JP7828876B2 - Adhesive sheet with release liner - Google Patents

Description

This invention relates to an adhesive sheet with a release liner.

Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) exhibit a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to a substrate under pressure. Taking advantage of this property, adhesives are widely used in the form of adhesive sheets for purposes such as joining parts and surface protection. For example, adhesive sheets having an adhesive layer on one surface of a substrate are preferably used as surface protection sheets to prevent damage (scratches, dirt, corrosion, etc.) to the surface of various articles during processing and transportation. Such adhesive sheets can be distributed, stored, and processed in a form where the adhesive surface is protected by a release sheet before use. Patent Document 1 is a prior art document disclosing this type of conventional technology.

Japanese Patent Publication No. 2012-224811

For adhesive sheets, silicone-based release sheets with excellent ease of peeling are widely used (for example, Patent Document 1). However, depending on the application and usage of the adhesive sheet, the use of silicone-based release sheets may be undesirable. For example, in applications where the adhesive sheet is used for surface protection of optical components, the silicone material contained in the silicone-based release sheet may be transferred from the peeling surface of the release sheet to the adhesive surface, and further to the adherend, potentially altering the surface properties of the adherend after the adhesive sheet is peeled off. Furthermore, in applications such as inside precision equipment, it may be desirable to avoid the use of silicone materials that can generate siloxane gas. In such cases, non-silicone-based release sheets, such as those having a release layer formed with a release agent other than silicone material (non-silicone-based release agent), are used. However, these non-silicone-based release sheets tend to have less ease of peeling from the adhesive surface (release sheet peelability) compared to silicone-based release sheets, resulting in reduced peelability.

This invention was created in view of the above circumstances, and aims to provide an adhesive sheet with a non-silicone release sheet that has release sheet peelability comparable to that of a silicone-based release sheet.

This specification provides an adhesive sheet with a release sheet, comprising an adhesive sheet having an adhesive layer and a non-silicone release sheet disposed on the surface of the adhesive layer. The adhesive layer contains an acrylic polymer. The acrylic polymer is a polymer of monomer components including alkyl (meth)acrylate (m1) having an alkyl group with 6 to 17 carbon atoms at its ester terminus. Here, the alkyl group with 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group with 1 carbon atom. By using an adhesive containing an acrylic polymer of the above structure, an adhesive sheet can be obtained that exhibits release properties comparable to those of a silicone release sheet, even when using a non-silicone release sheet.

In several preferred embodiments, the alkyl (meth)acrylate (m1) comprises at least one selected from n-heptyl acrylate and n-octyl acrylate. The effects of the techniques disclosed herein are preferably achieved by using at least one selected from n-heptyl acrylate and n-octyl acrylate as the monomer component of the acrylic polymer.

In some embodiments, the monomer component includes a monomer (m2) having a hydroxyl group. By using a monomer having a hydroxyl group, the side chains of the acrylic polymer have hydroxyl groups. Such hydroxyl groups can serve as crosslinking sites when using crosslinking agents such as isocyanate-based or epoxy-based crosslinking agents.

In some preferred embodiments, the adhesive layer comprises an isocyanate-based crosslinking agent. In embodiments using an isocyanate-based crosslinking agent, the techniques disclosed herein are preferably implemented.

In some embodiments, the adhesive layer contains a zirconium-containing compound. Using a zirconium-containing compound as a catalyst makes it easier to achieve both aging (typically a crosslinking reaction) and pot life in the adhesive layer. The use of a zirconium-based catalyst is also desirable from the standpoint of reducing environmental impact. Furthermore, using a zirconium-containing compound as a catalyst makes it easier to form a colorless adhesive. This can be an advantageous feature when the adhesive sheet is used in optical applications.

In some preferred embodiments, the non-silicone release sheet comprises a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate. The non-silicone release treatment layer is formed from a material containing a long-chain alkyl release treatment agent. In embodiments using a release sheet having a release treatment layer containing a long-chain alkyl release treatment agent, a desired level of easy release can be preferably achieved.

In some embodiments, the adhesive sheet comprises a substrate and an adhesive layer disposed on at least one surface of the substrate. Such an adhesive sheet with a substrate offers excellent processability and handling properties, and can be preferably used, for example, as a surface protection film that is removed (peeled) from the adherend after use.

The adhesive sheet disclosed herein has an adhesive surface protected by a release liner, so the adhesive surface is kept smooth and can be uniformly adhered to the substrate. Furthermore, by using a non-silicone release liner, contamination of the substrate by silicone materials does not occur. This can be an advantageous feature, for example, in optical applications where specific optical properties are required. Therefore, the adhesive sheet disclosed herein is preferably used in optical applications, specifically in a manner in which it is attached to optical components.

Furthermore, the adhesive sheet disclosed herein is suitable, for example, as a surface protection film. After a surface protection film is applied to an object to be protected, and its protective purpose is achieved, it is usually peeled off (re-peeled) from the object. Since such a surface protection film is required not to alter the object before or after protection, the use of an adhesive sheet with a non-silicone release liner that does not cause contamination of the protected surface with silicone material after peeling off may be advantageous.

This is a schematic cross-sectional view showing the structure of an adhesive sheet with a release liner according to one embodiment.

Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art.
In the following drawings, components and parts that perform the same function may be denoted by the same reference numeral and described accordingly, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic representations for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

In this specification, "adhesive" refers to a material that, as described above, exhibits a soft solid (viscoelastic) state in the temperature range near room temperature and has the property of easily adhering to an adherend by pressure. The adhesive referred to here may generally be a material having the property of satisfying the complex tensile modulus E ^* (1 Hz) < ^10⁷ dyne/ ^cm² , as defined in "CA Dahlquist, “Adhesion: Fundamentals and Practice”, McLaren & Sons (1966), p. 143" (typically a material having the above property at 25°C).

In this specification, biomass-derived carbon refers to carbon derived from biomass materials, i.e., materials derived from renewable organic resources (renewable carbon). The above-mentioned biomass materials typically refer to materials derived from biological resources (typically photosynthetic plants) that can be sustainably reproduced if sunlight, water, and carbon dioxide are present. Therefore, materials derived from fossil resources that are depleted by use after extraction (fossil resource-based materials) are excluded from the concept of biomass materials as used herein. The biomass-carbon ratio of the adhesive (layer) and adhesive sheet, i.e., the proportion of biomass-derived carbon in the total carbon contained in the adhesive (layer) and adhesive sheet, can be estimated from the carbon isotope content with mass number 14, measured in accordance with ASTM D6866.

<Example of the configuration of an adhesive sheet with a release liner>
The adhesive sheet with a release sheet disclosed herein comprises an adhesive sheet having an adhesive layer and a non-silicone release sheet disposed on the surface of the adhesive layer. The adhesive sheet may be an adhesive sheet with a substrate having the adhesive layer on one or both sides of a non-peelable substrate (support substrate), or it may be a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate) in which the adhesive layer is held by the release sheet. Hereinafter, the support substrate may simply be referred to as the "substrate." The concept of an adhesive sheet as used herein may include adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet may be in roll form or sheet form. It may also be an adhesive sheet processed into various shapes.

Figure 1 schematically shows the structure of an adhesive sheet with a release sheet according to one embodiment. This adhesive sheet with a release sheet 100 includes an adhesive sheet 1 having an adhesive layer 21 and a release sheet 31 laminated on the surface (adhesive surface) 21A of the adhesive layer 21. The adhesive sheet 1 is configured as a single-sided adhesive sheet with a base material, comprising a sheet-like support base material (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A side thereof. The adhesive layer 21 is fixedly provided on the first surface 10A side of the support base material 10, that is, without the intention of separating the adhesive layer 21 from the support base material 10. Such a single-sided adhesive sheet 1 is suitable as a surface protection film used by attaching its adhesive surface to the surface of an object to be protected (an object to be protected, for example, an optical component such as a polarizing plate). Before use, the adhesive sheet 1 has the form of an adhesive sheet 100 with a release liner, and the surface (adhesive surface) 21A of the adhesive layer 21 is protected by the release liner 31, at least on the side facing the adhesive layer 21, which is the release surface.

<Adhesive layer>
(Acrylic polymer)
The adhesive layer disclosed herein contains an acrylic polymer. The adhesive layer is typically an adhesive layer with an acrylic polymer as the base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of the rubbery polymer (a polymer exhibiting rubber elasticity in the temperature range around room temperature) contained in the adhesive layer. In this specification, unless otherwise specified, "main component" refers to a component present in an amount exceeding 50% by weight. Furthermore, the following description of components that may be contained in the adhesive and adhesive layer is also applicable to adhesive compositions used to form the adhesive (layer), unless otherwise specified.

In this specification, "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight of (meth)acrylic monomer. The content of (meth)acrylic monomer in the monomer component is preferably 70% by weight or more, and may be 80% by weight or more. In some embodiments, the content of (meth)acrylic monomer in the monomer component may be 90% by weight or more, 95% by weight or more, or 100% by weight. On the other hand, considering the balance of adhesive properties, in some embodiments, the proportion of (meth)acrylic monomer in the total monomer component may be, for example, less than 99% by weight, less than 95% by weight, or less than 93% by weight.

Furthermore, in this specification, "(meth)acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic. Therefore, the concept of (meth)acrylic monomer as used herein may encompass both monomers having an acryloyl group (acrylic monomer) and monomers having a methacryloyl group (methacrylic monomer).

The above-mentioned acrylic polymer typically uses a polymer of a monomer raw material containing one or more linear alkyl (meth)acrylates as the main monomer, and further containing one or more sub-monomers copolymerizable with the main monomer. The main monomer refers to a component accounting for more than 50% by weight of the total monomer components. Furthermore, linear alkyl (meth)acrylate refers to an alkyl (meth)acrylate having a linear alkyl group at its ester end. The linear alkyl group is a concept that includes both linear and branched alkyl groups, and does not include cyclic alkyl groups referred to as alicyclic alkyl groups. Furthermore, the sub-monomers refer to monomer components other than the linear alkyl (meth)acrylate used as the main monomer, and include functional group-containing monomers such as hydroxyl group-containing monomers and carboxyl group-containing monomers, as well as other copolymerizable monomers, as described later. In this specification, sub-monomers refer to monomer components other than alkyl (meth)acrylate (m1) and other linear alkyl (meth)acrylates in the monomer components.

The acrylic polymer used in the technology disclosed herein contains an alkyl (meth)acrylate (m1) having a specific chemical structure as a monomer component. Specifically, the alkyl (meth)acrylate (m1) is an alkyl (meth)acrylate having an alkyl group with 6 to 17 carbon atoms at its ester terminus, and the alkyl group with 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group with 1 carbon atom in the branch (also called a branching group). With an adhesive containing the acrylic polymer of the above structure, even when using a non-silicone release sheet, release sheet peelability comparable to that when using a silicone release sheet can be obtained. The reason for this is not to be interpreted in a particularly restrictive way, but from the results of the examples described later, the acrylic polymer synthesized using the alkyl (meth)acrylate (m1) as a monomer component has a relatively long linear or low-branching alkyl group in the side chain of the acrylic polymer. It is thought that such a side-chain alkyl group contributes to achieving the easy peelability of the non-silicone release sheet. The alkyl (meth)acrylate (m1) described above is included in the monomer component of the acrylic polymer as at least a part of the main monomer (chain alkyl (meth)acrylate). Hereinafter, a chain alkyl (meth)acrylate having a chain alkyl group with X carbon atoms at its ester end may be referred to as _C6-17 alkyl (meth)acrylate (for example, in the case of a chain alkyl (meth)acrylate having a chain alkyl group with 6 to 17 carbon atoms at its ester end, it may be referred to as _C6-17 alkyl (meth)acrylate).

The alkyl (meth)acrylate (m1) described above can also be represented by the following formula (1).
CH ₂ =C(R ¹ )COOR ² (1)
Here, ^R1 in formula (1) above is a hydrogen atom or a methyl group. ^R2 is an alkyl group having 6 to 17 carbon atoms, and is either a linear alkyl group or a branched alkyl group with 1 carbon atom. From the viewpoint of easy peelability on non-silicone release sheets, the number of carbon atoms in the alkyl(meth)acrylate (m1) alkyl group is preferably 7 or more, may be 8 or more, 9 or more, 10 or more, or 12 or more. The more carbon atoms in the alkyl group, the more effectively the effect and properties of making the alkyl group a long chain are expressed. Furthermore, from the viewpoint of adhesive formation, adhesive properties, aging rate, etc., the above number of carbon atoms is preferably 14 or less, more preferably 12 or less, even more preferably 10 or less, and particularly preferably 8 or less (for example, 7 or 8).

Specific examples of _C6-17 linear alkyl (meth)acrylates used as alkyl (meth)acrylate (m1) include n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, and n-heptadecyl (meth)acrylate. Specific examples of _C6-17 branched alkyl (meth)acrylates as alkyl (meth)acrylate (m1) include methylheptyl (meth)acrylate such as 2-octyl (meth)acrylate and isooctyl acrylate, methyloctyl (meth)acrylate, methylnonyl (meth)acrylate, methyldecyl (meth)acrylate, methyldodecyl (meth)acrylate, methyltridecyl (meth)acrylate, methyltetradecyl (meth)acrylate, methylpenta (meth)acrylate, and methylhexadecyl (meth)acrylate. Alkyl (meth)acrylate (m1) can be used alone or in combination of two or more types. Although not particularly limited, in some embodiments, alkyl acrylates are preferably used as alkyl (meth)acrylate (m1).

In some embodiments, _C6-17 linear alkyl (meth)acrylates are preferably used. Among these, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-dodecyl (meth)acrylate are more preferably used as the alkyl (meth)acrylate (m1), and n-heptyl (meth)acrylate and n-octyl (meth)acrylate are even more preferably used.

As the _C6-17 branched alkyl (meth)acrylate, either isoalkyl (meth)acrylate having an isoalkyl group in which the methyl group is branched at the carbon one position before the terminal of the branched alkyl group, or branched alkyl (meth)acrylate having a non-isobranched alkyl group in which the methyl group is branched at two or more carbon positions before the terminal of the branched alkyl group, such as 2-octyl (meth)acrylate, can be used. However, in some embodiments, branched alkyl (meth)acrylate having a non-isobranched alkyl group in which the side chain ends of the acrylic polymer are relatively long linear alkyl groups is preferred. For example, a _C6-17 branched alkyl (meth)acrylate in which the branched group (methyl group) of the branched alkyl group is bonded to the first or second carbon from the ester end can be preferably used.

The proportion of alkyl (meth)acrylate (m1) in the total monomer component is set according to its intended use and required properties. In some embodiments, the proportion of alkyl (meth)acrylate (m1) in the total monomer component may be, for example, 10% by weight or more, 30% by weight or more is appropriate, and in some preferred embodiments, it may be 50% by weight or more (for example, more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, 85% by weight or more, particularly preferably 90% by weight or more, 92% by weight or more, or 95% by weight or more. By increasing the amount of alkyl (meth)acrylate (m1) used, properties based on alkyl (meth)acrylate (m1) can be effectively expressed. On the other hand, from the viewpoint of copolymerizing functional group-containing monomers that serve as crosslinking points, the proportion of alkyl (meth)acrylate (m1) in the total monomer component may be, for example, less than 99% by weight, less than 98% by weight, or less than 97% by weight. In some other embodiments, the upper limit of the proportion of alkyl (meth)acrylate (m1) in the total monomer components may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effects of using other monomers.

The proportion of alkyl (meth)acrylate (m1) in the total amount of linear alkyl (meth)acrylate contained in the monomer component of the above acrylic polymer may be, for example, 10% by weight or more, 30% by weight or more is suitable, and in some preferred embodiments, it may be 50% by weight or more (for example, more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and may also be 95% by weight or more, or 99% by weight or more. By increasing the amount of alkyl (meth)acrylate (m1) used, properties based on alkyl (meth)acrylate (m1) can be effectively expressed. In some embodiments, an acrylic polymer with a monomer composition containing only alkyl (meth)acrylate (m1) is used as the linear alkyl (meth)acrylate. Therefore, the upper limit of the proportion of alkyl (meth)acrylate (m1) in the total amount of linear alkyl (meth)acrylate is 100% by weight. In some other embodiments, the proportion of alkyl (meth)acrylate (m1) in the total amount of the linear alkyl (meth)acrylate may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (for example, less than 50% by weight), from the viewpoint of obtaining the benefits of using linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1).

In some preferred embodiments, _C7-12 linear alkyl (meth)acrylate is used as the alkyl (meth)acrylate (m1). Among these, the use of _C7-8 linear alkyl (meth)acrylate is more preferred. The proportion of _C7-12 linear alkyl (meth)acrylate (more preferably _C7-8 linear alkyl (meth)acrylate) in the total monomer component may be, for example, 10% by weight or more, 30% by weight or more is appropriate, and in some preferred embodiments, it may be 50% by weight or more (for example, more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, and may also be 85% by weight or more, particularly preferably 90% by weight or more, may also be 92% by weight or more, and may also be 95% by weight or more. Furthermore, the proportion of _C7-12 linear alkyl (meth)acrylate (more preferably _C7-8 linear alkyl (meth)acrylate) in the total monomer components may be, for example, less than 99% by weight, less than 98% by weight, or less than 97% by weight. In some other embodiments, the upper limit of the proportion of _C7-12 linear alkyl (meth)acrylate (more preferably _C7-8 linear alkyl (meth)acrylate) in the total monomer components may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (for example, less than 50% by weight), from the viewpoint of obtaining the effects of using other monomers.

In some preferred embodiments, n-heptyl (meth)acrylate is used as the alkyl (meth)acrylate (m1). By using n-heptyl (meth)acrylate, the effects of the techniques disclosed herein can be particularly favorably exhibited. Among these, n-heptyl acrylate is particularly preferred from the viewpoint of adhesive properties.

The proportion of n-heptyl (meth)acrylate in the total monomer component is set according to its intended use and required properties. In some embodiments, the proportion of n-heptyl (meth)acrylate in the total monomer component may be, for example, 10% by weight or more, 30% by weight or more is appropriate, and in some preferred embodiments, it may be 50% by weight or more (for example, more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, 85% by weight or more, particularly preferably 90% by weight or more, 92% by weight or more, or 95% by weight or more. By increasing the amount of n-heptyl (meth)acrylate used, its effects can be effectively expressed. On the other hand, from the viewpoint of copolymerizing functional group-containing monomers that serve as crosslinking points, the proportion of n-heptyl (meth)acrylate in the total monomer component may be, for example, less than 99% by weight, less than 98% by weight, or less than 97% by weight. In some other embodiments, the proportion of n-heptyl (meth)acrylate in the total monomer components may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effects of using various monomers other than n-heptyl (meth)acrylate.

The proportion of n-heptyl (meth)acrylate in the total amount of linear alkyl (meth)acrylate contained in the monomer component of the above acrylic polymer may be, for example, 10% by weight or more, 30% by weight or more is suitable, and in some preferred embodiments, it may be 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and may also be 95% by weight or more, or 99% by weight or more. By increasing the amount of n-heptyl (meth)acrylate used, its effects can be effectively expressed. The technology disclosed herein can preferably be carried out in a manner in which an acrylic polymer with a monomer composition containing only n-heptyl (meth)acrylate is used as the linear alkyl (meth)acrylate. Therefore, the upper limit of the proportion of n-heptyl (meth)acrylate in the total amount of linear alkyl (meth)acrylate is 100% by weight. In some other embodiments, the proportion of n-heptyl (meth)acrylate in the total amount of the linear alkyl (meth)acrylate may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effects of using other linear alkyl (meth)acrylates.

In some embodiments, the monomer components constituting the acrylic polymer may include linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1), to the extent that they do not significantly impair the effects of the invention. Examples of linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1) include _C1-5 alkyl (meth)acrylate, C18 ₊ alkyl (meth)acrylate with 18 or more carbon atoms in the alkyl group, and _C6-17 branched alkyl (meth)acrylate with 2 or more carbon atoms in the branched group of the alkyl group. These can be used individually or in combination of two or more. Specific examples of _C1-5 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, and isopentyl (meth)acrylate. Specific examples of _C18+ alkyl (meth)acrylates include octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Specific examples of the above _C6-17 branched alkyl (meth)acrylates include 2-ethylhexyl (meth)acrylate, etc.

The proportion of linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1) in the monomer component is not particularly limited, but may be approximately 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1). In the embodiment in which the monomer component contains linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1), the proportion of linear alkyl (meth)acrylates other than alkyl (meth)acrylate (m1) in the monomer component may be, for example, 1% by weight or more, 10% by weight or more, or 30% by weight or more.

In this specification, "substantially free of monomer A (for example, a linear alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1) described above)" means that monomer A is not used intentionally, and it is permissible for monomer A to be unintentionally included in an amount of, for example, 0.1% by weight or less.

In some embodiments, the monomer component may include, as the linear alkyl (meth)acrylate, an alkyl (meth)acrylate having a biomass-derived alkyl group at its ester terminus (hereinafter also referred to as "biomass linear alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become a major concern, and there is a desire to reduce the use of fossil fuel-based materials such as petroleum. Under these circumstances, there is also a need to reduce the use of fossil fuel-based materials in the field of adhesives. By using biomass linear alkyl (meth)acrylate, it is possible to suitably realize an acrylic adhesive composition that takes into consideration the reduction of reliance on fossil fuel-based materials.

The biomass-derived alkyl (meth)acrylate is not particularly limited and, for example, is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant raw materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the biomass-derived alkanol has three or more carbon atoms, the alkanol may be linear or branched. In some embodiments, an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass-derived alkyl (meth)acrylate used in the synthesis of acrylic polymers. In such a biomass-derived alkyl (meth)acrylate, the more carbon atoms the alkanol has, the higher the ratio of biomass-derived carbons to the total number of carbon atoms in the biomass-derived alkyl (meth)acrylate, i.e., the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the above-mentioned biomass-derived linear alkyl (meth)acrylate, a high number of carbon atoms in the biomass-derived linear alkyl group is desirable in terms of reducing dependence on fossil fuel-based materials. On the other hand, if the number of carbon atoms in the linear alkyl group constituting the linear alkyl (meth)acrylate is too high, it tends to become difficult to obtain adhesive properties such as adhesion strength, and it may also be disadvantageous in terms of productivity, such as synthesis, handling, and cost. In embodiments where an ester of biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass-derived linear alkyl (meth)acrylate, it is desirable to use a material that balances adhesive properties with a reduction in dependence on fossil fuel-based materials (more specifically, the biomass carbon ratio of the above-mentioned linear alkyl (meth)acrylate).

In the technologies disclosed herein, biomass linear alkyl (meth)acrylate can be used in place of the alkyl (meth)acrylate (m1) or any other linear alkyl (meth)acrylate. In embodiments where two or more compounds are used as linear alkyl (meth)acrylates in the synthesis of acrylic polymers, at least a portion of them (e.g., one or two, or all of them) can be biomass linear alkyl (meth)acrylate. In several preferred embodiments, using biomass linear alkyl (meth)acrylate as alkyl (meth)acrylate (m1) allows for a reduction in reliance on fossil fuel-based materials while favorably achieving the effects of the technologies disclosed herein.

The number of carbon atoms in the alkyl group of the biomass-type alkyl (meth)acrylate is preferably 14 or less, more preferably 12 or less, even more preferably 10 or less, and particularly preferably 8 or less (for example, 7 or 8) from the viewpoint of adhesive formation, adhesive properties, and aging rate. Furthermore, the number of carbon atoms is preferably 7 or more. For example, in embodiments where an ester of biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass-type alkyl (meth)acrylate, increasing the number of carbon atoms in the alkyl group can increase the biomass carbon ratio of the synthesized acrylic polymer.

In several preferred embodiments, an n-heptyl (meth)acrylate having an n-heptyl group derived from biomass (hereinafter also referred to as "biomass heptyl (meth)acrylate") is used as the alkyl (meth)acrylate (m1). By using biomass heptyl (meth)acrylate, the effects of the disclosed technology can be particularly favorably exhibited while reducing dependence on fossil fuel-based materials. Among these, biomass heptyl acrylate is particularly preferred from the viewpoint of adhesive properties.

The proportion of biomass linear alkyl (meth)acrylate (e.g., biomass n-heptyl (meth)acrylate) in the total linear alkyl (meth)acrylate used as the monomer component of the above-mentioned acrylic polymer may be, for example, 1% by weight or more, 10% by weight or more is appropriate, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), may be 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more. By increasing the proportion of biomass linear alkyl (meth)acrylate used, the biomass carbon ratio of the acrylic polymer can be improved while effectively exhibiting its effects. The technology disclosed herein can preferably be implemented in a manner in which an acrylic polymer with a monomer composition containing only biomass linear alkyl (meth)acrylate as the linear alkyl (meth)acrylate is used. Therefore, the upper limit of the proportion of biomass-derived linear alkyl (meth)acrylate in the total linear alkyl (meth)acrylate is 100% by weight. In some other embodiments, the proportion of biomass-derived linear alkyl (meth)acrylate in the total linear alkyl (meth)acrylate may be 95% by weight or less, 70% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less.

In some embodiments, the monomer component of the acrylic polymer preferably contains a monomer (m2) having a hydroxyl group. The hydroxyl group-containing monomer (m2) is included in the monomer component as a secondary monomer. By using the hydroxyl group-containing monomer (m2), the side chains of the acrylic polymer have hydroxyl groups. Such hydroxyl groups can serve as crosslinking sites when using crosslinking agents such as isocyanate-based or epoxy-based crosslinking agents. The hydroxyl group-containing monomer (m2) can be used individually or in combination of two or more types.

In a hydroxyl group-containing monomer (m2), the length of the side chain containing the hydroxyl group is not particularly limited. The number of carbon atoms in the hydroxyl group-containing side chain of the hydroxyl group-containing monomer (m2) may be, for example, two or more, preferably three or more. Here, the hydroxyl group-containing side chain in the hydroxyl group-containing monomer (m2) refers to a chain-like structure bonded to a (meth)acryloyl group, for example, in the case of a hydroxyl group-containing (meth)acrylic monomer. By using a hydroxyl group-containing monomer (m2) with hydroxyl groups in a relatively long side chain, the hydroxyl groups that become crosslinking points and the crosslinking agent are brought into close proximity, and it is believed that aging (crosslinking reaction) proceeds rapidly. Furthermore, by appropriately setting the length of the side chain of the hydroxyl group-containing monomer (m2) based on its relationship to the chain length of the alkyl group of the alkyl (meth)acrylate (m1), the crosslinking reaction can be moderately controlled, thereby favorably achieving both crosslinking reaction progress and a practical pot life. The hydroxyl group-containing monomer (m2) may be biomass-derived or non-biomass-derived.

As the hydroxyl group-containing monomer (m2), hydroxyl group-containing (meth)acrylic monomers are preferably used. Specific examples of the above hydroxyl group-containing (meth)acrylic monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; and hydroxyalkyl (meth)acrylamides such as N-hydroxypropyl (meth)acrylamide and N-hydroxybutyl (meth)acrylamide. Among these, hydroxyalkyl (meth)acrylates are preferred, and 4-hydroxybutyl (meth)acrylate is more preferred. The above hydroxyl group-containing (meth)acrylic monomers can be used individually or in combination of two or more.

In some preferred embodiments, a (meth)acrylic monomer having a hydroxyalkyl group with three or more carbon atoms is used as the hydroxyl group-containing (meth)acrylic monomer. Among these, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with three or more carbon atoms at the ester terminus are more preferred, and among these, compounds in which the alkyl group constituting the hydroxyalkyl group is linear are even more preferred. The number of carbon atoms in the hydroxyalkyl group of the hydroxyalkyl (meth)acrylate is, for example, 3 to 10, preferably 4 to 10, and may also be 4 to 8 or 4 to 6.

In embodiments using hydroxyl group-containing monomers (m2), the content of hydroxyl group-containing monomers (m2) in the monomer component can be appropriately set according to the intended use and required characteristics. In some embodiments, the content of hydroxyl group-containing monomers (m2) is, for example, 0.01% by weight or more of the total monomer component, may be 0.1% by weight or more, and more than 0.5% by weight is appropriate. In some preferred embodiments, it may be 1% by weight or more (e.g., more than 1% by weight), 2% by weight or more, or 3% by weight or more. Furthermore, in some embodiments, the content of hydroxyl group-containing monomers (m2) in the total monomer component may be, for example, less than 15% by weight, and 10% by weight or less is appropriate. In some preferred embodiments, it may be 8% by weight or less, 6% by weight or less, or 5% by weight or less. By using an appropriate amount of hydroxyl group-containing monomers (m2) within the above range, the cohesive force is improved, making it easier to adjust to a good adhesive strength that allows for re-peelability, and thus easily forming an adhesive suitable for, for example, re-peelable surface protection applications.

While not particularly limited, in some embodiments, the proportion of hydroxyl group-containing monomers (m2) in the sub-monomers used as monomer components of the acrylic polymer is suitable to be 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more. For example, it may be 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of hydroxyl group-containing monomers (m2) in the total copolymerizable monomer is 100% by weight, but for example, it may be 95% by weight or less.

Furthermore, in some embodiments, the monomer component of the acrylic polymer may include a monomer having a carboxyl group as a secondary monomer. By using a carboxyl group-containing monomer, the side chains of the acrylic polymer have carboxyl groups. Such carboxyl groups can act as crosslinking sites when using a crosslinking agent, such as an epoxy crosslinking agent. Using a carboxyl group-containing monomer makes it easier to obtain an adhesive with appropriate cohesive force. The carboxyl group-containing monomer can be used individually or in combination of two or more types.

Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and other ethylenically unsaturated monocarboxylic acids; and ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid. Furthermore, the carboxyl group-containing monomer may also be a monomer having a metal salt (e.g., an alkali metal salt) of the carboxyl group. As the carboxyl group-containing monomer, carboxyl group-containing (meth)acrylic monomers are preferably used. The above carboxyl group-containing (meth)acrylic monomers can be used individually or in combination of two or more types.

In embodiments using carboxyl group-containing monomers, the length of the side chain containing the carboxyl group in the monomer is not particularly limited. The number of carbon atoms in the carboxyl group-containing side chain of the carboxyl group-containing monomer may be, for example, 1 or more, 2 or more, and preferably 3 or more. For example, one or more (meth)acrylic monomers having carboxyl groups with 3 or more carbon atoms can be selected and used from the Light Ester series or Light Acrylate series available from Kyoeisha Chemical Co., Ltd. Specific examples include, for example, the trade names "Light Ester HO-MS(N)" (2-methacryloyloxyethyl succinic acid) and "HOA-MPE(N)" (2-acryloyloxyethyl-2-hydroxyethyl phthalic acid).

In some embodiments, the amount of carboxyl group-containing monomer used in the monomer component forming the acrylic polymer may be, for example, less than 10% by weight, less than 8% by weight, less than 5% by weight, less than 3% by weight, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, or less than 0.1% by weight. The techniques disclosed herein can preferably be implemented in embodiments in which the monomer component substantially does not contain carboxyl group-containing monomers. By limiting or eliminating the use of carboxyl group-containing monomers, the adhesive strength can be easily adjusted to a suitable range for re-peelability, making it easier to form adhesives suitable, for example, for re-peelable surface protection applications.

The monomer component forming the acrylic polymer may include other copolymerizable monomers copolymerizable with the alkyl (meth)acrylate (m1) described above. The other copolymerizable monomers are defined as copolymerizable monomers different from the alkyl (meth)acrylate (m1), linear alkyl (meth)acrylates other than the alkyl (meth)acrylate (m1), the hydroxyl group-containing monomer (m2), and the carboxyl group-containing monomer. Other non-limiting examples of copolymerizable monomers include: acid anhydride group-containing monomers; sulfonic acid group or phosphate group-containing monomers; epoxy group-containing monomers; cyano group-containing monomers; amide group-containing monomers such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide; amino group-containing monomers such as aminoethyl(meth)acrylate and N,N-dimethylaminoethyl(meth)acrylate; monomers having nitrogen atom-containing rings such as N-vinyl-2-pyrrolidone and N-(meth)acryloylmorpholine; imide group-containing monomers; and other functional group-containing monomers, as well as vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cyclohexyl(meth)acrylate, cyclopentyl(meth)acrylate, iso Examples include cycloalkyl (meth)acrylates such as bornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylate (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylate (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and others. Other copolymerizable monomers can be used individually or in combination of two or more.

The monomer component constituting the acrylic polymer may or may not contain the other copolymerizable monomers mentioned above. Furthermore, the amount of the other copolymerizable monomers is not particularly limited and can be appropriately selected depending on the purpose and application. The content of other copolymerizable monomers in the monomer component is appropriately less than 30% by weight, preferably less than 10% by weight, may be less than 8% by weight, more preferably less than 5% by weight, and may be less than 3% by weight (e.g., less than 1% by weight). The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain other copolymerizable monomers.

The biomass-carbon ratio of the monomer components constituting the above-mentioned acrylic polymer (the biomass-carbon ratio of the acrylic polymer) may be, for example, 1% or more, 10% or more is appropriate, preferably 30% or more, more preferably 50% or more (for example, more than 50%), and may also be 70% or more, 80% or more, or even 90% to 100%. By designing in this way, an acrylic adhesive that takes into consideration the reduction of reliance on fossil fuel-based materials can be obtained.

The method for obtaining acrylic polymers is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. Employing solution polymerization can be advantageous from the viewpoint of transparency and tackiness. As for the monomer supply method during solution polymerization, a batch supply method where all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc., can be appropriately employed. The polymerization temperature during solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, around 20°C to 170°C (typically around 40°C to 140°C).

The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators (e.g., azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN), or peroxide-based initiators, etc.) depending on the type of polymerization method. The amount of polymerization initiator used can be the usual amount; for example, it can be selected from a range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of monomer component.

While not particularly limited, the weight-average molecular weight (Mw) of the acrylic polymer is usually appropriate to be approximately 10 × ^10⁴ or higher. Using an acrylic polymer with such an Mw makes it easier to obtain an adhesive that exhibits good cohesiveness. In some embodiments, the Mw of the acrylic polymer is appropriate to be, for example, 30 × ^10⁴ or higher, preferably 50 × ^10⁴ or higher, and may also be 70 × ^10⁴ or higher, from the viewpoint of re-peelable adhesive strength and cohesive strength. By setting the Mw of the acrylic polymer to a predetermined value or higher, the cohesive strength of the adhesive is improved, and it is easier to prevent the occurrence of adhesive residue on the surface of the adherend. Furthermore, from the viewpoint of adhesion to the adherend, the Mw of the acrylic polymer is usually appropriate to be approximately 500 × ^10⁴ or lower, may also be 300 × ^10⁴ or lower, and may also be 100 × ^10⁴ or lower (for example, less than 100 × ^10⁴ ). By setting Mw below a predetermined value, the adhesive tends to have appropriate fluidity, making it easier to obtain wettability (adhesion) to the adherend. Good wettability allows, for example, in surface protection applications, the surface protection film to not peel off the adherend during use, thus effectively fulfilling its protective function. In acrylic polymers obtained by solution polymerization, it is particularly significant that its Mw falls within the aforementioned preferred range.

The Mw of acrylic polymers can be measured by gel permeation chromatography (GPC) and determined as a value equivalent to standard polystyrene. Specifically, it can be measured using the "HLC-8220GPC" (manufactured by Tosoh Corporation) GPC measuring device under the following conditions. The same applies to the examples described later.
[GPC measurement conditions]
Sample concentration: 0.2% by weight (tetrahydrofuran solution)
Sample injection volume: 10 μL
Eluent: Tetrahydrofuran (THF)
Flow rate: 0.6 mL/min; Column temperature (measurement temperature): 40°C
column:
Sample columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation)
Reference column: One "TSKgel SuperH-RC" column (manufactured by Tosoh Corporation)
Detector: Differential refractometer (RI)
Standard sample: Polystyrene

(Crosslinking agent)
In some embodiments, the adhesive layer contains a crosslinking agent. The crosslinking agent may help to increase the cohesive force of the adhesive. The crosslinking agent can be selected from various crosslinking agents known in the field of adhesives. Examples of such crosslinking agents include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, amine crosslinking agents, and the like. The crosslinking agent can be used alone or in combination of two or more. The crosslinking agent may be biomass-derived or non-biomass-derived.

The amount of crosslinking agent used is not particularly limited. The amount of crosslinking agent can be selected from, for example, 0.1 to 20 parts by weight per 100 parts by weight of the acrylic polymer. From the viewpoint of achieving a good balance between improved cohesive force and adhesion to the adherend, the amount of crosslinking agent per 100 parts by weight of the acrylic polymer is usually preferably 10 parts by weight or less, but may also be 8 parts by weight or less, 6 parts by weight or less, or 0.5 parts by weight or more, and may also be 1 part by weight or more. By setting the amount of crosslinking agent within an appropriate range, the cohesive force of the adhesive can be increased, the occurrence of adhesive residue on the adherend can be prevented, and adhesion to the adherend can be obtained.

In some embodiments, the adhesive layer preferably contains an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent can be used individually or in combination of two or more types. The isocyanate-based crosslinking agent may be biomass-derived or non-biomass-derived. Furthermore, the isocyanate-based crosslinking agent may be used in combination with other crosslinking agents, such as epoxy-based crosslinking agents.

As the isocyanate crosslinking agent, a polyisocyanate crosslinking agent having two or more isocyanate groups per molecule is preferably used. The number of isocyanate groups per molecule of the polyisocyanate crosslinking agent is preferably 2 to 10, for example 2 to 4, and typically 2 or 3. Examples of the above polyisocyanate crosslinking agent include aromatic polyisocyanates such as tolylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate. More specifically, for example, lower aliphatic polyisocyanates such as butylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl diisocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), trimethylolpropane/hex Examples include isocyanate adducts such as sharkmethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate HL"), isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), and isocyanurate of pentamethylene diisocyanate (manufactured by Mitsui Chemicals, trade name "Stavio D-370N"); polyisocyanates such as polyether polyisocyanate and polyester polyisocyanate; adducts of these polyisocyanates with polyols; and polyfunctionalized polyisocyanates obtained by isocyanurate bonding, biuret bonding, allophanate bonding, etc. For example, in applications where transparency is required for the adhesive, the use of aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, or isocyanurate derivatives of such aliphatic diisocyanates, is preferred. In embodiments using isocyanate-based crosslinking agents, the proportion of aliphatic polyisocyanates (such as aliphatic diisocyanates or isocyanurates of aliphatic diisocyanates) in the total amount of isocyanate-based crosslinking agents is preferably more than 50% by weight, may be 70% or more by weight, or 90% or more by weight (for example, 95-100% by weight).

When using an isocyanate-based crosslinking agent, the amount used may be, for example, approximately 0.1 parts by weight or more, 0.5 parts by weight or more, 1.0 part by weight or more, or more than 1.5 parts by weight, per 100 parts by weight of the acrylic polymer. From the viewpoint of obtaining a higher usage effect, in some preferred embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is, for example, 2.0 parts by weight or more (e.g., more than 2.0 parts by weight), more preferably 2.5 parts by weight or more, and may be 3.0 parts by weight or more, or 3.5 parts by weight or more. Also, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is usually appropriate to be 20 parts by weight or less, but may be 10 parts by weight or less, 8 parts by weight or less, or 6 parts by weight or less. In some preferred embodiments, the amount of the above-mentioned isocyanate-based crosslinking agent used may be 5 parts by weight or less (e.g., less than 5 parts by weight), or 4.5 parts by weight or less (e.g., less than 4.0 parts by weight). By controlling the amount of isocyanate-based crosslinking agent used within an appropriate range, the cohesive force of the adhesive can be increased, preventing adhesive residue from forming on the substrate and achieving good adhesion. Furthermore, limiting the amount of isocyanate-based crosslinking agent makes it easier to form a transparent adhesive.

While not particularly limited, the technology disclosed herein can preferably be implemented in an embodiment comprising an adhesive layer containing an acrylic polymer and a crosslinking agent. In some embodiments, the total amount of the acrylic polymer and crosslinking agent in the adhesive layer is appropriately approximately 85% to 100% by weight, preferably approximately 90% or more by weight (e.g., more than 90%), and may also be approximately 95% or more by weight, approximately 98% or more by weight, or approximately 99% or more by weight (e.g., more than 99%). In the above adhesive composition, the amount of optional additives used is limited. This is preferable from the viewpoint of preventing contamination of the adherend by optional additives (e.g., low molecular weight components).

(catalyst)
Furthermore, the adhesive layer preferably contains a catalyst. By using a catalyst, the curing reaction of the adhesive composition (typically the crosslinking reaction of the crosslinking agent described above) can be efficiently advanced, making it easier to achieve stable adhesion from an early stage after the adhesive sheet is manufactured. The catalyst is also called a crosslinking catalyst. Examples of catalysts include tin (Sn)-containing compounds (tin-based catalysts), zirconium (Zr)-containing compounds (zirconium-based catalysts), titanium (Ti)-containing compounds (titanium-based catalysts), hafnium (Hf)-containing compounds (hafnium-based catalysts), iron (Fe)-containing compounds (iron-based catalysts), aluminum (Al)-containing compounds (aluminum-based catalysts), zinc (Zn)-containing compounds (zinc-based catalysts), bismuth (Bi)-containing compounds (bismuth-based catalysts), and the like. These are typically organic compounds having a metal in their active center, and are also called organometallic catalysts. Catalysts can be used individually or in combination of two or more.

In several preferred embodiments, a compound containing a Group IV element is used as a catalyst. Using a Group IV element-containing compound as a catalyst allows for rapid aging and sufficient pot life. Because Group IV element-containing compounds allow for good catalyst addition without the use of tin-based catalysts, which have been widely used due to their high catalytic activity, an adhesive that is environmentally friendly and safe can be obtained. Furthermore, Group IV element-containing compounds tend to exhibit less color change, such as discoloration, compared to other catalysts such as iron-based catalysts. Therefore, for example, in applications where transparency and optical properties are required for the adhesive, the use of a Group IV element-containing compound as a catalyst is preferable. Moreover, using a suitable Group IV element-containing compound can highly suppress contamination of the adherend surface. Group IV element-containing compounds can be used individually or in combination of two or more. Suitable Group IV element-containing compounds include zirconium-containing compounds (zirconium-based catalysts), titanium-containing compounds (titanium-based catalysts), and hafnium-containing compounds (hafnium-based catalysts), with zirconium-containing compounds being preferred. Using zirconium-containing compounds, it is possible to obtain adhesives with excellent transparency.

Suitable examples of zirconium-containing compounds (organozirconium-containing compounds) as catalysts are not particularly limited, and include, for example, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, zirconium octolate compounds, and the like. More specifically, zirconium alkoxides such as tetraethoxyzirconium, tetra-n-propoxyzirconium, tetra-i-propoxyzirconium, tetra-n-butoxyzirconium (n-butylzirconate), tetra-i-butoxyzirconium, tetra-sec-butoxyzirconium, tetra-t-butoxyzirconium; triethoxy-mono(acetylacetonate)zirconium, tri-n-propoxy-mono(acetylacetonate)zirconium, tri-i-propoxy-mono(acetylacetonate)zirconium, tri-n-butoxy-mono(acetylacetonate)zirconium, tri-sec-butoxy-mono(acetylacetonate)zirconium, tri-t-butoxy-mono(acetylacetonate)zirconium, diethoxy-bis(acetylacetonate) Tris(acetylacetonate) zirconium, di-n-propoxy-bis(acetylacetonate) zirconium, di-i-propoxy-bis(acetylacetonate) zirconium, di-n-butoxy-bis(acetylacetonate) zirconium, di-sec-butoxy-bis(acetylacetonate) zirconium, di-t-butoxy-bis(acetylacetonate) zirconium, monoethoxy-tris(acetylacetonate) zirconium, mono-n-propoxy-tris(acetylacetonate) zirconium, mono-i-propoxy-tris(acetylacetonate) zirconium, mono-n-butoxy-tris(acetylacetonate) zirconium, mono-sec-butoxy-tris(acetylacetonate) zirconium, mono-t-butoxy-tris(acetylacetonate) zirconium Tetrakis(acetylacetonate) zirconium, triethoxy-mono(ethylacetacetate) zirconium, tri-n-propoxy-mono(ethylacetacetate) zirconium, tri-i-propoxy-mono(ethylacetacetate) zirconium, tri-n-butoxy-mono(ethylacetacetate) zirconium, tri-sec-butoxy-mono(ethylacetacetate) zirconium, tri-t-butoxy-mono(ethylacetacetate) zirconium, diethoxy-bis(ethylacetacetate) zirconium, di-n-propoxy-bis(ethylacetacetate) zirconium, di-i-propoxy-bis(ethylacetacetate) zirconium, di-n-butoxy-bis(ethylacetacetate) zirconium, di-sec-butoxy-bis(ethylacetacetate) zirconium Zirconium acetate, di-t-butoxy bis(ethyl acetate) zirconium, monoethoxy tris(ethyl acetate) zirconium, mono-n-propoxy tris(ethyl acetate) zirconium, mono-i-propoxy tris(ethyl acetate) zirconium, mono-n-butoxy tris(ethyl acetate) zirconium, mono-sec-butoxy tris(ethyl acetate) zirconium, mono-t-butoxy tris(ethyl acetate) zirconium, tetrakis(ethyl acetate) zirconium, mono(acetylacetonate) tris(ethyl acetate) zirconium, bis(acetylacetonate) bis(ethyl acetate) zirconium, tris(acetylacetonate) Examples include zirconium chelates such as mono(ethylacetoacetate)zirconium; and others. The above zirconium-containing compounds can be used individually or in combination of two or more.

The titanium-containing compounds (organotitanium-containing compounds) are not particularly limited, and examples include tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, and titanium ethylacetoacetate. More specifically, tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium, tetra-n-butoxytitanium, tetra-n-butoxytitanium dimer, tetra-i-butoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium, titanium di-2-ethylhexyloxybis(2-ethyl-3-hydroxyhexyloxide), titanium lactate, titanium lactate ammonium salt, titanium diisopropoxybis(triethanolamine), tetrakis(2-ethylhexyloxy)titanium, titanium-i-propoxyoctylene glycolate, di-i-propoxybis(acetylacetonate)titanium, propanedioxytitanium bis(ethylacetoacetate), tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, titanium stearate, di-i-propoxytitanium diisostearate, (2- n-butoxycarbonylbenzoyloxy)tributoxytitanium, di-n-butoxybis(triethanolamine)titanium, triethoxymono(acetylacetonate)titanium, tri-n-propoxymono(acetylacetonate)titanium, tri-i-propoxymono(acetylacetonate)titanium, tri-n-butoxymono(acetylacetonate)titanium, tri-sec-butoxymono(acetylacetonate)titanium, tri -t-butoxy mono(acetylacetonate) titanium, diethoxy bis(acetylacetonate) titanium, di-n-propoxy bis(acetylacetonate) titanium, di-n-butoxy bis(acetylacetonate) titanium, di-sec-butoxy bis(acetylacetonate) titanium, di-t-butoxy bis(acetylacetonate) titanium, monoethoxy tris(acetylacetonate) titanium, mono-n-propoxy tris(a Titanium cetylacetonate, mono-i-propoxy tris(acetylacetonate) titanium, mono-n-butoxy tris(acetylacetonate) titanium, mono-sec-butoxy tris(acetylacetonate) titanium, mono-t-butoxy tris(acetylacetonate) titanium, tetrakis(acetylacetonate) titanium, triethoxy mono(ethylacetoacetate) titanium, tri-n-propoxy mono(ethylacetoacetate) Titanium tate, tri-i-propoxy mono(ethyl acetacetate) titanium, tri-n-butoxy mono(ethyl acetacetate) titanium, tri-sec-butoxy mono(ethyl acetacetate) titanium, tri-t-butoxy mono(ethyl acetacetate) titanium, diethoxy bis(ethyl acetacetate) titanium, di-n-propoxy bis(ethyl acetacetate) titanium, di-i-propoxy bis(ethyl acetacetate) Titanium tate, di-n-butoxy-bis(ethylacetacetate) titanium, di-sec-butoxy-bis(ethylacetacetate) titanium, di-t-butoxy-bis(ethylacetacetate) titanium, monoethoxy-tris(ethylacetacetate) titanium, mono-n-propoxy-tris(ethylacetacetate) titanium, mono-i-propoxy-tris(ethylacetacetate) titanium, mono-n-butoxy-tris(ethylacetacetate) Examples include titanium triacetate, mono-sec-butoxytris(ethylacetate)titanium, mono-t-butoxytris(ethylacetate)titanium, tetrakis(ethylacetate)titanium, mono(acetylacetonate)tris(ethylacetate)titanium, bis(acetylacetonate)bis(ethylacetate)titanium, tris(acetylacetonate)mono(ethylacetate)titanium, etc. The above titanium-containing compounds can be used individually or in combination of two or more.

As hafnium-containing compounds (organic hafnium-containing compounds), compounds are used in which zirconium or titanium in the above-mentioned zirconium-containing compounds and titanium-containing compounds is replaced with hafnium. Examples include hafnium tetraacetylacetonate; hafnium pentanedionate; hafnium alkoxides such as tetramethoxyhafnium, tetraethoxyhafnium, tetrabutoxyhafnium, and tetrapentoxyhafnium; etc. The above hafnium-containing compounds can be used individually or in combination of two or more.

Other examples of catalysts include tin-containing compounds (organotin-containing compounds) such as dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, and butyltin oxide; aluminum-containing compounds (organoaluminum-containing compounds) such as aluminum secondary butoxide, aluminum trisacetylacetonate, aluminum bisethylacetoacetate, and aluminum trisethylacetoacetate; and iron-containing compounds (organoiron-containing compounds) such as ferric narcem.

In some embodiments, the catalyst used in the adhesive layer does not contain tin-containing compounds. While the techniques disclosed herein do not exclude the use of tin-based catalysts, they enable the achievement of desired catalytic additive effects (rapid aging and sufficient pot life) without the use of tin-based catalysts, which have been widely used due to their high catalytic activity. By minimizing the use of tin-based catalysts, adhesives that are environmentally friendly and safe can be obtained.

The amount of catalyst used is not particularly limited. The amount of catalyst used can be, for example, approximately 0.0001 parts by weight or more per 100 parts by weight of the acrylic polymer, with approximately 0.001 parts by weight or more being appropriate, and approximately 0.005 parts by weight or more (e.g., 0.01 parts by weight or more). In some preferred embodiments, the amount of catalyst used per 100 parts by weight of the acrylic polymer is approximately 0.02 parts by weight or more, and may be approximately 0.03 parts by weight or more. Using the catalyst within the above range tends to easily form an adhesive with good peelability. Furthermore, the amount of catalyst used can be, for example, approximately 1 part by weight or less per 100 parts by weight of the acrylic polymer, with approximately 0.5 parts by weight or less being appropriate, and approximately 0.1 parts by weight or less being appropriate, and may be approximately 0.05 parts by weight or less. By using an appropriate amount of catalyst, the crosslinking reaction rate can be adjusted. Also, by limiting the amount of catalyst used, contamination of the adherend caused by the catalyst can be suppressed.

(Other ingredients)
Furthermore, the adhesive layer composition used to form the adhesive layer may optionally contain a compound that induces keto-enol tautomerism as a crosslinking retarder. For example, a compound that induces keto-enol tautomerism can be preferably used in an adhesive composition containing an isocyanate-based crosslinking agent. This can extend the pot life of the adhesive composition. Various β-dicarbonyl compounds can be used as compounds that induce keto-enol tautomerism. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionyl acetate esters such as ethyl propionyl acetate; isobutyryl acetate esters such as ethyl isobutyryl acetate; malonic acid esters such as methyl malonate and ethyl malonate; and the like. Among these, acetylacetone and acetoacetate esters are particularly preferred. The compounds that induce keto-enol tautomerism can be used individually or in combination of two or more.

The amount of the compound that causes keto-enol tautomerism may be, for example, 1 part by weight or more, preferably 5 parts by weight or more, and may be, for example, 15 parts by weight or more, per 100 parts by weight of the acrylic polymer contained in the adhesive composition. In some embodiments, from the viewpoint of obtaining a sufficient pot life, the amount of the compound that causes keto-enol tautomerism may be, for example, 30 parts by weight or more, preferably 60 parts by weight or more, and may be 120 parts by weight or more, per 100 parts by weight of the acrylic polymer contained in the adhesive composition. Furthermore, the above amount may be, for example, 200 parts by weight or less, preferably 180 parts by weight or less, and may be, for example, 160 parts by weight or less, and may be 140 parts by weight or less.

The above adhesive layer may further contain various conventionally known additives as needed. Examples of such additives include surface lubricants, leveling agents, tackifying resins, release modifiers (surfactants, etc.), plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, preservatives, light stabilizers, UV absorbers, polymerization inhibitors, silane coupling agents, etc. The content of these optional additives can be appropriately set according to the intended use. The amount of the above optional additive used is, for example, less than 10 parts by weight per 100 parts by weight of acrylic polymer, and is appropriately about 3 parts by weight or less. In some preferred embodiments, it is about 1 part by weight or less (e.g., less than 1 part by weight), may be 0.5 parts by weight or less, 0.3 parts by weight or less, or 0.1 parts by weight or less (e.g., less than 0.1 parts by weight). By limiting the amount of optional additives used (especially low molecular weight components such as release modifiers and antistatic agents), contamination of the adherend caused by the optional additives can be suppressed. From a similar viewpoint, the proportion of acrylic polymer in the adhesive layer should be 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more (for example, 90% by weight or more and 99.9% by weight or less), and may be 95% by weight or more.

(Method for forming an adhesive layer)
The form of the adhesive composition used to form the adhesive layer is not particularly limited, but aqueous adhesive compositions, solvent-type adhesive compositions, etc., are preferred. Here, an aqueous adhesive composition refers to an adhesive composition in which an adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) mainly composed of water, and a typical example is an aqueous dispersion type adhesive composition in which the adhesive is dispersed in water. A solvent-type adhesive composition refers to an adhesive composition in which an adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-type adhesive composition, one or more organic solvents that can be used in the above-mentioned solution polymerization (such as toluene and ethyl acetate) can be used without particular limitation. From the viewpoint of adhesive properties, etc., the technology disclosed herein can preferably be implemented in an embodiment comprising an adhesive layer formed from a solvent-type adhesive composition. The effects of the technology disclosed herein are preferably realized in an embodiment comprising a solvent-type adhesive layer formed from a solvent-type adhesive composition.

The formation of an adhesive (layer) from an adhesive composition can be carried out by conventionally known methods. For example, in the case of a substrate-less double-sided adhesive sheet, an adhesive sheet can be formed by applying the adhesive composition to a release surface (release surface) and then curing the adhesive composition to form an adhesive layer (a layer consisting of adhesive) on the surface. In the case of an adhesive sheet with a substrate, a method of forming the adhesive layer by directly applying (typically coating) the adhesive composition to the substrate and curing it (direct method) can be preferably employed. Alternatively, a method of forming an adhesive layer on a release surface (release surface) by applying the adhesive composition and curing it, and then transferring the adhesive layer to the substrate (transfer method), may also be employed. The release surface can be the surface of a release sheet or the back surface of a substrate that has undergone a release treatment. Furthermore, the curing of the adhesive composition can be carried out by subjecting the adhesive composition to curing treatments such as drying, crosslinking, polymerization, and cooling. Two or more curing treatments may be performed simultaneously or in stages.

The adhesive composition can be applied using known or conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, die coaters, bar coaters, knife coaters, and spray coaters. Alternatively, the adhesive composition may be applied by impregnation or curtain coating methods.
From the viewpoint of promoting the crosslinking reaction and improving manufacturing efficiency, it is preferable to dry the adhesive composition under heating. The drying temperature can be, for example, around 40 to 150°C, and is usually preferably around 60 to 130°C. After drying the adhesive composition, aging may be performed for the purpose of adjusting the migration of components within the adhesive layer, promoting the crosslinking reaction, and alleviating any strain that may exist in the substrate or adhesive layer.

(Thickness)
While not particularly limited, the thickness of the adhesive layer is suitable to be approximately 1 μm or more, and preferably approximately 3 μm or more (for example, approximately 5 μm or more). From the viewpoint of adhesion to the adherend, the above thickness is preferably approximately 10 μm or more, more preferably approximately 14 μm or more, and even more preferably approximately 17 μm or more. The above thickness can also be, for example, approximately 100 μm or less, suitable to be approximately 50 μm or less (for example, approximately 30 μm or less), and preferably approximately 25 μm or less. An adhesive layer having the above thickness is suitable as an adhesive layer for surface protective film applications.

(Gel fraction)
While not particularly limited, the gel fraction of the adhesive layer is preferably 70% or more. Adhesives with a gel fraction of 70% or more are less prone to deformation or damage such as dents caused by external forces during manufacturing, and are less likely to change in appearance. Such adhesives tend to form adhesive sheets with a smooth surface, which is preferable when forming them into transparent adhesive sheets and performing inspection of the adherend through the sheet, as it enables high-precision inspection. Furthermore, by setting a high gel fraction, it is easier to form an adhesive with excellent re-peelability. From this viewpoint, the gel fraction is more preferably over 80%, may be over 85% (e.g., 90% or more), may be 92% or more, or may be 94% or more (e.g., 95% or more). The gel fraction may be 100%, but from the viewpoint of adhesion to the adherend, it may be, for example, less than 99% or less than 95% (e.g., 94% or less).

The gel fraction of the adhesive layer is measured by the following method. Take 1 g of W from the adhesive layer and wrap it in a porous PTFE (polytetrafluoroethylene) sheet to make a sample. Place the sample in a glass bottle and immerse it in ethyl acetate solution and leave it for 7 days. Then remove the sample and dry it at 130°C for 2 hours. Weigh the dried sample and subtract the weight of the porous PTFE sheet to obtain the weight of the dried adhesive, W2 g. Substitute W1 and W2 into the following formula to calculate the gel fraction [%].
Gel fraction [%] = (W2/W1) × 100
As the porous PTFE sheet, you can use the product name "TEMISH" manufactured by Nitto Denko Corporation or an equivalent product.

(Biomass carbon ratio)
In some embodiments, the adhesive layer contains biomass-derived material, and its biomass-carbon ratio may be above a predetermined value. The biomass-carbon ratio of the adhesive layer is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass-carbon ratio of the adhesive means that less fossil resource-based material, such as petroleum, is used. From this viewpoint, a higher biomass-carbon ratio of the adhesive is preferable. For example, the biomass-carbon ratio of the adhesive layer may be 55% or more, may be 60% or more, may be 70% or more, may be 75% or more, may be 80% or more, and may be greater than 80%. The upper limit of the biomass-carbon ratio is 100% by definition, may be 99% or less, may be 95% or less, or 90% or less from the viewpoint of material availability. From the viewpoint of easily exhibiting good adhesive performance, in some embodiments, the biomass-carbon ratio of the adhesive layer may be, for example, 90% or less, may be 85% or less, or 80% or less.

<Base material>
The material of the support substrate used as a support for the adhesive sheet disclosed herein is not particularly limited, and for example, a resin film can be preferably used. The resin film may be formed from various resin materials into a film shape. The resin material is preferably one that can form a resin film with excellent properties of one or more of the following: transparency, mechanical strength, thermal stability, moisture shielding, isotropy, etc. For example, a resin film composed of a resin material whose main component (i.e., a component present in an amount greater than 50% by weight) is polyester such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate; cellulose such as diacetylcellulose and triacetylcellulose; polycarbonates; acrylic polymers such as polymethyl methacrylate; etc. can preferably be used as the substrate. Other examples of resin materials constituting the above-mentioned resin film include styrene polymers such as polystyrene and acrylonitrile-styrene copolymers; polyolefins, such as polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, ethylene-propylene copolymers, etc.; polyvinyl chlorides; polyamides such as nylon 6, nylon 6,6, and aromatic polyamides; etc. Alternatively, a resin film composed of resin materials mainly consisting of polyimides, polysulfones, polyethersulfones, polyetheretherketones, polyphenylene sulfides, fluororesins, polyvinyl alcohols, polyvinyl acetates, polyvinylidene chlorides, polyvinyl butyrals, polyarylates, polyoxymethylenes, epoxy resins, etc. may be used as a substrate. The resin materials constituting the above-mentioned resin film may be a blend of two or more of these.

In this specification, "resin film" refers to a non-porous structure, typically a substantially void-free (void-free) resin film. Therefore, the above-mentioned resin film is a concept distinct from foamed films, nonwoven fabrics, and woven fabrics.

Other examples of substrates include foamed sheets made from foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made from various fibrous materials (which may include natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate) alone or in blends; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and glass. Substrates with composite structures of these materials may also be used. Examples of such composite substrates include, for example, a substrate with a structure in which metal foil and the above-mentioned plastic film are laminated, and a plastic sheet reinforced with inorganic fibers such as glass cloth.

The base material may be made from biomass-derived materials or from non-biomass-derived materials. From the viewpoint of producing adhesive sheets while considering the reduction of reliance on fossil fuel-based materials, biomass-derived base materials (typically resin films) are preferably used.

Furthermore, the base material may be formed using recyclable materials or recycled materials (also called recycled materials). Resin film is preferably used as such recycled material. Since resin film (e.g., polyester film such as PET film) is recyclable, regardless of whether plant-derived materials are used, sustainable reproduction is possible by reusing used resin film, thereby reducing the environmental burden. Such recyclable resin film or recycled resin film is also called recycled film. The above-mentioned recycled material (e.g., recycled film) may be formed from biomass-derived materials or from non-biomass-derived materials.

In some preferred embodiments, the base material is a resin film (polyester resin film) formed from a resin (polyester resin) whose main component is polyester (containing more than 50% by weight). For example, a resin film (PET film) where the polyester is mainly PET, or a resin film (PEN film) where the polyester is mainly PEN, etc., can be preferably used.

The substrate may have a single-layer structure or a multi-layer structure. Therefore, the resin film that can be used as the substrate may also have a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure). A single-layer resin film can preferably be used as the substrate.

The above-mentioned substrate (typically a resin film) may contain various additives as needed, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, UV absorbers, antistatic components, plasticizers, colorants (pigments, dyes, etc.), and fillers.

The adhesive layer side surface of the substrate may be subjected to surface treatments such as chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, or ionization radiation treatment. Such surface treatments may, for example, enhance the adhesion between the substrate and the adhesive layer. In some embodiments, the adhesive layer side surface of the substrate may be treated with a primer. In some embodiments, the back surface of the substrate may be treated with a hard coat. This improves the scratch resistance of the back surface of the substrate, allowing for superior protective performance when the adhesive sheet is used as a protective sheet. Furthermore, in some other embodiments, the substrate may be treated with an antistatic treatment to suppress the generation of static electricity. The substrate may also be treated with various other treatments such as anti-fouling, anti-fingerprint, anti-glare, and anti-reflective properties.

The thickness of the substrate can be appropriately selected considering the application, purpose, and usage of the adhesive sheet. From the perspective of strength and workability, a substrate with a thickness of approximately 10 μm or more is suitable, preferably approximately 20 μm or more, more preferably approximately 30 μm or more (e.g., 35 μm or more). Furthermore, from the viewpoint of cost, a substrate thickness of approximately 200 μm or less is suitable, preferably approximately 150 μm or less, more preferably approximately 100 μm or less, and even more preferably approximately 75 μm or less (e.g., 50 μm or less). A substrate having the above thickness is suitable, for example, as a substrate for a surface protection film.

<Release Sheet>
The release sheet used in the adhesive sheet with release sheet disclosed herein is a non-silicone release sheet. Non-silicone release sheets are used to protect the adhesive surface during distribution, storage, and processing of the adhesive sheet before use in applications where the use of silicone release sheets is undesirable, and can also be used in the formation of the adhesive layer and the manufacture of the adhesive sheet. In this specification, "release sheet" is also called a release sheet and includes what are called release films and release liners. Furthermore, "non-silicone release sheet" refers to a release sheet in which at least the surface on the adhesive sheet side (release surface) is made of a material that does not contain silicone material, and for example, the entire release sheet may be made of a material that does not contain silicone material. Examples of non-silicone release sheets include release sheets having a release layer formed with a release agent other than silicone material (non-silicone release agent).

Examples of non-silicone release sheets include release sheets having a release treatment layer on the surface of a substrate such as a resin film or paper; fluorine-based release sheets having a single-layer or multi-layer structure made of fluorine-based polymers (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, etc.); and polyolefin-based release sheets having a single-layer or multi-layer structure made of polyolefin-based resins (polyethylene, polypropylene, etc.).

In some embodiments, a non-silicone release sheet comprises a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate. Here, "release sheet substrate" refers to a substrate used for forming a release sheet, i.e., a substrate for release sheets, used to distinguish it from the aforementioned substrate for adhesive sheets, and is not particularly limited beyond that. Various plastic films can be used as the release sheet substrate. In this specification, "plastic film" typically refers to a non-porous sheet and is a concept distinct from, for example, nonwoven fabrics (i.e., not including nonwoven fabrics). As the substrate, a resin film with a non-porous structure, typically substantially free of air bubbles (voidless), can be preferably used. The resin film may have a single-layer structure or a multilayer structure of two or more layers (e.g., a three-layer structure).

Examples of materials for the above-mentioned plastic film include polyolefin resins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyvinyl chloride resins; polyvinylidene chloride resins; polyvinyl alcohol resins; ethylene-vinyl acetate copolymer resins; ethylene-vinyl alcohol copolymer resins; cellulose resins such as triacetylcellulose; acetate resins; polycarbonate resins; polyamide resins; and others. A release sheet substrate formed from one or more of these resins may also be used. Among these, a preferred release sheet substrate is a polyester resin film (e.g., PET film) formed from a polyester resin. Similar to the substrate for adhesive sheets, release sheet substrates made from biomass-derived materials or recycled materials (recycled film, etc.) are preferably used.

The plastic film used as the release sheet substrate may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, the plastic film may have a single-layer structure or a multilayer structure including two or more sublayers. The plastic film may contain known additives that can be used in substrates, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, UV absorbers, colorants such as pigments and dyes, lubricants, fillers, plasticizers, antistatic agents, slip agents, antiblocking agents, and nucleating agents. In a multilayer plastic film, each additive may be incorporated into all sublayers or into only some of the sublayers.

In some embodiments, the non-silicone release treatment layer disposed on the release sheet substrate is a release treatment layer that does not contain silicone material, and may be a release treatment layer formed by a non-silicone release treatment agent such as a long-chain alkyl release treatment agent, an aliphatic carboxylic acid ester release treatment agent, a fluorine release treatment agent, or a molybdenum sulfide release treatment agent. While not particularly limited, a release treatment layer formed by at least one selected from long-chain alkyl release treatment agents and aliphatic carboxylic acid ester release treatment agents is preferred as it is easier to form a release treatment layer without uneven coating or whitening. Among these, a release treatment layer formed from a material containing a long-chain alkyl release treatment agent is particularly preferred because it easily provides excellent easy peelability.

As a long-chain alkyl-based stripping agent, one containing a long-chain alkyl group-containing compound having a linear or branched alkyl group with 6 or more carbon atoms is used. The number of carbon atoms in the alkyl group of the long-chain alkyl group-containing compound is preferably 8 or more, more preferably 12 or more. Examples of the alkyl group include octyl, decyl, lauryl, octadecyl, and behenyl groups. Examples of long-chain alkyl group-containing compounds include various long-chain alkyl group-containing polymer compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, and long-chain alkyl group-containing quaternary ammonium salts. From the viewpoint of heat resistance and stain resistance, long-chain alkyl group-containing polymer compounds are preferred. Furthermore, from the viewpoint of effectively obtaining water repellency with small amounts of use, polymer compounds having long-chain alkyl groups in their side chains are more preferred. The long-chain alkyl group-containing compounds can be used individually or in combination of two or more.

Examples of polymer compounds having long-chain alkyl groups as side chains include acrylic polymers obtained by polymerizing monomer components containing alkyl (meth)acrylates having alkyl groups with six or more carbon atoms, and polymers obtained by reacting a polymer having a reactive group with an alkyl group-containing compound that can react with the reactive group. Examples of the reactive group include hydroxyl groups, amino groups, carboxyl groups, and acid anhydrides. Examples of compounds having these reactive groups include polyvinyl alcohol, butyral resin, ethylene-vinyl alcohol resin, polyethyleneimine, polyethyleneamine, reactive group-containing polyester resin, and reactive group-containing poly(meth)acrylic resin. Among these, acrylic polymers, polyvinyl alcohol, butyral resin, and ethylene vinyl alcohol resin are preferred from the viewpoint of easy peelability and handling.

Examples of alkyl group-containing compounds that can react with the reactive group, used in reactions with polymers having the above-mentioned reactive group, include: long-chain alkyl group-containing isocyanates such as octyl isocyanate, decyl isocyanate, lauryl isocyanate, octadecyl isocyanate, and behenyl isocyanate; long-chain alkyl group-containing acid chlorides such as octyl chloride, decyl chloride, lauryl chloride, octadecyl chloride, and behenyl chloride; long-chain alkyl group-containing amines; and long-chain alkyl group-containing alcohols. Among these, long-chain alkyl group-containing isocyanates are preferred from the viewpoint of easy peelability and handling, and octadecyl isocyanate is particularly preferred.

The amount of alkyl group-containing compound that can react with the above-mentioned reactive group should preferably be an appropriate amount that achieves the desired peelability without causing transfer to the adhesive surface or contamination of the adherend. While not particularly limited, it is appropriate to react the alkyl group-containing compound in an amount of 100 parts by weight or more (for example, 200 parts by weight or more, and even 300 parts by weight or more) per 100 parts by weight of the polymer having the reactive group. Furthermore, it is appropriate to use 1000 parts by weight or less (for example, 800 parts by weight or less, and even 700 parts by weight or less) per 100 parts by weight of the polymer having the reactive group.

Furthermore, the aliphatic carboxylic acid ester that may be included in the stripping agent is one obtained by reacting an aliphatic carboxylic acid with an alcohol. The aliphatic carboxylic acid component is preferably a mono or dicarboxylic acid having 6 to 36 carbon atoms, and more preferably an aliphatic saturated monocarboxylic acid having 6 to 36 carbon atoms. Specific examples of aliphatic carboxylic acids include palmitic acid, stearic acid, valeric acid, caproic acid, capric acid, lauric acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, tetrariacontanoic acid, montanic acid, glutaric acid, adipic acid, and azelaic acid. The aliphatic carboxylic acid can be used alone or in combination of two or more. The alcohol used to produce the aliphatic carboxylic acid ester is a saturated or unsaturated monohydric or polyhydric alcohol. The alcohol may have substituents such as fluorine atoms or aryl groups. For example, saturated alcohols with 30 or fewer carbon atoms are preferred, and aliphatic saturated alcohols with 30 or fewer carbon atoms are more preferred. The above aliphatic alcohols include alicyclic alcohols. Specific examples of the alcohols mentioned above include octanol, decanol, dodecanol, stearyl alcohol, behenyl alcohol, ethylene glycol, diethylene glycol, glycerin, pentaerythritol, 2,2-dihydroxyperfluoropropanol, neopentylene glycol, ditrimethylolpropane, and dipentaerythritol. Alcohols can be used individually or in combination of two or more.

Specific examples of the above-mentioned aliphatic carboxylic acid esters include beeswax (a mixture mainly composed of myricyl palmitate), stearyl stearate, behenyl behenate, octyldodecyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, and pentaerythritol tetrastearate. Aliphatic carboxylic acid esters can be used individually or in combination of two or more.

While not particularly limited, the non-silicone-based release treatment layer typically contains 70% by weight or more of the release agent, such as the long-chain alkyl group-containing compound or aliphatic carboxylic acid ester. The content of the release agent in the release treatment layer may be 80% by weight or more, or even 90% by weight or more. The upper limit of the release agent content may be, for example, 99% by weight or less.

The release treatment layer may optionally contain known additives such as antistatic agents, colorants, surfactants, plasticizers, tackifiers, low molecular weight polymers, surface lubricants, leveling agents, antioxidants, corrosion inhibitors, light stabilizers, UV absorbers, polymerization inhibitors, and fillers.

Non-silicone release sheets can be manufactured by known methods, or commercially available non-silicone release sheets may be obtained and used. For example, a release sheet having a non-silicone release treatment layer on a release sheet substrate can be manufactured by applying a solution containing a non-silicone release treatment agent (release treatment agent composition) to the surface of the release sheet substrate using a suitable coater (such as a gravure roll coater), removing the solvent by drying, and performing appropriate curing.

The thickness of the peel-off layer is not particularly limited and is set to an appropriate thickness that provides the desired peelability. For example, a thickness of 1 nm or more is suitable, preferably 5 nm or more, more preferably 10 nm or more, and also suitable to be around 200 nm or less, preferably 100 nm or less, and may even be 50 nm or less.

The overall thickness of the release liner is not particularly limited. From the viewpoint of strength and dimensional stability, a thickness of 5 μm or more is appropriate, preferably 10 μm or more, and may be 20 μm or more. By protecting the adhesive surface with a release liner of sufficient thickness, the smoothness of the adhesive surface is easily maintained. Furthermore, from the viewpoint of handling the release liner (e.g., ease of winding), a thickness of 300 μm or less is appropriate, preferably 200 μm or less, more preferably 100 μm or less, and may also be 75 μm or less, 50 μm or less, or 35 μm or less. By setting the thickness of the release liner to a predetermined value or less, peeling from the adhesive sheet becomes smoother.

<Adhesive Sheet Characteristics>
The adhesive sheet with a release sheet disclosed herein has a peeling force (release sheet peeling force) when peeling the non-silicone-based release sheet from the adhesive layer surface of the adhesive sheet, which is comparable to the peeling force when a silicone-based release sheet is used. Although not particularly limited, in some embodiments, the release sheet peeling force is preferably less than 0.50 N/50 mm, preferably 0.30 N/50 mm or less, may be 0.20 N/50 mm or less, or 0.10 N/50 mm or less. The lower the release sheet peeling force, the better the peeling workability tends to be. In some preferred embodiments, the release sheet peeling force is less than 0.07 N/50 mm, more preferably 0.05 N/50 mm or less, may be 0.04 N/50 mm or less, may be 0.03 N/50 mm or less, or 0.02 N/50 mm or less. The technology disclosed herein makes it possible to achieve the above-described easy peelability for non-silicone release sheets. The lower limit of the release force of the release sheet may be, for example, 0.01 N/50 mm or more. By having a release force of the release sheet above a predetermined value, the adhesive surface can be well protected by the release sheet. The release force of the release sheet is measured under the conditions of 23°C, 50% RH atmosphere, tensile speed of 0.3 m/min, and peel angle of 180°. Specifically, it is measured by the method described in the examples below.

The adhesive strength of the adhesive sheet can be appropriately set according to the intended use and application location, and is not limited to a specific range. In some embodiments, the adhesive sheet (preferably a surface protective film) preferably has an adhesive strength to a glass plate (initial adhesive strength to glass) of 2.0 N/25 mm or less, measured under conditions of a temperature of 23°C, 50% RH, a peeling angle of 180°, and a tensile speed of 0.3 m/min. An adhesive sheet (preferably a surface protective film) that satisfies this characteristic has a low peeling force when peeling from the adherend (e.g., the object to be protected), making it easy to peel off. From the viewpoint of peelability, the above initial adhesive strength to glass is more preferably 1.0 N/25 mm or less, even more preferably 0.5 N/25 mm or less, and particularly preferably 0.1 N/25 mm or less (e.g., less than 0.1 N/25 mm). From the viewpoint of adhesion to the substrate and substrate protection, the initial adhesive strength to glass is appropriately 0.01 N/25 mm or higher, but may also be 0.03 N/25 mm or higher, or 0.05 N/25 mm or higher. Specifically, the initial adhesive strength to glass is measured by the method described in the examples below.

In some embodiments, the adhesive sheet preferably has transparency with a total light transmittance of approximately 50% or more. A transparent adhesive sheet with a total light transmittance of 80% or more (e.g., 85% or more) is more preferable. The upper limit of the total light transmittance may be around 99% or less (e.g., 95% or less) in applications where transparency is required. Such a transparent adhesive sheet is preferable because it allows for high-precision inspection, for example, when inspecting an object through the adhesive sheet. Such an adhesive sheet is suitable as an optical surface protection film. The value of the total light transmittance can be a value measured in accordance with JIS K 7361-1.

<Application>
The adhesive sheet disclosed herein can be used for a variety of applications. The adhesive sheet disclosed herein is suitable, for example, as a surface protection film that is applied to an object to be protected and, once its protective purpose has been achieved, is usually peeled off (re-peeled off) from the object to be protected. Since surface protection films are generally required not to alter the object to be protected before and after protection, it may be advantageous to use an adhesive sheet with a non-silicone release sheet that does not cause contamination of the protected surface with silicone material after peeling off. The object to be protected by the above surface protection film is not particularly limited and can be used as a protective film for various products, components, etc. Furthermore, the adhesive sheet with a non-silicone release sheet disclosed herein is particularly suitable for optical applications where predetermined optical properties are required, as it does not cause contamination of the adherend by silicone material. For example, the adhesive sheet disclosed herein is particularly suitable as an optical surface protection film that protects the surface of optical components (for example, optical components used as components of liquid crystal display panels, such as polarizers and waveplates) during processing and transportation of said optical components. More specifically, surface protection films are suitable for protecting optical components used as components of liquid crystal display panels, plasma display panels (PDPs), organic electroluminescent (EL) displays, etc., during manufacturing, transportation, etc. In particular, they are useful as surface protection films applied to optical components such as polarizing plates (polarizing films, e.g., reflective polarizing films), wave plates, phase difference plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets for liquid crystal display panels.

Furthermore, since the adhesives disclosed herein may, in some embodiments, contain acrylic polymers with a high biomass-carbon ratio, they can be used as a substitute for conventional acrylic adhesives (i.e., acrylic adhesives with a low biomass-carbon ratio) in various applications, thereby contributing to reducing reliance on fossil fuel-based materials. The adhesive sheets disclosed herein can typically be preferably used as adhesive sheets (e.g., surface protective films) with reduced reliance on fossil fuel-based materials.

The matters disclosed in this specification include the following:
[1] An adhesive sheet with a release sheet comprising an adhesive sheet having an adhesive layer and a non-silicone release sheet disposed on the surface of the adhesive layer,
The adhesive layer contains an acrylic polymer,
The acrylic polymer is a polymer of a monomer component containing an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 17 carbon atoms at its ester terminus, wherein the alkyl group having 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group with 1 carbon atom, and is an adhesive sheet with a release liner.
[2] The adhesive sheet with a release sheet according to [1] above, wherein the alkyl (meth)acrylate (m1) comprises at least one selected from n-heptyl acrylate and n-octyl acrylate.
[3] The adhesive sheet with a release sheet according to [1] or [2] above, wherein the monomer component comprises a monomer having a hydroxyl group (m2).
[4] The adhesive sheet with a release liner according to any one of [1] to [3] above, wherein the adhesive layer contains an isocyanate-based crosslinking agent.
[5] The adhesive sheet with a release liner according to any one of [1] to [4] above, wherein the adhesive layer contains a zirconium-containing compound.
[6] The non-silicone release sheet comprises a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate.
The non-silicone release treatment layer is formed of a material containing a long-chain alkyl release treatment agent, wherein the adhesive sheet with a release sheet is as described in any of [1] to [5] above.
[7] The adhesive sheet with a release sheet according to any one of [1] to [6] above, wherein the adhesive sheet comprises a base material and the adhesive layer disposed on at least one surface of the base material.
[8] The adhesive sheet is an adhesive sheet with a release sheet as described in any of [1] to [7] above, which is used by being attached to an optical component.
[9] The adhesive sheet is an adhesive sheet with a release sheet as described in any of [1] to [8] above, used as a surface protective film.

The following describes several embodiments of the present invention, but the invention is not intended to be limited to those shown in these embodiments. In the following description, "parts" refers to weight unless otherwise specified.

<Example of preparation>
(Preparation of acrylic polymer (A1))
In a flask equipped with a refluxer, stirrer, nitrogen gas inlet tube, and thermometer, 96 parts of n-heptyl acrylate (HpA) and 4 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components were charged with ethyl acetate (polymerization solvent) to a solid content concentration of 36%. 0.3 parts of azobisisobutyronitrile (AIBN) was then added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 4 hours while maintaining the liquid temperature in the flask at approximately 60°C. The mixture was then aged at 70°C for 4 hours to obtain a solution of acrylic polymer (A1). The weight-average molecular weight (Mw) of the obtained acrylic polymer (A1) was 760,000. Note that HpA is a compound synthesized using biomass-derived heptyl alcohol, and has a biomass-derived heptyl group at its ester terminus.

(Preparation of acrylic polymer (A2))
In a flask equipped with a refluxer, stirrer, nitrogen gas inlet tube, and thermometer, 96 parts of n-lauryl acrylate (LA) and 4 parts of 4HBA as monomer components were charged with ethyl acetate (polymerization solvent) to a solid content of 30%. 0.2 parts of AIBN were then added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 5 hours while maintaining the liquid temperature in the flask at around 60°C. After that, the mixture was aged at 70°C for 2 hours to obtain a solution of acrylic polymer (A2). The Mw of the obtained acrylic polymer (A2) was 570,000.

(Preparation of acrylic polymer (A3))
A solution of acrylic polymer (A3) was obtained by the same method as the preparation of acrylic polymer (A2), except that n-octyl acrylate (n-OcA) was used as the monomer component instead of LA. The Mw of the obtained acrylic polymer (A3) was 800,000.

(Preparation of acrylic polymer (A4))
A solution of acrylic polymer (A4) was obtained by the same method as the preparation of acrylic polymer (A1), except that 2-ethylhexyl acrylate (2EHA) was used as the monomer component instead of HpA. The Mw of the obtained acrylic polymer (A4) was 410,000.

(Preparation of acrylic polymer (A5))
In a flask equipped with a refluxer, stirrer, nitrogen gas inlet tube, and thermometer, 96 parts of n-pentyl acrylate (n-PnA) and 4 parts of 4HBA as monomer components were charged with ethyl acetate (polymerization solvent) to a solid content concentration of 30%. 0.2 parts of AIBN were then added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60°C. After that, the mixture was aged at 70°C for 2 hours to obtain a solution of acrylic polymer (A5). The Mw of the obtained acrylic polymer (A5) was 770,000.

(Preparation of acrylic polymer (A6))
A solution of acrylic polymer (A6) was obtained by the same method as the preparation of acrylic polymer (A2), except that isostearyl acrylate (i-StA) was used as the monomer component instead of LA. The Mw of the obtained acrylic polymer (A6) was 49,000.

<Example 1>
(Preparation of adhesive composition)
The acrylic polymer (A1) solution obtained above was diluted with ethyl acetate until the solid content concentration reached 30%. To this solution, 3.5 parts (solid content) of an isocyanate crosslinking agent (trade name "Coronate HX", isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh Corporation) and 0.035 parts (solid content) of a zirconium catalyst (trade name "ZC-150", zirconium tetraacetylacetonate, manufactured by Matsumoto Fine Chemical Co., Ltd.) were added per 100 parts of the solid content of the solution. Acetylacetone was then added to the diluted polymer solution to a concentration of 8%, and the mixture was stirred to obtain the acrylic adhesive composition according to this example.

(Making adhesive sheets)
The acrylic adhesive composition immediately after compounding was applied to a polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T100C38", thickness 38 μm), and the solvent was removed by drying at 130°C for 20 seconds to form an adhesive layer (thickness 21 μm). Subsequently, the surface of the adhesive layer was covered with a non-silicone release sheet (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T100H25 [UH18]", thickness 25 μm), and left to stand at room temperature (23°C) for 4 days to obtain the adhesive sheet with release sheet according to this example. The non-silicone release sheet has a release treatment layer formed on the surface of a polyester film substrate with a release treatment agent containing pentaerythritol fatty acid ester and octadecyl isocyanate.

<Examples 2-12 and Comparative Examples 1-6>
Adhesive sheets with release sheets for each example were obtained in the same manner as in Example 1, except that the type of acrylic polymer, the amount of crosslinking agent used (solids), the type and amount of catalyst used (solids), and the type of release sheet were changed as shown in Table 1.
In the example using a tin catalyst, 0.015 parts (solids) of dioctyl tin dilaurate (manufactured by Tokyo Fine Chemical Co., Ltd., trade name "Envirizer OL-1") was used as the tin catalyst, per 100 parts of the solids content of the acrylic polymer solution, and acetylacetone was added after dilution to a concentration of 3% of the polymer solution.
As the silicone-based release sheet, one prepared by the following method was used. 100 parts of a silicone-based release agent (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KS-847T") were mixed with 3.3 parts of a silicone curing catalyst (manufactured by Shin-Etsu Chemical Co., Ltd., product name "CAT-PL-50T"), and diluted to a concentration of 0.3% with a mixed solvent containing toluene, n-hexane, and methyl ethyl ketone in a weight ratio of 1:2:1 to obtain a silicone-based release agent composition. This release agent composition was applied to a 25 μm thick polyester film (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T100-25") and dried at 130°C for 1 minute to produce a silicone-based release sheet having a 20 nm thick silicone-based release treatment layer on the polyester film after drying.

(Initial adhesion to glass)
Adhesive sheets were cut to a size of 25 mm in width and 80 mm in length. These sheets were then pressed onto a clean soda-lime glass plate, which had been cleaned by rubbing it 10 times back and forth with a clean cloth soaked in ethanol, using a 2 kg roller to press them down once back and forth to create a sample for evaluating adhesive strength. After leaving the evaluation sample at room temperature for 30 minutes, the adhesive strength [N/25 mm] was measured at 23°C and 50% RH using a tensile testing machine (Shimadzu Corporation, product name "Autograph AG-50NX") under conditions of a peel angle of 180° and a tensile speed of 0.3 m/min. Two measurements were performed for each example (n=2), and the average value was taken as the initial adhesive strength to glass [N/25 mm]. As the adherend glass plate, a soda-lime glass plate (product number "S200423") manufactured by Matsunami Glass Co., Ltd. or an equivalent product was used.

(Contamination)
The surface of the substrate (the side of the glass plate from which the adhesive sheet was removed) was observed visually in a darkroom under fluorescent light after measuring the initial adhesion strength to glass. If no change was observed in the surface condition of the substrate, it was judged to be acceptable.

(Peelability of release sheet)
The adhesive sheet was cut to a size of 50 mm in width and 80 mm in length. The back of the adhesive sheet was fixed to an acrylic plate with double-sided tape (Nitto Denko Corporation, product name "No. 5000NS"). Under conditions of 23°C and 50% RH, the release sheet was peeled from the adhesive surface of the adhesive sheet using a tensile testing machine (Shimadzu Corporation, product name "Autograph AG-50NX") at a peel angle of 180° and a tensile speed of 0.3 m/min, and the peel force [N/50 mm] at this time was measured. For each example, the measurement was performed twice (n=2), and the maximum value among them was taken as the release sheet peel force [N/50 mm].

(Water contact angle of the glass plate surface after removal of adhesive sheet)
An adhesive sheet was pressed onto a glass slide using a 2 kg roller, completing one back-and-forth motion, to prepare an evaluation sample. After leaving the evaluation sample at room temperature for 30 minutes, the adhesive sheet was peeled off the glass slide at a constant angle and speed, and the water contact angle [°] of the glass slide surface was measured at 23°C and a 50% RH atmosphere. The contact angle was measured using a contact angle meter (Kyowa Interface Science Co., Ltd., product name "CA-X") with the droplet method (θ/2 method). The amount of distilled water droplets was 2 μL, and the standing time from droplet placement to measurement was 2000 milliseconds. For each example, five measurements were performed (n=5), and the average value was used. As the adherend glass plate, a soda-lime glass plate (product number "S1214") manufactured by Matsunami Glass Co., Ltd. or an equivalent product was used.

Table 1 shows an overview of each case and its evaluation results.

As shown in Table 1, when an acrylic polymer synthesized using 2EHA (a branched alkyl group with 8 carbon atoms and a branched alkyl group with 2 carbon atoms) as the linear alkyl (meth)acrylate was used, Comparative Example 1, which used a silicone-based release sheet, showed a low release force of 0.02 N/50 mm and excellent release properties. However, in Comparative Example 2, which used a non-silicone-based release sheet, the release force increased to 0.07 N/50 mm, and a tendency for the release properties to decrease was observed. On the other hand, when HpA (a linear alkyl group with 7 carbon atoms) was used as the monomer component of the acrylic polymer contained in the adhesive, in Comparative Example 4, which used a silicone-based release sheet, the initial adhesion to glass was 0.06 N/25 mm and the release sheet peeling force was 0.02 N/50 mm. In contrast, in Example 1, which used a non-silicone-based release sheet, the initial adhesion to glass was 0.05 N/25 mm and the release sheet peeling force was 0.03 N/50 mm. This confirmed that even when using a non-silicone-based release sheet, the release sheet peeling performance was comparable to that when using a silicone-based release sheet. In Examples 2 to 4, which used the same acrylic polymer as Example 1 but changed the amount of crosslinking agent and the type of catalyst, good release sheet peeling performance was also confirmed.

Furthermore, in Examples 5 to 12, which used an acrylic polymer adhesive synthesized using alkyl (meth)acrylate (specifically LA, n-OcA) as a monomer component, where the alkyl group has 6 to 17 carbon atoms and is either a linear alkyl group or a branched alkyl group with 1 carbon atom, good peelability of the release sheet was confirmed. On the other hand, even when the alkyl group of the alkyl (meth)acrylate used as the monomer component was a linear alkyl group, when the alkyl group had 5 carbon atoms (Comparative Example 5: using n-PnA), the release force tended to be high, and good peelability of the release sheet could not be obtained. Also, in Comparative Example 6, where i-StA with 18 carbon atoms in the alkyl group was used as the linear alkyl (meth)acrylate, the viscosity was too low, making it impossible to form an adhesive layer with a uniform film thickness, and thus the adhesive sheet could not be evaluated.

Furthermore, when the water contact angle of the glass plate surface after peeling off the adhesive sheet was measured, it was 16° for Example 1, 41° for Comparative Example 1, 43° for Comparative Example 2, and 20° for Comparative Example 4. In Example 1, the water contact angle did not increase before and after the application of the adhesive sheet. Also, from a comparison between Comparative Examples 1 and 2, and between Example 1 and Comparative Example 4, an increase in the water contact angle of the adherend surface was observed in the cases using silicone-based release sheets, compared to cases using non-silicone-based release sheets, even with short application times. This is thought to be due to the transfer of the silicone material of the release sheet to the adherend. The difference in water contact angles between Example 1, Comparative Example 4, and Comparative Examples 1 and 2 is thought to be due to differences in catalyst types. Furthermore, when the contamination resistance of Examples 1 to 12 and Comparative Examples 1 to 5 was evaluated, all passed at a visual level (no change in surface condition was observed).

From the above results, it can be seen that by using an adhesive containing an acrylic polymer which is a polymer of a monomer component containing alkyl (meth)acrylate (m1) having an alkyl group with 6 to 17 carbon atoms at its ester terminus, and where the alkyl group with 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group with 1 carbon atom, it is possible to achieve release sheet peelability comparable to that of a silicone-based release sheet, even when using a non-silicone-based release sheet.

The above describes specific examples of the present invention in detail, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above.

1. Adhesive sheet 10. Base material (supporting base material)
10A 1st side 10B 2nd side (back)
21 Adhesive layer 21A Adhesive surface 31 Release sheet 100 Adhesive sheet with release sheet

Claims (6)

An adhesive sheet with a release sheet comprises an adhesive sheet having an adhesive layer and a non-silicone release sheet disposed on the surface of the adhesive layer,
The adhesive sheet comprises a base material and an adhesive layer disposed on at least one surface of the base material, wherein the base material is a resin film.
The adhesive layer contains an acrylic polymer,
The acrylic polymer is a polymer of monomer components containing an alkyl (meth)acrylate (m1) having an alkyl group with 6 to 17 carbon atoms at its ester terminus, where the alkyl group with 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group with 1 carbon atom.
The alkyl (meth)acrylate (m1) comprises at least one selected from n-heptyl acrylate and n-octyl acrylate.
The non-silicone release sheet comprises a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate.
The aforementioned non-silicone release layer is formed from a material containing a long-chain alkyl release agent, and is an adhesive sheet with a release liner. The adhesive sheet with a release liner according to claim 1 , wherein the monomer component comprises a monomer (m2) having a hydroxyl group. The adhesive layer comprises an isocyanate-based crosslinking agent, as described in claim 1 or 2, for an adhesive sheet with a release liner. The adhesive layer comprises a zirconium-containing compound, as described in claim 1 or 2, for the adhesive sheet with a release liner. The adhesive sheet is used by being attached to an optical component, as described in claim 1 or 2. The adhesive sheet is used as a surface protective film, and is an adhesive sheet with a release liner according to claim 1 or 2.