Adhesive for repeated bending device, adhesive sheet, repeated bending laminate member and repeated bending device

Abstract

To provide an adhesive for repeated bending device that suppresses occurrence of floating or peeling and is excellent in restoring property from a bending state, even when placed in a bending state for a long time by applying to a repeated bending device.SOLUTION: An adhesive for a repeated bending device for adhering one bending member constituting a device that is repeatedly bent and other bending member, in which when a creep compliance value measured after 3757 second by continuing applying stress of 3000 Pa to the adhesive is set to maximum compliance J(t)max (MPa-1), and the creep compliance value measured after 3757 seconds with the stress applied to the relevant adhesive of 0 Pa is set to J(t)min (MPa-1), and the creep restoring rate calculated from the following formula (I) is 70% or larger. Creep restoring rate (%)=(1-J(t)min / J(t)max)×100 (I).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive and an adhesive sheet for a device that is repeatedly bent, as well as a repeatedly bent laminated member and a repeatedly bent device. [Background technology]

[0002] In recent years, flexible displays have been proposed as displays for electronic devices, which are a type of device. In addition to displays that are curved only once, repeatedly bent displays that can be repeatedly bent (folded) have also been proposed.

[0003] In the above-mentioned repeatedly bendable display, it is considered that one bendable member (flexible member) constituting the flexible display and another flexible member are bonded together by an adhesive layer of an adhesive sheet. However, when a conventional adhesive sheet is used in a repeatedly bendable display, problems arise in that lifting or peeling occurs at the interface between the adhesive layer and the adherend.

[0004] Patent Document 1 discloses a pressure-sensitive adhesive that aims to prevent the pressure-sensitive adhesive layer from lifting or peeling even when repeatedly bent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-108555 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, in the above-mentioned repeatedly bent display, it may be fixed in a bent state for a long period of time. When the pressure-sensitive adhesive sheet described in Patent Document 1 is used in a repeatedly bent display for such an application, lifting or peeling may occur at the interface between the pressure-sensitive adhesive layer and the adherend. Furthermore, even after being released from the bent state, deformation may occur in the pressure-sensitive adhesive layer, causing the flexible display to remain bent significantly and become solidified in that bent state.

[0007] The present invention has been made in consideration of the above-described circumstances, and aims to provide an adhesive and adhesive sheet for repeatedly flexed devices that suppress lifting and peeling even when applied to a repeatedly flexed device and left in a flexed state for a long period of time, and that have excellent recovery properties from a flexed state, as well as a repeatedly flexed laminate member and a repeatedly flexed device that suppress lifting and peeling even when left in a flexed state for a long period of time, and that have excellent recovery properties from a flexed state. [Means for solving the problem]

[0008] In order to achieve the above object, first, the present invention provides a pressure-sensitive adhesive for repeatedly bending devices, which is used to bond one flexible member and another flexible member that constitute a device that is repeatedly bent, and which is characterized in that a creep compliance value measured after 3757 seconds of continuously applying a stress of 3000 Pa to the pressure-sensitive adhesive is defined as a maximum creep compliance J(t) max (MPa -1 ) and then the stress applied to the adhesive is set to 0 Pa, and the creep compliance value measured after 3757 seconds is taken as the minimum creep compliance J(t) min (MPa -1 ) and the creep recovery rate calculated from the following formula (I) is 70% or more (Invention 1). Creep recovery rate (%) = (1 - J(t) min / J(t) max )×100 …(I)

[0009] According to the above invention (Invention 1), when a laminate formed by bonding one flexible member and another flexible member with a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive is placed in a bent state, the pressure-sensitive adhesive layer itself is unlikely to deform, and after being released from the bent state, the laminate is likely to return to its pre-bending shape over time. As a result, even when the laminate is placed in a bent state for a long period of time, lifting or peeling is unlikely to occur at the interface between the pressure-sensitive adhesive layer and the adherend, and the laminate has excellent recovery properties from the bent state.

[0010] In the above invention (invention 1), the pressure-sensitive adhesive is preferably an acrylic pressure-sensitive adhesive (invention 2).

[0011] Secondly, the present invention provides an adhesive sheet having an adhesive layer for bonding one flexible member and another flexible member that constitute a device that is repeatedly bent, characterized in that the adhesive layer is made of the adhesive for repeatedly bent devices (Inventions 1 and 2) (Invention 3).

[0012] In the above invention (invention 3), it is preferable that the adhesive strength of the pressure-sensitive adhesive sheet to polyimide is 1.0 N / 25 mm or more (invention 4).

[0013] In the above inventions (Inventions 3 and 4), the adhesive strength of the pressure-sensitive adhesive sheet to the gas barrier layer of the gas barrier film is preferably 3.0 N / 25 mm or more (Invention 5).

[0014] In the above inventions (Inventions 3 to 5), the thickness of the pressure-sensitive adhesive layer is preferably 1 μm or more and 300 μm or less (Invention 6).

[0015] In the above inventions (Inventions 3 to 6), it is preferable that the pressure-sensitive adhesive sheet has two release sheets, and the pressure-sensitive adhesive layer is sandwiched between the release sheets so as to contact the release surfaces of the two release sheets (Invention 7).

[0016] Thirdly, the present invention provides a repeatedly flexed laminated member comprising one flexible member and another flexible member that constitute a device that is repeatedly flexed, and an adhesive layer that bonds the one flexible member and the other flexible member to each other, wherein the adhesive layer is made of the adhesive for repeatedly flexed devices (Inventions 1 and 2) (Invention 8).

[0017] Fourthly, the present invention provides a repeatedly flexed device (Invention 9) comprising the repeatedly flexed laminated member (Invention 8). [Effects of the Invention]

[0018] The pressure-sensitive adhesive and pressure-sensitive adhesive sheet for repeatedly flexed devices according to the present invention are less likely to cause lifting or peeling at the interface between the pressure-sensitive adhesive layer and the adherend, and are also excellent in recovery from the flexed state, even when applied to a repeatedly flexed device and left in a flexed state for a long period of time.Furthermore, the repeatedly flexed laminated member and repeatedly flexed device according to the present invention are less likely to cause lifting or peeling at the interface between the pressure-sensitive adhesive layer and the adherend, and are also excellent in recovery from the flexed state, even when left in a flexed state for a long period of time. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 2] FIG. 1 is a cross-sectional view of a repeatedly bent laminated member according to an embodiment of the present invention. [Figure 3] FIG. 1 is an explanatory diagram (side view) illustrating a static bending test. [Figure 4] FIG. 1 is an explanatory diagram (side view) illustrating the amount of deformation of a test piece as a test result of a bending test. [Figure 5] 1 is a cross-sectional view of a repeated bending device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described. [Adhesive for repeated bending devices] The pressure-sensitive adhesive for a repeatedly flexing device according to this embodiment (hereinafter, sometimes simply referred to as "pressure-sensitive adhesive") is an adhesive for bonding one flexible member and another flexible member that constitute a repeatedly flexing device. The repeatedly flexing device and the flexible member will be described later.

[0021] The pressure-sensitive adhesive according to this embodiment has a creep compliance value measured 3757 seconds after continuously applying a stress of 3000 Pa to the pressure-sensitive adhesive (3757 seconds after the start of application of the stress of 3000 Pa) as the maximum creep compliance J(t) max (MPa -1 ) and then the stress applied to the adhesive is set to 0 Pa, and the creep compliance value measured 3757 seconds later (3757 seconds after the applied stress is set to 0 Pa) is taken as the minimum creep compliance J(t) min (MPa -1 ) and the creep recovery rate calculated from the following formula (I) is 70% or more. Creep recovery rate (%) = (1 - J(t) min / J(t) max )×100 …(I) Details of the method for measuring creep compliance J(t) are as shown in the test examples described below.

[0022] When a laminate formed by bonding one flexible member to another flexible member with a pressure-sensitive adhesive layer is placed in a bent state, the pressure-sensitive adhesive layer is constantly under stress. If this state continues for a long period of time, even after the bent state is released, the pressure-sensitive adhesive layer deforms, causing the laminate to harden in the bent state and making it difficult to restore to its original shape. However, the pressure-sensitive adhesive according to this embodiment has a creep recovery rate of 70% or more, which makes the pressure-sensitive adhesive layer itself less likely to deform and, after being released from a bent state, easily restores to its pre-bent shape over time. As a result, even when the laminate is placed in a bent state for a long period of time, lifting or peeling is unlikely to occur at the interface between the pressure-sensitive adhesive layer and the adherend (flexion resistance effect), and the laminate exhibits excellent recovery from the bent state (recovery effect). These effects may be referred to hereinafter as "flexion resistance and recovery effect." This excellent flexion resistance and recovery effect is also fully exhibited when the flexible member in the laminate is a polyimide film or a gas barrier film, or a laminate containing them. Furthermore, the above-mentioned bending resistance effect is fully exhibited even when the film is bent in a low-temperature environment (for example, −20° C.) where interfacial peeling is particularly likely to occur.

[0023] From the viewpoint of the flex resistance and recovery effect, the creep recovery rate must be 70% or more, preferably 75% or more, particularly preferably 80% or more, and even more preferably 85% or more. The upper limit of the creep recovery rate is not particularly limited, but is usually preferably 99% or less, particularly preferably 95% or less, and even more preferably 90% or less.

[0024] Maximum creep compliance J(t) of the adhesive according to this embodiment max is the lower limit, 10 MPa -1 Preferably, it is 50 MPa or more. -1 More preferably, it is 90 MPa or more. -1 It is preferable that the pressure is 110 MPa or more, and more preferably 110 MPa or more. -1 It is preferable that the maximum creep compliance J(t) is equal to or greater than this. This results in a pressure-sensitive adhesive with more appropriate stress relaxation properties. maxThe upper limit is usually 2000 MPa from the viewpoint of the cohesive strength of the adhesive. -1 It is preferable that the pressure is not more than 1000 MPa. -1 It is preferable that the resistance is not more than 500 MPa. -1 It is preferable that:

[0025] In addition, the minimum creep compliance J(t) of the adhesive according to this embodiment min The upper limit is 600MPa. -1 Preferably, it is 300 MPa or less. -1 More preferably, it is 100 MPa or less, and particularly 100 MPa or less. -1 It is preferable that the pressure is not more than 80 MPa. -1 It is preferable that the minimum creep compliance J(t) is less than or equal to 1. This results in a pressure-sensitive adhesive with superior recovery properties. min The lower limit is not particularly limited, but is usually 0 MPa. -1 More preferably, it is 5 MPa or more. -1 It is preferable that the pressure is 10 MPa or more, and more preferably 10 MPa or more. -1 It is preferable that this is equal to or greater than this.

[0026] The type of pressure-sensitive adhesive according to the present embodiment is not particularly limited as long as it satisfies the above-mentioned physical properties, and may be, for example, any of an acrylic pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyurethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, etc. Furthermore, the pressure-sensitive adhesive may be any of an emulsion type, a solvent-based type, or a solventless type, and may be any of a cross-linked type or a non-cross-linked type. Among these, an acrylic pressure-sensitive adhesive is preferred because it easily satisfies the above-mentioned physical properties and is also excellent in adhesive properties, optical properties, etc., and a solvent-based acrylic pressure-sensitive adhesive is particularly preferred.

[0027] Specifically, the pressure-sensitive adhesive according to this embodiment is preferably an adhesive obtained 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). Such an adhesive is likely to satisfy the above-mentioned physical properties and also likely to provide good adhesive strength. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

[0028] (1) Components of adhesive composition P (1-1) (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 (reactive functional group-containing monomer).

[0029] The (meth)acrylic acid ester polymer (A) can exhibit desirable adhesiveness by containing a (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. 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.

[0030] 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, 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 the creep recovery rate mentioned above, (meth)acrylic acid esters having an alkyl group containing 1 to 8 carbon atoms are preferred, and (meth)acrylic acid esters having an alkyl group containing 4 to 8 carbon atoms are particularly preferred. Specifically, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, with n-butyl acrylate and 2-ethylhexyl acrylate being particularly preferred. These may be used alone or in combination of two or more.

[0031] The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, 60% by mass or more, more preferably 80% by mass or more, particularly preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 98% by mass or more of a (meth)acrylic acid alkyl ester having an alkyl group containing 1 to 20 carbon atoms. By containing the (meth)acrylic acid alkyl ester in an amount equal to or greater than the above range, it is possible to impart suitable adhesiveness to the (meth)acrylic acid ester polymer (A) and to easily adjust the creep recovery rate to a higher value. Furthermore, the (meth)acrylic acid alkyl ester having an alkyl group containing 1 to 20 carbon atoms is preferably contained in an amount equal to or less than 99.9% by mass, particularly preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. By containing the (meth)acrylic acid alkyl ester in an amount equal to or less than the above range, it is possible to incorporate desired amounts of other monomer components into the (meth)acrylic acid ester polymer (A).

[0032] The (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and reacts with the crosslinking agent (B) described below via the reactive functional group derived from the reactive functional group-containing monomer, thereby forming a crosslinked structure (three-dimensional network structure), and a pressure-sensitive adhesive having the desired cohesive strength is obtained. The pressure-sensitive adhesive is likely to satisfy the creep recovery rate described above.

[0033] Preferred examples of the reactive functional group-containing monomer contained in the (meth)acrylic acid ester polymer (A) as a monomer unit constituting the polymer 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), a monomer having an amino group in the molecule (amino group-containing monomer), etc. These reactive functional group-containing monomers may be used alone or in combination of two or more.

[0034] Among the reactive functional group-containing monomers, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred. Hydroxyl group-containing monomers make it easy to adjust the crosslink density, and therefore, tend to satisfy the creep recovery rate described above.

[0035] 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 ease of satisfying the creep recovery rate mentioned above, 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, 4-hydroxybutyl (meth)acrylate, and the like are preferred, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0036] 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.

[0037] The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a reactive functional group-containing monomer in an amount of at least 0.1 mass%, more preferably at least 0.5 mass%, and even more preferably at least 1.0 mass%. The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a reactive functional group-containing monomer in an amount of at most 10 mass%, more preferably at most 7 mass%, more preferably at most 5 mass%, and even more preferably at most 2 mass%. When the (meth)acrylic acid ester polymer (A) contains, as a monomer unit, the reactive functional group-containing monomer in the above-mentioned amount, the crosslinking reaction with the crosslinking agent (B) results in an appropriate cohesive strength of the resulting pressure-sensitive adhesive, making it easier to satisfy the creep recovery rate requirement described above.

[0038] 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.

[0039] Here, "free of carboxyl group-containing monomers" means that the carboxyl group-containing monomers are substantially not contained, and in addition to not containing any carboxyl group-containing monomers at all, the carboxyl group-containing monomers may be contained to an extent that the carboxyl groups do not cause corrosion of the transparent conductive film, metal wiring, etc. Specifically, the carboxyl group-containing monomers may be contained 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, as monomer units.

[0040] The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. The other monomers are preferably monomers that do not contain reactive functional groups, so as not to inhibit the aforementioned action of the reactive functional group-containing monomer. Examples of such monomers include non-reactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, (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.

[0041] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0042] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 500,000 or more, more preferably 600,000 or more, particularly preferably 700,000 or more, and even more preferably 800,000 or more. The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 1,700,000 or less, more preferably 1,500,000 or less, and particularly preferably 1,300,000 or less. When the weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is within the above range, the aforementioned creep recovery rate is more likely to be satisfied. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0043] 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.

[0044] (1-2) Crosslinking agent (B) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) and forms a three-dimensional network structure when the pressure-sensitive adhesive composition P containing the crosslinking agent (B) is heated or otherwise triggered, thereby improving the cohesive strength of the resulting pressure-sensitive adhesive and making it easier to satisfy the creep recovery rate described above.

[0045] The crosslinking agent (B) may be any agent that reacts with the reactive groups 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 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.

[0046] 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 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. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

[0047] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably 0.01 parts by mass or more, particularly preferably 0.06 parts by mass or more, and even more preferably 0.10 parts by mass or more, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). The content is preferably 1.50 parts by mass or less, more preferably 0.80 parts by mass or less, particularly preferably 0.60 parts by mass or less, and even more preferably 0.40 parts by mass or less. When the content of the crosslinking agent (B) is within the above range, the aforementioned creep recovery rate is more likely to be satisfied.

[0048] (1-3) Various additives If desired, various additives commonly used in acrylic pressure-sensitive adhesives, such as a silane coupling agent, an ultraviolet absorber, an antistatic agent, a tackifier, an antioxidant, a light stabilizer, a softener, a filler, a refractive index adjuster, etc., can be added to the pressure-sensitive adhesive composition P. Note that polymerization solvents and dilution solvents described below are not included in the additives constituting the pressure-sensitive adhesive composition P.

[0049] The pressure-sensitive adhesive composition P preferably contains the above-mentioned silane coupling agent, which improves the adhesion of the resulting pressure-sensitive adhesive layer to the flexible member that is the adherend, resulting in more preferable adhesive strength.

[0050] The silane coupling agent is preferably 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.

[0051] Examples of such silane coupling agents include silicon compounds containing a polymerizable unsaturated group, such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercaptopropyltrimethoxysilane, such as 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane. Examples of such compounds include capryl group-containing silicon compounds, 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 compounds 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.

[0052] The content of the silane coupling agent in the pressure-sensitive adhesive composition P is preferably 0.01 parts by mass or more, particularly preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). Furthermore, the content is preferably 1 part by mass or less, particularly preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less. By having the content of the silane coupling agent within the above range, the resulting pressure-sensitive adhesive layer has improved adhesion to the flexible member that is the adherend, resulting in greater adhesive strength.

[0053] (2) Preparation of adhesive composition P The adhesive composition P can be produced by producing a (meth)acrylic acid ester polymer (A), mixing the resulting (meth)acrylic acid ester polymer (A) with a crosslinking agent (B), and adding additives as desired.

[0054] The (meth)acrylic acid ester polymer (A) can be produced 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) is preferably carried out by a solution polymerization method, optionally using a polymerization initiator. Polymerizing the (meth)acrylic acid ester polymer (A) by a solution polymerization method facilitates increasing the molecular weight of the resulting polymer and adjusting the molecular weight distribution, and also makes it possible to reduce the production of low molecular weight compounds. Therefore, the pressure-sensitive adhesive is less likely to become biased due to long-term bending, resulting in superior recovery from a bent state.

[0055] Examples of the polymerization solvent used in the solution polymerization method include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone, and two or more of these may be used in combination.

[0056] Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of the 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].

[0057] 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.

[0058] 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.

[0059] Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B), and optionally additives and a dilution solvent, are added to the solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a pressure-sensitive adhesive composition P (coating solution) diluted with the solvent.

[0060] In addition, when any of the above components is used in a solid state, or when precipitation occurs when the component is mixed with other components in an undiluted state, the component may be dissolved or diluted in advance alone in a dilution solvent and then mixed with the other components.

[0061] 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.

[0062] The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within a 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 becomes 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.

[0063] (3) Manufacture of adhesives The pressure-sensitive adhesive according to the present embodiment is preferably obtained by crosslinking the pressure-sensitive adhesive composition P. The crosslinking of the pressure-sensitive adhesive composition P can usually be carried out by a heat treatment. Note that 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.

[0064] The heating temperature for the heat treatment is preferably 50 to 150° C., particularly preferably 70 to 120° C. The heating time is preferably 10 seconds to 10 minutes, particularly preferably 50 seconds to 2 minutes.

[0065] 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.

[0066] By the above heat treatment (and curing), the (meth)acrylic acid ester polymer (A) is sufficiently crosslinked via the crosslinking agent (B) to form a crosslinked structure, thereby obtaining a pressure-sensitive adhesive.

[0067] [Adhesive sheet] The adhesive sheet of this embodiment has an adhesive layer for bonding one flexible member and another flexible member that constitute a repeatedly bending device, and the adhesive layer is made of the adhesive described above.

[0068] FIG. 1 shows a specific configuration of an example of the pressure-sensitive adhesive sheet according to this embodiment. 1, an adhesive sheet 1 according to one embodiment is composed of two release sheets 12a and 12b and an adhesive layer 11 sandwiched between the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. 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 being subjected to a release treatment.

[0069] (1) Components (1-1) Adhesive layer The adhesive layer 11 is made of the adhesive according to the embodiment described above, and is preferably made of an adhesive obtained by crosslinking the adhesive composition P.

[0070] The thickness of the pressure-sensitive adhesive layer 11 in the pressure-sensitive adhesive sheet 1 according to the present embodiment (measured in accordance with JIS K7130) is preferably 1 μm or more, more preferably 5 μm or more, particularly preferably 10 μm or more, and even more preferably 15 μm or more. When the thickness of the pressure-sensitive adhesive layer 11 has the above-mentioned lower limit, the desired adhesive strength is easily exerted, and lifting or peeling at the interface between the pressure-sensitive adhesive layer and the adherend is less likely to occur. Furthermore, the thickness of the pressure-sensitive adhesive layer 11 has an upper limit of preferably 300 μm or less, more preferably 150 μm or less, particularly preferably 90 μm or less, and from the viewpoint of obtaining a thinner repeatedly flexed device, it is even more preferably 40 μm or less. When the thickness of the pressure-sensitive adhesive layer 11 has the above-mentioned upper limit, the stress applied to the pressure-sensitive adhesive layer is relatively small, making it easier to restore from a flexed state, and the adhesion between the pressure-sensitive adhesive layer and the adherend is easily maintained, resulting in better flex resistance and restoration effect. The pressure-sensitive adhesive layer 11 may be formed as a single layer, or may be formed by laminating multiple layers.

[0071] The total light transmittance (measured in accordance with JIS K7361-1:1997) of the pressure-sensitive adhesive layer 11 in the pressure-sensitive adhesive sheet 1 according to this embodiment is preferably 80% or more, more preferably 90% or more, particularly preferably 95% or more, and even more preferably 99% or more. When the total light transmittance is within the above range, the transparency is high, making the sheet suitable for optical applications (for repeated bending displays).

[0072] (1-2) Release sheet Release sheets 12a and 12b protect adhesive layer 11 until adhesive sheet 1 is used, and are peeled off when adhesive sheet 1 (adhesive layer 11) is to be used. In adhesive sheet 1 according to this embodiment, one or both of release sheets 12a and 12b are not necessarily required.

[0073] Examples of materials that can be used as the release sheets 12a and 12b 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 can also be used.

[0074] The release surfaces of the release sheets 12a and 12b (particularly the surfaces in contact with the pressure-sensitive adhesive layer 11) 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. Preferably, one of the release sheets 12a and 12b is a heavy-release type release sheet with a high release strength, and the other is a light-release type release sheet with a low release strength.

[0075] There are no particular restrictions on the thickness of the release sheets 12a and 12b, but it is usually about 20 to 150 μm.

[0076] (2) Adhesive strength The adhesive strength of the pressure-sensitive adhesive sheet 1 according to this embodiment to polyimide is preferably 1.0 N / 25 mm or more as a lower limit, more preferably 3.0 N / 25 mm or more, particularly preferably 5.0 N / 25 mm or more, and even more preferably 6.5 N / 25 mm or more. When the lower limit of the adhesive strength of the pressure-sensitive adhesive sheet 1 to polyimide is as described above, even when a polyimide film or the like is used as the adherend, lifting or peeling is less likely to occur at the interface between the pressure-sensitive adhesive layer and the adherend when the adherend is left in a flexed state for a long period of time. On the other hand, the upper limit of the adhesive strength is not particularly limited, but reworkability may be required. From this perspective, the adhesive strength is preferably 30.0 N / 25 mm or less, more preferably 25.0 N / 25 mm or less, and particularly preferably 20.0 N / 25 mm or less. 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, and the specific test method is as shown in the test examples described below.

[0077] The adhesive strength of the pressure-sensitive adhesive sheet 1 according to the present embodiment to a gas barrier layer of a gas barrier film (e.g., a gas barrier film having a gas barrier layer made of modified polysilazane) is preferably 3.0 N / 25 mm or more as a lower limit, more preferably 4.0 N / 25 mm or more, particularly preferably 5.0 N / 25 mm or more, and even more preferably 7.0 N / 25 mm or more. When the pressure-sensitive adhesive sheet 1 has the above-mentioned lower limit of the adhesive strength to a gas barrier film, even when the gas barrier film is used as an adherend, lifting or peeling is less likely to occur at the interface between the pressure-sensitive adhesive layer and the adherend when the gas barrier film is left in a flexed state for a long period of time. On the other hand, there is no particular upper limit to the adhesive strength, but reworkability may be required. From this perspective, the adhesive strength is preferably 30.0 N / 25 mm or less, more preferably 25.0 N / 25 mm or less, and particularly preferably 20.0 N / 25 mm or less.

[0078] The adhesive strength of the pressure-sensitive adhesive sheet 1 according to the present embodiment to soda-lime glass is preferably 5.0 N / 25 mm or more, more preferably 6.0 N / 25 mm or more, particularly preferably 7.0 N / 25 mm or more, and even more preferably 8.0 N / 25 mm or more. When the adhesive strength of the pressure-sensitive adhesive sheet 1 to soda-lime glass is within the above range, lifting or peeling is less likely to occur at the interface between the pressure-sensitive adhesive layer and the adherend, even when the adherend is made of various materials. On the other hand, the upper limit of the adhesive strength is not particularly limited, but is generally preferably 50.0 N / 25 mm or less, more preferably 40.0 N / 25 mm or less. From the viewpoint of reworkability, which allows the pressure-sensitive adhesive sheet to be reattached in the event of a misapplication, 30.0 N / 25 mm or less is particularly preferred, and 20.0 N / 25 mm or less is even more preferred.

[0079] (3) Manufacturing of adhesive sheets As an example of manufacturing the adhesive sheet 1, a case where the adhesive composition P is used will be described. A coating solution of the adhesive composition P is applied to the release surface of one of the release sheets 12a (or 12b), and a heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, after which the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. If a curing period is required, a curing period is allowed, or if no curing period is required, the coating layer becomes the adhesive layer 11 as is. In this way, the adhesive sheet 1 is obtained. The conditions for the heat treatment and curing are as described above.

[0080] In another manufacturing example of the pressure-sensitive adhesive sheet 1, a coating liquid of the pressure-sensitive adhesive composition P is applied to the release surface of one release sheet 12a, followed by heat treatment to thermally crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a release sheet 12a with a coating layer. Furthermore, a coating liquid of the pressure-sensitive adhesive composition P is applied to the release surface of the other release sheet 12b, followed by heat treatment to thermally crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a release sheet 12b with a coating layer. The release sheet 12a with a coating layer and the release sheet 12b with a coating layer are then bonded together so that the two coating layers are in contact with each other. If a curing period is required, a curing period is allowed; if no curing period is required, the laminated coating layers become the pressure-sensitive adhesive layer 11 as is. This manufacturing example allows stable manufacturing even when the pressure-sensitive adhesive layer 11 is relatively thick.

[0081] The coating solution of the pressure-sensitive adhesive composition P can be applied by, for example, bar coating, knife coating, roll coating, blade coating, die coating, gravure coating, or the like.

[0082] [Repeatedly bent laminated member] As shown in Figure 2, the repeatedly bent laminated member 2 of this embodiment is composed of a first flexible member 21 (one flexible member), a second flexible member 22 (another flexible member), and an adhesive layer 11 located between them and bonding the first flexible member 21 and the second flexible member 22 to each other.

[0083] The pressure-sensitive adhesive layer 11 in the repeatedly folded laminated member 2 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 described above.

[0084] The repeatedly bent laminated member 2 is a repeatedly bent device itself or a member constituting part of a repeatedly bent device. The repeatedly bent device is preferably a display that can be repeatedly bent (including folded), but is not limited to this. Examples of such repeatedly bent devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays that use a plastic substrate (film) as a substrate, foldable displays, etc., and may also be touch panels.

[0085] The first flexible member 21 and the second flexible member 22 are members that can be repeatedly bent (including folded), and examples thereof 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 enhancement film, a contrast enhancement 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.

[0086] Among the above, it is preferable that one of the first flexible member 21 and the second flexible member 22 is a gas barrier film or a laminate having a gas barrier film on the adhesive layer 11 side. It is particularly preferable that the other of the first flexible member 21 and the second flexible member 22 is a polyimide film or a laminate having a polyimide film on the adhesive layer 11 side. Gas barrier films and polyimide films generally have low adhesion to adhesive layers, but the adhesive layer 11 of the present embodiment makes it difficult for lifting or peeling to occur at the interface between the adhesive layer and the adherend, even when the gas barrier film or polyimide film is the adherend and the adhesive layer is left in a bent state for a long period of time.

[0087] 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, particularly preferably 0.5 to 7 GPa, and even more preferably 1 to 5 GPa. When the Young's modulus of the first flexible member 21 and the second flexible member 22 is within this range, it becomes easy to repeatedly bend each flexible member.

[0088] The thickness of each of first flexible member 21 and second flexible member 22 is preferably 10 to 3000 μm, particularly preferably 25 to 1000 μm, and further preferably 50 to 500 μm. When the thickness of first flexible member 21 and second flexible member 22 is within this range, each flexible member can be easily bent repeatedly.

[0089] To manufacture the above-mentioned repeatedly bent laminated member 2, as an example, one release sheet 12a of the adhesive sheet 1 is peeled off and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to one surface of the first flexible member 21.

[0090] Thereafter, the other release sheet 12b is peeled from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the second flexible member 22 to obtain the repeatedly bent laminated member 2. As another example, the bonding order of the first flexible member 21 and the second flexible member 22 may be reversed.

[0091] [Repeated bending device] The repeatedly flexed device according to this embodiment includes the above-mentioned repeatedly flexed laminate member 2, and may be configured with only the repeatedly flexed laminate member 2, or may be configured with one or more repeatedly flexed laminate members 2 and other flexible members. When laminating one repeatedly flexed laminate member 2 with another repeatedly flexed laminate member 2, or when laminating a repeatedly flexed laminate member 2 with another flexible member, it is preferable to laminate them via the adhesive layer 11 of the adhesive sheet 1 described above.

[0092] In the repeatedly flexed device according to this embodiment, the adhesive layer is made of the adhesive described above. Therefore, even when the device is left in a flexed state for a long period of time, lifting or peeling is unlikely to occur at the interface between the adhesive layer 11 and the adherend (first flexing member 21 and second flexing member 22) (flexion resistance effect), and the device exhibits excellent recovery from a flexed state (recovery effect). This excellent flex resistance and recovery effect is fully exhibited even when the adherend is a polyimide film, a gas barrier film, or a laminate containing the same. Furthermore, the above-mentioned flex resistance effect is fully exhibited even when the device is flexed in a low-temperature environment (e.g., −20°C), where interfacial peeling is particularly likely to occur. The above-mentioned flex resistance and recovery effect can be evaluated, for example, by a static flex test.

[0093] In the static bending test, a test specimen was prepared by sandwiching a pressure-sensitive adhesive layer between two repeatedly bent laminated members and measuring 200 mm x 50 mm. As shown in Figure 3, the test specimen S was bent between two upright glass plates (holding plates P) for 24 hours at -20°C or 23°C and 50% RH. The distance between the two holding plates P was set to 4 mm (bending diameter of the test specimen S: 4 mm). The test specimen S was held so that the approximate center of the long side (200 mm) of the test specimen S was the bent portion, with both short sides (50 mm) facing upward. After the static bending test, the test specimen S was removed from between the two holding plates P and placed on a flat plate at 23°C and 50% RH, with the convex side of the bent portion facing upward, as shown in Figure 4. The height h from the surface of the plate to the apex of the bent part (deformed part) is measured as the static bending deformation (mm) immediately after the test and one hour after the test. The static bending deformation (mm) immediately after the test and the static bending deformation (mm) one hour after the test are used to calculate the recovery rate (%) according to the following formula (II), and the recovery rate (%) can be used to evaluate the recovery from the bent state (recovery effect). Recovery rate (%) = (1 - static bending deformation amount after 1 hour of testing / static bending deformation amount immediately after testing) × 100 ... (II)

[0094] In addition, when the test piece S is removed from the static bending test, it is visually checked whether there is any lifting or peeling at the interface between the pressure-sensitive adhesive layer and each repeatedly bent laminated member at the bent portion. This allows the bending resistance effect to be evaluated.

[0095] The static bending deformation amount in a static bending test at -20°C is preferably 12 mm or less immediately after the test, particularly preferably 10 mm or less, and even more preferably 8 mm or less. One hour after the test, it is preferably 3 mm or less, and even more preferably 1 mm or less. The static bending deformation amount in a static bending test at 23°C is preferably 18 mm or less immediately after the test, particularly preferably 15 mm or less, and even more preferably 10 mm or less. One hour after the test, it is preferably 5 mm or less, and even more preferably 3 mm or less. It is preferable that the lower limit of each static bending deformation amount is 0 mm.

[0096] An example of a repetitive bending device in this embodiment is shown in Fig. 5. Note that the repetitive bending device according to the present invention is not limited to this repetitive bending device.

[0097] 5, the repeatedly flexed device 3 according to this embodiment is configured by laminating, from top to bottom, a cover film 31, a first adhesive layer 32, a polarizing film 33, a second adhesive layer 34, a touch sensor film 35, a third adhesive layer 36, an organic EL element 37, a fourth adhesive layer 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.

[0098] At least one of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, and the fourth pressure-sensitive adhesive layer 38 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1. It is preferable that two or more of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, and the fourth pressure-sensitive adhesive layer 38 are the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1, and it is most preferable that all of the pressure-sensitive adhesive layers 32, 34, 36, and 38 are the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1.

[0099] The cover film 31 is preferably a gas barrier film having a gas barrier layer on the first adhesive layer 32 side, or a laminate having a gas barrier film (with the gas barrier layer on the adhesive layer 11 side) on the first adhesive layer 32 side. In this case, it is preferable that at least the first adhesive layer 32 is the adhesive layer 11 of the adhesive sheet 1 described above. Furthermore, for example, when the TFT substrate 39 includes a polyimide film, and particularly when the TFT substrate 39 has a polyimide film on the fourth adhesive layer 38 side, it is preferable that at least the fourth adhesive layer 38 is the adhesive layer 11 of the adhesive sheet 1 described above.

[0100] In the repeatedly flexed device 3, even when left in a flexed state for a long period of time, lifting or peeling is unlikely to occur at the interface between the adhesive layer consisting of the adhesive layer 11 of the adhesive sheet 1 and the flexible member bonded by the adhesive layer (flexion resistance effect), and the device has excellent recovery from a flexed state (recovery effect). This excellent flex resistance and recovery effect is fully exhibited even when the adherend is a polyimide film or a gas barrier film, or a laminate containing them. Furthermore, the above-mentioned flex resistance effect is fully exhibited even when the device is flexed in a low-temperature environment (e.g., -20°C) at which interfacial peeling is particularly likely to occur.

[0101] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended 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.

[0102] For example, either or both of release sheets 12a and 12b in pressure-sensitive adhesive sheet 1 may be omitted, and a desired flexible member may be laminated in place of release sheets 12a and / or 12b. [Example]

[0103] 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.

[0104] Example 1 1. Preparation of (meth)acrylic acid ester polymer (A) A (meth)acrylic acid ester polymer (A) was prepared by copolymerizing 54 parts by mass of n-butyl acrylate, 45 parts by mass of 2-ethylhexyl acrylate, and 1 part by mass of 4-hydroxybutyl acrylate by solution polymerization. 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 found to be 800,000.

[0105] 2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; same below) of the (meth)acrylic acid ester polymer (A) obtained in step 1 above, 0.25 parts by mass of trimethylolpropane-modified xylylene diisocyanate (XDI; manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") as the crosslinking agent (B), and 0.20 parts by mass of 3-glycidoxypropyltrimethoxysilane as the silane coupling agent were mixed, stirred thoroughly, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition.

[0106] 3. Manufacturing of adhesive sheets The obtained adhesive composition coating solution was applied by a knife coater to the release-treated surface of a heavy-release release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), one side of which was a polyethylene terephthalate film treated with a silicone-based release agent, and the coating layer was then heat-treated at 90°C for 1 minute to form a coating layer.

[0107] Next, the coating layer on the heavy-release release sheet obtained above was attached to a light-release release sheet (manufactured by Lintec Corporation, product name "SP-PET381130"), one side of which was a polyethylene terephthalate film treated with a silicone-based release agent, so that the release-treated side of the light-release release sheet was in contact with the coating layer, and the sheet was cured for 7 days under conditions of 23°C and 50% RH to produce a pressure-sensitive adhesive sheet with a 25µm thick adhesive layer, i.e., a pressure-sensitive adhesive sheet consisting of heavy-release release sheet / adhesive layer (thickness: 25µm) / light-release release sheet. The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant-pressure thickness gauge (manufactured by Teclock Corporation, product name "PG-02").

[0108] Here, the formulations (solid content equivalent) of the pressure-sensitive adhesive compositions when the (meth)acrylic acid ester polymer (A) is taken as 100 parts by mass (solid content equivalent) are shown in Table 1. 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 4HBA: 4-hydroxybutyl acrylate MMA: methyl methacrylate HEA: 2-hydroxyethyl acrylate ACMO: N-acryloylmorpholine IBXA: Isobornyl acrylate [Crosslinking agent (B)] XDI: Trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") TDI: Trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515")

[0109] [Examples 2 to 9, Comparative Examples 1 to 3] A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the types and proportions of each monomer constituting the (meth)acrylic acid ester polymer (A), the weight-average molecular weight (Mw) of the (meth)acrylic acid ester polymer (A), and the type and blending amount of the crosslinking agent (B) were changed as shown in Table 1.

[0110] [Production Example 1] A polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., product name "PET50A4100", thickness: 50 μm) with one side subjected to an easy-adhesion treatment was used as a base material. A composition (manufactured by JSR Corporation, product name "Optstar Z7530") containing an ultraviolet (UV) curable resin and reactive silica was applied onto one side (the smooth surface without the easy-adhesion treatment) of the base material using a Meyer bar to form a coating film, and the coating film was dried at 70 °C for 1 minute. Then, using a conveyor-type UV light irradiation device (manufactured by Fusion UV Systems, Inc., product name "F600V"), the coating film was irradiated with UV under the following conditions to cure the coating film and form an anchor coat layer with a thickness of 1 μm. <UV Irradiation Conditions> ·UV lamp: High-pressure mercury lamp ·Line speed: 20 m / min ·Integrated light quantity: 120 mJ / cm 2 ·Illuminance: 200 mW / cm 2 ·Lamp height: 104 mm

[0111] Next, a coating material mainly composed of perhydropolysilazane (manufactured by Merck Performance Materials, product name "AZ-110a-20") was applied onto the surface of the above anchor coat layer by the spin coating method. Then, it was heated at 120 °C for 1 minute to form a polysilazane layer containing perhydropolysilazane. The thickness of the formed polysilazane layer was 200 nm.

[0112] Next, a plasma ion implantation device was used to implant argon (Ar) plasma ions into the surface of the polysilazane layer to form a gas barrier layer made of modified polysilazane. In this way, a gas barrier film was obtained having a gas barrier layer made of modified polysilazane on one side of the substrate (PET film). Note that the modification of polysilazane proceeds from the surface of the polysilazane layer. Therefore, the degree of modification does not affect the surface condition of the gas barrier layer, and therefore does not affect flex resistance, etc.

[0113] [Test Example 1] (Creep Compliance Measurement) The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets prepared in the Examples and Comparative Examples were laminated together to form a 0.5 mm thick laminate. A cylindrical object with a diameter of 8 mm (height of 0.5 mm) was punched out from the resulting pressure-sensitive adhesive layer laminate to serve as a sample.

[0114] A stress of 3000 Pa was applied to the above sample using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") under the following conditions, and then the applied stress was reduced to 0 Pa and maintained for a while. During this time, the creep compliance J(t) (MPa -1 The creep compliance measured 3757 seconds after the start of the application of a stress of 3000 Pa was taken as the maximum creep compliance J(t). max (MPa -1 ) and the creep compliance measured 3757 seconds after the applied stress was set to 0 Pa was defined as the minimum creep compliance J(t). min (MPa -1 ) was decided. Measurement temperature: 25℃ Measurement points when stress is applied: 1000 points (logarithmic plot) Measurement points when unloading stress: 1000 points (logarithmic plot)

[0115] Obtained minimum creep compliance J(t) min (MPa -1 ) and maximum creep compliance J(t) max (MPa -1) and the creep recovery rate (%) was calculated based on the following formula (I). The results are shown in Table 2. Creep recovery rate (%) = (1 - J(t) min / J(t) max )×100 …(I)

[0116] [Test Example 2] (Measurement of adhesive strength) The light-release release sheets were peeled off from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive 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 heavy-release release sheet / pressure-sensitive adhesive layer / PET film laminate. The resulting laminate was cut to a width of 25 mm and a length of 110 mm.

[0117] On the other hand, the following three types of adherends were prepared. (1) A laminate (the polyimide film side is the adherend side) consisting of a soda-lime glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name "Soda-lime Glass", thickness: 1.1 mm) and a polyimide film with an adhesive layer (manufactured by Toray DuPont Co., Ltd., product name "Kapton 100PI", polyimide film thickness: 25 μm, adhesive layer thickness: 5 μm) attached to one side of the plate. (2) A laminate (gas barrier layer facing the adherend surface) in which the gas barrier film produced in Production Example 1 was attached to one side of a soda-lime glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name "Soda-lime Glass", thickness: 1.1 mm) via an adhesive. (3) Soda lime glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name "Soda Lime Glass", thickness: 1.1 mm)

[0118] The heavy-release release sheet was peeled from the laminate at 23°C and 50% RH, and the exposed adhesive layer was attached to each of the adherends. The laminate was then pressurized at 0.5 MPa and 50°C for 20 minutes in a Kurihara Manufacturing Co., Ltd. autoclave. After leaving the laminate at 23°C and 50% RH for 24 hours, the adhesive strength (N / 25 mm) was measured using a tensile tester (Orientec Co., Ltd., Tensilon) at a peel rate of 300 mm / min and a peel angle of 180°. Measurements were conducted in accordance with JIS Z0237:2009 except for the conditions described above. The results are shown in Table 2.

[0119] [Test Example 3] (Measurement of total light transmittance) The pressure-sensitive adhesive layer 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.

[0120] [Test Example 4] (Evaluation of restorability) In an environment of 23°C and 50% RH, the light-release release sheet was peeled from the pressure-sensitive adhesive sheets prepared in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was laminated to one side of a polyimide (PI) film (manufactured by Toray DuPont Co., Ltd., product name "Kapton 100PI," thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the heavy-release release sheet was peeled off, and the exposed pressure-sensitive adhesive layer was laminated to the gas barrier layer side of the gas barrier film (Young's modulus: 4.2 GPa) prepared in Production Example 1. The laminate was then pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., and then left at 23°C and 50% RH for 24 hours. The resulting laminate consisting of PI film / pressure-sensitive adhesive layer / gas barrier film was cut into a 50 mm wide x 200 mm long specimen.

[0121] The obtained test specimen was held in a bent state between two holding plates (4 mm apart) made of upright glass plates for 24 hours in an environment of -20°C or 23°C and 50% RH, as shown in Figure 3. Tests were performed both when the test specimen was bent so that the gas barrier film side faced the other side and when the PI film side faced the other side.

[0122] After the static bending test, the test piece was placed on a flat plate as shown in Figure 4. Immediately after the test and one hour after the test, the height h from the surface of the flat plate to the apex of the bent part (deformed part) was measured as the static bending deformation (mm).

[0123] The recovery rate (%) was calculated from the static flexural deformation (mm) immediately after the test and the static flexural deformation (mm) one hour after the test according to the following formula (II), and the recovery was evaluated according to the following criteria. The results are shown in Table 2. Recovery rate (%) = (1 - static bending deformation amount after 1 hour of testing / static bending deformation amount immediately after testing) × 100 ... (II) <Resilience evaluation criteria> ◎: Recovery rate is 85% or more 〇: Recovery rate is 75% or more but less than 85% ×: Recovery rate is less than 75%

[0124] [Test Example 5] (Evaluation of bending resistance) Test specimens similar to those in Test Example 4 were prepared and held in a bent state between two upright glass plates (4 mm apart) as shown in Figure 3 for 12 hours under conditions of -20°C or 23°C and 50% RH. The test was conducted both with the test specimen bent so that the gas barrier film side faced the other side and with the PI film side facing the other side. After the test, the interface between the pressure-sensitive adhesive layer and the adherend at the bent portion was visually inspected for any lifting or peeling, and the bending resistance was evaluated according to the following criteria. The results are shown in Table 2. <Evaluation criteria for bending resistance> Good: No lifting or peeling at the interface between the adhesive layer and the adherend at the bent portion ×: Lifting or peeling occurs at the interface between the adhesive layer and the adherend at the bent portion

[0125] In the static bending test at −20° C. in Comparative Example 1, the bending resistance was evaluated as ×, so measurement and evaluation of recovery property were not carried out.

[0126] [Table 1]

[0127] [Table 2]

[0128] As can be seen from Table 2, when the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the example was laminated with two flexible members (polyimide film / gas barrier film) and left in a bent state for a long period of time, no lifting or peeling occurred at the interface between the pressure-sensitive adhesive layer and the flexible member, and the sheet had excellent recovery from the bent state. This effect was fully demonstrated not only in a room temperature environment, but also when bent in a low-temperature environment of -20°C. [Industrial Applicability]

[0129] The present invention is suitable for bonding one flexible member (particularly a polyimide film or a laminate including a polyimide film) and another flexible member (a gas barrier film or a laminate including a gas barrier film) that constitute a repeatedly flexed device. [Explanation of symbols]

[0130] 1...Adhesive sheet 11...Adhesive layer 12a, 12b...Release sheet 2...Repeatedly bent laminated member 21...First flexible member 22...Second flexible member S...Test piece P...Retaining plate 3...Repeated bending device 31...Cover film 32...First adhesive layer 33...Polarizing film 34...Second adhesive layer 35...Touch sensor film 36...Third adhesive layer 37...Organic EL element 38...Fourth adhesive layer 39...TFT substrate

Claims

1. A pressure-sensitive adhesive for repeatedly flexed devices for bonding one flexible member and another flexible member that constitute a device that is repeatedly flexed, The creep compliance value measured after 3757 seconds of applying a stress of 3000 Pa to the adhesive was defined as the maximum creep compliance J(t). ｍａｘ (MPa －１ ) and then the stress applied to the pressure-sensitive adhesive is set to 0 Pa, and the creep compliance value measured after 3757 seconds is defined as the minimum creep compliance J(t). ｍｉｎ (MPa －１ ) and the creep recovery rate calculated from the following formula (I) is 70% or more.

1. A pressure-sensitive adhesive for a repeatedly flexed device, comprising: Cleave response rate (%) = (1 - J(t)) ｍｉｎ / J(t) ｍａｘ )×100 …(I)

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