JP7720901B2 - Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet.
This application claims priority based on Japanese Patent Application No. 2021-030200, filed on February 26, 2021, the entire contents of which are incorporated herein by reference.

Generally, adhesives (also known as pressure-sensitive adhesives; the same applies hereinafter) are soft solids (viscoelastic bodies) at temperatures near room temperature, and have the property of easily adhering to adherends when pressure is applied. Taking advantage of these properties, adhesives are widely used in a variety of industrial fields, from home appliances to automobiles, various machinery, electrical equipment, and electronic devices, as a joining method that is easy to work with and provides reliable adhesion, typically in the form of an adhesive sheet containing a layer of the adhesive. Various types of adhesives, such as acrylic adhesives, rubber adhesives, and polyester adhesives, are used depending on the purpose, location of use, required properties, etc. For example, Patent Documents 1 to 3 disclose prior art related to polyester adhesives.

Japanese Patent No. 4914132 Japanese Patent No. 6687997 Japanese Patent Application Publication No. 2020-79372

Adhesive sheets are preferably used for fixing components in electronic devices such as mobile phones, smartphones, and tablet computers. Most adhesive sheets for electronic devices use acrylic adhesives with an acrylic polymer as the base polymer. Other examples of adhesives used in the above applications include synthetic rubber adhesives with a rubber block copolymer, such as a styrene-butadiene block copolymer, as the base polymer.

Recently, environmental issues such as global warming have become a major concern, spurring a desire to reduce the use of fossil fuel-based materials, such as petroleum. It is also desirable to reduce the use of fossil fuel-based materials in the above-mentioned adhesive sheets for electronic devices. However, both the above-mentioned acrylic adhesives and synthetic rubber adhesives are primarily made from fossil fuels, such as petroleum. In reality, reducing the use of fossil fuel-based materials is difficult, and there are limits to switching to renewable organic resources. Polyester-based adhesives are an example of an adhesive that can reduce dependence on fossil fuel-based materials while offering adhesive properties equal to or superior to those of acrylic and synthetic rubber adhesives. Polyester-based adhesives offer excellent properties, such as chemical resistance, water resistance, durability, and optical properties (transparency), making them suitable for a variety of applications, including mobile electronic devices. Furthermore, because the polyester polymers used in polyester-based adhesives can be synthesized using biomass materials (e.g., Patent Documents 1 and 2), the use of such polyester-based polymers can reduce the use of petroleum-based materials. Biomass materials typically refer to materials derived from biological resources (typically, plants that perform photosynthesis) that can be sustainably reproduced in the presence of sunlight, water, and carbon dioxide.

However, because polyester polymers typically have crosslinking points only at the ends of the polymer chain, it is difficult to achieve an effective crosslinked structure compared to acrylic polymers. This polymer structure can hinder the achievement of required performance, for example, in applications involving the bonding and fixing of portable electronic devices. Specifically, adhesives used in portable electronic devices must have sufficient adhesive strength for bonding and fixing, while also possessing the holding power (high-temperature holding power) necessary to prevent slippage even at high temperatures. Portable electronic devices contain heat-generating components such as batteries within a limited internal space. Prolonged use of portable electronic devices increases the internal temperature due to the heat generated by the batteries. Therefore, adhesives used in portable electronic devices must also possess high-temperature holding power. Furthermore, repeated exposure to high and room temperatures within portable electronic devices can cause internal shrinkage of the adherend material. Therefore, adhesives must possess the holding power necessary to prevent slippage even in the face of such shrinkage. As mentioned above, polyester polymers often have a structure that makes it relatively difficult to increase the degree of crosslinking, making it difficult to improve high-temperature holding power through crosslinking. For example, if an attempt is made to increase the degree of crosslinking by increasing the amount of crosslinking agent in order to improve holding power, there is a concern that the gel fraction will increase, resulting in a decrease in flexibility and adhesive strength, and a decrease in impact resistance. Compared to acrylic adhesives, polyester-based pressure-sensitive adhesives tend to find it more difficult to achieve both high-temperature holding power and other adhesive properties (typically adhesive strength).

The present invention was created in light of the above circumstances, and aims to provide a pressure-sensitive adhesive composition that contains a polyester-based polymer synthesized using biomass materials and that is capable of achieving both adhesive strength and high-temperature retention. Another related aim is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that contains a polyester-based polymer synthesized using biomass materials.

According to the present specification, there is provided a pressure-sensitive adhesive composition comprising a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon. This pressure-sensitive adhesive composition further comprises a tackifying resin. Furthermore, the weight-average molecular weight of the polyester-based polymer is 30,000 or more.

The above-mentioned adhesive composition is prepared using a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon (bio content of 50% or more), thereby reducing dependence on fossil-based materials. Furthermore, the above-mentioned adhesive composition further contains a tackifying resin, and the weight-average molecular weight (Mw) of the polyester-based polymer is 30,000 or more. Therefore, improved adhesive strength can be achieved based on the effects of the polyester-based polymer and tackifying resin. Furthermore, high-temperature holding power can be achieved based on the Mw of the polyester-based polymer. An adhesive composition with the above-mentioned composition can achieve an adhesive that combines adhesive strength and high-temperature holding power.

In addition, adhesive compositions with the above-described composition are likely to provide good repulsion resistance. For example, in recent years, displays with curved shapes, such as three-dimensional shapes, have been put to practical use as displays for organic EL display devices used in electronic devices such as smartphones. It is desirable for adhesives used in such applications to be durable against bending and have adhesive reliability that prevents lifting or peeling when a highly elastic component attached to the curved surface of the display is subjected to a repulsive force that causes the component to return to its original shape. Because adhesives that can exhibit the above-described repulsion resistance tend to have excellent adhesive reliability against bending, they are also preferably used in applications where they are attached to the three-dimensional or other curved surfaces of portable electronic devices, for example.

In some preferred embodiments of the technology disclosed herein (including pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets; the same applies hereinafter), the weight-average molecular weight of the polyester-based polymer is greater than 60,000. By using a polyester-based polymer with the above Mw, it is easier to achieve better high-temperature retention.

In some embodiments, the glass transition temperature of the polyester polymer is 0°C or lower. By using a polyester polymer with a glass transition temperature (Tg) of 0°C or lower, good adhesive properties (e.g., adhesive strength) are likely to be obtained.

In some preferred embodiments, the polyester-based polymer contains an aromatic ring. Introducing an aromatic ring into a polyester-based polymer tends to provide excellent high-temperature retention.

In some preferred embodiments, the tackifier resin is selected from terpene phenolic resins and polymerized rosin esters. By using one or more tackifier resins selected from terpene phenolic resins and polymerized rosin esters, it is possible to achieve a better balance between adhesive strength and high-temperature retention.

In some preferred embodiments, the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring. By incorporating an aromatic ring into both the polyester polymer and the tackifier resin, high-temperature retention is more likely to be achieved. Furthermore, the polyester polymer and the tackifier resin tend to have excellent compatibility.

In some preferred embodiments, the pressure-sensitive adhesive composition further contains a crosslinking agent. The content of the crosslinking agent is 5 parts by weight or less per 100 parts by weight of the polyester polymer. According to the technology disclosed herein, it is possible to obtain a cohesive strength that achieves high-temperature holding power with the limited amount of crosslinking agent used as described above. This can be an advantageous feature in achieving both high-temperature holding power and other adhesive properties such as adhesive strength. An isocyanate-based crosslinking agent is preferably used as the crosslinking agent. Of these, it is particularly preferable that the isocyanate-based crosslinking agent be an aliphatic isocyanate-based compound. By using an aliphatic isocyanate-based compound as the crosslinking agent, the degree of crosslinking can be effectively increased.

The pressure-sensitive adhesive composition according to some embodiments further comprises a crosslinking agent and a crosslinking catalyst. The crosslinking catalyst does not contain a tin-based compound. From the standpoint of environmental impact and safety, it is preferable to reduce the amount of tin-containing compounds (typically organotin compounds) used. The pressure-sensitive adhesive composition disclosed herein can efficiently form a crosslinked structure that is suitable for achieving both adhesive strength and high-temperature retention without using a tin-based crosslinking catalyst, which generally tends to have excellent reaction speed.

The present specification also provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon. In this pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer further contains a tackifying resin. The weight-average molecular weight of the polyester-based polymer is 30,000 or more. Because the pressure-sensitive adhesive sheet of the above configuration uses a polyester-based polymer with a bio-content of 50% or more as the pressure-sensitive adhesive, it can reduce dependence on fossil resource-based materials. Furthermore, by using a polyester-based polymer having the above Mw in combination with a tackifying resin, it is possible to achieve both adhesive strength and high-temperature retention.

In some preferred embodiments, the PSA sheet has a 180-degree peel strength against a stainless steel plate of 10 N/20 mm or more, and has a holding strength that prevents it from falling in a holding strength test conducted at 80°C with a load of 1 kg for 1 hour. PSA sheets that satisfy these two characteristics adhere well to the adherend and are likely to exhibit high adhesive reliability without peeling or slippage, even when used in environments exposed to high temperatures, for example.

The adhesive sheets disclosed herein have adhesive reliability that combines adhesive strength with high-temperature retention, making them suitable for use in portable electronic devices that require high performance. The interiors of portable electronic devices may contain heat-generating elements such as batteries, and may be exposed to temperatures of, for example, 40°C or higher, making the use of adhesive sheets with excellent high-temperature retention particularly beneficial. Thus, this specification provides a portable electronic device that uses any of the adhesive sheets disclosed herein, or in other words, a portable electronic device that includes the adhesive sheet.

1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to one embodiment. FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. 1 is a front view schematically illustrating an example of a portable electronic device configured to include an adhesive sheet. FIG. 1 is a schematic diagram illustrating a method for testing repulsion resistance.

Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.
In the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and duplicated explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the PSA sheet of the present invention that is actually provided as a product.

The pressure-sensitive adhesive sheet disclosed herein is configured to include a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet may be in the form of a substrate-less double-sided pressure-sensitive adhesive sheet having, for example, a first adhesive surface formed by one surface of the pressure-sensitive adhesive layer and a second adhesive surface formed by the other surface of the pressure-sensitive adhesive layer. Alternatively, the pressure-sensitive adhesive sheet disclosed herein may be in the form of a substrate-attached pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is laminated on one or both surfaces of a supporting substrate. Hereinafter, the supporting substrate may also be simply referred to as the "substrate."

<Example of adhesive sheet configuration>
The structure of a PSA sheet according to one embodiment is shown schematically in FIG. 1 . This PSA sheet 1 is configured as a substrate-less double-sided PSA sheet comprising a PSA layer 21. The PSA sheet 1 is used by attaching a first adhesive surface 21A, which is formed by one surface (first surface) of the PSA layer 21, and a second adhesive surface 21B, which is formed by the other surface (second surface) of the PSA layer 21, to different locations on an adherend. The locations to which the PSA surfaces 21A and 21B are attached may be locations on different members, or may be different locations on a single member. Before use (i.e., before attachment to an adherend), the PSA sheet 1 may be a component of a release-liner PSA sheet 100, as shown in FIG. 1 , in which the first adhesive surface 21A and the second adhesive surface 21B are protected by release liners 31 and 32, each of which serves as a release surface at least on the side facing the PSA layer 21. For example, a sheet-like substrate (liner substrate) configured such that one side serves as a release surface by providing a release layer made of a release treatment agent on that side can be preferably used as release liners 31, 32. Alternatively, release liner 32 can be omitted, and release liner 31, which has release surfaces on both sides, can be used, and this can be superimposed on PSA sheet 1 and wound spirally to form a PSA sheet with release liner in a form (roll form) in which second PSA surface 21B is protected by being in contact with the back surface of release liner 31.

The structure of a PSA sheet according to another embodiment is shown schematically in Figure 2. This PSA sheet 2 is configured as a substrate-attached single-sided PSA sheet comprising a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and an PSA layer 21 provided on the first surface 10A side of the support substrate 10. The PSA layer 21 is fixedly provided on the first surface 10A side of the support substrate 10, i.e., without any intention of separating the PSA layer 21 from the support substrate 10. As shown in Figure 2, the PSA sheet 2 before use may be a component of a release-liner-attached PSA sheet 200 in which the surface (adhesive surface) 21A of the PSA layer 21 is protected by a release liner 31, at least the side facing the PSA layer 21 being a release surface. Alternatively, the release liner 31 may be omitted, and a support substrate 10 having a second surface 10B as a release surface may be used, with the PSA sheet 2 rolled up so that the adhesive surface 21A is in contact with the second surface (rear surface) 10B of the support substrate 10 and protected.

The structure of a PSA sheet according to yet another embodiment is shown schematically in Figure 3. This PSA sheet 3 is configured as a substrate-attached double-sided PSA sheet comprising a sheet-like support substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B, a first PSA layer 21 fixedly provided on the first side 10A, and a second PSA layer 22 fixedly provided on the second side 10B. As shown in Figure 3, the PSA sheet 3 before use may be a component of a release-liner PSA sheet 300 in which the surface (first adhesive surface) 21A of the first PSA layer 21 and the surface (second adhesive surface) 22A of the second PSA layer 22 are protected by release liners 31, 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used. This may be superimposed on the PSA sheet 3 and wound into a spiral shape to form a release-liner PSA sheet in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31 (roll form).

The release liner may be one having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or one made of a low-adhesion material such as a polyolefin resin (e.g., polyethylene or polypropylene) or a fluorine-based resin. The release treatment layer may be formed by surface treating the liner substrate with a release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. In the field of electronic devices, release liners having a release treatment layer on the surface of a resin film or a release liner made of a low-adhesion material are preferred to avoid the generation of paper dust.

The concept of adhesive sheet here can include things called adhesive tape, adhesive film, adhesive labels, etc. The adhesive sheet may be in roll form or in sheet form, and may be cut or punched into an appropriate shape depending on the application and mode of use.

<Adhesive Layer>
(Polyester-based polymer)
The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer containing a polyester-based polymer. In other words, the pressure-sensitive adhesive layer and the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contain a polyester-based polymer (hereinafter, unless otherwise specified, the description of the pressure-sensitive adhesive layer also applies to the pressure-sensitive adhesive composition). Such pressure-sensitive adhesives and pressure-sensitive adhesive compositions containing a polyester-based polymer are also referred to as polyester-based pressure-sensitive adhesives and polyester-based pressure-sensitive adhesive compositions. The polyester-based polymer is typically included in the pressure-sensitive adhesive layer as a base polymer. Here, the term "base polymer" refers to the main component of a rubbery polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) included in the pressure-sensitive adhesive layer. In this specification, unless otherwise specified, the term "main component" refers to a component that accounts for more than 50% by weight. In this specification, the term "polyester-based polymer" refers to a polymer obtained by polycondensation of a dicarboxylic acid and a diol.

The polyester polymer contained in the adhesive layer contains 50% or more of its constituent carbon derived from biomass. In other words, the biomass carbon ratio (also referred to as the "bio-ratio") of the polyester polymer is 50% or more. Using a polyester polymer with a bio-ratio equal to or greater than a predetermined value can reduce the adhesive's dependence on fossil-based materials. In some embodiments, the bio-ratio of the polyester polymer is 52% or more, preferably 55% or more, and may be, for example, 60% or more. The bio-ratio of the polyester polymer is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. It may be 85% or more, or even 88% or more. While the upper limit of the bio-ratio is 100% by definition, in some embodiments, the bio-ratio of the polyester polymer may be, for example, 95% or less. When adhesive performance is more important, it may be 92% or less, 90% or less, or 85% or less. By using a biomass-derived compound for at least one (for example, both) of the dicarboxylic acid and the diol used in the synthesis of the polyester-based polymer, the bio content of the polyester-based polymer can be increased to 50% or more.

As used herein, biomass-derived carbon refers to carbon (renewable carbon) derived from biomass materials, i.e., materials derived from renewable organic resources. Biomass materials typically refer to materials derived from biological resources (typically, plants that perform photosynthesis) that can be sustainably reproduced in the presence of sunlight, water, and carbon dioxide. Therefore, materials derived from fossil resources that are depleted through use after mining (fossil resource-based materials) are excluded from the concept of biomass materials. The biomass content of a polyester-based polymer, i.e., the proportion of biomass-derived carbon in the total carbon contained in the polyester-based polymer, can be estimated from the content of the carbon isotope with mass number 14 measured in accordance with ASTM D6866. The same applies to the examples described below.

The weight-average molecular weight (Mw) of the polyester polymer is 30,000 or more. By using a polyester polymer with a Mw of a predetermined value or more, the cohesive strength of the pressure-sensitive adhesive layer is increased, and the holding power, and therefore the high-temperature holding power, are improved. In some embodiments, the Mw of the polyester polymer is suitably greater than 50,000. From the viewpoint of obtaining better high-temperature holding power, it is preferably greater than 60,000, more preferably greater than 70,000, even more preferably greater than 80,000, particularly preferably greater than 90,000, and may even be greater than 95,000. In some preferred embodiments, the Mw of the polyester polymer is greater than 100,000, more preferably greater than 110,000 (e.g., greater than 110,000), even more preferably greater than 120,000, and may even be greater than 125,000. By using such a high-molecular-weight polyester polymer, excellent resilience is easily obtained. The upper limit of the Mw of the polyester polymer is usually about 30 × 10 ^{or less} , and from the viewpoint of adhesive strength etc., it is preferably about 20 × 10 ^{or less} , more preferably about 15 × 10 ^or less, and may be, for example, about 12 × 10 or ^less .

In this specification, the Mw of a polyester polymer refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As a GPC device, for example, a model "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) can be used. More specifically, GPC measurement can be performed under the following conditions. Measurements are also performed in the examples described below using the same method.
[GPC measurement]
Column: TSKgel GMH-H(S)
Column temperature: 40°C
Eluent: THF (containing 0.1% by weight of amine components)
Flow rate: 0.5mL/min
Injection volume: 100μL
Detector: differential refractometer (RI)
Standard sample: polystyrene (PS)

The glass transition temperature (Tg) of the polyester polymer is advantageously approximately 15°C or lower, preferably approximately 0°C or lower, more preferably approximately -15°C or lower, even more preferably approximately -20°C or lower, and particularly preferably approximately -25°C or lower (e.g., approximately -30°C or lower). Using a polyester polymer with a low Tg can favorably improve adhesive strength. Furthermore, from the perspective of the cohesive strength of the pressure-sensitive adhesive layer, the Tg of the polyester polymer is typically approximately -80°C or higher, preferably approximately -60°C or higher, more preferably approximately -45°C or higher, even more preferably approximately -40°C or higher, and may even be approximately -35°C or higher. The Tg of the polyester polymer can be adjusted by appropriately changing the monomer composition (i.e., the types and amounts of monomers used in the synthesis of the polymer).

The Tg of a polyester polymer is measured using the following method. A disc-shaped test specimen measuring 2 mm thick and 8 mm in diameter is prepared from the polyester polymer to be measured. This test specimen is sandwiched between parallel plates for shear testing, and the peak value of tan δ (loss modulus G''/storage modulus G') is determined at a frequency of 1 Hz using a measuring device (ARES, manufactured by Rheometric Scientific). The temperature at this peak value is taken as the Tg (glass transition temperature) [°C]. Measurements are performed in the same manner in the examples described below.

(dicarboxylic acid)
The dicarboxylic acid used in the synthesis of the polyester polymer may be any of aliphatic dicarboxylic acids, dimer acids, alicyclic dicarboxylic acids, unsaturated dicarboxylic acids, and aromatic dicarboxylic acids. Specific examples of dicarboxylic acids include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid, sebacic acid, thiodipropionic acid, and diglycolic acid; dimer acids obtained by dimerizing fatty acids such as oleic acid and erucic acid; 1,2-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 4-methyl-1,2 Examples of suitable dicarboxylic acids include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, norbornanedicarboxylic acid, and adamantanedicarboxylic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, and dodecenyl succinic anhydride; aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, orthophthalic acid, benzylmalonic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-dicarboxydiphenyl ether, and naphthalenedicarboxylic acid; and derivatives thereof. Derivatives of the dicarboxylic acids include derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters. By appropriately selecting and using one or more of these dicarboxylic acids, a polyester polymer suitable for achieving both adhesive strength and high-temperature holding power can be obtained.

As the dicarboxylic acid, it is preferable to use a plant-derived dicarboxylic acid from the viewpoint of obtaining a polyester polymer with a bio-content of 50% or more. Suitable examples of such dicarboxylic acids include sebacic acid derived from plants (e.g., castor oil) and dimer acids derived from fatty acids such as oleic acid and erucic acid. Plant-derived dicarboxylic acids can be used alone or in combination of two or more.

From the perspective of reducing dependence on petroleum-derived materials, it is appropriate that the weight proportion of plant-derived dicarboxylic acids relative to the total amount (total weight) of dicarboxylic acids as monomer components of the polyester polymer be approximately 1% by weight or more, preferably approximately 10% by weight or more, more preferably approximately 50% by weight or more, even more preferably approximately 70% by weight or more, and particularly preferably approximately 80% by weight or more. It may be approximately 90% by weight or more, or even approximately 95% by weight or more (e.g., 95-100% by weight). The upper limit of the weight proportion of the plant-derived dicarboxylic acids is 100% by weight. From the perspective of adhesive properties such as high-temperature retention, it is appropriate that the weight proportion be approximately 99% by weight or less, preferably approximately 95% by weight or less, or even approximately 90% by weight or less.

In some preferred embodiments, dimer acid is used as the plant-derived dicarboxylic acid. The use of dimer acid allows for the enhancement of the biomass content of the polyester polymer while maintaining favorable adhesive properties. Dimer acids can be used singly or in combination. In embodiments using dimer acid as the dicarboxylic acid, the weight ratio of dimer acid to the total amount (total weight) of dicarboxylic acids as monomer components of the polyester polymer is suitably approximately 1% by weight or more, preferably approximately 10% by weight or more, more preferably approximately 50% by weight or more, even more preferably approximately 70% by weight or more, and particularly preferably approximately 80% by weight or more. It may even be approximately 90% by weight or more, or even approximately 95% by weight or more (e.g., 95-100% by weight). By using a predetermined amount or more of dimer acid, the polymer can be designed based on the properties of the dimer acid. Furthermore, the upper limit of the weight proportion of the dimer acid is 100% by weight, and from the viewpoint of adhesive properties such as high-temperature retention, it is appropriate to use approximately 99% by weight or less, preferably approximately 95% by weight or less, and may be approximately 90% by weight or less.

In some embodiments, sebacic acid may be used as the plant-derived dicarboxylic acid. The use of sebacic acid can also increase the biomass content of the polyester-based polymer. In embodiments using sebacic acid as the dicarboxylic acid, the weight percentage of sebacic acid relative to the total amount (total weight) of dicarboxylic acids as monomer components of the polyester-based polymer may be approximately 1% by weight or more, for example, approximately 10% by weight or more, approximately 50% by weight or more, approximately 70% by weight or more, or approximately 90% by weight or more (e.g., 95-100% by weight). Furthermore, the weight percentage of sebacic acid may be approximately 95% by weight or less, and, from the viewpoint of adhesive properties such as high-temperature retention, may be approximately 75% by weight or less, or approximately 60% by weight or less. The technology disclosed herein can be implemented in either an embodiment in which the dicarboxylic acid as a monomer component used in the synthesis of the polyester-based polymer contains sebacic acid or an embodiment in which sebacic acid is not contained. For example, the weight percentage of the sebacic acid may be approximately 50% by weight or less, approximately 30% by weight or less, approximately 10% by weight or less, approximately 3% by weight or less, or less than 1% by weight, and the dicarboxylic acid used in the synthesis of the polyester-based polymer may be substantially free of sebacic acid.

The molecular weight of the plant-derived dicarboxylic acid is not particularly limited, and is suitably 100 or greater, and may be 150 or greater. The higher the molecular weight of the plant-derived dicarboxylic acid, the easier it is to increase the bio-content of the polyester polymer. From this perspective, the molecular weight of the plant-derived dicarboxylic acid may be 250 or greater, 350 or greater, 450 or greater, or 500 or greater (e.g., 550 or greater). On the other hand, from the perspective of monomer availability and ease of synthesis, the molecular weight of the plant-derived dicarboxylic acid is suitably approximately 1,000 or less, and may be, for example, 800 or less, 700 or less, or 600 or less. A suitable example of a dicarboxylic acid having the above molecular weight is dimer acid.

In this specification, the molecular weight of a dicarboxylic acid is the molecular weight calculated from the chemical formula. In addition, in embodiments where two or more dicarboxylic acids (e.g., the plant-derived dicarboxylic acids described above) are used, the molecular weight of the dicarboxylic acid (e.g., the plant-derived dicarboxylic acids described above) is the sum (total value) of the products of the molecular weights and weight fractions of the individual dicarboxylic acids.

Aromatic dicarboxylic acids are preferably used as the dicarboxylic acid used in the synthesis of the polyester polymer disclosed herein. Using a dicarboxylic acid containing an aromatic dicarboxylic acid tends to increase cohesive strength and improve high-temperature holding power. By including an aromatic dicarboxylic acid as the dicarboxylic acid, the amount of crosslinking agent used can be reduced, making it easier to improve high-temperature holding power while maintaining or improving adhesive strength. Suitable examples of aromatic dicarboxylic acids include isophthalic acid, terephthalic acid, and orthophthalic acid, with terephthalic acid being more preferred. These can be used alone or in combination of two or more.

The technology disclosed herein also encompasses embodiments in which the biomass content of polyester polymers is increased by using a biomass-derived aromatic dicarboxylic acid. In some embodiments, biomass-derived terephthalic acid and its derivatives can be used as the dicarboxylic acid. The method for obtaining the biomass-derived dicarboxylic acid is not particularly limited. For example, biomass-derived terephthalic acid can be obtained by obtaining isobutanol from corn, sugars, or wood, converting it to isobutylene, dimerizing it to obtain isooctene, and synthesizing p-xylene through radical cleavage, recombination, and cyclization, which is then oxidized to obtain terephthalic acid (WO 2009/079213).

In embodiments in which aromatic dicarboxylic acids are used as dicarboxylic acids, the weight percentage of aromatic dicarboxylic acids relative to the total amount (total weight) of dicarboxylic acids in the monomer components of the polyester polymer is not particularly limited, but is suitably approximately 1% by weight or more. From the viewpoint of improving high-temperature retention, it is preferably approximately 3% by weight or more, more preferably approximately 5% by weight or more, and even more preferably approximately 7% by weight or more. The upper limit of the weight percentage of the aromatic carboxylic acid is not limited to a specific range, as it may vary depending on the type of other dicarboxylic acid, etc., and is suitably approximately 50% by weight or less. From the viewpoint of adhesive properties such as adhesive strength, it is preferably approximately 30% by weight or less, more preferably approximately 20% by weight or less, even more preferably approximately 15% by weight or less, and particularly preferably approximately 10% by weight or less.

In some embodiments, dicarboxylic acids (e.g., aliphatic dicarboxylic acids) derived from fossil resources may be used to obtain the desired adhesive properties, taking into consideration productivity, efficiency, and cost. Examples of such dicarboxylic acids (e.g., aliphatic dicarboxylic acids) include dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, and azelaic acid. Of these, adipic acid is preferably used as the aliphatic dicarboxylic acid. The above dicarboxylic acids (e.g., aliphatic dicarboxylic acids) derived from fossil resources may be used alone or in combination of two or more.

The molecular weight of the dicarboxylic acid used as a monomer component in the synthesis of the polyester-based polymer disclosed herein is not particularly limited, and is suitably 100 or greater, and may be 150 or greater. In some embodiments, the molecular weight of the dicarboxylic acid used may be 200 or greater, 250 or greater, 350 or greater, 450 or greater, or 500 or greater (e.g., 530 or greater). On the other hand, from the standpoint of monomer availability and ease of synthesis, the molecular weight of the dicarboxylic acid is suitably approximately 1,000 or less, and may be, for example, 800 or less, 700 or less, or 600 or less (e.g., 550 or less). The polyester-based polymers disclosed herein (polyester-based polymers having an Mw greater than a specified value and preferably having a Tg within a specified range) are preferably synthesized using dicarboxylic acids having molecular weights within the above ranges.

(diol)
As the diol used in the synthesis of the polyester polymer disclosed herein, any of (poly)alkylene glycols, aliphatic diols, dimer diols, alicyclic diols, aromatic diols, and unsaturated diols can be used. Specific examples of the diol include (poly)alkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, and polytetramethylene glycol; 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, and 2,2,4-trimethyl-1,6 aliphatic diols such as 1,2-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; dimer diols (e.g., dimer diols derived from fatty acids such as oleic acid and erucic acid); alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; and aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and their ethylene oxide and propylene oxide adducts. By appropriately selecting and using one or more of these diols, a polyester-based polymer suitable for achieving both adhesive strength and high-temperature holding power can be obtained.

In some embodiments, the diol is preferably a (poly)alkylene glycol, an aliphatic diol, or an alicyclic diol, with a (poly)alkylene glycol or an aliphatic diol being more preferred. By combining these diols (preferably ethylene glycol or an aliphatic diol) with the above-mentioned dicarboxylic acid (preferably a dimer acid or an aromatic dicarboxylic acid), a polyester-based polymer with excellent adhesive properties can be preferably obtained. Suitable examples include (poly)ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. From the standpoint of reactivity, etc., ethylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol are more preferred. These can be used alone or in combination of two or more. The (poly)alkylene glycols, aliphatic diols, and alicyclic diols may be derived from plants or fossil resources. In this specification, the term "(poly)ethylene glycol" is used to encompass ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol.

The weight proportion of (poly)alkylene glycols, aliphatic diols, and alicyclic diols (preferably the weight proportion of ethylene glycol and aliphatic diols) relative to the total amount (total weight) of diols in the monomer components of the polyester polymer is not particularly limited, but is suitably approximately 50% by weight or more. From the viewpoint of obtaining good adhesive properties, it is preferably approximately 70% by weight or more, more preferably approximately 80% by weight or more, even more preferably approximately 90% by weight or more, and particularly preferably approximately 95% by weight or more (e.g., 99-100% by weight). Furthermore, the weight proportion of the (poly)alkylene glycols, aliphatic diols, and alicyclic diols (preferably the weight proportion of ethylene glycol and aliphatic diols) may be, for example, approximately 95% by weight or less.

In some preferred embodiments, (poly)ethylene glycol is used as the diol. By combining (poly)ethylene glycol with an appropriate dicarboxylic acid, excellent adhesive properties (adhesion strength and high-temperature retention) can be preferably achieved. In embodiments using (poly)ethylene glycol as the diol, the weight percentage of the (poly)ethylene glycol relative to the total amount (total weight) of diols as monomer components of the polyester-based polymer is preferably approximately 1 wt% or more, preferably approximately 10 wt% or more, more preferably approximately 50 wt% or more, even more preferably approximately 80 wt% or more, and particularly preferably approximately 90 wt% or more (e.g., 95-100 wt%). By using a predetermined amount of (poly)ethylene glycol or more, the polymer can be designed based on the properties of (poly)ethylene glycol. Furthermore, for example, the use of (poly)ethylene glycol facilitates the production of a pressure-sensitive adhesive layer with low haze. Furthermore, the weight percentage of the (poly)ethylene glycol may be approximately 95 wt% or less, approximately 70 wt% or less, or approximately 50 wt% or less. The (poly)ethylene glycol may be derived from plants or fossil resources. The (poly)ethylene glycols may be used alone or in combination of two or more.

In some embodiments, it is preferable to use a plant-derived diol as the diol, from the viewpoint of obtaining a polyester polymer with a bio-content of 50% or more. Examples of such diols include biomass diols obtained using biomass ethanol as a raw material (e.g., biomass (poly)ethylene glycol), fatty acid esters derived from plants (e.g., castor oil), dimer diols derived from fatty acids such as oleic acid and erucic acid, and butanediol produced using glucose. Plant-derived diols can be used alone or in combination of two or more.

In some embodiments, with a view to reducing dependence on petroleum-derived materials, the weight percentage of plant-derived diols relative to the total amount (total weight) of diols as monomer components of the polyester-based polymer may be approximately 1% by weight or more, approximately 10% by weight or more, approximately 50% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more (e.g., 95-100% by weight). Furthermore, the weight percentage of the plant-derived diols may be approximately 95% by weight or less, approximately 70% by weight or less, or approximately 50% by weight or less. Even in embodiments in which a relatively low amount of plant-derived diols is used and a petroleum-derived diol is used, for example, by using a petroleum-derived diol with a relatively low molecular weight, the polyester-based polymer can have a bio-content greater than or equal to a predetermined value. From this perspective, the weight percentage of the plant-derived diols may be approximately 30% by weight or less, approximately 10% by weight or less, or approximately 3% by weight or less (e.g., less than 1% by weight). The technology disclosed herein can also be preferably implemented in an embodiment in which the diol used as a monomer component in the synthesis of the polyester polymer does not substantially contain a plant-derived diol.

In some embodiments, dimer diol is used as the plant-derived diol. The use of dimer diol can also increase the bio-content of polyester polymers. Dimer diols can be used singly or in combination. In embodiments using dimer diol as the diol, the weight percentage of dimer diol relative to the total amount (total weight) of diols as monomer components of the polyester polymer may be approximately 1% by weight or more, for example, approximately 10% by weight or more, approximately 50% by weight or more, approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more (e.g., 95-100% by weight). The weight percentage of dimer diol may also be approximately 95% by weight or less, approximately 85% by weight or less, or approximately 60% by weight or less. The technology disclosed herein can be implemented in either an embodiment in which the diol used as a monomer component in the synthesis of a polyester polymer contains dimer diol, or an embodiment in which dimer diol is not contained. For example, the weight proportion of the dimer diol may be approximately 50% by weight or less (e.g., less than 50% by weight), approximately 30% by weight or less, approximately 10% by weight or less, approximately 3% by weight or less, or less than 1% by weight, and the diol used in the synthesis of the polyester-based polymer may be substantially free of dimer diol.

The molecular weight of the diol is not particularly limited. From the standpoint of monomer availability and ease of synthesis, the molecular weight of the diol is suitably 500 or less, and may be 300 or less, 150 or less, 100 or less, or 80 or less. The molecular weight of the diol is suitably 50 or greater, and may be, for example, greater than 100. In embodiments using diols within the above molecular weight range, polyester-based polymers that combine adhesive strength and high-temperature retention can be preferably synthesized. Furthermore, in embodiments where the diol is derived from fossil resources, the molecular weight of the fossil-based diol is suitably 500 or less, and may be 300 or less. The smaller the molecular weight of the fossil-based diol, the higher the bio-content of the polyester-based polymer. From this standpoint, the molecular weight of the fossil-based diol may be 150 or less, 100 or less, or 80 or less. The molecular weight of the fossil-based diol is suitably 50 or greater, and may be, for example, greater than 100. A suitable example of a diol having the above molecular weight is ethylene glycol.

In this specification, the molecular weight of a diol can be calculated from its chemical formula. In addition, in embodiments in which two or more diols (e.g., the diols derived from fossil resources) are used, the molecular weight of the diol (e.g., the diols derived from fossil resources) is the sum (total value) of the products of the molecular weights and weight fractions of the individual diols.

The polyester polymers disclosed herein may be essentially composed of the dicarboxylic acids and diols described above. However, for purposes such as introducing desired functional groups or adjusting molecular weight, other copolymerization components besides dicarboxylic acids and diols may be copolymerized within the scope of the technology disclosed herein, provided that the effects of the technology disclosed herein are not impaired. Examples of such other copolymerization components include polycarboxylic acids containing three or four or more carboxy groups (trivalent or higher polycarboxylic acids such as trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, trimesic acid, and trimer acid), polyols containing three or four or more hydroxyl groups per molecule (pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, and adamantanetriol), monocarboxylic acids, monoalcohols, hydroxycarboxylic acids, and lactones. The above-mentioned other copolymerization components may be used alone or in combination of two or more. These other copolymerization components may be plant-derived or not. The proportion of the other copolymerization component in the monomer components of the polyester-based polymer is suitably, for example, less than 10 wt %, and may be less than 3 wt %, typically less than 1 wt % (or even less than 0.1 wt %). The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer components of the polyester-based polymer are substantially free of the other copolymerization component.

While there are no particular limitations on the monomer components used in the synthesis of the polyester polymers disclosed herein, the total proportion of dicarboxylic acids and diols is suitably approximately 90% by weight or more, preferably approximately 95% by weight or more, more preferably approximately 98% by weight or more, and even more preferably approximately 99% by weight or more (e.g., 99-100% by weight). The technology disclosed herein is preferably implemented in an embodiment using a polyester polymer synthesized substantially from dicarboxylic acids and diols.

In some preferred embodiments, the monomer components of the polyester-based polymer use a combination of dimer acid as the dicarboxylic acid and (poly)ethylene glycol as the diol. By using a combination of dimer acid and (poly)ethylene glycol, it is possible to preferably synthesize a polyester-based polymer having a Mw of a predetermined value or greater and suitable for achieving both adhesive strength and high-temperature retention. The combined proportion of dimer acid and (poly)ethylene glycol in the total monomer components of the polyester-based polymer is suitably approximately 50% by weight or greater, preferably approximately 60% by weight or greater, more preferably approximately 70% by weight or greater, even more preferably approximately 80% by weight or greater, and may even be approximately 90% by weight or greater (e.g., 99-100% by weight).

In some preferred embodiments, the polyester polymer contains an aromatic ring within the polymer molecule. A polyester polymer containing an aromatic ring is more likely to achieve high-temperature holding power. The aromatic ring is introduced into the polymer by using a monomer (aromatic dicarboxylic acid or aromatic diol) having an aromatic ring. In embodiments in which the polyester polymer contains an aromatic ring, the copolymerization ratio of the aromatic ring-containing monomer (typically an aromatic dicarboxylic acid or aromatic diol) is not particularly limited, but is suitably approximately 1 wt% or more. From the viewpoint of improving high-temperature holding power, it is preferably approximately 3 wt% or more, more preferably approximately 5 wt% or more, and even more preferably approximately 7 wt% or more. The upper limit of the copolymerization ratio of the aromatic ring-containing monomer is suitably, for example, approximately 30 wt% or less. From the viewpoint of adhesive properties such as adhesive strength, it is preferably approximately 15 wt% or less, more preferably approximately 12 wt% or less, even more preferably approximately 10 wt% or less, and particularly preferably approximately 8 wt% or less.

The method for obtaining the polyester polymer disclosed herein is not particularly limited, and any polymerization method known as a synthetic method for polyester polymers can be appropriately employed. The monomer raw material used in the synthesis of the polyester polymer can be, for example, a mixture of monomers in such a way that 0.95 to 1.05 equivalents (preferably 0.98 to 1.02 equivalents) of dicarboxylic acid per equivalent of diol. By combining dicarboxylic acid and diol in the above ratio, a high molecular weight polyester polymer is easily obtained. Furthermore, the polymer can be moderately crosslinked (for example, by reaction with a crosslinking agent such as an isocyanate-based crosslinking agent) to enhance cohesive strength.

In the technology disclosed herein, the weight ratio of dicarboxylic acid to diol as monomer components used in the synthesis of polyester-based polymers is not particularly limited, and an appropriate weight ratio can be set taking into consideration the desired polymer properties, synthesis, and other factors. In some embodiments, the ratio of the weight of dicarboxylic acid A1 to the weight of diol A2 used as the monomer components (weight ratio A1/A2) may be 10/90 or greater, or 30/70 or greater. In some preferred embodiments, the weight ratio (A1/A2) is approximately 50/50 or greater, more preferably 60/40 or greater, even more preferably 70/30 or greater, or may be 80/20 or greater, or even 90/10 or greater. For example, by increasing the weight ratio of dicarboxylic acid as described above, the properties inherent in the dicarboxylic acid can be favorably expressed. Furthermore, in embodiments using plant-derived dicarboxylic acids, the bio-content of the resulting polyester-based polymer can be effectively increased. Furthermore, the weight ratio (A1/A2) may be, for example, 95/5 or less, or 85/15 or less. In some embodiments, from the viewpoint of favorably expressing the properties based on the diol, the weight ratio (A1/A2) may be 75/25 or less, or may be 50/50 or less (e.g., 30/70 or less). In embodiments using a plant-derived diol, the above weight ratio allows the polyester-based polymer to have a high bio-content. Note that in embodiments using plant-derived materials for both the dicarboxylic acid and the diol, a polyester-based polymer having a bio-content equal to or greater than a predetermined value can be obtained, regardless of the weight ratio of the dicarboxylic acid to the diol.

The polyester polymers disclosed herein can be obtained by polycondensation of dicarboxylic acids and diols, similar to conventional polyesters. More specifically, polyester polymers can be synthesized by allowing the reaction between the carboxyl groups of the dicarboxylic acid and the hydroxyl groups of the diol to proceed, typically while removing the water produced by the reaction (produced water) from the reaction system. Methods for removing the produced water from the reaction system include blowing an inert gas into the reaction system and removing the produced water along with the inert gas; azeotropic dehydration using a reaction water removal solvent such as toluene or xylene; and distilling the produced water from the reaction system under reduced pressure (decompression method).

The reaction temperature and reaction time during the above reaction (including esterification and polycondensation), as well as the degree of vacuum (pressure within the reaction system) when a vacuum method is used, can be appropriately set so as to efficiently produce a polyester polymer with the desired properties (e.g., molecular weight). While not particularly limited, a reaction temperature of approximately 150°C or higher (e.g., 180°C to 260°C) is typically appropriate. Maintaining a reaction temperature within this range ensures a good reaction rate, improves productivity, and helps prevent or suppress degradation of the resulting polyester polymer. The reaction time is also not particularly limited and can be approximately 3 to 48 hours (e.g., 10 to 30 hours). When a vacuum method is used, although not particularly limited, a degree of vacuum of 10 kPa or less (typically 10 kPa to 0.1 kPa) is typically appropriate, e.g., 4 kPa to 0.1 kPa. Maintaining the pressure within the reaction system within this range allows the water produced by the reaction to be efficiently distilled out of the system, making it easier to maintain a good reaction rate. Furthermore, when the reaction temperature is relatively high, by setting the pressure in the reaction system to the above-mentioned lower limit or higher, it is easy to prevent the distillation of the raw materials, dicarboxylic acid and diol, outside the system. From the viewpoint of maintaining a stable pressure in the reaction system, it is usually appropriate to set the pressure in the reaction system to 0.1 kPa or higher.

As with the synthesis of general polyesters, a known or conventional catalyst can be used in an appropriate amount for esterification and condensation in the above reaction. Examples of such catalysts include various metal compounds, such as titanium-based, germanium-based, antimony-based, tin-based, and zinc-based compounds; strong acids, such as p-toluenesulfonic acid and sulfuric acid; and others. The amount of catalyst used can be appropriately determined depending on factors such as the reaction rate, so a detailed explanation will be omitted here.

In the above process for synthesizing a polyester polymer by reacting a dicarboxylic acid with a diol, a solvent may or may not be used. The synthesis can be carried out substantially without the use of organic solvents (meaning, for example, that the intentional use of an organic solvent as a reaction solvent during the reaction is excluded). Synthesizing a polyester polymer substantially without the use of organic solvents and preparing a polyester pressure-sensitive adhesive using such a polyester polymer are preferred because they meet the demand for reducing the use of organic solvents in the manufacturing process.

In the above reaction, there is generally a correlation between the molecular weight of the polyester polymer synthesized and the viscosity of the reaction system, so this can be used to control the molecular weight of the polyester polymer. For example, by continuously or intermittently measuring (monitoring) the torque of the stirrer and the viscosity of the reaction system during the reaction, it is possible to accurately synthesize a polyester polymer that meets the target molecular weight.

(Tackifying resin)
The PSA layer (and PSA composition) disclosed herein contains a tackifier resin. By combining a polyester polymer having a Mw of a predetermined value or more with a tackifier resin, the tackifier resin effectively exhibits the adhesive strength-enhancing effect. The tackifier resin can be one or more selected from various known tackifier resins, such as phenolic tackifier resins, terpene tackifier resins, modified terpene tackifier resins, rosin tackifier resins, hydrocarbon tackifier resins, epoxy tackifier resins, polyamide tackifier resins, elastomer tackifier resins, and ketone tackifier resins.

Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, alkyl phenolic resins, and rosin phenolic resins.
Terpene phenolic resin refers to a polymer containing terpene residues and phenol residues, and is a concept that encompasses both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and phenol-modified terpene resins (phenol-modified terpene resins) of terpenes or their homopolymers or copolymers. Suitable examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d/l- (dipentene)). Hydrogenated terpene phenolic resins refer to hydrogenated terpene phenolic resins having a structure obtained by hydrogenating such terpene phenolic resins. They are also sometimes called hydrogenated terpene phenolic resins.
Alkylphenol resins are resins (oil-based phenolic resins) obtained from alkylphenols and formaldehyde. Examples of alkylphenol resins include novolac and resol types.
Rosin phenolic resins are typically phenol-modified products of rosins or the various rosin derivatives described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenolic resins include those obtained by adding phenol to rosins or the various rosin derivatives described above using an acid catalyst and then thermally polymerizing the resulting mixture.
Of these phenolic tackifying resins, terpene phenol resins, hydrogenated terpene phenol resins and alkylphenol resins are preferred, terpene phenol resins and hydrogenated terpene phenol resins are more preferred, and terpene phenol resins are particularly preferred.

Examples of terpene-based tackifying resins include polymers of terpenes (e.g., monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene, and dipentene. The tackifying resin may be a homopolymer of one type of terpene, or a copolymer of two or more types of terpenes. Examples of homopolymers of one type of terpene include α-pinene polymer, β-pinene polymer, and dipentene polymer.
Examples of modified terpene resins include those obtained by modifying the above-mentioned terpene resins, such as styrene-modified terpene resins and hydrogenated terpene resins.

The term "rosin-based tackifying resin" as used here encompasses both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; and modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins, etc.).

Rosin derivative resins are typically derivatives of the rosins described above. The term "rosin-based resin" as used herein encompasses derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). Examples include rosin esters, such as unmodified rosin esters (esters of unmodified rosin and alcohols) and modified rosin esters (esters of modified rosin and alcohols); unsaturated fatty acid-modified rosins (rosins modified with unsaturated fatty acids); unsaturated fatty acid-modified rosin esters (rosin esters modified with unsaturated fatty acids); rosin alcohols (rosins or the above-mentioned rosin derivatives, including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters), in which the carboxyl groups of these rosins have been reduced; and metal salts of rosins or the above-mentioned rosin derivatives. Specific examples of rosin esters include methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, and the like of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.).

Examples of hydrocarbon-based tackifying resins include various hydrocarbon-based resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, and coumarone-indene resins.

In some preferred embodiments, the tackifier resin comprises one or more phenolic tackifier resins (e.g., terpene phenolic resins) or rosin-based tackifier resins (polymerized rosin esters, etc.). More preferably, the tackifier resin is one or more selected from terpene phenolic resins and polymerized rosin esters. By selecting and using an appropriate tackifier resin from among terpene phenolic resins and polymerized rosin esters, it is possible to achieve a better balance between adhesive strength and high-temperature retention.

It is particularly preferred to use a tackifier resin containing one or more phenolic tackifier resins (e.g., terpene phenolic resins) as the tackifier resin. Phenolic tackifier resins tend to have better compatibility with polyester polymers than other tackifier resins (e.g., rosin-based tackifier resins). The technology disclosed herein can be preferably implemented, for example, in an embodiment in which approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the total tackifier resin is terpene phenolic resin. Approximately 50% by weight or more of the total tackifier resin may be terpene phenolic resin, or approximately 80% by weight or more (e.g., approximately 90% by weight or more) may be terpene phenolic resin. Substantially all of the tackifier resin (e.g., approximately 95% by weight to 100% by weight, or even approximately 99% by weight to 100% by weight) may be terpene phenolic resin.

In some embodiments, a tackifier resin having an aromatic ring in the molecule is preferably used as the tackifier resin. Tackifier resins containing aromatic rings are more likely to provide high-temperature retention. Suitable examples of tackifier resins having aromatic rings include phenolic tackifier resins. Of these, terpene phenolic resins are more preferred. The technology disclosed herein is particularly preferably implemented in an embodiment in which the polyester polymer in the adhesive layer contains an aromatic ring and the tackifier resin also contains an aromatic ring. By having both the polyester polymer and the tackifier resin have a structure containing an aromatic ring, better high-temperature retention is more likely to be achieved. Furthermore, by both the polyester polymer and the tackifier resin having an aromatic ring, they have excellent compatibility and can effectively exhibit the desired adhesive properties.

In embodiments using a tackifier resin having an aromatic ring in the molecule, it is preferable to use a tackifier resin with a high aromatic ring ratio. For tackifier resins having a phenol structure as the aromatic ring, a tackifier resin with a high phenol ratio is preferably used. Using a tackifier resin with a high aromatic ring ratio (e.g., phenol ratio) tends to provide excellent repulsion resistance. It also tends to provide superior high-temperature retention. The aromatic ring ratio (e.g., phenol ratio) of the tackifier resin is, for example, 10% by weight or more. From the viewpoint of repulsion resistance, it is preferably 15% by weight or more, more preferably 20% by weight or more, even more preferably 25% by weight or more, and particularly preferably 30% by weight or more. The upper limit of the aromatic ring ratio (e.g., phenol ratio) of the tackifier resin is, for example, 65% by weight or less. From the viewpoint of adhesive strength, etc., it may be 50% by weight or less, 40% by weight or less, or 35% by weight or less.

As used herein, the aromatic ring ratio (e.g., phenol ratio) of a tackifier resin refers to the aromatic ring ratio (e.g., phenol ratio) calculated from ^{a 1H} -NMR spectrum measured with a nuclear magnetic resonance (NMR) device. For example, when a tackifier resin has the chemical structure shown below, in the ^1H -NMR spectrum, peaks with chemical shifts between 7.5 and 6.3 ppm are thought to be derived from the phenol skeleton, and peaks with chemical shifts between 5.6 and 0.1 ppm are thought to be derived from the pinene skeleton.
If the total integral value of the former peak is designated as A and the total integral value of the latter peak is designated as B, the molar ratio of the phenol skeleton to the pinene skeleton in the tackifier resin can be calculated by dividing these values by the number of H atoms contained in the repeating unit of each skeleton.
Molar ratio [phenol skeleton:pinene skeleton] = [A/3:B/16]
Next, the weight ratio of the phenol skeleton to the pinene skeleton in the tackifier resin can be calculated by multiplying the calculated molar ratio by the molecular weight of phenol (molecular weight 94.1) and pinene (molecular weight 136.2), respectively.
Weight ratio [phenol skeleton:pinene skeleton] = [(A/3) x 94.1:(B/16) x 136.2]
Then, when the weight ratio of the phenol skeleton thus determined is a and the weight ratio of the pinene skeleton is b, the aromatic ring ratio (phenol ratio) of the tackifier resin can be calculated by the following formula.
Aromatic ring ratio (%) = 100 x (a/(a+b))
As the NMR apparatus, for example, an "AVANCE III-400" (manufactured by Bruker Biospin) can be used. More specifically, ¹ H-NMR spectrum measurement can be performed under the following conditions. Measurements are also performed in the examples described below using the same method.
[ ¹ H-NMR measurement]
Observation frequency: 400MHz
Measurement temperature: 23℃
Measurement solvent: 1,1,2,2-tetrachloroethane-d ₂ (TCE-d ₂ )
Measured concentration: 33mg/mL

In some embodiments, a plant-derived tackifier resin (plant-based tackifier resin) is preferably used as the tackifier resin from the viewpoint of increasing the bio content of the entire PSA layer. A plant-based tackifier resin is composed of components at least partially derived from plants. The resin may be entirely plant-derived, or a portion of the resin may be plant-derived and the other portion may be derived from fossil resources. Examples of plant-based tackifier resins include the rosin-based tackifier resins, terpene-based tackifier resins, terpene phenolic resins, hydrogenated terpene phenolic resins, and rosin phenolic resins described above. One plant-based tackifier resin may be used alone, or two or more plant-based tackifier resins may be used in combination. In some embodiments, the proportion of the plant-based tackifier resin in the total amount of tackifier resins contained in the PSA layer may be 30% by weight or more (e.g., 50% by weight or more, typically 80% by weight or more), and the proportion of the plant-based tackifier resin in the total amount of tackifier resins may be 90% by weight or more (e.g., 95% by weight or more, typically 99 to 100% by weight). The technology disclosed herein can be practiced in an embodiment that is substantially free of tackifying resins other than vegetable tackifying resins.

The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving cohesive strength, in some embodiments, the softening point (softening temperature) of the tackifier resin is suitably approximately 50°C or higher. A tackifier resin having a softening point (softening temperature) of approximately 80°C or higher (preferably approximately 100°C or higher, e.g., approximately 115°C or higher) can be preferably used. In other embodiments, the softening point of the tackifier resin used may be approximately 120°C or higher (e.g., 135°C or higher or 145°C or higher). The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin having the above softening point accounts for more than 50% by weight (more preferably more than 70% by weight, e.g., more than 90% by weight) of the total tackifier resin contained in the adhesive layer. For example, phenolic tackifier resins (e.g., terpene phenolic resins) or rosin-based tackifier resins (e.g., polymerized rosin esters) having such softening points can be preferably used. In some preferred embodiments, a terpene phenol resin having a softening point of approximately 120°C or higher (more preferably 135°C or higher, for example 145°C or higher) can be used. The upper limit of the softening point of the tackifier resin is not particularly limited. In terms of adhesive strength, etc., in some embodiments, a tackifier resin having a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower, even more preferably less than 160°C, for example 155°C or lower or 150°C or lower) can be preferably used. The softening point of the tackifier resin can be measured based on the softening point test method (ring and ball method) specified in JIS K2207.

Although not particularly limited, tackifier resins with an acid value limited to a predetermined value or less are preferably used. Tackifier resins with low acid values are preferred because they do not inhibit the crosslinking reaction during adhesive formation. Furthermore, adhesives containing tackifier resins with acid values limited to a predetermined value or less tend to have excellent durability. From this perspective, the acid value of the tackifier resin is preferably approximately 20 mgKOH/g or less, preferably less than 10 mgKOH/g, more preferably less than 7 mgKOH/g, and even more preferably less than 4 mgKOH/g (e.g., 0 to 4 mgKOH/g), and may even be less than 3 mgKOH/g (e.g., less than 1 mgKOH/g). The acid value of the tackifier resin can be measured by potentiometric titration as specified in JIS K 0070:1992.

The amount of tackifier resin can be, for example, greater than 0 parts by weight per 100 parts by weight of polyester polymer, or may be approximately 3 parts by weight or more (e.g., approximately 5 parts by weight or more). In some preferred embodiments, the amount of tackifier resin per 100 parts by weight of polyester polymer is approximately 10 parts by weight or more, more preferably approximately 20 parts by weight or more, even more preferably approximately 30 parts by weight or more, and particularly preferably approximately 35 parts by weight or more. The greater the amount of tackifier resin used, the more likely it is that excellent adhesive strength will be obtained. There is no particular upper limit to the amount of tackifier resin. From the viewpoint of compatibility with the polyester polymer and adhesiveness, in some embodiments, the amount of tackifier resin per 100 parts by weight of polyester polymer is typically approximately 120 parts by weight or less, preferably less than 80 parts by weight, and more preferably approximately 70 parts by weight or less (e.g., approximately 50 parts by weight or less). For example, it is effective to use a tackifier resin in the amount described above for a polyester polymer having a Tg of 0°C or less.

(Crosslinking agent)
The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer preferably contains a crosslinking agent as an optional component. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a partially crosslinked form, or an intermediate or composite form thereof. The crosslinking agent is usually contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction. Note that the crosslinking agent used to crosslink the polyester polymer may also function as a chain extender.

There are no particular restrictions on the type of crosslinking agent, and any suitable crosslinking agent may be selected from conventionally known crosslinking agents. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents may be used alone or in combination of two or more. Of these, isocyanate-based crosslinking agents are preferred.

As an isocyanate-based crosslinking agent, a polyfunctional isocyanate-based compound (a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. Isocyanate-based crosslinking agents can be used alone or in combination of two or more.

Examples of polyfunctional isocyanate compounds include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and aromatic polyisocyanate compounds.
Specific examples of the aliphatic polyisocyanate compound include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

Specific examples of alicyclic polyisocyanate compounds include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

Specific examples of aromatic polyisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. , 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, and the like.

Examples of polyfunctional isocyanates include polyfunctional isocyanate compounds having an average of two or more isocyanate groups per molecule. Such polyfunctional isocyanate compounds may be multimers (e.g., dimers or trimers) of bifunctional or trifunctional or higher isocyanates, derivatives (e.g., addition reaction products of polyhydric alcohols with two or more molecules of polyfunctional isocyanates), polymers, etc. Examples of polyfunctional isocyanate compounds include dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts with isocyanurate structures), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and the like. Commercially available products of such polyfunctional isocyanate compounds include those manufactured by Asahi Kasei Chemicals Corporation under the trade names "Duranate TPA-100" and "Duranate D101," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

A crosslinking agent that does not contain an aromatic ring is preferably used. For example, among the isocyanate-based crosslinking agents mentioned above, it is preferable to use an isocyanate-based compound that does not contain an aromatic ring. By using an isocyanate-based compound that does not contain an aromatic ring as a crosslinking agent, the degree of crosslinking can be effectively increased with little crosslinking inhibition in a pressure-sensitive adhesive composition containing a polyester-based polymer and a tackifying resin. Typical examples of the above-mentioned isocyanates that do not contain an aromatic ring include aliphatic isocyanate compounds. A particularly preferred embodiment is one in which both the polyester-based polymer and the tackifying resin have aromatic rings and an isocyanate-based compound that does not contain an aromatic ring (typically an aliphatic isocyanate compound) is used as the crosslinking agent.

In some embodiments, it is preferable to use two or more crosslinking agents (preferably isocyanate-based crosslinking agents) with different numbers of functional groups. Using two or more crosslinking agents with different numbers of functional groups makes it easier to achieve a good balance of multiple properties (e.g., high-temperature holding power, repulsion resistance, etc.). The "functional group" refers to a crosslinking reactive group, such as an isocyanate group in the polyfunctional isocyanate compound described above. In some preferred embodiments, one or more bifunctional crosslinking agents are used in combination with one or more trifunctional or higher crosslinking agents (e.g., trifunctional crosslinking agents). The combined use of a bifunctional crosslinking agent and a trifunctional or higher crosslinking agent facilitates the production of an adhesive with excellent repulsion resistance, achieving both high-temperature holding power and repulsion resistance. The bifunctional crosslinking agent primarily functions as a chain extender, extending the chain length of the polyester polymer during curing of the adhesive composition, thereby contributing to improved repulsion resistance. Meanwhile, the use of a trifunctional or higher crosslinking agent is believed to enhance the cohesive strength of the adhesive and achieve high-temperature holding power. The technology disclosed herein is not limited to the above interpretation. As the bifunctional crosslinking agent and trifunctional or higher functional crosslinking agent, any bifunctional or trifunctional or higher functional crosslinking agent can be used from among the various crosslinking agents described above without any particular limitation. In some preferred embodiments, an isocyanate compound is preferably used as the bifunctional or trifunctional or higher functional crosslinking agent.

In embodiments where a bifunctional crosslinking agent is used as the crosslinking agent, the amount of bifunctional crosslinking agent used is not particularly limited. For example, from the perspective of obtaining the desired effect of the bifunctional crosslinking agent, the amount of bifunctional crosslinking agent used per 100 parts by weight of polyester-based polymer is appropriately approximately 0.01 parts by weight or more, preferably approximately 0.1 parts by weight or more, more preferably approximately 0.5 parts by weight or more, even more preferably approximately 0.8 parts by weight or more, and may be approximately 1.5 parts by weight or more, or even approximately 3 parts by weight or more. Furthermore, the amount of bifunctional crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 10 parts by weight or less, preferably approximately 7 parts by weight or less, and may be 4 parts by weight or less.

In embodiments using a trifunctional or higher crosslinking agent as the crosslinking agent, the amount of trifunctional or higher crosslinking agent used is not particularly limited. For example, to obtain the desired effect of the trifunctional or higher crosslinking agent, the amount of trifunctional or higher crosslinking agent used per 100 parts by weight of polyester-based polymer is approximately 0.01 parts by weight or more, preferably approximately 0.1 parts by weight or more, more preferably approximately 0.5 parts by weight or more, even more preferably approximately 1 part by weight or more, and particularly preferably approximately 2 parts by weight or more (e.g., approximately 2.5 parts by weight or more). Using an appropriate amount of trifunctional or higher crosslinking agent increases cohesive strength and facilitates the achievement of excellent properties (adhesion strength, high-temperature retention, etc.). Furthermore, the amount of trifunctional or higher crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 8 parts by weight or less, preferably approximately 5 parts by weight or less, and may be 4 parts by weight or less.

In embodiments in which a bifunctional crosslinking agent and a trifunctional or higher functional crosslinking agent are used in combination, the ratio of the bifunctional crosslinking agent to the trifunctional or higher functional crosslinking agent is appropriately set so as to achieve a good balance of the desired adhesive properties (adhesive strength, high-temperature holding power, repulsion resistance, etc.), and is not limited to a specific range. The ratio ( _CB / _{CA )} of the amount of trifunctional or higher functional crosslinking agent _CB to the amount of bifunctional crosslinking agent CA is, for example, 0.1 or more, and from the viewpoint of improving cohesive strength, it is appropriate to be 0.3 or more, preferably 0.5 or more, more preferably 0.8 or more, and may be 1.5 or more, or may be 2 or more. Furthermore, the ratio ( _CB / _CA ) is, for example, 10 or less, and from the viewpoint of improving repulsion resistance, it is preferably 7 or less, more preferably 5 or less, and may be 4 or less, 2.5 or less, or 1.5 or less.

The amount of crosslinking agent used is not particularly limited. For example, the amount of crosslinking agent used per 100 parts by weight of polyester-based polymer can be approximately 0.005 parts by weight or more (e.g., 0.01 parts by weight or more, typically 0.1 parts by weight or more). From the perspective of improving cohesive strength, the amount of crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 0.5 parts by weight or more, preferably approximately 1 part by weight or more, more preferably approximately 2 parts by weight or more (e.g., more than 2 parts by weight), and even more preferably 2.5 parts by weight or more. Furthermore, the amount of crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 12 parts by weight or less, for example, approximately 10 parts by weight or less, preferably approximately 8 parts by weight or less, and preferably approximately 5 parts by weight or less. According to the technology disclosed herein, cohesive strength that exhibits favorable high-temperature retention can be obtained with the amount of crosslinking agent used limited as described above. The amount of crosslinking agent used per 100 parts by weight of polyester-based polymer is more preferably 4 parts by weight or less, and even more preferably approximately 3.5 parts by weight or less.

In embodiments using an isocyanate-based crosslinking agent, the amount used is not particularly limited. The amount of isocyanate-based crosslinking agent used can be, for example, approximately 0.5 parts by weight or more and approximately 10 parts by weight or less per 100 parts by weight of polyester-based polymer. From the perspective of improving cohesive strength, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 1 part by weight or more, preferably approximately 2 parts by weight or more (e.g., more than 2 parts by weight), more preferably approximately 2.5 parts by weight or more, even more preferably 2.8 parts by weight or more, and may be approximately 3.5 parts by weight or more, approximately 4.0 parts by weight or more, or even 4.5 parts by weight or more. Furthermore, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polyester-based polymer is typically approximately 8 parts by weight or less, preferably approximately 5 parts by weight or less. According to the technology disclosed herein, cohesive strength sufficient to exhibit favorable high-temperature retention can be obtained with the amount of isocyanate-based crosslinking agent limited as described above. The amount of isocyanate-based crosslinking agent used per 100 parts by weight of polyester-based polymer is more preferably 4.5 parts by weight or less, even more preferably approximately 4.2 parts by weight or less, particularly preferably 3.8 parts by weight or less (e.g., 3.5 parts by weight or less), and may be approximately 3.2 parts by weight or less.

(Crosslinking catalyst)
In the technology disclosed herein, in order to more effectively promote the crosslinking reaction, it is preferable to use a crosslinking catalyst in addition to the crosslinking agent. Examples of the crosslinking catalyst include zirconium-containing compounds (zirconium-based catalysts) such as zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, and zirconium octylate compounds; tin (Sn)-containing compounds (tin-based catalysts) such as dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, and butyltin oxide; aluminum sec-butoxide, aluminum sec-butoxide, and the like. Examples of the organometallic catalyst include aluminum-containing compounds (aluminum-based catalysts) such as aluminum trisacetylacetonate, aluminum bisethylacetoacetate, and aluminum trisethylacetoacetate; iron-containing compounds (iron-based catalysts) such as ferric naphthem; and titanium-containing compounds (titanium-based catalysts) such as tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, and titanium ethylacetoacetate. The crosslinking catalysts can be used alone or in combination of two or more.

In some preferred embodiments, from the standpoint of environmental impact and safety, the crosslinking catalyst does not contain a tin-containing compound. By using a non-tin-based compound as the crosslinking catalyst, the amount of tin-based compounds (typically organotin compounds) used in the adhesive can be reduced. The adhesive composition disclosed herein can efficiently form a good crosslinked structure that can achieve both adhesive strength and high-temperature retention without using a tin-based crosslinking catalyst, which generally tends to have excellent reaction speed. Furthermore, in some embodiments, the crosslinking catalyst does not contain an iron-based catalyst. For example, in use cases where the adhesive requires transparency and optical properties, it is desirable to avoid the use of iron-based compounds, which may discolor the adhesive.

There are no particular restrictions on the amount of crosslinking catalyst used. The amount of crosslinking catalyst used can be, for example, approximately 0.001 parts by weight or more, suitably approximately 0.01 parts by weight or more, and may be approximately 0.05 parts by weight or more (e.g., 0.10 parts by weight or more), per 100 parts by weight of polyester-based polymer. Furthermore, the amount of crosslinking catalyst used can be, for example, approximately 3 parts by weight or less, suitably approximately 1 part by weight or less, and may be approximately 0.3 parts by weight or less, per 100 parts by weight of polyester-based polymer.

(hydrolysis stabilizer)
The adhesive composition disclosed herein may also contain a hydrolysis stabilizer (also referred to as a hydrolysis inhibitor). Addition of a hydrolysis stabilizer inhibits hydrolysis reactions in the adhesive, making it easier to achieve good durability. The hydrolysis stabilizer is not particularly limited, and known or commonly used hydrolysis stabilizers can be used. Examples include oxazoline group-containing compounds, epoxy group-containing compounds, and carbodiimide group-containing compounds. Of these, carbodiimide group-containing compounds are preferred. One hydrolysis stabilizer can be used alone, or two or more can be used in combination.

Carbodiimide group-containing compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, and monofunctional cyclic carbodiimides. Here, a monofunctional cyclic carbodiimide refers to a compound having one carbodiimide group within its molecular structure, in which the first and second nitrogen atoms of the carbodiimide group are bonded by a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof. The linking group may contain a heteroatom or a substituent. Suitable examples of carbodiimide group-containing compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, and monofunctional cyclic carbodiimides.

The amount of hydrolysis stabilizer (preferably a carbodiimide group-containing compound) used is not particularly limited, but to ensure that the effects of the hydrolysis stabilizer are optimally manifested, it is appropriate to use an amount of approximately 0.05 parts by weight or more per 100 parts by weight of polyester polymer, preferably approximately 0.1 parts by weight or more, for example, approximately 0.3 parts by weight or more. The upper limit of the amount of hydrolysis stabilizer used is, for example, approximately 5 parts by weight or less per 100 parts by weight of polyester polymer, preferably approximately 3 parts by weight or less, for example, 1 part by weight or less.

(Other additives)
In addition to the above-mentioned components, the pressure-sensitive adhesive composition may contain, as necessary, various additives commonly used in the field of pressure-sensitive adhesives, such as leveling agents, fillers, plasticizers, softeners, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, etc. As for the above-mentioned various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed description thereof will be omitted.

(Adhesive composition)
The adhesive layer (layer made of adhesive) disclosed herein is formed from an adhesive composition containing the above-mentioned polyester polymer and tackifier resin. From the viewpoint of adhesive properties, etc., a solvent-based adhesive composition containing an adhesive in an organic solvent is preferred. As the organic solvent, organic solvents such as toluene and ethyl acetate can be used.

As described above, this specification provides a pressure-sensitive adhesive composition containing one or more of the components that can be contained in the pressure-sensitive adhesive layer disclosed herein. Specifically, the pressure-sensitive adhesive composition contains a polyester polymer in which 50% or more of the constituent carbon is biomass-derived carbon and has an Mw of 30,000 or more, and may further contain a tackifying resin. Such a pressure-sensitive adhesive composition can reduce dependence on fossil resource-derived materials and form a pressure-sensitive adhesive that combines adhesive strength and high-temperature retention. The pressure-sensitive adhesive composition may further contain components such as a crosslinking agent, a crosslinking catalyst, and a hydrolysis stabilizer. Details of the components that can be contained in the pressure-sensitive adhesive composition are as described for the pressure-sensitive adhesive layer, so repeated explanation will be omitted.

(Formation of Pressure-Sensitive Adhesive Layer)
A pressure-sensitive adhesive layer can be formed from a pressure-sensitive adhesive composition by a conventionally known method. For example, in the case of a substrate-less double-sided pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition can be applied to a surface (release surface) having releasability, and then the pressure-sensitive adhesive composition is cured to form a pressure-sensitive adhesive layer on the surface, thereby forming a pressure-sensitive adhesive sheet. In the case of a pressure-sensitive adhesive sheet with a substrate, a method (direct method) in which a pressure-sensitive adhesive composition is directly applied (typically coated) to the substrate and cured to form a pressure-sensitive adhesive layer can be preferably employed. Alternatively, a method (transfer method) in which a pressure-sensitive adhesive composition is applied to a surface (release surface) having releasability and cured to form a pressure-sensitive adhesive layer on the surface, and then the pressure-sensitive adhesive layer is transferred to the substrate may also be employed. The release surface may be the surface of a release liner, the back surface of a release-treated substrate, or the like. The pressure-sensitive adhesive composition can be cured by subjecting the pressure-sensitive adhesive composition to a curing treatment such as drying, crosslinking, polymerization, or cooling. Two or more curing treatments may be performed simultaneously or in stages. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be a pressure-sensitive adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

The pressure-sensitive adhesive composition can be applied using a known or commonly used coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a die coater, a bar coater, a knife coater, a spray coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation, curtain coating, or the like.
The pressure-sensitive adhesive composition can be dried at room temperature or under heating. From the viewpoints of promoting the crosslinking reaction and improving production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150°C, and is usually preferably about 40 to 130°C. After drying the pressure-sensitive adhesive composition, it is preferable to further perform aging for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist in the substrate or pressure-sensitive adhesive layer. The aging conditions are not particularly limited, and can be, for example, about 70°C or less (typically about 40 to 70°C) for one day or more (e.g., three days or more).

(Adhesive layer thickness)
In the pressure-sensitive adhesive sheet disclosed herein, the thickness of the pressure-sensitive adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. Considering the balance between adhesion to the adherend and high-temperature retention, the thickness of the pressure-sensitive adhesive layer can be, for example, approximately 2 μm to 500 μm. From the viewpoint of adhesion to the adherend, the thickness of the pressure-sensitive adhesive layer is typically 3 μm or more, preferably 5 μm or more. From the viewpoint of easily realizing a pressure-sensitive adhesive sheet that exhibits higher high-temperature retention, in some embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 8 μm or more, preferably 12 μm or more, 15 μm or more, or even 18 μm or more. Furthermore, from the viewpoint of reducing the thickness of the pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer may be, for example, 200 μm or less, 150 μm or less, 100 μm or less, 70 μm or less, 50 μm or less, or 30 μm or less. In embodiments where greater emphasis is placed on thinning, the thickness of the pressure-sensitive adhesive layer may be, for example, 25 μm or less, or 22 μm or less. When the PSA sheet disclosed herein is a double-sided PSA sheet having PSA layers on both sides of a substrate, the thicknesses of the PSA layers may be the same or different.

(Bio content of adhesive layer)
The technology disclosed herein is implemented using a PSA containing a polyester polymer with a bio-content of 50% or more, and therefore the PSA layer (and the PSA composition; the same applies hereinafter unless otherwise specified) has a bio-content of a predetermined value or more. While not particularly limited, the bio-content of the PSA layer may be approximately 30% or more (e.g., more than 30%), suitably approximately 40% or more, and preferably 50% or more. A high bio-content of the PSA layer means that the amount of fossil resource-based materials, such as petroleum, used is reduced. By designing the PSA layer to have a high bio-content, the PSA layer's overall dependence on fossil resource-based materials can be reduced. For example, the bio-content of the PSA layer may be 55% or more, 60% or more, 70% or more, or 75% or more. While the upper limit of the bio-content is 100% by definition, the PSA layer disclosed herein may typically have a bio-content of less than 100% because its components may contain materials derived from fossil resources. In order to facilitate obtaining performance (e.g., high-temperature retention) suitable for use in portable electronic devices, in some embodiments, the bio-ratio of the adhesive layer may be, for example, less than 90%, or, when adhesive performance is more important, less than 80% or less than 70%.

The bio content of the adhesive layer, i.e., the proportion of biomass-derived carbon in the total carbon contained in the adhesive layer, can be estimated from the carbon isotope content with mass number 14 measured in accordance with ASTM D6866. The bio content of the substrate and the bio content of the adhesive sheet, described below, can also be estimated using a similar method.

<Base material>
The PSA sheet disclosed herein may be in the form of a substrate-attached PSA sheet having a PSA layer on one or both sides of the substrate. Various sheet-like substrates can be used as the substrate, such as resin films, paper, cloth, rubber sheets, foam sheets, metal foils, and composites thereof. In the field of electronic devices, substrates that are less likely to generate dust (e.g., fine fibers or particles such as paper dust) are preferably used. From this perspective, substrates that do not contain fibrous materials such as paper or cloth are preferred, and for example, resin films, rubber sheets, foam sheets, metal foils, and composites thereof can be preferably used.

Examples of resin films include polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate; vinyl chloride resin films; polyolefin films such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; vinylidene chloride resin films; vinyl acetate resin films; polystyrene films; polyacetal films; polyimide films; polyamide films; fluororesin films; cellophane; etc. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polyolefin sheets. Examples of metal foils include aluminum foil and copper foil.

Resin films are suitable for use as the substrate. Resin films are preferred as they offer excellent dimensional stability, thickness accuracy, economy (cost), processability, and tensile strength. Furthermore, resin films (e.g., polyester films such as PET film, described below) are recyclable. Therefore, regardless of whether plant-derived materials are used, reusing used resin films allows for sustainable reproduction and reduces environmental impact. Such recyclable or recycled resin films are also referred to as recycled films. The recyclability of such resin films can also be applied to resin films used in the release liners described above. In this specification, "resin film" typically refers to a non-porous film, a concept distinct from so-called nonwoven fabrics or woven fabrics.

In some embodiments, a polyester film may be preferably used as the substrate from the viewpoints of strength and processability. The polyester resin constituting the polyester film is typically a polyester resin containing, as its main component, a polyester obtained by polycondensation of a dicarboxylic acid and a diol.

Examples of dicarboxylic acids that constitute the polyester include phthalic acid, isophthalic acid, terephthalic acid, 2-methylterephthalic acid, 5-sulfoisophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylketonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. aromatic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc.; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc.; aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanoic acid, etc.; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, etc.; derivatives thereof (for example, lower alkyl esters of the above dicarboxylic acids such as terephthalic acid, etc.); etc. These can be used alone or in combination of two or more.

Examples of diols constituting the polyester include aliphatic diols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, and polyoxytetramethylene glycol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; and aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These can be used alone or in combination of two or more. From the standpoint of transparency, etc., aliphatic diols are preferred, and ethylene glycol is particularly preferred. The proportion of the aliphatic diol (preferably ethylene glycol) in the diol constituting the polyester is preferably 50% by weight or more (e.g., 80% by weight or more, typically 95% by weight or more). The diol may be composed essentially of ethylene glycol alone. As the ethylene glycol, biomass-derived ethylene glycol (typically, biomass ethylene glycol obtained using biomass ethanol as a raw material) can be preferably used. For example, the proportion of biomass-derived ethylene glycol in the ethylene glycol constituting the polyester may be, for example, 50% by weight or more, preferably 75% by weight or more, or may be 90% by weight or more, or may be 95% by weight or more. Substantially all of the ethylene glycol may be biomass-derived ethylene glycol.

Examples of polyester resin films include polyethylene terephthalate (PET) film, polybutylene terephthalate (PBT) film, polyethylene naphthalate (PEN) film, polybutylene naphthalate film, etc.

When the substrate disclosed herein is a polyester film substrate, the polyester film substrate may contain, in addition to polyester, a polymer other than the above-mentioned polyester. Suitable examples of the polymer other than polyester include those polymer materials other than polyesters among the various polymer materials exemplified as resin films that can constitute the substrate. When the polyester film substrate disclosed herein contains, in addition to polyester, a polymer other than the above-mentioned polyester, the content of the polymer other than polyester is suitably less than 100 parts by weight per 100 parts by weight of polyester, preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less. The content of the polymer other than polyester may be 5 parts by weight or less, or even 1 part by weight or less, per 100 parts by weight of polyester. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which 99.5 to 100% by weight of the polyester film substrate is polyester.

In some other embodiments, a polyolefin film may be preferably used as the substrate from the viewpoint of strength and flexibility. A polyolefin film is a film whose main component is a polymer in which an α-olefin is the main monomer (the main component among the monomer components). The proportion of the polymer is usually 50% by weight or more (e.g., 80% by weight or more, typically 90 to 100% by weight). Specific examples of polyolefins include those in which ethylene is the main monomer (polyethylene) and those in which propylene is the main monomer (polypropylene). The polyethylene may be a homopolymer of ethylene, a copolymer of ethylene and another olefin (e.g., one or more α-olefins having 3 to 10 carbon atoms), or a copolymer of ethylene and a monomer other than an olefin (e.g., one or more ethylenically unsaturated monomers selected from vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, etc.). The polypropylene may be a homopolymer of propylene, a copolymer of propylene and another olefin (for example, one or more α-olefins having 2, 4 to 10 carbon atoms), or a copolymer of propylene and a monomer other than an olefin. The substrate disclosed herein may contain only one of the above polyolefins, or may contain two or more polyolefins.

When the substrate disclosed herein is a polyolefin film substrate, the polyolefin film substrate may contain, in addition to a polyolefin, a polymer other than the above-mentioned polyolefin. Suitable examples of the polymer other than the above-mentioned polyolefin include those polymer materials other than polyolefins among the various polymer materials exemplified as resin films that can constitute the substrate. When the polyolefin film substrate disclosed herein contains, in addition to a polyolefin, a polymer other than the above-mentioned polyolefin, the content of the polymer other than the above-mentioned polyolefin is suitably less than 100 parts by weight per 100 parts by weight of polyolefin, preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less. The content of the polymer other than polyolefin may be 5 parts by weight or less, or even 1 part by weight or less, per 100 parts by weight of polyolefin. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which 99.5 to 100% by weight of the polyolefin film substrate is polyolefin.

The substrate disclosed herein preferably contains a biomass material from the perspective of reducing the amount of fossil resource-based materials used. Biomass materials that can constitute the substrate are not particularly limited, but examples include biomass polyesters such as biomass PET and biomass polytrimethylene terephthalate (biomass PTT); polylactic acid; biomass polyethylenes such as biomass high-density polyethylene (biomass HDPE), biomass low-density polyethylene (biomass LDPE), and biomass linear low-density polyethylene (biomass LLDPE); biomass polyolefins such as biomass poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); biomass polyamides such as polyhexamethylene sebacamide and poly(xylylene sebacamide); biomass polyurethanes such as biomass polyester ether urethane and biomass polyether urethane; cellulose-based resins; and the like. These can be used alone or in combination of two or more. Among these, biomass PET and biomass PTT are preferred, with biomass HDPE, biomass LDPE, biomass LLDPE, biomass PP, and biomass PET being particularly preferred. Since the above biomass materials are resin materials, they can be preferably applied to configurations in which the substrate is a resin film. By using the above biomass materials, the amount of fossil resource-based materials used can be reduced in PSA sheets with a resin film (preferably a polyolefin film) as the substrate.

In PSA sheets having a substrate, the bio content of the substrate is preferably 20% or more, and more preferably 35% or more. When greater emphasis is placed on reducing the amount of fossil resource-based materials used, the bio content of the substrate may be, for example, 50% or more, 70% or more, 85% or more, or 90% or more. The upper limit of the bio content is 100% or less, but in some embodiments, taking into account processability, strength, etc., the bio content of the substrate may be, for example, 80% or less, 60% or less, 40% or less, or less than 20%.

The substrate may be transparent, or may have light-blocking or light-reducing properties. In some embodiments, a colorant may be incorporated into the substrate (e.g., a resin film). This allows the light transmittance (light-blocking properties) of the substrate to be adjusted. Adjusting the light transmittance (e.g., perpendicular light transmittance) of the substrate can also be useful for adjusting the light transmittance of the substrate and, further, the light transmittance of a pressure-sensitive adhesive sheet containing the substrate.

As with the colorants that can be contained in the adhesive layer, conventionally known pigments and dyes can be used as colorants. There are no particular restrictions on the colorant, and it can be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearlescent, etc.

The substrate may be colored by a colored layer disposed on the surface of a base film (preferably a resin film). In a substrate having such a configuration including a base film and a colored layer, the base film may or may not contain a colorant. The colored layer may be disposed on either one surface of the base film, or on both surfaces. In a configuration in which colored layers are disposed on both surfaces of the base film, the configurations of the colored layers may be the same or different. By disposing the colored layer, the color and transparency of the PSA sheet can be adjusted, allowing for desired design, light-blocking properties, and concealing properties to be achieved. The color of the colored layer is not particularly limited, and various colors can be adopted depending on the purpose. In some embodiments, the colored layer may be a black layer (e.g., a black printed layer) formed, for example, by black printing.

The colored layer can be formed, for example, by applying a colored layer-forming composition containing a colorant and a binder to the base film. Materials known in the fields of paint or printing can be used as the binder without particular limitations. Examples include polyurethane, phenolic resin, epoxy resin, urea melamine resin, and polymethyl methacrylate. The colored layer-forming composition can be, for example, solvent-based, UV-curable, or heat-curable. The colored layer can be formed using any method conventionally used to form colored layers, without particular limitations. For example, methods of forming a colored layer (printed layer) by printing, such as gravure printing, flexographic printing, or offset printing, are preferably used.

The colored layer may have a single-layer structure consisting of a single layer, or a multilayer structure containing two, three, or more sub-colored layers. A multilayer colored layer containing two or more sub-colored layers can be formed, for example, by repeatedly applying (e.g., printing) a colored layer-forming composition. The color and amount of colorant contained in each sub-colored layer may be the same or different. For colored layers intended to impart light-blocking properties, a multilayer structure is particularly useful from the perspective of preventing the occurrence of pinholes and increasing the reliability of preventing light leakage.

The colorant used to color the colored layer can be appropriately selected from known pigments and dyes depending on the desired color. Examples of white pigments include, but are not limited to, titanium dioxide, zinc oxide, and white lead. Examples of black pigments include carbon black, acetylene black, pine soot, and graphite. These can be used alone or in combination of two or more.

The content of the colorant is not limited to a specific range, as it is set depending on the required color, light transmittance, etc., but it is appropriate for it to be approximately 1% by weight or more in the colored layer, preferably 2% by weight or more (e.g., 5% by weight or more), and may be 15% by weight or more. Furthermore, it is appropriate for the content of the colorant to be approximately 65% by weight or less, preferably 30% by weight or less (e.g., 15% by weight or less), and may be 8% by weight or less.

The overall thickness of the color layer is typically 0.1 μm or more, preferably 0.5 μm or more, and more preferably 0.7 μm or more. The overall thickness of the color layer may be approximately 0.8 μm or more, or may be approximately 1 μm or more. In some other embodiments, to obtain sufficient light-blocking properties, the overall thickness of the color layer may be 2 μm or more (e.g., 3 μm or more), or even 4 μm or more. Furthermore, the overall thickness of the color layer is typically 10 μm or less, preferably 7 μm or less, and more preferably 5 μm or less. In some embodiments, the overall thickness of the color layer can be approximately 3 μm or less, or even approximately 2 μm or less. In a color layer including two or more sub-color layers, the thickness of each sub-color layer is typically preferably about 0.5 μm to 2 μm.

The surface of the substrate (e.g., a resin film, rubber sheet, foam sheet, etc.) on which the adhesive layer is to be disposed (the surface facing the adhesive layer) may be subjected to a known or conventional surface treatment, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the formation of a primer layer. Such a surface treatment may be intended to improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the substrate. Alternatively, the substrate may not be subjected to a surface treatment that improves anchoring ability on the surface facing the adhesive layer. When a primer layer is formed, the primer (primer) used for the formation is not particularly limited and can be appropriately selected from known primers. The thickness of the primer layer is not particularly limited and can be, for example, greater than 0.01 μm. It is usually appropriate to set it to 0.1 μm or greater, and it may be 0.2 μm or greater to enhance its effectiveness. The thickness of the primer layer is preferably less than 1.0 μm, and may be 0.7 μm or less, or 0.5 μm or less. Generally, primers are highly dependent on fossil resource-derived materials, so not having an undercoat layer that is too thick can be advantageous from the perspective of reducing the bio-ratio of the PSA sheet, as described below.

In the case of a single-sided PSA sheet in which a PSA layer is provided on one side of a substrate, the side of the substrate on which the PSA layer is not formed (the back surface) may be treated with a release agent (back surface treatment agent). The back surface treatment agent that can be used to form the back surface treatment layer is not particularly limited, and silicone-based back surface treatment agents, fluorine-based back surface treatment agents, long-chain alkyl back surface treatment agents, and other known or commonly used treatment agents can be used depending on the purpose and application. Back surface treatment agents can be used alone or in combination of two or more.

The substrate (e.g., a resin film substrate) may contain various additives, such as fillers (inorganic fillers, organic fillers, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, and colorants (pigments, dyes, etc.), as needed. The blending ratio of the various additives is usually about 30% by weight or less (e.g., 20% by weight or less, typically 10% by weight or less). For example, if the substrate contains a pigment (e.g., a white pigment), the blending ratio should be about 0.1 to 10% by weight (e.g., 1 to 8% by weight, typically 1 to 5% by weight).

The thickness of the substrate is not particularly limited and can be selected appropriately depending on the purpose, but is generally approximately 1 μm to 500 μm. From the perspective of substrate handleability, the thickness of the substrate may be, for example, 1.5 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, or 4.5 μm or more. Furthermore, from the perspective of reducing the thickness of the PSA sheet, in some embodiments, the thickness of the substrate may be, for example, 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, 20 μm or less, 10 μm or less, 7 μm or less, less than 5 μm, or less than 4 μm.

<Adhesive sheet>
The thickness (total thickness) of the PSA sheet disclosed herein (which includes a PSA layer, and in a substrate-attached PSA sheet, further includes a substrate but does not include a release liner) is not particularly limited and can be, for example, in the range of approximately 2 μm to 1000 μm. In some embodiments, the thickness of the PSA sheet is preferably about 5 μm to 500 μm (e.g., 10 μm to 300 μm, typically 15 μm to 200 μm), taking into consideration adhesive properties and the like. Alternatively, in some embodiments where thinning is important, the thickness of the PSA sheet may be 100 μm or less (e.g., 5 μm to 100 μm), 70 μm or less (e.g., 5 μm to 70 μm), 45 μm or less (e.g., 5 μm to 45 μm), or 30 μm or less (e.g., 5 μm to 30 μm).

In the PSA sheet disclosed herein, it is preferable that approximately 30% or more (e.g., more than 30%) of the total carbon contained in the PSA sheet is biomass-derived carbon. That is, it is preferable that the PSA sheet has a biomass-derived content of 30% or more. By using a PSA sheet with such a high biomass-derived content, the amount of fossil resource-derived materials used can be reduced. From this perspective, it can be said that the higher the biomass-derived content of the PSA sheet, the more preferable it is. The biomass-derived content of the PSA sheet is preferably 40% or more, and may be 50% or more, 60% or more, 70% or more, or even 75% or more. Although the upper limit of the biomass-derived content is 100% by definition, using all of the materials constituting the PSA sheet from plants may not be efficient in terms of productivity, performance, etc., so the biomass-derived content of the PSA sheet may be less than 100%. From the viewpoint of easily obtaining performance suitable for portable electronic device applications (e.g., high-temperature retention), in some embodiments, the biomass-derived content of the PSA sheet may be, for example, 90% or less. When adhesive performance is more important, the biomass-derived content may be 80% or less, or even 70% or less.
In a substrate-less pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer, the bio content of the pressure-sensitive adhesive layer and the bio content of the entire pressure-sensitive adhesive sheet are the same.

In some embodiments, the PSA sheet preferably has a 180-degree peel strength (adhesion strength to SUS) against a stainless steel plate of 10 N/20 mm or more. Because PSA sheets exhibiting these characteristics firmly bond to the adherend, they are typically preferred for use in applications where re-peeling is not intended. From the perspective of achieving a more reliable bond, the adhesive strength may be, for example, 11 N/20 mm or more, preferably 12 N/20 mm or more, 13 N/20 mm or more, 14 N/20 mm or more, or 15 N/20 mm or more. There is no particular upper limit to the adhesive strength, and in some embodiments, the adhesive strength may be, for example, 50 N/20 mm or less, 30 N/20 mm or less, or 25 N/20 mm or less. The adhesive strength to SUS is specifically measured by the method described in the Examples below.

The adhesive sheet disclosed herein preferably has a holding power such that it does not fall within one hour of a holding power test conducted at 80°C under a 1 kg load for one hour. An adhesive sheet exhibiting such high-temperature holding power can also exhibit good holding performance at temperatures higher than room temperature (e.g., temperatures above 40°C). It is appropriate for the adhesive sheet to have a slippage distance of 5.0 mm or less (e.g., 3.0 mm or less) after the holding power test. From the perspective of exhibiting higher holding performance, the slippage distance is preferably less than 2.0 mm, more preferably less than 1.0 mm, even more preferably less than 0.5 mm, and particularly preferably less than 0.3 mm (e.g., 0.1 mm or less). The lower limit of the slippage distance is 0.0 mm, which means that no slippage is observed in the holding power test. The holding power test is specifically conducted using the method described in the Examples below.

The adhesive sheets disclosed herein may also have a passable level of repulsion resistance (i.e., no peeling) in the repulsion resistance test measured using a 125 μm thick PET film in the examples described below. Adhesive sheets with the above repulsion resistance are durable against bending, and can exhibit reliable adhesion without lifting or peeling, even when attached to curved surfaces such as three-dimensional shapes.

<Application>
The applications of the PSA sheets disclosed herein are not particularly limited, and they can be used for a variety of applications without limitation. For example, the PSA sheets can be attached to components constituting electronic devices, for example, for purposes such as fixing, joining, and reinforcing the components. The PSA sheets disclosed herein, for example, in the form of double-sided PSA sheets, can be preferably used for applications involving fixing or joining components. In such applications, it is particularly useful for the PSA sheets to exhibit good adhesive strength and holding power. The double-sided PSA sheets may be substrate-less or may have a substrate. From the perspective of thinning, in some embodiments, substrate-less double-sided PSA sheets or substrate-attached double-sided PSA sheets using a thin substrate can be preferably employed. As the thin substrate, a substrate having a thickness of 10 μm or less (e.g., less than 5 μm) can be preferably used.

The adhesive sheets disclosed herein are suitable for use in, for example, fixing components in portable electronic devices. Because the adhesive sheets disclosed herein have adhesive reliability that combines adhesive strength and high-temperature retention, they are suitable for use in portable electronic devices that require high performance. Because the interiors of portable electronic devices may contain heat-generating elements such as batteries, they may be exposed to temperatures of, for example, 40°C or higher, making the use of adhesive sheets with excellent high-temperature retention particularly beneficial. Non-limiting examples of the portable electronic device include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular devices, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as an accessory, earwear devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. The adhesive sheet disclosed herein can be preferably used, for example, for the purpose of fixing a pressure-sensitive sensor to other components within such portable electronic devices equipped with a pressure-sensitive sensor. In some preferred embodiments, the adhesive sheet can be used to fix a pressure-sensitive sensor and other members in an electronic device (typically a portable electronic device) that has a function that enables an absolute position to be specified on a plate (typically a touch panel) corresponding to the screen using a device for indicating a position on the screen (typically a pen-type or mouse-type device) and a device for detecting the position. In this specification, "portable" does not simply mean being portable, but rather means having a level of portability that allows an individual (a standard adult) to carry it relatively easily.

In addition, some preferred embodiments of the PSA sheet have good repulsion resistance, and because of this repulsion resistance, they exhibit excellent adhesive reliability even when bent, making them suitable for use in applications where they are attached to the curved surfaces of portable electronic devices with curved shapes, such as three-dimensional shapes (e.g., portable electronic devices equipped with curved displays). As mentioned above, the interiors of portable electronic devices can reach high temperatures, so it is particularly significant that the PSA sheet can exhibit adhesive reliability without lifting or peeling even in such high-temperature conditions.

Materials (adherend materials) to which the adhesive sheets disclosed herein can be attached include, but are not limited to, metal materials such as copper, iron, aluminum, and stainless steel; various resin materials (typically plastic materials); and inorganic materials such as glass. Examples of such resin materials include polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, polycarbonate resins, and liquid crystal polymers. The adhesive sheets disclosed herein are particularly suitable for bonding the above-mentioned metal materials, polyester resins such as PET, polyimide resins, aramid resins, polyphenylene sulfide resins, and polycarbonate resins. The above materials may be component materials for products such as portable electronic devices. The adhesive sheets disclosed herein may be attached to components made of the above-mentioned materials.

Figure 4 is a schematic example of a portable electronic device (smartphone) that uses the adhesive sheet disclosed herein. As shown in Figure 4, a battery (heat-generating element) 540 is built into the housing 520 of the portable electronic device 500. The portable electronic device 500 also includes an adhesive sheet 550. In this configuration example, the adhesive sheet 550 is in the form of a double-sided adhesive sheet (double-sided adhesive sheet) that secures the components that make up the portable electronic device 500. The portable electronic device 500 is equipped with a touch panel 570 whose display unit also functions as an input unit. The adhesive sheet disclosed herein is preferably used as a component (component joining means) for such portable electronic devices.

The matters disclosed by this specification include the following:
[1] A portable electronic device,
The device comprises a housing and a touch panel whose display unit also functions as an input unit,
A heat generating element (e.g., a battery) is built into the housing,
Among the many members constituting the portable electronic device, at least the first member and the second member are joined by an adhesive sheet,
the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon;
The pressure-sensitive adhesive layer further comprises a tackifying resin,
The weight average molecular weight of the polyester polymer is 30,000 or more.
[2] The portable electronic device according to [1] above, wherein the weight average molecular weight of the polyester-based polymer is greater than 60,000.
[3] The portable electronic device according to [1] or [2] above, wherein the glass transition temperature of the polyester polymer is 0° C. or lower.
[4] The portable electronic device according to any one of [1] to [3] above, wherein the polyester-based polymer contains an aromatic ring.
[5] The portable electronic device according to any one of [1] to [4] above, wherein the tackifier resin is selected from a terpene phenol resin and a polymerized rosin ester.
[6] The portable electronic device according to any one of [1] to [5] above, wherein the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring.
[7] The portable electronic device according to any one of [1] to [6], wherein the pressure-sensitive adhesive layer further contains a crosslinking agent, and the content of the crosslinking agent is 5 parts by weight or less relative to 100 parts by weight of the polyester-based polymer.
[8] The portable electronic device according to [7], wherein the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent as the crosslinking agent.
[9] The portable electronic device according to [8], wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound.
[10] The portable electronic device according to any one of [1] to [9] above, wherein the pressure-sensitive adhesive layer further contains a crosslinking agent and a crosslinking catalyst, and the crosslinking catalyst does not contain a tin-based compound.

[11] A pressure-sensitive adhesive composition comprising a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
further comprising a tackifying resin;
The pressure-sensitive adhesive composition, wherein the polyester polymer has a weight average molecular weight of 30,000 or more.
[12] The pressure-sensitive adhesive composition according to the above [11], wherein the weight-average molecular weight of the polyester polymer is greater than 60,000.
[13] The pressure-sensitive adhesive composition according to the above [11] or [12], wherein the glass transition temperature of the polyester polymer is 0°C or lower.
[14] The pressure-sensitive adhesive composition according to any one of the above [11] to [13], wherein the polyester polymer contains an aromatic ring.
[15] The pressure-sensitive adhesive composition according to any one of the above [11] to [14], wherein the tackifier resin is selected from a terpene phenol resin and a polymerized rosin ester.
[16] The pressure-sensitive adhesive composition according to any one of the above [11] to [15], wherein the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring.
[17] The pressure-sensitive adhesive composition according to any one of the above [11] to [16], further comprising a crosslinking agent, the content of the crosslinking agent being 5 parts by weight or less per 100 parts by weight of the polyester-based polymer.
[18] The pressure-sensitive adhesive composition according to the above [17], wherein the crosslinking agent is an isocyanate-based crosslinking agent.
[19] The pressure-sensitive adhesive composition according to the above [18], wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound.
[20] The pressure-sensitive adhesive composition according to any one of the above [11] to [19], further comprising a crosslinking agent and a crosslinking catalyst, wherein the crosslinking catalyst does not contain a tin-based compound.
[21] The pressure-sensitive adhesive composition according to any one of the above [11] to [20], wherein the weight-average molecular weight of the polyester polymer is greater than 100,000.
[22] The pressure-sensitive adhesive composition according to any one of [11] to [20] above, comprising a bifunctional crosslinking agent and a trifunctional or higher crosslinking agent as the crosslinking agent.

[31] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
The pressure-sensitive adhesive layer further comprises a tackifying resin,
The pressure-sensitive adhesive sheet, wherein the weight average molecular weight of the polyester polymer is 30,000 or more.
[32] The pressure-sensitive adhesive sheet according to [31] above, wherein the weight average molecular weight of the polyester polymer is greater than 60,000.
[33] The pressure-sensitive adhesive sheet according to the above [31] or [32], wherein the glass transition temperature of the polyester polymer is 0°C or lower.
[34] The pressure-sensitive adhesive sheet according to any one of [31] to [33] above, wherein the polyester polymer contains an aromatic ring.
[35] The pressure-sensitive adhesive sheet according to any one of [31] to [34] above, wherein the tackifier resin is selected from a terpene phenol resin and a polymerized rosin ester.
[36] The pressure-sensitive adhesive sheet according to any one of the above [31] to [35], wherein the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring.
[37] The pressure-sensitive adhesive sheet according to any one of [31] to [36] above, wherein the pressure-sensitive adhesive layer further contains a crosslinking agent, and the content of the crosslinking agent is 5 parts by weight or less relative to 100 parts by weight of the polyester-based polymer.
[38] The pressure-sensitive adhesive sheet according to the above [37], wherein the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent as the crosslinking agent.
[39] The pressure-sensitive adhesive sheet according to the above [38], wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound.
[40] The pressure-sensitive adhesive sheet according to any one of [31] to [39] above, wherein the pressure-sensitive adhesive layer further comprises a crosslinking agent and a crosslinking catalyst, and the crosslinking catalyst does not contain a tin-based compound.
[41] The pressure-sensitive adhesive sheet according to any one of [31] to [40] above, which has a 180-degree peel strength against a stainless steel plate of 10 N/20 mm or more and does not fall in a holding power test carried out under conditions of 80°C, a load of 1 kg, and 1 hour.
[42] The pressure-sensitive adhesive sheet according to any one of [31] to [41] above, wherein the weight average molecular weight of the polyester polymer is greater than 100,000.
[43] The pressure-sensitive adhesive sheet according to any one of [31] to [42] above, wherein the pressure-sensitive adhesive layer contains, as crosslinking agents, a bifunctional crosslinking agent and a trifunctional or higher crosslinking agent.

[51] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
An adhesive sheet that has a 180-degree peel strength of 10 N/20 mm or more against a stainless steel plate and does not fall off in a holding power test conducted under conditions of 80°C, 1 kg load, and 1 hour.
[52] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer further comprises a crosslinking agent and a crosslinking catalyst, and the crosslinking catalyst does not contain a tin-based compound.
[53] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
the pressure-sensitive adhesive layer further comprises a tackifying resin and a crosslinking agent,
A pressure-sensitive adhesive sheet, wherein the polyester polymer contains an aromatic ring, the tackifier resin also contains an aromatic ring, and the crosslinking agent does not contain an aromatic ring.
[54] The pressure-sensitive adhesive sheet according to any one of [51] to [53] above, wherein the weight average molecular weight of the polyester polymer is 30,000 or more.
[55] The pressure-sensitive adhesive sheet according to any one of [51] to [54] above, wherein the weight average molecular weight of the polyester polymer is greater than 60,000.
[56] The pressure-sensitive adhesive sheet according to any one of [51] to [55] above, wherein the glass transition temperature of the polyester polymer is 0°C or lower.
[57] The pressure-sensitive adhesive sheet according to any one of [51] to [56] above, wherein the polyester polymer contains an aromatic ring.
[58] The pressure-sensitive adhesive layer further contains a tackifying resin,
The pressure-sensitive adhesive sheet according to any one of [51] to [57] above, wherein the tackifier resin is selected from terpene phenol resins and polymerized rosin esters.
[59] The pressure-sensitive adhesive layer further contains a tackifying resin,
The pressure-sensitive adhesive sheet according to any one of [51] to [58] above, wherein the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring.
[60] The pressure-sensitive adhesive sheet according to any one of [51] to [59] above, wherein the pressure-sensitive adhesive layer further contains a crosslinking agent, and the content of the crosslinking agent is 5 parts by weight or less per 100 parts by weight of the polyester-based polymer.
[61] The pressure-sensitive adhesive sheet according to the above [60], wherein the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent as the crosslinking agent.
[62] The pressure-sensitive adhesive sheet according to the above [61], wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound.
[63] The pressure-sensitive adhesive sheet according to any one of [51] to [62] above, wherein the pressure-sensitive adhesive layer further comprises a crosslinking agent and a crosslinking catalyst, and the crosslinking catalyst does not contain a tin-based compound.
[64] The pressure-sensitive adhesive sheet according to any one of [51] to [63] above, which has a 180-degree peel strength against a stainless steel plate of 10 N/20 mm or more and does not fall in a holding power test carried out under conditions of 80°C, a load of 1 kg, and 1 hour.
[65] The pressure-sensitive adhesive sheet according to any one of [51] to [64] above, wherein the weight average molecular weight of the polyester polymer is greater than 100,000.
[66] The pressure-sensitive adhesive sheet according to any one of [51] to [65] above, wherein the pressure-sensitive adhesive layer contains, as crosslinking agents, a bifunctional crosslinking agent and a trifunctional or higher crosslinking agent.

[71] The pressure-sensitive adhesive sheet according to any one of [31] to [65] above, which is used in a portable electronic device.
[72] A portable electronic device comprising the pressure-sensitive adhesive sheet according to any one of [31] to [65] above.

[81] A pressure-sensitive adhesive composition comprising a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
A pressure-sensitive adhesive composition further comprising a crosslinking agent and a crosslinking catalyst, wherein the crosslinking catalyst does not contain a tin-based compound.
[82] A pressure-sensitive adhesive composition comprising a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
further comprising a tackifying resin and a crosslinker;
A pressure-sensitive adhesive composition, wherein the polyester polymer contains an aromatic ring, the tackifying resin also contains an aromatic ring, and the crosslinking agent does not contain an aromatic ring.
[83] The pressure-sensitive adhesive composition according to the above [81] or [82], wherein the weight-average molecular weight of the polyester polymer is 30,000 or more.
[84] The pressure-sensitive adhesive composition according to any one of the above [81] to [83], wherein the weight average molecular weight of the polyester polymer is greater than 60,000.
[85] The pressure-sensitive adhesive composition according to any one of the above [81] to [84], wherein the glass transition temperature of the polyester polymer is 0°C or lower.
[86] The pressure-sensitive adhesive composition according to any one of the above [81] to [85], wherein the polyester polymer contains an aromatic ring.
[87] The pressure-sensitive adhesive composition according to any one of the above [81] to [86], further comprising a tackifier resin, wherein the tackifier resin is selected from a terpene phenol resin and a polymerized rosin ester.
[88] Further comprising a tackifying resin,
The pressure-sensitive adhesive composition according to any one of the above [81] to [87], wherein the polyester polymer contains an aromatic ring, and the tackifier resin also contains an aromatic ring.
[89] The pressure-sensitive adhesive composition according to any one of the above [81] to [88], further comprising a crosslinking agent, the content of the crosslinking agent being 5 parts by weight or less per 100 parts by weight of the polyester polymer.
[90] The pressure-sensitive adhesive composition according to the above [89], wherein the crosslinking agent is an isocyanate-based crosslinking agent.
[91] The pressure-sensitive adhesive composition according to the above [90], wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound.
[91] The pressure-sensitive adhesive composition according to any one of the above [81] to [90], further comprising a crosslinking agent and a crosslinking catalyst, wherein the crosslinking catalyst does not contain a tin-based compound.
[92] The pressure-sensitive adhesive composition according to any one of the above [81] to [91], wherein the weight-average molecular weight of the polyester polymer is greater than 100,000.
[93] The pressure-sensitive adhesive composition according to any one of the above [81] to [92], comprising a bifunctional crosslinking agent and a trifunctional or higher crosslinking agent as the crosslinking agent.

The following describes several examples of the present invention, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Evaluation method>
[Adhesion strength to SUS]
The adhesive sheet is cut to a size of 20 mm wide and 150 mm long to prepare a measurement sample. In an environment of 23 ° C. and 50% RH, the adhesive surface of the measurement sample is exposed, and the adhesive surface is pressed against a stainless steel plate (SUS304BA plate) as an adherend by rolling a 2 kg rubber roller back and forth once. This is left in an environment of 23 ° C. and 50% RH for 30 minutes, and then, in the same environment, the peel strength (adhesion to SUS) [N/20 mm] is measured using a tensile tester in accordance with JIS Z0237:2000 at a peel angle of 180 degrees and a tensile speed of 300 mm/min. A universal tension-compression tester (apparatus name "Tension-Compression Tester, TCM-1kNB", manufactured by Minebea Co., Ltd.) can be used as the tensile tester.

[High temperature holding power]
The adhesive sheet is cut to a size of 10 mm wide and 100 mm long to prepare a measurement sample (test piece). In an environment of 23 ° C and 50% RH, the adhesive surface of the measurement sample is pressed against a Bakelite plate (phenolic resin plate) as an adherend, with a 2 kg roller moving back and forth once over an adhesion area of 10 mm wide and 20 mm long. The adherend to which the test piece is attached in this manner is suspended in an environment at 80 ° C with the length direction of the test piece vertical and left for 30 minutes. Next, a load of 1 kg is applied to the free end of the test piece, and in accordance with JIS Z0237, the test piece is left in an environment at 80 ° C with the load applied for 1 hour. After this, the distance (displacement length, hereinafter also referred to as the displacement distance) [mm] of the test piece from the initial attachment position is measured. If the test piece falls from the Bakelite plate within 1 hour, it is evaluated as "dropped" (failed).

When measuring adhesive strength to SUS and high-temperature holding power, if necessary (for example, in the case of a substrate-less double-sided PSA sheet, or a substrate-backed PSA sheet that is prone to deformation), the PSA sheet to be measured can be reinforced by attaching an appropriate backing material. For example, a PET film with a thickness of approximately 50 μm can be used as the backing material, and this backing material was used in the examples.

[Rebound resistance test]
5(a), a polycarbonate (PC) plate 50 measuring 30 mm in length, 10 mm in width, and 2 mm in thickness and a PET film 60 measuring 100 mm in length, 10 mm in width, and 125 μm in thickness were prepared, and the PC plate 50 and the PET film 60 were overlapped so that one end of each was aligned in the longitudinal direction, and the remaining portion of the PET film 60 protruded beyond the other end of the PC plate 50. Commercially available double-sided adhesive tape (manufactured by Nitto Denko Corporation, "No. 5000NS") was used for the above-mentioned fixation.
The PSA sheet according to each example, both adhesive surfaces of which are protected by two release liners, is cut to a size of 10 mm x 10 mm to prepare PSA sheet sample 70. The surface of PC board 50 opposite the fixing surface of the PET film is placed upward, and one release liner is peeled off from PSA sheet sample 70. PSA sheet sample 70 is then attached and fixed to the top surface of PC board 50 such that the other longitudinal end of PC board 50 coincides with one side of PSA sheet sample 70. The fixing is performed by rolling a 2 kg roller back and forth once over the top surface of PSA sheet sample 70 protected by the other release liner.
Next, in an environment of 23°C and 50% RH, the other release liner of the adhesive sheet sample piece 70 attached to the PC board 50 is peeled off, and as shown in (b) of Figure 5, the protruding portion (70 mm long) of the PET film 60 fixed to the PC board 50 is folded back toward the PC board 50, so that the adhesive sheet sample piece 70 and the other end (free end) of the PET film 60 are aligned, and a 0.1 kg roller is moved back and forth once from above the PET film 60, thereby fixing the other end of the folded PET film 60 to the upper surface of the PC board 50 via the adhesive sheet sample piece 70. Whether the PET film 60 peels from the adhesive sheet sample piece 70 is observed for 24 hours each in an environment of 60°C and 95% RH and in an environment of room temperature (23°C), and the adhesive holding strength of the adhesive sheet sample piece 70 in the thickness direction of the adhesive sheet based on the elastic repulsion of the folded PET film 60 is evaluated as repulsion resistance.
The adhesive sheet sample piece 70 and the PET film 60 were evaluated as having good repulsion resistance (i.e., passed) when the adhesive sheet sample piece 70 and the PET film 60 were maintained in a 60°C, 95% RH, and room temperature environment for 24 hours, as shown in Fig. 5(c) when the adhesive sheet sample piece 70 and the PET film 60 were maintained in a room temperature environment for 24 hours.

<Synthesis Example>
(Synthesis Example 1)
A four-neck separable flask was equipped with a stirrer, thermometer, nitrogen tube, and water separation tube, and was charged with 100 g of ethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 62), 700 g of dimer acid (product name "Pripol 1009", manufactured by Croda, molecular weight 567), 63 g of terephthalic acid (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 166), 0.46 g of di-n-butyltin oxide (manufactured by Kishida Chemical Co., Ltd., molecular weight 249) as a polymerization catalyst, and 40 g of xylene as a reaction water discharge solvent. The mixture was heated to 180°C while stirring in a nitrogen atmosphere and maintained at this temperature. After a while, outflow and separation of reaction water was observed, and the reaction began to progress. The reaction was continued for approximately 24 hours, yielding a polyester-based polymer (A1) with a bio content of 81%. The weight-average molecular weight (Mw) of this polyester-based polymer (A1) was 100,000, and the glass transition temperature (Tg) was -33°C.

(Synthesis Example 2)
A four-neck separable flask was equipped with a stirrer, thermometer, nitrogen tube, and water separation tube. 100 g of ethylene glycol (Tokyo Chemical Industry Co., Ltd., molecular weight 62), 915 g of dimer acid (product name "Pripol 1009", Croda, molecular weight 567), 0.46 g of di-n-butyltin oxide (Kishida Chemical Co., Ltd., molecular weight 249) as a polymerization catalyst, and 40 g of xylene as a reaction water discharge solvent were charged. The mixture was heated to 180°C while stirring in a nitrogen atmosphere and maintained at this temperature. After a while, outflow and separation of reaction water was observed, and the reaction began to progress. The reaction was continued for approximately 24 hours, yielding a polyester-based polymer (A2) with a bio content of 89%. The Mw of this polyester-based polymer (A2) was 100,000, and the glass transition temperature (Tg) was -36°C.

(Synthesis Example 3)
A three-necked separable flask was equipped with a stirrer, thermometer, and vacuum pump. 97.8 g of dimer acid (product name "Pripol 1009", manufactured by Croda, molecular weight 567), 102.2 g of dimer diol (product name "Pripol 2033", manufactured by Croda, molecular weight 537), and 0.2 g of dibutyltin oxide (manufactured by Kanto Chemical Co., Ltd.) were charged and heated to 200 ° C. while stirring in a reduced pressure atmosphere (2.0 kPa or less), and this temperature was maintained. The reaction was continued for about 5 hours, yielding a polyester-based polymer (A3) with a bio content of 99% or more. The Mw of this polyester-based polymer (A3) was 28,000.

(Synthesis Example 4)
A polyester-based polymer (A4) having a higher molecular weight than the polyester-based polymer (A1) was obtained in the same manner as in Synthesis Example 1, except that the reaction time in Synthesis Example 1 was changed to about 36 hours. The monomer composition of this polyester-based polymer (A4) was the same as that of the polyester-based polymer (A1), and the Mw was 130,000.

<Example 1>
A pressure-sensitive adhesive composition (pressure-sensitive adhesive solution) was prepared by blending 100 parts of the polyester polymer (A1), 40 parts of a terpene phenol resin (trade name "YS Polystar S145", manufactured by Yasuhara Chemical Co., Ltd., phenol ratio 22%, hereinafter sometimes referred to as "S145") as a tackifier resin, 3 parts of an isocyanurate of hexamethylene diisocyanate (trade name "Coronate HX", manufactured by Tosoh Corporation) as a crosslinking agent, 0.13 parts of an organic zirconium compound (trade name "Orgatix ZC-162", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 0.5 parts of a carbodiimide group-containing compound (trade name "Carbodilite V-03", manufactured by Nisshinbo Chemical Inc.) as a hydrolysis stabilizer, and adding ethyl acetate. This adhesive solution was applied to the release-treated surface of a release-treated polyethylene terephthalate (PET) film (trade name "Diafoil MRF#38", manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 20 μm, and the coating was dried for 3 minutes at 120° C. to obtain an adhesive layer. Thereafter, the adhesive layer was attached to the release-treated surface of a release-treated PET film (trade name "Diafoil MRE#38", manufactured by Mitsubishi Chemical Corporation) and left for a further 3 days at 50° C. to obtain a substrateless adhesive sheet according to this example.

<Example 2>
The adhesive composition of this example was prepared in the same manner as in Example 1, except that 0.01 parts of an organic tin compound (trade name "dibutyltin(IV) dilaurate", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the crosslinking catalyst instead of the organic zirconium compound, and the substrate-less adhesive sheet of this example was obtained in the same manner as in Example 1, except that this adhesive composition was used.

<Example 3>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 1, except that the amount of crosslinking agent used was changed to 2 parts per 100 parts of polyester-based polymer (A1), and a substrate-less pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that this pressure-sensitive adhesive composition was used.

<Example 4>
The amount of crosslinking agent used was changed to 4 parts per 100 parts of polyester polymer (A1), and 0.13 parts of an organoaluminum compound (trade name "Nasem Aluminum", manufactured by Nippon Chemical Industry Co., Ltd.) was used as the crosslinking catalyst instead of the organozirconium compound. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 1, and a substrate-less pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except for using this pressure-sensitive adhesive composition.

<Examples 5 to 7>
A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 4, except that the type and amount of crosslinking catalyst used was changed as shown in Table 1, and a substrate-less pressure-sensitive adhesive sheet according to each example was obtained in the same manner as in Example 4, except that the pressure-sensitive adhesive composition obtained was used. In Table 1, the iron-based catalyst is an organic iron compound (trade name "Nasem Ferric", manufactured by Nippon Chemical Industry Co., Ltd.), and the titanium-based catalyst is an organic titanium compound (trade name "Orgatix TA-30", manufactured by Matsumoto Fine Chemical Co., Ltd.).

<Example 8>
A polyester-based polymer (A2) was used instead of the polyester-based polymer (A1), and the amount of crosslinking agent used was changed to 5 parts (5.3 parts) per 100 parts of the polyester-based polymer (A2). A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 2, except for using this pressure-sensitive adhesive composition.

<Example 9>
As the tackifier resin, 40 parts of polymerized rosin ester (trade name "Pensel D-125", manufactured by Arakawa Chemical Industries, Ltd., phenol ratio 0%, hereinafter sometimes referred to as "D125") was used instead of the terpene phenol resin, and the amount of crosslinking agent used was changed to 5 parts (5.3 parts) per 100 parts of polyester-based polymer (A1). A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 2, except for using this pressure-sensitive adhesive composition.

Examples 10 and 11
Except for using polyester-based polymer (A3) instead of polyester-based polymer (A1), a pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 1 or Example 2. Except for using the resulting pressure-sensitive adhesive composition, a substrate-less pressure-sensitive adhesive sheet according to each example was obtained in the same manner as in Example 1 or Example 2.

<Example 12>
The adhesive composition of this example was prepared in the same manner as in Example 1, except that no tackifier resin was used, and the substrateless adhesive sheet of this example was obtained in the same manner as in Example 1, except that this adhesive composition was used.

<Example 13>
100 parts of polyester polymer (A4) was blended with 40 parts of a terpene phenol resin (trade name "YS Polystar G150", manufactured by Yasuhara Chemical Co., Ltd., phenol ratio 32%, hereinafter sometimes referred to as "G150") as a tackifier resin, 2 parts of an isocyanurate of hexamethylene diisocyanate (trade name "Coronate HX", manufactured by Tosoh Corporation, hereinafter sometimes referred to as "trifunctional crosslinker") as a crosslinking agent, 0.03 parts of an organic zirconium compound (trade name "Orgatix ZC-162", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 0.5 parts of a carbodiimide group-containing compound (trade name "Carbodilite V-03", manufactured by Nisshinbo Chemical Inc.) as a hydrolysis stabilizer, and ethyl acetate was added to prepare a pressure-sensitive adhesive composition (pressure-sensitive adhesive solution). A substrateless pressure-sensitive adhesive sheet (thickness 20 μm) according to this example was obtained in the same manner as in Example 1, except that the resulting pressure-sensitive adhesive composition was used.

<Example 14>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 13, except that 100 parts of the polyester polymer (A4) were used, 40 parts of a terpene phenol resin (trade name "YS Polystar S145", manufactured by Yasuhara Chemical Co., Ltd., phenol ratio 22%) as a tackifier resin, 3 parts of an isocyanurate of hexamethylene diisocyanate (trade name "Coronate HX", manufactured by Tosoh Corporation) as a crosslinking agent, and 0.01 parts of an organotin compound (trade name "dibutyltin(IV) dilaurate", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a crosslinking catalyst. A substrate-less pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 13, except that this pressure-sensitive adhesive composition was used.

<Example 15>
100 parts of polyester polymer (A1) was mixed with 40 parts of terpene phenol resin (trade name "YS Polystar S145", manufactured by Yasuhara Chemical Co., Ltd., phenol ratio 22%) as a tackifier resin, 1 part of an isocyanurate of hexamethylene diisocyanate (trade name "Coronate HX", manufactured by Tosoh Corporation) as a crosslinking agent, and 5 parts of a bifunctional crosslinking agent (trade name "Duranate D101", manufactured by Asahi Kasei Corporation), 0.03 parts of an organic zirconium compound (trade name "Orgatix ZC-162", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 0.5 parts of a carbodiimide group-containing compound (trade name "Carbodilite V-03", manufactured by Nisshinbo Chemical Inc.) as a hydrolysis stabilizer, and ethyl acetate was added to prepare a pressure-sensitive adhesive composition (pressure-sensitive adhesive solution). A substrateless pressure-sensitive adhesive sheet (thickness 20 μm) according to this example was obtained in the same manner as in Example 1, except that the obtained pressure-sensitive adhesive composition was used.

<Examples 16-17>
The adhesive compositions of each example were prepared in the same manner as in Example 15, except that the type of tackifier resin and the proportion of crosslinking agent used were changed as shown in Table 3, and the substrate-less adhesive sheets of each example were obtained in the same manner as in Example 15, except that the obtained adhesive compositions were used.

The adhesive strength to SUS and high-temperature holding power of the pressure-sensitive adhesive sheets obtained in each example were measured using the methods described above. The results are shown in Tables 1 and 3. In addition, a rebound resistance test was conducted for Examples 2, 9', and 13-17. The results are shown in Tables 2 and 3. Note that Example 9' is a modification of Example 9 in which the amount of crosslinker (product name "Coronate HX") used in the pressure-sensitive adhesive composition of Example 9 was changed from 5.3 parts to 4.4 parts.

As shown in Tables 1 to 3, among PSA compositions containing a polyester-based polymer with a biocontent of 50% or more, Examples 1 to 9 and 13 to 17, which used PSA compositions containing a polyester-based polymer with an Mw of 30,000 or more and a tackifier resin, had adhesive strengths to SUS of 10 N/20 mm or more and passed the high-temperature holding power test. In particular, as can be seen from a comparison between Examples 5 and 8, compositions using a polyester-based polymer containing an aromatic ring in the molecule achieved a better balance of adhesive strength and high-temperature holding power. On the other hand, Examples 10 and 11, which used a polyester-based polymer with an Mw of less than 30,000, failed the high-temperature holding power test. Furthermore, Example 12, which did not use a tackifier resin, had inferior adhesive strength to SUS compared to Examples 1 to 9. Note that in the measurement of adhesive strength to SUS in Example 10, cohesive failure occurred in the PSA layer.
The above results show that a pressure-sensitive adhesive containing a polyester-based polymer in which 50% or more of the constituent carbon is biomass-derived carbon and a tackifying resin, wherein the polyester-based polymer has an Mw of 30,000 or more, can achieve both adhesive strength and high-temperature retention.

As shown in Tables 2 and 3, the PSA sheets of Examples 9' and 13-17, which are modifications of Examples 2 and 9, passed the repulsion resistance test. For Examples 2, 9', and 13-14, the use of a high-molecular-weight polyester polymer is believed to have contributed to the improved repulsion resistance. In particular, Examples 13-14, which used a polyester polymer with an Mw of 130,000, achieved particularly excellent results in the repulsion resistance test. For Examples 15-17, compared to Example 2, the use of a bifunctional and trifunctional crosslinking agent in combination is believed to have improved repulsion resistance. More specifically, the use of a bifunctional crosslinking agent is thought to have lengthened the polyester polymer chain during the crosslinking reaction, resulting in improved repulsion resistance. Although not specifically shown in the tables, Examples 13 and 16-17, which used a tackifier resin with a high phenol ratio, tended to exhibit better repulsion resistance compared to Examples 14-15. This is consistent with the fact that the rebound resistance test results of Examples 13 and 14 are superior to those of Example 9', which used a tackifier resin with a phenol ratio of 0%.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above.

1, 2, 3: Adhesive sheet 10: Support substrate 10A: First surface 10B: Second surface (rear surface)
21 Adhesive layer (first adhesive layer)
21A Adhesive surface (first adhesive surface)
21B Second adhesive surface 22 Adhesive layer (second adhesive layer)
22A Adhesive surface (second adhesive surface)
31, 32 Release liner 100, 200, 300 Pressure-sensitive adhesive sheet with release liner

Claims (12)

A pressure-sensitive adhesive composition comprising a polyester polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
further comprising a tackifying resin;
The polyester polymer is copolymerized with an aromatic dicarboxylic acid in a ratio of 1% by weight or more and 30% by weight or less,
The pressure-sensitive adhesive composition, wherein the weight average molecular weight of the polyester polymer exceeds 100,000 . The pressure-sensitive adhesive composition according to claim 1 , wherein the polyester polymer has a glass transition temperature of 0° C. or lower. The pressure-sensitive adhesive composition according to claim 1 or 2 , wherein the tackifier resin is selected from a terpene phenolic resin and a polymerized rosin ester. The pressure- sensitive adhesive composition according to any one of claims 1 to 3 , wherein the tackifier resin contains an aromatic ring. 5. The pressure-sensitive adhesive composition according to claim 1 , further comprising a crosslinking agent, the content of which is 5 parts by weight or less relative to 100 parts by weight of the polyester polymer. The pressure-sensitive adhesive composition according to claim 5 , wherein the crosslinking agent comprises an isocyanate-based crosslinking agent. The pressure-sensitive adhesive composition according to claim 6 , wherein the isocyanate-based crosslinking agent is an aliphatic isocyanate-based compound. The pressure-sensitive adhesive composition according to any one of claims 1 to 7 , further comprising a crosslinking agent and a crosslinking catalyst, wherein the crosslinking catalyst does not contain a tin-based compound. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a polyester polymer in which 50% or more of the constituent carbon is biomass-derived carbon,
The pressure-sensitive adhesive layer further comprises a tackifying resin,
The polyester polymer is copolymerized with an aromatic dicarboxylic acid in a ratio of 1% by weight or more and 30% by weight or less,
The weight average molecular weight of the polyester polymer is more than 100,000 . 10. The pressure-sensitive adhesive sheet according to claim 9 , which has a 180-degree peel strength from a stainless steel plate of 10 N/20 mm or more and does not fall in a holding power test carried out under conditions of 80°C, a load of 1 kg, and 1 hour. The pressure-sensitive adhesive sheet according to claim 9 or 10, which is used in a portable electronic device. A portable electronic device comprising the pressure-sensitive adhesive sheet according to claim 9 or 10 .