Adhesive composition and laminate comprising the same

Abstract

The present invention provides a pressure-sensitive adhesive composition that easily achieves both appropriate cohesive force and stress relaxation properties even at a high solid content concentration, and a laminate including the same.SOLUTION: The pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic polymer, and the structure of the crosslinked part after crosslinking in the (meth) acrylic polymer has a permanent dynamic covalent bond. The laminate of the present invention is a laminate comprising a first member, a second member, and a pressure-sensitive adhesive layer for bonding these members, wherein the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a laminate comprising the same. In particular, the present invention relates to a pressure-sensitive adhesive composition containing a (meth)acrylic polymer having a para-bonding dynamic covalent bond and a laminate comprising the same. [Background technology]

[0002] When a pressure-sensitive adhesive layer is formed using a pressure-sensitive adhesive composition containing a (meth)acrylic polymer, the solid content concentration of the pressure-sensitive adhesive composition is adjusted using an organic solvent from the viewpoint of coatability.

[0003] For example, a pressure-sensitive adhesive composition used in a polarizing plate in a liquid crystal panel may suffer from problems such as peeling, cracking, etc., due to stress caused by thermal shrinkage of the polarizing plate at high temperatures. To prevent such problems, a pressure-sensitive adhesive composition for a polarizing plate is required to have an appropriate cohesive strength and stress relaxation property.

[0004] However, if a polymer with a molecular weight of several hundred thousand is used to obtain a cohesive strength suitable for use as a pressure-sensitive adhesive, it is necessary to increase the crosslink density, which inevitably leads to problems such as inability to relax stress and peeling.

[0005] Therefore, in adhesive compositions for polarizing plates, a small amount of crosslinking agent is generally added to an ultra-high molecular weight (meth)acrylic polymer with a molecular weight of 1 million or more, so that when made into an adhesive sheet, it achieves both appropriate cohesive strength and stress relaxation properties.

[0006] Patent Document 1 discloses such a pressure-sensitive adhesive composition for polarizing plates.

[0007] In recent years, research has been conducted into bonds called dynamic covalent bonds, in which covalent bonds exhibit dissociation and recombination behavior in response to external stimuli such as heat or light. Patent Documents 2 and 3 disclose pressure-sensitive adhesives containing polymers with such dynamic covalent bonds. These dynamic covalent bonds are called dissociative dynamic covalent bonds, in that the bonds dissociate in response to external stimuli but recombine when the external stimuli are removed.

[0008] Furthermore, among dynamic covalent bonds, novel crosslinking structures have been reported called parabolic dynamic covalent bonds or bond-exchange dynamic covalent bonds, in which bonds do not completely dissociate in the intermediate reaction state under external stimuli, but rather new bond formation and dissociation occur simultaneously. For example, Patent Document 4 discloses an adhesive composition using a polyester resin having parabolic dynamic covalent bonds. Also, Non-Patent Document 1 discloses a (meth)acrylic polymer having parabolic dynamic covalent bonds. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5583001 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-241137 [Patent Document 3] Japanese Patent Application Publication No. 2022-169989 [Patent Document 4] International Publication No. 2023 / 063386 [Non-patent literature]

[0010] [Non-Patent Document 1] Lessard.JJet al. “Catalyst-Free Vitrimers from Vinyl Polymers”,Macromolecules,2019,52,2105-2111 Summary of the Invention [Problem to be solved by the invention]

[0011] When an ultra-high molecular weight (meth)acrylic polymer such as that described in Patent Document 1 is used, the viscosity increases, and therefore it is necessary to reduce the solid content concentration when coating the polymer on a polarizing plate, etc. Furthermore, since the polymer has low solubility in solvents, it is necessary to reduce the solid content concentration, which requires a large amount of solvent, resulting in problems such as reduced productivity, increased transportation costs, and environmental harm caused by the use of a large amount of solvent.

[0012] Therefore, an object of the present invention is to provide a pressure-sensitive adhesive composition that can easily achieve both appropriate cohesive strength and stress relaxation properties when made into a pressure-sensitive adhesive sheet even when the solid content is high, and a laminate containing the same. [Means for solving the problem]

[0013] The present inventors have found that the above problems can be solved by the present invention having the following aspects. <<Aspect 1>> A pressure-sensitive adhesive composition comprising a (meth)acrylic polymer, wherein the structure of a crosslinked portion of the (meth)acrylic polymer after crosslinking has a normal dynamic covalent bond. <<Aspect 2>> The pressure-sensitive adhesive composition according to aspect 1, wherein, in a measurement of holding power at 80°C of a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition, the amount of displacement 200 hours after the start of measurement is more than 0 μm and not more than 1000 μm, and the amount of displacement 50 hours after the start of measurement is less than 90% of the amount of displacement 200 hours. Aspect 3 2. The pressure-sensitive adhesive composition according to aspect 1, wherein the (meth)acrylic polymer has a molecular weight of 1,000,000 or less. Aspect 4 2. The pressure-sensitive adhesive composition according to aspect 1, wherein the (meth)acrylic polymer contains 60 to 99.9 mass % of a (meth)acrylic acid alkyl ester in which the alkyl group has 4 to 18 carbon atoms. Aspect 5 The pressure-sensitive adhesive composition according to aspect 1, wherein the normal dynamic covalent bond is any one of a vinylogous urethane bond, a vinylogous urea bond, and a vinylogous amide bond. Aspect 6 A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of aspects 1 to 5. Aspect 7 A laminate comprising a first member, a second member, and a pressure-sensitive adhesive layer bonding them together, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive composition according to any one of aspects 1 to 5. Aspect 8 8. The laminate of embodiment 7, wherein the first member and the second member are optical members. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of a laminate. [Figure 2] FIG. 2 is a cross-sectional view schematically showing another example of the laminate. DETAILED DESCRIPTION OF THE INVENTION

[0015] <<Adhesive Composition>> The pressure-sensitive adhesive composition contains a (meth)acrylic polymer, and the structure of the crosslinked portion of the (meth)acrylic polymer after crosslinking has a normal dynamic covalent bond. In this specification, (meth)acrylic means methacrylic or acrylic, (meth)acrylate means methacrylate or acrylate, and (meth)acryloyl means methacryloyl or acryloyl.

[0016] The present inventors have discovered that a (meth)acrylic polymer having a para-bond dynamic covalent bond at the crosslinking portion can achieve both adequate cohesive strength and stress relaxation properties even at a relatively low molecular weight. Because such a relatively low-molecular-weight (meth)acrylic polymer has low viscosity even when dissolved in a small amount of solvent, a pressure-sensitive adhesive composition containing this polymer can be applied at a higher solids concentration than conventional pressure-sensitive adhesive compositions. This has enabled the provision of a pressure-sensitive adhesive composition that can improve handling while reducing production costs and / or is environmentally friendly.

[0017] The reason why a (meth)acrylic polymer having a normal dynamic covalent bond at the crosslinking moiety can achieve both adequate cohesive strength and stress relaxation despite its relatively low molecular weight is that when a pressure-sensitive adhesive layer containing this (meth)acrylic polymer is subjected to stress, the crosslinking moiety is exchanged with an adjacent crosslinking moiety through an exchange reaction without breaking the bond, allowing the pressure-sensitive adhesive layer to continue to shift position slightly over time. This is thought to prevent stress from concentrating on a part of the pressure-sensitive adhesive layer and becoming a starting point for peeling, and to relieve the stress. This is thought to have enabled the achievement of both adequate cohesive strength and stress relaxation, which are particularly required for optical laminates.

[0018] This PSA composition preferably shifts slightly when subjected to stress. For example, when measuring the holding power of a PSA sheet formed from this PSA composition at 80°C, the amount of shift 200 hours after the start of measurement may be more than 0 μm, 1 μm or more, 10 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, or 250 μm or more, or may be 3000 μm or less, 1000 μm or less, 500 μm or less, or 250 μm or less. In this specification, the holding power is measured by the method described in the Examples below.

[0019] In measuring the holding power of the pressure-sensitive adhesive sheet at 80°C, the amount of deviation 100 hours after the start of measurement may be more than 0 μm, 1 μm or more, 10 μm or more, 50 μm or more, 100 μm or more, or 150 μm or more, or may be 1000 μm or less, 500 μm or less, 300 μm or less, or 150 μm or less.

[0020] When measuring the holding power of the pressure-sensitive adhesive sheet at 80°C, the amount of deviation 50 hours after the start of measurement may be more than 0 μm, 1 μm or more, 10 μm or more, 50 μm or more, 80 μm or more, or 100 μm or more, or may be 1000 μm or less, 500 μm or less, 200 μm or less, or 100 μm or less.

[0021] When measuring the holding power of the pressure-sensitive adhesive sheet at 80°C, the amount of displacement 50 hours after the start of measurement may be less than 90%, 80% or less, 60% or less, or 50% or less of the amount of displacement 200 hours after the start of measurement, or may be 10% or more, 30% or more, or 50% or more.

[0022] (Meth)acrylic polymer The (meth)acrylic polymer has a weight-average molecular weight (Mw) of, for example, 100,000 or more. The weight-average molecular weight may be 150,000 or more, 200,000 or more, or 300,000 or more, or 1,000,000 or less, 800,000 or less, 500,000 or less, or 400,000 or less. In particular, a molecular weight of 800,000 or less is preferred, and 500,000 or less is more preferred. Even within this range, a pressure-sensitive adhesive composition containing this (meth)acrylic polymer can impart sufficient cohesive strength. Furthermore, by having a molecular weight within this range, the pressure-sensitive adhesive composition containing this (meth)acrylic polymer can be coated at a high solids concentration.

[0023] The polydispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (meth)acrylic polymer, can be 15.0 or less, 10.0 or less, 8.0 or less, 6.0 or less, or 5.0 or less, and may be 1.5 or more, 2.0 or more, 3.0 or more, or 4.0 or more. For example, the polydispersity of the (meth)acrylic polymer may be 1.5 or more and 15.0 or less, or 2.0 or more and 8.0 or less.

[0024] The weight average molecular weight and number average molecular weight can be determined by GPC (gel permeation chromatography) under the conditions described in the Examples, using standard polystyrene equivalents.

[0025] (Meth)acrylic polymer-monomer The monomer composition for obtaining a (meth)acrylic polymer is not particularly limited as long as it can provide a (meth)acrylic polymer having a normal dynamic covalent bond at a crosslinking moiety. Such a monomer composition can contain a (meth)acrylic monomer that is normally used for obtaining a (meth)acrylic pressure-sensitive adhesive composition and a crosslinking monomer capable of forming a crosslinking moiety, and the crosslinking monomer can form a normal dynamic covalent bond at the crosslinking moiety.

[0026] (Meth)acrylic polymer-crosslinkable monomer The crosslinkable monomer that can be contained in the monomer composition is not particularly limited as long as it has a crosslinking moiety that has a normal dynamic covalent bond after being polymerized into a polymer. The crosslinkable monomer can be a side-chain crosslinkable monomer that can form a crosslinking moiety at the side chain. The crosslinking moiety can be formed from the monomer by polymerization or can be formed by a separate crosslinking agent.

[0027] The chemical bond constituting the normal dynamic covalent bond is not particularly limited, but examples thereof include an ester bond, a urethane bond, an imine bond, a vinylogous urethane bond, a vinylogous urea bond, and a vinylogous amide bond. Therefore, a monomer that brings about these chemical bonds in the polymer can be used as the crosslinkable monomer. Among these, the vinylogous urethane bond, the vinylogous urea bond, and the vinylogous amide bond are particularly preferred because they can be exchanged in the polymer without a catalyst for the exchange reaction.

[0028] The vinylogous urethane bond, vinylogous urea bond, and vinylogous amide bond are -X-CO-CH2-CO-R 1 The compound can be obtained by reacting a compound represented by the formula: with a primary amine. When X in the compound is O, it becomes a vinylogous urethane bond, when it is N, it becomes a vinylogous urea bond, and when it is CH2, it becomes a vinylogous amide bond. 1 represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 3 or less carbon atoms.

[0029] Compounds that can form vinylogous urethane bonds have the -O-CO-CH2-CO-R group in the side chain. 1 The vinyl-based monomer may be a vinyl monomer having a group, such as 2-(methacryloyloxy)ethyl acetoacetate (AAEM). The compound capable of forming a vinyl-based bond has a -N-CO-CH2-CO-R group in the side chain. 1 The compound capable of forming a vinyl amide bond can be a vinyl monomer having a -CH2-CO-CH2-CO-R group in the side chain. 1 The monomer may be a vinyl monomer having a group.

[0030] The primary amine may be a compound containing two or more, particularly three or more, primary amino groups, such as ethylenediamine, propylenediamine, 1,4-diaminobutane, 1,5-diaminopentane, hexamethylenediamine, 1,8-diaminooctane, bis(2-aminoethyl)amine, tris(2-aminoethyl)amine, tris(3-aminopropyl)amine, bis(hexamethylene)triamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N,N'-bis(2-aminoethyl)-1,3-propanediamine, N,N'-bis(3-aminopropyl)ethylenediamine, 1,2-bis(2-aminoethoxy)ethane, 1,4-butanediol bis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether, etc. Among these, tris(2-aminoethyl)amine may be particularly used.

[0031] The molar ratio of the reactive group of the compound to the amino group of the primary amine for forming a vinylogous urethane bond, vinylogous urea bond, or vinylogous amide bond may be, for example, 1:0.1 or more, 1:0.3 or more, 1:0.5 or more, 1:0.75 or more, 1:1 or more, 1:1.5 or more, or 1:2 or more, or 1:10 or less, 1:5 or less, 1:3 or less, 1:2 or less, 1:1 or less, 1:0.5 or less, or 1:0.3 or less. For example, this molar ratio can be in the range of 1:0.3 to 1:3, or 1:0.5 to 1:2.

[0032] To provide a para-bond dynamic covalent bond in the polymer that undergoes transesterification, polymer side chains, crosslinkers, and transesterification catalysts such as those described in US Pat. No. 5,649,297 can be used.

[0033] The crosslinkable monomer may be contained in a total amount of 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.8% by mass or more, or 1.0% by mass or more in the monomer composition for obtaining the (meth)acrylic polymer by polymerization, and may be contained in an amount of 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, 1.5% by mass or less, or 1.0% by mass or less.

[0034] (Meth)acrylic polymer-(meth)acrylic monomer Examples of (meth)acrylic monomers that can be contained in the monomer composition include, but are not limited to, (meth)acrylic acid alkyl esters, alkoxyalkyl (meth)acrylates, etc. For example, in addition to these monomers, other monomers such as (meth)acrylic hydroxyl group-containing monomers, (meth)acrylic carboxy group-containing monomers, and (meth)acrylic nitrogen-containing monomers can also be contained.

[0035] For example, the (meth)acrylic monomer is CH2=CR 2 -COO-R 3 The (meth)acrylic acid alkyl ester may be represented by the chemical formula: 2 is a hydrogen atom or a methyl group, and R3 is a linear or branched alkylene group. 3 The number of carbon atoms in R may be 1 or more, 2 or more, 3 or more, or 4 or more, and may be 20 or less, 18 or less, 15 or less, 12 or less, 10 or less, or 8 or less. For example, R 3 The number of carbon atoms can be in the range of 1 to 20, 1 to 10, or 2 to 8.

[0036] For example, examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca(meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, n-stearyl (meth)acrylate, and isostearyl (meth)acrylate.

[0037] For example, the (meth)acrylic acid alkyl ester may be contained in the monomer composition in an amount of 10% by mass or more, 50% by mass or more, 30% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more, or in an amount of 99.9% by mass or less, 99.5% by mass or less, 99% by mass or less, 98% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, 60% by mass or less, or 40% by mass or less.

[0038] An alkoxyalkyl (meth)acrylate is a monomer in which at least one hydrogen atom of the alkyl group of a (meth)acrylic acid alkyl ester is substituted with an alkoxy group or a compound having an alkoxy group. For example, this monomer is CH═CR 4 -COO-R5 where R 4 is a hydrogen atom or a methyl group, and R 5 represents a linear or branched alkyl or aralkyl group having 14 or less carbon atoms, and at least one of the hydrogen atoms constituting the group is a group -O-(C n H 2n O) m -R 6 n represents an integer of 1 to 4; m represents 0 or an integer of 1 to 10; R 6 constitutes a straight or branched chain alkyl group having 14 or less carbon atoms.

[0039] Specific examples of alkoxyalkyl (meth)acrylates include methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, ethyl carbitol acrylate, 2-ethylhexyl-diglycol acrylate, and methoxy-polyethylene glycol acrylate, and among these, 2-methoxyethyl (meth)acrylate is particularly preferred.

[0040] The alkoxyalkyl (meth)acrylate may be contained in the monomer composition in an amount of 10% by mass or more, 50% by mass or more, 30% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more, or may be contained in an amount of less than 99% by mass, 98% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, 60% by mass or less, or 40% by mass or less.

[0041] (Meth)acrylic hydroxyl group-containing monomers are CH2=CR 7 -COO-R 8 hydroxyalkyl (meth)acrylates represented by the formula —OH, where R 7 is a hydrogen atom or a methyl group, and R 8is a straight-chain or branched-chain alkylene group. The number of carbon atoms in R7 can be in the range of 1 to 10, 2 to 5, or 2 to 4.

[0042] Specific examples of (meth)acrylic hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0043] The (meth)acrylic hydroxyl group-containing monomer is contained in the monomer composition in an amount of, for example, 0.1% by mass or more and 10% by mass or less. The hydroxyl group-containing monomer may be contained in the monomer composition in an amount of 0.3% by mass or more, 0.5% by mass or more, 0.8% by mass or more, or 1.0% by mass or more, or 8.0% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, or 1.5% by mass or less.

[0044] Examples of (meth)acrylic carboxy group-containing monomers include β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, succinic acid mono(meth)acryloyloxyethyl ester, ω-carboxypolycaprolactone mono(meth)acrylate, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid, and the content of structural units derived from the carboxy group-containing monomer is preferably 0 to 6 mass% based on the entire (meth)acrylic polymer.

[0045] Examples of the (meth)acrylic nitrogen-containing monomer include amide monomers such as acrylamide, N-isopropylacrylamide, dimethylacrylamide, diethylacrylamide, and diacetoneacrylamide, and amine monomers such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, and the amine monomers are preferably used, preferably in an amount of 0 to 6% by mass.

[0046] <(Meth)acrylic polymers - others> The monomer composition may further contain other monomers, such as (meth)acrylic acid esters having an aromatic ring group, such as benzyl (meth)acrylate, 2-naphthyl acrylate, and phenoxyethyl acrylate, styrene-based monomers, such as styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene, vinyl carboxylic acid esters, such as vinyl acetate, and (meth)acryloyl group-containing macromonomers.

[0047] The monomer composition may be substantially free of the monomers listed above as optional components. As used herein, "substantially free" means that the component may be contained within a range that does not impair the advantageous effects of the present invention. For example, "substantially free" of a component in a composition may mean that the component is contained in an amount of less than 0.50% by mass, less than 0.30% by mass, less than 0.20% by mass, less than 0.10% by mass, or less than 0.05% by mass.

[0048] (Meth)acrylic polymer-polymerization initiator The monomer composition for forming the (meth)acrylic polymer may further contain a polymerization initiator, which may be an organic peroxide, an azo compound, or the like that can be used in normal radical polymerization.

[0049] The polymerization initiator can be used in an amount of 0.01 parts by mass or more and 2.0 parts by mass or less, or 0.1 parts by mass or more and 1.0 part by mass or less, relative to 100 parts by mass of the total monomer components.

[0050] (Meth)acrylic polymer-solvent The monomer composition may contain a solvent depending on the polymerization method. For example, when a copolymer is obtained by solution polymerization, an organic solvent capable of dissolving the monomer components can be used. For example, it is preferable to use an organic solvent that is particularly resistant to chain transfer during the polymerization reaction, such as an ester or a ketone. In particular, ethyl acetate, methyl ethyl ketone, acetone, etc. can be used in terms of the solubility of the monomer components and the ease of the polymerization reaction.

[0051] The PSA composition may be substantially free of a catalyst for converting the crosslinking points into normal dynamic covalent bonds at 100°C or below or 80°C or below. "Substantially containing" here means that the catalyst is contained in an amount sufficient to achieve the advantageous effects of the present invention by converting the crosslinking points into normal dynamic covalent bonds. For example, the molar ratio of such a catalyst to the theoretical amount of normal dynamic covalent bonds may be 1.0 or less, 0.5 or less, 0.1 or less, 0.05 or less, 0.01 or less, 0.005 or less, or 0.001 or less. Examples of such catalysts include acid catalysts and base catalysts, and specific examples include, but are not limited to, zinc acetate and its hydrate, zinc acetylacetonate and its hydrate, tetraisopropyl titanate, antimony trioxide, dibutyltin dioctylate, dibutyltin dilaurate, monobutyltin oxide, dibutyltin oxide, potassium tert-butoxide, bismuth triflate, triazabicyclodecene, diazabicycloundecene, and triethylamine.

[0052] (Meth)acrylic polymer - other components The monomer composition may contain other components as long as the advantageous effects of the present invention are not impaired. For example, the monomer component may contain an emulsifier, a dispersant, a dispersion medium, etc. depending on the polymerization method.

[0053] (Meth)acrylic polymer - polymerization method The polymerization method for the (meth)acrylic polymer is not particularly limited, and the (meth)acrylic polymer can be polymerized by known methods such as solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization, etc. When producing a pressure-sensitive adhesive composition using the copolymer, it is preferable to obtain the copolymer by solution polymerization, from the viewpoint that the treatment process is relatively simple and can be carried out in a short time.

[0054] <Crosslinking agent> The pressure-sensitive adhesive composition may contain a crosslinking agent that does not form a normal dynamic covalent bond, as long as the advantageous effects of the present invention are achieved. By incorporating such a crosslinking agent, the gel fraction, cohesive strength, and stress relaxation rate of the pressure-sensitive adhesive composition can be adjusted to appropriate ranges. As the crosslinking agent, an isocyanate-based crosslinking agent known in the art can be used, such as a crosslinking agent having two or more isocyanate groups or isocyanurate groups and a hydrocarbon group having 1 to 20 carbon atoms, optionally containing an oxygen atom.

[0055] Furthermore, an epoxy-based crosslinking agent can be used as the crosslinking agent. As the epoxy-based crosslinking agent, an epoxy compound having two or more epoxy groups in one molecule can be used, and specifically, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, mN,N-diglycidylaminophenyl glycidyl ether, N,N-diglycidyl toluidine, and N,N-diglycidylaniline can be used.

[0056] Furthermore, a metal chelate crosslinking agent can be used as the crosslinking agent, such as a compound in which an alkoxide, acetylacetone, ethyl acetoacetate, or the like is coordinated with a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium.Specific examples of the metal chelate crosslinking agent include aluminum isopropylate, aluminum secondary butylate, aluminum ethyl acetoacetate diisopropylate, aluminum trisethyl acetoacetate, and aluminum trisacetylacetonate.

[0057] The crosslinking agent that does not form a normal dynamic covalent bond may not be contained in the pressure-sensitive adhesive composition. For example, the crosslinking agent may be present in an amount of 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, or 1.0 parts by mass or less, 0.5 parts by mass or less, 0.3 parts by mass or less, 0.2 parts by mass or less, 0.1 parts by mass or less, or 0.05 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic polymer.

[0058] The gel fraction of the PSA composition after the crosslinking agent crosslinks the copolymer may be 50% or more, 60% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more, or 100% or less, 98% or less, 95% or less, 90% or less, 85% or less, or 80% or less. The gel fraction is a value determined by immersing a sample in ethyl acetate, filtering out the ethyl acetate-insoluble matter, and measuring the weight percentage of this insoluble matter relative to the total weight of the sample.

[0059] In addition to the above components, the pressure-sensitive adhesive composition may contain components selected from a silane coupling agent, an antistatic agent, an ultraviolet absorber, an antioxidant, a tackifying resin, a plasticizer, an antifoaming agent, a filler, a stabilizer, a softener, and a wettability adjuster, as long as the effects of the present invention are not impaired.

[0060] <Silane coupling agent> The PSA composition may contain a silane coupling agent. A PSA composition containing a silane coupling agent can maintain good adhesion between the adherend and the PSA layer.

[0061] The silane coupling agent may be any silane coupling agent known in the art, such as vinyltrimethoxysilane or other polymerizable unsaturated group-containing silicon compounds; 3-glycidoxypropyltrimethoxysilane or other epoxy structure-containing silicon compounds; 3-aminopropyltrimethoxysilane or other amino group-containing silicon compounds; 3-chloropropyltrimethoxysilane; and oligomeric silane coupling agents. Among these, silane coupling agents having a functional group that reacts with the functional group contained in the (meth)acrylic polymer or its monomer component are particularly preferred because they are less likely to peel under high humidity and heat conditions.

[0062] The silane coupling agent may be contained in the pressure-sensitive adhesive composition in an amount of 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer, or in an amount of 1.0 part by mass or less, 0.5 parts by mass or less, 0.3 parts by mass or less, or 0.2 parts by mass or less.

[0063] <Antistatic Agent> The PSA composition may contain an antistatic agent made of an ionic compound. Examples of the antistatic agent include ionic compounds that contain an anion and a cation and are liquid or solid at 25°C.

[0064] The antistatic agent may be contained in the pressure-sensitive adhesive composition in an amount of 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, or 2.0 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer, or 10 parts by mass or less, 5.0 parts by mass or less, 3.0 parts by mass or less, or 2.0 parts by mass or less.

[0065] <solvent> The pressure-sensitive adhesive composition may contain a solvent to adjust the coating properties. The type of solvent may be the same as the above-mentioned polymerization solvent for polymerizing the (meth)acrylic polymer.

[0066] The PSA composition contains a solvent, which allows the solids concentration to be adjusted. The solids concentration of the PSA composition may be 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, or 60% by mass or less, 55% by mass or less, 50% by mass or less, or 45% by mass or less. For example, the solids concentration of the PSA composition may be 20% by mass or more and 55% by mass or less, or 30% by mass or more and 50% by mass or less.

[0067] Adhesive sheet The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet may include the pressure-sensitive adhesive layer and a substrate layer. The substrate layer is not particularly limited and may be a release substrate.

[0068] The pressure-sensitive adhesive layer can be obtained, for example, by drying and / or crosslinking the pressure-sensitive adhesive composition. The pressure-sensitive adhesive layer may contain the pressure-sensitive adhesive composition in an amount of 50% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more, or 100% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less.

[0069] <<Laminate>> The laminate includes a first member, a second member, and a pressure-sensitive adhesive layer that bonds them together, and the pressure-sensitive adhesive layer may be formed from the pressure-sensitive adhesive composition described above and may be one used in the pressure-sensitive adhesive sheet described above.

[0070] The pressure-sensitive adhesive layer can be formed by applying a pressure-sensitive adhesive composition to the first and / or second member as the adherend, or to the surface of a release film (separator), drying the composition at, for example, 50°C to 150°C depending on the type of solvent, and then attaching a release film to the side of the pressure-sensitive adhesive layer that is not in contact with other layers. After forming the pressure-sensitive adhesive layer, the pressure-sensitive adhesive composition can be cured, for example, for 3 to 10 days in an environment of 23°C to 50°C, to adjust the gel fraction of the pressure-sensitive adhesive composition to the above-mentioned range.

[0071] Examples of methods for applying the pressure-sensitive adhesive composition include known methods such as spin coating, knife coating, roll coating, bar coating, blade coating, die coating, and gravure coating, and in particular blade coating.

[0072] The thickness of the pressure-sensitive adhesive layer may be 5 μm or more, 7 μm or more, 10 μm or more, or 15 μm or more, or 50 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less. For example, the thickness of the pressure-sensitive adhesive layer may be 5 μm or more and 50 μm or less, or 10 μm or more and 30 μm or less.

[0073] The first and second members to be adhered are not particularly limited, but examples thereof include optical members, such as glass substrates, polarizing plates, and optical films such as retardation films.

[0074] FIG. 1 is a cross-sectional view schematically showing an example of a laminate.

[0075] 1, laminate 100 includes a glass substrate 10 as a first member, a polarizing film 30 as a second member, and an adhesive layer 20 that bonds them together. Polarizing film 30 has a polycycloolefin-based film or triacetyl cellulose film 32, a polyvinyl alcohol film 34 on 32, and a polycycloolefin-based film or triacetyl cellulose film 36 on 34. Glass substrate 10 and polycycloolefin-based film or triacetyl cellulose film 32 are bonded together by adhesive layer 20.

[0076] FIG. 2 is a cross-sectional view schematically showing another example of the laminate.

[0077] As shown in FIG. 2 , the laminate 200 includes a glass substrate 10 as a first member, a polycycloolefin film (retardation film) 32 as a second member, and a polarizing film 130 as a third member, with adhesive layers 20 and 22 bonding these together. More specifically, the polycycloolefin film 32 and the polarizing film 130 are bonded together by the adhesive layer 20. The glass substrate 10 and the polycycloolefin film 32 are bonded together by the adhesive layer 22. The polarizing film 130 includes a layer 38 that is a polycycloolefin film (second polycycloolefin film) or a triacetyl cellulose film, a polyvinyl alcohol film 34 on the layer 38, and a polycycloolefin film or a triacetyl cellulose film 36 on the polyvinyl alcohol film 34. The polycycloolefin film (first polycycloolefin film) 32 and the layer (second polycycloolefin film) 38 are bonded together by the adhesive layer 20.

[0078] 1 and 2, the pressure-sensitive adhesive layers 20 and 22 are formed on the surface of an adherend. Examples of methods for forming the pressure-sensitive adhesive composition on the surface of an adherend include a transfer method in which the pressure-sensitive adhesive composition is applied to the surface of a release film (separator) with good smoothness, the coating is dried, and then the coating is transferred to the surface of a specific resin film.

[0079] The laminate can be used, for example, in an image display device, particularly a liquid crystal display device. More specifically, the laminate can be used, for example, in an image display device for a touch panel. In this case, the glass substrate included in the laminate may be a glass substrate for a liquid crystal display device.

[0080] The image display device may be, for example, a TFT (thin film transistor) liquid crystal display device used in liquid crystal televisions, computer monitors, mobile phones, tablets, and the like.

[0081] The present invention will be explained in more detail in the following examples, but the present invention is not limited thereto. [Example]

[0082] <Production example> Example 1 A flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser was charged with 99 parts by mass of n-butyl acrylate (BA), 1 part by mass of 2-(methacryloyloxy)ethyl acetoacetate (AAEM), 0.06 parts by mass of n-dodecyl mercaptan (NDM), and 60 parts by mass of ethyl acetate. The contents were then heated to 70°C while nitrogen gas was introduced into the flask. Next, 0.005 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to the flask, which had been thoroughly purged with nitrogen gas, while stirring. The contents were heated and cooled for 2 hours and 30 minutes to maintain the temperature at 70°C. The temperature was then raised, and the mixture was refluxed for 2 hours. After the reaction was completed, the mixture was diluted with ethyl acetate to obtain a pressure-sensitive adhesive composition with a solids concentration of 45%. The adhesive composition of Example 1 was obtained by blending 0.35 parts by mass of tris(2-aminoethyl)amine (TREN) with 100 parts by mass of the solid content of the obtained adhesive composition.

[0083] Example 2 A pressure-sensitive adhesive composition of Example 2 was obtained in the same manner as in Example 1, except that the amounts of AAEM and TREN used were changed as shown in Table 1.

[0084] Comparative Example 1 A PSA composition of Comparative Example 1 was obtained in the same manner as in Example 1, except that furfuryl methacrylate and 4,4'-bismaleimidodiphenylmethane were used in place of AAEM and TREN in the amounts shown in Table 1. The copolymer obtained in Comparative Example 1 can be reversibly crosslinked by the Diels-Alder reaction of bismaleimide. That is, the copolymer obtained in Comparative Example 1 does not have a normal dynamic covalent bond, but has a dissociative dynamic covalent bond.

[0085] Comparative Example 2 The PSA composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that 4-hydroxybutyl acrylate (4HBA) was used instead of AAEM and TREN, and that the isocyanate-based crosslinking agent was used in the amount shown in Table 1. In the copolymer obtained in Comparative Example 2, the hydroxyl groups of 4HBA were crosslinked with the isocyanate-based crosslinking agent.

[0086] Test Method <Weight average molecular weight (Mw) and number average molecular weight (Mn)> Mw and Mn were determined in terms of standard polystyrene using GPC (gel permeation chromatography) under the following conditions.

[0087] Measuring device: HLC-8120GPC (Tosoh) GPC column configuration: The following five columns (all manufactured by Tosoh) (1) TSK-GEL HXL-H (guard column) (2) TSK-GEL G7000HXL (3) TSK-GEL GMHXL (4) TSK-GEL GMHXL (5) TSK-GEL G2500HXL Sample concentration: 1.0 mg / cm 3 Dilute with tetrahydrofuran so that Mobile phase solvent: tetrahydrofuran Flow rate: 1.0cm 3 / min Column temperature: 40℃

[0088] <Preparation of Polarizing Plate with Pressure-Sensitive Adhesive Layer> A predetermined amount of each of the pressure-sensitive adhesive compositions obtained above was applied to a release-treated PET film and dried at 90°C for 4 minutes to form a 20µm-thick pressure-sensitive adhesive layer. Thereafter, a 130µm-thick polarizing plate (polarizer protective film (triacetylcellulose) / polarizer / polarizer protective film (triacetylcellulose)) was attached to the side of the pressure-sensitive adhesive layer where the release-treated PET film was not attached, and the resulting sheet was aged for 7 days in an environment of 23°C / 50% RH to prepare pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Examples 1 and 2 and Comparative Examples 1 and 2.

[0089] <Holding force measurement> The resulting polarizing plate with adhesive layer was cut to a width of 15 mm to prepare a test specimen. The release-treated PET film was peeled off from the test specimen, and the exposed adhesive layer was attached to a glass plate with an adhesive area of ​​15 mm x 15 mm. The test specimen was then placed in an autoclave adjusted to 50°C / 5 atm for 20 minutes for pressure bonding. After pressure bonding, the specimen was removed from the autoclave and placed in an oven at 80°C for 20 minutes. After this, the glass plate and adhesive sheet were placed vertically under the same conditions, and a 500g load was applied in the shear direction of the adhesive surface. The displacement of the test specimen was measured 50, 100, and 200 hours after the start of load application.

[0090] <Peeling evaluation> The polarizing plate with the adhesive layer was cut to a size of 75 mm x 130 mm to prepare a test specimen. The release-treated PET film was peeled off from the test specimen, and the exposed adhesive layer was attached to a glass plate. The resulting laminate was then placed in an autoclave adjusted to 50°C / 5 atm for 20 minutes to prepare a test specimen. The specimen was then left in an 80°C dry environment for 500 hours, and peeling was visually observed and evaluated according to the following criteria. ◎: No defects ○: A thin line of haze can be seen △: Areas where the substrate is floating above the polarizing plate can be seen ×: Lifting of the substrate was observed on more than 1 / 3 of the short side of the test piece.

[0091] "result" The results are shown in Table 1 below.

[0092] JPEG2026012055000001.jpg107170

[0093] With the pressure-sensitive adhesive compositions of Examples 1 and 2, the slight amount of slippage after 50 hours increased slightly after 200 hours, indicating that slippage occurred over a long period of time. These pressure-sensitive adhesive compositions were evaluated as having good peel resistance, which is thought to be because they were able to absorb stress by slight slippage when subjected to stress. [Explanation of symbols]

[0094] 10 Glass substrate 20,22 Adhesive layer 30,130 Polarizing film 32 Phase difference film (polycycloolefin film) 34 Polyvinyl alcohol (PVA) film 36 Polycycloolefin film or triacetyl cellulose film 38 Polycycloolefin film or triacetyl cellulose film 100,200 laminate

Claims

1. A pressure-sensitive adhesive composition comprising a (meth)acrylic polymer, wherein a structure of a crosslinked portion of the (meth)acrylic polymer after crosslinking has a normal dynamic covalent bond.

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein, in a measurement of holding power at 80°C of a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition, the amount of displacement 200 hours after the start of measurement is more than 0 μm and 1000 μm or less, and the amount of displacement 50 hours after the start of measurement is less than 90% of the amount of displacement 200 hours.

3. The pressure-sensitive adhesive composition according to claim 1 , wherein the (meth)acrylic polymer has a molecular weight of 1,000,000 or less.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic polymer contains 60 to 99.9 mass % of a (meth)acrylic acid alkyl ester having an alkyl group having 4 to 18 carbon atoms.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the normal dynamic covalent bond is any one of a vinylogous urethane bond, a vinylogous urea bond, and a vinylogous amide bond.

6. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of claims 1 to 5.

7. A laminate comprising a first member, a second member, and a pressure-sensitive adhesive layer that bonds them together, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive composition according to any one of claims 1 to 5.

8. The laminate according to claim 7 , wherein the first member and the second member are optical members.

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