Adhesives and adhesive sheets

Abstract

To provide an adhesive and an adhesive sheet which have excellent antistatic properties.SOLUTION: Provided is an adhesive for bonding optical members, comprising 100 ppm to 6000 ppm of an aromatic ring-containing monomer. The adhesive is preferably an acrylic adhesive and, preferably, specifically contains a (meth)acrylic acid ester polymer. The (meth)acrylic acid ester polymer preferably contains, as a monomer unit constituting the polymer, an aromatic ring-containing monomer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004]

[0001] The present invention relates to an antistatic adhesive and an adhesive sheet.

Background Art

[0002] In recent years, in touch panels which are display devices in mobile electronic devices such as smartphones and tablet terminals, many projection-type capacitive touch panels are used. As such a projection-type capacitive touch panel in mobile electronic devices, for example, a structure in which, in order from the bottom, a liquid crystal display device (LCD), an adhesive layer, a transparent conductive film (tin-doped indium oxide: ITO), a glass substrate, a transparent conductive film (ITO), and a protective layer such as strengthened glass are laminated has been proposed.

[0003] As a display component constituting the above liquid crystal display device, a liquid crystal cell is generally used. A liquid crystal cell is generally formed by arranging two transparent electrode substrates having alignment layers with the alignment layers facing inward, at a predetermined interval by spacers, sealing the periphery thereof, and sandwiching a liquid crystal material between the two transparent electrode substrates. Usually, polarizing plates are adhered to the outside of the two transparent electrode substrates in the liquid crystal cell via adhesive layers, respectively.

[0004] The above adhesive layer is often used as an adhesive sheet having the adhesive layer and a release sheet (and in some cases, further a polarizing plate). The release sheet or the polarizing plate on which the above adhesive layer is laminated is usually made of a plastic material. Therefore, the electrical insulation is high, and static electricity is likely to be generated when peeling the release sheet. If the polarizing plate is bonded to the liquid crystal cell with the static electricity thus generated remaining, the alignment of liquid crystal molecules may be disturbed, and the presence of static electricity causes problems such as attracting dust and dirt.

[0005] Therefore, in order to obtain effective antistatic performance, it has been proposed to add an antistatic agent to an adhesive composition (for example, Patent Documents 1 and 2).

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-316377 [Patent Document 2] Japanese Patent Publication No. 2008-95081 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, when conventional antistatic agents are added to adhesive compositions, there is a concern that durability under high-temperature conditions may be reduced. Therefore, there is a need for a technology that can achieve the desired antistatic performance even with a reduced amount of antistatic agent.

[0008] This invention has been made in view of the above circumstances, and aims to provide an adhesive and an adhesive sheet with excellent antistatic properties. [Means for solving the problem]

[0009] To achieve the above objective, firstly, the present invention provides an adhesive for bonding optical members, characterized in that it contains an aromatic ring-containing monomer in an amount of 100 ppm or more and 6000 ppm or less (Invention 1).

[0010] The adhesive according to the above invention (Invention 1) exhibits antistatic properties by containing aromatic ring-containing monomers in the above-mentioned amounts. Therefore, even if the amount of antistatic agent added is reduced (including when the amount added is zero) to obtain the desired antistatic properties, excellent antistatic performance can be obtained. Furthermore, because the upper limit of the aromatic ring-containing monomer content is as stated above, deterioration of the durability of the adhesive in optical components due to the aromatic ring-containing monomer is suppressed.

[0011] In the above invention (Invention 1), an acrylic adhesive is preferable (Invention 2).

[0012] In the above inventions (Inventions 1 and 2), it is preferable to include a (meth)acrylic acid ester polymer (Invention 3).

[0013] In the above invention (Invention 3), it is preferable that the (meth)acrylic acid ester polymer contains an aromatic ring-containing monomer as a monomer unit constituting the polymer (Invention 4).

[0014] In the above inventions (Inventions 3 and 4), it is preferable that the (meth)acrylic acid ester polymer is crosslinked with a crosslinking agent (Invention 5).

[0015] In the above inventions (Inventions 1 to 5), it is preferable that the optical member is a polarizing plate (Invention 6).

[0016] Secondly, the present invention provides an adhesive sheet comprising an optical member and an adhesive layer, wherein the adhesive layer is made of the adhesive (Inventions 1 to 6) (Invention 7).

[0017] In the above invention (Invention 7), it is preferable that the optical member is a polarizing plate (Invention 8).

[0018] Thirdly, the present invention provides 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, wherein the adhesive layer is made of the adhesive (Inventions 1 to 6) (Invention 9). [Effects of the Invention]

[0019] The adhesive and adhesive sheet according to the present invention can achieve excellent antistatic performance even with a reduced amount of antistatic agent added. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view of an adhesive sheet according to the first embodiment of the present invention. [Figure 2] Cross-sectional view of the adhesive sheet according to the second embodiment of the present invention.

Mode for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described. 〔Adhesive〕 The adhesive according to one embodiment of the present invention is an adhesive for bonding optical members, and preferably contains an aromatic ring-containing monomer at 100 ppm or more and 6000 ppm or less. When the optical adhesive contains the aromatic ring-containing monomer in the above amount, the adhesive exhibits antistatic properties. Therefore, in order to obtain the desired antistatic properties, excellent antistatic performance can be obtained even if the addition amount of the antistatic agent is reduced (including the case where the addition amount is 0). Further, since the upper limit value of the content of the aromatic ring-containing monomer is as described above, deterioration of the durability of the adhesive in the optical member due to the aromatic ring-containing monomer is suppressed.

[0022] From the viewpoint of antistatic properties, the content of the aromatic ring-containing monomer in the adhesive is preferably 100 ppm or more, more preferably 250 ppm or more, still more preferably 500 ppm or more, particularly preferably 800 ppm or more, and even more preferably 1200 ppm or more. Further, from the viewpoint of the durability of the adhesive in the optical member, the content of the aromatic ring-containing monomer in the adhesive is preferably 6000 ppm or less, more preferably 5500 ppm or less, particularly preferably 5000 ppm or less, even more preferably 4000 ppm or less, and most preferably 3000 ppm or less.

[0023] In this embodiment, the aromatic ring-containing monomer is preferably an acrylic monomer having an aromatic ring, and in particular, a (meth)acrylic acid ester having an aromatic ring is preferred. Examples of aromatic rings include benzene rings, naphthalene rings, anthracene rings, biphenyl rings, fluorene rings, etc., with benzene rings being preferred among them. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same applies to other similar terms.

[0024] Examples of aromatic ring-containing monomers include phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate; phenoxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate and phenoxybutyl (meth)acrylate; aromatic ring and ethylene glycol-containing (meth)acrylates such as phenyldiethylene glycol (meth)acrylate and phenoxydiethylene glycol (meth)acrylate; ethoxylated o-phenylphenol acrylate, ethylene oxide-modified cresol (meth)acrylate, and ethylene oxide-modified nonylphenol (meth)acrylate. Among these, phenoxyalkyl (meth)acrylate is preferred from the viewpoint of antistatic properties, phenoxyethyl (meth)acrylate is particularly preferred, and phenoxyethyl acrylate is even more preferred. These may be used alone or in combination of two or more.

[0025] The type of adhesive according to this embodiment is not particularly limited, as long as it is suitable for optical applications and does not hinder the antistatic effect of aromatic ring-containing monomers. For example, it may be any of acrylic adhesives, polyester adhesives, polyurethane adhesives, rubber adhesives, silicone adhesives, etc. Furthermore, the adhesive may be emulsion type, solvent type, or solvent-free type, and may be crosslinked type or non-crosslinked type. Among these, acrylic adhesives are preferred because they have excellent adhesive properties, optical properties, etc. Among acrylic adhesives, crosslinked types are preferred, and thermal crosslinked types are even more preferred.

[0026] The adhesive according to this embodiment preferably contains a (meth)acrylic acid ester polymer and an aromatic ring-containing monomer, from the viewpoint of suitability for optical applications, and in particular, it is preferable that the adhesive is obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A), a crosslinking agent (B), and an aromatic ring-containing monomer (C). The adhesive obtained by crosslinking adhesive composition P can obtain the desired cohesive force and exhibit durability suitable for optical applications. In this specification, the concept of "polymer" is also included in the concept of "copolymer".

[0027] 1. Components of adhesive composition P (1) (meth)acrylic acid ester polymer (A) In this embodiment, the (meth)acrylic acid ester polymer (A) preferably contains aromatic ring-containing monomers as monomer units constituting the polymer. When aromatic ring-containing monomers are used in the polymerization of the (meth)acrylic acid ester polymer (A), depending on the polymerization conditions, it is possible to leave unpolymerized aromatic ring-containing monomers in the polymerization solution during the polymerization of the (meth)acrylic acid ester polymer (A). In this case, there is the advantage that it is not necessary to separately add aromatic ring-containing monomers (C) to the adhesive (adhesive composition P). Furthermore, when the (meth)acrylic acid ester polymer (A) uses aromatic ring-containing monomers as constituent monomer units, the cohesive force of the resulting adhesive becomes more suitable, and excellent durability is more easily obtained in optical applications.

[0028] As mentioned above, examples of aromatic ring-containing monomers include those described above, but it is preferable to use the same aromatic ring-containing monomer (C) contained in adhesive composition P for polymerization of the (meth)acrylic acid ester polymer (A).

[0029] The (meth)acrylic acid ester polymer (A) preferably contains 1 to 40% by mass of aromatic ring-containing monomers as monomer units, more preferably 6 to 35% by mass, particularly preferably 12 to 30% by mass, and even more preferably 18 to 25% by mass. When the (meth)acrylic acid ester polymer (A) contains aromatic ring-containing monomers in the above amounts as monomer units, the cohesive force of the resulting adhesive becomes more suitable, and it becomes easier to obtain better durability in optical applications.

[0030] In this embodiment, the (meth)acrylic acid ester polymer (A) preferably contains a reactive group-containing monomer as a monomer unit constituting the polymer, which has a reactive group in its molecule that reacts with the crosslinking agent (B). The reactive group derived from this reactive group-containing monomer reacts with the crosslinking agent (B) to form a crosslinked structure (three-dimensional network structure), and an adhesive having the desired cohesive force is obtained.

[0031] Preferred examples of the reactive group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). Among these, hydroxyl group-containing monomers that exhibit excellent reactivity with the crosslinking agent (B) are preferred.

[0032] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylate esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, hydroxyalkyl (meth)acrylate esters having a hydroxyalkyl group with 1 to 4 carbon atoms are preferred from the viewpoint of the reactivity of the hydroxyl group in the resulting (meth)acrylate ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers. Specifically, for example, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0033] Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. These may be used individually or in combination of two or more.

[0034] Examples of amino group-containing monomers include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used individually or in combination of two or more. Note that nitrogen atom-containing monomers, as described later, are excluded from this list of amino group-containing monomers.

[0035] The (meth)acrylic acid ester polymer (A) preferably contains 0.1 to 20% by mass of reactive group-containing monomers as monomer units constituting the polymer, more preferably 0.5 to 12% by mass, particularly preferably 1 to 8% by mass, and even more preferably 2 to 5% by mass. When the (meth)acrylic acid ester polymer (A) contains the above amounts of reactive group-containing monomers as monomer units, a good crosslinked structure is formed in the resulting adhesive, making it easier to obtain better durability in optical applications.

[0036] Furthermore, it is preferable that the (meth)acrylic acid ester polymer (A) does not contain carboxyl group-containing monomers as monomer units constituting the polymer. Since carboxyl groups are acidic components, by not containing carboxyl group-containing monomers, it is possible to suppress problems caused by acid (corrosion, changes in resistance, etc.) even when the object to which the adhesive is applied has transparent conductive films such as tin-doped indium oxide (ITO) or metal films present. However, it is permissible to include a predetermined amount of carboxyl group-containing monomers to the extent that such problems do not occur. Specifically, it is permissible to include carboxyl group-containing monomers as monomer units in the (meth)acrylic acid ester polymer (A) in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

[0037] In this embodiment, the (meth)acrylic acid ester polymer (A) preferably contains an alkyl (meth)acrylic acid ester as a monomer unit constituting the polymer. This allows for the development of good tackiness. The alkyl group may be linear or branched.

[0038] As for alkyl (meth)acrylate esters, from the viewpoint of adhesiveness, alkyl (meth)acrylate esters with 1 to 20 carbon atoms in the alkyl group are preferred. Examples of alkyl (meth)acrylate esters with 1 to 20 carbon atoms in the alkyl group include methyl (meth)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, and stearyl (meth)acrylate. Among these, from the viewpoint of further improving adhesiveness, alkyl (meth)acrylate esters with 1 to 8 carbon atoms in the alkyl group are preferred, and methyl (meth)acrylate, n-butyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate are particularly preferred. These can be used individually or in combination of two or more types.

[0039] The (meth)acrylic acid ester polymer (A) preferably contains 40 to 99% by mass of alkyl (meth)acrylate as a monomer unit constituting the polymer, particularly preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass. When the lower limit of the alkyl (meth)acrylate content is as described above, the resulting adhesive is more likely to exhibit adhesive strength suitable for optical applications. Furthermore, when the upper limit of the alkyl (meth)acrylate content is as described above, other monomer components such as aromatic ring-containing monomers can be introduced into the (meth)acrylic acid ester polymer (A) in suitable amounts.

[0040] The above (meth)acrylic acid ester polymer (A) preferably contains monomers having an alicyclic structure within the molecule (alicyclic structure-containing monomers) as monomer units constituting the polymer. Since alicyclic structure-containing monomers are bulky, it is presumed that their presence in the polymer widens the spacing between polymer molecules, making the resulting adhesive highly flexible. On the other hand, the alicyclic structure-containing monomers themselves can impart a certain degree of hardness to the polymer. Therefore, by having alicyclic structure-containing monomers as constituent monomer units in the (meth)acrylic acid ester polymer (A), it becomes easier to obtain better durability in optical applications.

[0041] In monomers containing an alicyclic structure, the carbon rings of the alicyclic structure may be saturated or may have some unsaturated bonds. Furthermore, the alicyclic structure may be monocyclic or polycyclic, such as bicyclic or tricyclic structures. Similarly, from the viewpoint of adjusting the physical properties of the resulting adhesive, the alicyclic structure is preferably polycyclic. Moreover, considering the compatibility between the (meth)acrylic acid ester polymer (A) and other components, the polycyclic structure is particularly preferably bicyclic to tetracyclic. Similarly, from the viewpoint of adjusting the physical properties of the resulting adhesive, the number of carbon atoms in the alicyclic structure (referring to the total number of carbon atoms in the ring-forming portion, and the total number of carbon atoms if multiple rings exist independently) is usually preferably 5 or more, and particularly preferably 7 or more. On the other hand, there is no particular upper limit to the number of carbon atoms in the alicyclic structure, but similar to the above, from the viewpoint of compatibility, it is preferably 15 or less, and particularly preferably 10 or less.

[0042] Examples of monomers containing the alicyclic structure mentioned above include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. Among these, dicyclopentanyl (meth)acrylate (10 carbon atoms in the alicyclic structure), adamantyl (10 carbon atoms in the alicyclic structure), or isobornyl (7 carbon atoms in the alicyclic structure) are preferred because they exhibit superior durability, with isobornyl (meth)acrylate being particularly preferred. These may be used individually or in combination of two or more.

[0043] The (meth)acrylic acid ester polymer (A) preferably contains 1 to 25% by mass of alicyclic structure-containing monomers as monomer units constituting the polymer, more preferably 2 to 15% by mass, particularly preferably 3 to 10% by mass, and even more preferably 4 to 7% by mass. Having the alicyclic structure-containing monomer content within the above range makes it easier to obtain superior durability in optical applications.

[0044] The (meth)acrylic acid ester polymer (A) may optionally contain other monomers as monomer units constituting the polymer. Among the other monomers, monomers that do not contain reactive functional groups are preferred in order not to inhibit the aforementioned effects of the reactive functional group-containing monomers. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used individually or in combination of two or more.

[0045] The (meth)acrylic acid ester polymer (A) is preferably a linear polymer. Being a linear polymer makes it easier for molecular chains to intertwine, which in turn makes it easier to obtain an adhesive with the desired cohesive force.

[0046] Furthermore, it is preferable that the (meth)acrylic acid ester polymer (A) is a solution polymer obtained by a solution polymerization method. Being a solution polymer makes it easier to obtain a high molecular weight polymer, which can be expected to improve cohesive strength, thus making it easier to obtain an adhesive with excellent durability.

[0047] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0048] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 600,000 to 3,000,000, more preferably 900,000 to 2,600,000, particularly preferably 1,200,000 to 2,400,000, and even more preferably 1,600,000 to 2,200,000. When the weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is within the above range, excellent durability is more easily obtained in optical applications. The weight-average molecular weight in this specification is the value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0049] In the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more types.

[0050] (2) Crosslinking agent (B) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) upon heating of the adhesive composition P, enabling the formation of a good three-dimensional network structure. This improves the cohesive strength of the resulting adhesive, making it easier to obtain excellent durability in optical applications.

[0051] The crosslinking agent (B) can be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A). Examples include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, and ammonium salt crosslinking agents. Among these, if the reactive group of the (meth)acrylic acid ester polymer (A) is a hydroxyl group, it is preferable to use an isocyanate crosslinking agent that has excellent reactivity with hydroxyl groups. The crosslinking agent (B) can be used alone or in combination of two or more types.

[0052] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds 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 their biuret and isocyanurate forms, as well as adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

[0053] The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.001 to 2 parts by mass, more preferably 0.01 to 1 part by mass, particularly preferably 0.05 to 0.5 parts by mass, and even more preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). Having the crosslinking agent (B) content within the above range makes it easier to obtain superior durability in optical applications.

[0054] (3) Aromatic ring-containing monomer (C) The type of aromatic ring-containing monomer (C) is as described above. Furthermore, the content of aromatic ring-containing monomer (C) in the adhesive composition P is the same as the content of aromatic ring-containing monomer in the adhesive, as described above.

[0055] (4) Various additives The adhesive composition P may optionally contain various additives commonly used in acrylic adhesives, such as silane coupling agents, antistatic agents, rust inhibitors, ultraviolet absorbers, tackifiers, antioxidants, light stabilizers, softeners, and refractive index modifiers. The polymerization solvent and diluent solvent described later are not included in the additives constituting the adhesive composition P.

[0056] The adhesive composition P preferably contains a silane coupling agent. This improves adhesion to the adherend, whether the optical component is a plastic or glass component, resulting in superior durability.

[0057] As a silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in its molecule is preferred, which has good compatibility with the (meth)acrylic acid ester polymer (A) and is light-transmitting.

[0058] Examples of such silane coupling agents include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane. Examples include amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; 3-isocyanatetopropyltriethoxysilane; or condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These may be used individually or in combination of two or more.

[0059] Among the silane coupling agents listed above, from the viewpoint of achieving both antistatic properties and durability, it is preferable to use any of the following: a silicon compound having an epoxy structure, a silicon compound containing a mercapto group, a silicon compound containing an alkyl group, or a condensate of a silicon compound containing a mercapto group and a silicon compound containing an alkyl group. It is more preferable to use a silicon compound having an epoxy structure and a silicon compound containing a mercapto group in combination, or a silicon compound having an epoxy structure and a silicon compound containing an alkyl group in combination, or a silicon compound having an epoxy structure and a condensate of a silicon compound containing a mercapto group and a silicon compound containing an alkyl group in combination. In particular, it is preferable to use a silicon compound having an epoxy structure and a condensate of a silicon compound containing a mercapto group and a silicon compound containing an alkyl group in combination, and it is even more preferable to use 3-glycidoxypropyltrimethoxysilane and a condensate of 3-mercaptopropyltrimethoxysilane and methyltrimethoxysilane in combination.

[0060] The content of the silane coupling agent in the adhesive composition P is preferably 0.01 to 3 parts by mass, more preferably 0.1 to 2 parts by mass, particularly preferably 0.2 to 1 part by mass, and even more preferably 0.3 to 0.6 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). Having the silane coupling agent content within the above range makes it easier to obtain superior durability in optical applications.

[0061] Furthermore, when a silicon compound having an epoxy structure and a condensate of a mercapto group-containing silicon compound and an alkyl group-containing silicon compound are used in combination as silane coupling agents in the adhesive composition P, the content of the silicon compound having an epoxy structure is preferably 0.01 to 3 parts by mass, particularly preferably 0.05 to 1 part by mass, and even more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of (meth)acrylic acid ester polymer (A). The content of the condensate of a mercapto group-containing silicon compound and an alkyl group-containing silicon compound is preferably 0.01 to 3 parts by mass, particularly preferably 0.05 to 1 part by mass, and even more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of (meth)acrylic acid ester polymer (A). When the content of the silane coupling agents (silicon compound having an epoxy structure and condensate of a mercapto group-containing silicon compound and an alkyl group-containing silicon compound) is within the above ranges, it becomes easier to obtain better durability in optical applications.

[0062] The adhesive composition P may contain an antistatic agent to obtain the desired antistatic properties. However, in this embodiment, since the aromatic ring-containing monomer (C) has antistatic properties, the amount of antistatic agent can be less than usual. Specifically, the amount of antistatic agent in the adhesive composition P is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, particularly preferably 1 to 10 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). By using such a small amount of antistatic agent, it is possible to suppress the decrease in the durability of the adhesive layer 11 in the optical member due to the antistatic agent.

[0063] Examples of antistatic agents include ionic compounds, anionic surfactants, alkali metal salts, cationic surfactants, and nonionic surfactants. Among these, it is preferable to use at least one selected from ionic compounds and alkali metal salts.

[0064] Preferred ionic compounds include nitrogen-containing onium salts, sulfur-containing onium salts, and phosphorus-containing onium salts. Preferred alkali metal salts include lithium salts and potassium salts. These may be used individually or in combination of two or more. Among the above, nitrogen-containing onium salts are preferred, ionic compounds of nitrogen-containing onium salts are particularly preferred, and pyridinium salt-based ionic compounds are even more preferred.

[0065] 2. Manufacturing of adhesives In the manufacture of the adhesive, firstly, the polymerization of the (meth)acrylic acid ester polymer may be carried out so that the content of aromatic ring-containing monomers remaining in the adhesive (adhesive composition P) is 100 ppm or more and 6000 ppm or less. Secondly, aromatic ring-containing monomers may be added to a system (polymerization solution) containing a polymer as the main adhesive, preferably a (meth)acrylic acid ester polymer, so that the content of aromatic ring-containing monomers in the adhesive (adhesive composition P) is 100 ppm or more and 6000 ppm or less.

[0066] Adhesive composition P can preferably be prepared by polymerizing a (meth)acrylic acid ester polymer (A), and then adding a crosslinking agent (B) and, optionally, an aromatic ring-containing monomer (C), additives, etc., to the polymerized solution of the (meth)acrylic acid ester polymer (A) obtained (which may optionally contain an aromatic ring-containing monomer (C)).

[0067] (Meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer using a radical polymerization method. Polymerization of (meth)acrylic acid ester polymer (A) is preferably carried out by solution polymerization using a polymerization initiator if desired. At this time, by adjusting the polymerization conditions (polymerization temperature, etc.) and the amount of crosslinking agent, an unpolymerized aromatic ring-containing monomer may remain in the polymerization solution in a desired amount. However, the present invention is not limited thereto, and polymerization may also be carried out without a solvent. Examples of polymerization solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more types may be used in combination.

[0068] Examples of polymerization initiators include azo compounds and organic peroxides, and two or more may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane1-carbonitride), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

[0069] Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

[0070] Furthermore, in the polymerization process described above, the weight-average molecular weight of the resulting polymer can be adjusted by incorporating a chain transfer agent such as 2-mercaptoethanol.

[0071] Once the (meth)acrylic acid ester polymer (A) is obtained, a crosslinking agent (B), and optionally a diluent, aromatic ring-containing monomer (C), additives, etc., are added to the polymerization solution of the (meth)acrylic acid ester polymer (A), and the mixture is thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). If any of the above components are used in solid form, or if precipitation occurs when mixed with other components in an undiluted state, that component may be dissolved or diluted in a diluent solvent beforehand before mixing with the other components.

[0072] Examples of the diluent solvents used 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; alcohols such as methanol, ethanol, propanol, butanol, and 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.

[0073] The concentration and viscosity of the coating solution prepared in this manner are not particularly limited, as long as they are within the range of coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. Note that the addition of a diluent is not a necessary condition when obtaining the coating solution; if the adhesive composition P has a viscosity suitable for coating, a diluent may not be added. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used directly as the diluent.

[0074] An adhesive is obtained by crosslinking the adhesive composition P. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. This heat treatment can also be combined with the drying treatment to volatilize the diluent solvent, etc., from the coating film of the adhesive composition P applied to the desired object.

[0075] The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

[0076] After heat treatment, a curing period of 1 to 2 weeks at room temperature (e.g., 23°C, 50% RH) may be allowed if necessary. If a curing period is required, the adhesive will be formed after the curing period has elapsed; if a curing period is not required, the adhesive will be formed after the heat treatment is completed.

[0077] Through the above heat treatment (and curing), the (meth)acrylic acid ester polymer (A) is crosslinked via the crosslinking agent (B), and an adhesive is obtained.

[0078] 3. Physical properties of adhesives The gel fraction of the above adhesive is preferably 30-90%, more preferably 40-80%, particularly preferably 50-70%, and even more preferably 55-64%. This allows the adhesive to exhibit good cohesive strength and superior durability. The method for measuring the gel fraction of the adhesive is as shown in the test examples described later.

[0079] [Adhesive sheet] The adhesive sheet according to this embodiment has an adhesive layer made of the adhesive described above. A specific configuration of an example of the adhesive sheet according to this embodiment is shown in Figures 1 and 2.

[0080] As shown in Figure 1, the adhesive sheet 1A according to the first embodiment consists of a release sheet 12, an adhesive layer 11 laminated on the release surface of the release sheet 12, and an optical member 13 laminated on the adhesive layer 11.

[0081] Furthermore, as shown in Figure 2, the adhesive sheet 1B according to the second embodiment consists of two release sheets 12a and 12b, and an adhesive layer 11 sandwiched between 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. In this specification, the release surface of a release sheet refers to the surface of the release sheet that has release properties, and includes both surfaces that have undergone a release treatment and surfaces that exhibit release properties even without a release treatment.

[0082] 1. Each component (1) Adhesive layer The adhesive layer 11 is composed of the adhesive described above, and preferably, an adhesive formed by crosslinking the adhesive composition P.

[0083] In the adhesive sheets 1A and 1B according to this embodiment, the thickness of the adhesive layer 11 (a value measured in accordance with JIS K7130) is preferably 1 μm or more, more preferably 5 μm or more, particularly preferably 10 μm or more, and even more preferably 15 μm or more. This makes it easier to obtain the desired adhesive strength and exhibit the desired antistatic properties. Furthermore, the thickness of the adhesive layer 11 is preferably 100 μm or less, more preferably 75 μm or less, particularly preferably 50 μm or less, and even more preferably 30 μm or less. This results in good processability. The adhesive layer 11 may be formed as a single layer or as multiple layers laminated together.

[0084] (2) Release sheet The release sheets 12, 12a, and 12b protect the adhesive layer 11 until the adhesive sheets 1A and 1B are used, and are peeled off when the adhesive sheets 1A and 1B (adhesive layer 11) are used. In the adhesive sheet 1A according to this embodiment, the release sheet 12 is not necessarily required. Also, in the adhesive sheet 1B according to this embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

[0085] Examples of release sheets 12, 12a, and 12b include 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, fluororesin film, etc. Crosslinked films of these can also be used. Furthermore, laminated films of these may also be used.

[0086] It is preferable that the release surfaces of the above-mentioned release sheets 12, 12a, and 12b (especially the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of release agents used in the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax-based release agents. It is also preferable that the release agent used in the release treatment contains an antistatic agent or an aromatic ring-containing monomer. This improves the antistatic performance when the release sheets 12, 12a, and 12b are peeled from the adhesive layer 11. It is preferable that one of the release sheets 12a and 12b be a heavy-peel type release sheet with a high peeling force, and the other release sheet be a light-peel type release sheet with a low peeling force.

[0087] There are no particular restrictions on the thickness of the release sheets 12, 12a, and 12b, but they are usually around 20 to 150 μm.

[0088] (3) Optical components Examples of optical members 13 in the adhesive sheet 1A according to this embodiment include polarizing plates (polarizing films), polarizers, phase difference plates (phase difference films), viewing angle compensation films, brightness enhancement films, contrast enhancement films, liquid crystal polymer films, diffusion films, and semi-transparent reflective films. Among these, polarizing plates (polarizing films) are particularly suitable as optical members 13 laminated with the adhesive (adhesive layer 11) in this embodiment because they are prone to shrinkage and undergo large dimensional changes, thus requiring durability.

[0089] The thickness of the optical element 13 varies depending on its type, but for example, in the case of a polarizing plate, it is preferably 10 μm to 500 μm, particularly preferably 50 μm to 300 μm, and even more preferably 80 μm to 150 μm.

[0090] 2. Physical properties (1)Surface resistivity In measuring surface resistivity, a laminate of the adhesive layer 11 of adhesive sheets 1A and 1B and a polyethylene terephthalate (PET) film with a thickness of 50 μm is used as the sample. When a voltage of 100V is applied to the sample for 30 seconds under conditions of 23°C and 50% relative humidity, the surface resistivity of the adhesive side of the adhesive layer 11 (the side opposite to the PET film) is preferably 3.1 GΩ / sq or less, more preferably 3 GΩ / sq or less, particularly preferably 2.6 GΩ / sq or less, and even more preferably 2.1 GΩ / sq or less. This results in excellent antistatic properties, and for example, it is possible to effectively suppress the generation of static electricity when peeling the release sheets 12, 12a, and 12b from the adhesive layer 11. The lower limit of the above surface resistivity is not particularly limited, but it is usually preferably 0.1 GΩ / sq or more, particularly preferably 0.4 GΩ / sq or more, and even more preferably 0.7 GΩ / sq or more, from the viewpoint of compatibility with durability.

[0091] The above surface resistivity values ​​were measured in accordance with JIS K6911, and the details of the measurement method for this surface resistivity are shown in the test examples described later.

[0092] (2) Adhesive strength The adhesive strength of adhesive sheets 1A and 1B to soda-lime glass is preferably 0.1 to 50 N / 25 mm, more preferably 0.8 to 25 N / 25 mm, particularly preferably 0.8 to 10 N / 25 mm, and even more preferably 1 to 5 N / 25 mm. When the lower limit of the adhesive strength is as described above, excellent durability is easily obtained in optical applications. Furthermore, when the upper limit of the adhesive strength is as described above, good reworkability is obtained, and if a bonding error occurs, expensive liquid crystal cells and the like can be reused. From the viewpoint of achieving both antistatic properties and durability, the adhesive strength is preferably 1.2 to 4 N / 25 mm, particularly preferably 1.5 to 3 N / 25 mm, and even more preferably 1.6 to 2.5 N / 25 mm.

[0093] Herein, the adhesive strength referred to herein basically means the adhesive strength measured by the 180-degree peel method in accordance with JIS Z0237:2009. The measurement sample shall be 25 mm wide and 100 mm long, and the measurement sample shall be attached to the substrate, pressurized at 0.5 MPa and 50°C for 20 minutes, left for 24 hours under normal pressure, 23°C, and 50% RH conditions, and then measured at a peeling speed of 300 mm / min.

[0094] 3. Manufacturing of adhesive sheets As an example of the manufacturing of adhesive sheets 1A and 1B, we will describe the case in which the above-mentioned adhesive composition P is used.

[0095] To manufacture the adhesive sheet 1A, a solution containing the adhesive composition P (coating solution) is applied to the release surface of the release sheet 12, and the adhesive composition P is thermally crosslinked by heat treatment to form a coating layer. Then, the optical member 13 is laminated onto this adhesive layer 11. If a curing period is required, a curing period is allowed; if a curing period is not required, the coating layer becomes the adhesive layer 11 as is. This yields the adhesive sheet 1A. The conditions for heat treatment and curing are as described above.

[0096] Furthermore, to manufacture the adhesive sheet 1B, a coating solution containing the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and the adhesive composition P is thermally crosslinked by heat treatment to form a coating layer. Then, the release surface of the other release sheet 12b (or 12a) is placed on top of this adhesive layer 11. If a curing period is required, a curing period is allowed; if a curing period is not required, the coating layer becomes the adhesive layer 11 as is. This yields the adhesive sheet 1B. The conditions for heat treatment and curing are as described above.

[0097] Methods for applying the coating solution of the above-mentioned adhesive composition P include, for example, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0098] 4. Use of adhesive sheets Here, we will describe a method for manufacturing a touch panel comprising, for example, a liquid crystal cell with a transparent conductive film formed on one side, a polarizing plate laminated on the transparent conductive film, and a polarizing plate laminated on the other side of the liquid crystal cell. In the first method, two adhesive sheets 1A using polarizing plates as optical members 13 are prepared, the release sheet 12 of the first adhesive sheet 1A is peeled off and the exposed adhesive layer 11 is bonded to the transparent conductive film formed on one side of the liquid crystal cell, and the release sheet 12 of the second adhesive sheet 1A is peeled off and the exposed adhesive layer 11 is bonded to the other side of the liquid crystal cell.

[0099] In the second method, two adhesive sheets 1B are prepared. One release sheet 12a (or 12b) of the first adhesive sheet 1B is peeled off, and the exposed adhesive layer 11 is bonded to the transparent conductive film formed on one side of the liquid crystal cell. Then, one release sheet 12a (or 12b) of the second adhesive sheet 1B is peeled off, and the exposed adhesive layer 11 is bonded to the other side of the liquid crystal cell. Next, the other release sheet 12b (or 12a) of the first adhesive sheet 1B is peeled off, and the exposed adhesive layer 11 is bonded to the polarizing plate. Similarly, the other release sheet 12b (or 12a) of the second adhesive sheet 1B is peeled off, and the exposed adhesive layer 11 is bonded to the polarizing plate.

[0100] The adhesive layer 11 in the adhesive sheets 1A and 1B according to this embodiment has excellent antistatic properties, so it can effectively suppress the generation of static electricity when peeling off the release sheets 12, 12a, and 12b from the adhesive layer 11. This makes it possible to suppress, for example, the disruption of the orientation of liquid crystal molecules when laminating a polarizing plate to a liquid crystal cell.

[0101] Furthermore, the adhesive layer 11 in the adhesive sheets 1A and 1B according to this embodiment can exhibit excellent antistatic performance even with a reduced amount of antistatic agent added, and can suppress a decrease in durability caused by the antistatic agent. Moreover, if the content of aromatic ring-containing monomer is below a predetermined amount, a decrease in durability caused by the aromatic ring-containing monomer can be suppressed. As a result, the adhesive layer 11 has excellent durability, and even under high-temperature conditions, lifting, peeling, foaming, etc., between the adhesive layer 11 and the optical member 13 or the adherend is prevented or suppressed. In particular, even when the optical member 13 is a polarizing plate, the stress that may be generated by the deformation of the polarizing plate can be absorbed and mitigated by the adhesive layer 11, thereby exhibiting excellent durability.

[0102] In this specification, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "preferably greater than X" or "preferably less than Y." Similarly, when "greater than or equal to X" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "less than or equal to Y" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y."

[0103] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it. Accordingly, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0104] For example, the release sheet 12 of adhesive sheet 1A may be omitted, and either the release sheets 12a or 12b of adhesive sheet 1B may be omitted. [Examples]

[0105] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0106] [Example 1] 1. Preparation of (meth)acrylic acid ester polymers In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 72 parts by mass of n-butyl acrylate, 20 parts by mass of phenoxyethyl acrylate, 5 parts by mass of isobornyl acrylate, 3 parts by mass of 2-hydroxyethyl acrylate, 200 parts by mass of ethyl acetate, and 0.06 parts by mass of 2,2'-azobisisobutyronitrile were charged, and the air in the reaction vessel was replaced with nitrogen gas. Under this nitrogen atmosphere, the reaction solution was heated to 60°C while stirring and reacted for 16 hours, after which it was cooled to room temperature. At this point, the molecular weight of a portion of the obtained solution was measured by the method described later, and the formation of a (meth)acrylic acid ester polymer (A) with a weight-average molecular weight of 1.75 million was confirmed.

[0107] 2. Preparation of adhesive composition 100 parts by mass (on a solid content basis; the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained in step (1) above, 0.15 parts by mass of trimethylolpropane-modified xylylene diisocyanate (manufactured by Mitsui Chemicals, product name "Takenate D110N") as a crosslinking agent (B), 6.0 parts by mass of 1-decylpyridium bis(fluorosulfonyl)imide as an antistatic agent (C), 0.2 parts by mass of 3-glycidoxypropyltrimethoxysilane and 0.2 parts by mass of a condensate of 3-mercaptopropyltrimethoxysilane and methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "X-41-1810") as silane coupling agents were mixed, stirred thoroughly, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition.

[0108] 3. Manufacturing of adhesive sheets The obtained adhesive composition coating solution was applied using a knife coater to the peeled surface of a heavy-peel type release sheet (Lintec Corporation, product name "SP-PET752150"), in which one side of a polyethylene terephthalate film had been peeled with a silicone-based release agent, and then heated at 90°C for 1 minute to form a coating layer.

[0109] Next, the coating layer on the heavy-peel release sheet obtained above and a light-peel release sheet (Lintec Corporation, product name "SP-PET381031"), which was obtained by peeling one side of a polyethylene terephthalate film with a silicone-based release agent, were bonded together so that the peeled surface of the light-peel release sheet was in contact with the coating layer, thereby producing an adhesive sheet consisting of a heavy-peel release sheet / adhesive coating layer (thickness: 20 μm) / light-peel release sheet.

[0110] The thickness of the adhesive layer mentioned above was measured in accordance with JIS K7130 using a constant-pressure thickness measuring instrument (Teclock Co., Ltd., product name "PG-02") (the same applies hereafter).

[0111] [Example 2] The release liner was peeled off the adhesive sheet manufactured in Example 1 to expose the adhesive layer. The adhesive sheet was then heated at 100°C dry for 3 minutes to obtain the adhesive sheet according to Example 2.

[0112] [Example 3] The release liner was peeled off the adhesive sheet manufactured in Example 1 to expose the adhesive layer. The adhesive sheet was then heated at 100°C dry for 1 minute to obtain the adhesive sheet according to Example 3.

[0113] [Example 4] In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 72 parts by mass of n-butyl acrylate, 20 parts by mass of phenoxyethyl acrylate, 5 parts by mass of isobornyl acrylate, 3 parts by mass of 2-hydroxyethyl acrylate, 200 parts by mass of ethyl acetate, and 0.08 parts by mass of 2,2'-azobisisobutyronitrile were charged, and the air in the reaction vessel was replaced with nitrogen gas. Under this nitrogen atmosphere, the reaction solution was heated to 60°C while stirring and reacted for 16 hours, after which it was cooled to room temperature. At this point, the molecular weight of a portion of the obtained solution was measured by the method described later, and the formation of a (meth)acrylic acid ester polymer (A) with a weight-average molecular weight of 1.8 million was confirmed.

[0114] 100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained in the above process, 0.15 parts by mass of trimethylolpropane-modified xylylene diisocyanate (manufactured by Mitsui Chemicals, product name "Takenate D110N") as a crosslinking agent (B), 6.0 parts by mass of 1-decylpyridium bis(fluorosulfonyl)imide as an antistatic agent (C), 0.2 parts by mass of 3-glycidoxypropyltrimethoxysilane and 0.2 parts by mass of a condensate of 3-mercaptopropyltrimethoxysilane and methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "X-41-1810") as silane coupling agents, and 0.15 parts by mass of phenoxyethyl acrylate monomer were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition.

[0115] Using the coating solution of the obtained adhesive composition, an adhesive sheet was manufactured in the same manner as in Example 1.

[0116] [Example 5] An adhesive sheet was manufactured in the same manner as in Example 4, except that the amount of phenoxyethyl acrylate monomer in the adhesive composition was changed to 0.50 parts by mass.

[0117] [Example 6] An adhesive sheet was manufactured in the same manner as in Example 4, except that the amount of phenoxyethyl acrylate monomer in the adhesive composition was changed to 1.00 part by mass.

[0118] [Example 7] An adhesive sheet was manufactured in the same manner as in Example 4, except that the amount of phenoxyethyl acrylate monomer in the adhesive composition was changed to 3.00 parts by mass.

[0119] [Comparative Example 1] The release liner was peeled off the adhesive sheet manufactured in Example 1 to expose the adhesive layer. The adhesive sheet was then heated at 100°C dry for 10 minutes to obtain the adhesive sheet according to Comparative Example 1.

[0120] [Comparative Example 2] An adhesive sheet was manufactured in the same manner as in Example 4, except that the amount of phenoxyethyl acrylate monomer in the adhesive composition was changed to 5.00 parts by mass.

[0121] The weight-average molecular weight (Mw) mentioned above is the weight-average molecular weight in polystyrene terms, measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). <Measurement conditions> • GPC measuring device: Tosoh Corporation, HLC-8020 • GPC column (passes through in the following order): Manufactured by Tosoh Corporation TSK Guard Column HXL-H TSK gel GMHXL (x2) TSK gel G2000HXL • Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0122] [Test Example 1] (Measurement of PhEA monomer content) The light-peel release liner was peeled off from the adhesive sheets produced in the examples and comparative examples, and the exposed adhesive layer was attached to a polyethylene terephthalate (PET) film (thickness: 50 μm). After cutting this laminate to a size of 40 mm x 25 mm, the heavy-peel release liner was peeled off and used as a sample. In the case of the adhesive sheets in Examples 2 and 3 and Comparative Example 1, the light-peel release liner had already been peeled off, so the adhesive layer after the predetermined heat treatment was attached to the PET film.

[0123] The above samples were placed in vials and set in autosamplers (Shimadzu Corporation, product name "GC-2010" / PerkinElmer, product name "TurboMatrix 40"), heated at 120°C for 20 minutes, and then the content (ppm) of phenoxyethyl acrylate monomer (PhEA monomer) in the adhesive was measured by flame ionization detection (FID). The results are shown in Table 1.

[0124] [Test Example 2] (Measurement of gel fraction) The adhesive sheets produced in the examples and comparative examples were cut to a size of 80 mm x 80 mm, and each adhesive layer was wrapped in a polyester mesh (mesh size 200). The mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. This mass was denoted as M1.

[0125] Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. Afterward, the adhesive was removed and air-dried for 24 hours at 23°C and 50% relative humidity, followed by 12 hours of drying in an oven at 80°C. After drying, its mass was measured using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. This mass was denoted as M2. The gel fraction (%) is expressed as (M2 / M1) × 100. The gel fraction (%) of the adhesive was then derived. The results are shown in Table 1.

[0126] [Test Example 3] (Measurement of surface resistivity) The light-peel release liner was peeled off from the adhesive sheets manufactured in the examples and comparative examples, and the exposed adhesive layer was attached to a polyethylene terephthalate (PET) film (thickness: 50 μm). After cutting this laminate to a size of 40 mm × 40 mm, the heavy-peel release liner was peeled off, and the surface resistivity of the adhesive surface of the exposed adhesive layer was measured in accordance with JIS K6911. Specifically, under conditions of 23°C and 50% RH, the surface resistivity (GΩ / sq) of the adhesive surface of the adhesive layer was measured after applying a voltage of 100 V for 30 seconds to the adhesive sheet from which the heavy-peel release liner had been peeled off, using a resistivity meter (Mitsubishi Analytec Co., Ltd., product name "Highresta UP MCP-HT450"). The results are shown in Table 1.

[0127] [Test Example 4] (Measurement of Adhesion) The release liner was peeled off from the adhesive sheets produced in the examples and comparative examples, and the exposed adhesive layer was attached to a polyethylene terephthalate (PET) film (thickness: 50 μm). This laminate was cut to a size of 25 mm x 110 mm and used as a sample.

[0128] The heavy-peel release sheet was peeled off the above sample, and the sample was attached to soda-lime glass (manufactured by Kawamura Kyuzo Shoten Co., Ltd., product name "FL 1.1t 105±0.2×140±0.2") via the exposed adhesive layer. The sample was then pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. After that, it was left for 24 hours under normal pressure, 23°C, and 50% RH conditions, and then the adhesive strength was measured using a tensile testing machine (manufactured by A&D Co., Ltd., product name "TENSILON RTG-1225") in accordance with JIS Z0237:2009, under conditions of a peeling speed of 300 mm / min and a peeling angle of 180°. The results are shown in Table 1.

[0129] [Test Example 5] (Evaluation of Durability) The release liner was peeled off from the adhesive sheets prepared in the examples and comparative examples to expose the adhesive layer. Next, a 100 μm thick polarizing plate, made by protecting one side of a polyvinyl alcohol film polarizer with a triacetylcellulose film and the other side with a cycloolefin polymer film, was laminated to the adhesive layer so that the exposed surface of the adhesive layer and the surface of the cycloolefin polymer film were in contact. The polarizing plate was then cut to a size of 200 mm × 150 mm so that the polarization axis and the long side of the polarizing plate were parallel. After that, it was cured at 23°C and 50% RH for 7 days to obtain a polarizing plate with an adhesive layer.

[0130] The heavy-peel release sheet was peeled off the polarizing plate with the adhesive layer mentioned above, and the plate was attached to alkali-free glass (Corning, product name "Eagle XG") via the exposed adhesive layer. The plate was then subjected to 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho, and this was used as a sample.

[0131] The above samples were placed in an 85°C dry environment, and visual inspection was conducted after 250 hours, 500 hours, and 750 hours to check for foaming, lifting, peeling, and the presence of streaks. The evaluation criteria were as follows. The results are shown in Table 1. ○: No foaming, lifting, peeling, or streaking occurred. ×: Foaming, lifting, peeling, or streaking occurred.

[0132] [Table 1]

[0133] As can be seen from Table 1, the adhesive sheets manufactured in the examples exhibited excellent antistatic properties as well as superior durability. [Industrial applicability]

[0134] The adhesive and adhesive sheet according to the present invention are suitable for bonding optical components, particularly polarizing plates, that require antistatic properties and durability. [Explanation of Symbols]

[0135] 1A, 1B... Adhesive sheets 1A'... Polarizing plate with adhesive layer 11…Adhesive layer 12, 12a, 12b… Release sheets 13…Optical components

Claims

1. An acrylic adhesive for bonding optical components, It contains aromatic ring-containing monomers in an amount of 100 ppm or more and 4000 ppm or less. The aromatic ring-containing monomer is an acrylic monomer having a benzene ring. It contains (meth)acrylic acid ester polymer and an antistatic agent, The (meth)acrylic acid ester polymer contains monomers having an alicyclic structure within the molecule as monomer units constituting the polymer. An adhesive characterized by the following features.

2. The adhesive according to claim 1, characterized in that the (meth)acrylic acid ester polymer contains an aromatic ring-containing monomer as a monomer unit constituting the polymer.

3. The adhesive according to claim 1 or 2, characterized in that the (meth)acrylic acid ester polymer is crosslinked with a crosslinking agent.

4. The adhesive according to any one of claims 1 to 3, characterized in that the optical component is a polarizing plate.

5. An adhesive sheet comprising an optical component and an adhesive layer, The adhesive layer comprises the adhesive described in any one of claims 1 to 4. An adhesive sheet characterized by the following features.

6. The adhesive sheet according to claim 5, characterized in that the optical element is a polarizing plate.

7. Two release sheets, An adhesive layer sandwiched between the two release sheets so as to be in contact with the release surfaces of the two release sheets, An adhesive sheet equipped with, The adhesive layer comprises the adhesive described in any one of claims 1 to 6. An adhesive sheet characterized by the following features.

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