CN111621246B - Adhesive for repeatedly bending device, adhesive sheet, repeatedly bending laminated member, and repeatedly bending device - Google Patents

Abstract

The invention provides an adhesive for a repeatedly bending device, which has excellent bending resistance even when the adhesive is applied to the repeatedly bending device and is placed in a long-term bending state. The adhesive for a repeatedly bending device is used for bonding one bendable member and another bendable member constituting a repeatedly bent device, and the maximum relaxation modulus value measured when the adhesive is deformed by 10% is set as the maximum relaxation modulus G (t) based on JIS K7244-1 _max (MPa), the adhesive is continuously deformed by 10% from the time of measurement to the time of 3757 seconds after the maximum relaxation modulus G (t) max, and the minimum relaxation modulus value measured in the period is set as the minimum relaxation modulus G (t) _min (MPa), and a change in relaxation modulus Δ logG (t) calculated by the following formula (I) is 0.33 to 1.50. Δ logG (t) = logG (t) _max ‑logG(t) _min ···(I)。

Description

Adhesive for repeatedly bending device, adhesive sheet, repeatedly bending laminated member, and repeatedly bending device

Technical Field

The present invention relates to an adhesive for a repeatedly bending device, an adhesive sheet, a repeatedly bending laminated member, and a repeatedly bending device.

Background

In recent years, a bendable display has been proposed as a display body (display) of an electronic device which is one of devices. As the flexible display, in addition to a flexible display in which only one-time curved surface molding is performed, a repeated bending display for repeated bending (bending) use has been proposed.

In the above-described repeated bending display, it is considered that one bendable member (bendable member) and the other bendable member constituting the bendable display are bonded to each other via an adhesive layer of an adhesive sheet. However, when a conventional adhesive sheet is used in a display device which is repeatedly bent, there is a problem that the adhesive layer floats or peels off at the interface between the adhesive layer and the adherend.

Patent document 1 discloses an adhesive that has a technical problem of being able to suppress the occurrence of floating or peeling of an adhesive layer even when repeatedly bent.

Documents of the prior art

Patent literature

Patent document 1: japanese patent laid-open publication No. 2016-108555

Disclosure of Invention

Technical problem to be solved by the invention

On the other hand, in the display device which is repeatedly bent as described above, the display device may be fixed in a state of being bent for a long period of time. When the adhesive sheet described in patent document 1 is used for a display with repeated bendability for the above-mentioned application, floating or peeling occurs at the interface between the adhesive layer and the adherend, and sufficient bending resistance cannot be obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive and an adhesive sheet for a repeatedly bending device, which are excellent in bending resistance even when applied to the repeatedly bending device and left in a long-term bent state, and a repeatedly bending laminated member and a repeatedly bending device, which are excellent in bending resistance even when left in a long-term bent state.

Means for solving the problems

In order to achieve the above object, the first aspect of the present invention provides an adhesive for a repeatedly bendable device for bonding one bendable member and another bendable member constituting the repeatedly bendable device, wherein a maximum relaxation modulus value measured when the adhesive is deformed by 10% is defined as a maximum relaxation modulus G (t) in accordance with JIS K7244-1 _max (MPa), the maximum relaxation modulus G (t) is measured _max The adhesive was continuously deformed by 10% from the start to 3757 seconds, and the minimum relaxation modulus value measured during this time was set as the minimum relaxation modulus G (t) _min (MPa) a change in relaxation modulus DeltalogG (t) calculated by the following formula (I) of 0.33 to 1Under 50.

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

According to the above invention (invention 1), when a laminated body in which one bendable member and another bendable member are bonded to each other by an adhesive layer made of the adhesive is placed in a bent state, the difference between the stress generated outside the bent portion of the adhesive layer and the stress generated inside the bent portion is reduced, and the stress of the entire adhesive layer is easily relaxed. Further, it is easy to suppress the occurrence of a defect in which a difference in thickness of the adhesive layer (deformation of the adhesive layer) occurs around the bent portion due to excessive fluidity of the adhesive. By these actions, even when the laminate is left in a long-term bent state, the laminate is less likely to float or peel at the interface between the adhesive layer and the adherend, i.e., can exhibit excellent bending resistance.

In the above invention (invention 1), the gel fraction is preferably 40% to 95% (invention 2).

In the above inventions (inventions 1 and 2), the adhesive is preferably an acrylic adhesive (invention 3).

The second aspect of the present invention provides an adhesive sheet comprising an adhesive layer for bonding one bendable member and another bendable member constituting a device which is repeatedly bent, wherein the adhesive layer is composed of the adhesive for repeatedly bending devices (inventions 1 to 3) (invention 4).

In the above invention (invention 4), the adhesive sheet preferably has an adhesive force to polyimide of 1.0N/25mm or more (invention 5).

In the above inventions (inventions 4 and 5), the adhesive sheet preferably has an adhesive force to the gas barrier layer of the gas barrier film of 1.0N/25mm or more (invention 6).

In the above inventions (inventions 4 to 6), the adhesive agent layer preferably has a thickness of 1 μm to 300 μm (invention 7).

In the above inventions (inventions 4 to 7), it is preferable that the adhesive sheet includes two release sheets, and the adhesive layer is sandwiched between the release sheets so as to be in contact with release surfaces of the two release sheets (invention 8).

Third, the present invention provides a repeatedly bending laminated member, comprising: one bendable member and another bendable member constituting a device which is repeatedly bent, and an adhesive layer which bonds the one bendable member and the another bendable member to each other, wherein the adhesive layer is composed of the adhesive for repeatedly bending devices (inventions 1 to 3) (invention 9).

The present invention fourth provides a repeating bending device comprising the repeating bending laminated member (invention 9) (invention 10).

Effects of the invention

The adhesive and the adhesive sheet for a repeatedly bendable device according to the present invention are less likely to cause floating or peeling at the interface between the adhesive layer and the adherend even when applied to a repeatedly bendable device and left in a long-term bent state, and have excellent bending resistance. In addition, the repeatedly bendable laminated member and the repeatedly bendable device of the present invention are less likely to cause floating or peeling at the interface between the adhesive layer and the adherend even when left in a long-term bent state, and have excellent bending resistance.

Drawings

Fig. 1 is a sectional view of an adhesive sheet according to an embodiment of the present invention.

Fig. 2 is a sectional view of a repeating curved laminated member according to an embodiment of the present invention.

Fig. 3 is an explanatory view (side view) illustrating the static bending test.

FIG. 4 is a cross-sectional view of a recurved bend device in accordance with one embodiment of the present invention.

Description of the reference numerals

1: an adhesive sheet; 11: an adhesive layer; 12a, 12b: a release sheet; 2: repeatedly bending the laminated member; 21: a first bendable member; 22: a second bendable member; s: a test piece; p: a holding plate; 3: repeatedly bending the device; 31: coating a film; 32: a first adhesive layer; 33: a polarizing film; 34: a second adhesive layer; 35: a touch sensor film (touch sensor film); 36: a third adhesive layer; 37: an organic EL element; 38: a fourth adhesive layer; 39: and a TFT substrate.

Detailed Description

Hereinafter, embodiments of the present invention will be described.

[ adhesive for repeatedly bending device ]

The adhesive for a repeating bending device of the present embodiment (hereinafter, may be simply referred to as "adhesive") is used for bonding one bendable member and another bendable member constituting the repeating bending device. The recurve bending device and the bendable member are described later.

The maximum relaxation modulus value measured when the adhesive is deformed by 10% is defined as the maximum relaxation modulus G (t) in the adhesive of the present embodiment based on JIS K7244-1 _max (MPa), the maximum relaxation modulus G (t) is measured _max The adhesive was continuously deformed by 10% from the start to 3757 seconds, and the minimum relaxation modulus value measured during this time was set as the minimum relaxation modulus G (t) _min (MPa), and a change in relaxation modulus Δ logG (t) calculated by the following formula (I) is 0.33 to 1.50.

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

The details of the method for measuring the relaxation modulus G (t) are shown in the test examples described later.

When a laminate in which one bendable member and another bendable member are bonded to each other with an adhesive layer is placed in a bent state, stress in a tensile direction is applied to the outside of a bent portion of the adhesive layer, and stress in a compressive direction is applied to the inside of the bent portion of the adhesive layer. In this way, since different stresses are applied to the outside of the bent portion and the inside of the bent portion, the adhesive layer has reduced adhesion to the adherend and is likely to float or peel. However, when the variation value of the relaxation modulus of the adhesive of the present embodiment is 0.33 or more, the stress difference described above is reduced, and the stress of the entire adhesive layer is easily relaxed. This makes it easy to maintain the adhesion between the adhesive layer and the adherend. On the other hand, if the variation value of the relaxation modulus is 1.50 or less, it is easy to suppress a problem that the fluidity of the adhesive becomes too large and a difference in thickness of the adhesive layer (deformation of the adhesive layer) occurs around the bent portion. In this case, even when the laminate is left in a long-term bent state, the adhesive layer is less likely to float or peel at the interface between the adhesive layer and the adherend, and the adhesive layer does not have a difference in thickness. That is, excellent bending resistance can be exhibited. This effect can be sufficiently exhibited even in an environment of a low temperature (for example, -20 ℃) in which interfacial separation is likely to occur. In addition, even when the bendable member in the laminate is a polyimide film or a gas barrier film, or a laminate containing a polyimide film or a gas barrier film, the excellent bending resistance can be sufficiently exhibited.

From the viewpoint of the above-described bending resistance, the relaxation modulus variation Δ logG (t) needs to be 0.33 or more, preferably 0.45 or more, particularly preferably 0.50 or more, and more preferably 0.55 or more. In addition, the relaxation modulus variation value Δ logG (t) needs to be 1.50 or less, preferably 1.20 or less from the viewpoint of the above-described bending resistance, and is particularly preferably 0.95 or less, more preferably 0.89 or less from the viewpoint of suppressing deformation of the adhesive agent layer.

The maximum relaxation modulus G (t) of the adhesive of the present embodiment _max Preferably 0.0001MPa or more, more preferably 0.001MPa or more, particularly preferably 0.01MPa or more, and further preferably 0.017MPa or more. In addition, the maximum relaxation modulus G (t) _max Preferably 1MPa or less, particularly preferably 0.1MPa or less, and more preferably 0.04MPa or less. By bringing the maximum relaxation modulus G (t) _max Within the above range, the relaxation modulus variation Δ logG (t) easily satisfies the above value.

In addition, the minimum relaxation modulus G (t) of the adhesive of the present embodiment _min Preferably 0.0001MPa or more, particularly preferably 0.0005MPa or more, and more preferably 0.001MPa or more. In addition, the minimum relaxation modulus G (t) _min Preferably 0.1MPa or less, particularly preferably 0.01MPa or less, and more preferably 0.005MPa or less. By making the minimum relaxation modulus G (t) _min Within the above range, the relaxation modulus variation Δ logG (t) easily satisfies the above value.

The gel fraction of the pressure-sensitive adhesive of the present embodiment is preferably 40% or more, more preferably 50% or more, particularly preferably 60% or more, and further preferably 65% or more. Thus, the adhesive exhibits a suitable cohesive force, and therefore, when it is repeatedly bent, the occurrence of floating or peeling at the interface between the adhesive layer and the adherend can be suppressed. On the other hand, the gel fraction of the adhesive of the present embodiment is preferably 95% or less, more preferably 90% or less, particularly preferably 87% or less, and further preferably 84% or less. This makes it possible to suitably exhibit flexibility and stress relaxation property of the adhesive, and the above-mentioned bending resistance is further excellent. The method for measuring the gel fraction in the present specification is as shown in the test examples described later.

The type of the adhesive of the present embodiment is not particularly limited as long as the above physical properties are satisfied, and may be any of, for example, an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, a silicone adhesive, and the like. The adhesive may be any of emulsion type, solvent type, and non-solvent type, and may be any of crosslinking type and non-crosslinking type. Among them, acrylic adhesives which easily satisfy the above-mentioned excellent physical properties, adhesive physical properties, optical characteristics, and the like are preferable, and particularly, solvent-type acrylic adhesives are preferable.

Specifically, the adhesive of the present embodiment is preferably an adhesive obtained by crosslinking an adhesive composition containing a (meth) acrylate polymer (a) and a crosslinking agent (B) (hereinafter, may be referred to as "adhesive composition P"). In the case of the adhesive, the above-mentioned physical properties are easily satisfied, and a good adhesive force is easily obtained. In the present specification, the term (meth) acrylic acid means acrylic acid and methacrylic acid. Other similar terms are also the same. Further, "polymer" also includes the concept of "copolymer".

(1) Components of the adhesive composition P

(1-1) (meth) acrylate ester Polymer (A)

The (meth) acrylate polymer (a) preferably contains, as monomer units constituting the polymer, an alkyl (meth) acrylate and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer).

By containing the (meth) acrylic acid ester polymer (a) as a monomer unit constituting the polymer, excellent adhesiveness can be exhibited. The alkyl (meth) acrylate is preferably an alkyl (meth) acrylate in which the alkyl group has 1 to 20 carbon atoms. The alkyl group may be linear or branched, and may have a cyclic structure.

Examples of the alkyl (meth) acrylate having an alkyl group having 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 them, from the viewpoint of the above-mentioned relaxation modulus fluctuation value, a (meth) acrylate having an alkyl group with 1 to 8 carbon atoms is preferable, and a (meth) acrylate having an alkyl group with 4 to 8 carbon atoms is particularly preferable. Specifically, n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable. These alkyl (meth) acrylates may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer (a) contains, as a monomer unit constituting the polymer, preferably 60% by mass or more, more preferably 80% by mass or more, particularly preferably 90% by mass or more, and further preferably 95% by mass or more of an alkyl (meth) acrylate having 1 to 20 carbon atoms and an alkyl group. In addition, from the viewpoint of further improving the maximum relaxation modulus, an alkyl (meth) acrylate having 1 to 20 carbon atoms and containing an alkyl group in an amount of 98 mass% or more is preferable as a monomer unit constituting the polymer. When the amount of the alkyl (meth) acrylate is not less than the above amount, the (meth) acrylate polymer (a) can be provided with appropriate tackiness, and the relaxation modulus variation value can be easily adjusted to a high value. The alkyl (meth) acrylate having 1 to 20 carbon atoms preferably contains 99.9% by mass or less, particularly preferably 99.5% by mass or less, and more preferably 99.0% by mass or less of an alkyl group. When the amount of the alkyl (meth) acrylate is equal to or less than the above amount, other monomer components can be introduced into the (meth) acrylate polymer (a) in a desired amount.

The (meth) acrylate polymer (a) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and reacts with a crosslinking agent (B) described later via a reactive functional group derived from the reactive functional group-containing monomer, whereby a crosslinked structure (three-dimensional network structure) can be formed, and an adhesive having a desired cohesive force can be obtained. The adhesive easily satisfies the above-mentioned relaxation modulus variation value (and gel fraction).

Examples of the reactive functional group-containing monomer contained in the (meth) acrylate 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), and a monomer having an amino group in the molecule (amino group-containing monomer). These reactive functional group-containing monomers may be used alone or in combination of two or more.

Among the above reactive functional group-containing monomers, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred. Since the hydroxyl group-containing monomer easily adjusts the crosslinking density, the above-mentioned relaxation modulus fluctuation value (and gel fraction) can be easily satisfied.

Examples of the hydroxyl group-containing monomer include hydroxyalkyl (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 the above hydroxyl group-containing monomers, hydroxyalkyl (meth) acrylates having a hydroxyalkyl group having 1 to 4 carbon atoms are preferable from the viewpoint of easiness of satisfying the above relaxation modulus fluctuation value (and gel fraction). Specifically, for example, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and the like are preferably mentioned, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate is particularly preferably mentioned. These hydroxyl group-containing monomers may be used alone or in combination of two or more.

Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid, and among these, acrylic acid is preferable from the point of the adhesive force of the obtained (meth) acrylate polymer (a). These carboxyl group-containing monomers may be used alone or in combination of two or more.

The lower limit of the content of the reactive functional group-containing monomer in the (meth) acrylate polymer (a) is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and more preferably 1.0% by mass or more, as a monomer unit constituting the polymer. In addition, the (meth) acrylate polymer (a) preferably contains 10% by mass or less, more preferably 7% by mass or less, particularly preferably 5% by mass or less, and further preferably 2% by mass or less of the reactive functional group-containing monomer as a monomer unit constituting the polymer in terms of the above limit. When the (meth) acrylate polymer (a) contains the reactive functional group-containing monomer as a monomer unit in the above amount, the cohesive force of the obtained adhesive becomes appropriate by the crosslinking reaction with the crosslinking agent (B), and the relaxation modulus fluctuation value (and gel fraction) described above can be easily satisfied.

It is also preferable that the (meth) acrylate polymer (a) does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, since the carboxyl group-containing monomer is not contained, even when a substance which causes a problem due to an acid, for example, a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, a metal mesh, or the like is present on an object to which the adhesive is to be attached, the problem (corrosion, change in resistance value, or the like) caused by the acid can be suppressed.

The "not containing a carboxyl group-containing monomer" means that the monomer contains almost no carboxyl group-containing monomer, and the monomer is allowed to contain the carboxyl group-containing monomer to such an extent that corrosion of the transparent conductive film, the metal wiring, or the like due to the carboxyl group does not occur, in addition to not containing the carboxyl group-containing monomer at all. Specifically, the (meth) acrylate polymer (a) is allowed to contain a carboxyl group-containing monomer as a monomer unit in an amount of 0.1% by mass or less, preferably in an amount of 0.01% by mass or less, and more preferably in an amount of 0.001% by mass or less.

The (meth) acrylate polymer (a) may contain other monomers as a monomer unit constituting the polymer, as required. In order not to inhibit the above-mentioned action of the reactive functional group-containing monomer, as the other monomer, a monomer not containing a reactive functional group is preferable. Examples of the monomer include non-reactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone; alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, vinyl acetate, and styrene. These other monomers may be used alone or in combination of two or more.

The polymerization form of the (meth) acrylate polymer (a) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth) acrylate polymer (a) is preferably 40 ten thousand or more, more preferably 50 ten thousand or more, particularly preferably 60 ten thousand or more, further preferably 70 ten thousand or more, and most preferably 80 ten thousand or more. The weight average molecular weight of the (meth) acrylate polymer (a) is preferably 220 ten thousand or less, more preferably 180 ten thousand or less, particularly preferably 160 ten thousand or less, and further preferably 130 ten thousand or less. When the weight average molecular weight of the (meth) acrylate polymer (a) is within the above range, the above-mentioned relaxation modulus fluctuation value and gel fraction are easily satisfied. The weight average molecular weight in the present specification is a value in terms of standard polystyrene measured by a Gel Permeation Chromatography (GPC) method.

In the adhesive composition P, one kind of the (meth) acrylate polymer (a) may be used alone, or two or more kinds may be used in combination.

(1-2) crosslinking agent (B)

The crosslinking agent (B) crosslinks the (meth) acrylate polymer (a) to form a three-dimensional network structure using, as a trigger (trigger), heating or the like of the adhesive composition P containing the crosslinking agent (B). This improves the cohesive force of the obtained adhesive, and the relaxation modulus fluctuation value (and gel fraction) can be easily satisfied.

The crosslinking agent (B) may be a substance that reacts with the reactive group of the (meth) acrylate polymer (a), and examples thereof 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 the above crosslinking agents, isocyanate crosslinking agents having excellent reactivity with the reactive functional group-containing monomer are preferably used. The crosslinking agent (B) may be used singly or in combination of two or more.

The isocyanate-based crosslinking agent includes at least a polyisocyanate compound. Examples of the polyisocyanate compound 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 derivatives thereof; and adducts of the compounds with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanates are preferable from the viewpoint of reactivity with hydroxyl groups, and trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene diisocyanate is particularly preferable.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 part by mass or more, particularly preferably 0.04 part by mass or more, and more preferably 0.08 part by mass or more, relative to 100 parts by mass of the (meth) acrylate polymer (a). The content is preferably 1.50 parts by mass or less, more preferably 1.00 parts by mass or less, particularly preferably 0.60 parts by mass or less, and further preferably 0.40 parts by mass or less. When the content of the crosslinking agent (B) is within the above range, the above-mentioned relaxation modulus variation value and gel fraction are easily satisfied.

(1-3) various additives

Various additives generally used in acrylic adhesives, for example, silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index modifiers, and the like can be added to the adhesive composition P as needed. The polymerization solvent or the dilution solvent described later is not included in the additive constituting the adhesive composition P.

The adhesive composition P preferably contains the silane coupling agent. This improves the adhesion between the obtained adhesive layer and a flexible member as an adherend, and improves the adhesion.

The silane coupling agent is preferably an organosilicon compound having at least 1 alkoxysilyl group in the molecule, which has good compatibility with the (meth) acrylate polymer (a) and light transmittance.

Examples of the silane coupling agent 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; mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane and the like; amino-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane; or condensates of at least one of these compounds with an alkyl-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, or the like. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent in the adhesive composition P is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and more preferably 0.1 part by mass or more, relative to 100 parts by mass of the (meth) acrylate polymer (a). The content is preferably 1 part by mass or less, particularly preferably 0.5 part by mass or less, and further preferably 0.3 part by mass or less. When the content of the silane coupling agent is in the above range, the adhesion between the obtained adhesive layer and a flexible member as an adherend is improved, and the adhesion is further increased.

(2) Preparation of adhesive composition P

The adhesive composition P can be prepared by: the (meth) acrylic ester polymer (A) is prepared, and the resulting (meth) acrylic ester polymer (A) is mixed with the crosslinking agent (B) while adding additives as needed.

The (meth) acrylate polymer (a) can be produced by polymerizing a mixture of monomers constituting the polymer by a general radical polymerization method. The polymerization of the (meth) acrylate polymer (a) is preferably carried out by a solution polymerization method using a polymerization initiator as needed. By polymerizing the (meth) acrylate polymer (a) by a solution polymerization method, the obtained polymer can be easily increased in molecular weight and adjusted in molecular weight distribution, and the production of low molecular weight products can be further reduced. Therefore, even when the gel fraction is small and the degree of crosslinking is reduced, the adhesive is less likely to shift with repeated bending, and an adhesive which is less likely to float or peel even when repeatedly bent is easily obtained.

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 kinds thereof may be used simultaneously.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used simultaneously. As the azo-based compound, there may be mentioned, examples thereof include 2,2' -azobisisobutyronitrile, 2' -azobis (2-methylbutyronitrile), 1' -azobis (cyclohexane-1-carbonitrile), 2' -azobis (2, 4-dimethylvaleronitrile), 2' -azobis (2, 4-dimethyl-4-methoxyvaleronitrile) 2,2' -azobis (2-methylpropionic acid) dimethyl ester, 4' -azobis (4-cyanovaleric acid), 2' -azobis (2-hydroxymethylpropionitrile), 2' -azobis [2- (2-imidazolin-2-yl) propane ], and the like.

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

In the polymerization step, a chain transfer agent such as 2-mercaptoethanol is added to adjust the weight average molecular weight of the obtained polymer.

After the (meth) acrylate polymer (a) is obtained, the crosslinking agent (B) and, if necessary, additives and a diluting solvent are added to a solution of the (meth) acrylate polymer (a), and the mixture is thoroughly mixed, thereby obtaining a solvent-diluted adhesive composition P (coating solution).

In the case where a solid substance is used or a precipitate is generated when the solid substance is mixed with another component in an undiluted state, any of the above components may be dissolved or diluted in a diluting solvent in advance and then mixed with another component.

Examples of the diluting 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 solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution prepared in the above manner are not particularly limited as long as the coating solution can be applied, and may be appropriately selected depending on the case. For example, the adhesive composition P may be diluted so that the concentration thereof is 10 to 60 mass%. In addition, when obtaining the coating solution, it is not essential to add a diluting solvent or the like, and the diluting solvent may not be added as long as the adhesive composition P has a viscosity capable of being coated or the like. In this case, the adhesive composition P is a coating solution in which the polymerization solvent of the (meth) acrylate polymer (a) is directly used as a dilution solvent.

(3) Preparation of Adhesives

The adhesive constituting the adhesive layer 11 of the present embodiment is preferably formed by crosslinking the adhesive composition P. The crosslinking of the adhesive composition P can generally be carried out by heat treatment. Further, the drying treatment when evaporating the diluent solvent or the like from the coating film of the adhesive composition P applied to the desired object may also be used as the heating treatment.

The heating temperature of the heating treatment is preferably 50 to 150 ℃, particularly preferably 70 to 120 ℃. The heating time is preferably 10 seconds to 10 minutes, and particularly preferably 50 seconds to 2 minutes.

After the heat treatment, a maturation period of about 1 to 2 weeks may be set as required at room temperature (e.g., 23 ℃ C., 50% RH). When the curing period is required, an adhesive is formed after the curing period, and when the curing period is not required, an adhesive is formed directly after the heat treatment is completed.

By the above-mentioned heat treatment (and curing), the (meth) acrylate polymer (a) can be sufficiently crosslinked via the crosslinking agent (B) to form a crosslinked structure, thereby obtaining an adhesive.

[ adhesive sheet ]

The adhesive sheet of the present embodiment includes an adhesive layer for bonding one bendable member and another bendable member constituting a repeated bending device, and the adhesive layer is made of the adhesive.

Fig. 1 shows a specific configuration of an example of the pressure-sensitive adhesive sheet of the present embodiment.

As shown in fig. 1, the adhesive sheet 1 of one embodiment is composed of two release sheets 12a and 12b and an adhesive layer 11, and the adhesive layer 11 is 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. The release surface of the release sheet in the present specification means a surface having releasability in the release sheet, and includes any one of a surface subjected to a release treatment and a surface showing releasability even if the release treatment is not performed.

(1) Constituent elements

(1-1) adhesive agent layer

The adhesive layer 11 is composed of the adhesive of the above embodiment, and preferably is composed of an adhesive obtained by crosslinking the adhesive composition P.

The lower limit of the thickness (value measured in accordance with JIS K7130) of the adhesive layer 11 in the adhesive sheet 1 of the present embodiment is preferably 1 μm or more, more preferably 5 μm or more, particularly preferably 10 μm or more, and further preferably 15 μm or more. When the lower limit of the thickness of the adhesive layer 11 is set to the above value, a desired adhesive force is easily exhibited, and floating or peeling at the interface between the adhesive layer and the adherend is less likely to occur. 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 still more preferably 40 μm or less, from the viewpoint of obtaining a thinner device which is repeatedly bent. If the upper limit value of the thickness of the adhesive agent layer 11 is as described above, the difference between the stress received outside the bent portion and the stress received inside the bent portion becomes small, and the stress of the entire adhesive agent layer due to the above-described variation in the relaxation modulus can be more easily relaxed, so that the bending resistance is more excellent. The adhesive layer 11 may be formed of a single layer or may be formed by stacking a plurality of layers.

The total light transmittance (value measured in accordance with JIS K7361-1 1997) of the adhesive layer 11 of the adhesive sheet 1 of the present embodiment is preferably 80% or more, more preferably 90% or more, particularly preferably 95% or more, and further preferably 99% or more. When the total light transmittance is as described above, the transparency is high, and the optical film is suitably used for optical applications (for a display device which is repeatedly bent).

(1-2) Release sheet

The release sheets 12a, 12b protect the adhesive layer 11 until the time of using the adhesive sheet 1, and are released when using the adhesive sheet 1 (adhesive layer 11). In the adhesive sheet 1 of the present embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

Examples of the release sheets 12a and 12b include a polyethylene film, a polypropylene film, a polybutylene film, a polybutadiene film, a polymethylpentene film, a polyvinyl chloride film, a vinyl chloride copolymer film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, a polyurethane film, an ethylene vinyl acetate film, an ionomer resin film, an ethylene- (meth) acrylic acid copolymer film, an ethylene- (meth) acrylate copolymer film, a polystyrene film, a polycarbonate film, a polyimide film, and a fluororesin film. In addition, crosslinked films of these films may also be used. Further, a laminated film of these films may be used.

The release surfaces (particularly, the surfaces in contact with the adhesive agent layer 11) of the release sheets 12a and 12b are preferably subjected to a release treatment. Examples of the release agent used for the release treatment include alkyd based, silicone based, fluorine based, unsaturated polyester based, polyolefin based, and paraffin based release agents. Of the release sheets 12a and 12b, one release sheet is preferably a heavy release type release sheet having a large release force, and the other release sheet is preferably a light release type release sheet having a small release force.

The thickness of the release sheets 12a and 12b is not particularly limited, but is usually about 20 to 150 μm.

(2) Adhesive force

The lower limit of the adhesive force of the adhesive sheet 1 of the present embodiment to polyimide is preferably 1.0N/25mm or more, more preferably 3.0N/25mm or more, particularly preferably 5.0N/25mm or more, and further preferably 6.0N/25mm or more. When the lower limit of the adhesive strength of the adhesive sheet 1 to polyimide is the above value, even when a polyimide film or the like is used as an adherend and left to be bent for a long period of time, the adhesive sheet is less likely to float or peel at the interface between the adhesive layer and the adherend, and is more excellent in bending resistance. On the other hand, the upper limit of the above-mentioned adhesive force is not particularly limited, but is usually preferably 50N/25mm or less, more preferably 40N/25mm or less, and from the viewpoint of reworkability to enable re-adhesion of the adhesive sheet when an adhesion error occurs in the adhesive sheet, is particularly preferably 30N/25mm or less, and more preferably 20N/25mm or less. The adhesive force in the present specification is basically an adhesive force measured by a 180-degree peel method in accordance with JIS Z0237:2009, and a specific test method is shown in test examples described later.

The lower limit of the adhesion of the adhesive sheet 1 of the present embodiment to the gas barrier layer of the gas barrier film (for example, a gas barrier film having a gas barrier layer made of a modified polysilazane) is preferably 1.0N/25mm or more, more preferably 2.0N/25mm or more, particularly preferably 3.0N/25mm or more, and further preferably 4.0N/25mm or more. When the lower limit of the adhesion force of the adhesive sheet 1 to the gas barrier film is set as described above, even when the gas barrier film is left in a long-term bent state as an adherend, the adhesive sheet is less likely to float or peel at the interface between the adhesive layer and the adherend, and the bending resistance is further excellent. On the other hand, the upper limit of the above-mentioned adhesive force is not particularly limited, but is usually preferably 50N/25mm or less, more preferably 40N/25mm or less, and from the viewpoint of reworkability to enable re-adhesion of the adhesive sheet when an adhesion error occurs in the adhesive sheet, is particularly preferably 30N/25mm or less, and more preferably 20N/25mm or less.

The lower limit of the adhesive force of the adhesive sheet 1 of the present embodiment to soda-lime glass is preferably 1.0N/25mm or more, more preferably 3.0N/25mm or more, particularly preferably 5.2N/25mm or more, and further preferably 6.4N/25mm or more. When the lower limit of the adhesive force of the adhesive sheet 1 to soda-lime glass is as described above, even when a member made of various materials is used as an adherend, the adhesive sheet is less likely to float or peel at the interface between the adhesive layer and the adherend. On the other hand, the upper limit of the above-mentioned adhesive force is not particularly limited, but is usually preferably 50N/25mm or less, more preferably 40N/25mm or less, and from the viewpoint of reworkability to enable re-adhesion of the adhesive sheet when an adhesion error occurs in the adhesive sheet, is particularly preferably 30N/25mm or less, and more preferably 20N/25mm or less.

(3) Production of adhesive sheet

The case of using the adhesive composition P will be described as one example of the production of the adhesive sheet 1. A coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12 b), heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, and then the release surface of the other release sheet 12b (or 12 a) is superposed on the coating layer. When the curing period is required, the coating layer becomes the adhesive layer 11 by providing the curing period, and when the curing period is not required, the coating layer directly becomes the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. The conditions for the heat treatment and aging are as described above.

As another production example of the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12a with a coating layer. Further, the coating solution of the adhesive composition P is applied to the release surface of the other release sheet 12b, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12b with a coating layer. Then, the coated release sheet 12a and the coated release sheet 12b are bonded to each other so that the two coated layers are in contact with each other. When the curing period is required, the stacked coating layers become the adhesive layer 11 by providing the curing period, and when the curing period is not required, the stacked coating layers directly become the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. This production example enables stable production even when the adhesive layer 11 is thick.

Examples of the method for applying the coating solution of the adhesive composition P include a bar coating method, a blade coating method, a roll coating method, a blade coating method, a die coating method, and a gravure coating method.

[ repeatedly bending the laminated Member ]

As shown in fig. 2, the repeated bending laminated member 2 of the present embodiment includes a first bendable member 21 (one bendable member), a second bendable member 22 (the other bendable member), and an adhesive layer 11, and the adhesive layer 11 is located between the first bendable member 21 and the second bendable member 22 and bonds the first bendable member 21 and the second bendable member 22 to each other.

The adhesive layer 11 in the repeatedly bent and laminated member 2 is the adhesive layer 11 of the adhesive sheet 1.

The repeatedly bending laminated member 2 is a repeatedly bending device itself or a member constituting a part of the repeatedly bending device. The repetitive bending device is preferably a display capable of repetitive bending (including bending), but is not limited thereto. Examples of the repeatedly bending device include an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a liquid crystal display using a plastic substrate (film) as a substrate, a foldable display, and the like, and may be a touch panel.

The first bendable member 21 and the second bendable member 22 are members that can be repeatedly bent (including bent), and examples thereof include a coating 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 luminance improvement Film, a contrast improvement Film, a diffusion Film, a transflective 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.

Of the above members, one of the first bendable member 21 and the second bendable member 22 is preferably a gas barrier film or a laminate having a gas barrier film on the adhesive layer 11 side. In particular, the other of the first bendable member 21 and the second bendable member 22 is preferably a polyimide film or a laminate including a polyimide film on the adhesive layer 11 side. The gas barrier film and the polyimide film generally have low adhesion to the adhesive layer, but according to the adhesive layer 11 of the present embodiment, even if the gas barrier film or the polyimide film is an adherend, the bending resistance is excellent, and the adhesive layer is less likely to float or peel at the interface between the adhesive layer and the adherend.

The Young's modulus of each of the first bendable member 21 and the second bendable member 22 is preferably 0.1 to 10GPa, particularly preferably 0.5 to 7GPa, and still more preferably 1 to 5GPa. When the young's modulus of the first bendable member 21 and the second bendable member 22 is in this range, the respective bendable members can be easily bent repeatedly.

The thickness of each of the first bendable member 21 and the second bendable member 22 is preferably 10 to 3000 μm, particularly preferably 25 to 1000 μm, and more preferably 50 to 500 μm. By setting the thicknesses of the first bendable member 21 and the second bendable member 22 in this range, repeated bending of each bendable member is facilitated.

In order to manufacture the above-described repeatedly bent laminated member 2, one release sheet 12a of the adhesive sheet 1 is peeled off, and the adhesive layer 11 exposed from the adhesive sheet 1 is bonded to one surface of the first bendable member 21.

Then, the other release sheet 12b is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the adhesive layer 11 exposed from the adhesive sheet 1 and the second bendable member 22 are bonded to obtain the repeatedly bent laminated member 2. Further, as another example, the order of fitting the first bendable member 21 and the second bendable member 22 may be interchanged.

[ repeated bending device ]

The repeating bending device of the present embodiment includes the repeating bending laminated member 2 described above, and may be configured by only the repeating bending laminated member 2, or may be configured by including one or a plurality of repeating bending laminated members 2 and another bendable member. When one of the repeatedly bent and laminated member 2 and the other repeatedly bent and laminated member 2 are laminated, or when the repeatedly bent and laminated member 2 and the other bendable member are laminated, it is preferable to perform lamination via the adhesive layer 11 of the adhesive sheet 1.

Since the adhesive layer of the repeated bending device of the present embodiment is composed of the adhesive described above, even when the device is left in a long-term bent state, the adhesive layer 11 is less likely to cause lifting or peeling at the interface with the adherend (the first bendable member 21 and the second bendable member 22), and excellent bending resistance can be exhibited. This effect can be sufficiently exhibited even in an environment at a low temperature (for example, -20 ℃) where surface peeling is likely to occur. In addition, even when the adherend is a polyimide film or a gas barrier film, or a laminate containing a polyimide film or a gas barrier film, the excellent bending resistance can be sufficiently exhibited. The bending resistance can be evaluated by, for example, a static bending test.

In the static bending test, a laminate having a size of 200mm × 50mm in which the adhesive layer is sandwiched between two repeatedly bent laminate members was used as a test piece. As shown in FIG. 3, the test piece was subjected to an environment of-20 ℃ or an environment of 23 ℃ and 50% RHS is held between holding plates P composed of two glass plates set upright in a bent state for 5 minutes or 24 hours. At this time, the distance between the two holding plates P was set to 4mm (the bending diameter of the test piece S:

) The test piece S is held so that the two short sides (50 mm) of the test piece S are positioned above the test piece S, with the bent portion being substantially the center of the long side (200 mm) of the test piece S. After the static bending test, the test piece S was taken out from between the two holding plates P, and it was visually confirmed whether or not the adhesive layer at the bent portion floated or peeled off at the interface between the adhesive layer and each of the repeatedly bent laminated members.

Fig. 4 shows a repeating bending device as an example of the present embodiment. In addition, the repeated bending device of the present invention is not limited to this repeated bending device.

As shown in fig. 4, the bending device 3 of the present embodiment is configured by laminating a coating 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 in this order from top to bottom. The cover film 31, the polarizing film 33, the touch sensor film 35, the organic EL element 37, and the TFT substrate 39 correspond to a flexible member.

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. Preferably, 2 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, and most preferably, all of the adhesive layers 32, 34, 36, and 38 are the adhesive layers 11 of the adhesive sheet 1.

The coating 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 (the gas barrier layer is on the adhesive layer 11 side) on the first adhesive layer 32 side. In this case, at least the first adhesive layer 32 is preferably the adhesive layer 11 of the adhesive sheet 1. Further, for example, when the TFT substrate 39 includes a polyimide film, particularly when the polyimide film is provided 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.

In the above-described repeated bending device 3, even when left in a long-term bent state, the adhesive layer composed of the adhesive layer 11 of the adhesive sheet 1 is less likely to cause floating or peeling at the interface between the adhesive layer and the bendable member bonded by the adhesive layer, and excellent bending resistance can be exhibited. This effect can be sufficiently exhibited even in an environment at a low temperature (for example, -20 ℃) where interfacial peeling is likely to occur. In addition, even when the bendable member is a polyimide film or a gas barrier film, or a laminate containing a polyimide film or a gas barrier film, the excellent bending resistance can be sufficiently exhibited.

The above-described embodiments are described for the convenience of understanding the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments also covers all design changes or equivalents which fall within the technical scope of the present invention.

For example, either one or both of the release sheets 12a, 12b in the adhesive sheet 1 may be omitted, and further, a desired bendable member may be laminated instead of the release sheets 12a and/or 12b.

Examples

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

1. Preparation of (meth) acrylate Polymer (A)

The (meth) acrylate 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 a solution polymerization method. The molecular weight of the (meth) acrylate polymer (a) was measured by the method described later, and as a result, the weight average molecular weight (Mw) was 80 ten thousand.

2. Preparation of adhesive composition

A coating solution of an adhesive composition was obtained by mixing 100 parts by mass (in terms of solid content; the same applies hereinafter) of the (meth) acrylic ester polymer (A) obtained in the above step 1, 0.25 part by mass of trimethylolpropane-modified xylylene diisocyanate (XDI; product name "TD-75" manufactured by Soken Chemical & Engineering Co., ltd.) as a crosslinking agent (B), and 0.20 part by mass of 3-glycidoxypropyltrimethoxysilane as a silane coupling agent, followed by sufficient stirring and dilution with methyl ethyl ketone.

3. Preparation of adhesive sheet

The obtained coating solution of the adhesive composition was coated on the release-treated surface of a heavy release type release sheet (manufactured by Lintec Corporation, product name "SP-PET 752150") which was obtained by subjecting one surface of a polyethylene terephthalate film to a release treatment using a silicone-based release agent, using a blade coater. Then, the coating layer was heat-treated at 90 ℃ for 1 minute to form a coating layer.

Then, the light release sheet and the coating layer were laminated so that the coating layer on the heavy release sheet obtained above was in contact with the release-treated surface of the light release sheet (product name "SP-PET381130" manufactured by linec Corporation) obtained by subjecting one surface of the polyethylene terephthalate film to a release treatment using a silicone-based release agent, and the resultant was aged at 23 ℃ and 50% rh for 7 days, thereby producing an adhesive sheet having an adhesive layer with a thickness of 25 μm, that is, an adhesive sheet composed of a heavy release sheet/an adhesive layer (thickness: 25 μm)/a light release sheet. The thickness of the adhesive layer was measured by a constant pressure thickness measuring instrument (TECLOCK co., ltd., product name "PG-02") based on JIS K7130.

Here, the blending amounts (solid content equivalent) of the adhesive compositions when the (meth) acrylate polymer (a) is 100 parts by mass (solid content equivalent) are shown in table 1. The details of the abbreviations and the like shown in table 1 are as follows.

[ (meth) acrylic ester Polymer (A) ]

BA: acrylic acid n-butyl ester

2EHA: 2-ethylhexyl acrylate

4HBA: acrylic acid 4-hydroxybutyl ester

AA: acrylic acid

2HPA: 2-hydroxypropyl acrylate

MA: acrylic acid methyl ester

HEA: 2-Hydroxyethyl acrylate

[ crosslinking agent (B) ]

XDI: trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical & Engineering Co., ltd., product name "TD-75")

TDI: trimethylolpropane-modified toluene diisocyanate (TOYOCHEM CO., LTD., product name "BHS 8515")

Examples 2 to 10 and comparative examples 1 to 2

An adhesive sheet was produced in the same manner as in example 1, except that the kind and ratio of each monomer constituting the (meth) acrylate polymer (a), the weight average molecular weight (Mw) of the (meth) acrylate polymer (a), and the kind and blending amount of the crosslinking agent (B) were changed as shown in table 1.

[ preparation example 1]

A polyethylene terephthalate (PET) film (manufactured by inc., product name "PET50a4100" having a thickness of 50 μm) having one surface subjected to an easy adhesion treatment was used as a substrate, a composition containing an Ultraviolet (UV) curable resin and a reactive silica (manufactured by JSR Corporation, product name "opsar Z7530") was applied to one surface (a smooth surface not subjected to an easy adhesion treatment) of the substrate using a meyer rod to form a coating film, and the coating film was dried at 70 ℃ for 1 minute. Then, the coating film was irradiated with UV under the following conditions using a conveyor belt type UV light irradiation apparatus (manufactured by Fusion corporation, product name "F600V") to cure the coating film, thereby forming an anchor coat layer having a thickness of 1 μm.

< UV irradiation conditions >

"UV lamp: high-pressure mercury lamp

Line speed: 20 m/min

"cumulative light amount: 120mJ/cm ²

"illuminance: 200mW/cm ²

"light height: 104mm

Then, a coating material (product name "AZ-110a-20" manufactured by Merck Performance Materials) containing perhydropolysilazane as a main component was applied on the surface of the above-described anchor layer by a spin coating method. Then, the mixture was heated at 120 ℃ for 1 minute to form a polysilazane layer containing perhydropolysilazane. The thickness of the polysilazane layer formed was 200nm.

Then, argon (Ar) was plasma-based ion-implanted into the surface of the polysilazane layer using a plasma-based ion implantation apparatus, thereby forming a gas barrier layer made of a modified polysilazane. In this way, a gas barrier film having a gas barrier layer composed of a modified polysilazane on one surface of a base material (PET film) was obtained. In addition, the modification of polysilazane proceeds from the surface of the polysilazane layer. Therefore, the degree of modification does not affect the surface state of the gas barrier layer, and therefore does not affect the bending resistance and the like.

[ test example 1] (measurement of gel fraction)

The adhesive sheets prepared in examples and comparative examples were cut into 80mm × 80mm pieces, the adhesive layers were wrapped in a polyester mesh (product name: tetoron mesh # 200), the masses thereof were weighed with a precision balance, and the masses of the individual meshes were subtracted from each other, thereby calculating the masses of the adhesives themselves. The mass at this time is denoted as M1.

Subsequently, the adhesive wrapped in the polyester net was immersed in ethyl acetate at room temperature (23 ℃ C.) for 24 hours. Then, the adhesive was taken out, air-dried at a temperature of 23 ℃ and a relative humidity of 50% for 24 hours, and further dried in an oven at 80 ℃ for 12 hours. After drying, the mass of the adhesive itself was calculated by weighing it with a precision balance and subtracting the mass of the web alone. The mass at this time is denoted as M2. Gel fraction (%) is expressed as (M2/M1). Times.100. The results are shown in Table 2.

[ test example 2] (measurement of relaxation modulus)

The adhesive layers of the adhesive sheets prepared in examples and comparative examples were laminated in layers to prepare a laminate having a thickness of 0.5 mm. The laminate of the obtained adhesive layer was punched into a cylinder (height: 0.5 mm) having a diameter of 8mm, and this was used as a sample.

The sample was subjected to deformation of the adhesive by 10% under the following conditions using a viscoelasticity measuring apparatus (product name "MCR302" manufactured by Anton Paar GmbH) in accordance with JIS K7244-1, and the relaxation modulus G (t) (MPa) was measured. From the measurement results, the maximum relaxation modulus G (t) was derived _max (MPa) and the maximum relaxation modulus G (t) measured _max Minimum relaxation modulus G (t) measured from the beginning to 3757 seconds later _min (MPa)。

Measuring temperature: 25 deg.C

Measurement points: 1000 points (logarithmic curve)

From the maximum relaxation modulus G (t) obtained _max (MPa) and minimum relaxation modulus G (t) _min (MPa), the relaxation modulus variation value DeltalogG (t) is calculated from the following formula (I). The results are shown in Table 2.

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

[ test example 3] (measurement of adhesive force)

The light release sheet was peeled from the pressure-sensitive adhesive sheets obtained in examples and comparative examples, and the exposed pressure-sensitive adhesive layer was bonded to an easy-adhesion layer of a polyethylene terephthalate (PET) film (TOYOBO C o., ltd., product name "PET a4300" having a thickness of 100 μm) having an easy-adhesion layer, to obtain a laminate of the heavy release sheet/the pressure-sensitive adhesive layer/the PET film. The obtained laminate was cut into a width of 25mm and a length of 110 mm.

On the other hand, the following 3 kinds of adherends were prepared.

( 1) Soda-lime Glass plate (manufactured by Nippon Sheet Glass co., ltd., product name "soda-lime Glass", thickness: 1.1mm )

( 2) In a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., ltd., product name "soda-lime Glass", thickness: 1.1 mm) was attached to one surface of the adhesive layer (DU PONT-TORAY co., ltd., product name "kapton 100PI", thickness of polyimide film: 25 μm, thickness of adhesive layer: 5 μm) was formed on the surface of the polyimide film (the polyimide film side was the surface to be bonded) )

( 3) A coating was formed on a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., ltd., product name "soda-lime Glass", thickness: 1.1 mm) of the gas barrier film prepared in preparation example 1 was attached to one surface of the substrate (the gas barrier layer was the surface to be bonded) )

The heavy-release type release sheet was peeled from the laminate in an environment of 23 ℃ and 50% rh to attach the exposed adhesive layer to each of the adherends, and the laminate was pressurized at 0.5MPa and 50 ℃ for 20 minutes using an autoclave manufactured by Kurihara manual co., ltd. Then, after being left for 24 hours under the conditions of 23 ℃ and 50% rh, the adhesive force (N/25 mm) at the time of peeling the laminate of the PET film and the adhesive layer from the adherend was measured using a tensile tester (ORIENTEC co., ltd. manufacturing, tensillon) at a peeling speed of 300 mm/minute and a peeling angle of 180 degrees. The conditions other than those described herein were measured in accordance with JIS Z0237: 2009. The results are shown in Table 2.

[ test example 4] (measurement of Total light transmittance)

The adhesive layers of the adhesive sheets obtained in examples and comparative examples were bonded to glass, and the bonded adhesive layers were used as measurement samples. The total light transmittance (%) of the above-mentioned measurement sample was measured by a haze meter (NIPPON DENSHOKU INDUSTRIES CO., LTD., product name "NDH-5000") based on JIS K7361-1. The results are shown in Table 2.

[ test example 5] (static bending test)

The light-release type release sheets were peeled from the adhesive sheets prepared in examples and comparative examples in an environment of 23 ℃ and 50% RH, and the exposed adhesive layer was bonded to one surface of a Polyimide (PI) film (DU PONT-TORAY CO., manufactured by LTD., product name "kapton 100PI", thickness: 25 μm, young's modulus: 3.4 GPa). Then, the heavy-release type release sheet was peeled off, and the exposed adhesive layer was bonded to the gas barrier layer surface of the gas barrier film (Young's modulus: 4.2 GPa) prepared in preparation example 1. Then, the mixture was pressurized at 0.5MPa and 50 ℃ for 20 minutes using an autoclave manufactured by Kurihara Manual Co., ltd, and then allowed to stand at 23 ℃ and 50% RH for 24 hours. The laminate composed of the PI film/adhesive layer/gas barrier film obtained in the above manner was cut into a width of 50mm and a length of 200mm, and the cut product was used as a sample (test piece).

The obtained sample was held in a bent state between holding plates (mutual distance: 4 mm) composed of two glass plates set upright for 5 minutes or 24 hours in an environment of-20 ℃ or an environment of 23 ℃ and 50% RH as shown in FIG. 3. At this time, the test was performed for both cases where the specimen was bent so that the gas barrier film side was opposed to the specimen bent so that the PI film side was opposed. For each sample after the test, it was visually confirmed whether or not the adhesive layer was lifted or peeled off at the interface between the adhesive layer and the adherend at the bent portion, or whether or not the adhesive layer was deformed. The 5 samples of each example were tested, and the bending resistance was evaluated by the following criteria. The results are shown in Table 2.

< evaluation criteria for bending resistance >

Very good: in 5 of the 5 samples, no lifting or peeling occurred at the interface between the adhesive layer and the adherend at the bent portion, and the adhesive layer was not deformed.

Good: although 5 samples out of 5 samples did not float or peel at the interface between the adhesive layer and the adherend in the bent portion, the adhesive layer of 1 to 2 samples out of 5 samples underwent small deformation.

And (delta): in 1 to 4 samples out of 5 samples, lifting or peeling occurred at the interface between the adhesive layer of the bent portion and the adherend, and the adhesive layer of the sample in which lifting or peeling did not occur was not deformed.

X: in 5 samples out of the 5 samples, the adhesive layer at the bent portion was floated or peeled off from the interface between the adhesive layer and the adherend.

In comparative example 2, since the evaluation was x in the static bending test for 5 minutes, the static bending test for 24 hours was not performed.

[ Table 1]

As is clear from table 2, the adhesive layer of the adhesive sheet of the example was free from floating or peeling at the interface between the adhesive layer and the bendable member when 2 bendable members (polyimide film/gas barrier film) were bonded and placed in a bent state, and was excellent in bending resistance. This effect can be sufficiently exhibited not only in a normal temperature environment but also in a low temperature environment of-20 ℃.

Industrial applicability

The present invention is suitable for bonding one bendable member (particularly, a polyimide film or a laminate containing a polyimide film) and another bendable member (a gas barrier film or a laminate containing a gas barrier film) that constitute a repeated bending device.

Claims (12)

1. An adhesive for a repeatedly bendable device for bonding one bendable member and another bendable member constituting a repeatedly bendable device,

the maximum relaxation modulus value measured when the adhesive was deformed by 10% was defined as the maximum relaxation modulus G (t) in accordance with JIS K7244-1 _max (MPa), from the measurement to the maximum relaxation modulus G (t) _max The adhesive was continuously deformed by 10% from the start to 3757 seconds, and the minimum relaxation modulus value measured during this time was set as the minimum relaxation modulus G (t) _min (MPa) a change in relaxation modulus DeltalogG (t) calculated by the following formula (I) is 0.33 to 1.50,

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

the minimum relaxation modulus G (t) _min Is 0.0001MPa or more and 0.005MPa or less.

2. An adhesive for a repeatedly bendable device for bonding one bendable member and another bendable member constituting a repeatedly bendable device,

the maximum relaxation modulus value measured when the adhesive is deformed by 10% is defined as the maximum relaxation modulus value in accordance with JIS K7244-1Yu modulus G (t) _max (MPa), from the measurement to the maximum relaxation modulus G (t) _max The adhesive was continuously deformed by 10% from the start to 3757 seconds, and the minimum relaxation modulus value measured during this time was set as the minimum relaxation modulus G (t) _min (MPa) a change in relaxation modulus DeltalogG (t) calculated by the following formula (I) is 0.33 to 1.50,

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

the maximum relaxation modulus G (t) _max Is 0.0001MPa or more and 0.04MPa or less.

3. An adhesive for a repeatedly bendable device for bonding one bendable member and another bendable member constituting a repeatedly bendable device,

the maximum relaxation modulus value measured when the adhesive was deformed by 10% was defined as the maximum relaxation modulus G (t) in accordance with JIS K7244-1 _max (MPa), from the measurement to the maximum relaxation modulus G (t) _max The adhesive was continuously deformed by 10% from the start to 3757 seconds, and the minimum relaxation modulus value measured during this time was set as the minimum relaxation modulus G (t) _min (MPa), a relaxation modulus change value DeloglG (t) calculated by the following formula (I) is 0.33 or more and 1.50 or less,

ΔlogG(t)＝logG(t) _max -logG(t) _min ···(I)

the adhesive is formed by crosslinking an adhesive composition containing a (methyl) acrylate polymer (A) with the weight-average molecular weight of more than 70 ten thousand and less than 160 ten thousand and a crosslinking agent (B).

4. The adhesive for a repeatedly bending device according to any one of claims 1 to 3, wherein a gel fraction is 40% or more and 95% or less.

5. The adhesive for a repeatedly bending device according to claim 1 or 2, wherein the adhesive is an acrylic adhesive.

6. An adhesive sheet having an adhesive layer for bonding one bendable member and another bendable member constituting a device capable of repeated bending,

the adhesive layer is composed of the adhesive for a repeated bending device according to any one of claims 1 to 3.

7. The adhesive sheet according to claim 6, wherein the adhesive force of the adhesive sheet to polyimide is 1.0N/25mm or more.

8. The adhesive sheet according to claim 6, wherein the adhesive sheet has an adhesive force of 1.0N/25mm or more to a gas barrier layer of a gas barrier film.

9. The adhesive sheet according to claim 6, wherein the thickness of the adhesive layer is 1 μm or more and 300 μm or less.

10. The adhesive sheet according to claim 6,

the adhesive sheet is provided with 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.

11. A repeatedly bending laminated member is provided with: one bendable member and another bendable member constituting a device which is repeatedly bent, and an adhesive layer which adheres the one bendable member and the another bendable member to each other,

the adhesive layer is composed of the adhesive for a repeated bending device according to any one of claims 1 to 3.

12. A recurrently bending device comprising the recurrently bending laminated structure according to claim 11.

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