JP7656446B2 - Adhesive sheet - Google Patents

Description

The present invention relates to an adhesive sheet with light diffusing properties.

In recent years, stereoscopic image display devices that display images in three dimensions have been proposed as a type of display, and among these, liquid crystal display devices with a structure in which two liquid crystal cells are stacked are known (Patent Document 1, etc.). Such liquid crystal display devices display images in three dimensions by manipulating the brightness of the image in each liquid crystal cell and sending different light information to each eye.

JP 2015-114371 A

However, in such liquid crystal display devices, as the resolution of the displayed image increases, moire is likely to occur due to interference between liquid crystal cells, making the displayed image difficult to see. In addition, display devices such as liquid crystal display devices are required to display images without unevenness, and are required to have high durability in high-temperature and high-humidity environments, particularly when used in vehicles.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide an adhesive sheet that is less likely to cause moire and uneven image display when, for example, two liquid crystal cells are bonded together, and that also has excellent durability.

To achieve the above object, first, the present invention provides an adhesive sheet having a composite adhesive layer including a light diffusing adhesive layer containing light diffusing microparticles and a transparent adhesive layer not containing light diffusing microparticles, characterized in that the dynamic hardness (DHT115-1) measured on the surface on the transparent adhesive layer side is 0.007 or more, and the haze value of the composite adhesive layer is 70% or more and 99% or less (Invention 1).

The adhesive sheet according to the above invention (Invention 1) has the above-mentioned configuration and physical properties, so that when, for example, two liquid crystal cells are bonded together, moire and image display unevenness are unlikely to occur, and the sheet also has excellent durability.

In the above invention (Invention 1), it is preferable that the dynamic hardness (DHT115-1) measured on the surface on the side of the light-diffusing adhesive layer is 0.007 or more (Invention 2).

In the above inventions (Inventions 1 and 2), it is preferable that the adhesive strength of the surface on the transparent adhesive layer side to soda-lime glass is 1 N/25 mm or more and 80 N/25 mm or less (Invention 3).

In the above inventions (Inventions 1 to 3), it is preferable that the adhesive strength of the surface on the light-diffusing adhesive layer side to soda-lime glass is 1 N/25 mm or more and 80 N/25 mm or less (Invention 4).

In the above inventions (Inventions 1 to 4), it is preferable that the thickness of the composite adhesive layer is 70 μm or more and 3000 μm or less (Invention 5).

In the above inventions (Inventions 1 to 5), it is preferable that two release sheets are provided, and the composite adhesive layer is sandwiched between the release sheets so as to contact the release surfaces of the two release sheets (Invention 6).

In the above inventions (Inventions 1 to 6), it is preferable to use it to bond two hard plates together (Invention 7).

Secondly, the present invention provides an adhesive sheet having a composite adhesive layer including a light diffusing adhesive layer containing light diffusing microparticles and a transparent adhesive layer not containing light diffusing microparticles, characterized in that the storage shear modulus G' of the transparent adhesive layer is 0.07 MPa or more and 10 MPa or less, and the haze value of the composite adhesive layer is 70% or more and 99% or less (Invention 8).

In the above invention (Invention 8), it is preferable that the storage shear modulus G' of the light diffusing adhesive layer is 0.07 MPa or more and 10 MPa or less (Invention 9).

The adhesive sheet of the present invention, for example when two liquid crystal cells are bonded together, is less likely to cause moire and uneven image display, and also has excellent durability.

1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. 1 is a cross-sectional view of a liquid crystal display member according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Adhesive sheet]
The pressure-sensitive adhesive sheet according to one embodiment of the present invention has a composite pressure-sensitive adhesive layer including a light-diffusing pressure-sensitive adhesive layer containing light-diffusing microparticles and a transparent pressure-sensitive adhesive layer not containing light-diffusing microparticles. In this specification, "not containing light-diffusing microparticles" means "not substantially containing light-diffusing microparticles", and includes not only not containing any light-diffusing microparticles, but also containing light-diffusing microparticles in an amount that does not impair the effect of this embodiment. The amount is preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less, more preferably 0.001% by mass or less, and most preferably 0% by mass.

In the adhesive sheet according to this embodiment, the dynamic hardness (DHT115-1; hereinafter may be omitted) measured on the surface on the transparent adhesive layer side is preferably 0.007 or more, and the haze value of the composite adhesive layer is preferably 70% or more and 99% or less. The method for measuring the dynamic hardness (DHT115-1) in this specification is as shown in the test example described later. The haze value in this specification is a value measured in accordance with JIS K7136:2000.

In the adhesive sheet according to this embodiment, the dynamic hardness is 0.007 or more, so that the sheet has excellent durability under high temperature and high humidity conditions. For example, in a laminate obtained by bonding two liquid crystal cells (glass plates in the test) via the composite adhesive layer of the adhesive sheet according to this embodiment, even when the laminate is left under high temperature and high humidity conditions, for example, 60°C and 95% RH conditions, for 1000 hours, the occurrence of air bubbles and peeling is suppressed at the interface between the composite adhesive layer and the liquid crystal cell (glass plate).

Here, when liquid crystal cells, which are hard bodies, are bonded together with an adhesive layer, the adhesive layer is compressed in the thickness direction because neither of them has flexibility, and the stress of the compression is stored in the adhesive layer. This residual stress acts as a repulsive force on the two liquid crystal cells. When the adhesive layer is a light-diffusing adhesive layer, it is presumed that the repulsive force is strong or weak (uneven) depending on the density (shade) of the light-diffusing fine particles per surface area of the light-diffusing adhesive layer in contact with the liquid crystal cell. It is presumed that the unevenness of the repulsive force of the adhesive layer against the liquid crystal cell caused in this way disturbs the orientation of the liquid crystal cell and causes unevenness in the displayed image. In the adhesive sheet according to this embodiment, the physical properties of the adhesive layer are specified by the dynamic hardness that represents the local elastic behavior from the surface of the adhesive layer to the thickness direction of the adhesive layer, thereby suppressing the unevenness of the displayed image.

In addition, when a transparent adhesive layer that does not have light diffusing microparticles is present in addition to the light diffusing adhesive layer, as in the composite adhesive layer of the adhesive sheet according to this embodiment, it is presumed that the transparent adhesive layer can alleviate the stress unevenness caused by the density of the light diffusing microparticles in the light diffusing adhesive layer due to the compression of the liquid crystal cells, which are two hard plates. This makes it possible to more effectively prevent unevenness from occurring in the displayed image. In other words, by having a transparent adhesive layer as described above in addition to the light diffusing adhesive layer, the ability to prevent image display unevenness caused by bonding liquid crystal cells together is improved.

In addition, in the adhesive sheet according to this embodiment, the haze value of the composite adhesive layer is 70% or more, so that when two liquid crystal cells are bonded together using the composite adhesive layer, moire is less likely to occur, and image display unevenness is even less likely to occur. The haze value of the composite adhesive layer is 99% or less, so that visibility of the image displayed by the liquid crystal cell is ensured.

From the viewpoint of durability described above, the dynamic hardness measured on the surface on the transparent adhesive layer side is preferably 0.007 or more, more preferably 0.009 or more, particularly preferably 0.011 or more, and even more preferably 0.012 or more. From the viewpoint of preventing display unevenness, the dynamic hardness is preferably 10 or less, more preferably 1 or less, particularly preferably 0.1 or less, and even more preferably 0.05 or less.

From the viewpoint of suppressing the occurrence of moire, the haze value of the composite adhesive layer is preferably 70% or more, more preferably 80% or more, particularly preferably 84% or more, even more preferably 87% or more, and most preferably 90% or more. From the viewpoint of visibility of the displayed image, the haze value of the composite adhesive layer is preferably 99% or less, more preferably 98% or less, and particularly preferably 97% or less.

The dynamic hardness measured on the surface on the light-diffusing adhesive layer side is preferably 0.007 or more, more preferably 0.009 or more, particularly preferably 0.010 or more, and even more preferably 0.011 or more. This makes the durability of the laminate described above even better. On the other hand, from the viewpoint of preventing display unevenness, the dynamic hardness is preferably 10 or less, more preferably 1 or less, particularly preferably 0.1 or less, and even more preferably 0.05 or less.

The storage shear modulus G' of the transparent adhesive layer and the storage shear modulus G' of the light diffusing adhesive layer are preferably within the ranges specified in the embodiments described below. This makes it easier for the dynamic hardness to fall within the above-mentioned range. The method for measuring the storage shear modulus G' in this specification is as shown in the test examples described below.

The gel fraction of the adhesive constituting the transparent adhesive layer is preferably 30% or more, more preferably 40% or more, particularly preferably 50% or more, and even more preferably 55% or more. The gel fraction is preferably 90% or less, more preferably 80% or less, particularly preferably 70% or less, and even more preferably 60% or less. When the gel fraction is in the above range, the dynamic hardness and storage shear modulus G' of the transparent adhesive layer tend to be in the preferred range. The method for measuring the gel fraction of the adhesive in this specification is as shown in the test example described later.

The gel fraction of the adhesive constituting the light diffusing adhesive layer is preferably 30% or more, more preferably 40% or more, particularly preferably 50% or more, and even more preferably 55% or more. The gel fraction is preferably 90% or less, more preferably 80% or less, particularly preferably 70% or less, and even more preferably 65% or less. When the gel fraction is in the above range, the dynamic hardness and storage shear modulus G' of the light diffusing adhesive layer tend to be in the preferred range.

In this embodiment, the composite adhesive layer may be composed of two layers, a light-diffusing adhesive layer and a transparent adhesive layer, or may be composed of three layers, a transparent adhesive layer, a light-diffusing adhesive layer and a transparent adhesive layer, laminated in that order. A preferred example of the composite adhesive layer in this embodiment is one composed of two layers, a light-diffusing adhesive layer and a transparent adhesive layer, which will be described below with reference to the drawings.

As shown in FIG. 1, the adhesive sheet 1 according to this embodiment is composed of two release sheets 3a, 3b and a composite adhesive layer 2 sandwiched between the two release sheets 3a, 3b so as to be in contact with the release surfaces of the two release sheets 3a, 3b. However, the release sheets 3a, 3b are not essential components of the adhesive sheet 1, and are peeled off and removed when the adhesive sheet 1 is used. In this specification, the release surface of the release sheet refers to the surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without a release treatment.

In this embodiment, the composite adhesive layer 2 is made up of two layers: a light-diffusing adhesive layer 21 that contacts the release sheet 3a, and a transparent adhesive layer 22 that contacts the release sheet 3b.

1. Each element 1-1. Composite adhesive layer The type of adhesive constituting the light diffusion adhesive layer 21 and the transparent adhesive layer 22 of the composite adhesive layer 2 in this embodiment is not particularly limited as long as the desired physical properties are obtained. For example, any of acrylic adhesives, polyester adhesives, polyurethane adhesives, rubber adhesives, silicone adhesives, etc. may be used. The adhesive may be any of emulsion type, solvent type, or solventless type, and may be any of crosslinked type or non-crosslinked type. Among them, acrylic adhesives that are excellent in adhesive properties, optical properties, etc. are preferred. As the acrylic adhesive, a crosslinked type is preferred, and a thermal crosslinked type is more preferred.

The adhesive constituting the light diffusing adhesive layer 21 and the adhesive constituting the transparent adhesive layer 22 may be the same or different, but it is preferable that both are acrylic adhesives, particularly non-active energy ray curable acrylic adhesives. This makes it easier to satisfy the above-mentioned physical properties (dynamic hardness and storage shear modulus G'). In that case, the composition other than the light diffusing microparticles may be the same or different. Also, the monomer composition of the main polymer may be the same or different.

The following describes a case where the adhesive constituting the light-diffusing adhesive layer 21 and the adhesive constituting the transparent adhesive layer 22 are both acrylic adhesives that are not curable with active energy rays, but the present invention is not limited to this.

The adhesive constituting the light-diffusing adhesive layer 21 and the adhesive constituting the transparent adhesive layer 22 are preferably made by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B) from the viewpoint of strengthening the cohesive force between the polymers. In the case of the light-diffusing adhesive layer 21, the adhesive composition P further contains light-diffusing microparticles (C).

The adhesive obtained from such adhesive composition P is likely to satisfy the above-mentioned physical properties (dynamic hardness, storage shear modulus G') and can exhibit the desired optical properties, adhesive strength, etc. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, the term "polymer" includes the concept of "copolymer."

(1) Components of the Pressure-Sensitive Adhesive Composition (1-1) (Meth)acrylic Acid Ester Polymer (A)
In the present embodiment, the (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a reactive group-containing monomer having in the molecule a reactive group that reacts with the crosslinking agent (B). The reactive group derived from the reactive group-containing monomer reacts with the crosslinking agent (B) to form a crosslinked structure (three-dimensional network structure), thereby obtaining a pressure-sensitive adhesive having the desired cohesive strength.

Preferred examples of the reactive group-containing monomer include a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), and a monomer having an amino group in the molecule (amino group-containing monomer). Among these, a hydroxyl group-containing monomer or a carboxyl group-containing monomer that has excellent reactivity with the crosslinking agent (B) is preferred.

Examples of hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, from the viewpoint of the reactivity of the hydroxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers, a (meth)acrylic acid hydroxyalkyl ester having a hydroxyalkyl group having 1 to 4 carbon atoms is preferred. Specifically, for example, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred. These may be used alone or in combination of two or more.

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

Examples of amino group-containing monomers include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used alone or in combination of two or more. The amino group-containing monomers exclude the nitrogen atom-containing monomers described below.

The (meth)acrylic acid ester polymer (A) preferably contains reactive group-containing monomers as monomer units constituting the polymer in an amount of 1% by mass or more as a lower limit, more preferably 7% by mass or more, particularly preferably 13% by mass or more, even more preferably 22% by mass or more, and most preferably 26% by mass or more. The (meth)acrylic acid ester polymer (A) preferably contains reactive group-containing monomers as monomer units constituting the polymer in an amount of 45% by mass or less as an upper limit, more preferably 40% by mass or less, particularly preferably 35% by mass or less, and even more preferably 30% by mass or less. When the (meth)acrylic acid ester polymer (A) contains reactive group-containing monomers as monomer units in the above amount, a good crosslinking structure is formed in the resulting adhesive, and it becomes easier to set the dynamic hardness and storage shear modulus G' in a preferred range. In addition, when light-diffusing fine particles (C) are contained, the dispersibility of the light-diffusing fine particles (C) in the resulting adhesive tends to be good.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, by not containing a carboxyl group-containing monomer, even if the target to which the adhesive is applied contains a material that may be damaged by acid, such as a transparent conductive film or a metal film such as tin-doped indium oxide (ITO), the damage (corrosion, change in resistance value, etc.) caused by acid can be suppressed. However, it is acceptable to contain a predetermined amount of a carboxyl group-containing monomer to the extent that such damage does not occur. Specifically, it is acceptable to contain a carboxyl group-containing monomer as a monomer unit in the (meth)acrylic acid ester polymer (A) in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

It is preferable that the (meth)acrylic acid ester polymer (A) contains an alkyl (meth)acrylic acid ester as a monomer unit constituting the polymer. This allows the polymer to exhibit good adhesion. The alkyl group may be linear or branched.

From the viewpoint of adhesion, the (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group. Examples of the (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among these, from the viewpoint of further improving adhesion, a (meth)acrylic acid ester having an alkyl group with 4 to 8 carbon atoms is preferred, and n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, or isooctyl (meth)acrylate is particularly preferred. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 20% by mass or more of (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer, more preferably 30% by mass or more, particularly preferably 40% by mass or more, and even more preferably 45% by mass or more. When the lower limit of the content of the (meth)acrylic acid alkyl ester is as described above, the (meth)acrylic acid ester polymer (A) can exhibit suitable adhesiveness. In addition, when the light diffusing fine particles (C) are contained, there is a tendency that the dispersibility of the light diffusing fine particles (C) in the adhesive can be improved, and the (meth)acrylic acid ester polymer (A) is prevented from losing the desired adhesiveness. On the other hand, the (meth)acrylic acid ester polymer (A) preferably contains 90% by mass or less of (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer, more preferably 80% by mass or less, particularly preferably 70% by mass or less, and even more preferably 60% by mass or less. When the upper limit of the (meth)acrylic acid alkyl ester content is as described above, other monomer components such as reactive functional group-containing monomers can be introduced into the (meth)acrylic acid ester polymer (A) in suitable amounts.

It is also preferable that the (meth)acrylic acid ester polymer (A) contains a monomer having an alicyclic structure in the molecule (alicyclic structure-containing monomer) as a monomer unit constituting the polymer. The alicyclic structure-containing monomer increases the glass transition temperature of the polymer and increases the dynamic hardness and storage shear modulus G' of the resulting adhesive. In addition, since the alicyclic structure-containing monomer is bulky, it is presumed that the presence of this in the polymer increases the spacing between the polymers, reducing the viscosity of the coating liquid and making it easier to thicken the adhesive layer.

The carbon ring of the alicyclic structure in the alicyclic structure-containing monomer may be a saturated structure or may have an unsaturated bond in part. The alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure. From the above viewpoint, a polycyclic alicyclic structure (polycyclic structure) is preferable, and a polycyclic structure having two to four rings is particularly preferable. From the above viewpoint, the number of carbon atoms in the alicyclic structure (meaning the total number of carbon atoms in the portion forming the ring, and in the case where multiple rings exist independently, means the total number of carbon atoms) is preferably 5 to 15, and particularly preferably 7 to 10.

Specific examples of the alicyclic structure-containing monomer include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, etc., and among these, dicyclopentanyl (meth)acrylate (alicyclic structure carbon number: 10), adamantyl (meth)acrylate (alicyclic structure carbon number: 10), or isobornyl (meth)acrylate (alicyclic structure carbon number: 7) is preferred, as they exhibit superior durability, and isobornyl (meth)acrylate is particularly preferred. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer, it preferably contains the alicyclic structure-containing monomer in an amount of 1% by mass or more, particularly preferably 5% by mass or more, and even more preferably 7% by mass or more. In addition, the content of the alicyclic structure-containing monomer is preferably 20% by mass or less, particularly preferably 15% by mass or less, and even more preferably 10% by mass or less. By having the content of the alicyclic structure-containing monomer in the above range, it becomes easier to adjust the dynamic hardness and storage shear modulus G' to the preferred range.

It is also preferable that the (meth)acrylic acid ester polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer. By having the nitrogen atom-containing monomer exist as a constituent unit in the polymer, a predetermined polarity is imparted to the adhesive, and it can be made to have excellent affinity even for an adherend having a certain degree of polarity such as glass. As the nitrogen atom-containing monomer, a monomer having a nitrogen-containing heterocycle is preferable from the viewpoint of imparting appropriate rigidity to the (meth)acrylic acid ester polymer (A). In addition, from the viewpoint of increasing the degree of freedom of the portion derived from the nitrogen atom-containing monomer in the higher-order structure of the adhesive that is constituted, it is preferable that the nitrogen atom-containing monomer does not contain a reactive unsaturated double bond group other than one polymerizable group used in polymerization to form the (meth)acrylic acid ester polymer (A).

Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, and N-vinylphthalimide. Among these, N-(meth)acryloylmorpholine is preferred because it exhibits superior adhesive strength. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, it is preferable that the nitrogen atom-containing monomer is contained in an amount of 1 mass% or more, particularly preferably 3 mass% or more, and more preferably 5 mass% or more. In addition, the (meth)acrylic acid ester polymer (A) preferably contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer in an amount of 20 mass% or less, particularly preferably 15 mass% or less, and more preferably 10 mass% or less. When the content of the nitrogen atom-containing monomer is within the above range, the resulting adhesive can fully exhibit excellent adhesive strength to glass.

If desired, the (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer. As the other monomer, a monomer that does not contain a reactive functional group is preferable so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) is preferably a linear polymer. A linear polymer makes it easier for molecular chains to become entangled, which is expected to improve cohesive strength, making it easier to obtain an adhesive with excellent durability under high temperature and high humidity conditions.

The (meth)acrylic acid ester polymer (A) is preferably a solution polymer obtained by a solution polymerization method. By using a solution polymer, it is easier to obtain a high molecular weight polymer, and it is expected that the cohesive strength will be improved, so that it is easier to obtain an adhesive that has excellent durability under high temperature and high humidity conditions.

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

The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 200,000 or more, more preferably 300,000 or more, particularly preferably 400,000 or more, and even more preferably 500,000 or more. This can increase the dynamic hardness and storage shear modulus G' of the resulting adhesive.

The upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 1.5 million or less, more preferably 1.2 million or less, particularly preferably 1 million or less, and even more preferably 800,000 or less. When the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is as described above, the dynamic hardness and storage shear modulus G' of the resulting adhesive can be reduced, and the adhesive layer can be easily thickened. The weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

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

(1-2) Crosslinking agent (B)
The crosslinking agent (B) may be any that reacts with the reactive group of the (meth)acrylic acid ester polymer (A), and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among the above, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with hydroxyl groups and carboxy groups, or an epoxy-based crosslinking agent that has excellent reactivity with carboxy groups. The crosslinking agent (B) may be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and their biurets, isocyanurates, and adducts which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

Examples of epoxy crosslinking agents include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine, etc. Among these, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane is preferred from the viewpoint of reactivity with carboxy groups.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). The content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.4 parts by mass or less. When the content of the crosslinking agent (B) is within the above range, the aforementioned physical properties and adhesive strength of the resulting adhesive tend to be favorable.

(1-3) Light diffusing fine particles (C)
The light diffusing fine particles (C) may be any as long as the composite pressure-sensitive adhesive layer 2 having the obtained light diffusing pressure-sensitive adhesive layer 21 satisfies the above-mentioned haze value.

Examples of the light-diffusing fine particles include inorganic fine particles such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide; organic light-transmitting fine particles such as acrylic resin, polystyrene resin, polyethylene resin, and epoxy resin; and fine particles made of silicon-containing compounds having an intermediate structure between inorganic and organic, such as silicone resin (for example, the Tospearl series manufactured by Momentive Performance Materials Japan). Among them, acrylic resin fine particles and fine particles made of silicon-containing compounds having an intermediate structure between inorganic and organic are preferred from the viewpoint of responding to high-definition adhesive layers. Furthermore, fine particles made of silicon-containing compounds having an intermediate structure between inorganic and organic are particularly preferred because they exert their effect even with a small amount of addition and maintain good adhesion. The above light-diffusing fine particles may be used alone or in combination of two or more types.

Examples of the acrylic resin particles include homopolymers of methyl methacrylate and copolymers of methyl methacrylate with monomers such as vinyl acetate, styrene, methyl acrylate, and ethyl acrylate.

The shape of the light diffusing microparticles is preferably spherical microparticles that diffuse light uniformly. The average particle size of the light diffusing microparticles measured by the centrifugal sedimentation light transmission method is preferably 1.0 μm or more as a lower limit, more preferably 2.0 μm or more, particularly preferably 3.0 μm or more, and even more preferably 4.0 μm or more. On the other hand, the upper limit is preferably 10.0 μm or less, particularly preferably 7.0 μm or less, and even more preferably 5.0 μm or less. By being within the above average particle size range, the obtained adhesive can easily obtain a haze value in the above range while satisfying high total light transmittance.

The average particle size measured by the centrifugal sedimentation light transmission method was measured using a centrifugal automatic particle size distribution analyzer (CAPA-700, manufactured by Horiba, Ltd.) using a measurement sample made by thoroughly mixing 1.2 g of fine particles and 98.8 g of isopropyl alcohol.

The content of the light diffusing microparticles in the adhesive composition P is preferably 1 part by mass or more, more preferably 3 parts by mass or more, particularly preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). The content of the light diffusing microparticles is preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). When the content of the light diffusing microparticles is in the above range, the composite adhesive layer 2 having the obtained light diffusing adhesive layer 21 is more likely to satisfy the above-mentioned haze value, and also more likely to satisfy the above-mentioned dynamic hardness and storage shear modulus G'.

(1-4) Various Additives If desired, various additives that are commonly used in acrylic adhesives, such as a silane coupling agent, an antirust agent, an ultraviolet absorber, an antistatic agent, a tackifier, an antioxidant, a light stabilizer, a softener, a refractive index adjuster, etc., may be added to the adhesive composition P. Note that polymerization solvents and dilution solvents described below are not included in the additives constituting the adhesive composition P.

Among the above, it is preferable that the adhesive composition P contains a silane coupling agent. This improves adhesion to the adherend, whether the adherend is a plastic plate or a glass member, and provides the aforementioned durability.

As the silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the (meth)acrylic acid ester polymer (A) and has optical transparency, is preferred.

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

The content of the silane coupling agent in the adhesive composition P is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). The content is preferably 1.2 parts by mass or less, more preferably 0.8 parts by mass or less, and even more preferably 0.4 parts by mass or less.

(2) Preparation of adhesive composition The adhesive composition P can be produced by producing a (meth)acrylic acid ester polymer (A), mixing the (meth)acrylic acid ester polymer (A) with a crosslinking agent (B), and adding additives, etc., as desired. In the case of the light diffusing adhesive layer 21, light diffusing fine particles (C) are further blended.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator as desired. However, the present invention is not limited to this, and the polymerization may be carried out without a solvent. Examples of polymerization solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more types may be used in combination.

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

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

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

Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B) and, if desired, a dilution solvent, light-diffusing particles (C), additives, etc. are added to the solution of the (meth)acrylic acid ester polymer (A) and thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). Note that, if any of the above components is in a solid state or if precipitation occurs when mixed with other components in an undiluted state, the component may be dissolved or diluted alone in a dilution solvent before mixing with the other components.

Examples of the dilution solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution thus prepared are not particularly limited as long as they are within the range that allows coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that the concentration is 10 to 60 mass %. Note that the addition of a dilution solvent or the like is not a necessary condition for obtaining the coating solution, and if the adhesive composition P has a viscosity that allows coating, it is not necessary to add a dilution solvent. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) itself serves as the dilution solvent.

(3) Formation of adhesive layer In the present embodiment, the light diffusing adhesive layer 21 and the transparent adhesive layer 22 are preferably each made of an adhesive obtained by crosslinking (a coating layer of) the adhesive composition P. The crosslinking of the adhesive composition P can usually be performed by a heat treatment. This heat treatment can also serve as a drying treatment for volatilizing a diluting solvent or the like from the coating layer of the adhesive composition P applied to a desired object.

The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, 50% RH) if necessary. If this curing period is required, the adhesive will be formed after the curing period has elapsed. If no curing period is required, the adhesive will be formed after the heat treatment has been completed.

The above heat treatment (and curing) allows the (meth)acrylic acid ester polymer (A) to be sufficiently crosslinked via the crosslinking agent (B).

The composite adhesive layer 2 in this embodiment can be obtained by laminating a light diffusing adhesive layer 21 and a transparent adhesive layer 22. The lamination may be performed before or after curing each adhesive layer. However, in order to increase the adhesion between the light diffusing adhesive layer 21 and the transparent adhesive layer 22, it is preferable to laminate each adhesive layer before curing.

(4) Thickness of the adhesive layer The total thickness of the composite adhesive layer 2, in this embodiment, the total thickness of the light diffusion adhesive layer 21 and the transparent adhesive layer 22, is preferably 70 μm or more as a lower limit, particularly preferably 110 μm or more, and more preferably 140 μm or more. By setting the lower limit of the total thickness of the composite adhesive layer 2 as above, it becomes easier to satisfy the above-mentioned haze value, and it becomes easier to relax the stress of the adhesive layer against the compression of the liquid crystal cell, which is two hard plates, and the prevention of image display unevenness is further improved. On the other hand, the total thickness of the composite adhesive layer 2 is preferably 3000 μm or less as an upper limit, particularly preferably 1000 μm or less, more preferably 500 μm or less, and most preferably 420 μm or less. By setting the upper limit of the total thickness of the composite adhesive layer 2 as above, it is possible to prevent image blurring and a decrease in total light transmittance.

The thickness of the light diffusing adhesive layer 21 is preferably 10 μm or more as a lower limit, particularly preferably 20 μm or more, and more preferably 40 μm or more. By setting the lower limit of the thickness of the light diffusing adhesive layer 21 as above, it becomes easier to satisfy the above-mentioned haze value. On the other hand, the thickness of the light diffusing adhesive layer 21 is preferably 300 μm or less as an upper limit, particularly preferably 100 μm or less, and more preferably 80 μm or less. By setting the upper limit of the thickness of the light diffusing adhesive layer 21 as above, it is possible to prevent image blurring and a decrease in total light transmittance.

The thickness of the transparent adhesive layer 22 is preferably 20 μm or more as a lower limit, particularly preferably 40 μm or more, and more preferably 80 μm or more. By setting the lower limit of the thickness of the transparent adhesive layer 22 as above, it becomes easier to relax the stress of the adhesive layer against the compression of the liquid crystal cell, which is two hard plates, and the prevention of image display unevenness is further improved. On the other hand, the thickness of the transparent adhesive layer 22 is preferably 2700 μm or less as an upper limit, particularly preferably 900 μm or less, more preferably 420 μm or less, and most preferably 340 μm or less. By setting the upper limit of the thickness of the transparent adhesive layer 22 as above, it is possible to prevent image blurring and a decrease in total light transmittance.

The release sheets 3a and 3b protect the composite pressure-sensitive adhesive layer 2 until the pressure-sensitive adhesive sheet 1 is used, and are peeled off when the pressure-sensitive adhesive sheet 1 (composite pressure-sensitive adhesive layer 2) is used. In the pressure-sensitive adhesive sheet 1 according to this embodiment, one or both of the release sheets 3a and 3b are not necessarily required.

Examples of the release sheets 3a and 3b that can be used include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, polyurethane films, ethylene vinyl acetate films, ionomer resin films, ethylene-(meth)acrylic acid copolymer films, ethylene-(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, and fluororesin films. Crosslinked films of these films can also be used. Furthermore, laminated films of these films can also be used.

It is preferable that the release surfaces of the release sheets 3a and 3b (particularly the surfaces that come into contact with the composite adhesive layer 2) are subjected to a release treatment. Examples of release agents used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

Of the release sheets 3a and 3b, it is preferable that one of the release sheets is a heavy release type release sheet having a large release force and the other is a light release type release sheet having a small release force. For example, the release sheet 3a on the side in contact with the light diffusing adhesive layer 21 may be a light release type release sheet and the release sheet 3b on the side in contact with the transparent adhesive layer 22 may be a heavy release type release sheet, or the release sheet 3a on the side in contact with the light diffusing adhesive layer 21 may be a heavy release type release sheet and the release sheet 3b on the side in contact with the transparent adhesive layer 22 may be a light release type release sheet.

There are no particular limitations on the thickness of the release sheets 3a and 3b, but it is usually about 20 to 150 μm.

2. Manufacturing of the adhesive sheet As an example of manufacturing the adhesive sheet 1, a coating solution of the adhesive composition P for forming the transparent adhesive layer 22 is applied to the release surface of one release sheet 3a, and a heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 3a with a coating layer. Also, a coating solution of the adhesive composition P for forming the light diffusing adhesive layer 21 is applied to the release surface of the other release sheet 3b, and a heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 3b with a coating layer. Then, the release sheet 3a with the coating layer and the release sheet 3b with the coating layer are bonded together so that both coating layers are in contact with each other. Here, a plurality of release sheets with coating layers may be prepared, and the coating layers may be bonded together in a desired number and in a desired stacking order. If a curing period is required, a curing period is provided, and if a curing period is not required, the above-mentioned laminated coating layers become the composite adhesive layer 2 as they are. This provides the pressure-sensitive adhesive sheet 1 having the composite pressure-sensitive adhesive layer 2, which is a laminate of the light-diffusing pressure-sensitive adhesive layer 21 and the transparent pressure-sensitive adhesive layer 22. The conditions for the heat treatment and curing are as described above.

The coating layer for forming the transparent adhesive layer 22 and the coating layer for forming the light diffusing adhesive layer 21 may each be sandwiched between two release sheets, and one of the release sheets may be peeled off when the coating layer for forming the transparent adhesive layer 22 and the coating layer for forming the light diffusing adhesive layer 21 are bonded together.

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

3. Physical Properties (1) Adhesive Strength The adhesive strength of the transparent adhesive layer 22 side of the adhesive sheet 1 according to the present embodiment to soda lime glass is preferably 1N/25mm or more, more preferably 10N/25mm or more, particularly preferably 30N/25mm or more, and even more preferably 40N/25mm or more, from the viewpoint of durability. The adhesive strength is preferably 80N/25mm or less, more preferably 70N/25mm or less, particularly preferably 60N/25mm or less, and even more preferably 50N/25mm or less. This provides good reworkability, and allows the adherend to be reused even if a bonding error occurs.

The adhesive strength of the surface of the light diffusing adhesive layer 21 side of the adhesive sheet 1 according to this embodiment to soda lime glass is preferably 1 N/25 mm or more, more preferably 10 N/25 mm or more, particularly preferably 20 N/25 mm or more, and even more preferably 30 N/25 mm or more, from the viewpoint of durability. The adhesive strength is preferably 80 N/25 mm or less, more preferably 60 N/25 mm or less, particularly preferably 50 N/25 mm or less, and even more preferably 40 N/25 mm or less. This provides good reworkability, and allows the adherend to be reused even if a lamination error occurs.

Here, the adhesive strength in this specification basically refers to the adhesive strength measured by the 180-degree peeling method in accordance with JIS Z0237:2009. The measurement sample is 25 mm wide and 100 mm long, and the measurement sample is attached to the adherend and pressurized at 0.5 MPa and 50°C for 20 minutes, and then left for 24 hours under normal pressure, 23°C, and 50% RH, and then measured at a peeling speed of 300 mm/min.

(2) Total Light Transmittance The total light transmittance of the composite pressure-sensitive adhesive layer 2 in the pressure-sensitive adhesive sheet 1 according to the present embodiment is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. If the total light transmittance is within the above range, the transparency is very high, and the sheet is particularly suitable for optical applications (displays). The method for measuring the total light transmittance is as shown in the test examples described later.

4. Other embodiments The adhesive sheet according to this embodiment has a composite adhesive layer including a light-diffusing adhesive layer containing light-diffusing microparticles and a transparent adhesive layer not containing light-diffusing microparticles, and the storage shear modulus G' of the transparent adhesive layer is 0.07 MPa or more and 10 MPa or less, and the haze value of the composite adhesive layer is 70% or more and 99% or less. When, for example, two liquid crystal cells are bonded using such an adhesive sheet, moire and image display unevenness are unlikely to occur, as in the above-mentioned embodiment. In addition, the durability is excellent under high temperature and high humidity conditions, particularly due to the action of the storage shear modulus G'.

In the adhesive sheet according to the embodiment described above, the physical properties of the adhesive layer are defined by the dynamic hardness, which represents the local elastic behavior from the surface of the adhesive layer in the thickness direction of the adhesive layer. In contrast, in the adhesive sheet according to the present embodiment, the physical properties of each of the adhesive layers are defined by the storage shear modulus G', which represents the overall elastic behavior of each of the light diffusing adhesive layer and the transparent adhesive layer. This also provides excellent durability, as with the adhesive sheet according to the embodiment described above, and makes it possible to suppress unevenness in the displayed image when liquid crystal cells are bonded together.

From the viewpoint of durability, the storage shear modulus G' of the transparent adhesive layer is preferably 0.10 MPa or more, more preferably 0.13 MPa or more, particularly preferably 0.17 MPa or more, and even more preferably 0.20 MPa or more. From the viewpoint of preventing display unevenness, the storage shear modulus G' of the transparent adhesive layer is preferably 5 MPa or less, more preferably 1 MPa or less, particularly preferably 0.7 MPa or less, and even more preferably 0.4 MPa or less.

The storage shear modulus G' of the light diffusing adhesive layer is preferably 0.07 MPa or more, more preferably 0.08 MPa or more, particularly preferably 0.09 MPa or more, and even more preferably 0.10 MPa or more. This provides better durability as described above. From the viewpoint of preventing display unevenness, the storage shear modulus G' of the light diffusing adhesive layer is preferably 10 MPa or less, more preferably 5 MPa or less, particularly preferably 0.7 MPa or less, and even more preferably 0.4 MPa or less.

The thickness of each layer and the composite adhesive layer, and the physical properties other than the dynamic hardness are the same as those of the previously described embodiment. The transparent adhesive layer and the light diffusing adhesive layer having the above physical properties can be preferably formed using the adhesive (adhesive composition P) described in the previously described embodiment.

[Method for producing laminate]
In one embodiment of the present invention, the pressure-sensitive adhesive sheet according to the above-mentioned embodiment can be used to manufacture a laminate in which two hard plates are bonded together with a pressure-sensitive adhesive layer. In a method for manufacturing a laminate according to one embodiment of the present invention, the light-diffusing pressure-sensitive adhesive layer 21 of the composite pressure-sensitive adhesive layer 2 in the pressure-sensitive adhesive sheet 1 is bonded to one hard plate, and then the transparent pressure-sensitive adhesive layer 22 of the composite pressure-sensitive adhesive layer 2 is bonded to the other hard plate.

When two hard plates are bonded together with an adhesive layer, generally, the first hard plate is bonded to one side of the adhesive layer, and then the second hard plate is bonded to the other side of the adhesive layer. At this time, the second hard plate to be bonded later is pressed strongly against the adhesive layer so as not to trap air at the interface with the adhesive layer. In this case, the contact portion of the adhesive layer with the second hard plate, especially the contact portion that comes into contact first, is easily deformed, and if a light-diffusing adhesive layer is present at the contact portion, the dispersion state of the light-diffusing fine particles is easily disturbed, and the uniformity of light diffusion may decrease. However, as described above, if the light-diffusing adhesive layer is bonded to one (first) hard plate first, and then the transparent adhesive layer is bonded to the other (second) hard plate, the deformation of the light-diffusing adhesive layer can be suppressed and the uniformity of light diffusion can be well maintained. As a result, for example, when two liquid crystal cells are bonded together as a hard plate, the occurrence of moire can be uniformly suppressed, and unevenness in the displayed image can be more effectively suppressed.

In this specification, the term "hard plate" refers to a plate-like member that is hard enough to barely bend. Examples of such hard plates include glass plates, plastic plates, and plates on which various functional layers (transparent conductive films, metal layers, silica layers, hard coat layers, anti-glare layers, etc.) are provided, as well as display modules such as liquid crystal (LCD) modules (liquid crystal cells), light-emitting diode (LED) modules, and organic electroluminescence (organic EL) modules, optical members as part of a display module, and laminates including a display module.

[Liquid crystal display components]
A liquid crystal display member according to one embodiment of the present invention is configured to include a first liquid crystal cell, a second liquid crystal cell, and an adhesive layer that bonds them together. This adhesive layer is the composite adhesive layer of the adhesive sheet according to the embodiment described above. Due to the action of the composite adhesive layer, this liquid crystal display member is less likely to suffer from moire and image display unevenness, and also has excellent durability under high temperature and high humidity conditions.

A preferred example of the adhesive layer in this embodiment is a composite adhesive layer consisting of two layers, a light-diffusing adhesive layer and a transparent adhesive layer, which will be described below with reference to the drawings.

As shown in FIG. 2, the liquid crystal display member 4 according to this embodiment is configured to include a first liquid crystal cell 5a, a second liquid crystal cell 5b, and a composite adhesive layer 2 that bonds them together. In this embodiment, the composite adhesive layer 2 is composed of two layers: a light-diffusing adhesive layer 21 that contacts the first liquid crystal cell 5a, and a transparent adhesive layer 22 that contacts the second liquid crystal cell 5b.

The light-diffusing adhesive layer 21 and the transparent adhesive layer 22 are the light-diffusing adhesive layer 21 and the transparent adhesive layer 22 in the adhesive sheet 1 described above, and the details of their configuration are as described above.

The first liquid crystal cell 5a and the second liquid crystal cell 5b are those that are commonly used in liquid crystal (LCD) displays, particularly liquid crystal displays that display three-dimensional images, and are not particularly limited. Note that the "liquid crystal cell" is sometimes called a "liquid crystal panel," "liquid crystal module," "liquid crystal display element," etc.

The first liquid crystal cell 5a and the second liquid crystal cell 5b are typically hard plates, and their thickness is typically about 0.5 to 5.0 mm, and preferably about 1.0 to 3.0 mm.

A preferred method for manufacturing the liquid crystal display member 4 will be described. However, the present invention is not limited to this. First, the release sheet 3a (preferably a light-release type release sheet) is peeled off from the adhesive sheet 1 to expose the light-diffusing adhesive layer 21, and the exposed light-diffusing adhesive layer 21 is attached to one side of the first liquid crystal cell 5a. At this time, the adhesive sheet 1 maintains a state in which the flexible release sheet 3b is attached to the side opposite to the side in contact with the liquid crystal cell 5a. Therefore, the stress unevenness of the light-diffusing adhesive layer 21 generated when attached to the liquid crystal cell 5a is immediately eliminated. In addition, when attached to the liquid crystal cell 5a, the transparent adhesive layer 22 plays the role of a cushioning material, and can suppress the application of excessive pressure to the liquid crystal cell 5a. These actions can prevent the alignment of the liquid crystal cell 5a, which causes image display unevenness when the liquid crystal display member 4 is formed, at this stage.

Next, the release sheet 3b (preferably a heavy release type release sheet) is peeled off from the adhesive sheet 1 (composite adhesive layer 2) attached to the first liquid crystal cell 5a to expose the transparent adhesive layer 22, and the second liquid crystal cell 5b is attached to the exposed transparent adhesive layer 22. Here, stress is generated in the composite adhesive layer 2 by bonding with the liquid crystal cell 5b. However, since the composite adhesive layer 2 has the transparent adhesive layer 22, the stress on the light diffusing adhesive layer 21 is relaxed, and the occurrence of stress unevenness due to the density of the light diffusing fine particles is prevented. In the liquid crystal display member 4 obtained in this manner, the alignment of the liquid crystal cells 5a and 5b is prevented from being disturbed due to the stress unevenness caused by the light diffusing adhesive layer 21 in the composite adhesive layer 2, and thus the occurrence of unevenness in the displayed image is suppressed, and the displayed image is displayed satisfactorily.

In addition, the release sheet 3b (preferably a light release type release sheet) may be peeled off first from the adhesive sheet 1, the transparent adhesive layer 22 and the second liquid crystal cell 5b may be bonded together, and then the release sheet 3a (preferably a heavy release type release sheet) may be peeled off, and the light diffusing adhesive layer 21 and the first liquid crystal cell 5a may be bonded together.

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

For example, the composite adhesive layer 2 in the adhesive sheet 1 may have a structure of three or more layers. Also, one of the release sheets 3a and 3b in the adhesive sheet 1 may be omitted.

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

[Production Example 1] (Preparation of Coating Layer with Release Sheet for Light Diffusing Pressure Sensitive Adhesive Layer)
1. Preparation of (meth)acrylic acid ester polymer 25 parts by mass of n-butyl acrylate, 25 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of isobornyl acrylate, 10 parts by mass of N-acryloylmorpholine, and 30 parts by mass of 2-hydroxyethyl acrylate were copolymerized by a solution polymerization method to prepare a (meth)acrylic acid ester polymer (A). The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was 500,000.

2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; the same below) of the (meth)acrylic acid ester polymer (A) obtained in the above step 1, 0.2 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515") as a crosslinking agent (B), 15 parts by mass of fine particles (manufactured by Momentive Performance Materials Japan Co., Ltd., product name "Tospearl 145", average particle size: 4.5 μm) made of silicone resin (a silicon-containing compound having an intermediate structure between inorganic and organic) as light diffusing fine particles (C), and 0.3 parts by mass of 3-glycidoxypropyltrimethoxysilane as a silane coupling agent were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an adhesive composition.

Here, the formulations (solid content equivalent) of the pressure-sensitive adhesive composition when the (meth)acrylic acid ester polymer (A) is taken as 100 parts by mass (solid content equivalent) are shown in Table 1. The details of the abbreviations and the like shown in Table 1 are as follows.
[(Meth)acrylic acid ester polymer (A)]
BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate IBXA: isobornyl acrylate ACMO: N-acryloylmorpholine HEA: 2-hydroxyethyl acrylate AA: acrylic acid
[Crosslinking agent (B)]
TDI: Trimethylolpropane modified tolylene diisocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515")
XDI: Trimethylolpropane modified xylylene diisocyanate (manufactured by Soken Chemical Industries, Ltd., product name "TD-75")
Epoxy: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, product name "TETRAD-C")
[Light diffusing particles (C)]
D1: Microparticles made of silicone resin (a silicon-containing compound having an intermediate structure between inorganic and organic) with an average particle size of 4.5 μm (manufactured by Momentive Performance Materials Japan, product name "Tospearl 145", refractive index: 1.43)
D2: Spherical polymethyl methacrylate-polystyrene copolymer microparticles having an average particle size of 5.0 μm (manufactured by Sekisui Chemical Co., Ltd., product name "XX-23LA", refractive index: 1.525)

3. Formation of coating layer The coating solution of the adhesive composition obtained in the above step 2 was applied to the release-treated surface of a light-release type release sheet (manufactured by Lintec Corporation, product name "SP-PET381031"), one side of which was treated for release with a silicone-based release agent, using a knife coater, and then heated at 90°C for 1 minute to form a coating layer (thickness: 50 μm). This resulted in a coating layer with a release sheet consisting of a coating layer (thickness: 50 μm) of a light-release type release sheet/light-diffusing adhesive layer. In addition, for test examples, the coating layer with the release sheet was aged for 7 days under conditions of 23°C and 50% RH to obtain a light-diffusing adhesive layer with a release sheet.

The thickness of the coating layer is measured in accordance with JIS K7130 using a constant pressure thickness gauge (manufactured by Techlock Corporation, product name "PG-02") (same below).

[Production Examples 2 to 7] (Preparation of Coating Layer with Release Sheet for Light Diffusing Pressure Sensitive Adhesive Layer)
A coating layer with a release sheet for a light-diffusing adhesive layer and a light-diffusing adhesive layer with a release sheet were prepared in the same manner as in Production Example 1, except that the types and ratios of the monomers constituting the (meth)acrylic acid ester polymer (A), the weight-average molecular weight (Mw) of the (meth)acrylic acid ester polymer (A), the type and amount of the crosslinking agent (B), the type and amount of the light-diffusing microparticles (C), and the amount of the silane coupling agent were changed as shown in Table 1.

[Production Example 8] (Preparation of Coating Layer with Release Sheet for Light Diffusing Pressure Sensitive Adhesive Layer)
A coating layer with a release sheet for a light diffusing pressure-sensitive adhesive layer and a light diffusing pressure-sensitive adhesive layer with a release sheet were prepared in the same manner as in Production Example 1, except that the type and ratio of each monomer constituting the (meth)acrylic acid ester polymer (A) was changed as shown in Table 1, and 5.5 parts by mass of ε-caprolactone-modified tris-(2-acryloxyethyl)isocyanurate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-9300-1CL") as an active energy ray-curable component and 0.5 parts by mass of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide as a photopolymerization initiator were further added. The light diffusing pressure-sensitive adhesive layer was made of an active energy ray-curable pressure-sensitive adhesive.

[Production Examples 9 to 10] (Preparation of Coating Layer with Release Sheet for Transparent Adhesive Layer)
A coating layer with a release sheet and a transparent adhesive layer with a release sheet, each consisting of a coating layer (thickness: 50 μm) of a heavy release type release sheet/transparent adhesive layer, were prepared in the same manner as in Production Example 1, except that the types and ratios of the monomers constituting the (meth)acrylic acid ester polymer (A) and the blended amount (no blend) of the light diffusing microparticles (C) were changed as shown in Table 1, and the light release type release sheet was replaced by a coating layer on the release-treated surface of a heavy release type release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), and the coating layer was prepared in the same manner as in Production Example 1, each consisting of a heavy release type release sheet/transparent adhesive layer.

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

Example 1
The coating layer for the light diffusing adhesive layer prepared in Production Example 1 and the coating layer for the transparent adhesive layer prepared in Production Example 9 were laminated together, and then aged for 7 days under conditions of 23° C. and 50% RH. In this manner, an adhesive sheet (light diffusing adhesive layer + transparent adhesive layer = composite adhesive layer) consisting of a light release type release sheet/light diffusing adhesive layer (50 μm)/transparent adhesive layer (50 μm)/heavy release type release sheet was produced.

[Examples 2 to 8, Comparative Examples 1 to 3]
Pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the type of light-diffusing pressure-sensitive adhesive layer (Production Examples 1 to 8) and the type of transparent pressure-sensitive adhesive layer (Production Examples 9 to 10), as well as the thickness and total thickness of the transparent pressure-sensitive adhesive layer, were changed as shown in Table 2. The thickness of the transparent pressure-sensitive adhesive layer was changed by laminating a desired number of coating layers (50 μm) of the transparent pressure-sensitive adhesive layer of the transparent pressure-sensitive adhesive sheet produced in each production example.

[Test Example 1] (Measurement of gel fraction)
The light-diffusing adhesive layer with a release sheet and the transparent adhesive layer with a release sheet produced in each production example (except for production example 8) were cut to a size of 80 mm x 80 mm. Each adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass was measured using a precision balance. The mass of the mesh alone was subtracted to calculate the mass of the adhesive alone. This mass was designated M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The adhesive was then removed and air-dried for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%, and then dried in an oven at 80°C for 12 hours. After drying, the mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. This mass was designated M2. The gel fraction (%) was expressed as (M2/M1) x 100. The gel fraction of the adhesive was calculated in this way. The results are shown in Table 2.

The light-diffusing adhesive layer produced in Production Example 8 was irradiated with active energy rays (ultraviolet rays; UV) under the following conditions to cure the light-diffusing adhesive layer to form a cured adhesive layer. The gel fraction (after UV) of the adhesive in this cured adhesive layer was calculated in the same manner as above. The results are shown in Table 2.

<Activated energy ray irradiation conditions>
- Uses high pressure mercury lamp - Illuminance 200mW/ ^cm2 , light quantity 1000mJ/ ^cm2
・UV illuminance/light intensity meter used is "UVPF-A1" manufactured by iGraphics Co., Ltd.

[Test Example 2] (Measurement of dynamic hardness)
From the adhesive sheet produced in the embodiment and comparative example (except comparative example 3), the heavy release type release sheet is peeled off, and the exposed transparent adhesive layer is attached and fixed to a glass plate.Then, the light release type release sheet is peeled off, and the exposed light diffusion adhesive layer is pressed with a dynamic ultra-microhardness tester (manufactured by Shimadzu Corporation, product name "Shimadzu Dynamic Ultra-Microhardness Tester DUH-W201S"), and in an environment of 23°C, a diamond triangular pyramid indenter with a ridge angle of 115° is pressed at a load speed of 0.0142mN/sec until the depth reaches 4μm or the test force reaches 1mN, and after holding for 15 seconds, the pressing depth D (μm) and the test force P (mN) are read, and the dynamic hardness (DHT115-1) is calculated by the following formula.
Dynamic hardness (DHT115-1) = 3.8584 x P/D ²
(where 3.8584 is a constant determined by the shape of the indenter.)

The light release type release sheet was also peeled off from the adhesive sheets produced in the Examples and Comparative Examples (other than Comparative Example 3), and the exposed light diffusing adhesive layer was attached and fixed to a glass plate. Next, the heavy release type release sheet was peeled off, and the exposed transparent adhesive layer was tested in the same manner as above to determine the dynamic hardness (DHT115-1).

On the other hand, the heavy release type release sheet was peeled off from the adhesive sheet produced in Comparative Example 3, and the exposed transparent adhesive layer was attached and fixed to a glass plate. Next, active energy rays (ultraviolet rays; UV) were irradiated through the light release type release sheet under the same conditions as in Test Example 1 to cure the composite adhesive layer. Then, the light release type release sheet was peeled off, and the exposed light diffusing adhesive layer after curing with active energy rays was tested in the same manner as above to determine the dynamic hardness (DHT115-1; after UV). The transparent adhesive layer after curing with active energy rays was also tested in the same manner as above to determine the dynamic hardness (DHT115-1; after UV). The respective results are shown in Table 2.

[Test Example 3] (Measurement of storage shear modulus G')
A plurality of light-diffusing adhesive layers and transparent adhesive layers prepared in each Production Example (except Production Example 8) were laminated to obtain a laminate having a thickness of 800 μm. A cylindrical body having a diameter of 8 mm (height of 800 μm) was punched out from the obtained laminate of adhesive layers to obtain a sample.

The storage shear modulus G' (MPa) of the above samples was measured under the following conditions by a torsional shear method using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR301") in accordance with JIS K7244-1. The results are shown in Table 2.
Measurement frequency: 1Hz
Measurement temperature: 23°C

A cylinder was also obtained from the light-diffusing adhesive layer produced in Production Example 8 in the same manner as above. This cylinder was irradiated with active energy rays (ultraviolet rays; UV) under the same conditions as in Test Example 1 to cure the active energy ray-curable adhesive, thereby obtaining a sample after active energy ray curing. The storage shear modulus G' (MPa; after UV) at 23°C was measured for the obtained sample after active energy ray curing in the same manner as above. The results are shown in Table 2.

[Test Example 4] (Haze value measurement)
The composite adhesive layer of the adhesive sheet produced in the examples and comparative examples was attached to soda lime glass to prepare a measurement sample. After background measurement was performed on the soda lime glass, the haze value (%) of the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000") in accordance with JIS K7136:2000. The results are shown in Table 2.

[Test Example 5] (Measurement of total light transmittance)
The composite adhesive layer of the adhesive sheet produced in the Examples and Comparative Examples was attached to soda lime glass to prepare a measurement sample. After background measurement was performed on the soda lime glass, the total light transmittance (%) of the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000") in accordance with JIS K7361-1:1997. The results are shown in Table 2.

[Test Example 6] (Measurement of adhesive strength)
The light release type release sheet was peeled off from the adhesive sheet produced in the Examples and Comparative Examples, and the exposed light diffusing adhesive layer was attached to an easy adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 100 μm) having an easy adhesion layer, to obtain a laminate of heavy release type release sheet/composite adhesive layer/PET film. The obtained laminate was cut into a width of 25 mm and a length of 100 mm.

In an environment of 23°C and 50% RH, the heavy release type release sheet was peeled off from the laminate, and the exposed transparent adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.), and then pressurized for 20 minutes at 0.5 MPa and 50°C in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. After that, it was left for 24 hours under conditions of 23°C and 50% RH, and this was used as a sample. Then, using a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon"), the adhesive strength (transparent adhesive layer; N/25 mm) was measured under conditions of a peel speed of 300 mm/min and a peel angle of 180 degrees (except for Comparative Example 3). Measurements were performed under conditions other than those described here in accordance with JIS Z0237:2009.

For the adhesive sheet of Comparative Example 3, the above sample was irradiated with active energy rays (ultraviolet rays; UV) through the PET film under the same conditions as in Test Example 1 to harden the composite adhesive layer to form a cured composite adhesive layer. The adhesive strength (N/25 mm; after UV) of the cured composite adhesive layer was measured in the same manner as above. The results are shown in Table 2.

In addition, the adhesive strength (N/25 mm) of the light-diffusing adhesive layer side was measured for all adhesive sheets in the same manner as described above (Comparative Example 3 is the adhesive strength after UV curing). The results are shown in Table 2.

[Test Example 7] (Evaluation of Moire Suppression)
The light release type release sheet in the pressure-sensitive adhesive sheet produced in the Examples and Comparative Examples was peeled off, and the exposed light-diffusing pressure-sensitive adhesive layer was attached to the surface of the display screen of a tablet terminal (manufactured by Apple Inc., product name "iPad (registered trademark)", resolution: 264 ppi). Next, the heavy release type release sheet in the pressure-sensitive adhesive sheet was peeled off, and a liquid crystal mask having a lattice of 20 ppi to 180 ppi (in 20 ppi increments) was attached to the exposed transparent pressure-sensitive adhesive layer, to obtain a liquid crystal display.

The screen of the tablet terminal was set to full green display (RGB values (R, G, B) = 0, 255, 0), and the liquid crystal display was evaluated for moire suppression based on the degree of moire when visually observed from a direction of 60 degrees from the normal to the screen on the liquid crystal mask side, according to the following criteria. The results are shown in Table 2.
.circle.: No moire occurred in the liquid crystal displays for all the liquid crystal masks.
◯: Moire did not occur in most of the liquid crystal displays related to the liquid crystal mask.
×: Moire occurred in the liquid crystal displays for all the liquid crystal masks.

[Test Example 8] (Evaluation of Image Display Unevenness Prevention)
The first and second liquid crystal cells were prepared, and the first liquid crystal cell was adsorbed by an adsorption device. Next, the light release type release sheet in the adhesive sheet produced in the examples and comparative examples was peeled off, and the exposed light-diffusing adhesive layer was attached to one side of the first liquid crystal cell. Next, the heavy release type release sheet in the adhesive sheet was peeled off, and the second liquid crystal cell was attached to the exposed transparent adhesive layer using an atmospheric pressure laminator (manufactured by Suntec Co., Ltd., product name "TMS-SA") at an attachment speed of 30 mm/sec and a roller pressure of 0.3 MPa. Specifically, while one end of the second liquid crystal cell was supported by a glass press, the second liquid crystal cell was pressed against the transparent adhesive layer from the other end side of the second liquid crystal cell by a roller, the roller was rotated and moved to one end of the second liquid crystal cell, and finally the glass press was removed.

Thereafter, in the state where the first and second liquid crystal cells were laminated together, an image was displayed using white light as a backlight, and the displayed image was visually observed from the first liquid crystal cell side, and the prevention of image display unevenness was evaluated according to the following criteria. The results are shown in Table 2.
◎: The image was displayed without any unevenness.
.smallcircle.: Slight unevenness occurred in the displayed image, but was at a level that caused no practical problems.
×: Unevenness occurred in the displayed image.

[Test Example 9] (Evaluation of durability)
The composite adhesive layer of the adhesive sheet produced in each of the Examples and Comparative Examples was sandwiched between two soda lime glass plates (manufactured by Nippon Sheet Glass Co., Ltd., thickness: 0.7 mm), autoclaved for 30 minutes under conditions of 50°C and 0.5 MPa, and then left for 24 hours at normal pressure, 23°C, and 50% RH.

The obtained laminates (except for Comparative Example 3) were stored for 1000 hours under high temperature and high humidity conditions of 60° C. and 95% RH. The state of the interface between the composite pressure-sensitive adhesive layer and the adherend (soda-lime glass plate) was then visually inspected, and durability was evaluated according to the following criteria. The results are shown in Table 2.
. . . No air bubbles were generated.
◯: A small amount of air bubbles were generated, but the level was not problematic for practical use.
×: Many bubbles were generated.

For the adhesive sheet of Comparative Example 3, the laminate was irradiated with active energy rays through one of the soda lime glass plates under the same conditions as in Test Example 1 to harden the composite adhesive layer. Thereafter, it was stored under high temperature and high humidity conditions as described above, and durability was evaluated. The results are shown in Table 2.

As can be seen from Table 2, the adhesive sheet produced in the example was less prone to moire and image display unevenness, and also had excellent durability.

The adhesive sheet according to the present invention can be suitably used in a stereoscopic image display device.

Reference Signs List 1: Adhesive sheet 2: Composite adhesive layer 21: Light diffusing adhesive layer 22: Transparent adhesive layer 3a, 3b: Release sheet 4: Liquid crystal display member 5a: First liquid crystal cell 5b: Second liquid crystal cell

Claims (7)

A pressure-sensitive adhesive sheet having a composite pressure-sensitive adhesive layer including a light-diffusing pressure-sensitive adhesive layer containing light-diffusing fine particles and a transparent pressure-sensitive adhesive layer not containing light-diffusing fine particles,
The dynamic hardness (DHT115-1) measured on the surface of the transparent pressure-sensitive adhesive layer is 0.007 or more,
The haze value of the composite pressure-sensitive adhesive layer is 70% or more and 99% or less,
the pressure-sensitive adhesive constituting the transparent pressure-sensitive adhesive layer is obtained by crosslinking a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B);
The (meth)acrylic acid ester polymer (A) contains, as a monomer unit constituting the polymer, a monomer having an alicyclic structure in the molecule.
A pressure-sensitive adhesive sheet characterized by: The adhesive sheet according to claim 1, characterized in that the dynamic hardness (DHT115-1) measured on the surface of the light-diffusing adhesive layer side is 0.007 or more. The adhesive sheet according to claim 1 or 2, characterized in that the adhesive strength of the surface of the transparent adhesive layer to soda lime glass is 1 N/25 mm or more and 80 N/25 mm or less. The adhesive sheet according to any one of claims 1 to 3, characterized in that the adhesive strength of the surface of the light-diffusing adhesive layer to soda-lime glass is 1 N/25 mm or more and 80 N/25 mm or less. The adhesive sheet according to any one of claims 1 to 4, characterized in that the thickness of the composite adhesive layer is 70 μm or more and 3000 μm or less. It has two release sheets,
6. The pressure-sensitive adhesive sheet according to claim 1, wherein the composite pressure-sensitive adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the release sheets. The adhesive sheet according to any one of claims 1 to 6, characterized in that it is used to bond two hard plates.

Images