WO2024024686A1

WO2024024686A1 - Flexible display laminate and flexible display

Info

Publication number: WO2024024686A1
Application number: PCT/JP2023/026864
Authority: WO
Inventors: 寛之古野; 慎吾田邉; 努早坂; 克哲福田; 智文石; 剛史入江
Original assignee: 東洋インキＳｃホールディングス株式会社; トーヨーケム株式会社
Priority date: 2022-07-26
Filing date: 2023-07-21
Publication date: 2024-02-01
Also published as: JP2024016815A

Abstract

The present disclosure provides a flexible display laminate in which an adhesive layer is provided on a light-transmitting flexible substrate, said adhesive layer being formed from an acrylic adhesive containing a low-polarity additive and an acrylic copolymer that contains a repeating unit derived from a (meth)acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms. Also provided is a flexible display including said laminate.

Description

Flexible display laminates and flexible displays

The present disclosure provides a laminate for a flexible display comprising a light-transmissive flexible base material and an adhesive layer, the laminate comprising a light-transmissive flexible base material, an adhesive layer, and a polarizing plate in this order. The present invention relates to an adhesive layer for forming the adhesive layer and a laminate having the adhesive layer. The laminate can be used for flexible displays.

In recent years, input devices that use a combination of an image display device such as a liquid crystal display (LCD) or an organic electroluminescence (organic EL) display (OLED) and a touch panel have become popular. A transparent conductive film used in a touch panel is laminated on a member such as a support glass via an adhesive layer. Further, a polarizing plate film used in an image device is attached to a liquid crystal module or an organic EL module via an adhesive layer.

The mainstream image display device was a flat display using a glass substrate, but in recent years, foldable displays, rollable displays, etc. using flexible base materials such as plastic have been used. A flexible display has been developed. These flexible displays have various advantages over conventional flat displays using glass substrates, such as being lighter, thinner, more flexible, and more attractive in terms of design. has.

In order to be able to use it for a foldable display, it must have suitability (flexibility) to accommodate the bending of the display. Generally, flexibility is required to have the property of not causing foaming, lifting, or peeling (dynamic flexibility) when repeatedly bent.

In order to solve these problems, Patent Document 1 contains a resin syrup produced by partially polymerizing a (meth)acrylate monomer and a photoinitiator, and the adhesive layer has a storage modulus of 25° C. and 1 Hz. An optically transparent pressure-sensitive adhesive sheet is disclosed in which the pressure is 1.0×10 ⁶ to 1.0×10 ⁷ Pa. Further, Patent Document 2 discloses an adhesive layer formed of an adhesive containing a base polymer, a photocurable compound, and a photoinitiator.

Japanese Patent Application Publication No. 2020-517800 JP2020-097737A

However, when such a conventional adhesive layer is repeatedly bent by a flexible display, the adherends bonded together by the adhesive layer may become misaligned, or the adhesive layer protruding from the edges may come into contact with surrounding materials. The bendability may deteriorate due to the bending, and the bendability cannot be said to be sufficient.
Furthermore, in recent years, colorless polyimide, which is a transparent version of polyimide and has overwhelming mechanical properties, has been used as a light-transmitting flexible base material for foldable displays. As a result, the durability required for the adhesive layer has become more stringent, but if a laminate made by bonding the adhesive layer and colorless polyimide is repeatedly bent, the adhesive layer will lift at the bent part. There are problems in that the adherends may be misaligned with each other, or foaming may occur in the adhesive layer, causing whitening due to the bubbles. In addition, even products that are found to have no problems in normal repeated bending tests may cause misalignment between adherends, lifting of the adhesive layer, or foaming in the adhesive layer when bent at a higher speed than expected. There have also been problems with this.

Therefore, an object of the present disclosure is to provide a laminate in which adherends bonded together do not shift even when bent repeatedly or at high speeds, and the adhesive layer does not protrude from the edges. Furthermore, even when a highly polar base material such as colorless polyimide is used as a light-transmitting flexible base material, a laminate for a flexible display that does not cause display defects at bent parts and has improved visibility. The purpose is to provide an excellent flexible display.

The inventors of the present invention have made extensive studies and have found that the problem can be solved in the following embodiments.
That is, the present disclosure provides a laminate for a flexible display comprising an adhesive layer on a light-transmissive flexible base material, the light transmittance of which is calculated based on the OWRK method from the contact angle of water and the contact angle of diiodomethane. The polar term component of the surface free energy of the flexible substrate is 3.0 mN/m or more, and the surface free energy of the adhesive layer calculated based on the OWRK method from the contact angle of water and the contact angle of diiodomethane is the polar term component is 0.5 mN/m or less, the mass per unit area of the adhesive layer is 10 to 100 g/m ² , the adhesive layer is formed from an acrylic adhesive, and the acrylic adhesive layer is formed from an acrylic adhesive; The adhesive contains 25% by mass or less of repeating units derived from a hydroxyl group-containing monomer in 100% by mass of the acrylic copolymer, 10% by mass or less of repeating units derived from an acid-containing monomer, and 100% by mass or less of repeating units derived from an amide group-containing monomer. 15% by mass or less of repeating units derived from amino group-containing monomers, and 75 to 75% of repeating units derived from (meth)acrylic acid alkyl esters in which the alkyl group has 4 or more carbon atoms. Provided is a laminate for a flexible display characterized by containing 90% by mass of an acrylic copolymer and a low polarity additive.

According to the present disclosure, it is possible to provide a laminate in which bonded adherends do not shift even when repeatedly bent or bent at high speed, and the adhesive layer does not protrude from the end portions. Furthermore, even when a highly polar base material such as colorless polyimide is used as a light-transmitting flexible base material, a laminate for a flexible display that does not cause display defects at bent parts and has improved visibility. This makes it possible to provide an excellent flexible display.
Further, by using the laminate of the present disclosure, a flexible display with excellent visibility can be provided.

FIG. 1 is a schematic cross-sectional view partially showing a laminate according to an embodiment of the present disclosure. 1 is a schematic cross-sectional view partially showing a flexible display that is an example of the use of a laminate according to an embodiment of the present disclosure.

Hereinafter, configuration examples of the laminate and flexible display of the present disclosure will be described, but the present disclosure is not limited thereto.
Further, in this specification, a numerical range specified using "~" includes the numerical values written before and after "~" as the lower limit value and upper limit value range. Furthermore, "film" and "sheet" are not distinguished by thickness. In other words, the term "sheet" in this specification includes a thin film, and the term "film" in this specification includes a thick sheet.
In addition, the adherend refers to the other party to which the adhesive layer of the adhesive sheet is attached, and for example, in the case of a laminate for a flexible display that includes a light-transmitting flexible base material, an adhesive layer, and a polarizing plate in this order. refers to a light-transmissive flexible base material and a polarizing plate.
Unless otherwise noted, the various components appearing in this specification may be used individually or in combination of two or more.

《Adhesive layer for flexible display》
The adhesive layer used in the laminate of the present disclosure is characterized in that the polar component of the surface free energy calculated from the contact angle of water and the contact angle of diiodomethane based on the OWRK method is 0.5 mN/m or less. do.
As a result, even if it is repeatedly bent or bent at high speed, the bonded adherends do not shift, and the adhesive layer does not protrude from the edges. Furthermore, even when a highly polar base material such as colorless polyimide is used as the light-transmitting flexible base material, no display defects occur at the bent portion.

<Polar component of surface free energy>
The polar term component of the surface free energy is 0.5 mN/m or less. The smaller the polar term component of the surface free energy of the pressure-sensitive adhesive layer is, the more preferable it is, and it is preferably 0 mN/m or more. Further, it is preferably 0.3 mN/m or less, more preferably 0.2 mN/m or less. By adjusting the polar component to 0.5 mN/m or less, an adhesive layer is created that does not whiten the bent portion even when bent repeatedly or at high speed, and does not cause misalignment between adherends bonded together. can get. Although the mechanism by which such an effect is obtained is unknown, even if the adhesive layer exhibits strong adhesion to the adherend, strong intermolecular attraction due to dipole interaction is responsible for the development of the adhesive force. It is presumed that this is because the adhesive layer follows the adherend without peeling off when shearing force is applied during bending due to the non-contribution of the adhesive layer.

The polar component of the surface free energy can be controlled to 0.5 mN/m or less by lowering the polarity of the resin used for the adhesive and by adding low polarity additives that are unevenly distributed on the surface after coating. .

The surface free energy is calculated based on the OWRK method from the contact angle of water and diiodomethane at 25°C.
Specifically, the contact angle of each liquid is measured 1 second after the droplet has landed, with the volume of the droplet being 1 μl. The device used to measure the contact angle is not particularly limited, but examples include automatic contact angle meter DM-501Hi manufactured by Kyowa Interface Science Co., Ltd. The polar term component of the surface free energy is calculated by the OWRK method together with the dispersion term component.

<Gel fraction>
The adhesive layer of the present disclosure preferably has a gel fraction of 55 to 90% by mass, more preferably 60 to 80% by mass. When the gel fraction is 55% by mass or more, the cohesive force of the adhesive is improved, a strong adhesive layer is obtained, and the adhesive layer is less likely to protrude from the end portion when folded. When the content is 90% by mass or less, the stress relaxation property of the adhesive is improved, a flexible adhesive layer is easily obtained, the adhesion is improved, and displacement between adherends during bending can be further suppressed.

[Gel fraction measurement method]
The gel fraction can be determined as the insoluble content in a solvent such as ethyl acetate. Specifically, as expressed by Formula 1 below, the mass fraction (unit: mass) of the insoluble component after immersing the adhesive layer in ethyl acetate at 50°C for 1 day relative to the adhesive layer before immersion %).
(Formula 1)
Gel fraction (mass%) = (Y/X) x 100
X = Mass of adhesive layer before dipping (g)
Y=mass of adhesive layer after immersion (g)
Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction. The gel fraction (the amount of crosslinked structure introduced) can be adjusted to a desired range by the method of introducing the crosslinked structure, the type and amount of the crosslinking agent, etc.

<Adhesive>
The adhesive layer is formed of an adhesive.
The adhesive resin is an acrylic adhesive. By using an acrylic adhesive as the adhesive, it becomes easier to balance various performances while adjusting the polar component of the surface free energy to 0.5 mN/m or less.

[Acrylic adhesive]
Acrylic adhesives are mainly composed of acrylic copolymers, which are (meth)acrylic acid ester polymers, and contain low polarity additives as described below, as well as curing agents and other additives as necessary. obtain. (Meth)acrylic ester includes acrylic ester and methacrylic ester. A monomer is a monomer having an ethylenically unsaturated group.

(Acrylic copolymer)
Acrylic copolymers are monomer polymers containing one or more types of acrylic monomers such as (meth)acrylic acid alkyl esters. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and (meth)acrylate. Isobutyl acid, t-butyl (meth)acrylate, isoamyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, (meth)acrylate 2-ethylhexyl acid, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, (meth)acrylate Isodecyl acid, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate Examples include those having a linear or branched alkyl group such as , and those having a cyclic alkyl group such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate.

It is preferable that the acrylic copolymer is copolymerized with a monomer containing a unit derived from (meth)acrylic acid (ester) having a functional group. By including a functional group, cohesive force can be imparted to the adhesive layer, and by using a curing agent in the adhesive, the cohesive force of the adhesive layer can be further improved, making it easier to suppress extrusion during bending.

In the (meth)acrylic acid (ester) having a functional group, the functional group may be at least one selected from a carboxyl group, a hydroxyl group, an amino group, an amide group, an oxyalkylene group, an epoxy group, and an isocyanate group. Preferably, it is at least one selected from a carboxyl group, a hydroxy group, an amino group, and an amide group, and even more preferably at least one selected from a carboxyl group and a hydroxy group, or both.
Examples of the monomer (or acid-containing monomer) unit having a carboxyl group include acrylic acid and methacrylic acid.
A monomer unit having a hydroxyl group is a repeating unit derived from a monomer having a hydroxyl group. Examples of monomers having a hydroxyl group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; Examples include (meth)acrylic acid [(mono, di, or poly)alkylene glycol] such as meth)acrylic acid mono(diethylene glycol), and (meth)acrylic acid lactones such as monocaprolactone (meth)acrylic acid.
Monomer units having an amino group include monomers containing a primary amino group such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate, monomers containing a secondary amino group such as t-butylaminoethyl (meth)acrylate, and ethyl Tertiary amino group-containing monomers such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, allylamine, vinylpyridine, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, Examples include repeating units derived from monomers having an amino group such as vinyloxazole.
Examples of monomer units having an amide group include cyclic amides such as (meth)acrylamide, N-vinyl lactams, vinylmorpholine, and (meth)acryloylmorpholine, and N-vinyl carbons such as N-vinylformamide and N-vinylacetamide. Examples include acid amides, acrylamide, N,N-dimethylacrylamide, and the like. N-vinyl lactams are monomers having a cyclic lactam ring, such as N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-ε-caprolactam, and their hydrogen atoms. Examples include compounds having a structure in which one or more of them is substituted with a substituent. Examples of substituents include alkyl groups having 1 to 20 carbon atoms, alkyl groups having 2 to 20 carbon atoms, aryl groups having 6 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, and carboxyester groups having 3 to 20 carbon atoms. , an amino group having 1 to 20 carbon atoms, and does not include acidic groups such as a hydroxyl group, a carboxylic acid (salt) group, a sulfonic acid (salt) group, or a hypophosphorous acid (salt) group.
Monomer units having an oxyalkylene group include methoxytriethylene glycol (meth)acrylate, methoxypolyethylene glycol #400 (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxytripropylene glycol (meth)acrylate, and methoxypolypropylene glycol. (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, 2-ethylhexylcarbitol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate Examples include acrylate.
Examples of the monomer unit having an isocyanate group include 2-isocyanate ethyl (meth)acrylate, 3-isocyanate propyl (meth)acrylate, and 4-isocyanate butyl (meth)acrylate.
Examples of the monomer unit having an epoxy group include repeating units derived from monomers having a glycidyl group such as glycidyl (meth)acrylate.

The content of the hydroxyl group-containing monomer is 25% by mass or less, more preferably 20% by mass or less, based on 100% by mass of the acrylic copolymer. In addition, in the present disclosure, when a certain monomer is n mass % (or contained n mass %) in 100 mass % of the acrylic copolymer, it means that the repeating unit derived from that monomer is n mass % of the copolymer. %. Moreover, the fact that a certain monomer is n mass % or less (or n mass % or less is contained) in 100 mass % of the acrylic copolymer may also include an embodiment in which the monomer is 0 mass %.
The amount of the acid-containing monomer is 10% by mass or less, more preferably 7% by mass or less, based on 100% by mass of the acrylic copolymer.
The amount of the amide group-containing monomer in 100% by mass of the acrylic copolymer is 15% by mass or less, more preferably 10% by mass or less, and most preferably 7% by mass or less.
The amino group-containing monomer is present in an amount of 15% by mass or less based on 100% by mass of the acrylic copolymer, more preferably 10% by mass or less, and most preferably 7% by mass or less.
The proportion of the oxyalkylene group-containing monomer is preferably 30% by mass or less, more preferably 15% by mass or less, and most preferably 12% by mass or less.
Among other monomers copolymerizable with acrylic monomers, monomers with a water/octanol partition coefficient log Kow of 2.22 or less at 25°C and monomers that are optionally miscible with water should be added in an amount of 20% by mass or less. It is preferably at most 15% by mass, more preferably at most 12% by mass.
Each of the monomers mentioned above in this paragraph can be present in an amount of 0% by weight or more (ie, even 0% by weight) based on 100% by weight of the acrylic copolymer. For example, in 100% by mass of the acrylic copolymer, the hydroxyl group-containing monomer may be 0.5% by mass or more, and the acid-containing monomer may be 0.2% by mass or more. In one embodiment, out of 100% by weight of the acrylic copolymer, the hydroxyl group-containing monomer is 0.5% by weight or more, the acid-containing monomer is 0.2% by weight or more, and each of the other monomers mentioned above in this paragraph is 0% by weight. % by mass or more.
The (meth)acrylic acid alkyl ester in which the alkyl group has 4 or more carbon atoms is present in an amount of 75 to 90% by mass, preferably 78 to 88% by mass, based on 100% by mass of the acrylic copolymer. By using this type of monomer as the main component, the polarity of the acrylic copolymer becomes low. The number of carbon atoms in the alkyl group is typically 16 or less.

The (meth)acrylic copolymer may have other monomer units in addition to the above-mentioned monomer units, if necessary. Other monomers may be used as long as they are copolymerizable with the above-mentioned acrylic monomers, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, myristic acid. Examples include carboxylic acid vinyl esters such as vinyl, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, and vinyl benzoate, and styrene. Among these, vinyl acetate, vinyl propionate, and vinyl butyrate are hydrophilic with a water/octanol partition coefficient log Kow of 2.30 or less at 25°C, so in order to lower the polarity of the acrylic copolymer, the following It is preferable to lower the passing ratio.
The value of log Kow can be calculated using software called HSPiP (Steven Abbott, Hiroshi Yamamoto), for example, based on the structural formula of the monomer.

(Manufacture of acrylic copolymer)
Acrylic copolymers can be produced by polymerizing a monomer mixture.
For polymerization, known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization are possible, but solution polymerization is preferred. Preferred examples of the solvent used in solution polymerization include acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone.
The polymerization temperature is preferably a boiling point reaction of 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

The polymerization initiator used for polymerization is preferably a radical polymerization initiator. Radical polymerization initiators are generally peroxides and azo compounds.
Peroxides include, for example, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5- Dialkyl peroxides such as di(t-butylperoxy)hexyne-3;
Peroxy esters such as t-butylperoxybenzoate, t-butylperoxyacetate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide oxide, ketone peroxide such as methylcyclohexanone peroxide;
2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t- peroxyketals such as butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valate;
Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylcyclohexane-2,5-dihydroperoxide;
Diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide;
Examples include peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile);
2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2 2,2'-azobispropionitrile such as '-azobis(2-hydroxymethylpropionitrile);
Examples include 1,1'-azobis-1-alkane nitrile such as 1,1'-azobis(cyclohexane-1-carbonitrile).

The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the monomer mixture.

(Mass average molecular weight (Mw))
The weight average molecular weight of the acrylic copolymer is preferably 800,000 to 1,800,000, more preferably 1,000,000 to 1,500,000. If it is in the range of 800,000 to 1,800,000, the cohesive force will be further improved, and the adhesive layer will be less likely to protrude from the edge when folded. Note that the mass average molecular weight is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

(hardening agent)
It is preferable that the acrylic pressure-sensitive adhesive contains a curing agent. The curing agent to be added to the pressure-sensitive adhesive is preferably one that reacts with the functional group of the monomer having the above-mentioned functional group by heat or the like to form a bond. By adding a curing agent, the cohesive force of the adhesive layer is improved, and the durability and stain resistance are further improved.

As the curing agent, from among known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, carbodiimide compounds, metal chelate compounds, butylated melamine compounds, etc. It can be selected appropriately in consideration of reactivity. For example, if the polymer in the adhesive contains a hydroxyl group as a functional group, an isocyanate compound can be used.

The isocyanate compound is an isocyanate having two or more isocyanate groups. The isocyanate compound is preferably an isocyanate monomer such as an aromatic polyisocyanate, an aliphatic polyisocyanate, an araliphatic polyisocyanate, an alicyclic polyisocyanate, or a burette, nurate, or adduct thereof.

Aromatic polyisocyanates include, for example, 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6- Tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4',4 ”-triphenylmethane triisocyanate and the like.

Aliphatic polyisocyanates include, for example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, Examples include dodecamethylene diisocyanate and 2,4,4-trimethylhexamethylene diisocyanate.

Aroaliphatic polyisocyanates include, for example, ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, Examples include 1,4-tetramethylxylylene diisocyanate and 1,3-tetramethylxylylene diisocyanate.

Alicyclic polyisocyanates include, for example, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4 -cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), 1,4-bis(isocyanatomethyl)cyclohexane, and the like.

The buret body is a self-condensation product having buret bonds formed by self-condensation of isocyanate monomers. Examples of the buret body include hexamethylene diisocyanate burette bodies.

The nurate is a trimer of isocyanate monomers. Examples include hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, and tolylene diisocyanate trimer.

The adduct is a difunctional or more functional isocyanate compound obtained by reacting an isocyanate monomer with a difunctional or more functional low-molecular active hydrogen-containing compound. Examples of adducts include compounds obtained by reacting trimethylolpropane and hexamethylene diisocyanate, compounds obtained by reacting trimethylolpropane and tolylene diisocyanate, compounds obtained by reacting trimethylolpropane and xylylene diisocyanate, and trimethylolpropane. Examples include a compound obtained by reacting propane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

The isocyanate compound is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or a nurate, which is a reaction product of an isocyanate monomer and a trifunctional low-molecular active hydrogen-containing compound. Isocyanate compounds include trimethylolpropane adduct of hexamethylene diisocyanate, nurate of hexamethylene diisocyanate, trimethylolpropane adduct of tolylene diisocyanate, nurate of tolylene diisocyanate, trimethylolpropane adduct of isophorone diisocyanate, and isophorone diisocyanate. Nurate forms are preferred, and trimethylolpropane adducts of hexamethylene diisocyanate, trimethylolpropane adducts of tolylene diisocyanate, and trimethylolpropane adducts of isophorone diisocyanate are more preferred.

Epoxy compounds include, for example, glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylene diamine, 1,3-bis(N,N'- (diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane, and the like.

Examples of aziridine compounds include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, 4, Examples include 4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

The carbodiimide compound is preferably a high molecular weight polycarbodiimide produced by subjecting a diisocyanate compound to a decarboxylation condensation reaction in the presence of a carbodiimidation catalyst. The commercial product of the high molecular weight polycarbodiimide is preferably the Carbodilite series manufactured by Nisshinbo Co., Ltd. Among them, Carbodilite V-03, 07, and 09 are preferred because they have excellent compatibility with organic solvents.

The metal chelate is preferably a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium, and acetylacetone or ethyl acetoacetate. Examples of the metal chelate include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethylacetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

The curing agent preferably contains 0.02 to 4.0 parts by mass, more preferably 0.04 to 1.0 parts by mass, and 0.02 to 4.0 parts by mass, more preferably 0.04 to 1.0 parts by mass, based on 100 parts by mass of the acrylic copolymer in the adhesive. It is more preferable to contain 0.04 to 0.4 parts by mass. When the content is 0.02 parts by mass or more, the cohesive force is further improved, and when the content is 4 parts by mass or less, it becomes easier to achieve both cohesive force and flexibility, which is preferable.

In addition to the silane coupling agent and chlorinated polyolefin described below, acrylic adhesives can contain various resins, oils, softeners, dyes, pigments, antioxidants, and ultraviolet absorbers as optional ingredients as long as they can solve the problem. It can contain additives, weathering stabilizers, plasticizers, fillers, anti-aging agents, antistatic agents and the like.

The polar component of the adhesive layer can be adjusted to 0.5 mN/m or less by lowering the polarity of the resin used in the adhesive, or by adding low polarity additives that are unevenly distributed on the surface after coating. Can be mentioned.

For example, when lowering the polarity of an acrylic copolymer, use a (meth)acrylic acid alkyl ester whose alkyl group has 1 to 3 carbon atoms, a hydroxyl group-containing monomer, an acid-containing monomer, an amide group-containing monomer, or an amino group-containing monomer. Among monomers that can be copolymerized with , oxyalkylene group-containing monomers, or other acrylic monomers, monomers with a water/octanol partition coefficient log Kow at 25°C of 2.22 or less and are optionally miscible with water. One example is lowering the ratio of monomers and increasing the ratio of (meth)acrylic acid alkyl esters in which the alkyl group has 4 or more carbon atoms.

Specifically, the (meth)acrylic acid alkyl ester whose alkyl group has 1 to 3 carbon atoms is preferably 25% by mass or less, and 20% by mass or less based on 100% by mass of the acrylic copolymer. is more preferable, more preferably 18% by mass or less, still more preferably 15% by mass or less.
The content of the hydroxyl group-containing monomer is preferably 5% by mass or less, more preferably 2% by mass or less based on 100% by mass of the acrylic copolymer.
The acid-containing monomer is preferably 5% by mass or less, more preferably 2% by mass or less, and most preferably 1% by mass or less based on 100% by mass of the acrylic copolymer.
The amide group-containing monomer is preferably less than 5% by mass, more preferably 3% by mass or less, and most preferably 1% by mass or less based on 100% by mass of the acrylic copolymer.
The amino group-containing monomer is preferably less than 5% by weight, more preferably 3% by weight or less, and most preferably 1% by weight or less based on 100% by weight of the acrylic copolymer.
The proportion of the oxyalkylene group-containing monomer is preferably less than 20% by mass, more preferably 10% by mass or less, and most preferably 5% by mass or less.
Among other monomers copolymerizable with acrylic monomers, monomers with a water/octanol partition coefficient log Kow of 2.22 or less at 25°C and monomers that are optionally miscible with water should be used in an amount of less than 10% by mass. It is preferably at most 5% by mass, more preferably at most 3% by mass, even more preferably at most 1% by mass.
Each of the monomers mentioned above in this paragraph can be present in an amount of 0% by weight or more (ie, even 0% by weight) based on 100% by weight of the acrylic copolymer.
The (meth)acrylic acid alkyl ester in which the alkyl group has 4 or more carbon atoms is preferably 80% by mass or more based on 100% by mass of the acrylic copolymer, and more preferably 85% by mass or more.

Examples of a method for blending low polarity additives that are unevenly distributed on the surface after coating include a method of adding a silane coupling agent, a chlorinated polyolefin, or a combination thereof to the adhesive.
The individual or total amount of these low polarity additives is preferably 0.05 parts by mass or more and 0.5 parts by mass or less, based on 100 parts by mass of the resin component of the acrylic copolymer. More preferably, the content is .1 part by mass or more and 0.3 parts by mass or less.
At this time, the polar term component of the surface free energy of the acrylic copolymer before adding the low polarity additive (that is, without adding the low polarity additive) must be 2.0 mN/m or less. is preferable, and more preferably 1.5 mN/m or less.

As a silane coupling agent, an alkoxysilane compound having a (meth)acryloxy group, an alkoxysilane compound having a vinyl group, an alkoxysilane compound having an amino group, an alkoxysilane compound having a mercapto group, or an alkoxysilane compound having an epoxy group. etc.
Specifically, commercially available products include, for example, KBM403 (3-glycidoxypropyltrimethoxysilane), KBE403 (3-glycidoxypropyltriethoxysilane), and KBM303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane). methoxysilane) (manufactured by Shin-Etsu Chemical Co., Ltd.), BYK-325N (polyether-modified polymethylalkylsiloxane) (manufactured by BYK Chemie Japan Co., Ltd.), and the like.

Examples of chlorinated polyolefins include chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic-modified chlorinated polypropylene, chlorinated polyethylene, and chlorinated ethylene vinyl acetate (EVA) copolymers, which are compatible with acrylic copolymers and the like. Chlorinated polypropylene or chlorinated ethylene vinyl acetate copolymer is preferred from the viewpoint of good polarity and effective reduction of polarity.
Specific examples of commercially available products include Super Chron 390S (chlorinated polypropylene, chlorine content 36%) and Super Chron BX (chlorinated EVA, chlorine content 18%) (manufactured by Nippon Paper Industries Co., Ltd.). It will be done.

《Laminated body for flexible display》
A flexible display laminate includes an adhesive layer on a light-transmitting flexible base material. For example, it has a structure of base material/adhesive layer/polarizing plate. It is preferable to provide the light-transmitting flexible substrate, the adhesive layer, and the polarizing plate in this order. As a result, a laminate with excellent transparency and flexibility can be obtained.

FIG. 1 shows an example of a schematic cross-sectional view partially showing a laminate according to an embodiment of the present disclosure. In FIG. 1, 3 is a light-transmitting flexible base material (cover panel), 1 is an adhesive layer, and 4 is a polarizing plate.

In the laminate shown in FIG. 1, a light-transmitting flexible base material (cover panel) is attached to a polarizing plate via an adhesive layer.

[Light-transmitting flexible base material]
A transparent plastic substrate may be used as the light-transmissive flexible substrate (cover panel).
In the present disclosure, the polar term component of the surface free energy of the light-transmitting flexible substrate is 3.0 mN/m or more, preferably 4.0 mN/m or more. The adhesion due to the polar attraction between the adhesive layer having a polar term component of 0.5 mN/m or less and the light-transmitting flexible base material having a polar term component of 3.0 mN/m or more is not too strong; The adhesive layer follows the movement of the base material during repeated bending, making it difficult for whitening of the bent portion and misalignment of adherends due to the adhesive layer to occur. It is preferable to use a light-transmissive flexible base material having a resistance of 4.0 mN/m or more because the effects of the present disclosure are more excellent. Although the upper limit of the polar term component of the surface free energy of the light-transmitting flexible substrate is not particularly limited, it is typically 10 mN/m or less.

Examples of materials for such a light-transmitting flexible base material include acrylic resins such as polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, polycycloolefin, and polyimide. It will be done. In particular, PET film or polyimide is preferred, and polyimide is most preferred in terms of durability. Plastic materials can be used alone or in combination of two or more.

The adhesive layer used in the laminate of the present disclosure has excellent bending resistance, so even when colorless polyimide, which is a transparent polyimide, is used as the base material, it suppresses misalignment and whitening between adherends. It can be made into a laminate.

Among the transparent plastic substrates mentioned above, the light-transmitting flexible substrate (cover panel) is a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate that can be used under harsh conditions such as high temperature or high temperature and high humidity. A transparent plastic base material whose deformation is suppressed or prevented can be suitably used.

The light-transmitting flexible base material may be subjected to surface treatment such as plasma treatment, corona treatment, flame treatment, UV treatment, etc., if necessary. Even with transparent plastic substrates such as polyethylene (PE) and polypropylene (PP), which have a polar component value of less than 3.0 mN/m when untreated, the polar component can be reduced by applying the above surface treatment. It becomes possible to make the value 3.0 mN/m or more, and it can be used in the embodiment of the present disclosure.

The thickness of the light-transmitting flexible base material is not particularly limited, and is preferably, for example, 100 to 2000 μm, more preferably 200 to 1000 μm.

<Manufacture of laminates for flexible displays>
A method for manufacturing a laminate includes, for example, peeling off a release film from a pressure-sensitive adhesive sheet having release films on both sides of the pressure-sensitive adhesive layer, and applying the pressure-sensitive adhesive layer to an adherend such as a light-transmitting flexible substrate or a polarizing plate. can be pasted to form a laminate. Alternatively, after directly forming an adhesive layer on a light-transmitting flexible substrate, a laminate may be formed by pasting an adhesive layer provided on an adherend or another adhesive sheet to the adhesive layer. can.

[Adhesive sheet]
Adhesive sheets can be manufactured according to normal manufacturing methods. For example, an adhesive may be directly applied to one side of a release film to form a pressure-sensitive adhesive layer to a predetermined thickness after drying, and another release film may be attached to the adhesive layer. , Apply adhesive to one side of each of the two release films so that the dry thickness becomes a predetermined thickness to form two adhesive layers, and then apply each adhesive layer to each other. It can be produced by a method such as pasting.

When applying the adhesive, a conventional coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, or spray coater can be used.

The adhesive sheet may have the form of an adhesive tape wound into a roll by cutting it into an appropriate width and winding it into a roll.

The thickness of the adhesive layer is not particularly limited, and is preferably, for example, 10 to 500 μm, more preferably 50 to 200 μm. It is preferable that the thickness of the adhesive layer is 10 to 500 μm because it is easy to obtain sufficient cohesive force, there is no displacement or protrusion of the end portion of the adhesive layer, and flexibility during high-speed bending can be achieved.

The mass per unit area of the adhesive layer (hereinafter also referred to as coating amount) is 10 to 100 g/m ² , preferably 25 to 70 g/m ² . By setting the mass per unit area of the adhesive layer within this range, it is possible to obtain an adhesive layer that does not whiten at the bent portion even when repeatedly bent and does not cause misalignment between adherends. If the coating amount is 10 g/m ² or more, the adhesive layer will be sufficient to follow the adherend during bending, and the occurrence of edge displacement due to lifting can be further suppressed. When the coating amount is 100 g/m ² or less, it is possible to further suppress the pressure-sensitive adhesive layer from protruding from the edges during bending.

The release film is not particularly limited, but a transparent plastic base material can be suitably used. Examples of materials for the transparent plastic base material include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetylcellulose, polysulfone, polyarylate, and polycycloolefin. Examples include. In addition, plastic materials can be used individually or in combination of 2 or more types.

Among the transparent plastic substrates mentioned above, the release film is a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate that suppresses or prevents deformation under harsh conditions such as high temperature or high temperature and high humidity. A plastic base material can be suitably used.

The release film may have either a single layer or a multilayer form. Further, the surface of the transparent substrate may be subjected to appropriate surface treatment such as physical treatment such as corona discharge treatment and plasma treatment, and chemical treatment such as undercoating treatment.

《Flexible display》
The flexible display preferably includes the laminate of the present disclosure and an optical element. Thereby, the display of the present disclosure has excellent flexibility and visibility. For example, the optical element can be attached to the polarizing plate of the laminate via an additional adhesive layer.
The optical element is not particularly limited, and includes, for example, a liquid crystal element, an organic EL element, and the like.

FIG. 2 shows an example of a schematic cross-sectional view partially showing a display, which is an example of how the adhesive sheet of the present disclosure is used. In FIG. 2, 3 is a light-transmitting flexible base material (cover panel), 1 is a first adhesive layer, 4 is a polarizing plate, 5 is a second adhesive layer, and 6 is a barrier layer such as silicon nitride. , 7 is an organic EL layer, 8 is a support such as polyimide, and 9 is an organic EL cell. Note that the configuration of the display is not limited to that shown in FIG. 2.

In the display shown in FIG. 2, a light-transmitting flexible base material (cover panel) is attached to a polarizing plate via an adhesive layer (first adhesive layer) of the present disclosure, and It is attached to the organic EL cell via an adhesive layer (second adhesive layer). In this way, the adhesive sheet of the present disclosure has a transparent adhesive layer formed from the above-mentioned adhesive applied to a light-transmitting flexible base material (cover panel) and a polarizing plate, and further includes an adhesive layer for a polarizing plate. The laminate can be used in a form in which it is attached to an organic EL via a laminate.
For example, in FIG. 2, the adhesive layer of the present disclosure can be used as both the first adhesive layer and the second adhesive layer.
In general, when comparing the first adhesive layer and the second adhesive layer, the quality required for the adhesive layer is higher for the first adhesive layer, and the adhesive of the present disclosure has higher quality requirements. It is preferably used in the first adhesive layer because it has good adhesion and adhesion to materials. At this time, as the adhesive for forming the second adhesive layer, the adhesive of the present disclosure may be used, or a conventionally known adhesive may be used.

There are no particular restrictions on the usage of the display, but examples include organic EL televisions, organic EL smartphones, organic EL tablets, organic EL smart watches, etc.

Next, the present invention will be described in further detail with reference to Examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, "parts" means "parts by mass,""%" means "% by mass," and "RH" means relative humidity. Further, the blending amounts in the table are parts by mass. Note that a blank column in the table indicates that the corresponding component was not blended.
The method for measuring the mass average molecular weight of the acrylic copolymer is as shown below.

<Measurement of mass average molecular weight of acrylic copolymer>
The mass average molecular weight (Mw) can be measured using a GPC "LC-GPC system" manufactured by Shimadzu Corporation, using polystyrene of known molecular weight as a standard substance.
Equipment name: Shimadzu Corporation, LC-GPC system “Prominence”
Columns: 4 GMHXL columns manufactured by Tosoh Corporation and 1 column HXL-H manufactured by Tosoh Corporation were connected.
Mobile phase solvent: Tetrahydrofuran Flow rate: 1.0ml/min Column temperature: 40°C

<Production example of acrylic copolymer>
(Acrylic copolymer (R9))
20 parts of methyl acrylate (MA) and 2-acrylic acid were placed in a reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen introduction tube. 43.2 parts of ethylhexyl (2EHA), 35 parts of dodecyl acrylate (DOA), 1 part of 4-hydroxybutyl acrylate (4HBA), 0.8 part of acrylic acid (AA), 2,2'-azo as an initiator. 0.2 part of bisisobutyronitrile (hereinafter simply referred to as "AIBN") was charged, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. Thereafter, the reaction was started by heating to 50° C. while stirring under a nitrogen atmosphere. Thereafter, the reaction solution was allowed to react at 50°C for 4 hours. After the reaction was completed, it was cooled and diluted with ethyl acetate to obtain a copolymer (R9) solution with a nonvolatile content of 30%. The mass average molecular weight of the obtained copolymer (R9) was 890,000.

(Acrylic copolymer (R10-R11, R35-R62)
Acrylic copolymers (R10 to R11, R35 to R62) were produced in the same manner as in the production of acrylic copolymer (R9), except that the composition and blending amount (parts by mass) were changed as shown in Table 1. .

Tables 1, 2, and 3 show the composition, blending amount (nonvolatile parts by mass), and weight average molecular weight (Mw) of the obtained acrylic copolymers (R9 to R11, R35 to R62).

The abbreviations in the table are as follows.
MA: Methyl acrylate (alkyl group has 1 carbon number)
EA: Ethyl acrylate (alkyl group has 2 carbon atoms)
2EHA: 2-ethylhexyl acrylate (alkyl group has 8 carbon atoms)
BA: Butyl acrylate (alkyl group has 4 carbon atoms)
DOA: Dodecyl acrylate (alkyl group has 12 carbon atoms)
IBXA: Isobornyl acrylate (alkyl group (cyclic structure) has 10 carbon atoms)
TDA: tridecyl acrylate (alkyl group has 13 carbon atoms)
IBXMA: Isobornyl methacrylate (alkyl group (cyclic structure) has 10 carbon atoms)
nHA: n-heptyl acrylate (alkyl group has 7 carbon atoms)
IAA: Isoamyl acrylate (alkyl group (branched) carbon number 5)
4HBA: 4-Hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate AA: DMAEA acrylate: 2-dimethylaminoethyl acrylate ACMO: Acryloylmorpholine MDEA: Methoxydiethylene glycol acrylate
a1: (meth)acrylic acid alkyl ester monomer whose alkyl group has 1 to 3 carbon atoms
a2: (meth)acrylic acid alkyl ester monomer whose alkyl group has 4 or more carbon atoms
a3: Hydroxyl group-containing monomer
a4: Acid-containing monomer
a5: Monomer containing amino group
a6: Amide group-containing monomer
a7: Oxyalkylene group-containing monomer

(Example 1)
<Preparation of adhesive>
Per 100 parts of nonvolatile content of the acrylic copolymer (R9), 0.14 parts of hexamethylene diisocyanate trimethylolpropane adduct D-160N as a curing agent, and 0.1 part of KBM-403 as a low polarity additive. of the mixture was added, and ethyl acetate was further blended so that the nonvolatile content was 20%, and the mixture was stirred to obtain an adhesive.

<Preparation of adhesive sheet>
The above adhesive was applied to a polyethylene terephthalate separator (release film 1) with a thickness of 75 μm so that the thickness after drying was 50 μm, and the adhesive layer was formed by drying with hot air at 100 ° C. for 2 minutes. did. Next, a 50 μm thick polyethylene terephthalate separator (release film 2) was attached to this adhesive layer to obtain a first adhesive sheet.

<Preparation of laminate>
One separator was peeled off from the adhesive sheet, and the exposed adhesive layer was coated with CPI (colorless polyimide, manufactured by KOLON, 50 μm, polar component 4) as a light-transmitting flexible base material in an atmosphere of 25° C. and 50% relative humidity. .5 mN/m) using a laminator, peel off the other separator, and bond to a PET film with a thickness of 188 μm using a laminator to form the PET film/adhesive layer/light-transparent flexible group. A laminate of materials was obtained.

(Examples 2 to 40, Comparative Examples 1 to 12)
As shown in Tables 4 to 7, adhesive sheets were obtained in the same manner as in Example 1, except that the types and amounts (parts by mass) of the acrylic copolymer, curing agent, and additives were changed. Thereafter, the adhesive layer was attached to the light-transmitting flexible substrate shown in Tables 4 to 7 to obtain a laminate of PET film/adhesive layer/light-transmitting flexible substrate.

《Evaluation of adhesive layer》
The physical property values of the adhesive layer and the laminate were measured and evaluated by the following methods. The results are shown in Tables 4-7.

<Measurement of mass (coating amount) per unit area of adhesive layer>
The obtained adhesive sheet was cut into a size of 100 mm x 100 mm, and the mass was measured (mass W (g)). Separately, a 75 μm thick polyethylene terephthalate separator (release film 1) and a 50 μm thick polyethylene terephthalate separator (release film 2) used in the adhesive sheet were cut into 100 mm x 100 mm sizes and their mass was measured. (mass W75 (g) and mass W50 (g), respectively).
Coating amount (g/m ² )=(W-W75-W50)/0.01

<Measurement of gel fraction>
The obtained adhesive sheet was cut into a size of 30 mm x 100 mm, the polyethylene terephthalate separator (release film 2) with a thickness of 50 μm was peeled off, and the exposed adhesive layer was cut into a weighed 300 mesh stainless steel wire mesh (mass W0 ), and then a 75 μm thick polyethylene terephthalate separator (release film 1) was peeled off to prepare a sample. The weighed mass of the sample was designated as W1, and the mass of the sample left still in ethyl acetate for 24 hours, dried at 100° C. for 1 hour, and weighed was designated as W2, and was calculated using the following formula.
Gel fraction (%) = {(W2-W0)/(W1-W0)}×100

<Measurement of polar component of surface free energy>
A polyethylene terephthalate separator (release film 2) having a thickness of 50 μm was peeled off from the obtained pressure-sensitive adhesive sheet to expose the pressure-sensitive adhesive layer for measurement.
For the measurement, MSA manufactured by KRUSS was used, and the contact angle was calculated using the OWRK method from the contact angle 1 second after 1 μl each of water and diiodomethane landed on the adhesive layer or the light-transmitting flexible substrate, and the polar term was calculated using the OWRK method. I asked for it.

<Evaluation of whitening of bent parts, deviation of edges, and protrusion of edges by standard bending test>
Using the obtained laminate, the inner diameter (diameter) when bent was set to 3 mm using a bending tester (manufactured by Yuasa System Equipment Co., Ltd.) in an atmosphere of 25 ° C. and 50% relative humidity as a normal test. One cycle consisted of bending and opening 180 degrees, and 300,000 cycles were repeated at a pace of 30 reciprocations per minute.
The appearance after the test was evaluated based on the following criteria for whitening at the bent portion and misalignment of the edge of the adherend. In either case, the higher the numerical value of the evaluation standard, the better it is, and if it is 3 or more, it is practical.
Appearance: The presence or absence of air bubbles in the test laminate, the misalignment of the edges of the adherends, and the presence or absence of protrusion of the edges of the adhesive layer were visually evaluated under the following conditions.

[Whitening of bent parts]
5: No air bubbles are observed within a range of 5 mm on each side from the bent part.
4: The number of bubbles is 1 or more and 10 or less within a range of 5 mm on each side from the bent part.
3: There are 11 or more bubbles and 50 or less bubbles within a range of 5 mm on each side from the bent part.
2: There are 51 or more bubbles and 100 or less bubbles within a range of 5 mm on each side from the bent part.
1: There are 100 or more bubbles within a range of 5 mm on each side from the bent part.

[Misalignment of edges]
5: The gap between the PET film and the light-transmitting flexible base material is less than 1 mm.
4: The deviation between the PET film and the light-transmitting flexible base material is 1 mm or more and less than 2 mm.
3: The deviation between the PET film and the light-transmitting flexible base material is 2 mm or more and less than 3 mm.
2: The misalignment between the PET film and the light-transmitting flexible base material is 3 mm or more and less than 4 mm.
1: The gap between the PET film and the light-transmitting flexible base material is 4 mm or more.

[Protruding edges]
5: The protrusion from the edge of the adhesive layer is less than 100 μm.
4: The protrusion from the edge of the adhesive layer is 100 μm or more and less than 200 μm.
3: The protrusion from the edge of the adhesive layer is 200 μm or more and less than 300 μm.
2: The protrusion from the edge of the adhesive layer is 300 μm or more and less than 400 μm.
1: The protrusion from the edge of the adhesive layer is 400 μm or more.

<Evaluation of whitening of bent parts, deviation of edges, and protrusion of edges by high-speed bending test>
The test was conducted using a standard bending test with a reciprocating pace of 120 reciprocations per minute and a cycle count of 100,000 cycles, and evaluation was performed using the same evaluation criteria as in the standard bending test.

The abbreviations in the table are as follows.
<Curing agent>
D-110N: Trimethylolpropane adduct of xylylene diisocyanate D-160N: Trimethylolpropane adduct of hexamethylene diisocyanate EX-313: Polyfunctional epoxy compound (glycerol polyglycidyl ether)
D-370N: Isocyanurate of 1,5-pentamethylene diisocyanate DID: Trimethylolpropane adduct of decamethylene diisocyanate <Additive>
KBM-403: Epoxy silane KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.
KBE-403: Epoxy silane KBE-403 manufactured by Shin-Etsu Chemical Co., Ltd.
KBM-303: Epoxy silane KBM-303 manufactured by Shin-Etsu Chemical Co., Ltd.
BYK-325N: Silicon-containing surface conditioner manufactured by BYK-Chemie Japan Co., Ltd. BYK-325N
390S: Chlorinated polyolefin 390S manufactured by Nippon Paper Industries Co., Ltd.
BX: Chlorinated EVA BX manufactured by Nippon Paper Industries Co., Ltd.

<Light-transmitting flexible base material>
CPI: Colorless polyimide (manufactured by KOLON, 50 μm, polar component 4.5 mN/m)
P-CPI: Plasma-treated colorless polyimide (treated with the above CPI, 50 μm, polar term component 7.6 mN/m))
PET: Polyethylene terephthalate (manufactured by Toyobo Co., Ltd., 50 μm, polar component 5.8 mN/m)
PMMA: Polymethyl methacrylate (manufactured by Mitsubishi Chemical Corporation, 53 μm, polar component 6.8 mN/m)
C-HDPE: Corona-treated product of high-density polyethylene (manufactured by NT Film Co., Ltd., 50 μm) (polar term component 4.8 mN/m)
C-OPP: Corona-treated product of stretched polypropylene (manufactured by Toyobo Co., Ltd., 40 μm) (polar component 4.6 mN/m)

For the corona treatment when creating C-HDPE and C-OPP, we used the Navitas corona treatment equipment Plasma Dyne at a speed of 100 mm/sec, and the distance between the corona discharge nozzle and the substrate was 20 mm. One sweep was made from one end of the material to the other.

From the results shown in Tables 4 to 7, the adhesive layer of the present disclosure did not cause any displacement between adherends bonded together even when repeatedly bent, and the adhesive layer did not protrude from the edges. Furthermore, even when colorless polyimide was used as the light-transmitting flexible base material, it was confirmed that the bent portion did not whiten due to foaming. As a result, a display including a laminate having an adhesive layer according to the present disclosure has excellent flexibility, and thereby a display with excellent visibility can be obtained.
On the other hand, the adhesive layers of Comparative Examples 1 to 12 could not satisfy all of the above characteristics.

1 First adhesive layer 3 Light-transparent flexible base material (cover panel)
4 Polarizing plate 5 Second adhesive layer 6 Barrier layer 7 Organic EL layer 8 Support 9 Organic EL cell

Claims

A flexible display laminate comprising an adhesive layer on a light-transmitting flexible base material,
The polar term component of the surface free energy of the light-transmitting flexible base material calculated based on the OWRK method from the contact angle of water and the contact angle of diiodomethane is 3.0 mN/m or more,
The polar term component of the surface free energy of the adhesive layer calculated based on the OWRK method from the contact angle of water and the contact angle of diiodomethane is 0.5 mN/m or less,
The mass per unit area of the adhesive layer is 10 to 100 g/m 2 ,
The adhesive layer is formed from an acrylic adhesive,
The acrylic adhesive contains 25% by mass or less of repeating units derived from a hydroxyl group-containing monomer in 100% by mass of the acrylic copolymer, 10% by mass or less of repeating units derived from an acid-containing monomer, and contains an amide group. 15% by mass or less of repeating units derived from monomers, 15% by mass or less of repeating units derived from amino group-containing monomers, and repeating units derived from (meth)acrylic acid alkyl esters in which the alkyl group has 4 or more carbon atoms. 1. A laminate for a flexible display, comprising an acrylic copolymer containing 75 to 90% by mass of the following: and a low polarity additive.
2. The flexible display according to claim 1, wherein the polar term component of the surface free energy of the adhesive layer calculated based on the OWRK method from the contact angle of water and the contact angle of diiodomethane is 0.2 mN/m or less. laminate for use.
The flexible flexible material according to claim 1, wherein the adhesive layer has a mass per unit area of 25 to 70 g/m 2 and a gel fraction of the adhesive layer of 60 to 80% by mass. Laminate for display.
The laminate for a flexible display according to claim 1, comprising 0.02 to 4.0 parts by mass of a curing agent based on 100 parts by mass of the acrylic copolymer.
The laminate for a flexible display according to any one of claims 1 to 4, further comprising a polarizing plate on the adhesive layer.
A flexible display comprising the laminate according to claim 5 and an optical element.