JP2020139038A - Adhesive for repeated bending device, adhesive sheet, repeated bending laminate member and repeated bending device - Google Patents

Abstract

To provide an adhesive for repeated bending device that can suppress damage such as cracks of a bending member, when repeated bending by applying to a repeated bending device and when placed in a bending state for a long time.SOLUTION: An adhesive for a repeated bending device for adhering one bending member constituting a device that is repeatedly bent and other bending member, in which when shear stress (τ) generated when the adhesive is strained by a shear strain amount (γ) of 0.01 to 200% under the condition of -20°C is measured, in a region where the shear stress (τ) linearly changes to shear strain amount (γ), an average value of a ratio (τ/γ) of the shear stress (τ) to the shear strain amount (γ) is 3.0×108 Pa or smaller.SELECTED DRAWING: Figure 1

Description

The present invention relates to adhesives and pressure-sensitive adhesives for devices that are repeatedly bent, as well as repeatedly bent laminated members and repeatedly bent devices.

In recent years, a flexible flexible display has been proposed as a display body (display) of an electronic device, which is a kind of device. As the bendable display, in addition to the one in which the curved surface is formed only once, the repeatedly bendable display for the purpose of repeatedly bending (bending) has been proposed.

In the repetitive bending display as described above, it is conceivable that one flexible member (flexible member) constituting the flexible display and another flexible member are bonded to each other by an adhesive layer of an adhesive sheet. Be done. However, when a conventional pressure-sensitive adhesive sheet is used for a repeatedly bent display, there arises a problem that floating or peeling occurs at the interface between the pressure-sensitive adhesive layer and the adherend.

Patent Document 1 discloses a pressure-sensitive adhesive having an object of suppressing the occurrence of floating and peeling of the pressure-sensitive adhesive layer even when repeatedly bent.

Japanese Unexamined Patent Publication No. 2016-108555

By the way, in the repeatedly bending display as described above, the flexible member may be damaged such as cracks due to the repeated bending. Such damage also occurs when the repeatedly bent display is fixed in the bent state for a long period of time. With the conventional adhesive sheet as disclosed in Patent Document 1, it is not possible to sufficiently suppress damage such as cracks in the flexible member.

The present invention has been made in view of the above-mentioned actual conditions, and when it is repeatedly bent by being applied to a repeatedly bending device or when it is left in a bent state for a long period of time, the bending member is damaged such as cracks. Adhesives and adhesive sheets for repetitive bending devices that can suppress repeated bending, and repeated bending that can suppress damage such as cracks in flexible members even when repeatedly bent or left in a bent state for a long period of time It is an object of the present invention to provide a bending laminated member and a repeating bending device.

In order to achieve the above object, first, the present invention is an adhesive for a repetitive bending device for bonding one flexible member constituting a device to be repeatedly bent and another flexible member. , When the shear stress (τ) generated when the pressure-sensitive adhesive is distorted at a shear strain amount (γ) of 0.01 to 200% under the condition of −20 ° C. is measured, the shear stress (τ). shear in the region changes linearly with respect to the strain amount (gamma), the average value of the shear stress (tau) the ratio of (τ / γ) relative to the shear strain amount (gamma) is equal to or less than 3.0 × 10 8 ^Pa Provided is a pressure-sensitive adhesive for a repetitive bending device, characterized in that (Invention 1).

In the above invention (Invention 1), the load on the flexible member at the time of bending is caused by the average value of the ratio (τ / γ) of the shear stress (τ) to the above-mentioned shear strain amount (γ) being in the above range. It is possible to reduce the damage such as cracks of the flexible member.

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

Secondly, the present invention is an adhesive sheet having an adhesive layer for adhering one flexible member constituting a device to be repeatedly bent and another flexible member, and the adhesive layer is a pressure-sensitive adhesive layer. Provided is a pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive for a repeating bending device (Invention 1 and 2) (Invention 3).

In the above invention (Invention 3), the adhesive strength of the pressure-sensitive adhesive sheet to polyimide is preferably 4.0 N / 25 mm or more (Invention 4).

In the above inventions (Inventions 3 and 4), the thickness of the pressure-sensitive adhesive layer is preferably 1 μm or more and 300 μm or less (Invention 5).

In the above inventions (Inventions 3 to 5), the pressure-sensitive adhesive sheet includes two release sheets, and the pressure-sensitive adhesive layer is sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets. (Invention 6).

Thirdly, in the present invention, 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. Provided is a repeatedly bent laminated member comprising the above, wherein the pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive for the repeatedly bent device (Invention 1 and 2) (Invention 7).

Fourth, the present invention provides a repetitive bending device including the bending laminated member (Invention 7) (Invention 8).

The pressure-sensitive adhesive and the pressure-sensitive adhesive sheet for a repetitive bending device according to the present invention suppress damage such as cracks in a flexible member when it is repeatedly bent by being applied to a repetitive bending device and when it is left in a bent state for a long period of time. be able to. Further, the repeatedly bent laminated member and the repeatedly bent device according to the present invention can suppress breakage such as cracks of the flexible member even when repeatedly bent or left in a bent state for a long period of time.

It is sectional drawing of the adhesive sheet which concerns on one Embodiment of this invention. It is sectional drawing of the repeated bending laminated member which concerns on one Embodiment of this invention. It is explanatory drawing (side view) explaining the static bending test. It is explanatory drawing (side view) explaining the dynamic bending test. It is sectional drawing of the repeated bending device which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described.
[Adhesive for repeated bending device]
The adhesive for a repetitive bending device according to the present embodiment (hereinafter, may be simply referred to as "adhesive") is for bonding one flexible member constituting the repetitive bending device to another flexible member. Adhesive. The repetitive bending device and the flexible member will be described later.

In the pressure-sensitive adhesive according to the present embodiment, the shear stress (τ) generated when the pressure-sensitive adhesive is distorted at a shear strain amount (γ) of 0.01 to 200% under the condition of −20 ° C. was measured. In the case, the average value (τ / γ) of the ratio (τ / γ) of the shear stress (τ) to the shear strain amount (γ) in the region where the shear stress (τ) linearly changes with respect to the shear strain amount (γ) (hereinafter, “ sometimes referred to average ratio "between τ and gamma.) is less than or equal to 3.0 × ¹⁰ 8 Pa. The details of the above-mentioned shear stress (τ) and the above-mentioned average value measurement method are as shown in the test examples described later.

When a laminate formed by laminating one flexible member and another flexible member with an adhesive layer is placed in a bent state, stress in the tensile direction is applied to the outside of the bent portion of the adhesive layer, and the adhesive Stress in the compression direction is applied inside the bent portion of the layer. Therefore, in the above-mentioned laminated body, when it is repeatedly bent or when it is left in a bent state for a long period of time, the flexible member is liable to be damaged such as cracks. However, the adhesive according to the present embodiment, the average ratio of the γ and τ described above is not more than 3.0 × 10 8 ^Pa, the above-mentioned stress is applied to the bending member is reduced, as a result , The occurrence of breakage in the flexible member is well suppressed. Such an effect is sufficiently exhibited even in a low temperature environment (for example, −20 ° C.) where the flexible member is likely to be damaged. On the other hand, when the average ratio of the τ and γ exceeds 3.0 × 10 8 ^Pa, it is impossible to sufficiently reduce the occurrence of stress due to bending, and can not be prevented the occurrence of breakage of the flexible member Become. From this point of view, the average ratio of τ and γ is preferably 1.0 × 10 ⁸ Pa or less, particularly preferably 5.0 × 10 ⁷ Pa or less, and further 1.3 × 10 ⁷ Pa. preferably less, and most preferably not more than 8.00 × ¹⁰ 6 Pa.

Further, the lower limit of the average ratio of τ and γ is not particularly limited from the viewpoint of suppressing the occurrence of breakage of the flexible member. However, from the viewpoint of easily achieving excellent processability and cohesive force, it is preferably 1.0 × 10 ⁵ Pa or more, particularly preferably 5.0 × 10 ⁵ Pa or more, and further 1 It is preferably 0.0 × 10 ⁶ Pa or more.

The type of the pressure-sensitive adhesive according to the present embodiment is not particularly limited as long as the above physical properties are satisfied, and for example, an acrylic pressure-sensitive adhesive, a polyester-based pressure-sensitive adhesive, a polyurethane-based pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, and the like. It may be any of. Further, the pressure-sensitive adhesive may be an emulsion type, a solvent type or a solvent-free type, and may be either a crosslinked type or a non-crosslinked type. Among them, an acrylic pressure-sensitive adhesive that easily satisfies the above-mentioned physical properties and is excellent in adhesive physical properties, optical properties, etc. is preferable, and a solvent-type acrylic pressure-sensitive adhesive is particularly preferable.

Specifically, the pressure-sensitive adhesive according to the present embodiment is referred to as a pressure-sensitive composition containing a (meth) acrylic acid ester polymer (A) and a cross-linking agent (B) (hereinafter referred to as "sticky composition P"). In some cases, it is preferable that the adhesive is obtained by cross-linking). With such an adhesive, it is easy to satisfy the above-mentioned physical properties, and it is easy to obtain good adhesive strength. In addition, in this specification, (meth) acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, the concept of "polymer" shall be included in "polymer".

(1) Component (1-1) (meth) acrylic acid ester polymer (A) of adhesive composition P
The (meth) acrylic acid ester polymer (A) is a (meth) acrylic acid alkyl ester and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer) as a monomer unit constituting the polymer. And are preferably contained.

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

Examples of the (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, propyl (meth) acrylic acid, and n- (meth) acrylic acid. Butyl, n-pentyl (meth) acrylic acid, n-hexyl (meth) acrylic acid, 2-ethylhexyl (meth) acrylic acid, isooctyl (meth) acrylic acid, n-decyl (meth) acrylic acid, (meth) acrylic acid Examples thereof include n-dodecyl, myristyl (meth) acrylate, palmityl (meth) acrylate, and stearyl (meth) acrylate. Among them, a (meth) acrylic acid ester having an alkyl group having 1 to 8 carbon atoms is preferable, and an alkyl group having 4 to 8 carbon atoms is preferable from the viewpoint that the average ratio of τ and γ can be easily adjusted to the above-mentioned range. (Meta) acrylic acid esters are particularly preferred. Specifically, n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable. These may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer (A) preferably contains 60% by mass or more of the (meth) acrylic acid ester alkyl ester having 1 to 20 carbon atoms of the alkyl group as the monomer unit constituting the polymer. , 80% by mass or more, particularly preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 98% by mass or more. When the amount of the (meth) acrylic acid alkyl ester is equal to or more than the above amount, the (meth) acrylic acid ester polymer (A) can be imparted with suitable adhesiveness, and the average ratio of τ and γ is described above. It will be easy to adjust to the range. Further, it is preferable that the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms of the alkyl group is contained in an amount of 99.9% by mass or less, particularly preferably 99.5% by mass or less, and further 99.0. It is preferably contained in an amount of% by mass or less. By setting the amount of the (meth) acrylic acid alkyl ester to the above amount or less, a desired amount of other monomer components can be introduced into the (meth) acrylic acid ester polymer (A).

The (meth) acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and thus via a reactive functional group derived from the reactive functional group-containing monomer. , Reacts with the cross-linking agent (B) described later, thereby forming a cross-linked structure (three-dimensional network structure), and a pressure-sensitive adhesive having a desired cohesive force can be obtained. The pressure-sensitive adhesive easily satisfies the above-mentioned average ratio of τ and γ.

The reactive functional group-containing monomer contained in the (meth) acrylic acid ester polymer (A) as a monomer unit constituting the polymer includes a monomer having a hydroxyl group in the molecule (monomer containing a hydroxyl group) and a carboxy in the molecule. Preferred examples include a monomer having a group (carboxy group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like. One of these reactive functional group-containing monomers may be used alone, or two or more thereof may be used in combination.

Among the above reactive functional group-containing monomers, a hydroxyl group-containing monomer or a carboxy group-containing monomer is preferable, and a hydroxyl group-containing monomer is particularly preferable. Since the hydroxyl group-containing monomer can easily adjust the crosslink density in the formed pressure-sensitive adhesive to a desired range, it can easily satisfy the above-mentioned average ratio of τ and γ.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and (meth). ) Hydroxyalkyl esters of (meth) acrylates such as 3-hydroxybutyl acrylate and 4-hydroxybutyl (meth) acrylate can be mentioned. Among the above, a (meth) acrylic acid hydroxyalkyl ester having a hydroxyalkyl group having 1 to 4 carbon atoms is preferable from the viewpoint that the average ratio of τ and γ can be easily adjusted within the above-mentioned range. Specifically, for example, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and the like are preferable, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate are particularly preferable. Be done. These may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Of these, acrylic acid is preferable from the viewpoint of the adhesive strength of the obtained (meth) acrylic acid ester polymer (A). These may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer as a lower limit value of 0.1% by mass or more as a monomer unit constituting the polymer, particularly 0.5. It is preferably contained in an amount of 1.0% by mass or more, and more preferably 1.0% by mass or more. Further, the (meth) acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer as an upper limit value of 10% by mass or less, and 7% by mass or less, as a monomer unit constituting the polymer. It is more preferably contained, particularly preferably 4% by mass or less, and further preferably 2% by mass or less. When the (meth) acrylic acid ester polymer (A) contains a reactive functional group-containing monomer in the above amount as a monomer unit, the cohesive force of the adhesive obtained by the cross-linking reaction with the cross-linking agent (B) is appropriate. It becomes easy to satisfy the above-mentioned average ratio of τ and γ.

It is also preferable that the (meth) acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Since the carboxy group is an acid component, a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, etc. Even when a metal mesh or the like is present, it is possible to suppress those defects (corrosion, change in resistance value, etc.) due to acid.

Here, "not containing a carboxy group-containing monomer" means that the carboxy group-containing monomer is substantially not contained, and in addition to containing no carboxy group-containing monomer, a transparent conductive film using a carboxyl group, metal wiring, etc. It is permissible to contain a carboxy group-containing monomer to the extent that the corrosion of the above does not occur. Specifically, in the (meth) acrylic acid ester polymer (A), as a monomer unit, 0.1% by mass or less, preferably 0.01% by mass or less, more preferably 0.001 of a carboxy group-containing monomer. It is permissible to contain it in an amount of mass% or less.

If desired, the (meth) acrylic acid ester polymer (A) may contain another monomer as a monomer unit constituting the polymer. As the other monomer, a monomer containing no reactive functional group is preferable so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include non-reactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, and (meth) such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate. Acrylic acid alkoxyalkyl ester, vinyl acetate, styrene and the like can be mentioned. These may be used alone or in combination of two or more.

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

The weight average molecular weight of the (meth) acrylic acid ester polymer (A) is preferably 500,000 or more, more preferably 600,000 or more, and particularly preferably 700,000 or more. The weight average molecular weight of the (meth) acrylic acid ester polymer (A) is preferably 2 million or less, more preferably 1.5 million or less, and particularly preferably 1.2 million or less. When the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is within the above range, the average ratio of τ and γ can be easily adjusted to the above range. The weight average molecular weight in the present specification is a standard polystyrene-equivalent value measured by a gel permeation chromatography (GPC) method.

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

(1-2) Crosslinking agent (B)
The cross-linking agent (B) cross-links the (meth) acrylic acid ester polymer (A) with the heating of the adhesive composition P containing the cross-linking agent (B) as a trigger to form a three-dimensional network structure. .. As a result, the cohesive force of the obtained pressure-sensitive adhesive is improved, and the average ratio of τ and γ can be easily adjusted within the above-mentioned range.

The cross-linking agent (B) may be any one that reacts with the reactive group of the (meth) acrylic acid ester polymer (A), and is, for example, an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, or an amine-based cross-linking agent. , Melamine-based cross-linking agent, aziridine-based cross-linking agent, hydrazine-based cross-linking agent, aldehyde-based cross-linking agent, oxazoline-based cross-linking agent, metal alkoxide-based cross-linking agent, metal chelate-based cross-linking agent, metal salt-based cross-linking agent, ammonium salt-based cross-linking agent, etc. Can be mentioned. Among the above, it is preferable to use an isocyanate-based cross-linking agent having excellent reactivity with a reactive functional group-containing monomer. As the cross-linking agent (B), one type can be used alone, or two or more types can be used in combination.

The isocyanate-based cross-linking agent contains 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, isophorone diisocyanates, and alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate. , And their biurets, isocyanurates, and adducts, which are reactants with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Of these, from the viewpoint of reactivity with hydroxyl groups, trimethylolpropane-modified aromatic polyisocyanate, particularly trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene diisocyanate is preferable.

The content of the cross-linking agent (B) in the adhesive composition P is preferably 0.01 part by mass or more with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A), and in particular, 0. It is preferably 04 parts by mass or more, and more preferably 0.08 parts by mass or more. 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 0.40 parts by mass. It is preferably parts by mass or less. When the content of the cross-linking agent (B) is within the above range, it becomes easy to adjust the average ratio of τ and γ to the above range.

(1-3) Various Additives If desired, the adhesive composition P contains various additives usually used for acrylic pressure-sensitive adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, and tackifiers. Agents, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters and the like can be added. The polymerization solvent and the dilution solvent described later are not included in the additives constituting the adhesive composition P.

The adhesive composition P preferably contains the above-mentioned silane coupling agent. As a result, in the obtained pressure-sensitive adhesive layer, the adhesiveness with the flexible member which is an adherend is improved, and the adhesive strength becomes more preferable.

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

Examples of such a silane coupling agent include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacrypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glyceride. Silicon compounds having an epoxy structure such as sidoxypropylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyl Mercapto group-containing silicon compounds such as dimethoxymethylsilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyl Amino group-containing silicon compounds such as dimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanuspropyltriethoxysilane, or at least one of these, methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltri. Examples thereof include a condensate with an alkyl group-containing silicon compound such as methoxysilane. These may be used individually by 1 type and may be used in combination of 2 or more type.

The content of the silane coupling agent in the adhesive composition P is preferably 0.01 part by mass or more with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A), and is particularly 0.05. It is preferably 1 part by mass or more, and more preferably 0.1 part by mass or more. 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 obtained pressure-sensitive adhesive layer has improved adhesion to the flexible member, which is an adherend, and has a larger adhesive strength.

(2) Production of Adhesive Composition P The adhesive composition P produced a (meth) acrylic acid ester polymer (A), and the obtained (meth) acrylic acid ester polymer (A) and a cross-linking agent. It can be produced by mixing with (B) and adding an additive if desired.

The (meth) acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by an ordinary radical polymerization method. The polymerization of the (meth) acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator, if desired. By polymerizing the (meth) acrylic acid ester polymer (A) by the solution polymerization method, it becomes easy to increase the molecular weight of the obtained polymer and adjust the molecular weight distribution, and further reduce the formation of the low molecular weight polymer. Is possible. Therefore, even when the gel fraction is relatively small and the degree of cross-linking is loosened, it is difficult for the adhesive to be biased due to repeated bending.

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

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane1-carbonitrile), and 2 , 2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis (2-methylpropionate) , 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis (2-hydroxymethylpropionitrile), 2,2'-azobis [2- (2-imidazolin-2-yl)) Propane] and the like.

Examples of the organic peroxide include benzoyl peroxide, t-butylperbenzoate, cumenehydroperoxide, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, and di (2-ethoxyethyl) peroxy. Examples thereof include dicarbonate, t-butylperoxyneodecanoate, t-butylperoxyvivarate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

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

Once the (meth) acrylic acid ester polymer (A) is obtained, a cross-linking agent (B) and, if desired, an additive and a diluting solvent are sufficiently added to the solution of the (meth) acrylic acid ester polymer (A). To obtain a tacky composition P (coating solution) diluted with a solvent.

If any of the above components is in the form of a solid, or if precipitation occurs when the component is mixed with another component in an undiluted state, the component is used alone as a diluting solvent in advance. It may be dissolved or diluted and then mixed with other ingredients.

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, methanol, ethanol, propanol and butanol. Alcohols such as 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 are used.

The concentration and viscosity of the coating solution prepared in this manner may be any range as long as it can be coated, and is not particularly limited and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so as to have a concentration of 10 to 60% by mass. It should be noted that the addition of a diluting solvent or the like is not a necessary condition when obtaining the coating solution, and the diluting solvent may not be added as long as the adhesive composition P has a coatable viscosity or the like. In this case, the adhesive composition P becomes a coating solution using the polymerization solvent of the (meth) acrylic acid ester polymer (A) as it is as a diluting solvent.

(3) Production of Adhesive The adhesive according to the present embodiment is preferably obtained by cross-linking the adhesive composition P. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. This heat treatment can also be used as a drying treatment for volatilizing the diluting solvent or the like from the coating film of the adhesive composition P applied to the desired object.

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

After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23 ° C., 50% RH). When this curing period is required, an adhesive is formed after the curing period has elapsed, and when the curing period is not required, after the heat treatment is completed.

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

[Adhesive sheet]
The pressure-sensitive adhesive sheet according to the present embodiment has a pressure-sensitive adhesive layer for adhering one flexible member and another flexible member constituting the repeatedly bending device, and the pressure-sensitive adhesive layer is the above-mentioned pressure-sensitive adhesive. It consists of.

FIG. 1 shows a specific configuration as an example of the pressure-sensitive adhesive sheet according to the present embodiment.
As shown in FIG. 1, the adhesive sheet 1 according to the embodiment is in contact with the two release sheets 12a and 12b and the release surfaces of the two release sheets 12a and 12b. , 12b and the pressure-sensitive adhesive layer 11 sandwiched between the two. The peeling surface of the release sheet in the present specification refers to a surface of the release sheet that has peelability, and includes both a surface that has been peeled and a surface that exhibits peelability without peeling. ..

(1) Components (1-1) Adhesive Layer The adhesive layer 11 is composed of the adhesive according to the above-described embodiment, and is preferably composed of a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition P. ..

The thickness of the pressure-sensitive adhesive layer 11 (value measured according to JIS K7130) in the pressure-sensitive adhesive sheet 1 according to the present embodiment is preferably 1 μm or more, more preferably 5 μm or more, and particularly 10 μm as a lower limit value. It is preferably more than that, and more preferably 15 μm or more. When the lower limit of the thickness of the pressure-sensitive adhesive layer 11 is the above, it is easy to exert a desired adhesive force, and floating or peeling is less likely to occur at the interface between the pressure-sensitive adhesive layer and the adherend. Further, the thickness of the pressure-sensitive adhesive layer 11 is preferably 300 μm or less, more preferably 150 μm or less, particularly preferably 90 μm or less as an upper limit value, and a thinner repetitive bending device can be obtained. From the viewpoint, it is more preferably 40 μm or less. Further, when the upper limit of the thickness of the pressure-sensitive adhesive layer 11 is the above, the stress applied to the bent portion is likely to be reduced, and the stress applied to the whole is likely to be reduced due to the average ratio of τ and γ. .. The pressure-sensitive adhesive layer 11 may be formed as a single layer, or may be formed by laminating a plurality of layers.

The total light transmittance (value measured in accordance with JIS K7361-1: 1997) of the pressure-sensitive adhesive layer 11 in the pressure-sensitive adhesive sheet 1 according to the present embodiment is preferably 80% or more, preferably 90% or more. Is more preferable, and particularly preferably 95% or more, and further preferably 99% or more. When the total light transmittance is the above, the transparency is high and it is suitable for optical applications (for repetitive bending displays).

(1-2) Release Sheet The release sheets 12a and 12b protect the pressure-sensitive adhesive layer 11 until the time when the pressure-sensitive adhesive sheet 1 is used, and are peeled off when the pressure-sensitive adhesive sheet 1 (the pressure-sensitive adhesive layer 11) is used. In the pressure-sensitive adhesive sheet 1 according to the present embodiment, one or both of the release sheets 12a and 12b are not always necessary.

Examples of the 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, and polybutylene. Telephthalate 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, fluorine A resin film or the like is used. In addition, these crosslinked films are also used. Further, these laminated films may be used.

It is preferable that the peeling surfaces (particularly the surfaces in contact with the pressure-sensitive adhesive layer 11) of the release sheets 12a and 12b are subjected to a peeling treatment. Examples of the release agent used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. Of the release sheets 12a and 12b, it is preferable that one of the release sheets is a heavy release type release sheet having a large release force and the other release sheet is 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 Strength The adhesive strength of the pressure-sensitive adhesive sheet 1 according to the present embodiment to the polyimide is preferably 4.0 N / 25 mm or more, more preferably 5.0 N / 25 mm or more, and particularly 6 It is preferably 0.0 N / 25 mm or more. When the lower limit of the adhesive force of the adhesive sheet 1 to the polyimide is as described above, the adhesive layer is formed even when a polyimide film or the like is used as an adherend, when it is repeatedly bent or when it is left in a bent state for a long period of time. Floating or peeling is unlikely to occur at the interface between the and the adherend. On the other hand, the upper limit of the adhesive strength is not particularly limited, and is preferably 30.0 N / 25 mm or less, more preferably 25.0 N / 25 mm or less, and particularly 20.0 N / 25 mm or less. It is preferable to have. The adhesive strength in the present specification basically refers to the adhesive strength measured by the 180-degree peeling method according to JIS Z0237: 2009, and the specific test method is as shown in the test example described later. ..

The adhesive strength of the pressure-sensitive adhesive sheet 1 according to the present embodiment to soda lime glass is preferably 5.0 N / 25 mm or more, more preferably 6.0 N / 25 mm or more, and particularly 7.0 N / 25 mm or more as a lower limit value. It is preferably 25 mm 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 interface between the adhesive layer and the adherend is more likely to float or peel off. It is unlikely to occur. On the other hand, the upper limit of the adhesive strength is not particularly limited, but usually, it is preferably 50.0 N / 25 mm or less, more preferably 40.0 N / 25 mm or less, and it is possible to prevent a bonding error of the adhesive sheet 1. From the viewpoint of reworkability that enables the adhesive sheet 1 to be reattached, it is particularly preferably 30.0 N / 25 mm or less, and further preferably 20.0 N / 25 mm or less.

(3) Production of Adhesive Sheet As an example of production of the adhesive sheet 1, a case where the adhesive composition P is used will be described. The coating liquid of the adhesive composition P is applied to the peeling surface of one of the release sheets 12a (or 12b), heat-treated to heat-crosslink the adhesive composition P to form a coating layer, and then the coating is applied. The peeling surface of the other peeling sheet 12b (or 12a) is superposed on the layer. When the curing period is required, the curing period is set, and when the curing period is not required, the coating layer becomes the adhesive layer 11 as it is. As a result, the adhesive sheet 1 is obtained. The conditions for heat treatment and curing are as described above.

As another production example of the pressure-sensitive adhesive sheet 1, a coating liquid of the pressure-sensitive adhesive composition P is applied to the peel-off surface of one of the release sheets 12a, and heat treatment is performed to thermally crosslink the pressure-sensitive adhesive composition P to obtain a coating layer. Is formed to obtain a release sheet 12a with a coating layer. Further, the coating liquid of the adhesive composition P is applied to the peeling surface of the other release sheet 12b, heat-treated to heat-crosslink the adhesive composition P to form a coating layer, and the coating layer is attached. To obtain the release sheet 12b of. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are bonded so that both coating layers are in contact with each other. When the curing period is required, the curing period is set, and when the curing period is not required, the laminated coating layer becomes the pressure-sensitive adhesive layer 11. As a result, the adhesive sheet 1 is obtained. According to this production example, stable production is possible even when the pressure-sensitive adhesive layer 11 is relatively thick.

As a method of applying the coating liquid of the adhesive composition P, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method and the like can be used.

[Repeated bending laminated member]
As shown in FIG. 2, the repetitive bending laminated member 2 according to the present embodiment includes a first flexible member 21 (one flexible member) and a second flexible member 22 (another flexible member). , Which is located between them and includes an adhesive layer 11 for bonding the first flexible member 21 and the second flexible member 22 to each other.

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

The repetitive bending laminated member 2 is a repetitive bending device itself or a member forming a part of the repetitive bending device. The repetitive bending device is preferably, but is not limited to, a display capable of repeated bending (including bending). Examples of such a repetitive 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 a touch panel. It may be.

The first flexible member 21 and the second flexible member 22 are members capable of repeated bending (including bending), and are, for example, a cover film, a barrier film, a hard coat film, and a polarizing film (plate plate). , Polarizer, retardation film (phase difference plate), viewing angle compensation film, brightness improvement film, contrast improvement film, diffusion film, transflective reflective film, electrode film, transparent conductive film, metal mesh film, film sensor (touch) Sensor film), liquid crystal polymer film, light emitting polymer film, film-like liquid crystal module, organic EL module (organic EL film, organic EL element), electronic paper module (film-like electronic paper), TFT (Thin Film Transistor) substrate, etc. Be done.

Among the above, in the repetitive bending laminated member 2 according to the present embodiment, it is preferable that one of the first flexible member 21 and the second flexible member 22 is a hard coat film. In general, a hard coat film is liable to be damaged such as cracks when bent. However, according to the pressure-sensitive adhesive layer 11 in the present embodiment, even when the repeatedly bent laminated member 2 is repeatedly bent or fixed in a bent state for a long period of time, the hard coat film is easily damaged. Can be suppressed.

The Young's modulus of the first flexible member 21 and the second flexible member 22 is preferably 0.1 to 10 GPa, particularly preferably 0.5 to 7 GPa, and further preferably 1 to 5 GPa. It is preferable to have. When the Young's modulus of the first flexible member 21 and the second flexible member 22 is within such a range, it becomes easy to repeatedly bend each flexible member.

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 further preferably 50 to 500 μm. .. When the thickness of the first flexible member 21 and the second flexible member 22 is within such a range, it becomes easy to repeatedly bend each flexible member.

In order to manufacture the repeatedly bent laminated member 2, as an example, one of the release sheets 12a of the pressure-sensitive adhesive sheet 1 is peeled off, and the exposed pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 is removed from one of the first flexible members 21. Stick it on the surface of.

After that, the other release sheet 12b is peeled from the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1, the exposed pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 and the second flexible member 22 are bonded to each other, and the repeatedly bent laminated member 2 is attached. To get. Further, as another example, the bonding order of the first flexible member 21 and the second flexible member 22 may be changed.

[Repeat bending device]
The repetitive bending laminated member 2 according to the present embodiment includes the repetitive bending laminated member 2 described above, and may be composed of only the repetitive bending laminated member 2, one or a plurality of repetitive bending laminated members 2, and another. It may be configured to include a flexible member. When laminating one repeatedly bent laminated member 2 and another repeatedly bent laminated member 2, or when laminating the repeatedly bent laminated member 2 and another flexible member, the adhesive layer 11 of the adhesive sheet 1 described above is used. It is preferable to laminate through.

In the repetitive bending device according to the present embodiment, since the pressure-sensitive adhesive layer 11 is made of the above-mentioned adhesive, cracks and the like in the flexible member can be generated even when the pressure-sensitive adhesive layer 11 is repeatedly bent or left in a bent state for a long period of time. The occurrence of damage can be suppressed. This effect is fully exhibited even in a low temperature environment (for example, −20 ° C.) where damage is likely to occur. Further, this effect is fully exhibited even when the adherend is a hard coat film. Such bending resistance can be evaluated by, for example, a static bending test and a dynamic bending test.

In the static bending test, a laminate having an adhesive layer sandwiched between two flexible members having a size of 200 mm × 50 mm is used as a test piece. As shown in FIG. 3, this test piece S is bent between a holding plate P composed of two glass plates erected in an environment of 23 ° C., 50% RH, or -20 ° C. Hold for 1 minute or 24 hours. At this time, the distance between the two holding plates P is 7 mm (bending diameter of the test piece S: 7 mmφ) when placed in an environment of 23 ° C. and 50% RH, and when placed in an environment of −20 ° C. 8 mm (bending diameter of test piece S: 8 mmφ). Further, the test piece S is held so that the substantially central portion of the long side (200 mm) of the test piece S is a bent portion and both short sides (50 mm) of the test piece S are located on the upper side. After performing this static bending test, the test piece S is taken out from between the two holding plates P, and it is visually confirmed whether or not the flexible member is damaged such as a crack.

On the other hand, in the dynamic bending test, a laminated body having an adhesive layer sandwiched between two flexible members having a size of 150 mm × 50 mm is used as a test piece. As shown in FIG. 4, this test piece S is placed between two holding plates P of a surface condition no-load U-shaped expansion / contraction tester in an environment of 23 ° C., 50% RH, or -20 ° C. Hold. One of the two holding plates P maintains a parallel relationship with the other holding plate P, and can move back and forth with respect to the other holding plate P. When placed in an environment of 23 ° C. and 50% RH, the distance between the two holding plates P shall be changed from 86 mm to 7 mm (bending diameter of test piece S: 7 mmφ, stroke: 79 mm). Further, when placed in an environment of −20 ° C., the distance between the two holding plates P shall be changed from 86 mm to 8 mm (bending diameter of test piece S: 7 mmφ, stroke: 78 mm). The test piece S is fixed to the holding plate P so that the substantially central portion of the long side (150 mm) thereof becomes a bent portion and both short sides (50 mm) of the test piece S are located on the upper side. In that state, the test piece S is bent 30,000 times at a bending speed (reciprocating speed of the holding plate P) of 30 rpm. After performing this dynamic bending test, the test piece S is taken out from between the two holding plates P, and it is visually confirmed whether or not the flexible member is damaged such as a crack.

A repetitive bending device as an example in this embodiment is shown in FIG. The repetitive bending device according to the present invention is not limited to the repetitive bending device.

As shown in FIG. 5, the repetitive bending device 3 according to the present embodiment includes a cover film 31, a first pressure-sensitive adhesive layer 32, a polarizing film 33, and a second pressure-sensitive adhesive layer 34 in this order from the top. The touch sensor film 35, the third adhesive layer 36, the organic EL element 37, the fourth adhesive layer 38, and the TFT substrate 39 are laminated. 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 the flexible member.

At least one of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, and the fourth pressure-sensitive adhesive layer 38 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 described above. is there. Any two or more of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, and the fourth pressure-sensitive adhesive layer 38 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 described above. It is preferable that all the pressure-sensitive adhesive layers 32, 34, 36, and 38 are the pressure-sensitive adhesive layers 11 of the pressure-sensitive adhesive sheet 1.

The cover film 31 is preferably a hard coat film or a laminate provided with the hard coat film. In this case, at least the first pressure-sensitive adhesive layer 32 is preferably the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 described above. Further, for example, when the TFT substrate 39 contains a polyimide film, particularly when the polyimide film is provided on the adhesive layer 11 side, at least the fourth adhesive layer 38 is the adhesive layer of the adhesive sheet 1 described above. It is preferably 11.

In the repetitive bending device 3, even when it is repeatedly bent or left in a bent state for a long period of time, the occurrence of breakage such as cracks in the flexible member is suppressed. This effect is fully exhibited even in a low temperature environment (for example, −20 ° C.) where damage is likely to occur. Further, this effect is sufficiently exhibited even when the flexible member is a hard coat film or a laminated body containing the same.

The embodiments described above have been described for facilitating the understanding of the present invention, and have not been described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

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

Hereinafter, 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.

[Example 1]
1. 1. Preparation of (meth) Acrylic Acid Ester Polymer (A) 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 were copolymerized by a solution polymerization method. , (Meta) acrylic acid ester polymer (A) was prepared. When the molecular weight of this (meth) acrylic acid ester polymer (A) was measured by the method described later, the weight average molecular weight (Mw) was 800,000.

2. 2. Preparation of Adhesive Composition 100 parts by mass (solid content conversion value; the same applies hereinafter) of the (meth) acrylic acid ester polymer (A) obtained in the above step 1 and trimethylolpropane-modified xiri as a cross-linking agent (B). 0.25 parts by mass of range isocyanate (XDI; manufactured by Soken Kagaku Co., Ltd., product name "TD-75") and 0.20 parts by mass of 3-glycidoxypropyltrimethoxysilane as a silane coupling agent were mixed. A coating solution of the adhesive composition was obtained by thoroughly stirring and diluting with methyl ethyl ketone.

3. 3. Manufacture of Adhesive Sheet Peeling of a heavy-release type release sheet (manufactured by Lintec, product name "SP-PET752150") in which one side of a polyethylene terephthalate film is peeled off with a silicone-based release agent from the obtained coating solution of the adhesive composition. The treated surface was coated with a knife coater. Then, the coating layer was heat-treated at 90 ° C. for 1 minute to form a coating layer.

Next, the coating layer on the heavy release type release sheet obtained above and the light release type release sheet obtained by peeling one side of the polyethylene terephthalate film with a silicone-based release agent (manufactured by Lintec Corporation, product name "SP-PET381130"). The adhesive layer having a thickness of 25 μm was formed by laminating the light peeling type peeling sheet so that the peeled surface of the light peeling type peeling sheet was in contact with the coating layer and curing under the conditions of 23 ° C. and 50% RH for 7 days. An adhesive sheet having the structure, that is, a heavy release type release sheet / an adhesive layer (thickness: 25 μm) / a light release type release sheet, was produced. The thickness of the adhesive layer is a value measured using a constant pressure thickness measuring device (manufactured by Teclock Co., Ltd., product name "PG-02") in accordance with JIS K7130.

Here, Table 1 shows each formulation (solid content conversion value) of the adhesive composition when the (meth) acrylic acid ester polymer (A) is 100 parts by mass (solid content conversion value). Details of the abbreviations and the like shown in Table 1 are as follows.
[(Meta) acrylic acid ester polymer (A)]
BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate 4HBA: 4-hydroxybutyl acrylate MMA: HEA methacrylate HEA: 2-hydroxyethyl acrylate ACMO: acryloylmorpholin IBXA: isobornyl acrylate [crosslinker (B)]
XDI: Trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical Co., Ltd., product name "TD-75")
TDI: Trimethylolpropane-modified toluene diisocyanate (manufactured by Toyochem, product name "BHS8515")

[Examples 2 to 10, Comparative Examples 1 and 2]
The type and proportion of each monomer constituting the (meth) acrylic acid ester polymer (A), the weight average molecular weight (Mw) of the (meth) acrylic acid ester polymer (A), and the type and composition of the cross-linking agent (B). An adhesive sheet was produced in the same manner as in Example 1 except that the amount was changed as shown in Table 1.

[Manufacturing Example 1]
100 parts by mass of ethoxylated (6 mol) polyglycerin hexaacrylate (manufactured by Sakamoto Pharmaceutical Co., Ltd., product name "TE-6") and (meth) acrylic group-modified silica nanofiller (manufactured by Nissan Chemical Industry Co., Ltd., product name "MEK-" AC-2140Z ") 235 parts by mass and 5 parts by mass of a photopolymerization initiator (manufactured by BASF, product name" IRGACURE184 ") are mixed and diluted with methyl ethyl ketone to obtain a hard coat layer having a solid content concentration of 50% by mass. A coating solution of the forming composition was prepared.

The obtained coating liquid was applied to the easily adhesive-treated surface of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET50A4100", thickness: 50 μm) on which one side was easily adhered. After coating with, the obtained coating film was dried at 80 ° C. for 1 minute. Subsequently, the coating film was cured by irradiation with ultraviolet rays (light intensity: 170 mJ / cm ² ) to form a hard coat layer having a thickness of 5 μm.

As described above, a hard coat film in which a hard coat layer is laminated on the PET film is manufactured.

[Test Example 1] (Measurement of adhesive strength)
The light release type release sheet is peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and the exposed adhesive layer is a polyethylene terephthalate (PET) film having an easy adhesive layer (manufactured by Toyo Boseki Co., Ltd., product name "PET A4300"). , Thickness: 100 μm), and a laminated body of a heavy peeling type release sheet / adhesive layer / PET film was obtained. The obtained laminate was cut into a width of 25 mm and a length of 110 mm.

On the other hand, the following two types of adherends were prepared.
(1) Soda lime glass plate (manufactured by Nippon Sheet Glass, product name "soda lime glass", thickness: 1.1 mm)
(2) Polyimide film with adhesive layer (manufactured by Toray DuPont, product name "" on one side of a soda lime glass plate (manufactured by Nippon Plate Glass Co., Ltd., product name "soda lime glass", thickness: 1.1 mm)) Capton 100PI ”, polyimide film thickness: 25 μm, adhesive layer thickness: 5 μm) laminated body (polyimide film side is the adherend surface)

In an environment of 23 ° C. and 50% RH, the heavy release type release sheet was peeled off from the laminate, the exposed adhesive layer was attached to each of the adherends, and the autoclave manufactured by Kurihara Seisakusho Co., Ltd. The pressure was increased at 5 MPa and 50 ° C. for 20 minutes. Then, after leaving it to stand for 24 hours under the conditions of 23 ° C. and 50% RH, it was formed with a PET film under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180 degrees using a tensile tester (Tensilon manufactured by Orientec). The adhesive strength (N / 25 mm) when the laminate with the adhesive layer was peeled off from the adherend was measured. Conditions other than those described here were measured in accordance with JIS Z0237: 2009. The results are shown in Table 2.

[Test Example 2] (Measurement of total light transmittance)
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples was bonded to glass, and this was used as a measurement sample. After performing background measurement with glass, the above measurement sample is subjected to all light rays using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "NDH-5000") according to JIS K7361-1: 1997. The transmittance (%) was measured. The results are shown in Table 2.

[Test Example 3] (Measurement of shear strain-shear stress)
A plurality of pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets produced in Examples and Comparative Examples were laminated to obtain a laminated body having a thickness of 0.5 mm. A cylinder (height 0.5 mm) having a diameter of 8 mm was punched out from the obtained laminated body of the pressure-sensitive adhesive layer, and this was used as a sample.

For the above sample, the shear strain amount (γ) was changed from 0.01 to 200% under the following conditions using a viscoelasticity measuring device (manufactured by Antoniopaar, product name “MCR302”), and the shear at that time was changed. The stress (τ) was measured.
Measurement temperature: -20 ° C
Measurement points: 44-point plot

From the obtained measurement results, a region in which the shear stress (τ) linearly changes with respect to the shear strain amount (γ) was identified. Then, the ratio (τ / γ) of the shear stress (τ) to the shear strain amount (γ) was calculated for each measurement point existing in the region. Further, the average value of the obtained ratios (τ / γ) was calculated. The results are shown in Table 2.

[Test Example 4] (Static bending test)
In an environment of 23 ° C. and 50% RH, the light peeling type release sheet was peeled off from the pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was produced as a base material in Production Example 1. It was affixed to the surface of the flexible hard coat film opposite to the hard coat layer. Next, the heavy-release type release sheet was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to one surface of a polyimide (PI) film (manufactured by Toray DuPont, product name "Kapton 100PI", thickness: 25 μm). .. Then, the mixture was pressurized at 0.5 MPa and 50 ° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho, and then left to stand for 24 hours under the conditions of 23 ° C. and 50% RH. The laminate composed of the flexible hard coat film / adhesive layer / PI film thus obtained was cut into a width of 50 mm and a length of 200 mm, and this was used as a test piece.

The obtained test piece was placed in an environment of 23 ° C. and 50% RH, and as shown in FIG. 3, the surface on the flexible hard coat film side was outside between the holding plates made of two glass plates erected. It was held for 1 minute or 24 hours in a state of being bent so as to be. The bending diameter in the bent state was set to 7 mmφ.

It was confirmed whether or not the flexible hard coat film had cracks in the test piece after the bending was completed. Table 2 shows the case where no cracks occur as “⊚”, the case where cracks occur only at the ends as “◯”, and the cases where cracks occur in areas other than the ends as “x”. The test piece evaluated as "x" in the 1-minute bending test was not subjected to the 24-hour bending test.

Further, the test piece obtained in the same manner as above was subjected to a bending test in the same manner as described above except that the temperature condition was changed to −20 ° C. and the bending diameter was changed to 8 mmφ. The results are also shown in Table 2.

[Test Example 5] (Dynamic bending test)
The laminate composed of the flexible hard coat film / adhesive layer / PI film obtained in the same manner as in Test Example 4 was cut into 150 mm × 50 mm, and this was used as a test piece. As shown in FIG. 4, both ends of the obtained test piece were fixed to two holding plates of a surface state no-load U-shaped expansion / contraction tester (manufactured by Yuasa System Co., Ltd., product name "DLDMLH-FS"). At this time, the test piece was fixed so that the surface on the flexible hard coat film side was on the outside when bent. Then, the test piece was bent 30,000 times at a bending diameter of 7 mmφ, a stroke of 79 mm, and a bending speed of 30 rpm in an environment of 23 ° C. and 50% RH.

It was confirmed whether or not the flexible hard coat film had cracks in the test piece after the bending was completed. Table 2 shows the case where no cracks occur as “⊚”, the case where cracks occur only at the ends as “◯”, and the cases where cracks occur in areas other than the ends as “x”.

Further, the test piece obtained in the same manner as above was subjected to a bending test in the same manner as described above except that the temperature condition was changed to −20 ° C. and the bending diameter was changed to 8 mmφ and the stroke was changed to 78 mm. The results are also shown in Table 2.

As can be seen from Table 2, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the example was obtained when two flexible members (flexible hard coat film / polyimide film) were laminated and a static bending test and a dynamic bending test were performed. In addition, it was possible to suppress the occurrence of cracks in the flexible member. This effect was fully exhibited not only in a normal temperature environment but also in a low temperature environment of −20 ° C.

The present invention is suitable for bonding one flexible member and another flexible member constituting the repetitive bending device.

1 ... Adhesive sheet 11 ... Adhesive layer 12a, 12b ... Peeling sheet 2 ... Repeated bending laminated member 21 ... First flexible member 22 ... Second flexible member S ... Test piece P ... Holding plate

Claims (8)

An adhesive for a repetitive bending device for bonding one flexible member and another flexible member constituting the device to be repeatedly bent.
When the shear stress (τ) generated when the pressure-sensitive adhesive is distorted at a shear strain amount (γ) of 0.01 to 200% under the condition of −20 ° C. is measured, the shear stress (τ) is in the region changes linearly with respect to shear strain amount (gamma), the average value of the shear stress (tau) the ratio of (τ / γ) relative to the shear strain amount (gamma) is equal to or less than 3.0 × 10 8 ^Pa Adhesive for repetitive bending devices. The pressure-sensitive adhesive for a repetitive bending device according to claim 1, wherein the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive. An adhesive sheet having an adhesive layer for adhering one flexible member and another flexible member constituting a device that is repeatedly bent.
A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive for a repetitive bending device according to claim 1 or 2. The adhesive sheet according to claim 3, wherein the adhesive force of the adhesive sheet with respect to polyimide is 4.0 N / 25 mm or more. The pressure-sensitive adhesive sheet according to claim 3 or 4, wherein the thickness of the pressure-sensitive adhesive layer is 1 μm or more and 300 μm or less. The adhesive sheet includes two release sheets.
The adhesive sheet according to any one of claims 3 to 5, wherein the pressure-sensitive adhesive layer is sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets. One flexible member and another flexible member constituting a device that is repeatedly bent,
A repeatedly bent laminated member including an adhesive layer for bonding the one flexible member and the other flexible member to each other.
A repetitive bending laminated member, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive for a repetitive bending device according to claim 1 or 2. A repetitive bending device comprising the repetitive bending laminated member according to claim 7.

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