KR102528272B1 - Adhesive for flexible display, adhesive sheet, flexible laminate member and flexible display - Google Patents

Abstract

An object of the present invention is to provide a pressure-sensitive adhesive for a flexible display, a pressure-sensitive adhesive sheet, a flexible laminated member, and a flexible display that can withstand repeated bending when applied to a flexible display and has excellent bending resistance.
As a means for solving these problems, as an adhesive for a flexible display for bonding one flexible member and another flexible member constituting a flexible display together, the storage elastic modulus G' (-20) at -20 ° C is 0.05 MPa. Or more, less than 1 MPa, based on the storage elastic modulus G' (-20) and the storage elastic modulus G' (40) at 40 ° C., the elastic modulus change rate derived from the following formula (1) is 350% or more, 10000 A pressure-sensitive adhesive for a flexible display having % or less is provided.
Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One)

Description

Adhesive for flexible display, adhesive sheet, flexible laminated member and flexible display

The present invention relates to a pressure-sensitive adhesive for a flexible display, a pressure-sensitive adhesive sheet, a flexible laminated member, and a flexible display.

BACKGROUND OF THE INVENTION [0002] Recently, a bendable display, a so-called flexible display, has been proposed as a display body (display) of electronic devices. A flexible display is expected to have a wide range of applications, for example, as a stationary display that is bent and installed on a columnar pillar, or as a mobile display that can be bent or rounded and carried. .

Examples of types of flexible displays include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays using plastic films as substrates, and the like.

In the flexible display as described above, it is considered common to bond one bendable member (flexible member) constituting the flexible display to another flexible member using a pressure-sensitive adhesive layer of an adhesive sheet. Here, what is shown in patent documents 1 and 2 is known as a conventional adhesive sheet for display which cannot be bent here, for example.

A flexible display may be repeatedly bent (bent) as described in Patent Literature 3 rather than being curved only once. When a conventional pressure-sensitive adhesive sheet is used for a flexible display for such a purpose, lines are formed in the pressure-sensitive adhesive layer in the repeatedly bent portion, or cloudiness occurs, resulting in a deterioration in appearance and a problem in that visibility as a display deteriorates. .

Japanese Unexamined Patent Publication No. 2015-174907 Japanese Unexamined Patent Publication No. 2016-774 Japanese Unexamined Patent Publication No. 2016-2764

The present invention was made in view of such a reality, and the purpose of providing a pressure-sensitive adhesive for a flexible display, an adhesive sheet, a flexible laminated member, and a flexible display that can withstand repeated bending when applied to a flexible display and has excellent bending resistance to be

In order to achieve the above object, first, the present invention is a pressure-sensitive adhesive for a flexible display for bonding one flexible member and another flexible member constituting a flexible display, which has a storage modulus G '(-20) at -20 ° C. is 0.05 MPa or more and less than 1 MPa, and based on the storage modulus G' (-20) and the storage modulus G' (40) at 40 ° C., the elastic modulus change rate derived from the following formula (1) is 350 It provides an adhesive for a flexible display characterized in that % or more and 10000% or less (Invention 1).

Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One)

The pressure-sensitive adhesive according to the above invention (invention 1) has the above-described G '(-20) and the rate of change of elastic modulus, so that it is flexible with excellent stress relaxation properties, and when applied to a flexible display and repeatedly bent, the pressure-sensitive adhesive layer Formation of lines or cloudiness is suppressed, and bending resistance is excellent.

In the above invention (Invention 1), it is preferable that the gel fraction is 60% or more and 100% or less (Invention 2).

In the above inventions (Inventions 1 and 2), it is preferable that the main polymer of the pressure-sensitive adhesive for flexible display has a glass transition temperature (Tg) of -80°C or higher and -40°C or lower (Invention 3).

Second, the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer for bonding one flexible member and another flexible member constituting a flexible display, wherein the pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive for the flexible display (Inventions 1 to 3) An adhesive sheet as characterized is provided (Invention 4).

In the above invention (invention 4), it is preferable that the pressure-sensitive adhesive sheet includes two release sheets, and the pressure-sensitive adhesive layer is held by the release sheet so as to contact the release surfaces of the two release sheets. do (Invention 5).

Thirdly, the present invention is a flexible laminated member provided with one flexible member and another flexible member constituting a flexible display, and an adhesive layer for bonding the one flexible member and the other flexible member together, wherein the adhesive layer, Provided is a flexible laminated member characterized in that it is the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet (Invention 4 and 5) (Invention 6).

In the above invention (Invention 6), it is preferable that at least one of the one flexible member and the other flexible member is a flexible display element (Invention 7).

In the above inventions (Inventions 6 and 7), it is preferable that the Young's moduli of the one flexible member and the other flexible member are 0.1 to 10 GPa, respectively (Invention 8).

In the above inventions (Inventions 6 to 8), it is preferable that the one flexible member and the other flexible member each have a thickness of 10 to 3000 μm (Invention 9).

In the above inventions (Inventions 6 to 9), it is preferable that the interlayer adhesion between the one flexible member and the other flexible member is 1 to 30 N/25 mm (Invention 10).

Fourth, the present invention provides a flexible display characterized by having the flexible laminated member (Invention 6 to 10) (Invention 11).

The pressure-sensitive adhesive and pressure-sensitive adhesive sheet for a flexible display according to the present invention, and/or the flexible laminated member and the pressure-sensitive adhesive layer of the flexible display are excellent in bending resistance when repeatedly bent.

1 is a cross-sectional view of an adhesive sheet according to an embodiment of the present invention.
2 is a cross-sectional view of a flexible laminated member according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

[Adhesive for flexible display]

An adhesive for a flexible display according to the present embodiment (hereinafter, sometimes simply referred to as “adhesive”) is an adhesive for bonding one flexible member constituting a flexible display to another flexible member. A flexible display and a flexible member will be described later.

The pressure-sensitive adhesive according to the present embodiment has a storage modulus G' at -20°C (sometimes described as "G'(-20)" in the present specification) of 0.05 MPa or more and less than 1 MPa, and G' Based on (-20) and storage modulus G' at 40 ° C. (sometimes expressed as "G' (40)" in this specification), the rate of change in elastic modulus derived by the following formula (1) is It is 350% or more and 10000% or less.

Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One)

In addition, G'(-20) and G'(40) are values measured by a method based on JIS K7244-6, and specific measurement methods are as shown in the test examples described later.

The pressure-sensitive adhesive according to the present embodiment has the above-described G' (-20) and the rate of change of elastic modulus, so that it is flexible with excellent stress relaxation properties, and when applied to a flexible display and repeatedly bent, lines are formed in the pressure-sensitive adhesive layer. or cloudiness is suppressed, and bending resistance is excellent. Therefore, when the flexible display using the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the present embodiment is repeatedly bent at a predetermined portion, deterioration in appearance or deterioration in visibility at the bent portion is suppressed.

From the above viewpoint, G'(-20) is preferably 0.9 MPa or less, particularly preferably 0.8 MPa or less. The lower limit of G'(-20) is not particularly limited, but is preferably 0.10 MPa or more, and particularly preferably 0.30 MPa or more.

Moreover, it is preferable that the said elastic modulus change rate is 6000 % or less, and it is especially preferable that it is 3000 % or less. In addition, the lower limit of the rate of change of elastic modulus is preferably 500% or more, particularly preferably 800% or more, from the viewpoint of ensuring appropriate interlayer adhesion.

G'(40) is preferably 0.005 to 0.28 MPa, particularly preferably 0.008 to 0.18 MPa, and more preferably 0.01 to 0.1 MPa, from the viewpoint of making it easy to satisfy the above elastic modulus change rate.

The pressure-sensitive adhesive according to the present embodiment preferably has a gel fraction of 60% or more, particularly preferably 65% or more, and more preferably 70% or more. Further, the gel fraction is preferably 100% or less, particularly preferably 95% or less, and more preferably 90% or less. The pressure-sensitive adhesive according to the present embodiment has more excellent bending resistance while maintaining stress relaxation properties by having a gel fraction of 60% or more. In addition, the measuring method of the gel fraction is as showing in the test example mentioned later.

The glass transition temperature (Tg) of the main polymer of the pressure-sensitive adhesive according to the present embodiment (as a polymer constituting the pressure-sensitive adhesive, the polymer having the largest blending ratio) is preferably -40°C or lower, particularly preferably -45°C or lower, It is more preferable that it is -50 degrees C or less. The glass transition temperature (Tg) is preferably -80°C or higher, particularly preferably -75°C or higher, and more preferably -70°C or higher. When the glass transition temperature (Tg) of the main polymer of the pressure-sensitive adhesive according to the present embodiment is -40°C or lower, the elastic modulus is less likely to change in the temperature range of actual use of the pressure-sensitive adhesive, and the above-described elastic modulus change rate is easily satisfied. lose In addition, the measuring method of glass transition temperature (Tg) is as showing in the test example mentioned later.

The type of the pressure-sensitive adhesive according to the present embodiment is not particularly limited as long as it satisfies the above physical properties, and may be, for example, acrylic pressure-sensitive adhesive, polyester-based pressure-sensitive adhesive, polyurethane-based pressure-sensitive adhesive, rubber-based pressure-sensitive adhesive, silicone pressure-sensitive adhesive, or the like. do. In addition, the adhesive may be of an emulsion type, solvent type or non-solvent type, and may be of a crosslinking type or a non-crosslinking type.

Among the above, it is preferable to use an acrylic pressure-sensitive adhesive that easily satisfies the above-mentioned physical properties and has excellent adhesive properties, optical properties, and the like. The acrylic pressure-sensitive adhesive may contain a main polymer that is not crosslinked, or may contain a main polymer crosslinked by a crosslinking agent. Considering the ease of satisfying the above-mentioned physical properties, it is preferable to contain a main polymer crosslinked by a crosslinking agent. Here, the main polymer of the acrylic pressure-sensitive adhesive is usually a (meth)acrylic acid ester polymer. In addition, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same goes for other similar terms. In addition, "polymer" shall also include the concept of "copolymer".

The adhesive according to the present embodiment is an adhesive composition (hereinafter sometimes referred to as “adhesive composition P”) containing a (meth)acrylic acid ester polymer (A) as a main polymer and a crosslinking agent (B) described below. It is preferable that it is crosslinked. The adhesive obtained by crosslinking the adhesive composition P (hereinafter sometimes referred to as “adhesive Q”) easily satisfies the above-mentioned physical properties.

(1) Components of adhesive composition P

(1-1) (meth)acrylic acid ester polymer (A)

The (meth)acrylic acid ester polymer (A) is a (meth)acrylic acid alkyl ester having 2 to 20 carbon atoms in an alkyl group as monomer units constituting the polymer, and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer). It is preferable to contain

The (meth)acrylic acid ester polymer (A) can express desirable adhesiveness by containing, as a monomer unit constituting the polymer, a (meth)acrylic acid alkyl ester having 2 to 20 carbon atoms in an alkyl group. As the (meth)acrylic acid alkyl ester having an alkyl group having 2 to 20 carbon atoms, those having a glass transition temperature (Tg) as a homopolymer of -40°C or lower (hereinafter sometimes referred to as "low Tg alkyl acrylate") are preferable. By containing such a low-Tg alkyl acrylate as a constituting monomer unit, it becomes easy to set the glass transition temperature (Tg) of the main polymer of the pressure-sensitive adhesive according to the present embodiment within the above-mentioned range, and furthermore, the above-mentioned elastic modulus change rate is satisfied. It gets easier.

Examples of the low Tg alkyl acrylate include n-butyl acrylate (Tg -55°C), n-octyl acrylate (Tg -65°C), isooctyl acrylate (Tg -58°C), 2-ethylhexyl acrylate (Tg -70℃), isononyl acrylate (Tg -58℃), isodecyl acrylate (Tg -60℃), isodecyl methacrylate (Tg -41℃), n-lauryl methacrylate (Tg -65℃) ), tridecyl acrylate (Tg -55°C), tridecyl methacrylate (-40°C), and the like are preferably used. Among them, from the viewpoint of more effectively reducing the rate of change in elastic modulus, as the low-Tg alkyl acrylate, the Tg of the homopolymer is more preferably -45°C or lower, and is particularly preferably -50°C or lower. Specifically, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These may be used independently and may be used in combination of 2 or more type. In addition, the alkyl group in the (meth)acrylic acid alkyl ester having 2 to 20 carbon atoms in the alkyl group refers to a linear, branched or cyclic alkyl group.

The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, 60% by mass or more of a low-Tg alkyl acrylate as a lower limit, particularly preferably 80% by mass or more, It is more preferable to contain 90 mass % or more. By containing 60 mass % or more of the said low-Tg alkylacrylate, it becomes easy to set the glass transition temperature (Tg) of the main polymer of the adhesive according to this embodiment to the above-mentioned range.

Further, the (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, 99.9% by mass or less of the above-mentioned low-Tg alkyl acrylate as an upper limit, particularly preferably 99% by mass or less. And it is more preferable to contain 98% by mass or less. By containing 99.9 mass % or less of the said low-Tg alkyl acrylate, another monomer component (especially a reactive functional group containing monomer) can be introduce|transduced in a suitable amount in (meth)acrylic acid ester polymer (A).

On the other hand, the (meth)acrylic acid ester polymer (A) has a glass transition temperature (Tg) as a homopolymer in order to easily set the glass transition temperature (Tg) of the main polymer of the pressure-sensitive adhesive according to the present embodiment to the range described above. It is preferable to reduce the content of monomers exceeding 0°C (hereinafter sometimes referred to as "hard monomers") as little as possible. Specifically, in the (meth)acrylic acid ester polymer (A), as a monomer unit constituting the polymer, the content of the hard monomer as an upper limit is preferably 15% by mass or less, particularly 10% by mass or less. It is preferable, and it is more preferable to set it as 5 mass % or less. Moreover, the reactive functional group containing monomer mentioned later is also included in this hard monomer.

Examples of the hard monomer include methyl acrylate (Tg 10° C.), methyl methacrylate (Tg 105° C.), ethyl methacrylate (Tg 65° C.), n-butyl methacrylate (Tg 20° C.), meta Isobutyl acrylate (Tg 48 ° C), t-butyl methacrylate (Tg 107 ° C), n-stearyl acrylate (Tg 30 ° C), n-stearyl methacrylate (Tg 38 ° C), cyclohexyl acrylate ( Tg 15℃), cyclohexyl methacrylate (Tg 66℃), phenoxyethyl acrylate (Tg 5℃), phenoxyethyl methacrylate (Tg 54℃), benzyl methacrylate (Tg 54℃), isoacrylate Bornyl (Tg 94 ℃), isobornyl methacrylate (Tg 180 ℃), acryloylmorpholine (Tg 145 ℃), adamantyl acrylate (Tg 115 ℃), adamantyl methacrylate (Tg 141 ℃ ), acrylic monomers such as acrylic acid (Tg 103°C), dimethylacrylamide (Tg 89°C), and acrylamide (Tg 165°C), vinyl acetate (Tg 32°C), and styrene (Tg 80°C).

The (meth)acrylic acid ester polymer (A) reacts with a crosslinking agent (B) described later via a reactive functional group derived from the reactive functional group-containing monomer by containing a reactive functional group-containing monomer as a monomer unit constituting the polymer, As a result, a cross-linked structure (three-dimensional network structure) is formed, and a pressure-sensitive adhesive having a desired cohesive force is obtained.

The (meth)acrylic acid ester polymer (A) contains, as a monomer unit constituting the polymer, a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxy group-containing monomer) , a monomer having an amino group in the molecule (amino group-containing monomer), and the like are preferable. Among these, a hydroxyl group-containing monomer is especially preferable. Many of the hydroxyl group-containing monomers have a glass transition temperature (Tg) of 0°C or less, and it is easy to set the glass transition temperature (Tg) of the main polymer of the pressure-sensitive adhesive according to the present embodiment to the above range.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, ( (meth)acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; and the like. Among them, from the viewpoint of the glass transition temperature (Tg), the reactivity of the hydroxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B), and copolymerizability with other monomers, 2-hydroxyethyl acrylate, It is preferable that it is at least 1 of 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate. These may be used independently and may be used in combination of 2 or more type.

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. Especially, acrylic acid is preferable from the viewpoint of the reactivity of the carboxy group in the obtained (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers. These may be used independently and may be used in combination of 2 or more type.

Examples of the amino group-containing monomer include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used independently and may be used in combination of 2 or more type.

The (meth)acrylic acid ester polymer (A) preferably contains, as a lower limit, 0.1% by mass or more of a reactive functional group-containing monomer as a monomer unit constituting the polymer, particularly preferably 0.5% by mass or more, and 1 It is more preferable to contain more than mass %. Further, the (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, 30% by mass or less of a reactive functional group-containing monomer as an upper limit, particularly preferably 20% by mass or less, , It is preferable to further contain 8 mass % or less. When the (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer, particularly a hydroxyl group-containing monomer in the above amount as a monomer unit, the gel fraction of the resulting adhesive tends to fall within the above-mentioned range.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer, particularly acrylic acid, which is also a hard monomer, as a monomer unit constituting the polymer. Since the carboxy group is an acid component, by not containing a carboxy group-containing monomer, problems are caused by acid on the object to which the adhesive is attached, for example, a transparent conductive film such as tin-doped indium oxide (ITO) or a metal Even when a film, metal mesh, etc. are present, their problems (corrosion, change in resistance value, etc.) due to acid can be suppressed.

The (meth)acrylic acid ester polymer (A) may contain other monomers as a monomer unit constituting the polymer as desired. As the other monomer, a monomer that does not contain a reactive functional group is preferable even in order not to interfere with the action of the reactive functional group-containing monomer. Examples of such other monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, as well as glass transition temperatures (Tg) as homopolymers exceeding -40°C; and monomers having a temperature of 0°C or less (hereinafter sometimes referred to as "heavy-Tg alkyl acrylate"). Examples of heavy Tg alkyl acrylates include ethyl acrylate (Tg -20°C), isobutyl acrylate (Tg -26°C), 2-ethylhexyl methacrylate (Tg -10°C), n-lauryl acrylate ( Tg -23°C), isostearyl acrylate (Tg -18°C), and the like. These may be used independently and may be used in combination of 2 or more type.

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

The lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 200,000 or more, particularly preferably 400,000 or more, and more preferably 600,000 or more. Problems, such as leaching of an adhesive, are suppressed as the lower limit of the weight average molecular weight of a (meth)acrylic acid ester polymer (A) is more than the said. In addition, the weight average molecular weight in this specification is a standard polystyrene conversion value measured by the gel permeation chromatography (GPC) method.

The upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 2,000,000 or less, particularly preferably 1,500,000 or less, and more preferably 900,000 or less. When the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is below the above, the interlayer adhesion of the resulting adhesive tends to fall within a suitable range described later.

Moreover, in the adhesive composition P, (meth)acrylic acid ester polymer (A) may be used individually by 1 type, and may be used in combination of 2 or more type.

(1-2) crosslinking agent (B)

When the adhesive composition P containing the crosslinking agent (B) is heated, the crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) to form a three-dimensional network structure. As a result, the cohesive force of the pressure-sensitive adhesive to be obtained is improved, and the gel fraction of the pressure-sensitive adhesive is easily within the above-mentioned range, furthermore excellent in bending resistance.

The crosslinking agent (B) may be any one that reacts with the reactive group of the (meth)acrylic acid ester polymer (A), and examples thereof include an isocyanate crosslinking agent, an epoxy crosslinking agent, an amine crosslinking agent, a melamine crosslinking agent, an aziridine crosslinking agent, and 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, when the reactive group of the (meth)acrylic acid ester polymer (A) is a hydroxyl group, it is preferable to use an isocyanate-based crosslinking agent having excellent reactivity with hydroxyl groups, and the reactivity of the (meth)acrylic acid ester polymer (A) When the group is a carboxy group, it is preferable to use an epoxy-based crosslinking agent having excellent reactivity with a carboxy group. Moreover, a crosslinking agent (B) can be used individually by 1 type or in combination of 2 or more types.

The isocyanate-based crosslinking 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 diisocyanate, and hydrogenated diphenylmethane diisocyanate. Adducts that are reactants with alicyclic polyisocyanates such as isocyanates, their biurets and isocyanurates, and low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane and castor oil sieve, and the like. Among them, from the viewpoint of reactivity with hydroxyl groups, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylol-propane-modified xylylene diisocyanate, are preferable.

Examples of the epoxy-based crosslinking agent include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, Ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl aniline, diglycidyl amine, etc. are mentioned. Among them, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane is preferable from the viewpoint of reactivity with a carboxyl group.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and 0.1 part by mass or more with respect to 100 parts by mass of the (meth)acrylic acid ester polymer (A). it is more preferable The content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and more preferably 5 parts by mass or less. When the content of the crosslinking agent (B) is in the above range, the gel fraction of the pressure-sensitive adhesive obtained is more likely to fall within the above range.

(1-3) Various additives

In the adhesive composition P, as desired, various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters, etc. may be added. can be added. In addition, the polymerization solvent and dilution solvent mentioned later shall not be included in the additives constituting the adhesive composition P.

(2) Preparation of adhesive composition P

The adhesive composition P can be prepared by preparing a (meth)acrylic acid ester polymer (A), mixing the resulting (meth)acrylic acid ester polymer (A) with a crosslinking agent (B), and adding additives as desired. there is.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. Polymerization of the (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator as desired. As a polymerization solvent, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone etc. are mentioned, for example, You may use 2 or more types together.

As a polymerization initiator, an azo compound, an organic peroxide, etc. are mentioned, You may use 2 or more types together. Examples of the azo-based compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), and 1,1'-azobis(cyclohexane 1-carbonitrile). tril), 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] etc. are mentioned.

Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propylperoxydicarbonate, and di(2-ethoxyethyl)peroxydicarbonate. , t-butylperoxyneodecanoate, t-butylperoxypivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

Moreover, in the said polymerization process, the weight average molecular weight of the polymer obtained can be adjusted by mix|blending a chain transfer agent, such as 2-mercaptoethanol.

When the (meth)acrylic acid ester polymer (A) is obtained, to the solution of the (meth)acrylic acid ester polymer (A), a crosslinking agent (B) and/or optionally additives and a diluting solvent are added and sufficiently mixed, A solvent-diluted adhesive composition P (coating solution) is obtained.

In addition, in the case of using any of the above components in a solid state, or when precipitation occurs when mixed with other components in an undiluted state, the component is dissolved or diluted in advance in a diluting solvent alone Then, you may mix with other components.

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, butanol, and 1-methyl Alcohols such as toxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone and cyclohexanone, esters such as ethyl acetate and butyl acetate, cellosolve solvents such as ethyl cellosolve, etc. this is used

The concentration/viscosity of the coating solution prepared in this way is not particularly limited as long as it is within a range that can be coated, and can be appropriately selected according to the situation. For example, it is diluted so that the concentration of adhesive composition P may become 10-60 mass %. In addition, in obtaining the coating solution, addition of a diluting solvent is not a necessary condition, and as long as the adhesive composition P has a coatingable viscosity or the like, it is not necessary to add a diluting solvent. In this case, the adhesive composition P is a coating solution in which the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used as a diluting solvent.

(3) Manufacture of adhesive Q

Preferred adhesive Q as the adhesive according to the present embodiment is formed by crosslinking the adhesive composition P. Crosslinking of the adhesive composition P can usually be performed by heat treatment. In addition, this heat treatment can also serve as a drying treatment when volatilizing a diluting solvent or the like from a coating film of the adhesive composition P applied to a desired object.

The heating temperature of the heat treatment is preferably 50 to 150°C, particularly preferably 70 to 120°C. Moreover, it is preferable that it is 10 second - 10 minutes, and, as for heating time, it is preferable that it is 50 second - 2 minutes especially.

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at normal temperature (for example, 23°C, 50% RH) as needed. When this curing period is required, the adhesive Q is formed after the curing period has elapsed, and when the curing period is unnecessary, after the end of the heat treatment.

By the heat treatment (and curing) described above, the (meth)acrylic acid ester polymer (A) is sufficiently crosslinked via the crosslinking agent (B) to form a crosslinked structure, and the adhesive Q is obtained. This pressure-sensitive adhesive Q particularly easily satisfies the storage elastic modulus and elastic modulus change rate described above.

[adhesive sheet]

The adhesive sheet according to the present embodiment has an adhesive layer for bonding one flexible member constituting a flexible display with another flexible member, and the adhesive layer is made of the above-described adhesive.

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 pressure-sensitive adhesive sheet 1 according to one embodiment includes two release sheets 12a and 12b and the release surfaces of the two release sheets 12a and 12b so as to be in contact with each other. It is composed of an adhesive layer 11 sandwiched between sheets of release sheets 12a and 12b. In addition, the release surface of a release sheet in this specification refers to the surface which has release property in a release sheet, and includes both the surface which has been subjected to the release treatment and the surface which exhibits release property even without the release treatment.

(1) Components

(1-1) adhesive layer

The pressure-sensitive adhesive layer 11 is composed of the pressure-sensitive adhesive according to the above-described embodiment, and preferably composed of the pressure-sensitive adhesive Q formed by crosslinking the pressure-sensitive adhesive composition P.

The thickness of the pressure-sensitive adhesive layer 11 in the pressure-sensitive adhesive sheet 1 according to the present embodiment (value measured based on JIS K7130) is preferably 5 μm or more as a lower limit, particularly preferably 10 μm or more, and 20 μm or more. It is more preferable that it is micrometer or more. In addition, as for the thickness of the adhesive layer 11, as an upper limit, it is preferable that it is 300 micrometers or less, it is more preferable that it is 200 micrometers or less, and it is especially preferable that it is 100 micrometers or less. When the thickness of the pressure-sensitive adhesive layer 11 is within the above range, it is easy to exert desired adhesive force, and the bending resistance becomes more excellent. In addition, the pressure-sensitive adhesive layer 11 may be formed as a single layer, or may be formed by laminating a plurality of layers.

(1-2) release sheet

The release sheets 12a and 12b protect the pressure-sensitive adhesive layer 11 until the time of use of the pressure-sensitive adhesive sheet 1, and are peeled off when the pressure-sensitive adhesive sheet 1 (pressure-sensitive adhesive layer 11) is used. In the adhesive sheet 1 according to 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 polybutene film, a polybutadiene film, a polymethylpentene film, a polyvinyl chloride film, a vinyl chloride copolymer film, a polyethylene terephthalate film, and polyethylene. Naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene/(meth)acrylic acid copolymer film, ethylene/(meth)acrylic acid ester copolymer film, polystyrene film, poly A carbonate film, a polyimide film, a fluororesin film or the like is used. Moreover, these crosslinked films are also used. Moreover, these laminated|multilayer films may be sufficient.

It is preferable that a peeling treatment is performed on the peeling surfaces (particularly, the surfaces in contact with the pressure-sensitive adhesive layer 11) of the peeling sheets 12a and 12b. Examples of release agents used in the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax release agents. Among the release sheets 12a and 12b, it is preferable that one release sheet 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) physical properties (total light transmittance)

The total light transmittance (value measured based on JIS K7361-1: 1997) of the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 according to the present embodiment is preferably 80% or more, particularly preferably 90% or more, It is more preferable that it is 99% or more. When the total light transmittance is 80% or more, the transparency is high, and it is suitable for an optical use (for a display body). When the pressure-sensitive adhesive layer 11 is composed of the pressure-sensitive adhesive Q, it is easy to satisfy the total light transmittance.

(3) Manufacture of adhesive sheet

As an example of production of the PSA sheet 1, a case in which the PSA composition P is used will be described. A coating liquid of adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and heat treatment is performed to thermally cross-link the adhesive composition P to form a coating layer. The release surface of the side release sheet 12b (or 12a) is overlapped. When a curing period is required, a curing period is provided, and when a curing period is unnecessary, the coating layer becomes the pressure-sensitive adhesive layer 11 as it is. In this way, the pressure-sensitive adhesive sheet 1 is obtained. The heat treatment and curing conditions are as described above.

As another production example of the PSA sheet 1, a coating liquid of the PSA composition P is applied to the release surface of one release sheet 12a, and heat treatment is performed to thermally crosslink the PSA composition P to form a coating layer, The release sheet 12a with a coating layer is obtained. Further, the coating liquid 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 forming a release sheet with a coating layer. (12b) is obtained. And the release sheet 12a with an application layer and the release sheet 12b with an application layer are bonded together so that both application layers may contact each other. When a curing period is required, a curing period is provided, and when a curing period is not required, the above-described laminated coating layer becomes the pressure-sensitive adhesive layer 11 as it is. In this way, the pressure-sensitive adhesive sheet 1 is obtained. According to this manufacturing, even if it is a case where the adhesive layer 11 is thick, it becomes possible to manufacture stably.

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, or the like can be used.

[Flexible laminated member]

As shown in FIG. 2 , the flexible laminated member 2 according to the present embodiment includes a first flexible member 21 (one flexible member), a second flexible member 22 (another flexible member), and their It is comprised by providing the adhesive layer 11 located in between, and bonding the 1st flexible member 21 and the 2nd flexible member 22 mutually.

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

The flexible laminated member 2 is a flexible display itself or a member constituting a part of the flexible display. Here, the flexible display is a bendable display, preferably a display capable of repeated bending (including bending), for example, 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 flexible member 21 and the second flexible member 22 are bendable members, preferably members capable of repeated bending (including bending), and include, for example, a cover film, a barrier film, a polarizing film , polarizer, retardation film, viewing angle compensation film, luminance enhancement film, contrast enhancement film, diffusion film, transflective reflective film, electrode film, transparent conductive film, metal mesh film, film sensor, liquid crystal polymer film, light emitting polymer film, on film A liquid crystal module, an organic EL module (organic EL film), an electronic paper module (film-like electronic paper), etc. are mentioned.

Among the above, at least one of the first flexible member 21 and the second flexible member 22 is a flexible display element, specifically, a liquid crystal polymer film, a light emitting polymer film, a film-like liquid crystal module, an organic EL module (organic EL film) or an electronic paper module (film-like electronic paper).

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 more preferably 1.0 to 5 GPa. When the Young's moduli of the first flexible member 21 and the second flexible member 22 are within these ranges, repeated bending of each flexible member becomes easy.

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 more preferably 50 to 500 μm. When the thicknesses of the first flexible member 21 and the second flexible member 22 fall within these ranges, repeated bending of each flexible member becomes easy.

The interlayer adhesion (adhesive force) between the first flexible member 21 and the second flexible member 22 is preferably 1 N/25 mm or more as a lower limit value, particularly preferably 2 N/25 mm or more, and 5 N/25 mm or more. It is more preferable that it is 25 mm or more. When the interlayer adhesion is 1 N/25 mm or more, the bending resistance as a flexible display is excellent. Moreover, as for the said interlayer adhesiveness, as an upper limit, it is preferable that it is 30 N/25 mm or less, it is more preferable that it is 25 N/25 mm or less, and it is especially preferable that it is 20 N/25 mm or less. When the interlayer adhesion is 20 N/25 mm or less, it can be said that the rework property is excellent. Thereby, even if it is a case where bonding error between flexible members arises, both can be peeled easily, and reuse of a flexible member (especially expensive flexible member) is attained.

Here, the interlayer adhesive force (adhesive force) in this specification basically refers to the adhesive force measured by the 180-degree peeling method conforming to JIS Z0237:2009, but the measurement sample was 25 mm wide, 100 After preparing a laminate composed of the first flexible member / pressure-sensitive adhesive layer / second flexible member with a length of mm, pressurized at 0.5 MPa and 50 ° C. for 20 minutes, and then under normal pressure, 23 ° C., 50% RH conditions for 24 hours After leaving it to stand, it shall be measured at a peeling rate of 300 mm/min.

In order to manufacture the flexible laminated member 2, as an example, one release sheet 12a of the pressure-sensitive adhesive sheet 1 is peeled off, and the pressure-sensitive adhesive layer 11 exposed on the pressure-sensitive adhesive sheet 1 is removed by first flexible It is bonded to one side of the member 21.

After that, the other release sheet 12b is peeled from the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1, and the pressure-sensitive adhesive layer 11 exposed on the pressure-sensitive adhesive sheet 1 and the second flexible member 22 are bonded together. Together, the flexible laminated member 2 is obtained. In addition, as another example, you may change the bonding order of the 1st flexible member 21 and the 2nd flexible member 22.

[Flexible display]

The flexible display according to the present embodiment includes the flexible laminated member 2 described above, may be composed of only the flexible laminated member 2, or includes one or a plurality of flexible laminated members 2 and other flexible members. may be constituted by When one flexible laminated member 2 and another flexible laminated member 2 are laminated, or when the flexible laminated member 2 and another flexible member are laminated, the pressure-sensitive adhesive layer 11 of the aforementioned pressure-sensitive adhesive sheet 1 It is preferable to laminate via.

Since the flexible display according to the present embodiment is a product in which flexible members are laminated using the pressure-sensitive adhesive layer 11 having excellent bending resistance, when it is repeatedly bent at a predetermined portion, at the bent portion of the pressure-sensitive adhesive layer 11 It is suppressed that an external appearance deteriorates and visibility deteriorates.

The embodiments described above are described for facilitating understanding of the present invention, and are not 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, one or both of the release sheets 12a and 12b in the adhesive sheet 1 may be omitted, and a desired optical member may be laminated instead of the release sheets 12a and/or 12b.

(Example)

Hereinafter, the present invention will be described more specifically by examples and the like, but the scope of the present invention is not limited to these examples and the like.

[Example 1]

1. Preparation of (meth)acrylic acid ester polymer (A)

47.8 parts by mass of n-butyl acrylate, 47.8 parts by mass of 2-ethylhexyl acrylate, 4 parts by mass of acrylic acid, and 0.4 parts by mass of 2-hydroxypropyl acrylate were copolymerized to prepare a (meth)acrylic acid ester polymer (A). When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method mentioned later, the weight average molecular weight (Mw) was 600,000.

2. Preparation of adhesive composition

100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained in the above step 1 (solid content conversion value; as follows), and trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem, product name "BHS8515") as a crosslinking agent (B) 0.9 By mixing parts by mass, stirring sufficiently, and diluting with methyl ethyl ketone, a coating solution of the adhesive composition was obtained.

3. Manufacture of adhesive sheet

The coating solution of the obtained adhesive composition was coated with a knife coater on the release-treated surface of a heavy release type release sheet (manufactured by Lintex, product name "SP-PET752150") in which one side of a polyethylene terephthalate film was subjected to release treatment with a silicone-based release agent. Then, the coated layer was subjected to heat treatment at 90°C for 1 minute to form a coated layer.

Next, an easy-peelable release sheet (manufactured by Lintec, product name "SP-PET382120") in which the coating layer on the heavy-peelable release sheet obtained above and one side of the polyethylene terephthalate film were subjected to release treatment with a silicone-based release agent was prepared. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 25 μm, that is, a heavy-release type release sheet / pressure-sensitive adhesive layer (thickness : 25 μm)/An adhesive sheet having a configuration of an easy-peelable type release sheet was produced. In addition, the thickness of the adhesive layer is a value measured using a static pressure thickness meter (manufactured by Techrox Co., Ltd., product name "PG-02") in accordance with JIS K7130.

Here, Table 1 shows each formulation (value in terms of solid content) of the adhesive composition when the (meth)acrylic acid ester polymer (A) is 100 parts by mass (value in terms of solid content). In addition, the details of the abbreviation or the like described in Table 1 are as follows.

[(meth)acrylic acid ester polymer (A)]

BA: n-butyl acrylate

2EHA: 2-ethylhexyl acrylate

AA: acrylic acid

2HPA: 2-hydroxypropyl acrylate

4HBA: 4-hydroxybutyl acrylate

MMA: methyl methacrylate

HEA: 2-hydroxyethyl acrylate

ACMO: N-Acryloylmorpholine

IBXA: isobornyl acrylate

[Crosslinking agent (B)]

TDI: Trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem, product name "BHS8515")

XDI: Trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical Co., Ltd., product name "TD-75")

Epoxy system: 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "TETRAD-C")

[Examples 2 to 3, Comparative Examples 1 to 5]

Table 1 shows the type and ratio 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/or the type and compounding amount of the crosslinking agent (B). A pressure-sensitive adhesive sheet was manufactured in the same manner as in Example 1 except for changing as shown in .

[Test Example 1] (Measurement of glass transition temperature)

The glass transition temperature (Tg) of the (meth)acrylic acid ester polymer (A) produced and used in Examples and Comparative Examples was measured by a differential scanning calorimetry device (manufactured by TA Instruments Japan, product name "DSC Q2000"). , It was measured at a heating/cooling rate of 20°C/min. The results are shown in Table 1.

[Test Example 2] (Measurement of storage modulus (G'))

A plurality of layers of the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples were laminated to obtain a laminate having a thickness of 3 mm. From the obtained laminated body of the pressure-sensitive adhesive layer, a cylinder having a diameter of 8 mm (height 3 mm) was punched out, and this was used as a sample.

The storage modulus (G') (MPa) of the sample was measured under the following conditions by a torsional shear method using a viscoelasticity meter (DYNAMIC ANALAYZER, manufactured by REOMETRIC) in accordance with JIS K7244-6. The results are shown in Table 1.

Measurement frequency: 1Hz

Measurement temperature: -20℃, 0℃, 23℃, 40℃

In addition, when the storage elastic modulus at -20 ° C. is G' (-20) and the storage elastic modulus at 40 ° C. is G' (40), the elastic modulus change rate derived from the following formula (1) was calculated. The results are shown in Table 1.

Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One)

[Test Example 3] (Measurement of gel fraction)

The PSA sheets obtained in Examples and Comparative Examples were cut to a size of 80 mm × 80 mm, the PSA layer was wrapped with a polyester mesh (mesh size 200), and the mass was weighed with a precision balance. By subtracting the mass, the mass of only the adhesive was calculated. Let the mass at this time be M1.

Next, the adhesive wrapped with the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. After that, the adhesive was taken out and air-dried for 24 hours in an environment of a temperature of 23°C and a relative humidity of 50%, and further, it was dried in an oven at 80°C for 12 hours. After drying, the mass was measured with a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. Let the mass at this time be M2. The gel fraction (%) is represented by (M2/M1) x 100. The results are shown in Table 1.

[Test Example 4] (Measurement of total light transmittance)

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet obtained in Examples and Comparative Examples was bonded to glass, and this was used as a sample for measurement. After performing the background measurement on the glass, the total light transmittance (%) of the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "NDH-2000") in accordance with JIS K7361-1:1997. Measured. The results are shown in Table 1.

[Test Example 5] (Measurement of adhesive force (adhesive force between layers))

In an environment of 23°C and 50% RH, an easy-peelable release sheet was peeled from the adhesive sheet obtained in Examples and Comparative Examples, and the exposed adhesive layer was formed as a polyethylene terephthalate film (manufactured by Toyobo, product name) as a first flexible member. "Cosmo Shine 4300", thickness: 100 µm) was bonded to one side. Next, the heavy release type release sheet is peeled off, and the exposed pressure-sensitive adhesive layer is a polyethylene terephthalate film (manufactured by Oike Kogyo Co., Ltd., ITO film) provided with a transparent conductive film made of tin-doped indium oxide (ITO) on one side as a second flexible member , thickness: 125 μm) was bonded to the surface on the side of the transparent conductive film. And after pressurizing at 0.5 MPa and 50 degreeC for 20 minutes with the Kurihara Sesakujo Co., Ltd. autoclave, it was left to stand on 23 degreeC and 50%RH conditions for 24 hours. The thus obtained laminate (flexible laminated member) composed of the PET film/pressure-sensitive adhesive layer/ITO film was cut into a 25 mm width and 100 mm length, and this was used as a sample.

With respect to the above sample, using a universal tensile tester (manufactured by Orientex Co., Ltd., product name "Tensiron UTM-4-100"), the PET film was bonded under the conditions of a peeling speed of 300 mm/min and a peeling angle of 180 degrees, and the adhesion between the layers was measured. Adhesion (N/25 mm) was measured. Conditions other than those described here were measured in accordance with JIS Z 0237:2009. The results are shown in Table 1.

[Test Example 6] (Measurement of Young's modulus of flexible member)

The first and second flexible members (PET film and ITO film) used in Test Example 5 were cut into test pieces of 10 mm x 70 mm. Then, the Young's modulus at 23°C and 50% RH was measured in accordance with JIS K7161:1994. Specifically, the test piece was subjected to a tensile test at a speed of 200 mm/min after setting the distance between the chucks to 20 mm with a universal tensile tester (manufactured by Orientex Co., Ltd., product name "Tensiron RTA-T-2M"). , Young's modulus (unit: GPa) was measured. As a result, the Young's modulus of both the PET film and the ITO film was 4.2 GPa.

[Test Example 7] (Flexibility test)

In an environment of 23° C. and 50% RH, the easy-peelable release sheet was peeled from the adhesive sheet obtained in Examples and Comparative Examples, and the exposed adhesive layer was coated with a polyethylene terephthalate film (manufactured by Toyobo, product name “Cosmo Shine 4300”). , thickness: 100 μm). Next, the heavy release type release sheet was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to one side of another polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., product name "Cosmo Shine 4300", thickness: 100 µm). And after pressurizing at 0.5 MPa and 50 degreeC for 20 minutes with the Kurihara Sesakujo Co., Ltd. autoclave, it was left to stand on 23 degreeC and 50%RH conditions for 24 hours. The thus-obtained laminate composed of the PET film/adhesive layer/PET film was cut into a 50 mm width and 200 mm length, and this was used as a sample.

The obtained sample was repeatedly bent under the following conditions using a durability tester (manufactured by Yuasa Systems Co., Ltd., product name "Flat body unloaded U-shaped stretch tester"). Then, the sample was placed on a horizontal table, one end of the sample in the longitudinal direction was fixed to the table surface, and the vertical distance (curvature amount) of the other end of the sample from the table surface was measured. The results are shown in Table 1.

Minimum bending diameter: 4mmφ

Number of bends: 30000 times

Test temperature: 23℃

In addition, with respect to the sample after completion of the said test, the external appearance of the bent part was visually evaluated according to the following criteria. The results are shown in Table 1.

◎: No line at the bend

○: There is a line at the bent part, but the line is hardly noticed when viewed from the front.

△: There is a line at the bending part, and the existence of the line can be confirmed when viewed from the front, but the line is not cloudy.

x: The line of a bending part exists, and the said line is clouded and conspicuous. Or peeling between the adhesive and the substrate has occurred.

[Table 1]

As can be seen from Table 1, the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets of Examples were excellent in bending resistance and also in optical properties. In addition, the flexible laminated members obtained using the PSA sheets of Examples had good interlayer adhesion.

INDUSTRIAL APPLICABILITY The present invention is suitable for bonding one flexible member (eg various films) constituting a flexible display to another flexible member (eg display element).

DESCRIPTION OF SYMBOLS 1: adhesive sheet 11: adhesive layer
12a, 12b: release sheet 2: flexible laminated member
21: first flexible member 22: second flexible member

Claims (15)

As an adhesive for a flexible display for bonding one flexible member and another flexible member constituting a flexible display,
The storage modulus G'(-20) at -20°C is 0.05 MPa or more and less than 1 MPa,
Based on the storage modulus G' (-20) and the storage modulus G' (40) at 40 ° C, the rate of change in elastic modulus derived from the following formula (1) is 700% or more and 10000% or less,
Solvent type adhesive
A pressure-sensitive adhesive for a flexible display, characterized in that.
Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One) According to claim 1,
A pressure-sensitive adhesive for a flexible display, characterized in that the gel fraction is 60% or more and 100% or less. According to claim 1,
A pressure-sensitive adhesive for a flexible display, characterized in that the main polymer of the pressure-sensitive adhesive for a flexible display has a glass transition temperature (Tg) of -80°C or more and -40°C or less. According to claim 1,
The pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive,
The main polymer of the acrylic pressure-sensitive adhesive is a (meth)acrylic acid ester polymer polymerized by solution polymerization.
A pressure-sensitive adhesive for a flexible display, characterized in that. delete A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer for bonding one flexible member and another flexible member constituting a flexible display,
The pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive for a flexible display according to claim 1.
An adhesive sheet characterized in that. According to claim 6,
The pressure-sensitive adhesive sheet includes two release sheets,
The pressure-sensitive adhesive layer is held by the release sheet so as to come into contact with the release surfaces of the two release sheets.
An adhesive sheet characterized in that. One flexible member and another flexible member constituting the flexible display;
An adhesive layer for bonding the one flexible member and the other flexible member together
As a flexible laminated member having a,
The pressure-sensitive adhesive layer is the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to claim 6.
Flexible laminated member, characterized in that. According to claim 8,
A flexible laminated member characterized in that at least one of the one flexible member and the other flexible member is a flexible display element. According to claim 8,
A flexible laminated member characterized in that Young's moduli of the one flexible member and the other flexible member are 0.1 to 10 GPa, respectively. According to claim 8,
A flexible laminated member characterized in that the one flexible member and the other flexible member each have a thickness of 10 to 3000 μm. According to claim 8,
A flexible laminated member characterized in that the interlayer adhesion between the one flexible member and the other flexible member is 1 to 30 N/25 mm. A flexible display comprising the flexible laminated member according to any one of claims 8 to 12. One flexible member and another flexible member constituting the flexible display;
An adhesive layer for bonding the one flexible member and the other flexible member together
As a flexible display having a flexible laminated member having, repeatedly bent,
The pressure-sensitive adhesive layer,
The storage modulus G'(-20) at -20°C is 0.05 MPa or more and less than 1 MPa,
Based on the storage modulus G' (-20) and the storage modulus G' (40) at 40 ° C, the rate of change in elastic modulus derived from the following formula (1) is 700% or more and 10000% or less,
Composed of adhesive for flexible display
Characterized in that the flexible display.
Modulus change rate (%) = (G'(-20)/G'(40)) × 100... (One) According to claim 14,
A flexible display characterized in that it is possible to repeatedly bend 30,000 times at a minimum bending diameter of 4 mmφ.

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