JP7664064B2 - Active energy ray-curable adhesive sheet and laminate - Google Patents

Description

The present invention relates to an adhesive sheet having an active energy ray-curable adhesive layer, and a laminate obtained using the adhesive layer of the adhesive sheet.

In recent years, various mobile electronic devices such as mobile phones and tablet terminals are equipped with displays that use display modules that have liquid crystal elements, light-emitting diodes (LED elements), organic electroluminescence (organic EL) elements, etc.

In such displays, a protective panel is usually provided on the front side of the display module. A gap is provided between the protective panel and the display module so that even if the protective panel is deformed by an external force, the deformed protective panel will not collide with the display module.

However, the presence of such a gap, i.e., an air layer, causes a problem of large light reflection loss due to the difference in refractive index between the protective panel and the air layer, and between the air layer and the display module, resulting in a deterioration in the image quality of the display.

It has therefore been proposed to improve the image quality of the display by filling the gap between the protective panel and the display module with an adhesive layer. However, a frame-shaped printed layer may exist as a step on the display module side of the protective panel. If the adhesive layer does not conform to the step, it will float near the step, which will cause a reflection loss of light. For this reason, the adhesive layer is required to have the ability to conform to the step.

In order to solve the above problems, Patent Document 1 discloses an adhesive layer that fills the gap between a protective panel and a display module, the adhesive layer having a shear storage modulus (G') of 1.0 x ¹⁰⁵ Pa or less at 25°C and 1 Hz and a gel fraction of 40% or more.

JP 2010-97070 A

In Patent Document 1, an attempt is made to improve step-following ability by lowering the storage modulus of the adhesive layer at room temperature. However, when the storage modulus at room temperature is lowered as described above, the storage modulus at high temperatures drops more than necessary, causing problems under durability conditions. For example, when the adhesive layer is subjected to high temperature and high humidity conditions and then returned to room temperature and humidity, problems occur in which the adhesive layer whitens and air bubbles are generated near steps.

While glass plates have generally been used as the protective panels, plastic plates may be used in recent years due to demands for thinner, lighter panels. In high-temperature environments, gas (outgassing) may be generated from these plastic plates. When such plastic plates are used, the outgassing may cause air bubbles or lifting/peeling (blistering) between the plastic plate and the adhesive layer.

The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide an active energy ray-curable adhesive sheet and laminate having an adhesive layer that is excellent in step conformability as well as in resistance to moist heat whitening, durability, and blister resistance.

In order to achieve the above object, first, the present invention provides an adhesive sheet having an adhesive layer having a thickness of 50 to 400 μm, which is obtained by thermally crosslinking an adhesive composition that contains a (meth)acrylic acid ester copolymer (A) having a weight average molecular weight of 200,000 to 900,000 and containing, as monomer units constituting the polymer, 5 to 20 mass % of a monomer having a carboxyl group or 15 to 30 mass % of a monomer having a hydroxyl group, an active energy ray curable component (B), and a crosslinking agent (C), and the content of the active energy ray curable component (B) is 10 to 50 parts by mass per 100 parts by mass of the (meth)acrylic acid ester copolymer (A) (Invention 1).

In the above invention (Invention 1), by thermally crosslinking an adhesive composition containing a (meth)acrylic acid ester copolymer having a small weight average molecular weight and a predetermined amount of hydroxyl or carboxyl groups, the resulting adhesive layer has excellent step conformability and resistance to moist heat whitening, as well as suitable durability. In addition, since the adhesive composition contains a large amount of an active energy ray-curable component, the adhesive layer is cured by irradiation with active energy rays, and the adhesive layer thus cured has excellent durability and blister resistance.

In the above invention (Invention 1), the content of the crosslinking agent (C) in the adhesive composition is preferably 0.01 to 5 parts by mass per 100 parts by mass of the (meth)acrylic acid ester copolymer (A) (Invention 2).

In the above inventions (Inventions 1 and 2), it is preferable that the ratio of the storage modulus at 23°C after the pressure-sensitive adhesive layer is irradiated with active energy rays to the storage modulus at 23°C before the pressure-sensitive adhesive layer is 1.1 to 10 (Invention 3).

In the above inventions (Inventions 1 to 3), it is preferable that the ratio of the storage modulus at 85°C after the pressure-sensitive adhesive layer is irradiated with active energy rays to the storage modulus at 85°C before the pressure-sensitive adhesive layer is 1.1 to 10 (Invention 4).

In the above inventions (Inventions 1 to 4), it is preferable that the adhesive sheet has two release sheets, and the adhesive layer is sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets (Invention 5).

Secondly, the present invention provides a laminate comprising two hard plates and an adhesive layer sandwiched between the two hard plates, the adhesive layer being characterized in that the adhesive layer is the adhesive layer of the adhesive sheet (Inventions 1 to 5) cured by irradiation with active energy rays (Invention 6).

In the above invention (Invention 6), it is preferable that at least one of the hard plates has a step on the surface facing the adhesive layer (Invention 7).

In the above invention (Invention 7), it is preferable that the step is due to the presence or absence of a printed layer (Invention 8).

In the above inventions (Inventions 6 to 8), it is preferable that at least one of the hard plates includes a polarizing plate (Invention 9).

In the above inventions (Inventions 6 to 9), it is preferable that at least one of the hard plates includes a plastic plate (Invention 10).

In the above inventions (Inventions 6 to 8), it is preferable that one of the two hard plates is a display module or a part thereof, and the other of the two hard plates is a protective plate having a frame-shaped step on the surface facing the adhesive layer (Invention 11).

In the above inventions (Inventions 6 to 11), it is preferable that the total light transmittance of the pressure-sensitive adhesive layer is 80% or more (Invention 12).

The adhesive layer of the active energy ray curable adhesive sheet according to the present invention has excellent step conformability, and after irradiation with active energy rays, it also has excellent resistance to moist heat whitening, durability and blister resistance. In a laminate obtained using such an active energy ray curable adhesive sheet, even if there is a step on the adhesive layer side, the adhesive layer conforms to the step, so there is no floating or air bubbles near the step. In addition, the adhesive layer in the laminate after irradiation with active energy rays also has excellent resistance to moist heat whitening, durability and blister resistance.

1 is a cross-sectional view of an active energy ray-curable adhesive sheet according to one embodiment of the present invention. FIG. 2 is a cross-sectional view of a laminate according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Adhesive sheet]
As shown in Fig. 1, the active energy ray-curable adhesive sheet (sometimes simply referred to as "adhesive sheet" in this specification) 1 according to this embodiment is composed of two release sheets 12a, 12b and an adhesive layer 11 sandwiched between the two release sheets 12a, 12b so as to be in contact with the release surfaces of the two release sheets 12a, 12b. Note that the release surface of the release sheet in this specification refers to a surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without being subjected to a release treatment.

1. Pressure-sensitive adhesive layer The pressure-sensitive adhesive layer 11 is an active energy ray-curable pressure-sensitive adhesive layer obtained by thermally crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester copolymer (A) having a weight average molecular weight of 200,000 to 900,000 and containing 5 to 20 mass% of a monomer having a carboxyl group (carboxyl group-containing monomer) or 15 to 30 mass% of a monomer having a hydroxyl group (hydroxyl group-containing monomer) as a monomer unit constituting a polymer, an active energy ray-curable component (B), and a crosslinking agent (C). In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms.

The adhesive layer 11 in the adhesive sheet 1 is formed by thermally crosslinking the adhesive composition P, specifically, the (meth)acrylic acid ester copolymer (A) is in a crosslinked state with the crosslinking agent (C). On the other hand, the active energy ray curable component (B) has not yet cured and is present in the adhesive layer 11 in a state in which it is blended in the adhesive composition P. This active energy ray curable component (B) polymerizes and cures when the adhesive layer 11 is irradiated with active energy rays during use of the adhesive sheet 1 (when bonding to an adherend).

(1) (Meth)acrylic acid ester copolymer (A)
The (meth)acrylic acid ester copolymer (A) is the main adhesive agent in the adhesive composition P. The (meth)acrylic acid ester copolymer (A) contains 5 to 20% by mass of a carboxyl group-containing monomer or 15 to 30% by mass of a hydroxyl group-containing monomer as a monomer unit constituting the polymer. When the content of the carboxyl group-containing monomer or the hydroxyl group-containing monomer is within the above range, the crosslinked structure formed by the (meth)acrylic acid ester copolymer (A) and the crosslinking agent (C) becomes good, and the adhesive layer 11 has suitable durability. In addition, the adhesive layer 11 obtained from the adhesive composition P containing the (meth)acrylic acid ester copolymer (A) having the content of the carboxyl group-containing monomer or the hydroxyl group-containing monomer within the above range is subjected to high temperature and high humidity conditions (for example, 240 hours under conditions of 85°C and 85% RH) after curing, and then whitening is suppressed when the adhesive layer 11 is returned to normal temperature and normal humidity, that is, it has excellent resistance to moist heat whitening. When the (meth)acrylic acid ester copolymer (A) contains the above amount of carboxyl group-containing monomer or hydroxyl group-containing monomer as a monomer unit, a predetermined amount of carboxyl group or hydroxyl group remains in the obtained adhesive. Carboxyl group and hydroxyl group are hydrophilic groups, and when such hydrophilic groups are present in a predetermined amount in the adhesive, even if the adhesive is placed under high temperature and high humidity conditions, it is presumed that the moisture that has penetrated into the adhesive under the high temperature and high humidity conditions will be easily released from the adhesive when the adhesive returns to normal temperature and humidity, and as a result, whitening of the adhesive is suppressed.

If the content of the carboxyl group-containing monomer as a monomer unit in the (meth)acrylic acid ester copolymer (A) is less than 5% by mass, or if the content of the hydroxyl group-containing monomer is less than 15% by mass, the adhesive layer 11 will have poor resistance to wet heat whitening. On the other hand, if the content of the carboxyl group-containing monomer exceeds 20% by mass, or if the content of the hydroxyl group-containing monomer exceeds 30% by mass, the coatability of the adhesive composition P will deteriorate.

From the above viewpoints, it is preferable that the (meth)acrylic acid ester copolymer (A) contains, as a monomer unit constituting the polymer, 7 to 15% by mass, particularly 8 to 12% by mass of a carboxyl group-containing monomer, or 17 to 28% by mass, particularly 20 to 25% by mass of a hydroxyl group-containing monomer.

Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, (meth)acrylic acid is preferred, and acrylic acid is particularly preferred, in terms of the reactivity of the carboxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, 2-hydroxyethyl (meth)acrylate is preferred in terms of the reactivity of the hydroxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester copolymer (A) preferably contains, as a monomer unit constituting the polymer, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms, and more preferably contains this as the main component. This allows the resulting adhesive to exhibit favorable adhesive properties.

Examples of (meth)acrylic acid alkyl esters having an alkyl group with 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among these, from the viewpoint of further improving adhesion, (meth)acrylic acid esters having an alkyl group with 1 to 8 carbon atoms are preferred, and methyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are particularly preferred. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester copolymer (A) preferably contains 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of (meth)acrylic acid alkyl esters having an alkyl group with 1 to 20 carbon atoms as monomer units constituting the polymer. The upper limit of the content of (meth)acrylic acid alkyl esters having an alkyl group with 1 to 20 carbon atoms is preferably the remainder excluding carboxyl group-containing monomers and hydroxyl group-containing monomers.

If desired, the (meth)acrylic acid ester copolymer (A) may contain other monomers as monomer units constituting the polymer. As the other monomer, a monomer that does not contain a reactive functional group is preferable so as not to interfere with the action of the carboxyl group-containing monomer or the hydroxyl group-containing monomer. Examples of such other monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, (meth)acrylic acid esters having an aliphatic ring such as cyclohexyl (meth)acrylate, non-crosslinkable acrylamides such as acrylamide and methacrylamide, (meth)acrylic acid esters having a non-crosslinkable tertiary amino group such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate, vinyl acetate, styrene, etc. These may be used alone or in combination of two or more.

The polymerization mode of the (meth)acrylic acid ester copolymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylic acid ester copolymer (A) is 200,000 to 900,000, and preferably 250,000 to 700,000. The weight average molecular weight in this specification is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

Since the weight average molecular weight of the (meth)acrylic acid ester copolymer (A), which is the main component of the adhesive composition P, is relatively small as described above, the adhesive layer 11 obtained by thermally crosslinking the adhesive composition P has excellent step conformability. If the weight average molecular weight of the (meth)acrylic acid ester copolymer (A) exceeds 900,000, the step conformability is poor. On the other hand, if the weight average molecular weight of the (meth)acrylic acid ester copolymer (A) is less than 200,000, the adhesive layer 11 after irradiation with active energy rays has poor durability. In addition to the above viewpoints, in consideration of step conformability and durability, it is particularly preferable that the weight average molecular weight of the (meth)acrylic acid ester copolymer (A) is 300,000 to 500,000, and in consideration of blister resistance, it is particularly preferable that the weight average molecular weight of the (meth)acrylic acid ester copolymer (A) is 500,000 to 700,000.

In addition, in the adhesive composition P, the (meth)acrylic acid ester copolymer (A) may be used alone or in combination of two or more kinds.

(2) Active energy ray-curable component (B)
The pressure-sensitive adhesive layer 11 formed becomes an active energy ray-curable pressure-sensitive adhesive layer by containing the active energy ray-curable component (B) in the pressure-sensitive adhesive composition P. By containing the active energy ray-curable component (B), the pressure-sensitive adhesive layer 11 becomes excellent in step conformability and durability.

The active energy ray curable component (B) is not particularly limited as long as it is a component that is cured by irradiation with active energy rays without interfering with the effects of the present invention, and may be any of a monomer, oligomer, or polymer, or a mixture thereof. Among them, preferred examples include polyfunctional acrylate monomers having a molecular weight of less than 1000, which have excellent compatibility with the (meth)acrylic acid ester copolymer (A) and the like.

Examples of polyfunctional acrylate monomers having a molecular weight of less than 1000 include bifunctional monomers such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, di(acryloxyethyl)isocyanurate, and allylated cyclohexyl di(meth)acrylate; trimethylolpropane tri(meth)acrylate, dipenta Examples of such trifunctional compounds include erythritol tri(meth)acrylate, propionic acid modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, and ε-caprolactone modified tris-(2-(meth)acryloxyethyl)isocyanurate; tetrafunctional compounds such as diglycerol tetra(meth)acrylate and pentaerythritol tetra(meth)acrylate; pentafunctional compounds such as propionic acid modified dipentaerythritol penta(meth)acrylate; and hexafunctional compounds such as dipentaerythritol hexa(meth)acrylate and caprolactone modified dipentaerythritol hexa(meth)acrylate. These compounds may be used alone or in combination of two or more.

As the active energy ray curable component (B), an active energy ray curable acrylate oligomer can also be used. This acrylate oligomer preferably has a weight average molecular weight of 50,000 or less. Examples of such acrylate oligomers include polyester acrylates, epoxy acrylates, urethane acrylates, polyether acrylates, polybutadiene acrylates, silicone acrylates, etc.

Here, the polyester acrylate oligomer can be obtained, for example, by esterifying the hydroxyl groups of a polyester oligomer having hydroxyl groups at both ends obtained by condensation of a polyvalent carboxylic acid and a polyhydric alcohol with (meth)acrylic acid, or by esterifying the terminal hydroxyl groups of an oligomer obtained by adding an alkylene oxide to a polyvalent carboxylic acid with (meth)acrylic acid. The epoxy acrylate oligomer can be obtained, for example, by reacting (meth)acrylic acid with the oxirane ring of a bisphenol-type epoxy resin or a novolac-type epoxy resin to esterify it. In addition, a carboxyl-modified epoxy acrylate oligomer in which this epoxy acrylate oligomer is partially modified with a dibasic carboxylic acid anhydride can also be used. The urethane acrylate oligomer can be obtained, for example, by esterifying a polyurethane oligomer obtained by reacting a polyether polyol or a polyester polyol with a polyisocyanate with (meth)acrylic acid. Polyol acrylate oligomers can be obtained by esterifying the hydroxyl groups of polyether polyol with (meth)acrylic acid.

The weight average molecular weight of the acrylate oligomer is preferably 50,000 or less, more preferably 500 to 50,000, and even more preferably 3,000 to 40,000. These acrylate oligomers may be used alone or in combination of two or more.

Also, as the active energy ray-curable component (B), an adduct acrylate polymer in which a group having a (meth)acryloyl group has been introduced into the side chain can be used. Such an adduct acrylate polymer can be obtained by using a copolymer of a (meth)acrylic acid ester and a monomer having a crosslinkable functional group in the molecule, and reacting a part of the crosslinkable functional group of the copolymer with a compound having a group that reacts with the (meth)acryloyl group and the crosslinkable functional group.

The (meth)acrylic acid ester preferably contains an alkyl (meth)acrylic acid ester having an alkyl group with 1 to 20 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more.

The monomer having a crosslinkable functional group in the molecule preferably contains at least one functional group selected from hydroxyl, carboxyl, amino and amide groups. Examples of such monomers include hydroxyalkyl esters of (meth)acrylic acid such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; acrylamides such as N-methylol methacrylamide; monoalkylaminoalkyl (meth)acrylates such as monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate and monoethylaminopropyl (meth)acrylate; ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid and citraconic acid. These monomers may be used alone or in combination of two or more.

Preferable examples of compounds having a group that reacts with a (meth)acryloyl group and a crosslinkable functional group include 2-methacryloyloxyethyl isocyanate, 2-(0-[1'-methylpropylideneamino]carboxyamino)ethyl methacrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, 2-acryloyloxyethyl isocyanate, 2-acryloyloxyethyl succinate, 2-acryloyloxyethyl hexahydrophthalimide, ω-carboxy-polycaprolactone monoacrylate, monohydroxyethyl phthalate acrylate, and 2-hydroxy-3-phenoxypropyl acrylate. These compounds may be used alone or in combination of two or more.

The weight average molecular weight of the adduct acrylate polymer is preferably about 50,000 to 900,000, and particularly preferably about 100,000 to 300,000.

The active energy ray curable component (B) may be one selected from the above-mentioned polyfunctional acrylate monomers, acrylate oligomers, and adduct acrylate polymers, or two or more may be combined, or may be combined with other active energy ray curable components.

The content of the active energy ray curable component (B) in the adhesive composition P must be 10 to 50 parts by mass, preferably 15 to 45 parts by mass, and particularly preferably 25 to 40 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester copolymer (A). By having a content of the active energy ray curable component (B) of 10 parts by mass or more, the adhesive layer 11 after irradiation with active energy rays has improved cohesive force, and even if outgassing occurs from the plastic plate in a high-temperature environment, the occurrence of bubbles, floating, and peeling is suppressed, resulting in excellent blister resistance. In other words, if the content of the active energy ray curable component (B) is less than 10 parts by mass, the adhesive layer 11 after irradiation with active energy rays does not have excellent blister resistance. On the other hand, if the content of the active energy ray curable component (B) exceeds 50 parts by mass, the adhesive strength of the adhesive layer 11 before the active energy ray irradiation becomes too high, making it difficult to smoothly peel off the release sheets 12a and 12b from the adhesive layer 11, and there is a risk that the adhesive layer 11 will be destroyed when the release sheets 12a and 12b are peeled off. In addition, since the adhesive layer 11 after the active energy ray irradiation has an adhesive strength (against a glass substrate) of about 10 N/25 mm or more, the bonded state between the hard plates can be firmly maintained.

(3) Crosslinking agent (C)
The pressure-sensitive adhesive composition P contains a crosslinking agent (C) that crosslinks the (meth)acrylic acid ester copolymer (A) to form a three-dimensional network structure, thereby improving the cohesive strength of the resulting pressure-sensitive adhesive. In addition, the pressure-sensitive adhesive can be provided with durability after irradiation with active energy rays.

The crosslinking agent (C) may be any that reacts with the reactive group (carboxyl group or hydroxyl group) possessed by the (meth)acrylic acid ester copolymer (A), and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. The crosslinking agent (C) may be used alone or in combination of two or more.

When the (meth)acrylic acid ester copolymer (A) contains a carboxyl group-containing monomer, it is preferable to use at least one selected from an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent, which have excellent reactivity with carboxyl groups, as the crosslinking agent (C), and it is particularly preferable to use an epoxy-based crosslinking agent. When the (meth)acrylic acid ester copolymer (A) contains a hydroxyl group-containing monomer, it is preferable to use an isocyanate-based crosslinking agent, which has excellent reactivity with hydroxyl groups.

Examples of epoxy crosslinking agents include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl aniline, and diglycidyl amine.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and their biuret and isocyanurate forms, as well as adducts which are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

The content of the crosslinking agent (C) in the adhesive composition P is preferably 0.01 to 5 parts by mass, particularly 0.05 to 1 part by mass, per 100 parts by mass of the (meth)acrylic acid ester copolymer (A). If the content of the crosslinking agent (C) is 0.01 parts by mass or more, the adhesive after irradiation with active energy rays can be given an improved durability effect. If the content of the crosslinking agent (C) exceeds 5 parts by mass, the degree of crosslinking becomes excessive, and the step-following ability of the resulting adhesive may decrease. In addition, a large amount of the carboxyl group or hydroxyl group of the (meth)acrylic acid ester copolymer (A) reacts with the crosslinking agent (C), and the amount of the carboxyl group or hydroxyl group remaining in the adhesive decreases, and the above-mentioned resistance to wet heat whitening may decrease. In addition to the above, from the viewpoint of obtaining the most preferable durability, the content of the crosslinking agent (C) is preferably 0.05 to 0.4 parts by mass, and from the viewpoint of obtaining the most preferable blister resistance, the content of the crosslinking agent (C) is preferably 0.3 to 1 part by mass.

(4) Photopolymerization initiator (D)
When ultraviolet rays are used as the active energy rays to be irradiated to the pressure-sensitive adhesive layer 11, the pressure-sensitive adhesive composition P preferably further contains a photopolymerization initiator (D). By containing the photopolymerization initiator (D) in this manner, the active energy ray-curable component (B) can be cured efficiently, and the polymerization curing time and the irradiation dose of the active energy rays can be reduced.

Examples of such photopolymerization initiators (D) include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzof Examples of the benzoxanthone include phenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiary-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ester, oligo[2-hydroxy-2-methyl-1[4-(1-methylvinyl)phenyl]propanone], and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. These may be used alone or in combination of two or more.

The photopolymerization initiator (D) is preferably used in an amount ranging from 2 to 15 parts by mass, and particularly from 4 to 12 parts by mass, per 100 parts by mass of the active energy ray-curable component (B).

(5) Various Additives If desired, various additives commonly used in acrylic pressure-sensitive adhesives, such as a silane coupling agent, an antistatic agent, a tackifier, an antioxidant, an ultraviolet absorber, a light stabilizer, a softener, a filler, and a refractive index adjuster, may be added to the pressure-sensitive adhesive composition P.

In particular, from the viewpoint of improving durability, it is preferable to add a silane coupling agent as an additive to the adhesive composition P. The silane coupling agent is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule, and has good compatibility with the (meth)acrylic acid ester copolymer (A). In addition, when the adhesive sheet 1 is used for optical purposes, a silane coupling agent having optical transparency is preferable.

Examples of such silane coupling agents include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; epoxy structure-containing silicon compounds such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane. , 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and other amino group-containing silicon compounds, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These may be used alone or in combination of two or more.

The amount of the silane coupling agent added is preferably 0.01 to 1.0 parts by mass, and more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester copolymer (A).

(6) Production of adhesive composition The adhesive composition P can be produced by producing a (meth)acrylic acid ester copolymer (A), mixing the obtained (meth)acrylic acid ester copolymer (A) with an active energy ray-curable component (B) and a crosslinking agent (C), and, if desired, adding a photopolymerization initiator (D) and/or an additive.

The (meth)acrylic acid ester copolymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. The polymerization of the (meth)acrylic acid ester copolymer (A) can be carried out by a solution polymerization method or the like, using a polymerization initiator as desired. Examples of polymerization solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more types may be used in combination.

Examples of polymerization initiators include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.

In addition, in the above polymerization process, the weight average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

Once the (meth)acrylic acid ester copolymer (A) is obtained, the active energy ray curable component (B), the crosslinking agent (C), and optionally the photopolymerization initiator (D) and additives are added to the solution of the (meth)acrylic acid ester copolymer (A) and thoroughly mixed to obtain the adhesive composition P.

(7) Formation of Pressure-Sensitive Adhesive Layer The pressure-sensitive adhesive layer 11 is formed by thermally crosslinking the pressure-sensitive adhesive composition P. That is, the crosslinking of the pressure-sensitive adhesive composition P is performed by a heat treatment. This heat treatment can also serve as a drying treatment after application of the pressure-sensitive adhesive composition P.

The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes. After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, 50% RH) as necessary. If this curing period is required, the adhesive layer is formed after the curing period has elapsed, and if no curing period is required, the adhesive layer is formed after the heat treatment is completed.

The above heat treatment (and curing) allows the (meth)acrylic acid ester copolymer (A) to be effectively crosslinked via the crosslinking agent (C).

The thickness of the adhesive layer 11 formed (measured according to JIS K7130) is 50 to 400 μm, preferably 70 to 300 μm, and particularly preferably 90 to 250 μm. The adhesive layer 11 may be formed as a single layer or as a laminate of multiple layers.

If the thickness of the adhesive layer 11 is less than 50 μm, sufficient conformability to unevenness cannot be obtained, and if the thickness of the adhesive layer 11 is more than 400 μm, processability decreases.

2. Release Sheet As the release sheets 12a and 12b, for example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. are used. Crosslinked films of these are also used. Furthermore, laminated films of these may be used.

It is preferable that the release surfaces of the release sheets 12a and 12b (particularly the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of release agents used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 12a and 12b is a heavy release type release sheet with a large release force, and the other is a light release type release sheet with a small release force.

There are no particular limitations on the thickness of the release sheets 12a and 12b, but it is usually about 20 to 150 μm.

3. Manufacturing of adhesive sheet In one manufacturing example of the adhesive sheet 1, the coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed, and then the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. If a curing period is required, a curing period is left, and if no curing period is required, the coating layer becomes the adhesive layer 11 as it is. This results in the adhesive sheet 1. Note that no irradiation of active energy rays is performed at this stage.

In another example of the production of the adhesive sheet 1, the coating liquid of the adhesive composition P is applied to the release surface of one of the release sheets 12a, and a heat treatment is performed to thermally crosslink the adhesive composition P, forming a coating layer, to obtain the release sheet 12a with the coating layer. Also, the coating liquid of the adhesive composition P is applied to the release surface of the other release sheet 12b, and a heat treatment is performed to thermally crosslink the adhesive composition P, forming a coating layer, to obtain the release sheet 12b with the coating layer. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are bonded together so that both coating layers are in contact with each other. If a curing period is required, a curing period is provided, and if a curing period is not required, the laminated coating layer becomes the adhesive layer 11 as it is. This results in the adhesive sheet 1. According to this production example, stable production is possible even when the adhesive layer 11 is thick.

Methods for applying the coating solution of the adhesive composition P include, for example, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

4. Physical Properties The ratio of the storage modulus at 23° C. after the pressure-sensitive adhesive layer 11 is irradiated with active energy rays to the storage modulus at 23° C. before the pressure-sensitive adhesive layer 11 is irradiated with active energy rays (storage modulus after active energy ray irradiation/storage modulus before active energy ray irradiation) is preferably 1.1 to 10, particularly preferably 1.2 to 7. The storage modulus in this specification is a value measured by a torsional shear method at a measurement frequency of 1 Hz in accordance with JIS K7244-6.

As described above, the storage modulus of the adhesive layer 11 at 23°C increases after irradiation with active energy rays (curing), and the cured adhesive layer 11 has excellent durability and conformability to uneven surfaces. Furthermore, in addition to the above viewpoints, when considering blister resistance, it is particularly preferable that the storage modulus ratio is 3 to 7.

The ratio of the storage modulus at 85°C after the pressure-sensitive adhesive layer 11 is irradiated with active energy rays to the storage modulus at 85°C before the pressure-sensitive adhesive layer 11 is irradiated with active energy rays (storage modulus after active energy ray irradiation/storage modulus before active energy ray irradiation) is preferably 1.1 to 10, and more preferably 1.3 to 7. Furthermore, in addition to the above viewpoints, taking into account blister resistance, the storage modulus ratio is particularly preferably 3 to 7.

As described above, the storage modulus of the adhesive layer 11 at 85°C increases after irradiation with active energy rays (curing), so that the cured adhesive layer 11 has excellent durability even at high temperatures.

If the storage modulus ratio at 23°C or 85°C is less than 1.1, the durability improvement effect described above may not be obtained. On the other hand, if the storage modulus ratio at 23°C or 80°C exceeds 10, the adhesive strength of the cured adhesive layer 11 may decrease, and sufficient durability may not be obtained.

The storage modulus of the adhesive layer 11 at 23°C before irradiation with active energy rays is preferably 0.01 to 0.2 MPa, more preferably 0.04 to 0.15 MPa, and even more preferably 0.07 to 0.1 MPa. The storage modulus of the adhesive layer 11 at 85°C before irradiation with active energy rays is preferably 0.01 to 0.1 MPa, more preferably 0.01 to 0.06 MPa, and even more preferably 0.02 to 0.04 MPa. The adhesive layer 11 before irradiation with active energy rays has excellent step-following properties due to having the above-mentioned storage modulus.

The storage modulus of the adhesive layer 11 at 23°C after irradiation with active energy rays is preferably 0.02 to 2 MPa, more preferably 0.05 to 1 MPa, and even more preferably 0.1 to 0.6 MPa. The storage modulus of the adhesive layer 11 at 85°C after irradiation with active energy rays is preferably 0.02 to 0.5 MPa, more preferably 0.02 to 0.2 MPa, and even more preferably 0.03 to 0.1 MPa. By having the above-mentioned storage modulus, the adhesive layer 11 after irradiation with active energy rays has excellent durability and blister resistance.

In the above adhesive sheet 1, the adhesive layer 11 before irradiation with active energy rays has excellent conformability to unevenness, so even if the adherend has unevenness, voids or air bubbles are unlikely to form between the unevenness and the adhesive layer 11, and the adhesive layer 11 can fill the unevenness. In addition, the adhesive layer 11 is cured by irradiation with active energy rays, and thus has excellent resistance to moist heat whitening, durability, and blister resistance.

The adhesive layer 11 of the adhesive sheet 1 according to this embodiment is preferably used to bond two hard plates together, as described below.

[Laminate]
2, the laminate 2 according to this embodiment is composed of a first hard plate 21, a second hard plate 22, and an adhesive layer 11 located therebetween and sandwiched between the first hard plate 21 and the second hard plate 22. Moreover, in the laminate 2 according to this embodiment, the first hard plate 21 has a step on the surface on the adhesive layer 11 side, specifically, a step due to the presence or absence of a printed layer 3.

The first hard plate 21 and the second hard plate 22 are not particularly limited as long as the adhesive layer 11 can be adhered to them. In addition, the first hard plate 21 and the second hard plate 22 may be made of the same material or different materials.

The first hard plate 21 and the second hard plate 22 may be, for example, a glass plate, a plastic plate, a metal plate, a semiconductor plate, or a laminate thereof, or a plate-shaped hard product such as a display module or a solar cell module. Since the adhesive layer 11 in this embodiment has excellent blister resistance, it is preferable that at least one of the first hard plate 21 and the second hard plate 22 includes a plastic plate.

The glass plate is not particularly limited, and examples thereof include chemically strengthened glass, alkali-free glass, quartz glass, soda-lime glass, barium-strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, barium borosilicate glass, etc. The thickness of the glass plate is not particularly limited, but is usually 0.1 to 5 mm, and preferably 0.2 to 2 mm.

The above-mentioned plastic plate is not particularly limited, but examples thereof include acrylic plates and polycarbonate plates. The thickness of the plastic plate is not particularly limited, but is usually 0.2 to 5 mm, and preferably 0.4 to 3 mm.

In addition, various functional layers (transparent conductive film, metal layer, silica layer, hard coat layer, anti-glare layer, etc.) may be provided on one or both sides of the above glass plate or plastic plate, metal wiring may be formed, or optical components may be laminated.

Examples of the optical components include polarizing plates (polarizing films), polarizers, retardation plates (retardation films), viewing angle compensation films, brightness enhancement films, contrast enhancement films, liquid crystal polymer films, diffusion films, hard coat films, semi-transmissive reflective films, etc.

Examples of the display module include a liquid crystal (LCD) module, a light emitting diode (LED) module, an organic electroluminescence (OLED) module, and electronic paper. These display modules usually have the above-mentioned glass plates, plastic plates, optical members, and the like laminated therein. For example, a polarizing plate is laminated in the LCD module, and the polarizing plate forms one surface of the LCD module.

In the laminate 2 according to this embodiment, at least one of the first hard plate 21 and the second hard plate 22 preferably has a polarizing plate. In addition, the second hard plate 22 in the laminate 2 according to this embodiment is preferably a display module or a part thereof (e.g., an optical member such as a polarizing plate), and the first hard plate 21 is preferably a protective plate made of a plastic plate or the like. In this case, the printing layer 3 is generally formed in a frame shape on the adhesive layer 11 side of the first hard plate 21.

The material constituting the printing layer 3 is not particularly limited, and known materials for printing may be used. The thickness of the printing layer 3, i.e., the height of the step, is preferably 3 to 45 μm, more preferably 5 to 35 μm, particularly preferably 7 to 25 μm, and even more preferably 7 to 15 μm.

The thickness of the printed layer 3 (height of the step) is preferably 3 to 30% of the thickness of the adhesive layer 11, more preferably 3.2 to 20%, and even more preferably 3.5 to 15%. This allows the adhesive layer 11 to reliably conform to the step caused by the printed layer 3, and prevents floating or air bubbles from occurring near the step.

The adhesive layer 11 of the laminate 2 according to this embodiment is obtained by curing the adhesive layer 11 of the adhesive sheet 1 described above by irradiating it with active energy rays. Here, active energy rays refer to electromagnetic waves or charged particle beams that have an energy quantum, and specific examples include ultraviolet rays and electron beams. Among active energy rays, ultraviolet rays are particularly preferred because they are easy to handle.

The irradiation with ultraviolet rays can be performed by a high pressure mercury lamp, a fusion H lamp, a xenon lamp, or the like, and the irradiation amount of the ultraviolet rays is preferably about 50 to 1000 mW/cm ² in terms of illuminance. The light amount is preferably 50 to 10000 mJ/cm ² , more preferably 80 to 5000 mJ/cm ² , and particularly preferably 200 to 2000 mJ/cm ^2. On the other hand, the irradiation with electron beams can be performed by an electron beam accelerator, or the like, and the irradiation amount of the electron beams is preferably about 10 to 1000 krad.

When the adhesive layer 11 in the adhesive sheet 1 is irradiated with active energy rays, the active energy ray curable component (B) polymerizes and hardens. The adhesive layer 11 hardened by irradiation with active energy rays has excellent durability, resistance to moist heat whitening, and resistance to blistering.

To manufacture the laminate 2, for example, first, one release sheet 12a (or 12b) of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the first hard plate 21 (or the second hard plate 22). Next, the other release sheet 12b (or 12a) is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the second hard plate 22 (or the first hard plate 21).

When the adhesive layer 11 and the first hard plate 21 are bonded together in the above process, the adhesive layer 11 has excellent step-following properties, so that gaps are unlikely to form between the step caused by the printing layer 3 and the adhesive layer 11, and the adhesive layer 11 can fill the step.

Then, active energy rays are irradiated onto the adhesive layer 11 from either the first hard plate 21 or the second hard plate 22 side to harden the adhesive layer 11. At this time, the hard plate on the side irradiated with active energy rays needs to be transparent to active energy rays.

In the laminate 2 described above, the adhesive layer 11 before irradiation with active energy rays has excellent step-following properties, so that voids or bubbles are unlikely to form between the step of the printing layer 3 and the adhesive layer 11. In addition, the adhesive layer 11 hardened by irradiation with active energy rays is suppressed from whitening when returned to room temperature after being subjected to high temperature and high humidity conditions, and has excellent resistance to humidity and heat whitening. Furthermore, even when the adhesive layer 11 irradiated with active energy rays is subjected to high temperature and high humidity conditions, the generation of bubbles and the like near the step is prevented, and the adhesive layer 11 has excellent durability. Furthermore, when at least one of the first hard plate 21 and the second hard plate 22 includes a plastic plate, even if outgassing is generated from the plastic plate under high temperature conditions, the adhesive layer 11 irradiated with active energy rays has excellent blister resistance, so that the generation of bubbles, lifting, and peeling is suppressed.

The excellent resistance to moist heat whitening of the adhesive layer 11 cured by irradiation with active energy rays can be evaluated as follows. For example, both sides of the adhesive layer 11 are sandwiched between two pieces of alkali-free glass with a thickness of 1.1 mm, and active energy rays with the above-mentioned illuminance and amount of light are irradiated through the alkali-free glass from at least one side to obtain a laminate. The laminate is stored for 240 hours under conditions of 85°C and 85% RH (humid heat conditions), and then taken out under normal temperature and humidity conditions of 23°C and 50% RH. At this time, it is confirmed that the degree of whitening of the adhesive layer 11 is small.

The degree of whitening can also be quantitatively evaluated by the haze value. Specifically, it can be evaluated by the haze value (%) of the laminate after the moist heat condition (measured according to JIS K7136:2000; the same applies below) minus the haze value (%) before the moist heat condition (the increase in the haze value after the moist heat condition). The increase in the haze value after the moist heat condition is preferably less than 5.0 points, and more preferably less than 1.0 point. In the above evaluation, it is preferable to use an alkali-free glass with a haze value of approximately 0%. The haze value of the adhesive layer after the moist heat condition is preferably 1.0% or less, more preferably 0.9% or less, and even more preferably 0.8% or less.

The adhesive layer 11 preferably has a total light transmittance (measured in accordance with JIS K7361-1:1997) of 80% or more, more preferably 90% or more, and even more preferably 99% or more. A total light transmittance of 80% or more provides high transparency and is suitable for optical applications. The total light transmittance of the adhesive layer 11 usually does not change much before and after irradiation with active energy rays.

The above-described embodiments are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, one of the release sheets 12a, 12b in the adhesive sheet 1 may be omitted. Also, the first hard plate 21 may have a step other than the printed layer 3, or may not have a step. Furthermore, not only the first hard plate 21 but also the second hard plate 22 may have a step on the adhesive layer 11 side.

The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

Example 1
1. Preparation of (meth)acrylic acid ester copolymer 60 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of methyl methacrylate, and 20 parts by mass of 2-hydroxyethyl acrylate were copolymerized to prepare a (meth)acrylic acid ester copolymer (A). The molecular weight of this (meth)acrylic acid ester copolymer (A) was measured by the method described below, and the weight average molecular weight was 600,000.

2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; the same applies below) of the (meth)acrylic acid ester copolymer (A) obtained in the above step (1), 25 parts by mass of polyethylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-400") as the active energy ray curable component (B), 0.23 parts by mass of trimethylolpropane modified tolylene diisocyanate (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L") as the isocyanate-based crosslinking agent (C), 0.2 parts by mass of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-403") as the silane coupling agent, and 0.5 parts by mass of 1-hydroxycyclohexylphenyl ketone (manufactured by BASF, product name "Irgacure 184") as the photopolymerization initiator (D) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an adhesive composition with a solid content concentration of 33% by mass.

The formulation of the pressure-sensitive adhesive composition is shown in Table 1. Details of the abbreviations and the like shown in Table 1 are as follows.
[(Meth)acrylic acid ester copolymer]
2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate MMA: methyl methacrylate HEA: 2-hydroxyethyl acrylate AA: acrylic acid
[Active energy ray curable component]
A400: Polyethylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-400")
A9300-1CL: ε-caprolactone-modified tris-(2-acryloxyethyl) isocyanurate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "A-9300-1CL")
[Crosslinking agent]
TDI: Trimethylolpropane modified tolylene diisocyanate (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L")
Epoxy: 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, product name "TETRAD-C")

3. Manufacture of adhesive sheet The obtained adhesive composition coating solution was applied to the release-treated surface of a heavy release type release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), one side of which was treated with a silicone-based release agent, using a knife coater so that the thickness after drying was 100 μm, and then heated at 100 ° C. for 4 minutes to form a coating layer. Similarly, the obtained adhesive composition coating solution was applied to the release-treated surface of a light release type release sheet (manufactured by Lintec Corporation, product name "SP-PET382120"), one side of which was treated with a silicone-based release agent, using a knife coater so that the thickness after drying was 100 μm, and then heated at 100 ° C. for 4 minutes to form a coating layer.

Then, the heavy release type release sheet with the coating layer obtained above and the light release type release sheet with the coating layer obtained above were laminated together so that both coating layers were in contact with each other, and cured for 7 days under conditions of 23°C and 50% RH to produce an adhesive sheet consisting of heavy release type release sheet/adhesive layer (thickness: 200 μm)/light release type release sheet. The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant pressure thickness gauge (manufactured by Techclock, product name "PG-02").

[Examples 2 to 4, Comparative Examples 1 to 3]
Except for changing the ratio of each monomer constituting the (meth)acrylic acid ester copolymer (A), the weight average molecular weight of the (meth)acrylic acid ester copolymer (A), the type and amount of the active energy ray curable component (B), the type and amount of the crosslinking agent (C), the amount of the photopolymerization initiator (D), the amount of the silane coupling agent, and the thickness of the adhesive layer as shown in Table 1, adhesive sheets were produced in the same manner as in Example 1.

The weight average molecular weight (Mw) mentioned above is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement).
<Measurement conditions>
GPC measuring device: Tosoh Corporation, HLC-8020
GPC columns (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (x2)
TSK gel G2000HXL
Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[Test Example 1] (Measurement of storage modulus)
The light release type release sheet and the heavy release type release sheet were peeled off from the pressure-sensitive adhesive sheet obtained in the Examples or Comparative Examples, and the pressure-sensitive adhesive layer was laminated in multiple layers to a thickness of 0.6 mm. A cylindrical body with a diameter of 8 mm (height of 0.6 mm) was punched out from the resulting laminate of pressure-sensitive adhesive layers, and this was used as a sample (sample before UV irradiation).

The storage modulus (MPa) of the above sample was measured by a torsional shear method using a viscoelasticity measuring device (MCR300, manufactured by Physica) in accordance with JIS K7244-6 under the following conditions.
Measurement frequency: 1Hz
Measurement temperature: 23℃, 85℃

In addition, the same sample as above was irradiated with ultraviolet light under the following conditions using an ultraviolet light irradiation device (manufactured by iGraphics, product name "iGrantage ECS-401GX type") to cure the adhesive layer, thereby obtaining a sample after ultraviolet light irradiation. The storage modulus (MPa) of the obtained sample after ultraviolet light irradiation was measured in the same manner as the sample before ultraviolet light irradiation.
[Ultraviolet light irradiation conditions]
Light source: high pressure mercury lamp Light quantity: 1000mJ/ ^cm2
・Illuminance: 200mW/ ^cm2

From the above measurement results, the ratio of the storage modulus after UV irradiation to the storage modulus before UV irradiation at 23°C and 85°C (storage modulus after UV irradiation/storage modulus before UV irradiation) was calculated. The measurement results and calculation results are shown in Table 2.

[Test Example 2] (Processability Evaluation)
The light release type release sheet was peeled off from the adhesive sheet obtained in the examples or comparative examples, and the peeling state of the light release type release sheet at this time was evaluated as processability. The light release type release sheet that could be peeled off smoothly from the adhesive layer was evaluated as good processability (○), and the adhesive layer was destroyed with the peeling of the light release type release sheet was evaluated as poor processability (×). The results are shown in Table 2.

[Test Example 3] (Evaluation of resistance to wet heat whitening)
A laminate was obtained by sandwiching the adhesive layer of the adhesive sheet obtained in the Examples or Comparative Examples between two pieces of 1.1 mm thick alkali-free glass, and irradiating ultraviolet light through one of the pieces of glass under the ultraviolet irradiation conditions of Test Example 1. The haze value (%) of the laminate was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH2000").

The laminate was then stored for 240 hours under humid heat conditions of 85°C and 85% RH. After that, it was returned to room temperature and humidity of 23°C and 50% RH, and the haze value (%) of the laminate was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH2000"). The haze value was measured within 30 minutes after the laminate was returned to room temperature and humidity.

Based on the above results, the haze value increase (points) after the moist heat conditions was calculated by subtracting the haze value before the moist heat conditions from the haze value after the moist heat conditions. A haze value increase of less than 1.0 point after the moist heat conditions was evaluated as having good moist heat whitening resistance (○), a haze value increase of 1.0 point or more but less than 5.0 points after the moist heat conditions was evaluated as being within the appropriate range for moist heat whitening resistance (△), and a haze value increase of 5.0 points or more after the moist heat conditions was evaluated as having poor moist heat whitening resistance (×). The results are shown in Table 2.

[Test Example 4] (Step-following ability and durability test)
(a) Preparation of evaluation samples On the surface of a glass plate (manufactured by NSG Precision, product name "Corning Glass Eagle XG", length 90 mm x width 50 mm x thickness 0.5 mm), ultraviolet-curable ink (manufactured by Teikoku Ink Co., Ltd., product name "POS-911 Black") was screen-printed in a frame shape (outer dimensions: length 90 mm x width 50 mm, width 5 mm) to a coating thickness of 8 μm and 15 μm. Next, the printed ultraviolet-curable ink was cured by irradiation with ultraviolet light (80 W/cm ² , two metal halide lamps, lamp height 15 cm, belt speed 10 to 15 m/min), and a stepped glass plate having a printed step (step height: 8 μm and 15 μm) was prepared.

The adhesive sheet obtained in the Example or Comparative Example was cut into a shape of 90 mm length x 50 mm width, and the light release type release sheet was removed to expose the adhesive layer. Then, using a laminator (manufactured by Fujipla Inc., product name "LPD3214"), the adhesive sheet was laminated onto a stepped glass plate so that the adhesive layer covered the entire frame-shaped print.

After lamination, the heavy-release release sheet was peeled off, and a glass plate (manufactured by NSG Precision, product name "Corning Glass Eagle XG", 90 mm length x 50 mm width x 0.5 mm thickness) was laminated onto the exposed adhesive layer surface using the laminator described above to prepare a sample for evaluation.

(b) Evaluation of step conformity (initial stage) The obtained evaluation sample was pressurized in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. at 0.5 MPa and 50° C. for 30 minutes. Thereafter, the presence or absence of air bubbles in the adhesive layer (especially in the vicinity of the step caused by the printing layer) was visually confirmed. As a result, the sample with no air bubbles was evaluated as ◎, the sample with almost no air bubbles was evaluated as ○, and the sample with air bubbles was evaluated as × (evaluation of initial step conformity). The results are shown in Table 2.

(c) Evaluation of durability (step-following ability after durability test) Next, the above evaluation samples (1) and (2) were stored for 240 hours under humid heat conditions of 85°C and 85% RH. After that, the presence or absence of air bubbles in the adhesive layer (especially in the vicinity of the step caused by the printing layer) was visually confirmed. As a result, the sample with no air bubbles was evaluated as ◎, the sample with almost no air bubbles was evaluated as ○, and the sample with air bubbles was evaluated as × (evaluation of durability (step-following ability after durability test)). The results are shown in Table 2.

[Test Example 5] (Total light transmittance measurement)
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet obtained in the Examples or Comparative Examples was attached to glass to prepare a measurement sample. After background measurement was performed on the glass, the total light transmittance (%) of the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-2000) in accordance with JIS K7361-1:1997. The results are shown in Table 2.

[Test Example 6] (Evaluation of blister resistance)
A polyethylene terephthalate film (ITO film, manufactured by Oike Kogyo Co., Ltd.) having a thickness of 125 μm was prepared, on one side of which a transparent conductive film made of tin-doped indium oxide (ITO) was provided by sputtering.

The adhesive layer of the adhesive sheet obtained in the Examples or Comparative Examples was sandwiched between the transparent conductive film of the ITO film and a 1 mm thick polycarbonate plate (manufactured by Mitsubishi Gas Chemical Company, product name "Iupilon Sheet MR58"), and ultraviolet light was irradiated through the polycarbonate plate under the ultraviolet irradiation conditions of Test Example 1 to obtain a laminate.

The obtained laminate was autoclaved for 30 minutes at 50°C and 0.5 MPa, and then left for 15 hours. It was then stored for 72 hours under endurance conditions of 85°C and 85% RH. The adhesive layer was then visually inspected for the presence of bubbles, lifting, or peeling. As a result, samples with no bubbles, lifting, or peeling were rated as ◎, samples with almost no bubbles, lifting, or peeling were rated as ○, and samples with bubbles, lifting, or peeling were rated as × (evaluation of blister resistance). The results are shown in Table 2.

As can be seen from Table 2, the adhesive sheets obtained in the examples had excellent processability. In addition, the adhesive layers obtained in the examples had excellent step conformability before UV irradiation, and had excellent resistance to moist heat whitening, durability, and blister resistance after UV irradiation.

The active energy ray-curable pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, for bonding a display module to a protective plate having a step, particularly a plastic plate.

Reference Signs List 1: active energy ray-curable adhesive sheet 11: adhesive layer 12a, 12b: release sheet 2: laminate 21: first hard plate 22: second hard plate 3: printed layer

Claims (11)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of an active energy ray-curable acrylic pressure-sensitive adhesive containing at least an acrylic active energy ray-curable component , the pressure-sensitive adhesive sheet being used for bonding two hard plates together,
The thickness of the pressure-sensitive adhesive layer is 50 to 400 μm,
a ratio of a storage modulus at 23°C after irradiating the pressure-sensitive adhesive layer with active energy rays to a storage modulus at 23°C before irradiating the pressure-sensitive adhesive layer with active energy rays is 1.1 to 10;
the pressure-sensitive adhesive layer has a storage modulus at 23° C. before irradiation with active energy rays of 0.01 to 0.2 MPa;
the pressure-sensitive adhesive layer has a storage modulus at 23° C. after irradiation with active energy rays of 0.02 to 2 MPa;
the pressure-sensitive adhesive layer has a storage modulus at 85° C. before irradiation with active energy rays of 0.01 to 0.06 MPa;
the pressure-sensitive adhesive layer has a storage modulus at 85° C. after irradiation with active energy rays of 0.02 to 0.5 MPa;
The adhesive layer is sandwiched between two pieces of alkali-free glass having a thickness of 1.1 mm, and an active energy ray is irradiated through one of the pieces of glass to obtain a laminate, which is then stored under humid heat conditions of 85°C and 85% RH for 240 hours, and then taken out under normal temperature and humidity conditions of 23°C and 50% RH, and the haze value after the humid heat conditions is calculated by subtracting the haze value (%) before the humid heat conditions from the haze value (%), and the increase in haze value after the humid heat conditions is less than 5.0 points. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of an active energy ray-curable acrylic pressure-sensitive adhesive containing at least an acrylic active energy ray-curable component , the pressure-sensitive adhesive sheet being used for bonding two hard plates together,
The thickness of the pressure-sensitive adhesive layer is 50 to 400 μm,
the pressure-sensitive adhesive layer has a storage modulus at 23° C. before irradiation with active energy rays of 0.01 to 0.2 MPa;
a ratio of a storage modulus at 85°C after irradiating the pressure-sensitive adhesive layer with active energy rays to a storage modulus at 85°C before irradiating the pressure-sensitive adhesive layer with active energy rays is 1.1 to 10;
the pressure-sensitive adhesive layer has a storage modulus at 85° C. before irradiation with active energy rays of 0.01 to 0.06 MPa;
the pressure-sensitive adhesive layer has a storage modulus at 85° C. after irradiation with active energy rays of 0.02 to 0.5 MPa;
The adhesive layer is sandwiched between two pieces of alkali-free glass having a thickness of 1.1 mm, and an active energy ray is irradiated through one of the pieces of glass to obtain a laminate, which is then stored under humid heat conditions of 85°C and 85% RH for 240 hours, and then taken out under normal temperature and humidity conditions of 23°C and 50% RH, and the haze value after the humid heat conditions is calculated by subtracting the haze value (%) before the humid heat conditions from the haze value (%), and the increase in haze value after the humid heat conditions is less than 5.0 points. The active energy ray-curable adhesive sheet according to claim 2, characterized in that the storage modulus of the adhesive layer at 23°C after irradiation with active energy rays is 0.02 to 2 MPa. The pressure-sensitive adhesive sheet includes two release sheets,
The active energy ray-curable adhesive sheet according to any one of claims 1 to 3, characterized in that the adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the two release sheets. The active energy ray-curable adhesive sheet according to any one of claims 1 to 4, characterized in that the adhesive layer contains a carboxyl group or a hydroxyl group. Two hard boards,
A laminate comprising a pressure-sensitive adhesive layer sandwiched between the two hard plates,
The pressure-sensitive adhesive layer is a laminate obtained by curing the pressure-sensitive adhesive layer of the active energy ray-curable pressure-sensitive adhesive sheet according to any one of claims 1 to 5 by irradiation with active energy rays. The laminate according to claim 6, characterized in that at least one of the hard plates has a step on the surface facing the adhesive layer. The laminate according to claim 7, characterized in that the step is due to the presence or absence of a printed layer. The laminate according to any one of claims 6 to 8, characterized in that at least one of the hard plates includes a polarizing plate. The laminate according to any one of claims 6 to 9, characterized in that at least one of the hard plates includes a plastic plate. One of the two hard plates is a display module or a part thereof;
9. The laminate according to claim 6, wherein the other of the two hard plates is a protective plate having a frame-shaped step on a surface facing the pressure-sensitive adhesive layer.

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