JP7790105B2 - Adhesive layer and adhesive sheet - Google Patents

Description

The present invention relates to an adhesive layer, and in particular to a thin adhesive layer and adhesive sheet suitable for use in the joints between housings and components of portable electronic devices.

Adhesive tapes and sheets are excellent for workability as they can bond substrates and components without the need for heat or other energy, and as a highly reliable bonding method, they are used in various industrial fields, such as office equipment and home appliances, for applications such as securing components. As these office equipment become more functional, they are also becoming smaller and thinner, and there is a particularly high demand for smaller and thinner devices, such as personal computers, digital video cameras, electronic organizers, mobile phones, PHS phones, smartphones, game consoles, and e-books. For these portable electronic devices, along with thinner main components, thinner adhesive tapes are also being required.

As a transparent thin-film double-sided adhesive tape with excellent adhesive strength and high-temperature retention, suitable for fastening components such as mobile electronic devices like mobile phones and thin-film displays, for bonding optical disk substrates, and for fastening polarizing plates, for example, Patent Document 1 proposes a double-sided adhesive tape having a total thickness of 30 μm or less, with each of the adhesive layers on each side being 2 to 10 μm thick, in which adhesive layers are formed on both sides of a core material and comprise an adhesive composition containing an acrylic ester copolymer containing 90% by mass or more of butyl acrylate units and a weight-average molecular weight of 700,000 or more, and a specific amount of a tackifier.

For example, Patent Document 2 proposes a pressure-sensitive adhesive containing a polyester resin that has, as essential ingredients, an aromatic dicarboxylic acid, a glycol having hydrocarbon in the side chain, and a trivalent or higher polyhydric alcohol and/or a trivalent or higher polycarboxylic acid, and that is obtained by polycondensing a specific amount of the polyhydric alcohol and/or polycarboxylic acid, thereby obtaining a pressure-sensitive adhesive with excellent adhesive properties and heat resistance. The polyester resin exhibits sufficient adhesive strength with finger pressure, and has excellent adhesiveness, mechanical strength, and particularly excellent heat resistance, making it suitable for a wide range of applications.

Japanese Patent Application Laid-Open No. 2007-169327 Japanese Patent Application Laid-Open No. 2007-99879

However, the technologies disclosed in Patent Documents 1 and 2 do not provide sufficient adhesive strength to various adherends in thin films, and further improvement is required. Furthermore, the acrylic adhesives used in the technology disclosed in Patent Document 1 generally have a low modulus of elasticity and low cohesive strength, so when used to form a thin adhesive layer, adhesive residue tends to remain when peeled off, leaving room for further improvement.

Polyester-based adhesives have also been investigated as adhesives with a high modulus of elasticity and high cohesive strength (resistance to cracking and leaving residue when peeled off), but the polyester-based adhesive disclosed in the technology of Patent Document 2 above does not disclose its use in thin films. Furthermore, when made into thin films, sufficient adhesive strength is not exhibited, leaving further improvements required.

Traditionally, acrylic adhesives have been widely used, but in recent years, polyester adhesives have also been increasingly used. Compared to acrylic adhesives, polyester adhesives have higher heat resistance, making them ideal for use in electronic components and other applications. They also work well with ester films such as polyethylene terephthalate (PET), making them suitable for use in many applications where acrylic adhesives are difficult to use. Furthermore, with growing calls in recent years for addressing environmental impact, polyester adhesives can be depolymerized to return them to oligomers and monomers during disposal, making them more environmentally friendly than acrylic adhesives when it comes to recycling.

In view of this background, the present invention provides a pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet that, even though thin, has good adhesive strength to various adherends such as SUS, polyimide, and polypropylene , and exhibits little change in adhesive strength over time. In some cases, a thin-film pressure-sensitive adhesive sheet is provided that, when bonded with a thin-film pressure-sensitive adhesive layer, has low initial adhesive strength but increases adhesive strength over time.

The present inventors have noticed that the adhesive strength of polyester-based adhesives is little dependent on the thickness of the adhesive layer, and have discovered that by using a polyester-based resin as the resin constituting the adhesive composition to form a polyester-based adhesive, it is possible to reduce the thickness of the adhesive layer while maintaining adhesive strength.
The reason why adhesive strength is less dependent on the thickness of the adhesive layer is not clear, but it is thought that this is because polyester-based adhesives have a high elastic modulus and are less likely to deform, so the energy required to deform the adhesive bulk is less and does not contribute much to adhesive strength, and therefore the adhesion between interfaces contributes more to adhesive strength.
Furthermore, when a polyester-based adhesive is used to achieve strong adhesive strength in a thin film, it is preferable that the adhesive have high interfacial adhesion, as described above. In order to improve adhesion, it is important to increase polarity, and increasing the ester bond concentration is thought to be effective. On the other hand, since it is necessary for the adhesive to be compatible with thin films, the softness of the adhesive must also be taken into consideration, and it is preferable that the adhesive have a low glass transition temperature (Tg). Taking these factors into consideration, we have designed the adhesive and found that the above-mentioned problems can be more effectively solved by introducing a certain amount of aliphatic dicarboxylic acid with a relatively short carbon difference.

That is, the present invention has the following aspects [1] to [14].
[1] A pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing a polyester resin (i) having a structural moiety derived from a polycarboxylic acid (a) and a structural moiety derived from a polyol component (b),
The thickness of the pressure-sensitive adhesive layer is 18 μm or less,
The pressure-sensitive adhesive layer contains 60 mol % or more of structural moieties derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms among the structural moieties derived from the polycarboxylic acids (a).
[2] The pressure-sensitive adhesive layer according to [1], wherein the structural moiety derived from the polyol component (b) contains a structural moiety derived from at least one selected from the group consisting of ethylene glycol, 2-methyl-1,3-propanediol, and neopentyl glycol.
[3] The pressure-sensitive adhesive layer according to [1] or [2], wherein the structural moiety derived from the aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms is a structural moiety derived from adipic acid.
[4] The pressure-sensitive adhesive layer according to any one of [1] to [3], wherein the polyester resin (i) has an ester bond concentration of 9 to 12.5 mmol/g.
[5] The pressure-sensitive adhesive layer according to any one of [1] to [4], wherein the glass transition temperature of the polyester resin (i) is −50 to −10° C.
[6] The pressure-sensitive adhesive layer according to any one of [1] to [5], wherein the polyester resin (i) having a structural moiety derived from the polyvalent carboxylic acid (a) and a structural moiety derived from the polyol component (b) is crosslinked with a crosslinking agent (ii).
[7] The pressure-sensitive adhesive layer according to [6], wherein the crosslinking agent (ii) is an isocyanate-based crosslinking agent (ii-1).
[8] A pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer according to any one of [1] to [7] and a substrate, wherein the substrate is laminated on one surface of the pressure-sensitive adhesive layer, and the other surface is a release-treated sheet.
[9] The pressure-sensitive adhesive sheet according to [8], wherein the substrate is a polyester resin sheet.
[10] A pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer according to any one of [1] to [7] and a release-treated sheet, wherein the release-treated sheet is laminated on both sides of the pressure-sensitive adhesive layer.
[11] The pressure-sensitive adhesive sheet according to [8] or [9], wherein the adherend is a polyimide.
[12] The pressure-sensitive adhesive sheet according to [8] or [9], which is for fixing electronic components.
[13] The pressure-sensitive adhesive sheet according to any one of [8] to [12], wherein X/Y≧0.5, where X is the adhesive strength (N/25 mm) measured under the following measurement conditions and Y is the thickness (μm) of the pressure-sensitive adhesive layer.
[Measurement conditions for adhesive strength (N/25 mm)]
The adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, the release film was peeled off, and the adhesive layer side was placed against a SUS-BA plate as an adherend, and a 2 kg roller was used to pressurize and 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 speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N), and this was taken as the adhesive strength.
[14] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer crosslinked with a pressure-sensitive adhesive composition containing a polyester resin (i') having a structural moiety derived from a polyvalent carboxylic acid (a) and a structural moiety derived from a polyol component (b),
The thickness of the pressure-sensitive adhesive layer is 18 μm or less,
A pressure-sensitive adhesive sheet having an adhesive strength over time of 5 N/25 mm or more as measured under the following measurement conditions.
[Measurement conditions for adhesive strength over time (N/25 mm)]
The pressure-sensitive adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, and the pressure-sensitive adhesive layer was then placed on a SUS-BA plate as an adherend, and a 2 kg roller was used to press and adhere it. After leaving the sheet to stand for 24 hours in the same atmosphere, the 180-degree peel strength (N/25 mm) was measured at a peel speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N), and this was taken as the adhesive strength over time.

The pressure-sensitive adhesive layer of the present invention, even when thin, has excellent adhesive strength to various adherends such as SUS, polyimide, and polypropylene . Furthermore, the pressure-sensitive adhesive layer of the present invention shows little change in adhesive strength between the initial state and over time, i.e., the pressure-sensitive adhesive layer of the present invention exhibits sufficient adhesive strength from the beginning.
Therefore, the pressure-sensitive adhesive layer of the present invention is suitable for use as a single-sided or double-sided pressure-sensitive adhesive sheet for polyimide, a single-sided or double-sided pressure-sensitive adhesive sheet used for bonding optical components, a single-sided or double-sided pressure-sensitive adhesive sheet for fixing components of portable electronic devices, a single-sided or double-sided pressure-sensitive adhesive sheet for fixing electronic components, etc.

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 acids such as carboxylic acids, but also derivatives of carboxylic acids such as salts of carboxylic acids, anhydrides of carboxylic acids, halides of carboxylic acids, and esters of carboxylic acids.

A pressure-sensitive adhesive layer according to one embodiment of the present invention is a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing a polyester resin (i) having a structural moiety derived from a polyvalent carboxylic acid (a) and a structural moiety derived from a polyol component (b),
The thickness of the pressure-sensitive adhesive layer is 18 μm or less,
The polycarboxylic acid (a) is characterized in that it contains 60 mol % or more of structural moieties derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms among the structural moieties derived from the polycarboxylic acids (a).
Furthermore, a pressure-sensitive adhesive sheet according to one embodiment of the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer crosslinked with a pressure-sensitive adhesive composition containing a polyester resin (i′) having a structural moiety derived from a polyvalent carboxylic acid (a) and a structural moiety derived from a polyol component (b),
The thickness of the pressure-sensitive adhesive layer is 18 μm or less,
It is characterized in that the adhesive strength over time measured under specific measurement conditions is 5 N/25 mm or more.
Hereinafter, each component contained in the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer of the present invention will be described in order.

<Polyester Resins (i) and (i')>
The polyester resin (i) used in the present invention has structural moieties derived from the polycarboxylic acid (a) and structural moieties derived from the polyol component (b), and contains 60 mol % or more, preferably 70 mol % or more, particularly preferably 75 mol % or more of structural moieties derived from the aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms among the structural moieties derived from the polycarboxylic acid (a).
The upper limit is usually 100 mol %, preferably 98 mol %. Since the pressure-sensitive adhesive layer of the present invention contains the polyester resin (i) containing a specific amount of a structural moiety derived from an aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms, it can have excellent adhesive strength to various adherends even when it is a thin film, and can have little change in adhesive strength between the initial state and over time.
The polyester resin (i') used in the present invention has a structural portion derived from the polycarboxylic acid (a) and a structural portion derived from the polyol component (b).

[Structural moiety derived from polycarboxylic acid (a)]
The polyester resin (i) is characterized in that, as the structural moieties derived from the polycarboxylic acids (a), structural moieties derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms (including the carbon atoms of the carboxy groups) account for 60 mol % or more of the total polycarboxylic acids (a).

(Structural moiety derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms)
Examples of structural moieties derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms include structural moieties derived from straight-chain aliphatic dicarboxylic acids such as malonic acids, dimethylmalonic acids, succinic acids, glutaric acids, adipic acids, pimelic acids, suberic acids, and diglycolic acids having 8 or less carbon atoms; structural moieties derived from aliphatic dicarboxylic acids having an alkyl group on the side chain such as methylsuccinic acids, 2,2-dimethylglutaric acids, 1,3-dimethylglutaric acids, and dimethyladipic acids; structural moieties derived from sulfur-containing dicarboxylic acids such as thiodipropionic acids; and structural moieties derived from unsaturated group-containing aliphatic dicarboxylic acids such as fumaric acids, maleic acids, and itaconic acids. Of these, structural moieties derived from straight-chain aliphatic dicarboxylic acids are preferred. These may be contained alone or in combination of two or more. Among these, structural moieties derived from adipic acids are preferred because of their excellent adhesive strength to various adherends and little change in adhesive strength between the initial stage and over time.
Furthermore, it is preferable that the structural moiety derived from the aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms is a structural moiety derived from adipic acid, since this provides excellent adhesive strength to various adherends even in the form of a thin film and little change in adhesive strength between the initial state and over time.

The content of structural moieties derived from the aliphatic dicarboxylic acids (a1) having 8 or fewer carbon atoms is typically 60 mol% or more, preferably 70 mol% or more, and particularly preferably 75 mol% or more, relative to the structural moieties derived from the polycarboxylic acids (a). The upper limit of the content of structural moieties derived from the aliphatic dicarboxylic acids (a1) having 8 or fewer carbon atoms is typically 100 mol%, preferably 98 mol%. When the content of structural moieties derived from the aliphatic dicarboxylic acids (a1) having 8 or fewer carbon atoms is equal to or greater than the above-mentioned value, the adhesive strength to various adherends is excellent, and there tends to be less change in adhesive strength between initial and aging.

(Structural moieties derived from other polycarboxylic acids)
The structural moiety derived from the polyvalent carboxylic acid (a) contained in the polyester resin (i) may contain, in addition to the structural moiety derived from the aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms, structural moieties derived from other polyvalent carboxylic acids such as dicarboxylic acids having 9 or more carbon atoms, aromatic dicarboxylic acids, and trivalent or higher polyvalent carboxylic acids. These may be contained alone or in combination of two or more kinds.

Examples of structural moieties derived from dicarboxylic acids having 9 or more carbon atoms include structural moieties derived from aliphatic dicarboxylic acids such as trimethyladipic acids, pimelic acids, azelaic acids, thiodipropionic acids, diglycolic acids having 9 or more carbon atoms, and 1,9-nonanedicarboxylic acids; and structural moieties derived from alicyclic 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.

Examples of the structural units derived from aromatic dicarboxylic acids include structural moieties derived from aromatic dicarboxylic acids such as phthalic acids, terephthalic acids, isophthalic acids, benzylmalonic acids, diphenic acids, 4,4'-oxydibenzoic acids, and naphthalenedicarboxylic acids such as 1,8-naphthalenedicarboxylic acids, 2,3-naphthalenedicarboxylic acids, and 2,7-naphthalenedicarboxylic acids.

Examples of the structural moiety derived from the trivalent or higher polyvalent carboxylic acids include structural moieties derived from trimellitic acids, pyromellitic acids, adamantanetricarboxylic acids, trimesic acids, etc.

Among the structural moieties derived from the other polycarboxylic acids described above, it is preferable to contain structural moieties derived from aromatic dicarboxylic acids, particularly structural moieties derived from asymmetric aromatic dicarboxylic acids, in order to reduce the crystallinity of the polyester resin (i).

Examples of the structural moiety derived from the asymmetric aromatic dicarboxylic acids include structural moieties derived from phthalic acids, isophthalic acids, 1,8-naphthalenedicarboxylic acids, and 2,3-naphthalenedicarboxylic acids. Among these, structural moieties derived from isophthalic acids are particularly preferred in terms of reactivity.

The content of the structural moieties derived from the aromatic dicarboxylic acids, particularly the structural moieties derived from asymmetric aromatic dicarboxylic acids, relative to the structural moieties derived from the polycarboxylic acid (a), is typically 1 to 40 mol %, preferably 2 to 30 mol %, and particularly preferably 3 to 25 mol %. If the content of structural moieties derived from aromatic dicarboxylic acids is too high, the initial adhesive strength and tackiness tend to decrease.

The structural units derived from polycarboxylic acids (a) contained in the polyester resin (i') are not particularly limited, but it is preferable that the polyester resin (i') contain structural units derived from polycarboxylic acids (a) similar to those contained in the polyester resin (i).

[Structural moiety derived from polyol component (b)]
Examples of the structural moiety derived from the polyol component (b) contained in the polyester resins (i) and (i') include a structural moiety derived from a dihydric alcohol (b1) and a structural moiety derived from a trihydric or higher polyol (b2). These may be contained alone or in combination of two or more. In particular, in the present invention, it is preferred that the polyester resins (i) and (i') contain a structural moiety derived from a dihydric alcohol (b1) and a structural moiety derived from a trihydric or higher polyol (b2).

(Structural moiety derived from dihydric alcohol (b1))
Examples of the structural moiety derived from the dihydric alcohol (b1) include structural moieties derived from aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol, oleic acid, and dimer diol derived from erucic acid;
Structural moieties derived from alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol;
Examples of structural moieties include those derived from aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and ethylene oxide adducts and propylene oxide adducts thereof.
Further examples include structural moieties derived from fatty acid esters derived from castor oil, glycerol monostearate, etc. Among these, structural moieties derived from aliphatic diols are preferred.

Furthermore, the structural moieties derived from the above-mentioned aliphatic diols can also be distinguished as structural moieties derived from aliphatic diols with a straight-chain structure and structural moieties derived from aliphatic diols having a hydrocarbon group in the side chain.

In such cases, the content of structural moieties derived from linear aliphatic diols relative to the structural moieties derived from polyol component (b) is 1 to 100 mol%, preferably 10 to 80 mol%, more preferably 20 to 75 mol%, and particularly preferably 40 to 70 mol%. If this content ratio is too low, the reactivity of polyester resins (i) and (i') during production tends to decrease. However, if this content ratio is too high, polyester resins (i) and (i') tend to crystallize, reducing the initial adhesive strength of the adhesive.

The structural moiety derived from the linear aliphatic diol is preferably a structural moiety derived from a linear aliphatic diol having 2 to 18 carbon atoms. In particular, structural moieties derived from aliphatic diols having 4 or fewer carbon atoms are preferred, as they facilitate increasing the thin film adhesive strength by increasing the polarity through an increase in the ester bond concentration. Specifically, structural moieties derived from ethylene glycol, 1,3-propanediol, and 1,4-butanediol are preferred, with ethylene glycol being particularly preferred.

The content of structural moieties derived from an aliphatic diol having a hydrocarbon group in the side chain is 5 to 100 mol%, preferably 20 to 90 mol%, more preferably 25 to 80 mol%, and particularly preferably 28 to 60 mol%, relative to the structural moieties derived from polyol component (b). If this content ratio is too low, polyester resins (i) and (i') tend to crystallize, reducing the initial adhesive strength of the adhesive. If this content ratio is too high, the reactivity of polyester resin (i) during production tends to decrease.

Examples of structural moieties derived from aliphatic diols having a hydrocarbon group in the side chain include structural moieties derived from dipropylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol, and dimer diol. Among these, structural moieties derived from 2,2-dimethyl-1,3-propanediol (neopentyl glycol) and 2-methyl-1,3-propanediol are preferred.

(Structural moiety derived from trivalent or higher polyol (b2))
In the present invention, it is preferable that the structural moiety derived from the polyol component (b) contains a structural moiety derived from a trivalent or higher polyol (b2), in order to form a reactive site with the crosslinking agent (ii) described below and increase the cohesive strength.

The content of structural moieties derived from such trivalent or higher polyol (b2) is preferably 20 mol% or less, more preferably 0.1 to 10 mol%, and particularly preferably 0.5 to 5 mol%, relative to the structural moieties derived from polyol component (b). If the content of such trivalent or higher polyol (b2) is too high, it tends to make it difficult to produce polyester resins (i) and (i').

Examples of structural moieties derived from trivalent or higher polyols (b2) include structural moieties derived from 2-ethyl-2-hydroxymethyl-1,3-propanediol (trimethylolpropane), trimethylolethane, glycerin, pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, and 1,2,6-hexanetriol. Among these, those containing structural moieties derived from trimethylolpropane are particularly preferred, as they are relatively less likely to form gels.

In the present invention, in terms of adhesive strength to various adherends and minimal change in adhesive strength between initial and aging, it is preferable that the structural moiety derived from polyol component (b) contains a structural moiety derived from at least one selected from the group consisting of ethylene glycol, 2-methyl-1,3-propanediol, and neopentyl glycol, and it is particularly preferable that the structural moiety derived from polyol component (b) contains a structural moiety derived from ethylene glycol and/or neopentyl glycol. When both such structural moieties are contained, the ethylene glycol/neopentyl glycol (molar ratio) is preferably 10/90 to 10/90, particularly 20/75 to 25/80, and even more preferably 40/60 to 70/30.

The content of structural units derived from at least one selected from the group consisting of ethylene glycol, 2-methyl-1,3-propanediol, and neopentyl glycol is typically 70 mol% or more, preferably 80 mol% or more, and particularly preferably 90 mol% or more, relative to the structural units derived from polyol component (b). The upper limit is 100 mol%.

In the present invention, the proportions (compositional proportions) of structural moieties derived from each component of the polyester resins (i) and (i') can be determined by known methods using NMR, such as 1H-NMR measurement (proton-type nuclear magnetic resonance spectroscopy) at a resonance frequency of 400 MHz or ^13C -NMR measurement (carbon-type nuclear magnetic resonance spectroscopy).

The polyester resins (i) and (i') used in the present invention may contain, in addition to structural moieties derived from the polycarboxylic acids (a) and the polyol component (b), structural moieties derived from compounds having both a carboxylic acid and a hydroxyl group in the molecule (e.g., lactic acid), to the extent that the effects of the present invention are not impaired. However, because structural moieties derived from lactic acid are prone to hydrolysis, it is preferable not to contain them.

[Production of Polyester Resins (i) and (i')]
The polyester resins (i) and (i') of the present invention can be produced by polycondensation reaction of the above-mentioned polycarboxylic acid (a) and the above-mentioned polyol component (b) as raw materials in the presence of a catalyst by a known method. That is, since the polyester resins (i) and (i') are obtained by polycondensation reaction of the polycarboxylic acid (a) and the polyol component (b), they have structural moieties derived from the polycarboxylic acid (a) and the polyol component (b).
In the polycondensation reaction, an esterification reaction or an ester exchange reaction is carried out first, followed by the polycondensation reaction. When a high molecular weight is not required, the product may be produced by only the esterification reaction or the ester exchange reaction.

The blending ratio of the polycarboxylic acid (a) and polyol component (b) is preferably 1 to 2 equivalents of polyol component (b) per equivalent of polycarboxylic acid (a), and particularly preferably 1.1 to 1.7 equivalents. If the blending ratio of polyol component (b) is too low, the acid value tends to be high, making it difficult to achieve a high molecular weight, while if it is too high, the yield tends to decrease.

[Esterification reaction or transesterification reaction]
In the esterification reaction or transesterification reaction, a catalyst is usually used, and 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, and one or more of these are used. Among these, antimony trioxide, tetrabutyl titanate, germanium dioxide, and zinc acetate are preferred from the viewpoint of the balance between high catalytic activity and the hue of the resulting reaction product.

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 or transesterification reaction is preferably 200 to 300°C, particularly preferably 210 to 280°C, and even more preferably 220 to 260°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 catalyst as used in the above esterification reaction or transesterification reaction is further compounded in an equivalent amount; the reaction temperature is preferably set to 220-280°C, and particularly preferably 230-270°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 tends not to proceed sufficiently; if it is too high, side reactions such as decomposition tend to occur.

The ester bond concentration of the polyester resins (i) and (i') obtained above is preferably 9 to 12.5 mmol/g, more preferably 9.2 to 11.5 mmol/g, and even more preferably 9.5 to 11.0 mmol/g. If the ester group concentration is too low, the polarity of the polyester resins (i) and (i') will decrease, which will tend to result in poor initial adhesion and thin film adhesive strength.

The ester bond concentration (mmol/g) refers to the number of moles of ester bonds per gram of polyester resin (i) or (i'), and can be calculated from the amounts charged. The calculation is performed by dividing the number of moles of the polycarboxylic acid (a) or the polyol component (b), whichever is charged less frequently, by the total weight of the final product. An example of the calculation formula is shown below.
When the polycarboxylic acid (a) and the polyol component (b) are charged in equal molar amounts, either of the following calculation formulas may be used.
Furthermore, when a monomer having both a carboxylic acid and a hydroxyl group is used, or when polyester is produced from caprolactone or the like, the calculation method will be changed appropriately.

<When the amount of polycarboxylic acid (a) is small>
Ester bond concentration (mmol/g) = [(A1/α1 × m1 + A2/α2 × m2 + A3/α3 × m3 ...) / Z] × 1000
A: Amount (g) of polycarboxylic acid (a) charged
α: Molecular weight of polycarboxylic acid (a) m: Number of carboxyl groups per molecule of polycarboxylic acid (a) Z: Finished weight (g)
<When the amount of polyol component (b) is small>
Ester group concentration (mmol/g)=[(B1/β1×n1+B2/β2×n2+B3/β3×n3...)/Z]×1000
B: Amount of polyol component (b) charged (g)
β: molecular weight of polyol component (b); n: number of hydroxyl groups per molecule of polyol component (b); Z: finished weight (g);

The ester bond concentrations of the polyester resins (i) and (i') can also be determined by known methods using NMR, such as ^1H -NMR measurement (proton-type nuclear magnetic resonance spectroscopy) or ^13C -NMR measurement (carbon-type nuclear magnetic resonance spectroscopy) at a resonance frequency of 400 MHz.

Methods for adjusting the ester bond concentration within a predetermined range include, for example, selecting a polyol having 4 or fewer carbon atoms as the polyol component (b), increasing the content of linear carboxylic acids having 8 or fewer carbon atoms as the polycarboxylic acids (a), or increasing the content of dicarboxylic acids with fewer carbon atoms, or a combination of both.

The glass transition temperature (Tg) of the polyester resins (i) and (i') is preferably −70 to −10° C., particularly preferably −50 to −15° C., and further preferably −45 to −20° C. If the glass transition temperature (Tg) is too high, the adhesive strength of the thin film tends to decrease, whereas if it is too low, the heat resistance and cohesive strength tend to decrease.
The glass transition temperature can be adjusted by, for example, introducing an aromatic skeleton or changing the alkyl chain length of the polycarboxylic acid (a) or the polyol component (b).

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

The weight-average molecular weight of the polyester resins (i) and (i') is preferably 2,000 to 500,000, more preferably 5,000 to 200,000, and particularly preferably 50,000 to 100,000. If the weight-average molecular weight is too high, handling properties will be reduced, requiring a large amount of solvent and increasing the environmental load. If the weight-average molecular weight is too low, adhesive properties will tend to be reduced.

The weight-average molecular weight is a weight-average molecular weight converted into a standard polystyrene molecular weight, and is 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.

The acid value of the polyester resins (i) and (i') is preferably 10 mgKOH/g or less in order to prevent hydrolysis and improve durability, more preferably 5 mgKOH/g or less, particularly preferably 2 mgKOH/g or less, particularly preferably 1 mgKOH/g or less, and most preferably 0.5 mgKOH/g or less. If the acid value is too high, durability tends to decrease.
The acid value can be adjusted, for example, by increasing the proportion of the polyol component (b) during the esterification reaction or transesterification reaction, or by adjusting the reaction conditions. The lower limit of the acid value is usually 0 mgKOH/g.

The acid values of the polyester resins (i) and (i') are determined by neutralization titration in accordance with JIS K0070.
The acid value in the present invention refers to the content of carboxy groups in the polyester resins (i) and (i'). The carboxy groups include those in a carboxylate ion state in which the carboxy groups are neutralized with a basic compound.

The heat of crystalline fusion of the polyester resins (i) and (i') as measured by a differential scanning calorimeter (DSC) is preferably 10 J/g or less, more preferably 5 J/g or less, even more preferably 2 J/g or less, and particularly preferably no heat of crystalline fusion. If the heat of crystalline fusion is too large, crystallinity will occur, which tends to result in poor storage stability of the resin solution, poor stability at low temperatures when made into an adhesive sheet, and poor adhesive strength in thin films.

Methods for adjusting the heat of crystalline fusion within a predetermined range include, for example, appropriately using polycarboxylic acids (a) having alkyl groups on the side chains or polyol components (b) having alkyl groups on the side chains, or using three or more, preferably four or more, copolymerizable monomer components.

The heat of crystalline fusion mentioned above refers to the energy consumed when heating and melting a crystallized substance, and can be measured using a differential scanning calorimeter (DSC).

The pressure-sensitive adhesive composition used in the present invention preferably contains, in addition to the polyester resin (i) or (i'), a crosslinking agent (ii), a hydrolysis inhibitor (iii), a urethanization catalyst (iv), and an antioxidant (v).

[Crosslinking agent (ii)]
The pressure-sensitive adhesive composition used in the present invention preferably contains a crosslinking agent (ii). By containing the crosslinking agent (ii), the polyester resins (i) and (i') are crosslinked by the crosslinking agent (ii), resulting in excellent cohesive strength and improved performance as a pressure-sensitive adhesive.

Examples of such crosslinking agents (ii) include isocyanate-based crosslinking agents (ii-1) and polyepoxy-based crosslinking agents, as well as crosslinking agents having functional groups that react with at least one of the hydroxyl groups and carboxyl groups contained in the polyester-based resins (i) and (i'). It is also possible to use polyfunctional acrylic monomers or urethane acrylate oligomers that increase cohesive strength even without reacting with the polyester-based resin (i). Of these, it is particularly preferable to use isocyanate-based crosslinking agents (ii-1), as they can achieve a good balance between initial adhesion, mechanical strength, and heat resistance.

Examples of such isocyanate-based crosslinking agents (ii-1) include polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, and triphenylmethane triisocyanate. Other examples include adducts of the above polyisocyanates with polyol compounds such as trimethylolpropane, as well as biuret and isocyanurate forms of these polyisocyanate compounds. The above polyisocyanate compounds may also be used in which the isocyanate moiety is blocked with phenol, lactam, or the like. These isocyanate-based crosslinking agents (ii-1) may be used alone or in combination.

For such isocyanate-based crosslinking agents (ii-1), aromatic polyisocyanate-based compounds are preferred, and trifunctional aromatic isocyanate-based compounds are preferred because of their good compatibility with the polyester-based resins (i) and (i').

The content of crosslinking agent (ii) can be selected appropriately depending on the molecular weight of polyester resins (i) and (i') and the intended use. However, it is generally preferable to contain crosslinking agent (ii) in a ratio such that the reactive groups contained in crosslinking agent (ii) are 0.2 to 10 equivalents per equivalent of at least one of the hydroxyl groups and carboxyl groups contained in polyester resins (i) and (i'), with 0.5 to 5 equivalents being particularly preferred, 0.8 to 4 equivalents being even more preferred, and 1.1 to 3 equivalents being even more preferred. If the equivalent number of reactive groups contained in crosslinking agent (ii) is too small, cohesive strength tends to decrease, while if it is too large, flexibility tends to decrease.

The content of such crosslinking agent (ii) is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 8 parts by weight, even more preferably 0.5 to 6 parts by weight, and especially preferably 1 to 4 parts by weight, per 100 parts by weight of polyester resins (i) and (i'). If the content of such crosslinking agent is too low, cohesive strength tends to decrease, while if the content is too high, flexibility tends to decrease and the required adhesive strength tends to be difficult to achieve.

In addition, in the reaction between polyester resins (i) and (i') and crosslinking agent (ii), organic solvents that do not have functional groups that react with these components 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 types.

<Hydrolysis inhibitor (iii)>
The hydrolysis inhibitor (iii) is not particularly limited, and conventionally known compounds can be used, such as compounds that react with and bond to the carboxylic acid terminal groups of the polyester resins (i) and (i'), specifically compounds having functional groups such as carbodiimide groups, epoxy groups, and oxazoline groups. Of these, carbodiimide group-containing compounds are preferred because they are highly effective in eliminating the catalytic activity of protons derived from the carboxyl terminal groups.

As the carbodiimide group-containing compound used in the present invention, a known carbodiimide having one or more carbodiimide groups (—N═C═N—) in the molecule can usually be used. However, in order to improve durability under high temperature and high humidity conditions, a compound having two or more carbodiimide groups in the molecule, i.e., a polyvalent carbodiimide compound, is preferred, and a compound having three or more, further five or more, and particularly seven or more carbodiimide groups in the molecule is particularly preferred.
The number of carbodiimide groups in a molecule is usually 50 or less, and if there are too many carbodiimide groups, the molecular structure becomes too large, which tends to reduce compatibility.

The carbodiimide group-containing compound used in the present invention preferably has a high weight-average molecular weight from the standpoint of hydrolysis resistance. The weight-average molecular weight of the carbodiimide group-containing compound is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 3,000 or more. The upper limit of the weight-average molecular weight is typically 50,000.

In addition, carbodiimide group-containing compounds are preferably low in volatility, and therefore it is preferable to use compounds with a high number-average molecular weight, typically 300 to 10,000, and preferably 1,000 to 5,000.

If the molecular weight of the carbodiimide group-containing compound is too small, hydrolysis resistance tends to decrease. Furthermore, if the molecular weight is too large, compatibility with polyester resins (i) and (i') tends to decrease.

The carbodiimide equivalent weight of the carbodiimide group-containing compound is preferably 50 to 10,000, particularly preferably 100 to 1,000, and even more preferably 150 to 500. The carbodiimide equivalent weight refers to the chemical formula weight per carbodiimide group.

It is also preferable to use, as the carbodiimide group-containing compound, a polycarbodiimide compound produced by subjecting a diisocyanate to a decarboxylation condensation reaction in the presence of a carbodiimide catalyst.

[Polycarbodiimide Compounds]
The polycarbodiimide compound can be obtained by subjecting an organic diisocyanate compound to a condensation reaction.
Examples of the organic diisocyanate compound include aromatic diisocyanate compounds such as 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate;
Examples of the diisocyanate include acyclic aliphatic diisocyanates such as hexamethylene diisocyanate, and aliphatic diisocyanates such as cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexane diisocyanate, and 2,5(2,6)-bis(isocyanatomethyl)bicyclo[2.2.1]heptane. These may be used alone or in combination of two or more.
Among these, aromatic diisocyanate compounds are preferred, and tetramethylxylene diisocyanate is more preferred, in that they can provide a pressure-sensitive adhesive composition with excellent moist heat resistance.

A polycarbodiimide compound can be obtained by subjecting the above organic diisocyanate compound to a decarboxylation condensation reaction using a known carbodiimide catalyst in a conventional manner.

The polycarbodiimide compound is preferably an aromatic polycarbodiimide compound, as this allows for a pressure-sensitive adhesive with minimal haze change even under high-temperature, high-humidity conditions and excellent moisture and heat resistance.

Furthermore, the polycarbodiimide compound used in the present invention is preferably one in which at least one of the terminal isocyanate groups of the polycarbodiimide compound is substituted with a substituent derived from a hydrophilic organic compound.

[Polycarbodiimide compound in which at least one terminal isocyanate group is substituted with a substituent derived from a hydrophilic organic compound]
Next, a polycarbodiimide compound in which at least one of the terminal isocyanate groups is substituted with a substituent derived from a hydrophilic organic compound will be described.
First, the hydrophilic organic compound will be described.

[Hydrophilic organic compound]
The hydrophilic organic compound is a compound having a substituent with an active hydrogen that is reactive with the terminal isocyanate group of the polycarbodiimide compound, and further having one or more heteroatoms in the molecule in addition to the substituent.

Examples of the substituent having an active hydrogen that is reactive with the isocyanate group include a hydroxyl group, a primary amino group, a secondary amino group, an imino group, an isocyanate group, and a carboxy group. Among these, a hydroxyl group, a primary amino group, a secondary amino group, and an imino group are preferred. These substituents may be contained alone or in combination of two or more types in the hydrophilic organic compound.

The number of substituents having active hydrogen atoms reactive with the isocyanate group in the hydrophilic organic compound is typically two or less, and preferably one. Furthermore, the substituent is preferably located at the end of the hydrophilic organic compound.

Examples of compounds having a substituent with an active hydrogen that is reactive with the isocyanate group and further having one or more heteroatoms in the molecule in addition to the substituent include compounds containing an oxyalkylene structure, compounds containing a hydroxy polyester structure, compounds containing a hydroxyalkyl sulfonic acid structure, compounds containing a dialkylamino alcohol structure, compounds containing a hydroxycarboxylic acid alkyl ester structure, and compounds containing a dialkylamino alkylamine structure. Of these, compounds containing an oxyalkylene structure are preferred.

It is also preferable that the ends of the hydrophilic organic compound are blocked with an alkoxy group or a phenoxy group.

Among these, hydrophilic organic compounds that are preferred are compounds containing an oxyalkylene structure end-blocked with an alkoxy group or a phenoxy group, as they cause little change in haze even under high-temperature, high-humidity conditions.

The oxyalkylene structure-containing compound terminally blocked with an alkoxy group or a phenoxy group includes, for example, a compound represented by the following formula (1):
R ₁ -O-(CH ₂ -CHR ₂ -O)m-H...(1)
In the above formula (1), R ₁ represents an alkyl group having 1 to 4 carbon atoms or a phenyl group, R ₂ represents a hydrogen atom or a methyl group, and m is an integer of 4 to 100.

Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, an isobutyl group, and a t-butyl group.

Specific examples of compounds represented by formula (1) above include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, and polypropylene glycol monophenyl ether. Of these, polyethylene glycol monomethyl ether is preferred.

The weight-average molecular weight of the hydrophilic organic compound is preferably 200 or more, and more preferably 400 or more. The upper limit of the weight-average molecular weight is usually 5,000 or less, preferably 4,000 or less, more preferably 2,000 or less, and even more preferably 1,000 or less. If the weight-average molecular weight is too small, compatibility with the polyester resin decreases, and furthermore, haze change under high-temperature, high-humidity conditions tends to increase. If the weight-average molecular weight is too large, adhesive strength tends to decrease.

The polycarbodiimide compound in which at least one of the terminal isocyanate groups is substituted with a substituent derived from a hydrophilic organic compound can be obtained by reacting the polycarbodiimide compound with the hydrophilic organic compound.

The reaction between the polycarbodiimide compound and the hydrophilic organic compound is carried out by heating the polycarbodiimide compound typically to 50 to 200°C, preferably 100 to 180°C, adding the hydrophilic organic compound, and then further reacting at 80 to 200°C for 0.5 to 5 hours.

In this way, a polycarbodiimide compound can be obtained in which at least one of the terminal isocyanate groups is substituted with a substituent derived from a hydrophilic organic compound.

Commercially available polycarbodiimide compounds include, for example, Carbodilite (registered trademark) V-09GB, V-02B, V-04K, V-04PF, and V-07 manufactured by Nisshinbo Chemical Inc., and Elastostab H01 manufactured by BASF, with Carbodilite V-09GB being particularly preferred.

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

Examples of the glycidyl ester compounds include benzoic acid glycidyl ester, t-Bu-benzoic 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 diglycidyl ester. Examples of suitable glycidyl esters include glycidyl esters of ...

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.

The oxazoline group-containing compound is preferably a bisoxazoline compound. 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 Examples of suitable oxazoline include 2,2'-ethylenebis(4-methyl-2-oxazoline), 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 viewpoint of reactivity with polyester.
Furthermore, the above-mentioned bisoxazoline compounds can be used alone or in combination of two or more kinds, as long as the object of the present invention is achieved.

These hydrolysis inhibitors (iii) preferably have low volatility, and therefore it is preferable to use one with a high molecular weight.

The amount of hydrolysis inhibitor (iii) added 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 polyester resins (i) and (i'). If this amount is too high, turbidity tends to occur due to poor compatibility with polyester resins (i) and (i'), while if the amount is too low, sufficient durability tends to be difficult to achieve.

The amount of the hydrolysis inhibitor (iii) is preferably optimized depending on the acid values of the polyester resins (i) and (i'). The molar ratio ((β)/(α)) of the total acid value (α) of the polyester resins (i) in the pressure-sensitive adhesive composition to the total amount of functional groups (β) of the hydrolysis inhibitor (iii) in the pressure-sensitive adhesive composition is preferably 0.5≦(β)/(α), particularly preferably 1≦(β)/(α)≦1000, and even more preferably 1.5≦(β)/(α)≦100.
If the content ratio of (β) to (α) is too high, the compatibility with the polyester resins (i) and (i') tends to decrease, and the adhesive strength, cohesive strength, and durability performance tend to decrease, and if the content ratio of (β) to (α) is low, the moist heat resistance performance tends to decrease.

[Urethanization catalyst (iv)]
The pressure-sensitive adhesive composition used in the present invention preferably contains a urethanization catalyst (iv) from the viewpoint of reaction rate.

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

Examples of the organometallic compounds include zirconium-based compounds, iron-based compounds, tin-based compounds, titanium-based compounds, lead-based compounds, cobalt-based compounds, and zinc-based compounds.

Examples of the zirconium compound include zirconium naphthenate and zirconium acetylacetonate.
Examples of the iron-based compound include iron acetylacetonate and iron 2-ethylhexanoate.
Examples of the tin compounds include dibutyltin dichloride, dibutyltin oxide, and dibutyltin dilaurate.
Examples of the titanium compounds include dibutyltitanium dichloride, tetrabutyltitanium, and butoxytitanium trichloride.
Examples of the lead-based 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 the zinc-based 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 (iv), organometallic compounds are preferred in terms of reaction rate and pot life of the PSA layer, with zirconium compounds being particularly preferred. Furthermore, it is preferable to use acetylacetone in combination with the urethane-forming catalyst (iv) as a catalytic action inhibitor. The inclusion of acetylacetone is preferred in that it inhibits catalytic action at low temperatures and extends the pot life.

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

[Antioxidant (v)]
The pressure-sensitive adhesive composition used in the present invention preferably contains an antioxidant (v) in order to increase the stability of the resin.

Examples of the antioxidant (v) include hindered phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, and phosphoric acid-based antioxidants. 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 antioxidants consisting of hindered phenol-based compounds are particularly preferred.

Examples of hindered phenol-based antioxidants include antioxidants that have a hindered phenol structure in which a group with significant steric hindrance, such as a tertiary 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.

The content of antioxidant (v) 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, per 100 parts by weight of polyester resins (i) and (i'). If the content is too low, adhesive residue on the adherend tends to be more likely to occur, while if the content is too high, adhesive properties tend to deteriorate.

In addition to the polyester resin (i) or (i'), crosslinking agent (ii), hydrolysis inhibitor (iii), urethanization catalyst (iv), and antioxidant (v) described above, the adhesive composition used in the present invention may contain additives such as tackifying resins, softeners, UV absorbers, stabilizers, and antistatic agents, as well as inorganic or organic fillers, metal powders, pigments, and other powdery or particulate additives, within a range that does not impair the effects of the present invention (e.g., 10% by weight or less of the adhesive composition). These may be used alone or in combination of two or more. Furthermore, the adhesive composition may contain small amounts of impurities contained in the manufacturing raw materials of the components of the adhesive composition.

The pressure-sensitive adhesive composition can be obtained, for example, by preparing the polyester resin (i) or (i') and any necessary optional components, and blending and dispersing them during the production of the polyester resin (i), or by blending them with the polyester resin (i) or (i') and dispersing them using a mixing roller or the like. In this case, the components may be dispersed as a solution using a solvent, or may be dispersed without a solvent. It is preferable that the polyester resin be the main component. The main component accounts for 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and particularly preferably 90% by weight or more. A low content of polyester resin tends to result in poor heat resistance.

<Adhesive Layer>
The pressure-sensitive adhesive layer of the present invention is obtained by crosslinking (curing) the pressure-sensitive adhesive composition. The pressure-sensitive adhesive layer can be obtained by coating and drying the pressure-sensitive adhesive composition, as will be described in detail later in the description of the method for producing a pressure-sensitive adhesive sheet.

The pressure-sensitive adhesive layer of the present invention has a thickness of 18 μm or less, preferably 15 μm or less, more preferably 12 μm or less, even more preferably 8 μm or less, and especially preferably 3 μm or less. The lower limit is usually 0.1 μm. Generally, the thicker the pressure-sensitive adhesive layer, the higher the adhesive strength tends to be. However, the pressure-sensitive adhesive layer of the present invention has excellent adhesive strength to various adherends, despite its thin thickness.

The thickness of the adhesive layer can be measured using a Digimatic Indicator (ID-C112B, manufactured by Mitutoyo Corporation). In the case of adhesive sheets, which will be described later, the thickness can be determined by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive sheet.

The gel fraction of the pressure-sensitive adhesive layer is preferably 10% by weight or more from the standpoint of durability and adhesive strength, and is particularly preferably 15 to 80% by weight, even more preferably 20 to 70% by weight, especially 30 to 55% by weight, and most preferably 35 to 45% by weight. If the gel fraction is too low, the cohesive strength will decrease, which tends to reduce durability. However, if the gel fraction is too high, there is a concern that the adhesive strength will decrease due to the increased cohesive strength.

The gel fraction is an indicator of the degree of crosslinking and is calculated, for example, by the following method: the adhesive layer is wrapped in a 200-mesh SUS wire mesh and immersed in toluene at 23°C for 24 hours, and the gel fraction is calculated as the weight percentage of the undissolved adhesive component remaining in the wire mesh after immersion relative to the weight of the adhesive component before immersion.

<Adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention has the pressure-sensitive adhesive layer.
A first aspect of the pressure-sensitive adhesive sheet of the present invention is a sheet having the pressure-sensitive adhesive layer and a substrate, in which the substrate is laminated on one side of the pressure-sensitive adhesive layer and the other side is release-treated.
A second aspect of the pressure-sensitive adhesive sheet of the present invention comprises the pressure-sensitive adhesive layer and a release-treated sheet, with the release-treated sheet laminated on both sides of the pressure-sensitive adhesive layer.
That is, the pressure-sensitive adhesive sheet of the present invention may be a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of a supporting substrate, or may be a substrateless double-sided pressure-sensitive adhesive sheet that does not have a substrate.
In the present invention, the term "sheet" also includes "film" and "tape."

The pressure-sensitive adhesive sheet of the first aspect can be produced according to a known method for producing pressure-sensitive adhesive sheets. For example, the pressure-sensitive adhesive composition can be applied to one surface of a substrate, followed by drying to form a pressure-sensitive adhesive layer, and then a release-treated sheet can be attached to the surface (the surface opposite the surface that contacts the substrate) and cured as necessary.

Alternatively, the pressure-sensitive adhesive composition can be applied to the release-treated sheet, dried to form a pressure-sensitive adhesive layer, and then a substrate can be attached to the surface (the side opposite to the surface that comes into contact with the release-treated sheet), followed by curing as necessary.

Examples of the substrate 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; synthetic resin sheets made of cycloolefin polymers; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; woven and nonwoven fabrics made of glass fiber, natural fibers, synthetic fibers, etc. Of these, polyester resin sheets are preferred, with polyethylene terephthalate being more preferred.

The release-treated sheet can be, for example, the above-mentioned base material that has been treated with a release agent. Among these, it is preferable to use a silicone-based release sheet.

The above-mentioned adhesive composition may 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.

Furthermore, the drying conditions after applying the pressure-sensitive adhesive composition are preferably a drying temperature of 60 to 140°C, and particularly preferably 80 to 120°C. Furthermore, the drying time is preferably 0.5 to 30 minutes, and particularly preferably 1 to 5 minutes.

The conditions for the above-mentioned curing treatment are typically a temperature between room temperature (23°C) and 70°C, and a time period between 1 and 30 days. Specifically, the treatment can be carried out under conditions such as 1 to 20 days at 23°C, preferably 3 to 14 days at 23°C, or 1 to 10 days at 40°C.

The adhesive sheet of the second embodiment can also be produced according to a known method for producing an adhesive sheet. For example, the adhesive composition is applied to a release-treated sheet, followed by drying to form an adhesive layer, and a separate release-treated sheet is then attached to the surface of the adhesive layer (the surface opposite to the surface that contacts the release-treated sheet), thereby obtaining the adhesive sheet of the second embodiment. The release-treated sheet used in the second embodiment can be the same as that exemplified in the first embodiment. The coating method, drying conditions, and curing conditions may also be similar to those in the first embodiment.

When using the resulting adhesive sheet or substrate-less double-sided adhesive sheet, the release-treated sheet is peeled off from the adhesive layer, and the adhesive layer is then bonded to the adherend.

The pressure-sensitive adhesive sheet of the present invention preferably has an adhesive strength of 5 N/25 mm or more, more preferably 6 N/25 mm or more, and particularly preferably 7 N/25 mm or more, as measured under the following measurement conditions. The upper limit is not particularly limited, but is usually 100 N/25 mm.
[Measurement conditions for adhesive strength (N/25 mm)]
The adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, the release film was peeled off, and the adhesive layer side was placed against a SUS-BA plate as an adherend, and a 2 kg roller was used to pressurize and 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 speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N), and this was taken as the adhesive strength.
The SUS-BA plate is made by cold rolling SUS304 and then bright annealing (non-oxidation annealing), or by skin-pass rolling to enhance the gloss.

Furthermore, when the adhesive strength (N/25 mm) measured under the above measurement conditions is X and the thickness (μm) of the adhesive layer is Y, the adhesive sheet of the present invention preferably satisfies X/Y ≧ 0.5, more preferably ≧ 1.0, and particularly preferably ≧ 1.5.

The pressure-sensitive adhesive sheet of the present invention preferably has an adhesive strength over time measured under the following conditions of 5 N/25 mm or more, more preferably 6 N/25 mm or more, and particularly preferably 7 N/25 mm or more. The upper limit is not particularly limited, but is usually 100 N/25 mm.
[Measurement conditions for adhesive strength over time (N/25 mm)]
The pressure-sensitive adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, and the pressure-sensitive adhesive layer was then placed on a SUS-BA plate as an adherend, and a 2 kg roller was used to press and adhere it. After leaving the sheet to stand for 24 hours in the same atmosphere, the 180-degree peel strength (N/25 mm) was measured at a peel speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N), and this was taken as the adhesive strength.
The SUS-BA plate is made by cold rolling SUS304 and then bright annealing (non-oxidation annealing), or by skin-pass rolling to enhance the gloss.

Furthermore, when the adhesive strength over time (N/25 mm) measured under the above measurement conditions is Z and the thickness of the adhesive layer (μm) is Y, the adhesive sheet of the present invention preferably satisfies Z/Y≧1.0, more preferably Z/Y≧2.0, and particularly preferably Z/Y≧3.0.

The pressure-sensitive adhesive sheet of the present invention can be used to bond various components, and is particularly suitable for use as a single-sided or double-sided pressure-sensitive adhesive sheet for polyimide, a single-sided or double-sided pressure-sensitive adhesive sheet used to bond optical components, and a single-sided or double-sided pressure-sensitive adhesive sheet for fixing components in portable electronic devices and electronic components.

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 the examples below, the ester bond concentration, glass transition temperature, weight average molecular weight, acid value, heat of crystalline fusion of the polyester resin, and gel fraction of the pressure-sensitive adhesive layer were measured according to the methods described above.

The polyester resin was produced using the following method.

[Production Example 1: Production of Polyester Resin (i-1)]
Thermometer, stirrer, distillation column, nitrogen inlet tube and vacuum device equipped reactor, as polycarboxylic acids (a), 46.2 parts adipic acid, 13.1 parts isophthalic acid, as polyol component (b), 13.1 parts ethylene glycol and 26.8 parts neopentyl glycol, 0.8 parts trimethylolpropane, as a catalyst, tetrabutyl titanate 0.01 parts was charged, the internal temperature was gradually increased to 250 ° C., and an esterification reaction was carried out over 4 hours. Thereafter, the internal temperature was increased to 260 ° C., and as a catalyst, 0.01 parts tetrabutyl titanate was charged, the pressure was reduced to 1.33 hPa, and a polymerization reaction was carried out over 3 hours, producing a polyester resin (i-1).
The composition (molar ratio) of the obtained polyester resin (i-1) was adipic acid/isophthalic acid/ethylene glycol/neopentyl glycol/trimethylolpropane=80/20/44.2/54.5/1.3, the ester bond concentration was 10.0 mmol/g, the heat of crystalline fusion was 0 J/g, the weight average molecular weight was 78,000, the glass transition temperature (Tg) was −30° C., and the acid value was 0.1 mgKOH/g.

Production Examples 2 to 5 and Comparative Production Examples 1 and 2 were prepared in the same manner as Production Example 1, except that the resin compositions shown in Table 1 below were used.
The resin compositions and physical properties of the polyester resins (i-1) to (i-7) prepared are shown in Table 1 below.

Comparative Production Example 3: Production of acrylic resin (b-1)
A four-necked round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 5 parts of acrylic acid, 65 parts of butyl acrylate, 30 parts of methyl acrylate, 150 parts of ethyl acetate, and 45 parts of acetone. After heating to reflux, 0.03 parts of azobisisobutyronitrile (AIBN) was added as a polymerization initiator and the reaction was carried out at the ethyl acetate reflux temperature for 3 hours. After the reaction, the mixture was diluted with ethyl acetate to obtain an acrylic resin (b-1) solution (weight average molecular weight (Mw) 1.2 million, glass transition temperature calculated by Fox's equation -35°C, solids content 25%, viscosity 5,000 mPa s (25°C)).

Next, the following components were prepared.
[Crosslinking agent (ii)]
Isocyanate-based crosslinking agent (ii-1A): "Coronate L55E" (manufactured by Tosoh Corporation)
Isocyanate-based crosslinking agent (ii-2A): "Coronate HX" (manufactured by Tosoh Corporation)
[Hydrolysis inhibitor (iii)]
Carbodiimide compound (iii-1): an aromatic polycarbodiimide compound whose terminals are substituted with substituents derived from aromatic monoisocyanates, "Carbodilite V-09GB" (manufactured by Nisshinbo Chemical Inc.), weight-average molecular weight: 6,000
[Urethanization catalyst (iv)]
Zirconium-based compound (iv-1): Orgatics ZC-150 (manufactured by Matsumoto Fine Chemical Co., Ltd.) diluted with acetylacetone to a solids concentration of 1% [antioxidant (v)]
Hindered phenolic antioxidant (v-1): "IRGANOX 1010" (manufactured by BASF)

Next, the polyester resins (i-1) to (i-3) obtained above were used to prepare adhesive compositions as described below, and adhesive sheets for the examples and comparative examples were fabricated.

[Example 1]
The polyester resin (i-1) obtained above was diluted with ethyl acetate to a solid content concentration of 50%, and 1.5 parts (solid content) of an isocyanate crosslinking agent (ii-1A), 0.5 parts (solid content) of a carbodiimide compound (iii-1), 0.02 parts (solid content) of a zirconium compound (iv-1), and 0.1 parts of a hindered phenol antioxidant (v-1) were blended with 100 parts of the diluted solid content, followed by stirring and mixing 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 5 μm, and then dried for 1 minute at 100° C. to form a pressure-sensitive adhesive layer. Thereafter, a release-treated PET sheet (release sheet) 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 a pressure-sensitive adhesive sheet.

[Examples 2 to 8, Comparative Examples 1 to 4]
A pressure-sensitive adhesive composition was prepared and a pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the ingredients were blended as shown in Table 2 below.

[Examples 9 and 10, Comparative Example 5]
An adhesive composition was prepared and an adhesive sheet was obtained in the same manner as in Example 1, except that the ingredients were blended as shown in Table 3 below so that the thickness of the adhesive layer after drying was 10 μm.

[Examples 11 and 12, Comparative Examples 6 and 7]
An adhesive composition was prepared and an adhesive sheet was obtained in the same manner as in Example 1, except that the ingredients were blended as shown in Table 4 below so that the thickness of the adhesive layer after drying was 2 μm.

The following evaluations were carried out using the resulting adhesive sheets of the Examples and Comparative Examples. Because adhesive strength varies depending on the thickness of the adhesive layer, evaluation criteria were set according to the thickness of the adhesive layer. The results for Examples 1 to 8 and Comparative Examples 1 to 4, in which the adhesive layer was 5 μm thick, are shown in Table 5 below. The results for Examples 9 and 10 and Comparative Example 5, in which the adhesive layer was 10 μm thick, are shown in Table 6 below. The results for Examples 11 and 12 and Comparative Examples 6 and 7, in which the adhesive layer was 2 μm thick, are shown in Table 7.

<Adhesion strength (peel strength) (against SUS)>
A SUS-BA plate was prepared as the adherend. The pressure-sensitive adhesive sheet obtained above was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, and the release film was then 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 to pressurize and adhere it. 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 speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N) and evaluated according to the following criteria.
The SUS-BA plate refers to a plate obtained by cold rolling SUS304 and then bright annealing (non-oxidation annealing), or by skin-pass rolling to enhance the luster.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 5 μm)
〇...7N/25mm or more.
△: 5N/25mm or more, less than 10N/25mm.
×...Less than 5N/25mm.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 10 μm)
〇...12N/25mm or more.
×...Less than 12N/25mm.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 2 μm)
〇...5N/25mm or more.
×...Less than 5N/25mm.

<Adhesion strength (peel strength) (against PI)>
A polyimide (PI) adherend (100 μm thick film, manufactured by Toray DuPont Co., Ltd.) was attached to a SUS-BA plate with double-sided tape to prepare a PI adherend. The pressure-sensitive adhesive sheet obtained above was cut to a 25 mm x 200 mm size under an environment of 23°C and 50% RH, after which the release film was peeled off. The adhesive layer side was placed against the PI adherend, and the PI adherend was pressed and adhered by reciprocating pressure with a 2 kg roller. After leaving the sheet to stand for 30 minutes under the same atmosphere, the 180° peel strength (N/25 mm) was measured at a peel speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N) and evaluated according to the following criteria.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 5 μm)
〇...13N/25mm or more.
△: 10N/25mm or more, less than 13N/25mm.
×...Less than 10N/25mm.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 10 μm)
〇...15N/25mm or more.
×...Less than 15N/25mm.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 2 μm)
〇...5N/25mm or more.
×...Less than 5N/25mm.

<Adhesive strength (peel strength) (against PP)>
A polypropylene (PP) plate (manufactured by Nippon Test Panel Co., Ltd., PP 2.0 x 70 x 150 mm) was prepared as the adherend. The pressure-sensitive adhesive sheet obtained above was cut to 25 mm x 200 mm in an environment of 23 °C and 50% RH, after which the release film was peeled off, and the pressure-sensitive adhesive layer side was placed against a polypropylene (PP) plate and pressure-applied by reciprocating a 2 kg roller. 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 speed of 300 mm/min using an autograph (manufactured by Shimadzu Corporation, Autograph AGS-H 500N) and evaluated according to the following criteria.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 5 μm)
〇...5N/25mm or more.
△: 1N/25mm or more, less than 5N/25mm.
×...Less than 1N/25mm.
(Evaluation criteria for a pressure-sensitive adhesive layer thickness of 10 μm)
〇...5N/25mm or more.
×...Less than 5N/25mm.

<Adhesive strength over time (peel strength after 24 hours)>
A SUS304-BA plate was prepared as the adherend. The pressure-sensitive adhesive sheet obtained above was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, after which the release film was peeled off and the pressure-sensitive adhesive layer side was placed against the SUS-BA plate, and a 2 kg roller was applied back and forth to pressurize and adhere the sheet. After leaving the sheet to stand for 24 hours in the same atmosphere, the 180° peel strength (N/25 mm) was measured at a peel speed of 300 mm/min using an autograph (Shimadzu Corporation, Autograph AGS-H 500N).
Examples 11 and 12 and Comparative Examples 6 and 7 were evaluated according to the following criteria.
(Evaluation criteria)
〇...5N/25mm or more.
×...Less than 5N/25mm.

<Initial rate>
The ratio of A/B was calculated, where the value of "adhesive strength (peel strength) (to SUS)" measured above is A and the value of "adhesive strength over time (peel strength after 24 hours)" is B. A higher initial ratio indicates that adhesive strength is developed from the beginning, and that performance is being exerted more effectively.
(Evaluation criteria)
〇...Over 70%.
×...Less than 70%.

<Holding force (cohesive force)>
The pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 obtained above were attached to SUS304 as an adherend in accordance with JIS Z-0237, with an attachment area of 25 mm x 25 mm, and then left to stand at 80°C for 20 minutes. A load of 1 kg was then applied to each of the sheets, and the time until the sheets fell off, or for sheets that did not fall off after being left to stand for 24 hours, the condition after 24 hours was visually observed and evaluated according to the following criteria.
(Evaluation criteria)
◯: No falling even after being left standing for 24 hours.
×: Falling occurred during 24 hours of standing.

The above results demonstrate that the pressure-sensitive adhesive layers (pressure-sensitive adhesive sheets) of Examples 1 to 10, which contain a specific amount or more of a structural moiety derived from an aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms as a structural moiety derived from a polyvalent carboxylic acid (a), have excellent adhesive strength to various adherends even when thin, and exhibit sufficient adhesive strength from the beginning.
On the other hand, the pressure-sensitive adhesive layers (pressure-sensitive adhesive sheets) of Comparative Examples 1 to 5, which do not contain a structural moiety derived from an aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms, had inferior adhesive strength to various adherends compared to the pressure-sensitive adhesive layers of the Examples, and furthermore, had low initial modulus and did not exhibit sufficient adhesive strength from the beginning.
The pressure-sensitive adhesive layers (pressure-sensitive adhesive sheets) of Examples 11 and 12, even though they were very thin at 2 μm, exhibited excellent adhesion to various substrates and exhibited sufficient adhesion from the beginning. On the other hand, the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) of Comparative Example 6, which did not contain a structural moiety derived from an aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms, had a lower initial modulus than the pressure-sensitive adhesive layers of the Examples, and did not exhibit sufficient adhesion from the beginning. However, by using a polyester-based pressure-sensitive adhesive layer, it was confirmed that the adhesive strength over time was excellent compared to Comparative Example 7, which used an acrylic-based pressure-sensitive adhesive layer. The Z/Y value using this adhesive strength over time was sufficiently high compared to acrylic resins.
Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

The pressure-sensitive adhesive of the present invention has excellent effects even when used in thin films, and can be used in single-sided or double-sided pressure-sensitive adhesive sheets for polyimides, single-sided or double-sided pressure-sensitive adhesive sheets used for bonding optical components, single-sided or double-sided pressure-sensitive adhesive sheets for fixing components in portable electronic devices, and single-sided or double-sided pressure-sensitive adhesive sheets for fixing electronic components.

Claims (12)

A pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing a polyester resin (i) having a structural moiety derived from a polyvalent carboxylic acid (a) and a structural moiety derived from a polyol component (b) and a crosslinking agent (ii) ,
The thickness of the pressure-sensitive adhesive layer is 18 μm or less,
the content of the polyester resin (i) is 80% by weight or more of the pressure-sensitive adhesive composition,
Among the structural moieties derived from the polycarboxylic acids (a), 60 mol % or more of structural moieties derived from aliphatic dicarboxylic acids (a1) having 8 or less carbon atoms are contained ,
The structural moiety derived from the polyvalent carboxylic acid (a) further contains a structural moiety derived from an aromatic dicarboxylic acid,
The pressure-sensitive adhesive layer, wherein the crosslinking agent (ii) is an isocyanate-based crosslinking agent (ii-1) . The pressure-sensitive adhesive layer according to claim 1, characterized in that the structural moiety derived from the polyol component (b) contains a structural moiety derived from at least one member selected from the group consisting of ethylene glycol, 2-methyl-1,3-propanediol, and neopentyl glycol. The pressure-sensitive adhesive layer according to claim 1 or 2, characterized in that the structural moiety derived from the aliphatic dicarboxylic acid (a1) having 8 or less carbon atoms is a structural moiety derived from adipic acid. The pressure-sensitive adhesive layer according to any one of claims 1 to 3, characterized in that the ester bond concentration of the polyester resin (i) is 9.0 to 12.5 mmol/g. The pressure-sensitive adhesive layer according to any one of claims 1 to 4, characterized in that the glass transition temperature of the polyester resin (i) is -50 to -10°C. The pressure-sensitive adhesive layer according to any one of claims 1 to 5, characterized in that the polyester resin (i) having a structural moiety derived from the polycarboxylic acid (a) and a structural moiety derived from the polyol component (b) is crosslinked with a crosslinking agent (ii). A pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer according to any one of claims 1 to 6 and a substrate, wherein the substrate is laminated on one side of the pressure-sensitive adhesive layer, and the other side is a release-treated sheet. 8. The pressure-sensitive adhesive sheet according to claim 7 , wherein the substrate is a polyester resin sheet. A pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer according to any one of claims 1 to 6 and a release-treated sheet, characterized in that the release-treated sheet is laminated on both sides of the pressure-sensitive adhesive layer. 9. The pressure-sensitive adhesive sheet according to claim 7 , wherein the adherend is a polyimide. The pressure-sensitive adhesive sheet according to claim 7 or 8 , which is used to fix electronic components. The pressure-sensitive adhesive sheet according to any one of claims 7 to 11 , wherein X/Y≧0.5 is satisfied, where X is the adhesive strength (N/25 mm) measured under the following measurement conditions, and Y is the thickness (μm) of the pressure-sensitive adhesive layer.
[Measurement conditions for adhesive strength X (N/25 mm)]
The adhesive sheet was cut to 25 mm x 200 mm in an environment of 23°C and 50% RH, the release film was peeled off, and the adhesive layer side was placed against a SUS-BA plate as an adherend, and a 2 kg roller was used to press and adhere it. After leaving it 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 adhesive strength was defined as Adhesive Strength X.