JP2018150547A - Adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive that is excellent in blister resistance and step followability, and an adhesive sheet.SOLUTION: An adhesive is obtained by crosslinking an adhesive composition containing a (meth) acrylate polymer (A) that has a weight average molecular weight of 200,000-900,000, and contains, as a monomer unit constituting the polymer, a monomer having a hydroxy group of more than 10 mass% and 30 mass% or less, a crosslinker (B), and a crosslinking promoter (C), where the adhesive has a gel fraction of 30-95%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an adhesive and an adhesive sheet that can be used for a touch panel and the like.

  Various mobile electronic devices such as mobile phones and tablet terminals in recent years include a display using a display module having a liquid crystal element, a light emitting diode (LED element), an organic electroluminescence (organic EL) element, and the like. Is increasingly becoming a touch panel.

  In the display as described above, a protective panel is usually provided on the surface side of the display module. With the reduction in thickness and weight of electronic devices, the protective panel has been changed from a conventional glass plate to a plastic plate such as an acrylic plate or a polycarbonate plate.

  Here, a gap is provided between the protection panel and the display module so that the deformed protection panel does not collide with the display module even when the protection panel is deformed by an external force.

  However, if there is a gap as described above, that is, an air layer, the difference in refractive index between the protective panel and the air layer, and the reflection loss of light due to the difference in refractive index between the air layer and the display module is large. There is a problem that the image quality deteriorates.

  Therefore, it has been proposed to improve the image quality of the display by filling the gap between the protective panel and the display module with an adhesive layer. However, a frame-like printed layer may exist as a step on the display module side of the protective panel. If the pressure-sensitive adhesive layer does not follow the step, the pressure-sensitive adhesive layer floats in the vicinity of the step, thereby causing light reflection loss. For this reason, the pressure-sensitive adhesive layer is required to have a step following ability.

In order to solve the above-described problem, Patent Document 1 discloses that the shear storage elastic modulus (G ′) at 25 ° C. and 1 Hz is 1.0 as an adhesive layer that fills the gap between the protective panel and the display module. × is at 10 5 ^Pa or less, and a gel fraction discloses a pressure-sensitive adhesive layer is 40% or more.

JP 2010-97070 A

  In patent document 1, it is going to improve level | step difference followability by making low the storage elastic modulus at the time of normal temperature in an adhesive layer. However, when the storage elastic modulus at normal temperature is lowered as described above, the storage elastic modulus at high temperature is unnecessarily lowered, causing a problem under durability conditions. For example, when high-temperature and high-humidity conditions are applied, bubbles may be generated near the step, or outgas may be generated from the plastic plate, which is a protective panel, and blisters such as bubbles, floats, and peeling may occur. To do. On the other hand, when the pressure-sensitive adhesive layer is hardened in order to improve the blister resistance, the step following ability is lowered.

  This invention is made | formed in view of the above actual conditions, and it aims at providing the adhesive and adhesive sheet which are excellent in both blister resistance and level | step difference followability.

  In order to achieve the above object, first, the present invention has a weight average molecular weight of 200,000 to 900,000, and a monomer having a hydroxyl group is more than 10% by mass and 30% by mass or less as a monomer unit constituting the polymer. A pressure-sensitive adhesive obtained by crosslinking a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer (A), a crosslinking agent (B), and a crosslinking accelerator (C). The pressure-sensitive adhesive is characterized by comprising 40 to 90% (Invention 1).

  In the said invention (invention 1), the crosslinking agent (B) is activated by the catalytic action of the crosslinking accelerator (C), and the crosslinking reaction between the (meth) acrylate polymer (A) and the crosslinking agent (B). Proceeds efficiently, and the cohesive strength of the resulting adhesive improves. The pressure-sensitive adhesive layer made of a pressure-sensitive adhesive having such a strong cohesive force and having a gel fraction within the above range is excellent in blister resistance, and is not too hard, so that it can be step following. Also excellent. That is, according to the pressure-sensitive adhesive according to the invention (Invention 1), it is possible to achieve both the blister resistance and the step following ability, which are usually in a trade-off relationship.

  In the said invention (invention 1), content of the said crosslinking accelerator (C) in the said adhesive composition is 0.001-1 with respect to 100 mass parts of said (meth) acrylic acid ester polymers (A). It is preferable that it is a mass part (invention 2).

  In the said invention (invention 1), it is preferable that the said crosslinking accelerator (C) is an organotin compound (invention 3).

  In the said invention (invention 1-3), it is preferable that the said (meth) acrylic acid ester polymer (A) does not contain the monomer which has a carboxyl group as a monomer unit which comprises the said polymer (invention 4).

  In the said invention (invention 1-4), it is preferable that the said crosslinking agent (B) is an isocyanate type crosslinking agent (invention 5).

  In the said invention (invention 1-5), the said (meth) acrylic acid ester polymer (A) contains the hard monomer whose glass transition temperature as a homopolymer is 70 degreeC or more as a monomer unit which comprises the said polymer. It is preferable to do this (Invention 6).

  In the said invention (invention 1-6), it is preferable that the said (meth) acrylic acid ester polymer (A) contains (meth) acrylic-acid 2-ethylhexyl as a monomer unit which comprises the said polymer (invention). 7).

  In the said invention (invention 1-7), it is preferable that the said adhesive composition contains a silane coupling agent (D) further (invention 8).

  Secondly, the present invention includes two release sheets, and an adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets, and the adhesive layer is the adhesive ( A pressure-sensitive adhesive sheet comprising the inventions 1 to 8) is provided (invention 9).

  In the said invention (invention 9), it is preferable that the said adhesive layer is arrange | positioned between two patterned transparent conductive films, or between the patterned transparent conductive film and a cover material or a display body module ( Invention 10).

  The pressure-sensitive adhesive and pressure-sensitive adhesive sheet according to the present invention are excellent in both blister resistance and step followability.

It is sectional drawing of the adhesive sheet which concerns on one Embodiment of this invention. It is sectional drawing which shows one structural example of a touchscreen.

Hereinafter, embodiments of the present invention will be described.
[Adhesive]
The pressure-sensitive adhesive according to this embodiment has a weight average molecular weight of 200,000 to 900,000, and contains a monomer having a hydroxyl group (hydroxyl group-containing monomer) in an amount of more than 10% by mass and 30% by mass or less as a monomer unit constituting the polymer. An adhesive composition containing a (meth) acrylic acid ester polymer (A), a crosslinking agent (B), and a crosslinking accelerator (C) (hereinafter sometimes referred to as “adhesive composition P”). Are crosslinked and have a gel fraction of 40 to 90%. In the present specification, (meth) acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Further, the “polymer” includes the concept of “copolymer”.

  In the pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition P, the cross-linking agent (B) is activated by the catalytic action of the cross-linking accelerator (C), and cross-links with the (meth) acrylate polymer (A). The crosslinking reaction with the agent (B) proceeds efficiently. The compound as the crosslinking agent (B) has a plurality of functional groups in one molecule, and in a normal reaction, some functional groups in one molecule remain without reacting, but the crosslinking accelerator (C ) Is present, it is presumed that all functional groups in one molecule of the compound can react with the reactive functional group (hydroxyl group) of the (meth) acrylic acid ester polymer (A). For this reason, a crosslinked structure becomes strong and the cohesive force of the obtained adhesive improves. The pressure-sensitive adhesive layer made of a pressure-sensitive adhesive having such a strong cohesive force and having a gel fraction within the above range is excellent in blister resistance, and is not too hard, so that it can be step following. Also excellent. In other words, according to the pressure-sensitive adhesive according to the present embodiment, it is possible to achieve both the blister resistance and the step following ability that are normally in a trade-off relationship.

  Therefore, as an example, when the pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive is applied to the surface on the side where the level difference of the plastic plate is present, the pressure-sensitive adhesive layer follows the level difference, so there are no floating or bubbles in the vicinity of the level difference. It will be a thing. In addition, even when the laminate of the pressure-sensitive adhesive layer and the plastic plate is in a durable condition, generation of bubbles or the like in the vicinity of the step is suppressed, and even if outgas is generated from the plastic plate, bubbles, floats, Generation | occurrence | production of blisters, such as peeling, is suppressed.

(1) (Meth) acrylic acid ester polymer (A)
Examples of the hydroxyl group-containing monomer contained in the (meth) acrylic acid ester polymer (A) as a monomer unit constituting the polymer include 2-hydroxyethyl (meth) acrylate and 2-hydroxy (meth) acrylate. Hydroxyalkyl (meth) acrylates such as propyl, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate Examples include esters. Among them, 2-hydroxyethyl (meth) acrylate is preferred from the viewpoint of the reactivity of the hydroxyl group in the resulting (meth) acrylic acid ester polymer (A) with the crosslinking agent (B) and the copolymerizability with other monomers. Is preferred. These may be used alone or in combination of two or more.

  As described above, the (meth) acrylic acid ester polymer (A) contains a hydroxyl group-containing monomer in an amount of more than 10% by mass and 30% by mass or less as a monomer unit constituting the polymer. When the content of the hydroxyl group-containing monomer is 10% by mass or less, the above-described strong cross-linked structure is not formed, and the resulting pressure-sensitive adhesive is inferior in blister resistance. On the other hand, when the content of the hydroxyl group-containing monomer exceeds 30% by mass, desired tackiness cannot be obtained.

  Here, when the touch panel or the like is placed in a high-temperature and high-humidity environment, moisture enters the pressure-sensitive adhesive layer, and when the touch panel or the like returns to room temperature, the pressure-sensitive adhesive layer is whitened and transparency is reduced. There is a problem of "humid heat whitening". When the (meth) acrylic acid ester polymer (A) contains a hydroxyl group-containing monomer in the above range, a predetermined amount of hydroxyl groups will remain in the pressure-sensitive adhesive layer. A hydroxyl group is a hydrophilic group, and when such a hydrophilic group is present in a predetermined amount in the pressure-sensitive adhesive layer, even if the pressure-sensitive adhesive layer is placed under high-temperature and high-humidity conditions, The compatibility with the moisture that has penetrated into the layer is good, and as a result, whitening of the pressure-sensitive adhesive layer is suppressed, and the pressure-sensitive adhesive layer is excellent in resistance to moist heat whitening.

  From the above viewpoint, the (meth) acrylic acid ester polymer (A) preferably contains 12 to 25% by mass, particularly 15 to 20% by mass, of a hydroxyl group-containing monomer as a monomer unit constituting the polymer. It is preferable to do.

  The (meth) acrylic acid ester polymer (A) preferably does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. The carboxyl group (acid) tends to reduce the catalytic action of the crosslinking accelerator (C), but the (meth) acrylic acid ester polymer (A) does not have a carboxyl group, so that the crosslinking accelerator (C). The catalytic action can be sufficiently exhibited. In addition, when the (meth) acrylic acid ester polymer (A) does not have a carboxyl group, the resulting pressure-sensitive adhesive is a case where a defect is caused by an acid, such as a transparent conductive film or a metal wiring. Even so, it is possible to suppress the problems caused by the acid. For example, it is possible to suppress corrosion of the transparent conductive film and metal wiring, and change of the resistance value of the transparent conductive film.

  Here, “not containing a monomer having a carboxyl group” means substantially not containing a monomer having a carboxyl group, and contains no carboxyl group-containing monomer at all, or a crosslinking accelerator (C ) Is allowed to contain the carboxyl group-containing monomer to such an extent that the deterioration of the catalytic action and the problems such as the transparent conductive film and the metal wiring do not occur. Specifically, the (meth) acrylic acid ester polymer (A) contains a carboxyl group-containing monomer as a monomer unit in an amount of 0.1% by mass or less, preferably 0.01% by mass or less. It is acceptable.

  The (meth) acrylic acid ester polymer (A) preferably contains a (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group as a monomer unit constituting the polymer. Thereby, the obtained adhesive can express preferable adhesiveness. In addition, the below-mentioned hard monomer is removed from the (meth) acrylic acid alkyl ester.

  Examples of the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include, for example, methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, ( N-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate , Myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, and the like. Among these, from the viewpoint of further improving adhesiveness, (meth) acrylic acid esters having 1 to 8 carbon atoms in the alkyl group are preferable, and n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are particularly preferable. More preferred is 2-ethylhexyl (meth) acrylate. According to (meth) acrylic acid 2-ethylhexyl, the dielectric constant of the obtained adhesive can be lowered and the response accuracy of the touch panel can be improved. In addition, these may be used independently and may be used in combination of 2 or more type.

  The (meth) acrylic acid ester polymer (A) contains 30 to 85% by mass of a (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms as the monomer unit constituting the polymer. The content is preferably 40 to 75% by mass, more preferably 50 to 65% by mass.

  Further, the (meth) acrylic acid ester polymer (A) preferably contains a hard monomer having a glass transition temperature (Tg) as a homopolymer of 70 ° C. or more as a monomer unit constituting the polymer. By including the hard monomer as a monomer unit constituting the (meth) acrylic acid ester polymer (A), the resulting pressure-sensitive adhesive has improved cohesive force and is more excellent in blister resistance. In particular, when 2-ethylhexyl (meth) acrylate is used as the monomer unit constituting the (meth) acrylic acid ester polymer (A), the cohesive force tends to be low, so the hard monomer is used. It is preferable. The glass transition temperature (Tg) as a homopolymer of the hard monomer is preferably 75 to 200 ° C, and particularly preferably 80 to 180 ° C.

  Examples of the hard monomer include methyl methacrylate (Tg 105 ° C.), isobornyl acrylate (Tg 94 ° C.), isobornyl methacrylate (Tg 180 ° C.), acryloylmorpholine (Tg 145 ° C.), adamantyl acrylate (Tg 115 ° C.), and adamantyl methacrylate. (Tg 141 ° C.), dimethylacrylamide (Tg 89 ° C.), acrylamide (Tg 165 ° C.) and the like. These may be used alone or in combination of two or more.

  Among the hard monomers, methyl methacrylate, isobornyl acrylate and acryloyl morpholine are more preferable from the viewpoint of exerting the performance of the hard monomer while preventing adverse effects on other properties such as adhesion and transparency, and methacrylic acid. Methyl is particularly preferred.

  The (meth) acrylic acid ester polymer (A) preferably contains 10 to 45% by mass of the hard monomer as a monomer unit constituting the polymer, and particularly preferably contains 15 to 30% by mass. By containing the hard monomer in an amount of 10% by mass or more, an effect of improving blister resistance by the monomer unit can be expected. On the other hand, by setting the hard monomer content to 45% by mass or less, the relative shortage of other monomer units in the (meth) acrylic acid ester polymer (A) is prevented, and the pressure-sensitive adhesive obtained The adhesiveness and the step following ability can be made excellent.

  The (meth) acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. The other monomer is preferably a monomer that does not contain a reactive functional group in order not to interfere with the action of the hydroxyl group-containing monomer. Such other monomers include, for example, (meth) acrylic acid alkoxyalkyl esters such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, and aliphatic rings such as cyclohexyl (meth) acrylate (meta ) Acrylic acid ester, (meth) acrylic acid N, N-dimethylaminoethyl, (meth) acrylic acid N, N-dimethylaminopropyl, etc. (meth) acrylic acid ester having acetic acid tertiary amino group, acetic acid Examples include vinyl and styrene. These may be used alone or in combination of two or more.

  The polymerization mode of the (meth) acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

  The weight average molecular weight of the (meth) acrylic acid ester polymer (A) is 200,000 to 900,000, preferably 300,000 to 800,000, particularly preferably 400,000 to 600,000. In addition, the weight average molecular weight in this specification is the value of polystyrene conversion measured by the gel permeation chromatography (GPC) method.

  When the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is within a relatively low range as described above, a pressure-sensitive adhesive excellent in both blister resistance and step followability can be obtained. When the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is less than 200,000, the blister resistance is inferior, and the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is 900,000. When it exceeds, it will be inferior to level | step difference followability.

  In the adhesive composition P, the (meth) acrylic acid ester polymer (A) may be used singly or in combination of two or more.

(2) Crosslinking agent (B)
When the adhesive composition P is crosslinked, the crosslinking agent (B) reacts with a hydroxyl group derived from a hydroxyl group-containing monomer constituting the (meth) acrylic acid ester polymer (A). Thereby, the structure where (meth) acrylic acid ester polymer (A) was bridge | crosslinked with the crosslinking agent (B) is formed.

  The crosslinking agent (B) may be any one that reacts with the reactive group (the hydroxyl group of the hydroxyl group-containing monomer that is a monomer unit) of the (meth) acrylic acid ester polymer (A). For example, an isocyanate crosslinking agent Epoxy crosslinking agent, amine crosslinking agent, melamine crosslinking agent, aziridine crosslinking agent, hydrazine crosslinking agent, aldehyde crosslinking agent, oxazoline crosslinking agent, metal alkoxide crosslinking agent, metal chelate crosslinking agent, metal salt Examples thereof include an ammonium-based crosslinking agent and an ammonium salt-based crosslinking agent. Among these, it is preferable to use an isocyanate-based crosslinking agent that is excellent in reactivity with a hydroxyl group and that exhibits an excellent catalytic action of the crosslinking accelerator (C). In addition, a crosslinking agent (B) can be used individually by 1 type or in combination of 2 or more types.

  The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and the like. , And their biuret bodies, isocyanurate bodies, and adduct bodies that are a reaction product with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Of these, trimethylolpropane-modified aromatic polyisocyanate, particularly trimethylolpropane-modified tolylene diisocyanate is preferred from the viewpoint of reactivity with hydroxyl groups and the catalytic action of the crosslinking accelerator (C).

  One molecule of the polyisocyanate compound has a plurality of isocyanate groups. In the pressure-sensitive adhesive according to this embodiment, when the pressure-sensitive adhesive composition P contains the crosslinking accelerator (C), all the isocyanate groups possessed by one molecule of the polyisocyanate compound are (meth) acrylic acid ester polymers ( It is presumed that the cohesive force is improved by reacting with the reactive functional group (hydroxyl group) of A), and both the blister resistance and the step following ability are excellent.

  It is preferable that content of the crosslinking agent (B) in the adhesive composition P is 0.01-2 mass parts with respect to 100 mass parts of (meth) acrylic acid ester polymer (A), especially 0. The amount is preferably 0.05 to 1 part by mass, and more preferably 0.10 to 0.20 part by mass. When the content of the crosslinking agent (B) is within the above range, the resulting pressure-sensitive adhesive is excellent in both the blister resistance and the step following ability described above.

(3) Crosslinking accelerator (C)
The crosslinking accelerator (C) is not particularly limited as long as it activates the crosslinking agent (B) and improves the reaction efficiency between the (meth) acrylic acid ester polymer (A) and the crosslinking agent (B). Examples of the crosslinking accelerator (C) include organotin compounds; amino compounds such as N, N, N ′, N′-tetramethylhexanediamine, triethylamine, and imidazole; metal complexes such as aluminum complexes; paratoluenesulfonic acid, Examples include acid catalysts such as phosphoric acid, hydrochloric acid, and ammonium chloride. Among these, an organotin compound is preferable from the viewpoint of catalytic action.

  Examples of the organic tin compound include organic tin compounds such as dimethyltin dichloride; organic compounds such as dimethyltin dilaurate, dimethyltin di (2-ethylhexanoate), dimethyltin diacetate, dibutyltin dilaurate, dihexyltin diacetate, and dioctyltin dilaurate. Fatty acid salts of tin compounds; thioglycolic acid ester salts of organic tin compounds such as dimethyltin bis (isooctylthioglycolic acid ester) salt, dioctyltin bis (isooctylthioglycolic acid ester) salt; tin octylate, tin decanoate And metal soaps. Among these, fatty acid salts of organotin compounds are preferable from the viewpoint of catalytic action, and dibutyltin dilaurate is particularly preferable. In addition, a crosslinking accelerator (C) may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the crosslinking accelerator (C) in the adhesive composition P is preferably 0.001 to 1 part by mass with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A). It is preferable that it is 0.005-0.8 mass part, Furthermore, it is preferable that it is 0.01-0.7 mass part. When the content of the crosslinking accelerator (C) is within the above range, the catalytic action by the crosslinking accelerator (C) is effectively exhibited, and the adhesiveness is not inhibited.

(4) Silane coupling agent (D)
The adhesive composition P preferably further contains a silane coupling agent (D). Thereby, when a to-be-adhered body has a glass member, the adhesive obtained will improve adhesiveness with the glass member. Further, even if the adherend is a plastic plate, the obtained pressure-sensitive adhesive has improved adhesion to the plastic plate and is more excellent in blister resistance.

  The silane coupling agent (D) is an organosilicon compound having at least one alkoxysilyl group in the molecule, has good compatibility with the (meth) acrylic acid ester polymer (A), and has light transmittance. What has is preferable.

  Examples of the silane coupling agent (D) include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, Mercapto groups such as silicon compounds having an epoxy structure such as 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane Contains amino groups such as silicon compounds, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane Silicon compound, 3-chloropropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, or at least one of them, and alkyl groups such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane Examples include condensates with silicon compounds. These may be used individually by 1 type and may be used in combination of 2 or more type.

  The content of the silane coupling agent (D) in the adhesive composition P is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A). In particular, it is preferably 0.05 to 0.5 parts by mass, more preferably 0.1 to 0.3 parts by mass.

(5) Various additives For the adhesive composition P, if necessary, various additives usually used for acrylic pressure-sensitive adhesives, such as reaction inhibitors, refractive index adjusters, antistatic agents, tackifiers, oxidation agents, etc. Inhibitors, UV absorbers, light stabilizers, softeners, fillers, and the like can be added.

  In the pressure-sensitive adhesive composition P in this embodiment, the reaction between the (meth) acrylic acid ester polymer (A) and the crosslinking agent (B) easily proceeds due to the catalytic action of the crosslinking accelerator (C). In order to ensure this, it is also preferable to contain a reaction inhibitor.

  Examples of the reaction inhibitor include acetylacetone, ethyl acetoacetate, octylene glycol and the like, and among them, acetylacetone is preferable. These may be used individually by 1 type and may be used in combination of 2 or more type. In addition, said reaction inhibitor volatilizes normally at the drying process when forming an adhesive layer.

  It is preferable that content of the reaction inhibitor in the adhesive composition P is 0.01-10 mass parts with respect to 100 mass parts of (meth) acrylic acid ester polymer (A), especially 0.05. It is preferably ˜8 parts by mass, more preferably 0.1 to 5 parts by mass.

(6) Manufacture of adhesive composition Adhesive composition P manufactures (meth) acrylic acid ester polymer (A), and the obtained (meth) acrylic acid ester polymer (A) is made into a crosslinking agent ( B), a crosslinking accelerator (C), and, if desired, a silane coupling agent (D) and additives can be added.

  The (meth) acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomer units constituting the polymer by an ordinary radical polymerization method. The polymerization of the (meth) acrylic acid ester polymer (A) can be performed by a solution polymerization method or the like using a polymerization initiator as desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like. Two or more kinds may be used in combination.

  Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more kinds may be used in combination. Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane 1-carbonitrile), 2 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2′-azobis (2-methylpropionate) 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis (2-hydroxymethylpropionitrile), 2,2′-azobis [2- (2-imidazolin-2-yl) Propane] and the like.

  Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, and di (2-ethoxyethyl) peroxy. Examples include dicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

  In addition, in the said superposition | polymerization process, the weight average molecular weight of the polymer obtained can be adjusted by mix | blending chain transfer agents, such as 2-mercaptoethanol.

  Once the (meth) acrylic acid ester polymer (A) is obtained, the solution of the (meth) acrylic acid ester polymer (A) is added to the crosslinking agent (B), the crosslinking accelerator (C), and optionally silane coupling. The adhesive composition P (coating solution) diluted with the solvent is obtained by adding the agent (D), the diluting solvent and the additive and mixing them well.

  Examples of the dilution solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and ethylene chloride, methanol, ethanol, propanol, butanol, Alcohols such as 1-methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve solvents such as ethyl cellosolve are used.

  The concentration / viscosity of the coating solution thus prepared is not particularly limited as long as it can be coated, and can be appropriately selected depending on the situation. For example, it dilutes so that the density | concentration of the adhesive composition P may be 10-60 mass%. In addition, when obtaining a coating solution, addition of a dilution solvent etc. is not a necessary condition, and if a viscosity etc. which can be coated with the adhesive composition P are not necessary, a dilution solvent does not need to be added. In this case, the adhesive composition P becomes a coating solution using the polymerization solvent of the (meth) acrylic acid ester polymer (A) as a dilution solvent.

(7) Production of pressure-sensitive adhesive The pressure-sensitive adhesive according to this embodiment is preferably one obtained by crosslinking the pressure-sensitive adhesive composition P. The crosslinking of the pressure-sensitive adhesive composition P can be usually performed by heat treatment. In addition, this heat processing can also serve as the drying process at the time of volatilizing the dilution solvent of the adhesive composition P, etc.

  When performing heat processing, it is preferable that heating temperature is 50-150 degreeC, and it is especially preferable that it is 70-120 degreeC. The heating time is preferably 30 seconds to 10 minutes, particularly preferably 50 seconds to 2 minutes. After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23 ° C., 50% RH). When this curing period is necessary, after the curing period has elapsed, and when the curing period is unnecessary, an adhesive is formed after the heat treatment.

  By the heat treatment (and curing), the (meth) acrylic acid ester polymer (A) is sufficiently crosslinked through the crosslinking agent (B), and the above-described effects can be exhibited.

(8) Gel fraction The gel fraction of the adhesive which concerns on this embodiment is 40 to 90%, Preferably it is 50 to 85%, Most preferably, it is 60 to 80%. When the gel fraction is less than 40%, the cohesive force of the pressure-sensitive adhesive is insufficient and blister resistance is lowered. On the other hand, if the gel fraction exceeds 90%, the adhesive strength becomes too low and the durability is lowered or the step following performance is lowered. In addition, the measuring method of a gel fraction is as showing to the test example mentioned later.

[Adhesive sheet]
As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 according to this embodiment includes two release sheets 12a and 12b and the two release sheets 12a so as to be in contact with the release surfaces of the two release sheets 12a and 12b. , 12b and an adhesive layer 11 sandwiched between the two layers. In addition, the release surface of the release sheet in this specification refers to a surface having peelability in the release sheet, and includes both a surface that has been subjected to a release treatment and a surface that exhibits peelability without being subjected to a release treatment. .

(1) Adhesive layer The adhesive layer 11 is comprised from the adhesive mentioned above, ie, it is comprised from the adhesive formed by bridge | crosslinking the adhesive composition P. As shown in FIG.

  The thickness of the pressure-sensitive adhesive layer 11 (measured according to JIS K7130) is preferably 10 to 400 μm, particularly preferably 20 to 300 μm, and more preferably 50, depending on the height of the step. It is preferable that it is -250 micrometers. When the thickness of the pressure-sensitive adhesive layer 11 is 10 μm or more, good step followability is exhibited, and when the thickness of the pressure-sensitive adhesive layer 11 is 400 μm or less, workability is improved. The pressure-sensitive adhesive layer 11 may be formed as a single layer or may be formed by laminating a plurality of layers.

(2) Release sheet The release sheets 12a and 12b are not particularly limited, and known plastic films can be used. For example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene acetate A vinyl film, an ionomer resin film, an ethylene / (meth) acrylic acid copolymer film, an ethylene / (meth) acrylic acid ester copolymer film, a polystyrene film, a polycarbonate film, a polyimide film, a fluororesin film, or the like is used. These crosslinked films are also used. Furthermore, these laminated films may be sufficient.

  It is preferable that the peeling surface (especially the surface in contact with the pressure-sensitive adhesive layer 11) of the release sheets 12a and 12b is subjected to a peeling treatment. Examples of the release agent used for the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax release agents. Of the release sheets 12a and 12b, one release sheet is preferably a heavy release release sheet having a high release force, and the other release sheet is preferably a light release release sheet having a low release force.

  Although there is no restriction | limiting in particular about the thickness of release sheet 12a, 12b, Usually, it is about 20-150 micrometers.

(3) Production of pressure-sensitive adhesive sheet As one production example of the pressure-sensitive adhesive sheet 1, a coating liquid of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and heat treatment is performed for adhesion. After cross-linking the composition P and forming a coating layer, the release surface of the other release sheet 12b (or 12a) is overlaid on the coating layer. When a curing period is required, a curing period is set, and when the curing period is unnecessary, the coating layer becomes the pressure-sensitive adhesive layer 11 as it is. Thereby, the said adhesive sheet 1 is obtained. The conditions for the heat treatment and curing are as described above.

  As another production example of the pressure-sensitive adhesive sheet 1, a coating liquid of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of one release sheet 12 a, a heat treatment is performed to cross-link the pressure-sensitive adhesive composition P, and a coating layer To obtain a release sheet 12a with a coating layer. Moreover, the coating liquid of the said adhesive composition P is apply | coated to the peeling surface of the other peeling sheet 12b, heat processing is performed, the adhesive composition P is bridge | crosslinked, an application layer is formed, and an application layer is attached. A release sheet 12b is obtained. And the peeling sheet 12a with an application layer and the peeling sheet 12b with an application layer are bonded together so that both application layers may mutually contact. When the curing period is necessary, the curing period is set, and when the curing period is unnecessary, the above-mentioned laminated application layer becomes the pressure-sensitive adhesive layer 11 as it is. Thereby, the said adhesive sheet 1 is obtained. According to this production example, even when the pressure-sensitive adhesive layer 11 is thick, it can be stably produced.

  For example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, or the like can be used as a method for applying the coating solution of the adhesive composition P.

(4) Adhesive strength A transparent conductive film made of tin-doped indium oxide (ITO) is provided on the pressure-sensitive adhesive layer 11 side of the laminate obtained by laminating the pressure-sensitive adhesive layer 11 on a base material made of a polyethylene terephthalate film having a thickness of 100 μm. When the obtained transparent conductive film is attached to the transparent conductive film, the adhesive strength of the laminate to the transparent conductive film is preferably 5 to 80 N / 25 mm, particularly 10 to 70 N / 25 mm. It is preferable that it is 15-50 N / 25mm. When the adhesive force is in the above range, for example, the constituent members of the touch panel are securely bonded.

  In addition, although the adhesive force here means the adhesive force measured by the 180 degree peeling method according to JIS Z0237: 2009, the measurement sample has a width of 25 mm and a length of 100 mm, and the measurement sample is attached. After being applied to the body by applying pressure at 0.5 MPa and 50 ° C. for 20 minutes, the sample was left for 24 hours under conditions of normal pressure, 23 ° C. and 50% RH, and then measured at a peeling rate of 300 mm / min. To do.

(5) Use of pressure-sensitive adhesive sheet By using the pressure-sensitive adhesive sheet 1, for example, the capacitive touch panel 2 shown in FIG. 2 can be manufactured. The touch panel 2 includes a display module 3, a first film sensor 5 a laminated thereon via an adhesive layer 4 a, and a second film sensor 5 b laminated thereon via an adhesive layer 4 b. And the cover material 6 laminated | stacked through the adhesive layer 11 on it is comprised.

  The pressure-sensitive adhesive layer 11 in the touch panel 2 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1.

  Examples of the display module 3 include a liquid crystal (LCD) module, a light emitting diode (LED) module, an organic electroluminescence (organic EL) module, and electronic paper.

  The pressure-sensitive adhesive layers 4a and 4b may be formed by the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1, or may be formed by other pressure-sensitive adhesives or pressure-sensitive adhesive sheets. In the latter case, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 4 includes an acrylic pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a polyester-based pressure-sensitive adhesive, and a polyvinyl ether-based pressure-sensitive adhesive. However, among them, an acrylic pressure-sensitive adhesive is preferable.

  The 1st film sensor 5a and the 2nd film sensor 5b are normally comprised from the base film 51 and the patterned transparent conductive film 52, respectively. Although it does not specifically limit as the base film 51, For example, a polyethylene terephthalate film, an acrylic film, a polycarbonate film etc. are used.

  Examples of the transparent conductive film 52 include metals such as platinum, gold, silver and copper, oxides such as tin oxide, indium oxide, cadmium oxide, zinc oxide and zinc dioxide, tin-doped indium oxide (ITO), and zinc oxide-doped oxide. Examples include composite oxides such as indium, fluorine-doped indium oxide, antimony-doped tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide, and non-oxidized compounds such as chalcogenide, lanthanum hexaboride, titanium nitride, and titanium carbide. Among these, those made of tin-doped indium oxide (ITO) are preferable.

  One of the transparent conductive film 52 of the first film sensor 5a and the transparent conductive film 52 of the second film sensor 5b normally constitutes a circuit pattern in the X-axis direction, and the other constitutes a circuit pattern in the Y-axis direction. .

  The transparent conductive film 52 of the second film sensor 5b in the present embodiment is located above the second film sensor 5b in FIG. 2, but is not limited to this, and the second film sensor It may be located below 5a. Moreover, although the transparent conductive film 52 of the 1st film sensor 5a is located in the upper side of the 1st film sensor 5a in FIG. 2, it is not limited to this, The 1st film sensor 5a It may be located on the lower side.

  The cover material 6 is mainly composed of a glass plate or a plastic plate. The glass plate is not particularly limited. For example, chemically strengthened glass, alkali-free glass, quartz glass, soda lime glass, barium / strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, barium borosilicate glass. Etc. The plastic plate is not particularly limited, and examples thereof include an acrylic plate made of polymethyl methacrylate and the like, and a polycarbonate plate.

  In addition, a functional layer such as a hard coat layer, an antireflection layer, or an antiglare layer may be provided on one side or both sides of the glass plate or plastic plate, or a hard coat film, an antireflection film, or an antiglare film. Such optical members may be laminated.

  In the present embodiment, the cover material 6 has a step on the surface on the pressure-sensitive adhesive layer 11 side, and specifically has a step due to the presence or absence of the printing layer 7. The print layer 7 is generally formed in a frame shape on the pressure-sensitive adhesive layer 11 side of the cover material 6.

  The material which comprises the printing layer 7 is not specifically limited, The well-known material for printing is used. The thickness of the printing layer 7, that is, the height of the step, is preferably 3 to 45 μm, more preferably 5 to 35 μm, particularly preferably 7 to 25 μm, and preferably 7 to 15 μm. Further preferred.

  Further, the thickness of the printing layer 7 (height of the step) is preferably 3 to 30% of the thickness of the pressure-sensitive adhesive layer 11, particularly preferably 3.2 to 20%, and more preferably 3 It is preferable that it is 5 to 15%. As a result, the pressure-sensitive adhesive layer 11 can easily follow the step formed by the printing layer 7, and the occurrence of floating or bubbles in the vicinity of the step is suppressed.

An example of the manufacturing method of the touch panel 2 will be described below.
One release sheet 12a is peeled from the pressure-sensitive adhesive sheet 1, and the exposed pressure-sensitive adhesive layer 11 is bonded to the second film sensor 5b so as to be in contact with the patterned transparent conductive film 52 of the second film sensor 5b. To do. On the other hand, the pressure-sensitive adhesive layer 4b provided on the release sheet is bonded to the first film sensor 5a so as to be in contact with the patterned transparent conductive film 52 of the first film sensor 5a.

  Then, the release film remaining on the pressure-sensitive adhesive layer 4b is peeled off, and the exposed pressure-sensitive adhesive layer 4b is opposite to the surface on which the pressure-sensitive adhesive layer 11 is laminated in the second film sensor 5b (second surface). Both are bonded so that it may touch the exposed surface of the base film 51 of the film sensor 5b. Thereby, the laminated body by which the peeling sheet 12b, the adhesive layer 11, the 2nd film sensor 5b, the adhesive layer 4b, and the 1st film sensor 5a are laminated | stacked one by one is obtained.

  Next, the pressure-sensitive adhesive layer 4a provided on the release sheet is bonded to the surface of the laminate on the first film sensor 5a side (exposed surface of the base film 51 of the first film sensor 5a). Subsequently, the other release sheet 12b is peeled from the laminate, and the cover material 6 is pasted so that the printed layer 7 side of the cover material 6 contacts the pressure-sensitive adhesive layer 11 with respect to the exposed pressure-sensitive adhesive layer 11. Match. Thereby, the structure by which the cover material 6, the adhesive layer 11, the 2nd film sensor 5b, the adhesive layer 4b, the 1st film sensor 5a, the adhesive layer 4a, and a peeling sheet are laminated | stacked one by one is obtained.

  Finally, the release sheet is peeled off from the structure, and the structure is bonded to the display module 3 so that the exposed pressure-sensitive adhesive layer 4 a is in contact with the display module 3. Thereby, the touch panel 2 shown in FIG. 2 is manufactured.

  When the pressure-sensitive adhesive layer 11 and the cover material 6 are bonded in the above process, since the pressure-sensitive adhesive layer 11 is excellent in step following ability, it is difficult to form a gap between the step formed by the printing layer 7 and the pressure-sensitive adhesive layer 11. The agent layer 11 can fill the step. Further, even when the touch panel 2 is placed under a high temperature and high humidity condition, it is possible to prevent bubbles, floats, peeling, and the like from occurring near the step.

  Further, when the cover material 6 is a plastic plate, even if outgas is generated from the plastic plate under high temperature and high humidity conditions, the pressure-sensitive adhesive layer 11 is excellent in blister resistance, and thus blisters such as bubbles, floats, and peeling. Is suppressed from occurring.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, one of the release sheets 12a and 12b in the pressure-sensitive adhesive sheet 1 may be omitted.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, the scope of the present invention is not limited to these Examples etc.

[Example 1]
1. Preparation of (meth) acrylic acid ester copolymer 62.5 parts by mass of 2-ethylhexyl acrylate, 22.5 parts by mass of methyl methacrylate and 15 parts by mass of 2-hydroxyethyl acrylate were copolymerized to produce (meth) acrylic. An acid ester polymer (A) was prepared. When the molecular weight of this (meth) acrylic acid ester polymer (A) was measured by the method described later, the weight average molecular weight (Mw) was 500,000.

2. Preparation of Adhesive Composition 100 parts by mass of the (meth) acrylic acid ester polymer (A) obtained in the above step (1) (in terms of solid content; the same applies hereinafter) and trimethylolpropane as a crosslinking agent (B) 0.23 parts by mass of modified tolylene diisocyanate (manufactured by Nippon Polyurethane Co., Ltd., product name “Coronate L”) and dibutyltin dilaurate as a crosslinking accelerator (C) (product name “BXX3778-10” manufactured by Toyochem Co.) 0.005 3 parts by mass, 0.25 parts by mass of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name “KBM-403”) as a silane coupling agent (D), and acetylacetone as a reaction inhibitor Mixing 2.5 parts by mass, sufficiently stirring, and diluting with methyl ethyl ketone, a pressure-sensitive adhesive composition having a solid content concentration of 36% by mass A coating solution was obtained.

Here, Table 1 shows the composition of the adhesive composition. Details of the abbreviations and the like described in Table 1 are as follows.
[(Meth) acrylic acid ester polymer (A)]
2EHA: 2-ethylhexyl acrylate MMA: methyl methacrylate HEA: 2-hydroxyethyl acrylate

3. Production of pressure-sensitive adhesive sheet Peeling of a heavy-peelable release sheet (product name "SP-PET752150", manufactured by Lintec Corporation), in which one side of a polyethylene terephthalate film was subjected to a release treatment with a silicone-based release agent The treated surface was coated with a knife coater so that the thickness after drying was 25 μm, and then heat treated at 90 ° C. for 1 minute to form a coated layer. Similarly, a release treatment of a light release release sheet (product name “SP-PET382120” manufactured by Lintec Corporation) in which one side of a polyethylene terephthalate film was release-treated with a silicone-based release agent was applied to the obtained adhesive composition coating solution. The surface was coated with a knife coater so that the thickness after drying was 25 μm, and then heat-treated at 90 ° C. for 1 minute to form a coating layer.

  Subsequently, the heavy release type release sheet with the coating layer obtained above and the light release type release sheet with the coating layer obtained above were bonded so that both coating layers were in contact with each other. By curing for 7 days under the condition of 50% RH, a pressure-sensitive adhesive sheet having a structure of heavy release type release sheet / pressure-sensitive adhesive layer (thickness: 50 μm) / light release type release sheet was produced. The thickness of the pressure-sensitive adhesive layer is a value measured using a constant pressure thickness measuring instrument (manufactured by Teclock, product name “PG-02”) in accordance with JIS K7130.

[Examples 2-6, Comparative Examples 1-2]
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except that the amounts of the crosslinking agent (B), crosslinking accelerator (C) and silane coupling agent (D) were changed as shown in Table 1.

Here, the above-mentioned weight average molecular weight (Mw) is a polystyrene-reduced weight average molecular weight measured under the following conditions (GPC measurement) using gel permeation chromatography (GPC).
<Measurement conditions>
GPC measurement device: manufactured by Tosoh Corporation, HLC-8020
GPC column (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (× 2)
TSK gel G2000HXL
・ Measurement solvent: Tetrahydrofuran ・ Measurement temperature: 40 ° C.

[Test Example 1] (Measurement of adhesive strength)
The light release type release sheet was peeled off from the pressure sensitive adhesive sheets obtained in Examples and Comparative Examples, and the exposed pressure sensitive adhesive layer was easily made of a polyethylene terephthalate film (PET A4300, manufactured by Toyobo Co., Ltd., thickness: 100 μm) having an easy adhesion layer. Bonded to the adhesive layer. The laminate was cut into a width of 25 mm and a length of 100 mm, and this was used as a sample. The peelable release sheet was peeled from the sample, and the exposed adhesive layer was a polyethylene terephthalate film (made by Oike Kogyo Co., Ltd., ITO film, thickness provided with a transparent conductive film made of tin-doped indium oxide (ITO) on one side. : 125 μm).

  Then, after leaving for 24 hours under conditions of normal pressure, 23 ° C., and 50% RH, using a tensile tester (Orientec, Tensilon), according to JIS Z0237: 2009, a peeling rate of 300 mm / min, The adhesive strength (N / 25 mm) was measured under the condition of a peeling angle of 180 °. The results are shown in Table 1.

[Test Example 2] (Measurement of gel fraction)
The pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples were cut into a size of 80 mm × 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), the mass was weighed with a precision balance, and the mesh By subtracting the single mass, the mass of the adhesive alone was calculated. The mass at this time is M1.

  Next, the pressure-sensitive adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23 ° C.) for 24 hours. Thereafter, the pressure-sensitive adhesive was taken out, air-dried for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 50%, and further dried in an oven at 80 ° C. for 12 hours. After drying, the mass was weighed with a precision balance, and the mass of the pressure sensitive adhesive alone was calculated by subtracting the mass of the mesh alone. The mass at this time is M2. The gel fraction (%) is represented by (M2 / M1) × 100. The results are shown in Table 1.

[Test Example 3] (Evaluation of step following ability)
(A) Preparation of sample for evaluation On the surface of a glass plate (manufactured by NSG Precision, product name “Corning Glass Eagle XG”, length 90 mm × width 50 mm × thickness 0.5 mm), an ultraviolet curable ink (made by Teikoku Ink, The product name “POS-911 Black”) was screen-printed in a frame shape (outside: vertical 90 mm × width 50 mm, width 5 mm) so that the coating thickness was any one of 5 μm, 10 μm, and 15 μm. Next, irradiation with ultraviolet rays (80 W / cm ² , ^two metal halide lamps, lamp height of 15 cm, belt speed of 10 to 15 m / min) is performed to cure the printed ultraviolet curable ink, and a level difference due to printing (level difference) A stepped glass plate having a thickness of any one of 5 μm, 10 μm, and 15 μm was produced.

  The light release type release sheet was peeled off from the pressure sensitive adhesive sheets obtained in Examples and Comparative Examples, and the exposed pressure sensitive adhesive layer was easily made of a polyethylene terephthalate film (PET A4300, manufactured by Toyobo Co., Ltd., thickness: 100 μm) having an easy adhesion layer. Bonded to the adhesive layer. Next, the heavy release type release sheet was peeled off to expose the pressure-sensitive adhesive layer. Then, using a laminator (product name “LPD3214”, manufactured by Fuji Plastics Co., Ltd.), the laminate is laminated on each stepped glass plate so that the adhesive layer covers the entire frame-like print, and this is used as an evaluation sample. did.

(B) Evaluation of Evaluation Sample After the obtained evaluation sample was autoclaved for 30 minutes under the conditions of 50 ° C. and 0.5 MPa, it was further stored for 72 hours under wet heat conditions of 85 ° C. and 85% RH. . Thereafter, the pressure-sensitive adhesive layer (particularly in the vicinity of the step due to the printing layer) was visually confirmed, and the step following property was evaluated according to the following criteria. The results are shown in Table 1.
(Double-circle): There was no bubble, floating, and peeling at all.
○: Only bubbles with a diameter of 0.1 mm or less were generated.
Δ: Bubbles having a diameter of more than 0.1 mm were generated, and the diameter of the largest bubble was 0.2 mm or less.
X: Bubbles with a diameter of more than 0.2 mm, floating or peeling occurred.

[Test Example 4] (Blister resistance evaluation)
Polyethylene terephthalate film (manufactured by Oike Kogyo Co., Ltd., ITO film, thickness) provided with a transparent conductive film made of tin-doped indium oxide (ITO) on one side of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet obtained in Examples and Comparative Examples 125 μm) transparent conductive film and polycarbonate (PC) plate (Mitsubishi Gas Chemical Co., Ltd., Iupilon sheet MR58, thickness: 1 mm) or polymethyl methacrylate (PMMA) acrylic plate (Mitsubishi Gas Chemical Co., Ltd., Iupilon Sheet MR200, thickness: 1 mm) to obtain a laminate.

The obtained laminate was autoclaved for 30 minutes under the conditions of 50 ° C. and 0.5 MPa, and then allowed to stand at normal pressure, 23 ° C. and 50% RH for 15 hours. Subsequently, it was stored for 72 hours under 85 ° C. and 85% RH durability conditions. Thereafter, it was visually confirmed whether or not the pressure-sensitive adhesive layer had bubbles, floating or peeling, and blister resistance was evaluated according to the following criteria. The results are shown in Table 1.
A: There were no bubbles, no floating, and no peeling.
○: Only bubbles with a diameter of 0.1 mm or less were generated.
X: Bubbles with a diameter of more than 0.1 mm, floating or peeling occurred.

  As can be seen from Table 1, the pressure-sensitive adhesive sheets obtained in the examples were excellent in both step following ability and blister resistance.

  The pressure-sensitive adhesive sheet of the present invention can be suitably used for bonding, for example, a display module in a touch panel and a cover material having a step, particularly a plastic plate.

DESCRIPTION OF SYMBOLS 1 ... Adhesive sheet 11 ... Adhesive layer 12a, 12b ... Release sheet 2 ... Touch panel 3 ... Display body module 4a, 4b ... Adhesive layer 5a ... 1st film sensor 5b ... 2nd film sensor 51 ... Base film 52 ... Transparent conductive film 6 ... Cover material 7 ... Print layer

Claims (10)

(Meth) acrylic acid ester polymer (A) having a weight average molecular weight of 200,000 to 900,000 and containing a monomer having a hydroxyl group of more than 10% by mass and 30% by mass or less as a monomer unit constituting the polymer;
A crosslinking agent (B);
A pressure-sensitive adhesive obtained by crosslinking a pressure-sensitive adhesive composition containing a crosslinking accelerator (C),
A pressure-sensitive adhesive having a gel fraction of 40 to 90%.   Content of the said crosslinking accelerator (C) in the said adhesive composition is 0.001-1 mass part with respect to 100 mass parts of said (meth) acrylic acid ester polymers (A), It is characterized by the above-mentioned. The pressure-sensitive adhesive according to claim 1.   The pressure-sensitive adhesive according to claim 1 or 2, wherein the crosslinking accelerator (C) is an organotin compound.   The said (meth) acrylic acid ester polymer (A) does not contain the monomer which has a carboxyl group as a monomer unit which comprises the said polymer, The adhesive as described in any one of 1-3 characterized by the above-mentioned. .   The pressure-sensitive adhesive according to claim 1, wherein the crosslinking agent (B) is an isocyanate-based crosslinking agent.   The said (meth) acrylic acid ester polymer (A) contains the hard monomer whose glass transition temperature as a homopolymer is 70 degreeC or more as a monomer unit which comprises the said polymer. The pressure-sensitive adhesive according to any one of 5.   The said (meth) acrylic acid ester polymer (A) contains (meth) acrylic-acid 2-ethylhexyl as a monomer unit which comprises the said polymer, The any one of Claims 1-6 characterized by the above-mentioned. The adhesive as described in.   The pressure-sensitive adhesive composition according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive composition further contains a silane coupling agent (D). Two release sheets,
An adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets;
The said adhesive layer consists of an adhesive as described in any one of Claims 1-8, The adhesive sheet characterized by the above-mentioned.   The pressure-sensitive adhesive layer according to claim 9, wherein the pressure-sensitive adhesive layer is disposed between two patterned transparent conductive films or between the patterned transparent conductive film and a cover material or a display module. Sheet.

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