Adhesive composition, adhesive sheet, optical laminate, and image display device

Abstract

This adhesive composition includes a monomer component M and / or a polymer thereof, the monomer component M including a monomer a that contains an aromatic ring and does not contain a nitrogen atom, a monomer b that contains a ring structure that includes a nitrogen atom, and a monomer c that contains a hydroxyl group. The sum of the monomer a content and the monomer b content of the monomer component M is at least 50 wt%. The monomer b content of the monomer component M is 0.1–8 wt%. The adhesive composition is suited to forming an adhesive sheet that has a high refractive index and is better suited for use in an image display device that can be used in various environments.

Description

Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, optical laminate, and image display device

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, an optical laminate, and an image display device.

[0002] 2. Description of the Related Art In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices), have rapidly become widespread.

[0003] An image display device generally includes an optical laminate including optical elements such as a polarizing film and a retardation film. In such an optical laminate, a bonding layer is usually disposed between adjacent optical elements to bond them together. An example of the bonding layer is a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition.

[0004] A high refractive index pressure-sensitive adhesive sheet can be advantageous for use in an image display device. For example, when an image display device is equipped with a high refractive index optical member, unnecessary reflection can be suppressed by combining it with a high refractive index pressure-sensitive adhesive sheet.

[0005] Patent Document 1 discloses a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive sheet with a high refractive index. Patent Document 1 also describes that the pressure-sensitive adhesive composition can suppress whitening when subjected to high-temperature, high-humidity conditions and then returned to normal temperature and humidity.

[0006] Patent No. 6307189

[0007] With the expansion of applications, image display devices can be used in a variety of environments. In consideration of the possibility of use in a variety of environments, the pressure-sensitive adhesive composition of Patent Document 1 still has room for improvement.

[0008] An object of the present invention is to provide a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive sheet having a high refractive index and that can form a pressure-sensitive adhesive sheet that is more suitable for use in image display devices that can be used in a variety of environments.

[0009] [1] A pressure-sensitive adhesive composition according to an embodiment of the present invention includes at least one selected from the group consisting of monomer component M and polymers thereof, wherein the monomer component M includes monomer a having an aromatic ring but no nitrogen atom, monomer b having a ring structure containing a nitrogen atom, and monomer c having a hydroxyl group, wherein the sum of the content of monomer a and the content of monomer b in the monomer component M is 50% by weight or more, and the content of monomer b in the monomer component M is 0.1 to 8% by weight. [2] In the pressure-sensitive adhesive composition described in [1] above, the content of a (meth)acrylic monomer in the monomer component M may be 50% by weight or more. [3] In the pressure-sensitive adhesive composition described in [1] or [2] above, the monomer component M may include monomer a having one aromatic ring per molecule. [4] In the pressure-sensitive adhesive composition described in any of [1] to [3] above, the monomer component M may include monomer b having an aliphatic ring structure as the ring structure. [5] In the pressure-sensitive adhesive composition described in any one of [1] to [4] above, the monomer component M may include the monomer b containing a cyclic amide structure as the ring structure. [6] In the pressure-sensitive adhesive composition described in any one of [1] to [5] above, the monomer component M may include the monomer b which is an N-vinyl cyclic amide. [7] In the pressure-sensitive adhesive composition described in any one of [1] to [6] above, the content of the monomer c in the monomer component M may be 12 wt% or more. [8] In the pressure-sensitive adhesive composition described in any one of [1] to [7] above, the monomer component M may further include a (meth)acrylic acid alkyl ester having a C1 to C20 alkyl group in the side chain. [9] In the pressure-sensitive adhesive composition described in any one of [1] to [8] above, the monomer component M may further include a (meth)acrylic acid alkyl ester having a C5 to C20 alkyl group in the side chain.

[10] In the pressure-sensitive adhesive composition according to the above [9], the content of the (meth)acrylic acid alkyl ester in the monomer component M may be 14 wt % or more.

[11] In the pressure-sensitive adhesive composition according to any one of [1] to

[10] above, the monomer component M may be substantially free of a carboxyl group-containing monomer.

[12] The pressure-sensitive adhesive composition according to any one of [1] to

[11] above may further contain a tackifier.

[13] In the pressure-sensitive adhesive composition according to

[12] above, the content of the tackifier in the pressure-sensitive adhesive composition may be 0.1 to 10 parts by weight per 100 parts by weight of the monomer component M.

[14] The pressure-sensitive adhesive composition according to any one of [1] to

[13] above may be a photocurable pressure-sensitive adhesive composition containing a photopolymerization initiator.

[15] In the pressure-sensitive adhesive composition according to

[14] above, the content of the photopolymerization initiator in the pressure-sensitive adhesive composition may be 0.001 part by weight or more per 100 parts by weight of the monomer component M.

[16] The pressure-sensitive adhesive composition according to any one of [1] to

[15] above may further contain an antioxidant.

[17] The pressure-sensitive adhesive composition according to any one of [1] to

[16] above may further contain a silane coupling agent.

[18] A pressure-sensitive adhesive sheet according to an embodiment of the present invention is a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition according to any one of [1] to

[17] above.

[19] An optical laminate according to an embodiment of the present invention comprises the pressure-sensitive adhesive sheet according to

[18] above and an optical film.

[20] An image display device according to an embodiment of the present invention comprises the optical laminate according to

[19] above.

[0010] According to an embodiment of the present invention, a pressure-sensitive adhesive composition can be provided that can form a pressure-sensitive adhesive sheet having a high refractive index and that can form a pressure-sensitive adhesive sheet that is more suitable for use in image display devices that can be used in a variety of environments.

[0011] FIG. 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 2 is a schematic view for explaining an example of a method for forming the pressure-sensitive adhesive sheet of the present invention from the pressure-sensitive adhesive composition of the present invention. FIG. 3 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention.

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention.

[0013] [Terminology, etc.] In this specification, when the expression "weight" appears, it may be read as "mass," which is commonly used as an SI unit indicating weight, and vice versa.

[0014] In this specification, the expression "(meth)acrylic" means "acrylic and / or methacrylic", the expression "(meth)acrylate" means "acrylate and / or methacrylate", the expression "(meth)allyl" means "allyl and / or methallyl", and the expression "(meth)acrolein" means "acrolein and / or methacrolein".

[0015] When the pressure-sensitive adhesive composition contains a polymer of the monomer component M (including a partially polymerized product described below), the weight of the polymer is converted into the weight of each monomer before polymerization in calculating the monomer content.

[0016] <<1. Pressure-sensitive adhesive composition>> A pressure-sensitive adhesive composition according to an embodiment of the present invention (hereinafter referred to as "pressure-sensitive adhesive composition A") contains at least one selected from the group consisting of monomer component M and polymers thereof. Monomer component M contains (I) monomer a having an aromatic ring but no nitrogen atom, (II) monomer b having a ring structure containing a nitrogen atom, and (III) monomer c having a hydroxyl group. The sum of the content of monomer a and the content of monomer b in monomer component M is 50% by weight or more. The content of monomer b in monomer component M is 0.1 to 8% by weight. According to studies by the present inventors, a pressure-sensitive adhesive composition A in which monomer component M contains specific monomers a, b, and c and in which the contents of each of the monomers in monomer component M are specified is suitable for forming a pressure-sensitive adhesive sheet that has a high refractive index, is inhibited from whitening under high temperature and high humidity conditions, and is inhibited from foaming under environments where temperature changes are repeated.

[0017] <1-1. Monomer Component M> Monomer component M may contain a (meth)acrylic monomer. The (meth)acrylic monomer that monomer component M may contain may correspond to Monomer a, Monomer b, or Monomer c. Monomer component M may also contain a (meth)acrylic monomer that does not correspond to Monomer a, Monomer b, or Monomer c. The content of the (meth)acrylic monomer in monomer component M may be 50% by weight or more, in which case a (meth)acrylic pressure-sensitive adhesive sheet can be formed. The content may be 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, 97% by weight or more, 98% by weight or more, 99% by weight or more, or even 100% by weight.

[0018] In this specification, the term "(meth)acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. The (meth)acrylic monomer is preferably a monomer having one (meth)acryloyl group (in other words, a monofunctional (meth)acrylic monomer).

[0019] <1-1-a. Monomer a> Monomer a is a monomer that contains an aromatic ring and does not contain a nitrogen atom.

[0020] The aromatic ring may be a fused ring or a heterocyclic ring (heterocycle). Examples of heteroatoms that can be contained in the heterocycle as ring-constituting atoms include at least one selected from the group consisting of sulfur atoms and oxygen atoms. The heteroatom may be a sulfur atom. Examples of aromatic rings are a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, an indene ring, an azulene ring, and a thiophene ring. Monomer a may have a structure in which one or more non-heterocyclic aromatic rings are fused with one or more heterocycles, such as a dinaphthothiophene structure.

[0021] The aromatic ring may have one or more substituents (excluding ethylenically unsaturated groups, as described below) on the ring-constituting atoms, or may have no substituents. Examples of the substituents include alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, and glycidyloxy groups. However, the substituents are not limited to the above examples, as long as they do not contain a nitrogen atom. The substituent may contain carbon atoms, and in such cases, the number of carbon atoms contained in the substituent may be, for example, 1 to 4, 1 to 3, or even 1 to 2. One example of an aromatic ring has no substituents on the ring-constituting atoms. Another example of an aromatic ring has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms) on the ring-constituting atoms.

[0022] The number of aromatic rings contained in one molecule of monomer a is, for example, 1, and may be 2 or more. The upper limit of the number of aromatic rings is not particularly limited and may be, for example, 16 or less. The upper limit may be 12 or less, 8 or less, 6 or less, 5 or less, 4 or less, 3 or less, or even 2 or less. Monomer component M may contain monomer a containing one aromatic ring in one molecule. Monomer component M may be substantially free of monomer a containing two or more aromatic rings in one molecule.

[0023] In this specification, "substantially free" means that the content is less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.01 wt%, and even more preferably less than 0.001 wt%. Furthermore, with regard to a component whose content in the PSA composition A is specified by a range of parts by weight relative to 100 parts by weight of the monomer component M, "substantially free" means that the content is less than 0.1 part by weight, preferably less than 0.05 part by weight, more preferably less than 0.01 part by weight, and even more preferably less than 0.001 part by weight.

[0024] In the monomer a, the aromatic ring is preferably located on a side chain. In other words, the monomer a may have an aromatic ring on a side chain. The monomer a preferably has at least one aromatic ring and at least one ethylenically unsaturated group in one molecule. As the monomer a, a compound having one ethylenically unsaturated group in one molecule (in other words, a monofunctional monomer) is preferably used.

[0025] Examples of ethylenically unsaturated groups are (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and adhesiveness, acryloyl groups are more preferred. In other words, monomer a preferably contains an aromatic ring-containing (meth)acrylic monomer, more preferably an aromatic ring-containing acrylic monomer. An example of an aromatic ring-containing (meth)acrylic monomer is an aromatic ring-containing (meth)acrylate. Specific examples of aromatic ring-containing (meth)acrylates will be described later.

[0026] The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. An example of the linking group includes one or more selected from the group consisting of alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups in which one or more hydrogen atoms in these groups have been substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O-), and thiooxy groups (-S-). In one example of Monomer A, the aromatic ring and the ethylenically unsaturated group are bonded directly. In another example of Monomer A, the aromatic ring and the ethylenically unsaturated group are bonded via a linking group selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. The number of carbon atoms in the alkylene group and oxyalkylene group that can be included in the linking group is, for example, 1 to 4, and may be 1 to 3, or even 1 to 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group that can be contained in the linking group is, for example, 1 to 8, and may be 1 to 6, 1 to 4, 1 to 3, 2 to 3, or even 1 to 2, 2, or 1.

[0027] Specific examples of the monomer a include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds may be used alone or in combination of two or more.

[0028] The monomer component M may contain a monomer having one aromatic ring (preferably a carbon ring) and at least one ethylenically unsaturated group in one molecule (aromatic ring-single-unit-containing monomer). A pressure-sensitive adhesive composition A containing a aromatic ring-single-unit-containing monomer as the monomer a is particularly suitable for forming a pressure-sensitive adhesive sheet that is suppressed from discoloring due to exposure to light.

[0029] Examples of aromatic ring unit-containing monomers include carbon aromatic ring-containing (meth)acrylates such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and chlorobenzyl (meth)acrylate; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo bromine-substituted aromatic ring-containing (meth)acrylates such as 6-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6-(4,6-dibromo-2-s-butylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, and 2,6-dibromo-4-dodecylphenyl acrylate; carbon-containing aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having a vinyl substituent on a heteroaromatic ring.

[0030] Monomer component M may contain a monomer (multiple aromatic ring-containing monomer) having two or more aromatic rings (preferably carbon rings) and at least one ethylenically unsaturated group in one molecule. Pressure-sensitive adhesive composition A containing a multiple aromatic ring-containing monomer as monomer a is particularly suitable for forming a pressure-sensitive adhesive sheet with a higher refractive index. However, when emphasis is placed on suppressing coloration due to light exposure, monomer component M may be substantially free of multiple aromatic ring-containing monomers.

[0031] Examples of the aromatic ring-containing monomer include a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are directly bonded, a monomer having a condensed ring, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure. Among these, a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group (for example, phenoxybenzyl (meth)acrylate described below) is preferably used.

[0032] The linking group connecting two or more aromatic rings may contain atoms such as P, Ge, Te, Se, N, S, Si, etc., and these atoms may be bonded to an oxygen atom. However, the linking group does not have to contain any of the above atoms. Examples of linking groups include an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n -; n is 1 to 3, preferably 1), a thiooxyalkylene group (e.g., -S-(CH2) n -; n is 1 to 3, preferably 1), a straight chain alkylene group (-(CH2) n -; n is 1 to 6, preferably 1 to 3), and the above-mentioned oxyalkylene group, the above-mentioned thiooxyalkylene group, and the above-mentioned straight-chain alkylene group in which the alkylene group is partially or completely halogenated. The linking group may contain one or more types selected from the group consisting of an oxy group, a thiooxy group, an oxyalkylene group, and a straight-chain alkylene group. Specific examples of monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate, thiophenoxybenzyl (meth)acrylate, and benzyl benzyl (meth)acrylate.

[0033] Examples of the monomer having a structure in which two or more non-fused aromatic rings are directly bonded include biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, and vinyl group-containing biphenyl. Specific examples include o-phenylphenol (meth)acrylate, biphenyl (meth)acrylate, and biphenylmethyl (meth)acrylate.

[0034] Examples of monomers having a condensed ring include naphthalene ring-containing (meth)acrylates, anthracene ring-containing (meth)acrylates, vinyl group-containing naphthalenes, and vinyl group-containing anthracenes. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

[0035] Examples of monomers having a fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. Note that, since monomers having a fluorene structure have a structure in which two benzene rings are directly bonded, they are included in the concept of monomers having a structure in which two or more non-fused aromatic rings are directly bonded.

[0036] Examples of the monomer having a dinaphthothiophene structure are (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, and (meth)allyl group-containing dinaphthothiophene. Specific examples include (meth)acryloyloxymethyldinaphthothiophene (e.g., a compound having a structure in which a CHCH(R)C(O)OCH group is bonded to the 5th or 6th position of the dinaphthothiophene ring; R is a hydrogen atom or a methyl group), (meth)acryloyloxyethyldinaphthothiophene (e.g., a compound having a structure in which a CHCH(R)C(O)OCH(CH) group or a CHCH(R)C(O)OCHCH group is bonded to the 5th or 6th position of the dinaphthothiophene ring; R is a hydrogen atom or a methyl group), vinyldinaphthothiophene (e.g., a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), and (meth)allyloxydinaphthothiophene. Incidentally, a monomer having a dinaphthothiophene structure is included in the concept of a monomer having a fused ring because it has a naphthalene structure and also has a structure in which a thiophene ring and two naphthalene structures are fused together.

[0037] Examples of monomers having a dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophenes and vinyl group-containing dibenzothiophenes. Note that, since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are fused, they are included in the concept of monomers having fused rings. Neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly bonded.

[0038] Monomer a may have a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in the various monomers a described above. Monomers having such a structure can be understood as ethoxylated products of the original monomers. The number of repeating oxyethylene units (—CHCHO—) in the oxyethylene chain is, for example, 1 to 8, and may be 1 to 6, 1 to 4, 1 to 3, or even 1 to 2, or even 1. Examples of monomer a that is an ethoxylated product include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate.

[0039] Monomer a may contain a high refractive index monomer. In this specification, the high refractive index monomer means a monomer having a refractive index of 1.51 or more, 1.53 or more, 1.55 or more, 1.56 or more, 1.57 or more, 1.58 or more, 1.59 or more, 1.60 or more, 1.61 or more, 1.62 or more, 1.63 or more, 1.64 or more, 1.65 or more, 1.66 or more, 1.67 or more, 1.68 or more, or even 1.69 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, and may be, for example, 3.00 or less, 2.50 or less, 2.00 or less, 1.90 or less, 1.80 or less, or even 1.70 or less. The high refractive index monomer may be used alone or in combination of two or more.

[0040] The refractive index of the monomer can be measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. The Abbe refractometer may be a DR-M4 model manufactured by ATAGO or an equivalent (e.g., DR-M2 model). If the nominal value of the refractive index at 25°C is provided by the monomer manufacturer, etc., this nominal value can be used as the refractive index.

[0041] Examples of high refractive index monomers are phenoxybenzyl acrylate (refractive index 1.566), 1-naphthylmethyl acrylate (refractive index 1.595), ethoxylated o-phenylphenol acrylate (refractive index 1.578 when the number of repeating oxyethylene units is 1), benzyl acrylate (refractive index 1.519), phenoxyethyl acrylate (refractive index 1.517), phenoxydiethylene glycol acrylate (refractive index 1.510), 6-acryloyloxymethyldinaphthothiophene (refractive index 1.75), 6-methacryloyloxymethyldinaphthothiophene (refractive index 1.726), 5-acryloyloxyethyldinaphthothiophene (refractive index 1.786), 6-acryloyloxyethyldinaphthothiophene (refractive index 1.722), 6-vinyldinaphthothiophene (refractive index 1.802), and 5-vinyldinaphthothiophene (refractive index 1.793). However, the high refractive index monomer is not limited to the above examples.

[0042] The content of monomer a in monomer component M is, for example, 20% by weight or more, and may be 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 42% by weight or more, 45% by weight or more, 47% by weight or more, 50% by weight or more, 51% by weight or more, 52% by weight or more, 53% by weight or more, 54% by weight or more, 55% by weight or more, 56% by weight or more, 57% by weight or more, 58% by weight or more, 59% by weight or more, or even 60% by weight or more. The upper limit of the content is, for example, 99% by weight or less, and may be 95% by weight or less, 90% by weight or less, 88% by weight or less, 87% by weight or less, 85% by weight or less, 83% by weight or less, 80% by weight or less, 78% by weight or less, 75% by weight or less, 73% by weight or less, 70% by weight or less, 69% by weight or less, 68% by weight or less, 67% by weight or less, 66% by weight or less, 65% by weight or less, 64% by weight or less, 63% by weight or less, 62% by weight or less, 61% by weight or less, or even 60% by weight or less.

[0043] Monomer component M may contain one or more types of monomer a. Monomer component M may contain one or more types of monomer a selected from the above-mentioned examples. Monomer a may be a (meth)acrylic monomer. When monomer component M contains two or more types of monomer a, at least one of the monomers a may be a (meth)acrylic monomer.

[0044] <1-1-b. Monomer b> Monomer b is a monomer containing a ring structure containing a nitrogen atom (hereinafter referred to as an "N-containing ring structure"). According to studies by the present inventors, the polarity of monomer b and the rigidity that it can impart to a polymer after polymerization may contribute to suppressing whitening of a PSA sheet due to humidification and suppressing deformation of the PSA sheet due to temperature changes and foaming caused thereby in a PSA composition A containing monomers a, b, and c as monomer components M. The nitrogen atom is preferably contained in the N-containing ring structure as a ring-constituting atom.

[0045] The N-containing ring structure may have one or more substituents (excluding ethylenically unsaturated groups) on the ring-constituting atoms, or may have no substituents. Examples of the substituents are the same as the examples described above as the substituents that the aromatic ring contained in monomer a may have. The substituent may or may not have a nitrogen atom.

[0046] The number of N-containing ring structures contained in one molecule of monomer b is, for example, 1, and may be 2 or more. The upper limit of the number of N-containing ring structures is not particularly limited and is, for example, 5 or less. The upper limit may be 4 or less, 3 or less, or even 2 or less. Monomer component M may contain monomer b containing one N-containing ring structure in one molecule. Monomer component M may be substantially free of monomer b containing two or more N-containing ring structures in one molecule.

[0047] In the monomer b, the N-containing ring structure is preferably located in a side chain. In other words, the monomer b may have the N-containing ring structure in a side chain. The monomer b preferably has at least one N-containing ring structure and at least one ethylenically unsaturated group in one molecule. As the monomer b, a compound having one ethylenically unsaturated group in one molecule (in other words, a monofunctional monomer) is preferably used.

[0048] Examples of the ethylenically unsaturated group are the same as those described above in the description of monomer A. Monomer B may be a (meth)acrylic monomer having a (meth)acryloyl group as the ethylenically unsaturated group, or may be a monomer having a vinyl group or a (meth)allyl group as the ethylenically unsaturated group.

[0049] The N-containing ring structure and the ethylenically unsaturated group may be bonded directly or via a linking group. Examples of the linking group are the same as those described above in the description of Monomer a. The ethylenically unsaturated group may be bonded to a nitrogen atom, which is a ring-constituting atom of the N-containing ring structure.

[0050] The N-containing ring structure may be a 3-membered ring, a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, or an 8-membered ring or more. The N-containing ring structure may be a 5-membered ring or a 6-membered ring, or may be a 5-membered ring.

[0051] The N-containing ring structure may be an alicyclic structure. In other words, the monomer component M may contain a monomer b containing an alicyclic structure as the N-containing ring structure. The alicyclic structure may or may not contain a carbon-carbon double bond.

[0052] An example of an aliphatic ring structure is a cyclic amide structure. In other words, the monomer component M may contain a monomer b containing a cyclic amide structure as an N-containing ring structure. The cyclic amide structure and the ethylenically unsaturated group may be bonded directly or via a linking group. The ethylenically unsaturated group may be bonded to a nitrogen atom that is a ring-constituting atom of the cyclic amide structure. The ethylenically unsaturated group may be a vinyl group. The monomer component M may contain a monomer b that is an N-vinyl cyclic amide.

[0053] Examples of N-vinyl cyclic amides are N-vinyl-2-pyrrolidone (NVP), N-vinyl-2-piperidone, N-vinyl-2-caprolactam, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, and vinylmethyloxazolidinone.

[0054] Examples of the monomer b other than the N-vinyl cyclic amide include heterocycle-containing monomers such as (meth)acryloylmorpholine, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole, vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, (meth)acryloylpiperidine, and N-methylvinylpyrrolidone.

[0055] The content of monomer b in monomer component M is 0.1 to 8 wt%. The lower limit of the content may be 0.2 wt% or more, 0.5 wt% or more, 0.7 wt% or more, 1 wt% or more, 1.2 wt% or more, 1.5 wt% or more, 1.7 wt% or more, 2 wt% or more, 2.2 wt% or more, 2.5 wt% or more, 2.7 wt% or more, or even 3 wt% or more. The upper limit of the content may be 7.7 wt% or less, 7.5 wt% or less, 7.2 wt% or less, 7 wt% or less, 6.7 wt% or less, 6.5 wt% or less, 6.2 wt% or less, 6 wt% or less, 5.7 wt% or less, 5.5 wt% or less, 5.2 wt% or less, or even 5 wt% or less.

[0056] Monomer component M may contain one or more types of monomer b. Monomer component M may contain one or more types of monomer b selected from the above-mentioned examples. Monomer b may be a (meth)acrylic monomer. When monomer component M contains two or more types of monomer b, at least one of the monomers b may be a (meth)acrylic monomer.

[0057] The sum of the content of monomer a and the content of monomer b in monomer component M may be 51% by weight or more, 52% by weight or more, 54% by weight or more, 55% by weight or more, 57% by weight or more, 59% by weight or more, 60% by weight or more, 62% by weight or more, 64% by weight or more, 65% by weight or more, 67% by weight or more, 69% by weight or more, or even 70% by weight or more. The upper limit of the above sum is 99.9% by weight or less, and may be 99.5% by weight or less, 99% by weight or less, 97% by weight or less, 95% by weight or less, 92% by weight or less, 90% by weight or less, 88% by weight or less, 86% by weight or less, 85% by weight or less, 84% by weight or less, 82% by weight or less, 80% by weight or less, 78% by weight or less, 76% by weight or less, 75% by weight or less, 74% by weight or less, 72% by weight or less, 70% by weight or less, 68% by weight or less, 66% by weight or less, or even 65% by weight or less.

[0058] <1-1-c. Monomer c> Monomer c is a hydroxyl group-containing monomer. Monomer c has at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule.

[0059] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of the monomer A. The monomer C may be a (meth)acrylic monomer.

[0060] Examples of monomer c include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. Monomer c is preferably 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate.

[0061] The content of monomer c in monomer component M may be, for example, 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, 3% by weight or more, 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 9% by weight or more, 10% by weight or more, 11% by weight or more, 12% by weight or more, 13% by weight or more, 14% by weight or more, 15% by weight or more, 16% by weight or more, 17% by weight or more, 18% by weight or more, 19% by weight or more, 20% by weight or more, or even 21% by weight or more. The upper limit of the content may be, for example, 30% by weight or less, 29% by weight or less, 28% by weight or less, 27% by weight or less, 26% by weight or more, 25% by weight or less, 24% by weight or less, 23% by weight or less, 22% by weight or less, 21% by weight or less, 20% by weight or less, 19% by weight or less, 18% by weight or less, or even 17% by weight or less. The content of monomer c may be 12% by weight or more, 15% by weight or more, 17% by weight or more, or even 20% by weight or more. According to studies by the present inventors, when the content of monomer c is 12% by weight or more, the balance between monomer b and monomer c in PSA composition A containing monomer a, monomer b, and monomer c as monomer component M may be particularly suitable for suppressing whitening of the PSA sheet due to humidification, and suppressing deformation of the PSA sheet due to thermal changes and foaming resulting therefrom.

[0062] Monomer component M may contain one or more types of monomer c. Monomer component M may contain one or more types of monomer c selected from the above-mentioned examples. Monomer c may be a (meth)acrylic monomer. When monomer component M contains two or more types of monomer c, at least one of the monomers c may be a (meth)acrylic monomer.

[0063] The sum of the contents of monomer a, monomer b, and monomer c in the monomer component M is, for example, 50.1% by weight or more, and may be 51% by weight or more, 52% by weight or more, 55% by weight or more, 57% by weight or more, 60% by weight or more, 62% by weight or more, 64% by weight or more, 65% by weight or more, 67% by weight or more, 69% by weight or more, 70% by weight or more, 72% by weight or more, 74% by weight or more, 75% by weight or more, 77% by weight or more, 79% by weight or more, or even 80% by weight or more. The upper limit of the above sum is 100% by weight, and may be 99% by weight or less, 97% by weight or less, 95% by weight or less, 92% by weight or less, 90% by weight or less, 88% by weight or less, 86% by weight or less, 85% by weight or less, 84% by weight or less, 82% by weight or less, 80% by weight or less, 78% by weight or less, 76% by weight or less, 75% by weight or less, 74% by weight or less, 72% by weight or less, 70% by weight or less, 68% by weight or less, 66% by weight or less, 65% by weight or less, 64% by weight or less, 62% by weight or less, or even 60% by weight or less.

[0064] <1-1-d. (Meth)acrylic acid alkyl ester> Monomer component M may further contain a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms on the side chain. The number of carbon atoms in the alkyl group may be 18 or less, 16 or less, 14 or less, 12 or less, or even 10 or less. The alkyl group may be linear or branched. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-dodecyl(meth)acrylate (lauryl(meth)acrylate), n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, and octadecyl(meth)acrylate.

[0065] Monomer component M may further contain a (meth)acrylic acid alkyl ester having an alkyl group having 5 to 20 carbon atoms in its side chain. The number of carbon atoms in the alkyl group may be 18 or less, 16 or less, 14 or less, 12 or less, or even 10 or less. The lower limit of the number of carbon atoms may be 6 or more, 7 or more, or even 8 or more. The alkyl group may be linear or branched. It is believed that the greater the carbon number of the alkyl group, the stronger the hydrophobicity of the (meth)acrylic acid alkyl ester. According to studies by the present inventors, a (meth)acrylic acid alkyl ester having an alkyl group having 5 or more carbon atoms in its side chain may contribute to suppressing whitening of the PSA sheet due to humidification in a PSA composition A containing monomer a, monomer b, and monomer c as monomer component M.

[0066] The content of the (meth)acrylic acid alkyl ester in the monomer component M may be, for example, 49.9% by weight or less, 49% by weight or less, 45% by weight or less, 40% by weight or less, 39% by weight or less, 37% by weight or less, 35% by weight or less, 34% by weight or less, 32% by weight or less, 30% by weight or less, 29% by weight or less, 27% by weight or less, 25% by weight or less, 24% by weight or less, 22% by weight or less, or even 20% by weight or less. The lower limit of the content may be, for example, 1% by weight or more, 2% by weight or more, 5% by weight or more, 7% by weight or more, 9% by weight or more, 10% by weight or more, 12% by weight or more, 14% by weight or more, 15% by weight or more, 17% by weight or more, 19% by weight or more, or even 20% by weight or more. The monomer component M may be substantially free of a (meth)acrylic acid alkyl ester.

[0067] The content of the (meth)acrylic acid alkyl ester having an alkyl group having 5 to 20 carbon atoms on the side chain in the monomer component M may be 14% by weight or more, 15% by weight or more, 16% by weight or more, 17% by weight or more, 18% by weight or more, 19% by weight or more, or even 20% by weight or more.

[0068] <1-1-e. Other Monomers> The monomer component M may contain other monomers in addition to those described above. Examples of other monomers that may be contained in the monomer component M are listed below. However, the other monomers listed below exclude those corresponding to monomer a, monomer b, and monomer c.

[0069] An example of the other monomer is an aliphatic ring-containing monomer. The aliphatic ring-containing monomer has at least one aliphatic ring and at least one ethylenically unsaturated group in one molecule. The monomer component M may contain one or more aliphatic ring-containing monomers.

[0070] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The aliphatic ring-containing monomer may be a (meth)acrylic monomer.

[0071] Examples of the aliphatic ring-containing monomer are cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate.

[0072] The content of the alicyclic monomer in the monomer component M is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 10% by weight or less, 7% by weight or less, 5% by weight or less, or even 4% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. The monomer component M may be substantially free of the alicyclic monomer.

[0073] Another example of the other monomer is a carboxyl group-containing monomer. The carboxyl group-containing monomer has at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer component M may contain one or more types of carboxyl group-containing monomers.

[0074] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The carboxyl group-containing monomer may be a (meth)acrylic monomer.

[0075] Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0076] The content of the carboxyl group-containing monomer in the monomer component M is, for example, 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, 3% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. The monomer component M may be substantially free of a carboxyl group-containing monomer.

[0077] The monomer component M may contain monomers other than those mentioned above.

[0078] <1-2. Tackifier> The PSA composition A may further contain a tackifier. The tackifier can contribute to improving the adhesive strength of a PSA sheet formed from the PSA composition A. Furthermore, according to studies by the present inventors, the tackifier may contribute to suppressing initial foaming of a PSA sheet formed from the PSA composition A.

[0079] <1-2-1. Acrylic Oligomer> An example of a tackifier is an acrylic oligomer. In this specification, the term "acrylic oligomer" refers to a polymer containing, as a monomer unit constituting the acrylic oligomer, a monomer unit derived from a monomer having at least one (meth)acryloyl group per molecule. In this specification, the acrylic oligomer is defined as an oligomer containing a monomer unit derived from an acrylic monomer.

[0080] The weight average molecular weight (Mw) of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,000 to 20,000, still more preferably 1,500 to 10,000, and particularly preferably 2,000 to 8,000.

[0081] The Mw of the acrylic oligomer can be determined in terms of polystyrene by gel permeation chromatography (GPC). For example, Mw can be measured using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions: Column: TSKgel Super HZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: Tetrahydrofuran Flow rate: 0.6 mL / min

[0082] The acrylic oligomer is preferably an acrylic oligomer obtained from a monomer composition containing, as an essential component, a (meth)acrylic acid ester having a cyclic structure in the molecule, and more preferably an acrylic oligomer obtained from a monomer composition containing, as essential components, a (meth)acrylic acid ester having a cyclic structure in the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group.

[0083] The (meth)acrylic acid ester having a cyclic structure in the molecule may be of one type only, or of two or more types.

[0084] The (meth)acrylic acid alkyl ester having a linear or branched alkyl group may be of one type only, or of two or more types.

[0085] The cyclic structure in the (meth)acrylic acid ester having a cyclic structure in the molecule may be either an aromatic ring or a non-aromatic ring.

[0086] Examples of aromatic rings include aromatic carbocycles (for example, monocyclic carbocycles such as a benzene ring, and condensed carbocycles such as a naphthalene ring), and various aromatic heterocycles.

[0087] Examples of non-aromatic rings include non-aromatic aliphatic rings (non-aromatic alicyclic rings) (e.g., cycloalkane rings such as cyclopentane ring, cyclohexane ring, cycloheptane ring, and cyclooctane ring; cycloalkene rings such as cyclohexene ring), non-aromatic bridged rings (e.g., bicyclic hydrocarbon rings such as pinane, pinene, bornane, norbornane, and norbornene; tricyclic or higher aliphatic hydrocarbon rings (bridged hydrocarbon rings) such as adamantane), and non-aromatic heterocycles (e.g., epoxy ring, oxolane ring, and oxetane ring). Examples of tricyclic or higher aliphatic hydrocarbon rings (tricyclic or higher bridged hydrocarbon rings) include dicyclopentanyl, dicyclopentenyl, adamantyl, tricyclopentanyl, and tricyclopentenyl groups.

[0088] Specific examples of (meth)acrylic acid esters having a cyclic structure in the molecule include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, and 1,2-dimethyl-2,3-dimethyl-2,4 ... (meth)acrylic acid esters having an aliphatic hydrocarbon ring with three or more rings, such as 2-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate; (meth)acrylic acid esters having an aromatic ring, such as aryl (meth)acrylate esters such as phenyl (meth)acrylate, aryloxyalkyl (meth)acrylate esters such as phenoxyethyl (meth)acrylate, and arylalkyl (meth)acrylate esters such as benzyl (meth)acrylate; and the like.

[0089] As the (meth)acrylic acid ester having a cyclic structure in the molecule, a non-aromatic ring-containing (meth)acrylic acid ester is preferred, in terms of being able to further exhibit the effects of the present invention, more preferred are cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), and dicyclopentanyl methacrylate (DCPMA), and even more preferred are dicyclopentanyl acrylate (DCPA) and dicyclopentanyl methacrylate (DCPMA).

[0090] The content of the (meth)acrylic acid ester having a cyclic structure in the molecule in all the monomers that can be used to constitute the acrylic oligomer is preferably 10 parts by weight to 90 parts by weight, and more preferably 20 parts by weight to 80 parts by weight, relative to 100 parts by weight of all the monomers.

[0091] Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, ... Examples of (meth)acrylic acid alkyl esters include those in which the alkyl group has 1 to 20 carbon atoms, such as isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Of these, methyl methacrylate (MMA) is preferred.

[0092] The content of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group in all the monomers that can be used to constitute the acrylic oligomer is preferably 10 to 90 parts by weight, more preferably 20 to 80 parts by weight, and even more preferably 20 to 60 parts by weight, relative to 100 parts by weight of all the monomers.

[0093] The total monomers (monomer composition) that can be used to form the acrylic oligomer may contain, in addition to the (meth)acrylic acid ester having a cyclic structure in the molecule and the (meth)acrylic acid alkyl ester having a linear or branched alkyl group, other monomers (copolymerizable monomers) that can be copolymerized with these monomers. The content of the other monomers (copolymerizable monomers) in the total monomers (monomer composition) that can be used to form the acrylic oligomer is preferably less than 50 parts by weight, more preferably 40 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 20 parts by weight or less, relative to 100 parts by weight of the total monomers.

[0094] Examples of such other monomers (copolymerizable monomers) include (meth)acrylic acid alkoxyalkyl esters (e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.), carboxyl group-containing monomers (e.g., acid anhydride group-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, maleic anhydride, etc.), hydroxyl group-containing monomers (e.g., hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc.); vinyl alcohol; allyl alcohol; ol; etc.), amide group-containing monomers (e.g., (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, etc.), amino group-containing monomers (e.g., aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, etc.), cyano group-containing monomers (e.g., acrylonitrile, methacrylonitrile, etc.), sulfonic acid group-containing monomers (e.g., sodium vinyl sulfonate, etc.), phosphate group-containing monomers (e.g., 2-hydroxyethyl acryloyl phosphate, etc.), isocyanate group-containing monomers (e.g., 2-methacryloyloxyethyl isocyanate, etc.), imide group-containing monomers (e.g., cyclohexylmaleimide, isopropylmaleimide, etc.), and the like.

[0095] The total monomers (monomer composition) that can be used to form the acrylic oligomer particularly preferably contain (1) at least one monomer selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and (2) methyl methacrylate. In this case, the content of monomer (1) is preferably 30 to 70 parts by weight, and the content of monomer (2) is preferably 30 to 70 parts by weight, per 100 parts by weight of the total monomers (monomer composition) that can be used to form the acrylic oligomer.

[0096] The acrylic oligomer can be produced by any appropriate polymerization method. Examples of the polymerization method include a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, and a polymerization method using active energy ray irradiation (active energy ray polymerization method). Among these, the bulk polymerization method and the solution polymerization method are preferred, and the solution polymerization method is more preferred.

[0097] Examples of solvents that can be used in the polymerization include organic solvents such as esters such as ethyl acetate and n-butyl acetate, aromatic hydrocarbons such as toluene and benzene, aliphatic hydrocarbons such as n-hexane and n-heptane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Only one type of solvent may be used, or two or more types may be used.

[0098] In the polymerization, any appropriate polymerization initiator (for example, a thermal polymerization initiator or a photopolymerization initiator) can be used. The polymerization initiator may be one type or two or more types. When solution polymerization is performed, it is preferable to use an oil-soluble polymerization initiator.

[0099] Any appropriate thermal polymerization initiator can be used as the thermal polymerization initiator. The thermal polymerization initiator may be one type only or two or more types. Examples of the thermal polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1- azo-based initiators such as 2,2'-azobis(2,4,4-trimethylpentane) and 2,2'-azobis(2,4,4-trimethylpentane); and peroxide-based initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane.

[0100] The amount of the thermal polymerization initiator used is preferably 0.1 to 15 parts by weight, for example, based on 100 parts by weight of all the monomers (monomer composition) that can be used to form the acrylic oligomer.

[0101] Any appropriate photopolymerization initiator can be used as the photopolymerization initiator. The photopolymerization initiator may be one type only, or two or more types may be used. Examples of the photopolymerization initiator include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

[0102] The amount of the photopolymerization initiator used is preferably 0.001 to 0.5 parts by weight, for example, relative to 100 parts by weight of all the monomers (monomer composition) that can be used to form the acrylic oligomer.

[0103] During polymerization of the acrylic oligomer, a chain transfer agent may be used to adjust the molecular weight (preferably to adjust Mw to 1,000 to 30,000). Examples of the chain transfer agent include 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octyl mercaptan, t-nonyl mercaptan, dodecyl mercaptan (lauryl mercaptan), t-dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolic acid esters of ethylene glycol, thioglycolic acid esters of neopentyl glycol, thioglycolic acid esters of pentaerythritol, and α-methylstyrene dimer. Among these, α-thioglycerol and methyl thioglycolate are preferred, and α-thioglycerol is particularly preferred. The chain transfer agent may be one type or two or more types.

[0104] The amount of the chain transfer agent used is, for example, preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, and even more preferably 0.3 to 10 parts by weight, relative to 100 parts by weight of all monomers (monomer composition) that can be used to constitute the acrylic oligomer.

[0105] The glass transition temperature (Tg) of the acrylic oligomer is preferably 20°C to 300°C, more preferably 30°C to 300°C, and even more preferably 40°C to 300°C.

[0106] <1-2-2. Other Tackifiers> Other examples of tackifiers include various tackifier resins such as rosin-based resins, terpene-based resins, hydrocarbon-based resins, epoxy-based resins, polyamide-based resins, elastomer-based resins, phenol-based resins, and ketone-based resins. These tackifiers can be used alone or in combination of two or more. When combined with a monomer component M capable of forming a (meth)acrylic pressure-sensitive adhesive sheet, rosin-based resins (e.g., polymerized rosin esters) and terpene-based resins (e.g., terpene phenol resins) are preferred.

[0107] Examples of rosin-based resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.) obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc.; and various other rosin derivatives. Examples of rosin derivatives include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., esterified rosin), and those obtained by esterifying modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with alcohols (i.e., esterified modified rosin); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with unsaturated fatty acid; and unsaturated fatty acid modified rosins obtained by modifying rosin esters with unsaturated fatty acid. rosin esters; rosin alcohols obtained by reducing the carboxyl groups of unmodified rosin, modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), unsaturated fatty acid modified rosin, or unsaturated fatty acid modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and then thermally polymerizing the resulting mixture; and the like.

[0108] Examples of terpene resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modified terpene resins obtained by modifying these terpene resins (phenol-modified, aromatic-modified, hydrogenation-modified, hydrocarbon-modified, etc.); etc. Examples of modified terpene resins include terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpene resins.

[0109] Examples of hydrocarbon resins include various hydrocarbon resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, and coumarone-indene resins.

[0110] The softening point of the tackifier resin is not particularly limited. In one embodiment, a resin having a softening point (softening temperature) of approximately 80°C or higher (preferably approximately 110°C or higher, more preferably approximately 135°C or higher) can be preferably used. For example, terpene resins (such as terpene phenol resins) and rosin resins (such as esterified products of polymerized rosin) having such softening points can be preferably used. Furthermore, for example, terpene phenol resins having a softening point of approximately 135°C or higher (even approximately 140°C or higher) can be preferably used. The upper limit of the softening point of the tackifier resin is not particularly limited and can be, for example, approximately 200°C or lower (typically approximately 180°C or lower). The softening point of the tackifier resin can be measured in accordance with the softening point test method (ring and ball method) specified in Japanese Industrial Standards (JIS) K2207.

[0111] The content of the tackifier in the PSA composition A is, for example, 0.1 to 10 parts by weight per 100 parts by weight of the monomer component M. The lower limit of the content may be 0.2 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight or more, 1 part by weight or more, 1.5 parts by weight or more, 2 parts by weight or more, 2.5 parts by weight or more, or even 3 parts by weight or more. The upper limit of the content may be 9.5 parts by weight or less, 9 parts by weight or less, 8.5 parts by weight or less, 8 parts by weight or less, 7.5 parts by weight or less, 7 parts by weight or less, 6.5 parts by weight or less, 6 parts by weight or less, 5.5 parts by weight or less, 5 parts by weight or less, 4.5 parts by weight or less, 4 parts by weight or less, 3.5 parts by weight or less, or even 3 parts by weight or less.

[0112] The PSA composition A may contain one or more tackifiers. The PSA composition A may contain one or more tackifiers selected from the above-mentioned examples.

[0113] <1-3. Aspects of Pressure-Sensitive Adhesive Composition> An example of the pressure-sensitive adhesive composition A is a first composition containing a monomer component M. The first composition may be a photocurable pressure-sensitive adhesive composition. In the first composition, a portion of the monomer component M may be in the form of a partial polymer. The weight-average molecular weight (Mw) of the partial polymer may be greater than 10,000, or may be 20,000 or more, greater than 20,000, 30,000 or more, greater than 30,000, 40,000 or more, 50,000 or more, 75,000 or more, or even 100,000 or more. The Mw of the partial polymer can be evaluated by GPC.

[0114] Another example of the pressure-sensitive adhesive composition A is a second composition containing a base polymer that is a polymer of a monomer component M. The polymer that is the base polymer has a structural unit formed by polymerization of a monomer a. The second composition may be a thermosetting pressure-sensitive adhesive composition.

[0115] <1-3-1. Photocurable pressure-sensitive adhesive composition (first composition)> The pressure-sensitive adhesive composition A may be a photocurable pressure-sensitive adhesive composition containing a photopolymerization initiator. Note that being a photocurable pressure-sensitive adhesive composition is a particularly preferred embodiment in terms of environmental protection and sustainability, since the amount of energy required to form a pressure-sensitive adhesive sheet can be reduced compared to a thermosetting pressure-sensitive adhesive composition that mainly uses heat to form a pressure-sensitive adhesive sheet.

[0116] Components that may be contained in the photocurable pressure-sensitive adhesive composition A will be described.

[0117] [1-3-1a. Photopolymerization initiator] The photopolymerization initiator that may be contained in the photocurable pressure-sensitive adhesive composition A may be a photoradical generator that generates radicals when exposed to visible light and / or ultraviolet light having a wavelength of 450 nm or less.

[0118] The photopolymerization initiator may have an absorption peak in a wavelength region exceeding 340 nm, or may have an absorption peak in a wavelength region of 340 nm or less. The photopolymerization initiator preferably has an absorption peak in a wavelength region of 340 nm or less.

[0119] Examples of the photopolymerization initiator include benzoin ethers such as benzoin methyl ether, benzoin isopropyl ether, and benzil dimethyl ketal; substituted benzoin ethers such as anisole methyl ether; substituted acetophenones such as 2,2-diethoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone; α-hydroxyalkylphenones such as 1-hydroxycyclohexyl-phenyl ketone; substituted alpha-ketol such as 2-methyl-2-hydroxypropiophenone; aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride; photoactive oximes such as 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime; and benzophenone compounds such as benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, acrylated benzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, and 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone. Thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and 2,4-diethylthioxanthone; 2,4,6-trichloro-s-triazine, 2-phenyl-4,6-bis(trichloromethyl)-s-triazine, 2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, and 2-(p-tolyl)-4,6-bis(trichloromethyl)-s-triazine , 2-piperonyl-4,6-bis(trichloromethyl)-s-triazine, 2,4-bis(trichloromethyl)-6-styryl-s-triazine, 2-(naphth-1-yl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxy-naphth-1-yl)-4,6-bis(trichloromethyl)-s-triazine, 2,4-trichloromethyl-(piperonyl)-6-triazine, 2,4-trichloromethyl-(4'-methoxystyryl)-6-triazine and other triazine-based compounds;Oxime ester compounds such as 1,2-octanedione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)], O-(acetyl)-N-(1-phenyl-2-oxo-2-(4'-methoxy-naphthyl)ethylidene)hydroxylamine; phosphine compounds such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; quinone compounds such as 9,10-phenanthrenequinone, camphorquinone, and ethylanthraquinone; borate compounds; carbazole compounds; imidazole compounds; and titanocene compounds.

[0120] Specific examples of the photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one (Omnirad 651, manufactured by IGM Resins), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad 819, manufactured by IGM Resins), and 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)2-methylpropan-1-one (Omnirad 127, manufactured by IGM Resins). However, the photopolymerization initiator that can be contained in the photocurable pressure-sensitive adhesive composition A is not limited to the above examples.

[0121] The content of the photopolymerization initiator in the photocurable pressure-sensitive adhesive composition A is, for example, 0.001 to 10 parts by weight, and may be 0.01 to 5 parts by weight, 0.05 to 3 parts by weight, or even 0.1 to 2 parts by weight per 100 parts by weight of the monomer component M. In the photocurable pressure-sensitive adhesive composition A, the content of the photopolymerization initiator having an absorption peak in a wavelength region of 340 nm or less may be within the above range.

[0122] The photocurable pressure-sensitive adhesive composition A may contain one or more photopolymerization initiators.

[0123] [1-3-1b. Crosslinking Agent] The photocurable pressure-sensitive adhesive composition A may further contain a crosslinking agent. An example of the crosslinking agent is a polyfunctional monomer having two or more polymerizable functional groups in one molecule. The polyfunctional monomer may be a (meth)acrylic monomer. Examples of the polyfunctional monomer are a monomer having two or more C=C bonds in one molecule, and a monomer having one or more C=C bonds and one or more polymerizable functional groups such as epoxy groups, aziridine groups, oxazoline groups, hydrazine groups, methylol groups, etc. in one molecule. The polyfunctional monomer is preferably a monomer having two or more C=C bonds in one molecule.

[0124] Examples of polyfunctional monomers include (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol diacrylate (N Polyfunctional acrylates (such as ester compounds of polyhydric alcohols and (meth)acrylic acid) such as 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tetramethylolmethane tri(meth)acrylate; allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl di(meth)acrylate, and hexyl di(meth)acrylate. The polyfunctional monomer is preferably a polyfunctional acrylate, and more preferably trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, or dipentaerythritol hexa(meth)acrylate.

[0125] The content of the crosslinking agent in the photocurable pressure-sensitive adhesive composition A varies depending on the molecular weight, the number of functional groups, etc., but may be, for example, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, or even 0.1 parts by weight or less per 100 parts by weight of the monomer component M. The lower limit of the content may be, for example, 0.001 parts by weight or more, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.015 parts by weight or more, 0.02 parts by weight or more, 0.025 parts by weight or more, or even 0.03 parts by weight or more. The photocurable pressure-sensitive adhesive composition A may be substantially free of a crosslinking agent.

[0126] The photocurable pressure-sensitive adhesive composition A may contain one or more crosslinking agents.

[0127] [1-3-1c. Antioxidant] The photocurable pressure-sensitive adhesive composition A may further contain an antioxidant. The pressure-sensitive adhesive composition A may contain one or more antioxidants.

[0128] Examples of antioxidants include phenolic antioxidants, hindered phenolic antioxidants, amine antioxidants, and phosphite antioxidants.

[0129] Examples of the phenolic antioxidants include monophenolic antioxidants, bisphenolic antioxidants, and polymeric phenolic antioxidants. Examples of the monophenolic antioxidants include 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, and stearin-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate. Examples of the bisphenol antioxidant are 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane. Examples of the polymeric phenolic antioxidant are 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, bis[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid]glycol ester, 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-S-triazine-2,4,6-(1H,3H,5H)trione, and tocopherol.

[0130] The hindered phenolic antioxidant may have a structure in which a tertiary butyl group is bonded to at least one carbon atom adjacent to the carbon atom on the aromatic ring to which the phenolic OH group is bonded. Examples of the hindered phenolic antioxidant include dibutylhydroxytoluene (BHT); Irganox 1010, Irganox 1010FF, Irganox 1035, Irganox 1035FF, Irganox 1076, Irganox 1076FD, Irganox 1076DWJ, Irganox 1098, Irganox 109 ... Irganox 1135, Irganox 1330, Irganox 1726, Irganox 1425WL, Irganox 1520L, Irganox 245, Irganox 245FF, Irganox 259, Irganox 3114, Irganox 565 and Irganox 295 (all of which are trade names manufactured by BASF).

[0131] The amine antioxidant is preferably a hindered amine antioxidant. The hindered amine antioxidant may have at least one hindered piperazine group in one molecule. Examples of hindered amine antioxidants include Adeka STAB LA-63, Adeka STAB LA-63P, Adeka STAB LA-52, and Adeka STAB LA-57 (all of which are trade names, manufactured by ADEKA Corporation).

[0132] Examples of the phosphite antioxidants are triphenyl phosphite, diphenyl isodecyl phosphite, and phenyl diisodecyl phosphite; and Adeka STAB 2112, Adeka STAB 2112RG, Adeka STAB 1178, and Adeka STAB 3010 (all of which are trade names, manufactured by ADEKA Corporation).

[0133] The content of the antioxidant in the photocurable pressure-sensitive adhesive composition A is, for example, 5 parts by weight or less, and may be 3 parts by weight or less, 1 part by weight or less, 0.8 parts by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, or even 0.1 parts by weight or less, relative to 100 parts by weight of the monomer component M. The lower limit of the content may be, for example, 0.01 parts by weight or more, 0.03 parts by weight or more, or even 0.05 parts by weight or more. The photocurable pressure-sensitive adhesive composition A may be substantially free of an antioxidant.

[0134] The photocurable pressure-sensitive adhesive composition A may contain one or more antioxidants.

[0135] [1-3-1d. Silane Coupling Agent] The photocurable pressure-sensitive adhesive composition A may further contain a silane coupling agent.

[0136] The content of the silane coupling agent in the photocurable pressure-sensitive adhesive composition A is, for example, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or even 0.5 parts by weight or less per 100 parts by weight of the monomer component M. The lower limit of the content may be, for example, 0.1 parts by weight or more, 0.2 parts by weight or more, or even 0.3 parts by weight or more. The photocurable pressure-sensitive adhesive composition A may be substantially free of a silane coupling agent.

[0137] [1-3-1e. Additives] The photocurable pressure-sensitive adhesive composition A may further contain additives other than those described above. Examples of the additives include a chain transfer agent, a viscosity modifier, a plasticizer, a softener, an antioxidant, a filler, a colorant, a surfactant, an antistatic agent, and an ultraviolet absorber.

[0138] [1-3-1f. Solvent] The content of the solvent in the photocurable pressure-sensitive adhesive composition A is, for example, 5 wt % or less, and may be 4 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or even 0.5 wt % or less. The photocurable pressure-sensitive adhesive composition A may be substantially free of a solvent.

[0139] [1-3-1g. Viscosity] The viscosity of the photocurable pressure-sensitive adhesive composition A is preferably 5 to 100 poise at 25° C. The pressure-sensitive adhesive composition A having a viscosity in the above range is particularly suitable for forming a coating layer, which will be described later.

[0140] <1-3-2. Thermosetting type (second composition)> The pressure-sensitive adhesive composition A may be a thermosetting type pressure-sensitive adhesive composition. Components that may be contained in the thermosetting type pressure-sensitive adhesive composition A will be described.

[0141] [1-3-2a. Base polymer] The thermosetting pressure-sensitive adhesive composition A usually contains a base polymer, which is a polymer of a monomer component M. The base polymer can be formed by various known polymerization methods, such as solution polymerization, radiation polymerization using electron beams, ultraviolet rays, or the like, bulk polymerization, or emulsion polymerization. The polymerization is typically radical polymerization. The base polymer may be any of a random copolymer, a block copolymer, a graft copolymer, or the like. However, the method for forming the base polymer is not limited to the above examples.

[0142] The weight average molecular weight (Mw) of the base polymer is, for example, 700,000 or more, and may be 800,000 or more, 900,000 or more, or even 1,000,000 or more. The upper limit of Mw may be, for example, 2,000,000 or less, 1,800,000 or less, 1,600,000 or less, or even 1,500,000 or less.

[0143] As the polymerization solvent for solution polymerization, known polymerization solvents such as ethyl acetate and toluene can be used. Solution polymerization can be carried out, for example, using a polymerization initiator and under a stream of an inert gas such as nitrogen. The polymerization conditions are, for example, 50 to 70°C and 5 to 30 hours.

[0144] The polymerization initiator, chain transfer agent, emulsifier, etc. used in the radical polymerization are not particularly limited and can be selected appropriately.

[0145] [1-3-2b. Crosslinking agent] The thermosetting pressure-sensitive adhesive composition A may further contain a crosslinking agent. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, a peroxide-based crosslinking agent, an epoxy-based crosslinking agent, an imine-based crosslinking agent, and a polyfunctional metal chelate. The thermosetting pressure-sensitive adhesive composition A preferably contains an isocyanate-based crosslinking agent and / or a peroxide-based crosslinking agent, and more preferably contains an isocyanate-based crosslinking agent.

[0146] As the isocyanate-based crosslinking agent, a compound having at least two isocyanate groups (isocyanate compound) can be used. The number of isocyanate groups contained in the isocyanate compound is preferably 3 or more. The upper limit of the number of isocyanate groups is not particularly limited, and is, for example, 5. Examples of the isocyanate compound include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds.

[0147] Examples of aromatic isocyanate compounds are phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate.

[0148] Examples of the alicyclic isocyanate compound are 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

[0149] Examples of aliphatic isocyanate compounds are trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0150] The isocyanate-based crosslinking agent may be a polymer (dimer, trimer, pentamer, etc.) of the above-mentioned isocyanate compound, an adduct obtained by adding the compound to a polyhydric alcohol such as trimethylolpropane, a urea-modified compound, a biuret-modified compound, an allophanate-modified compound, an isocyanurate-modified compound, a carbodiimide-modified compound, or a urethane prepolymer obtained by adding the compound to a polyether polyol, a polyester polyol, an acrylic polyol, a polybutadiene polyol, a polyisoprene polyol, or the like.

[0151] The isocyanate-based crosslinking agent is preferably an aromatic isocyanate compound and its derivatives, more preferably tolylene diisocyanate and its derivatives, in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent. From the viewpoint of reactivity, a TDI-based crosslinking agent is more suitable than xylylene diisocyanate and its derivatives, in other words, a xylylene diisocyanate-based (XDI-based) crosslinking agent. The isocyanate-based crosslinking agent may contain an adduct of a polyhydric alcohol and tolylene diisocyanate as the TDI-based crosslinking agent. A specific example of the adduct is a trimethylolpropane / tolylene diisocyanate trimer adduct.

[0152] Commercially available isocyanate crosslinking agents can be used. Examples of commercially available products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation), Takenate D-101E, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500, and Takenate 600 (all manufactured by Mitsui Chemicals, Inc.). Of these, Takenate D-101E and Takenate D110N are preferred.

[0153] The isocyanate-based crosslinking agents may be used alone or in combination of two or more.

[0154] The content of the crosslinking agent in the thermosetting adhesive composition A is, for example, 0.01 to 20 parts by weight relative to 100 parts by weight of the base polymer.

[0155] [1-3-2c. Antioxidant] The thermosetting pressure-sensitive adhesive composition A may further contain an antioxidant. The pressure-sensitive adhesive composition A may contain one or more antioxidants.

[0156] Examples of the antioxidant are the same as those mentioned above in the description of the photocurable pressure-sensitive adhesive composition A.

[0157] The content of the antioxidant in the thermosetting pressure-sensitive adhesive composition A is, for example, 5 parts by weight or less, and may be 3 parts by weight or less, 1 part by weight or less, 0.8 parts by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, or even 0.1 parts by weight or less, relative to 100 parts by weight of the monomer component M. The lower limit of the content may be, for example, 0.01 parts by weight or more, 0.03 parts by weight or more, or even 0.05 parts by weight or more. The thermosetting pressure-sensitive adhesive composition A may be substantially free of an antioxidant.

[0158] The thermosetting pressure-sensitive adhesive composition A may contain one or more antioxidants.

[0159] [1-3-2d. Silane Coupling Agent] The thermosetting pressure-sensitive adhesive composition A may further contain a silane coupling agent.

[0160] The content of the silane coupling agent in the thermosetting pressure-sensitive adhesive composition A is, for example, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or even 0.5 parts by weight or less per 100 parts by weight of the monomer component M. The lower limit of the content may be, for example, 0.1 parts by weight or more, 0.2 parts by weight or more, or even 0.3 parts by weight or more. The thermosetting pressure-sensitive adhesive composition A may be substantially free of a silane coupling agent.

[0161] [1-3-1e. Additives] The thermosetting pressure-sensitive adhesive composition A may further contain additives other than those described above. Examples of the additives include chain transfer agents, viscosity modifiers, plasticizers, softeners, antioxidants, fillers, colorants, surfactants, antistatic agents, and ultraviolet absorbers.

[0162] The thermosetting pressure-sensitive adhesive composition A may be substantially free of a photocuring agent such as a photopolymerization initiator.

[0163] 2. Pressure-sensitive adhesive sheet An example of a pressure-sensitive adhesive sheet according to an embodiment of the present invention is shown in Fig. 1. Pressure-sensitive adhesive sheet 1 in Fig. 1 is a pressure-sensitive adhesive sheet formed from pressure-sensitive adhesive composition A.

[0164] <2-1. Properties> <2-1-1. Refractive Index> The pressure-sensitive adhesive sheet 1 may have a refractive index of 1.460 or more. The refractive index may be 1.465 or more, 1.470 or more, 1.475 or more, 1.480 or more, 1.485 or more, 1.490 or more, 1.495 or more, 1.500 or more, 1.505 or more, 1.510 or more, 1.515 or more, 1.520 or more, 1.525 or more, 1.530 or more, or even 1.532 or more. The upper limit of the refractive index is, for example, 1.700 or less. Some optical films that can be provided in the optical laminate have a high refractive index. For example, using a pressure-sensitive adhesive sheet 1 with a high refractive index to bond the optical film is advantageous in reducing reflected light at the interface between the optical film and the pressure-sensitive adhesive sheet 1.

[0165] In this specification, the refractive index of a pressure-sensitive adhesive sheet refers to the refractive index of the pressure-sensitive adhesive sheet surface. The refractive index of a pressure-sensitive adhesive sheet can be measured using a prism coupler at a measurement temperature of 25°C and a measurement wavelength of 594 nm. For pressure-sensitive adhesive sheets with a thickness of less than 20 μm, measurement in the optical propagation mode is generally suitable. For pressure-sensitive adhesive sheets with a thickness of 20 μm or more, measurement in the critical angle mode is generally suitable. A commercially available measuring device can be used as the prism coupler, such as a Metricon Model 2010 / M prism coupler or an equivalent.

[0166] <2-1-2. Adhesive strength> The adhesive strength of the pressure-sensitive adhesive sheet 1 determined by the following test may be 10 N / 25 mm or more, 11 N / 25 mm or more, 12 N / 25 mm or more, 13 N / 25 mm or more, 14 N / 25 mm or more, 15 N / 25 mm or more, 16 N / 25 mm or more, 17 N / 25 mm or more, 18 N / 25 mm or more, or even 19 N / 25 mm or more. The upper limit of the adhesive strength is, for example, 50 N / 25 mm or less.

[0167] (Adhesion Strength Test) A test specimen is prepared as a laminate of the PSA sheet 1 to be evaluated and an evaluation base sheet. The evaluation base sheet is not limited as long as it does not peel from the PSA sheet 1 during the peel test from the alkali-free glass surface performed in this test and allows for the peel test (180° peel test). For example, a polyethylene terephthalate (PET) sheet can be used as the evaluation base sheet. The bonding surface of the PSA sheet 1 in the evaluation base sheet may be subjected to an adhesion-enhancing treatment such as corona treatment. As long as the above conditions are met, the base sheet or release liner used to form the PSA sheet 1 may also be used as the evaluation base sheet. The test specimen is prepared so that the portion of the evaluation base sheet to which the PSA sheet 1 is bonded has a rectangular shape measuring 25 mm wide x 80 mm long, and the portion consisting of only the evaluation base sheet has a rectangular shape measuring 25 mm wide x 170 mm long. The overall shape of the test specimen is a rectangle measuring 25 mm wide x 250 mm long.

[0168] Next, the test piece is placed on the alkali-free glass via the adhesive sheet 1, and a 2 kg hand roller is rolled back and forth once to press the pieces together. The alkali-free glass is glass that is substantially free of alkali components (alkali metal oxides). Specifically, the weight ratio of alkali components in the glass is, for example, 1000 ppm (by weight, the same applies below) or less, and even 500 ppm or less. The alkali-free glass is, for example, in the form of a plate and has a thickness of 0.5 mm or more. To perform measurements more accurately, it is recommended that the bonding surface of the adhesive sheet 1 on the alkali-free glass be cleaned using isopropyl alcohol or the like.

[0169] Next, the test piece bonded to the alkali-free glass is left at room temperature (23°C ± 5°C) for 30 minutes, and then placed in a pressure degassing apparatus (autoclave) and autoclaved for 15 minutes at a temperature of 50°C and a pressure of 0.5 MPa. After the treatment, the test piece is left at room temperature for 12 hours. Next, a peel test is performed at a peel angle of 180° and a peel speed of 300 mm / min to peel the test piece from the alkali-free glass. The maximum force (peel strength) measured during peeling can be identified as the adhesive strength of the pressure-sensitive adhesive sheet 1.

[0170] <2-1-3. Chromaticity> (Chromaticity) The chromaticity of the pressure-sensitive adhesive sheet 1 is measured according to the CIE1976 L standard defined in JIS Z8781-4:2013. * , a * , b * Color space chromaticity b * The chromaticity b may be expressed as an absolute value of 2.0 or less. * A low absolute value of chromaticity b means that coloring such as yellowing is suppressed. * The absolute value of chromaticity b may be 1.7 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.5 or less, 0.4 or less, 0.3 or less, or even 0.2 or less. * The lower limit of the absolute value of is 0, and may be 0.1 or more. The above chromaticity may be the chromaticity before carrying out the light fastness test described below.

[0171] (After light resistance test) The chromaticity of the pressure-sensitive adhesive sheet 1 after the light resistance test was the same as the chromaticity b * The chromaticity b after the light fastness test may be 2.5 or less, 2.2 or less, 2.0 or less, 1.8 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less, when expressed as an absolute value. * The lower limit of the absolute value of is 0, and may be 0.1 or more, 0.2 or more, or even 0.3 or more. Here, the light resistance test is a test performed using a weather resistance tester (for example, a Super Xenon Weather Meter SX75 manufactured by Suga Test Instruments Co., Ltd. or an equivalent product) at an irradiance of 120 W / m 2 This test involves exposing the pressure-sensitive adhesive sheet 1 to light for 240 hours under radiation conditions of wavelength 300 to 400 nm and a set temperature of 30°C.

[0172] Chromaticity b of adhesive sheet 1 * can be evaluated using a commercially available colorimeter capable of measurements in accordance with JIS Z8781-4:2013.

[0173] The pressure-sensitive adhesive sheet 1 can have any combination of two or more properties selected from the group consisting of the refractive index, adhesive strength, and chromaticity described above.

[0174] The gel fraction of the pressure-sensitive adhesive sheet 1 is, for example, 50% or more, and may be 75% or more, 80% or more, or even 85% or more.

[0175] The thickness of the pressure-sensitive adhesive sheet 1 is, for example, 2 to 500 μm, and may be 2 to 300 μm, 2 to 200 μm, or even 2 to 150 μm. The upper limit of the thickness may be 100 μm or less, 70 μm or less, 60 μm or less, 55 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, or even 30 μm or less. The lower limit of the thickness may be 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, 45 μm or more, or even 50 μm or more.

[0176] The pressure-sensitive adhesive sheet 1 can be used in, for example, an optical laminate or an image display device, but the uses of the pressure-sensitive adhesive sheet 1 are not limited to the above examples.

[0177] <2-2. Manufacturing Method> The pressure-sensitive adhesive sheet 1 can be formed from the photocurable pressure-sensitive adhesive composition A, for example, by irradiating light 14 onto a first laminate 10 comprising, in this order, a base sheet 11, a coating layer 12 containing the pressure-sensitive adhesive composition A, and a release liner 13 (see FIG. 2 ). The coating layer 12 is cured by irradiation with light 14 to form the pressure-sensitive adhesive sheet 1. Irradiation with light 14 is typically carried out from the side of the base sheet 11. In this case, the light 14 passes through the base sheet 11 and reaches the coating layer 12, curing the coating layer 12. However, irradiation with light 14 may also be carried out from the side of the release liner 13, or from both the side of the release liner 13 and the side of the base sheet 11.

[0178] The formed pressure-sensitive adhesive sheet 1 is sandwiched between the base sheet 11 and the release liner 13 until the release liner 13 is peeled off, and constitutes part of the second laminate 17. By peeling the release liner 13 from the second laminate 17, a third laminate 15 including the base sheet 11 and the pressure-sensitive adhesive sheet 1 is obtained. In the third laminate 15, the surface of the pressure-sensitive adhesive sheet 1 is exposed to the outside. An optical film can be laminated onto the exposed surface of the pressure-sensitive adhesive sheet 1 directly or via another layer.

[0179] The light 14 is, for example, visible light or ultraviolet light having a wavelength shorter than 450 nm. The light may include light having a wavelength in the same region as the absorption wavelength of the photopolymerization initiator contained in the pressure-sensitive adhesive composition A. Light having a wavelength of 300 nm or less and cut out using a filter or the like may be irradiated. Cutting out short-wavelength light is suitable for suppressing deterioration of the base sheet 11 and / or release liner 13 due to the light 14. The light source 18 of the light 14 is, for example, a light irradiation device equipped with an ultraviolet irradiation lamp. Examples of ultraviolet irradiation lamps include ultraviolet LEDs, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, microwave-excited mercury lamps, black light lamps, chemical lamps, germicidal lamps, low-pressure discharge mercury lamps, and excimer lasers. Two or more ultraviolet irradiation lamps may be combined. The ultraviolet LED allows the irradiated ultraviolet light band to be narrower than when other light sources are used.

[0180] The light source 18 may be an LED. Compared to black light sources, LEDs not only allow for easier adjustment of illuminance, but also tend to have a longer light source life. Compared to black light sources that use mercury, LEDs are also superior in terms of reducing environmental impact. When using an ultraviolet LED as the light source, an LED having a peak wavelength of 325 to 350 nm may be selected. As an LED having a peak wavelength of 325 to 350 nm, an LED having a peak wavelength of 340±10 nm may be selected.

[0181] Focusing on the peak wavelength of the light 14, the peak wavelength of the light 14 irradiated onto the first laminate 10 (specifically, the coating layer 12) may be 325 nm to 350 nm. The peak wavelength of the light 14 is preferably 340±10 nm (330 nm to 350 nm), may be 340±5 nm (335 nm to 345 nm), may be 340±2 nm (338 nm to 342 nm), or may be 340 nm. The peak wavelength refers to the wavelength at which the intensity of the light 14 reaches a maximum value in a spectrum showing the relationship between the wavelength and intensity of the light 14. The light 14 may further have a peak wavelength in a wavelength range other than 325 nm to 350 nm, but preferably does not have such a peak wavelength.

[0182] The illuminance of the light 14 irradiated onto the first laminate 10 (specifically, the coating layer 12) is, for example, 2.0 to 30 mW / cm 2 The illuminance is 2.5 mW / cm 2 Above, 3.0mW / cm 2 Above, 3.5mW / cm 2 Above, 4.0mW / cm 2 Above, 5.0mW / cm 2 Above, 6.0mW / cm 2 Above, 7.0mW / cm 2 Above, 8.0mW / cm 2 Above, 9.0mW / cm 2 or more, and even 10 mW / cm 2 The upper limit of the illuminance may be, for example, 25 mW / cm 2 less than 20 mW / cm 2 It may be the following:

[0183] The time for irradiating the first laminate 10 (specifically, the coating layer 12) with the light 14 is, for example, 10 to 1,000 seconds, and may be 60 seconds or more, 100 seconds or more, 150 seconds or more, or even 200 seconds or more. The upper limit of the time is, for example, 800 seconds or less, and may be 600 seconds or less, 500 seconds or less, 400 seconds or less, 300 seconds or less, or even 250 seconds or less. The irradiation with the light 14 may be continuous or intermittent.

[0184] The integrated light amount of the light 14 on the first laminate 10 (specifically, the coating layer 12) is, for example, 25 mJ / cm 2 or more, and 100 mJ / cm 2 Above, 500mJ / cm 2 Above, 1000mJ / cm 2 Above, 1500mJ / cm 2 Above, 1700mJ / cm 2 Above, 2000mJ / cm 2 Above, 2200mJ / cm 2 Above, 2400mJ / cm 2 or more, and even 2500 mJ / cm 2 The upper limit of the integrated light amount is not particularly limited, and may be, for example, 30,000 mJ / cm 2 or less, and 20,000 mJ / cm 2 Below, 10000mJ / cm2 Below 5000 mJ / cm 2 It may be the following:

[0185] The light 14 may be irradiated onto the first laminate 10 in multiple stages. The illuminance and / or the integrated amount of light of the light 14 in each stage may be the same or different from each other. Furthermore, the light sources in each stage may be the same or different from each other.

[0186] An example of the substrate of the release liner 13 (hereinafter referred to as the "liner substrate") is a resin film. Examples of resins that can be contained in the liner substrate include polyesters such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone, polycarbonate, polyamide, polyimide, polyolefin, (meth)acrylic resins, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, polyarylate, and polyphenylene sulfide. The resin is preferably a polyester such as polyethylene terephthalate.

[0187] The release liner 13 may include a layer other than the liner substrate. The release liner 13 may include a release layer. The release liner 13 includes, for example, a liner substrate and a release layer formed on one surface of the liner substrate. This release liner 13 can be used so that the release layer faces the coating layer 12. The release layer is typically a cured layer of a release agent composition containing a release agent. Various release agents can be used as the release agent, such as silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, fatty acid amide-based release agents, and silica powder.

[0188] The release liner 13 may be in the form of a sheet or a continuous piece.

[0189] An example of the substrate sheet 11 is a resin film. Examples of the resin contained in the substrate sheet 11 are the same as the examples of the resin that can be contained in the liner substrate.

[0190] The thickness of the base sheet 11 is, for example, 10 to 200 μm, and may be 25 to 150 μm.

[0191] The base sheet 11 may have a release layer on the surface facing the coating layer 12. Examples of the release layer that may be provided on the base sheet 11 are the same as the examples of the release layer that may be provided on the release liner 13. Both the release liner 13 and the base sheet 11 may have a release layer.

[0192] For the base sheet 11 , a sheet having a greater peel strength from the pressure-sensitive adhesive sheet 1 than the release liner 13 can usually be selected.

[0193] The base sheet 11 may be in the form of a sheet or a continuous sheet.

[0194] The first laminate 10 can be formed, for example, by forming a coating layer 12 on a base sheet 11 (or a release liner 13), and then placing the release liner 13 (or base sheet 11) on the formed coating layer 12. Alternatively, the first laminate 10 may be formed by applying the PSA composition A in a pouring manner into the space between the base sheet 11 and the release liner 13, which are held at a predetermined distance so that their main surfaces face each other.

[0195] The coating layer 12 can be formed by various coating methods such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

[0196] The thickness of the coating layer 12 can be adjusted depending on the desired thickness of the PSA sheet 1, and may be, for example, 2 to 500 μm, 2 to 300 μm, 2 to 200 μm, or even 2 to 150 μm. The upper limit of the thickness may be 100 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, or even 20 μm or less. The lower limit of the thickness may be 5 μm or more, 10 μm or more, or even 15 μm or more.

[0197] The first laminate 10 may include a long base sheet 11, a long coating layer 12, and a long release liner 13, or in other words, may be long. The long first laminate 10 can be obtained, for example, by forming the coating layer 12 between the base sheet 11 and the release liner 13 while conveying them after they have been unwound from a roll.

[0198] The pressure-sensitive adhesive sheet 1 can be formed from the thermosetting pressure-sensitive adhesive composition A, for example, by drying a coating film of the pressure-sensitive adhesive composition A provided on a substrate sheet. Heat can be used for drying. A release film may be used for the substrate sheet. The pressure-sensitive adhesive sheet 1 formed on the release film can be transferred to another layer that may be included in the optical laminate. A known film can be used for the release film. The substrate sheet may be another layer that may be included in the optical laminate.

[0199] The drying temperature of the coating film is, for example, 130° C. or lower, and may be 125° C. or lower, 120° C. or lower, 110° C. or lower, or even 100° C. or lower. The drying temperature is, for example, 60° C. or higher, and may be 80° C. or higher. The drying time of the coating film can be appropriately adjusted depending on the composition of the pressure-sensitive adhesive composition A, and may be, for example, 30 to 300 seconds, 40 to 240 seconds, or even 60 to 180 seconds.

[0200] <<3. Optical Laminate>> An example of an optical laminate according to an embodiment of the present invention is shown in Fig. 3. The optical laminate 20A in Fig. 3 includes a pressure-sensitive adhesive sheet 1 and an optical film 2. The pressure-sensitive adhesive sheet 1 and the optical film 2 are laminated to each other. The optical laminate 20A can be used as an optical film with a pressure-sensitive adhesive sheet.

[0201] Examples of the optical film 2 include a polarizing film, a retardation film, and a laminate film including a polarizing film and / or a retardation film. However, the optical film 2 is not limited to the above examples. The optical film 2 may also include a glass film.

[0202] The optical film 2 may be a polarizing film, and the pressure-sensitive adhesive sheet 1 may be in contact with the optical film 2 .

[0203] The polarizing film includes a polarizer. The polarizing film typically includes a polarizer and a protective film (transparent protective film). The protective film is disposed, for example, in contact with a main surface (the surface having the largest area) of the polarizer. The polarizer may be disposed between two protective films. The protective film may be disposed on at least one surface of the polarizer.

[0204] The polarizer is not particularly limited, and examples thereof include a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film, which has been uniaxially stretched after adsorbing a dichroic substance such as iodine or a dichroic dye; a polyene-based oriented film such as a dehydrated polyvinyl alcohol or a dehydrochlorinated polyvinyl chloride; etc. A polarizer typically comprises a polyvinyl alcohol film (polyvinyl alcohol films include an ethylene-vinyl acetate copolymer partially saponified film) and a dichroic substance such as iodine.

[0205] The thickness of the polarizer is not particularly limited and may be, for example, 80 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, 15 μm or less, or even 12 μm or less. The lower limit of the polarizer thickness is not particularly limited and may be, for example, 1 μm or more, 5 μm or more, or even 10 μm or more. In some cases, the lower limit of the polarizer thickness may be 15 μm or more. A thin polarizer (for example, a thickness of 20 μm or less) has reduced dimensional change and can contribute to improving the durability of the optical laminate, particularly durability at high temperatures.

[0206] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 42.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0207] The polarizer can be produced by any appropriate method. Specifically, the polarizer may be produced from a single-layer resin film or a laminate of two or more layers.

[0208] A method for producing a polarizer from the above-mentioned single-layer resin film typically includes subjecting the resin film to a dyeing treatment with a dichroic substance such as iodine or a dichroic dye and a stretching treatment. Examples of the resin film that can be used include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and partially saponified ethylene-vinyl acetate copolymer-based films. This method may further include an insolubilization treatment, a swelling treatment, a crosslinking treatment, and the like. Such production methods are well known and commonly used in the art, and therefore a detailed description thereof will be omitted.

[0209] A polarizer obtained using the laminate can be produced, for example, using a laminate of a resin substrate and a resin film or resin layer (typically, a PVA-based resin layer). Specifically, a polarizer can be produced by applying a PVA-based resin solution to a resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, a PVA-based resin layer containing a halide and a PVA-based resin is preferably formed on one side of the resin substrate. The stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, the stretching may further include, if necessary, in-air stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. In addition, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting a laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching treatment, it is possible to increase the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of the PVA in advance, problems such as a decrease in orientation or dissolution of the PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the PVA molecular orientation disorder and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide, thereby achieving high optical properties. Furthermore, by shrinking the laminate in the width direction by a drying shrinkage treatment, high optical properties can be achieved. A polarized film can be obtained by laminating a protective film on the peeled surface of the obtained resin substrate / polarizer laminate after peeling the resin substrate, or on the surface opposite to the peeled surface. Details of such a method for manufacturing a polarizer are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

[0210] The material for the protective film may be, for example, a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture-blocking properties, isotropy, etc. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The material for the protective film may be a thermosetting resin or an ultraviolet-curable resin such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone-based resin. When the polarizing film has two protective films, the materials of the two protective films may be the same or different. For example, a protective film made of a thermoplastic resin may be bonded to one main surface of the polarizer via an adhesive, and a protective film made of a thermosetting resin or an ultraviolet-curable resin may be bonded to the other main surface of the polarizer. The protective film may contain one or more optional additives, such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, color inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants.

[0211] The thickness of the protective film can be determined as appropriate, but is generally about 10 to 200 μm in view of strength, workability such as handling, thinness, and the like.

[0212] The polarizer and the protective film are usually adhered to each other via an aqueous adhesive or the like. Examples of aqueous adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex, aqueous polyurethane, and aqueous polyester. Examples of adhesives other than the above-mentioned adhesives include ultraviolet-curable adhesives and electron beam-curable adhesives. Electron beam-curable polarizing film adhesives exhibit suitable adhesiveness to various protective films. The adhesive may contain a metal compound filler.

[0213] In the polarizing film, a retardation film or the like can be formed on the polarizer instead of the protective film. Another protective film or a retardation film or the like can be further provided on the protective film.

[0214] The protective film may have a hard coat layer on the surface opposite to the surface bonded to the polarizer, and may also be subjected to treatments for purposes such as anti-reflection, anti-sticking, diffusion, and anti-glare.

[0215] The polarizing film may be a circular polarizing film.

[0216] The thickness of the polarizing film is, for example, 500 μm or less, and may be 300 μm or less, 200 μm or less, 100 μm or less, or even 60 μm or less. The lower limit of the thickness may be, for example, 10 μm or more, 25 μm or more, or even 40 μm or more.

[0217] The retardation film is a film having birefringence in the in-plane direction and / or the thickness direction, and is, for example, a stretched resin film or a film in which a liquid crystal material is oriented and fixed.

[0218] The retardation film may be a λ / 4 plate, a λ / 2 plate, an anti-reflection retardation film (see, for example, paragraphs 0221, 0222, and 0228 of JP 2012-133303 A), a viewing angle compensation retardation film (see, for example, paragraphs 0225 and 0226 of JP 2012-133303 A), or an inclined orientation retardation film for viewing angle compensation (see, for example, paragraph 0227 of JP 2012-133303 A). The retardation film is not limited to the above examples as long as it has birefringence in the in-plane direction and / or the thickness direction. There are also no limitations on the retardation value, arrangement angle, three-dimensional birefringence, whether the retardation film is single-layer or multi-layer, etc. of the retardation film. Known films can be used as the retardation film.

[0219] The thickness of the optical film 2 is, for example, 1 to 200 μm.

[0220] The optical film 2 may be a single layer or a laminated film composed of two or more layers. When the optical film 2 is a laminated film, the pressure-sensitive adhesive sheet 1 may be used to bond the layers together.

[0221] Another example of an optical laminate according to an embodiment of the present invention is shown in Figure 4. Optical laminate 20B in Figure 4 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 1, and an optical film 2 are layered in this order. By peeling off release liner 3, optical laminate 20B can be used as an optical film with a pressure-sensitive adhesive sheet.

[0222] The release liner 3 is typically a resin film. Examples of resins that make up the release liner 3 include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the release liner 3 that comes into contact with the pressure-sensitive adhesive sheet 1 may be subjected to a release treatment. The release treatment is, for example, a treatment with a silicone compound. However, the release liner 3 is not limited to the above examples. The release liner 3 is peeled off when the optical laminate 20B is used, for example, when it is attached to the image forming layer.

[0223] Another example of an optical laminate according to an embodiment of the present invention is shown in Fig. 5. Optical laminate 20C in Fig. 5 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, and a polarizing film 2A are layered in this order. After peeling off release liner 3, optical laminate 20C can be used by being attached to, for example, an image-forming layer.

[0224] A known adhesive sheet can be used as the adhesive sheet 4. The adhesive sheet 1 may also be used as the adhesive sheet 4.

[0225] Another example of an optical laminate according to an embodiment of the present invention is shown in Fig. 6. Optical laminate 20D in Fig. 6 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, a polarizing film 2A, and a protective film 5 are layered in this order. After peeling off the release liner 3, optical laminate 20D can be used by being attached to, for example, an image-forming layer.

[0226] The protective film 5 has the function of protecting the optical film 2 (polarizing film 2A), which is the outermost layer, during distribution and storage of the optical laminate 20D and when the optical laminate 20D is incorporated into an image display device. The protective film 5 may also function as a window to the external space when incorporated into an image display device. The protective film 5 is typically a resin film. Examples of resins constituting the protective film 5 include polyesters such as PET, polyolefins such as polyethylene and polypropylene, acrylics, cycloolefins, polyimides, and polyamides, with polyesters being preferred. However, the protective film 5 is not limited to the above examples. The protective film 5 may be a glass film or a laminate film including a glass film. The protective film 5 may be subjected to surface treatments such as anti-glare, anti-reflection, and anti-static.

[0227] The protective film 5 may be bonded to the optical film 2 by any adhesive. Bonding by an adhesive sheet 1 is also possible.

[0228] Another example of an optical laminate according to an embodiment of the present invention is shown in Fig. 7. The optical laminate 20E in Fig. 7 has a layered structure in which a polarizing film 2A, a first adhesive layer 30, a first retardation film 2B, a second adhesive layer 35, a second retardation film 2C, a pressure-sensitive adhesive sheet 1, and a release liner 3 are layered in this order. After the release liner 3 is peeled off, the optical laminate 20E can be used by being attached to, for example, an image forming layer.

[0229] In the optical laminate 20E, the polarizing film 2A has a laminated structure in which a first protective film 26A, a polarizer 25, and a second protective film 26B are laminated in this order.

[0230] The first protective film 26A can be formed of, for example, any appropriate resin film that can be used as a protective layer for the polarizer 25. Specific examples of resins that serve as the main component of the resin film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based resins, polyvinyl alcohol-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyethersulfone-based resins, polysulfone-based resins, polystyrene-based resins, cycloolefin-based resins such as polynorbornene, polyolefin-based resins, (meth)acrylic-based resins, and acetate-based resins.

[0231] The optical laminate 20E is typically disposed on the viewing side of an image display device (e.g., an organic EL display device), and the first protective film 26A is disposed on the viewing side. Therefore, the first protective film 26A may be subjected to surface treatment such as hard coat (HC) treatment, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc., as needed.

[0232] The thickness of the first protective film 26A is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 15 μm to 35 μm. If the above-mentioned surface treatment is applied, the thickness of the first protective film 26A includes the thickness of the surface treatment layer.

[0233] The second protective film 26B can be formed of, for example, any appropriate resin film that can be used as a protective layer for the polarizer 25. When the second protective film 26B is formed of a resin film, the same explanation as for the first protective film 26A can be applied. Furthermore, for example, the second protective film 26B can be a solidified or cured layer of a coating film of an organic solvent solution containing a resin. When the second protective film 26B is a solidified or cured layer of a coating film of an organic solvent solution containing a resin, adhesion to the polarizer 25 can be improved.

[0234] In one embodiment, the resin (base polymer) forming the solidified or cured layer may have a glass transition temperature (Tg) of 85°C or higher and a weight average molecular weight (Mw) of 25,000 or higher. By having the Tg and Mw of the resin within these ranges, excellent durability in high-temperature, high-humidity environments can be achieved despite the film's very thin thickness. The Tg of the resin is preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and particularly preferably 120°C or higher. The Tg may be, for example, 200°C or lower. The Mw of the resin is preferably 30,000 or higher, more preferably 35,000 or higher, and even more preferably 40,000 or higher. The Mw may be, for example, 150,000 or lower.

[0235] As the resin, any suitable resin can be used as long as it can form a solidified or cured product (e.g., a thermoset product) of the coating film of the organic solvent solution. Thermoplastic resins or thermosetting resins having the above-mentioned Tg and Mw are preferred, and thermoplastic resins are more preferred. Only one type of resin may be used, or two or more types may be used in combination.

[0236] Examples of thermoplastic resins include acrylic resins and epoxy resins. Acrylic resins and epoxy resins may be used in combination.

[0237] Acrylic resins typically contain, as their main component, repeating units derived from (meth)acrylic acid ester monomers having a linear or branched structure. Acrylic resins may contain repeating units derived from any appropriate copolymerizable monomer depending on the purpose. Examples of copolymerizable monomers (comonomers) include carboxyl group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, aromatic ring-containing (meth)acrylates, and heterocyclic ring-containing vinyl monomers. By appropriately setting the type, number, combination, and copolymerization ratio of the monomer units, an acrylic resin having the above-mentioned predetermined Mw can be obtained. Specific examples of acrylic resins include boron-containing acrylic resins and lactone ring-containing acrylic resins described in

[0034] to

[0056] of JP 2021-117484 A.

[0238] As the epoxy resin, an epoxy resin having an aromatic ring is preferably used. By using an epoxy resin having an aromatic ring as the epoxy resin, the adhesion between the second protective film 26B and the polarizer 25 can be improved. Furthermore, the anchoring strength of the first adhesive layer 30 adjacent to the second protective film 26B can be improved. Examples of epoxy resins having an aromatic ring include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and bisphenol S-type epoxy resins; novolac-type epoxy resins such as phenol novolac epoxy resins, cresol novolac epoxy resins, and hydroxybenzaldehyde phenol novolac epoxy resins; multifunctional epoxy resins such as glycidyl ether of tetrahydroxyphenylmethane, glycidyl ether of tetrahydroxybenzophenone, and epoxidized polyvinylphenol; naphthol-type epoxy resins, naphthalene-type epoxy resins, and biphenyl-type epoxy resins. Bisphenol A-type epoxy resins, biphenyl-type epoxy resins, and bisphenol F-type epoxy resins are preferably used. Only one type of epoxy resin may be used, or two or more types may be used in combination.

[0239] The second protective film 26B can be formed by applying an organic solvent solution of the resin to form a coating film, and then solidifying or thermally curing the coating film. Any suitable organic solvent capable of dissolving or uniformly dispersing an acrylic resin or an epoxy resin can be used as the organic solvent. Specific examples of organic solvents include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone. The resin concentration in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. Such a resin concentration allows for the formation of a uniform coating film.

[0240] The solution may be applied to any suitable substrate or to the polarizer 25. When the solution is applied to the substrate, the solidified or cured product (resin layer) of the coating film formed on the substrate is transferred to the polarizer 25. When the solution is applied to the polarizer 25, the second protective film 26B is formed directly on the polarizer 25 by drying (solidifying) or curing the coating film. Preferably, the solution is applied to the polarizer 25, and the second protective film 26B is formed directly on the polarizer 25. With this configuration, the adhesive layer or pressure-sensitive adhesive layer required for transfer can be omitted, thereby further thinning the polarizing film 2A. Any suitable method can be used to apply the solution. Specific examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (such as comma coating).

[0241] The second protective film 26B can be formed by solidifying or thermally curing the applied film of the solution. The heating temperature for solidification or thermal curing is preferably 100°C or less, and more preferably 50°C to 70°C. If the heating temperature is within this range, adverse effects on the polarizer 25 can be prevented. The heating time can vary depending on the heating temperature. The heating time can be, for example, 1 minute to 10 minutes.

[0242] The second protective film 26B (essentially, the organic solvent solution of the resin) may contain any appropriate additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; hindered phenol-based, phosphorus-based, sulfur-based, and other antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic fillers; resin modifiers; organic or inorganic fillers; plasticizers; lubricants; and flame retardants. The type, number, combination, and amount of additives can be appropriately determined depending on the purpose.

[0243] When the second protective film 26B is a solidified or hardened layer of a coating film of an organic solvent solution containing a resin, the thickness of the second protective film 26B is preferably 0.05 μm to 10 μm, more preferably 0.08 μm to 5 μm, even more preferably 0.1 μm to 1 μm, and particularly preferably 0.2 μm to 0.7 μm.

[0244] The first retardation film 2B may have any appropriate optical and / or mechanical properties depending on the purpose. The first retardation film 2B typically has a slow axis. In one embodiment, the angle θ between the slow axis of the first retardation film 2B and the absorption axis of the polarizer 25 is, for example, 40° to 50°, preferably 42° to 48°, and more preferably about 45°. If the angle θ is within this range, by using a λ / 4 plate as the first retardation film 2B, an optical laminate 20E having excellent circular polarization properties (and, as a result, excellent antireflection properties) can be obtained.

[0245] The first retardation film 2B preferably has a refractive index characteristic that satisfies the relationship nx>ny≧nz. In one embodiment, the first retardation film 2B can function as a λ / 4 plate. In this case, the in-plane retardation Re(550) of the first retardation film 2B is, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm. Note that "ny = nz" here encompasses not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, there may be cases where ny < nz, as long as the effects of the present invention are not impaired.

[0246] The Nz coefficient of the first retardation film 2B is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained optical laminate 20E is used in an image display device, an extremely excellent reflected hue can be achieved.

[0247] The first retardation film 2B may exhibit a reverse dispersion wavelength characteristic in which the retardation value increases with the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases with the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value hardly changes with the wavelength of the measurement light. In one embodiment, the first retardation film 2B exhibits a reverse dispersion wavelength characteristic. In this case, the Re(450) / Re(550) of the first retardation film 2B is, for example, 0.8 or more and less than 1, preferably 0.8 or more and 0.95 or less. With such a configuration, extremely excellent antireflection properties can be achieved.

[0248] The absolute value of the photoelastic coefficient of the first retardation film 2B is preferably 2×10 -11 m 2 / N or less, more preferably 2.0 × 10 -13 m 2 / N ~ 1.5 x 10 -11 m 2 / N, more preferably 1.0 × 10 -12 m 2 / N ~ 1.2 × 10 -11 m 2 When the absolute value of the photoelastic coefficient is in this range, the retardation is less likely to change when shrinkage stress occurs during heating. As a result, thermal unevenness in the resulting image display device can be effectively prevented.

[0249] The first retardation film 2B is typically made of a stretched resin film. The thickness of the first retardation film 2B is, for example, 70 μm or less, preferably 60 μm or less, more preferably 10 μm to 50 μm, and even more preferably 20 μm to 45 μm. If the thickness of the first retardation film 2B is within this range, good bendability can be ensured, making it suitable for flexible applications.

[0250] The first retardation film 2B can be composed of any appropriate resin film that can satisfy the above characteristics. Typical examples of such resins include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, and acrylic-based resins. These resins may be used alone or in combination (e.g., blended or copolymerized). When the first retardation film 2B is composed of a resin film that exhibits reverse dispersion wavelength characteristics, polycarbonate-based resins or polyester carbonate-based resins (hereinafter sometimes simply referred to as polycarbonate-based resins) can be suitably used.

[0251] As the polycarbonate-based resin, any suitable polycarbonate-based resin can be used as long as the effects of the present invention can be obtained. For example, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of an alicyclic diol, an alicyclic dimethanol, di-, tri- or polyethylene glycol, and an alkylene glycol or spiroglycol. Preferably, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, a structural unit derived from an alicyclic dimethanol and / or a structural unit derived from di-, tri- or polyethylene glycol; more preferably, it contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from di-, tri- or polyethylene glycol. The polycarbonate-based resin may contain a structural unit derived from another dihydroxy compound as needed. Details of polycarbonate-based resins that can be suitably used for the first retardation film 2B and methods for forming the first retardation film 2B are described in, for example, JP 2014-10291 A, JP 2014-26266 A, JP 2015-212816 A, JP 2015-212817 A, and JP 2015-212818 A, the disclosures of which are incorporated herein by reference.

[0252] In one embodiment, an organic solvent is brought into contact with the surface of the first retardation film 2B on the second adhesive layer 35 side, and then the second adhesive layer 35 is provided on the contact surface. This allows a compatible region in which the composition continuously changes toward the second adhesive layer 35 side of the first retardation film 2B. The formation of a compatible region in which the components of the first retardation film 2B and the components of the second adhesive layer 35 are compatible can improve the adhesion between the first retardation film 2B and the second retardation film 2C. On the other hand, from the viewpoint of strictly suppressing moisture penetration into the first retardation film 2B, it is preferable not to provide a compatible region. Therefore, it is preferable to form the compatible region as needed, taking into account the adhesion strength between the first retardation film 2B and the second retardation film 2C, the application or use environment of the optical laminate 20E, etc. Details of the method for forming the compatible region are described in JP 2019-56820 A, the disclosure of which is incorporated herein by reference.

[0253] The second retardation film 2C can be typically a so-called positive C plate whose refractive index characteristics satisfy the relationship nz > nx = ny. By using a positive C plate as the second retardation film 2C, reflection in oblique directions can be effectively prevented, and the anti-reflection function can be extended to a wide viewing angle.

[0254] The thickness direction retardation Rth(550) of the second retardation film 2C is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, even more preferably −90 nm to −200 nm, and particularly preferably −100 nm to −180 nm. Here, "nx = ny" encompasses not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the second retardation film 2C can be less than 10 nm.

[0255] The second retardation film 2C having the refractive index characteristic of nz > nx = ny can be formed from any appropriate material. The second retardation film 2C is preferably made of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the second retardation film 2C include the liquid crystal compound and the method for forming the retardation layer described in paragraphs

[0020] to

[0028] of JP 2002-333642 A. In this case, the thickness of the second retardation film 2C is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

[0256] Any appropriate adhesive may be used as the adhesive constituting the first adhesive layer 30 and the second adhesive layer 35. Examples of the adhesive include those described above for the optical laminate 20A.

[0257] The optical laminate according to the embodiment of the present invention may have any configuration as long as it includes the pressure-sensitive adhesive sheet 1 and the optical film 2 .

[0258] The pressure-sensitive adhesive sheet 1 can be disposed between any layers included in the optical laminate. In other words, the pressure-sensitive adhesive sheet 1 may be a so-called interlayer pressure-sensitive adhesive layer.

[0259] The optical laminate according to the embodiment of the present invention can be distributed and stored, for example, as a rolled body obtained by rolling up a strip-shaped optical laminate, or as a sheet-shaped optical laminate.

[0260] The optical laminate according to the embodiment of the present invention is typically used in an image display device, such as a liquid crystal display, an EL display such as an organic EL display, or an inorganic EL display.

[0261] <<4. Image Display Device>> An example of an image display device according to an embodiment of the present invention is shown in Figure 8. The image display device 21 of Figure 8 has a layered structure in which a substrate 7, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 6, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, a polarizing film 2A, and a protective film 5 are layered in this order. The image display device 21 has the optical laminate 20D of Figure 6 (excluding the release liner 3). The image display device 21 may have the optical laminates 20A, 20B, 20C, and 20E of Figures 3 to 5 and 7 instead of the optical laminate 20D. The substrate 7 and the image forming layer 6 may have the same configurations as the substrate and the image forming layer, respectively, of known image display devices.

[0262] The image display device 21 in FIG. 8 may be an organic EL display or a liquid crystal display. However, the image display device 21 is not limited to this example. The image display device 21 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 21 may be used for home appliances, in-vehicle applications, public information displays (PID), or the like. The image display device 21 may be used in a virtual reality (VR) device or an augmented reality (AR) device.

[0263] The image display device 21 may have any configuration as long as it includes the pressure-sensitive adhesive sheet 1 and / or the optical laminate according to an embodiment of the present invention.

[0264] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0265] <Preparation of Pressure-Sensitive Adhesive Composition> [Monomer Syrup A1] As shown in Table 1, 60 parts by weight of benzyl acrylate (BzA), 20 parts by weight of 2-ethylhexyl acrylate (2EHA), 15 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 5 parts by weight of N-vinylpyrrolidone (NVP) as monomer components M, and 0.15 parts by weight of 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)2-methylpropan-1-one (Omnirad 127, manufactured by IGM Resins) and 0.05 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one (Omnirad 651, manufactured by IGM Resins) as photopolymerization initiators were placed in a four-neck flask. Next, the liquid in the flask was irradiated with ultraviolet light under a nitrogen atmosphere to obtain a monomer syrup A1 in which the monomer component M was partially polymerized. The monomer syrup A1 contains a partial polymer of the monomer component M. The ultraviolet light irradiation was continued until the viscosity of the liquid in the flask reached approximately 20 Pa s (measurement conditions: BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30°C).

[0266] Monomer syrups A2 to A4, A31 to A34 were obtained in the same manner as for Monomer syrup A1, except that the types and amounts of monomers contained in Monomer Component M and the types and amounts of photopolymerization initiators were changed as shown in Table 1. The abbreviations in Table 1 are as follows.

[0267] (Monomers) BzA: benzyl acrylate POB-A: phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A") BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate 4HBA: 4-hydroxybutyl acrylate NVP: N-vinylpyrrolidone (Photopolymerization initiators) Omnirad 127: 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)2-methylpropan-1-one (manufactured by IGM Resins, trade name "Omnirad 127") Omnirad 651: 2,2-dimethoxy-1,2-diphenylethan-1-one (manufactured by IGM Resins, trade name "Omnirad 651")

[0268] The alkyl groups of BA and 2EHA, which are alkyl acrylates, have 4 and 8 carbon atoms, respectively.

[0269] Omnirad 127 used as the photopolymerization initiator does not have an absorption peak in the wavelength region of 340 nm or less, whereas Omnirad 651 has an absorption peak in the wavelength region of 340 nm or less.

[0270]

[0271] [Adhesive composition B1] As shown in Table 2, 0.05 parts by weight of 1,9-nonanediol diacrylate (NDDA) as a crosslinking agent, 0.3 parts by weight of γ-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones Co., Ltd., trade name "KBM-403") as a silane coupling agent, and 1 part by weight of the acrylic oligomer ODM as a tackifier were added to 100 parts by weight of monomer syrup A1 to obtain adhesive composition B1. ODM is a copolymerized oligomer of dicyclopentanyl methacrylate (DCPMA) and methyl methacrylate (MMA), and the copolymerization ratio (weight ratio) of DCPMA to MMA was 60:40.

[0272] [Adhesive compositions B2 to B13, B31 to B35] Adhesive compositions B2 to B13, B31 to B35 were obtained in the same manner as for adhesive composition B1, except that the types and amounts of monomer syrup, crosslinking agent, antioxidant, silane coupling agent, and tackifier used were changed as shown in Table 2 below. The results are shown in Table 2. The abbreviations in Table 2 are as follows.

[0273] (Crosslinking agent) NDDA: 1,9-nonanediol diacrylate (Antioxidant) Irganox 1010: Hindered phenol-based antioxidant (manufactured by BASF, product name "Irganox 1010") (Silane coupling agent) KBM-403: γ-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones, product name "KBM-403") (Tackifier) ​​ODM: Acrylic copolymer oligomer of dicyclopentanyl methacrylate (DCPMA) and methyl methacrylate (MMA). The copolymerization ratio (weight ratio) of DCPMA to MMA is 60:40

[0274]

[0275] <Preparation of Pressure-Sensitive Adhesive Sheet> [Preparation of Release Liner] A silicone-based release agent composition was obtained by mixing 30 parts by weight of an addition reaction curable silicone (LTC761 containing a hexenyl group-containing polyorganosiloxane, a 30 wt% toluene solution, manufactured by Dow Corning Toray), 0.9 parts by weight of a release control agent (BY24-850 containing an unreactive silicone resin, manufactured by Dow Corning Toray), 2 parts by weight of a curing catalyst (SRX212 containing a platinum catalyst, manufactured by Dow Corning Toray), and a toluene / hexane mixed solvent (volume ratio 1:1) as a dilution solvent. The concentration of silicone solids in the release agent composition was 1.0 wt%. Next, the release agent composition was applied with a wire bar to one side of a liner substrate (Lumirror XD500P, a polyester film, 75 μm thick), and heated at 130° C. for 1 minute to prepare a release liner having a release layer (thickness 60 nm) on one side.

[0276] [Preparation of Pressure-Sensitive Adhesive] (Example 1) Pressure-Sensitive Adhesive Composition B1 was applied to one side of a substrate sheet (PET separator, manufactured by Mitsubishi Plastics, MRF38) using an applicator to form a coating layer. Next, the release liner described above was placed on the formed coating layer to obtain a first laminate. The release liner was placed so that the release layer was in contact with the coating layer. Next, a light source with an illuminance of 2.5 mW / cm was applied from the substrate sheet side of the first laminate. 2 and cumulative light intensity of 2400 mJ / cm 2 The adhesive sheet was irradiated with ultraviolet light from a black light source under the conditions of (a) and (b). No ultraviolet light was irradiated from the release liner side. The coating layer was cured as described above, to obtain a PSA sheet (thickness: 50 μm) of Example 1 sandwiched between the base sheet and the release liner. The illuminance of the light was measured using an illuminance meter (U0-T36T2, manufactured by Topcon Technohouse Co., Ltd.) near the surface of the base sheet where the ultraviolet light was incident.

[0277] (Examples 2 to 13, Comparative Examples 1 to 5) Pressure-sensitive adhesive sheets (thickness 50 μm) of Examples 2 to 13 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that pressure-sensitive adhesive compositions B2 to B13, B31 to B35 were used instead of pressure-sensitive adhesive composition B1.

[0278] <Evaluation of Pressure-Sensitive Adhesive Sheets> [Refractive Index] For each of the produced pressure-sensitive adhesive sheets, the release liner was peeled off to expose the surface, and the refractive index was measured in critical angle mode using a prism coupler (manufactured by Metricon, model "2010M") at a measurement temperature of 25°C and a measurement wavelength of 594 nm.

[0279] [Adhesive Strength] The adhesive strength of each prepared pressure-sensitive adhesive sheet was evaluated using the method described above. A PET sheet with a corona treatment applied to the adhesive sheet bonding surface was used as the evaluation substrate sheet. The size of the alkali-free glass was a 10 cm x 10 cm square, and the bonding surface of the adhesive sheet on the alkali-free glass was cleaned with isopropyl alcohol before bonding the adhesive sheet. A bench-top precision universal testing machine (Shimadzu Corporation, AGS-50NX) was used for the peel test, and the portion of the evaluation substrate sheet of the test piece to which the adhesive sheet was not bonded was pulled with the chuck of the testing machine to perform peeling.

[0280] [Chromaticity b* For each pressure-sensitive adhesive sheet produced, the base sheet was peeled off, and an alkali-free glass plate (0.7 mm thick) was attached to the exposed surface, followed by a single stroke of a hand roller with a mass of 2 kg. Next, the release liner was peeled off, and an alkali-free glass plate (0.7 mm thick) was attached to the exposed surface while slowly applying a load with a finger to prepare a test specimen. Next, the test specimen was pressure-bonded in its thickness direction using a vacuum laminator (manufactured by NPC Corporation, LM-50x50-S) (vacuum time: 3 minutes + pressing time: 1 minute + holding time: 3 minutes). Next, the test specimen was placed in a pressure degassing apparatus (autoclave) and autoclaved for 15 minutes at a temperature of 50°C and a pressure of 0.5 MPa. Next, in a measurement environment of 23°C, the light transmittance of the test piece for light with wavelengths of 300 nm to 800 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer (UH4150, manufactured by Hitachi High-Technologies), and the chromaticity b * asked for.

[0281] Chromaticity after light fastness test b * The light resistance test was carried out using a Super Xenon Weather Meter (SX75, manufactured by Suga Test Instruments Co., Ltd.) as a weather resistance tester, and was carried out at an irradiance of 120 W / m 2 of light with a wavelength of 340 to 400 nm. 2 The experiment was carried out under radiation conditions of a set temperature of 30°C and an exposure time of 240 hours. * The measurement was carried out 24 hours after the light resistance test was completed.

[0282] [Appearance Evaluation] The following appearance evaluation was carried out for each of the produced pressure-sensitive adhesive sheets.

[0283] (Appearance 1: Initial foaming) Color b * The appearance of the test pieces prepared in the evaluation of (1) after autoclave treatment was visually observed immediately after treatment and evaluated according to the following criteria: A: No foaming was observed, and the adhesive sheet and the alkali-free glass plate were in complete contact. B: Slight foaming was observed, but the adhesive sheet and the alkali-free glass plate were in complete contact over time. D (Unacceptable): Foaming was observed.

[0284] (Appearance 2: Whitening under high temperature and humidity conditions) Chromaticity b * The autoclave-treated test pieces prepared for the evaluation of 1) were left to stand for 240 hours in a thermostatic chamber (Lightspec thermo-hygrostat LHL-113, manufactured by Espec Corporation) maintained at 85°C and 85% RH. After standing, the test pieces were removed from the thermostatic chamber and the appearance was visually observed 10 minutes and 1 day after removal, and evaluated according to the following criteria: A: No whitening observed B: Slight whitening observed, which is not a problem in practical use D (unacceptable): Whitening observed

[0285] (Appearance 3: Foaming under repeated temperature changes) Color b * A heat shock test was carried out on the autoclave-treated test specimens prepared in the evaluation of 1) using a small thermal shock apparatus (TSE-12-A, manufactured by Espec Corp.) in which the test specimens were repeatedly exposed to environments of -40°C and 85°C. The test was carried out for 200 cycles, with 30 minutes of exposure to -40°C followed by 30 minutes of exposure to 85°C as one cycle. After the heat shock test was completed, the test specimens were removed from the small thermal shock apparatus and their appearance was visually observed and evaluated according to the following criteria: A: No foaming was observed D (Unacceptable): Foaming was observed

[0286] (Appearance 4: foaming / peeling under high temperature environment) Chromaticity b * The autoclave-treated test pieces prepared for the evaluation of (1) were left to stand for 240 hours in a thermostatic chamber (Espec Corporation, thermo-hygrostat PSL-2J) maintained at 85°C. After standing, the test pieces were removed from the thermostatic chamber and the appearance was visually inspected 1 hour after removal and evaluated according to the following criteria: A: No foaming or peeling of the adhesive sheet was observed B: Slight foaming was observed, at a level that is not problematic for practical use D (unacceptable): Foaming or peeling of the adhesive sheet was observed

[0287] The evaluation results are shown in Table 3.

[0288]

[0289] As shown in Table 3, each of the pressure-sensitive adhesive sheets of the Examples had a refractive index of 1.530 or higher, and compared to the Comparative Examples, whitening in a high-temperature, high-humidity environment (Appearance 2) and foaming in an environment with repeated temperature changes (Appearance 3) were suppressed.

[0290] The pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition of the present invention can be used in image display devices such as EL displays and liquid crystal displays.

Claims

1. A pressure-sensitive adhesive composition comprising at least one selected from the group consisting of monomer component M and polymers thereof, wherein the monomer component M comprises: monomer a which contains an aromatic ring and no nitrogen atom; monomer b which contains a ring structure containing a nitrogen atom; and monomer c which contains a hydroxyl group; the sum of the content of monomer a and the content of monomer b in the monomer component M is 50% by weight or more; and the content of monomer b in the monomer component M is 0.1 to 8% by weight.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the (meth)acrylic monomer in the monomer component M is 50% by weight or more.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M includes the monomer a containing one aromatic ring in one molecule.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M includes the monomer b containing an aliphatic ring structure as the ring structure.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M includes the monomer b containing a cyclic amide structure as the ring structure.

6. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M includes the monomer b which is an N-vinyl cyclic amide.

7. The pressure-sensitive adhesive composition according to claim 1, wherein the content of said monomer c in said monomer component M is 12% by weight or more.

8. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M further comprises a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms on the side chain.

9. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M further comprises a (meth)acrylic acid alkyl ester having an alkyl group having 5 to 20 carbon atoms on the side chain.

10. The pressure-sensitive adhesive composition according to claim 9, wherein the content of said (meth)acrylic acid alkyl ester in said monomer component M is 14% by weight or more.

11. The pressure-sensitive adhesive composition according to claim 1, wherein the monomer component M is substantially free of carboxyl group-containing monomers.

12. The adhesive composition of claim 1, wherein the adhesive composition further comprises a tackifier.

13. The pressure-sensitive adhesive composition according to claim 12, wherein the content of the tackifier in the pressure-sensitive adhesive composition is 0.1 to 10 parts by weight per 100 parts by weight of the monomer component M.

14. The adhesive composition according to claim 1, which is a photocurable adhesive composition containing a photopolymerization initiator.

15. The pressure-sensitive adhesive composition according to claim 14, wherein the content of the photopolymerization initiator in the pressure-sensitive adhesive composition is 0.001 parts by weight or more per 100 parts by weight of the monomer component M.

16. The pressure-sensitive adhesive composition of claim 1, wherein the pressure-sensitive adhesive composition further comprises an antioxidant.

17. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition further comprises a silane coupling agent.

18. A pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 17.

19. An optical laminate comprising the pressure-sensitive adhesive sheet according to claim 18 and an optical film.

20. An image display device comprising the optical laminate according to claim 19.

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