JP7815643B2 - Polyester-based resin composition, pressure-sensitive adhesive composition, pressure-sensitive adhesive, pressure-sensitive adhesive sheet and laminate, and polyester-based resin (A) and its production method - Google Patents

Description

The present invention relates to a polyester resin composition, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and a laminate containing the same, as well as a polyester resin (A) and a method for producing the same. More specifically, the present invention relates to a polyester resin composition made from environmentally friendly recycled raw materials that has excellent storage stability in solution and, when made into a pressure-sensitive adhesive, has excellent adhesive properties such as adhesive strength, holding power, and humidity and heat durability, as well as a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and a laminate containing the same. The present invention also relates to a polyester resin (A) used in such a polyester resin composition and a method for producing the same.

In recent years, with the aim of making products smaller and lighter, adhesives have come to be used to join parts together, and instead of the commonly used acrylic resins, adhesives using polyester resins, which have superior adhesive strength, are being considered.

On the other hand, the use of recycled raw materials has recently been recommended as part of measures to combat the depletion of fossil resources and global warming, and there is a demand for resin compositions and adhesive compositions made from recycled raw materials that are environmentally friendly.

Thermoplastic polyester resin (hereinafter sometimes referred to as "recycled PET") used as such a recycled raw material is a noteworthy recycled raw material, as recycling methods have been established for it from PET bottles (hereinafter sometimes referred to as "PET bottles") and the like.

For example, Patent Document 1 discloses that by adding a hydrolysis inhibitor to a polyester-based adhesive having a glass transition temperature of -10°C or lower, a highly durable polyester adhesive with excellent adhesive properties and transparency can be obtained, even when exposed to high temperatures and high humidity. More specifically, it is known that polyester-based adhesives are prone to hydrolysis, and the above-mentioned composition discloses that it is possible to meet the more stringent humidity and heat resistance conditions that are sometimes required of adhesives.

Patent Document 2 also discloses that a polyester adhesive layer containing a polyester polymerized using a dimer acid as the dicarboxylic acid component and a dimer diol as the diol component, in which the diol component contains 1.04 to 2.10 moles of hydroxyl groups per mole of carboxyl groups in the dicarboxylic acid component, and a tackifier, requires a small amount of organic solvent, can be applied thickly, and has excellent adhesion, retention, and repulsion resistance.

Furthermore, Patent Document 3 discloses a reactive adhesive that uses recycled PET.

JP 2017-115149 A JP 2014-169419 A Patent No. 6892020

However, while the technology disclosed in Patent Document 1 may potentially result in an environmentally friendly adhesive by using plant-derived raw materials, it still imposes a high environmental load. Furthermore, when an aromatic polycarboxylic acid is used in combination as a polycarboxylic acid component, the high melting point of the monomer means that the esterification reaction does not proceed unless the reaction is carried out at a high temperature for a long period of time, which is problematic as it tends to leave behind carboxylic acids. Furthermore, carrying out a reaction at a high temperature for a long period of time consumes a large amount of energy, which may ultimately result in a higher environmental load. Furthermore, carrying out a reaction at a high temperature for a long period of time may increase the likelihood of side reactions or may result in the decomposition of the polyester due to thermal history, resulting in the generation of carboxylic acids. Furthermore, there is also the problem that an increase in the carboxylic acid concentration may cause the carboxylic acid to react with the hydrolysis inhibitor, which crosslinks the polymer, resulting in an increase in the viscosity of the adhesive solution during storage.
As a method for introducing an aromatic carboxylic acid component, there is also a method of using an ester of an aromatic dicarboxylic acid such as dimethyl terephthalate or dimethyl isophthalate, but these substances have the disadvantage that they are highly sublimable and tend to clog the inside of the rectification column of the reactor or the distillation line.

Furthermore, the technology disclosed in Patent Document 2 primarily uses plant-derived raw materials, which reduces the environmental impact, but the resin is too soft, which results in a low elastic modulus when made into an adhesive sheet, and a tendency for adhesive properties such as adhesive strength when made into a double-sided adhesive tape, making it still unsatisfactory. In response to this, it is possible to improve adhesive properties, including adhesive strength, by adding a tackifier, etc., but this increases the number of essential components, which poses a problem of reduced design freedom.

Furthermore, while the technology in Patent Document 3 describes the use of recycled PET in a polyester polyol composition for reactive adhesives, it makes no mention of high-molecular-weight polyesters suitable for use in pressure-sensitive adhesives. Furthermore, even if low-molecular-weight polyesters are used directly in pressure-sensitive adhesive applications, it is difficult to achieve a balance between durability and adhesive strength, and they also have poor suitability for thick coatings, making them difficult to use in pressure-sensitive adhesives. Furthermore, evaluations of boiling treatments and other processes have been conducted on two-component reactive polyurethane adhesives using the polyester polyol compositions, and while a certain level of water resistance has been found, when used as pressure-sensitive adhesives, more stringent evaluations of humidity and heat resistance are often required, and there is a problem of insufficient durability unless measures to prevent hydrolysis are taken.

As such, it has been disclosed that adhesives can be made using plant-derived raw materials to create environmentally friendly adhesives. However, growing plants takes several years to several decades, or even hundreds of years in the worst case scenario, which is extremely time-consuming. Recycling waste resin, on the other hand, allows unwanted resin to be used at any time, and is therefore considered a better method when considering the environmental impact in terms of time.

Against this background, the present invention aims to provide a polyester resin composition that uses recycled PET and other environmentally friendly recycled materials, which, when made into an adhesive solution, has excellent storage stability and adhesive properties such as adhesive strength and holding power; an adhesive composition, adhesive agent, adhesive sheet, and laminate containing the polyester resin; and a polyester resin (A) used in such a polyester resin composition and a method for producing the same.

However, the present inventors conducted extensive research based on the following concept and discovered that by forming a resin composition containing a specific polyester resin (A) containing structural units derived from a thermoplastic polyester resin (excluding polyester resin (A)) (a1), structural units derived from an aliphatic dicarboxylic acid (a2), and structural units derived from a polyol (a3), and a hydrolysis inhibitor (B), it is possible to obtain a polyester resin composition that is environmentally friendly, has excellent storage stability when made into an adhesive solution, and is excellent in adhesive properties such as adhesive strength and holding power, and thus completed the present invention.

In general, polyester-based adhesives use, for example, aromatic polycarboxylic acids, aliphatic polycarboxylic acids, and alicyclic polycarboxylic acids in appropriately controlled composition ratios to ensure their physical properties. However, as mentioned above, when aromatic polycarboxylic acids are used, there is the problem that the acid value tends to remain.

In contrast, recycled thermoplastic polyester resins have almost no acid value, and when they are subjected to transesterification, esterification, and polycondensation reactions with aliphatic polycarboxylic acids and polyol components, polyester resins with low glass transition temperatures (Tg) can be produced again. In addition, since there is no need to consume carboxylic acids derived from aromatic dicarboxylic acids in the esterification reaction, it is possible to produce polyester resins with almost no acid value.
Therefore, since the hydrolysis inhibitor that reacts with carboxylic acid does not react with this polyester resin having a very low acid value at first, the storage stability of the polyester resin solution is improved. In other words, it is possible to create a situation where carboxylic acid is not generated from the polyester resin until it is placed in a severe environment such as a high temperature and high humidity, and a product that is easy to handle is obtained.

The present invention has the following aspects [1] to [14].
[1] A resin composition containing a polyester-based resin (A) and a hydrolysis inhibitor (B), wherein the polyester-based resin (A) contains structural units derived from a thermoplastic polyester resin (excluding the polyester-based resin (A)) (a1), structural units derived from an aliphatic polycarboxylic acid (a2), and structural units derived from a polyol (a3), and the polyester-based resin composition has a glass transition temperature of 40°C or lower.
[2] The polyester-based resin composition according to the above [1], wherein the acid value of the polyester-based resin (A) is 0.5 mg KOH/g or less.
[3] The polyester-based resin composition according to the above [1] or [2], wherein the acid value of the polyester-based resin composition is 0.5 mg KOH/g or less.
[4] The polyester-based resin composition according to any one of [1] to [3], wherein the polyester-based resin (A) has a hydroxyl value of 15 mg KOH/g or less.
[5] The polyester-based resin composition according to any one of [1] to [4], wherein the polyester-based resin (A) is obtained using a polyol (a3) having hydroxyl groups in a molar ratio of 1.2 or more per mole of carboxy groups of polycarboxylic acids including the aliphatic polycarboxylic acids (a2).
[6] The polyester resin composition according to any one of [1] to [5] above, wherein the hydrolysis inhibitor (B) is a polyvalent carbodiimide compound (B1).
[7] The polyester resin composition according to any one of [1] to [6], further comprising a crosslinking agent (C).
[8] A pressure-sensitive adhesive composition containing the polyester resin composition according to any one of [1] to [7] above.
[9] A pressure-sensitive adhesive obtained using the pressure-sensitive adhesive composition described in [8] above.
[10] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive according to [9] above.
[11] A laminate having a release-treated sheet on one side thereof and a base sheet or a release-treated sheet on the other side thereof via the pressure-sensitive adhesive layer according to [10] above.
[12] A polyester-based resin (A) containing structural units derived from a thermoplastic polyester resin (excluding polyester-based resin (A)) (a1), structural units derived from an aliphatic polycarboxylic acid (a2), and structural units derived from a polyol (a3), and having a glass transition temperature of 40°C or lower and a hydroxyl value of 15 mgKOH/g or lower.
[13] A method for producing a polyester-based resin (A) having a glass transition temperature of 40°C or lower and a hydroxyl value of 15 mgKOH/g or lower, the method comprising copolymerizing a thermoplastic polyester resin (excluding the polyester-based resin (A)) (a1), an aliphatic polycarboxylic acid (a2), and a polyol (a3).
[14] A method for producing a polyester-based resin (A) containing structural units derived from a thermoplastic polyester (excluding the polyester-based resin (A)) (a1), structural units derived from an aliphatic polycarboxylic acid (a2), and structural units derived from a polyol (a3), and having a glass transition temperature of 40°C or lower, the method comprising: decomposing the thermoplastic polyester (a1) by a reaction between the thermoplastic polyester (a1) and the aliphatic polycarboxylic acid (a2), and then copolymerizing a copolymerization component containing the polyol (a3).

The polyester resin composition of the present invention is a polyester resin composition that is highly recyclable and environmentally friendly, and has a low environmental impact during the manufacturing process. Furthermore, it has excellent storage stability when made into a resin composition solution, and when made into an adhesive, it has excellent adhesive strength and holding power.
Therefore, it can be effectively used as an environmentally friendly material for single-sided or double-sided pressure-sensitive adhesive sheets used for laminating optical components, single-sided or double-sided pressure-sensitive adhesive sheets for fixing components of portable electronic devices, and single-sided or double-sided pressure-sensitive adhesive sheets for fixing electronic components.

The configuration of the present invention will be described in detail below, but these are merely examples of preferred embodiments.
In the present invention, the term "carboxylic acids" includes not only carboxylic acids but also carboxylic acid derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters.
In the present invention, the term "α and/or β (α and β are optional constituents or components)" means three combinations: α only, β only, and α and β.

The polyester resin composition (hereinafter referred to as "the polyester resin composition") according to one embodiment of the present invention comprises a thermoplastic polyester resin (excluding polyester resin (A)) (a1), an aliphatic polycarboxylic acid (a2), and a polyol (a3), and is a resin composition containing polyester resin (A) having a glass transition temperature of 40°C or less, and hydrolysis inhibitor (B). The polyester resin (A) is described in detail below.

<Polyester Resin (A)>
In general, polyester resins have, as their resin structure, structural units derived from polycarboxylic acids and structural units derived from polyols, and are usually obtained by polymerizing polymerization components containing polycarboxylic acids and polyols.

The polyester resin (A) used in this polyester resin composition contains structural units derived from a thermoplastic polyester resin (a1), structural units derived from an aliphatic polycarboxylic acid (a2), which is a polycarboxylic acid, and structural units derived from a polyol (a3). In particular, it is preferable that the polyester resin (A) be obtained by polymerizing polymerization components including a thermoplastic polyester resin (a1), an aliphatic polycarboxylic acid (a2), and a polyol (a3).

[Thermoplastic polyester resin (a1)]
As the thermoplastic polyester resin (a1), polyethylene terephthalate (hereinafter, sometimes referred to as "PET") is preferably used. The PET is a polyester resin obtained by polymerizing terephthalic acids and ethylene glycol, and may be further modified with a substance such as isophthalic acids, phthalic anhydrides, adipic acids, cyclohexanedicarboxylic acids, sebacic acids, 1,3-butanediol, 1,4-butanediol, or cyclohexanedimethanol, as necessary.

In addition, commercially available unused PET bottles, PET film, crushed leftovers from the manufacture of other PET products, and recycled PET recovered from waste and washed can also be used. Of these, the use of recycled PET is preferable from an environmental perspective. Washed and pelletized PET is available on the market.

The intrinsic viscosity (IV) of the above-mentioned PET is preferably 0.50 to 0.90 dL/g. This range allows the polycondensation reaction between PET and other raw materials to be carried out at 260°C or less.

The above-mentioned PET preferably contains 0.1 to 5% by weight of a diethylene glycol component, more preferably 0.5 to 2.5% by weight. If the content is too low, the crystallinity of the polyester resin (A) will be high, making it difficult to melt and prone to remaining undissolved during production. If the content is too high, it will affect the overall resin composition, making stable production more likely to be affected.

The acid value of the above-mentioned PET is preferably 50 mgKOH/g or less, more preferably 10 mgKOH/g or less, and even more preferably 5 mgKOH/g or less. If the acid value is too high, the acid value tends to increase when the polyester resin (A) is produced.

The content of structural units derived from the thermoplastic polyester resin (a1) in the copolymerization components of polyester resin (A) is preferably 1 to 90% by weight, more preferably 5 to 80% by weight, even more preferably 10 to 60% by weight, particularly preferably 15 to 50% by weight, and especially preferably 20 to 40% by weight, of all structural units derived from the copolymerization components. If the content is too low, the contribution to the global environment will be small, and the cohesive strength will be reduced, which will tend to reduce adhesive strength and prevent sufficient adhesive performance. If the content is too high, the initial adhesive strength (tack) will tend to decrease. For the sake of the global environment, it is preferable that thermoplastic polyester resin (a1) is derived from recycled materials, and the more recycled-derived structural units there are, the better.

The content of structural units derived from dicarboxylic acids derived from the thermoplastic polyester resin (a1) in the copolymerization components of polyester resin (A) is preferably 1 mol % or more and less than 90 mol %, more preferably 5 to 80 mol %, even more preferably 10 to 60 mol %, particularly preferably 15 to 50 mol %, and especially preferably 20 to 40 mol % based on all structural units derived from polycarboxylic acids. If this content is too low, the contribution to the global environment will be reduced, and further, the cohesive strength will decrease, resulting in reduced adhesive strength and insufficient adhesive performance. If the content is too high, the initial adhesive strength (tack) will tend to decrease.

[Aliphatic polycarboxylic acids (a2)]
Examples of the aliphatic polycarboxylic acid (a2) in the copolymerization component of the polyester resin (A) include linear alkyl dicarboxylic acids such as malonic acids, succinic acids, glutaric acids, adipic acids, pimelic acids, azelaic acids, sebacic acids, 1,9-nonanedicarboxylic acids, and decanedicarboxylic acids; dicarboxylic acids having an alkyl group in the side chain such as dimethylmalonic acids, trimethyladipic acids, 2,2-dimethylglutaric acids, 1,3-diethylglutaric acids, and dimer acids; unsaturated group-containing dicarboxylic acids such as fumaric acids, maleic acids, and itaconic acids; and acyclic aliphatic dicarboxylic acids such as thiodipropionic acids and diglycolic acids. These may be used alone or in combination of two or more. Among these, it is preferable to use linear alkyl dicarboxylic acids and dimer acids because they can easily lower the glass transition temperature and adjust the adhesive properties, and it is more preferable to use succinic acid, adipic acid, sebacic acid, and dimer acids because of their ease of availability.

In order to be more environmentally friendly, it is also preferable that the aliphatic polycarboxylic acids (a2) have a high biomass content, and among these, it is particularly preferable to use plant-derived aliphatic polycarboxylic acids. Examples of plant-derived aliphatic polycarboxylic acids include sebacic acids derived from castor oil, succinic acids derived from corn, and dimer acids derived from rapeseed oil.

The "dimer acids" are those containing as a main component a dimer of an unsaturated fatty acid having an average carbon number of 10 to 26, preferably a dimer of an unsaturated fatty acid having an average carbon number of 12 to 24, and more preferably a dimer of an unsaturated fatty acid having an average carbon number of 14 to 22. Specific examples of dimer acids include dicarboxylic acids derived from unsaturated fatty acids such as oleic acids, linoleic acids, linolenic acids, and erucic acids.
Here, the term "main component" refers to a component whose content is 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more of the total.

Examples of the dimer acids include dimer acids derived from the unsaturated fatty acids listed above, and hydrogenated dimer acids. Among these, hydrogenated dimer acids are preferred because they are more likely to prevent crystallization.

The raw materials used for the above dimer acids are usually plants or beef tallow, but as already mentioned, it is preferable to use plant-derived raw materials that are environmentally friendly.

The content of structural units derived from such aliphatic polycarboxylic acids (a2) is preferably 99 mol% or less, more preferably 5 to 90 mol%, and particularly preferably 50 to 70 mol%, based on the total amount of structural units derived from polycarboxylic acids. If this content ratio is too high, the adhesive strength may decrease or the resin may crystallize, making it difficult to achieve sufficient adhesive performance.

In addition to the aliphatic polycarboxylic acids (a2), alicyclic polycarboxylic acids and aromatic polycarboxylic acids can also be used as the polycarboxylic acid component of the polyester resin (A).

Examples of the alicyclic polycarboxylic acids include cyclic aliphatic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acids, 1,2-cyclohexanedicarboxylic acids, 1,3-cyclopentanedicarboxylic acids, 1,4-cyclohexanedicarboxylic acids, 2,5-norbornanedicarboxylic acids, and adamantanedicarboxylic acids.
These alicyclic polycarboxylic acids may be used alone or in combination of two or more.

Examples of the aromatic polycarboxylic acids include benzene-based dicarboxylic acids such as phthalic acids, terephthalic acids, isophthalic acids, benzylmalonic acids, diphenic acids, 4,4'-oxydibenzoic acids, naphthalenedicarboxylic acids such as 1,8-naphthalenedicarboxylic acids, 2,3-naphthalenedicarboxylic acids, and 2,7-naphthalenedicarboxylic acids; and heterocyclic dicarboxylic acids such as furandicarboxylic acids and thiophenedicarboxylic acids (pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, etc.). These may be used alone or in combination of two or more. Among these, terephthalic acids, isophthalic acids, and furandicarboxylic acids are preferred due to their ease of availability.

When the aromatic polycarboxylic acids are introduced, they are preferably used in small amounts, preferably 30 mol % or less, and more preferably 10 mol % or less, based on the total structural units derived from the polycarboxylic acids. If the content is too high, the reactivity of the aromatic polycarboxylic acids will be slow, which will tend to extend the reaction time and increase the burden on the global environment. Furthermore, since carboxylic acids are likely to remain, the storage stability of the resin solution will tend to be poor.

The above aromatic polycarboxylic acids are likely to be introduced substantially through the thermoplastic polyester resin (a1), so there is no need to specifically charge and incorporate them as aromatic polycarboxylic acids.

[Polyol (a3)]
Examples of the polyol (a3) in the copolymerization component of the polyester resin (A) include linear aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,18-octadecanediol; propylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, and 1-methyl -1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,3,5-trimethyl-1,3-pentanediol, 2-methyl-1,6-hexanediol, 2 aliphatic diols having hydrocarbon groups in the side chains such as 1,4-methyl-1,8-octanediol, 2-methyl-1,9-nonanediol, dimer diol, 4-methyl-1,7-heptanediol, 3-methyl-1,6-hexanediol, 1-methyl-1,6-hexanediol, 4-methyl-1,9-nonanediol, and 3-methyl-1,9-nonanediol; 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,3-cyclobutanediol, and hydrogenated bisphenols and aromatic diols such as bisphenol A, 9,9-bis(hydroxyphenyl)fluorene, 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and ethylene oxide adducts or propylene oxide adducts thereof.

As the polyol (a3), it is preferable to use, for example, a trivalent or higher aliphatic polyhydric alcohol, such as trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, or 1,2,6-hexanetriol. Among these, it is particularly preferable to use trimethylolpropane, as it is relatively less likely to form gels.

These structural units derived from polyol (a3) may be present in polyester resin (A) either alone or in combination of two or more.

Of these, it is preferable to have both structural units derived from a linear aliphatic diol and structural units derived from an aliphatic diol having a hydrocarbon group on the side chain, as this allows the glass transition temperature to be controlled so as not to cause crystallization. It is particularly preferable to have structural units derived from at least one type of linear aliphatic diol selected from ethylene glycol, 1,3-propanediol, and 1,4-butanediol as structural units derived from aliphatic diols having a hydrocarbon group on the side chain, and structural units derived from at least one type of aliphatic diol selected from neopentyl glycol and 2-butyl-2-ethyl-1,3-propanediol as structural units derived from aliphatic diols having a hydrocarbon group on the side chain.

When such polyester resin (A) has structural units derived from a linear aliphatic diol, the content is preferably 5 to 90 mol % of the structural units derived from the polyhydric alcohol, and even more preferably 20 to 80 mol %. If the content is too low, the cohesive strength tends to be insufficient, while if the content is too high, crystallization tends to occur more easily, resulting in insufficient adhesive properties.

Furthermore, the structural units derived from polyol (a3) may include structural units derived from polyester diol, structural units derived from polyether diol, structural units derived from polycaprolactone diol, structural units derived from polycarbonate diol, etc., in order to easily obtain a polymer of the desired molecular weight.

Examples of structural units derived from the polyester diols include structural units derived from polyester diols obtained by dehydrating diol components such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1,8-octanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,10-decanediol, and octadecanediol with dicarboxylic acid components or derivatives thereof such as succinic acid, methylsuccinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanoic acid, 1,14-tetradecanedioic acid, terephthalic acid, isophthalic acid, and anhydrides or lower alkyl esters of these acids, either alone or in mixture. Commercially available polyester diols used to introduce such structural units into polyester resin (A) include, for example, polyester diols of 3-methyl-1,5-pentanediol and adipic acid, trade names of which include "Kuraray Polyol P-510," "Kuraray Polyol P-1010," "Kuraray Polyol P-2010," "Kuraray Polyol P-3010," and "Kuraray Polyol P-5010" (all manufactured by Kuraray Co., Ltd.).

Examples of structural units derived from the polyether diol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol obtained by ring-opening polymerization of ethylene oxide, propylene oxide, tetrahydrofuran, etc., as well as structural units derived from copolyethers copolymerized with these. Commercially available polyether diols used to introduce such structural units into polyester resin (A) include polyether diols obtained by adding propylene oxide to propylene glycol under the trade names "ADEKA POLYETHER P-400," "ADEKA POLYETHER P-1000," "ADEKA POLYETHER P-2000," and "ADEKA POLYETHER P-3000" (all manufactured by Asahi Denka Kogyo Co., Ltd.).

Examples of the structural units derived from the polycaprolactone diol include structural units derived from caprolactone-based polyester diols obtained by ring-opening polymerization of cyclic ester monomers such as ε-caprolactone and δ-valerolactone. Commercially available polycaprolactone diols used to introduce such structural units into polyester resin (A) include those under the trade names "PLACCEL L205AL," "PLACCEL L212AL," "PLACCEL L220AL," "PLACCEL L220PL," and "PLACCEL L230AL" (all manufactured by Daicel Chemical Industries, Ltd.).

Examples of structural units derived from the above-mentioned polycarbonate diols include structural units derived from carbonate diols such as propylene carbonate diol, hexamethylene carbonate diol, and 3-methylpentene carbonate diol, as well as structural units derived from polycarbonate diols obtained by dealcoholization reactions of polyhydric alcohols such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 1,9-nonanediol with dialkyl carbonates such as diethylene carbonate and dimethyl carbonate. Commercially available polycarbonate diols used to introduce such structural units into polyester resin (A) include, for example, trade names "PLACCEL CD205," "PLACCEL CD210," "PLACCEL CD220," "PLACCEL CD205PL," "PLACCEL CD210PL," and "PLACCEL CD220PL" (all manufactured by Daicel Chemical Industries, Ltd.).

It is also preferable that the polyol (a3) has a high biomass content in consideration of the global environment, and in this case, it is also preferable to use a plant-derived polyol.
Examples of the plant-derived polyol include isosorbide, fatty acid ester diols derived from castor oil, bioethylene glycol, bio-1,3-propane glycol, biobutylene glycol, etc. Among these, bioethylene glycol is preferred.

The polyester resin (A) used in the polyester resin composition preferably contains at least one structural unit selected from the group consisting of structural units derived from trivalent or higher aromatic polycarboxylic acids and structural units derived from trivalent or higher aliphatic polyhydric alcohols, in order to introduce a branched skeleton. In other words, it is preferable that the polyester resin (A) contains at least one selected from the group consisting of the trivalent or higher aromatic polycarboxylic acids and the trivalent or higher aliphatic polyhydric alcohols as a copolymerization component. In particular, when forming a crosslinked structure by reacting with the crosslinking agent (C) described below, the introduction of a branched skeleton increases the number of reaction sites in the resin, allowing for the production of a strong pressure-sensitive adhesive layer with a high crosslink density. In particular, from the perspective of versatility, it is preferable for the resin to contain structural units derived from trimethylolpropane.

When at least one selected from the group consisting of trivalent or higher aromatic polycarboxylic acids and trivalent or higher aliphatic polyhydric alcohols is used for the purpose of introducing a branched skeleton into the polyester resin (A), the content of structural units derived from trivalent or higher aromatic polycarboxylic acids relative to all structural units derived from polycarboxylic acids, or the content of structural units derived from trivalent or higher polyhydric alcohols relative to all structural units derived from polyhydric alcohols, is preferably in the range of 0.1 to 5 mol%, more preferably 0.3 to 3 mol%, and even more preferably 0.5 to 2 mol%, respectively. If the content of either or both is too high, the mechanical properties such as elongation at break of the coating film (coating film that becomes the pressure-sensitive adhesive layer) formed by application of the resulting pressure-sensitive adhesive composition will tend to decrease, resulting in reduced adhesive strength, and gelation will also tend to occur during polymerization.

Furthermore, the polyester resin (A) may contain structural units derived from an oxycarboxylic acid compound, which is a compound having a hydroxyl group and a carboxyl group in its molecular structure.
Examples of the oxycarboxylic acid compound constituting the structural unit derived from the oxycarboxylic acid compound include 5-hydroxyisophthalic acid, p-hydroxybenzoic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenylacetic acid, 6-hydroxy-2-naphthoic acid, 4,4-bis(p-hydroxyphenyl)valeric acid, etc. These may be used alone or in combination of two or more.

[Production of polyester resin (A)]
The polyester resin (A) can be produced by polycondensation of copolymer components containing the thermoplastic polyester resin (a1), the aliphatic polycarboxylic acid (a2), and the polyol (a3) in the presence of a catalyst by a known method, and in the polycondensation reaction, an esterification reaction and/or a transesterification reaction is first carried out, followed by the polycondensation reaction. When a high molecular weight is not required, the polyester resin (A) may be produced by only the esterification reaction or the transesterification reaction.

A catalyst is used in such an esterification reaction and/or transesterification reaction. Specific examples include titanium-based catalysts such as tetraisopropyl titanate and tetrabutyl titanate, antimony-based catalysts such as antimony trioxide, germanium-based catalysts such as germanium dioxide, and catalysts such as zinc acetate, manganese acetate, and dibutyltin oxide. One or more of these may be used. Among these, antimony trioxide, tetrabutyl titanate, germanium dioxide, and zinc acetate are preferred in terms of the balance between high catalytic activity and the hue of the resulting reaction product. The above catalysts may also be pre-contained in the thermoplastic polyester resin (a1).

The amount of the catalyst is preferably 1 to 10,000 ppm based on the total copolymerization components (by weight), particularly preferably 10 to 5,000 ppm, and even more preferably 20 to 3,000 ppm. If the amount is too small, the polymerization reaction tends to proceed insufficiently, while if the amount is too large, there is no benefit such as shortening the reaction time, and side reactions tend to occur more easily.

The reaction temperature during the esterification reaction and/or transesterification reaction is preferably 200 to 300°C, particularly preferably 220 to 280°C, and even more preferably 240 to 270°C. If the reaction temperature is too low, the reaction tends not to proceed sufficiently, while if it is too high, side reactions such as decomposition tend to occur easily. Furthermore, the pressure during the reaction is usually atmospheric pressure.

The reaction conditions for the polycondensation reaction carried out after the above esterification reaction or transesterification reaction are as follows: the same amount of catalyst as used in the above esterification reaction or transesterification reaction is further compounded; the reaction temperature is preferably 200 to 280°C, and particularly preferably 210 to 270°C; the reaction system is gradually reduced in pressure until the reaction is finally carried out at 5 hPa or less. If the reaction temperature is too low, the reaction will not proceed sufficiently and it will be difficult to reach the desired molecular weight; if the reaction temperature is too high, side reactions such as decomposition will tend to occur.

In carrying out the esterification reaction or transesterification reaction, (i) the thermoplastic polyester resin (a1), the aliphatic polycarboxylic acid (a2), and the polyol (a3) can be simultaneously charged and reacted, or (ii) the thermoplastic polyester resin (a1) and the aliphatic polycarboxylic acid (a2) can be charged in advance, the thermoplastic polyester resin (a1) can be depolymerized in advance, and then the polyol (a3) can be charged and reacted.Furthermore, (iii) the thermoplastic polyester resin (a1) and the polyol (a3) can be charged in advance, the thermoplastic polyester resin (a1) can be depolymerized in advance, and then the aliphatic polycarboxylic acid (a2) can be charged and reacted.
Among these, method (ii) is preferred in that it can increase the depolymerization temperature, improve the depolymerization reactivity, and increase the esterification/transesterification reaction rate.

In this way, polyester resin (A) is obtained that contains structural units derived from thermoplastic polyester resin (a1), structural units derived from aliphatic polycarboxylic acids (a2), and structural units derived from polyol (a3).

The polyester resin (A) is preferably obtained using a polyol (a3) having hydroxyl groups in a molar ratio of 1.2 or more per mole of carboxy groups of the polycarboxylic acids, including the aliphatic polycarboxylic acids (a2). It is more preferable that the molar ratio is 1.25 to 2.5, and even more preferably 1.3 to 1.7. In other words, if the molar ratio is less than 1.2, the esterification reaction and/or transesterification reaction will be insufficient, and the acid value of the polyester resin (A) will tend to be high. Furthermore, if the molar ratio is too high, too much glycol will be distilled off, resulting in waste.

[Physical properties of polyester resin (A)]
The number average molecular weight of the polyester resin (A) is preferably 3,000 or more, more preferably 3,500 to 50,000, even more preferably 4,000 to 40,000, particularly preferably 5,000 to 30,000, especially preferably 6,000 to 20,000, and most preferably 7,000 to 15,000. If the number average molecular weight is too large, handling properties will be reduced, requiring a large amount of solvent and the environmental load will tend to increase, whereas if the number average molecular weight is too small, adhesive properties and coating properties will tend to decrease.

The weight-average molecular weight of the polyester resin (A) is preferably 10,000 to 500,000, more preferably 20,000 to 300,000, particularly preferably 30,000 to 250,000, especially preferably 40,000 to 200,000, and most preferably 50,000 to 150,000. If the weight-average molecular weight is too high, handling properties will be reduced, requiring a large amount of solvent and tending to increase the environmental load. If the weight-average molecular weight is too low, adhesive properties and coating properties will tend to be reduced.

The number average molecular weight and weight average molecular weight are number average molecular weight and weight average molecular weight converted into standard polystyrene molecular weight, and are measured using a high performance liquid chromatograph (manufactured by Tosoh Corporation, "HLC-8320GPC") equipped with two columns: TSKgel SuperMultipore HZ-M (exclusion limit molecular weight: 2 × 10 ⁶ , number of theoretical plates: 16,000 plates/column, packing material: styrene-divinylbenzene copolymer, packing particle size: 4 μm) connected in series.

Furthermore, when the polyester resin (A) contains structural units derived from an aliphatic polyol, the content of acyclic aliphatic diols having 2 to 20 carbon atoms among the structural units derived from the aliphatic polyol is preferably 10 mol % or more, more preferably 30 mol % or more, and particularly preferably 50 mol % or more, from the viewpoint of initial adhesive strength when used as an adhesive.

The composition of the polyester resin (A) can be measured by a known method using NMR, etc. Specifically, when using NMR, the measurement can be performed by ¹ H-NMR measurement (proton-type nuclear magnetic resonance spectroscopy) or ¹³ C-NMR measurement (carbon-type nuclear magnetic resonance spectroscopy) at a resonance frequency of 400 MHz.

Furthermore, the glass transition temperature (Tg) of the polyester resin (A) must be 40°C or lower, preferably -90 to 20°C, particularly preferably -60 to 0°C, and even more preferably -50 to -20°C. If the glass transition temperature (Tg) is too high, the adhesive strength when used as an adhesive tends to decrease, while if it is too low, the heat resistance and cohesive strength tend to decrease.

The glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC) (for example, the Q20 differential scanning calorimeter manufactured by TA Instruments). The measurement temperature range is -90 to 100°C, and the temperature rise rate is 10°C/min.

The heat of crystalline fusion of the polyester resin (A) is usually 10 J/g or less, preferably 5 J/g or less, more preferably 2 J/g or less, and particularly preferably no heat of crystalline fusion. If the heat of crystalline fusion is too large, crystals tend to form, reducing the storage stability of the resin solution and reducing the stability and adhesive properties at low temperatures when made into a pressure-sensitive adhesive sheet.
The "heat of fusion of crystals" refers to the energy consumed when a crystallized substance is heated and melted, and can be measured by a differential scanning calorimeter (DSC).

Methods for adjusting the heat of crystalline fusion include, for example, appropriately using polycarboxylic acids with alkyl groups on the side chains or polyols with alkyl groups on the side chains, or using three or more, preferably four or more, copolymerizable monomer components.

The acid value of the polyester resin (A) is preferably 0.5 mgKOH/g or less, more preferably 0.3 mgKOH/g or less, and particularly preferably 0.1 mgKOH/g or less, in order to prevent reaction with the hydrolysis inhibitor (B) over time and to improve storage stability. If the acid value is too high, storage stability tends to be poor.
The acid value can be adjusted, for example, by increasing the proportion of polyol during the esterification reaction or transesterification reaction, adjusting the reaction conditions, or increasing the amount of thermoplastic polyester resin used as the aromatic carboxylic acid component. The lower limit of the acid value is usually 0 mgKOH/g.

The acid value of the polyester resin (A) is determined by neutralization titration in accordance with JIS K0070.
The "acid value of the polyester resin (A)" means the content of carboxy groups in the polyester resin (A). The carboxy groups include those in a carboxylate ion state in which the carboxy groups are neutralized with a basic compound.

The hydroxyl value of the polyester resin (A) is preferably 15 mgKOH/g or less, more preferably 2 to 12 mgKOH/g, even more preferably 3 to 11 mgKOH/g, and particularly preferably 4 to 10 mgKOH/g. If the hydroxyl value is too low, it becomes difficult to adjust the gel fraction of the resulting pressure-sensitive adhesive layer to the desired value, and it tends to be difficult to obtain the desired adhesive properties. Furthermore, if the hydroxyl value is too high, it means that there are many terminal groups, and the adhesive properties tend to deteriorate due to a low molecular weight or excessive branching.

The hydroxyl value of the polyester resin (A) is determined by neutralization titration in accordance with JIS K 0070.

The content of the polyester resin (A) in the entire polyester resin composition is preferably 50 parts by weight or more, particularly preferably 70 to 99 parts by weight, and even more preferably 80 to 98 parts by weight. It is most preferably 90 to 97 parts by weight. If the content is too low, the adhesive properties tend to decrease.

Next, we will explain the hydrolysis inhibitor (B) used together with the polyester resin (A) in this polyester resin composition.

<Hydrolysis inhibitor (B)>
The hydrolysis inhibitor (B) is contained in order to ensure long-term durability when the polyester resin composition is used as a pressure-sensitive adhesive composition.
As the hydrolysis inhibitor (B), a conventionally known compound can be used, for example, a compound that reacts with the carboxyl terminal of the polyester resin (A) to bond, specifically, for example, a compound containing a functional group such as a carbodiimide group, an epoxy group, an oxazoline group, etc. Among these, a carbodiimide group-containing compound is preferred because of its high effect of eliminating the catalytic activity of protons derived from the carboxyl terminal.

When the above-mentioned carbodiimide group-containing compound is used as the hydrolysis inhibitor (B), its carbodiimide equivalent weight is preferably 50 to 10,000, particularly 100 to 1,000, and even more preferably 150 to 500. The carbodiimide equivalent weight refers to the chemical formula weight per carbodiimide group.

As the carbodiimide group-containing compound, a known carbodiimide having one or more carbodiimide groups (-N=C=N-) in the molecule may typically be used. However, to improve durability under high temperature and humidity conditions, a compound having two or more carbodiimide groups in the molecule, i.e., a polyvalent carbodiimide compound (B1), is preferred. Compounds having three or more, preferably five or more, and especially seven or more carbodiimide groups in the molecule are particularly preferred. The number of carbodiimide groups in the molecule is typically 50 or less; if there are too many carbodiimide groups, the molecular structure becomes too large, tending to reduce compatibility. It is also preferred to use a high-molecular-weight polycarbodiimide produced by the decarboxylation condensation reaction of a diisocyanate in the presence of a carbodiimidization catalyst.

Furthermore, from the standpoint of storage stability, it is preferable for the high-molecular-weight polycarbodiimide to have its terminal isocyanate groups blocked with a blocking agent. Examples of blocking agents include compounds containing active hydrogen that reacts with isocyanate groups, or compounds containing isocyanate groups. Examples include monoalcohols, monocarboxylic acids, monoamines, and monoisocyanates each having one substituent selected from a carboxy group, an amino group, and an isocyanate group.

Examples of such high molecular weight polycarbodiimides include those obtained by the decarboxylation condensation reaction of the following diisocyanates:

Such diisocyanates include, for example, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 3,3'-dimethyl-4,4'-diphenylether diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate. These can be used alone or in combination of two or more. Such high molecular weight polycarbodiimides can be synthesized or commercially available products can be used.

Commercially available examples of the carbodiimide group-containing compounds include the "Carbodilite (registered trademark)" series manufactured by Nisshinbo Chemical Inc. Among these, "Carbodilite (registered trademark) V-01," "V-02B," "V-03," "V-04K," "V-04PF," "V-05," "V-07," "V-09," and "V-09GB" are preferred due to their excellent compatibility with organic solvents.

Preferred examples of the epoxy group-containing compound include glycidyl ester compounds and glycidyl ether compounds.

Specific examples of the above glycidyl ester compounds include, for example, benzoic acid glycidyl ester, t-butylbenzoic acid glycidyl ester, p-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, lauric acid glycidyl ester, palmitic acid glycidyl ester, behenic acid glycidyl ester, versatic acid glycidyl ester, oleic acid glycidyl ester, linoleic acid glycidyl ester, linolenic acid glycidyl ester, behenolic acid glycidyl ester, stearolic acid glycidyl ester, terephthalic acid diglycidyl ester, and isophthalic acid. Examples include diglycidyl ester, diglycidyl phthalate ester, diglycidyl naphthalenedicarboxylic acid ester, diglycidyl methyl terephthalate ester, diglycidyl hexahydrophthalate ester, diglycidyl tetrahydrophthalate ester, diglycidyl cyclohexanedicarboxylic acid ester, diglycidyl adipic acid ester, diglycidyl succinate ester, diglycidyl sebacic acid ester, diglycidyl dodecanedioate, diglycidyl octadecanedicarboxylic acid ester, triglycidyl trimellitate, and tetraglycidyl pyromellitic acid ester, and these can be used alone or in combination of two or more.

Specific examples of the glycidyl ether compound include phenyl glycidyl ether, o-phenyl glycidyl ether, 1,4-bis(β,γ-epoxypropoxy)butane, 1,6-bis(β,γ-epoxypropoxy)hexane, 1,4-bis(β,γ-epoxypropoxy)benzene, 1-(β,γ-epoxypropoxy)-2-ethoxyethane, 1-(β,γ-epoxypropoxy)-2-benzyloxyethane, 2,2-bis-[p-(β,γ-epoxypropoxy)phenyl]propane, and bisglycidyl polyethers obtained by reacting bisphenols such as 2,2-bis-(4-hydroxyphenyl)propane and 2,2-bis-(4-hydroxyphenyl)methane with epichlorohydrin. These compounds can be used alone or in combination of two or more.

Preferred examples of the oxazoline group-containing compound include bisoxazoline compounds. Specific examples include 2,2'-bis(2-oxazoline), 2,2'-bis(4-methyl-2-oxazoline), 2,2'-bis(4,4-dimethyl-2-oxazoline), 2,2'-bis(4-ethyl-2-oxazoline), 2,2'-bis(4,4'-diethyl-2-oxazoline), 2,2'-bis(4-propyl-2-oxazoline), 2,2'-bis(4-butyl-2-oxazoline), and 2,2'-bis(4-hexyl-2-oxazoline). 2,2'-bis(4-phenyl-2-oxazoline), 2,2'-bis(4-cyclohexyl-2-oxazoline), 2,2'-bis(4-benzyl-2-oxazoline), 2,2'-p-phenylenebis(2-oxazoline), 2,2'-m-phenylenebis(2-oxazoline), 2,2'-o-phenylenebis(2-oxazoline), 2,2'-p-phenylenebis(4-methyl-2-oxazoline), 2,2'-p-phenylenebis(4,4-dimethyl-2-oxazoline), 2,2'-m-phenylenebis(4-methyl-2-oxazoline), 2,2'-m-phenylenebis(4,4-dimethyl-2-oxazoline), 2,2'-ethylenebis(2-oxazoline), 2,2'-tetramethylenebis(2-oxazoline), 2,2'-hexamethylenebis(2-oxazoline), 2,2'-octamethylenebis(2-oxazoline), 2,2'-decamethylenebis(2-oxazoline), 2,2'-ethylene Examples of suitable olefin copolymers include 2,2'-tetramethylenebis(4,4-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethanebis(2-oxazoline), 2,2'-cyclohexylenebis(2-oxazoline), and 2,2'-diphenylenebis(2-oxazoline). Of these, 2,2'-bis(2-oxazoline) is most preferred from the standpoint of reactivity with the polyester resin (A). These olefin copolymers can be used alone or in combination of two or more.

The hydrolysis inhibitor (B) preferably has low volatility, and therefore it is preferable to use one with a large number average molecular weight, which is usually 300 to 10,000, preferably 1,000 to 5,000.
Furthermore, from the viewpoint of hydrolysis resistance, it is preferable to use a hydrolysis inhibitor (B) having a high weight-average molecular weight. The weight-average molecular weight of the hydrolysis inhibitor (B) is preferably 500 or more, more preferably 1000 or more, even more preferably 2000 or more, and particularly preferably 3000 or more. The upper limit of the weight-average molecular weight is usually 50,000. That is, if the weight-average molecular weight of the hydrolysis inhibitor (B) is too small, hydrolysis resistance tends to decrease, and if the weight-average molecular weight is too large, compatibility with the polyester resin (A) tends to decrease.

The content of the hydrolysis inhibitor (B) is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, and even more preferably 0.2 to 3 parts by weight, per 100 parts by weight of the polyester resin (A). If the content is too high, turbidity tends to occur due to poor compatibility with the polyester resin (A), while if the content is too low, sufficient durability tends to be difficult to achieve.

The content of the hydrolysis inhibitor (B) is preferably optimized depending on the acid value of the polyester resin (A), and the molar ratio [(y)/(x)] of the total number of moles (y) of functional groups of the hydrolysis inhibitor (B) in the polyester resin composition to the total number of moles (x) of acidic functional groups of the polyester resin (A) in the polyester resin composition is preferably 0.5≦(y)/(x), particularly preferably 1≦(y)/(x)≦10,000, and even more preferably 10≦(y)/(x)≦1,000.
If the molar ratio of (y) to (x) is too low, the moist heat resistance tends to decrease, whereas if the molar ratio of (y) to (x) is too high, the compatibility with the polyester resin (A) tends to decrease, and the adhesive strength, cohesive strength, and durability tend to decrease.

The acid value of the polyester resin composition containing the polyester resin (A) and hydrolysis inhibitor (B) is preferably 0.5 mg KOH/g or less, more preferably 0.3 mg KOH/g or less, and particularly preferably 0.1 mg KOH/g or less. If the acid value is too high, storage stability tends to be poor.

In addition, the polyester resin (A) and hydrolysis inhibitor (B) may be stored in the form of a solution dissolved in an organic solvent. In this case, if the molecular weight of the polyester resin (A) is too high and/or the acid value is too high, the storage stability of the solution tends to decrease.

Examples of organic solvents that do not have functional groups that react with the polyester resin (A) and hydrolysis inhibitor (B) include esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatics such as toluene and xylene. These can be used alone or in combination of two or more.

In addition to the essential components, polyester resin (A) and hydrolysis inhibitor (B), the polyester resin composition may also preferably contain a crosslinking agent (C), a tackifier (D), a urethanization catalyst (E), an antioxidant (F), and the like. These preferred optional components are described below.

<Crosslinking agent (C)>
Examples of the crosslinking agent (C) include epoxy compounds and polyisocyanate compounds (C1). Among these, polyisocyanate compounds (C1) are preferred. That is, crosslinking the polyester resin (A) with the polyisocyanate compound (C1) in particular results in excellent cohesive strength, and can improve the performance as a pressure-sensitive adhesive.

Examples of such polyisocyanate compounds (C1) include aromatic isocyanate crosslinking agents such as tolylene diisocyanate crosslinking agents such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate crosslinking agents such as 1,3-xylylene diisocyanate, diphenylmethane crosslinking agents such as diphenylmethane-4,4-diisocyanate, and naphthalene diisocyanate crosslinking agents such as 1,5-naphthalene diisocyanate; isophorone diisocyanate, 1,4-cyclohexane diisocyanate, and 4,4'-dicyclohexyl Examples of suitable crosslinking agents include alicyclic isocyanate crosslinking agents such as methane diisocyanate, methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, and norbornane diisocyanate; aliphatic isocyanate crosslinking agents such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; and adducts of the above isocyanate compounds with polyol compounds such as trimethylolpropane, as well as biuret and isocyanurate forms of these isocyanate compounds. The polyisocyanate compounds may also be used in which the isocyanate moiety is blocked with phenol, lactam, or the like. These polyisocyanate compounds may be used alone or in combination.

When using a crosslinking agent (C) such as a polyisocyanate compound (C1), its content can be selected appropriately depending on the molecular weight of the polyester resin (A) and the intended use. However, it is generally preferable to contain the crosslinking agent (C) in a ratio such that the reactive groups contained in the crosslinking agent (C) are 0.2 to 10 equivalents per equivalent of at least one of the hydroxyl groups and carboxyl groups contained in the polyester resin (A), with 0.5 to 5 equivalents being particularly preferred, and 0.5 to 3 equivalents being even more preferred. If the equivalent number of reactive groups contained in such crosslinking agent (C) is too small, cohesive strength tends to decrease, while if it is too large, flexibility tends to decrease.

The content of such crosslinking agent (C) can be selected appropriately depending on the molecular weight of the polyester resin (A) and the intended use, but is typically preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, even more preferably 0.3 to 3 parts by weight, and particularly preferably 0.5 to 2 parts by weight, per 100 parts by weight of polyester resin (A). If the amount of such crosslinking agent (C) added is too small, cohesive strength tends to decrease, while if it is too large, flexibility tends to decrease.

In addition, in the reaction between the polyester resin (A) and the crosslinking agent (C), organic solvents that do not have functional groups that react with (A) and (C) can be used, such as esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatics such as toluene and xylene. These can be used alone or in combination of two or more.

<Tackifier (D)>
In the present polyester resin composition, it is also preferred to contain a tackifier (D) in order to improve the adhesive properties.

The tackifier (D) is not particularly limited, and conventionally known tackifiers can be used. Examples of the tackifier (D) include hydrocarbon-based tackifier resins, terpene-based resins, phenol-based resins, rosin-based resins, xylene resins, epoxy-based resins, polyamide-based resins, ketone-based resins, and elastomer-based resins. These may be used alone or in combination of two or more. Of these, hydrocarbon-based tackifier resins and terpene-based resins are preferred. It is particularly preferred that the tackifier (D) contain at least one hydrocarbon-based tackifier resin, with the hydrocarbon-based tackifier resin preferably accounting for 30% by weight or more of the total tackifier, preferably 50% by weight or more, and more preferably 70% by weight or more.

Examples of the hydrocarbon-based tackifying resin include various hydrocarbon resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (such as styrene-olefin copolymers), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, and coumarone-indene resins. Commercially available products include "FTR6100," "FTR6110," "FTR6125," "FTR8100," "FTR8120," and "FMR0150" manufactured by Mitsui Chemicals, Inc.

Examples of the terpene resin include terpene resin, terpene phenol resin, and aromatic-modified terpene resin. Specific examples include α-pinene polymer, β-pinene polymer, dipentene polymer, and terpene resins obtained by phenol-modifying, aromatic-modifying, hydrogenating-modifying, or hydrocarbon-modifying these. Commercially available products include Yasuhara Chemical's YS Polystar S145, YS Resin PX1000, YS Resin PX1250, YS Polystar T160, YS Polystar T145, YS Polystar T130, YS Resin TO115, YS Polystar G150, YS Polystar G125, YS Polystar U130, and Clearon P125. Terpene resins are preferred due to their excellent adhesion to non-polar substrates such as polypropylene.

The phenolic resins that can be used include, for example, condensates of formaldehyde with various phenols such as phenol, m-cresol, 3,5-xylenol, p-alkylphenol, and resorcinol. Other examples include resols obtained by subjecting the phenols and formaldehyde to an addition reaction in the presence of an alkali catalyst; novolaks obtained by subjecting the phenols and formaldehyde to a condensation reaction in the presence of an acid catalyst; and rosin-modified phenolic resins obtained by adding phenol to rosins, such as unmodified or modified rosin or their derivatives, in the presence of an acid catalyst, followed by thermal polymerization.

Examples of the rosin-based resin include rosin resin, polymerized rosin resin, hydrogenated rosin resin, rosin ester resin, hydrogenated rosin ester resin, rosin phenolic resin, and polymerized rosin ester. Specific examples include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin, as well as modified rosins that have been hydrogenated, disproportionated, polymerized, or otherwise chemically modified, and derivatives of these. Commercially available products include Hariestar TF, Haritack 8LJA, Haritack PH, Haritack FK100, and Haritack PCJ manufactured by Harima Chemicals.

The tackifier (D) preferably has an acid value of 30 mgKOH/g or less, particularly 10 mgKOH/g or less, even more preferably 6 mgKOH/g or less, and especially preferably 3 mgKOH/g or less. When multiple types of tackifier (D) are used in combination, it is preferable that their average be within the above range.

The softening point of the tackifier (D) (measured, for example, by the ring and ball method) is preferably 80 to 170°C, particularly 90 to 160°C, more preferably 100 to 155°C, even more preferably 120 to 150°C, and particularly preferably 135 to 150°C. A softening point within the above range is preferred, as it can improve adhesive properties (adhesive strength, cohesive strength).

The tackifier (D) is preferably plant-derived in order to maintain a high biomass content throughout the polyester resin composition. Examples of plant-derived tackifiers include terpene resins and rosin resins.

When the tackifier (D) is used, its content is preferably 2 to 200 parts by weight, more preferably 5 to 150 parts by weight, even more preferably 8 to 100 parts by weight, particularly preferably 10 to 80 parts by weight, and most preferably 20 to 50 parts by weight, per 100 parts by weight of the polyester resin (A). A content within the above range tends to improve adhesive properties (adhesive strength, cohesive strength).

<Urethanization catalyst (E)>
In view of the reaction rate, the polyester resin composition preferably further contains a urethanization catalyst (E).

Examples of the urethane-forming catalyst (E) include organometallic compounds and tertiary amine compounds. These can be used alone or in combination of two or more.

Examples of the organometallic compounds include zirconium compounds, iron compounds, tin compounds, titanium compounds, lead compounds, cobalt compounds, and zinc compounds.
Examples of zirconium compounds include zirconium naphthenate and zirconium acetylacetonate.
Examples of iron compounds include iron acetylacetonate and iron 2-ethylhexanoate.
Examples of tin compounds include dibutyltin dichloride, dibutyltin oxide, and dibutyltin dilaurate.
Examples of titanium compounds include dibutyltitanium dichloride, tetrabutyltitanium, and butoxytitanium trichloride.
Examples of lead compounds include lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate.
Examples of the cobalt-based compounds include cobalt 2-ethylhexanoate and cobalt benzoate.
Examples of zinc compounds include zinc naphthenate and zinc 2-ethylhexanoate.
Examples of the tertiary amine compound include triethylamine, triethylenediamine, and 1,8-diazabicyclo-(5,4,0)-undecene-7.

Among these urethane-forming catalysts (E), organometallic compounds are preferred, with zirconium compounds being particularly preferred, in terms of reaction rate and pot life of the resulting pressure-sensitive adhesive layer. Furthermore, it is preferable to use acetylacetone in combination with the urethane-forming catalyst (E) as a catalytic inhibitor. The inclusion of acetylacetone is preferred in that it inhibits catalytic activity in the solution and extends the pot life.

When the urethane catalyst (E) is used, its content is preferably 0.0001 to 1 part by weight, particularly 0.001 to 0.1 parts by weight, and even more preferably 0.01 to 0.05 parts by weight, per 100 parts by weight of the polyester resin (A). If the content is too low, the aging time until the crosslinking reaction is complete tends to be long, while if it is too high, the adhesive properties tend to deteriorate.

<Antioxidant (F)>
The polyester resin composition preferably contains an antioxidant (F) in order to improve the stability of the resin.

Examples of the antioxidant (F) include hindered phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, phosphoric acid-based antioxidants, etc. Among these, at least one selected from the group consisting of hindered phenol-based antioxidants, amine-based antioxidants, and phosphoric acid-based antioxidants is preferred, and hindered phenol-based antioxidants are particularly preferred.
Examples of hindered phenol-based antioxidants include antioxidants having a hindered phenol structure in which a group with large steric hindrance, such as a t-butyl group, is bonded to at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring to which the phenolic hydroxyl group is bonded.

When the antioxidant (F) is used, the content thereof is preferably 0.01 to 10 parts by weight, more preferably 0.03 to 8 parts by weight, and even more preferably 0.05 to 5 parts by weight, relative to 100 parts by weight of the polyester resin (A).
If the content is too low, the resulting pressure-sensitive adhesive layer tends to leave adhesive residue on the adherend, whereas if the content is too high, the adhesive properties tend to deteriorate.

In addition to the preferred components, namely the crosslinking agent (C), tackifier (D), urethanization catalyst (E), and antioxidant (F), the polyester resin composition may also contain additives such as softeners, UV absorbers, stabilizers, and antistatic agents, as well as inorganic or organic fillers, metal powders, pigments, and other powdery or particulate additives, provided that the effects of the present invention are not impaired. Furthermore, the polyester resin composition may contain small amounts of impurities contained in the raw materials used to manufacture the components of the polyester resin composition. These may be used alone or in combination of two or more.

The polyester resin composition obtained in this way is a highly recyclable and environmentally friendly polyester resin composition, which has a low environmental impact during the manufacturing process. Furthermore, it has excellent storage stability when made into a resin composition solution, and when made into an adhesive, it has excellent adhesive strength and holding power.

A pressure-sensitive adhesive composition according to one embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive composition") contains the polyester-based resin composition, and preferably consists of the polyester-based resin composition.
Moreover, a pressure-sensitive adhesive according to one embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive") is obtained by using the pressure-sensitive adhesive composition described above.

A pressure-sensitive adhesive sheet according to one embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive sheet") has a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive of the present invention, and the pressure-sensitive adhesive layer is preferably formed on one or both sides of a supporting substrate. The pressure-sensitive adhesive sheet will now be described.
In the present invention, the term "sheet" is used to include "film" and "tape."

<Adhesive sheet>
The present pressure-sensitive adhesive sheet can be produced according to a known general method for producing a pressure-sensitive adhesive sheet. For example, the present pressure-sensitive adhesive composition is coated on a substrate, dried, a release sheet is attached to the surface of the pressure-sensitive adhesive layer opposite to the substrate surface, and the sheet is cured as necessary to obtain the present pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a pressure-sensitive adhesive on a substrate.

The adhesive sheet of the present invention can also be obtained by coating the adhesive composition on a release sheet, drying it, laminating a substrate to the adhesive layer surface opposite the release sheet surface, and curing the composition as necessary.

Also, a substrateless double-sided PSA sheet can be produced by forming a PSA layer on a first release sheet and then laminating a second release sheet to the PSA layer surface opposite the first release sheet surface.

When using the resulting pressure-sensitive adhesive sheet or substrate-less double-sided pressure-sensitive adhesive sheet, the release sheet covering the pressure-sensitive adhesive layer is peeled off to expose the pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer is bonded to an adherend.

Examples of substrates that can be used in this pressure-sensitive adhesive sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/isophthalate copolymer; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride/vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; polyimide; and sheets made of at least one synthetic resin selected from the group consisting of cycloolefin polymers; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven and knitted fabrics and nonwoven fabrics made of glass fiber, natural fibers, synthetic fibers, etc. These substrates can be used as a single layer or as a multi-layer structure in which two or more types are laminated.

Of these, substrates made of polyethylene terephthalate and polyimide are particularly preferred, with substrates made of polyethylene terephthalate being particularly preferred due to their excellent adhesion to pressure-sensitive adhesives.

Foam substrates, such as foam sheets made of synthetic resin foams such as polyurethane foam, polyethylene foam, and polyacrylate foam, can also be used as the substrate. Of these, polyethylene foam and polyacrylate foam are preferred because they offer an excellent balance of conformability to the adherend and adhesive strength.

The thickness of the substrate is preferably, for example, 1 to 1000 μm, particularly preferably 2 to 500 μm, and even more preferably 3 to 300 μm.

The release sheet used in this pressure-sensitive adhesive sheet can be, for example, a sheet made of any of the synthetic resins exemplified above as the substrate, or paper, cloth, nonwoven fabric, etc., that has been subjected to a release treatment. It is preferable to use a silicone-based release sheet.

The adhesive composition can be applied using, for example, a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, etc.

The drying conditions for the coated layer are preferably a drying temperature of 60 to 140°C, particularly preferably 80 to 120°C, and a drying time of 0.5 to 30 minutes, particularly preferably 1 to 5 minutes.

The curing conditions for the dried coating layer are a temperature of 0 to 70°C and a time of typically 1 to 30 days. Specifically, curing can be carried out, for example, at 23°C for 1 to 20 days, preferably at 23°C for 3 to 14 days, or at 40°C for 1 to 10 days.

The thickness of the adhesive layer in the present adhesive sheet (including substrate-less double-sided adhesive sheets, etc.) is set appropriately depending on the application, but is typically preferably 0.1 to 500 μm, particularly preferably 5 to 200 μm, and even more preferably 10 to 100 μm. If the thickness of such an adhesive layer is too thin, the adhesive strength tends to decrease, while if it is too thick, it becomes difficult to apply uniformly and problems such as the inclusion of air bubbles in the coating film tend to occur. When considering impact absorption, a thickness of 50 μm or more is preferable. Furthermore, for applications such as double-sided tape used on electronic components, a thin film may be required, in which case a thickness of 0.5 to 5 μm is preferable.

The thickness of the adhesive layer is determined using a Mitutoyo ID-C112B gauge by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive sheet.

From the standpoint of durability and adhesive strength, the gel fraction of the adhesive layer of this adhesive sheet is preferably 10% by weight or more, particularly preferably 20-80% by weight, even more preferably 30-70% by weight, and most preferably 35-45% by weight. If the gel fraction is too low, the cohesive strength tends to decrease, resulting in a decrease in holding power. However, if the gel fraction is too high, the cohesive strength tends to increase, resulting in a decrease in adhesive strength.

The gel fraction is an indicator of the degree of crosslinking and can be calculated, for example, by the following method. A pressure-sensitive adhesive sheet (without a release sheet) consisting of a polymer sheet substrate (e.g., PET film) on which a pressure-sensitive adhesive layer is formed is wrapped in a 200-mesh SUS wire mesh and immersed in toluene at 23°C for 24 hours. The gel fraction is calculated as the weight percentage of the undissolved pressure-sensitive adhesive component remaining in the wire mesh after immersion relative to the weight of the pressure-sensitive adhesive component before immersion. Note that the weight of the substrate is subtracted.

Furthermore, if necessary, the present pressure-sensitive adhesive sheet may be provided with a release sheet on the outside of the pressure-sensitive adhesive layer to protect its surface. Furthermore, in a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is formed on one side of the substrate, it is also possible to apply a release treatment to the surface of the substrate opposite the pressure-sensitive adhesive layer, thereby utilizing the release-treated surface to protect the pressure-sensitive adhesive layer.

As such, the present pressure-sensitive adhesive can be used to bond a variety of components, particularly as single- or double-sided pressure-sensitive adhesive sheets used to bond optical components, or for fixing components in portable electronic devices or electronic components. Furthermore, regardless of whether the entire product is in sheet form, it can be used as a laminate with a variety of configurations, such as having a release sheet on one side, via the present pressure-sensitive adhesive layer, and a substrate sheet or release sheet on the other side, or having a substrate sheet on one side, via the present pressure-sensitive adhesive layer, and the same or a different substrate sheet on the other side.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Note that "parts" and "%" in the examples are by weight.

In addition, the number average molecular weight, weight average molecular weight, glass transition temperature, hydroxyl value, acid value, and gel fraction of the adhesive layer of the polyester resin in the examples below were measured according to the methods described above.

Polyester resin (A) was produced by the following method (see Table 1).

[Production Examples 1 to 3, 5 to 7]
[Production of Polyester Resin (A) [A-1, A-2, A-3, A'-1, A'-3, A'-4)]
Polycarboxylic acids, polyol, and thermoplastic polyester resin were blended in a reactor equipped with a thermometer, a stirrer, a rectification column, a nitrogen inlet tube, and a vacuum device, and tetrabutyl titanate was charged as a catalyst in an amount of 0.2 mmol/mole relative to the polycarboxylic acids. The internal temperature was gradually increased to 260°C under conditions where the top of the rectification column could be kept at 100°C or less, and esterification and transesterification reactions were carried out until the top of the rectification column reached 50°C or less. Thereafter, tetrabutyl titanate was charged as a catalyst in an amount of 0.2 mmol/mole relative to the polycarboxylic acids at an internal temperature of 260°C, the pressure was reduced to 1.33 to 2.66 hPa, and a polymerization reaction was carried out over 2 to 3 hours to produce polyester resin (A).

The molar composition of the resulting polyester resin (A) is shown in Table 1 below. Its physical properties are also shown in Table 2 below.

Furthermore, the esterification reaction time in each production example was measured as described below, and the condition of the reactor after the reaction product was removed was evaluated as described below. The results are also shown in Table 2 below.
<Esterification reaction time>
The time from the start of the esterification and transesterification reactions until the temperature at the top of the distillation column fell to 50°C or less was measured.
<Reaction vessel after resin removal>
After the resin was removed, the state of the lid of the reactor was visually inspected and evaluated according to the following criteria.
(Evaluation criteria)
〇: Little or no white powder adhesion ×: Much white powder adhesion

[Production Example 4]
[Production of Polyester Resin (A) [A-4]]
Polycarboxylic acids and a thermoplastic polyester resin were blended in a reactor equipped with a thermometer, a stirrer, a rectification column, a nitrogen inlet tube, and a vacuum device. Tetrabutyl titanate was added as a catalyst at 0.2 mmol/mole relative to the polycarboxylic acids, and the thermoplastic polyester resin was depolymerized at an internal temperature of 260°C for 2 hours. Next, the polyol components shown in Table 1 below were added, and the temperature was gradually increased to 260°C while keeping the top of the rectification column below 100°C. Esterification and transesterification reactions were carried out until the top of the rectification column reached 50°C or below. Thereafter, tetrabutyl titanate was added as a catalyst at 0.2 mmol/mole relative to the polycarboxylic acids at an internal temperature of 260°C, the pressure was reduced to 1.33 to 2.66 hPa, and the polymerization reaction was carried out over 2 to 3 hours to produce polyester resin (A).
The molar composition ratios of the resulting polyester resins (A) are shown in Table 1. Their physical properties are also shown in Table 2. Furthermore, the esterification reaction times and the conditions of the reactor after the reaction product was removed in the above-mentioned production examples are also shown in Table 2.

In regards to the evaluation of the reactor after removing the resin in Production Examples 5 to 7 in Table 2 above, a supplementary explanation is that in these examples in which polyester resin (A) [A'-1, A'-3, A'-4] was produced, a large amount of terephthalic acid residue (white powder deposits) remained on the reactor lid after the reaction product was removed. Such a large amount of residue could cause the composition to become distorted and also required a lot of effort to clean.

Next, prior to preparing the adhesive composition, the following components were prepared:

[Hydrolysis inhibitor (B)]
Polyvalent carbodiimide compound (B1): "Carbodilite V-09GB, solid content concentration 70%" (manufactured by Nisshinbo Chemical Inc.)

[Crosslinking agent (C)]
Polyisocyanate compound (C1): "Coronate L55E, solid content concentration 55%" (manufactured by Tosoh Corporation)

[Examples 1 to 4, Comparative Examples 1 to 5]
The polyester resin [(A) or (A')] was diluted with ethyl acetate to a solids concentration of 50% (±1%), and the hydrolysis inhibitor (B) was added thereto in the blending ratio (solids ratio) shown in Table 3 below, thereby preparing a pressure-sensitive adhesive solution for forming a pressure-sensitive adhesive layer.

The resulting adhesive solution was applied to a release-treated polyethylene terephthalate (PET) film so that the thickness after drying was 50 μm, and then dried at 100°C for 5 minutes to form nine types of adhesive layers, designated Examples 1 to 4 and Comparative Examples 1 to 5.

The following evaluations were performed on the adhesive solutions and adhesive layers of Examples 1 to 4 and Comparative Examples 1 to 5. The evaluation results are shown in Table 3 below.

<Storage stability>
The initial fluidity of the obtained adhesive solution was confirmed, and then the adhesive solution was left to stand at 40°C for one month, after which it was confirmed whether the fluidity was maintained, and the storage stability was evaluated according to the following criteria.
(Evaluation criteria)
○・・・Liquidity ×・・・No or very low liquidity

<Moist heat durability>
The resulting pressure-sensitive adhesive layer was cut into a size of 25 mm wide x 200 mm long and then placed in an environment of 85°C and 85% RH for 250 hours. The weight-average molecular weight of the sample before and after placement was measured using GPC, and the "weight-average molecular weight after placement/weight-average molecular weight before placement" was calculated. A decrease in this value indicates that hydrolysis has progressed and the molecular weight of the resin has decreased, indicating that the pressure-sensitive adhesive layer has deteriorated due to moist heat. Therefore, the moist heat durability was evaluated according to the following criteria.
(Evaluation criteria)
〇: 0.9 or more ×: less than 0.9

[Examples 5 to 7, Comparative Examples 6 and 7]
The polyester resin (A) was diluted with ethyl acetate to a solids concentration of 50%, and a polyvalent carbodiimide compound (B1) and a polyvalent isocyanate compound (C1) were blended in the blending ratios (solids proportions) shown in Table 4 below. 0.02 parts (solids) of a zirconium compound (manufactured by Matsumoto Fine Chemical Co., Ltd., "Orgatix ZC-150") diluted with acetylacetone to a solids concentration of 1% as a urethanization catalyst (E) and 0.1 parts of a hindered phenol antioxidant (manufactured by BASF, "IRGANOX1010") were added, stirred, and mixed to obtain a pressure-sensitive adhesive composition.
The obtained pressure-sensitive adhesive composition was applied to a polyethylene terephthalate (PET) film (thickness: 38 μm) so that the thickness after drying would be approximately 25 μm, and then dried for 3 minutes at 100° C. to form a pressure-sensitive adhesive layer. Thereafter, a release-treated PET film (release film) was attached to the pressure-sensitive adhesive layer to protect its surface, and the layer was aged for 10 days in an atmosphere at a temperature of 40° C. to obtain five types of pressure-sensitive adhesive sheets, which are Examples 5 to 7 and Comparative Examples 6 and 7.

The following evaluations were performed on each of the pressure-sensitive adhesive sheets of Examples 5 to 7 and Comparative Examples 6 and 7. The evaluation results are shown in Table 4 below.

<Adhesion strength (peel strength) (against SUS)>
A SUS-BA plate was prepared as the adherend. The pressure-sensitive adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, and the release film was peeled off. The pressure-sensitive adhesive layer side was placed against the SUS-BA plate, and a 2 kg roller was applied back and forth under pressure to adhere the sheet. After leaving the sheet to stand for 30 minutes in the same atmosphere, the 180-degree peel strength (N/25 mm) was measured at a peel rate of 300 mm/min using an autograph (Shimadzu Corporation, "Autograph AGS-H 500N"), and the peel state was visually observed. The adhesive strength was then evaluated according to the following criteria.
(Evaluation criteria)
◯: The peel strength was 10 N/25 mm or more and interfacial peeling occurred.
× Peel strength was less than 10 N/25 mm, or cohesive failure occurred.

<Holding force (cohesive force)>
The pressure-sensitive adhesive sheet obtained above was attached to an adherend of SUS304 in accordance with JIS Z-0237 with an attachment area of 25 mm × 25 mm, and then allowed to stand at 80°C for 20 minutes. A load of 1 kg was then applied to the sheet, and the time until it fell was measured, and the holding power (cohesion) was evaluated according to the following criteria.
(Evaluation criteria)
◯: No falling after being left standing for 24 hours.
×: Falling occurred during 24 hours of standing.

The results in Table 3 above show that the adhesive solutions of Examples 1 to 4 had excellent storage stability and also excellent moist heat durability. On the other hand, the adhesive solutions of Comparative Examples 1 to 3 underwent a crosslinking reaction after the addition of the hydrolysis inhibitor (B1), resulting in gelation or loss of fluidity, and therefore had poor storage stability. Furthermore, although Comparative Examples 4 and 5, in which the hydrolysis inhibitor (B1) was not added, had excellent storage stability, when the dried adhesive solutions were evaluated for moist heat durability, hydrolysis had progressed, the molecular weight had decreased, and the solution had poor moist heat durability.

Furthermore, the results in Table 4 above show that the pressure-sensitive adhesive sheets of Examples 5 to 7 contain the hydrolysis inhibitor (B-1) in the pressure-sensitive adhesive layer, but have adhesive strength and holding power (cohesion) comparable to those of the pressure-sensitive adhesive sheets of Comparative Examples 6 and 7, which do not contain the hydrolysis inhibitor (B-1).

When examined together with the results in Table 2, it can be seen that the polyester resins of Production Examples 1 to 4 produced using recycled PET have higher reactivity than the polyester resins of Production Examples 5 to 7, which used terephthalic acid or ethylene glycol monomers, resulting in lower acid values and superior storage stability. Furthermore, the esterification reaction time could be significantly shortened due to two factors: [1] the less reactive terephthalic acid had already reacted as recycled PET, and [2] most or part of the ethylene glycol, which has a low boiling point, had already reacted as recycled PET (leading to a rapid rise in internal temperature). Furthermore, the absence of terephthalic acid, which is prone to sublimation, meant that the lid of the reaction vessel was very clean and did not require cleaning.
On the other hand, in the polyester resins of Production Examples 5 to 7, the reactivity of terephthalic acid was low, so the acid value of the final product was high, the esterification reaction time was long, and furthermore, the sublimation of terephthalic acid caused it to adhere to the lid of the reaction vessel, making the reaction vessel very dirty. This required solvents and glycols for cleaning, which further increased the environmental load.

The polyester resin composition, adhesive solution, adhesive composition, and adhesive containing the same of the present invention are not only environmentally friendly, but also have excellent storage stability and humidity and heat resistance, and exhibit excellent adhesive properties to adherends. They can be used in single-sided or double-sided adhesive sheets for laminating optical components, single-sided or double-sided adhesive sheets for fixing components in portable electronic devices, and single-sided or double-sided adhesive sheets for fixing electronic components.

Claims (14)

A resin composition containing a polyester resin (A) and a hydrolysis inhibitor (B),
the polyester-based resin (A) contains a structural unit derived from a thermoplastic polyester resin (excluding the polyester-based resin (A)) (a1), a structural unit derived from an aliphatic polycarboxylic acid (a2), and a structural unit derived from a polyol (a3);
The structural units derived from the polyol (a3) include a structural unit derived from a linear aliphatic diol and a structural unit derived from an aliphatic diol having a hydrocarbon group in a side chain,
The acid value of the thermoplastic polyester resin (a1) is 50 mgKOH/g or less,
The polyester resin (A) has a glass transition temperature of 40°C or lower,
A polyester resin composition characterized in that the content of the hydrolysis inhibitor (B) is 0.01 to 10 parts by weight per 100 parts by weight of the polyester resin (A). The polyester resin composition according to claim 1, characterized in that the acid value of the polyester resin (A) is 0.5 mg KOH/g or less. The polyester resin composition according to claim 1 or 2, characterized in that the acid value of the polyester resin composition is 0.5 mg KOH/g or less. The polyester resin composition according to any one of claims 1 to 3, characterized in that the hydroxyl value of the polyester resin (A) is 15 mgKOH/g or less. The polyester resin composition according to any one of claims 1 to 4, characterized in that the polyester resin (A) is obtained using a polyol (a3) having hydroxyl groups in a molar ratio of 1.2 or more per mole of carboxy groups of polycarboxylic acids, including the aliphatic polycarboxylic acids (a2). The polyester resin composition according to any one of claims 1 to 5, characterized in that the hydrolysis inhibitor (B) is a polyvalent carbodiimide compound (B1). The polyester resin composition according to any one of claims 1 to 6, further comprising a crosslinking agent (C). A pressure-sensitive adhesive composition comprising the polyester resin composition described in any one of claims 1 to 7. An adhesive obtained using the adhesive composition of claim 8. An adhesive sheet having an adhesive layer containing the adhesive of claim 9. A laminate comprising the adhesive layer of claim 10, a release-treated sheet on one side, and a base sheet or a release-treated sheet on the other side. The polyester-based resin (A) comprises structural units derived from a thermoplastic polyester resin (excluding polyester-based resin (A)) (a1), structural units derived from an aliphatic polycarboxylic acid (a2), and structural units derived from a polyol (a3), and the structural units derived from the polyol (a3) include structural units derived from a linear aliphatic diol and structural units derived from an aliphatic diol having a hydrocarbon group in its side chain; the polyester-based resin (A) has a glass transition temperature of 40°C or lower, a hydroxyl value of 15 mgKOH/g or lower, and the acid value of the polyester-based resin (a1) is 50 mgKOH/g or lower. A method for producing a polyester-based resin (A) having a glass transition temperature of 40°C or lower and a hydroxyl value of 15 mgKOH/g or lower, comprising copolymerizing a thermoplastic polyester resin (a1) (excluding the polyester-based resin (A)), an aliphatic polycarboxylic acid (a2), and a polyol (a3), the method comprising the steps of:
The polyol (a3) includes a linear aliphatic diol and an aliphatic diol having a hydrocarbon group in a side chain,
The method for producing a polyester resin (A), wherein the thermoplastic polyester resin (a1) has an acid value of 50 mg KOH/g or less. A method for producing a polyester-based resin (A) containing structural units derived from a thermoplastic polyester resin (excluding the polyester-based resin (A)) (a1), structural units derived from an aliphatic polycarboxylic acid (a2), and structural units derived from a polyol (a3), and having a glass transition temperature of 40°C or lower, comprising:
The structural units derived from the polyol (a3) include a structural unit derived from a linear aliphatic diol and a structural unit derived from an aliphatic diol having a hydrocarbon group in a side chain,
a thermoplastic polyester resin (a1) having an acid value of 50 mgKOH/g or less, decomposing the thermoplastic polyester resin (a1) by a reaction between the thermoplastic polyester resin (a1) and an aliphatic polycarboxylic acid (a2), and then copolymerizing a copolymerization component containing a polyol (a3).