TWI829805B - Adhesive sheet, manufacturing method thereof, and image display device manufacturing method - Google Patents

Abstract

The adhesive sheet (5) of the present invention contains an acrylic base polymer having a cross-linked structure, a photopolymerizable multifunctional compound having two or more photopolymerizable functional groups in one molecule, and a photopolymerization initiator. The adhesive composition is formed into a layered photocurable adhesive sheet. The adhesive sheet preferably has a storage elastic modulus of 100-250 kPa at 25°C and 1 Hz and a gel fraction of 25-70%. The storage elastic modulus of the adhesive sheet at 25°C and 1 Hz after light-hardening the adhesive composition is preferably 180 to 400 kPa.

Description

Adhesive sheet, manufacturing method thereof, and image display device manufacturing method

The present invention relates to a photocurable adhesive sheet and its manufacturing method. Furthermore, the present invention relates to a method of manufacturing an image display device using the adhesive sheet.

Liquid crystal display devices and organic EL (Electroluminescence) display devices are widely used as various image display devices such as mobile phones, smart phones, car navigation devices, computer monitors, and televisions. In order to prevent damage to the image display panel due to impact from the outer surface, a front transparent plate (also called a "cover window", etc.) such as a transparent resin plate or a glass plate is sometimes installed on the viewing side of the image display panel. ). In addition, in recent years, devices including a touch panel on the viewing side of the image display panel have become popular.

In an image display device in which a front transparent member such as a front transparent plate or a touch panel is arranged in front of an image display panel, the image display panel and the front transparent member are bonded together via an adhesive sheet. In addition, an adhesive sheet may be provided between the touch panel and the front transparent plate. By using an adhesive sheet to bond and fix the components, there is an advantage that the front transparent component is less likely to peel off due to impact such as falling, compared to the case where the front transparent component is only fixed to the casing.

A colored layer (decoration) for the purpose of decoration or light-shielding is formed on the periphery of the front transparent member. printing layer). If an adhesive is bonded to a transparent member with a decorative printing layer, bubbles are likely to be generated around the printed step portion. Therefore, a method is adopted to suppress abnormalities such as air bubbles by using a thicker adhesive sheet to provide step absorption. In addition, by using a thicker adhesive sheet, impact resistance tends to be improved.

A method of using an adhesive sheet containing a photocurable adhesive composition for laminating a front transparent member has been proposed (for example, see Patent Document 1 and Patent Document 2). The photocurable adhesive composition contains photopolymerizable polyfunctional monomers or oligomers in an unreacted state. The adhesive sheet before light curing has high fluidity, so it has excellent step absorption, which can prevent air bubbles from being mixed into the laminating interface or near the printing step. By irradiating the adhesive sheet with active light for photohardening after bonding it to the adherend, the fluidity of the adhesive is reduced and the holding power is improved.

[Prior technical literature] [Patent Document]

[Patent Document 1] International Publication No. 2013/161666

[Patent Document 2] Japanese Patent Application Publication No. 2014-227453

In an image display device in which the size of the front transparent member such as the cover window is larger than that of the display panel, the front transparent member is bonded to the casing through an adhesive tape or the like in an area further outside the outer periphery of the display panel. That is, the front transparent member is fixed by bonding it to the casing using an adhesive tape or the like, and bonding it to the surface of the display panel using an adhesive sheet for interlayer filling.

In recent years, display devices have been becoming narrower or borderless, centered on mobile devices such as smartphones. Along with narrowing edges or becoming frameless, image display devices have been developed in which the size of the display panel 10 is equal to or larger than the size of the front transparent member 7 . In this structure, the case 9 and the front transparent member 7 cannot be fixed with an adhesive tape or the like, and the front transparent member 7 needs to be fixed only with the adhesive sheet 5 (see FIG. 2 ). Along with this, the adhesive sheet is required to have higher adhesion strength and to prevent peeling due to impact such as falling.

In addition, as the bezel becomes narrower or frameless, higher dimensional stability is also required when assembling image display devices or transporting unfinished products. The photocurable adhesive sheet used for laminating the front transparent member is soft before photocuring and has excellent step absorption. The adhesive sheet that is flexible in order to have step-absorbing properties has high fluidity in the state before light hardening after being bonded to the adherend. If external force is applied during transportation or processing, it will be easily deformed. , so misalignment may occur between bonded components. In addition, when the fluidity of the adhesive is high, there are processability problems such as defects in the adhesive sheet when the release sheet temporarily adhered to the surface of the adhesive sheet is peeled off.

In view of the above, an object of the present invention is to provide an adhesive sheet that can achieve both step absorption and processability in the state before photocuring and has excellent impact resistance and bonding durability after photocuring.

The present invention relates to a photocurable adhesive sheet in which an adhesive composition is formed into a layer. The adhesive composition constituting the photocurable adhesive sheet contains: an acrylic base polymer having a cross-linked structure, a photopolymerizable multifunctional compound, and a photopolymerization initiator. The photopolymerizable polyfunctional compound is a compound having two or more photopolymerizable functional groups in one molecule, and preferably a compound having three or more photopolymerizable functional groups in one molecule is used.

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

The acrylic base polymer having a cross-linked structure contained in the adhesive sheet is preferably a base polymer in which a cross-linked structure formed by an isocyanate cross-linking agent is introduced into an acrylic base polymer with a weight average molecular weight of 300,000 or more. things. The acrylic base polymer preferably contains 5 to 30 parts by weight of the hydroxyl-containing monomer based on 100 parts by weight of the total monomer components. The adhesive sheet preferably contains 1 to 6 parts by weight of the photopolymerizable multifunctional compound based on 100 parts by weight of the acrylic base polymer.

The above-mentioned adhesive sheet can be formed by coating a composition including an acrylic base polymer, a cross-linking agent, and a photopolymerizable polyfunctional compound in a layer on the base material, and introducing cross-linking into the acrylic base polymer. It is formed by the cross-linked structure formed by the agent.

The adhesive sheet of the present invention is used, for example, for bonding a transparent member in an image display device in which a transparent member is arranged on a viewing side surface. Attach the adhesive sheet to the transparent member, and then The material is irradiated with active light to photoharden the adhesive composition, thereby forming an image display device.

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

The adhesive sheet of the present invention can achieve both step absorption and workability before photocuring, and has excellent impact resistance and bonding durability after photocuring. An image display device with a cover window or the like bonded to the viewing side surface using the adhesive sheet of the present invention has excellent adhesion reliability and can also cope with narrow edges or frameless applications.

1, 2: Release film

3:Polarizing plate

4: Adhesive sheet

5: Adhesive sheet

6:Image display unit

7: Front transparent panel

8:Glass plate

9: Shell

10:Image display panel

71:Transparent board

76: Printing layer

90: gap

93: Taiwan

95: Test specimen

97:Metal Ball

99:Director

100:Image display device

FIG. 1 is a cross-sectional view showing an example of the structure of an adhesive sheet with a release film.

FIG. 2 is a cross-sectional view showing a configuration example of the image display device.

FIG. 3 is a cross-sectional view showing an example of a laminated structure of an optical film with an adhesive sheet.

FIG. 4 is a cross-sectional view showing an example of a laminated structure of an optical film with an adhesive sheet.

Figure 5A is a photograph showing the inter-layer adhesion test.

Figure 5B is an observation photograph of a sample with striped bubbles produced during the interlayer adhesion test.

Fig. 6 is a schematic diagram showing the arrangement of specimens in the impact resistance test.

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

[Physical properties of adhesive sheets]

The adhesive sheet of the present invention is formed by forming an adhesive composition into a layer. The adhesive composition contains: an acrylic base polymer having a cross-linked structure, a photopolymerizable multifunctional compound, and a photopolymerization initiator. agent, and the adhesive sheet has photohardening properties. The adhesive sheet is preferably highly transparent. The total light transmittance of the adhesive sheet is preferably above 85%, more preferably above 90%. The haze of the adhesive sheet is preferably 1.5% or less, more preferably 1% or less.

From the perspective of making the adhesive sheet have step absorption and preventing air bubbles from being mixed near the printing step, the storage elastic modulus G' _25°C of the adhesive sheet before light curing at a temperature of 25°C and a frequency of 1Hz is smaller than It is preferably 250 kPa or less, more preferably 200 kPa or less, still more preferably 180 kPa or less. On the other hand, from the viewpoint of suppressing misalignment after bonding the adhesive sheet to the adherend and ensuring processing dimensional stability, the G' _25°C of the adhesive sheet before light hardening is preferably 100 kPa or more, more preferably 110kPa or more.

The storage elastic modulus of the adhesive sheet before light hardening 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, and further preferably 5.5 kPa or more. If the storage elastic modulus at a frequency of 10 ^-7 Hz is within the above range, the adhesive sheet is less likely to undergo plastic deformation under low-speed strain, and the plasticity of the adhesive sheet during transportation and processing of unfinished products after being bonded to the adherend is The deformation strain is small, so the processing dimensional stability tends to be improved.

The storage elastic modulus of the adhesive sheet before light hardening 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, and further preferably 10 kPa or less. If the storage elastic modulus at a frequency of 10 ^-7 Hz is within the above range, the adhesive will have moderate softness in a high temperature environment, thus ensuring step absorption.

If the adhesive sheet is bonded to the adherend and then photocured, the storage elastic modulus of the adhesive sheet increases due to the photopolymerization reaction (photocuring) of the photopolymerizable polyfunctional compound. The storage elastic modulus G' of the adhesive sheet after light hardening at 25°C and a frequency of 1Hz is preferably at least 180 kPa at _25°C , more preferably at least 200 kPa, and further preferably at least 210 kPa. The higher the G' _25°C of the adhesive sheet after photocuring, the higher the bonding reliability tends to be.

On the other hand, from the viewpoint of providing the adhesive sheet with appropriate viscosity, ensuring wettability, and having bonding durability against impact such as being dropped, the G' _25°C of the adhesive sheet after light curing is preferably 400 kPa. or less, more preferably 350 kPa or less, still more preferably 300 kPa or less, particularly preferably 280 kPa or less.

The glass transition temperature of the adhesive sheet after light hardening 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 adhesive sheet after light hardening is preferably -20°C or higher, more preferably -15°C or higher, and further preferably -13°C or higher. By setting the glass transition temperature within the above range, the adhesive sheet has appropriate viscosity even in a low-temperature region, and therefore tends to have excellent impact resistance.

The peak value of the loss tangent tan δ (that is, tan δ at the glass transition temperature) of the adhesive sheet after light hardening is preferably 1.5 or more, more preferably 1.6 or more, further preferably 1.7 or more, and particularly preferably 1.75 or more. Adhesive sheets with a larger peak value of tan δ tend to have greater adhesive behavior and excellent impact resistance.

The upper limit of the peak value of tan δ of the adhesive sheet after light hardening is not particularly limited, but it is usually 3.0 or less. From the viewpoint of adhesive holding power, the peak value of tan δ is preferably 2.5 or less, more preferably 2.3 or less, and still more preferably 2.1 or less.

In the measurement of the physical properties of the adhesive sheet after light curing, an adhesive sheet that has been light cured so that the residual C=C bond quantified by infrared spectroscopy becomes 15% or less is used. The storage elastic modulus G', glass transition temperature, and peak value of tan δ of the adhesive sheet can be determined by viscoelasticity measurement. In the absence of special circumstances, the measurement frequency is 1Hz. The glass transition temperature is the temperature (peak temperature) at which tan δ becomes maximum. tanδ is the ratio G"/G' of the storage elastic modulus G' and the loss elastic modulus G". The storage elastic modulus G' is equivalent to the part that is stored as elastic energy when the material is deformed, and is an indicator of the degree of hardness. The greater the storage elastic modulus of the adhesive sheet, the higher the subsequent holding power, and the more likely it is to suppress the tendency to peel off due to strain. The loss elastic modulus G" is equivalent to the part of the loss energy lost due to internal friction during deformation of the material, and represents the degree of viscosity. The larger tan δ is, the stronger the tendency of viscosity, and the more liquid the deformation behavior becomes. , and the tendency for the resilience energy to become smaller.

From the viewpoint of ensuring processing dimensional stability by setting G' _25°C to 100 kPa or more and having appropriate flexibility for imparting step absorption, the gel fraction of the adhesive sheet before photocuring is preferably: 25~70%. The gel fraction of the adhesive sheet before light hardening is preferably 30 to 65%, further preferably 33 to 60%, and even more preferably 35 to 55%. From the viewpoint of balancing adhesion reliability and impact resistance, the gel fraction of the adhesive sheet after light curing is preferably 65 to 95%, more preferably 70 to 93%, and further preferably 75 to 90%. .

The gel fraction of the adhesive sheet can be determined in the form of components insoluble in solvents such as ethyl acetate. Specifically, the adhesive that constitutes the adhesive sheet can be immersed in ethyl acetate at 23°C for 7 days. The insoluble component is calculated as the weight fraction (unit: weight %) of the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of cross-linking, and the more cross-linked parts of the polymer, the greater the gel fraction becomes. The gel fraction (the amount of the cross-linked structure introduced) can be adjusted to a desired range by the method of introducing the cross-linked structure, the type and amount of the cross-linking agent, etc.

The adhesion force of the adhesive sheet before light hardening is preferably 4N/10mm or more, more preferably 6N/10mm or more, further preferably 7N/10mm or more, especially 8N/10mm or more. By setting the adhesive force of the adhesive sheet before light curing to the above range, it is possible to prevent the adhesive sheet from peeling off or being dislocated from the adherend during transportation and processing of the unfinished product after being bonded to the adherend. Furthermore, by setting the adhesive force of the adhesive sheet before light curing to the above range, the release film 2 (light release film) temporarily adhered to one side of the adhesive sheet 5 can be peeled off and bonded to the adherend. , when peeling off the release film 1 (releasable film) temporarily adhered to the other side, the peeling at the interface between the adherend and the adhesive sheet 5 is suppressed.

The adhesion strength of the adhesive sheet after light hardening is preferably 4N/10mm or more, and more preferably 4.5 N/10mm or more, more preferably 5N/10mm or more. By setting the adhesive force of the photo-cured adhesive sheet within the above range, it is possible to prevent the adhesive sheet from being peeled off from the adherend when stress due to strain or impact due to dropping or the like occurs.

The adhesion force can be determined by a peeling test with a stretching speed of 300 mm/min and a peeling angle of 180°, using a glass plate as the adherend. Unless otherwise specified, the adhesion force is the measured value at 25°C.

The thickness of the adhesive sheet is not particularly limited and may be set according to the type or shape of the adherend. When a member with a printed step, such as a front transparent plate, is used as the adherend, it is preferable that the thickness of the adhesive sheet is greater than the thickness of the printed step. The thickness of the adhesive sheet used when bonding the front transparent plate (cover window) is preferably 30 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. By increasing the thickness of the adhesive sheet, step absorption and impact resistance tend to become higher. The upper limit of the thickness of the adhesive sheet is not particularly limited, but from the viewpoint of the productivity of the adhesive sheet, it is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 250 μm or less.

[Composition of adhesive]

The composition of the adhesive is not particularly limited. Acrylic polymers, polysiloxane polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate/vinyl chloride copolymers, and modified adhesives can be appropriately selected. Polyolefin, epoxy, fluorine, natural rubber, synthetic rubber and other rubber-based polymers are used as the base polymer. In particular, it has excellent optical transparency, exhibits moderate adhesive properties such as wettability, cohesiveness, and adhesiveness, and is also excellent in weather resistance and heat resistance. In other words, an acrylic adhesive containing an acrylic base polymer introduced with a cross-linked structure can be preferably used.

<Basic polymer>

The acrylic base polymer contains (meth)acrylic acid alkyl ester as the main monomer component. In addition, in this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having a carbon number of 1 to 20 in the alkyl group can be preferably used. The alkyl (meth)acrylate may have a branched alkyl group, and the alkyl (meth)acrylate may have a cyclic alkyl group.

Specific examples of alkyl (meth)acrylate having a chain alkyl group include: (methyl)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylate Isobutyl acrylate, 2nd butyl (meth)acrylate, 3rd butyl (meth)acrylate, amyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate , Hexyl (meth)acrylate, Heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, Octyl (meth)acrylate, Isooctyl (meth)acrylate, (Methyl) Nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate Ester, isotridecyl (meth)acrylate, myristyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, (meth)acrylate Cetyl acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nineteen (meth)acrylate Alkyl esters, etc.

基酯等具有二環式脂肪族烴環之(甲基)丙烯酸酯；(甲基)丙烯酸雙環戊酯、(甲基)丙烯酸雙環戊氧基乙酯、(甲基)丙烯酸三環戊酯、(甲基)丙烯酸1-金剛烷基酯、(甲基)丙烯酸2-甲基-2-金剛烷基酯、(甲基)丙烯酸2-乙基-2-金剛烷基酯等具有三環以上之脂肪族烴環之(甲基)丙烯酸酯。 Specific examples of the alkyl (meth)acrylate having an alicyclic alkyl group include: (meth)cyclopentyl acrylate, (meth)cyclohexyl acrylate, (meth)cycloheptyl acrylate, (Meth)acrylic acid cycloalkyl esters such as (meth)cyclooctyl acrylate; (meth)acrylic acid isopropyl esters

(meth)acrylate with a bicyclic aliphatic hydrocarbon ring such as ester; dicyclopentyl (meth)acrylate, dicyclopentoxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, etc. have three or more rings. (meth)acrylate of aliphatic hydrocarbon ring.

The amount of alkyl (meth)acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more relative to the total amount of monomer components constituting the acrylic base polymer. From the viewpoint of keeping the glass transition temperature (Tg) of the base polymer within an appropriate range, the acrylic base polymer has a chain alkyl group having 4 to 10 carbon atoms relative to the total amount of the monomer components. The amount of alkyl acrylate is preferably 30% by weight or more, more preferably 40% by weight or more, and still more preferably 45% by weight or more.

The acrylic base polymer preferably contains an acrylic monomer unit having a crosslinkable functional group as a copolymer component. By providing the base polymer with a functional group capable of crosslinking, the base polymer can react with the crosslinking agent to adjust the gel fraction of the adhesive to a desired range.

Examples of the acrylic monomer having a crosslinkable functional group include a hydroxyl group-containing monomer or a carboxyl group-containing monomer. For example, when an isocyanate-based cross-linking agent is used, a cross-linked structure is introduced through the reaction of a hydroxyl group and an isocyanate group. When using epoxy cross-linking agent, by carboxyl The cross-linked structure is introduced through the reaction between the base and the epoxy group. Among them, it is preferable to use a hydroxyl-containing monomer as a copolymer component of the base polymer, and to introduce a cross-linked structure through an isocyanate-based cross-linking agent. When the base polymer contains a hydroxyl-containing monomer as a monomer component, there is a tendency to improve the cross-linking properties of the base polymer and suppress the whitening of the adhesive in a high temperature and high humidity environment, thereby obtaining a product with higher transparency. Adhesive.

Examples of the hydroxyl-containing monomer include: (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 4-hydroxybutyl ester, (meth)acrylic acid 6- Hydroxyhexyl ester, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate or (4-hydroxymethylcyclohexyl) (meth)acrylate ) methyl ester and other (meth)acrylate. Among these, 2-hydroxyethyl acrylate (Tg of homopolymer: -15°C) is preferred in terms of its greater contribution to improving adhesive strength and its ability to suppress whitening of the adhesive sheet in a high-humidity environment. ) and 4-hydroxybutyl acrylate (Tg of homopolymer: -32°C). 4-hydroxybutyl acrylate is particularly preferable in that it has a low Tg and contributes greatly to increasing the storage elastic modulus by forming intermolecular hydrogen bonds.

Relative to the total amount of monomer components constituting the acrylic base polymer, the amount of the hydroxyl-containing monomer is preferably 5 to 30 wt%, more preferably 8 to 25 wt%, and further preferably 10 to 20 wt%. By increasing the amount of hydroxyl-containing monomers, the unreacted functional groups of the cross-linking agent are reduced, so the cross-linking degree (gel fraction) can be increased with a smaller cross-linking dose, thereby taking into account the adhesive sheet before light hardening. Processability, processing dimensional stability and step absorption. In addition, since the unreacted hydroxyl groups after cross-linking will form intermolecular hydrogen bonds, it is possible to obtain an adhesive sheet with a G' _25°C of more than 100 kPa even if the gel fraction is less than 70%.

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

When an adhesive sheet is used for bonding to a touch panel sensor, in order to prevent corrosion of the electrodes caused by acid components, the adhesive sheet preferably contains less acid. Furthermore, when an adhesive sheet is used for adhering to a polarizing plate, in order to suppress polyvinylization of the polyvinyl alcohol-based polarizing element caused by an acid component, the adhesive sheet preferably contains less acid. In such an acid-free adhesive sheet, the content of organic acid monomers such as (meth)acrylic acid is preferably 100 ppm or less, more preferably 70 ppm or less, and still more preferably 50 ppm or less. The organic acid monomer content of the adhesive sheet can be determined by the following method: immerse the adhesive sheet in pure water, heat it at 100°C for 45 minutes, and use an ion chromatograph to quantify the acid monomer extracted from the water. .

In order to reduce the acid monomer content in the adhesive sheet, it is preferable that the amount of organic acid monomer components such as (meth)acrylic acid among the monomer components constituting the acrylic base polymer is small. Therefore, in order to make the adhesive sheet acid-free, it is preferable that the base polymer substantially does not contain organic acid monomers (carboxyl group-containing monomers) as monomer components. In the acid-free adhesive sheet, the amount of the carboxyl group-containing monomer is preferably 0.5 parts by weight or less, more preferably 0.1 parts by weight or less, and still more preferably 100 parts by weight of the monomer components of the base polymer in total. It is 0.05 parts by weight or less, preferably 0.

、乙烯基吡

、乙烯基吡 咯、乙烯基咪唑、乙烯基

唑、乙烯基

啉、(甲基)丙烯醯基

啉、N-乙烯基羧酸醯胺類、N-乙烯基己內醯胺等乙烯基系單體；丙烯腈、甲基丙烯腈等氰基丙烯酸酯系單體等。該等中，就由提高凝聚力帶來之接著力提高效果較高之方面而言，較佳為N-乙烯基吡咯啶酮。 The acrylic base polymer may also contain nitrogen-containing monomers as constituent monomer components. Examples of nitrogen-containing monomers include: N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperdine

, Vinylpyr

, vinylpyrrole, vinylimidazole, vinyl

Azole, vinyl

pholine, (meth)acrylyl

Vinyl monomers such as phosphine, N-vinyl carboxylic acid amide, N-vinyl caprolactam, etc.; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile, etc. Among these, N-vinylpyrrolidone is preferable in terms of the higher effect of improving the adhesion force by increasing the cohesive force.

By making the acrylic base polymer contain highly polar monomers such as hydroxyl-containing monomers, carboxyl-containing monomers, and nitrogen-containing monomers as constituent monomer components, the cohesive force of the adhesive can be improved and the adhesiveness can be maintained at high temperatures. tendency to improve. On the other hand, if the content of the highly polar monomer is too large, the glass transition temperature may become high and the adhesiveness or impact resistance at low temperatures may decrease. Therefore, relative to the total amount of monomer components constituting the acrylic base polymer, the amount of highly polar monomers (the total of hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen-containing monomers) is preferably 10~ 45% by weight, more preferably 15 to 40% by weight, further preferably 18 to 35% by weight. Moreover, relative to the total amount of monomer components constituting the acrylic base polymer, the amount of nitrogen-containing monomers is preferably 3 to 25% by weight, more preferably 5 to 20% by weight, and still more preferably 7 to 15% by weight. %.

As monomer components other than the above, the acrylic base polymer may also include anhydride group-containing monomers, (meth)acrylic acid caprolactone adducts, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Vinyl monomers such as vinyl acetate, vinyl propionate, styrene, and α-methylstyrene; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; glycidyl (meth)acrylate esters and other epoxy group-containing monomers; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, methoxypolypropylene glycol ( Diol acrylate monomers such as meth)acrylate; tetrahydrofurfuryl (meth)acrylate, fluoro(meth)acrylate, polysiloxy (meth)acrylate or 2-methyl(meth)acrylate Acrylate monomers such as oxyethyl ester, etc.

The acrylic base polymer preferably contains the largest amount of alkyl (meth)acrylate among the above-mentioned monomer components. The characteristics of the adhesive sheet are easily affected by the type of the most abundant monomer (main monomer) among the monomers constituting the acrylic base polymer. For example, when the main monomer of the acrylic base polymer is alkyl (meth)acrylate having a chain alkyl group with a carbon number of 6 or less, the peak value of tan δ tends to increase and the impact resistance tends to improve. . Especially when C ₄ alkyl acrylate such as butyl acrylate is the main monomer, the peak value of tan δ tends to increase. The amount of alkyl (meth)acrylate having a chain alkyl group with a carbon number of 6 or less is preferably 30 to 80% by weight, more preferably 35 to 80% by weight relative to the total amount of monomer components constituting the acrylic base polymer. 75% by weight, more preferably 40 to 70% by weight. 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, further preferably -15°C or lower. After introducing a cross-linked structure into the acrylic base polymer, the glass transition temperature can be calculated based on the theoretical Tg based on the composition of the polymer. The theoretical Tg is calculated by the following Fox formula based on the glass transition temperature Tg _i of the homopolymer of the monomer components constituting the acrylic base polymer and the weight fraction _Wi of each monomer component.

1/Tg=Σ(W _i /Tg _i )

Tg is the glass transition temperature (unit: K) of the base polymer, _Wi is the weight fraction of the monomer component i that constitutes the base polymer (copolymerization ratio on a weight basis), and Tg _i is the homopolymer of the monomer component i. The glass transition temperature (unit: K). As the glass transition temperature of the homopolymer, the value described in the Polymer Handbook 3rd Edition (John Wiley & Sons, Inc., 1989) can be used. For the Tg of the homopolymer of the monomer not described in the above literature, it is sufficient to use the peak temperature of the loss tangent (tanδ) obtained from dynamic viscoelasticity measurement.

The acrylic base polymer can be obtained by polymerizing the above monomer components by various known methods such as solution polymerization, emulsion polymerization, and block polymerization. From the viewpoint of the balance of characteristics such as adhesive strength and holding power of the adhesive, or the cost, the solution polymerization method is preferred as the polymerization method. As a solvent for solution polymerization, ethyl acetate, toluene, etc. are usually used. The solution concentration is usually about 20~80% by weight. As the polymerization initiator, azo-based initiators, peroxide-based initiators, and redox-based initiators that combine a peroxide and a reducing agent (for example, persulfate and The combination of sodium bisulfite, the combination of peroxide and sodium ascorbate) and other thermal polymerization initiators. The usage amount of the polymerization initiator is not particularly limited. For example, relative to 100 parts by weight of the total amount of monomer components forming the base polymer, it is preferably about 0.005 to 5 parts by weight, and more preferably about 0.02 to 3 parts by weight.

In order to adjust the molecular weight of the base polymer, chain transfer agents can also be used. The chain transfer agent can receive free radicals from growing polymer links, causing elongation of the polymer to cease, and the chain transfer agent receiving free radicals can attack the monomer and initiate polymerization again. Therefore, by using a chain transfer agent, the increase in the molecular weight of the base polymer can be suppressed without reducing the free radical concentration in the reaction system. As the chain transfer agent, for example, α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, and 2-ethylhexyl thioglycolate can be preferably used. , 2,3-dimercapto-1-propanol and other thiols.

The amount of chain transfer agent used is not particularly limited. When the amount of chain transfer agent used is too large, the molecular weight of the base polymer may decrease, and the processability and processing dimensional stability of the adhesive sheet before light curing may decrease. Therefore, the usage amount of the chain transfer agent is preferably 1 part by weight or less, more preferably 0.3 part by weight or less, and still more preferably 0.15 part by weight or less based on 100 parts by weight of the total amount of monomer components constituting the base polymer. , preferably 0.1 parts by weight or less.

The viscoelasticity of the adhesive sheet before light hardening is easily affected by the composition and molecular weight of the base polymer. The greater the molecular weight of the base polymer, the greater the G' _25°C , and the greater the processability and processing dimensional stability tend to be. Therefore, the weight average molecular weight of the acrylic base polymer is preferably 300,000 or more, more preferably 350,000 or more, and still more preferably 400,000 or more. On the other hand, if the molecular weight of the base polymer is too large, the step absorptivity tends to decrease. Therefore, the weight average molecular weight of the base polymer is preferably 1.5 million or less, more preferably 1 million or less, further preferably 800,000 or less, and particularly preferably 650,000 or less. Furthermore, the molecular weight of the base polymer refers to the molecular weight of the polymer before the cross-linked structure is incorporated.

<Cross-linked structure of base polymer>

As a method of introducing a cross-linked structure into the base polymer, the following methods are generally listed: (1) After polymerizing the base polymer having a functional group capable of reacting with the cross-linking agent, the cross-linking agent is added to allow the base polymer to react with the cross-linking agent. The method of linking agent reaction; and (2) the method of introducing a branched structure (cross-linked structure) into the polymer chain by including a photopolymerizable polyfunctional compound in the polymerization component of the base polymer, etc.

The base polymer of the adhesive sheet of the present invention has the properties introduced by the method (1) above. link structure. Furthermore, the adhesive composition constituting the adhesive sheet contains a photopolymerizable polyfunctional compound, and the crosslinked structure of (2) above is introduced by laminating the adhesive sheet and the adherend and then photocuring the adhesive composition. That is, in the adhesive sheet of the present invention, before light curing, the base polymer has a cross-linked structure formed by a (thermal) cross-linking agent such as an isocyanate cross-linking agent. In the photo-hardened adhesive sheet, in addition to the cross-linked structure formed by an isocyanate cross-linking agent, etc., a photopolymerizable polyfunctional compound (photopolymerizable polyfunctional compound (photopolymerizable) such as polyfunctional (meth)acrylate) is also introduced into the base polymer. Cross-linking agent) to form a cross-linked structure.

<Cross-linking agent>

After polymerizing the base polymer, a cross-linking agent is added and heated if necessary to introduce a cross-linked structure into the base polymer. In order to distinguish it from a cross-linked structure introduced by a photopolymerizable polyfunctional compound, cross-linking using an isocyanate cross-linking agent, etc. is sometimes described as "thermal cross-linking". However, when a cross-linking structure is introduced using a cross-linking agent, , or without heating. By introducing a thermal cross-linked structure into the acrylic base polymer, the processability and processing dimensional stability of the adhesive sheet before light curing can be improved.

唑啉系交聯劑、氮丙啶系交聯劑、碳二醯亞胺系交聯劑、金屬螯合物系交聯劑等。 Examples of the crosslinking agent include compounds that react with functional groups such as hydroxyl groups and carboxyl groups contained in the base polymer. Specific examples of the cross-linking agent include isocyanate-based cross-linking agents, epoxy-based cross-linking agents,

Oxazoline-based cross-linking agents, aziridine-based cross-linking agents, carbodiimide-based cross-linking agents, metal chelate-based cross-linking agents, etc.

Among them, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferred because they have high reactivity with the hydroxyl group or carboxyl group of the base polymer and can easily introduce a cross-linked structure. These cross-linking agents It reacts with functional groups such as hydroxyl or carboxyl groups introduced into the base polymer to form a cross-linked structure. In acid-free adhesives whose base polymer does not contain carboxyl groups, it is preferable to use an isocyanate cross-linking agent to form a cross-linked structure through the reaction between the hydroxyl groups in the base polymer and the isocyanate cross-linking agent.

As the isocyanate cross-linking agent, a polyisocyanate having two or more isocyanate groups in one molecule can be used. Examples of isocyanate-based crosslinking agents include lower aliphatic polyisocyanates such as butyl diisocyanate and hexamethylene diisocyanate; cyclopentyl diisocyanate, cyclohexyl diisocyanate, and isophorone diisocyanate. and other alicyclic isocyanates; 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate and other aromatic isocyanates; trimethylolpropane/toluene diisocyanate trimerization Body adducts (such as "Coronate L" manufactured by Tosoh Corporation), trimethylolpropane/hexamethylene diisocyanate trimer adducts (such as "Coronate HL" manufactured by Tosoh Corporation), benzene Trimethylolpropane adduct of dimethyl diisocyanate (for example, "Takenate D110N" manufactured by Mitsui Chemicals Co., Ltd.), isocyanurate body of hexamethylene diisocyanate (for example, "Takenate D110N" manufactured by Tosoh Corporation) Coronate HX") and other isocyanate adducts, etc.

By adjusting the amount of cross-linking agent added, the gel fraction of the adhesive sheet can be adjusted to a specified range. In order to achieve a gel fraction of the adhesive sheet before light hardening of 25 to 70%, the added amount of the cross-linking agent is preferably 0.03 to 0.5 parts by weight, more preferably 0.05 to 0.3, based on 100 parts by weight of the base polymer. Parts by weight, more preferably 0.06~0.25 parts by weight, particularly preferably 0.07~0.2 parts by weight. The greater the amount of cross-linking agent added, the higher the gel fraction of the adhesive sheet before light curing. With this, the G' _25°C tends to become larger.

<Photopolymerizable polyfunctional compound>

The photopolymerizable multifunctional compound contained in the adhesive sheet has two or more photopolymerizable functional groups in one molecule. The photopolymerizable functional group may be any one of radical polymerizability, cationic polymerization, and anionic polymerization. In terms of excellent reactivity, a radical having an unsaturated double bond (ethylenically unsaturated group) is preferred. Polymerizable functional groups. As the photopolymerizable polyfunctional compound, polyfunctional (meth)acrylate is preferred because of its high compatibility with the acrylic base polymer and because of its high photoradical reactivity. , especially multifunctional acrylates.

Examples of polyfunctional (meth)acrylates include hexylene glycol di(meth)acrylate, nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. (Meth)acrylate, polybutylene glycol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate Ester, alkylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin Difunctional (meth)acrylates such as di(meth)acrylate; pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated isocyanuric acid tri(methyl)acrylate ) acrylate and other trifunctional (meth)acrylates; di-trimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate and other tetrafunctional (Meth)acrylate; dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and other pentafunctional or higher (meth)acrylate.

From the viewpoint of appropriately adjusting viscoelasticity such as G' or tan δ of the photo-cured adhesive sheet, the molecular weight of the photopolymerizable polyfunctional compound is preferably 1,500 or less, more preferably 1,000 or less. many The functional group equivalent (g/eq) of the functional compound is preferably 50 to 500, more preferably 70 to 300, and further preferably 80 to 200. In terms of showing appropriate compatibility with the base polymer, the photopolymerizable polyfunctional compound is preferably liquid at normal temperature.

The content of the photopolymerizable multifunctional compound in the photocurable adhesive sheet is preferably 1 to 6 parts by weight, more preferably 2 to 5 parts by weight, and still more preferably 100 parts by weight of the acrylic base polymer. It is 2.5~4 parts by weight. When the content of the photopolymerizable polyfunctional compound is small, the gel fraction and G' _25°C of the adhesive sheet after photocuring tend to be small and the subsequent retention tends to be insufficient. On the other hand, when the content of the photocurable polyfunctional compound is large, the adhesive sheet after photocuring may become too hard and the impact resistance may become insufficient. In addition, as the content of the photocurable polyfunctional compound increases, the ratio of the base polymer in the adhesive sheet (adhesive composition) before photocuring decreases, resulting in a tendency for the processability or processing dimensional stability to decrease.

From the viewpoint of improving the cohesion of the polymer in the photo-cured adhesive sheet and improving the adhesive holding power, it is preferable to use a compound having three or more photopolymerizable functional groups in one molecule as the photopolymerizable polyfunctional The compound is particularly preferably a polyfunctional acrylate having three or more functions. A bifunctional photopolymerizable compound and a trifunctional or higher photopolymerizable compound may be used together. The content of the photopolymerizable multifunctional compound with three or more functions in the photocurable adhesive sheet is preferably 0.5 to 5 parts by weight, more preferably 1 to 4.5 parts by weight, relative to 100 parts by weight of the acrylic base polymer. Preferably it is 2~4 parts by weight.

Even if it is only a bifunctional photopolymerizable compound, the adhesion retention after photocuring can be improved by increasing the amount added. However, if the amount of the photopolymerizable compound added is increased in order to improve the adhesion retention of the adhesive sheet after photocuring, the G' _25°C of the adhesive sheet before photocuring will decrease and the processability or processing dimensional stability will decrease. tendency.

<Adhesive composition>

A crosslinking agent, a photopolymerizable multifunctional compound, a photopolymerization initiator, a polymerization initiator, and optional oligomers or various additives are mixed into a base polymer to prepare an adhesive composition. The adhesive composition preferably has a viscosity suitable for coating on a substrate (for example, about 0.5~20 Pa.s). By adjusting the molecular weight of the base polymer, the added amount of the photopolymerizable multifunctional compound, the composition, molecular weight, added amount of other components (such as oligomers), etc., the viscosity of the adhesive composition can be made within an appropriate range. For purposes such as viscosity adjustment, viscosity-increasing additives can also be used.

(Photopolymerization initiator)

系光聚合起始劑、醯基氧化膦系光聚合起始劑等。相對於基礎聚合物100重量份，黏著劑組合物中之光聚合起始劑之含量較佳為0.01~5重量份，更佳為0.05~3重量份。 The photocurable adhesive composition contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketool photopolymerization initiators, and aromatic sulfonyl chloride photopolymerization initiators. agent, photoactive oxime-based photopolymerization initiator, benzoin-based photopolymerization initiator, benzil-based photopolymerization initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator, 9-oxysulfur

It is a photopolymerization initiator, a phosphine oxide photopolymerization initiator, etc. The content of the photopolymerization initiator in the adhesive composition is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight relative to 100 parts by weight of the base polymer.

(Oligomer)

For the purpose of adjusting the adhesive strength of the adhesive sheet or adjusting the viscosity, the adhesive composition can also be used Contains various oligomers. As an oligomer, for example, one having a weight average molecular weight of about 1,000 to 30,000 can be used. As the oligomer, an acrylic oligomer is preferred in terms of excellent compatibility with the acrylic base polymer.

Acrylic oligomers contain alkyl (meth)acrylate as a main monomer component. Among them, preferred ones include alkyl (meth)acrylate having a chain alkyl group (chain alkyl (meth)acrylate) and alkyl (meth)acrylate having an alicyclic alkyl group ( (Meth)alicyclic alkyl acrylate) as a constituent monomer component. Specific examples of the (meth)acrylic acid chain alkyl ester and (meth)acrylic acid cycloalkyl ester are as exemplified above as the constituent monomers of the acrylic 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 combining a low-Tg base polymer with a cross-linked structure and a high-Tg acrylic oligomer, the adhesive strength of the adhesive sheet tends to be improved. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but it is usually 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 above-mentioned Fox formula.

Among the exemplified alkyl (meth)acrylates, as the linear alkyl (meth)acrylate, the glass transition temperature is relatively high and the compatibility with the base polymer is excellent. Methyl acrylate. As the alicyclic alkyl (meth)acrylate, preferred are dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. That is, the acrylic oligomer preferably contains one or more selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate. Esters serve as monomer components.

The amount of alicyclic alkyl (meth)acrylate is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30~70% by weight. The amount of linear alkyl (meth)acrylate is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and still more preferably 30% by weight relative to the total amount of monomer components constituting the acrylic oligomer. ~70% by weight.

The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, further preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, the adhesive strength or adhesive holding power of the adhesive sheet tends to be improved.

Acrylic oligomers can be obtained by polymerizing the above-mentioned monomer components using various polymerization methods. During the polymerization of acrylic oligomers, various polymerization initiators can also be used. In addition, for the purpose of adjusting molecular weight, a chain transfer agent can also be used.

When the adhesive composition contains an oligomer component such as an acrylic oligomer, its content is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight based on 100 parts by weight of the above-mentioned base polymer. . When the oligomer content in the adhesive composition is within the above range, it is possible to improve the adhesion without reducing the processability and processing dimensional stability of the adhesive sheet before curing, especially the adhesive sheet after light curing. The tendency of the material to increase its adhesion.

(silane coupling agent)

For the purpose of adjusting the adhesion force, a silane coupling agent can also be added to the adhesive composition. When a silane coupling agent is added to the adhesive composition, the amount added is usually about 0.01 to 5.0 parts by weight, preferably about 0.03 to 2.0 parts by weight relative to 100 parts by weight of the base polymer.

(Other additives)

In addition to the above-exemplified ingredients, the adhesive composition may also include chain transfer agents, adhesion-imparting agents, plasticizers, softeners, anti-deterioration agents, fillers, colorants, ultraviolet absorbers, antioxidants, and surfactants. , anti-static agents and other additives.

[Adhesive sheet]

An adhesive sheet is formed on the base material by coating the adhesive composition on the base material and drying and removing the solvent if necessary. As the base material for forming the adhesive sheet, any appropriate base material can be used. The base material may also 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 containing various resin materials can be used. Examples of the resin material include polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate, acetate-based resins, polyether-based resins, polycarbonate-based resins, and polyamides. resin, polyimide resin, polyolefin resin, (meth)acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, poly Aryl ester resin, polyphenylene sulfide resin, etc. Among these, polyester-based resins such as polyethylene terephthalate are particularly preferred. The thickness of the film base material is preferably 10~200 μm, more preferably 25~150 μm. Examples of materials for the release layer include polysiloxane release agents, fluorine release agents, long-chain alkyl release agents, and fatty amide release agents. Release agent, etc. The thickness of the release layer is usually about 10~2000nm.

As a coating method for applying the adhesive composition to the base material, roll coating, contact roll coating, gravure coating, reverse coating, roller brushing, spray coating, dip roll coating, and rod coating can be used. Various methods such as type coating, blade coating, air knife coating, curtain coating, die lip coating, die nozzle coating, etc.

When the adhesive composition contains a solvent, it is preferable to dry the solvent after applying the adhesive composition to the substrate. As a drying method, a suitable method can be used appropriately depending on the purpose. The heating drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and further preferably 70°C to 170°C. The drying time can be appropriately adjusted. 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 the solvent is dried, in order to protect the surface of the adhesive sheet, it is preferred to attach a cover sheet. As the cover sheet, it is preferable to use a release film having a release layer on the contact surface with the adhesive sheet like the base film.

After the adhesive composition is coated on the base material, it is heated if necessary to introduce a cross-linked structure into the base polymer. The heating temperature or heating time can be set appropriately according to the type of cross-linking agent used, usually in the range of 20°C to 160°C and from 1 minute to 7 days. The heating used to dry the solvent can also serve as the heating used for cross-linking. As mentioned above, the introduction of the cross-linked structure does not necessarily involve heating.

In order to promote the formation of the cross-linked structure, a cross-linking catalyst can also be used. For example, as isocyanate Cross-linking catalysts for ester cross-linking agents include: tetra-n-butyl titanate, tetraisopropyl titanate, iron triacetyl acetonate, butyl tin oxide, dioctyl tin dilaurate, and dibutyl tin dilaurate. and other metal-based cross-linking catalysts (especially tin-based cross-linking catalysts), etc.

By bonding the release films 1 and 2 to the surface of the adhesive sheet 5, an adhesive sheet with the release films temporarily adhered to both sides as shown in Figure 1 can be obtained. The base material or cover sheet when forming the adhesive sheet can also be directly used as the release films 1 and 2.

When the release films 1 and 2 are provided on both sides of the 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. The peeling force when the self-adhesive sheet 5 peels off the release film temporarily adhered to one side and the peeling force when the self-adhesive sheet 5 peels off the release film temporarily adhered to the other side may be the same or different. When the peeling force between the two is different, first peel off the release film 2 (light peeling film) with a relatively small peeling force from the adhesive sheet 5, and then bond it to the first adherend, and then adjust the peeling force. The relatively large release film 1 (heavy release film) has excellent workability when it is peeled off and bonded to a second adherend.

[Image display device]

The adhesive sheet of the present invention can be used for laminating various transparent components or opaque components. The type of adherend is not particularly limited, and various resin materials, glass, metal, etc. can be cited. Since the adhesive sheet of the present invention has high transparency, it is suitable for bonding optical components of image display devices and the like. In particular, since the adhesive sheet of the present invention is excellent in step absorption and impact resistance, it can be preferably used to bond transparent members such as front transparent panels and touch panels to the viewing side surface of an image display device.

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

The polarizing plate 3 provided on the surface of the image display panel 10 and the printed layer 76 forming surface of the front transparent plate 7 are bonded together via the adhesive sheet 5 . There is no particular restriction on the order of lamination. The adhesive sheet 5 can be bonded to the image display panel 10 first, or the adhesive sheet 5 can be bonded to the front transparent panel 7 first. Moreover, the two can also be attached at the same time. From the viewpoint of lamination workability, etc., it is preferable to peel off one release film (light release film) 2, bond the exposed surface of the adhesive sheet 5 to the image display panel 10, and then peel off the other release film. The mold film 1 (heavy peeling film) is attached to the front transparent plate 7 with the exposed surface of the adhesive sheet.

It is preferable to remove air bubbles near the interface between the adhesive sheet 5 and the flat plate 71 of the front transparent plate 7 or the non-flat portions such as the printing layer 76 after the adhesive sheet 5 and the front transparent plate 7 are bonded. of deaeration. As a degassing method, appropriate methods such as heating, pressurization, and pressure reduction can be used. For example, it is preferable to perform lamination while suppressing the mixing of bubbles under reduced pressure and heating. Then, for the purpose of suppressing delayed bubbling, it is preferable to perform autoclave processing, which is equal to heating and pressing at the same time. by heating In the case of degassing, the heating temperature is usually around 40℃~150℃. In the case of pressurization, the pressure is usually around 0.05MPa~2MPa.

The adhesive sheet of the present invention has a storage elastic modulus G' at ₂₅ °C of 100 to 250 kPa before light curing and a gel fraction of 25 to 70%, so it can easily follow the step shape of the printing layer 76 and the like. It can suppress the generation of voids and is less likely to cause paste defects during processing or misalignment between components during transportation or processing. It has excellent processability and processing dimensional stability.

After the adhesive sheet before light curing is bonded to an adherend such as a front transparent plate, the adhesive composition constituting the adhesive sheet is light cured. The polymerization reaction of the photopolymerizable polyfunctional compound proceeds by light irradiation, and along with this, the storage elastic modulus of the adhesive sheet increases, and the bonding reliability between the adhesive sheet 5 and the front transparent member 70 improves.

The amount of irradiation light during photocuring is not particularly limited as long as it is within the range that can photoharden the adhesive sheet. For example, the cumulative light amount is about 50 to 10000 mJ/cm ² . The amount of irradiation light is preferably set so that the residual C=C bond becomes 15% or less. The amount of residual C=C bonds is quantified by infrared spectroscopy. The C=C bond amount of the adhesive sheet before light curing is set to 100%. The amount of C=C bonds after irradiation with active energy rays of 10000mJ/ ^cm2 is completely cured. The amount of C=C bonds in the sheet is set to 0%. If the amount of residual C=C bonds is 15% or less, the physical properties of the adhesive sheet will be approximately the same as when the amount of residual C=C bonds is 0%.

When there is a gap 90 between the casing 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 mentioned above, the adhesive sheet after light hardening is due to The storage elastic modulus is large, so the bonding reliability is excellent in a wide temperature range. Therefore, even when stress and strain are generated at the bonding interface of the adhesive sheet due to temperature changes during sealing with a resin material or the like, peeling at the bonding interface can be suppressed. In addition, the adhesive sheet after light hardening has a low glass transition temperature and a large peak value of tan δ, so it has excellent impact resistance and is not prone to peeling caused by impacts such as falling.

[Optical film with adhesive sheet]

In addition to the form in which a release film is temporarily adhered to both sides as shown in Figure 1, the adhesive sheet of the present invention can also be used as an adhesive-attached film to which the adhesive sheet is fixed to an optical film or the like. For example, in the form shown in FIG. 3 , the release film 1 is temporarily adhered to one side of the adhesive sheet 5 , and the polarizing plate 3 is fixed to the other side of the adhesive sheet 5 . In the form shown in FIG. 4 , an adhesive sheet 4 is further provided on the polarizing plate 3 , and the release film 2 is temporarily adhered to the adhesive sheet 4 .

As described above, in a form where an optical film such as a polarizing plate is bonded to an adhesive sheet in advance, the release film 1 temporarily adhered to the surface of the adhesive sheet 5 is peeled off and bonded to the front transparent member. Then the adhesive sheet 5 is light-hardened.

Example

The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

[Production of acrylic oligomer]

Mix 60 parts by weight of dicyclopentyl methacrylate (DCPMA), methyl methacrylate 40 parts by weight of (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 were mixed, and stirred at 70° C. for 1 hour under a nitrogen atmosphere. Then, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added, and the reaction was carried out at 70°C for 2 hours, and then the temperature was raised to 80°C and the reaction was carried out for 2 hours. Thereafter, the reaction liquid was heated to 130° C., toluene, the chain transfer agent and the unreacted monomer were dried and removed to obtain a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer is 5100.

[Example 1]

<Polymerization of basic polymer>

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, azobisisobutyronitrile (AIBN) as a thermal polymerization initiator: 0.2 parts by weight and α-thio as a chain transfer agent Glycerin (TGR): 0.065 parts by weight and 233 parts by weight of ethyl acetate were put into a reaction vessel equipped with a thermometer, a stirrer, a cooler and a nitrogen introduction pipe, and the mixture was stirred for 1 hour under a nitrogen atmosphere at 23°C and replaced with nitrogen. Thereafter, the reaction was carried out at 56°C for 5 hours, and then at 70°C for 3 hours to prepare an acrylic base polymer solution.

<Preparation of photocurable adhesive composition>

To the acrylic base polymer solution obtained above, the following post-addition components were added with respect to 100 parts by weight of the base polymer, and then uniformly mixed to prepare a photocurable adhesive composition.

(Ingredients added later)

Trimethylolpropane adduct of xylylene diisocyanate as isocyanate cross-linking agent ("Takenate D110N" manufactured by Mitsui Chemicals Co., Ltd.): 0.1 parts by weight; dipentaerythritol hexahydrate as photopolymerizable multifunctional monomer Acrylic ester (DPHA): 3.0 parts by weight; the above-mentioned acrylic oligomer: 5 parts by weight; 1-hydroxy-cyclohexyl-phenyl-ketone ("Irgacure 184" manufactured by BASF Corporation) as a photopolymerization initiator: 0.2 parts by weight; and 3-glycidoxypropyltrimethoxysilane ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent: 0.3 parts by weight.

<Production of adhesive sheet>

A polyethylene terephthalate (PET) film ("Diafoil MRF75" manufactured by Mitsubishi Chemical Corporation) with a thickness of 75 μm and a polysiloxane-based release layer provided on the surface is used as the base material (also serves as a heavy release film). The above-mentioned photocurable adhesive composition is coated on the base material, heated at 100°C for 3 minutes to remove the solvent, and then a 75 μm-thick PET film ("Diafoil" manufactured by Mitsubishi Chemical Corporation) that has been peeled off by polysiloxane on one side is laminated. MRE75"). The laminated body was aged for 3 days in an atmosphere of 25°C to perform cross-linking, and an adhesive sheet with a release film temporarily adhered to both sides was obtained.

[Example 2, Comparative Examples 1 to 5]

The types and amounts of the photopolymerizable polyfunctional monomers in the post-added components were changed as shown in Tables 1 and 2. Except for this, an adhesive sheet was obtained in the same manner as in Example 1.

[Example 3, Comparative Examples 6 and 7]

The added amount of the cross-linking agent (Takenate D110N) among the post-added components was changed as shown in Table 1 and Table 2. Except for this, an adhesive sheet was obtained in the same manner as in Example 1.

[Examples 4, 5, Comparative Examples 8, 9]

The amount of the chain transfer agent (TGR) added in the polymerization of the base polymer was changed as shown in Tables 1 and 2. Except for this, an adhesive sheet was obtained in the same manner as in Example 1.

[Example 6]

The added monomers in the polymerization of the base polymer were changed to 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): 12.9 parts by weight. Except for this, an adhesive sheet was obtained in the same manner as in Example 1.

[Example 7]

An adhesive sheet was obtained in the same manner as in Example 6 except that the acrylic oligomer was not included in the post-added component.

[Example 8]

The photopolymerizable polyfunctional monomer among the post-added components was changed as shown in Table 1. Except for this, an adhesive sheet was obtained in the same manner as in Example 6.

[evaluation]

<Weight average molecular weight>

The weight average molecular weight (Mw) of the base polymer and the acrylic oligomer was measured with a GPC (gel permeation chromatography) device (product name "HLC-8120GPC") manufactured by Tosoh Corporation. The measurement sample was a filtrate obtained by dissolving the base polymer in tetrahydrofuran to prepare a 0.1% by weight solution and filtering it through a 0.45 μm membrane filter. The measurement conditions of GPC are as follows.

(Measurement conditions)

Pipe string: Made by Tosoh Corporation, G7000HXL+GMHXL+GMHXL

×30cm(合計管柱長度：90cm) Pipe string size: 7.8mm each

×30cm (total string length: 90cm)

Tube string temperature: 40℃. Flow: 0.8mL/min

Injection volume: 100μL

Eluate: Tetrahydrofuran

Detector: Differential Refractometer (RI)

Standard sample: polystyrene

<Storage elastic modulus, glass transition temperature, and tan δ peak value of adhesive sheet>

Laminate 10 adhesive sheets to make a material with a thickness of approximately 1.5 mm and use it as a measurement sample. The "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific was used, and the dynamic viscoelasticity was measured under the following conditions.

(Measurement conditions)

Transformation mode: twist

Measuring frequency: 1Hz or 1×10 ^-7 Hz

Heating rate: 5℃/min

Shape: parallel plate 7.9mm

The storage elastic modulus is calculated by reading the storage elastic modulus G' at 25°C from the measurement results. The temperature (peak temperature) at which the loss tangent (tanδ) becomes maximum is defined as the glass transition temperature of the adhesive sheet. Also, read the tan δ value (peak value) at the glass transition temperature.

<Gel fraction>

Scrape about 0.2g of adhesive from the adhesive sheet and use it as a sample for gel fraction measurement. The sample for measuring the gel fraction of the adhesive sheet after light hardening is taken from the following sample for measuring the adhesive strength. The sample was wrapped with a porous polytetrafluoroethylene membrane ("NTF-1122" manufactured by Nitto Denko Co., Ltd.) with a pore diameter of 0.2 μm cut into a size of 100 mm × 100 mm, and the wrapping opening was tied with a kite string. Subtract the total weight of the previously measured porous polytetrafluoroethylene membrane and kite string (A) from the weight of the sample to calculate the weight of the adhesive sample (B). Dip the adhesive sample wrapped by the porous polytetrafluoroethylene film into about 50 mL of ethyl acetate at 23°C for 7 days to allow the sol component of the adhesive to dissolve out of the porous polytetrafluoroethylene film. After immersion, take out the adhesive wrapped by the porous polytetrafluoroethylene film, dry it at 130°C for 2 hours, leave it to cool for about 20 minutes, and then measure the dry weight (C). Calculate the gel fraction of the adhesive using the following formula.

Gel fraction (%)=100×(C-A)/B

<Adhesion>

Peel off the light release film from the self-adhesive sheet, laminate it to a PET film with a thickness of 50 μm, cut it into a width of 10 mm x a length of 100 mm, then peel off the heavy release film, and use a 5kg roller to press-bond it to the glass plate to prepare a sample for adhesion strength measurement. . Furthermore, a metal halide lamp (300 mW/cm ² ) was used to irradiate ultraviolet light with a cumulative light intensity of 3000 mJ/cm ² from the glass plate side to cure, thereby preparing a sample for measuring the adhesive strength of the photo-cured adhesive sheet. After maintaining the sample for adhesion strength measurement in an environment of 25°C or 65°C for 30 minutes, use a tensile testing machine to peel the test piece from the glass plate at a tensile speed of 300mm/min and a peeling angle of 180°. Determine the peel force.

<Step Absorption>

Cut the adhesive sheet into a size of 75mm x 45mm, peel off the light release film from the adhesive sheet, and use a laminating machine (pressure between rollers: 0.2MPa, feed speed: 100mm/min) to laminate it until it is cut into 100mm x 50mm The center of the PET film with a thickness of 125μm. Thereafter, the releasable film was peeled off, and a laminating machine (pressure between rollers: 0.2 MPa, feed speed: 100 mm/min) was used to laminate the glass with a thickness of 500 μm and black ink with a thickness of 20 μm printed in a frame shape on the peripheral edge. Board (100mm×50mm). The ink printing area of the glass plate is 5mm from both ends in the short side direction and 15mm from both ends in the long side direction. The area 5mm from the ends of the four sides of the adhesive sheet is connected to the black ink layer. The sample was processed in an autoclave (50°C, 0.5MPa) for 30 minutes, and then observed using a digital microscope with a magnification of 20 times to confirm whether there were bubbles near the boundary of the black ink printing area. The sample in which bubbles were not confirmed was evaluated as OK, and the sample in which bubbles were confirmed was evaluated as NG.

<Processability>

The light release film was peeled off from the adhesive sheet and laminated to a 100 μm thick PET film ("Cosmo Shine A4100" manufactured by Toyobo Co., Ltd.), and a press was used to press from the PET film side to prepare a sample for processability evaluation. After the sample was placed in an atmosphere with a temperature of 23° C. and a relative humidity of 50% for 1 week, the re-peel film was peeled off and the presence or absence of paste defects was visually observed. Those with no paste defects were evaluated as OK, and those with paste defects were evaluated as NG.

<Adhesion between layers>

(Preparation of test specimens)

Cut the adhesive sheet into a size of 75 mm × 45 mm, peel off the light release film from the adhesive sheet, and use a laminating machine (pressure between rollers: 0.2 MPa, feed speed: 100 mm/min) to laminate it to a glass plate with a thickness of 500 μm ( 100mm×50mm) in the center. The releasable film is peeled off from the self-adhesive sheet and bonded to a 500μm thick glass plate (50mm×100mm, ink) with a frame-like printed black ink of 30μm thickness on the periphery by vacuum pressure (surface pressure 0.3MPa, pressure 100Pa) The printed area is the same as that used in the step absorbency test). The sample was treated with an autoclave (50°C, 0.5MPa) for 30 minutes, and then a metal halide lamp (300mW/ ^cm2 ) was used to irradiate a cumulative light amount of 3000mJ/cm2 from the side of the glass plate with a printed layer of ^black ink. UV rays cause the adhesive sheet to light harden.

Keep the above sample at 60°C for 30 minutes. Then, as shown in Figure 5A, insert a polystyrene sheet with a thickness of 200 μm between the two glass plates until it is 1 mm away from the end of the adhesive sheet. Hold for 10 seconds. Use a digital microscope with a magnification of 20 times to observe the end of the adhesive sheet. Those in which striped bubbles (see Figure 5B) were generated or the adhesive sheet peeled off from the glass plate were evaluated as NG, and those in which neither bubbles nor peeling occurred were evaluated as OK.

<Impact resistance>

Except that the size of the glass plate without the printed layer of black ink was changed to 100 mm × 70 mm, the glass plate was bonded to both sides of the adhesive sheet in the same manner as the above-mentioned sample for the interlayer adhesion test. Carry out autoclave treatment and hardening of the adhesive to produce the test Use samples. As shown in FIG. 6 , both ends of the test sample 95 in the short side direction are placed on a stage 93 arranged at a distance of 60 mm so that the glass plate 7 provided with the printing layer 76 is on the lower side. A tape (not shown) secures the upper surface of the end portion of the glass plate 8 that is not provided with the printing layer to the table 80 . The test specimen 95 fixed to the table 93 with an adhesive tape is kept in an environment of -5°C for 24 hours, and then taken out to room temperature, and a metal ball 97 with a mass of 11g is dropped from a height of 300mm within 40 seconds. onto the glass plate 7 to perform an impact resistance test.

In the impact resistance test, in order to fix the falling position of the metal ball, a cylindrical guide 99 is used to make the metal ball 97 fall to the short side direction and the long side direction of the inner edge of the frame of the printing area of the printing layer 76 at positions 10mm apart from the corners. Two tests were conducted, and the test in which no peeling of the glass plate occurred in all tests was evaluated as OK, and the test in which peeling of the glass plate occurred in any one or both of the two tests was evaluated as NG.

[Evaluation results]

The formulation and evaluation results of the adhesive compositions used in the production of each adhesive sheet are shown in Table 1 and Table 2. In addition, in Table 1 and Table 2, each component is described by the following abbreviation.

<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

<Photopolymerizable multifunctional monomer>

HDDA: Hexanediol diacrylate ("NK Ester A-HD-N" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent 113g/eq)

APG400: Polypropylene glycol #400 (n=7) diacrylate ("NK Ester APG400" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent weight 268g/eq)

TMPTA: Trimethylolpropane triacrylate ("NK Ester A-TMPT" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent 99g/eq)

DPHA: dipentaerythritol hexaacrylate ("NK Ester A-DPH" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent 96g/eq)

The adhesive sheets of Examples 1 to 8 had good step absorption and processability before photocuring, and after photocuring, their interlayer adhesion and drop impact durability were both good.

Comparing Example 1 with Comparative Examples 1 to 3, the following tendency was found: as the amount of polyfunctional monomer added increases, the gel fraction of the adhesive sheet after photocuring increases, and with this increase, G' _25°C increases. The peak value of tanδ becomes smaller. In Comparative Example 1 in which the added amount of the polyfunctional monomer was smaller, the adhesion force after photocuring was higher than that in Example 1, but the adhesion retention force was lower, and peeling was confirmed in the interlayer adhesion test. In Comparative Examples 2 and 3 where a large amount of the polyfunctional monomer was added, the adhesive sheet had low viscosity and insufficient impact resistance. Furthermore, in Comparative Example 3, the interlayer adhesion also decreased due to the decrease in adhesive force. In addition, according to the comparison between Example 1 and Comparative Examples 1 to 3, it can be seen that as the amount of polyfunctional monomer added increases, the ratio of the base polymer in the adhesive composition decreases. Therefore, the adhesive sheet before photocuring The gel fraction and storage elastic modulus decrease.

In Comparative Examples 4 and 5, due to the large amount of polyfunctional monomer added, the gel fraction and storage elastic modulus of the adhesive sheet before light curing were small, and the processability of the adhesive sheet was reduced. Moreover, in Comparative Examples 4 and 5, even though the polyfunctional monomer was added in the same amount as in Comparative Example 3 (7 parts by weight relative to 100 parts by weight of the base polymer), the adhesive sheet after photocuring was G' _25℃ is small, and the adhesion between layers is insufficient.

Example 2 in which APG400, a bifunctional acrylate as a polyfunctional monomer, and DPHA, a hexafunctional acrylate, were used together showed the same characteristics as Example 1. In addition, Example 8 using TMPTA, a trifunctional acrylate as a polyfunctional monomer, showed the same characteristics as Example 6. From these results, it can be seen that by using a polyfunctional monomer having three or more polymerizable functional groups in one molecule, the addition amount of the polyfunctional monomer can be smaller compared to the case of using a difunctional monomer. At the same time, it can also improve the interlayer adhesion of the adhesive sheet after light hardening, so it can balance the processability of the adhesive sheet before light hardening and the interlayer adhesion of the adhesive sheet after light hardening.

Comparing Example 1, Example 3, Comparative Example 6 and Comparative Example 7, it can be seen that there is a tendency that as the added amount of the cross-linking agent increases, the gel fraction and storage elastic modulus of the adhesive sheet before light curing increase. Large, the glass transfer temperature of the adhesive sheet increases. In Comparative Example 6, in which the added amount of the cross-linking agent was small, the adhesive sheet before light curing was too soft, so the processability was poor. On the other hand, in Comparative Example 7 in which the crosslinking agent was added in a large amount, the adhesive sheet before photocuring was relatively hard, and the adhesiveness and step absorption were insufficient. In addition, in Comparative Examples 6 and 7, the adhesive sheets after photocuring had insufficient interlayer adhesion and impact resistance.

Comparing Example 1, Example 4, Comparative Example 8 and Comparative Example 9, the following tendency was found: as the amount of chain transfer agent added during polymerization of the base polymer increases, the molecular weight of the base polymer decreases. In Comparative Examples 8 and 9, since the molecular weight of the base polymer is small, the storage elastic modulus of the adhesive sheet before light curing is small and the processability is poor. Furthermore, in Comparative Examples 8 and 9, the tan δ peak value of the adhesive sheet after light curing was small, and the impact resistance was insufficient.

According to the comparison between Example 6 and Example 7, it can be seen that by adding oligomers to the adhesive composition, the adhesion of the adhesive sheet after light curing can be improved without significantly changing other properties.

According to the comparison between the above-mentioned Examples and Comparative Examples, it can be seen that the photo-curable adhesive sheet whose characteristics before and after photo-curing are within the specified range can achieve both step absorption and processability in the state before photo-curing. After hardening, it has excellent impact resistance and bonding durability.

1, 2: Release film

5: Adhesive sheet

Claims (12)

An adhesive sheet, which is a photocurable adhesive sheet formed by forming an adhesive composition into a layer, and the above-mentioned adhesive composition contains: an acrylic base polymer having a cross-linked structure; one molecule having 2 A photopolymerizable multifunctional compound with more than one photopolymerizable functional group; and a photopolymerization initiator. The above-mentioned acrylic base polymer with a cross-linked structure is based on 100 weight of an acrylic base polymer with a weight average molecular weight of more than 300,000. If a cross-linked structure formed by 0.03 to 0.5 parts by weight of isocyanate cross-linking agent has been introduced into Polyfunctional compound, the amount of the compound having more than 3 photopolymerizable functional groups in one molecule is 0.5 to 4 parts by weight relative to 100 parts by weight of the acrylic base polymer, and the adhesive sheet is at 25°C , the storage elastic modulus at 1Hz is 100~250kPa, and the gel fraction is 25~70%, and the storage elastic modulus at 25°C and 1Hz after light hardening of the above adhesive composition is 180~400kPa . For example, the adhesive sheet of claim 1 has a storage elastic modulus of 4.5 kPa or more at 25°C and 10 ^-7 Hz. The adhesive sheet according to claim 1 or 2, wherein the glass transition temperature after the above-mentioned adhesive composition is light-hardened is -3°C or lower. As claimed in claim 1 or 2, the adhesive sheet has a gel fraction of 65 to 95% after light-hardening the adhesive composition. The adhesive sheet according to claim 1 or 2, wherein the peak value of the loss tangent after photohardening the adhesive composition is 1.5 or more. For example, the adhesive sheet of claim 1 or 2 has an adhesion force to glass of 4N/10mm or more, and the adhesion force to glass after the above-mentioned adhesive composition is light-hardened is 4N/10mm or more. Such as the adhesive sheet of claim 1 or 2, wherein the acrylic base polymer contains 5 to 30 parts by weight of hydroxyl-containing monomers relative to 100 parts by weight of the total monomer components. The adhesive sheet of claim 1 or 2, wherein the adhesive composition includes an acrylic oligomer with a weight average molecular weight of 1,000 to 30,000. A method for manufacturing an adhesive sheet, which is the method for manufacturing an adhesive sheet according to any one of claims 1 to 8, and the manufacturing method will include an acrylic base polymer, a cross-linking agent, and a molecule having A composition of a photopolymerizable multifunctional compound with two or more photopolymerizable functional groups is coated on the substrate in a layered manner, The cross-linked structure formed by the above-mentioned cross-linking agent is introduced into the above-mentioned acrylic base polymer. An adhesive sheet with a release film, which is provided with: the adhesive sheet according to any one of claims 1 to 8; a first release film temporarily adhered to the first main surface of the adhesive sheet; and a first release film temporarily adhered to the first main surface of the adhesive sheet; A second release film on the second main surface of the above-mentioned adhesive sheet. An optical film with an adhesive layer, which includes: an optical film; a first adhesive sheet laminated on the first main surface of the above-mentioned optical film; and a second adhesive sheet laminated on the second main surface of the above-mentioned optical film, and The above-mentioned first adhesive sheet is the adhesive sheet according to any one of claims 1 to 8. A method of manufacturing an image display device, which is a method of manufacturing an image display device in which a transparent member having a step portion is disposed on the viewing side surface. The method is a method of manufacturing an image display device by using the adhesive sheet according to any one of claims 1 to 8. After the material is bonded to the above-mentioned transparent member, the above-mentioned adhesive sheet is irradiated with active light, thereby photohardening the adhesive composition of the above-mentioned adhesive sheet.