KR102691366B1 - Adhesive sheet, method for manufacturing the same and method for manufacturing image display unit - Google Patents

Abstract

The adhesive sheet 5 is a photocurable adhesive sheet in which a pressure-sensitive adhesive composition containing an acrylic base polymer with a crosslinked structure, a photopolymerizable multifunctional compound having two or more photopolymerizable functional groups per molecule, and a photopolymerization initiator is formed in a layered manner. The adhesive sheet preferably has a storage modulus of 100 to 250 kPa at 25°C and 1 Hz and a gel fraction of 25 to 70%. The storage modulus of the adhesive sheet at 25°C and 1 Hz after photocuring the adhesive composition is preferably 180 to 400 kPa.

Description

Adhesive sheet, method of manufacturing the same, and method of manufacturing an image display device {ADHESIVE SHEET, METHOD FOR MANUFACTURING THE SAME AND METHOD FOR MANUFACTURING IMAGE DISPLAY UNIT}

The present invention relates to a photocurable adhesive sheet and a method for producing the same. Additionally, the present invention relates to a method of manufacturing an image display device using the adhesive sheet.

Liquid crystal displays and organic EL displays are widely used as various image display devices such as mobile phones, smartphones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the external surface, a front transparent plate (also called a “cover window”, etc.) such as a transparent resin plate or glass plate is installed on the viewing side of the image display panel. There are cases where it is provided. Additionally, 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 disposed on the front surface of the image display panel, the image display panel and the front transparent member are joined through an adhesive sheet. Additionally, an adhesive sheet may be provided between the touch panel and the front transparent plate. By bonding and fixing the members together with an adhesive sheet, there is an advantage that peeling of the front transparent member due to impact such as dropping is less likely to occur compared to 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 bonded to a transparent member having a decorative printed layer, bubbles are likely to be generated around the printed step portion. Therefore, a method of suppressing problems such as air bubble mixing by providing step absorption by using a thick adhesive sheet is adopted. Additionally, impact resistance tends to improve by using a thick adhesive sheet.

A method of using an adhesive sheet made of a photocurable adhesive composition has been proposed for joining front transparent members (see, for example, Patent Document 1 and Patent Document 2). The photocurable adhesive composition contains a photopolymerizable polyfunctional monomer or oligomer in an unreacted state. Since the adhesive sheet before photocuring has high fluidity, it has excellent step absorption and can prevent air bubbles from entering the bonding interface or the vicinity of the printing step. By photocuring the adhesive sheet by irradiating actinic light after bonding to the adherend, the fluidity of the adhesive decreases and the adhesion holding power improves.

International Publication No. 2013/161666 Japanese Patent Publication No. 2014-227453

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 joined with an adhesive tape or the like in an area outside the outer periphery of the display panel. That is, the front transparent member is fixed by a combination of bonding to the housing using an adhesive tape or the like and bonding to the display panel surface using an adhesive sheet for interlayer filling.

In recent years, frame width narrowing and bezel-less display devices have been progressing, especially in mobile devices such as smartphones. With the narrowing of frame widths and becoming bezel-less, image display devices in which the size of the display panel 10 is equal to or larger than the size of the front transparent member 7 have also been developed. In this configuration, the housing 9 and the front transparent member 7 cannot be fixed with adhesive tape or the like, and it is necessary to secure the front transparent member 7 only with the adhesive sheet 5 (see Fig. 2). ). In line with this, adhesive sheets are required to have higher adhesive strength and are required to prevent peeling due to impacts such as dropping.

In addition, with narrowing of frame widths and becoming bezel-less, high dimensional stability has become required even when assembling image display devices or transporting unfinished products. The photocurable adhesive sheet used for joining front transparent members has a soft adhesive before photocuring and is excellent in level difference absorption. The adhesive sheet, which is flexible in order to absorb steps, has high adhesive fluidity in the state after bonding to the adherend but before photocuring, and is prone to deformation when an external force is applied during transportation or processing, so there is a problem between the bonding members. Positional misalignment may occur. In addition, when the fluidity of the adhesive is high, problems with processability, such as the adhesive falling off of the adhesive sheet, may occur when peeling off the release sheet temporarily attached to the surface of the adhesive sheet.

In light of the above, the purpose of the present invention is to provide an adhesive sheet that is compatible with step absorption and processability before photocuring, and has excellent impact resistance and adhesive durability after photocuring.

The present invention relates to a photocurable adhesive sheet in which the adhesive composition is formed in a layered form. The adhesive composition that makes up the photocurable adhesive sheet is. It contains an acrylic base polymer with a crosslinked structure, a photopolymerizable multifunctional compound, and a photopolymerization initiator. A photopolymerizable multifunctional 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 modulus of 100 to 250 kPa at 25°C and 1 Hz and a gel fraction of 25 to 70%. The adhesive sheet preferably has a storage modulus of 4.5 kPa or more at 25°C and 10 ^-7 Hz. The adhesive sheet preferably has an adhesive force to glass of 4N/10mm or more.

The acrylic base polymer having a crosslinked structure contained in the adhesive sheet is preferably an acrylic base polymer having a weight average molecular weight of 300,000 or more, and a crosslinked structure using 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 based on a total of 100 parts by weight of the monomer components. The adhesive sheet preferably contains 1 to 6 parts by weight of a photopolymerizable multifunctional compound based on 100 parts by weight of the acrylic base polymer.

The pressure-sensitive adhesive sheet can be formed by applying a composition containing an acrylic base polymer, a crosslinking agent, and a photopolymerizable multifunctional compound in a layered form on a substrate, and introducing a crosslinking structure using a crosslinking agent into the acrylic base polymer.

The adhesive sheet of the present invention is used, for example, for bonding transparent members in an image display device in which the transparent members are disposed on the viewing side surface. After bonding the adhesive sheet and the transparent member, actinic light is irradiated on the adhesive sheet to photocure the adhesive composition, thereby forming an image display device.

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

The adhesive sheet of the present invention has both step absorption and processability in the state before photocuring, and is excellent in impact resistance and adhesive durability after photocuring. An image display device in which a cover window or the like is bonded to a viewing side surface using the adhesive sheet of the present invention has excellent bonding reliability and can cope with narrowing of the frame width and becoming bezel-less.

1 is a cross-sectional view showing a configuration example of an adhesive sheet provided with a release film.
Fig. 2 is a cross-sectional view showing a configuration example of an image display device.
Figure 3 is a cross-sectional view showing an example of a lamination structure of an optical film provided with an adhesive sheet.
Fig. 4 is a cross-sectional view showing an example of a lamination structure of an optical film provided with an adhesive sheet.
FIG. 5A is a photograph showing an interlayer adhesion test.
Figure 5b is an observation photograph of a sample in which stripe-shaped bubbles were generated in an interlayer adhesion test.
Figure 6 is a schematic diagram showing the arrangement of samples in an impact resistance test.

Fig. 1 shows a pressure-sensitive adhesive sheet including a release film in which release films 1 and 2 are temporarily attached to both sides of the 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 adhesive sheet of the present invention is formed in a layered form of an adhesive composition containing an acrylic base polymer having a crosslinked structure, a photopolymerizable multifunctional compound, and a photopolymerization initiator, and has photocurability. The adhesive sheet preferably has high transparency. The total light transmittance of the adhesive sheet is preferably 85% or more, and more preferably 90% or more. The haze of the adhesive sheet is preferably 1.5% or less, and more preferably 1% or less.

From the viewpoint of providing the adhesive sheet with step absorption properties and preventing air bubbles from entering the vicinity of printing steps, the storage modulus G' _25°C at a temperature of 25°C and a frequency of 1 Hz of the adhesive sheet before photocuring is preferably 250 kPa or less. , 200 kPa or less is more preferable, and 180 kPa or less is further preferable. On the other hand, from the viewpoint of suppressing misalignment after bonding the adhesive sheet to the adherend and ensuring processing dimensional stability, G' _25°C of the adhesive sheet before photocuring is preferably 100 kPa or more, and more preferably 110 kPa or more. .

The storage modulus of the 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, and even more preferably 5.5 kPa or more. If the storage modulus at a frequency of 10 ^-7 Hz is within the above range, the adhesive sheet is unlikely to be plastically deformed due to low-speed distortion, and the plastic deformation distortion of the adhesive sheet during transportation and processing of the unfinished product after bonding to the adherend is small. Processing dimensional stability tends to improve.

The storage modulus of the 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, and still more preferably 10 kPa or less. If the storage modulus at a frequency of 10 ^-7 Hz is within the above range, the adhesive has appropriate softness in a high temperature environment, and step absorption can be ensured.

When photocuring is performed after bonding the adhesive sheet to an adherend, the storage modulus of the adhesive sheet increases due to the photopolymerization reaction (photocuring) of the photopolymerizable multifunctional compound. The storage modulus G' _25°C of the adhesive sheet after photocuring at 25°C and a frequency of 1 Hz is preferably 180 kPa or more, more preferably 200 kPa or more, and still more preferably 210 kPa or more. The higher the G' _25°C of the adhesive sheet after photocuring, the higher the adhesive reliability tends to be.

On the other hand, from the viewpoint of providing the adhesive sheet with appropriate viscosity to ensure wettability and adhesion durability against impacts such as dropping, G' _25°C of the adhesive sheet after photocuring is preferably 400 kPa or less, and 350 kPa. Below is more preferable, 300 kPa or less is further preferable, and 280 kPa or less is particularly preferable.

The glass transition temperature of the adhesive sheet after photocuring is preferably -3°C or lower, more preferably -5°C or lower, and even more preferably -6°C or lower. The glass transition temperature of the adhesive sheet after photocuring is preferably -20°C or higher, more preferably -15°C or higher, and 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 (i.e., tan δ at the glass transition temperature) of the adhesive sheet after photocuring is preferably 1.5 or more, more preferably 1.6 or more, still more preferably 1.7 or more, and particularly preferably 1.75 or more. do. PSA sheets with a large peak top value of tan δ tend to have large viscous behavior and excellent impact resistance.

The upper limit of the tan δ peak top value of the adhesive sheet after photocuring is not particularly limited, but is generally 3.0 or less. From the viewpoint of adhesion holding power, the peak top value of tanδ is preferably 2.5 or less, more preferably 2.3 or less, and still more preferably 2.1 or less.

To measure the physical properties of an adhesive sheet after photocuring, an adhesive sheet that has been photocured so that the remaining C=C bond, as quantified by infrared spectroscopy, is 15% or less is used. The storage elastic modulus G', glass transition temperature, and peak top value of tanδ of the adhesive sheet are determined by viscoelasticity measurement. Unless otherwise specified, the measurement frequency is 1 Hz. The glass transition temperature is the temperature at which tanδ is maximized (peak top temperature). tanδ is the ratio G"/G' of the storage modulus G' and the loss modulus G". The storage modulus G' corresponds to the portion stored as elastic energy when the material is deformed and is an indicator of the degree of hardness. The larger the storage modulus of the adhesive sheet, the higher the adhesion holding power, and the tendency is to suppress peeling due to distortion. The loss modulus G" corresponds to the loss energy portion that is dissipated due to internal friction etc. when the material is deformed, and indicates the degree of viscosity. The larger tanδ, the stronger the tendency for viscosity, the more liquid the deformation behavior, and the more elastic the rebound energy. tends to become smaller.

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

The gel fraction of the adhesive sheet can be determined as the insoluble content in a solvent such as ethyl acetate, and specifically, the insoluble component after immersing the adhesive constituting the adhesive sheet in ethyl acetate at 23°C for 7 days, the sample before immersion. It is calculated as a weight fraction (unit: weight %). Generally, the gel fraction of a polymer is similar to the degree of crosslinking, and the more crosslinked portions there are in the polymer, the larger the gel fraction. The gel fraction (amount of cross-linked structure introduced) can be adjusted to a desired range depending on the method of introducing the cross-linked structure, the type and amount of the cross-linking agent, etc.

The adhesive strength of the adhesive sheet before photocuring is preferably 4 N/10 mm or more, more preferably 6 N/10 mm or more, still more preferably 7 N/10 mm or more, and especially preferably 8 N/10 mm or more. When the adhesive strength of the adhesive sheet before photocuring is within the above range, peeling and misalignment of the adhesive sheet from the adherend during transportation and processing of the unfinished product after bonding to the adherend can be suppressed. In addition, since the adhesive strength of the adhesive sheet before photocuring is within the above range, the release film 2 (light release film) temporarily attached to one side of the adhesive sheet 5 is peeled off and bonded to the adherend, and then the other side is peeled off. When peeling off the release film 1 (heavy release film) temporarily attached to , peeling at the interface between the adherend and the adhesive sheet 5 can be suppressed.

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

The adhesive strength is determined by a peel test using a glass plate as the adherend at a tensile speed of 300 mm/min and a peel angle of 180°. Unless otherwise specified, adhesion is measured at 25°C.

The thickness of the adhesive sheet is not particularly limited and can be set depending on the type or shape of the adherend. When a member having printing steps, 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 steps. The thickness of the adhesive sheet used for bonding the front transparent plate (cover window) is preferably 30 μm or more, more preferably 40 μm or more, and still more preferably 50 μm or more. By increasing the thickness of the adhesive sheet, step absorption and impact resistance tend to increase. The upper limit of the thickness of the adhesive sheet is not particularly limited, but from the viewpoint of productivity of the adhesive sheet, etc., it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less.

[Composition of adhesive]

The composition of the adhesive is not particularly limited and includes acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy, fluorine, natural rubber, synthetic rubber, etc. A polymer such as a rubber-based polymer can be appropriately selected and used as the base polymer. In particular, an acrylic adhesive containing an acrylic base polymer into which a crosslinked structure is introduced is preferably used because it has excellent optical transparency, exhibits adhesive properties such as moderate wettability, cohesiveness, and adhesiveness, and is also excellent in weather resistance and heat resistance.

<Base polymer>

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

As the (meth)acrylic acid alkyl ester, an alkyl (meth)acrylic acid whose alkyl group has 1 to 20 carbon atoms is suitably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or a cyclic alkyl group.

Specific examples of (meth)acrylic acid alkyl esters having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, and (meth)acrylate. t-butyl acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid Octyl, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, Isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate , isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, aralkyl (meth)acrylate, etc.

Specific examples of alkyl (meth)acrylate having an alicyclic alkyl group include cycloalkyl (meth)acrylate such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. ester; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; Dicyclofentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclofentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl ( (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings, such as meth)acrylate and 2-ethyl-2-adamantyl (meth)acrylate.

The amount of alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic base polymer is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more. From the viewpoint of keeping the glass transition temperature (Tg) of the base polymer in an appropriate range, the acrylic base polymer contains 30% by weight of alkyl (meth)acrylate having a chain alkyl group of 4 to 10 carbon atoms relative to the total amount of constituent monomer components. It is preferable that it is more than 40% by weight, more preferably 40% by weight or more, and even more 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 adhesive can be adjusted to a desired range by reacting the base polymer with the crosslinking agent.

Examples of acrylic monomers having a crosslinkable functional group include hydroxy group-containing monomers and carboxyl group-containing monomers. For example, when an isocyanate-based crosslinking agent is used, a crosslinking structure is introduced through a reaction between a hydroxy group and an isocyanate group. When an epoxy-based crosslinking agent is used, a crosslinking structure is introduced through the reaction between the carboxyl group and the epoxy group. Among these, it is preferable to use a hydroxy group-containing monomer as a copolymerization component of the base polymer and to introduce a crosslinked structure using an isocyanate-based crosslinking agent. When the base polymer contains a hydroxy group-containing monomer as a monomer component, the crosslinkability of the base polymer increases and whitening of the adhesive in a high temperature and high humidity environment tends to be suppressed, resulting in a highly transparent adhesive.

As hydroxy group-containing monomers, (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 2-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylic acid 6-hydroxyhexyl, (meth)acrylic acid 8 - (meth)acrylic acid esters such as hydroxyoctyl, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, or (4-hydroxymethylcyclohexyl)-methyl (meth)acrylate. I can hear it. Among these, 2-hydroxyethyl acrylate (homopolymer Tg: -15°C) and 4-hydroxybutyl acrylate have a significant contribution to improving the adhesive strength and can suppress clouding of the adhesive sheet in a high-humidity environment. (Tg of homopolymer: -32°C) is preferred. 4-Hydroxybutyl acrylate is particularly preferred because it has a low Tg and greatly contributes to improving the storage modulus through the formation of intermolecular hydrogen bonds.

The amount of the hydroxy group-containing monomer relative to the total amount of monomer components constituting the acrylic base polymer is preferably 5 to 30% by weight, more preferably 8 to 25% by weight, and even more preferably 10 to 20% by weight. By increasing the amount of hydroxy group-containing monomer, the unreacted functional groups of the cross-linking agent are reduced, so the degree of cross-linking (gel fraction) can be increased with a small amount of cross-linking agent, making it possible to achieve both processability and processing dimensional stability of the adhesive sheet before photocuring and step absorption. there is. Additionally, since unreacted hydroxy groups form intermolecular hydrogen bonds after crosslinking, an 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 carboxyl 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 adhesive sheet is used to adhere a touch panel sensor, it is preferable that the adhesive sheet has a low acid content in order to prevent corrosion of the electrode by acid components. Additionally, when the adhesive sheet is used to adhere a polarizing plate, it is preferable that the adhesive sheet has a low acid content in order to suppress polyenylation of the polyvinyl alcohol-based polarizer by acid components. In such acid-free adhesive sheets, 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 is determined by immersing the adhesive sheet in pure water, heating it at 100°C for 45 minutes, and quantifying the acid monomer extracted into the water using an ion chromatograph.

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 in 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 does not substantially contain an organic acid monomer (carboxylic group-containing monomer) as a monomer component. In the acid-free adhesive sheet, the amount of the carboxyl group-containing monomer relative to a total of 100 parts by weight of the monomer component of the base polymer is preferably 0.5 part by weight or less, more preferably 0.1 part by weight or less, and still more preferably 0.05 part by weight or less, Ideally it is 0.

The acrylic base polymer may contain a nitrogen-containing monomer as a constituent monomer component. Nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, and vinylmor. Vinyl monomers such as polyline, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile. I can hear it. Among these, N-vinylpyrrolidone is preferable because it has a high effect of improving adhesion by improving cohesion.

When the acrylic base polymer contains a highly polar monomer such as a hydroxy group-containing monomer, a carboxyl group-containing monomer, or a nitrogen-containing monomer as a constituent monomer component, the cohesive force of the adhesive increases, and the adhesion retention at high temperatures tends to improve. On the other hand, if the content of the highly polar monomer is excessively large, the glass transition temperature may increase and the adhesion and impact resistance at low temperatures may decrease. Therefore, the amount of high polarity monomer (total of hydroxy group-containing monomer, carboxyl group-containing monomer, and nitrogen-containing monomer) relative to the total amount of monomer components constituting the acrylic base polymer is preferably 10 to 45% by weight, and more preferably 15 to 40% by weight. It is preferred, and 18 to 35% by weight is more preferred. Additionally, the amount of nitrogen-containing monomer relative to the total amount of monomer components constituting the acrylic base polymer is preferably 3 to 25% by weight, more preferably 5 to 20% by weight, and still more preferably 7 to 15% by weight.

Acrylic base polymers include monomer components other than the above, such as acid anhydride group-containing monomers, caprolactone adducts of (meth)acrylic acid, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, vinyl acetate, vinyl propionate, styrene, α-methylstyrene, etc. vinyl monomer; Cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; Epoxy group-containing monomers such as glycidyl (meth)acrylate; Glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; It may contain acrylic acid ester monomers such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, or 2-methoxyethyl (meth)acrylate.

The acrylic base polymer preferably has the highest content of alkyl (meth)acrylate among the monomer components. The characteristics of the adhesive sheet are likely to be influenced by the type of monomer (main monomer) with the highest content among the constituent monomers of the acrylic base polymer. For example, when the main monomer of the acrylic base polymer is an alkyl (meth)acrylate having a chain alkyl group of 6 or less carbon atoms, the peak top value of tan δ increases and impact resistance tends to improve. In particular, when acrylic acid C ₄ alkyl ester such as butyl acrylate is the main monomer, the peak top value of tan δ tends to increase. The amount of the (meth)acrylic acid alkyl ester having a chain alkyl group of 6 or less carbon atoms relative to the total amount of monomer components constituting the acrylic base polymer is preferably 30 to 80% by weight, more preferably 35 to 75% by weight, and 40 to 40% by weight. 70% by weight is more preferable. In particular, it is preferable that the content of butyl acrylate as a constituent monomer component is 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, and even more preferably -15°C or lower. After introducing a crosslinked structure into the acrylic base polymer, the glass transition temperature can be calculated based on the theoretical Tg from the composition of the polymer. Theoretical Tg is calculated from the glass transition temperature Tg _i of the homopolymer of the constituent monomer components of the acrylic base polymer and the weight fraction W _i of each monomer component using Fox's 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 (copolymerization ratio by weight) of monomer component i constituting the base polymer, and Tg _i is the glass transition temperature of the homopolymer of monomer component i ( 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 adopted. The peak top temperature of the loss tangent (tanδ) determined by dynamic viscoelasticity measurement may be used as the homopolymer Tg of a monomer not described in the above literature.

An acrylic base polymer is obtained by polymerizing the monomer component using various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. From the viewpoint of balance of characteristics such as adhesive strength and holding power of the adhesive and cost, etc., a solution polymerization method is suitable as a polymerization method. Ethyl acetate, toluene, etc. are generally used as solvents for solution polymerization. The solution concentration is usually about 20 to 80% by weight. As a polymerization initiator, a thermal polymerization initiator such as an azo-based initiator, a peroxide-based initiator, and a redox-based initiator combining a peroxide and a reducing agent (e.g., a combination of persulfate and sodium bisulfite, or a combination of peroxide and sodium ascorbate) It is preferably used. The amount of the polymerization initiator used is not particularly limited, but for example, it is preferably about 0.005 to 5 parts by weight, and more preferably about 0.02 to 3 parts by weight, based on 100 parts by weight of the total amount of monomer components forming the base polymer.

To adjust the molecular weight of the base polymer, a chain transfer agent may be used. The chain transfer agent can accept radicals from the growing polymer chain and stop the elongation of the polymer, and the chain transfer agent that has received the radicals can attack the monomer and start polymerization again. Therefore, by using a chain transfer agent, an increase in the molecular weight of the base polymer can be suppressed without lowering the radical concentration in the reaction system. Examples of chain transfer agents include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, and 2,3-dimercapto. Thiols such as -1-propanol are suitably used.

The amount of the chain transfer agent used is not particularly limited, but if the amount of the chain transfer agent used is excessively large, the molecular weight of the base polymer may decrease, and the processability and processing dimensional stability of the adhesive sheet before photocuring may decrease. Therefore, the amount of the chain transfer agent used is preferably 1 part by weight or less, more preferably 0.3 parts by weight or less, even more preferably 0.15 parts by weight or less, based on 100 parts by weight of the total amount of monomer components constituting the base polymer. Parts by weight or less is particularly preferable.

The viscoelasticity of the adhesive sheet before photocuring is likely to depend on the constituents and molecular weight of the base polymer. The larger the molecular weight of the base polymer, the larger G' _25°C and the tendency for processability and process dimensional stability to improve. 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 excessively large, step absorption 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 especially preferably 650,000 or less. In addition, the molecular weight of the base polymer refers to the molecular weight of the polymer before introduction of the crosslinked structure.

<Crosslinking structure of base polymer>

Methods for introducing a crosslinking structure into a base polymer generally include (1) a method of polymerizing a base polymer having a functional group capable of reacting with a crosslinking agent, then adding a crosslinking agent, and reacting the base polymer with the crosslinking agent; and (2) a method of introducing a branched structure (crosslinked structure) into the polymer chain by including a photopolymerizable multifunctional 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 method (1) above. Additionally, the adhesive composition constituting the adhesive sheet contains a photopolymerizable multifunctional compound, and the crosslinked structure of (2) above is introduced by photocuring the adhesive sheet and the adherend after bonding them. That is, in the pressure-sensitive adhesive sheet of the present invention, before photocuring, the base polymer has a crosslinking structure using a (thermal) crosslinking agent such as an isocyanate crosslinking agent. In the adhesive sheet after photocuring, in addition to the crosslinking structure using an isocyanate crosslinking agent or the like, a crosslinking structure using a photopolymerizable polyfunctional compound (photocrosslinking agent) such as polyfunctional (meth)acrylate is introduced into the base polymer.

<Cross-linking agent>

After polymerizing the base polymer, a crosslinking agent is added and, if necessary, heated, thereby introducing a crosslinked structure into the base polymer. In order to distinguish it from the crosslinking structure introduced by a photopolymerizable multifunctional compound, crosslinking by an isocyanate crosslinking agent, etc. may be described as "thermal crosslinking"; however, the introduction of a crosslinking structure by a crosslinking agent may not involve heating. . By introducing a thermal crosslinking structure to the acrylic base polymer, the processability and processing dimensional stability of the adhesive sheet before photocuring can be improved.

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

Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferable because they have high reactivity with the hydroxy group or carboxyl group of the base polymer and facilitate the introduction of a crosslinked structure. These cross-linking agents react with functional groups such as hydroxy groups and carboxyl groups introduced into the base polymer to form a cross-linked structure. In an acid-free adhesive in which the base polymer does not contain a carboxyl group, it is preferable to use an isocyanate-based crosslinking agent to form a crosslinked structure by reacting the hydroxy group in the base polymer with the isocyanate crosslinking agent.

As an isocyanate-based crosslinking agent, polyisocyanate having two or more isocyanate groups per molecule is used. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; Alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; Aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; Trimethylolpropane/tolylene diisocyanate trimer adduct (e.g., coating agent “Coronate L”), trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., coating agent “Coronate HL”) , trimethylolpropane adduct of xylylene diisocyanate (e.g., “Takenate D110N” manufactured by Mitsui Chemicals, isocyanurate form of hexamethylene diisocyanate (e.g., “Coronate HX” by coating agent), etc. Isocyanate adducts, etc. can be mentioned.

By adjusting the amount of crosslinking agent added, the gel fraction of the adhesive sheet can be adjusted to a predetermined range. In order to set the gel fraction of the adhesive sheet before photocuring to 25 to 70%, the amount of crosslinking agent added is preferably 0.03 to 0.5 parts by weight, more preferably 0.05 to 0.3 parts by weight, and 0.06 to 0.25 parts by weight, based on 100 parts by weight of the base polymer. Parts by weight are more preferable, and 0.07 to 0.2 parts by weight are particularly preferable. The larger the amount of crosslinking agent added, the higher the gel fraction of the adhesive sheet before photocuring, and the G' at _25°C tends to increase accordingly.

<Photopolymerizable multifunctional 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 of radically polymerizable, cationically polymerizable, and anionically polymerizable, but a radically polymerizable functional group having an unsaturated double bond (ethylenically unsaturated group) is preferred because of its excellent reactivity. As a photopolymerizable multifunctional compound, polyfunctional (meth)acrylate is preferable because of its high compatibility with an acrylic base polymer, and polyfunctional acrylate is especially preferable because of its high photo radical reactivity.

As polyfunctional (meth)acrylates, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and 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, tricyclodecane dimethanol di(meth) ) Bifunctional (meth)acrylic acid esters such as acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin di(meth)acrylate; trifunctional (meth)acrylic acid esters such as pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated isocyanuric acid tri(meth)acrylate; Tetrafunctional (meth)acrylic acid esters such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and pentaerythritol penta(meth)acrylate, etc., and dipentaerythritol hexa(meth)acrylate, and more pentafunctional (meth)acrylic acid esters.

From the viewpoint of appropriately adjusting the viscoelasticity such as G' and tan δ of the adhesive sheet after photocuring, the molecular weight of the photopolymerizable multifunctional compound is preferably 1500 or less, and more preferably 1000 or less. The functional group equivalent (g/eq) of the polyfunctional compound is preferably 50 to 500, more preferably 70 to 300, and still more preferably 80 to 200. Since it shows appropriate compatibility with the base polymer, the photopolymerizable multifunctional compound is preferably liquid at room 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 2.5 to 4 parts by weight, based on 100 parts by weight of the acrylic base polymer. . When the content of the photopolymerizable multifunctional compound is small, the gel fraction and G' _25°C of the adhesive sheet after photocuring are small, and the adhesion retention tends to be insufficient. On the other hand, when the content of the photocurable polyfunctional compound is high, the adhesive sheet after photocuring may become excessively hard and the impact resistance may become insufficient. Additionally, as the content of the photocurable multifunctional compound increases, the proportion of the base polymer in the adhesive sheet (adhesive composition) before photocuring decreases, and processability and processing dimensional stability tend to decrease.

From the viewpoint of increasing the cohesiveness of the polymer in the adhesive sheet after photocuring and increasing the adhesive holding power, it is preferable to use a compound having 3 or more photopolymerizable functional groups in one molecule as the photopolymerizable multifunctional compound, especially the trifunctional compound. The above multifunctional acrylates are preferred. A bifunctional photopolymerizable compound and a trifunctional or higher photopolymerizable compound may be used together. The content of the trifunctional or higher photopolymerizable polyfunctional compound in the photocurable adhesive sheet is preferably 0.5 to 5 parts by weight, more preferably 1 to 4.5 parts by weight, and 2 to 4 parts by weight, based on 100 parts by weight of the acrylic base polymer. It is more desirable.

It is possible to increase the adhesive holding power after photocuring by increasing the amount of the bifunctional photopolymerizable compound alone. However, if the amount of photopolymerizable compound added is increased in order to increase the adhesion retention of the adhesive sheet after photocuring, the G' _25°C of the adhesive sheet before photocuring decreases, and processability and processing dimensional stability tend to decrease. .

<Adhesive composition>

A crosslinking agent, a photopolymerizable multifunctional compound, a photopolymerization initiator, a polymerization initiator, and, if necessary, oligomers and various additives are mixed with the base polymer to prepare an adhesive composition. The adhesive composition preferably has a viscosity suitable for application to a substrate (for example, about 0.5 to 20 Pa·s). By adjusting the molecular weight of the base polymer, the amount of the photopolymerizable multifunctional compound added, the composition, molecular weight, and amount of other components (for example, oligomers), the viscosity of the adhesive composition can be adjusted to an appropriate range. For purposes such as viscosity adjustment, a thickening additive or the like may be used.

(Photopolymerization initiator)

The photocurable adhesive composition contains a photopolymerization initiator. As a photopolymerization initiator, a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, a photoactive oxime-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, and benzoate. Examples include phenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. 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, based on 100 parts by weight of the base polymer.

(oligomer)

The adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force or viscosity of the adhesive sheet. As an 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 preferred because it has excellent compatibility with an acrylic base polymer.

Acrylic oligomers contain (meth)acrylic acid alkyl ester as the main monomer component. Among them, as the constituent monomer components, (meth)acrylic acid alkyl ester (chain alkyl (meth)acrylate) having a chain alkyl group and (meth)acrylic acid alkyl ester (alicyclic alkyl (meth)acrylate) having an alicyclic alkyl group. It is desirable to include it. Specific examples of chain alkyl (meth)acrylate and alicyclic alkyl (meth)acrylate are as previously exemplified as constituent monomers 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, and particularly preferably 100°C or higher. The adhesion of the pressure-sensitive adhesive sheet tends to improve by using a low-Tg base polymer with a crosslinked structure in combination with a high-Tg acrylic oligomer. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but 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 using the Fox equation described above.

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

The amount of alicyclic alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight. The amount of linear alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 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, and still more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight in this range, the adhesive strength and adhesive holding power of the adhesive sheet tend to improve.

Acrylic oligomers are obtained by polymerizing the above monomer components using various polymerization methods. When polymerizing an acrylic oligomer, various polymerization initiators may be used. Additionally, 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 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 base polymer. When the oligomer content in the adhesive composition is within the above range, it is possible to improve the adhesiveness without reducing the processability and processing dimensional stability of the adhesive sheet before curing, and in particular, the adhesive strength of the adhesive sheet after photocuring tends to improve. there is.

(Silane coupling agent)

For the purpose of adjusting the adhesive force, a silane coupling agent may 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, based on 100 parts by weight of the base polymer.

(Other additives)

In addition to each component in the above examples, the adhesive composition may contain additives such as chain transfer agents, tackifiers, plasticizers, softeners, anti-deterioration agents, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents.

[Adhesive sheet]

An adhesive sheet is formed on the substrate by applying the adhesive composition to the substrate and drying off the solvent as needed. As the substrate used for forming the adhesive sheet, any suitable substrate can be used. The base material may be a release film provided with a release layer on the contact surface with the adhesive sheet.

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

Methods for applying the adhesive composition to the substrate include roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, Various methods such as die coaters are used.

When the adhesive composition contains a solvent, it is preferable to dry the solvent after application of the adhesive composition to the substrate. As a drying method, an appropriate method may be adopted depending on the purpose. The heat 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 for the drying time, an appropriate time may be 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 desirable to lay a cover sheet to protect the surface of the adhesive sheet. As a cover sheet, like the base film, it is preferable to use a release film provided with a release layer on the contact surface with the adhesive sheet.

After applying the adhesive composition on the substrate, heating is performed as necessary to introduce a crosslinked structure into the base polymer. The heating temperature and heating time can be set appropriately depending on the type of crosslinking agent used, and are usually in the range of 20°C to 160°C and range from 1 minute to about 7 days. Heating for drying the solvent may also serve as heating for crosslinking. As described above, introduction of the crosslinked structure does not necessarily have to involve heating.

A cross-linking catalyst may be used to promote the formation of a cross-linked structure. For example, crosslinking catalysts for isocyanate-based crosslinking agents include tetra-n-butyl titanate, tetraisopropyl titanate, ferric nasem, butyltin oxide, dioctyltin dilaurate, and dibutyltin dilaurate. Metal-based crosslinking catalysts (particularly tin-based crosslinking catalysts) can be used.

By bonding the release films 1 and 2 to the surface of the adhesive sheet 5, an adhesive sheet with release films temporarily attached to both sides is obtained, as shown in FIG. 1. The base material or cover sheet at the time of forming the adhesive sheet may be used as the release films 1 and 2 as is.

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 peeling the release film temporarily attached to one side from the adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other side from the adhesive sheet 5 are different even if they are the same. You can do it. When the peeling forces of the two are different, the release film 2 (easy-release film), which has a relatively small peeling force, is first peeled from the adhesive sheet 5 and bonded to the first adherend, and the peeling force is relatively small. Workability is excellent when peeling the large release film 1 (heavy release film) and bonding it to a second adherend.

[Image display device]

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

FIG. 2 is a cross-sectional view showing an example of a lamination structure of an image display device in which a front transparent plate 7 is bonded to the viewing side surface of the image display panel 10 through an adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 bonded to the viewing side surface of an image display cell 6, such as a liquid crystal cell or an organic EL cell, via an adhesive sheet 4. The front transparent plate 7 has a printing layer 76 provided on the periphery of one side of the transparent flat plate 71. The transparent plate 71 is, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate. The transparent plate 71 may have a touch panel function. As the touch panel, any type of touch panel, such as a resistive type, a capacitive type, an optical type, or an ultrasonic type, is 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 through the adhesive sheet 5. The order of bonding is not particularly limited, and bonding of the adhesive sheet 5 to the image display panel 10 may be performed first, or bonding of the adhesive sheet 5 to the front transparent plate 7 may be performed first. . Additionally, both joining can be performed simultaneously. From the viewpoint of workability of bonding, etc., after peeling off one release film (light release film) 2 and bonding the exposed surface of the adhesive sheet 5 to the image display panel 10, the other release film ( 1) It is desirable to peel off the (heavy release film) and bond the exposed surface of the adhesive sheet to the front transparent plate 7.

After bonding the adhesive sheet 5 and the front transparent plate 7, the interface between the adhesive sheet 5 and the flat plate 71 portion of the front transparent plate 7, the printing layer 76, etc. It is preferable that defoaming is performed to remove air bubbles near the burnt portion. As a degassing method, appropriate methods such as heating, pressurization, and decompression can be adopted. For example, it is preferable that bonding is performed while suppressing the mixing of air bubbles under reduced pressure and heating, and then, for the purpose of suppressing delay bubbles, etc., pressurization is performed simultaneously with heating through autoclave treatment or the like. 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.

The adhesive sheet of the present invention has a storage modulus G' at ₂₅ °C before photocuring of 100 to 250 kPa and a gel fraction of 25 to 70%, so it is easy to follow the shape of the steps such as the printed layer 76. The generation of voids can be suppressed, and it is difficult for adhesives to fall off during processing or misalignment between members during transportation or processing, providing excellent processability and processing dimensional stability.

After the adhesive sheet before photocuring is bonded to an adherend such as a front transparent plate, the adhesive composition constituting the adhesive sheet is photocured. By light irradiation, the polymerization reaction of the photopolymerizable multifunctional compound progresses, and accordingly, the storage elastic modulus of the adhesive sheet increases, and the reliability of adhesion between the adhesive sheet 5 and the front transparent member 70 increases.

The amount of irradiated light during photocuring is not particularly limited as long as it is within the range capable of photocuring the adhesive sheet, for example, the accumulated amount of light is about 50 to 10000 mJ/cm2. The amount of irradiated light is preferably set so that the remaining C=C bond is 15% or less. The amount of remaining C=C bonds is quantified by infrared spectroscopy, and is 100% of the amount of C=C bonds in the adhesive sheet before photocuring, and C= in the adhesive sheet completely cured by irradiating an active energy ray of 10,000 mJ/cm2. The amount of C bonds is set to 0%. When the amount of residual C=C bonds is 15% or less, the physical properties of the adhesive sheet are almost the same as when the amount of residual C=C bonds 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 to perform sealing. As described above, the pressure-sensitive adhesive sheet after photocuring has a high storage modulus and thus has excellent adhesion reliability over a wide temperature range. Therefore, even when stress distortion occurs at the bonded interface of the adhesive sheet due to temperature changes during sealing with a resin material or the like, peeling at the bonded interface can be suppressed. In addition, the adhesive sheet after photocuring has a low glass transition temperature and a large peak top value of tan δ, so it has excellent impact resistance and is unlikely to peel off due to impacts such as dropping.

[Optical film with adhesive sheet]

The adhesive sheet of the present invention can be used in a form in which a release film is temporarily attached to both sides as shown in FIG. 1, and can also be used as a film provided with an adhesive in 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 attached 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 a release film 2 is temporarily attached thereon.

In this way, in the form in which an optical film such as a polarizing plate is previously bonded to the adhesive sheet, the release film 1 temporarily attached to the surface of the adhesive sheet 5 is peeled off, bonded to the front transparent member, and then The adhesive sheet 5 may be photocured.

[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]

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 were mixed and incubated at 70°C in a nitrogen atmosphere. It was stirred for 1 hour. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator and reacted at 70°C for 2 hours, then heated to 80°C and allowed to react for 2 hours. Thereafter, the reaction solution was heated to 130°C, toluene, chain transfer agent, and unreacted monomer were removed by drying, and a solid acrylic oligomer was obtained. The weight average molecular weight of the acrylic oligomer was 5100.

[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, and 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 as a chain transfer agent. α-thioglycerol (TGR): 0.065 parts by weight was added together with 233 parts by weight of ethyl acetate, stirred for 1 hour in a nitrogen atmosphere at 23°C, and substituted with nitrogen. After that, the reaction was carried out at 56°C for 5 hours, followed by reaction 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 relative to 100 parts by weight of the base polymer, and then mixed uniformly to prepare a photocurable adhesive composition.

(post-added ingredients)

As an isocyanate-based crosslinking agent, a trimethylolpropane adduct of xylylene diisocyanate (“Takenate D110N” manufactured by Mitsui Chemicals): 0.1 part by weight;

As a photopolymerizable multifunctional monomer, dipentaerythritol hexaacrylate (DPHA): 3.0 parts by weight;

The acrylic oligomer: 5 parts by weight;

As a photopolymerization initiator, 1-hydroxy-cyclohexyl-phenyl-ketone (“Irgacure 184” manufactured by BASF): 0.2 parts by weight; and

As a silane coupling agent, 3-glycidoxypropyltrimethoxysilane (“KBM-403” manufactured by Shin-Etsu Chemical): 0.3 parts by weight.

<Production of adhesive sheet>

A polyethylene terephthalate (PET) film (“Diafoil MRF75” manufactured by Mitsubishi Chemical) with a thickness of 75 μm provided with a silicone-based release layer on the surface was used as a substrate (Kaneshige release film), and the photocurable adhesive composition was applied onto the substrate. After removing the solvent by heating at 100°C for 3 minutes, a PET film (“Diafoil MRE75” manufactured by Mitsubishi Chemical) with a thickness of 75 μm, one side of which was treated with silicone peeling, was bonded. This laminate was aged in an atmosphere of 25°C for 3 days to advance crosslinking, and an adhesive sheet with a release film temporarily attached to both sides was obtained.

[Example 2, Comparative Examples 1 to 5]

The type and addition amount of photopolymerizable multifunctional monomer in the post-addition component were changed as shown in Tables 1 and 2. Other than that, an adhesive sheet was obtained in the same manner as in Example 1.

[Example 3, Comparative Examples 6, 7]

The addition amount of the crosslinking agent (Takenate D110N) in the post-addition component was changed as shown in Tables 1 and 2. Other than that, an adhesive sheet was obtained in the same manner as in Example 1.

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

The addition amount of chain transfer agent (TGR) in polymerization of the base polymer was changed as shown in Tables 1 and 2. Other than that, an adhesive sheet was obtained in the same manner as in Example 1.

[Example 6]

The input 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. did. Other than that, 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 post-addition component did not include acrylic oligomer.

[Example 8]

The photopolymerizable multifunctional monomer in the post-addition component was changed as shown in Table 1. Other than that, 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 using a GPC (gel permeation chromatography) device manufactured by Cosmetics (product name “HLC-8120GPC”). The measurement sample used was a filtrate obtained by dissolving the base polymer in tetrahydrofuran to obtain a 0.1% by weight solution and filtering it through a 0.45 µm membrane filter. The measurement conditions of GPC are as follows.

(Measuring conditions)

Column: Tosoh Corporation, G7000HXL+GMHXL+GMHXL

Column size: 7.8mmϕ×30cm each (total column length: 90cm)

Column temperature: 40℃, flow rate: 0.8mL/min

Injection volume: 100μL

Eluent: tetrahydrofuran

Detector: Differential refractometer (RI)

Standard sample: polystyrene

<Storage modulus, glass transition temperature, and tanδ peak value of the adhesive sheet>

Ten adhesive sheets were laminated to a thickness of approximately 1.5 mm and were used as samples for measurement. Dynamic viscoelasticity measurements were performed using the “Advanced Rheometric Expansion System (ARES)” manufactured by Rheometric Scientific under the following conditions.

(Measuring conditions)

Deformation Mode: Torsion

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

Temperature increase rate: 5℃/min

Shape: Parallel plate 7.9mmϕ

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

<Gel fraction>

About 0.2 g of adhesive was scraped off from the adhesive sheet and used as a sample for measuring the gel fraction. The sample for measuring the gel fraction of the adhesive sheet after photocuring was collected from the sample for measuring adhesive force below. The sample was surrounded by a porous polytetrafluoroethylene film (“NTF-1122” manufactured by Nitto Denko) with a pore diameter of 0.2 μm cut to a size of 100 mm × 100 mm, and the surrounding spout was tied with a string. From the weight of this sample, the total weight (A) of the porous polytetrafluoroethylene film and lead string measured in advance was subtracted to calculate the weight (B) of the adhesive sample. An adhesive sample surrounded by a porous polytetrafluoroethylene film was immersed in about 50 mL of ethyl acetate at 23°C for 7 days, and the sol component of the adhesive was eluted out of the porous polytetrafluoroethylene film. After immersion, the adhesive surrounded by the porous polytetrafluoroethylene film was taken out, dried at 130°C for 2 hours, and left to cool for about 20 minutes, and then the dry weight (C) was measured. The gel fraction of the adhesive was calculated using the following equation.

Gel fraction (%)=100×(C-A)/B

<Adhesion>

Peel the light release film from the adhesive sheet, attach a PET film with a thickness of 50㎛, cut it into 10mm width Produced. Additionally, curing was performed by irradiating ultraviolet rays with an accumulated light amount of 3000 mJ/cm 2 using a metal halide lamp (300 mW/cm 2 ) from the glass plate side, and a sample for measuring the adhesion of the photo-cured adhesive sheet was produced. After holding the sample for measuring adhesion for 30 minutes in an environment of 25°C or 65°C, the test piece was peeled from the glass plate using a tensile tester under the conditions of a tensile speed of 300 mm/min and a peeling angle of 180°, and the peeling force was measured. Measured.

<Step absorbency>

Cut the adhesive sheet to a size of 75mm It was joined by (min). Afterwards, the heavy release film was peeled, and a 500㎛ thick glass plate (100mm x 50mm) with 20㎛ thick black ink printed on the periphery in a frame shape was placed on a roll laminator (pressure between rolls: 0.2MPa, transfer speed: 100mm/min). ) was joined by. 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 a black ink layer was in contact with an area 5 mm from both ends of the four sides of the adhesive sheet. This sample was treated in an autoclave (50°C, 0.5 MPa) for 30 minutes, and then observed under a digital microscope with a magnification of 20x to confirm the presence or absence of air bubbles near the border of the black ink printing area. Those in which no air bubbles were observed were evaluated as OK, and those in which air bubbles were identified were evaluated as NG.

<Processability>

The light release film was peeled from the adhesive sheet, bonded to a PET film (“Cosmoshine A4100” manufactured by Toyobo) with a thickness of 100 μm, and punched from the PET film side using a press to prepare a sample for evaluating processability. After leaving this sample in an atmosphere of temperature: 23°C and relative humidity of 50% for one week, the heavy release film was peeled off and the presence or absence of adhesive peeling was visually observed. Those in which adhesive removal was not observed were evaluated as OK, and those in which adhesive removal was observed were evaluated as NG.

<Interlayer adhesion>

(Production of test samples)

The adhesive sheet was cut to a size of 75 mm ) was joined by. The heavy release film was peeled from the adhesive sheet, and a 500㎛ thick glass plate (50mm It was joined by (surface pressure 0.3 MPa, pressure 100 Pa). After processing this sample in an autoclave (50°C, 0.5MPa) for 30 minutes, ultraviolet rays with an integrated light intensity of 3000mJ/cm2 were irradiated from the side of the glass plate with the black ink printing layer using a metal halide lamp (300mW/cm2). , the adhesive sheet was photocured.

After holding the sample in an environment at 60°C for 30 minutes, as shown in FIG. 5A, a polystyrene sheet with a thickness of 200 μm was inserted between two glass plates at a distance of 1 mm from the end of the adhesive sheet and held for 10 seconds. I supported it. The end of the adhesive sheet was observed with a digital microscope at a magnification of 20x. NG indicated that striped bubbles (see FIG. 5B) or peeling of the adhesive sheet from the glass plate occurred, and OK indicated that neither bubbles nor peeling occurred.

<Impact resistance>

Except that the size of the glass plate without the black ink printing layer was changed to 100 mm This was performed to produce a sample for testing. As shown in FIG. 6, both ends of the short side direction of the test sample 95 are placed on a stand 93 arranged at an interval of 60 mm so that the glass plate 7 on which the printing layer 76 is provided is at the lower side. It was stacked, and the upper surface of the end of the glass plate 8 without the printing layer was fixed on the base 80 with an adhesive tape (not shown). The test sample 95 fixed on the stand 93 with adhesive tape was held in an environment of -5°C for 24 hours, and then taken out to room temperature, and within 40 seconds, a metal sphere with a mass of 11 g was placed on the glass plate 7. (97) was dropped from a height of 300 mm to conduct an impact resistance test.

In the impact resistance test, a cylindrical guide 99 is used to keep the falling position of the metal sphere constant, and the print area of the print layer 76 is spaced 10 mm in each of the short and long side directions from the inner edge angle of the frame. A metal sphere 97 was dropped at a remote location. Two tests were performed, and in either test, the test where peeling of the glass plate did not occur was OK, and the test where peeling of the glass plate occurred in one or both of the two tests was rated NG.

[Evaluation results]

The formulation and evaluation results of the adhesive composition used in the production of each adhesive sheet are shown in Tables 1 and 2. In addition, in Tables 1 and 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 Shinnakamura Chemical Co., Ltd., functional group equivalent 113 g/eq)

APG400: Polypropylene glycol #400 (n=7) diacrylate (“NK Ester APG400” manufactured by Shinnakamura Chemical Co., Ltd., functional group equivalent weight 268 g/eq)

TMPTA: Trimethylpropane triacrylate (“NK Ester A-TMPT” manufactured by Shinnakamura Chemical Co., Ltd., functional group equivalent weight: 99 g/eq)

DPHA: Dipentaerythritol hexaacrylate (“NK Ester A-DPH” manufactured by Shinnakamura Chemical Co., Ltd., functional group equivalent weight 96 g/eq)

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

Comparing Example 1 with Comparative Examples 1 to 3, as the amount of polyfunctional monomer added increases, the gel fraction of the adhesive sheet after photocuring increases, G' at _25°C increases, and the peak top value of tanδ increases. There was a tendency for this to become smaller. In Comparative Example 1, in which the amount of polyfunctional monomer added was small, the adhesive strength after photocuring was higher than that of Example 1, but the adhesive holding strength was low, and peeling was confirmed in the interlayer adhesion test. In Comparative Examples 2 and 3, where the amount of polyfunctional monomer added was large, the viscosity of the adhesive sheet was low and the impact resistance was insufficient. Additionally, in Comparative Example 3, interlayer adhesion also decreased due to the decrease in adhesion. In addition, from the comparison of Example 1 and Comparative Examples 1 to 3, as the amount of polyfunctional monomer added increases, the ratio of the base polymer in the adhesive composition decreases, so the gel fraction and storage modulus of the adhesive sheet before photocuring decrease. You can see that it has been done.

In Comparative Examples 4 and 5, because the amount of polyfunctional monomer added was large, the gel fraction and storage modulus of the adhesive sheet before photocuring were small, and the processability of the adhesive sheet deteriorated. In addition, in Comparative Examples 4 and 5, despite adding an equivalent amount of polyfunctional monomer (7 parts by weight per 100 parts by weight of base polymer) as in Comparative Example 3, the G' of the adhesive sheet after photocuring was _25°C . It was small and the interlayer adhesion was insufficient.

Example 2, in which APG400, a bifunctional acrylate, and DPHA, a hexafunctional acrylate, were used together as polyfunctional monomers showed the same characteristics as Example 1. Additionally, Example 8, which used TMPTA, a trifunctional acrylate, as a polyfunctional monomer, showed the same characteristics as Example 6. From these results, by using a polyfunctional monomer having 3 or more polymerizable functional groups per molecule, the interlayer adhesion of the adhesive sheet after photocuring is improved even when the amount of polyfunctional monomer added is small compared to the case of using a bifunctional monomer. Since this can be done, it can be seen that both the processability of the adhesive sheet before photocuring and the interlayer adhesion of the adhesive sheet after photocuring can be achieved.

Comparing Example 1, Example 3, Comparative Example 6, and Comparative Example 7, as the amount of crosslinking agent added increases, the gel fraction and storage modulus of the adhesive sheet before photocuring tend to increase, and the glass transition temperature of the adhesive sheet tends to increase. You can see that there is this. In Comparative Example 6, in which the amount of crosslinking agent added was small, the adhesive sheet before photocuring was excessively flexible, so processability was poor. On the other hand, in Comparative Example 7, where the amount of crosslinking agent added was large, the adhesive sheet before photocuring was hard, and the adhesiveness and step absorption were insufficient. In addition, in Comparative Examples 6 and 7, the interlayer adhesion and impact resistance of the adhesive sheets after photocuring were insufficient.

When comparing Examples 1, 4, Comparative Examples 8, and 9, the molecular weight of the base polymer tended to decrease as the amount of chain transfer agent added during polymerization of the base polymer increased. In Comparative Examples 8 and 9, since the molecular weight of the base polymer was small, the storage modulus of the adhesive sheet before photocuring was small, and processability was poor. Additionally, in Comparative Examples 8 and 9, the tan δ peak top value of the 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 an oligomer to the pressure-sensitive adhesive composition, the adhesive strength 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 adhesive sheet whose properties before and after photocuring are within a predetermined range is capable of both step absorption and processability in the state before photocuring, and has impact resistance and adhesive durability after photocuring. You can see this excellence.

5: Adhesive sheet
1, 2: Release film
3: Polarizer
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 cross-linked structure; Photopolymerizable multifunctional compounds having two or more photopolymerizable functional groups in one molecule; A photocurable adhesive sheet in which an adhesive composition containing a photopolymerization initiator is formed in a layered form,
The acrylic base polymer having the crosslinked structure contains 5 to 30 parts by weight of a hydroxy group-containing monomer based on a total of 100 parts by weight of the monomer components, and 0.03 to 0.5 parts by weight per 100 parts by weight of the acrylic base polymer with a weight average molecular weight of 300,000 or more. A cross-linking structure using a polyisocyanate cross-linking agent was introduced,
The adhesive composition contains 1 to 6 parts by weight of the photopolymerizable multifunctional compound based on 100 parts by weight of the acrylic base polymer, and the amount of the compound having 3 or more photopolymerizable functional groups in one molecule is the acrylic base polymer. 1 to 4 parts by weight based on 100 parts by weight of base polymer,
The storage modulus at 25°C and 1Hz is 100 to 250 kPa,
The gel fraction is 25 to 70%,
An adhesive sheet having a storage modulus of 180 to 400 kPa at 25°C and 1 Hz after photocuring the adhesive composition. The adhesive sheet according to claim 1, wherein the adhesive sheet has a storage 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 adhesive composition has a glass transition temperature of -3°C or lower after photocuring. The adhesive sheet according to claim 1 or 2, wherein the gel fraction after photocuring the adhesive composition is 65 to 95%. The adhesive sheet according to claim 1 or 2, wherein the peak top value of the loss tangent after photocuring the adhesive composition is 1.5 or more. The adhesive sheet according to claim 1 or 2, wherein the adhesive strength to glass is 4 N/10 mm or more, and the adhesive strength to glass after photocuring the adhesive composition is 4 N/10 mm or more. delete delete delete delete The adhesive sheet according to claim 1 or 2, wherein the adhesive composition contains an acrylic oligomer having a weight average molecular weight of 1,000 to 30,000. A method for producing the adhesive sheet according to claim 1 or 2,
An acrylic base polymer containing 5 to 30 parts by weight of a hydroxyl group-containing monomer and having a weight average molecular weight of 300,000 or more based on a total of 100 parts by weight of monomer components, a polyisocyanate crosslinking agent, and a photopolymerizable multifunctional photopolymerizable functional group having two or more photopolymerizable functional groups in one molecule. Compound, the content of the polyisocyanate crosslinking agent is 0.03 to 0.5 parts by weight, the content of the photopolymerizable multifunctional compound is 1 to 6 parts by weight, based on 100 parts by weight of the acrylic base polymer, and among the photopolymerizable multifunctional compounds A composition in which the amount of a compound having three or more photopolymerizable functional groups per molecule is 1 to 4 parts by weight based on 100 parts by weight of the acrylic base polymer is applied in a layered form on a substrate,
A method for producing an adhesive sheet, comprising introducing a crosslinking structure using the polyisocyanate crosslinking agent into the acrylic base polymer. delete The adhesive sheet according to claim 1 or 2; a first release film temporarily attached to the first main surface of the adhesive sheet; and a second release film temporarily attached to the second main surface of the adhesive sheet. 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 claim 1 or 2. A method of manufacturing an image display device in which a transparent member having a stepped portion is disposed on a viewing side surface,
A method of manufacturing an image display device, wherein the adhesive composition of the adhesive sheet is photocured by irradiating actinic light to the adhesive sheet after bonding the adhesive sheet according to claim 1 or 2 to the transparent member.