Adhesive composition and adhesive sheet

Abstract

PROBLEM TO BE SOLVED: The present invention provides an adhesive composition and an adhesive sheet that can provide an adhesive layer with high cohesive force and durability even when a large amount of ionic compound is compounded. SOLUTION: The present invention relates to an adhesive composition which contains more than 10 mass parts of an ionic compound (B) and 0.5-10 mass parts of a crosslinking agent (C) per 100 mass parts of a (meth)acrylic polymer (A) that has a weight average molecular weight of 1,000,000 or more. The (meth)acrylic polymer (A) is a polymer of monomer components that contain 50-99.9 mass% of an alkoxyalkyl group-containing monomer and 0.1-10 mass% of a crosslinkable functional group-containing monomer.

Description

Adhesive composition and adhesive sheet

[0001] This invention relates to adhesive compositions and adhesive sheets. In particular, this invention relates to adhesive compositions and adhesive sheets that have both low surface resistivity and high durability.

[0002] Display devices such as liquid crystal displays utilize optical components such as polarizing plates and phase difference plates. These optical components are attached to other materials, such as glass or plastic, via an adhesive layer obtained from an adhesive composition.

[0003] Since display devices are used in a variety of environments, the adhesive layer must also exhibit the desired adhesive properties under various conditions. Among these, the interior of a car or other vehicle is a particularly harsh environment that can be high in temperature and humidity.

[0004] From the perspective of preventing static electricity buildup during peeling of the adhesive sheet from the separator and preventing malfunctions of the touch panel, the adhesive layer used in automotive displays (touch panels) is required to have low resistance. Furthermore, durability is required to prevent peeling or other defects from occurring on substrates such as glass and plastic, even in high-temperature and high-humidity environments.

[0005] One known method for reducing the surface resistivity of an adhesive layer is to incorporate an ionic compound into the adhesive composition that forms the adhesive layer. Patent documents 1 to 3 disclose such adhesive compositions.

[0006] Japanese Patent Publication No. 2019-200423, Japanese Patent Publication No. 2020-125436, International Publication No. 2018 / 181477

[0007] In recent years, the adhesive layers used in automotive displays have been required to have even lower resistance.

[0008] The inventors found that when a large amount of ionic compound is incorporated into the adhesive layer to reduce its resistance, the adhesive layer becomes plasticized and its cohesive force decreases. Furthermore, they found that when an even larger amount of ionic compound is incorporated into the adhesive layer, the ionic compound bleeds to the interface between the adhesive layer and the adherend, worsening its durability.

[0009] Therefore, the present invention provides an adhesive composition and an adhesive sheet that have high cohesive strength and durability in the adhesive layer, even when a large amount of ionic compounds are incorporated.

[0010] The present inventors have found that the above problems can be solved by the present invention having the following embodiments. Embodiment 1: An adhesive composition comprising more than 10 parts by mass of an ionic compound (B) and 0.5 to 10 parts by mass of a crosslinking agent (C) per 100 parts by mass of a (meth)acrylic polymer (A) having a weight-average molecular weight of 1 million or more, wherein the (meth)acrylic polymer (A) is a polymer of monomer components comprising 50 to 99.9% by mass of an alkoxyalkyl group-containing monomer and 0.1 to 10% by mass of a crosslinkable functional group-containing monomer. Embodiment 2: The adhesive composition according to Embodiment 1, wherein the ionic compound (B) is contained in an amount greater than 15 parts by mass and less than or equal to 20 parts by mass per 100 parts by mass of the (meth)acrylic polymer (A). <Aspect 3> The adhesive composition according to Aspect 1, wherein the (meth)acrylic polymer (A) is a polymer of monomer components containing 50 to 98.9% by mass of an alkoxyalkyl group-containing monomer, 0.1 to 10% by mass of a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and 1.0 to 49.8% by mass of an alkyl (meth)acrylate ester. <Aspect 4> The adhesive composition according to Aspect 1, wherein the ionic compound (B) is an alkali metal salt. <Aspect 5> The adhesive composition according to Aspect 1, wherein the ionic compound (B) has an anion that is a bis(fluorosulfonyl)imide anion or a bis(trifluoromethanesulfonyl)imide anion. <Aspect 6> The adhesive composition according to Aspect 1, further comprising 0.1 to 5 parts by mass of a silane coupling agent (D). <Aspect 7> The adhesive composition according to Aspect 6, wherein the silane coupling agent (D) has an acetoacetoxy group. <Aspect 8> Having an adhesive layer formed by the adhesive composition described in any one of aspects 1 to 7, wherein the surface resistivity of the adhesive layer is 1.0 × 10 ７ ~9.9 x 10 ７ An adhesive sheet with the properties Ω / □.

[0011] Figure 1 illustrates the layer configuration of an in-cell liquid crystal panel.

[0012] Adhesive Composition The adhesive composition of the present invention comprises 100 parts by mass of an ionic compound (B) and 0.5 to 10 parts by mass of a crosslinking agent (C) per 100 parts by mass of a (meth)acrylic polymer (A) having a weight-average molecular weight of 1 million or more, wherein the (meth)acrylic polymer (A) is a polymer of monomer components containing 50 to 99.9% by mass of alkoxyalkyl group-containing monomers and 0.1 to 10% by mass of crosslinkable functional group-containing monomers. In this specification, "(meth)acrylic" means methacrylic or acrylic, "(meth)acrylate" means methacrylate or acrylate, and "(meth)acryloyl" means methacryloyl or acryloyl. Furthermore, when "α to β" (α and β are arbitrary numerical values) is written, it means that the entire numerical range from α to β is included.

[0013] The present inventors have found that such an adhesive composition can provide an adhesive layer with high cohesive force and high durability while achieving a very low surface resistivity. This is thought to be due to the fact that the (meth)acrylic polymer (A) contains a relatively large amount of alkoxyalkyl group-containing monomers, thereby increasing its compatibility with the ionic compound (B) and suppressing the bleeding of the ionic compound at the interface between the adhesive layer and the adherend, as well as the use of a high molecular weight (meth)acrylic polymer (A) and a relatively large amount of crosslinking agent, which makes plasticization of the adhesive layer less likely to occur even if a large amount of ionic compound (B) is present.

[0014] <(meth)acrylic polymer (A)> The adhesive composition contains a (meth)acrylic polymer (A) having a weight-average molecular weight of 1 million or more, where the (meth)acrylic polymer (A) is a polymer of monomer components containing 50 to 99.9% by mass of alkoxyalkyl group-containing monomers and 0.1 to 10% by mass of crosslinkable functional group-containing monomers.

[0015] The weight-average molecular weight (Mw) of the (meth)acrylic polymer (A) is 1 million or more. It may be 1.2 million or more, 1.3 million or more, 1.4 million or more, or 1.5 million or more, and may be 2.5 million or less, 2.2 million or less, 2 million or less, 1.8 million or less, or 1.65 million or less. For example, its weight-average molecular weight may be 1.2 million to 2.5 million or 1.4 million to 2 million. Within this range, the adhesive composition can be given high cohesive strength and durability.

[0016] The weight-average molecular weight is determined using GPC (gel permeation chromatography) under the following conditions, converted to standard polystyrene equivalent. <GPC Measurement Conditions> Measurement device: HLC-8120GPC (Tosoh Corporation) GPC column configuration: The following five-section column (all Tosoh Corporation) (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: 1.5 mg / cm³ ３ To achieve this, dilute with tetrahydrofuran. Mobile phase solvent: tetrahydrofuran. Flow rate: 1.0 ml / min. Column temperature: 40°C.

[0017] <(meth)acrylic polymer (A) - alkoxyalkyl group-containing monomer> The monomer composition for obtaining (meth)acrylic polymer (A) contains an alkoxyalkyl group-containing monomer. The alkoxyalkyl group-containing monomer is not particularly limited as long as it is a monomer having an alkoxyalkyl group and a polymerizable group, but for example, as a polymerizable group, there can be a group having a polymerizable double bond such as a vinyl group or a (meth)acryloyl group. In particular, as an alkoxyalkyl group-containing monomer, alkoxyalkyl (meth)acrylate can be given.

[0018] Alkoxyalkyl (meth)acrylate is a monomer in which at least one hydrogen atom of the alkyl group of alkyl (meth)acrylate is substituted with an alkoxy group or a compound having an alkoxy group. Alkoxyalkyl (meth)acrylate may be alkoxypolyalkylene glycol (meth)acrylate, but preferably does not contain an oxyalkylene group.

[0019] For example, this monomer is represented by CH ２ =CR １ -COO-R ２ where R １ is a hydrogen atom or a methyl group, and R ２ represents a linear or branched alkyl group or aralkyl group having 14 or fewer carbon atoms, and at least one of the hydrogen atoms constituting these groups is a group -O-(C ｎ H ２ｎ O) ｍ -R ３ substituted, n represents an integer of 1 to 4, m represents an integer of 0 or 1 to 10, and R ３ constitutes a linear or branched alkyl group having 14 or fewer carbon atoms. However, m is preferably 0.

[0020] Specifically, examples of alkoxyalkyl (meth)acrylate 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, methoxy-polyethylene glycol acrylate, ethoxy-diethylene glycol acrylate, etc. Among these, 2-methoxyethyl (meth)acrylate is particularly preferred.

[0021] The alkoxyalkyl group-containing monomer is contained in the monomer composition in an amount of 50% by mass or more and 99.9% by mass or less. For example, the alkoxyalkyl group-containing monomer may be contained in the monomer composition in an amount of 51% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more, and may be contained in an amount of 99.9% by mass or less, 99.5% by mass or less, 99.0% by mass or less, 98% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less. For example, the alkoxyalkyl (meth)acrylate may be contained in the monomer composition in an amount of 70% by mass or more and 99.9% by mass or less, or 85% by mass or more and 99.9% by mass or less.

[0022] Multiple types of alkoxyalkyl group-containing monomers may be used in combination. When alkoxypolyalkylene glycol (meth)acrylate is used in combination, the amount of alkoxypolyalkylene glycol (meth)acrylate can be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, relative to the total amount of alkoxyalkyl group-containing monomers. The amount of alkoxyalkyl (meth)acrylate that does not contain an oxyalkylene group can be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more.

[0023] When the content of alkoxyalkyl group-containing monomers in the (meth)acrylic polymer (A) is in the high range described above, the compatibility between the (meth)acrylic polymer and ionic compounds commonly used in this field increases, and bleeding of the ionic compounds to the interface between the adhesive layer and the adherend can be suppressed.

[0024] <(meth)acrylic polymer (A) - Crosslinkable functional group-containing monomer> The monomer composition for obtaining (meth)acrylic polymer (A) includes a crosslinkable functional group-containing monomer. The crosslinkable functional group of the crosslinkable functional group-containing monomer can act as a crosslinking site that reacts with the crosslinking agent contained in the adhesive composition, thereby adjusting the gel fraction of the resulting adhesive layer to an appropriate range.

[0025] Examples of monomers containing crosslinkable functional groups include monomers containing hydroxyl groups and monomers containing carboxyl groups.

[0026] The hydroxyl group-containing monomer is not particularly limited as long as it is a monomer having a hydroxyl group and a polymerizable group. For example, polymerizable groups include groups having polymerizable double bonds such as vinyl groups and (meth)acryloyl groups.

[0027] Examples of 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.

[0028] Examples of carboxyl group-containing monomers include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, or their anhydrides (such as maleic anhydride).

[0029] The crosslinkable functional group-containing monomer is contained in the monomer composition in an amount of 0.1% by mass or more and 10% by mass or less. For example, the crosslinkable functional 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, and may be contained in an amount of 10% by mass or less, 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. For example, the crosslinkable functional group-containing monomer may be contained in the monomer composition in an amount of 0.3% by mass or more and 5.0% by mass or less, or 0.5% by mass or more and 2.0% by mass or less. Hydroxyl group-containing monomers and carboxyl group-containing monomers can also be contained in the monomer composition within these ranges, respectively.

[0030] <(meth)acrylic polymer (A) - other monomer components> The monomer composition for obtaining (meth)acrylic polymer (A) may also contain other monomers other than alkoxyalkyl group-containing monomers and crosslinkable functional group-containing monomers, to the extent that the advantageous effects of the present invention can be obtained.

[0031] Other monomers include alkyl (meth)acrylates, for example, alkyl (meth)acrylates in which the alkyl group has 1 to 20 carbon atoms. The alkyl group in alkyl (meth)acrylate is either linear or branched, and the number of carbon atoms in the alkyl group can be in the range of 1 to 20, 1 to 10, or 2 to 8.

[0032] Examples of alkyl (meth)acrylates 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, isostearyl (meth)acrylate, etc.

[0033] Other monomers include, for example, nitrogen-containing monomers such as (meth)acrylamide, N-(meth)acryloylpiperidine, N-vinylpyrrolidone, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, and N,N-diethylaminoethyl methacrylate; (meth)acrylic acid esters having aromatic ring groups such as benzyl (meth)acrylate, 2-naphthyl acrylate, and phenoxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene; vinyl carboxylate esters such as vinyl acetate; and macromonomers containing vinyl (meth)acryloyl groups.

[0034] Other monomers may be contained in the monomer composition in amounts of 0% by mass or more, 1.0% by mass or more, 5.0% by mass or more, 10% by mass or more, or 15% by mass or more, and may be contained in amounts of 49.8% by mass or less, 49% by mass or less, 45% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, or less than 1.0% by mass. For example, other monomers may be contained in the monomer composition in amounts of 1.0% by mass or more and 49.8% by mass or less, or 1.0% by mass or more and 10% by mass or less.

[0035] Other monomers may not be substantially present in the monomer composition. In this specification, "substantially absent" means that the component may be present as long as it does not impair the advantageous effects of the present invention. For example, substantially absent from the composition may mean that the component is present in an amount of less than 1.0% by mass, 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.

[0036] <(Meth)acrylic polymer (A) - Polymerization initiator> (Meth)acrylic polymer (A) can be polymerized using known polymerization initiators. As polymerization initiators, organic peroxides and azo compounds that can be used in radical polymerization can be used. Specifically, examples of polymerization initiators include organic peroxides such as t-butyl hydroperoxide, cumene hydrooxide, dicumyl peroxide, and benzoyl peroxide, and azo compounds such as 2,2'-azobis-iso-butyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile.

[0037] The polymerization initiator can be used in an amount of 0.01 parts by mass or more and 2.0 parts by mass or 0.03 parts by mass or more and 1.0 part by mass per 100 parts by mass of the total monomer components.

[0038] <(meth)acrylic polymer (A) - solvent> The monomer composition may contain a solvent depending on the polymerization method. For example, when obtaining a polymer by solution polymerization, an organic solvent capable of dissolving the monomer components can be used.

[0039] Specifically, examples of organic solvents include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, t-butylbenzene, xylene, and aromatic naphtha; aliphatic or alicyclic hydrocarbons such as n-hexane, n-heptane, dipentene, petroleum spirits, petroleum naphtha, and turpentine oil; esters such as ethyl acetate, n-butyl acetate, n-amyl acetate, and methyl benzoate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; glycol ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; and alcohols such as methyl alcohol, ethyl alcohol, and t-butyl alcohol. These organic solvents can be used individually or in combination of two or more. For example, it is particularly preferable to use organic solvents that do not easily cause chain transfer during polymerization reactions, such as esters and ketones. In particular, ethyl acetate, methyl ethyl ketone, and acetone can be used from the viewpoint of monomer solubility and ease of polymerization reaction.

[0040] <(Meth)acrylic polymer (A) - Other components> The monomer composition may contain other components as long as they do not impair the advantageous effects of the present invention. For example, the monomer component may contain a chain transfer agent, and depending on the polymerization method, it may also contain emulsifiers, dispersants, dispersion media, etc.

[0041] Examples of chain transfer agents include cyanoacetic acid, bromoacetic acid, or alkyl esters thereof having 1 to 8 carbon atoms; aromatic compounds such as anthracene, phenanthrene, and fluorene; aromatic nitro compounds such as p-nitroaniline, nitrobenzene, and p-nitrobenzoic acid; benzoquinone derivatives such as benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone; borane derivatives such as tributylborane; halogenated hydrocarbons such as carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, and 3-chloro-1-propene; aldehydes such as chloral and fural hydrate; alkyl mercaptans having 1 to 18 carbon atoms; aromatic mercaptans such as thiophenol and toluene mercaptan; mercaptoacetic acid, alkyl esters of mercaptoacetic acid having 1 to 10 carbon atoms; hydroxyalkyl mercaptans having 1 to 12 carbon atoms; and terpenes such as pinene and terpinolene.

[0042] <(Meth)acrylic polymer (A) - Polymerization method> The polymerization method for (meth)acrylic polymer (A) is not particularly limited and can be polymerized by known methods such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. When producing an adhesive composition using the polymer, it is preferable to obtain the polymer by solution polymerization from the viewpoint that the processing steps are relatively simple and can be carried out in a short time.

[0043] <Ionic compound (B)> The adhesive composition contains more than 10 parts by mass of ionic compound (B). It is believed that the adhesive composition containing ionic compound (B) can achieve high compatibility and antistatic properties because the oxygen atoms of the alkoxyalkyl group of the (meth)acrylic polymer (A) coordinate to the ionic group contained in ionic compound (B).

[0044] The ionic compound (B) may contain both a cation and anion, and preferably an alkali metal salt in which the cation is an alkali metal can be used. The ionic compound (B) may be solid or liquid at 25°C.

[0045] Examples of cations constituting ionic compounds (B) include inorganic cations and organic cations. An example of an inorganic cation is Li ＋ Na ＋ _K ＋ Examples of alkali metals include the following. Examples of organic cations include pyridinium cation, piperidinium cation, pyrrolidinium cation, pyrroline cation, pyrrole cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, pyrazolinium cation, tetraalkylammonium cation, trialkylsulfonium cation, tetraalkylphosphonium cation, and derivatives thereof. Among these cations, Li is particularly important from the viewpoint of antistatic properties. ＋ Na ＋ _K ＋ Alkali metals such as Li are preferred, ＋ That is particularly preferable.

[0046] The anion constituting the ionic compound (B) is not particularly limited as long as it can form an ionic compound by ionic bonding with the cation, for example, F － , Cl － , Br － , I － AlCl ４ － Al ２ Cl ７ － BF ４ － , PF ６ － SCN － , ClO ４ － NO ３ － ,CH ３ COO － CF ３ COO－ , CH ３ SO ３ － , CF ３ SO ３ － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) ２ N － , (CF ３ SO ２ ) ３ C － , AsF ６ － , SbF ６ － , NbF ６ － , TaF ６ － , F(HF)n － , (CN) ２ N － , C ４ F ９ SO ３ － , (C ２ F ５ SO ２ ) ２ N － , C ３ F7COO － and (CF ３ SO ２ )(CF ３ CO)N － can be mentioned. Among them, as a preferable anion, in addition to the high antistatic property due to the high ionic dissociation ability, and the high durability due to the high thermal decomposition temperature, particularly (FSO ２ ) ２ N － (bis(fluorosulfonyl)imide anion) or (CF ３ SO ２ ) ２ N － (bis(trifluoromethanesulfonyl)imide anion) can be mentioned.

[0047] Ionic compounds (B) are composed of these cations and anions, and specifically include lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tris(trifluoromethanesulfonyl)methide, potassium bis(trifluoromethanesulfonyl)imide, potassium bis(fluorosulfonyl)imide, 1-ethylpyridinium hexafluorophosphate, 1-butyl-4-pyridinium hexafluorophosphate, 1-hexyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium bis(fluorosulfonyl)imide, and 1-octyl-4-methylpyridinium Examples of suitable materials include umbis(trifluoromethanesulfonyl)imide, (N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N,N-tributyl-N-methylammonium bis(trifluoromethanesulfonyl)imide, 1-octylpyridinium fluorosulfoniumimide, 1-octyl-3-methylpyridinium, and trifluorosulfoniumimide. Among these, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide are preferred, and lithium bis(trifluoromethanesulfonyl)imide is particularly preferred.

[0048] The ionic compound (B) may be contained in the adhesive composition in an amount of more than 10 parts by mass, 11 parts by mass or more, 12 parts by mass or more, 15 parts by mass or more, more than 15 parts by mass, or 17 parts by mass or more per 100 parts by mass of (meth)acrylic polymer (A), and may be contained in an amount of 25 parts by mass or less, 22 parts by mass or less, 20 parts by mass or less, or 19 parts by mass or less. For example, the ionic compound may be contained in an amount of 12 parts by mass or more and 25 parts by mass or more and 15 parts by mass or less per 100 parts by mass of (meth)acrylic polymer (A). When the content of the ionic compound is within such a range, it is easy to achieve both sufficient surface resistivity and durability.

[0049] <Crosslinking agent (C)> The adhesive composition contains 0.5 to 10 parts by mass of crosslinking agent (C) per 100 parts by mass of (meth)acrylic polymer (A). By including crosslinking agent (C), the gel fraction of the resulting adhesive layer can be set to an appropriate range. As crosslinking agent (C), isocyanate-based crosslinking agents known in this field can be used, for example, a crosslinking agent having two or more isocyanate groups or isocyanurate groups and optionally a hydrocarbon group having 1 to 20 carbon atoms and containing an oxygen atom can be used.

[0050] Specifically, the isocyanate crosslinking agent is not particularly limited as long as it is a crosslinking agent that can crosslink with functional group-containing monomers at room temperature or under heating. Examples include isocyanate monomers such as xylylene diisocyanate, tolylene diisocyanate, chlorphenyl diisocyanate, and hexamethylene diisocyanate, isocyanate compounds obtained by adding these monomers to divalent or higher alcohol compounds such as trimethylolpropane, and isocyanurates. In addition, urethane prepolymer type isocyanates obtained by adding isocyanate compounds to known polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc., can also be used as isocyanate crosslinking agents.

[0051] Furthermore, epoxy crosslinking agents can be used as the crosslinking agent (C). As the epoxy crosslinking agent, epoxy compounds having two or more epoxy groups in one molecule can be used. 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, m-N,N-diglycidylaminophenylglycidyl ether, N,N-diglycidyltoluidine, and N,N-diglycidylaniline can be used.

[0052] Furthermore, a metal chelating crosslinking agent can be used as the crosslinking agent (C). As the metal chelating crosslinking agent, compounds in which alkoxides, acetylacetone, ethyl acetoethyl, etc. are coordinated to polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium can be used. Specifically, aluminum isopropylate, aluminum secondary butyrate, aluminum ethyl acetacetate / diisopropylate, aluminum trisethyl acetacetate, and aluminum trisacetylacetonate can be used.

[0053] The crosslinking agent (C) may be contained in the adhesive composition in an amount of 0.5 parts by mass or more, 0.8 parts by mass or more, 1.0 part by mass or more, or 1.2 parts by mass or more per 100 parts by mass of (meth)acrylic polymer (A), and may be contained in an amount of 10 parts by mass or less, 5.0 parts by mass or less, 3.0 parts by mass or less, 2.0 parts by mass or less, or 1.5 parts by mass or less per 100 parts by mass of (meth)acrylic polymer (A). For example, the crosslinking agent may be contained in an amount of 0.5 parts by mass or more and 5.0 parts by mass or 0.8 parts by mass or more and 3.0 parts by mass per 100 parts by mass of (meth)acrylic polymer (A).

[0054] <Silane coupling agent (D)> The adhesive composition may contain a silane coupling agent (D). An adhesive layer obtained from an adhesive composition containing a silane coupling agent (D) can maintain good adhesion to a glass substrate.

[0055] As the silane coupling agent (D), silane coupling agents known in this field can be used, for example, polypolymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane; 3-chloropropyltrimethoxysilane; oligomer-type silane coupling agents; and silicon compounds having an acetacetoxy group such as acetoacetoxypropyltrimethoxysilane. Among these, silane coupling agents having a functional group that reacts with the (meth)acrylic polymer (A) or its monomer component are particularly preferred in that they are less likely to cause the adhesive layer to peel off from the adherend in a high-humidity, high-temperature environment.

[0056] The silane coupling agent (D) is preferably a silane coupling agent having an acetoacetoxy group. These silane coupling agents (D) not only maintain good adhesion between the glass substrate and the adhesive layer, but also prevent excessive increase in adhesive strength even after the adhesive sheet has been exposed to a high-temperature environment, allowing for easy removal of the adhesive sheet from the substrate when necessary.

[0057] The silane coupling agent (D) may be contained in the 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 per 100 parts by mass of (meth)acrylic polymer (A), and may be contained in an amount of 5.0 parts by mass or less, 3.0 parts by mass or less, 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 per 100 parts by mass of (meth)acrylic polymer (A). For example, the silane coupling agent may be contained in an amount of 0.05 parts by mass or more and 1.0 parts by mass or less, or 0.1 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of (meth)acrylic polymer (A).

[0058] <Solvent> The adhesive composition may contain a solvent to adjust its applicability. The type of solvent may be the same as the polymerization solvent used to polymerize the (meth)acrylic polymer (A) described above.

[0059] The solid content concentration of the adhesive composition can be adjusted by including a solvent. The solid content concentration of the adhesive composition may be 10% by mass or more, 12% by mass or more, 14% by mass or more, or 16% by mass or more, and may be 40% by mass or less, 30% by mass or less, 20% by mass or less, or 18% by mass or less. For example, the solid content concentration of the adhesive composition may be 10% by mass or more and 30% by mass or less, or 12% by mass or more and 20% by mass or less.

[0060] In addition to the above components, the adhesive composition may also contain components selected from ultraviolet absorbers, antioxidants, tackifying resins, plasticizers, defoamers, fillers, stabilizers, softeners, and wettability modifiers, to the extent that they do not impair the effects of the present invention.

[0061] 《Adhesive Sheet》 The adhesive sheet of the present invention has an adhesive layer formed by the adhesive composition described above. The adhesive sheet may have the adhesive layer on a base layer.

[0062] The adhesive layer can be formed by applying an adhesive composition to the surface of the optical component or substrate layer that is the adherend, drying it at, for example, 50°C to 150°C depending on the type of solvent, then applying a release film to the side of the adhesive layer that is not in contact with other layers, and finally curing it for, for example, 3 to 10 days in an environment of 23°C to 50°C.

[0063] Methods for applying the adhesive composition include known methods such as spin coating, knife coating, roll coating, bar coating, blade coating, die coating, and gravure coating, with blade coating being particularly noteworthy.

[0064] The thickness of the adhesive layer may be 5 μm or more, 7 μm or more, 10 μm or more, or 15 μm or more, and may be 50 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less. For example, the thickness of the adhesive layer may be 5 μm or more and 50 μm or less, or 10 μm or more and 30 μm or less.

[0065] The surface resistivity of the adhesive layer was 1.0 × 10 when measured by the method described in the examples. ９ Ω / □ or less, 5.0×10 ８ Ω / □ or less, 2.0×10８ Ω / □ or less, 1.0×10 ８ Ω / □ or less, 5.0×10 ７ Ω / □ or less, or 3.0×10 ７ Ω / □ or less may also be acceptable, 1.0×10 ７ Ω / □ or more, 2.0×10 ７ Ω / □ or more, or 3.0×10 ７ Ω / □ or more may also be acceptable. When the surface resistivity is within the above range, it is preferable from the viewpoint of antistatic properties.

[0066] When the adhesive sheet has a base material layer, various base material films can be used as the base material layer that supports the adhesive layer. As the base material film, a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, a composite of these, etc. can be used. Among them, a resin film can be preferably adopted.

[0067] The resin film mentioned here is typically a non-porous resin sheet, which is formed by shaping various resin materials into a film shape.

[0068] Examples of the resin film include polyolefin-based resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester-based resin films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); vinyl chloride-based resin films; vinyl acetate-based resin films; polyimide-based resin films; polyamide-based resin films; fluororesin films; cellophane; etc. Among them, a PET film can be particularly used.

[0069] In the adhesive sheet of the present invention, when a polarizing plate is used for the base material and the thickness of the adhesive layer is 25 μm, after being attached to a glass adherend and left in a 95°C environment for 3 hours, the adhesive force is preferably 20.0 N / 25 mm or less, more preferably 18.0 N / 25 mm or less, still more preferably 15.0 N / 25 mm or less, and particularly preferably 10.0 N / 25 mm or less. That the adhesive force after being left in a 95°C environment for 3 hours is within the above range means that the reworkability is excellent.

[0070] 《Laminate》 In one embodiment, the present invention is a laminate. This laminate includes a first member, a second member, and an adhesive layer that adheres them together, the adhesive layer being formed from the adhesive composition described above. At least one of the first member and the second member may be the substrate layer described above, and the other may be an optical member. Both the first member and the second member may be optical members.

[0071] The laminate can be used, for example, in image display devices, particularly liquid crystal display devices. More specifically, the laminate can be used as part of touch panels, particularly automotive touch panels, and can be part of on-cell liquid crystal panels and in-cell liquid crystal panels. Each of these components is very expensive, and if the adhesive layer does not have reworkability, the entire component will have to be discarded if any slight misalignment occurs during adhesion. Therefore, it is preferable that the adhesive layer has reworkability.

[0072] Figure 1 shows an in-cell liquid crystal panel as an example of a laminate including an adhesive layer formed from the above-described adhesive composition. This in-cell liquid crystal panel 1 may have a first polarizing film 30a, a first adhesive layer 20a, a first transparent substrate 10a, a liquid crystal layer 4, a touch sensing function unit 5, a second transparent substrate 10b, a second adhesive layer 20b, and a second polarizing film 30b in this order, but the touch sensing function unit 5 can be configured in various positions in relation to the liquid crystal layer 4.

[0073] The first and second polarizing films are bonded to the first and second adhesive layers, respectively, and a polarizer having a transparent protective film on one or both sides is generally used. The polarizer is not particularly limited, but a polarizer made of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferably used. As the material constituting the transparent protective film, for example, a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, etc., can be used, and examples include cellulose resins such as triacetylcellulose and cyclic olefin resins. The polarizer and the transparent protective film are bonded together with a well-known adhesive.

[0074] An anchor layer may be present between the polarizing film and the adhesive layer. The anchor layer can be formed from a composition comprising a conductive polymer and a binder. Examples of conductive polymers include polyaniline and polythiophene, and examples of binders include polyurethane resins, polyester resins, and acrylic resins.

[0075] The first and second transparent substrates are bonded to the first and second adhesive layers, respectively, and can be made of glass or a polymer film. Examples of polymer films include films containing polyethylene terephthalate, cyclic olefin resin, polycarbonate, etc. When the transparent substrate is made of glass, its thickness can be, for example, about 0.1 mm to 1 mm. When the transparent substrate is made of a polymer film, its thickness can be, for example, about 10 μm to 200 μm. The transparent substrate may have an easy-adhesion layer or a hard coat layer on its surface.

[0076] The present invention will be described in more detail by the following examples, but the present invention is not limited thereto.

[0077] <Production Example> <Production of (meth)acrylic polymer (A1)> 98.5 parts by mass of 2-methoxyethyl acrylate, 1 part by mass of 4-hydroxybutyl acrylate, 0.5 parts by mass of acrylic acid, and 100 parts by mass of ethyl acetate were placed in a flask equipped with a stirring device, a nitrogen gas inlet tube, a thermometer, and a reflux condenser. The contents were then heated to 65°C while introducing nitrogen gas into the flask. Next, 0.05 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to the flask, which had been thoroughly purged with nitrogen gas, under stirring. The reaction was carried out for 6 hours while maintaining the temperature of the contents in the flask at 65°C.

[0078] After 6 hours, 300 parts by mass of ethyl acetate were added to the reaction mixture to obtain a solution containing (meth)acrylic polymer (A1). The Mw of the obtained (meth)acrylic polymer (A1), as measured by GPC, was 1.7 million.

[0079] <Production of (meth)acrylic polymers (A2) to (A4) and (A1') to (A2')> (meth)acrylic polymers (A2) to (A4) and (A1') to (A2') were produced in the same manner as (meth)acrylic polymer (A1), except that the types and / or amounts of raw materials were changed as shown in Table 1 below. In the case of (meth)acrylic polymer (A1'), 0.1 parts by mass of n-dodecyl mercaptan was added as a chain transfer agent and charged simultaneously with the monomer components in the reaction.

[0080]

[0081] <Preparation of Adhesive Composition> (Example 1) To 100 parts by mass of the solid content of a solution containing (meth)acrylic polymer (A1), 18 parts by mass of ionic compound (B1) (lithium bis(trifluoromethanesulfonyliimide)), 1 part by mass of isocyanate crosslinking agent (TD-75: manufactured by Soken Chemical Co., Ltd.), and 0.2 parts by mass of silane coupling agent (D1) (acetoacetoxypropyltrimethoxysilane) were added and thoroughly mixed to obtain an adhesive composition.

[0082] (Examples 2-10 and Comparative Examples 1-6) Adhesive compositions according to Examples 2-10 and Comparative Examples 1-5 were obtained in the same manner as in Example 1, except that the components to be blended were changed as shown in Table 2.

[0083] <Manufacturing of Polarizing Film with Adhesive Layer> The adhesive compositions obtained in each example were applied to the peeled PET film using a doctor blade at a liquid temperature of 25°C so that the film thickness after drying was 25 μm. Then, the film was dried at 90°C for 3 minutes to obtain an adhesive sheet having an adhesive layer with a thickness of 25 μm on the PET film.

[0084] A polarizing plate (COP film 40 μm / polarizing film 20 μm / TAC film 40 μm) was bonded to the PET film opposite the adhesive layer so that the COP film side was in contact with it, and the bonded plate was left to stand for 3 days at 50°C to produce a polarizing plate film with an adhesive layer.

[0085] <Test Method> <Surface Resistivity> The PET film was peeled from the adhesive layer of the polarizing film with an adhesive layer, and the surface resistivity of the adhesive layer was measured using a resistivity meter (Highresta UX MCP-HT800, manufactured by Nitto Seiko Analytech) at an applied voltage of 1000V in accordance with JIS-K-6911, under conditions of 23°C / 50%RH.

[0086] <Adhesion> A polarizing film with an adhesive layer was cut to a width of 25 mm to prepare test specimens. The PET film, which had been released from the test specimen, was peeled off, and the exposed adhesive layer was attached to an alkali-free glass plate. Then, they were held in an autoclave adjusted to 50°C / 5 atm for 20 minutes and pressed together. After pressing, they were left for 1 hour in a 23°C / 50% RH environment, and the adhesive-layered polarizing plate was pulled at the edge of the test specimen at a speed of 300 mm / min at an angle of 180° to the glass plate, and the adhesion strength was measured.

[0087] Furthermore, the adhesive strength after exposure to heat was measured under the same conditions, except that the samples were left in a 95°C environment for 3 hours after being pressed.

[0088] <Durability> Test specimens were prepared by cutting a polarizing film with an adhesive layer to a size of 160 mm (MD direction) x 90 mm (TD direction). After peeling the PET film from the test specimen, the polarizing film with the adhesive layer was attached to one side of a liquid crystal panel having a 2 mm thick alkali-free glass plate as a glass substrate, using a laminator roll so that the adhesive layer and the alkali-free glass plate were in contact. The resulting laminate was held in an autoclave adjusted to 50°C / 5 atm for 20 minutes to prepare a test plate. The test plate was left for 500 hours under conditions of 105°C, and the test plate was visually inspected for appearance defects such as foaming from the adhesive layer, cracks in the test plate, and peeling of the adhesive layer, and evaluated according to the following criteria: ○: No appearance defects △: Slight appearance defects are observed, but there are no problems in actual use ×: Appearance defects are present

[0089] Results: The results are shown in Table 2 below.

[0090]

[0091] In Comparative Example 1, despite containing a large amount of ionic compounds, the low molecular weight of the (meth)acrylic polymer (A1') resulted in insufficient cohesive force and delamination. In Comparative Example 2, the low compatibility between the (meth)acrylic polymer (A2') and the ionic compounds led to bleeding of the ionic compounds and subsequent delamination. In Comparative Example 3, despite containing a large amount of ionic compounds, the low amount of crosslinking agent resulted in defects during the durability test. In Comparative Examples 4 and 5, the low amount of added ionic compounds resulted in high durability but low surface resistivity.

[0092] In contrast, Examples 1 to 10 all exhibited acceptable durability and retained reworkability even after aging at 95°C for 3 hours after adhesion. However, Example 10, which used a silane coupling agent without an acetacetoxy group, showed high adhesive strength after aging at 95°C for 3 hours, and exhibited inferior reworkability compared to the other examples.

[0093] 1. In-cell liquid crystal panel 10a First transparent substrate 10b Second transparent substrate 20a First adhesive layer 20b Second adhesive layer 30a First polarizing film 30b Second polarizing film 4. Liquid crystal layer 5. Touch sensing function unit

Claims

1. An adhesive composition comprising 100 parts by mass of an (meth)acrylic polymer (A) having a weight-average molecular weight of 1 million or more, more than 10 parts by mass of an ionic compound (B), and 0.5 to 10 parts by mass of a crosslinking agent (C), wherein the (meth)acrylic polymer (A) is a polymer of monomer components containing 50 to 99.9% by mass of alkoxyalkyl group-containing monomers and 0.1 to 10% by mass of crosslinkable functional group-containing monomers.

2. The adhesive composition according to claim 1, wherein the ionic compound (B) is contained in an amount greater than 15 parts by mass and less than or equal to 20 parts by mass per 100 parts by mass of the (meth)acrylic polymer (A).

3. The adhesive composition according to claim 1, wherein the (meth)acrylic polymer (A) is a polymer of monomer components comprising 50 to 98.9% by mass of an alkoxyalkyl group-containing monomer, 0.1 to 10% by mass of a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and 1.0 to 49.8% by mass of an alkyl (meth)acrylate ester.

4. The adhesive composition according to claim 1, wherein the ionic compound (B) is an alkali metal salt.

5. The adhesive composition according to claim 1, wherein the ionic compound (B) has an anion which is a bis(fluorosulfonyl)imide anion or a bis(trifluoromethanesulfonyl)imide anion.

6. The adhesive composition according to claim 1, further comprising 0.1 to 5 parts by mass of a silane coupling agent (D).

7. The adhesive composition according to claim 6, wherein the silane coupling agent (D) has an acetoacetoxy group.

8. Having an adhesive layer formed by the adhesive composition according to any one of claims 1 to 7, wherein the surface resistivity of the adhesive layer is 1.0 × 10 ７ ~9.9 x 10 ７ An adhesive sheet with the properties Ω / □.

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