Adhesive composition, adhesive film for touch panel, and optical film with adhesive layer

Abstract

To provide an adhesive composition which has good step followability to frame printing arranged on a cover glass, and has both excellent step followability and durability, even if the cover glass and a sensor glass are stuck to each other.SOLUTION: There is provided an adhesive composition, wherein the acid value of an acrylic polymer, which is obtained by copolymerization of 100 pts.wt. of the total of monomers selected from a monomer group consisting of an alkyl acrylate monomer having 1 to 14 carbon atoms in an alkyl group, a branch structure alkyl group-containing monomer, and a nitrogen-containing vinyl monomer, with 0.1 to 10.0 pts.wt. of a hydroxyl group-containing copolymerizable vinyl monomer, without containing an alicyclic group-containing monomer, is 1 or less, and with respect to 100 pts.wt. of the total of at least the one or more monomers selected from the monomer group, 0.01 to 3.0 pts.wt. of an isocyanate compound and 0.01 to 2.0 pts.wt. of the silane coupling agent are contained as crosslinking agents.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive layer and an adhesive film used for bonding a cover glass (or touch sensor glass) of a touch panel member and a sensor glass (or sensor film). More specifically, it relates to an optical adhesive layer having good step-following properties for frame printing provided on the cover glass, and having excellent step-following properties and durability even when bonding the cover glass and the sensor glass, and a touch panel adhesive film and an optical film with an adhesive layer using the same.

Background Art

[0002] Examples of displays (display devices) to which touch panels are applied include liquid crystal displays (LCDs), electroluminescence displays (inorganic EL, organic EL), etc. Specific electronic devices using such touch panels include liquid crystal TVs, mobile terminals, mobile phones, electronic papers, e-book terminals, personal computers, etc.

[0003] For example, Patent Document 1 describes that in a liquid crystal device or a touch panel, in order to bond a light-transmitting member having a step in a light-shielding layer on a display surface, a shock-resistant and thick adhesive layer and an adhesive layer that is less likely to allow air bubbles to enter are used in combination. Further, Patent Document 2 describes a method of attaching between a touch panel and a surface protection layer such as a glass plate using a transparent adhesive sheet containing a cyclic olefin resin, a saturated polyisobutylene resin, an acrylic resin, a photoinitiator, etc. Further, Patent Document 3 describes a method of bonding between a touch panel and a protective transparent plate using a transparent adhesive sheet containing a polyoxyalkylene polymer having an alkenyl group, a compound having a hydrosilyl group, a hydrosilylation catalyst, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the display device described in Patent Document 1, bonding a light-transmitting member to the surface of the touch panel via an adhesive layer and an adhesive layer requires more labor than using only the adhesive layer, which causes an increase in cost and cannot be adopted for an inexpensive display device. Further, in the display device described in Patent Document 1, a light-shielding layer having a thickness of about 5 to 10 μm is formed so as to surround the outer periphery of the liquid crystal device. However, in order not to be affected by the printing step of the light-shielding layer, the regions of the adhesive layer and the adhesive layer are disposed within the frame of the light-shielding layer.

[0006] Further, Patent Document 2 discloses bonding a surface protection layer having a light-shielding layer to the surface of a touch panel via an adhesive layer having a specific storage elastic modulus. Although it is stated that no bubbles are generated when using this adhesive layer, after bonding the surface protection layer to the touch panel, the adhesive is cured by irradiating ultraviolet rays from the back side of the surface protection layer or the opposite side of the touch panel, so there is a problem that the back side of the light-shielding layer is not sufficiently irradiated with ultraviolet rays.

[0007] Further, Patent Document 3 discloses bonding a protective transparent plate having a black printing layer to the surface of a touch panel via a transparent adhesive sheet having a specific shear storage elastic modulus and gel fraction. It is stated that no foaming occurs at the bonding surface between the liquid crystal display panel and the protective transparent plate when using the transparent adhesive sheet of Patent Document 3. However, since the protective transparent plate made of transparent plastic is adhered to the liquid crystal panel via the transparent adhesive sheet, there is a problem that bubbles cannot be avoided at the corners where the step of the black printing layer occurs.

[0008] The present invention aims to provide an optical pressure-sensitive adhesive layer that has good step-following ability with respect to a frame print arranged on a cover glass, and that combines excellent step-following ability and durability even when the cover glass and sensor glass are bonded together, and an adhesive film using the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted extensive research and found that when the gel fraction of the adhesive layer and the strain value when a shear force is applied to the adhesive layer are within a predetermined range, both excellent step conformability and durability are achieved. The technical idea of ​​the present invention is to provide an adhesive layer having a gel fraction of 40 to 75%, a storage modulus of 100000 (10 to the power of 5) Pa or less at 1 Hz and 100°C measured by laminating the adhesive layer to a thickness of 1000 μm, a strain of 15% or more when a shear force of 500 Pa is applied continuously for 30 minutes under a load of 1 N, and a strain recovery force of 50% or more thereafter.

[0010] In order to solve the above-mentioned problems, the present invention provides a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer and a crosslinking agent, the acrylic polymer being a copolymer obtained by copolymerizing at least one monomer selected from the group of monomers consisting of an alkyl acrylate monomer having an alkyl group carbon number of C1 to C14, an alicyclic-containing monomer, a branched-structure alkyl group-containing monomer, and a nitrogen-containing vinyl monomer, and a hydroxyl group-containing copolymerizable vinyl monomer ... the pressure-sensitive adhesive layer has a gel fraction of 40 to 75%, a storage modulus of 1 Hz and 100°C measured after laminating the pressure-sensitive adhesive layer to a thickness of 1,000 µm is 100,000 Pa or less, and when a shear force of 500 Pa is continuously applied for 30 minutes under a load of 1 N, a strain of 15% or more and a strain recovery force thereafter of 50% or more are provided.

[0011] Also, the acid value of the acrylic polymer is 1 or less, and the pressure-sensitive adhesive composition contains an isocyanate compound as the crosslinking agent in an amount of 0.01 to 3.0 parts by weight based on 100 parts by weight in total of at least one or more monomers selected from the monomer group. When the pressure-sensitive adhesive layer after crosslinking the pressure-sensitive adhesive composition is laminated on one side of a substrate to a thickness of 175 μm, the adhesive strength is preferably 20 N / 25 mm or more, the total light transmittance is 90% or more, and the haze value is 1.0% or less.

[0012] Further, it is preferable that the pressure-sensitive adhesive composition contains a silane coupling agent in an amount of 0.01 to 2.0 parts by weight based on 100 parts by weight in total of at least one or more monomers selected from the monomer group.

[0013] Also, it is preferable that the hydroxyl group-containing copolymerizable vinyl monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate.

[0014] Further, the pressure-sensitive adhesive composition further contains 0.1 to 10 parts by weight of a polyfunctional acrylate monomer having 2 to 3 acryloyl groups in one molecule and 0.01 to 2.0 parts by weight of a photopolymerization initiator based on 100 parts by weight in total of at least one or more monomers selected from the monomer group. After the pressure-sensitive adhesive layer after crosslinking the pressure-sensitive adhesive composition is bonded to an adherend and then further subjected to ultraviolet curing by ultraviolet irradiation, the gel fraction of the pressure-sensitive adhesive layer is preferably 50 to 95%.

[0015] Further, the pressure-sensitive adhesive layer, which is a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition, is a pressure-sensitive adhesive layer that has been further subjected to ultraviolet curing by ultraviolet irradiation after being bonded to an adherend. The pressure-sensitive adhesive composition further contains, with respect to a total of 100 parts by weight of at least one or more monomers selected from the monomer group, 0.1 to 10 parts by weight of a polyfunctional acrylate monomer having 2 to 3 acryloyl groups in one molecule and 0.01 to 2.0 parts by weight of a photopolymerization initiator. After the ultraviolet curing, the gel fraction of the pressure-sensitive adhesive layer is preferably 50 to 95%.

[0016] The present invention also provides a pressure-sensitive adhesive film for a touch panel, in which the pressure-sensitive adhesive layer is laminated on one side of a base material.

[0017] The present invention also provides an optical film with a pressure-sensitive adhesive layer, in which the pressure-sensitive adhesive layer is laminated on at least one surface of an optical film.

Advantages of the Invention

[0018] According to the pressure-sensitive adhesive layer of the present invention, since the gel fraction of the pressure-sensitive adhesive layer and the strain value when a shearing force is applied to the pressure-sensitive adhesive layer are within a predetermined range, the step-following property to the frame printing disposed on the cover glass is good. Even when the cover glass and the sensor glass are bonded together, it is possible to provide an optical pressure-sensitive adhesive layer having excellent step-following property and durability, and a pressure-sensitive adhesive film using the same.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the present invention will be described based on preferred embodiments. The pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive layer formed by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer and a crosslinking agent. The acrylic polymer is a copolymer obtained by copolymerizing at least one monomer selected from a monomer group consisting of an alkyl acrylate monomer having 1 to 14 carbon atoms in the alkyl group, an alicyclic group-containing monomer, a branched-structure alkyl group-containing monomer, and a nitrogen-containing vinyl monomer, and a hydroxyl group-containing copolymerizable vinyl monomer. The acrylic polymer contains 0.1 to 10.0 parts by weight of the hydroxyl group-containing copolymerizable vinyl monomer with respect to 100 parts by weight in total of at least one monomer selected from the monomer group. The gel fraction of the pressure-sensitive adhesive layer is 40 to 75%. When the pressure-sensitive adhesive layer is laminated to a thickness of 1000 μm and measured, the storage elastic modulus at 1 Hz and 100 °C is 100,000 Pa or less, the strain when a shearing force of 500 Pa is continuously applied for 30 minutes under a load of 1 N is 15% or more, and the subsequent strain recovery force is 50% or more.

[0020] The acrylic polymer of the pressure-sensitive adhesive layer according to the present invention is a copolymer obtained by copolymerizing at least one monomer selected from a monomer group consisting of an alkyl acrylate monomer having 1 to 14 carbon atoms in the alkyl group, an alicyclic group-containing monomer, a branched-structure alkyl group-containing monomer, and a nitrogen-containing vinyl monomer as a monomer belonging to the first monomer group, and a hydroxyl group-containing copolymerizable vinyl monomer as a monomer belonging to the second monomer group, with one or more monomers each belonging to the first monomer group and the second monomer group. In the present specification, (meth)acrylate is a general term for acrylate and methacrylate.

[0021] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, as the alkyl acrylate monomer having an alkyl group with 1 to 14 carbon atoms, at least one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate and the like can be mentioned. The alkyl group of the alkyl acrylate monomer may be linear, branched or cyclic, but the alkyl group here is linear. The acrylate monomer having a branched alkyl group belongs to the monomer containing a branched structure alkyl group. Further, the acrylate monomer having a cyclic alkyl group belongs to the monomer containing an alicyclic group.

[0022] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, as the monomer containing an alicyclic group, at least one or more of cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, bicycloheptyl (meth)acrylate, bicyclooctyl (meth)acrylate, dimethylbicycloheptyl (meth)acrylate, dicyclopentanyl (meth)acrylate and the like can be mentioned. The monomer containing an alicyclic group may be an alicyclic alkyl (meth)acrylate monomer having an alkyl group with 1 to 18 carbon atoms.

[0023] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, examples of the branched-structure alkyl group-containing monomer include at least one or more of isopropyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, isopentyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isononyl (meth) acrylate, isodecyl (meth) acrylate, isoundecyl (meth) acrylate, isododecyl (meth) acrylate, isotridecyl (meth) acrylate, isotetradecyl (meth) acrylate, isopentadecyl (meth) acrylate, isohexadecyl (meth) acrylate, isoheptadecyl (meth) acrylate, isooctadecyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, and the like. The branched-structure alkyl group-containing monomer may be a branched-structure alkyl (meth) acrylate monomer having 1 to 18 carbon atoms in the alkyl group. The branched-structure alkyl group-containing monomer may have a branched structure in which the alkyl group has two or more branches (for example, two or more side chains with respect to the main chain), such as a t-butyl group.

[0024] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, examples of the nitrogen-containing vinyl monomer include vinyl monomers containing an amide bond, vinyl monomers containing an amino group, vinyl monomers having a nitrogen-containing heterocyclic structure, and the like. More specifically, cyclic nitrogen vinyl compounds having an N-vinyl-substituted heterocyclic structure such as N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methyl vinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyl oxazole, N-vinylmorpholine, N-vinylcaprolactam, N-vinyl lauryllactam; cyclic nitrogen vinyl compounds having an N-(meth)acryloyl-substituted heterocyclic structure such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth)acryloylazepane, N-(meth)acryloylazocan; cyclic nitrogen vinyl compounds having a heterocyclic structure having a nitrogen atom and an ethylenic unsaturated bond in the ring such as N-cyclohexylmaleimide, N-phenylmaleimide; unsubstituted or monoalkyl-substituted (meth)acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-t-butyl(meth)acrylamide; dialkyl-substituted (meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, N-methyl-N-isopropyl(meth)acrylamide;Dialkylamino (meth) acrylates such as N,N-dimethylaminomethyl (meth) acrylate, N,N-dimethylaminoethyl (meth) acrylate, N,N-dimethylaminopropyl (meth) acrylate, N,N-dimethylaminoisopropyl (meth) acrylate, N,N-dimethylaminobutyl (meth) acrylate, N,N-diethylaminomethyl (meth) acrylate, N,N-diethylaminoethyl (meth) acrylate, N-ethyl-N-methylaminoethyl (meth) acrylate, N-methyl-N-propylaminoethyl (meth) acrylate, N-methyl-N-isopropylaminoethyl (meth) acrylate, N,N-dibutylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate; N,N-dialkyl-substituted aminopropyl (meth) acrylamides such as N,N-dimethylaminopropyl (meth) acrylamide, N,N-diethylaminopropyl (meth) acrylamide, N,N-dipropylaminopropyl (meth) acrylamide, N,N-diisopropylaminopropyl (meth) acrylamide, N-ethyl-N-methylaminopropyl (meth) acrylamide, N-methyl-N-propylaminopropyl (meth) acrylamide, N-methyl-N-isopropylaminopropyl (meth) acrylamide; N-vinyl carboxamides such as N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide; (meth) acrylamides such as N-methoxymethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, diacetone acrylamide, N,N-methylenebis (meth) acrylamide; unsaturated carboxylic acid nitriles such as (meth) acrylonitrile; and the like. As the nitrogen-containing vinyl monomer, those not containing a hydroxyl group are preferred, and those not containing a hydroxyl group and a carboxyl group are more preferred. Examples of such monomers include the monomers exemplified above, for example, acrylic monomers containing an N,N-dialkyl-substituted amino group or an N,N-dialkyl-substituted amide group; N-vinyl-substituted lactams such as N-vinyl-2-pyrrolidone, N-vinylcaprolactam, and N-vinyl-2-piperidone; and N-(meth)acryloyl-substituted cyclic amines such as N-(meth)acryloylmorpholine and N-(meth)acryloylpyrrolidine are preferred.

[0025] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, examples of the hydroxyl group-containing copolymerizable vinyl monomer include at least one or more of hydroxyl group-containing alkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide. Among them, it is preferable that the hydroxyl group-containing copolymerizable vinyl monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. The acrylic polymer according to the present invention preferably contains 0.1 to 10.0 parts by weight, more preferably 0.2 to 5.0 parts by weight, and particularly preferably 0.2 to 4.0 parts by weight of the hydroxyl group-containing copolymerizable vinyl monomer with respect to 100 parts by weight in total of the monomers belonging to the first monomer group.

[0026] In the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, from the viewpoint of lowering the dielectric constant of the pressure-sensitive adhesive layer, it is preferable that the acrylic polymer does not contain a (meth)acrylate monomer having an aromatic group. Similarly, not only (meth)acrylate having an aromatic group, but also copolymerizable vinyl monomers having an aromatic group (such as styrene) can be not contained. Further, from the viewpoint of avoiding the influence on the corrosiveness to a substrate liable to corrosion such as the ITO surface of the transparent conductive film, the acid value of the acrylic polymer is preferably 1 or less.

[0027] The polymerization method of the copolymer used as the acrylic polymer is not particularly limited, and a known polymerization method such as a solution polymerization method or an emulsion polymerization method can be appropriately used. The acrylic polymer preferably contains 50 to 100% by weight of acrylic monomers such as (meth)acrylate monomers.

[0028] The pressure-sensitive adhesive composition can adjust characteristics such as required physical property values by blending a crosslinking agent and optionally arbitrary additives with the above acrylic polymer.

[0029] Examples of the crosslinking agent include at least one or more polyisocyanate compounds such as burette-modified products and isocyanurate-modified products of diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and adducts with polyols having a trivalent or higher valency such as trimethylolpropane and glycerin. It is preferable that the acrylic polymer has a hydroxyl group as a functional group capable of crosslinking with the isocyanate compound of the crosslinking agent, and it is also preferable to contain a monomer having these functional groups in the side chain. The content of the isocyanate compound used as the crosslinking agent is preferably 0.01 to 3.0 parts by weight with respect to 100 parts by weight in total of the monomers belonging to the first monomer group. Only the isocyanate compound may be used as the crosslinking agent.

[0030] The pressure-sensitive adhesive composition preferably further contains a silane coupling agent. Examples of the silane coupling agent include compounds having at least one organic functional group and at least one hydrolyzable group in one molecule, and the hydrolyzable group is an alkoxy group bonded to a silicon atom or the like. The silane coupling agent preferably has at least one type of organic functional group selected from the group consisting of an epoxy group, a (meth)acryloxy group, a mercapto group, and an amino group. Here, the (meth)acryloxy group means an acryloxy group (CH 2 =CHCOO-), or a methacryloxy group (CH 2 =C(CH 3 )COO-).

[0031] Examples of the silane coupling agent having an epoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 5,6-epoxyhexyltrimethoxysilane, 5,6-epoxyhexylmethyldimethoxysilane, 5,6-epoxyhexylmethyldiethoxysilane, 5,6-epoxyhexyltriethoxysilane, and the like. Examples of the silane coupling agent having a (meth)acryloxy group include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropyldimethylethoxysilane, 3-(meth)acryloxypropyldimethylmethoxysilane, and the like. Examples of the silane coupling agent having a mercapto group include 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropyltriethoxysilane, and the like. Examples of the silane coupling agent having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-(methylamino)propyltrimethoxysilane, 3-(methylamino)propyltriethoxysilane, and the like. In addition, an alkoxy oligomer (silicone alkoxy oligomer) containing the organic functional group and oligomerized can also be used as the silane coupling agent.

[0032] The content of the silane coupling agent is preferably 0.01 to 2.0 parts by weight with respect to 100 parts by weight in total of the monomers belonging to the first monomer group.

[0033] As other optional components, known additives such as antioxidants, surfactants, curing accelerators, plasticizers, fillers, crosslinking catalysts, crosslinking retarders, curing retarders, processing aids, anti-aging agents, etc. can be appropriately blended. These may be used alone or in combination of two or more.

[0034] The adhesive layer of the present invention can be obtained by crosslinking the adhesive composition after applying the adhesive composition to a substrate or a release film. The gel fraction of the adhesive layer after crosslinking is preferably 40 to 75%. Further, in order to obtain an optical adhesive layer having good step followability for the frame printing of the cover glass and excellent step followability and durability even when the cover glass and the sensor glass are bonded together, the storage elastic modulus at 1 Hz and 100 °C measured by laminating the adhesive layer to a thickness of 1000 μm is preferably 100,000 Pa or less, the strain when a shear force of 500 Pa is continuously applied for 30 minutes with a load of 1 N is preferably 15% or more, and the subsequent strain recovery force is preferably 50% or more.

[0035] When used for bonding between layers of optical members, etc., the adhesive layer after crosslinking the adhesive composition preferably has an adhesive strength of 20 N / 25 mm or more, a total light transmittance of 90% or more, and a haze value of 1.0% or less when laminated to a thickness of 175 μm on one side of the substrate. Examples of the adherend used in the adhesive strength test include a glass plate such as non-alkali glass and a resin film.

[0036] The adhesive layer of the present invention can also be an adhesive layer obtained by bonding the adhesive composition after crosslinking to an adherend and further performing ultraviolet curing by ultraviolet irradiation. In this case, the adhesive composition preferably contains an acrylic polymer, a crosslinking agent, a polyfunctional acrylate monomer, and a photoinitiator as essential components. This adhesive composition can further contain the above-mentioned silane coupling agent, etc. as optional components.

[0037] The polyfunctional acrylate monomer is not particularly limited as long as it is a compound having 2 to 3 acryloyl groups in one molecule. For example, diacrylates of dihydric alcohols (diols), diacrylates or triacrylates of trihydric alcohols (triols), diacrylates or triacrylates of tetrahydric alcohols (tetrols), etc. can be mentioned. Specific examples include ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, glycerol triacrylate, trimethylolethane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol triacrylate, etc., and one or more of these can be mentioned. Similarly to the polyfunctional acrylate monomer, a polyfunctional methacrylate monomer having 2 to 3 methacryloyl groups in one molecule can also be used. These polyfunctional monomers can be used singly or in combination of two or more in the pressure-sensitive adhesive composition. The polyfunctional monomer used in the pressure-sensitive adhesive composition of the present invention preferably has 2 to 3 polymerizable functional groups such as (meth)acryloyl groups in one molecule. The pressure-sensitive adhesive composition may not contain a monomer having 4 or more polymerizable functional groups in one molecule.

[0038] The photoinitiator is not particularly limited, and examples thereof include acetophenone-based photoinitiators, benzoin-based photoinitiators, benzophenone-based photoinitiators, thioxanthone-based photoinitiators, thioxanthone-based photoinitiators, etc. Examples of acetophenone-based photoinitiators include acetophenone, p-(tert-butyl)-1’,1’,1’-trichloroacetophenone, chloroacetophenone, 2’,2’-diethoxyacetophenone, hydroxylacetophenone, 2,2-dimethoxy-2’-phenylacetophenone, 2-aminoacetophenone, dialkylaminoacetophenone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, etc. Examples of benzoin-based photoinitiators include benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-2-methylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, benzyldimethyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, etc. Examples of benzophenone-based photoinitiators include benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, methyl-o-benzoylbenzoate, 4-phenylbenzophenone, hydroxylbenzophenone, hydroxylpropylbenzophenone, acrylylbenzophenone, 4,4’-bis(dimethylamino)benzophenone, etc. Examples of thioxanthone-based photoinitiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, diethylthioxanthone, dimethylthioxanthone, etc. Examples of other photoinitiators include α-acyl oxime ester, benzyl-(o-ethoxycarbonyl)-α-monoxime, acylphosphine oxide, phenylglyoxylic acid ester, 3-ketocoumarin, 2-ethylanthraquinone, camphorquinone, tetramethylthiuram sulfide, azobisisobutyronitrile, benzoyl peroxide, dialkyl peroxide, tert-butyl peroxypivalate, etc.

[0039] By using a polyfunctional acrylate monomer, a photopolymerization initiator, and ultraviolet irradiation, the acrylic polymer crosslinked with a crosslinking agent can be further cured by ultraviolet light to improve durability. The content of the polyfunctional acrylate monomer in the pressure-sensitive adhesive composition before crosslinking is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight in total of the monomers belonging to the first monomer group. Also, the content of the photopolymerization initiator is preferably 0.01 to 2.0 parts by weight with respect to 100 parts by weight in total of the monomers belonging to the first monomer group. The gel fraction of the pressure-sensitive adhesive layer after ultraviolet curing is preferably 50 to 95%.

[0040] When the pressure-sensitive adhesive layer according to the present invention is used for laminating between layers of an optical member, etc., in order to reduce the reflection of light at the interface between the pressure-sensitive adhesive layer and the optical member, it is desirable that the difference in refractive index be as small as possible. For this reason, the refractive index of the pressure-sensitive adhesive layer is preferably 1.47 to 1.50.

[0041] When the pressure-sensitive adhesive layer according to the present invention is used in an electronic device such as a touch panel, from the viewpoint of reducing electromagnetic field noise, the relative permittivity at a frequency of 100 kHz, measured by laminating the pressure-sensitive adhesive layer to a thickness of 1000 μm, is 1.50 to 5.50, and the dielectric loss is preferably 0.01 to 0.09.

[0042] The pressure-sensitive adhesive film of the present invention can be manufactured by forming the pressure-sensitive adhesive layer of the present invention on one surface of a base material or a release film. As the base material film used for forming the pressure-sensitive adhesive layer and the release film (separator) for protecting the adhesive surface, a resin film such as a polyester film can be used. On the surface of the base material film opposite to the side on which the pressure-sensitive adhesive layer of the resin film is formed, an antifouling treatment with a silicone-based, fluorine-based release agent, coating agent, silica fine particles, etc., and an antistatic treatment by applying or kneading an antistatic agent can be performed.

[0043] The release film is subjected to a release treatment on the surface that is joined to the adhesive surface of the pressure-sensitive adhesive layer with a silicone-based, fluorine-based release agent, etc. By aligning the surfaces of the release films that have been subjected to release treatment on both sides of a single adhesive layer, a structure of "release film / adhesive layer / release film" can also be formed. In this case, by sequentially or simultaneously peeling off the release films on both sides to expose the adhesive surfaces, it becomes possible to bond with optical members such as optical films. Examples of optical films include polarizing films, retardation films, antireflection films, antiglare films, ultraviolet absorption films, infrared absorption films, optical compensation films, brightness enhancement films, and the like.

[0044] The adhesive layer of the present invention can be suitably used for bonding the cover glass and the sensor glass of a touch panel because it can obtain good step-following performance even in the bonding of glass to glass such as cover glass and sensor glass. Also, when bonding a film member and a glass member, the adhesive film of the present invention obtained by laminating the adhesive layer of the present invention on one side of the film member can also be bonded to a glass member such as cover glass and sensor glass. The adhesive layer and the adhesive film of the present invention are suitable as an adhesive layer and an adhesive film for touch panels. As the step-following performance, for example, when the thickness of the adhesive layer is 175 μm, good step-following performance for a 42 μm printing step can be mentioned.

[0045] The adhesive film of the present invention can be used for bonding various optical films for peripheral members of liquid crystal display devices mainly including polarizing plates, various optical films for touch panels, various optical films for electronic papers, various optical films for organic ELs, and the like. Also, it can be made into an optical film with an adhesive layer in which the adhesive layer is laminated on at least one surface of these optical films. Specifically, structures such as "optical film / adhesive layer / optical film", "optical film / adhesive layer / release film", "optical film / adhesive layer", "optical film / adhesive layer / optical film / adhesive layer / optical film", "optical film / adhesive layer / optical film / adhesive layer / release film", "release film / adhesive layer / optical film / adhesive layer / release film" can be mentioned. For example, when having an adhesive layer protected by a release film, such as "optical film / adhesive layer / release film", the release film is peeled off to expose the adhesive layer, such as "optical film / adhesive layer", and by laminating with another optical film, a structure such as "optical film / adhesive layer / optical film" in which the adhesive layer is used for lamination between layers can be obtained.

[0046] The pressure-sensitive adhesive film of the present invention is suitably used for laminating a polarizing plate and a display panel. Examples of the display panel include a liquid crystal panel or an organic EL panel. The pressure-sensitive adhesive film of the present invention can be suitably used as the adhesive layer of a polarizing plate with an adhesive layer. As a constituent material of the polarizing plate, a retardation film having a retardation of λ / 4 or λ / 2 may be used. The adhesive layer of the present invention can be used for laminating the retardation film and the polarizing plate. According to the pressure-sensitive adhesive film of the present invention, since the adhesive layer has a low dielectric constant, it can be suitably used for laminating optical members between the polarizing plate and the backlight unit in an on-cell type display device in which a touch sensor is provided between the color filter and the polarizing plate.

Examples

[0047] Hereinafter, the present invention will be specifically described with reference to examples.

[0048] <Production of acrylic polymer> [Example 1] Nitrogen gas was introduced into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube to replace the air in the reaction apparatus with nitrogen gas. Then, 80 parts by weight of butyl acrylate, 20 parts by weight of methyl acrylate, 1.0 part by weight of 8-hydroxyoctyl acrylate, and 60 parts by weight of a solvent (ethyl acetate) were added to the reaction apparatus. Then, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours and reacted at 65°C for 6 hours to obtain an acrylic polymer solution used in Example 1. A part of the acrylic polymer was collected and used as a sample for measuring the acid value described later. [Examples 2 to 5 and Comparative Examples 1 to 3] Except that the composition of the monomers was made as described in groups (1) and (2) of Table 1 respectively, acrylic polymer solutions used in Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the acrylic polymer solution used in Example 1 above.

[0049] <Manufacture of Adhesive Composition, Adhesive Layer and Adhesive Film> [Example 1] To the acrylic polymer solution of Example 1 manufactured as described above, 0.5 part by weight of Coronate L (75% ethyl acetate solution of trimethylolpropane (TMP) adduct of tolylene diisocyanate (TDI) compound) and 0.2 part by weight of KBM-803 (3-mercaptopropyltrimethoxysilane) were added and stirred and mixed to obtain the adhesive composition of Example 1. This adhesive composition was applied onto a release film (a polyethylene terephthalate (PET) film coated with a silicone resin), and after removing the solvent by drying at 90°C, it was aged for 7 days in an atmosphere of 23°C and 50% RH to crosslink the adhesive composition, thereby obtaining the adhesive film of Example 1 having an adhesive layer formed on one side of the release film. [Examples 2 to 5 and Comparative Examples 1 to 3] Except that the composition of the additives was made as described in groups (3) to (6) of Table 1 respectively, adhesive films of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the adhesive film of Example 1 above. In the adhesive films of Examples 3 to 5 and Comparative Example 2, the adhesive layer formed by crosslinking the adhesive composition was irradiated with ultraviolet rays for further ultraviolet curing.

[0050]

Table 1

[0051] In Table 1, the total of the monomer group consisting of an alkyl (meth)acrylate monomer having an alkyl group with 1 to 14 carbon atoms, an alicyclic group-containing monomer, and a branched-structure alkyl group-containing monomer in group (1) was determined as 100 parts by weight. Also, as the addition ratios in groups (2) to (6), the numerical values in parts by weight are shown enclosed in parentheses. Incidentally, the group (2) is a monomer group composed of a hydroxyl group-containing copolymerizable vinyl monomer and a carboxyl group-containing copolymerizable vinyl monomer. The group (3) is a crosslinking agent. The group (4) is a silane coupling agent. The group (5) is a polyfunctional acrylate monomer. The group (6) is a photopolymerization initiator.

[0052] In addition, the compound names of the abbreviations of the respective components used in Table 1 are shown in Table 2. Incidentally, Coronate (registered trademark) L is a product name of Nippon Polyurethane Industry Co., Ltd., D-110N and D-170N are product names of Mitsui Chemicals, Inc., KBM-803 (described above), KBE-9007 (3-isocyanatopropyltriethoxysilane), and X-41-1805 (mercapto group-containing silicone alkoxy oligomer) are product names of Shin-Etsu Chemical Co., Ltd. TDI means tolylene diisocyanate, TMP means trimethylolpropane, XDI means xylylene diisocyanate, and HDI means hexamethylene diisocyanate. IRGACURE (registered trademark) 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE (registered trademark) 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR (registered trademark) 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one) are product names of BASF.

[0053]

Table 2

[0054] <Test Methods and Evaluation> From the pressure-sensitive adhesive films in Examples 1 to 5 and Comparative Examples 1 to 3, the release film (PET film coated with a silicone resin) was peeled off to expose the pressure-sensitive adhesive layer, and evaluation was performed by the following test methods and measurement methods.

[0055] <Measurement Method of Adhesive Strength> An adhesive film (optical film with an adhesive layer) serving as a sample was obtained by transferring an adhesive layer with a thickness of 175 μm onto one side of a polyester film with a thickness of 50 μm. The obtained adhesive film was bonded to the non-tin surface of alkali-free glass washed with acetone using a pressure roller, autoclaved under the conditions of 50 °C and 0.5 MPa for 20 minutes, then returned to an atmosphere of 23 °C × 50% RH, and allowed to stand for 1 hour. Subsequently, the peel strength of the adhesive film was measured using a tensile tester in accordance with JIS Z0237 "Test Methods for Adhesive Tapes and Adhesive Sheets", and the peel strength when peeling at a speed of 300 mm / min in the 180° direction was taken as the adhesive force (N / 25 mm) of the adhesive layer of the adhesive film.

[0056] <Measurement Method of Gel Fraction> The mass of the measurement sample of the adhesive layer was accurately measured, immersed in toluene for 24 hours, and then filtered through a 200-mesh wire mesh. Subsequently, the filtrate was dried at 100 °C for 1 hour, and the mass of the residue was accurately measured, and the gel fraction of the adhesive layer (crosslinked adhesive) was calculated from the following formula. Gel fraction (%) = mass of insoluble part (g) / mass of adhesive (g) × 100 For the adhesive films of Examples 3 to 5 and Comparative Example 2, the gel fraction of the adhesive layer was measured before and after ultraviolet irradiation after crosslinking by aging, and the value before ultraviolet irradiation was described on the left side of the right arrow (⇒), and the value after ultraviolet irradiation was described on the right side.

[0057] <Test Method for Durability> A 10 cm square adhesive film prepared in the same manner as in the method for measuring the adhesive force was bonded to the non-tin surface of alkali-free glass in the same manner to prepare a sample, which was left in a predetermined atmosphere (80 °C dry atmosphere or 60 °C × 90% RH atmosphere) for 250 hours, then taken out into a 23 °C × 50% RH atmosphere, and the state of the adhesive film was visually observed 1 hour later to judge the durability. ○·· There is no peeling or foaming of the adhesive film at all. △·· Peeling and foaming have occurred in a part of the adhesive film. ×·· Peeling and foaming have occurred throughout the adhesive film.

[0058] <Method for measuring storage elastic modulus> Using an adhesive layer with a thickness of 1000 μm as a sample, a dynamic viscoelasticity test was carried out with a shear rheometer (Anton Paar; apparatus name MCR301) under the condition of a frequency of 1 Hz. The measured value of the storage elastic modulus was the value at 100 °C.

[0059] <Test method for shear force-induced strain and restoring force> Using an adhesive layer with a thickness of 1000 μm as a sample, the strain A (%) when a shear force of 500 Pa was maintained for 30 minutes with a load of 1 N and the strain B (%) when the shear force was then set to 0 were measured. The shear-induced strain is obtained by the following formula when the thickness of the adhesive layer is y and the displacement in the shear direction (direction perpendicular to the thickness) is Δx. Shear strain = (Δx / y) × 100 (%) The restoring force of the strain is obtained by the following formula such that when strain B is 0% (returns to the shape before applying the load), the restoring force is 100%, and when strain B is equal to strain A (the strain remains permanently), the restoring force is 0%. Restoring force = (A - B) / A × 100 (%)

[0060] <Test method for step following property> An adhesive layer with a thickness of 175 μm was bonded to the surface of a 0.7 mm glass plate, and then a 1.1 mm cover glass having a printing step of 42 μm was bonded on it from above under the conditions of a pressure of 80 kPa and a vacuum degree of -100 kPa using a vacuum bonding apparatus. Further, the step following property was visually confirmed after autoclave treatment under the conditions of a temperature of 60 °C, 6 atmospheres, and 30 minutes. The criteria for visual confirmation were as follows. ○: Follows the printing step and there is no foaming around the printing step. △: There is slight foaming around the printing step. ×: There is foaming around the printing step.

[0061] <Method for measuring acid value> The acid value of the acrylic polymer was determined by dissolving the sample in a solvent (a mixture of diethyl ether and ethanol in a volume ratio of 2:1), and performing potentiometric titration using a potentiometric titrator (manufactured by Kyoto Electronics Industry Co., Ltd., AT-610) with a potassium hydroxide ethanol solution having a concentration of about 0.1 mol / l. The amount of the potassium hydroxide ethanol solution required to neutralize the sample was measured. Then, the acid value was determined from the following formula. Acid value = (B × f × 5.611) / S B = Amount (ml) of 0.1 mol / l potassium hydroxide ethanol solution used for titration f = Factor of 0.1 mol / l potassium hydroxide ethanol solution S = Mass (g) of the solid content of the sample

[0062] <Measurement method of total light transmittance> Measurement method of light transmittance: The total light transmittance was measured in accordance with JIS K7105, "Test Methods for Optical Properties of Plastics".

[0063] <Measurement method of haze value> Measurement method of haze value: The haze value was measured in accordance with JIS K7136, "Plastics - Method for Determining Haze of Transparent Materials".

[0064] Table 3 and Table 4 show the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 3. In the measurement results of the storage modulus in Table 3, 100,000 Pa was expressed as 1.0E+05 (1.0×10 5 ).

[0065]

Table 3

[0066]

Table 4

[0067] For the adhesive layers of Examples 1 to 5 according to the present invention, the gel fraction of the adhesive layer after crosslinking was 40 to 75%, the storage modulus at 1 Hz and 100 °C measured by laminating the adhesive layer to a thickness of 1000 μm was 100000 Pa or less, the strain when a shearing force of 500 Pa was continuously applied for 30 minutes with a load of 1 N was 15% or more, and the subsequent strain recovery force was 50% or more, and it was excellent in durability and step followability. Also, when laminated to a thickness of 175 μm on one side of the substrate, the adhesive strength was 20 N / 25 mm or more, and it was excellent in adhesive strength. Further, the total light transmittance was 90% or more and the haze value was 1.0% or less, and it was also excellent in optical properties. That is, according to the adhesive layers of Examples 1 to 5 according to the present invention, the requirements and problems in the prior art could be overcome.

[0068] The adhesive layer of Comparative Example 1 was produced using an adhesive composition having a low content of a hydroxyl group-containing copolymerizable vinyl monomer in an acrylic polymer. The gel fraction of the adhesive layer was 1%, the strain recovery force was low, and the durability and step followability were poor. The adhesive layer of Comparative Example 2 was UV-cured using a polyfunctional acrylate monomer having four acryloyl groups in one molecule. Therefore, the storage modulus at 1 Hz and 100 °C was high, and the durability and step followability were poor. The adhesive layer of Comparative Example 3 was produced using an adhesive composition not containing a crosslinking agent, and since the adhesive composition was not crosslinked, the gel fraction of the adhesive layer was 0%, the strain recovery force was low, and the durability and step followability were poor. Thus, the adhesive layers of Comparative Examples 1 to 3 could not overcome the requirements and problems in the prior art.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer, a crosslinking agent, and a silane coupling agent, The acrylic polymer is (A) an alkyl acrylate monomer having an alkyl group having a carbon number of C1 to C14; (C) a monomer containing a branched alkyl group; (D) a nitrogen-containing vinyl monomer, and at least one monomer selected from the monomer group consisting of: (E) a copolymer obtained by copolymerizing 0.1 to 10.0 parts by weight of at least one hydroxyl group-containing copolymerizable vinyl monomer in total without containing an alicyclic-containing monomer, The alkyl group of the alkyl acrylate monomer (A) having a carbon number of C1 to C14 is linear, the branched alkyl group-containing monomer (C) is a branched alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C18; the (E) hydroxyl group-containing copolymerizable vinyl monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; The acid value of the acrylic polymer is 1 or less, The pressure-sensitive adhesive composition is characterized in that it contains 0.01 to 3.0 parts by weight of an isocyanate compound as the crosslinking agent and 0.01 to 2.0 parts by weight of the silane coupling agent relative to a total of 100 parts by weight of at least one or more monomers selected from the monomer group.

2. An adhesive film for a touch panel, comprising a substrate and an adhesive layer formed by crosslinking the adhesive composition according to claim 1 laminated on one side thereof, the adhesive layer having a gel fraction of 40 to 75%.

3. An optical film with a pressure-sensitive adhesive layer, comprising an optical film and a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition according to claim 1 laminated on at least one surface of the optical film, the pressure-sensitive adhesive layer having a gel fraction of 40 to 75%.

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