Adhesive sheet, repeatedly flexed laminated member, and repeatedly flexed device

Abstract

Provided is a pressure-sensitive adhesive for repeatedly flexed devices that is inhibited from lifting or peeling even when applied to a repeatedly flexed device and left in a flexed state for a long period of time, and that has excellent recovery properties from a flexed state. The adhesive is for bonding one flexible member and another flexible member that constitute a device that is repeatedly bent, and the creep compliance value measured after 3757 seconds of applying a stress of 3000 Pa to the adhesive is called 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 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. Creep recovery rate (%) = (1 - J(t) min / J(t) max )×100 …(I)

Description

[Technical Field]

[0001] The present invention relates to adhesives and adhesive sheets for devices that are repeatedly bent, as well as repeatedly bent laminated members and repeatedly bent devices. [Background technology]

[0002] In recent years, flexible displays have been proposed as a type of device, specifically as a display element (display) for electronic devices. In addition to flexible displays that are curved only once, repeatedly flexible displays have also been proposed for applications where they are repeatedly bent (folded).

[0003] In a repeatedly flexible display as described above, it is conceivable to bond one flexible member (flexible member) constituting the flexible display to another flexible member using the adhesive layer of an adhesive sheet. However, using a conventional adhesive sheet in a repeatedly flexible display results in problems such as lifting and peeling at the interface between the adhesive layer and the adherend.

[0004] Patent Document 1 discloses an adhesive that addresses the issue of preventing lifting or peeling of the adhesive layer even when repeatedly bent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-108555 [Overview of the project] [Problems that the invention aims to solve]

[0006] On the other hand, in the case of the repeatedly flexed displays described above, they may be fixed in a flexed state for a long period of time. When the adhesive sheet described in Patent Document 1 is used for repeatedly flexed displays in such applications, lifting or peeling may occur at the interface between the adhesive layer and the adherend. Furthermore, even after being released from the flexed state, deformation may occur in the adhesive layer, causing the flexible display to remain significantly flexed and harden in that flexed state.

[0007] The present invention has been made in view of the above-mentioned circumstances, and aims to provide an adhesive and adhesive sheet for repeatedly bending devices that suppress the occurrence of lifting and peeling even when applied to a repeatedly bending device and left in a bent state for a long period of time, and that exhibit excellent resilience from a bent state, as well as a repeatedly bending laminated member and repeatedly bending device that suppress the occurrence of lifting and peeling even when left in a bent state for a long period of time, and that exhibit excellent resilience from a bent state. [Means for solving the problem]

[0008] To achieve the above objective, firstly, the present invention provides an adhesive for a repeatedly bending device for bonding one flexible member to another flexible member constituting a device that is repeatedly bent, wherein the creep compliance value measured after 3757 seconds by continuously applying a stress of 3000 Pa to the adhesive is the maximum creep compliance J(t) max ( MPa -1 The creep compliance value measured after 3757 seconds with the stress applied to the adhesive set to 0 Pa is called the minimum creep compliance J(t). min ( MPa -1 The invention provides an adhesive for repeatedly bending devices, characterized in that 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)

[0009] According to the above invention (Invention 1), when a laminate formed by bonding one flexible member and another flexible member with an adhesive layer made of the adhesive is placed in a bent state, it is difficult for the adhesive layer itself to deform, and after being released from the bent state, it is likely to restore to the shape before bending over time. Thereby, even when the above laminate is placed in a bent state for a long period of time, it is difficult for lifting or peeling to occur at the interface between the adhesive layer and the adherend, and it also has excellent restorability from the bent state.

[0010] In the above invention (Invention 1), it is preferable that the adhesive is an acrylic 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 constituting a device that is repeatedly bent, wherein the adhesive layer is composed of the adhesive for repeatedly bent devices (Inventions 1, 2) (Invention 3).

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

[0013] In the above inventions (Inventions 3, 4), it is preferable that the adhesive force of the adhesive sheet to the gas barrier layer of the gas barrier film is 3.0 N / 25 mm or more (Invention 5).

[0014] In the above inventions (Inventions 3 to 5), it is preferable that the thickness of the adhesive layer is 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 adhesive sheet includes two release sheets, and the 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 bendable laminated member comprising one flexible member and another flexible member constituting a device that is repeatedly bent, and an adhesive layer for bonding the one flexible member and the other flexible member to each other, wherein the adhesive layer is made of the adhesive for the repeatedly bendable device (Inventions 1, 2) (Invention 8).

[0017] Fourthly, the present invention provides a repetitive bending device characterized by comprising the repetitive bending laminated member (Invention 8) (Invention 9). [Effects of the Invention]

[0018] The adhesive and adhesive sheet for repeatedly bending devices according to the present invention are less prone to lifting or peeling at the interface between the adhesive layer and the adherend, and exhibit excellent recovery from the bending state, even when applied to a repeatedly bending device and left in a bent state for a long period of time. Furthermore, the repeatedly bending laminated member and repeatedly bending device according to the present invention are less prone to lifting or peeling at the interface between the adhesive layer and the adherend, and exhibit excellent recovery from the bending state, even when left in a bent state for a long period of time. [Brief explanation of the drawing]

[0019] [Figure 1] This is a cross-sectional view of an adhesive sheet according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view of a repeatedly bent laminated member according to one embodiment of the present invention. [Figure 3] This is an explanatory diagram (side view) illustrating the static bending test. [Figure 4] This is an explanatory diagram (side view) illustrating the amount of deformation of the test specimen as a result of a bending test. [Figure 5] This is a cross-sectional view of a repeatedly bending device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described below. [Adhesive for Repeated Flexing Device] The adhesive for a repeated flexing device according to this embodiment (hereinafter sometimes simply referred to as "adhesive") is an adhesive for bonding one flexural member and another flexural member constituting the repeated flexing device. The repeated flexing device and the flexural member will be described later.

[0021] The adhesive according to this embodiment has a creep compliance value measured 3757 seconds after continuously applying a stress of 3000 Pa to the adhesive (3757 seconds after the start of applying the stress of 3000 Pa) as the maximum creep compliance J(t) max (MPa -1 ), and then, with the stress applied to the adhesive being 0 Pa, the creep compliance value measured 3757 seconds after (3757 seconds after the applied stress is made 0 Pa) is 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 the creep compliance J(t) are as shown in the test examples described later.

[0022] When a laminate formed by bonding one flexible member to another with an adhesive layer is placed in a bent state, the adhesive layer is constantly under stress. If this state continues for a long time, even after being released from the bent state, deformation occurs in the adhesive layer, causing the laminate to harden in the bent state and making it difficult to restore to its original shape. However, the adhesive according to this embodiment has a creep recovery rate of 70% or more, making it difficult for the adhesive layer itself to deform, and allowing it to easily restore to its pre-bent shape over time after being released from the bent state. As a result, even when the above laminate is left in a bent state for a long period of time, lifting and peeling are less likely to occur at the interface between the adhesive layer and the adherend (bending resistance effect), and it exhibits excellent recovery from the bent state (restoration effect). These effects may hereafter be referred to as "bending resistance and restoration effect." This excellent bending resistance and restoration effect is fully exhibited even when the flexible member in the above laminate is a polyimide film or a gas barrier film, or a laminate containing the same. Furthermore, the above-mentioned bending resistance effect is fully demonstrated even when the material is bent in low-temperature environments (e.g., -20°C) where interfacial delamination is likely to occur.

[0023] From the viewpoint of the above-mentioned bending 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 it is usually preferably 99% or less, particularly preferably 95% or less, and even more preferably 90% or less.

[0024] The maximum creep compliance J(t) of the adhesive according to this embodiment max The lower limit is 10 MPa. -1 Preferably, it is 50 MPa or higher. -1 It is more preferable that the MPa is greater than or equal to 90 MPa. -1 Preferably, the above, and moreover, 110 MPa -1 The above is preferable. This results in an adhesive with more appropriate stress relaxation properties. Maximum creep compliance J(t) maxThe upper limit is typically 2000 MPa, considering the cohesive force of the adhesive. -1 Preferably, the following, and especially 1000 MPa -1 Preferably the following, and moreover 500 MPa -1 The following is preferable:

[0025] Furthermore, the minimum creep compliance J(t) of the adhesive according to this embodiment min The upper limit is 600 MPa. -1 Preferably, the following: 300 MPa -1 The following is more preferable, particularly 100 MPa -1 Preferably the following, and moreover 80 MPa -1 The following is preferable. This results in an adhesive with superior resilience. Minimum creep compliance J(t) min The lower limit is not particularly limited, but is usually 0 MPa. -1 It is preferable that the MPa is greater than or equal to 5 MPa, and is particularly 5 MPa. -1 Preferably, the above is true, and more preferably, 10 MPa. -1 It is preferable that the above conditions are met.

[0026] The type of adhesive according to this embodiment is not particularly limited as long as the above physical properties are satisfied, and may be any of the following: acrylic adhesive, polyester adhesive, polyurethane adhesive, rubber adhesive, silicone adhesive, etc. Furthermore, the adhesive may be emulsion type, solvent type, or solvent-free type, and may be crosslinked type or non-crosslinked type. Among these, acrylic adhesives are preferred because they easily satisfy the aforementioned physical properties and have excellent adhesive properties, optical properties, etc., and solvent-type acrylic adhesives are particularly preferred.

[0027] The 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 more likely to satisfy the aforementioned physical properties and to easily obtain 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 concept of "polymer" is also included in the concept of "polymer".

[0028] (1) Components of adhesive composition P (1-1)(meth)acrylic acid ester polymer (A) The (meth)acrylic acid ester polymer (A) preferably contains an alkyl (meth)acrylic acid ester and a monomer having a reactive functional group in its molecule (a monomer containing a reactive functional group) as monomer units constituting the polymer.

[0029] The (meth)acrylic acid ester polymer (A) can exhibit desirable tackiness by containing an alkyl (meth)acrylic acid ester as a monomer unit constituting the polymer. As the alkyl (meth)acrylic acid ester, an alkyl (meth)acrylic acid ester having 1 to 20 carbon atoms in the alkyl group is preferred. The alkyl group may be linear, branched, or have a cyclic structure.

[0030] Examples of alkyl (meth)acrylate esters having 1 to 20 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among these, from the viewpoint of the creep recovery rate mentioned above, (meth)acrylate esters having 1 to 8 carbon atoms in the alkyl group are preferred, and (meth)acrylate esters having 4 to 8 carbon atoms in the alkyl group are particularly preferred. Specifically, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These can be used individually or in combination of two or more types.

[0031] The (meth)acrylic acid ester polymer (A) preferably contains 60% by mass or more of alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group as monomer units constituting the polymer, 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. If the amount of alkyl (meth)acrylate ester is above the above amount, suitable tackiness can be imparted to the (meth)acrylic acid ester polymer (A), and the creep recovery rate can be easily adjusted to a higher value. Furthermore, it is preferable to contain 99.9% by mass or less of alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group, particularly preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. By setting the amount of alkyl (meth)acrylate ester to below the above amount, other monomer components can be introduced into the (meth)acrylic acid ester polymer (A) in desired amounts.

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

[0033] The (meth)acrylic acid ester polymer (A) contains, as monomer units, preferably, monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomer), monomers having a carboxyl group in the molecule (carboxyl group-containing monomer), and monomers having an amino group in the molecule (amino group-containing monomer). These reactive functional group-containing monomers may be used individually or in combination of two or more.

[0034] Among the above-mentioned monomers containing reactive functional groups, monomers containing hydroxyl groups or monomers containing carboxyl groups are preferred, and monomers containing hydroxyl groups are particularly preferred. Because the crosslinking density of hydroxyl group-containing monomers is easy to adjust, it is easier to satisfy the creep recovery rate mentioned above.

[0035] Examples of hydroxyl group-containing monomers include hydroxyalkyl esters of (meth)acrylates 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, hydroxyalkyl esters of (meth)acrylates having a hydroxyalkyl group with 1 to 4 carbon atoms are preferred from the viewpoint of easily satisfying the aforementioned creep recovery rate. Specifically, for example, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate 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 adhesiveness of the resulting (meth)acrylic acid ester polymer (A). These may be used individually or in combination of two or more.

[0037] The (meth)acrylic acid ester polymer (A) preferably contains at least 0.1% by mass of reactive functional group-containing monomers as monomer units constituting the polymer, more preferably at least 0.5% by mass, and even more preferably at least 1.0% by mass. Furthermore, the (meth)acrylic acid ester polymer (A) preferably contains at least 10% by mass of reactive functional group-containing monomers as monomer units constituting the polymer, more preferably at least 7% by mass, more preferably at least 5% by mass, and even more preferably at least 2% by mass. When the (meth)acrylic acid ester polymer (A) contains reactive functional group-containing monomers in the above amounts as monomer units, the cohesive force of the resulting adhesive becomes appropriate through the crosslinking reaction with the crosslinking agent (B), making it easier to satisfy the aforementioned creep recovery rate.

[0038] It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain carboxyl group-containing monomers as monomer units constituting the polymer. Since the carboxyl group is an acidic component, by not containing carboxyl group-containing monomers, it is possible to suppress problems caused by acid (corrosion, change in resistance, etc.) even when the object to which the adhesive is applied is a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, or a metal mesh.

[0039] Here, "carboxy group-containing monomer-free" means substantially free of carboxy group-containing monomers, including not only complete absence of carboxy group-containing monomers, but also the possibility of containing carboxy group-containing monomers to an extent that does not cause corrosion of transparent conductive films or metal wiring due to carboxyl groups. Specifically, it means that the (meth)acrylic acid ester polymer (A) may contain carboxy group-containing monomers as monomer units 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.

[0040] The (meth)acrylic acid ester polymer (A) may optionally contain other monomers as monomer units constituting the polymer. Among the other monomers, monomers that do not contain reactive functional groups are preferred in order not to inhibit the aforementioned effects of the reactive functional group-containing monomers. Examples of such monomers include unreactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, alkoxyalkyl (meth)acrylate esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used individually 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 (meth)acrylic acid 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. Furthermore, the weight-average molecular weight of (meth)acrylic acid 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 (meth)acrylic acid polymer (A) is within the above range, the aforementioned creep recovery rate is more easily satisfied. Note that the weight-average molecular weight in this specification is the value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0043] In the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more types.

[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, triggered by heating or other means of the adhesive composition P containing the crosslinking agent (B). This improves the cohesive force of the resulting adhesive, making it easier to satisfy the aforementioned creep recovery rate.

[0045] The crosslinking agent (B) can be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A), and examples include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, and ammonium salt crosslinking agents. Among these, it is preferable to use an isocyanate crosslinking agent that exhibits excellent reactivity with monomers containing reactive functional groups. The crosslinking agent (B) can be used alone or in combination of two or more types.

[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 their biuret and isocyanurate forms, as well as adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. 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 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). Furthermore, 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 easily satisfied.

[0048] (1-3) Various additives The adhesive composition P may optionally contain various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, and refractive index modifiers. The polymerization solvent and diluent described later are not included in the additives constituting the adhesive composition P.

[0049] The adhesive composition P preferably contains the above-mentioned silane coupling agent. This improves the adhesion between the resulting adhesive layer and the flexible member to be adhered, resulting in a more desirable adhesive strength.

[0050] As a silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in its molecule is preferred, which has good compatibility with the (meth)acrylic acid ester polymer (A) and is light-transmitting.

[0051] Examples of such silane coupling agents include polymerizable unsaturated silicon compounds 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, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyldimethoxymethylsilane. Examples include silicon compounds containing a capto group, amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, or condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These may be used individually or in combination of two or more.

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

[0053] (2) Manufacture of adhesive composition P The adhesive composition P can be produced by manufacturing a (meth)acrylic acid ester polymer (A), mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B), and optionally adding an additive.

[0054] (Meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. Polymerization of (meth)acrylic acid ester polymer (A) is preferably carried out by solution polymerization using a polymerization initiator if desired. Polymerizing (meth)acrylic acid ester polymer (A) by solution polymerization makes it easy to increase the molecular weight of the resulting polymer and adjust the molecular weight distribution, and further reduces the generation of low molecular weight products. As a result, uneven distribution of the adhesive due to prolonged bending is less likely to occur, and the recovery from the bent state is improved.

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

[0056] Examples of polymerization initiators include azo compounds and organic peroxides, and two or more may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane1-carbonitride), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2'-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 peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

[0058] Furthermore, in the polymerization process described above, the weight-average molecular weight of the resulting polymer can be adjusted by incorporating 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 diluent solvents are added to the solution of the (meth)acrylic acid ester polymer (A), and the mixture is thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution).

[0060] Furthermore, if any of the above components are used in solid form, or if precipitation occurs when mixed with other components in an undiluted state, that component may be dissolved or diluted in a diluent solvent beforehand before mixing with the other components.

[0061] Examples of the diluent solvents used 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 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 the range of 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% by mass. Note that the addition of a diluent is not a necessary condition when obtaining the coating solution; if the adhesive composition P has a viscosity suitable for coating, a diluent may not be added. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used directly as the diluent.

[0063] (3) Manufacturing of adhesives The adhesive according to this embodiment is preferably formed by crosslinking an adhesive composition P. Crosslinking of the adhesive composition P can usually be performed by heat treatment. This heat treatment can also be combined with a drying treatment to volatilize the diluent solvent, etc., from the coating film of the adhesive composition P applied to the desired object.

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

[0065] After heat treatment, a curing period of 1 to 2 weeks at room temperature (e.g., 23°C, 50% RH) may be allowed if necessary. If a curing period is required, the adhesive will be formed after the curing period has elapsed; if a curing period is not required, the adhesive will be formed after the heat treatment is completed.

[0066] Through 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, and an adhesive is obtained.

[0067] [Adhesive sheet] The adhesive sheet according to 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] Figure 1 shows a specific configuration of an adhesive sheet as an example according to this embodiment. As shown in Figure 1, an adhesive sheet 1 according to one embodiment consists 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 release properties, and includes both surfaces that have undergone a release treatment and surfaces that exhibit release properties even without a release treatment.

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

[0070] The thickness of the adhesive layer 11 in the adhesive sheet 1 according to this embodiment (a value measured in accordance with JIS K7130) is preferably 1 μm or more as a lower limit, more preferably 5 μm or more, particularly preferably 10 μm or more, and even more preferably 15 μm or more. When the lower limit of the thickness of the adhesive layer 11 is as described above, it is easier to achieve the desired adhesive strength, and lifting and peeling are less likely to occur at the interface between the adhesive layer and the adherend. Furthermore, the upper limit of the thickness of the adhesive layer 11 is preferably 300 μm or less, more preferably 150 μm or less, particularly preferably 90 μm or less, and even more preferably 40 μm or less from the viewpoint of obtaining a thinner, repeatedly bending device. When the upper limit of the thickness of the adhesive layer 11 is as described above, the stress on the adhesive layer becomes relatively small, making it easier to recover from the bent state, and the adhesion between the adhesive layer and the adherend is easier to maintain, resulting in a better bending resistance and recovery effect. The adhesive layer 11 may be formed as a single layer or as multiple layers laminated together.

[0071] The total light transmittance of the adhesive layer 11 in the adhesive sheet 1 according to this embodiment (a value measured in accordance with JIS K7361-1:1997) 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 as described above, the transparency is high and it becomes suitable for optical applications (for repeatedly bending displays).

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

[0073] Examples of release sheets 12a and 12b include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. Crosslinked films of these may also be used. Furthermore, laminated films of these may also be used.

[0074] It is preferable that the release surfaces of the above-mentioned release sheets 12a and 12b (especially the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of release agents used in the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax-based release agents. It is preferable that one of the release sheets 12a and 12b be a heavy-release type release sheet with a high release force, and the other release sheet be a light-release type release sheet with a low release force.

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

[0076] (2) Adhesive strength The adhesive strength of the adhesive sheet 1 to polyimide according to this embodiment 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 adhesive sheet 1 to polyimide is as described above, even when a polyimide film or the like is used as the adherend, lifting and peeling at the interface between the adhesive layer and the adherend becomes less likely to occur when it is left in a bent state for a long period of time. On the other hand, there is no particular limit to the upper limit of the adhesive strength, however reworkability may be required. From this viewpoint, 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. In this specification, adhesive strength basically refers to the adhesive strength measured by the 180-degree peel method in accordance with JIS Z0237:2009, and the specific test method is as shown in the test examples described later.

[0077] The adhesive strength of the adhesive sheet 1 according to this embodiment to the gas barrier film (for example, 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 lower limit of the adhesive strength of the adhesive sheet 1 to the gas barrier film is as described above, even when the gas barrier film is used as the adherend, lifting and peeling are less likely to occur at the interface between the adhesive layer and the adherend when it is left in a bent state for a long period of time. On the other hand, there is no particular limit to the upper limit of the adhesive strength, however reworkability may be required. From this viewpoint, 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 adhesive sheet 1 to soda-lime glass according to this embodiment is preferably 5.0 N / 25 mm or more as a lower limit, 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 lower limit of the adhesive strength of the adhesive sheet 1 to soda-lime glass is as described above, lifting and peeling at the interface between the adhesive layer and the adherend becomes less likely to occur when a member made of various materials is used as the adherend. On the other hand, the upper limit of the adhesive strength is not particularly limited, but is usually preferably 50.0 N / 25 mm or less, more preferably 40.0 N / 25 mm or less, and from the viewpoint of reworkability, which allows the adhesive sheet to be reapplied in the event of an application error, it is particularly preferably 30.0 N / 25 mm or less, and even more preferably 20.0 N / 25 mm or less.

[0079] (3) Manufacturing of adhesive sheets As an example of manufacturing the adhesive sheet 1, the case in which the above-mentioned adhesive composition P is used will be described. The coating liquid of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and the adhesive composition P is thermally crosslinked by heat treatment to form a coating layer. Then, the release surface of the other release sheet 12b (or 12a) is placed on top of the coating layer. If a curing period is required, a curing period is allowed, or if a curing period is not required, the coating layer becomes the adhesive layer 11. This gives rise to the adhesive sheet 1. The conditions for heat treatment and curing are as described above.

[0080] Another manufacturing example of the adhesive sheet 1 involves applying a coating solution of the adhesive composition P to the release surface of one release sheet 12a, performing a heat treatment to thermally crosslink the adhesive composition P, and forming a coating layer to obtain a release sheet 12a with a coating layer. Similarly, applying the coating solution of the adhesive composition P to the release surface of the other release sheet 12b, performing a heat treatment to thermally crosslink the adhesive composition P, and forming a coating layer to obtain a release sheet 12b with a coating layer. Then, the release sheets 12a and 12b with coating layers are bonded together so that both coating layers are in contact with each other. If a curing period is required, a curing period is observed; otherwise, the laminated coating layers become the adhesive layer 11. This yields the adhesive sheet 1. According to this manufacturing example, even when the adhesive layer 11 is relatively thick, stable manufacturing is possible.

[0081] For example, methods such as bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating can be used to apply the coating solution of the above-mentioned adhesive composition P.

[0082] [Repeatedly Bending Laminated Material] As shown in Figure 2, the repeatedly bendable laminated member 2 according to this embodiment comprises a first flexible member 21 (one flexible member), a second flexible member 22 (another flexible member), and an adhesive layer 11 located between them that bonds the first flexible member 21 and the second flexible member 22 to each other.

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

[0084] The repeatedly bending laminated member 2 is either the repeatedly bending device itself or a member that constitutes a part of the repeatedly bending device. The repeatedly bending device is preferably a display that can be repeatedly bent (including folding), but is not limited thereto. Examples of such repeatedly bending devices include organic electroluminescent (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays using a plastic substrate (film) as the 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 include cover films, barrier films, hard coat films, polarizing films (polarizing plates), polarizers, phase difference films (phase difference plates), viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transparent reflective films, electrode films, transparent conductive films, metal mesh films, film sensors (touch sensor films), liquid crystal polymer films, light-emitting polymer films, film-type liquid crystal modules, organic EL modules (organic EL films, organic EL elements), electronic paper modules (film-type electronic paper), TFT (Thin Film Transistor) substrates, etc.

[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 with a gas barrier film on the adhesive layer 11 side. Furthermore, 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 with a polyimide film on the adhesive layer 11 side. Although gas barrier films and polyimide films generally have low adhesion to adhesive layers, with the adhesive layer 11 in this embodiment, even if the adherend is a gas barrier film or a polyimide film, lifting or peeling is less likely to occur at the interface between the adhesive layer and the adherend, even when it is left in a bent state for a long period of time.

[0087] The Young's moduli of the first flexible member 21 and the second flexible member 22 are preferably 0.1 to 10 GPa, particularly preferably 0.5 to 7 GPa, and even more preferably 1 to 5 GPa. Having the Young's moduli of the first flexible member 21 and the second flexible member 22 within this range makes it easy to repeatedly bend each flexible member.

[0088] The thickness of the first flexible member 21 and the second flexible member 22 is preferably 10 to 3000 μm, particularly preferably 25 to 1000 μm, and even more preferably 50 to 500 μm. Having the thicknesses of the first flexible member 21 and the second flexible member 22 within this range makes it easy to repeatedly bend each flexible member.

[0089] To manufacture the above-mentioned repeatedly bending 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 side of the first flexible member 21.

[0090] Subsequently, the other release sheet 12b is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the second flexible member 22 to obtain a repeatedly flexible laminated member 2. Alternatively, 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 repeat bending device according to this embodiment comprises the repeat bending laminated member 2 described above, and may consist only of the repeat bending laminated member 2, or it may be configured with one or more repeat bending laminated members 2 and other flexible members. When laminating one repeat bending laminated member 2 with another repeat bending laminated member 2, or when laminating a repeat bending laminated 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 this embodiment, the repeatedly bending device has an adhesive layer made of the aforementioned adhesive, so even when left in a bent state for a long period of time, lifting or peeling is less likely to occur at the interface between the adhesive layer 11 and the adherend (first flexible member 21 and second flexible member 22) (bending resistance effect), and it exhibits excellent recovery from the bent state (restoration effect). This excellent bending resistance and restoration effect is fully exhibited even when the adherend is a polyimide film or a gas barrier film, or a laminate containing the same. Furthermore, the above bending resistance effect is fully exhibited even when bent in a low-temperature environment (e.g., -20°C) where interfacial delamination is likely to occur. The above bending resistance and restoration effect can be evaluated, for example, by a static bending test.

[0093] In the static bending test, the test specimen is a laminate consisting of two repeatedly bending laminated members sandwiching an adhesive layer, measuring 200 mm x 50 mm. As shown in Figure 3, this test specimen S is held in a bent state for 24 hours in an environment of -20°C or 23°C, 50% RH between two upright holding plates P made of glass plates. At this time, the distance between the two holding plates P is set to 4 mm (bending diameter of test specimen S: 4 mmφ), and the test specimen S is held so that the bending part is approximately in the center of the long side (200 mm) of the test specimen S, and both short sides (50 mm) of the test specimen S are positioned on the upper side. After this static bending test, the test specimen S is removed from between the two holding plates P, and as shown in Figure 4, the test specimen S is placed on a flat plate in an environment of 23°C, 50% RH with the convex direction of the bending part facing upwards. Then, 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 bend (deformation) is measured as the static bending deformation (mm). From the obtained static bending deformation (mm) immediately after the test and the static bending deformation (mm) one hour after the test, the recovery rate (%) is calculated based on the following formula (II), and the recovery ability (recovery effect) from the bent state can be evaluated based on this recovery rate (%). Recovery rate (%) = (1 - Static flexural deformation after 1 hour of testing / Static flexural deformation immediately after testing) × 100 …(II)

[0094] Furthermore, when the test piece S is removed from the static bending test described above, it is visually inspected to check for any lifting or peeling at the interface between the adhesive layer and each repeatedly bending laminated member in the bent portion. This allows for evaluation of the bending resistance effect.

[0095] The static bending deformation 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. Furthermore, it is preferably 3 mm or less, and especially preferably 1 mm or less, one hour after the test. The static bending deformation 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. Furthermore, it is preferably 5 mm or less, and especially preferably 3 mm or less, one hour after the test. In addition, the lower limit of the static bending deformation in all cases is preferably 0 mm.

[0096] Figure 5 shows an example of a repeatedly bending device in this embodiment. However, the repeatedly bending device according to the present invention is not limited to this device.

[0097] As shown in Figure 5, the repeatedly bending device 3 according to this embodiment is constructed 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 are all flexible members.

[0098] At least one of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 is the adhesive layer 11 of the adhesive sheet 1 described above. Preferably, two or more of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 are the adhesive layers 11 of the adhesive sheet 1 described above, and most preferably, all of the adhesive layers 32, 34, 36, and 38 are the adhesive layers 11 of the 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 on the first adhesive layer 32 side (with the gas barrier layer on the adhesive layer 11 side). In this case, at least the first adhesive layer 32 is preferably the adhesive layer 11 of the adhesive sheet 1 described above. Furthermore, for example, if the TFT substrate 39 includes a polyimide film, and especially if the polyimide film is provided on the fourth adhesive layer 38 side, at least the fourth adhesive layer 38 is preferably the adhesive layer 11 of the adhesive sheet 1 described above.

[0100] In the above-described repeatedly bending device 3, even when left in a bent state for a long period of time, lifting and peeling are unlikely to occur at the interface between the adhesive layer 11 of the adhesive sheet 1 and the flexible member bonded by the adhesive layer (bending resistance effect), and the device exhibits excellent recovery from a bent state (restoration effect). This excellent bending resistance and restoration 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 bending resistance effect is fully exhibited even when the device is bent in a low-temperature environment (e.g., -20°C) where interfacial delamination is likely to occur.

[0101] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it. Accordingly, 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 one or both of the release sheets 12a and 12b in the adhesive sheet 1 may be omitted, and a desired flexible member may be laminated in place of the release sheets 12a and / or 12b. [Examples]

[0103] The present invention will be described 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) (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 later and found to be a weight-average molecular weight (Mw) of 800,000.

[0105] 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 in step 1 above, 0.25 parts by mass of trimethylolpropane-modified xylylene diisocyanate (XDI; manufactured by Soken Chemical Co., Ltd., product name "TD-75") as a crosslinking agent (B), and 0.20 parts by mass of 3-glycidoxypropyltrimethoxysilane as a 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 resulting adhesive composition coating solution was applied using a knife coater to the release surface of a heavy-release type release sheet (Lintec Corporation, product name "SP-PET752150"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent. The coated layer was then heated at 90°C for 1 minute to form a coating layer.

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

[0108] Here, Table 1 shows the respective formulations (solid content equivalent) of the adhesive composition when (meth)acrylic acid ester polymer (A) is present in 100 parts by mass (solid content equivalent). Details of the abbreviations and other terms listed 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 Co., Ltd., product name "TD-75") TDI: Trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem Co., Ltd., product name "BHS8515")

[0109] [Examples 2-9, Comparative Examples 1-3] A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the types and proportions of the monomers constituting the (meth)acrylic acid ester polymer (A), the weight-average molecular weight (Mw) of the (meth)acrylic acid ester polymer (A), and the type and 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 being subjected to easy adhesion treatment was used as a base material. A composition (manufactured by JSR Corporation, product name "Opsstar Z7530") containing an ultraviolet (UV) curable resin and reactive silica was applied onto one side (the smooth surface not subjected to easy adhesion treatment) of the base material using a Mayer 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 perhydro polysilazane (manufactured by Merck Performance Materials, product name "AZ-110a-20") was applied onto the surface of the above anchor coat layer by spin coating. Then, it was heated at 120 °C for 1 minute to form a polysilazane layer containing perhydro polysilazane. The thickness of the formed polysilazane layer was 200 nm.

[0112] Next, using a plasma ion implantation device, argon (Ar) was plasma-implanted onto the surface of the polysilazane layer to form a gas barrier layer made of modified polysilazane. In this way, a gas barrier film having a gas barrier layer made of modified polysilazane on one side of the substrate (PET film) was obtained. Note that the modification of the 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 thus does not affect the flexibility or other properties.

[0113] [Test Example 1] (Measurement of creep compliance) Multiple adhesive layers from the adhesive sheets prepared in the examples and comparative examples were laminated to form a 0.5 mm thick laminate. From the resulting laminate of adhesive layers, a cylindrical object with a diameter of 8 mm (height 0.5 mm) was punched out and used as a sample.

[0114] For the above sample, a viscoelasticity measuring device (Anton Paar, product name "MCR302") was used to continuously apply a stress of 3000 Pa under the following conditions. After that, the applied stress was reduced to 0 Pa and maintained for a period of time. During that time, the creep compliance J(t)(MPa) was measured. -1 The creep compliance value measured 3757 seconds after the start of stress application at 3000 Pa was determined as the maximum creep compliance J(t). max ( MPa -1 The creep compliance value measured 3757 seconds after the applied stress was reduced to 0 Pa is defined as the minimum creep compliance J(t). min ( MPa -1 ) Measurement temperature: 25℃ Measurement points during stress application: 1000 points (logarithmic plot) Measurement points during stress unloading: 1000 points (logarithmic plot)

[0115] The obtained minimum creep compliance J(t) min ( MPa -1 ) and maximum creep compliance J(t) max ( MPa -1The 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 Adhesion) The light-peel release sheet was peeled off from the adhesive sheets obtained in the examples and comparative examples, and the exposed adhesive layer was laminated to the easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 100 μm) having an easy-adhesion layer, to obtain a laminate of heavy-peel release sheet / adhesive layer / PET film. The obtained 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 substrates were prepared. (1) A laminate formed by attaching a polyimide film with an adhesive layer (Toray DuPont, product name "Kapton 100PI", polyimide film thickness: 25 μm, adhesive layer thickness: 5 μm) 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) (the polyimide film side is the adhered surface). (2) A laminate in which a gas barrier film made in Manufacturing Example 1 is 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 (the gas barrier layer is the adhered surface). (3) Soda-lime glass sheet (manufactured by Nippon Sheet Glass Co., Ltd., product name "Soda-lime Glass", thickness: 1.1 mm)

[0118] Under conditions of 23°C and 50%RH, the heavy-peel release sheet was peeled from the laminate, and the exposed adhesive layer was attached to each of the above-mentioned adherends. The laminate was then pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. After leaving it for 24 hours under conditions of 23°C and 50%RH, the adhesive strength (N / 25mm) when the laminate of PET film and adhesive layer was peeled from the adherend was measured using a tensile testing machine (Tensilon, manufactured by Orientec Co., Ltd.) under conditions of peeling speed of 300 mm / min and peeling angle of 180 degrees. Measurements other than those described herein were performed in accordance with JIS Z0237:2009. The results are shown in Table 2.

[0119] [Test Example 3] (Measurement of total light transmittance) The adhesive layers of the adhesive sheets obtained in the examples and comparative examples were bonded to glass to serve as measurement samples. After background measurements were performed on the glass, the total light transmittance (%) of the measurement samples 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 Restorativeness) Under conditions of 23°C and 50%RH, the light-peel release liner was peeled off from the adhesive sheets prepared in the examples and comparative examples, and the exposed adhesive layer was laminated to one side of a polyimide (PI) film (Toray DuPont, product name "Kapton 100PI", thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the heavy-peel release liner was peeled off, and the exposed adhesive layer was laminated to the gas barrier layer surface of the gas barrier film (Young's modulus: 4.2 GPa) prepared in Production Example 1. Then, the laminate was pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., and left for 24 hours under conditions of 23°C and 50%RH. The laminate obtained in this way, consisting of PI film / adhesive layer / gas barrier film, was cut to a width of 50 mm and a length of 200 mm, and these were used as test specimens.

[0121] The obtained test specimens were held in a bent state for 24 hours in an environment of -20°C or 23°C, 50%RH, as shown in Figure 3, between two upright holding plates (distance between them: 4 mm). During this time, tests were conducted in both cases: when the test specimens were bent with the gas barrier film sides facing each other, and when they were bent with the PI film sides facing each other.

[0122] After performing the static bending test described above, the test specimen was placed on a flat plate as shown in Figure 4, and the height h from the surface of the flat plate to the apex of the bent (deformed) portion was measured as the amount of static bending deformation (mm) immediately after the test and one hour after the test.

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

[0124] [Test Example 5] (Evaluation of flexural resistance) A test specimen similar to that in Test Example 4 was prepared and held for 12 hours in a bent state between two upright glass plates (distance between them: 4 mm) in an environment of -20°C or 23°C, 50% RH, as shown in Figure 3. During this time, tests were conducted in both cases: when the test specimen was bent with the gas barrier film side facing the other, and when it was bent with the PI film side facing the other. After the tests, the interface between the 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 flexibility resistance> ○...There is no lifting or peeling at the interface between the adhesive layer and the adherend in the bent portion. ×...There is lifting or peeling at the interface between the adhesive layer and the adherend in the bent portion.

[0125] In the static bending test at -20°C for Comparative Example 1, the bending resistance was rated as "×", therefore, no measurement or evaluation regarding recovery was performed.

[0126] [Table 1]

[0127] [Table 2]

[0128] As can be seen from Table 2, the adhesive layer of the adhesive sheet in the example did not exhibit lifting or peeling at the interface between the adhesive layer and the flexible members when the two flexible members (polyimide film / gas barrier film) were bonded together and left in a bent state for a long period of time, and also exhibited excellent recovery from the bent state. This effect was fully demonstrated not only in a normal 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 containing a polyimide film) to another flexible member (a gas barrier film or a laminate containing a gas barrier film) that constitutes a repeatedly bending device. [Explanation of Symbols]

[0130] 1…Adhesive sheet 11…Adhesive layer 12a, 12b… Release sheets 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 elements 38…Fourth adhesive layer 39…TFT substrate

Claims

1. An adhesive sheet having an adhesive layer for bonding one flexible member to another flexible member that constitutes a device that is repeatedly bent, The creep compliance value measured after 3757 seconds by continuously applying a stress of 3000 Pa to the adhesive constituting the aforementioned adhesive layer is the maximum creep compliance J(t). ｍａｘ ( MPa －１ ) and thereafter, the creep compliance value measured after 3757 seconds with the stress applied to the adhesive set to 0 Pa is called the minimum creep compliance J(t). ｍｉｎ ( MPa －１ ) and the creep recovery rate calculated from the following formula (I) is 70% or more, The adhesive strength to the soda-lime glass after being attached, pressurized at 0.5 MPa and 50°C for 20 minutes, and then left for 24 hours under conditions of 23°C and 50% RH is 5.0 N / 25 mm or more (excluding 5.0 N / 25 mm). An adhesive sheet characterized by the following features. Cleave response rate (%) = (1 - J(t)) ｍｉｎ / J(t) ｍａｘ )×100 …(I)

2. The adhesive sheet according to claim 1, characterized in that the adhesive is an acrylic adhesive.

3. The adhesive sheet according to claim 1 or 2, characterized in that, after being attached to a polyimide, pressurized at 0.5 MPa and 50°C for 20 minutes, and then left for 24 hours under conditions of 23°C and 50% RH, the adhesive strength to the polyimide is 1.0 N / 25 mm or more.

4. The adhesive sheet according to any one of claims 1 to 3, characterized in that, after being attached to the gas barrier layer of a gas barrier film, pressurized at 0.5 MPa and 50°C for 20 minutes, and then left for 24 hours under conditions of 23°C and 50% RH, the adhesive strength to the gas barrier layer of the gas barrier film is 3.0 N / 25 mm or more.

5. The adhesive sheet according to any one of claims 1 to 4, characterized in that the thickness of the adhesive layer is 1 μm or more and 300 μm or less.

6. The adhesive sheet comprises two release sheets. The adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the two release sheets. The adhesive sheet according to any one of claims 1 to 5.

7. A device that is repeatedly bent comprises one flexible member and another flexible member, An adhesive layer that bonds the first flexible member and the other flexible member together. A repeatedly bent laminated member comprising, The adhesive layer is the adhesive layer of the adhesive sheet described in any one of claims 1 to 6. A repeatedly bending laminated member characterized by the following:

8. A repeat bending device characterized by comprising a repeat bending laminated member as described in claim 7.

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