JP6216519B2 - Adhesive composition, adhesive and adhesive sheet - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive (a material obtained by crosslinking a pressure-sensitive adhesive composition), and a pressure-sensitive adhesive sheet, and particularly relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet suitable for optical members. It is.

  In recent years, in various electronic devices, a touch panel that serves as both a display device and an input unit is often used. The types of touch panels are mainly resistive film type, capacitance type, optical type and ultrasonic type. Resistance film type includes analog resistance film type and matrix resistance film type. There are types and projection types.

  As a touch panel in a mobile electronic device such as a smartphone or a tablet terminal that has been attracting attention recently, a projected capacitive type is often used. As a projected capacitive touch panel in such mobile electronic devices, for example, in order from the bottom, a liquid crystal display (LCD), an adhesive layer, a transparent conductive film (tin-doped indium oxide: ITO), a glass substrate, a transparent conductive film ( ITO) and a laminate of protective layers such as tempered glass have been proposed.

  A liquid crystal cell is generally used as an optical component constituting the liquid crystal display device. In general, the liquid crystal cell is arranged such that the alignment layers of the two transparent electrode substrates on which the alignment layers are formed are placed inside, with a predetermined interval by a spacer, and the periphery thereof is sealed to form the two transparent electrode substrates. A liquid crystal material is sandwiched between them. Usually, a polarizing plate is bonded to the outside of two transparent electrode substrates in a liquid crystal cell via an adhesive.

  As an adhesive used by a touch panel, what is shown by patent documents 1 is known, for example. This pressure-sensitive adhesive contains 0.2 to 20 parts by weight of a carboxyl group-containing monomer as a copolymer component with respect to 100 parts by weight of an alkyl (meth) acrylate having an alkyl group having 4 to 14 carbon atoms as a monomer unit. 0.02 to 2 parts by weight of a peroxide and 0.005 to 5 parts by weight of an epoxy crosslinking agent as a crosslinking agent with respect to 100 parts by weight of the (meth) acrylic polymer and (meth) acrylic polymer. Containing.

JP 2009-242786 A

  As described above, in the touch panel, various optical members are bonded with an adhesive, particularly an acrylic adhesive. Here, the refractive index of the optical member is generally high, for example, 1.50 or more, but the refractive index of the acrylic pressure-sensitive adhesive is usually about 1.47. For this reason, there is a problem that the refractive index difference between the optical member and the pressure-sensitive adhesive layer is large and reflection occurs at the interface between them.

  Moreover, in the conventional adhesive used for the touch panel, when the touch panel is placed in a high temperature and high humidity environment, moisture enters the adhesive layer, and when the touch panel returns to room temperature, the adhesive layer There is a problem that whitening occurs and transparency decreases.

  The present invention has been made in view of such a situation, and is suitable for an optical member, has a high refractive index and is subjected to high-temperature and high-humidity conditions, and then is whitened when returned to normal temperature and normal humidity. It aims at providing the adhesive composition which can be suppressed, an adhesive, and an adhesive sheet.

  In order to achieve the above object, the present invention firstly includes a monomer having a plurality of aromatic rings as a monomer unit constituting a polymer, and a monomer having a hydroxyl group or a monomer having a carboxyl group (meta ) A pressure-sensitive adhesive composition mainly composed of an acrylic acid ester polymer, wherein the content of the monomer having an aromatic ring in the (meth) acrylic acid ester polymer is 10 to 70% by mass, When the (meth) acrylic acid ester polymer contains the monomer having the hydroxyl group as a monomer unit constituting the polymer, the content of the monomer having the hydroxyl group in the (meth) acrylic acid ester polymer is 12 to 50% by mass, and the (meth) acrylic acid ester polymer is a monomer unit constituting the polymer. When the monomer having a carboxyl group is contained, the content of the monomer having a carboxyl group in the (meth) acrylic acid ester polymer is 7 to 40% by mass. (Invention 1).

  When the (meth) acrylic acid ester polymer of the pressure-sensitive adhesive composition according to the invention (Invention 1) contains a predetermined amount of a monomer having a plurality of aromatic rings as constituent monomer units, the resulting pressure-sensitive adhesive has a high refractive index. It becomes. Moreover, the (meth) acrylic acid ester polymer of the adhesive composition according to the invention (Invention 1) contains a predetermined amount of a monomer having a hydroxyl group or a monomer having a carboxyl group as a constituent monomer unit. Is suppressed from whitening when it is returned to room temperature and humidity after being subjected to high temperature and high humidity conditions.

  In the above invention (Invention 1), the monomer having a plurality of aromatic rings is preferably a monomer having a biphenyl ring (Invention 2).

  In the said invention (invention 2), it is preferable that the monomer which has the said biphenyl ring is biphenyloxy structure containing (meth) acrylate (invention 3).

  In the said invention (invention 1-3), it is preferable that the said adhesive composition contains a crosslinking agent further (invention 4).

  In the said invention (invention 4), it is preferable that the said crosslinking agent is at least 1 sort (s) chosen from the group which consists of an isocyanate type crosslinking agent, an epoxy-type crosslinking agent, and an aziridine type crosslinking agent (invention 5).

  In the said invention (invention 4 and 5), content of the said crosslinking agent in the said adhesive composition is 0.001-5 mass parts with respect to 100 mass parts of said (meth) acrylic acid ester polymers. It is preferable (Invention 6).

  In the said invention (invention 1-6), it is preferable that the weight average molecular weights of the said (meth) acrylic acid ester polymer are 200,000-2 million (invention 7).

  2ndly this invention provides the adhesive formed by bridge | crosslinking the said adhesive composition (invention 1-7) (invention 8).

  In the said invention (invention 8), it is preferable that the refractive index of the said adhesive is 1.50 or more (invention 9).

  In the above inventions (Inventions 8 and 9), the pressure-sensitive adhesive having a thickness of 50 μm sandwiched between two non-alkali glasses having a thickness of 1.1 mm is stored at 85 ° C. and 85% RH for 120 hours. It is preferable that the pressure-sensitive adhesive has a haze value of 1.0% or less when returned to normal temperature and humidity of 23 ° C. and 50% RH (Invention 10).

  Thirdly, the present invention provides a pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive (inventions 8 to 10). (Invention 11)

  In the said invention (invention 11), it is preferable that the said base material is an optical member (invention 12).

  Fourthly, the present invention is an adhesive sheet comprising 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. The pressure-sensitive adhesive sheet is characterized in that the layer is composed of the pressure-sensitive adhesive (Invention 8 to 10) (Invention 13).

  In the said invention (invention 13), it is preferable that the said adhesive sheet is an adhesive sheet for bonding two glass substrates together (invention 14).

  According to the pressure-sensitive adhesive composition of the present invention, it is suitable for an optical member, has a high refractive index, and can suppress whitening when it is returned to room temperature and humidity after being subjected to high temperature and high humidity conditions. An adhesive and an adhesive sheet are obtained.

It is sectional drawing of the adhesive sheet which concerns on the 1st Embodiment of this invention. It is sectional drawing of the adhesive sheet which concerns on the 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described.
[Adhesive composition]
The pressure-sensitive adhesive composition according to the present embodiment (hereinafter referred to as “pressure-sensitive adhesive composition P”) contains a monomer having a plurality of aromatic rings (a monomer containing a plurality of aromatic rings) as a monomer unit constituting the polymer, The main component is a (meth) acrylic acid ester polymer (A) containing a monomer having a hydroxyl group (hydroxyl group-containing monomer) or a monomer having a carboxyl group (carboxyl group-containing monomer). Preferably, a crosslinking agent (B) is further added. contains. In this specification, (meth) acrylic acid ester means both acrylic acid ester and methacrylic acid ester. The same applies to other similar terms. Further, the “polymer” includes the concept of “copolymer”. The “main component” is a component that usually accounts for 50% by mass or more, preferably 80% by mass or more, particularly preferably 90% by mass or more, based on the total amount of nonvolatile components of the adhesive composition.

  When the (meth) acrylic acid ester polymer (A) contains an aromatic ring-containing monomer, the pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition P has a high refractive index. Specifically, the refractive index is 1.50 or more, particularly preferably 1.51 or more. A method for measuring the refractive index will be described later.

  Examples of the aromatic ring of the aromatic ring-containing monomer include, for example, naphthalene ring, anthracene ring, fluorene ring, biphenyl ring, terphenyl ring, azulene ring, phenanthrene ring, triphenylene ring, pyrene ring, chrysene ring, naphthacene ring, perylene ring, Pentacene ring, hexacene ring, coronene ring, trinaphthylene ring, indolizine ring, quinoline ring, isoindole ring, indole ring, isoquinoline ring, phthalazine ring, purine ring, naphthyridine ring, quinoxaline ring, quinazoline ring, cinnoline ring, pteridine ring, Examples thereof include a carbazole ring, a phenanthridine ring, an acridine ring, a perimidine ring, a phenanthroline ring, a phenazine ring, and a phenalene ring. Among these, an aromatic ring having 10 to 18 carbon atoms, particularly an aromatic ring having 12 carbon atoms is preferable, and specifically, a biphenyl ring, a naphthalene ring, an anthracene ring, a triphenylene ring, and the like are preferable, and a biphenyl ring is particularly preferable. According to the monomer containing a biphenyl ring, a high refractive index can be obtained while maintaining good adhesive properties.

  Examples of the aromatic ring-containing monomer include, for example, biphenyl ring-containing (meth) acrylate, naphthalene ring-containing (meth) acrylate, anthracene ring-containing (meth) acrylate, triphenyl ring-containing (meth) acrylate, vinyl group-containing biphenyl, vinyl group Containing naphthalene, vinyl group-containing anthracene, and the like are mentioned. Among them, biphenyl ring-containing (meth) acrylate that can obtain a high refractive index while maintaining good adhesive properties is preferable. These may be used alone or in combination of two or more.

  Here, as biphenyl ring containing (meth) acrylate, specifically, o-biphenyloxymethyl (meth) acrylate, m-biphenyloxymethyl (meth) acrylate, p-biphenyloxymethyl (meth) acrylate, o- Biphenyloxyethyl (meth) acrylate, m-biphenyloxyethyl (meth) acrylate, p-biphenyloxyethyl (meth) acrylate, o-biphenyloxypropyl (meth) acrylate, m-biphenyloxypropyl (meth) acrylate, p- Biphenyloxypropyl (meth) acrylate, (o-biphenyloxy) diethylene glycol (meth) acrylate, (m-biphenyloxy) diethylene glycol (meth) acrylate, (p-biphenyloxy) diethyl Glycol (meth) acrylate, (o-biphenyloxy) dipropylene glycol (meth) acrylate, (m-biphenyloxy) dipropylene glycol (meth) acrylate, (p-biphenyloxy) dipropylene glycol (meth) acrylate, ( o-biphenyloxy) polyethylene glycol (meth) acrylate, (m-biphenyloxy) polyethylene glycol (meth) acrylate, (p-biphenyloxy) polyethylene glycol (meth) acrylate, (o-biphenyloxy) polypropylene glycol (meth) acrylate , (M-biphenyloxy) polypropylene glycol (meth) acrylate, (p-biphenyloxy) polypropylene glycol (meth) acrylate, and the like.Among these, biphenyloxyethyl (meth) acrylate is preferable, and o-biphenyloxyethyl (meth) acrylate is particularly preferable from the viewpoint of achieving both transparency and high refractive index of the obtained pressure-sensitive adhesive.

  The (meth) acrylic acid ester polymer (A) contains 10 to 70% by mass, preferably 20 to 65% by mass, particularly preferably 25, of an aromatic ring-containing monomer as a monomer unit constituting the polymer. Contains ~ 60% by mass. When the content of the aromatic ring-containing monomer is less than 10% by mass, the refractive index of the obtained pressure-sensitive adhesive is not sufficiently high. On the other hand, when the content of the aromatic ring-containing monomer exceeds 70% by mass, adhesiveness suitable for optical use cannot be obtained.

  On the other hand, when the (meth) acrylic acid ester polymer (A) contains a hydroxyl group-containing monomer as a monomer unit constituting the polymer, the hydroxyl group-containing monomer is contained in an amount of 12 to 50% by mass, preferably 15 to 40%. It is contained by mass%, particularly preferably 17-35 mass%. Further, when the (meth) acrylic acid ester polymer (A) contains a carboxyl group-containing monomer as a monomer unit constituting the polymer, the carboxyl group-containing monomer is contained in an amount of 7 to 40% by mass, preferably 10%. It contains -35 mass%, Most preferably, it contains 10-20 mass%.

  When the (meth) acrylic acid ester polymer (A) contains the hydroxyl group-containing monomer or the carboxyl group-containing monomer in the above amount, the pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition P is subjected to high temperature and high humidity conditions. After applying, whitening when returning to normal temperature and humidity is suppressed. Details of the conditions of high temperature and high humidity will be described later.

  When the (meth) acrylic acid ester polymer (A) contains a hydroxyl group-containing monomer or a carboxyl group-containing monomer in the above amount, a predetermined amount of hydroxyl group or carboxyl is contained in the adhesive obtained by crosslinking the adhesive composition P. The group will remain. Hydroxyl groups and carboxyl groups are hydrophilic groups, and when such a hydrophilic group is present in the pressure-sensitive adhesive in a predetermined amount, even when the pressure-sensitive adhesive is placed under high-temperature and high-humidity conditions, Moisture that has entered the agent is easily removed from the adhesive when it returns to normal temperature and humidity, and as a result, whitening of the adhesive is suppressed. When the content of the hydroxyl group-containing monomer or the carboxyl group-containing monomer in the (meth) acrylic acid ester polymer (A) is less than the above range, the above-mentioned effects cannot be obtained. Or the refractive index cannot be made sufficiently high.

  Moreover, even when the adhesive composition P contains the crosslinking agent (B), if the content of the hydroxyl group-containing monomer or carboxyl group-containing monomer in the (meth) acrylic acid ester polymer (A) is in the above range. While maintaining the above-described effects, the crosslinked structure formed is good, and the resulting pressure-sensitive adhesive has excellent durability.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (meth ) (Meth) acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl acrylate and 4-hydroxybutyl (meth) acrylate, among others, from the viewpoint of reactivity with the crosslinking agent (B) and pot life ( Meth) acrylic acid 2-hydroxyethyl is preferred. These may be used alone or in combination of two or more.

  Preferred examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. These may be used alone or in combination of two or more.

  In the (meth) acrylic acid ester polymer (A), as a monomer unit constituting the polymer, in addition to the hydroxyl group-containing monomer, the carboxyl group-containing monomer, and the aromatic ring-containing monomer, the alkyl group has 1 to 20 carbon atoms. It is preferable to contain (meth) acrylic acid alkyl ester. Moreover, you may contain another monomer if desired.

  The (meth) acrylic acid ester polymer (A) contains a (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group as a monomer unit constituting the polymer. Can be expressed. Examples of the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth) acrylic acid n-. Butyl, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, (meth) acrylic acid Examples include n-dodecyl, myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, and the like. Among these, from the viewpoint of further improving the tackiness, (meth) acrylic acid esters having 1 to 8 carbon atoms in the alkyl group are preferable, and methyl (meth) acrylate and n-butyl (meth) acrylate are particularly preferable. 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) may contain 18 to 78% 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 20 to 65% by mass, more preferably 23 to 58% by mass.

  As said other monomer, the monomer which does not contain the reactive functional group is preferable also in order not to prevent the effect | action of the said hydroxyl-containing monomer or the said carboxyl 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 Non-crosslinkable acrylamide such as acrylic ester, acrylamide, methacrylamide, etc. Non-crosslinkable tertiary such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate Examples thereof include (meth) acrylic acid ester having an amino group, vinyl acetate, 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 preferably 200,000 to 2,000,000, particularly preferably 200,000 to 1,000,000, and more preferably 300,000 to 700,000. Is preferred. 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 less than 200,000, foaming may occur when the resulting adhesive is exposed to high temperature and high humidity conditions such as a whitening test. . Moreover, when the weight average molecular weight of the (meth) acrylic acid ester polymer (A) exceeds 2 million, it is possible to suppress whitening when the obtained adhesive is subjected to high temperature and high humidity conditions and then returned to normal temperature and normal humidity. It may disappear.

  In the adhesive composition P, the (meth) acrylic acid ester polymer (A) may be used singly or in combination of two or more. In addition, the adhesive composition P is a (meth) acrylic acid ester polymer that does not contain a hydroxyl group-containing monomer and a carboxyl group-containing monomer as constituent monomer units, and (meth) acrylic acid that does not contain an aromatic ring-containing monomer as constituent monomer units. An ester polymer may be further contained.

  The pressure-sensitive adhesive composition P preferably contains a crosslinking agent (B), but by containing this crosslinking agent (B), the (meth) acrylic acid ester polymer (A) is crosslinked to form a three-dimensional network. A structure can be formed and the durability of the resulting pressure-sensitive adhesive can be improved.

  The crosslinking agent (B) may be any functional group that is reactive with the functional group of the (meth) acrylic acid ester polymer (A), that is, a hydroxyl group or a carboxyl group. 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 crosslinking agent Agents, ammonium salt crosslinking agents, and the like. Among these, it is preferable to use an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, or an aziridine-based crosslinking agent. A crosslinking agent (B) can be used individually by 1 type or in combination of 2 or more types.

  Here, when the (meth) acrylic acid ester polymer (A) has a hydroxyl group, it is preferable to use an isocyanate-based crosslinking agent excellent in reactivity with the hydroxyl group, and the (meth) acrylic acid ester polymer When (A) has a carboxyl group, it is preferable to use an epoxy-based crosslinking agent and / or an aziridine-based crosslinking agent excellent in reactivity with the carboxyl group.

  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.

  Examples of the epoxy crosslinking agent include 1,3-bis (N, N′-diglycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl. Examples include ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl aniline, diglycidyl amine and the like.

  Examples of the aziridine-based crosslinking agent include diphenylmethane-4,4′-bis (1-aziridinecarboxamide), trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethanetri-β-aziridinyl. Propionate, toluene-2,4-bis (1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1- (2-methylaziridine), tris-1- (2-methylaziridine) phosphine, And trimethylolpropane tri-β- (2-methylaziridine) propionate.

  It is preferable that content of the crosslinking agent (B) in the adhesive composition P is 0.001-5 mass parts with respect to 100 mass parts of (meth) acrylic acid ester polymer (A), especially 0. It is preferably 0.005 to 2 parts by mass, and more preferably 0.01 to 1 part by mass. The durability improvement effect by the said crosslinking agent (B) is acquired as content of a crosslinking agent (B) is 0.001 mass part or more. When the content of the crosslinking agent (B) exceeds 5 parts by mass, the hydroxyl group or carboxyl group of the (meth) acrylic acid ester polymer (A) reacts with the crosslinking agent (B) in a large amount, and in the pressure-sensitive adhesive. Therefore, the amount of the remaining white is reduced, and the above-described whitening suppression effect may not be obtained.

  For the adhesive composition P, if necessary, various additives usually used for acrylic adhesives, for example, silane coupling agents, antistatic agents, tackifiers, antioxidants, ultraviolet absorbers, light stabilizers. An agent, a softening agent, a filler, a refractive index adjusting agent, and the like can be added.

  As the silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in the molecule, having good compatibility with the pressure-sensitive adhesive component and having light transmittance, for example, a substantially transparent one. Is preferred.

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

  It is preferable that the addition amount of a silane coupling agent is 0.01-1 mass part with respect to 100 mass parts of (meth) acrylic acid ester polymer (A), Especially 0.05-0.5 mass part. Preferably there is.

[Method for producing adhesive composition]
Adhesive composition P produces (meth) acrylic acid ester polymer (A), and the obtained (meth) acrylic acid ester polymer (A) is optionally added with a crosslinking agent (B) or an additive. It can be manufactured by adding.

  The (meth) acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers 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 organic peroxides 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, add a diluting solvent and optionally a crosslinking agent (B) or additive to the solution of the (meth) acrylic acid ester polymer (A). To obtain an adhesive composition P (coating solution) diluted with a solvent.

  Examples of the dilution solvent for diluting the adhesive composition P to form a coating solution include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, methylene chloride, ethylene chloride, and the like. Halogenated hydrocarbons, methanol, ethanol, propanol, butanol, alcohols such as 1-methoxy-2-propanol, acetone, methyl ethyl ketone, ketones such as 2-pentanone, isophorone, cyclohexanone, esters such as ethyl acetate and butyl acetate, ethyl A cellosolv solvent such as cellosolve is 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 10-40 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 the coating solution as it is.

[Adhesive]
The pressure-sensitive adhesive according to this embodiment is obtained by crosslinking the pressure-sensitive adhesive composition P. Here, when the adhesive composition P contains a crosslinking agent (B), the adhesive is formed by crosslinking the adhesive composition P. The pressure-sensitive adhesive composition P can be crosslinked 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 10 seconds to 10 minutes, particularly preferably 50 seconds to 2 minutes. Furthermore, it is particularly preferable to provide a curing period of about 1 to 2 weeks at room temperature (for example, 23 ° C., 50% RH) after the heat treatment.

  The (meth) acrylic acid ester polymer (A) is crosslinked by the heat treatment (and curing). When the adhesive composition P contains a crosslinking agent (B), the (meth) acrylic acid ester polymer (A) is crosslinked by the crosslinking agent (B) to form a three-dimensional network structure.

  The pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition P has a high refractive index by having a plurality of aromatic rings derived from the aromatic ring-containing monomer constituting the (meth) acrylic acid ester polymer (A). It becomes. Specifically, the refractive index is 1.50 or more, particularly preferably 1.51 or more. Here, the refractive index in this specification is a value measured using an Abbe refractometer (Attago's product is used in the test example) under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 23 ° C. The upper limit of the refractive index is not particularly limited, but is usually 1.9 or less.

  The gel fraction of the pressure-sensitive adhesive according to this embodiment is preferably 15 to 90%, particularly preferably 20 to 80%, and more preferably 30 to 70%. When the gel fraction is less than 15%, the cohesive force of the pressure-sensitive adhesive is insufficient, and durability and reworkability may be deteriorated. On the other hand, if the gel fraction exceeds 90%, the adhesive strength may be too low and the durability may be reduced. In addition, the said gel fraction is the value of the adhesive formed after the curing period passed (for example, after storing for 7 days in 23 degreeC and 50% RH environment). If it is unclear whether the curing period has elapsed, after storing again for 7 days in an environment of 23 ° C. and 50% RH, the gel fraction should be within the above range.

[Adhesive sheet]
As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 </ b> A according to the first embodiment is laminated on the pressure-sensitive adhesive layer 11, the pressure-sensitive adhesive layer 11 stacked on the release surface of the release sheet 12, and the pressure-sensitive adhesive layer 11. And the formed base material 13.

  In addition, as shown in FIG. 2, the adhesive sheet 1B according to the second embodiment includes the two release sheets 12a and 12b and the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. And the pressure-sensitive adhesive layer 11 sandwiched between the release sheets 12a and 12b. 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. .

  In any of the pressure-sensitive adhesive sheets 1A and 1B, the pressure-sensitive adhesive layer 11 is made of a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition P described above.

  The thickness of the pressure-sensitive adhesive layer 11 is appropriately determined according to the purpose of use of the pressure-sensitive adhesive sheets 1A and 1B, but is usually in the range of 5 to 100 μm, preferably 10 to 60 μm, for example, for optical members, particularly for polarizing plates. When used as an adhesive layer, it is preferably 10 to 50 μm, particularly preferably 15 to 30 μm.

  There is no restriction | limiting in particular as the base material 13, What was used as a base material sheet of a normal adhesive sheet can be used. For example, in addition to the desired optical member, woven or non-woven fabric using fibers such as rayon, acrylic, polyester, etc .; synthetic paper; paper such as fine paper, glassine paper, impregnated paper, coated paper; metal such as aluminum and copper Foil; Foam such as urethane foam and polyethylene foam; Polyester film such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyurethane film, polyethylene film, polypropylene film, cellulose film such as triacetyl cellulose, polyvinyl chloride film , Polyvinylidene chloride film, polyvinyl alcohol film, ethylene-vinyl acetate copolymer film, polystyrene film, polycarbonate film, acrylic resin film, norbornene resin film, cycloolefin Plastic film such as emission resin film; and the like of two or more kinds of those laminates. The plastic film may be uniaxially stretched or biaxially stretched.

  Examples of the optical member include a polarizing plate (polarizing film), a polarizer, a retardation plate (retarding film), a viewing angle compensation film, a brightness enhancement film, a contrast enhancement film, a liquid crystal polymer film, a diffusion film, and a transflective film. Etc.

  Although the thickness of the base material 13 changes with kinds, for example in the case of an optical member, they are 10 micrometers-500 micrometers normally, Preferably they are 50 micrometers-300 micrometers.

  As the release sheets 12, 12a, 12b, 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 vinyl acetate film, ionomer resin film, ethylene / (meth) acrylic acid copolymer film, ethylene / (meth) acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film A fluororesin film or the like is used. These crosslinked films are also used. Furthermore, these laminated films may be sufficient.

  The release surface of the release sheet (particularly the surface in contact with the pressure-sensitive adhesive layer 11) is preferably subjected to a release treatment. Examples of the release agent used for the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax release agents.

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

  In order to manufacture the pressure-sensitive adhesive sheet 1A, a solution (coating solution) containing the pressure-sensitive adhesive composition P is applied to the release surface of the release sheet 12, and a heat treatment is performed to form a coating layer. The substrate 13 is laminated on the substrate. 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 1A is obtained. In addition, about the conditions of heat processing and curing, it is as having mentioned above.

  Moreover, in order to manufacture the said adhesive sheet 1B, the coating solution containing the said adhesive composition P was apply | coated to the peeling surface of one peeling sheet 12a (or 12b), and the heat treatment was performed, and the coating layer was formed. Thereafter, 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 1B is obtained.

  As a method for applying the coating solution, 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.

  Here, for example, to manufacture a liquid crystal display device composed of a liquid crystal cell and a polarizing plate, a polarizing plate is used as the base material 13 of the pressure-sensitive adhesive sheet 1A, and the release sheet 12 of the pressure-sensitive adhesive sheet 1A is peeled off. What is necessary is just to bond the exposed adhesive layer 11 and a liquid crystal cell.

  For example, in order to manufacture a liquid crystal display device in which a retardation plate is disposed between a liquid crystal cell and a polarizing plate, as an example, first, one release sheet 12a (or 12b) of the adhesive sheet 1B is released. Then, the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet 1B and the phase difference plate are bonded together. Next, the release sheet 12 of the pressure-sensitive adhesive sheet 1A using a polarizing plate as the base material 13 is peeled off, and the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet 1A and the retardation plate are bonded. Furthermore, the other release sheet 12b (or 12a) is peeled from the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet B, and the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet B is bonded to the liquid crystal cell.

  For example, in order to manufacture a laminate of a liquid crystal cell having a glass substrate and a glass substrate having a desired functional layer, as an example, first, one release sheet 12a (or 12b) of the adhesive sheet 1B is peeled off. And the adhesive layer 11 which the adhesive sheet 1B exposed, and the surface by the side of the functional layer of a glass substrate are bonded. Next, the other release sheet 12b (or 12a) is peeled from the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet B, and the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet B and the glass substrate of the liquid crystal cell are bonded.

  The type of the glass substrate is not particularly limited. For example, alkali-free glass, quartz glass, soda lime glass, barium / strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, barium borosilicate glass, etc. Is mentioned. Although the thickness of a glass substrate is not specifically limited, Usually, it is 0.1-5 mm, Preferably it is 0.2-2 mm.

  Here, the pressure-sensitive adhesive layer 11 in the pressure-sensitive adhesive sheets 1A and 1B is, as described above, after the (meth) acrylic acid ester polymer (A) has a predetermined amount of hydroxyl group or carboxyl group, Whitening when the temperature is returned to room temperature is suppressed. For example, the pressure-sensitive adhesive layer 11 having a thickness of 50 μm sandwiched between two non-alkali glasses having a thickness of 1.1 mm is stored for 120 hours under conditions of 85 ° C. and 85% RH, and then 23 ° C. and 50%. When the RH is returned to normal temperature and normal humidity, whitening of the pressure-sensitive adhesive layer 11 is suppressed. Specifically, the haze value (value measured according to JIS K7136: 2000) at that time is preferably 1.0% or less, particularly preferably 0.9% or less, and further 0 .8% or less is preferable.

  In addition, it is preferable that the said adhesive layer 11 has the above haze values also at the normal state. When the haze value is 1.0% or less, the transparency is very high, which is suitable for optical applications.

  Moreover, it is preferable that 1 A of adhesive sheets have the adhesive force with respect to an alkali free glass of 0.1-50 N / 25mm, and it is especially preferable that it is 2-20 N / 25mm. When the adhesive strength is within the above range, it is possible to prevent floating or peeling between the glass plate and the adherend. 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 pressing and pasting the body (non-alkali glass) at 0.5 MPa and 50 ° C. for 20 minutes, it was left for 24 hours under conditions of normal pressure, 23 ° C. and 50% RH, and then the peeling speed was 300 mm / min. Shall be measured.

  According to the above pressure-sensitive adhesive sheets 1A and 1B, since the refractive index of the pressure-sensitive adhesive layer 11 is high, the difference in refractive index between the pressure-sensitive adhesive layer 11 and the optical member is small, and the occurrence of reflection at the interface between them is suppressed. The

  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, the release sheet 12 of the adhesive sheet 1A may be omitted, or one of the release sheets 12a and 12b in the adhesive sheet 1B 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 polymer In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen introduction tube, 40 parts by mass of n-butyl acrylate, o-biphenyloxyethyl acrylate (Shin Nakamura) Chemical Industry Co., Ltd., ALEN10) 50 parts by mass, acrylic acid 10 parts by mass, ethyl acetate 200 parts by mass, and 2,2′-azobisisobutyronitrile 0.18 parts by mass were charged, and the air in the reaction vessel was Replaced with nitrogen gas. While stirring in this nitrogen atmosphere, the reaction solution was heated to 60 ° C., reacted for 16 hours, and then cooled to room temperature. Here, the molecular weight of a part of the obtained solution was measured by a method described later, and production of a (meth) acrylic acid ester polymer (A) having a weight average molecular weight (Mw) of 400,000 was confirmed.

2. Preparation of Adhesive Composition As the (meth) acrylic acid ester polymer (A) obtained in the above step (1) 100 parts by mass (solid content conversion value; the same applies hereinafter) and an epoxy-based crosslinking agent (B), N, N, N ′, N′-tetraglycidyl-m-xylylenediamine (manufactured by Soken Chemical Co., Ltd., trade name “E-AX”) is mixed with 0.05 part by mass, sufficiently stirred, and ethyl acetate By diluting with, a coating solution of the adhesive composition 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]
BA: n-butyl acrylate ALEN10: o-biphenyloxyethyl acrylate AA: acrylic acid HEA: 2-hydroxyethyl acrylate

3. Production of pressure-sensitive adhesive sheet The release-treated surface of a release sheet (SP-PET3811, thickness: 38 μm, manufactured by Lintec Co., Ltd.) obtained by subjecting one side of a polyethylene terephthalate film to a silicone-based release agent. Then, after coating with a knife coater so that the thickness after drying was 25 μm, the coating layer was formed by heat treatment at 90 ° C. for 1 minute.

  Next, a release sheet (SP-PET3801, thickness: 38 μm, manufactured by Lintec Co., Ltd.) obtained by releasing one side of the polyethylene terephthalate film with a silicone release agent is placed on the exposed surface side of the coating layer. The pressure-sensitive adhesive sheet having a constitution of release sheet / pressure-sensitive adhesive layer (thickness: 25 μm) / release sheet was prepared by pasting so as to be in contact with each other and curing for 7 days under conditions of 23 ° C. and 50% RH.

[Examples 2 to 12, Comparative Examples 1 to 6]
Except for changing the type and ratio of each monomer constituting the (meth) acrylic acid ester polymer (A) and the type and blending amount of the crosslinking agent (B) as shown in Table 1, the same manner as in Example 1 was carried out. An adhesive sheet was produced.

The details of the crosslinking agent shown in Table 1 are as follows.
[Crosslinking agent]
Epoxy-based cross-linking agent: N, N, N ′, N′-tetraglycidyl-m-xylylenediamine (trade name “E-AX”, manufactured by Soken Chemical Co., Ltd.)
Aziridine-based cross-linking agent: trimethylolpropane tri-β-aziridinyl propionate (trade name “BXX5172” manufactured by Toyo Ink Co., Ltd.)
Isocyanate-based cross-linking agent: trimethylolpropane adduct xylylene diisocyanate (manufactured by Soken Chemical Co., Ltd., trade name “TD-75”)

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 gel fraction)
The pressure-sensitive adhesive sheets obtained in Examples or Comparative Examples were sampled to a size of 80 mm × 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass of the pressure-sensitive adhesive alone was weighed with a precision balance. . 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. The mass of only the pressure-sensitive adhesive after drying was weighed with a precision balance. The mass at this time is M2. The gel fraction (%) is represented by (M2 / M1) × 100. The results are shown in Table 2.

[Test Example 2] (Measurement of adhesive strength / zipping evaluation)
One release sheet was peeled off from the pressure-sensitive adhesive sheet obtained in Examples or Comparative Examples, and the exposed pressure-sensitive adhesive layer was bonded to a polyethylene terephthalate film (PET100A4300, Toyobo Co., Ltd., thickness: 100 μm) having an easy-adhesion layer. Thereafter, the laminate was cut to prepare a sample having a width of 25 mm and a length of 100 mm. After peeling the release sheet from this sample and pasting the sample on alkali-free glass (Corning, Eagle XG) through the exposed adhesive layer, 0.5 MPa at 50 ° C. in an autoclave manufactured by Kurihara Seisakusho, Pressurized for 20 minutes. Then, after leaving for 24 hours under the conditions of 23 ° C. and 50% RH, using a tensile tester (Orientec, Tensilon), the adhesive strength (N / 25 mm). The results are shown in Table 2.

Moreover, when peeling a sample in the said test, generation | occurrence | production of zipping was confirmed and the following references | standards evaluated. Zipping means that when peeling the adhesive sheet from the adherend, peeling sound is generated without peeling continuously and smoothly, or peeling stripes are formed in the adhesive layer. As a result, the peelability and sticking property are deteriorated. The results are shown in Table 2.
○: No zipping occurred △: Some zipping occurred (a level where there is no problem in peelability and sticking property)
X: Zipping occurs (a level with a problem in peelability or sticking property)

[Test Example 3] (Refractive index measurement)
About the adhesive layer of the adhesive sheet obtained by the Example or the comparative example, the refractive index was measured using the Abbe refractometer (made by Atago Co., Ltd.) on the conditions of measurement wavelength 589nm and measurement temperature 23 degreeC. The results are shown in Table 2.

[Test Example 4] (Moisture and heat whitening evaluation)
Two pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheet obtained in Examples or Comparative Examples were laminated to prepare a pressure-sensitive adhesive layer having a thickness of 50 μm. This pressure-sensitive adhesive layer was sandwiched between two sheets of non-alkali glass having a thickness of 1.1 mm, and the laminate was used as a sample. The obtained sample was stored for 120 hours under the conditions of 85 ° C. and 85% RH. Thereafter, the temperature was returned to room temperature and normal humidity of 23 ° C. and 50% RH, and the presence or absence of whitening was visually confirmed by the following criteria to evaluate moisture and heat whitening resistance, and the haze value of the pressure-sensitive adhesive layer was measured. The haze value was measured according to JIS K7136: 2000 within 30 minutes after returning the sample to room temperature and normal humidity. The results are shown in Table 2.
A: No whitening occurred immediately after returning to normal temperature and humidity.
○: Part of the whitening occurred, but no whitening occurred within 2 hours after returning to normal temperature and humidity.
X: Overall whitening. Or after partial whitening, it was not restored even when stored at normal temperature and humidity.

  As can be seen from Table 2, the pressure-sensitive adhesive of the pressure-sensitive adhesive layer obtained in the examples has a good adhesive force, a high refractive index (1.51 or more), and is excellent in moisture and heat whitening resistance. It was.

  The pressure-sensitive adhesive of the present invention is suitable for adhesion of optical members such as polarizing plates and glass substrates, and the pressure-sensitive adhesive sheet of the present invention is suitable as a pressure-sensitive adhesive sheet for optical members such as polarizing plates and glass substrates.

1A, 1B ... Adhesive sheet 11 ... Adhesive layer 12, 12a, 12b ... Release sheet 13 ... Base material

Claims (13)

As a monomer unit constituting the polymer, an adhesive composition containing as a main component a (meth) acrylic acid ester polymer containing a monomer having a plurality of aromatic rings and a monomer having a carboxyl group,
Content of the monomer having the aromatic ring in the (meth) acrylic acid ester polymer is 10 to 70% by mass,
The content of the monomer having a carboxyl group in the (meth) acrylic acid ester polymer is 10 to 40% by mass,
The adhesive composition, wherein the monomer having a plurality of aromatic rings is a monomer having a biphenyl ring. The pressure-sensitive adhesive composition according to claim 1 , wherein the monomer having a biphenyl ring is biphenyloxy structure-containing (meth) acrylate. The adhesive composition, adhesive composition according to claim 1 or 2, characterized in that it contains a further cross-linking agent. The pressure-sensitive adhesive composition according to claim 3 , wherein the crosslinking agent is at least one selected from the group consisting of an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and an aziridine-based crosslinking agent. The content of the crosslinking agent in the adhesive composition, the (meth) according to claim 3 or 4, characterized in that of the acrylic acid ester polymer 100 parts by weight, and 0.001 to 5 parts by weight The adhesive composition according to 1. The pressure-sensitive adhesive composition according to any one of claims 1 to 5 , wherein the (meth) acrylic acid ester polymer has a weight average molecular weight of 200,000 to 2,000,000. The adhesive which bridge | crosslinks the adhesive composition as described in any one of Claims 1-6 . The pressure-sensitive adhesive according to claim 7 , wherein a refractive index of the pressure-sensitive adhesive is 1.50 or more. The pressure-sensitive adhesive having a thickness of 50 μm sandwiched between two non-alkali glasses having a thickness of 1.1 mm is stored for 120 hours under conditions of 85 ° C. and 85% RH, and then at room temperature and normal humidity of 23 ° C. and 50% RH. The pressure-sensitive adhesive according to claim 7 or 8 , wherein the pressure-sensitive adhesive has a haze value of 1.0% or less. A pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer,
The said adhesive layer consists of an adhesive as described in any one of Claims 7-9 , The adhesive sheet characterized by the above-mentioned. The pressure-sensitive adhesive sheet according to claim 10 , wherein the substrate is an optical member. Two release sheets,
An adhesive sheet comprising 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 7-9 , The adhesive sheet characterized by the above-mentioned. The pressure-sensitive adhesive sheet according to claim 12 , wherein the pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet for bonding two glass substrates together.

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