JP7203624B2 - Optically transparent adhesive sheet, laminate sheet and laminated structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optically transparent pressure-sensitive adhesive sheet, a laminated sheet and a laminated structure.

An optically clear adhesive (OCA) sheet is a transparent adhesive sheet used for bonding optical members. As an example of use of the OCA sheet, in a display device, it is sometimes used for joining a display panel such as a liquid crystal module and a cover panel provided on the outermost surface of the display device. By filling the space between the display panel and the cover panel with the OCA sheet, the visibility of the screen of the display panel can be improved.

Documents disclosing prior art in the field related to OCA sheets include, for example, Patent Document 1. Patent Document 1 discloses a polyurethane (A) having a terminal (meth)acryloyl group and a weight average molecular weight of 10,000 to 300,000, a (meth)acrylic acid ester (B) having a hydroxyl group, and a specific structure ( Containing a meth) acrylic acid ester (C), a polymerizable monomer (D) other than components (A) to (C), and a photopolymerization initiator (E), and having an acid value of 0 to 5 mgKOH/g Disclosed is a transparent adhesive sheet having a refractive index of 1.50 to 1.60 obtained by curing a photocurable composition for a transparent adhesive sheet characterized by: Further, Patent Document 1 discloses that a transparent adhesive sheet has a three-layer structure, and the compositions of the layers on both sides and the central layer are changed to achieve a balance between the cohesive force and the adhesive force.

By the way, with the diversification of display devices, the use of resin panels as cover panels, which are more advantageous in terms of design, safety (prevention of shattering when broken) and price than conventional glass panels, has become increasingly popular in recent years. Consideration is being made. Therefore, an OCA sheet suitable for joining with a resin panel is desired.

JP 2016-20477 A

In order to realize an OCA sheet suitable for bonding a display panel and a touch panel main body, the present inventors have developed a multi-layer structure in which a first acrylic pressure-sensitive adhesive layer, a thermosetting polyurethane layer and a second acrylic pressure-sensitive adhesive layer are laminated. We have been developing an OCA sheet with The OCA sheet having this multilayer structure can obtain excellent flexibility due to the thermosetting polyurethane layer and excellent adhesiveness due to the first and second acrylic pressure-sensitive adhesive layers. It is possible to exhibit excellent characteristics such as being difficult to

However, this OCA sheet has uneven adhesive strength and viscoelasticity at the ends and the center in the flow direction, and it is not possible to obtain an OCA sheet with stable performance (hereinafter also referred to as production stability). there were.
In addition, when a laminated structure prepared by bonding an OCA sheet having a multilayer structure and a resin panel is left in a high-temperature and high-humidity environment, the OCA sheet may peel off.

The present invention has been made in view of the above-mentioned current situation, and provides an optically transparent pressure-sensitive adhesive sheet that is excellent in production stability and reliability in a high-temperature/high-humidity environment, and a laminated sheet and a laminate using the optically transparent pressure-sensitive adhesive sheet. The purpose is to provide a structure.

The optically transparent pressure-sensitive adhesive sheet of the present invention has a first acrylic pressure-sensitive adhesive layer, a first primer layer, a thermosetting polyurethane layer, a second primer layer, and a second acrylic pressure-sensitive adhesive layer in this order. The first primer layer and the second primer layer contain an acrylic resin and / or an ester resin and have a glass transition temperature of -7 ° C. or less, and the first acrylic pressure-sensitive adhesive layer And the glass transition temperature of the second acrylic pressure-sensitive adhesive layer is higher than the glass transition temperatures of the first primer layer and the second primer layer.

The acid content of the resin component constituting the first primer layer and the second primer layer is preferably 6 mol % or less.

The first primer layer and the second primer layer preferably have a thickness of 1 to 50 μm.

The laminated sheet of the present invention comprises the optically transparent adhesive sheet of the present invention, a first release film covering the first surface of the optically transparent adhesive sheet, and a second release film covering the other surface of the optically transparent adhesive sheet. and a release film are laminated.

The bonded structure of the present invention comprises a first adherend, a second adherend, and the optically transparent adhesive sheet for bonding the first adherend and the second adherend. It is characterized by having

According to the optically transparent pressure-sensitive adhesive sheet of the present invention, production stability and reliability under high-temperature and high-humidity environments can be enhanced. According to the laminated sheet of the present invention, the handleability of the optically transparent pressure-sensitive adhesive sheet of the present invention can be enhanced. According to the bonded structure of the present invention, it is possible to improve the reliability in a high-temperature/high-humidity environment.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which showed typically an example of the optically transparent adhesive sheet of this invention. It is a schematic diagram explaining the flow direction of an optically transparent adhesive sheet. It is a schematic diagram for demonstrating the evaluation method of adhesive strength. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which showed typically an example of the lamination sheet of this invention. 1 is a cross-sectional view schematically showing the configuration of a bonded structure of the present invention having a bezel-on bonded structure; FIG.

[Optical transparent adhesive sheet]
FIG. 1 is a cross-sectional view schematically showing an example of the optically transparent pressure-sensitive adhesive sheet of the present invention. The optically transparent adhesive sheet 10 shown in FIG. 1 includes a first acrylic adhesive layer 11, a first primer layer 12, a thermosetting polyurethane layer 13, a second and a second acrylic adhesive layer 15 constituting a second surface (adhesive surface) in this order. Thereby, interlayer adhesiveness can be suitably provided.

<Acrylic adhesive layer>
The first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 are obtained by curing an acrylic resin composition. The acrylic resin composition contains, for example, a (meth)acrylic acid ester polymer or a copolymer thereof (hereinafter also referred to as a (meth)acrylic copolymer) and a cross-linking agent. things are mentioned.

Examples of the (meth)acrylic copolymers include copolymers of (meth)acrylic acid alkyl esters and carboxyl group-containing monomers.

Examples of the (meth)acrylic acid alkyl ester include a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms (CH ₂ ═CR ¹ —COOR ² ; R ¹ is a hydrogen atom or a methyl group; ² is an alkyl group having 1 to 18 carbon atoms), and the alkyl group preferably has 4 to 12 carbon atoms.

Examples of (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 18 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (Meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate , isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate mentioned. These may be used individually by 1 type, and may use 2 or more types.

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloyloxyethyl succinate, ω-carboxypolycaprolactone mono(meth) Carboxyl group-containing (meth)acrylates such as acrylates; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid and maleic acid. These may be used individually by 1 type, and may use 2 or more types.

As the cross-linking agent, for example, a component capable of causing a cross-linking reaction with a cross-linkable functional group derived from a cross-linkable functional group-containing monomer contained in the (meth)acrylic copolymer can be used. include isocyanate compounds, metal chelate compounds, epoxy compounds and the like. The above crosslinking agents may be used singly or in combination of two or more.

From the viewpoint of suitably adjusting the glass transition temperature, the content of the cross-linking agent is preferably 0.01 to 20% by weight with respect to the entire (meth)acrylic copolymer, and is preferably 0.02. More preferably ~10% by weight.

The glass transition temperatures of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 are higher than the glass transition temperatures of the first primer layer 12 and the second primer layer 14, which will be described later.
The optically transparent adhesive sheet 10 has a first primer layer 12 and a second primer layer 14 between a first acrylic adhesive layer 11 and a second acrylic adhesive layer 15 and a thermosetting polyurethane layer 13. Therefore, it is possible to suitably impart interlayer adhesion, so that unevenness in viscoelasticity and adhesive strength at the ends and the central portion in the flow direction can be suppressed.
FIG. 2 is a schematic diagram for explaining the flow direction of the optically transparent adhesive sheet.
FIG. 2 shows an example of the manufacturing process of the optically transparent adhesive sheet 10. After the acrylic resin composition, the primer composition, etc. are applied by the discharge device 70, the sheet is transported by the transport rollers 80 and then by the rolls 60. By molding, the optically transparent pressure-sensitive adhesive sheet 10 is obtained. The direction of the arrow indicates the direction of progress of the manufacturing process.
As used herein, the term "flow direction" means the direction in which the optically transparent pressure-sensitive adhesive sheet 10 is manufactured (in the direction of the arrow).

The glass transition temperature of the first acrylic pressure-sensitive adhesive layer and the second acrylic pressure-sensitive adhesive layer is not particularly limited. °C or less is more preferable.
In addition, in this specification, a glass transition temperature means the glass transition temperature after bridge|crosslinking.
Here, the glass transition temperature can be determined by the starting point method in accordance with the provisions of JIS K7121. It can be obtained from a DSC curve stabilized by repeating the temperature increase from −100° C. to 150° C. at a temperature increase rate of 20° C./min.
The glass transition temperature can be adjusted by appropriately selecting the monomer components constituting the (meth)acrylic copolymer and the type and content of the crosslinking agent.

The thicknesses of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 are not particularly limited, but are preferably 3 to 100 μm, for example. If the thickness is less than 3 μm, delayed bubbles may occur. On the other hand, if the thickness exceeds 100 μm, it may not be possible to obtain flexibility (step followability) to the extent that the optically transparent pressure-sensitive adhesive sheet can be adhered to the surface of the adherend to conform to steps present on the surface thereof. . Further, when the optically transparent pressure-sensitive adhesive sheet is used for bonding substrates having different stretchability under environmental changes, such as bonding between a glass substrate and a resin substrate, the optically transparent pressure-sensitive adhesive sheet is used. There is a risk of peeling because it cannot follow the dimensional change of the base material when the environment changes. More preferably, the thickness of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 is 3 to 40 μm.

<Primer layer>
The first primer layer 12 and the second primer layer 14 are obtained by curing a primer composition. Examples of the primer composition include those containing a resin component and a cross-linking agent.
By having the first primer layer 12 and the second primer layer 14, the interlayer adhesion between the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 and the thermosetting polyurethane layer 13 is preferably can be given.

The resin component is an acrylic resin and/or an ester resin.
By using such a resin component, it is possible to satisfy the glass transition temperature to be described later, and to suitably impart interlayer adhesion.

As the acrylic resin, for example, a copolymer containing methyl methacrylate as a main component and copolymerized with a (meth)acrylic acid alkyl ester other than methyl methacrylate or a copolymerizable monomer is used.

Examples of alkyl esters of (meth)acrylic acid alkyl esters include methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, s-butyl ester, t-butyl ester, pentyl ester and isopentyl ester. , hexyl ester, heptyl ester, octyl ester, 2-ethylhexyl ester, isooctyl ester, nonyl ester, decyl ester, isodecyl ester, undecyl ester, dodecyl ester, tridecyl ester, tetradecyl ester, hexadecyl ester, octadecyl ester linear or branched alkyl esters having 1 to 30 carbon atoms, particularly 4 to 18 carbon atoms, such as eicosyl esters.

Examples of the above-mentioned copolymerizable monomer include carboxyl group-containing monomers such as (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid; maleic anhydride and itaconic anhydride; Acid anhydride monomers; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, (meth) acrylic 8-hydroxyoctyl acid, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, [4-(hydroxymethyl)cyclohexyl]methyl=acrylate, (meth)acrylic acid N-hydroxymethylamide, etc. hydroxyl group-containing monomers of; sulfonic acid group-containing monomers such as acids; phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; amino group-containing monomers such as dimethylaminoethyl methacrylate and t-butylaminoethyl methacrylate; Epoxy group-containing monomers; Others (meth)acrylamide, vinyl acetate, styrene, acrylonitrile and the like; The amount of the (meth)acrylic acid alkyl ester to be copolymerized with the methyl methacrylate and the copolymerizable monomer is preferably 50% by weight or less of the total monomer components.

Further, the acrylic resin used as the resin component of the primer layer may be selected from butyl glycidyl ether, phenyl glycidyl ether, nonylphenyl glycidyl ether, etc., when the carboxyl group-containing monomer or acid anhydride monomer is used as the copolymerizable monomer. Those modified with epoxy compounds and those amidated with primary or secondary amines such as monomethylamine, dimethylamine, monoethylamine and diethylamine can also be used. Furthermore, it is possible to obtain a polyethyleneimine-grafted product by grafting ethyleneimine or the like.

As the ester resin, a polyester resin containing polyester obtained by polycondensation of dicarboxylic acid and diol as a main component is used.

Examples of the dicarboxylic acid constituting the polyester resin include phthalic acid, isophthalic acid, terephthalic acid, 2-methylterephthalic acid, 5-sulfoisophthalic acid, 4,4′-diphenyldicarboxylic acid, and 4,4′-diphenyl ether. dicarboxylic acids, 4,4'-diphenylketonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, Aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid; Alicyclic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid Dicarboxylic acids; aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and dodecanoic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride and fumaric acid acids; derivatives thereof (for example, lower alkyl esters of the above dicarboxylic acids such as terephthalic acid); and the like. These can be used individually by 1 type or in combination of 2 or more types. In some embodiments, aromatic dicarboxylic acids can be preferably employed. Among the preferred dicarboxylic acids are terephthalic acid and 2,6-naphthalenedicarboxylic acid. For example, 50% by weight or more (for example, 80% by weight or more, typically 95% by weight or more) of the dicarboxylic acids constituting the polyester are terephthalic acid, 2,6-naphthalenedicarboxylic acid, or a combination thereof. is preferred. The dicarboxylic acid may consist essentially of terephthalic acid, essentially 2,6-naphthalenedicarboxylic acid, or essentially terephthalic acid and 2,6-naphthalenedicarboxylic acid.

Examples of the diol constituting the polyester resin include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-propanediol, 1,5-pentanediol, neopentyl glycol, and 1,4-butane. Aliphatic diols such as diols, 1,6-hexanediol, 1,8-octanediol, and polyoxytetramethylene glycol; 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, 1 ,4-cyclohexanedimethylol and other alicyclic diols, xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone and other aromatics family diols; and the like. These can be used individually by 1 type or in combination of 2 or more types. Of these, aliphatic diols are preferred from the viewpoint of transparency and the like, and ethylene glycol is particularly preferred. The ratio of the aliphatic diol (preferably ethylene glycol) to the diols constituting the polyester is preferably 50% by weight or more (for example, 80% by weight or more, typically 95% by weight or more). The diol may consist essentially of ethylene glycol.

Specific examples of the polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate, and the like.

As the cross-linking agent, the same one as described for the acrylic pressure-sensitive adhesive layer can be used.
Among them, an isocyanate compound and an epoxy compound are preferable, and the glass transition temperature can be suitably adjusted by using such a cross-linking agent.
The content of the cross-linking agent is preferably 0.01 to 20% by weight, preferably 0.02 to 10% by weight, relative to the entire primer composition, from the viewpoint of suitably adjusting the glass transition temperature. It is more preferable to have

The resin component preferably has an acid content of 6 mol % or less from the viewpoint of suitably imparting interlayer adhesive strength and suitably preventing unevenness in the adhesive strength and viscoelasticity of the optically transparent adhesive sheet 10 .
Further, when the optically transparent pressure-sensitive adhesive sheet of the present invention is used for laminating touch panels or the like, it is possible to suitably prevent corrosion of touch sensors.
The resin component more preferably has an acid content of 3 mol % or less, and further preferably does not contain an acid content.
Here, the acid content means the proportion of structural units derived from acidic groups contained in the resin component. In addition, a carboxyl group, a sulfo group, a sulfino group, a phosphoric acid group etc. are mentioned as an acidic group.

The first primer layer 12 and the second primer layer 14 have a glass transition temperature of −7° C. or lower.
By having such a glass transition temperature, adhesion between layers can be imparted, so unevenness in viscoelasticity and adhesive strength in the flow direction of the optically transparent adhesive sheet 10 can be suppressed, and production stability can be improved.
The resin component preferably has a glass transition temperature of -10°C or lower, more preferably -15°C or lower.
The glass transition temperature can be adjusted by appropriately selecting the type and content of the resin component and the cross-linking agent.

The first primer layer 12 and the second primer layer 14 preferably have a thickness of 1 to 50 μm, more preferably 10 to 25 μm.
If the thickness of the first primer layer 12 and the second primer layer 14 is less than 1 μm, the first primer layer 12 and the second primer layer 14 may not have sufficient interlayer adhesion. On the other hand, if the thickness of the first primer layer 12 and the second primer layer 14 exceeds 50 μm, the first primer layer 12 and the second primer layer 14 may easily undergo cohesive failure.

<Thermosetting polyurethane layer>
The thermosetting polyurethane layer 13 is obtained by curing thermosetting polyurethane. Since the thermosetting polyurethane can be formed into a film without using a solvent, the thermosetting polyurethane layer 13 containing the thermosetting polyurethane makes it possible to increase the thickness of the thermosetting polyurethane layer 13 . In addition, since the thermosetting polyurethane layer 13 contains thermosetting polyurethane, it has excellent flexibility and transparency even when formed into a thick film, and is highly reliable even in a high-temperature and high-humidity environment. An optically transparent pressure-sensitive adhesive sheet can be suitably obtained.

The thermosetting polyurethane is preferably not acrylic-modified, and preferably does not contain sites derived from acrylic acid esters, methacrylic acid esters, etc. in the main chain. When the thermosetting polyurethane is acrylic-modified, it becomes hydrophobic, so that moisture tends to aggregate under high temperature and high humidity conditions. Aggregation of this moisture causes whitening, foaming, etc., and may impair optical properties. Therefore, by using a thermosetting polyurethane that is not acrylic-modified, it is possible to prevent deterioration in optical properties due to whitening, foaming, etc. under high temperature and high humidity conditions. In the thermosetting polyurethane, the total amount of the monomer units derived from the polyol component and the monomer units derived from the polyisocyanate component is 80 mol% or more of the monomer units constituting the entire thermosetting polyurethane. Preferably.

The thermosetting polyurethane is a cured product of a thermosetting polyurethane composition. The thermosetting polyurethane composition preferably contains a polyol component and a polyisocyanate component. Both the polyol component and the polyisocyanate component can be liquid at room temperature (23° C.), and a thermosetting polyurethane can be obtained without using a solvent. Other components such as silane coupling agents, tackifiers, etc. can be added to either the polyol component or the polyisocyanate component, and are preferably added to the polyol component. When the thermosetting polyurethane layer 13 is produced, it is not necessary to remove the solvent, so a uniform and thick sheet can be formed. Further, the thermosetting polyurethane layer 13 can maintain its optical properties even when formed thick, and can sufficiently suppress coloring and foaming (generation of air bubbles at the interface with the adherend). Furthermore, the thermosetting polyurethane layer 13 can be thickened and is flexible, so that it has excellent impact resistance. The optically transparent adhesive sheet provided with the thermosetting polyurethane layer 13 can be used for bonding a transparent member having a transparent conductive film on its surface and a cover panel. It can also be used for bonding a transparent member having a transparent conductive film on its surface with another member. When the optically transparent adhesive sheet provided with the thermosetting polyurethane layer 13 is used for bonding the display panel and a transparent member (touch panel) having a transparent conductive film on the surface layer, the bezel is formed by the bezel arranged on the outer edge of the display panel. The step can be covered with an optically transparent adhesive sheet.

The polyol component is not particularly limited, and examples thereof include polyether polyol, polycaprolactone polyol, polycarbonate polyol, polyester polyol and the like. These may be used alone or in combination of two or more.

The above polyol component preferably has an olefin skeleton. That is, the main chain is preferably composed of polyolefin or a derivative thereof. Examples of the polyol component having an olefin skeleton include polybutadiene-based polyols such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, 1,2-polychloroprene polyol, and 1,4-polychloroprene polyol, and polyisoprene. system polyols, and those having their double bonds saturated with hydrogen, halogen, or the like. Further, the polyol component may be a polyol obtained by copolymerizing an olefin compound such as styrene, ethylene, vinyl acetate, acrylic acid ester, or the like with a polybutadiene-based polyol or the like, or a hydrogenated product thereof. The polyol component may have a linear structure or a branched structure. Only one type of the polyol component may be used, or two or more types may be used. The polyol component used in the thermosetting polyurethane preferably contains 80 mol % or more of a polyol component having an olefin skeleton, and more preferably consists only of a polyol component having an olefin skeleton.

The polyisocyanate component is not particularly limited, and conventionally known polyisocyanates can be used. Either a hydrophilic polyisocyanate having a hydrophilic unit or a hydrophobic polyisocyanate having no hydrophilic unit, Alternatively, both may be used. In addition, the hydrophilic polyisocyanate having the above-mentioned hydrophilic unit is not one in which hydrophilicity is improved only by a structure derived from an isocyanate group such as an isocyanurate structure or a biuret structure, but a functional group (hydrophilic polyisocyanate to which a functional unit) is added. By including a hydrophilic unit in the polyisocyanate component, an effect of suppressing whitening due to moisture absorption can be obtained.

An ethylene oxide unit is suitable as the hydrophilic unit. The content of the ethylene oxide unit is preferably 0.1% by weight or more and 20% by weight or less with respect to the entire thermosetting polyurethane composition. If the content is less than 0.1% by weight, the effect of suppressing whitening may not be obtained sufficiently. If the content exceeds 20% by weight, the compatibility with the low-polarity olefin-based polyol component, tackifier, plasticizer, etc. may decrease, thereby deteriorating optical properties such as haze. More preferably, the content of the ethylene oxide unit is 0.1 to 5% by weight. If the content exceeds 5% by weight, there is a risk that the amount of moisture absorbed in the high-temperature, high-humidity environment may become too large.

Examples of hydrophilic units other than ethylene oxide units include units containing a carboxylic acid group, a carboxylic acid alkali metal base, a sulfonic acid group, a sulfonic acid alkali metal base, a hydroxyl group, an amide group, an amino group, and the like. More specifically, polyacrylic acid, alkali metal salt of polyacrylic acid, sulfonic acid group-containing copolymer, alkali metal salt of sulfonic acid group-containing copolymer, polyvinyl alcohol, polyacrylamide, carboxymethylcellulose, alkali metal of carboxymethylcellulose salts, polyvinylpyrrolidone, and the like.

The polyisocyanate component is preferably a modified polyisocyanate obtained by reacting an aliphatic and/or alicyclic polyisocyanate having an isocyanate group with an ether compound having an ethylene oxide unit. By using an aliphatic and/or alicyclic polyisocyanate, coloring and discoloration are less likely to occur, and the transparency of the optically transparent pressure-sensitive adhesive sheet can be more reliably ensured over a long period of time. In addition, by forming a modified product obtained by reacting an ether compound having an ethylene oxide unit, the polyisocyanate component can suppress whitening by the action of the hydrophilic portion (ethylene oxide unit), and the hydrophobic portion (other units) can be suppressed. can exhibit compatibility with low-polarity tackifiers, plasticizers, and the like.

The thermosetting polyurethane composition preferably has an α ratio (number of moles of OH groups derived from the polyol component/number of moles of NCO groups derived from the polyisocyanate component) of 1 or more. If the α ratio is less than 1, the amount of the polyisocyanate component blended is excessive with respect to the blended amount of the polyol component. It can be difficult to secure. If the flexibility of the thermosetting polyurethane layer 13 is low, unevenness and steps present on the bonding surface cannot be covered, particularly when an optical member such as a touch panel is bonded. Moreover, when the α ratio is less than 1, there is a possibility that the adhesive force required for the optically transparent adhesive sheet cannot be ensured. The α ratio is preferably less than 2.0. If the α ratio is 2.0 or more, the thermosetting polyurethane composition may not sufficiently cure.

The thermosetting polyurethane may contain a silane coupling agent.
As the silane coupling agent, those having an epoxy group or an isocyanurate structure, and those having an epoxy group or an isocyanurate structure and an alkoxy group are preferably used. Examples of alkoxy groups include methoxy groups and ethoxy groups. The silane coupling agent having an epoxy group is not particularly limited. sidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The silane coupling agent having an isocyanurate structure is not particularly limited, and examples thereof include tris-(trimethoxysilylpropyl)isocyanurate.

The thermosetting polyurethane composition may further contain a plasticizer. The plasticizer is not particularly limited as long as it is a compound used for imparting flexibility to thermosetting polyurethane, but from the viewpoint of compatibility and weather resistance, it preferably contains a carboxylic acid plasticizer.

The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is used for the urethanization reaction, and examples thereof include organic tin compounds such as di-n-butyltin dilaurate, dimethyltin dilaurate, dibutyltin oxide and octane tin; organic titanium compounds; organic zirconium compounds; tin carboxylates; bismuth carboxylates; and amine-based catalysts such as triethylenediamine.

Various additives such as colorants, stabilizers, antioxidants, anti-staining agents, and flame retardants may be added to the above thermosetting polyurethane composition as necessary within a range that does not impede the required properties of the optically transparent pressure-sensitive adhesive sheet. may be added.

The thickness of the thermosetting polyurethane layer 13 is preferably 100-2000 μm. If the thickness is less than 100 μm, the flexibility of the entire optically transparent adhesive sheet is reduced, and when one surface of the optically transparent adhesive sheet is attached to the surface of the optical member, the optical member is coated with the optically transparent adhesive sheet. Unevennesses or steps present on the surface of the adhesive sheet cannot be covered, and the other surface of the optically transparent pressure-sensitive adhesive sheet and the surface of another optical member cannot be bonded together with sufficient adhesive strength. If the thickness exceeds 2000 μm, sufficient optical properties such as haze and total light transmittance may not be obtained. A more preferable lower limit of the thickness of the thermosetting polyurethane layer 13 is 150 μm, a still more preferable lower limit is 200 μm, and a particularly preferable lower limit is 250 μm. A more preferable upper limit of the thickness of the thermosetting polyurethane layer 13 is 1500 μm, and a further preferable upper limit is 1000 μm.

The optically transparent adhesive sheet 10 has a first acrylic adhesive layer 11, a first primer layer 12, a thermosetting polyurethane layer 13, a second primer layer 14 and a second acrylic adhesive layer 15 in this order. It suffices if the layer is provided, and may further include other layers. The first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 are preferably positioned on the outermost surface (the surface in contact with the adherend) of the optically transparent pressure-sensitive adhesive sheet 10, respectively. Moreover, the first acrylic pressure-sensitive adhesive layer 11 and the first primer layer 12, and the first primer layer 12 and the thermosetting polyurethane layer 13 are preferably in contact with each other. Moreover, the second acrylic pressure-sensitive adhesive layer 15 and the second primer layer 14, and the second primer layer 14 and the thermosetting polyurethane layer 13 are preferably in contact with each other.

<Optical transparent adhesive sheet>
In order to ensure performance as an optically transparent adhesive sheet, the optically transparent adhesive sheet 10 preferably has a haze of 1% or less, more preferably 0.5% or less. Further, the optically transparent pressure-sensitive adhesive sheet 10 of the present invention preferably has a total light transmittance of 90% or more. Haze and total light transmittance can be measured, for example, using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. Haze is measured by a method conforming to JIS K 7136, and total light transmittance is measured by a method conforming to JIS K 7361-1.

The thickness of the entire optically transparent adhesive sheet 10 is preferably 106 μm or more. Although the upper limit of the thickness of the entire optically transparent adhesive sheet 10 is not particularly limited, it is, for example, 3000 μm. The optically transparent pressure-sensitive adhesive sheet 10 preferably has a thickness that is at least three times the height of unevenness or steps present on the attachment surface of the adherend. A more preferable lower limit of the thickness is 500 μm, a further preferable lower limit is 750 μm, a preferable upper limit is 2000 μm, and a more preferable upper limit is 1750 μm.

The optically transparent pressure-sensitive adhesive sheet 10 is excellent in production stability because it has a property that the difference in viscoelasticity between the end portions and the central portion in the flow direction is extremely small. On the other hand, if the unevenness in viscoelasticity between the end portions and the central portion in the flow direction is large, an optically transparent pressure-sensitive adhesive sheet having stable properties cannot be obtained.
The optically transparent pressure-sensitive adhesive sheet 10 preferably has a difference of 0.02 or less in loss tangent (tan δ _{85° C.} ) at 85° C. between the ends and the center, more preferably 0.01 or less.
The end portion means a portion 0 to 30% from the end in the width direction, and the central portion means a portion 31 to 69% from the end in the width direction.
Here, the loss tangent can be measured using, for example, a viscoelasticity measuring device "Physica MCR301" manufactured by Anton Paar Germany GmbH. Measurement conditions are to use PP12 as a measurement plate, strain 0.1%, frequency 1 Hz, cell temperature 25 ° C. to 100 ° C. (heating rate 3 ° C./min), and adopt the measured value at the target temperature. can be done.

In the optically transparent pressure-sensitive adhesive sheet 10, the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 preferably have a pressure-sensitive adhesive strength to glass of 7 N/25 mm or more at room temperature (23°C). The optical transparent pressure-sensitive adhesive sheet 10 is sufficiently adhered to an adherend having a glass base material because both the adhesive strengths of the first and second acrylic pressure-sensitive adhesive layers to glass at room temperature are 7 N/25 mm or more. It can have stickiness. The adhesive strength at room temperature is the adhesive strength measured by a 180° peel test. The details of the test method of the 180° peel test will be described later. The adhesive strength at room temperature is more preferably 10 N/25 mm or more, and even more preferably 30 N/25 mm or more.

From the viewpoint of improving productivity, the optically transparent adhesive sheet 10 preferably has little difference in adhesive strength to glass at room temperature (23° C.) between the end portion and the central portion.
Specifically, the difference in adhesive strength to glass at room temperature (23° C.) is preferably less than 5 N/25 mm, more preferably less than 3 N/25 mm, between the end portion and the central portion.

In the optically transparent pressure-sensitive adhesive sheet 10, the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 preferably have a pressure-sensitive adhesive strength to glass of 1.0 N/25 mm or more at 85°C. The adhesive strength at 85°C is the adhesive strength measured by the 180° peel test. The optical transparent pressure-sensitive adhesive sheet of the present invention can be applied to an adherend having a glass substrate because both the adhesive strengths of the first and second acrylic pressure-sensitive adhesive layers to glass at 85° C. are 1.0 N/25 mm or more. On the other hand, sufficient adhesiveness can be maintained even in a high temperature and high humidity environment. Although the upper limit of the adhesive strength at 85° C. is not particularly limited, it is, for example, 15 N/25 mm.

FIG. 3 is a schematic diagram for explaining a method for evaluating adhesive strength. In the 180° peeling test, for example, an optically transparent adhesive sheet 10 cut into a length of 75 mm × width of 25 mm is used as a test piece, and one side of each test piece is attached to a slide glass 31 of length 75 mm × width 25 mm, and pressure is applied. The pressure is kept at 0.4 MPa for 30 minutes, and the optically transparent adhesive sheet 10 and the slide glass 31 are bonded together. Next, as shown in FIG. 3A, a PET sheet 32 is attached to the surface of the optically transparent adhesive sheet 10 opposite to the slide glass 31 . After that, after being left at a predetermined temperature for a certain period of time, as shown in FIG. The adhesive force of the optically transparent adhesive sheet 10 to the glass 31 is measured. As the PET sheet, for example, a PET sheet having a thickness of 125 μm (“Melinex (registered trademark) S” manufactured by Teijin DuPont Films Ltd.) or the like can be used.

[Method for producing optically transparent adhesive sheet]
The method of laminating the first acrylic pressure-sensitive adhesive layer 11, the thermosetting polyurethane layer 13, and the second acrylic pressure-sensitive adhesive layer 15 in this order is not particularly limited. The second acrylic pressure-sensitive adhesive layer 15 and the thermosetting polyurethane layer 13 are separately produced, the first primer layer 12 is formed on one side of the thermosetting polyurethane layer 13, and the second primer layer is formed on the other side. After forming 14, the first acrylic adhesive layer 11 is attached to the side where the first primer layer 12 is formed, and the second acrylic adhesive layer 15 is attached to the side where the second primer layer 14 is formed. method.

The method for producing the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 15 is not particularly limited. Membrane methods may also be used. Moreover, you may produce the 1st acrylic adhesive layer 11 and the 2nd acrylic adhesive layer 15 using the centrifugal molding method.

The method for producing the first primer layer 12 and the second primer layer 14 is not particularly limited, and for example, a general-purpose film-forming device or film-forming method such as various coating devices, bar coaters, or doctor blades may be used to coat the primer composition. may be Moreover, you may manufacture the 1st primer layer 12 and the 2nd primer layer 14 using the centrifugal molding method.

The method for producing the thermosetting polyurethane layer 13 is not particularly limited, and includes, for example, a method in which a thermosetting polyurethane composition is prepared and then the composition is molded while being thermoset by a conventionally known method. ingredients, a polyisocyanate component, a silane coupling agent, and a tackifier to prepare a thermosetting polyurethane composition; and curing the thermosetting polyurethane composition.

As a specific example of the manufacturing method, first, a masterbatch is prepared by adding a predetermined amount of tackifier to a polyol component and dissolving the mixture by heating and stirring. Subsequently, the obtained masterbatch, polyol component, polyisocyanate component, silane coupling agent, and, if necessary, other components such as a catalyst are mixed and stirred with a mixer or the like to form a liquid or gel. A thermosetting polyurethane composition is obtained. After that, the thermosetting polyurethane composition is immediately put into the molding device, and the curing reaction (crosslinking reaction) is performed while the thermosetting polyurethane composition is moved while sandwiched between the first and second release films. , the thermosetting polyurethane composition is semi-cured to obtain a sheet integrated with the first and second release films. After that, a thermosetting polyurethane layer 13 is obtained by causing a cross-linking reaction in a furnace for a certain period of time.

As a method for producing the thermosetting polyurethane layer 13, after preparing a thermosetting polyurethane composition before curing, general-purpose film-forming devices and methods such as various coating devices, bar coaters, and doctor blades are used. good too. Alternatively, the thermosetting polyurethane layer 13 may be produced using a centrifugal molding method.

[Laminated sheet]
A release film may be attached to both sides of the optically transparent pressure-sensitive adhesive sheet of the present invention. FIG. 4 is a cross-sectional view schematically showing an example of the laminated sheet of the present invention. The optically transparent adhesive sheet 10 of the present invention, the first release film 21 covering one surface of the optically transparent adhesive sheet 10, and the second release film 22 covering the other surface of the optically transparent adhesive sheet 10. A laminated laminate sheet 20 is also an aspect of the present invention. According to the laminated sheet of the present invention, both surfaces of the optically transparent pressure-sensitive adhesive sheet of the present invention can be protected by the first release film and the second release film until immediately before being attached to the adherend. As a result, the optically transparent pressure-sensitive adhesive sheet of the present invention is prevented from being degraded in pressure-sensitive adhesiveness and from being adhered with foreign matter. In addition, since the optically transparent pressure-sensitive adhesive sheet of the present invention is prevented from sticking to objects other than the adherend, the handleability is enhanced.

The first release film and the second release film may be a resin film such as a PET film, or may be a release-treated paper (release paper). The material and thickness of the first release film and the second release film may be the same or different.

The bonding strength (peel strength) of the optically transparent adhesive sheet of the present invention and the first release film and the bonding strength (peel strength) of the optically transparent adhesive sheet of the present invention and the second release film are preferably different. Since the bonding strength is different from each other in this way, only one of the first release film and the second release film (the release film with the lower bonding strength) is peeled off from the laminated sheet of the present invention. Then, one surface of the exposed optically transparent adhesive sheet and the first adherend are bonded together, and then the other of the first release film and the second release film (the bonding strength is high It becomes easy to peel off the second release film) and bond the exposed other surface of the optically transparent adhesive sheet to the second adherend.

At least one of the surface of the first release film in contact with the optically transparent pressure-sensitive adhesive sheet of the present invention and the surface of the second release film in contact with the optically transparent pressure-sensitive adhesive sheet of the present invention is provided with a release agent. A mold treatment (easy peeling treatment) may be applied. Examples of easy peeling treatment include silicone treatment.

[Laminated structure]
Applications of the optically transparent pressure-sensitive adhesive sheet of the present invention are not particularly limited. A laminated structure comprising a first adherend, a second adherend, and the optically transparent pressure-sensitive adhesive sheet for bonding the first adherend and the second adherend is also provided by the present invention. This is one aspect of the invention.

The optically transparent pressure-sensitive adhesive sheet of the present invention can be used for bonding a liquid crystal module and a cover panel. The visibility of the liquid crystal module can be improved by bonding the liquid crystal module and the cover panel with the optically transparent adhesive sheet and eliminating the air layer existing between the liquid crystal module and the cover panel. In this case, the first adherend and the second adherend are the liquid crystal module and the cover panel. When the liquid crystal module is arranged in a housing (bezel) having an opening in the display section, the bezel is arranged on the outer edge of the liquid crystal module. Therefore, a step corresponding to the thickness of the bezel is formed. The method of joining the liquid crystal module and the cover panel by overlapping an optically transparent adhesive sheet not only in the center of the liquid crystal module but also in the area where the bezel is arranged is also called "bezel-on lamination". A bonded structure formed by bezel-on bonding is also referred to as a “bezel-on bonded structure”.

Since the optically transparent pressure-sensitive adhesive sheet of the present invention is flexible and can be formed into a thick film, it can be applied to bezel-on lamination. The laminated structure of the present invention has a structure in which an optically transparent adhesive sheet and a support member are provided between a first base material and a second base material, and the support member is provided between the first base material and the support member. The optically transparent pressure-sensitive adhesive sheet has a step forming portion disposed on the outer edge, and includes: a thick film portion for bonding the first base material and the second base material; and an end portion sandwiched between the base material of the substrate.

FIG. 5 is a cross-sectional view schematically showing the configuration of the laminated structure of the present invention having a bezel-on laminated structure. The laminated structure 50 shown in FIG. 5 has a structure in which the optically transparent adhesive sheet 10 and the upper bezel (supporting member) 41 are provided between the first base material 51 and the second base material 52. However, for example, it may be a part of an electronic device such as a display device. The upper bezel 41 is integrated with the lower bezel 42 to form a housing (bezel) that accommodates the first base material 51 .

In the bonded structure 50 , the optically transparent adhesive sheet 10 includes a thick film portion that bonds a first base material 51 and a second base material 52 together, a step forming part of the upper bezel 41 , and the second base material 52 . and an end sandwiched between Since the end portion of the optically transparent adhesive sheet 10 is sandwiched between the second base material 52 and the step forming portion of the upper bezel 41, it is difficult to peel off. Since the optically transparent adhesive sheet 10 reaches the stepped portion of the upper bezel 41 , the entire upper surface of the first base material 51 is covered by the stepped portion of the upper bezel 41 or the optically transparent adhesive sheet 10 . It is possible to prevent moisture absorption of the first base material 51 . When the polarizing plate is positioned on the upper surface of the first base material 51, moisture absorption of the polarizing plate can be prevented. When the polarizing plate absorbs moisture, its performance deteriorates quickly, and the moisture absorbed in the high-temperature environment evaporates, which may cause delayed foaming.

The combination of the first base material 51 and the second base material 52 is not particularly limited. For example, a display device such as a display panel, a touch panel (glass substrate with an ITO transparent conductive film), a cover panel (cover glass) is configured. various members to be used. The type of display panel is not particularly limited, and examples thereof include a liquid crystal panel and an organic electroluminescence panel (organic EL panel). A polarizing plate, a retardation film, or the like may be arranged on the surface of the display panel to which the optically transparent adhesive sheet 10 is attached. By using the optically transparent adhesive sheet 10 to bond various members in the display device together, an air layer (air gap) in the display device can be eliminated, and the visibility of the display screen can be improved. Moreover, when a polarizing plate is arranged, the optically transparent adhesive sheet 10 can effectively prevent the polarizing plate from absorbing moisture. A combination in which the first base material 51 is a display panel such as a liquid crystal module and the second base material 52 is a cover panel (cover glass) or touch sensor glass is suitable.

Materials of the first base material 51 and the second base material 52 are not particularly limited, and examples thereof include glass and resin. The resin constituting the first base material 51 and/or the second base material 52 is not particularly limited, and examples thereof include polycarbonate, polymethyl methacrylate resin (PMMA), triacetyl cellulose (TAC), and the like. For example, when a polarizing plate is placed on the surface of the first substrate 51 to which the optically transparent adhesive sheet 10 is attached, the surface in contact with the optically transparent adhesive sheet 10 may be made of TAC. The polarizing plate may have a laminated structure of TAC, polyvinyl alcohol (PVA), and TAC, or may have the TAC surface of the laminated structure subjected to AG (anti-glare) treatment. HC (hard coat) treatment may be applied to the TAC surface of the laminate structure, or AG treatment and HC treatment may be applied to the TAC surface of the laminate structure.

The upper bezel 41 is a frame-shaped member arranged around the optically transparent adhesive sheet 10 when viewed from above, and at least a portion of the upper bezel 41 is arranged on the outer edge of the first base material 51 . A side surface of a portion (step forming portion) arranged on the outer edge of the first base material 51 forms a step. The shape of the side surface of the step forming portion is not particularly limited, and the side surface of the step forming portion may be perpendicular to the upper surface of the first base material 51 . When the first base material 51 is a display panel, the upper bezel 41 is arranged in the frame area of the display device. A light shielding portion 52A may be provided on the outer edge of 51 . The material of the upper bezel 41 is not particularly limited, and examples thereof include metal and resin.

The thickness (the size of the step) of the upper bezel 41 is not particularly limited, but is set to 200 to 1000 μm, for example. If the thickness of the upper bezel 41 exceeds 200 μm, the thickness of the optically transparent adhesive sheet 10 must be 300 μm or more, so an optically transparent adhesive sheet thicker than a normal optically transparent adhesive sheet is used.

The thickness of the thick film portion of the optically transparent adhesive sheet 10 is at least 1.5 times the thickness of the step forming portion of the upper bezel 41, and more preferably at least 2 times. As a result, a sufficient thickness can be secured at the edge of the optically transparent adhesive sheet 10 sandwiched between the stepped portion of the upper bezel 41 and the second base material 52, and peeling of the edge can be prevented. . The thickness of the thick film portion of the optically transparent adhesive sheet 10 in the bonded structure 50 is substantially the same as the thickness of the optically transparent adhesive sheet 10 before bonding. That is, the thickness of the optically transparent adhesive sheet 10 before bonding is preferably 1.5 times or more, more preferably 2 times or more, the thickness of the upper bezel 41 .

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

<Acrylic resin composition>
(A-1)
Acrylic resin ("SK1838" manufactured by Soken Chemical Co., Ltd.), epoxy-based cross-linking agent ("E-AX" manufactured by Soken Chemical Co., Ltd.) to be 0.15% by weight with respect to the total acrylic resin composition was added to prepare an acrylic resin composition (glass transition temperature after crosslinking: -5.2°C).

<Primer composition>
(P-1)
An isocyanate cross-linking agent (“DY-70” manufactured by Soken Chemical Co., Ltd.) is added to the resin component (“SK1875” manufactured by Soken Chemical Co., Ltd.) so that the total amount of the primer composition is 0.7% by weight. Then, a primer composition (glass transition temperature after cross-linking: -12.4°C, acid content: 0 mol%) was prepared.
(P-2)
To the resin component (“MPT-54” manufactured by Toagosei Co., Ltd.), an isocyanate-based cross-linking agent (“Hardener 02” manufactured by Toagosei Co., Ltd.) is added to the total primer composition so that it becomes 0.06% by weight. was added to prepare a primer composition (glass transition temperature after cross-linking: −18.7° C., 0 mol %).
(P-3)
To the resin component (“MPT-29” manufactured by Toagosei Co., Ltd.), an isocyanate-based cross-linking agent (“Hardener 02” manufactured by Toagosei Co., Ltd.) is added to the total primer composition so that it becomes 0.07% by weight. was added to prepare a primer composition (glass transition temperature after cross-linking: −4.3° C., 0 mol %).
(P-4)
To the resin component (“SZ8580” manufactured by Nippon Carbide Industry Co., Ltd.), an isocyanate-based cross-linking agent (“CK-121” manufactured by Nippon Carbide Industry Co., Ltd.) is added to the primer composition in an amount of 0.14% by weight. was added to prepare a primer composition (glass transition temperature after cross-linking: −18.5° C., 0 mol %).
(P-5)
The resin component (“KP-2984” manufactured by Nippon Carbide Industry Co., Ltd.) is added with an isocyanate cross-linking agent (“CK-121 manufactured by Nippon Carbide Industry Co., Ltd. ”) was added to prepare a primer composition (glass transition temperature after cross-linking: −7.2° C., containing acid content).
(P-6)
An isocyanate cross-linking agent ("BXX6450" manufactured by Toyochem Co., Ltd.) was added to the resin component ("BPS6660Q" manufactured by Toyochem Co., Ltd.) in an amount of 0.2% by weight with respect to the total primer composition, and the primer composition was prepared. A product (glass transition temperature: -26.0°C, 0 mol%) was produced.
The acid content is obtained by determining the ratio of structural units derived from acidic groups contained in each resin component.

<Glass transition temperature (Tg)>
The glass transition temperature (Tg) of (A-1) and (P-1) to (P-6) after crosslinking was measured using a differential scanning calorimeter (manufactured by NETZSCH, DSC3500A) under a nitrogen gas atmosphere. After obtaining a stabilized DSC curve by repeatedly heating a sample of about 10 mg from -100 ° C. to 150 ° C. at a heating rate of 20 ° C. per minute, by the starting point method in accordance with the provisions of JIS K7121. This is the calculated value.

<Thermosetting polyurethane composition>
(U-1)
Polyolefin polyol (“EPOL (registered trademark)” manufactured by Idemitsu Kosan Co., Ltd.) 85 parts by weight, IPDI (isophorone diisocyanate)-based polyisocyanate (“Desmodur I” manufactured by Sumika Bayer Urethane Co., Ltd.) 4.0 parts by weight, Modified polyisocyanate containing ethylene oxide unit (“Coronate 4022” manufactured by Tosoh Corporation) 4.0 parts by weight, tackifier (“Imarb P-100” manufactured by Idemitsu Kosan Co., Ltd.) 8.5 parts by weight, and a catalyst (dilauric acid Dimethyltin) (0.1 part by weight) was stirred and mixed using a reciprocating rotary stirrer agitator to prepare a polyurethane composition having an α ratio of 1.42. In the polyurethane composition, the mixing ratio (molar ratio) of the IPDI-based polyisocyanate (A) and the modified polyisocyanate (B) was A:B=2:1.
In addition, "Coronate 4022" manufactured by Tosoh Corporation is obtained by reacting an ether polyol having an average of 3 or more ethylene oxide units per molecule with a polyisocyanate starting from hexamethylene diisocyanate and/or a hexamethylene diisocyanate monomer. It is obtained.

(Example 1)
The thermosetting polyurethane composition (U-1) was cross-linked and cured under the conditions of a furnace temperature of 50 to 90° C. and a furnace time of several minutes. Thereafter, a crosslinking reaction was carried out with a heating device for 10 to 15 hours to prepare a thermosetting polyurethane layer composed of the thermosetting polyurethane composition (U-1). The thickness of the thermosetting polyurethane layer was 1460 µm.

On the other hand, after applying the acrylic resin composition (A-1) to the release film with a comma coater, drying in a drying oven at 80 ° C. to 120 ° C., further acrylic resin composition (A-1 ) was coated with a release film. After that, curing was completed by heating at 40° C. for 1 week to prepare an acrylic pressure-sensitive adhesive layer. The thickness of the acrylic adhesive layer was 10 µm.
One release film is peeled from the obtained acrylic pressure-sensitive adhesive layer, and the primer composition (P-1) is applied to the surface of the first acrylic pressure-sensitive adhesive layer from which the release film is peeled, and the temperature is 80 ° C. After drying in a drying oven at ~120°C, a release film was placed on the surface coated with the primer composition (P-1). After that, curing was completed by heating at 40° C. for 1 week to form a primer layer on one side of the acrylic pressure-sensitive adhesive layer. The thickness of the primer layer was 10 μm.

After that, two sheets of the acrylic pressure-sensitive adhesive layer on which the primer layer was formed and one sheet of the thermosetting polyurethane layer were prepared. Peel off the release film on the side where the primer layer is formed from the acrylic pressure-sensitive adhesive layer on which the first primer layer is formed, and on the surface of the first acrylic pressure-sensitive adhesive layer on which the primer layer is formed A thermoset polyurethane layer was laminated. Furthermore, the release film on the side where the primer layer is formed is peeled off from the acrylic pressure-sensitive adhesive layer on which the second primer layer is formed, and the acrylic adhesive layer on which the first primer layer of the thermosetting polyurethane layer is formed Acrylic adhesive layer (second acrylic adhesive layer and a second primer layer) were laminated. As a result, the release film, the first acrylic pressure-sensitive adhesive layer, the first primer layer, the thermosetting polyurethane layer, the second primer layer, the second acrylic pressure-sensitive adhesive layer and the release film were laminated in this order. An optically transparent pressure-sensitive adhesive sheet with a release film was produced. The thickness of the optically transparent adhesive sheet was 1500 μm.

Measurement of loss tangent (tan δ) of optically transparent adhesive sheet The loss tangent of the obtained optically transparent adhesive sheet was measured using a viscoelasticity measuring apparatus "Physica MCR301" manufactured by Anton Paar Germany GmbH. PP12 was used as the measurement plate, and the measurement conditions were a strain of 0.1%, a frequency of 1 Hz, and a cell temperature of 25° C. to 100° C. (heating rate of 3° C./min). Table 1 shows the loss tangent of the optically transparent pressure-sensitive adhesive sheet at 85°C.
The measurement of the loss tangent (tan δ) was performed for each of a portion (end portion) of 0 to 30% from the edge in the width direction and a portion (central portion) of 31 to 69% from the edge.

(Comparative example 1)
While transporting the polyurethane composition (B-1) sandwiched between a pair of release films (PET films whose surfaces have been subjected to a release treatment), the temperature inside the furnace is 50 to 90° C., and the time inside the furnace is several minutes. The sheet was crosslinked and cured under the conditions to obtain a sheet with a release film. Thereafter, a crosslinking reaction was performed with a heating device for 10 to 15 hours to prepare a thermosetting polyurethane layer containing the polyurethane composition (B-1) and provided with release films on both sides. The thickness of the thermosetting polyurethane layer was 1480 μm.

On the other hand, after applying the acrylic resin composition (A-1) to the release film with a comma coater, drying in a drying oven at 80 ° C. to 120 ° C., further acrylic resin composition (A-1 ) was coated with a release film. After that, curing was completed by heating at 40° C. for 1 week to prepare an acrylic pressure-sensitive adhesive layer. The thickness of the acrylic adhesive layer was 10 μm.

After that, two sheets of the acrylic pressure-sensitive adhesive layer with the release film and one sheet of the thermosetting polyurethane layer with the release film were prepared. One release film was peeled off from the first acrylic pressure-sensitive adhesive layer with a release film, and a thermosetting polyurethane layer was laminated on the surface of the first acrylic pressure-sensitive adhesive layer from which the release film was peeled. Furthermore, one release film is peeled off from the second release film-attached acrylic pressure-sensitive adhesive layer, and the first acrylic pressure-sensitive adhesive layer (first acrylic pressure-sensitive adhesive layer) of the thermosetting polyurethane layer is laminated. A second acrylic pressure-sensitive adhesive layer (second acrylic pressure-sensitive adhesive layer) was laminated on the surface opposite to the surface that was coated. As a result, an optically transparent pressure-sensitive adhesive sheet with a release film was produced in which the release film, the first acrylic pressure-sensitive adhesive layer, the thermosetting polyurethane layer, the second acrylic pressure-sensitive adhesive layer and the release film were laminated in this order. The thickness of the optically transparent adhesive sheet was 1500 μm.

(Examples 2 to 5 and Comparative Example 2)
Optically transparent adhesive sheets according to Examples 2 to 5 and Comparative Example 2 were prepared in the same manner as in Example 1, except that the type of primer composition and the thickness of the primer layer were changed.
In each of Examples 2 to 5 and Comparative Example 2, the second primer layer was made of the same type of primer composition and had the same thickness as the first primer layer.

The loss tangent was measured in the same manner as in Example 1 for the optically transparent pressure-sensitive adhesive sheets obtained in Examples 2-5 and Comparative Examples 1-2.

As can be seen from Table 1 above, in Examples 1 to 5, the loss tangent is small at the ends and the center measured at 85 ° C., so the difference in adhesive strength is small even in a high temperature environment, and the adhesive strength is stable. It was also confirmed that the production stability was excellent.
On the other hand, in Comparative Example 1 where no primer layer is formed, the glass transition temperature of the primer layer exceeds -7 ° C., which is higher than that of the acrylic pressure-sensitive adhesive layer. Due to the large difference in tangent, it was not possible to exhibit stable adhesive strength even in a high-temperature environment, and the production stability was also inferior.

10: Optically transparent adhesive sheet 11: First acrylic adhesive layer 12: First primer layer 13: Thermosetting polyurethane layer 14: Second primer layer 15: Second acrylic adhesive layer 20: Laminated sheet 21: First release film 22: Second release film 31: Slide glass
32: PET sheet
41: Upper bezel (support member)
42: Lower bezel 50: Bonded structure 51: First base material 52: Second base material 52A: Light shielding part 60: Roll 70: Ejection device 80: Transport roller

Claims (5)

Having a first acrylic pressure-sensitive adhesive layer, a first primer layer, a thermosetting polyurethane layer, a second primer layer, and a second acrylic pressure-sensitive adhesive layer in this order,
The first primer layer and the second primer layer contain an acrylic resin and / or an ester resin, and have a glass transition temperature of -7 ° C. or less,
The glass transition temperature of the first acrylic pressure-sensitive adhesive layer and the second acrylic pressure-sensitive adhesive layer is higher than the glass transition temperature of the first primer layer and the second primer layer. adhesive sheet. 2. The optically transparent pressure-sensitive adhesive sheet according to claim 1, wherein the resin component constituting said first primer layer and said second primer layer has an acid content of 6 mol % or less. 3. The optically transparent pressure-sensitive adhesive sheet according to claim 1, wherein the first primer layer and the second primer layer have a thickness of 1 to 50 μm. The optically transparent adhesive sheet according to any one of claims 1 to 3, a first release film covering one side of the optically transparent adhesive sheet, and a second release film covering the other side of the optically transparent adhesive sheet. A laminated sheet comprising a release film laminated thereon. The optically transparent pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which bonds a first adherend, a second adherend, and the first adherend and the second adherend. A laminated structure comprising:

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