Adhesive sheet, flexible member laminate, and flexible device

Abstract

To provide an adhesive sheet having an adhesive that allows both excellent bend resistance and resistance to humid heat whitening when applied to lamination of flexible members.SOLUTION: An adhesive sheet has an adhesive for bonding a first flexible member and a second flexible member, the adhesive containing a surfactant and the adhesive having a gel fraction of 20% or more and less than 85%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a flexible material laminate, and a flexible device. [Background technology]

[0002] A display member having a liquid crystal element, a light-emitting diode (LED) element, an organic electroluminescence (organic EL) element, or the like is laminated with other members (such as a protective panel for protecting the display member) to form a display (display) of a device such as an electronic device. Such a laminate of a display member and other members is generally formed by bonding the display member and other members together using an adhesive layer of an adhesive sheet.

[0003] In recent years, bendable displays, so-called flexible displays, have been proposed as displays for electronic devices. Flexible displays are expected to have a wide range of applications, for example, as stationary displays that are curved and installed on a cylindrical pillar, or as mobile displays that can be folded or rolled up for easy portability.

[0004] Examples of types of flexible displays include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), and liquid crystal displays that use a plastic film as a substrate.

[0005] Examples of such flexible displays include displays that are bent during molding and maintained in a bent state, and displays that are repeatedly bent during use.

[0006] Patent Document 1 discloses an adhesive sheet having an adhesive layer for bonding one flexible member to another flexible member that constitutes a flexible display. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-45213 Summary of the Invention [Problem to be solved by the invention]

[0008] As the flexible member bends, the pressure-sensitive adhesive layer used to attach the flexible member also bends (deforms), and therefore, even when the pressure-sensitive adhesive layer is repeatedly bent, it is required that the pressure-sensitive adhesive layer not peel off, float, or fall off from the flexible member (flex resistance).

[0009] In Patent Document 1, in order to impart flexibility to the adhesive layer, a polymer obtained by polymerizing a monomer having a low glass transition temperature (Tg) is used as the main component of the adhesive constituting the adhesive layer.

[0010] On the other hand, flexible devices such as flexible displays are used in various external environments, for example, in high-temperature and high-humidity environments. In such high-temperature and high-humidity environments, moisture easily penetrates into the adhesive layer, and the absorbed moisture can cause the adhesive layer to turn white (whitening). Whitening of the adhesive layer tends to occur more easily when a polymer obtained by polymerizing a monomer with a low glass transition temperature (Tg) is used.

[0011] Therefore, the pressure-sensitive adhesive layer disclosed in Patent Document 1 has a problem in that it is poor in preventing whitening of the pressure-sensitive adhesive layer (resistance to whitening due to humidity and heat).

[0012] The present invention has been made in consideration of the above circumstances, and aims to provide an adhesive sheet having an adhesive that can achieve both bending resistance and resistance to wet heat whitening, even when used for bonding flexible materials, etc. [Means for solving the problem]

[0013] The aspects of the present invention are as follows.

[0014] [1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive for bonding a first flexible member and a second flexible member, The adhesive contains a surfactant, The pressure-sensitive adhesive sheet has a gel fraction of 20% or more and less than 85%.

[0015] [2] The pressure-sensitive adhesive sheet according to [1], wherein the pressure-sensitive adhesive has a storage modulus of 0.01 MPa or more and 18 MPa or less at -20°C.

[0016] [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive.

[0017] [4] The pressure-sensitive adhesive sheet according to [3], wherein the acrylic pressure-sensitive adhesive has a crosslinked structure containing at least a (meth)acrylic acid ester polymer and a crosslinking agent.

[0018] [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the surfactant is at least one selected from a nonionic surfactant and an anionic surfactant.

[0019] [6] A flexible material laminate comprising a first flexible material, a second flexible material, and an adhesive that bonds the first flexible material and the second flexible material to each other, The flexible material laminate is one in which the adhesive is the adhesive contained in the adhesive sheet according to any one of [1] to [5].

[0020] [7] A flexible device comprising the flexible material laminate described in [6]. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that can achieve both bending resistance and resistance to wet heat whitening, even when used for bonding flexible members or the like. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a flexible material laminate according to one embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view of a flexible device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below based on specific embodiments.

[0024] (1. Adhesive sheet) As shown in FIG. 1, the adhesive sheet 1 according to this embodiment comprises an adhesive 10, a first release sheet 11, and a second release sheet 12. The adhesive 10 is formed in a layered form, constituting an adhesive layer. The adhesive will be described later. Two release sheets (first release sheet 11 and second release sheet 12) support the adhesive 10, and are arranged so that their release surfaces contact both main surfaces 10a and 10b of the adhesive, making them releasable from the adhesive. In other words, the adhesive 10 is releasably sandwiched between the two release sheets (first release sheet 11 and second release sheet 12). In this specification, the release surface of a 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. The release sheets will be described later.

[0025] The pressure-sensitive adhesive sheet according to this embodiment is used to bond a first member to a second member, and is particularly suitable for use in bonding bendable members (flexible members).

[0026] A flexible member is a member that maintains the function that the member is intended to perform even when it is bent, such as folded, etc. Examples of flexible members include members that are molded to bend during the manufacture of a device that includes the flexible member and that maintain the bent state, and members that are repeatedly bent during the use of a device that includes the flexible member.

[0027] In flexible devices made of flexible members, when the flexible device is bent, the adhesive bonding the flexible members also bends (deforms) along with the flexible members. In particular, flexible displays that are repeatedly bent during use are bent many times.

[0028] Therefore, the adhesive must have the property (flex resistance) of being resistant to lifting or peeling from the flexible member to which it is attached when repeatedly bent.

[0029] Furthermore, flexible devices are used in a variety of environments, and so they are required to be able to perform as intended even in such environments. High-temperature, high-humidity environments are particularly harsh and prone to adhesive defects. For example, in high-temperature, high-humidity environments, moisture can penetrate into the adhesive, causing it to turn white. When this type of adhesive discoloration (whitening) occurs, it can easily cause defects, such as a change in the color of the image displayed on the display, particularly in flexible displays.

[0030] However, there has been a problem in that it is difficult to achieve both flexibility resistance and suppression of whitening of the adhesive (resistance to wet heat whitening).

[0031] The present inventors have found that the above problems can be addressed by controlling the components and physical properties of the adhesive, as described below. The components of the adhesive sheet according to this embodiment will be described in detail below.

[0032] (1.1. Adhesive) As described above, in this embodiment, it is preferable that the adhesive bond the first flexible member and the second flexible member together.

[0033] The adhesive formed in layers may be composed of one layer (single layer) or two or more layers. When the adhesive has multiple layers, these multiple layers may be the same or different. The adhesive that comes into contact with the flexible member is preferably composed of an adhesive described below.

[0034] The thickness of the pressure-sensitive adhesive 10 formed in a layer is preferably 5 to 1000 μm, more preferably 10 to 500 μm, even more preferably 20 to 250 μm, particularly preferably 30 to 100 μm, and most preferably 40 to 70 μm. This provides adhesiveness that allows the first flexible member and the second flexible member to be bonded well, and thus excellent flex resistance. In particular, lifting or peeling of the pressure-sensitive adhesive is easily suppressed even when the member is repeatedly bent.

[0035] In this embodiment, the adhesive contains a surfactant and has a gel fraction within a predetermined range, which allows the adhesive to have both bending resistance and resistance to wet heat whitening.

[0036] (1.1.1. Gel Fraction) In this embodiment, the adhesive has a gel fraction of 20% or more and less than 85%. Gel is a polymer component with a three-dimensional network structure. Therefore, the adhesive has a predetermined three-dimensional network structure with a gel fraction within the above range. This allows the adhesive to exhibit suitable cohesive strength that can withstand repeated bending. As a result, the adhesive has excellent bending resistance.

[0037] From the viewpoint of flex resistance, the gel fraction of the pressure-sensitive adhesive is preferably 25 to 82%, more preferably 30 to 78%, even more preferably 35 to 74%, and particularly preferably 40 to 70%. The method for measuring the gel fraction of the pressure-sensitive adhesive will be described in detail in the Examples below.

[0038] (1.1.2. Surfactants) In this embodiment, the PSA preferably contains a surfactant (D) in addition to the three-dimensional network structure. The surfactant has a hydrophilic group. For example, in a PSA in a high-temperature, high-humidity environment, the hydrophilic group of the surfactant is thought to capture moisture that has penetrated into the PSA. Therefore, it is thought that whitening of the PSA is unlikely to occur even if moisture penetrates into the PSA. Furthermore, when the PSA is transferred from a high-temperature, high-humidity environment to a normal environment, it is thought that the captured moisture is released, which is thought to prevent the PSA from becoming cloudy due to excess moisture. Therefore, by including a surfactant, the PSA can exhibit good resistance to moist heat whitening.

[0039] Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. In this embodiment, nonionic surfactants and anionic surfactants are preferred, and from the viewpoint of the adhesive strength of the pressure-sensitive adhesive layer, nonionic surfactants are more preferred.

[0040] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrenated phenyl ethers, and block copolymers of polyoxyethylene and polyoxypropylene.

[0041] Examples of anionic surfactants include polyoxyethylene alkyl ether sulfates and salts thereof, polyoxyethylene alkyl phenyl ether sulfates and salts thereof, polyoxyethylene alkyl ether phosphates and salts thereof, and polyoxyethylene alkyl phenyl ether phosphates and salts thereof.

[0042] The content of the surfactant is preferably 0.01 to 4 mass%, more preferably 0.1 to 3 mass%, particularly preferably 0.3 to 2 mass%, even more preferably 0.5 to 1.5 mass%, and especially preferably 0.7 to 1.1 mass%, relative to 100 mass% of the adhesive, which provides good resistance to wet heat whitening.

[0043] (1.2. Physical properties of adhesive) In this embodiment, the adhesive preferably has the following physical properties in addition to the above-mentioned characteristics.

[0044] (1.2.1. Adhesive strength) In this embodiment, the adhesive strength of the adhesive to soda-lime glass is preferably 0.5 N / 25 mm or more and 100 N / 25 mm or less. This ensures sufficient adhesion to the adherend and excellent repeated bending resistance. As a result, peeling of the adhesive from the bonded members is suppressed. From the above perspective, the adhesive strength may be 1 to 75 N / 25 mm or 3 to 50 N / 25 mm. Taking reworkability into consideration, it may be 5 to 25 N / 25 mm or 7 to 15 N / 25 mm. Good reworkability allows easy peeling between flexible members even in the event of a bonding error, enabling the flexible members (especially expensive flexible members) to be reused. A method for measuring the adhesive strength of an adhesive will be described in detail in the Examples below.

[0045] (1.2.2. Storage modulus of adhesive) In this embodiment, the pressure-sensitive adhesive preferably has a storage modulus (G') of 0.001 MPa or more and 0.50 MPa or less at 23°C and a frequency of 1 Hz. The storage modulus is an index of the ease with which a pressure-sensitive adhesive deforms (its hardness). This allows the pressure-sensitive adhesive to adequately conform to bending even when repeatedly bent, preventing lifting or peeling from the member to which it is attached.

[0046] From the above viewpoints, the storage modulus of the pressure-sensitive adhesive at 23°C may be 0.005 to 0.30 MPa, 0.010 to 0.20 MPa, 0.015 to 0.10 MPa, 0.020 to 0.075 MPa, or 0.024 to 0.050 MPa.

[0047] The pressure-sensitive adhesive preferably has a storage modulus (G') of 0.01 MPa or more and 18 MPa or less at -20°C and a frequency of 1 Hz, which allows the pressure-sensitive adhesive to adequately conform to bending even at low temperatures and prevents lifting or peeling from the member to which it is attached.

[0048] From the above viewpoints, the storage modulus of the pressure-sensitive adhesive at -20°C may be 0.03 to 10 MPa, 0.06 to 5 MPa, 0.08 to 1 MPa, 0.10 to 0.50 MPa, or 0.11 to 0.20 MPa.

[0049] The pressure-sensitive adhesive preferably has a storage modulus (G') of 0.001 MPa or more and 0.30 MPa or less at 70°C and a frequency of 1 Hz. When the storage modulus at 70°C is within the above range, the pressure-sensitive adhesive can adequately conform to bending even at high temperatures, and is prevented from lifting or peeling from the member to which it is attached.

[0050] From the above viewpoint, the storage modulus of the pressure-sensitive adhesive at 70°C may be 0.003 to 0.2 MPa, 0.005 to 0.1 MPa, 0.006 to 0.030 MPa, or 0.007 to 0.022 MPa.

[0051] In this embodiment, of the storage moduli at the three temperatures (-20°C, 23°C, and 70°C), it is preferable that the storage moduli at two or more temperatures are within the above range, and it is more preferable that the storage moduli at all three temperatures are within the above range, thereby making it possible to improve the flex resistance of the pressure-sensitive adhesive over a wide temperature range.

[0052] The storage modulus of the adhesive can be adjusted, for example, by changing the composition of the adhesive (such as the type and amount of reactive functional groups, the molecular structure and glass transition temperature of the monomer composition used), the molecular weight of the material that constitutes the adhesive, etc., as described below.

[0053] The storage modulus (G') may be measured by a known method. For example, the pressure-sensitive adhesive is prepared into a sample of a predetermined size, and the sample is strained at a predetermined frequency within a predetermined temperature range using a dynamic viscoelasticity measuring device to measure the modulus. The storage modulus under the above conditions can be calculated from the measured modulus.

[0054] (1.2.3. Total light transmittance of adhesive) The total light transmittance of the pressure-sensitive adhesive according to this embodiment may be 80% or more, 90% or more, 95% or more, or 99% or more. This makes the pressure-sensitive adhesive suitable for optical applications where transparency is required. The upper limit of the total light transmittance is usually 100% or less. In this specification, when the pressure-sensitive adhesive is active energy ray-curable, the total light transmittance of the pressure-sensitive adhesive refers to the total light transmittance after exposure to active energy rays. The total light transmittance in this specification is a value measured in accordance with JIS K7361-1:1997.

[0055] (1.2.4. Haze value of adhesive) In this embodiment, the haze value of the pressure-sensitive adhesive may be 10% or less, 5% or less, 1% or less, or 0.5% or less. This makes the pressure-sensitive adhesive suitable for optical applications where transparency is required. The lower limit of the haze value is usually 0% or more. In this specification, when the pressure-sensitive adhesive is active energy ray-curable, the haze value of the pressure-sensitive adhesive is the haze value after exposure to active energy rays. Note that the haze value in this specification is a value measured in accordance with JIS K7136:2000.

[0056] (1.2.5. Humidity and heat haze value of adhesive) In this embodiment, the moist heat haze value of the adhesive may be 10% or less, 5% or less, 3% or less, 2% or less, 1% or less, 0.6% or less, or 0.4% or less. The moist heat haze value is the haze value of the adhesive after being exposed to a predetermined high-temperature and high-humidity environment for a predetermined period of time. When the moist heat haze value is within the above range, the adhesive tends to be less likely to whiten even in an environment where moisture easily penetrates the adhesive. The lower limit of the moist heat haze value is usually 0% or more. In this specification, when the adhesive is active energy ray-curable, the moist heat haze value of the adhesive is the moist heat haze value after exposure to active energy rays. A method for measuring the moist heat haze value will be described in the Examples below.

[0057] (1.2.6. Difference between the Haze Value and the Humidity Haze Value of the Adhesive) In this embodiment, the difference between the wet heat haze value and the haze value of the adhesive (wet heat haze value - haze value) may be 5% or less, 3% or less, or 1% or less. The difference between the wet heat haze value and the haze value is an indicator of the wet heat whitening resistance of the adhesive, and the smaller this difference, the better the wet heat whitening resistance. In this embodiment, satisfying this difference makes it easy to achieve both bending resistance and wet heat whitening resistance, even when used for bonding flexible materials, etc.

[0058] (1.3. Composition of Adhesive) The adhesive may have any composition as long as it contains a surfactant and has a gel fraction within the above-mentioned range. For example, the adhesive may be any of an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, a silicone adhesive, etc. The adhesive may be either a solvent-based or solventless adhesive, but a solvent-based adhesive is preferred. In this embodiment, the adhesive is not preferably an emulsion type (e.g., a water-dispersed type).

[0059] The pressure-sensitive adhesive may have a crosslinked structure as the three-dimensional network structure. Furthermore, the pressure-sensitive adhesive may be either active energy ray-curable or non-active energy ray-curable.

[0060] In this embodiment, from the viewpoint of ease of realizing the above-mentioned physical properties, and from the viewpoint of adhesive properties, optical properties, etc., an acrylic adhesive is preferred as the adhesive, an acrylic adhesive having a crosslinked structure is more preferred, and a solvent-type acrylic adhesive having a crosslinked structure is particularly preferred.

[0061] Specifically, the pressure-sensitive adhesive preferably has a crosslinked structure formed using at least a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B) as the three-dimensional network structure. In other words, the pressure-sensitive adhesive is preferably an adhesive obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a surfactant (D), a (meth)acrylic acid ester polymer (A), and a crosslinking agent (B). Such a pressure-sensitive adhesive is likely to satisfy the above-mentioned physical properties and easily obtain good adhesive strength.

[0062] In this case, the content of the surfactant (D) in the pressure-sensitive adhesive composition P is preferably 0.01 to 4 parts by mass, more preferably 0.1 to 3 parts by mass, more preferably 0.3 to 3 parts by mass, more preferably 0.5 to 1.5 parts by mass, or more preferably 0.7 to 1.2 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier to satisfy the above-mentioned physical properties and obtains good resistance to wet heat whitening.

[0063] Furthermore, from the perspective of the SDGs, the adhesive may be made from a material with a high biomass content, a material that can be recycled or reused, or a recycled or reused material. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

[0064] (1.3.1. (Meth)acrylic acid ester polymer (A)) The (meth)acrylic acid ester polymer (A) preferably contains, as monomer units constituting the polymer, a (meth)acrylic acid alkyl ester and a monomer having a reactive functional group in the molecule (a reactive functional group-containing monomer), which makes it easier to obtain a pressure-sensitive adhesive having a crosslinked structure and good adhesiveness.

[0065] Furthermore, the (meth)acrylic acid ester polymer (A) preferably contains an aromatic ring-containing monomer as a monomer unit constituting the polymer, which makes it easier to obtain the above-mentioned physical properties.

[0066] Therefore, the (meth)acrylic acid ester polymer (A) preferably contains, as monomer units constituting the polymer, an alkyl (meth)acrylate, a reactive functional group-containing monomer, and an aromatic ring-containing monomer.

[0067] By containing a (meth)acrylic acid alkyl ester, the resulting pressure-sensitive adhesive can exhibit desirable adhesiveness. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferred. The alkyl group may be linear or branched, or may have a cyclic structure.

[0068] Examples of (meth)acrylic acid alkyl esters having an alkyl group containing 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

[0069] Among these, from the viewpoint of physical properties related to flex resistance, (meth)acrylic acid esters having an alkyl group with 1 to 8 carbon atoms are preferred, (meth)acrylic acid esters having an alkyl group with 4 to 8 carbon atoms are more preferred, and (meth)acrylic acid esters having an alkyl group with 4 to 8 carbon atoms and a glass transition temperature (Tg) as a homopolymer of -40°C or less are even more preferred. Specifically, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-octyl (meth)acrylate are preferred, and n-butyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0070] The (meth)acrylic acid ester polymer (A) preferably contains 60 to 99.9 mass %, more preferably 70 to 99 mass %, even more preferably 80 to 98.5 mass %, and particularly preferably 90 to 98 mass % of (meth)acrylic acid alkyl esters, the alkyl groups of which contain 1 to 20 carbon atoms, as monomer units constituting the polymer. This allows the (meth)acrylic acid ester polymer (A) to have suitable adhesive properties and also makes it easier to improve the flex resistance of the resulting pressure-sensitive adhesive. Furthermore, it is possible to incorporate desired amounts of other monomer components into the (meth)acrylic acid ester polymer (A), making it easier to design pressure-sensitive adhesives that exhibit desired performance.

[0071] The (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and thus the (meth)acrylic acid ester polymer (A) reacts with the crosslinking agent (B) described below via the reactive functional group derived from the reactive functional group-containing monomer, forming a crosslinked structure as a three-dimensional network structure in the pressure-sensitive adhesive. As a result, a pressure-sensitive adhesive having the desired cohesive strength is obtained, and the pressure-sensitive adhesive is likely to satisfy the above-mentioned physical properties.

[0072] Preferred reactive functional group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). These reactive functional group-containing monomers may be used alone or in combination of two or more. Among these, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred. By including a hydroxyl group-containing monomer, physical properties related to flex resistance are easily satisfied, and resistance to wet heat whitening is also easily improved.

[0073] 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, as well as hydroxyl group-containing monomethacrylates such as glycerin monomethacrylate. Among the (meth)acrylic acid hydroxyalkyl esters, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 1 to 4 carbon atoms are preferred from the viewpoint of easily achieving physical properties related to bending resistance and wet heat whitening resistance. Specific examples include 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, with 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate being particularly preferred. Furthermore, a preferred hydroxyl group-containing monomethacrylate is glycerin monomethacrylate. These may be used alone or in combination of two or more.

[0074] 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 from the viewpoint of the adhesive strength of the resulting (meth)acrylic acid ester polymer (A). These may be used alone or in combination of two or more.

[0075] The (meth)acrylic acid ester polymer (A) may contain, as a monomer unit constituting the polymer, 0.1 to 20 mass %, 0.3 to 16 mass %, 0.6 to 12 mass %, 0.8 to 8 mass %, or 0.9 to 4 mass % of a reactive functional group-containing monomer, which allows the pressure-sensitive adhesive obtained by the crosslinking reaction with the crosslinking agent (B) to have an appropriate cohesive strength, making it easier to satisfy the above-mentioned physical properties.

[0076] It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Since a carboxy group is an acid component, the absence of a carboxy group-containing monomer can suppress acid-induced defects (corrosion, resistance change, etc.) even when the target to which the pressure-sensitive adhesive is applied includes a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, or a metal mesh, which may be affected by acid.

[0077] Here, "not containing a carboxyl group-containing monomer" means that the carboxyl group-containing monomer is substantially not contained, and includes not only the case where the carboxyl group-containing monomer is not contained at all, but also the case where the carboxyl group-containing monomer is contained to an extent that the carboxyl group does not cause corrosion of the transparent conductive film, metal wiring, etc. Specifically, the (meth)acrylic acid ester polymer (A) may contain the carboxyl group-containing monomer as a monomer unit 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.

[0078] Examples of aromatic ring-containing monomers include phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, ethoxylated-o-phenylphenol acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, biphenyl di(meth)acrylate, pentafluorobenzyl (meth)acrylate, etc. Among these, from the viewpoint of easily satisfying the above-mentioned physical properties, phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and phenoxybutyl (meth)acrylate are preferred, and from the viewpoint of easily making the above-mentioned physical properties more suitable, 2-phenoxyethyl (meth)acrylate is more preferred, and 2-phenoxyethyl acrylate is particularly preferred. These may be used alone or in combination of two or more.

[0079] The (meth)acrylic acid ester copolymer (A) may contain, as a monomer unit constituting the polymer, an aromatic ring-containing monomer in an amount of 0.1 to 15 mass%, 0.4 to 10 mass%, 0.8 to 5 mass%, 1.2 to 3 mass%, or 1.5 to 2 mass%, which makes it easier to satisfy the above-mentioned physical properties.

[0080] In this embodiment, the (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers that do not contain reactive functional groups are preferred 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.

[0081] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0082] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) may be 200,000 to 3,000,000, 400,000 to 2,400,000, 550,000 to 2,000,000, 700,000 to 1,600,000, or 800,000 to 1,300,000. This makes it easier for the resulting pressure-sensitive adhesive to satisfy the above-mentioned physical properties related to flex resistance. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0083] In the pressure-sensitive adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used singly or in combination of two or more kinds.

[0084] (1.3.2. Crosslinker (B)) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) to form a crosslinked structure, triggered by heating the pressure-sensitive adhesive composition P containing the crosslinking agent (B), etc. As a result, the cohesive strength of the resulting pressure-sensitive adhesive is improved, and the above-mentioned physical properties tend to be satisfied.

[0085] The crosslinking agent (B) may be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A). Examples 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 these, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with reactive functional group-containing monomers. The crosslinking agent (B) may be used alone or in combination of two or more.

[0086] The isocyanate crosslinking agent contains at least a polyisocyanate compound, such as 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 biuret and isocyanurate forms thereof, as well as adducts thereof that are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

[0087] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P may be 0.01 to 10 parts by mass, 0.03 to 5 parts by mass, 0.06 to 1 part by mass, 0.09 to 0.7 parts by mass, or 0.12 to 0.4 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A), which makes it easier to satisfy the above-mentioned physical properties.

[0088] (1.3.3. Silane Coupling Agent (C)) The pressure-sensitive adhesive composition P according to the present embodiment preferably contains a silane coupling agent (C), which not only improves adhesion to the adherend but also prevents lifting or peeling even when repeatedly bent.

[0089] The silane coupling agent is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the adhesive component, particularly the (meth)acrylic acid ester polymer (A), and has optical transparency.

[0090] 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. Examples of such silane compounds include amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane, as well as condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These compounds may be used alone or in combination of two or more.

[0091] The content of the silane coupling agent (C) may be 0.01 to 1 part by mass, 0.04 to 0.6 parts by mass, 0.08 to 0.3 parts by mass, or 0.1 to 0.22 parts by mass relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A), which makes it easier to achieve the above-mentioned properties.

[0092] (1.3.4. Other Additives) The adhesive composition P may contain additives commonly used in acrylic adhesives, if necessary. Examples of such additives include ultraviolet absorbers, infrared absorbers, tackifiers, colorants, antistatic agents, antioxidants, light stabilizers, softeners, rust inhibitors, fillers, refractive index adjusters, catalysts, etc. Note that polymerization solvents and dilution solvents, which will be described later, are not included in the additives constituting the adhesive composition P.

[0093] (1.4. Release sheet) The release sheets 11 and 12 protect the adhesive 10 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive 10) is to be used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 11 and 12 are not necessarily required.

[0094] Examples of materials that can be used as the release sheets 11 and 12 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 materials can also be used. Furthermore, laminated films of these materials may also be used. From the perspective of the SDGs, the material constituting the release sheets may be a highly biomass material, a recyclable or reusable material, or a recycled or reused material.

[0095] The release surfaces of release sheets 11, 12 (particularly the surfaces that come into contact with adhesive 10) are preferably subjected to a release treatment. Examples of release agents used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of release sheets 11, 12 is a heavy release type release sheet with high release strength, and the other is a light release type release sheet with low release strength.

[0096] In this embodiment, the peel force when the heavy release release sheet is peeled from the adhesive at a peel rate of 0.3 m / min may be 20 to 700 mN / 25 mm, 30 to 500 mN / 25 mm, 40 to 250 mN / 25 mm, 45 to 150 mN / 25 mm, 50 to 100 mN / 25 mm, or 55 to 80 mN / 25 mm. This peel force corresponds to the peel force when the light release release sheet is peeled from the adhesive sheet, the adhesive is laminated to a first member, and then the heavy release release sheet is peeled to laminate to a second member. This allows the heavy release release sheet to be smoothly peeled from the adhesive.

[0097] In this embodiment, the peel force when the light release type release sheet is peeled from the adhesive at a peeling rate of 0.3 m / min may be 5 to 600 mN / 25 mm, 10 to 300 mN / 25 mm, 15 to 150 mN / 25 mm, 20 to 100 mN / 25 mm, 25 to 75 mN / 25 mm, or 30 to 50 mN / 25 mm. This peel force corresponds to the peel force when the light release type release sheet is peeled from the adhesive sheet in order to bond the adhesive to a member. This prevents the adhesive that should remain on the heavy release type release sheet from unintentionally adhering to the light release type release sheet when peeling the light release type release sheet.

[0098] There are no particular restrictions on the thickness of the release sheets 11 and 12, but it is usually about 20 to 150 μm.

[0099] (1.5. Production of adhesive composition) The pressure-sensitive adhesive composition P containing the (meth)acrylic acid ester polymer (A), the crosslinking agent (B), and the surfactant (D) can be produced, for example, by first producing the (meth)acrylic acid ester polymer (A), and then mixing the resulting (meth)acrylic acid ester polymer (A), the crosslinking agent (B), and the surfactant (D). If necessary, a silane coupling agent (C) and other additives may be added.

[0100] The (meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) can be carried out by a solution polymerization method, using a polymerization initiator as needed. By polymerizing the (meth)acrylic acid ester polymer (A) using a solution polymerization method, it becomes easy to increase the molecular weight of the resulting polymer and adjust the molecular weight distribution, and it also becomes possible to reduce the production of low molecular weight substances. As a result, it is easy to obtain a pressure-sensitive adhesive that is excellent in resistance to repeated bending.

[0101] Examples of polymerization solvents used in solution polymerization include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone. One polymerization solvent may be used, or two or more polymerization solvents may be used in combination. Examples of polymerization initiators include azo compounds and organic peroxides, and two or more polymerization initiators may be used in combination. In the polymerization step, the weight-average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

[0102] Next, the crosslinking agent (B) and the surfactant (D) are added to the obtained solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a solvent-diluted pressure-sensitive adhesive composition P (coating solution). If necessary, a diluting solvent, a silane coupling agent (C), and other additives may be added.

[0103] In addition, if any of the above components is a solid component, or if it is a component that will precipitate when mixed with other components in an undiluted state, that component may be dissolved or diluted in advance alone in a dilution solvent and then mixed with the other components.

[0104] Examples of dilution solvents 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.

[0105] The concentration and viscosity of the prepared coating solution may be within a range that allows coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted to a concentration of 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 as long as the adhesive composition P has a viscosity that allows coating, the addition of a dilution solvent is not necessary. 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.

[0106] (1.6. Manufacturing of adhesives) The pressure-sensitive adhesive is preferably obtained by crosslinking the above-mentioned pressure-sensitive adhesive composition P. Crosslinking of the pressure-sensitive adhesive composition P can usually be carried out by heat treatment. This heat treatment can also serve as a drying treatment for volatilizing dilution solvents and the like from a coating film of the pressure-sensitive adhesive composition P applied to a desired object.

[0107] The heating temperature for the heat treatment is preferably 50 to 150° C., more preferably 70 to 120° C. The heating time is preferably 10 seconds to 10 minutes, more preferably 50 seconds to 2 minutes.

[0108] After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, relative humidity 50%). If curing is required, the adhesive having a crosslinked structure is obtained after the curing period has elapsed. If curing is not required, the adhesive having a crosslinked structure is obtained after the heat treatment is completed.

[0109] (1.7. Manufacturing of adhesive sheets) The method for producing the pressure-sensitive adhesive sheet 1 is not particularly limited, and it may be produced by a known method. For example, a coating solution of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of one of the first release sheets 11 (or second release sheet 12), and a heat treatment is carried out to crosslink the pressure-sensitive adhesive composition P, thereby forming a coating layer having a predetermined thickness. The release surface of the other second release sheet 12 (or first release sheet 11) is then superimposed on the formed coating layer. If curing is required, the coating layer will become the pressure-sensitive adhesive 10 after a predetermined curing period. Alternatively, if curing is not required, the coating layer will become the pressure-sensitive adhesive 10 as is. In this way, the pressure-sensitive adhesive sheet 1 is obtained.

[0110] In another method for producing the pressure-sensitive adhesive sheet 1, a coating solution of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of one of the first release sheets 11, followed by a heat treatment to crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a first release sheet 11 with a coating layer. Furthermore, a coating solution of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of the other of the second release sheets 12, followed by a heat treatment to crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a second release sheet 12 with a coating layer. The first release sheet 11 with the coating layer and the second release sheet 12 with the coating layer are then bonded together so that the two coating layers are in contact with each other. If curing is required, the coating layer becomes the pressure-sensitive adhesive 10 after a predetermined curing period. If curing is not required, the coating layer becomes the pressure-sensitive adhesive 10 as is. This produces the pressure-sensitive adhesive sheet 1. This production method allows stable production of pressure-sensitive adhesive 10 even when the pressure-sensitive adhesive 10 is thick.

[0111] Examples of methods for applying the coating solution of the adhesive composition P include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0112] (2. Flexible material laminate) As shown in Figure 2, the flexible material laminate 2 of this embodiment is composed of a first flexible material 21 (one flexible material), a second flexible material 22 (another flexible material), and an adhesive 10 located between them and bonding the first flexible material 21 and the second flexible material 22 to each other.

[0113] The adhesive 10 in the flexible material laminate 2 is the adhesive 10 of the adhesive sheet 1 described above.

[0114] The flexible material laminate 2 is a flexible device itself, or a material that constitutes part of a flexible device. The flexible device may be a device including a material that has been bent once during manufacturing and that maintains the bent state, or may be a device including a material that can be repeatedly bent (including folded). The flexible device is preferably a display, but is not limited to this. Examples of flexible devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays that use a plastic substrate (film) as a substrate, light-emitting diode (LED) displays, foldable displays, stretchable displays, and rollable displays. These may also be touch panels.

[0115] First flexible member 21 and second flexible member 22 are members that can be repeatedly bent (including folded), for example. Examples of flexible members include a cover film, a barrier film, a hard coat film, a polarizing film (polarizing plate), a polarizer, a retardation film (retardation plate), a viewing angle compensation film, a brightness improvement film, a contrast improvement film, a diffusion film, a semi-transmitting reflective film, an electrode film, a transparent conductive film, a metal mesh film, a film sensor (touch sensor film), a liquid crystal polymer film, a light-emitting polymer film, a film-like liquid crystal module, an organic EL module (organic EL film, organic EL element), an electronic paper module (film-like electronic paper), a TFT (Thin Film Transistor) substrate, and the like.

[0116] The Young's modulus of each of the first flexible member 21 and the second flexible member 22 is preferably 0.1 to 10 GPa, more preferably 0.5 to 7 GPa, and even more preferably 1 to 5 GPa, which makes it easier to repeatedly bend each flexible member.

[0117] The thickness of each of the first flexible member 21 and the second flexible member 22 is preferably 10 to 3000 μm, more preferably 25 to 1000 μm, and even more preferably 50 to 500 μm, which makes it easier to repeatedly bend each flexible member.

[0118] An example of manufacturing the flexible material laminate 2 is shown below. First, one second release sheet 12 of the adhesive sheet 1 is peeled off, and the exposed adhesive 10 of the adhesive sheet 1 is attached to one surface of the first flexible material 21.

[0119] Thereafter, the other first release sheet 11 is peeled from the adhesive 10 of the adhesive sheet 1, and the exposed adhesive 10 of the adhesive sheet 1 is bonded to the second flexible member 22 to obtain the flexible member laminate 2. As another example, the bonding order of the first flexible member 21 and the second flexible member 22 may be reversed.

[0120] (3. Flexible Devices) The flexible device according to this embodiment includes the above-described flexible material laminate 2, and may be configured with only the flexible material laminate 2, or may be configured with one or more flexible material laminates 2 and other flexible materials. When laminating one flexible material laminate 2 with another flexible material laminate 2, or when laminating a flexible material laminate 2 with another flexible material, it is preferable to laminate them via the adhesive 10 of the above-described adhesive sheet 1.

[0121] In the flexible device of this embodiment, each component is bonded together using the above-mentioned adhesive, so even when the device is repeatedly bent, the adhesive is prevented from lifting or peeling off from the bonded components, and whitening of the adhesive is prevented even when the device is exposed to a high-temperature, high-humidity environment.

[0122] A flexible device as an example of this embodiment is shown in Fig. 3. However, the flexible device according to the present invention is not limited to this flexible device.

[0123] 3, the flexible device 3 according to this embodiment is configured by laminating, from top to bottom, a cover film 31, a first adhesive 32, a polarizing film 33, a second adhesive 34, a touch sensor film 35, a third adhesive 36, an organic EL element 37, a fourth adhesive 38, and a TFT substrate 39. The cover film 31, polarizing film 33, touch sensor film 35, organic EL element 37, and TFT substrate 39 correspond to flexible members.

[0124] It is preferable that at least one layer of the first adhesive 32, the second adhesive 34, the third adhesive 36, and the fourth adhesive 38 is the adhesive 10 of the adhesive sheet 1 described above. It is preferable that two or more layers of the first adhesive 32, the second adhesive 34, the third adhesive 36, and the fourth adhesive 38 are the adhesive 10 of the adhesive sheet 1 described above, and it is most preferable that all of the adhesives 32, 34, 36, and 38 are the adhesive 10 of the adhesive sheet 1.

[0125] In this specification, when it is written "X to Y" (X and Y are any numbers), it means "X or more and Y or less" unless otherwise specified, and also includes the meaning "preferably greater than X" or "preferably smaller than Y." Furthermore, when it is written "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is written "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

[0126] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Example]

[0127] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0128] Example 1 1. Preparation of (meth)acrylic acid ester polymer A (meth)acrylic acid ester polymer (A) was prepared by copolymerizing 48.6 parts by mass of n-butyl acrylate, 48.6 parts by mass of 2-ethylhexyl acrylate, 1.8 parts by mass of 2-phenoxyethyl acrylate, and 1 part by mass of 4-hydroxybutyl acrylate. The molecular weight of the resulting (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was 1.2 million.

[0129] 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 HLC-8020 GPC columns (passed in the following order): Tosoh Corporation TSK guard column HXL-H TSK gel GMHXL (×2) TSK gel G2000HXL Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0130] 2. Preparation of adhesive composition 100 parts by mass (solid content equivalent: the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained above, 0.14 parts by mass of an isocyanate-based crosslinking agent (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") (B1) as the crosslinking agent (B), 0.20 parts by mass of 3-glycidoxypropyltrimethoxysilane (C1) as the silane coupling agent (C), and 0.5 parts by mass of a nonionic surfactant (manufactured by Daiichi Pharmaceutical Co., Ltd., product name "Noigen EA-87" (D1) as the surfactant (D) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of a pressure-sensitive adhesive composition.

[0131] 3. Manufacturing of adhesive sheets The obtained adhesive composition coating solution was applied to the release-treated surface of a heavy-release release sheet R1, one side of which was a polyethylene terephthalate film treated with a silicone-based release agent, using a knife coater to form a coating layer. The coating layer was then heated at 90°C for 1 minute to promote a crosslinking reaction, forming a coating layer made of an adhesive containing a crosslinked structure having at least a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B).

[0132] Next, the coating layer on the release sheet R1 obtained above was bonded to the release-treated surface of a light-release type release sheet R2, which was a polyethylene terephthalate film with one side treated with a silicone-based release agent, so that the release-treated surface contacted the coating layer. This was then cured for 7 days at 23°C and 50% relative humidity to produce a 50 μm-thick adhesive sheet. This adhesive sheet had a configuration of "release sheet R1 / adhesive (thickness: 50 μm) / release sheet R2." The adhesive thickness was measured in accordance with JIS K7130 using a constant-pressure thickness gauge (PG-02, manufactured by Teclock Corporation). It was also confirmed that the release strength from the adhesive of the resulting adhesive sheet was greater for release sheet R1 than for release sheet R2.

[0133] (Examples 2 to 5, Comparative Examples 1 to 6) Pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the composition and molecular weight of the (meth)acrylic acid ester polymer (A), the type and amount of the crosslinking agent (B), the amount of the silane coupling agent (C), and the type and amount of the surfactant (D) were changed as shown in Table 1. In Table 1, the amounts of the crosslinking agent (B), silane coupling agent (C), and surfactant (D) are expressed as amounts (in solids content) relative to 100 parts by mass (in solids content) of the (meth)acrylic acid ester polymer (A).

[0134] [Table 1]

[0135] Details of the abbreviations and other information listed in Table 1 are as follows: ((Meth)acrylic acid ester copolymer (A)) BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate PhEA: 2-phenoxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate GMMA: Glycerin monomethacrylate ACMO: N-acryloylmorpholine IBXA: Isobornyl acrylate HEA: 2-hydroxyethyl acrylate (Crosslinking agent (B)) B1: Isocyanate-based crosslinking agent (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") B2: Isocyanate-based crosslinking agent (Mitsui Chemicals, product name "Takenate D-101E") (Silane coupling agent (C)) C1: 3-glycidoxypropyltrimethoxysilane (Surfactant (D)) D1: Nonionic surfactant (manufactured by Daiichi Pharmaceutical Co., Ltd., product name "Noigen EA-87") D2: Anionic surfactant (manufactured by Daiichi Pharmaceutical Co., Ltd., product name "Plysurf A208F")

[0136] The resulting pressure-sensitive adhesive or pressure-sensitive adhesive sheet was subjected to the following measurements and evaluations.

[0137] (Evaluation of gel fraction of adhesive) The adhesives prepared in the Examples and Comparative Examples were cut to a size of 80 mm x 80 mm, and the adhesive layer was wrapped in a polyester mesh (product name: Tetron Mesh #200), and the mass was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated M1.

[0138] Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The mesh 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 mesh was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated M2. The gel fraction was calculated using the obtained M1 and M2 using the following formula. The results are shown in Table 2. Gel fraction (%) = (M2 / M1) × 100

[0139] (Measurement of adhesive strength) The release sheet R2 was peeled off from the adhesive sheets obtained in the Examples and Comparative Examples, and the exposed adhesive was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160", thickness: 100 μm) having an easy-adhesion layer to obtain a release sheet R1 / adhesive / PET film laminate. The resulting laminate was cut into a 25 mm wide, 100 mm long sample.

[0140] The release sheet R1 was peeled off from the sample at 23°C and 50% relative humidity, and the exposed adhesive was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). After leaving the sample at 23°C and 50% relative humidity for 24 hours, the adhesive strength (N / 25 mm) was measured using a tensile tester (manufactured by Orientec Co., Ltd., model "Tensilon") at a peel speed of 300 mm / min and a peel angle of 180 degrees. Measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 2.

[0141] (Release strength of release sheet) The peel strength of release sheet R2 (light release type release sheet) was measured as follows. The resulting pressure-sensitive adhesive sheet was cut into 25 mm widths to prepare a measurement sample. The surface of the measurement sample opposite the release-treated surface of release sheet R1 was fixed to a hard support plate with double-sided tape to prepare a laminate having a configuration of "release sheet R2 / adhesive / release sheet R1 / double-sided tape / hard support plate." Using a universal tensile tester (manufactured by Shimadzu Corporation, device name "Autograph (registered trademark) AG-IS"), release sheet R2 was peeled from the laminate at a measurement distance of 100 mm, a peel angle of 180°, and a peel speed of 0.3 m / min, and the load at this time was measured. The average value of the load over an 80 mm measurement distance, excluding the loads at the first 10 mm and the last 10 mm of the measurement distance, was used as the peel strength of release sheet R2. The results are shown in Table 2.

[0142] The release force of release sheet R1 (heavy release type release sheet) was measured as follows. Release sheet R2 was peeled from the obtained adhesive sheet, and the easy-adhesion side of PET (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360," thickness: 50 μm) with an easy-adhesion layer was attached to the exposed surface of the adhesive by thermal lamination (70°C, 1 m / min) to prepare a laminate sample. The obtained laminate sample was cut into a width of 25 mm to prepare a measurement sample. Next, the back of the easy-adhesion PET of the measurement sample was fixed to a hard support plate with double-sided tape to prepare a laminate with a configuration of "release sheet R1 / adhesive / easy-adhesion PET / double-sided tape / hard support."

[0143] The release sheet R1 of this laminate was peeled off using a universal tensile tester (Shimadzu Corporation, device name "Autograph (registered trademark) AG-IS") at a measurement distance of 100 mm, a peel angle of 180°, and a peel speed of 0.3 m / min, and the load at this time was measured. Of the measured loads, the loads at the first 10 mm and the last 10 mm of the measurement distance were excluded, and the average value of the load over 80 mm was taken as the peel strength of the release sheet R1. The results are shown in Table 2.

[0144] (Measurement of total light transmittance) The adhesive of the pressure-sensitive adhesive sheet obtained in the examples and comparative examples was attached to glass to prepare a measurement sample. After background measurement was performed on the glass, the total light transmittance (%) of the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7361-1:1997. The results are shown in Table 2.

[0145] (Haze value measurement) The haze values ​​(%) of the adhesives of the pressure-sensitive adhesive sheets obtained in the examples and comparative examples were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7136: 2000. The obtained haze values ​​(%) are shown in Table 2.

[0146] (Haze value measurement after wet heat test) Release sheet R2 was peeled off from the resulting adhesive sheet, and an ITO layer of a polyethylene terephthalate film (ITO-PET film, manufactured by Oike Industries Co., Ltd., thickness: 125 μm) with a tin-doped indium oxide (ITO) layer on one side was laminated to the exposed surface of the adhesive. Next, release sheet R1 was peeled off, and the ITO layer of another ITO-PET film was laminated to the exposed surface of the adhesive, yielding a laminate with an "ITO-PET film / adhesive / ITO-PET film" configuration. The resulting laminate was stored under humid heat conditions of 85°C and 85% relative humidity for 72 hours. After storage, the laminate was removed and allowed to stand for 1 hour. The haze value (%) of the laminate after standing was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7136:2000. The haze values ​​(%; humid heat haze) obtained after the humid heat test are shown in Table 2.

[0147] (storage modulus of adhesive) The pressure-sensitive adhesives prepared in the examples and comparative examples were laminated in multiple layers to form a 0.6 mm thick laminate, and a cylindrical object with a diameter of 8 mm (height of 0.6 mm) was punched out from the resulting pressure-sensitive adhesive laminate to prepare a sample for measuring storage modulus.

[0148] The storage modulus of the measurement samples was measured in accordance with JIS K7244-6 using a viscoelasticity measuring device (manufactured by Anton-Paar, model "MCR302") by the torsional shear method under the conditions of a measurement temperature range of -20 to 140°C, a measurement frequency of 1 Hz, and a heating rate of 4°C / min. From the measurement results, the storage moduli at -20°C, 23°C, and 70°C were calculated. The results are shown in Table 2.

[0149] (Evaluation of unevenness-following ability) On the surface of a glass plate (NSG Precision, product name "Corning Glass Eagle XG", 90 mm length x 50 mm width x 0.5 mm thickness), ultraviolet-curable ink (Teikoku Ink Co., Ltd., product name "POS-911 Sumi") was screen-printed in the shape of a picture frame (outer dimensions: 90 mm length x 50 mm width, 5 mm width). Then, ultraviolet light (80 W / cm 2The printed ultraviolet-curable ink was cured using a laser beam (two metal halide lamps, lamp height 15 cm, belt speed 10-15 m / min) to produce a stepped glass plate having steps (convexoconcave) caused by the printed layer (step height: 20 μm).

[0150] The release sheet R2 was peeled off from the adhesive sheets produced in the Examples and Comparative Examples, and the exposed adhesive was attached to the adhesive layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160", thickness: 100 μm) having an adhesive layer. Next, the release sheet R1 was peeled off to expose the adhesive, and the adhesive was laminated to a stepped glass plate using a laminator (manufactured by Fujipla Co., Ltd., product name "LPD3214") so that the adhesive covered the entire frame-shaped print. The sheet was then autoclaved for 20 minutes under conditions of 50 ° C and 0.5 MPa, and left for 24 hours at normal pressure, 23 ° C, and relative humidity of 50%.

[0151] The interface between the adhesive and the stepped glass plate near the step was visually inspected for air bubbles or peeling, and the conformability to the unevenness was evaluated according to the following criteria. A conformability to the unevenness of the adhesive of "○" is preferable. The results are shown in Table 2. ○: Conforms to uneven surfaces, no bubbles or peeling is observed ×: Bubbles and peeling were observed at the interface.

[0152] (Evaluation of blister resistance) The release sheet R2 was peeled off from the adhesive sheets obtained in the Examples and Comparative Examples, and the exposed adhesive was attached to an ITO vapor-deposited film (manufactured by Oike Kogyo Co., Ltd., product name "Tetlite TCFKH150NMH2-125-U6 / T2"). Furthermore, the release sheet R1 was peeled off from the adhesive sheet, and the exposed adhesive was attached to the polycarbonate layer side of a resin plate (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Iupilon Sheet MR58U," containing UV absorbers, thickness: 0.8 mm) consisting of a polycarbonate resin layer laminated with a polymethyl methacrylate resin layer, to obtain an evaluation sample. The evaluation sample was then autoclaved at 50°C and 0.5 MPa for 20 minutes.

[0153] The evaluation sample was left at normal pressure, 23°C, and 50% relative humidity for 12 hours, and then stored under high-temperature, high-humidity conditions of 85°C and 85% relative humidity for 72 hours. The condition of the interface between the adhesive and the adherend was then visually inspected, and blister resistance was evaluated according to the following criteria. A blister resistance rating of "Good" is preferred. The results are shown in Table 2. ○: No bubbles or peeling are observed at the interface ×: Bubbles and peeling were observed at the interface.

[0154] (Evaluation of bending resistance) In an environment of 23°C and 50% relative humidity, the release sheet R2 was peeled from the pressure-sensitive adhesive sheets prepared in the Examples and Comparative Examples, and the exposed adhesive was bonded to one side of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 38 μm, Young's modulus: 0.2 GPa). Next, the release sheet R1 was peeled off, and the exposed adhesive was bonded to one side of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 100 μm, Young's modulus: 0.2 GPa). Then, after applying pressure of 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., the laminate was left at 23°C and 50% relative humidity for 24 hours. The resulting laminate having a "PET film / adhesive / PET film" configuration was cut into a 50 mm width and 200 mm length, which was used as a sample.

[0155] The obtained sample was repeatedly bent at 23°C under the following conditions using a durability tester (manufactured by Yuasa System Co., Ltd., device name "Surface condition no-load U-shaped stretch tester model: DLDMLH-FS"). After the test, the interface between the adhesive and the adherend at the bent portion was visually inspected for any lifting or peeling, and the repeated bending resistance was evaluated according to the following criteria. A bending resistance of "○" is preferable. The results are shown in Table 2. <Test conditions> Bending direction: Bending so that the 38 μm thick PET film side faces Minimum bending diameter: 4mmφ Number of flexes: 200,000 Bending speed: 60rpm <Evaluation criteria for repeated bending resistance> ○: No peeling or lifting is observed at the interface ×: Peeling was observed at the interface

[0156] (Evaluation of resistance to wet heat whitening) The adhesive of the pressure-sensitive adhesive sheet prepared in the Examples and Comparative Examples was sandwiched between a 1.1 mm thick alkali-free glass plate and the same resin plate as used in the evaluation of blister resistance, and this was used as a sample. The obtained sample was autoclaved at 50°C and 0.5 MPa for 20 minutes, and then left at normal pressure, 23°C, and 50% RH for 24 hours.

[0157] The haze value (haze value before durability test; %) of each of the above samples was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7136:2000.

[0158] Next, the above sample was stored under humid heat conditions of 85°C and relative humidity of 85% for 120 hours (durability test), and then left at room temperature and humidity of 23°C and relative humidity of 50% for 6 hours. The haze value (haze value after durability test; %) of the sample was measured in the same manner as above.

[0159] Based on the difference in the haze value measured before and after the durability test, the resistance to wet heat whitening was evaluated according to the following criteria. A: The difference in haze value is less than 1.0%. B: The difference in haze value is 1.0% or more and 5% or less. C...The difference in haze value is more than 5%.

[0160] [Table 2]

[0161] From Table 2, it was confirmed that the pressure-sensitive adhesive sheets of Examples 1 to 5 were able to achieve both bending resistance and resistance to wet heat whitening. Furthermore, it was confirmed that they also had excellent conformability to irregularities and blister resistance. [Industrial Applicability]

[0162] The pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, to attach a flexible member. [Explanation of symbols]

[0163] 1...Adhesive sheet 10...Adhesive 11...First release sheet 12...Second release sheet 2...Flexible member laminate 21...First flexible member 22...Second flexible member 3. Flexible devices 31...Cover film 32...First adhesive 33...Polarizing film 34...Second adhesive 35...Touch sensor film 36...Third adhesive 37...Organic EL element 38...Fourth adhesive 39...TFT substrate

Claims

1. An adhesive sheet having an adhesive for bonding a first flexible member and a second flexible member, The adhesive contains a surfactant, A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive has a gel fraction of 20% or more and less than 85%.

2. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive has a storage modulus at -20°C of 0.01 MPa or more and 18 MPa or less.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive.

4. The pressure-sensitive adhesive sheet according to claim 3 , wherein the acrylic pressure-sensitive adhesive has a crosslinked structure containing at least a (meth)acrylic acid ester polymer and a crosslinking agent.

5. The pressure-sensitive adhesive sheet according to claim 1, wherein the surfactant is at least one selected from the group consisting of a nonionic surfactant and an anionic surfactant.

6. A flexible member laminate comprising a first flexible member, a second flexible member, and an adhesive that bonds the first flexible member and the second flexible member to each other, A flexible material laminate, wherein the adhesive is the adhesive contained in the adhesive sheet according to claim 1 .

7. A flexible device comprising the flexible member laminate according to claim 6.

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