JP2020083996A - Pressure-sensitive adhesive sheet and production method of the same, and production method of image display device - Google Patents

Abstract

To provide a pressure-sensitive adhesive sheet which has level difference absorbing property and excellent adhesion durability corresponding to impact resistance and strain stress in a wide temperature range.SOLUTION: A pressure-sensitive adhesive sheet (5) is a photocurable pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive composition containing an acrylic base polymer having a crosslinked structure, a photopolymerizable multifunctional compound having two or more photopolymerizable functional groups in a molecule and a photopolymerization initiator, formed in layers. The pressure-sensitive adhesive sheet has a storage elastic modulus of 100-250 kPa at 25°C and 1 Hz, and preferably a gel fraction of 25-70%. The storage elastic modulus of the pressure-sensitive adhesive sheet at 25°C and 1 Hz after photocuring of the pressure-sensitive adhesive composition is preferably 180-400 kPa.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photocurable pressure-sensitive adhesive sheet and a method for producing the same. Furthermore, the present invention relates to a method for manufacturing an image display device using the adhesive sheet.

Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile phones, smartphones, car navigation devices, personal computer monitors, and televisions. A front transparent plate (also referred to as a "cover window") such as a transparent resin plate or a glass plate is provided on the viewing side of the image display panel for the purpose of preventing damage to the image display panel due to an impact from the outer surface. Sometimes. Further, in recent years, devices having a touch panel on the viewing side of an image display panel have become widespread.

In an image display device in which a front transparent member such as a front transparent plate or a touch panel is arranged on the front surface of the image display panel, the image display panel and the front transparent member are bonded together via an adhesive sheet. Also, an adhesive sheet may be provided between the touch panel and the front transparent plate. By bonding and fixing the members with the adhesive sheet, there is an advantage that the front transparent member is less likely to be peeled off due to an impact such as a drop, as compared with the case where the front transparent member is fixed only to the housing.

A colored layer (decorative printing layer) for the purpose of decoration or light shielding may be formed on the periphery of the front transparent member. When an adhesive is attached to a transparent member having a decorative printing layer, bubbles are likely to be generated around the printing step portion. Therefore, a method is adopted in which a thick adhesive sheet is provided with step absorbability to suppress problems such as air bubble inclusion. In addition, impact resistance tends to be improved by using a thick PSA sheet.

A method has been proposed in which a pressure-sensitive adhesive sheet made of a photocurable pressure-sensitive adhesive composition is used for bonding the front transparent member (see, for example, Patent Document 1 and Patent Document 2). The photocurable pressure-sensitive adhesive composition contains a photopolymerizable polyfunctional monomer or oligomer in an unreacted state. Since the pressure-sensitive adhesive sheet before photocuring has high fluidity, it has excellent step absorbability, and can prevent air bubbles from being mixed into the bonding interface and the vicinity of the printing step. By irradiating the pressure sensitive adhesive sheet with an actinic ray after the bonding with the adherend to perform photo-curing, the fluidity of the pressure sensitive adhesive is lowered and the adhesive holding power is improved.

International Publication No. 2013/161666 JP, 2014-227453, A

In an image display device in which a front transparent member such as a cover window is larger in size than the display panel, the front transparent member and the housing are attached to each other by an adhesive tape or the like in a region outside the outer peripheral edge of the display panel. .. That is, the front transparent member is fixed by using both the attachment to the housing with an adhesive tape or the like and the attachment to the display panel surface with the interlayer filling adhesive sheet.

In recent years, mainly for mobile devices such as smartphones, display devices have become narrower and bezel-less. With the narrowing of the frame and the reduction of the bezel, an image display device in which the size of the display panel 10 is equal to or larger than the size of the front transparent member 7 has been developed. In such a configuration, the housing 9 and the front transparent member 7 cannot be fixed by an adhesive tape or the like, and the front transparent member 7 needs to be fixed only by the adhesive sheet 5 (see FIG. 2). Along with this, the pressure-sensitive adhesive sheet is required to have higher adhesive strength and to be prevented from being peeled off due to an impact such as a drop.

Further, with the narrowing of the frame and the reduction of the bezel, high dimensional stability is required even when the image display device is assembled and the work-in-process is conveyed. The photo-curable pressure-sensitive adhesive sheet used for bonding the front transparent member has a soft pressure-sensitive adhesive before photo-curing and is excellent in step absorbability. A pressure-sensitive adhesive sheet that has flexibility to absorb step differences has high fluidity of the pressure-sensitive adhesive after it is attached to the adherend and before photo-curing. When applied, it is likely to be deformed, which may cause displacement between the bonding members. Further, when the pressure-sensitive adhesive has a high fluidity, when peeling off the release sheet temporarily attached to the surface of the pressure-sensitive adhesive sheet, there may occur a problem of workability such as adhesive chipping of the pressure-sensitive adhesive sheet.

In view of the above, it is an object of the present invention to provide a pressure-sensitive adhesive sheet that can achieve both step absorbability and processability in the state before photo-curing, and that has excellent impact resistance and adhesive durability after photo-curing.

The present invention relates to a photocurable pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive composition is formed in layers. What is the pressure-sensitive adhesive composition that constitutes the photocurable pressure-sensitive adhesive sheet? It contains an acrylic base polymer having a crosslinked structure, a photopolymerizable polyfunctional compound, and a photopolymerization initiator. The photopolymerizable polyfunctional compound is a compound having two or more photopolymerizable functional groups in one molecule, and it is preferable to use a compound having three or more photopolymerizable functional groups in one molecule.

The adhesive sheet preferably has a storage elastic modulus at 25° C. and 1 Hz of 100 to 250 kPa and a gel fraction of 25 to 70%. The adhesive sheet preferably has a storage elastic modulus at 25° C. and 10 ⁻⁷ Hz of 4.5 kPa or more. The adhesive sheet preferably has an adhesive force to glass of 4 N/10 mm or more.

The acrylic base polymer having a crosslinked structure contained in the pressure-sensitive adhesive sheet is preferably an acrylic base polymer having a weight average molecular weight of 300,000 or more and a crosslinked structure introduced by an isocyanate crosslinking agent or the like. The acrylic base polymer preferably contains 5 to 30 parts by weight of a hydroxy group-containing monomer with respect to 100 parts by weight of the total of the monomer components. The pressure-sensitive adhesive sheet preferably contains 1 to 6 parts by weight of the photopolymerizable polyfunctional compound with respect to 100 parts by weight of the acrylic base polymer.

The pressure-sensitive adhesive sheet, a composition containing an acrylic base polymer, a cross-linking agent, and a photopolymerizable polyfunctional compound is applied in layers on a substrate, to introduce a cross-linking structure by the cross-linking agent into the acrylic base polymer. It can be formed by

The pressure-sensitive adhesive sheet of the present invention is used, for example, for bonding a transparent member in an image display device in which the transparent member is arranged on the viewing side surface. After the pressure-sensitive adhesive sheet and the transparent member are bonded together, the pressure-sensitive adhesive sheet is irradiated with actinic rays to photo-cur the pressure-sensitive adhesive composition, whereby an image display device can be formed.

The pressure-sensitive adhesive sheet after photocuring preferably has a storage elastic modulus at 25° C. and 1 Hz of 180 to 400 kPa. The glass transition temperature of the pressure-sensitive adhesive sheet after photocuring is preferably −3° C. or lower. The gel fraction of the pressure-sensitive adhesive sheet after photocuring is preferably 65 to 95%. The peak top value of loss tangent of the pressure-sensitive adhesive sheet after photocuring is preferably 1.5 or more. The adhesive force of the adhesive sheet after photocuring to glass is preferably 4 N/10 mm or more.

The pressure-sensitive adhesive sheet of the present invention can have both step absorbability and workability in a state before photo-curing, and has excellent impact resistance and adhesion durability after photo-curing. An image display device in which a cover window or the like is attached to the viewing side surface using the pressure-sensitive adhesive sheet of the present invention has excellent adhesion reliability and can be applied to narrow frame and bezelless.

It is sectional drawing which shows the structural example of the adhesive sheet with a release film. It is sectional drawing which shows the structural example of an image display apparatus. It is sectional drawing which shows the example of a laminated structure of the optical film with an adhesive sheet. It is sectional drawing which shows the example of a laminated structure of the optical film with an adhesive sheet. It is a photograph which shows a mode of an interlayer adhesion test. It is an observation photograph of a sample in which streak-like bubbles were generated in the interlayer adhesion test. It is a schematic diagram which shows arrangement|positioning of the sample in an impact resistance test.

FIG. 1 shows a release film-attached pressure-sensitive adhesive sheet in which release films 1 and 2 are temporarily attached to both surfaces of a pressure-sensitive adhesive sheet 5. FIG. 2 is a cross-sectional view showing a configuration example of an image display device in which the front transparent plate 7 is fixed using an adhesive sheet.

[Physical properties of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention is one in which a pressure-sensitive adhesive composition containing an acrylic base polymer having a crosslinked structure, a photopolymerizable polyfunctional compound, and a photopolymerization initiator is formed in layers, and is photocurable. Have. The pressure-sensitive adhesive sheet preferably has high transparency. The total light transmittance of the pressure-sensitive adhesive sheet is preferably 85% or more, more preferably 90% or more. The haze of the pressure-sensitive adhesive sheet is preferably 1.5% or less, more preferably 1% or less.

Adhesive sheet to have a thickness unevenness absorbability, from the viewpoint of preventing the mixing of air bubbles into the printing step vicinity, temperature 25 ° C. of the adhesive sheet before photocuring, the storage elastic modulus G _{'25 ° C.} at a frequency of 1Hz is, 250 kPa or less Is preferred, 200 kPa or less is more preferred, and 180 kPa or less is even more preferred. On the other hand, G'25 _{° C.} of the pressure-sensitive adhesive sheet before photocuring is preferably 100 kPa or more, and 110 kPa or more, from the viewpoint of suppressing positional deviation after attaching the pressure-sensitive adhesive sheet to an adherend and ensuring processing dimensional stability. Is more preferable.

The storage elastic modulus of the pressure-sensitive adhesive sheet before photocuring at a temperature of 25° C. and a frequency of 10 ⁻⁷ Hz is preferably 4.5 kPa or more, more preferably 5 kPa or more, still more preferably 5.5 kPa or more. When the storage elastic modulus at a frequency of 10 ⁻⁷ Hz is within the above range, the pressure-sensitive adhesive sheet is less likely to be plastically deformed due to low-speed strain, and the pressure-sensitive adhesive sheet during conveyance and processing of an in-process product after bonding with an adherend. Since the plastic deformation strain of is small, the processing dimensional stability tends to be improved.

The storage elastic modulus of the pressure-sensitive adhesive sheet before photocuring at a temperature of 25° C. and a frequency of 10 ⁻⁷ Hz is preferably 20 kPa or less, more preferably 15 kPa or less, still more preferably 10 kPa or less. When the storage elastic modulus at a frequency of 10 ⁻⁷ Hz is within the above range, the pressure-sensitive adhesive has appropriate softness in a high temperature environment, and therefore the step absorbability can be secured.

When photocuring is performed after the pressure-sensitive adhesive sheet is attached to the adherend, the storage elastic modulus of the pressure-sensitive adhesive sheet increases due to the photopolymerization reaction (photocuring) of the photopolymerizable polyfunctional compound. The pressure-sensitive adhesive sheet after photocuring has a storage elastic modulus G′ of _{25° C.} at 25° C. and a frequency of 1 Hz of preferably 180 kPa or more, more preferably 200 kPa or more, and further preferably 210 kPa or more. The higher the G′ _{25° C.} of the pressure-sensitive adhesive sheet after photocuring, the higher the adhesive reliability tends to be.

On the other hand, G'25 _{° C.} of the pressure-sensitive adhesive sheet after photocuring is preferably 400 kPa or less from the viewpoint of imparting appropriate viscosity to the pressure-sensitive adhesive sheet to ensure wettability and adhesive durability against impact such as dropping. , 350 kPa or less is more preferable, 300 kPa or less is further preferable, and 280 kPa or less is particularly preferable.

The glass transition temperature of the pressure-sensitive adhesive sheet after photocuring is preferably −3° C. or lower, more preferably −5° C. or lower, and further preferably −6° C. or lower. The glass transition temperature of the pressure-sensitive adhesive sheet after photocuring is preferably −20° C. or higher, more preferably −15° C. or higher, even more preferably −13° C. or higher. When the glass transition temperature is within the above range, the pressure-sensitive adhesive sheet has appropriate viscosity even in a low temperature region, and therefore tends to have excellent impact resistance.

The peak top value of the loss tangent tan δ (that is, tan δ at the glass transition temperature) of the pressure-sensitive adhesive sheet after photocuring is preferably 1.5 or more, more preferably 1.6 or more, still more preferably 1.7 or more. Particularly preferred is 75 or more. A pressure-sensitive adhesive sheet having a large tan δ peak top value tends to have large viscous behavior and excellent impact resistance.

The upper limit of the peak top value of tan δ of the pressure-sensitive adhesive sheet after photocuring is not particularly limited, but is generally 3.0 or less. From the viewpoint of adhesion retention, the peak top value of tan δ is preferably 2.5 or less, more preferably 2.3 or less, and further preferably 2.1 or less.

For the measurement of the physical properties of the pressure-sensitive adhesive sheet after photocuring, a pressure-sensitive adhesive sheet that has been photocured so that the residual C=C bond quantified by infrared spectroscopy is 15% or less is used. The storage elastic modulus G′ of the adhesive sheet, the glass transition temperature, and the peak top value of tan δ are determined by viscoelasticity measurement. The measurement frequency is 1 Hz unless otherwise specified. The glass transition temperature is a temperature at which tan δ has a maximum (peak top temperature). tan δ is the ratio G″/G′ of the storage elastic modulus G′ and the loss elastic modulus G″. The storage elastic modulus G'corresponds to a portion stored as elastic energy when the material is deformed and is an index indicating the degree of hardness. The larger the storage modulus of the pressure-sensitive adhesive sheet, the higher the adhesive holding force, and the more likely peeling due to strain is suppressed. The loss elastic modulus G″ corresponds to a loss energy portion dissipated by internal friction when the material is deformed, and represents the degree of viscosity. The larger tan δ, the stronger the tendency of viscosity, and the deformation behavior becomes liquid, The impact resilience energy tends to be small.

The gel fraction of the pressure-sensitive adhesive sheet before photocuring is 25% to 70% from the viewpoint of imparting appropriate flexibility for imparting step absorbability while securing processing dimensional stability by setting G'25 _{° C.} to 100 kPa or more. Is preferred. The gel fraction of the pressure-sensitive adhesive sheet before photocuring is more preferably 30 to 65%, further preferably 33 to 60%, particularly preferably 35 to 55%. From the viewpoint of achieving both adhesive reliability and impact resistance, the gel fraction of the pressure-sensitive adhesive sheet after photocuring is preferably 65 to 95%, more preferably 70 to 93%, further preferably 75 to 90%.

The gel fraction of the pressure-sensitive adhesive sheet can be obtained as an insoluble component in a solvent such as ethyl acetate, and specifically, the insoluble component after the pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet is immersed in ethyl acetate at 23° C. for 7 days. Is calculated as a weight fraction (unit:% by weight) of the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of cross-linking, the more cross-linked moieties in the polymer the greater the gel fraction. The gel fraction (introduced amount of the crosslinked structure) can be adjusted to a desired range depending on the method of introducing the crosslinked structure, the type and amount of the crosslinking agent, and the like.

The adhesive force of the pressure-sensitive adhesive sheet before photocuring is preferably 4 N/10 mm or more, more preferably 6 N/10 mm or more, further preferably 7 N/10 mm or more, and particularly preferably 8 N/10 mm or more. When the adhesive strength of the pressure-sensitive adhesive sheet before photocuring is within the above range, it is possible to prevent the pressure-sensitive adhesive sheet from peeling off or being displaced from the adherend during the transportation and processing of the work-in-process after being bonded to the adherend. Further, since the adhesive force of the pressure-sensitive adhesive sheet before photocuring is within the above range, the release film 2 (light release film) temporarily attached to one surface of the pressure-sensitive adhesive sheet 5 is peeled off and bonded to the adherend. After that, when the release film 1 (heavy release film) temporarily attached to the other surface is released, the release at the interface between the adherend and the adhesive sheet 5 can be suppressed.

The adhesive force of the pressure-sensitive adhesive sheet after photocuring is preferably 4 N/10 mm or more, more preferably 4.5 N/10 mm or more, still more preferably 5 N/10 mm or more. When the adhesive strength of the pressure-sensitive adhesive sheet after photocuring is within the above range, peeling of the pressure-sensitive adhesive sheet from the adherend can be prevented when stress due to strain or impact due to dropping or the like occurs.

The adhesive strength is obtained by a peel test with a glass plate as an adherend and a pulling speed of 300 mm/min and a peeling angle of 180°. Unless otherwise specified, the adhesive force is a value measured at 25°C.

The thickness of the pressure-sensitive adhesive sheet is not particularly limited and may be set according to the type and shape of the adherend. When a member having a printing step such as a front transparent plate is used as the adherend, it is preferable that the thickness of the adhesive sheet is larger than the thickness of the printing step. The thickness of the pressure-sensitive adhesive sheet used for bonding the front transparent plate (cover window) is preferably 30 μm or more, more preferably 40 μm or more, still more preferably 50 μm or more. Increasing the thickness of the pressure-sensitive adhesive sheet tends to increase step absorbability and impact resistance. The upper limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but from the viewpoint of the productivity of the pressure-sensitive adhesive sheet, it is preferably 500 μm or less, more preferably 300 μm or less, and further preferably 250 μm or less.

[Composition of adhesive]
The composition of the pressure-sensitive adhesive is not particularly limited, and includes acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate/vinyl chloride copolymers, modified polyolefins, epoxy systems, fluorine systems, natural rubbers, synthetic rubbers, etc. A rubber-based polymer as a base polymer can be appropriately selected and used. In particular, it contains an acrylic base polymer with a crosslinked structure introduced because it has excellent optical transparency, exhibits appropriate wettability, cohesiveness, adhesiveness, and other adhesive properties, and also has excellent weather resistance and heat resistance. An acrylic pressure sensitive adhesive is preferably used.

<Base polymer>
The acrylic base polymer contains a (meth)acrylic acid alkyl ester as a main constituent monomer component. In addition, in this specification, "(meth)acryl" means acryl and/or methacryl.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferably used. The alkyl group of the (meth)acrylic acid alkyl ester may have a branched structure, or may have a cyclic alkyl group.

Specific examples of the (meth)acrylic acid alkyl ester having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl acrylate (meth), and (meth). S-Butyl acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-Methyl acrylate (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate Undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridodecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, (meth) Examples thereof include cetyl acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and aralkyl (meth)acrylate.

Specific examples of the (meth)acrylic acid alkyl ester having an alicyclic alkyl group include (meth)acrylic acid cyclopentyl, (meth)acrylic acid cyclohexyl, (meth)acrylic acid cycloheptyl, (meth)acrylic acid cyclooctyl and the like. (Meth)acrylic acid cycloalkyl ester; (meth)acrylic acid isobornyl and other (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring; dicyclopentanyl (meth)acrylate, dicyclopentanyloxy Tricyclic ring such as ethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate The (meth)acrylic acid ester having the above aliphatic hydrocarbon ring may be mentioned.

The amount of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, based on the total amount of the monomer components constituting the acrylic base polymer. From the viewpoint of setting the glass transition temperature (Tg) of the base polymer in an appropriate range, the acrylic base polymer is the amount of (meth)acrylic acid alkyl ester having a chain alkyl group having 4 to 10 carbon atoms with respect to the total amount of constituent monomer components. Is preferably 30% by weight or more, more preferably 40% by weight or more, and further preferably 45% by weight or more.

The acrylic base polymer preferably contains an acrylic monomer unit having a crosslinkable functional group as a copolymerization component. Since the base polymer has a crosslinkable functional group, the gel fraction of the pressure-sensitive adhesive can be adjusted to a desired range by reacting the base polymer with the crosslinking agent.

Examples of the acrylic monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxy group-containing monomer. For example, when an isocyanate-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between a hydroxy group and an isocyanate group. When an epoxy-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between a carboxy group and an epoxy group. Above all, it is preferable to use a hydroxy group-containing monomer as a copolymerization component of the base polymer and introduce a crosslinked structure with an isocyanate crosslinking agent. When the base polymer contains a hydroxy group-containing monomer as a monomer component, the cross-linking property of the base polymer is enhanced and the cloudiness of the pressure-sensitive adhesive in a high temperature and high humidity environment tends to be suppressed, resulting in a highly transparent pressure-sensitive adhesive. Is obtained.

Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and (meth) Examples thereof include (meth)acrylic acid esters such as 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate and (4-hydroxymethylcyclohexyl)-methyl acrylate. Among these, 2-hydroxyethyl acrylate (Tg of homopolymer: −15° C.) and 4-acrylic acid 4-because they contribute greatly to the improvement of adhesive strength and can suppress clouding of the pressure-sensitive adhesive sheet in a high humidity environment. Hydroxybutyl (Tg of homopolymer: -32°C) is preferred. 4-Hydroxybutyl acrylate is particularly preferable because it has a low Tg and contributes greatly to the improvement of the storage elastic modulus due to the formation of intermolecular hydrogen bonds.

The amount of the hydroxy group-containing monomer is preferably 5 to 30% by weight, more preferably 8 to 25% by weight, still more preferably 10 to 20% by weight, based on the total amount of the monomer components constituting the acrylic base polymer. By increasing the amount of hydroxy group-containing monomer, the unreacted functional groups of the cross-linking agent will decrease, so the cross-linking degree (gel fraction) will be increased with a small amount of cross-linking agent, and the workability and processing of the pressure-sensitive adhesive sheet before photocuring It is possible to achieve both dimensional stability and step absorbability. In addition, since unreacted hydroxy groups form intermolecular hydrogen bonds after crosslinking, a pressure-sensitive adhesive sheet having a G′ of _{25° C.} of 100 kPa or more can be obtained even with a gel fraction of 70% or less.

Examples of the carboxy group-containing monomer include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

When the pressure-sensitive adhesive sheet is used for bonding the touch panel sensor, it is preferable that the pressure-sensitive adhesive sheet has a low acid content in order to prevent corrosion of the electrode due to an acid component. When the pressure-sensitive adhesive sheet is used for bonding a polarizing plate, it is preferable that the pressure-sensitive adhesive sheet has a small acid content in order to suppress polyeneization of the polyvinyl alcohol-based polarizer due to an acid component. In such an acid-free pressure-sensitive adhesive sheet, the content of an organic acid monomer such as (meth)acrylic acid is preferably 100 ppm or less, more preferably 70 ppm or less, and further preferably 50 ppm or less. .. The organic acid monomer content of the pressure-sensitive adhesive sheet is determined by immersing the pressure-sensitive adhesive sheet in pure water, heating at 100° C. for 45 minutes, and quantifying the acid monomer extracted in water by ion chromatography.

In order to reduce the content of the acid monomer in the pressure-sensitive adhesive sheet, it is preferable that the amount of the organic acid monomer component such as (meth)acrylic acid in the monomer component constituting the acrylic base polymer is small. Therefore, in order to make the pressure-sensitive adhesive sheet acid-free, it is preferable that the base polymer does not substantially contain an organic acid monomer (carboxy group-containing monomer) as a monomer component. In the acid-free pressure-sensitive adhesive sheet, the amount of the carboxy group-containing monomer is preferably 0.5 parts by weight or less, more preferably 0.1 parts by weight or less, and even more preferably 0.05 parts by weight or less based on 100 parts by weight of the total of the monomer components of the base polymer. Is more preferable, and ideally 0.

The acrylic base polymer may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl. Examples thereof include vinyl monomers such as carboxylic acid amides and N-vinylcaprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile. Among these, N-vinylpyrrolidone is preferable because it has a high effect of improving the adhesive force by improving the cohesive force.

Since the acrylic base polymer contains a high polar monomer such as a hydroxy group-containing monomer, a carboxy group-containing monomer, and a nitrogen-containing monomer as constituent monomer components, the cohesive force of the pressure-sensitive adhesive is enhanced and the adhesive retention at high temperature is improved. Tends to improve. On the other hand, when the content of the highly polar monomer is excessively high, the glass transition temperature becomes high, and the adhesiveness and impact resistance at low temperature may be deteriorated. Therefore, the amount of the highly polar monomer (the total of the hydroxy group-containing monomer, the carboxy group-containing monomer, and the nitrogen-containing monomer) is preferably 10 to 45% by weight, and 15 to 40% by weight, based on the total amount of the monomer components constituting the acrylic base polymer. Is more preferable, and 18 to 35% by weight is further preferable. Moreover, the amount of the nitrogen-containing monomer is preferably 3 to 25% by weight, more preferably 5 to 20% by weight, and further preferably 7 to 15% by weight, based on the total amount of the monomer components constituting the acrylic base polymer.

Acrylic base polymer, as monomer components other than the above, acid anhydride group-containing monomer, (meth)caprolactone adduct of acrylic acid, sulfonic acid group-containing monomer, phosphoric acid group-containing monomer, vinyl acetate, vinyl propionate, styrene, Vinyl-based monomers such as α-methylstyrene; cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate; polypropylene (meth)acrylate Glycol, methoxyethylene glycol (meth)acrylate, glycol acrylic ester monomer such as methoxy polypropylene glycol (meth)acrylate; tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate or (meth ) It may contain an acrylic acid ester monomer such as 2-methoxyethyl acrylate.

Among the above-mentioned monomer components, the acrylic base polymer preferably has the highest content of (meth)acrylic acid alkyl ester. The characteristics of the pressure-sensitive adhesive sheet are easily influenced by the type of the monomer (main monomer) having the highest content among the constituent monomers of the acrylic base polymer. For example, when the main monomer of the acrylic base polymer is a (meth)acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the peak top value of tan δ becomes large, and the impact resistance tends to be improved. is there. In particular, when an acrylic acid C ₄ alkyl esters, such as butyl acrylate is the major monomer, they tend to peak top value of tanδ increases. The amount of the (meth)acrylic acid alkyl ester having a chain alkyl group having a carbon number of 6 or less is preferably 30 to 80% by weight, more preferably 35 to 75% by weight, based on the total amount of monomer components constituting the acrylic base polymer. , 40 to 70% by weight is more preferable. In particular, the content of butyl acrylate as a constituent monomer component is preferably within the above range.

The glass transition temperature (Tg) of the acrylic base polymer is preferably −50° C. or higher. The glass transition temperature of the acrylic base polymer is preferably −5° C. or lower, more preferably −10° C. or lower, still more preferably −15° C. or lower. After introducing the crosslinked structure into the acrylic base polymer, the glass transition temperature may be calculated from the composition of the polymer based on the theoretical Tg. Theoretical Tg is a glass transition temperature Tg _i of the homopolymer constituent monomer components of the acrylic based polymer, the weight fraction W _i of each monomer component, is calculated by the Fox equation below.
1/Tg=Σ(W _i /Tg _i ).

Tg is the glass transition temperature of the base polymer (unit: K), W _i is the weight fraction of the monomer component i constituting the base polymer (copolymerization ratio on a weight basis), and Tg _i is the glass transition of the homopolymer of the monomer component i. Temperature (unit: K). As the glass transition temperature of the homopolymer, the values described in Polymer Handbook 3rd edition (John Wiley & Sons, Inc., 1989) can be adopted. For the Tg of a homopolymer of a monomer not described in the above literature, the peak top temperature of loss tangent (tan δ) measured by dynamic viscoelasticity may be adopted.

An acrylic base polymer is obtained by polymerizing the above-mentioned monomer components by various known methods such as solution polymerization, emulsion polymerization and bulk polymerization. The solution polymerization method is preferable as the polymerization method from the viewpoint of the balance of properties such as adhesive strength and holding power of the pressure-sensitive adhesive, and cost. As a solvent for solution polymerization, ethyl acetate, toluene and the like are generally used. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator, an azo-based initiator, a peroxide-based initiator, a redox-based initiator in which a peroxide and a reducing agent are combined (for example, a combination of persulfate and sodium hydrogen sulfite, a peroxide and ascorbine). A thermal polymerization initiator such as a sodium acid combination) is preferably used. The amount of the polymerization initiator used is not particularly limited, but is preferably about 0.005 to 5 parts by weight, and about 0.02 to 3 parts by weight with respect to 100 parts by weight of the total amount of the monomer components forming the base polymer. More preferable.

Chain transfer agents may be used to adjust the molecular weight of the base polymer. The chain transfer agent can receive a radical from the growing polymer chain to stop the elongation of the polymer, and at the same time, the chain transfer agent receiving the radical can attack the monomer to restart the polymerization. Therefore, by using the chain transfer agent, it is possible to suppress an increase in the molecular weight of the base polymer without lowering the radical concentration in the reaction system. Examples of the chain transfer agent include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Is preferably used.

The amount of chain transfer agent used is not particularly limited, but if the amount of chain transfer agent used is excessively large, the molecular weight of the base polymer will decrease, and the processability and processing dimensional stability of the pressure-sensitive adhesive sheet before photocuring will decrease. There is a case. Therefore, the amount of the chain transfer agent used is preferably 1 part by weight or less, more preferably 0.3 part by weight or less, still more preferably 0.15 part by weight or less with respect to 100 parts by weight of the total amount of the monomer components constituting the base polymer. It is preferably 0.1 parts by weight or less, and particularly preferably 0.1 part by weight or less.

The viscoelasticity of the pressure-sensitive adhesive sheet before photocuring is easily influenced by the constituent components and molecular weight of the base polymer. The larger the molecular weight of the base polymer, the larger the G'25 _°C , and the more the processability and the dimensional stability of the process tend to be improved. Therefore, the weight average molecular weight of the acrylic base polymer is preferably 300,000 or more, more preferably 350,000 or more, and further preferably 400,000 or more. On the other hand, when the molecular weight of the base polymer is excessively large, the step absorbability tends to decrease. Therefore, the weight average molecular weight of the base polymer is preferably 1,500,000 or less, more preferably 1,000,000 or less, further preferably 800,000 or less, particularly preferably 650,000 or less. The molecular weight of the base polymer refers to the molecular weight of the polymer before the introduction of the crosslinked structure.

<Crosslinked structure of base polymer>
As a method for introducing a crosslinked structure into a base polymer, generally, (1) a method in which a base polymer having a functional group capable of reacting with the crosslinker is polymerized, and then the crosslinker is added to react the base polymer with the crosslinker. And (2) a method of introducing a branched structure (crosslinked structure) into the polymer chain by including a photopolymerizable polyfunctional compound in the polymerization component of the base polymer.

The pressure-sensitive adhesive sheet of the present invention has a crosslinked structure in which the base polymer is introduced by the above method (1). Furthermore, the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet contains a photopolymerizable polyfunctional compound, and by performing photocuring after bonding the pressure-sensitive adhesive sheet and an adherend, the crosslinked structure of (2) above is obtained. be introduced. That is, in the pressure-sensitive adhesive sheet of the present invention, before photocuring, the base polymer has a crosslinked structure with a (heat) crosslinking agent such as an isocyanate crosslinking agent. In the pressure-sensitive adhesive sheet after photocuring, the base polymer has a crosslinked structure formed by a photopolymerizable polyfunctional compound (photocrosslinking agent) such as a polyfunctional (meth)acrylate, in addition to the crosslinked structure formed by an isocyanate crosslinking agent. ing.

<Crosslinking agent>
A cross-linking structure is introduced into the base polymer by adding a cross-linking agent after the base polymer is polymerized and heating it as necessary. In order to distinguish from the crosslinked structure introduced by the photopolymerizable polyfunctional compound, the crosslinking by the isocyanate crosslinking agent or the like may be described as "thermal crosslinking", but the introduction of the crosslinked structure by the crosslinking agent does not involve heating. It may be one. By introducing a heat-crosslinking structure into the acrylic base polymer, the processability and process dimensional stability of the pressure-sensitive adhesive sheet before photocuring can be improved.

Examples of the cross-linking agent include compounds that react with functional groups such as a hydroxy group and a carboxy group contained in the base polymer. Specific examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents.

Of these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferable because they have high reactivity with the hydroxy group and carboxy group of the base polymer and can easily introduce a crosslinked structure. These cross-linking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the base polymer to form a cross-linked structure. In the acid-free pressure-sensitive adhesive in which the base polymer does not contain a carboxy group, it is preferable to use an isocyanate cross-linking agent to form a cross-linked structure by reacting the hydroxy group in the base polymer with the isocyanate cross-linking agent.

As the isocyanate-based crosslinking agent, polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate cross-linking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; 2,4-tolylene diisocyanate. Aromatic isocyanates such as isocyanate, 4,4′-diphenylmethane diisocyanate and xylylene diisocyanate; trimethylol propane/tolylene diisocyanate trimer adduct (eg Tosoh's “Coronate L”), trimethylol propane/hexamethylene Diisocyanate trimer adduct (for example, "Coronate HL" manufactured by Tosoh), trimethylolpropane adduct of xylylene diisocyanate (for example, "Takenate D110N" manufactured by Mitsui Chemicals, isocyanurate body of hexamethylene diisocyanate (for example, "Tosoh" Coronate HX") and other isocyanate adducts.

By adjusting the addition amount of the crosslinking agent, the gel fraction of the pressure-sensitive adhesive sheet can be adjusted within a predetermined range. In order to adjust the gel fraction of the pressure-sensitive adhesive sheet before photocuring to 25 to 70%, the amount of the crosslinking agent added is preferably 0.03 to 0.5 part by weight, based on 100 parts by weight of the base polymer. 0.05 to 0.3 parts by weight is more preferable, 0.06 to 0.25 parts by weight is further preferable, and 0.07 to 0.2 parts by weight is particularly preferable. The larger the amount of the cross-linking agent added, the higher the gel fraction of the pressure-sensitive adhesive sheet before photocuring, and the higher _G'25°C tends to be.

<Photopolymerizable polyfunctional compound>
The photopolymerizable polyfunctional compound contained in the adhesive sheet has two or more photopolymerizable functional groups in one molecule. The photopolymerizable functional group may be radically polymerizable, cationically polymerizable, or anionically polymerizable, but since it has excellent reactivity, it has a radically polymerizable functional group having an unsaturated double bond (ethylenically unsaturated group). Is preferred. As the photopolymerizable polyfunctional compound, a polyfunctional (meth)acrylate is preferable because it has high compatibility with an acrylic base polymer, and a polyfunctional acrylate is particularly preferable because it has high photoradical reactivity.

As the polyfunctional (meth)acrylate, hexanediol di(methacrylate, nonanediol di(methacrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, neo Bifunctional (meth)acrylic acid esters such as pentyl glycol di(meth)acrylate and glycerin di(meth)acrylate; pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated trisocyanurate Trifunctional (meth)acrylic acid ester such as (meth)acrylate; tetrafunctional (meth), such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate Acrylic acid esters; pentafunctional or higher (meth)acrylic acid esters such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

The molecular weight of the photopolymerizable polyfunctional compound is preferably 1500 or less, more preferably 1000 or less, from the viewpoint of appropriately adjusting the viscoelasticity such as G′ and tan δ of the pressure-sensitive adhesive sheet after photocuring. The functional group equivalent (g/eq) of the polyfunctional compound is preferably 50 to 500, more preferably 70 to 300, and further preferably 80 to 200. It is preferable that the photopolymerizable polyfunctional compound is a liquid at room temperature because it exhibits an appropriate compatibility with the base polymer.

The content of the photopolymerizable polyfunctional compound in the photocurable pressure-sensitive adhesive sheet is preferably 1 to 6 parts by weight, more preferably 2 to 5 parts by weight, and 2.5 to 4 parts by weight with respect to 100 parts by weight of the acrylic base polymer. Weight parts are more preferred. When the content of the photopolymerizable polyfunctional compound is low, the gel fraction and G′ of _{25° C.} of the pressure-sensitive adhesive sheet after photocuring are small, and the adhesive retention tends to be insufficient. On the other hand, when the content of the photocurable polyfunctional compound is large, the pressure-sensitive adhesive sheet after the photocuring may be excessively hard and the impact resistance may be insufficient. Moreover, as the content of the photocurable polyfunctional compound increases, the ratio of the base polymer in the pressure-sensitive adhesive sheet (pressure-sensitive adhesive composition) before photocuring becomes smaller, and the processability and the process dimensional stability tend to decrease. There is.

From the viewpoint of enhancing the cohesiveness of the polymer in the pressure-sensitive adhesive sheet after photocuring and enhancing the adhesive holding power, it is preferable to use a compound having 3 or more photopolymerizable functional groups in one molecule as the photopolymerizable polyfunctional compound. In particular, a trifunctional or higher polyfunctional acrylate is preferable. You may use together a bifunctional photopolymerizable compound and a trifunctional or more than trifunctional photopolymerizable compound. The content of the tri- or more-functional photopolymerizable polyfunctional compound in the photocurable pressure-sensitive adhesive sheet is preferably 0.5 to 5 parts by weight, and 1 to 4.5 parts by weight with respect to 100 parts by weight of the acrylic base polymer. More preferably, 2 to 4 parts by weight is even more preferable.

Even with only a bifunctional photopolymerizable compound, it is possible to increase the adhesive holding power after photocuring by increasing the addition amount. However, if the amount of the photopolymerizable compound added is increased in order to improve the adhesive retention of the pressure-sensitive adhesive sheet after photo-curing, _G'25°C of the pressure-sensitive adhesive sheet before photo-curing becomes small, and the processability and processing dimensional stability are improved. Tends to decrease.
<Adhesive composition>
A pressure-sensitive adhesive composition is prepared by mixing a crosslinking agent, a photopolymerizable polyfunctional compound, a photopolymerization initiator polymerization initiator, and, if necessary, an oligomer and various additives with the base polymer. The pressure-sensitive adhesive composition preferably has a viscosity suitable for coating on a substrate (for example, about 0.5 to 20 Pa·s). The viscosity of the pressure-sensitive adhesive composition can be adjusted to an appropriate range by adjusting the molecular weight of the base polymer, the addition amount of the photopolymerizable polyfunctional compound, the composition of other components (eg, oligomer), the molecular weight, the addition amount, and the like. it can. A viscosity increasing additive or the like may be used for the purpose of adjusting viscosity.

(Photopolymerization initiator)
The photocurable pressure-sensitive adhesive composition contains a photopolymerization initiator. As the photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, a photoactive oxime photopolymerization initiator, Examples thereof include a benzoin photopolymerization initiator, a benzyl photopolymerization initiator, a benzophenone photopolymerization initiator, a ketal photopolymerization initiator, a thioxanthone photopolymerization initiator, and an acylphosphine oxide photopolymerization initiator. The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, based on 100 parts by weight of the base polymer.

(Oligomer)
The pressure-sensitive adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force of the pressure-sensitive adhesive sheet, adjusting the viscosity, and the like. As the oligomer, for example, one having a weight average molecular weight of about 1,000 to 30,000 is used. As the oligomer, an acrylic oligomer is preferable because it has excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains (meth)acrylic acid alkyl ester as a main constituent monomer component. Among them, as a constituent monomer component, a (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth)acrylate) and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl) Those containing (meth)acrylate are preferable. Specific examples of the chain alkyl (meth)acrylate and the alicyclic alkyl (meth)acrylate are as exemplified above as the constituent monomer of the acrylic base polymer.

The glass transition temperature of the acrylic oligomer is preferably 20°C or higher, more preferably 50°C or higher, further preferably 80°C or higher, particularly preferably 100°C or higher. By using a low Tg base polymer having a crosslinked structure introduced therein and a high Tg acrylic oligomer in combination, the adhesive force of the pressure-sensitive adhesive sheet tends to be improved. Although the upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, it is generally 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated by the Fox equation described above.

Among the exemplified (meth)acrylic acid alkyl esters, as the chain alkyl (meth)acrylate, methyl methacrylate is preferable because it has a high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer has, as constituent monomer components, at least one member selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate. Those containing are preferred.

The amount of the alicyclic alkyl(meth)acrylate based on the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and further preferably 30 to 70% by weight. The amount of the chain alkyl(meth)acrylate based on the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and further preferably 30 to 70% by weight.

1000-30000 are preferable, as for the weight average molecular weight of an acrylic oligomer, 1500-10000 are more preferable, 2000-8000 are still more preferable. By using an acrylic oligomer having a molecular weight within the above range, the adhesive force and adhesive holding force of the pressure-sensitive adhesive sheet tend to be improved.

The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components by various polymerization methods. At the time of polymerizing the acrylic oligomer, various polymerization initiators may be used. A chain transfer agent may be used for the purpose of adjusting the molecular weight.

When the pressure-sensitive adhesive composition contains an oligomer component such as an acrylic oligomer, the content thereof is preferably 0.1 to 10 parts by weight, and 0.2 to 5 parts by weight, relative to 100 parts by weight of the base polymer. More preferable. When the content of the oligomer in the pressure-sensitive adhesive composition is in the above range, it is possible to improve the adhesiveness without lowering the processability and the dimensional stability of the pressure-sensitive adhesive sheet before curing, and particularly, The adhesive strength of the pressure-sensitive adhesive sheet after photocuring tends to be improved.

(Silane coupling agent)
A silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the adhesive strength. When the silane coupling agent is added to the pressure-sensitive adhesive composition, the addition amount thereof is usually about 0.01 to 5.0 parts by weight, and 0.03 to 2.0 parts by weight with respect to 100 parts by weight of the base polymer. It is preferably about the same.

(Other additives)
In addition to the components exemplified above, the pressure-sensitive adhesive composition is a chain transfer agent, a tackifier, a plasticizer, a softening agent, a deterioration inhibitor, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, You may contain additives, such as an antistatic agent.

[Adhesive sheet]
A pressure-sensitive adhesive sheet is formed on the base material by applying the pressure-sensitive adhesive composition on the base material and drying and removing the solvent as necessary. Any appropriate base material is used as the base material used for forming the pressure-sensitive adhesive sheet. The base material may be a release film having a release layer on the contact surface with the adhesive sheet.

As the film base material of the release film, films made of various resin materials are used. Examples of the resin material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, Examples thereof include polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polyarylate resin, and polyphenylene sulfide resin. Among these, polyester resins such as polyethylene terephthalate are particularly preferable. 10-200 micrometers is preferable and, as for the thickness of a film base material, 25-150 micrometers is more preferable. Examples of the material of the release layer include a silicone-based release agent, a fluorine-based release agent, a long-chain alkyl-based release agent, and a fatty acid amide-based release agent. The thickness of the release layer is generally about 10 to 2000 nm.

The method for applying the pressure-sensitive adhesive composition on the substrate includes roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, and curtain coating. , Various methods such as lip coating and die coater are used.

When the pressure-sensitive adhesive composition contains a solvent, it is preferable to dry the solvent after coating the pressure-sensitive adhesive composition on the substrate. As a drying method, an appropriate method can be appropriately adopted depending on the purpose. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. As the drying time, an appropriate time can be appropriately adopted. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

After drying the solvent, it is preferable to attach a cover sheet to protect the surface of the pressure-sensitive adhesive sheet. As the cover sheet, it is preferable to use a release film having a release layer on the contact surface with the pressure-sensitive adhesive sheet, similar to the base film.

After coating the pressure-sensitive adhesive composition on the base material, heating is performed if necessary to introduce a crosslinked structure into the base polymer. The heating temperature and the heating time may be appropriately set depending on the type of the cross-linking agent used, and are usually in the range of 20° C. to 160° C. and about 1 minute to 7 days. The heating for drying the solvent may also serve as the heating for crosslinking. As described above, the introduction of the crosslinked structure is not necessarily accompanied by heating.

A crosslinking catalyst may be used to promote the formation of the crosslinked structure. For example, as a crosslinking catalyst for an isocyanate-based crosslinking agent, a metal-based crosslinking catalyst such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric ferric iron, butyltin oxide, dioctyltin dilaurate, or dibutyltin dilaurate (especially tin-based crosslinking catalyst) Etc.

By sticking the release films 1 and 2 on the surface of the pressure-sensitive adhesive sheet 5, as shown in FIG. 1, a pressure-sensitive adhesive sheet having release films temporarily attached to both surfaces thereof can be obtained. The base material and the cover sheet at the time of forming the adhesive sheet may be used as the release films 1 and 2 as they are.

When the release films 1 and 2 are provided on both surfaces of the pressure-sensitive adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. Even if the peeling force when peeling the release film temporarily attached to one surface from the adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other surface from the adhesive sheet 5 are the same, May be different. When the peeling forces of the two are different, the release film 2 (light release film) having a relatively small peeling force is peeled off from the pressure-sensitive adhesive sheet 5 first, and is bonded to the first adherend. It is excellent in workability when the release film 1 (heavy release film) having a large peeling force is peeled off and is bonded to the second adherend.

[Image display device]
The pressure-sensitive adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The type of adherend is not particularly limited, and various types of resin materials, glass, metals and the like can be mentioned. Since the pressure-sensitive adhesive sheet of the present invention has high transparency, it is suitable for bonding optical members such as image display devices. In particular, since the pressure-sensitive adhesive sheet of the present invention is excellent in step absorbability and impact resistance, it is suitably used for bonding a transparent member such as a front transparent plate or a touch panel to the viewing side surface of an image display device.

FIG. 2 is a cross-sectional view showing a laminated configuration example of the image display device in which the front transparent plate 7 is attached to the viewing side surface of the image display panel 10 via the adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 attached to the surface of the image display cell 6 such as a liquid crystal cell or an organic EL cell on the viewing side through an adhesive sheet 4. The front transparent plate 7 is provided with a printing layer 76 on the periphery of one surface of a transparent flat plate 71. As the transparent plate 71, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate is used. The transparent plate 71 may have a touch panel function. As the touch panel, a touch panel of any type such as a resistance film type, an electrostatic capacitance type, an optical type, an ultrasonic type or the like is used.

The polarizing plate 3 provided on the surface of the image display panel 10 and the surface of the front transparent plate 7 on which the print layer 76 is formed are attached to each other via the adhesive sheet 5. The order of bonding is not particularly limited, and the adhesive sheet 5 may be bonded to the image display panel 10 first, or the adhesive sheet 5 may be bonded to the front transparent plate 7 first. Good. Also, the both can be bonded at the same time. From the viewpoint of workability of bonding and the like, after peeling one release film (light release film) 2, the exposed surface of the adhesive sheet 5 is bonded to the image display panel 10, and then the other release film 1 It is preferable that the (heavy release film) is peeled off and the exposed surface of the adhesive sheet is attached to the front transparent plate 7.

After adhering the adhesive sheet 5 and the front transparent plate 7, defoaming for removing bubbles at the interface between the adhesive sheet 5 and the flat plate 71 portion of the front transparent plate 7 and in the vicinity of the non-flat portion such as the printing layer 76. Is preferably performed. As a defoaming method, an appropriate method such as heating, pressurizing, depressurizing or the like can be adopted. For example, it is preferable that the bonding is performed under reduced pressure and heating while suppressing the inclusion of air bubbles, and then the pressure is simultaneously applied with heating by autoclave treatment or the like for the purpose of suppressing delay bubbles. When degassing is performed by heating, the heating temperature is generally about 40 to 150°C. When pressurization is performed, the pressure is generally about 0.05 MPa to 2 MPa.

Since the pressure-sensitive adhesive sheet of the present invention has a storage elastic modulus G′ at _25° C. before photo-curing of 25° _C. of 100 to 250 kPa and a gel fraction of ₂₅ to 70%, it follows the step shape of the printing layer 76 and the like. It is easy to prevent the occurrence of voids, and is less likely to cause adhesive chipping during processing or positional deviation between members during transportation and processing, resulting in excellent workability and processing dimensional stability.

After adhering the pressure-sensitive adhesive sheet before photocuring to an adherend such as a front transparent plate, the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet is photocured. Due to the light irradiation, the polymerization reaction of the photopolymerizable polyfunctional compound proceeds, the storage elastic modulus of the pressure-sensitive adhesive sheet increases accordingly, and the adhesion reliability between the pressure-sensitive adhesive sheet 5 and the front transparent member 70 is enhanced.

The irradiation light amount at the time of photocuring is not particularly limited as long as it is a range in which the pressure-sensitive adhesive sheet can be photocured, and for example, the integrated light amount is about 50 to 10000 mJ/cm ² . The irradiation light amount is preferably set so that the residual C=C bond is 15% or less. The residual C=C bond amount was quantified by infrared spectroscopy, and the C=C bond amount of the pressure-sensitive adhesive sheet before photocuring was 100%, and the pressure-sensitive adhesive sheet was completely cured by irradiating an active energy ray of 10000 mJ/cm ^2. The C=C bond amount in is 0%. When the residual C=C bond amount is 15% or less, the physical properties of the pressure-sensitive adhesive sheet are almost the same as when the residual C=C bond amount is 0%.

When a gap 90 exists between the housing 9 and the front transparent plate 7, it is preferable to fill the gap 90 with a resin material or the like for sealing. As described above, the pressure-sensitive adhesive sheet after photocuring has a large storage elastic modulus, and therefore has excellent adhesion reliability in a wide temperature range. Therefore, even if stress strain occurs at the bonding interface of the pressure-sensitive adhesive sheet due to a temperature change during sealing with a resin material or the like, peeling at the bonding interface can be suppressed. Further, the adhesive sheet after photocuring has a low glass transition temperature and a large peak top value of tan δ, so that it has excellent impact resistance and is unlikely to peel off due to an impact such as dropping.

[Optical film with adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention can be used as a pressure-sensitive adhesive-attached film in which the pressure-sensitive adhesive sheet is fixed to an optical film or the like, in addition to the form in which release films are temporarily attached to both sides as shown in FIG. For example, in the form shown in FIG. 3, the release film 1 is temporarily attached to one surface of the adhesive sheet 5, and the polarizing plate 3 is attached to the other surface of the adhesive sheet 5. In the form shown in FIG. 4, the pressure-sensitive adhesive sheet 4 is further provided on the polarizing plate 3, and the release film 2 is temporarily attached thereon.

In this manner, in the form in which the optical film such as the polarizing plate is previously attached to the pressure-sensitive adhesive sheet, the release film 1 temporarily attached to the surface of the pressure-sensitive adhesive sheet 5 is peeled off and the front transparent member is attached. After that, the adhesive sheet 5 may be photocured.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Preparation of acrylic oligomer]
60 parts by weight of dicyclopentanyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent are mixed, and nitrogen is mixed. The mixture was stirred under an atmosphere at 70°C for 1 hour. Next, 0.2 part by weight of 2,2′-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, reacted at 70° C. for 2 hours, and then heated to 80° C. for 2 hours. It was made to react. After that, the reaction solution was heated to 130° C. to dry and remove toluene, the chain transfer agent and the unreacted monomer to obtain a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer was 5,100.

[Example 1]
<Polymerization of base polymer>
In a reaction vessel equipped with a thermometer, a stirrer, a cooler and a nitrogen gas introduction tube, as monomer components, butyl acrylate (BA): 64.5 parts by weight, cyclohexyl acrylate (CHA): 6.0 parts by weight, N -Vinylpyrrolidone (NVP): 9.6 parts by weight, 4-hydroxybutyl acrylate (4HBA): 10 parts by weight and isostearyl acrylate: 5.0 parts by weight, azoisobutyronitrile (AIBN as a thermal polymerization initiator) ): 0.2 parts by weight, and α-thioglycerol (TGR): 0.065 parts by weight as a chain transfer agent, together with 233 parts by weight of ethyl acetate, the mixture was stirred under a nitrogen atmosphere at 23° C. for 1 hour, and nitrogen was added. Substitution was made. Then, the reaction was carried out at 56° C. for 5 hours, and subsequently at 70° C. for 3 hours to prepare an acrylic base polymer solution.

<Preparation of photocurable pressure-sensitive adhesive composition>
A photo-curable pressure-sensitive adhesive composition was prepared by adding the following post-addition components to 100 parts by weight of the base polymer, and mixing the components uniformly with the acrylic base polymer solution obtained above.
(Post-addition ingredient)
As an isocyanate-based cross-linking agent, a trimethylolpropane adduct of xylylene diisocyanate (“Takenate D110N” manufactured by Mitsui Chemicals): 0.1 part by weight;
As a photopolymerizable polyfunctional monomer, dipentaerythritol hexaacrylate (DPHA): 3.0 parts by weight;
The above acrylic oligomer: 5 parts by weight;
As a photopolymerization initiator, 1-hydroxy-cyclohexyl-phenyl-ketone (manufactured by BASF, “Irgacure 184”): 0.2 parts by weight; and as a silane coupling agent, 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd. "KBM-403"): 0.3 parts by weight.

<Preparation of adhesive sheet>
A 75 μm thick polyethylene terephthalate (PET) film (“Diafoil MRF75” manufactured by Mitsubishi Chemical) having a silicone release layer on the surface is used as a base material (also a heavy release film), and the above photocurable adhesive is applied on the base material. The agent composition was applied and heated at 100° C. for 3 minutes to remove the solvent, and then a PET film (“DIAFOIL MRE75” manufactured by Mitsubishi Chemical Co., Ltd.) having a thickness of 75 μm, one surface of which was subjected to silicone release treatment, was attached. This laminate was aged in an atmosphere of 25° C. for 3 days to proceed with cross-linking to obtain a pressure-sensitive adhesive sheet having release films temporarily attached to both surfaces.

[Example 2, Comparative Examples 1 to 5]
The type and amount of the photopolymerizable polyfunctional monomer in the post-addition component were changed as shown in Tables 1 and 2. An adhesive sheet was obtained in the same manner as in Example 1 except for the above.

[Example 3, Comparative Examples 6 and 7]
The addition amount of the crosslinking agent (Takenate D110N) in the post-addition component was changed as shown in Tables 1 and 2. An adhesive sheet was obtained in the same manner as in Example 1 except for the above.

[Examples 4 and 5, Comparative Examples 8 and 9]
The amount of chain transfer agent (TGR) added in the polymerization of the base polymer was changed as shown in Tables 1 and 2. An adhesive sheet was obtained in the same manner as in Example 1 except for the above.

[Example 6]
The charged monomers in the polymerization of the base polymer were 2-ethylhexyl acrylate (2HEA): 62.9 parts by weight, NVP: 14.5 parts by weight, 4HBA: 9.7 parts by weight, and 2-hydroxyethyl acrylate (2HEA). : Changed to 12.9 parts by weight. An adhesive sheet was obtained in the same manner as in Example 1 except for the above.

[Example 7]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 6 except that the acrylic oligomer was not included in the post-addition component.

[Example 8]
The photopolymerizable polyfunctional monomer in the post-addition component was changed as shown in Table 1. An adhesive sheet was obtained in the same manner as in Example 6 except for the above.

[Evaluation]
<Weight average molecular weight>
The weight average molecular weight (Mw) of the base polymer and the acrylic oligomer was measured by a GPC (gel permeation chromatography) device (product name "HLC-8120GPC") manufactured by Tosoh Corporation. As a measurement sample, a filtrate obtained by dissolving a base polymer in tetrahydrofuran to prepare a 0.1% by weight solution and filtering the solution with a 0.45 μm membrane filter was used. The measurement conditions of GPC are as follows.
(Measurement condition)
Column: Tosoh Corp., G7000HXL+GMHXL+GMHXL
Column size: 7.8 mmφ x 30 cm each (total column length: 90 cm)
Column temperature: 40°C, flow rate: 0.8 mL/min
Injection volume: 100 μL
Eluent: Tetrahydrofuran Detector: Differential refractometer (RI)
Standard sample: polystyrene

<Storage elastic modulus of adhesive sheet, glass transition temperature, and tan δ peak value>
Ten adhesive sheets were laminated to have a thickness of about 1.5 mm as a measurement sample. Dynamic viscoelasticity was measured under the following conditions using "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific.
(Measurement condition)
Deformation mode: torsion Measurement frequency: 1 Hz or 1×10 ⁻⁷ Hz
Temperature rising rate: 5°C/min Shape: Parallel plate 7.9 mmφ

The storage elastic modulus was determined by reading the storage elastic modulus G′ at 25° C. from the measurement result. The temperature at which the loss tangent (tan δ) was maximized (peak top temperature) was defined as the glass transition temperature of the adhesive sheet. Further, the value of tan δ (peak top value) at the glass transition temperature was read.

<Gel fraction>
A sample for gel fraction measurement was prepared by scraping about 0.2 g of the adhesive from the adhesive sheet. Samples for measuring the gel fraction of the pressure-sensitive adhesive sheet after photocuring were collected from the following adhesive force measurement samples. The sample was wrapped with a porous polytetrafluoroethylene membrane (“NTF-1122” manufactured by Nitto Denko) having a pore size of 0.2 μm cut into a size of 100 mm×100 mm, and the wrapped mouth was tied with a tacho thread. The weight (B) of the pressure-sensitive adhesive sample was calculated by subtracting the total weight (A) of the weights of the porous polytetrafluoroethylene film and the taco yarn measured in advance from the weight of this sample. The pressure-sensitive adhesive sample wrapped with the porous polytetrafluoroethylene film was immersed in about 50 mL of ethyl acetate at 23° C. for 7 days to elute the sol component of the pressure-sensitive adhesive out of the porous polytetrafluoroethylene film. .. After the immersion, the pressure-sensitive adhesive wrapped with the porous polytetrafluoroethylene film was taken out, dried at 130° C. for 2 hours, allowed to cool for about 20 minutes, and then the dry weight (C) was measured. The gel fraction of the pressure-sensitive adhesive was calculated by the following formula.
Gel fraction (%)=100×(C−A)/B

<Adhesive strength>
After peeling the light release film from the adhesive sheet and pasting a PET film with a thickness of 50 μm and cutting it into a width of 10 mm and a length of 100 mm, the heavy release film is peeled off and pressure-bonded to the glass plate with a 5 kg roller. A force measurement sample was prepared. Further, ultraviolet rays having an integrated light quantity of 3000 mJ/cm ² were irradiated from the glass plate side with a metal halide lamp (300 mW/cm ² ) to cure, and a sample for measuring adhesive strength of the adhesive sheet after photocuring was prepared. After holding the adhesive strength measurement sample in an environment of 25° C. or 65° C. for 30 minutes, a tensile tester was used to peel the test piece from the glass plate under the conditions of a pulling speed of 300 mm/min and a peeling angle of 180°. Then, the peeling force was measured.

<Step absorbability>
A pressure-sensitive adhesive sheet was cut into a size of 75 mm×45 mm, a light release film was peeled from the pressure-sensitive adhesive sheet, and a roll laminator (pressure between rolls: 0.2 MPa, feed rate: 100 mm/min). Then, the heavy release film was peeled off, and a glass plate (100 mm×50 mm) having a thickness of 500 μm, in which a black ink having a thickness of 20 μm was printed in a frame shape on the peripheral portion, was placed on a roll laminator (pressure between rolls: 0.2 MPa, feed rate). : 100 mm/min). The ink printing area of the glass plate was 5 mm from both ends in the short side direction and 15 mm from both ends in the long side direction, and the black ink layer was in contact with the area 5 mm from the four side edges of the adhesive sheet. This sample was treated in an autoclave (50° C., 0.5 MPa) for 30 minutes and then observed with a digital microscope having a magnification of 20 times to confirm the presence or absence of air bubbles near the boundary of the black ink print area. Those in which no bubbles were confirmed were OK, and those in which bubbles were confirmed were NG.

<Workability>
The light release film was peeled from the pressure-sensitive adhesive sheet, adhered to a PET film having a thickness of 100 μm (“Cosmoshine A4100” manufactured by Toyobo), and punched from the PET film side using a press machine to prepare a sample for processability evaluation. .. This sample was allowed to stand in an atmosphere of temperature: 23° C. and relative humidity of 50% for 1 week, then the heavy release film was peeled off, and the presence or absence of adhesive crack was visually observed. The sample in which no adhesive chip was found was OK, and the sample in which no adhesive chip was found was NG.

<Interlayer adhesion>
(Preparation of test sample)
Cut the adhesive sheet into a size of 75 mm×45 mm, peel off the light release film from the adhesive sheet, and roll a roll laminator (pressure between rolls: 0.2 MPa, feed rate: 100 mm) at the center of a glass plate (100 mm×50 mm) with a thickness of 500 μm. /Minute) and pasted together. The heavy release film was peeled off from the adhesive sheet, and a glass plate with a thickness of 500 μm (50 mm × 100 mm, in which the black ink with a thickness of 30 μm was printed on the peripheral portion in a frame shape, the ink printing area was the same as that used in the step absorbency test). ) Were bonded by vacuum pressure bonding (surface pressure 0.3 MPa, pressure 100 Pa). This sample was treated in an autoclave (50° C., 0.5 MPa) for 30 minutes, and then a metal halide lamp (300 mW/cm ² ) was used to apply ultraviolet rays having an integrated light intensity of 3000 mJ/cm ² from the glass plate side having a black ink print layer. The pressure sensitive adhesive sheet was photocured by irradiation.

After holding the above sample in an environment of 60° C. for 30 minutes, as shown in FIG. 5A, a polystyrene sheet having a thickness of 200 μm was inserted between two glass plates to a distance of 1 mm from the end of the adhesive sheet. Hold for 10 seconds. The edge of the adhesive sheet was observed with a digital microscope with a magnification of 20 times. The striped bubbles (see FIG. 5B) or the ones in which the pressure-sensitive adhesive sheet was peeled from the glass plate were NG, and the ones in which neither bubbles nor peeling occurred were OK.

<Impact resistance>
As in the preparation of the sample for the interlayer adhesion test described above except that the size of the glass plate not provided with the black ink print layer was changed to 100 mm x 70 mm, the glass plate was attached to both sides of the adhesive sheet. The autoclave and the adhesive were cured to prepare a test sample. As shown in FIG. 6, both ends in the short side direction of the test sample 95 are placed on the table 93 with a 60 mm interval so that the glass plate 7 provided with the printing layer 76 is on the lower side. Then, the upper surface of the end portion of the glass plate 8 not provided with the printing layer was fixed on the base 80 with an adhesive tape (not shown). A test sample 95 fixed on a table 93 with an adhesive tape was held in an environment of -5°C for 24 hours, and then taken out to room temperature, and within 40 seconds, the metal ball 97 having a mass of 11 g was put on the glass plate 7. Was dropped from a height of 300 mm to perform an impact resistance test.

In the impact resistance test, a cylindrical guide 99 is used in order to keep the falling position of the metal ball constant, and is separated by 10 mm in each of the short side direction and the long side direction from the corner of the inner edge of the frame of the printing region of the printing layer 76. The metal ball 97 was dropped to the open position. The test was performed twice, and in each of the tests, the one in which peeling of the glass plate did not occur was OK, and the one in which peeling of the glass plate occurred in one or both of the two times was NG.

[Evaluation results]
Tables 1 and 2 show the composition and evaluation results of the pressure-sensitive adhesive composition used for producing each pressure-sensitive adhesive sheet. In addition, in Table 1 and Table 2, each component is described by the following abbreviations.
<Acrylic monomer>
BA: butyl acrylate 2HEA: 2-ethylhexyl acrylate CHA: cyclohexyl acrylate NVP: N-vinyl-2-pyrrolidone 4HBA: 4-hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate ISTA: isostearyl acrylate <light Polymerizable polyfunctional monomer>
HDDA: Hexanediol diacrylate (Shin-Nakamura Chemical Co., Ltd. "NK ester A-HD-N", functional group equivalent 113 g/eq)
APG400: Polypropylene glycol #400 (n=7) diacrylate (“NK Ester APG400” manufactured by Shin-Nakamura Chemical Co., functional group equivalent weight 268 g/eq)
TMPTA: trimethylpropane triacrylate ("NK Ester A-TMPT" manufactured by Shin-Nakamura Chemical Co., functional group equivalent 99g/eq)
DPHA: Dipentaerythritol hexaacrylate (“NK Ester A-DPH” manufactured by Shin-Nakamura Chemical Co., functional group equivalent weight 96 g/eq)

Each of the pressure-sensitive adhesive sheets of Examples 1 to 8 had good step absorbability and workability before photocuring, and also had good interlayer adhesion and drop impact durability after photocuring.

Comparing Example 1 with Comparative Examples 1 to 3, the gel fraction of the pressure-sensitive adhesive sheet after photocuring increased with an increase in the addition amount of the polyfunctional monomer, and the G′ _{25° C.} increased accordingly. And the peak top value of tan δ tended to decrease. In Comparative Example 1 in which the amount of the polyfunctional monomer added was small, the adhesive force after photocuring was higher than that in Example 1, but the adhesive holding force was low, and peeling was confirmed in the interlayer adhesion test. In Comparative Examples 2 and 3 in which the addition amount of the polyfunctional monomer was large, the viscosity of the pressure-sensitive adhesive sheet was low and the impact resistance was insufficient. Further, in Comparative Example 3, the interlayer adhesiveness was also reduced due to the decrease in the adhesive strength. In addition, from the comparison between Example 1 and Comparative Examples 1 to 3, since the ratio of the base polymer in the pressure-sensitive adhesive composition decreases with an increase in the addition amount of the polyfunctional monomer, the pressure-sensitive adhesive sheet before photocuring It can be seen that the gel fraction and the storage elastic modulus are lowered.

In Comparative Example 4 and Comparative Example 5, since the addition amount of the polyfunctional monomer was large, the gel fraction and the storage elastic modulus of the pressure-sensitive adhesive sheet before photocuring were small, and the workability of the pressure-sensitive adhesive sheet was deteriorated. Further, in Comparative Example 4 and Comparative Example 5, the pressure-sensitive adhesive sheet after photocuring was used in spite of the addition of the same amount of multifunctional monomer as in Comparative Example 3 (7 parts by weight to 100 parts by weight of the base polymer). G′ of _{25° C.} was small and the interlayer adhesion was insufficient.

In Example 2 in which the bifunctional acrylate APG400 and the hexafunctional acrylate DPHA were used in combination as the polyfunctional monomer, the same characteristics as in Example 1 were exhibited. Further, Example 8 using TMPTA which is a trifunctional acrylate as the polyfunctional monomer exhibited the same characteristics as Example 6. From these results, by using a polyfunctional monomer having three or more polymerizable functional groups in one molecule, compared with the case of using a bifunctional monomer, even when the addition amount of the polyfunctional monomer is small, the photocuring after photocuring is performed. Since the interlayer adhesive strength of the pressure-sensitive adhesive sheet can be improved, it can be seen that the workability of the pressure-sensitive adhesive sheet before photocuring and the interlayer adhesive strength of the pressure-sensitive adhesive sheet after photocuring can both be achieved.

Comparing Example 1, Example 3, Comparative Example 6 and Comparative Example 7, the gel fraction and the storage elastic modulus of the pressure-sensitive adhesive sheet before photocuring increased with the increase of the addition amount of the cross-linking agent. It can be seen that the glass transition temperature tends to increase. In Comparative Example 6 in which the addition amount of the crosslinking agent was small, the workability was poor because the pressure-sensitive adhesive sheet before photocuring was excessively soft. On the other hand, in Comparative Example 7 in which the amount of the cross-linking agent added was large, the pressure-sensitive adhesive sheet before photocuring was hard, and the adhesiveness and step absorbability were insufficient. Further, in both Comparative Example 6 and Comparative Example 7, the interlayer adhesive strength and impact resistance of the pressure-sensitive adhesive sheet after photocuring were insufficient.

Comparing Example 1, Example 4, Comparative Example 8 and Comparative Example 9, the molecular weight of the base polymer tended to decrease as the amount of the chain transfer agent added during the polymerization of the base polymer increased. In Comparative Example 8 and Comparative Example 9, since the base polymer had a small molecular weight, the storage elastic modulus of the pressure-sensitive adhesive sheet before photocuring was small and the processability was poor. In Comparative Example 8 and Comparative Example 9, the tan δ peak top value of the pressure-sensitive adhesive sheet after photocuring was small, and the impact resistance was insufficient.

From the comparison between Example 6 and Example 7, it can be seen that by adding the oligomer to the pressure-sensitive adhesive composition, the adhesive force of the pressure-sensitive adhesive sheet after photocuring can be improved without significantly changing other properties.

From the comparison of the above examples and comparative examples, the photocurable pressure-sensitive adhesive sheet having the properties before and after photocuring within a predetermined range is compatible with step absorbability and processability in the state before photocuring. It is possible, and it can be seen that after photocuring, the impact resistance and the adhesion durability are excellent.

5 Adhesive Sheet 1, 2 Release Film 3 Polarizing Plate 4 Adhesive Sheet 6 Image Display Cell 10 Image Display Panel 7 Front Transparent Plate 9 Housing 100 Image Display Device

Claims (16)

An acrylic base polymer having a crosslinked structure; a photopolymerizable polyfunctional compound having two or more photopolymerizable functional groups in one molecule; and a photopolymerization initiator-containing pressure-sensitive adhesive composition formed into a layered light. A curable adhesive sheet,
The storage elastic modulus at 25° C. and 1 Hz is 100 to 250 kPa,
Gel fraction is 25-70%,
A pressure-sensitive adhesive sheet having a storage elastic modulus of 180 to 400 kPa at 25° C. and 1 Hz after photocuring the pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet according to claim 1, which has a storage elastic modulus at 25° C. and 10 ⁻⁷ Hz of 4.5 kPa or more. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the glass transition temperature after photocuring the pressure-sensitive adhesive composition is -3°C or lower. The pressure-sensitive adhesive sheet according to claim 1, wherein a gel fraction of the pressure-sensitive adhesive composition after photocuring is 65 to 95%. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein a peak top value of loss tangent after photocuring the pressure-sensitive adhesive composition is 1.5 or more. The adhesive sheet according to any one of claims 1 to 5, wherein the adhesive force to glass is 4 N/10 mm or more, and the adhesive force to glass after photocuring the adhesive composition is 4 N/10 mm or more. .. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which comprises a compound having three or more photopolymerizable functional groups in one molecule as the photopolymerizable polyfunctional compound. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which contains 1 to 6 parts by weight of the photopolymerizable polyfunctional compound with respect to 100 parts by weight of the acrylic base polymer. The pressure-sensitive adhesive sheet according to claim 1, wherein the acrylic base polymer having a crosslinked structure has a crosslinked structure formed by a polyisocyanate compound introduced into a polymer having a weight average molecular weight of 300,000 or more. The pressure-sensitive adhesive sheet according to any one of claims 1 to 9, wherein the acrylic base polymer contains 5 to 30 parts by weight of a hydroxy group-containing monomer based on 100 parts by weight of a total of monomer components. The pressure-sensitive adhesive sheet according to any one of claims 1 to 10, wherein the pressure-sensitive adhesive composition contains an acrylic oligomer having a weight average molecular weight of 1,000 to 30,000. It is a manufacturing method of the adhesive sheet according to any one of claims 1 to 11,
A composition containing an acrylic base polymer, a cross-linking agent, and a photopolymerizable polyfunctional compound having two or more photopolymerizable functional groups in one molecule is applied in a layered manner on a substrate,
A method for producing a pressure-sensitive adhesive sheet, which comprises introducing a crosslinked structure by the crosslinking agent into the acrylic base polymer. The method for producing a pressure-sensitive adhesive sheet according to claim 12, wherein the acrylic base polymer has a weight average molecular weight of 300,000 or more. The pressure-sensitive adhesive sheet according to any one of claims 1 to 11, a first release film temporarily attached to a first main surface of the pressure-sensitive adhesive sheet, and a first release film temporarily attached to a second main surface of the pressure-sensitive adhesive sheet. A pressure-sensitive adhesive sheet with a release film, comprising a release film. An optical film; a first adhesive sheet laminated on the first main surface of the optical film; and a second adhesive sheet laminated on the second main surface of the optical film,
An optical film with an adhesive layer, wherein the first adhesive sheet is the adhesive sheet according to any one of claims 1 to 11. A method for manufacturing an image display device in which a transparent member having a step portion is arranged on the viewing side surface,
After sticking the pressure-sensitive adhesive sheet according to any one of claims 1 to 11 and the transparent member, the pressure-sensitive adhesive composition of the pressure-sensitive adhesive sheet is photocured by irradiating the pressure-sensitive adhesive sheet with an actinic ray. , A method for manufacturing an image display device.