JP7666913B2 - Transparent double-sided pressure-sensitive adhesive sheet and pressure-sensitive adhesive sheet laminate - Google Patents

Description

The present invention relates to a transparent double-sided adhesive sheet that can be used as a component for constructing image display devices such as personal computers, mobile terminals (PDA), game consoles, televisions (TV), car navigation systems, touch panels, pen tablets, etc.

In recent years, in order to improve the visibility of image display devices, the gap between an image display panel such as a liquid crystal display (LCD), plasma display (PDP), or electroluminescence display (ELD) and a protective panel or touch panel member placed on the front side (viewing side) of the image display panel has been filled with an adhesive to suppress reflection of incident light and outgoing light from the displayed image at the air layer interface.

As a method for filling the gaps between components of such image display devices with an adhesive, a method is known in which a liquid adhesive resin composition containing an ultraviolet-curable resin is filled into the gaps and then cured by irradiating the composition with ultraviolet light (Patent Document 1).

A method is also known in which gaps between components of an image display device are filled with an adhesive sheet. For example, Patent Document 2 discloses a method in which an adhesive sheet that has been primarily crosslinked with ultraviolet light is attached to the component of an image display device, and then the adhesive sheet is irradiated with ultraviolet light through the component of the image display device for secondary curing.

Patent Document 3 discloses a method for filling gaps between components of an image display device using an adhesive sheet made of a hot melt type adhesive composition whose main component is a urethane (meth)acrylate with a weight average molecular weight of 20,000 to 100,000 and whose loss tangent at 25°C is less than 1.

International Publication No. 2010/027041 Patent No. 4971529 International Publication No. 2010/038366

Incidentally, when two components of an image display device are attached using an adhesive sheet made of an adhesive resin composition containing a base resin, a crosslinking agent, and an ultraviolet polymerization initiator, the two components of the image display device are primarily attached via the adhesive sheet, and then ultraviolet light is irradiated from the outside of one of the components of the image display device to cure the adhesive sheet with ultraviolet light through the component of the image display device for secondary attachment. This method makes it possible to perform primary attachment while filling in any unevenness on the attachment surface, and further increases the adhesive reliability by finally curing the components.
However, when such an ultraviolet-sensitive adhesive sheet is exposed to ultraviolet light for a long period of time, the adhesive sheet itself deteriorates, producing decomposition products that may cause foaming or peeling.
Furthermore, some of the components of the image display device are susceptible to deterioration by ultraviolet light. In such cases, it is not possible to adhere two components of the image display device together using the method described above.
Furthermore, if the image display device components have ultraviolet absorbing properties, even if ultraviolet light is irradiated through the component, the ultraviolet light will not reach the adhesive sheet sufficiently, and therefore, even in such a case, it is not possible to adhere the two image display device components using the method described above.

On the other hand, as image display devices become thinner, new functions are being required of adhesive sheets. In order to prevent ultraviolet degradation of liquid crystals, organic EL elements, polarizing plates, etc., image display device components may be required to have an ultraviolet absorbing function, and this function has generally been ensured by polarizing plate protective films. However, as image display device components become thinner, polarizing plate protective films also become thinner, making it difficult to obtain sufficient ultraviolet absorbing function. For this reason, ultraviolet absorbing function is also being required of image display device components other than polarizing plate protective films, such as adhesives and adhesive sheets.

However, it is difficult to impart ultraviolet absorbing properties to the above-mentioned ultraviolet curing type adhesive sheet. On the other hand, unless a method is adopted in which the adhesive sheet is used to fill in the unevenness of the adherend surface while being primarily adhered, and then further cured and adhered secondarily, it is impossible to achieve both the ability to absorb steps when the adherend surface of the lamination member has unevenness, and the reliability of foaming resistance after lamination.

The present invention aims to provide a new transparent double-sided adhesive sheet that has ultraviolet absorbing properties and can be used for primary application using an adhesive sheet, and then further cured for secondary application.

The present invention provides a pressure-sensitive adhesive comprising a single layer or two or more layers of a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive resin composition containing a (meth)acrylic copolymer (A), a crosslinking agent (B), a photopolymerization initiator (C) having an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm, and an ultraviolet absorber (D),
The transparent double-sided pressure-sensitive adhesive sheet contains at least a polyfunctional (meth)acrylate as the crosslinking agent (B), and the pressure-sensitive adhesive layer is photocurable.

The transparent double-sided adhesive sheet for image display of the present invention has an ultraviolet absorbing function, and furthermore, after the primary application using the adhesive sheet, it can be further photocured for secondary application, so that it can achieve both step absorption when the adherend surface of the lamination member has irregularities and foaming resistance reliability after lamination.

An example of an embodiment of the present invention is described in detail below. However, the present invention is not limited to the following embodiment.

<This adhesive sheet>
A transparent double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention is a transparent double-sided pressure-sensitive adhesive sheet (referred to as "the pressure-sensitive adhesive sheet") made of a pressure-sensitive adhesive resin composition (referred to as "the pressure-sensitive adhesive composition") containing a (meth)acrylic copolymer (A), a crosslinking agent (B), a photopolymerization initiator (C) having an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm, and an ultraviolet absorber (D).

[(Meth)acrylic copolymer (A)]
The (meth)acrylic polymer used as the base polymer of the pressure-sensitive adhesive sheet can have properties such as the glass transition temperature (Tg) appropriately adjusted depending on the types and composition ratios of the acrylic monomers and methacrylic monomers used to polymerize it, as well as the polymerization conditions.

In this adhesive sheet, the term "base polymer" refers to the resin that is the main component of this adhesive sheet. It does not specify a specific content. As a guideline, this refers to a resin that accounts for 50% or more by mass of the resin contained in this adhesive sheet, preferably 65% or more by mass, and more preferably 80% or more by mass (including 100% by mass). When there are two or more types of base polymer, the total amount of these polymers corresponds to the above content.

Examples of the (meth)acrylic (co)polymer (A) include homopolymers of alkyl (meth)acrylates, as well as copolymers obtained by polymerizing a monomer component copolymerizable therewith, and more preferably copolymers containing an alkyl (meth)acrylate and one or more monomers selected from a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an amino group-containing monomer, an epoxy group-containing monomer, an amide group-containing monomer, and other vinyl monomers that are copolymerizable therewith, as monomer components.

More specifically, examples of such copolymers include copolymers composed of one or more monomers selected from a linear or branched alkyl (meth)acrylate having 4 to 18 carbon atoms in the side chain (hereinafter also referred to as "copolymerizable monomer A"), a carboxyl group-containing monomer copolymerizable therewith (hereinafter also referred to as "copolymerizable monomer B"), a vinyl monomer (hereinafter also referred to as "copolymerizable monomer C"), a (meth)acrylate having 1 to 3 carbon atoms in the side chain (hereinafter also referred to as "copolymerizable monomer D"), and a hydroxyl group-containing monomer (hereinafter "copolymerizable monomer E").

In addition, (a) a copolymer composed of a monomer component including a copolymerizable monomer A, a copolymerizable monomer B and/or a copolymerizable monomer C, and (b) a copolymer composed of a monomer component including a copolymerizable monomer A, a copolymerizable monomer B and/or a copolymerizable monomer C, and a copolymerizable monomer D and/or a copolymerizable monomer E can also be mentioned as particularly suitable examples. Specifically, a copolymer of copolymerizable monomers A and B, a copolymer of copolymerizable monomers A and C, a copolymer of copolymerizable monomers A, B and C, a copolymer of copolymerizable monomers A, B and D, a copolymer of copolymerizable monomers A, B and E, a copolymer of copolymerizable monomers A, B, D and E, a copolymer of copolymerizable monomers A, C and D, a copolymer of copolymerizable monomers A, C and E, a copolymer of copolymerizable monomers A, C, D and E, a copolymer of copolymerizable monomers A, B, C and D, a copolymer of copolymerizable monomers A, B, C and E, a copolymer of copolymerizable monomers A, B, C, D and E, a copolymer of copolymerizable monomers A, B, C, D and E.

Examples of the above-mentioned "copolymerizable monomer A" include n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, t-butylcyclohexyl Examples of such acrylates include silyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, isobornyl (meth)acrylate, 3,5,5-trimethylcyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

The copolymerizable monomer A is preferably contained in the total monomer components of the copolymer in an amount of 30% by mass or more and 90% by mass or less, more preferably 35% by mass or more or 88% by mass or less, and even more preferably 40% by mass or more or 85% by mass or less.

Examples of the "copolymerizable monomer B" include (meth)acrylic acid, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxyethylmaleic acid, 2-(meth)acryloyloxypropylmaleic acid, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxypropylsuccinic acid, crotonic acid, fumaric acid, maleic acid, and itaconic acid. These may be used alone or in combination of two or more. Note that "(meth)acrylic" is intended to encompass acrylic and methacrylic. Similarly, "(meth)acryloyl" is intended to encompass acryloyl and methacryloyl.

The above-mentioned "copolymerizable monomer C" may be a compound having a vinyl group in the molecule. Examples of such compounds include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 12 carbon atoms, functional monomers having functional groups such as a hydroxyl group, an amide group, and an alkoxylalkyl group in the molecule, polyalkylene glycol di(meth)acrylates, vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate, and aromatic vinyl monomers such as styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes. These may be used alone or in combination of two or more.

The copolymerizable monomer B and the copolymerizable monomer C are contained in the total monomer components of the copolymer in an amount of 1.2% by mass to 15% by mass or less, preferably 1.5% by mass or more or 10% by mass or less, particularly preferably 2% by mass or more or 8% by mass or less, in order to obtain excellent adhesive properties.

Examples of the "copolymerizable monomer D" include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, etc. These may be used alone or in combination of two or more.
The copolymerizable monomer D is preferably contained in an amount of 0% by mass or more and 70% by mass or less of the total monomer components of the copolymer, more preferably in an amount of 3% by mass or more or 65% by mass or less, and even more preferably in an amount of 5% by mass or more or 60% by mass or less.

Examples of the above-mentioned "copolymerizable monomer E" include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate. These may be used alone or in combination of two or more.

The copolymerizable monomer E is preferably contained in the total monomer components of the copolymer in an amount of 0% by mass or more and 30% by mass or less, more preferably 0% by mass or more or 25% by mass or less, and even more preferably 0% by mass or more or 20% by mass or less.

In addition to the above, acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride, epoxy group-containing monomers such as glycidyl (meth)acrylate, α-ethyl glycidyl acrylate, and 3,4-epoxybutyl (meth)acrylate, amino group-containing (meth)acrylic acid ester monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate, amide group-containing monomers such as (meth)acrylamide, N-t-butyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, diacetone (meth)acrylamide, maleic acid amide, and maleimide, and heterocyclic basic monomers such as vinylpyrrolidone, vinylpyridine, and vinylcarbazole can also be used as needed.

Specific examples of (meth)acrylic (co)polymers include, for example, monomer components (a) such as 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, isostearyl (meth)acrylate, butyl (meth)acrylate, ethyl (meth)acrylate, and methyl (meth)acrylate, and (meth)acrylic acid having a carboxyl group, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxyethylmaleic acid, 2-(meth)acryloyloxyethylmaleic acid, and 2-(meth)acryloyloxyethylmaleic acid. Examples of the monomer component (b) include 2-(meth)acryloyloxypropyl maleate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxypropyl succinate, crotonic acid, fumaric acid, maleic acid, and itaconic acid, and a monomer component (c) having an organic functional group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, glycerol (meth)acrylate, monomethyl maleate, monomethyl itaconate, vinyl acetate, glycidyl (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, fluorinated (meth)acrylate, and silicone (meth)acrylate, are (meth)acrylic acid ester copolymers obtained by copolymerizing the monomer component (b).

The mass average molecular weight of the (meth)acrylic (co)polymer is preferably 100,000 to 1,500,000, more preferably 150,000 or more or 1,300,000 or less, and even more preferably 200,000 or more or 1,200,000 or less.

When it is desired to obtain an adhesive composition with high cohesive strength, the mass average molecular weight is preferably 700,000 to 1,500,000, particularly 800,000 or more or 1,300,000 or less, from the viewpoint that the larger the molecular weight, the greater the cohesive strength obtained by entanglement of molecular chains. On the other hand, when it is desired to obtain an adhesive composition with high fluidity and stress relaxation, the mass average molecular weight is preferably 70,000 to 700,000, particularly 100,000 or more or 600,000 or less. In addition, when no solvent is used in forming an adhesive sheet or the like, it is difficult to use a polymer with a large molecular weight, so the mass average molecular weight of the acrylic copolymer is preferably 70,000 to 700,000, particularly 100,000 or more or 600,000 or less, and of these, particularly 150,000 or more or 500,000 or less.

(Acrylic Copolymer (A1))
An example of a preferred base polymer for the present pressure-sensitive adhesive sheet is a (meth)acrylic copolymer (A1) made of a graft copolymer having a macromonomer as a branch component.

When the adhesive sheet is constructed using the above-mentioned acrylic copolymer (A1) as a base resin, the adhesive sheet can exhibit self-adhesiveness while maintaining its sheet shape at room temperature, has hot-melt properties such that it melts or flows when heated in an uncrosslinked state, and can further be photocured, and after photocuring, it can exert excellent cohesive strength to adhere.
Therefore, when the acrylic copolymer (A1) is used as the base polymer of the present pressure-sensitive adhesive sheet, even in an uncrosslinked state, the sheet exhibits adhesiveness at room temperature (20°C), and also has the property of softening or flowing when heated to a temperature of 50 to 90°C, more preferably 60°C or higher or 80°C or lower.

The glass transition temperature of the copolymer constituting the backbone component of the acrylic copolymer (A1) is preferably from -70 to 0°C.
In this case, the glass transition temperature of the copolymer component constituting the trunk component refers to the glass transition temperature of a polymer obtained by copolymerizing only the monomer components constituting the trunk component of the acrylic copolymer (A1). Specifically, it means a value calculated by the Fox formula from the glass transition temperature and the composition ratio of a polymer obtained from a homopolymer of each component of the copolymer.
The Fox formula is a calculated value obtained by the following formula, and can be obtained using values described in Polymer Handbook [Polymer Handbook, J. Brandrup, Interscience, 1989].
1/(273+Tg)=Σ(Wi/(273+Tgi))
[In the formula, Wi represents the weight fraction of monomer i, and Tgi represents the Tg (°C) of a homopolymer of monomer i.]

The glass transition temperature of the copolymer component constituting the backbone component of the acrylic copolymer (A1) affects the flexibility of the pressure-sensitive adhesive sheet at room temperature and the wettability of the pressure-sensitive adhesive sheet to an adherend, i.e., the adhesiveness. Therefore, in order for the pressure-sensitive adhesive sheet to obtain appropriate adhesiveness (tackiness) at room temperature, the glass transition temperature is preferably -70°C to 0°C, and in particular -65°C or higher or -5°C or lower, and in particular -60°C or higher or -10°C or lower.
However, even if the glass transition temperatures of the copolymer components are the same, the viscoelasticity can be adjusted by adjusting the molecular weight. For example, the copolymer component can be made softer by decreasing its molecular weight.

Examples of the (meth)acrylic acid ester monomer contained in the trunk component of the acrylic copolymer (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and the like. ) acrylate, t-butylcyclohexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate, isobornyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3,5,5-trimethylcyclohexane acrylate, p-cumylphenol EO-modified (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, benzyl (meth)acrylate, and the like. In addition to these, hydroxyl group-containing (meth)acrylates having hydrophilic groups or organic functional groups, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and glycerol (meth)acrylate, (meth)acrylic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, monomethyl itaconate, and the like; carboxyl group-containing monomers such as butyl; acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; epoxy group-containing monomers such as glycidyl (meth)acrylate, α-ethyl glycidyl acrylate, and 3,4-epoxybutyl (meth)acrylate; amino group-containing (meth)acrylic acid ester monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; amide group-containing monomers such as (meth)acrylamide, N-t-butyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, diacetone acrylamide, maleic acid amide, and maleimide; and heterocyclic basic monomers such as vinyl pyrrolidone, vinyl pyridine, and vinyl carbazole.
In addition, various vinyl monomers copolymerizable with the above acrylic monomers or methacrylic monomers, such as styrene, t-butylstyrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkyl vinyl monomers, can also be used appropriately.

The backbone component of the acrylic copolymer (A1) preferably contains a hydrophobic (meth)acrylate monomer and a hydrophilic (meth)acrylate monomer as structural units.
When the backbone component of the acrylic copolymer (A1) is composed only of hydrophobic monomers, it is found that the copolymer tends to whiten when heated and wet. Therefore, it is preferable to also introduce a hydrophilic monomer into the backbone component to prevent whitening when heated and wet.

Specifically, the backbone component of the acrylic copolymer (A1) can be a copolymer component formed by random copolymerization of a hydrophobic (meth)acrylate monomer, a hydrophilic (meth)acrylate monomer, and a polymerizable functional group at the end of a macromonomer.

Here, examples of the hydrophobic (meth)acrylate monomer include n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, and nonyl (meth)acrylate. acrylate, isononyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and methyl methacrylate.
Examples of hydrophobic vinyl monomers include vinyl acetate, styrene, t-butylstyrene, α-methylstyrene, vinyltoluene, and alkyl vinyl monomers.

Examples of the hydrophilic (meth)acrylate monomer include methyl acrylate, (meth)acrylic acid, tetrahydrofurfuryl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, glycerol (meth)acrylate, and other hydroxyl group-containing (meth)acrylates, (meth)acrylic acid, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxyethylmale ... Examples of suitable monomers include carboxyl group-containing monomers such as 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, and monomethyl itaconate; acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; epoxy group-containing monomers such as glycidyl (meth)acrylate, α-ethyl glycidyl acrylate, and 3,4-epoxybutyl (meth)acrylate; alkoxy polyalkylene glycol (meth)acrylates such as methoxy polyethylene glycol (meth)acrylate; N,N-dimethylacrylamide; and hydroxyethylacrylamide.

(Branch component: macromonomer)
The acrylic copolymer (A1) preferably contains a repeating unit derived from a macromonomer introduced as a branch component of the graft copolymer.
A macromonomer is a polymer monomer having a terminal polymerizable functional group and a high molecular weight backbone component.

The glass transition temperature (Tg) of the macromonomer is preferably higher than the glass transition temperature of the copolymer component constituting the acrylic copolymer (A1).
Specifically, since the glass transition temperature (Tg) of the macromonomer affects the heat melting temperature (hot melt temperature) of the present pressure-sensitive adhesive sheet, the glass transition temperature (Tg) of the macromonomer is preferably 30°C to 120°C, and more preferably 40°C or higher or 110°C or lower, and even more preferably 50°C or higher or 100°C or lower.
If the glass transition temperature (Tg) is within this range, excellent processability and storage stability can be maintained by adjusting the molecular weight, and the composition can be adjusted so as to hot melt at a temperature of approximately 50°C to 80°C.
The glass transition temperature of a macromonomer refers to the glass transition temperature of the macromonomer itself, and can be measured by a differential scanning calorimeter (DSC).

In addition, in order to maintain a physically crosslinked state in the pressure-sensitive adhesive composition at room temperature, where the branch components are attracted to each other, and to enable the physical crosslinks to be broken down and fluidity to be obtained by heating to an appropriate temperature, it is also preferable to adjust the molecular weight and content of the macromonomer.
From such a viewpoint, the macromonomer is preferably contained in the acrylic copolymer (A1) in a proportion of 5% by mass to 30% by mass, more preferably 6% by mass or more or 25% by mass or less, and even more preferably 8% by mass or more or 20% by mass or less.
The number average molecular weight of the macromonomer is preferably 500 or more and less than 8,000, more preferably 800 or more or less than 7,500, and even more preferably 1,000 or more or less than 7,000.
As the macromonomer, a generally produced one (for example, a macromonomer manufactured by Toagosei Co., Ltd.) can be appropriately used.

The high molecular weight backbone component of the macromonomer is preferably composed of an acrylic polymer or a vinyl polymer.
Examples of the high molecular weight skeleton component of the macromonomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, and cyclohexyl (meth)acrylate. acrylate, heptyl (meth)acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate acrylate, isobornyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3,5,5-trimethylcyclohexane acrylate, p-cumylphenol EO-modified (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, benzyl (meth)acrylate, hydroxyalkyl (meth)acrylate, (meth)acrylic acid, glycidyl (meth)acrylate, (meth)acrylamide, N,N-dimethyl (meth)acrylamide, (meth)acrylonitrile, alkoxyalkyl (meth)acrylate, alkoxypolyalkylene glycol (meth)acrylate, and other (meth)acrylate monomers; styrene, t-butylstyrene, α-methylstyrene, vinyl toluene, alkyl vinyl monomers, alkyl vinyl esters, alkyl vinyl ethers, and hydroxyalkyl vinyl ethers, and other various vinyl monomers, which may be used alone or in combination of two or more.

Examples of the terminal polymerizable functional groups of the macromonomer include methacryloyl groups, acryloyl groups, vinyl groups, etc.

[Crosslinking agent (B)]
Examples of the crosslinking agent (B) include crosslinking agents having at least one crosslinkable functional group selected from a (meth)acryloyl group, an epoxy group, an isocyanate group, a carboxyl group, a hydroxyl group, a carbodiimide group, an oxazoline group, an aziridine group, a vinyl group, an amino group, an imino group, and an amide group, and one or more of these may be used in combination.
The crosslinkable functional group may be protected with a protecting group which can be removed.

Examples of such polyfunctional (meth)acrylates include 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polyalkoxy di(meth)acrylate, bisphenol F polya Alkoxy di(meth)acrylate, polyalkylene glycol di(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, ε-caprolactone modified tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyethylene glycol di(meth)acrylate, tris(acryloxyethyl)isocyanurate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate Examples of suitable monomers include UV-curable polyfunctional monomers such as di(meth)acrylate, di(meth)acrylate of hydroxypivalic acid neopen glycol adduct with ε-caprolactone, trimethylolpropane tri(meth)acrylate, alkoxylated trimethylolpropane tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate, as well as polyfunctional acrylic oligomers such as polyester (meth)acrylate, epoxy (meth)acrylate, urethane (meth)acrylate, and polyether (meth)acrylate, as well as polyfunctional acrylamide.

Among the above-mentioned polyfunctional (meth)acrylic acid ester monomers, from the viewpoint of improving the adhesion to the adherend and the effect of suppressing wet heat whitening, polyfunctional monomers or oligomers containing a polar functional group such as a hydroxyl group, a carboxyl group, an amide group, etc. Among them, it is preferable to use a polyfunctional (meth)acrylic acid ester having a hydroxyl group or an amide group.
From the viewpoint of preventing wet heat whitening, it is preferable that the (meth)acrylic acid ester copolymer (A1), i.e., the backbone component of the graft copolymer, contains a hydrophobic acrylate monomer and a hydrophilic acrylate monomer, and further, it is preferable to use a polyfunctional (meth)acrylic acid ester having a hydroxyl group as the crosslinking agent (B).
In order to adjust the effects of adhesion, moist heat resistance, heat resistance, etc., a monofunctional or polyfunctional (meth)acrylic acid ester which reacts with the crosslinking agent (B) may be further added.

From the viewpoint of balancing the flexibility and cohesive strength of the adhesive composition, the content of the crosslinking agent (B) is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the (meth)acrylic copolymer (A), and more preferably 0.5 parts by mass or more or 15 parts by mass or less, and even more preferably 1 part by mass or more or 13 parts by mass or less.

[Photopolymerization initiator (C)]
The photopolymerization initiator (C) used in the present pressure-sensitive adhesive sheet functions as a reaction initiation assistant in the crosslinking reaction of the crosslinking agent (B), and is preferably one that generates radicals by irradiation with visible light, for example, light in the wavelength region of 380 nm to 700 nm, to become the starting point of the polymerization reaction of the base resin. However, it may be one that generates radicals only by irradiation with visible light, or one that generates radicals by irradiation with light in a wavelength region other than the visible light region.

From this viewpoint, it is particularly preferable that the photopolymerization initiator (C) has an absorption coefficient at a wavelength of 405 nm of 10 mL/(g cm) or more, more preferably 15 mL/(g cm) or more, and even more preferably 25 mL/(g cm) or more.
The absorption coefficient in the present invention corresponds to the absorbance at an optical path length of 1 cm when the photopolymerization initiator is dissolved in methanol at a concentration of 1 g/L.

Examples of photopolymerization initiators having an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-(4-methylbenzyl)-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, bis(η ⁵ -2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, thioxanthone, and 2-chlorothioxanthanone. Examples of the photopolymerization initiator include 1-(4-(phenylthio), 2-(o-benzoyloxime)), 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-ethanone 1-(O-acetyloxime), camphorquinone, and triazine-based photopolymerization initiators.
These may be used alone or in combination of two or more of them, or may be used in combination with a photopolymerization initiator having an absorption coefficient of less than 10 mL/(g cm) at a wavelength of 405 nm.

Photopolymerization initiators are roughly classified into two types based on the radical generation mechanism: cleavage-type photopolymerization initiators that can generate radicals by cleaving and decomposing the single bond of the photopolymerization initiator itself, and hydrogen abstraction-type photopolymerization initiators that form an exciplex between a photoexcited initiator and a hydrogen donor in the system and can transfer hydrogen from the hydrogen donor.
Among these, the cleavage type photopolymerization initiator decomposes to another compound when generating radicals by light irradiation, and once excited, it no longer functions as a reaction initiator. Therefore, when the intramolecular cleavage type is used as the photopolymerization initiator (C) having an absorption wavelength in the visible light region, it is preferable compared to the case of using the hydrogen abstraction type, because after the adhesive sheet is crosslinked by light irradiation, the photoreactive photopolymerization initiator remains as an unreacted residue in the adhesive composition, which is less likely to cause unexpected changes over time of the adhesive sheet or promotion of crosslinking. In addition, regarding the coloring specific to the photopolymerization initiator, it is preferable to select one that does not absorb visible light by becoming a reaction decomposition product and loses color.
On the other hand, hydrogen abstraction type photopolymerization initiators do not produce decomposition products like cleavage type photopolymerization initiators during the radical generating reaction upon irradiation with active energy rays such as ultraviolet rays, and therefore are less likely to become volatile components after the reaction is completed, making it possible to reduce damage to the adherend.

Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), methyl phenylglyoxylate, 2-benzyl-2-dimethylamino-1- Examples include (4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and derivatives thereof.

Among these, acylphosphine oxide photoinitiators such as bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide are preferred because they are cleavage-type photopolymerization initiators that become decomposed products and lose color after the reaction.
Furthermore, in view of compatibility with an acrylic copolymer consisting of a graft copolymer having a macromonomer as a branch component, it is preferable to use 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, or the like as the photopolymerization initiator (C).

The content of the photopolymerization initiator (C) is not particularly limited. For example, it is preferably contained in an amount of 0.1 to 10 parts by mass, more preferably 0.2 parts by mass or more or 5 parts by mass or less, and even more preferably 0.5 parts by mass or more or 3 parts by mass or less, per 100 parts by mass of the (meth)acrylic copolymer (A). However, this range may be exceeded depending on the balance with other elements. The photopolymerization initiator may be used alone or in combination of two or more kinds.

[Ultraviolet absorber (D)]
The ultraviolet absorber (D) may be any substance capable of absorbing ultraviolet light. As a guideline, it is preferable for the addition of the ultraviolet absorber (D) to be a substance that can increase the absorbance of the transparent double-sided pressure-sensitive adhesive sheet at a wavelength of 380 nm to 0.3 or more, preferably 0.5 or more, and more preferably 1 or more.

The absorbance at a wavelength of 380 nm can be calculated from the following formula.
A ₃₈₀ = -Log (T ₃₈₀ /100)
A ₃₈₀ : absorbance at a wavelength of 380 nm
T ₃₈₀ : Transmittance (%) of the transparent double-sided pressure-sensitive adhesive sheet at 380 nm

The ultraviolet absorber (D) is preferably one having one or more structures selected from the group consisting of a benzotriazole structure, a benzophenone structure, a triazine structure, a benzoate structure, an oxalanilide structure, a salicylate structure, and a cyanoacrylate structure.
Among these, from the viewpoint of ultraviolet absorbing properties, those having one or more structures selected from the group consisting of a benzotriazole structure, a triazine structure, and a benzophenone structure are preferred.
From the viewpoint of compatibility with the acrylic copolymer consisting of a graft copolymer having a macromonomer as a branch component, it is preferable to use a benzotriazole structure or a benzophenone structure as the ultraviolet absorbent (D).

The content of the ultraviolet absorber (D) is not particularly limited. For example, it is preferably contained in an amount of 0.01 to 10 parts by mass, more preferably 0.1 parts by mass or more or 5 parts by mass or less, and even more preferably 0.2 parts by mass or more or 3 parts by mass or less, per 100 parts by mass of the (meth)acrylic copolymer (A). However, it may be contained in an amount exceeding this range in terms of the balance with other elements.

From the viewpoint of absorbing ultraviolet rays while initiating photopolymerization in the visible light region excluding said ultraviolet rays, the ratio of ultraviolet absorber (D) to 100 parts by mass of photopolymerization initiator (C) is preferably 25 to 400 parts by mass, and more preferably 50 parts by mass or more or 300 parts by mass or less, and even more preferably 80 parts by mass or more or 250 parts by mass or less. The ultraviolet absorbers can be used alone or in combination of two or more kinds.

[Other ingredients]
The pressure-sensitive adhesive sheet may contain other known components that are incorporated in ordinary pressure-sensitive adhesive compositions, such as tackifier resins, antioxidants, light stabilizers, metal deactivators, rust inhibitors, antiaging agents, moisture absorbents, hydrolysis inhibitors, sensitizers, antistatic agents, defoamers, and inorganic particles.
Furthermore, a reaction catalyst (such as a tertiary amine compound, a quaternary ammonium compound, or a tin laurate compound) may be appropriately contained as necessary.

[Preferable composition example]
An example of a particularly preferred composition of the pressure-sensitive adhesive composition includes an acrylic copolymer consisting of a graft copolymer having a macromonomer as a branch component as the (meth)acrylic copolymer (A), a polyfunctional (meth)acrylic acid ester compound such as a bifunctional or trifunctional compound as the crosslinking agent (B), a cleavage-type photopolymerization initiator as the photopolymerization initiator (C), and an ultraviolet absorber having a benzotriazole structure or a benzophenone structure as the ultraviolet absorber (D). However, the composition is not limited to this.

[Layer structure]
The pressure-sensitive adhesive sheet of the present invention may be a sheet consisting of a single layer, or a multi-layer sheet consisting of two or more laminated layers.
When the present pressure-sensitive adhesive sheet is to be a multi-layer pressure-sensitive adhesive sheet, i.e., when forming a pressure-sensitive adhesive sheet having a laminated structure with an intermediate layer and an outermost layer, it is preferable that the outermost layer is formed from the present pressure-sensitive adhesive composition.

When the pressure-sensitive adhesive sheet has a multi-layer structure, the ratio of the thickness of each outermost layer to the thickness of the intermediate layer is preferably 1:1 to 1:20, and more preferably 1:2 to 1:10.
It is preferable that the thickness of the intermediate layer is within the above range, since the contribution of the thickness of the adhesive layer in the laminate is not too large, and the intermediate layer is not too soft, which deteriorates workability in cutting and handling.
Furthermore, if the outermost layer is in the above range, it is preferable since it will not be inferior in conformity to uneven or curved surfaces and it will be possible to maintain adhesive strength and wettability to the adherend.

[Sheet thickness]
Regarding the thickness of this adhesive sheet, by making the sheet thinner it is possible to meet the demand for thinner walls. However, if the sheet is too thin, there is a possibility that, for example, if the adherend surface has unevenness, the sheet will not be able to adequately conform to the unevenness or will not be able to exert sufficient adhesive strength.
From this viewpoint, the thickness of the present pressure-sensitive adhesive sheet is preferably 20 to 500 μm, more preferably 25 μm or more or 350 μm or less, and even more preferably 50 μm or more or 250 μm or less.

(Characteristics)
The ultraviolet transmittance (JIS K7361-1) of this pressure-sensitive adhesive sheet at a wavelength of 380 nm is preferably 50% or less, more preferably 30% or less, and even more preferably 10% or less.

<Adhesive Sheet Laminate>
The pressure-sensitive adhesive sheet can be used alone as it is, or can be used by laminating it with other members.

(Present Adhesive Sheet Laminate)
For example, it is possible to form a pressure-sensitive adhesive sheet laminate (referred to as "the pressure-sensitive adhesive sheet laminate") by laminating a release film on one or both sides of the pressure-sensitive adhesive sheet.

In this case, it is preferable that one or both of the release films have a light transmittance of 40% or less for light having a wavelength of 410 nm or less. If at least one of the release films has a light transmittance of 40% or less for light having a wavelength of 410 nm or less, by laminating the release film to the present pressure-sensitive adhesive sheet, even if the present pressure-sensitive adhesive sheet contains a photopolymerization initiator (C) having an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm, the photopolymerization can be effectively prevented from proceeding due to irradiation with visible light.
From this viewpoint, it is preferable that one or both of the release films have a light transmittance for light having a wavelength of 410 nm or less of 40% or less, more preferably 30% or less, and even more preferably 20% or less.

Here, examples of release films having a light transmittance of 40% or less for light with a wavelength of 410 nm or less, that is, release films having the effect of partially blocking the transmission of visible light and ultraviolet light, include cast films or stretched films made of polyester-based, polypropylene-based, or polyethylene-based resins containing ultraviolet absorbers, which are coated with silicone resin and subjected to a release treatment. Examples of multi-layer cast films or stretched films made by forming a layer of resin not containing ultraviolet absorbers on one or both sides of a layer made of polyester-based, polypropylene-based, or polyethylene-based resin containing ultraviolet absorbers, are those coated with silicone resin on one side and subjected to a release treatment. Examples of cast films or stretched films made of polyester-based, polypropylene-based, or polyethylene-based resins are those coated with a paint containing ultraviolet absorbers on one side to provide an ultraviolet absorbing layer, and then coated with silicone resin on the ultraviolet absorbing layer to provide a release treatment. Examples of cast films or stretched films made of polyester-based, polypropylene-based, or polyethylene-based resins are those coated with a paint containing ultraviolet absorbers on one side to provide an ultraviolet absorbing layer, and then coated with silicone resin on the other side to provide a release treatment. Another example is a laminate in which one side of a resin film made of a polyester, polypropylene, or polyethylene resin, which has been release-treated, is laminated with a separately prepared resin film that has not been release-treated, via an adhesive layer or pressure-sensitive adhesive layer containing an ultraviolet absorber.

The release film may have other layers, such as an antistatic layer, a hard coat layer, or an anchor layer, if necessary.
If the thickness of the release film is too thick, the cutting processability is poor, and if the thickness is too thin, the handling property is poor and the PSA sheet may be easily dented. From this viewpoint, the thickness of the release film is preferably 20 μm or more and 300 μm or less, more preferably 25 μm or more or 250 μm or less, and even more preferably 38 μm or more or 200 μm or less.
When a release film is laminated on both sides, it is preferable that one release film has a different thickness or peeling force from the other release film.

As a preferred configuration example, there is mentioned a configuration in which a surface protection film having a light transmittance of 40% or less for light having a wavelength of 410 nm or less is laminated on one or both sides of the present pressure-sensitive adhesive sheet laminate.
By laminating a surface protection film having a light transmittance of 40% or less for light with a wavelength of 410 nm or less on at least one surface of the present pressure-sensitive adhesive sheet laminate, it is possible to effectively prevent photopolymerization from progressing due to irradiation with visible light, even if the present pressure-sensitive adhesive sheet contains a photopolymerization initiator (C) with an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm.
From this viewpoint, the surface protection film laminated on one or both sides of the present pressure-sensitive adhesive sheet laminate preferably has a light transmittance of 40% or less for light with a wavelength of 410 nm or less, more preferably 30% or less, and even more preferably 20% or less.

Here, as a surface protective film having a light transmittance of 40% or less for light having a wavelength of 410 nm or less, that is, a surface protective film having a function of partially blocking the transmission of visible light and ultraviolet light, for example, a laminated film having an ultraviolet absorbing layer formed by applying a slightly adhesive resin having removability to one side of a polyester-based, polypropylene-based, or polyethylene-based cast film or stretched film, and applying a paint containing an ultraviolet absorber to the other side can be mentioned. In addition, a polypropylene-based or polyethylene-based cast film or stretched film having a slightly adhesive resin having removability and containing an ultraviolet absorber to one side can be mentioned. In addition, a cast film or stretched film made of a polyester-based, polypropylene-based, or polyethylene-based resin containing an ultraviolet absorber can be mentioned, which is coated with a slightly adhesive resin having removability. In addition, a multilayer cast film or stretched film formed by forming a layer of a resin not containing an ultraviolet absorber on one or both sides of a layer made of a polyester-based, polypropylene-based, or polyethylene-based resin containing an ultraviolet absorber can be mentioned, which is coated with a slightly adhesive resin having removability to one side. In addition, a coating material containing an ultraviolet absorbent is applied to one side of a cast film or stretched film made of a polyester, polypropylene, or polyethylene resin to provide an ultraviolet absorbing layer, and a slightly adhesive resin having removability is applied on the ultraviolet absorbing layer. In addition, a coating material containing an ultraviolet absorbent is applied to one side of a cast film or stretched film made of a polyester, polypropylene, or polyethylene resin to provide an ultraviolet absorbing layer, and a slightly adhesive resin having removability is applied on the other side. In addition, a resin film made of a polyester, polypropylene, or polyethylene resin, one side of which is coated with a slightly adhesive resin having removability, and the other side of which is laminated with a resin film prepared separately, via an adhesive layer or adhesive layer containing an ultraviolet absorbent, can be mentioned.
The surface protective film may have other layers, such as an antistatic layer, a hard coat layer, or an anchor layer, if necessary.

(Laminate for Constituting the Present Image Display Device)
It is also possible to construct a laminate for constituting an image display device (referred to as "the laminate for constituting the image display device") by laminating two constituent members for an image display device via the present pressure-sensitive adhesive sheet.

In this case, the two components for the image display device may be, for example, any one of the group consisting of a touch sensor, an image display panel, a surface protection panel, and a polarizing film, or a combination of two or more types.

Specific examples of the laminate for constituting the present image display device include structures such as release sheet/present adhesive sheet/touch panel, release sheet/present adhesive sheet/protective panel, release sheet/present adhesive sheet/image display panel, image display panel/present adhesive sheet/touch panel, image display panel/present adhesive sheet/protective panel, image display panel/present adhesive sheet/touch panel/present adhesive sheet/protective panel, polarizing film/present adhesive sheet/touch panel, polarizing film/present adhesive sheet/touch panel/present adhesive sheet/protective panel, etc. However, the laminate is not limited to these lamination examples.
The above touch panel includes a structure in which a touch panel function is incorporated in a protection panel, and a structure in which a touch panel function is incorporated in an image display panel.

(Present image display device)
An image display device (referred to as "the image display device") can be constructed using the present pressure-sensitive adhesive sheet or the present laminate for constructing an image display device as described above.
As the image display device, for example, a liquid crystal display, an organic EL display, an inorganic EL display, electronic paper, a plasma display, a microelectromechanical system (MEMS) display, or the like can be configured.

<Features and usage of this adhesive sheet>
The adhesive sheet has an ultraviolet absorbing function and a curing property that allows it to be cured by irradiation with light of a wavelength other than the ultraviolet region, particularly visible light. By utilizing such properties of the adhesive sheet, a laminate for constituting an image display device can be produced, for example, as follows.

After forming the pressure-sensitive adhesive composition into a sheet (sheet preparation process), two components of an image display device are laminated via the pressure-sensitive adhesive sheet before photocuring (primary attachment process), and then the pressure-sensitive adhesive sheet is photocrosslinked and cured by irradiating it with light containing light rays with wavelengths in the visible light region (secondary attachment process), thereby producing a laminate for use in constructing an image display device.
The light containing light rays with wavelengths in the visible light region may also contain light in the ultraviolet region, i.e., light with wavelengths of 380 nm or less; however, when the laminated image display device components are components that are susceptible to deterioration by ultraviolet light, it is preferable to irradiate the adhesive sheet with light rays that do not substantially contain light with wavelengths of 380 nm or less, i.e., visible light, to photocrosslink and harden the adhesive sheet (secondary adhesion process).

(Sheet manufacturing process)
The pressure-sensitive adhesive composition can be formed into a sheet to produce the pressure-sensitive adhesive sheet.
As a method for forming the present pressure-sensitive adhesive resin composition into a sheet, any currently known method can be adopted.

In this case, as described above, the present pressure-sensitive adhesive resin composition may be formed into a sheet-like film on the release film to produce the present pressure-sensitive adhesive sheet.
The present pressure-sensitive adhesive resin composition may be formed into a sheet on a component of an image display device, and the present pressure-sensitive adhesive sheet may be laminated on the component of the image display device.

(Primary adhesion process)
If the present pressure-sensitive adhesive sheet has self-adhesive properties (tackiness), primary adhesion can be achieved simply by overlapping two image display device components with the present pressure-sensitive adhesive sheet interposed therebetween.

For example, if the adhesive sheet has an acrylic copolymer (A1) as the base polymer, which is a graft copolymer having a macromonomer as a branch component, not only can it maintain its sheet shape at room temperature while exhibiting self-adhesiveness, but also can have a moderate adhesiveness in an uncrosslinked state, for example, an adhesiveness that allows peeling (called "tackiness") in a normal state, i.e., near room temperature, making it easier to position when pasting. Furthermore, since it can be melted or flowed when heated in an uncrosslinked state (hot melt properties), the adhesive can be filled to conform to uneven parts such as printing steps, and can be filled without generating air bubbles.

The laminating device used for lamination can be a known device. Examples include an electric heat press equipped with a heating plate, a diaphragm type laminator, a roll laminator, a vacuum laminator, a hand roll, etc.

In addition, when the present pressure-sensitive adhesive sheet uses as a base polymer an acrylic copolymer (A1) consisting of a graft copolymer having a macromonomer as a branch component, it can provide excellent storage stability and cutting processability under normal conditions, i.e., room temperature conditions. Moreover, since it has self-adhesiveness (tackiness), it can obtain enough adhesiveness that it can be easily attached just by pressing the present pressure-sensitive adhesive sheet against an adherend, so that it is easy to position the adhesive material for application, and it is very convenient in terms of work.
Furthermore, since it has excellent shape retention, it can be processed into any shape in advance, and therefore the adhesive sheet formed on a release film can be cut in advance to match the dimensions of the image display device components to be laminated.
The cutting method in this case is generally punching with a Thompson blade, cutting with a super cutter or laser, and it is more preferable to half-cut while leaving a frame-like portion of the release film on either the front or back side to make it easier to peel off the release film.

If the adhesive sheet has hot melt properties, i.e., the property of becoming soft or fluid when heated, even if the surface to be adhered is uneven, the adhesive sheet can be heated to conform to the unevenness and fill the unevenness without any gaps.
In this case, the means for heating the pressure-sensitive adhesive sheet can be, for example, various thermostatic chambers, hot plates, electromagnetic heating devices, heating rolls, etc. In order to perform lamination and heating more efficiently, for example, an electric heating press, a diaphragm type laminator, a roll laminator, etc. are preferably used.

In this case, if the softening temperature of the pressure-sensitive adhesive sheet is 50° C. or higher, the processing characteristics and storage characteristics at room temperature can be sufficient. On the other hand, if the softening temperature of the pressure-sensitive adhesive sheet is 100° C. or lower, not only can thermal damage to the image display panel and front panel be suppressed, but also the pressure-sensitive adhesive sheet can be prevented from flowing too much and spilling out.
Therefore, the softening temperature of the present pressure-sensitive adhesive sheet is preferably 50 to 100°C, more preferably 55°C or higher or 95°C or lower, and even more preferably 60°C or higher or 90°C or lower.

When the present pressure-sensitive adhesive sheet is heated, it is preferable to laminate two image display device components with the present pressure-sensitive adhesive sheet interposed therebetween, and then heat the laminate in a reduced pressure environment.
By heating the laminate in a reduced pressure environment, it is possible to prevent air bubbles or foreign matter from being mixed into the pressure-sensitive adhesive sheet after lamination.

(Secondary adhesion process)
In the secondary adhesion process, the adhesive sheet is irradiated with light including light rays with wavelengths in the visible light range, preferably light that does not substantially include light with wavelengths of 380 nm or less, i.e., visible light, from the outside of at least one of the image display device constituent members through the image display device constituent member, to photocrosslink and harden the adhesive sheet.

By photocrosslinking in this manner, the adhesive sheet can be firmly crosslinked, and therefore can have adhesive strength and cohesive strength sufficient to withstand the gas pressure of outgassing generated from components of an image display device, such as a protective panel. Furthermore, because the adhesive sheet has ultraviolet absorbing properties, it is possible to suppress deterioration of the adhesive sheet itself and the components of the image display device due to ultraviolet light.

When irradiating with visible light, it is preferable to irradiate with visible light that does not substantially contain light with a wavelength in the ultraviolet region, for example, light with a wavelength of less than 365 nm.
Here, "substantially free of light with wavelengths of less than 365 nm" means that the emission intensity of light with wavelengths of less than 365 nm is less than 1 mW/ ^cm2 .

As a method for irradiating visible light that does not contain light with wavelengths in the ultraviolet region, as described above, a light source that emits only visible light that does not contain light with wavelengths in the ultraviolet region may be used.
Examples of light sources that emit only visible light include fluorescent lamps, LEDs, organic EL, and inorganic EL.
Alternatively, the adhesive composition may be irradiated through a filter that does not transmit light having wavelengths in the ultraviolet region. For example, the adhesive composition may be irradiated with visible light through a filter having a light transmittance of less than 10% at a wavelength of 380 nm and a light transmittance of 60% or more at a wavelength of 405 nm, using a light-emitting lamp such as a high-pressure mercury lamp, a metal halide lamp, a xenon arc lamp, or a carbon arc lamp that also emits light having wavelengths in the ultraviolet region, or sunlight, as a light source.
The filter may be a release film constituting the present pressure-sensitive adhesive sheet laminate, or a surface protection film to be laminated on the surface of the present pressure-sensitive adhesive sheet laminate.

In order to adjust the degree of visible light crosslinking, in addition to controlling the amount of visible light irradiated, it is also possible to adjust the degree of visible light crosslinking by irradiating visible light through the above-mentioned filter, thereby blocking some of the visible light transmission.

<Explanation of terms, etc.>
In addition, a "sheet" generally refers to a thin, flat product whose thickness is small relative to its length and width, as defined in JIS, and a "film" generally refers to a thin, flat product whose thickness is extremely small relative to its length and width, and whose maximum thickness is arbitrarily limited, and which is usually supplied in the form of a roll (Japanese Industrial Standard JIS K6900). However, the boundary between a sheet and a film is unclear, and there is no need to distinguish between the two in the present invention in terms of wording, so in the present invention, the term "film" includes "sheet", and the term "sheet" includes "film".
Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.

In this specification, when it is described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" or "preferably smaller than Y".
In addition, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified.

The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these.

The integrated light quantities at wavelengths of 405 nm and 365 nm measured in this example were measured using an integrated light meter (UIT-250, manufactured by Ushio Inc.).

[Example 1]
As the (meth)acrylic copolymer (A), 15 parts by mass of polymethyl methacrylate macromonomer (Tg 80° C.) having a number average molecular weight of 3,000, 81 parts by mass of butyl acrylate, and 4 parts by mass of acrylic acid (A-1, mass average molecular weight 300,000) were added to 1 kg of the copolymer, and 100 g of glycerin dimethacrylate (manufactured by NOF Corporation, Blenmar GMR) (B-1) was added as the crosslinking agent (B), 15 g of ESACURE KTO46 (C-1) (manufactured by Lamberti) was added as the photopolymerization initiator (C), and 5 g of 2,6-diphenyl-4-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine (manufactured by BASF, Tinuvin 1577) (D-1) was added as the ultraviolet absorber (D), and mixed uniformly to obtain a pressure-sensitive adhesive composition 1.
The photopolymerization initiator (C-1) had an absorption coefficient at 405 nm of 7.4×10 ¹ (mL/(g·cm)).

Next, the adhesive composition 1 was formed into a sheet having a thickness of 100 μm on a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Inc., Diafoil MRV, thickness 100 μm), and then covered with a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Inc., Diafoil MRQ, thickness 75 μm) to produce an adhesive sheet laminate 1.

[Example 2]
As the (meth)acrylic copolymer (A), 10 parts by mass of polymethyl methacrylate macromonomer (Tg 55 ° C.) having a number average molecular weight of 1400, and 90 parts by mass of 2-ethylhexyl acrylate (Tg: -70 ° C.) were randomly copolymerized to obtain an acrylic graft copolymer (A-2) (weight average molecular weight: 230,000) 1 kg, 50 g of tricyclodecane dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: DCP) (B-2) as a crosslinking agent (B), 15 g of Irgacure 369 (C-2) (manufactured by BASF Corporation) as a photopolymerization initiator (C), and 20 g of 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (manufactured by Johoku Chemical Co., Ltd., JF-80) (D-2) as an ultraviolet absorber (D) were uniformly mixed to prepare an adhesive resin composition 2.

Next, the adhesive composition 4 was applied to a thickness of 100 μm onto a release-treated polyethylene terephthalate film (manufactured by Mitsubishi Plastics, Inc., Diafoil MRV, thickness 100 μm), and then covered with a release-treated polyethylene terephthalate film (manufactured by Mitsubishi Plastics, Inc., Diafoil MRQ, thickness 75 μm) to produce an adhesive sheet laminate 2.
The photopolymerization initiator (C-2) had an absorption coefficient at 405 nm of 1.6×10 ² (mL/(g·cm)).

[Example 3]
As the (meth)acrylic copolymer (A), 76 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of vinyl acetate, and 4 parts by mass of acrylic acid (A-3, mass average molecular weight 400,000) were added to 1 kg of the copolymer, and 200 g of propoxylated pentaerythritol tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., ATM-4P) (B-3) was added as the crosslinking agent (B), 7 g of Irgacure 819 (C-3) (manufactured by BASF Corporation) was added as the photopolymerization initiator (C), and 10 g of 2,2'-dihydroxy-4-methoxybenzophenone (manufactured by Chemipro Chemical Co., Ltd., Kemisorb111) (D-3) was added as the ultraviolet absorber (D) and mixed uniformly to obtain a pressure-sensitive adhesive composition 3.
The photopolymerization initiator (C-3) had an absorption coefficient at 405 nm of 9.0×10 ² (mL/(g·cm)).

The adhesive resin composition 3 was sandwiched between two peel-treated polyethylene terephthalate films (Mitsubishi Plastics, Inc., Diafoil MRF, thickness 75 μm/Mitsubishi Plastics, Inc., Diafoil MRT, thickness 38 μm) and shaped into a sheet with a thickness of 100 μm to create an intermediate layer sheet (α).

To 1 kg of a pressure-sensitive adhesive solution (SK Dyne 1882, manufactured by Soken Chemical Engineering Co., Ltd., solid content concentration approximately 17%) made of a commercially available acrylic copolymer (A-4, mass average molecular weight 1.3 million), 1.85 g of L-45 (B-5) (manufactured by Soken Chemical Engineering Co., Ltd.) as an isocyanate-based crosslinking agent and 0.5 g of E-5XM (B-6) (manufactured by Soken Chemical Engineering Co., Ltd.) as an epoxy-based crosslinking agent were added to prepare pressure-sensitive adhesive composition 4.
The above-mentioned adhesive layer coating liquid was applied onto a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRV, thickness 100 μm) so that the film thickness after drying would be 20 to 30 μm, and then dried for 5 minutes at 80° C. This was aged at 23° C. for 7 days to react with the crosslinking agent, thereby preparing a sheet for adhesive layer (β).
Furthermore, the above-mentioned adhesive layer coating liquid was similarly applied to a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRQ, thickness 75 μm) so that the adhesive composition 4 had a film thickness after drying of 20 to 30 μm, and then dried for 5 minutes at 80° C. This was aged at 23° C. for 7 days to react with the crosslinking agent, thereby preparing a sheet for adhesive layer (β').

The PET films on both sides of the intermediate layer resin sheet (α) were sequentially peeled off and removed, and the adhesive surfaces of the adhesive layer resin sheets (β) and (β') were sequentially laminated to both surfaces of the intermediate layer sheet (α) to produce a laminate (thickness 150 μm) consisting of (β)/(α)/(β').

Light was irradiated from a high-pressure mercury lamp through the PET film remaining on the surfaces of (β) and (β') so that the integrated light amount at a wavelength of 365 nm was 1000 mJ/ ^cm2 and the integrated light amount at a wavelength of 405 nm was 1400 mJ/ ^cm2 , thereby photocrosslinking the intermediate layer resin sheet (α) and producing an adhesive sheet laminate 3.

[Example 4]
Adhesive sheet laminate 4 was produced in the same manner as in Example 1, except that a release film made of a PET film (thickness 100 μm) containing an ultraviolet absorber and coated with a silicone release agent was used instead of the release-treated polyethylene terephthalate film (Diafoil MRV, thickness 100 μm).

[Example 5]
The weak adhesive layer surface of a surface protection film consisting of weak adhesive layer (5 μm)/polyethylene terephthalate film (25 μm)/ultraviolet absorbing layer (3 μm) was laminated on the surface of the polyethylene terephthalate film (Diafoil MRV, thickness 100 μm) of the adhesive sheet laminate prepared in Example 1, to prepare an adhesive sheet laminate 5 consisting of a release film/adhesive sheet/release film/surface protection film structure.

[Comparative Example 1]
A pressure-sensitive adhesive sheet laminate 6 was prepared in the same manner as in Example 1, except that 15 g of ESACURE TZT (C-5) was added as the photopolymerization initiator instead of ESACURE KTO46 (C-1).
The absorption coefficient of the photopolymerization initiator (C-5) at 405 nm was less than 10 (mL/(g·cm)), which was too low to be measured.

[Comparative Example 2]
A pressure-sensitive adhesive sheet laminate 7 was prepared in the same manner as in Example 2, except that the ultraviolet absorber (D-2) was not added.

[Comparative Example 3]
To 1 kg of a pressure-sensitive adhesive solution (Soken Chemical Industries, Ltd., SK Dyne 1882, solids concentration about 17%) made of a commercially available acrylic copolymer (A-4, mass average molecular weight 1.3 million), 1.85 g of L-45 (B-5) (Soken Chemical Industries, Ltd.) as an isocyanate crosslinking agent, 0.5 g of E-5XM (B-6) (Soken Chemical Industries, Ltd.) as an epoxy crosslinking agent, and 10 g of 2,2'-dihydroxy-4-methoxybenzophenone (Kemisorb 111, Chemipro Chemical Industries, Ltd.) (D-3) as an ultraviolet absorber (D) were added and mixed uniformly to prepare a pressure-sensitive adhesive composition 7.

Next, the pressure-sensitive adhesive composition was applied onto a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Inc., Diafoil MRV, thickness 100 μm) so that the thickness after drying would be 50 μm, and then dried at 80° C. for 5 minutes to obtain a sheet-shaped pressure-sensitive adhesive composition 7 having a thickness of 50 μm.
Similarly, the adhesive composition was applied onto a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRQ, thickness 75 μm) so that the thickness after drying would be 50 μm, and then dried at 80° C. for 5 minutes to obtain a sheet-like adhesive composition 7 having a thickness of 50 μm. These were laminated to a thickness of 100 μm, and then covered with a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRQ, thickness 75 μm). This was aged at room temperature (23° C.) for 7 days to react with the crosslinking agent, and an adhesive sheet laminate 8 was produced.

<Evaluation>
[Optical properties]
The PET films on both sides of the adhesive sheet laminates produced in the Examples and Comparative Examples were sequentially peeled off, and the adhesive sheets were sandwiched between two sheets of soda lime glass (thickness 0.5 mm) and attached, and then autoclaved (70°C, gauge pressure 0.2 MPa, 20 minutes) for finish attachment. For the adhesive sheet laminates 1, 2, 4, 5, 6, and 7, a high-pressure mercury lamp with a UV cut filter was used to irradiate light at a wavelength of 405 nm to an integrated light amount of 3000 mJ/ ^cm2 , to prepare samples for evaluating optical properties.

The light transmittance of the prepared test piece in the wavelength range of 360 to 430 nm was measured using a spectrophotometer (manufactured by Shimadzu Corporation; device name "UV2450").
A sample having a light transmittance of less than 50% at 380 nm was judged to have UV absorbency of "○ (good)", and a sample having a light transmittance of 50% or more was judged to have UV absorbency of "× (poor)". The results are shown in Table 1.

[Adhesive strength]
For the adhesive sheets prepared in the examples and comparative examples, one release film was peeled off, and a polyethylene terephthalate film (manufactured by Toyobo Co., Ltd.; product name "Cosmoshine A4300", thickness 100 μm) was roll-pressed with a hand roller as a backing film. This was cut into strips of 10 mm width x 100 mm length, and the remaining release film was peeled off to expose the adhesive surface, which was roll-pasted to soda lime glass using a hand roller. After autoclaving (70 ° C, gauge pressure 0.2 MPa, 20 minutes) and finish-pasting, for adhesive sheet laminates 1, 2, 4, 5, 6, and 7, visible light was irradiated using a high-pressure mercury lamp through a UV cut filter so that the accumulated light amount at a wavelength of 405 nm was 3000 mJ / cm ² and the accumulated light amount at a wavelength of 365 nm was 5 mJ / cm ² or less to prepare an adhesive strength measurement sample.

The adhesive sheet was peeled off from the glass while pulling the backing film at an angle of 180° at a peeling speed of 60 mm/min, and the tensile strength was measured with a load cell to measure the 180° peel strength (N/cm) of the adhesive sheet to the glass, which is shown in Table 1 as "glass adhesion strength." The results are shown in Table 1.

[Roughness absorption]
A 20 μm thick print was applied to the peripheral portion (3 mm on the long side, 15 mm on the short side) of a 58 mm×110 mm×0.8 mm thick glass plate to prepare a glass plate 1 with a printed step having an opening of 52 mm×80 mm.
In addition, a 10 μm thick print was applied to the peripheral portion (3 mm on the long side, 15 mm on the short side) of a 58 mm x 110 mm x 0.8 mm thick glass plate to prepare a glass plate 2 with a printed step and an opening of 52 mm x 80 mm.
The release film on one side of the pressure-sensitive adhesive sheet laminate was peeled off, and the laminate was then roll-bonded to a soda-lime glass sheet measuring 54 mm×82 mm and 0.5 mm thick.
Next, the remaining release film was peeled off, and the four sides of the adhesive surface were pressed and bonded to the printed surfaces of the printed stepped glass plates 1 and 2 using a vacuum press so that they overlap the printed steps (absolute pressure 5 kPa, temperature 70°C, press pressure 0.04 MPa), and then autoclaved (70°C, gauge pressure 0.2 MPa, 20 minutes) for finish attachment. For the adhesive sheet laminates 1, 2, 4, 5, 6, and 7, a high-pressure mercury lamp was used through a UV cut filter to irradiate the printed glass side with light at a wavelength of 405 nm to an integrated light amount of 3000 mJ/ ^cm2 , to prepare evaluation samples.

For the evaluation samples, the glass plate 1 with a 20 μm printed step was judged to have excellent unevenness absorption if it could be bonded without any air bubbles near the step, the glass plate 2 with a 10 μm printed step was judged to have good unevenness absorption if it could be bonded without any air bubbles near the step, and the glass plates 1 and 2 with printed steps were judged to have poor unevenness absorption if air bubbles were found near the step. The results are shown in Table 1.

[Heat resistance]
The release film on one side of the pressure-sensitive adhesive sheet prepared in the examples and comparative examples was peeled off, and a COP film (100 μm manufactured by Nippon Zeon Co., Ltd.) was attached to the exposed surface with a hand roller. Next, the pressure-sensitive adhesive sheet was cut into 50 mm × 80 mm, and the remaining release film was peeled off, and the sheet was attached to a soda lime glass having a thickness of 0.5 mm with a hand roller, and autoclaved (temperature 80 ° C, pressure 0.4 MPa, 30 minutes). For pressure-sensitive adhesive sheet laminates 1, 2, 4, 5, 6, and 7, a high-pressure mercury lamp was used through a UV cut filter to irradiate light from the COP surface so that the accumulated light amount of a wavelength of 405 nm was 3000 mJ / cm ² , and an evaluation sample was prepared.

The evaluation samples were cured at 85°C for 6 hours, and samples that showed no change in appearance, such as foaming, were rated as having good heat resistance, while samples that showed foaming or peeling were rated as having poor heat resistance. The results are shown in Table 1.

[Light resistance]
One release film of the pressure-sensitive adhesive sheet laminate was peeled off, and the laminate was roll-bonded to a 150 mm x 200 mm, 2 mm thick soda lime glass. Next, the remaining release film was peeled off, and the exposed adhesive surface was roll-bonded to a 150 mm x 200 mm, 2 mm thick soda lime glass, and autoclaved (temperature 80°C, pressure 0.4 MPa, 30 minutes).
For the pressure-sensitive adhesive sheet laminates 1, 2, 4, 5, 6 and 7, light was irradiated using a high-pressure mercury lamp so that the integrated light amount at a wavelength of 405 nm was 3000 mJ/cm ² to prepare evaluation samples.

The evaluation samples were irradiated with ultraviolet light for 24 hours using a xenon lightfastness tester (Suntest CPS, manufactured by Atlas Co., Ltd.). Those that showed no lifting or peeling on the adhesive sheet were judged to have lightfastness of "○ (good)", and those that showed lifting or peeling were judged to have lightfastness of "× (poor)". The results are shown in Table 1.

The light transmittance in the wavelength range of 380 to 450 nm was measured using a spectrophotometer (Shimadzu Corporation; device name "UV2450") for the release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRV, thickness 100 μm) used in Example 1, the release film made of a PET film (thickness 100 μm) containing an ultraviolet absorber and coated with a silicone release agent used in Example 4, and the surface protection film used in Example 5. The results are shown in Table 2.

For the adhesive sheet laminate 1, adhesive sheet laminate 4, and adhesive sheet laminate 5, a release-treated polyethylene terephthalate film (Mitsubishi Plastics, Diafoil MRV, thickness 100 μm), a release film coated with a silicone release agent on a PET film (thickness 100 μm) containing an ultraviolet absorber used in Example 4, and a surface protective film were placed on the upside. The film side was irradiated with light from a fluorescent lamp (illuminance 1100 Lx) for 7 days. The accumulated light amount at a wavelength of 405 nm of the irradiated light was about 43 J/cm ² , and the accumulated light amount at a wavelength of 365 nm was about 1 mJ/cm ² or less and could not be measured.

The gel fraction of the adhesive was determined for adhesive sheet laminates 1 and 4 before and after light irradiation treatment using the following method. The results are shown in Table 2.

1) The pressure-sensitive adhesive composition is weighed (W1) and wrapped in a pre-weighed SUS mesh (W0).
2) The above SUS mesh is immersed in 100 mL of ethyl acetate for 24 hours.
3) Remove the SUS mesh and dry it at 75°C for 4.5 hours.
4) The weight (W2) after drying is determined, and the gel fraction of the pressure-sensitive adhesive composition is calculated using the following formula.
Gel fraction (%)=100×(W2−W0)/W1

Regarding storage stability, samples in which the gel fraction changed by less than 5 points before and after exposure to fluorescent light were rated as "○ (good)," and samples in which the gel fraction increased by 5 points or more after exposure to light were rated as "× (poor)." The results are shown in Table 2.

The pressure-sensitive adhesive sheet laminates of Examples 1 to 5 not only had excellent ultraviolet absorbing performance, but also had excellent quality by achieving both the ability to absorb irregularities during lamination and reliability after lamination of members.
In contrast, Comparative Example 1 used a photopolymerization initiator with an absorption coefficient of less than 10 mL/(g cm) at a wavelength of 405 nm, i.e., did not use a photopolymerization initiator with an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm, so the adhesive did not harden even when irradiated with light, and no adhesive strength after secondary attachment or reliability after lamination was obtained.
Comparative Example 2 did not contain the ultraviolet absorber (D) and could not obtain ultraviolet absorbing performance. Therefore, foaming of the pressure-sensitive adhesive sheet was observed in the light resistance test, and the lamination reliability was poor.
Comparative Example 3 is a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive composition is crosslinked by thermal crosslinking. Since it does not have a photocurable layer, it is inferior in terms of unevenness absorbency during application.

In addition, in Example 4, a PET film containing an ultraviolet absorber is used as the release film. This makes it possible to suppress the progress of the photocuring reaction of the adhesive composition before bonding to the member, resulting in an adhesive sheet laminate with excellent storage stability.

In addition, in Example 5, a surface protection film having an ultraviolet absorbing layer is laminated on the surface of the release film. This makes it possible to suppress the progress of the photocuring reaction of the adhesive composition before it is attached to a member, and to produce an adhesive sheet laminate with excellent storage stability.

Claims (14)

The adhesive layer comprises a single layer or two or more layers formed from an adhesive resin composition containing a (meth)acrylic copolymer (A), a crosslinking agent (B), a photopolymerization initiator (C) having an absorption coefficient of 10 mL/(g cm) or more at a wavelength of 405 nm, and an ultraviolet absorber (D);
The ultraviolet absorber (D) is contained in an amount of 0.1 parts by mass or more and 3 parts by mass or less based on 100 parts by mass of the (meth)acrylic copolymer (A),
The crosslinking agent (B) contains at least a polyfunctional (meth)acrylate, and
The adhesive layer is a photocurable, transparent, double-sided adhesive sheet (excluding those containing a multi-acrylate oligomer having 2-5 acrylate functional groups). The transparent double-sided pressure-sensitive adhesive sheet according to claim 1 , wherein the polyfunctional (meth)acrylate is a polyfunctional (meth)acrylic acid ester monomer. The transparent double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a curing property such that it is cured by visible light. The transparent double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3 , wherein the ( meth )acrylic copolymer (A) has a mass average molecular weight of 100,000 to 1,500,000. The transparent double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, characterized in that the ultraviolet absorber (D) has one or more structures selected from the group consisting of a benzotriazole structure, a triazine structure, and a benzophenone structure. The transparent double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , characterized in that the ultraviolet absorber (D) is contained in a ratio of 25 to 400 parts by mass per 100 parts by mass of the photopolymerization initiator (C). The (meth)acrylic copolymer (A) contains an acrylic copolymer consisting of a graft copolymer having a macromonomer as a branch component,
The crosslinking agent (B) contains a polyfunctional (meth)acrylic acid ester monomer ,
The photopolymerization initiator (C) contains a cleavage-type photopolymerization initiator,
The transparent double-sided pressure - sensitive adhesive sheet according to any one of claims 1 to 6 , characterized in that the ultraviolet absorber (D) contains an ultraviolet absorber having a benzotriazole structure or a benzophenone structure. The transparent double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive resin composition exhibits adhesiveness at room temperature (20°C) even in an uncrosslinked state, and has the property of softening or becoming fluid when heated to a temperature of 50 to 100 °C. 9. A pressure-sensitive adhesive sheet laminate comprising the transparent double-sided pressure-sensitive adhesive sheet according to claim 1 and a release film laminated thereon . 10. The pressure-sensitive adhesive sheet laminate according to claim 9 , wherein at least one of the release films has a light transmittance of 40% or less for light having a wavelength of 410 nm or less. 10. The pressure-sensitive adhesive sheet laminate according to claim 9 , comprising a surface protective film having a light transmittance of 40% or less for light having a wavelength of 410 nm or less laminated on the surface of at least one of the release films. 9. A laminate for use in constructing an image display device, comprising two constituent members laminated together with the transparent double-sided pressure-sensitive adhesive sheet according to claim 1 interposed therebetween . The laminate for use in constructing an image display device according to claim 12 , characterized in that the image display device component is a laminate consisting of any one or a combination of two or more of the group consisting of a touch sensor, an image display panel, a surface protection panel, and a polarizing film. An image display device constructed using the laminate for constituting an image display device according to claim 12 or 13 .