TW202413095A - Flexible display laminate and flexible display - Google Patents

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

Multilayer body for flexible display and flexible display

The present disclosure relates to an adhesive layer for forming a laminate, and a laminate having the adhesive layer. The laminate is a laminate for a flexible display including a light-transmitting flexible substrate and an adhesive layer, and includes the light-transmitting flexible substrate, the adhesive layer, and a polarizing plate in sequence. The laminate can be used in a flexible display.

In recent years, input devices that combine image display devices such as liquid crystal display (LCD) or organic electroluminescence (EL) display (organic light emitting diode (OLED)) with touch panels have become popular. The transparent conductive film used in the touch panel is laminated on a supporting glass or other components via an adhesive layer. In addition, the polarizing plate film used in the image device is attached to the liquid crystal module or organic EL module via an adhesive layer.

As the image display device, flat panel displays using glass substrates are the mainstream, but in recent years, flexible displays such as foldable displays and rollable displays using flexible substrates such as plastic have been developed. Compared with the previous flat panel displays using glass substrates, such flexible displays have various advantages such as lightness, thickness, flexibility, and excellent design.

In order to be used in foldable displays, it is necessary to have adaptability to the bend of the display (bendability). Generally speaking, the bendability requires a property that does not cause bubbling, lifting, or peeling when repeatedly bent (dynamic bendability).

In order to solve these problems, Patent Document 1 discloses an optically transparent adhesive sheet, which is characterized by comprising a resin syrup produced by partially polymerizing a (meth)acrylate monomer and a photoinitiator, and the storage elastic coefficient of the adhesive layer is 1.0×10 ⁶ Pa to 1.0×10 ⁷ Pa at 25°C and 1 Hz. In addition, Patent Document 2 discloses an adhesive layer formed of an adhesive comprising a base polymer, a photocurable compound, and a photoinitiator. [Prior Art Document] [Patent Document]

[Patent document 1] Japanese Patent Publication No. 2020-517800 [Patent document 2] Japanese Patent Publication No. 2020-097737

[Problem to be solved by the invention] However, in such a conventional adhesive layer, if the flexible display is repeatedly bent, the adherends bonded by the adhesive layer may be offset from each other, or the adhesive layer exposed from the end may contact the surrounding components and deteriorate the bending property, and the bending property cannot be said to be sufficient. Furthermore, in recent years, in foldable displays, colorless polyimide with overwhelming mechanical properties and transparent polyimide can be used as a light-transmitting flexible substrate. As a result, the durability required of the adhesive layer becomes more stringent, but if the laminate with the adhesive layer and colorless polyimide is repeatedly bent, there are problems such as the adhesive layer floating in the bent portion causing the adherends to shift, or bubbles in the adhesive layer causing whitening due to bubbles. In addition, even products that are considered to have no problems in normal repeated bending tests will have the following problems when bent at a higher speed than expected: the adherends will shift, the adhesive layer will float, and bubbles in the adhesive layer will cause problems during display.

Therefore, the purpose of the present disclosure is to provide a laminated body in which the adherends will not be offset from each other after bonding, and the adhesive layer will not be exposed from the end, regardless of repeated bending or high-speed bending. Furthermore, it is intended to provide a laminated body for a flexible display that will not cause display defects at the bent portion even when a highly polar substrate such as colorless polyimide is used as a light-transmitting flexible substrate, and a flexible display with excellent visibility. [Means for Solving the Problem]

The inventors of the present invention have made repeated efforts to study and found that the problem can be solved in the following aspects. That is, the present disclosure provides a multilayer body for a flexible display, comprising an adhesive layer on a light-transmitting flexible substrate, wherein the multilayer body for a flexible display is characterized in that the polar component of the surface free energy of the light-transmitting flexible substrate calculated based on the contact angle of water and the contact angle of diiodomethane and based on the Owens-Wendt-Rabel-Kaelble method (OWRK method) is 3.0 mN/m or more, and the polar component of the surface free energy of the adhesive layer calculated based on the contact angle of water and the contact angle of diiodomethane and based on the OWRK method is 0.5 mN/m or less, the mass per unit area of the adhesive layer is 10 g/m ² to 100 g/m ² , the adhesive layer is formed by an acrylic adhesive, and the acrylic adhesive comprises: an acrylic copolymer, wherein in 100% by mass of the acrylic copolymer, 25% by mass or less of repeating units derived from hydroxyl-containing monomers, 10% by mass or less of repeating units derived from acid-containing monomers, 15% by mass or less of repeating units derived from amide-containing monomers, 15% by mass or less of repeating units derived from amine-containing monomers, and 75% to 90% by mass of repeating units derived from (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 4 or more are contained; and a low-polarity additive. [Effects of the Invention]

The present disclosure can provide a laminate that does not cause offset between adherends after bonding and does not expose the adhesive layer from the end, regardless of repeated bending or high-speed bending. Furthermore, it can provide a laminate for a flexible display that does not cause display defects at the bent portion even when a highly polar substrate such as colorless polyimide is used as a light-transmitting flexible substrate, and a flexible display with excellent visibility. In addition, by using the laminate of the present disclosure, a flexible display with excellent visibility can be provided.

The following describes the structure examples of the laminate and flexible display disclosed in the present invention, but is not limited thereto. In addition, the numerical range determined by using "～" in this specification is set to include the numerical values recorded before and after "～" as the lower limit and upper limit. In addition, "film" or "sheet" is not distinguished according to thickness. In other words, the "sheet" in this specification also includes a thin film-like sheet, and the "film" in this specification also includes a sheet-like film with thickness. In addition, the so-called adherend refers to the other party of the adhesive layer to which the adhesive sheet is attached, for example, in the case of a laminate for a flexible display including a translucent flexible substrate, an adhesive layer, and a polarizing plate in sequence, it refers to the translucent flexible substrate and the polarizing plate. Unless otherwise specified, the various ingredients mentioned in this manual can be used individually or in combination of two or more.

《Adhesive layer for flexible display》 The characteristic of the adhesive layer used in the laminate disclosed in this disclosure is that the polar term component of the surface free energy calculated based on the contact angle of water and the contact angle of diiodomethane and the OWRK method is less than 0.5 mN/m. Thus, no matter whether it is repeated bending or high-speed bending, there will be no deviation between the adherends after bonding, and the adhesive layer will not be exposed from the end. Furthermore, even if a highly polar substrate such as colorless polyimide is used as a light-transmitting flexible substrate, no display defects will occur in the bent portion.

<Polar component of surface free energy> The polar component of surface free energy is 0.5 mN/m or less. The smaller the polar component of the surface free energy of the adhesive layer, the better, preferably 0 mN/m or more. In addition, it is preferably 0.3 mN/m or less, and more preferably 0.2 mN/m or less. By adjusting the polar component to 0.5 mN/m or less, an adhesive layer can be obtained in which the bent portion does not whiten regardless of repeated bending or high-speed bending, and the offset between the adherends after bonding will not occur. Although the mechanism of this effect is unknown, it is speculated that the reason is that even if the adhesive layer has strong adhesion to the adherend, the strong intermolecular attraction generated by dipole interaction does not contribute to the expression of the adhesion, so when shear force is applied by bending, the adhesive layer will not fall off from the adherend and follow it.

The method of reducing the polar component of the surface free energy to 0.5 mN/m or less can be achieved by reducing the polarity of the resin used in the adhesive and by adding a low-polarity additive that is preferentially present on the surface after application.

The surface free energy is calculated based on the contact angle of water and the contact angle of diiodomethane at 25°C using the OWRK method. Specifically, the contact angle of each liquid is measured 1 second after the droplet is dropped, with the volume of the droplet set to 1 μl. The device used for the contact angle measurement is not particularly limited, and an example thereof is the automatic contact angle meter DM-501Hi manufactured by Kyowa Interface Science Co., Ltd. The polar term component of the surface free energy is calculated together with the dispersion term component using the OWRK method.

<Gel fraction> The gel fraction of the adhesive layer disclosed herein is preferably 55% to 90% by mass, and more preferably 60% to 80% by mass. If the gel fraction is 55% by mass or more, the cohesive force of the adhesive is improved, a tough adhesive layer is obtained, and the adhesive layer is less likely to be exposed from the end when bending. If it is 90% by mass or less, the stress relaxation property of the adhesive is improved, a soft adhesive layer is easily obtained, the adhesion is improved, and the displacement of the adherends when bending can be further suppressed.

[Gel fraction measurement method] The gel fraction can be calculated as the insoluble component relative to a solvent such as ethyl acetate. Specifically, as shown in the following formula 1, it is calculated as the mass fraction (unit: mass %) of the insoluble component of the adhesive layer after immersion in ethyl acetate at 50°C for 1 day relative to the adhesive layer before immersion. (Formula 1) Gel fraction (mass %) = (Y/X) × 100 X = mass of adhesive layer before immersion (g) Y = mass of adhesive layer after immersion (g) In general, the gel fraction of a polymer is equal to the degree of crosslinking. The more crosslinked parts in the polymer, the greater the gel fraction. The gel fraction (the amount of cross-linked structure introduced) can be adjusted to the desired range according to the method of introducing the cross-linked structure, or the type and amount of the cross-linking agent.

<Adhesive> The adhesive layer is formed by an adhesive. The resin of the adhesive is an acrylic adhesive. By using an acrylic adhesive as the adhesive, the polar term component of the surface free energy is adjusted to less than 0.5 mN/m, and it is easy to achieve a balance of various performances.

[Acrylic Adhesive] Acrylic adhesives have acrylic copolymers as (meth)acrylate polymers as their main component, and include the low-polarity additives described below, and may contain hardeners and other additives as needed. The so-called (meth)acrylate includes acrylate and methacrylate. The so-called monomer is a monomer having an ethylenically unsaturated group.

(Acrylic copolymer) Acrylic copolymer is a polymer containing one or more monomers of acrylic monomers such as alkyl (meth)acrylate. Examples of alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isoamyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl ... Those having a linear or branched alkyl group such as octyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, or those having a cyclic alkyl group such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate.

Preferably, a monomer containing a unit derived from (meth)acrylic acid (ester) having a functional group is copolymerized in an acrylic copolymer. In addition to imparting cohesive force to the adhesive layer by including a functional group, the cohesive force of the adhesive layer can be further improved by using a hardener in the adhesive, thereby easily suppressing exposure during bending.

The functional group of the (meth)acrylic acid (ester) having a functional group is preferably at least one selected from a carboxyl group, a hydroxyl group, an amine group, an amide group, an alkylene oxide group, an epoxy group, and an isocyanate group, more preferably at least one selected from a carboxyl group, a hydroxyl group, an amine group, and an amide group, and further preferably at least one or both selected from a carboxyl group and a hydroxyl group. As the monomer (or acid-containing monomer) unit having a carboxyl group, acrylic acid and methacrylic acid can be cited. The monomer unit having a hydroxyl group is a repeated 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, (meth)acrylic acid [(mono-, di-, or poly-)alkylene glycol] such as (meth)acrylate mono(diethylene glycol), and (meth)acrylic acid lactones such as (meth)acrylate monocaprolactone. As monomer units having an amino group, there can be listed repetitive units derived from the following: monomers containing primary amino groups such as (meth) acrylate aminomethyl, (meth) acrylate aminoethyl, monomers containing secondary amino groups such as (meth) acrylate tertiary amino groups such as tertiary amino groups such as (meth) acrylate ethyl aminoethyl, (meth) acrylate dimethyl aminoethyl, (meth) acrylate diethyl aminoethyl, allylamine, vinyl pyridine, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazole, vinyl oxazole and other monomers having amino groups. Examples of monomer units having an amide group include (meth)acrylamide, N-vinyl lactams, vinyl morpholine, cyclic amides such as (meth)acryl morpholine, N-vinyl carboxylic acid amides such as N-vinylformamide and N-vinylacetamide, acrylamide, and N,N-dimethylacrylamide. N-vinyl lactams are monomers having a cyclic lactam ring, and examples thereof include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-ε-caprolactam, and compounds having a structure in which one or two or more hydrogen atoms of these are substituted with a substituent. As substituents, there can be listed: alkyl groups with 1 to 20 carbon atoms, alkyl groups with 2 to 20 carbon atoms, aryl groups with 6 to 20 carbon atoms, alkoxy groups with 1 to 20 carbon atoms, carboxyl ester groups with 3 to 20 carbon atoms, and amine groups with 1 to 20 carbon atoms, excluding acidic groups such as hydroxyl groups or carboxylic acid (salt) groups, sulfonic acid (salt) groups, and hypophosphite (salt) groups. Examples of monomer units having an oxyalkylene group include methoxytriethylene glycol (meth)acrylate, methoxypolyethylene glycol #400 (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxytripropylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, 2-ethylhexyl carbitol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, etc. Examples of monomer units having an isocyanate group include 2-isocyanateethyl (meth)acrylate, 3-isocyanatepropyl (meth)acrylate, 4-isocyanatebutyl (meth)acrylate, etc. As monomer units having an epoxy group, repeating units derived from monomers having a glycidyl group such as glycidyl (meth)acrylate can be cited.

The amount of the hydroxyl-containing monomer in the acrylic copolymer is 25% by mass or less, preferably 20% by mass or less. Furthermore, in the present disclosure, the amount of a monomer in the acrylic copolymer is n% by mass (or includes n% by mass) means that the repeating units derived from the monomer account for n% by mass of the copolymer. In addition, the amount of a monomer in the acrylic copolymer is n% by mass or less (or includes n% by mass or less), and the embodiment in which the monomer is 0% by mass may also be included. The amount of the acid-containing monomer in the acrylic copolymer is 10% by mass or less, preferably 7% by mass or less. The amount of the amide-containing monomer in the acrylic copolymer is 15% by mass or less, preferably 10% by mass or less, and most preferably 7% by mass or less. The amount of the monomer containing an amine group is 15% by mass or less, preferably 10% by mass or less, and optimally 7% by mass or less in 100% by mass of the acrylic copolymer. The ratio of the monomer containing an oxyalkylene group is preferably 30% by mass or less, more preferably 15% by mass or less, and optimally 12% by mass or less. Among the monomers copolymerizable with the acrylic monomer, the amount of the monomer having a water/octanol partition coefficient logKow of 2.22 or less at 25°C and the monomer capable of being mixed with water at will is preferably 20% by mass or less, more preferably 15% by mass or less, and optimally 12% by mass or less. The monomers described in this paragraph may be 0% by mass or more (i.e., may also be 0% by mass) in 100% by mass of the acrylic copolymer. For example, in 100% by mass of the acrylic copolymer, the hydroxyl-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, in 100% by mass of the acrylic copolymer, the hydroxyl-containing monomer may be 0.5% by mass or more, the acid-containing monomer may be 0.2% by mass or more, and the other monomers described in this paragraph may be 0% by mass or more. The (meth)acrylic acid alkyl ester having an alkyl carbon number of 4 or more is 75% by mass to 90% by mass in 100% by mass of the acrylic copolymer, preferably 78% by mass to 88% by mass. By using this type of monomer as the main component, the polarity of the acrylic copolymer is reduced. The carbon number of the alkyl group is typically 16 or less.

The (meth)acrylic copolymer may have other monomer units in addition to the above monomer units as needed. Other monomers can be copolymerized with the above acrylic monomers, for example: vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristic acid, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl benzoate-like carboxylic acid vinyl esters or styrene. Among them, vinyl acetate, vinyl propionate, and vinyl butyrate are hydrophilic when the water/octanol partition coefficient logKow at 25°C is less than 2.30. Therefore, in order to reduce the polarity of the acrylic copolymer, it is better to reduce the ratio as described below. The logKow value can be calculated, for example, based on the structural formula of its monomer using the HSPiP software (Steven Abbott, Hiroshi Yamamoto).

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

The polymerization initiator used in the polymerization is preferably a free radical polymerization initiator. Free radical polymerization initiators are generally peroxides and azo compounds. Examples of peroxides include: di-tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, α,α'-bis(tert-butylperoxy-m-isopropyl)benzene, 2,5-di(tert-butylperoxy)hexyne-3 and other dialkyl peroxides; tert-butyl peroxybenzoate, tert-butyl peroxyacetate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane and other peroxyesters; Ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Peroxy ketal such as 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate; Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylcyclohexane-2,5-dihydroperoxide; Diacyl peroxides such as benzoyl peroxide, decyl peroxide, lauryl peroxide, 2,4-dichlorobenzyl peroxide; Peroxy dicarbonates such as bis(tert-butylcyclohexyl) peroxy dicarbonate, etc.

Examples of azo compounds include: 2,2'-azobisisobutyronitrile (AIBN (2,2'-azobisisobutyronitrile)), 2,2'-azobis(2-methylbutyronitrile) and other 2,2'-azobisbutyronitrile; 2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile); 1,1'-azobis-1-alkanenitrile such as 1,1'-azobis(cyclohexane-1-carbonitrile), etc.

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

(Mass average molecular weight (Mw)) The mass average molecular weight of the acrylic copolymer is preferably 800,000 to 1.8 million, and more preferably 1 million to 1.5 million. If it is within the range of 800,000 to 1.8 million, the cohesive force is further improved, and the adhesive layer is less likely to be exposed from the end when bent. In addition, the mass average molecular weight is a value converted to polystyrene measured by gel permeation chromatography (GPC).

(Hardener) The acrylic adhesive preferably contains a hardener. As the hardener formulated in the adhesive, it is preferred that the hardener reacts with the functional group of the monomer having the functional group by heat or the like to form a bond. By formulating the hardener, the cohesion of the adhesive layer is improved, and the durability and stain resistance are further improved.

As the hardener, it is possible to appropriately select from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, carbodiimide compounds, metal chelate compounds, and butylated melamine compounds, taking into account the reactivity with the functional group of the polymer in the adhesive. For example, when the functional group of the polymer in the adhesive contains a hydroxyl 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 aromatic aliphatic polyisocyanate, an alicyclic polyisocyanate, and a biuret form, a urate form, and an adduct thereof.

Examples of the aromatic polyisocyanate include 1,3-phenylene diisocyanate, 4,4'-diphenylene diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4''-triphenylmethane triisocyanate.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI (hexamethylene diisocyanate)), pentamethylene diisocyanate, 1,2-propyl diisocyanate, 2,3-butyl diisocyanate, 1,3-butyl diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

Examples of the aromatic aliphatic polyisocyanate include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

Examples of the alicyclic polyisocyanate include 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI (isophorone diisocyanate), 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(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane.

The biuret form is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer. Examples of the biuret form include the biuret form of hexamethylene diisocyanate.

The urate body is a trimer of an isocyanate monomer, for example, a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, a trimer of toluene diisocyanate, etc.

The adduct is a difunctional or higher isocyanate compound formed by reacting an isocyanate monomer with a difunctional or higher compound containing low molecular weight active hydrogen. Examples of the adduct include a compound formed by reacting trihydroxymethylpropane with hexamethylene diisocyanate, a compound formed by reacting trihydroxymethylpropane with toluene diisocyanate, a compound formed by reacting trihydroxymethylpropane with xylylene diisocyanate, a compound formed by reacting trihydroxymethylpropane with isophorone diisocyanate, a compound formed by reacting 1,6-hexanediol with hexamethylene diisocyanate, and the like.

From the viewpoint of forming a sufficient cross-linked structure, the isocyanate compound is preferably a trifunctional isocyanate compound. The isocyanate compound is more preferably an adduct which is a reaction product of an isocyanate monomer and a trifunctional low molecular weight active hydrogen-containing compound, and a urate form. The isocyanate compound is preferably a trihydroxymethylpropane adduct of hexamethylene diisocyanate, a ureate of hexamethylene diisocyanate, a trihydroxymethylpropane adduct of toluene diisocyanate, a ureate of toluene diisocyanate, a trihydroxymethylpropane adduct of isophorone diisocyanate, or a ureate of isophorone diisocyanate, and more preferably a trihydroxymethylpropane adduct of hexamethylene diisocyanate, a trihydroxymethylpropane adduct of toluene diisocyanate, or a trihydroxymethylpropane adduct of isophorone diisocyanate.

Examples of epoxy compounds include glycerol diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

Examples of the aziridine compound include N,N'-diphenylmethane-4,4'-bis(1-carbonylaziridine), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

The carbodiimide compound is preferably a high molecular weight polycarbodiimide produced by subjecting a diisocyanate compound to a decarbonation condensation reaction in the presence of a carbodiimidization catalyst. The commercially available product of the high molecular weight polycarbodiimide is preferably the Carbodilite series of Nisshin Bosei Co., Ltd. Among them, Carbodilite V-03, 07, and 09 are preferred because of their excellent compatibility with organic solvents.

Preferred metal chelates include, for example, coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium with acetylacetone or ethyl acetylacetate. Examples of metal chelates include ethylacetylacetate aluminum diisopropyl alcohol ester, triacetylacetonate aluminum, diethylacetylacetate aluminum monoacetylacetonate, and alkylacetylacetate aluminum diisopropyl alcohol ester.

The curing agent preferably contains 0.02 to 4.0 parts by mass, more preferably 0.04 to 1.0 parts by mass, and even more preferably 0.04 to 0.4 parts by mass, relative to 100 parts by mass of the acrylic copolymer in the adhesive. If the content is 0.02 parts by mass or more, the cohesive force is further improved, and if the content is 4 parts by mass or less, it is easy to take into account both cohesive force and softness, which is preferred.

The acrylic adhesive may contain, in addition to the silane coupling agent and chlorinated polyolefin described below, various resins, oils, softeners, dyes, pigments, antioxidants, ultraviolet absorbers, weathering stabilizers, plasticizers, fillers, anti-aging agents, antistatic agents, etc. as optional components as long as they can solve the problem.

Methods for adjusting the polarity term component of the adhesive layer to 0.5 mN/m or less include: a method of reducing the polarity of the resin used in the adhesive, and a method of mixing a low-polarity additive that is preferentially present on the surface after application.

For example, in order to reduce the polarity of the acrylic copolymer, the ratio of (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms, or hydroxyl group-containing monomers, acid-containing monomers, amide group-containing monomers, amine group-containing monomers, oxyalkylene group-containing monomers, or monomers other than these monomers copolymerizable with acrylic monomers having a water/octanol partition coefficient logKow of 2.22 or less at 25°C and monomers miscible with water can be reduced, and the ratio of (meth)acrylic acid alkyl esters having an alkyl group with 4 or more carbon atoms can be increased.

Specifically, the amount of the (meth)acrylic acid alkyl ester having an alkyl group with 1 to 3 carbon atoms in the acrylic copolymer is preferably 25% by mass or less, more preferably 20% by mass or less, further preferably 18% by mass or less, further preferably 15% by mass or less. The amount of the hydroxyl-containing monomer in the acrylic copolymer is preferably 5% by mass or less, further preferably 2% by mass or less. The amount of the acid-containing monomer in the acrylic copolymer is preferably 5% by mass or less, further preferably 2% by mass or less, and optimally 1% by mass or less. The amount of the amide-containing monomer in the acrylic copolymer is preferably less than 5% by mass, more preferably 3% by mass or less, and optimally 1% by mass or less. The amount of the monomer containing an amine group in 100% by mass of the acrylic copolymer is preferably less than 5% by mass, more preferably less than 3% by mass, and most preferably less than 1% by mass. The ratio of the monomer containing an oxyalkylene group is preferably less than 20% by mass, more preferably less than 10% by mass, and most preferably less than 5% by mass. Among the monomers copolymerizable with the acrylic monomer, the amount of the monomer having a water/octanol partition coefficient logKow of 2.22 or less at 25°C and the monomer capable of being mixed with water at will is preferably less than 10% by mass, more preferably less than 5% by mass, further preferably less than 3% by mass, and most preferably less than 1% by mass. The monomers described in this paragraph may be 0% by mass or more (that is, may also be 0% by mass) in 100% by mass of the acrylic copolymer. The (meth)acrylic acid alkyl ester having an alkyl group with 4 or more carbon atoms is preferably 80% by mass or more, and more preferably 85% by mass or more, in 100% by mass of the acrylic copolymer.

As a method for mixing a low-polarity additive that tends to be present on the surface after application, there can be cited a method of adding a silane coupling agent, a chlorinated polyolefin, or a combination thereof to an adhesive. The amount of these low-polarity additives mixed individually or in total is preferably 0.05 mass parts or more and 0.5 mass parts or less, and more preferably 0.1 mass parts or more and 0.3 mass parts or less, relative to 100 mass parts of the resin component of the acrylic copolymer. At this time, the polar term component of the surface free energy of the acrylic copolymer before mixing the low-polarity additive (i.e., without the addition of the low-polarity additive) is preferably 2.0 mN/m or less, and more preferably 1.5 mN/m or less.

As silane coupling agents, there can be mentioned: alkoxysilane compounds having a (meth)acryloyloxy group, alkoxysilane compounds having a vinyl group, alkoxysilane compounds having an amino group, alkoxysilane compounds having an alkyl group, or alkoxysilane compounds having an epoxy group. As commercial products, specifically, for example, KBM403 (3-glycidyloxypropyltrimethoxysilane), KBE403 (3-glycidyloxypropyltriethoxysilane), KBM303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all manufactured by Shin-Etsu Chemical Co., Ltd.), BYK-325N (polyether modified polymethyl alkyl siloxane) (manufactured by BYK-Chemie Japan Co., Ltd.), etc. can be mentioned.

As chlorinated polyolefins, there are chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic acid-modified chlorinated polypropylene, chlorinated polyethylene, chlorinated ethylene vinyl acetate (EVA) copolymers, etc., and chlorinated polypropylene or chlorinated ethylene vinyl acetate copolymers are preferred from the viewpoint of good compatibility with acrylic copolymers and the like and effective reduction of polarity. As commercially available products, specifically, there are superchlon 390S (chlorinated polypropylene, chlorine content 36%) and superchlon BX (chlorinated EVA, chlorine content 18%) (all manufactured by Nippon Paper Industries, Ltd.).

《Multilayer for flexible display》 The multilayer for flexible display includes an adhesive layer on a light-transmitting flexible substrate. For example, it has a structure of substrate/adhesive layer/polarizing plate. Preferably, it includes a light-transmitting flexible substrate, an adhesive layer, and a polarizing plate in sequence. In this way, a multilayer with excellent transparency and bendability is formed.

Fig. 1 shows an example of a schematic cross-sectional view partially showing a laminated body of an embodiment of the present disclosure. In Fig. 1, 3 is a light-transmitting flexible substrate (cover plate), 1 is an adhesive layer, and 4 is a polarizing plate.

In the laminate shown in FIG1 , a light-transmissive flexible substrate (cover plate) is attached to a polarizing plate via an adhesive layer.

[Translucent flexible substrate] As a translucent flexible substrate (cover plate), a transparent plastic substrate can be used. In the present disclosure, the polar term component of the surface free energy of the translucent flexible substrate is 3.0 mN/m or more, preferably 4.0 mN/m or more. The adhesion caused by polar attraction between the adhesive layer having a polar term component of 0.5 mN/m or less and the translucent flexible substrate having a polar term component of 3.0 mN/m or more is not strong enough. When repeatedly bent, the adhesive layer follows the movement of the substrate, and it is not easy to cause whitening of the bent part or displacement of the adherends caused by the adhesive layer. If a translucent flexible substrate having a polar term component of 4.0 mN/m or more is used, the effect of the present disclosure is more excellent, so it is better. The upper limit of the polar term component of the surface free energy of the light-transmitting flexible substrate is not particularly limited, but is typically less than 10 mN/m.

Examples of the raw materials of such a light-transmitting flexible substrate include acrylic resins such as polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA), polycarbonate, polycycloolefin, polyimide and other plastic materials. PET film or polyimide is particularly preferred, and polyimide is the most preferred in terms of durability. The plastic material may be used alone or in combination of two or more.

Since the adhesive layer used in the laminate of the present disclosure has excellent bending resistance, even when a colorless polyimide obtained by making the polyimide transparent is used as a substrate, a laminate can be produced in which the deviation or whitening of adherends is suppressed.

As the light-transmitting flexible substrate (cover), among the above-mentioned transparent plastic substrates, a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate that suppresses or prevents deformation under severe conditions such as high temperature or high temperature and high humidity, can be preferably used.

The light-transmitting flexible substrate may be subjected to surface treatment such as plasma treatment, corona treatment, frame treatment, UV treatment, etc., as required. Even a transparent plastic substrate such as polyethylene (PE) or polypropylene (PP) whose polarity term component value is less than 3.0 mN/m when untreated can be set to a polarity term component value of 3.0 mN/m or more by performing the surface treatment, and can be used in the embodiments of the present disclosure.

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

<Manufacturing of laminates for flexible displays> Regarding the manufacturing method of the laminate, for example, a peeling film can be peeled off from an adhesive sheet having peeling films on both sides of an adhesive layer, and the adhesive layers can be attached to adherends such as a light-transmitting flexible substrate or a polarizing plate to form a laminate. Alternatively, an adhesive layer can be directly formed on a light-transmitting flexible substrate, and then an adherend or an adhesive layer included in another adhesive sheet can be attached to the adhesive layer to form a laminate.

[Adhesive sheet] The adhesive sheet can be manufactured by a common manufacturing method. For example, it can be manufactured by the following methods: a method in which an adhesive is directly applied to one side of a peeling film so that the thickness after drying becomes a predetermined thickness to form an adhesive layer, and another peeling film is attached thereto; or a method in which an adhesive is applied to each side of two peeling films so that the thickness after drying becomes a predetermined thickness to form two adhesive layers respectively, and then the adhesive layers are attached to each other.

When applying the adhesive, a conventional coater may be used, such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a rod coater, a scraper coater, or a spray coater.

The adhesive sheet may be cut into a suitable width and rolled into a roll to have a form of an adhesive tape rolled into a roll.

The thickness of the adhesive layer is not particularly limited, and is preferably 10 μm to 500 μm, more preferably 50 μm to 200 μm. If the thickness of the adhesive layer is 10 μm to 500 μm, sufficient cohesion can be easily obtained, the end of the adhesive layer is not offset or exposed, and the bendability during high-speed bending can be taken into account, so it is preferred.

The mass per unit area of the adhesive layer (hereinafter also referred to as the coating amount) is 10 g/m ² to 100 g/m ² , preferably 25 g/m ² to 70 g/m ² . By setting the mass per unit area of the adhesive layer to this range, an adhesive layer can be obtained that does not whiten at the bent portion and does not cause deviation between adherends even when repeatedly bent. If the coating amount is 10 g/m ² or more, the adhesive layer will sufficiently follow the adherend during bending, and the occurrence of edge deviation due to lifting can be further suppressed. By setting the coating amount to 100 g/ ^m2 or less, it is possible to further suppress the adhesive layer from being exposed from the edge when being bent.

As the release film, there is no particular limitation, and a transparent plastic substrate can be preferably used. Examples of the raw materials of the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose, polysulfone, polyarylate, polycycloolefin, and other plastic materials. Furthermore, the plastic material can be used alone or in combination of two or more.

As the release film, among the above-mentioned transparent plastic substrates, a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate that suppresses or prevents deformation under severe conditions such as high temperature or high temperature and high humidity, can be preferably used.

The release film may be in the form of a single layer or multiple layers. In addition, the surface of the transparent substrate may be subjected to appropriate surface treatments such as physical treatments such as corona discharge treatment and plasma treatment, and chemical treatments such as primer treatment.

《Flexible display》 The flexible display preferably includes the laminate disclosed herein and an optical element. Thus, the display disclosed herein has excellent bendability and visibility. For example, the optical element can be attached to the polarizing plate of the laminate via another adhesive layer. The optical element is not particularly limited, and examples thereof include liquid crystal elements, organic EL elements, etc.

FIG2 shows an example of a schematic cross-sectional view of a display partially showing an example of use of the adhesive sheet of the present disclosure. In FIG2, 3 is a light-transmitting flexible substrate (cover plate), 1 is a first adhesive layer, 4 is a polarizing plate, 5 is a second adhesive layer, 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 unit. In addition, the structure of the display is not limited to FIG2.

In the display shown in FIG. 2 , the light-transmitting flexible substrate (cover plate) is attached to the polarizing plate via the adhesive layer (first adhesive layer) disclosed herein, and then attached to the organic EL unit via the adhesive layer for the polarizing plate (second adhesive layer). In this way, the adhesive sheet disclosed herein can be attached to the light-transmitting flexible substrate (cover plate) and the polarizing plate using a transparent adhesive layer formed by the adhesive, and then the laminate is attached to the organic EL via the adhesive layer for the polarizing plate. For example, in FIG. 2 , the adhesive layer disclosed herein can be used for either the first adhesive layer or the second adhesive layer. Generally speaking, when comparing the first adhesive layer with the second adhesive layer, the first adhesive layer has higher requirements for the quality of the adhesive layer. The adhesive disclosed herein is preferably used for the first adhesive layer because of its good adhesion and adhesion to the substrate. At this time, the adhesive used to form the second adhesive layer can use the adhesive disclosed herein or a previously known adhesive.

There is no particular limitation on the use of the display, and examples thereof include organic EL TVs, organic EL smartphones, organic EL input boards, and organic EL smart watches. [Example]

Next, examples are shown to further explain the details, but the present invention is not limited to these. In the examples, unless otherwise specified, "parts" means "parts by mass", "%" means "% by mass", and "RH" means relative humidity. In addition, the blending amount in the table is part by mass. Furthermore, the blank column in the table means that the corresponding component is not blended. Furthermore, the method for determining the mass average molecular weight of the acrylic copolymer is as shown below.

<Measurement of the mass average molecular weight of acrylic copolymer> The mass average molecular weight (Mw) can be measured using the GPC "LC-GPC system" manufactured by Shimadzu Corporation, by converting polystyrene with a known molecular weight as a standard substance. Apparatus name: LC-GPC system "Prominence" manufactured by Shimadzu Corporation Column: Four GMHXL manufactured by Tosoh Corporation and one HXL-H manufactured by Tosoh Corporation are connected. Mobile phase solvent: Tetrahydrofuran Flow rate: 1.0 ml/min Column temperature: 40°C

<Example of producing acrylic copolymer> (Acrylic copolymer (R9)) In a reaction vessel (hereinafter simply referred to as "reaction vessel") including a stirrer, a thermometer, a reflux cooling tube, a dropping device, and a nitrogen inlet tube, 20 parts of methyl acrylate (MA), 43.2 parts of 2-ethylhexyl acrylate (2EHA), 35 parts of dodecyl acrylate (DOA), 1 part of 4-hydroxybutyl acrylate (4HBA), 0.8 parts of acrylic acid (AA), and 0.2 parts of 2,2'-azobisisobutyronitrile (hereinafter simply referred to as "AIBN") as an initiator were placed, and the atmosphere in the reaction vessel was replaced with nitrogen. Thereafter, the reaction was started by heating to 50°C while stirring in a nitrogen atmosphere. Thereafter, the reaction solution was reacted at 50°C for 4 hours. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain a copolymer (R9) solution with a non-volatile component of 30%. The mass average molecular weight of the obtained copolymer (R9) was 890,000.

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

The compositions, blending amounts (non-volatile mass fractions), and mass average molecular weights (Mw) of the obtained acrylic copolymers (R9 to R11, R35 to R62) are shown in Tables 1, 2, and 3.

[Table 1] Table 1 Acrylic acid copolymer R9 R10 R11 Single a1 MA 20 EA 20 a2 2EHA 43.2 68.2 69.2 BA DOA 35 IBXA 10 10 TDA IBXMA nHA IAA a3 4HBA 1 1 20 a4 AA 0.8 0.8 0.8 a7 MDEA Mw/million 89 82 82

[Table 2] Table 2 Acrylic acid copolymer R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R45 R46 R47 R48 R49 R50 R51 Single a1 MA twenty three 5 5.3 26.5 a2 2EHA 2.8 20 40 40 40 6.3 40 40 20 15 39.3 39.3 BA 30 39.3 40 38 23.3 15 DOA 76.3 75 70 44.5 47.3 46.3 48 48 48 48 45 48 41 48 43 43 72.8 a3 4HBA 0.5 2 2 0.5 0.5 0.5 0.5 0.5 0.5 1.5 0.5 1.5 0.5 1.5 0.5 0.5 0.5 2HEA 20 5 5 10 3.3 3.3 2 10.3 a4 AA 0.2 0.2 8 5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.5 0.2 0.2 0.2 0.2 0.2 a5 DMAEA 12 8 5 17 a6 ACMO 12 8 5 13 10 17 a7 MDEA 13 10 Mw/million 109 101 149 142 109 107 102 115 109 101 102 103 116 114 148 148 132

[table 3] table 3 Acrylic acid copolymer R52 R53 R54 R55 R56 R57 R58 R59 R60 R61 R62 Single a1 MA 10 EA 6.2 10 a2 2EHA 66.8 80.8 78.5 56 83.5 10 55 BA 49.1 78.8 20 20 DOA 38.7 18 75 65 IBXA 2 10 TDA 20.7 5 5 IBXMA 7.2 nHA 83.3 9 IAA 9 13.5 4.5 a3 4HBA 2.4 2.1 2.4 1.9 1.9 2.4 2.4 1.9 2 2HEA 7.8 8.1 8.1 6.6 8.1 8.1 8.1 8.1 a4 AA 2 2 2 2 2 2 2 2 11 a5 DMAEA 16 a6 ACMO 16 Mw/million 113 103 139 146 113 143 141 128 126 101 100

The abbreviations in the table are as follows. MA: Methyl acrylate (1 carbon number in the alkyl group) EA: Ethyl acrylate (2 carbon numbers in the alkyl group) 2EHA: 2-ethylhexyl acrylate (8 carbon numbers in the alkyl group) BA: Butyl acrylate (4 carbon numbers in the alkyl group) DOA: Dodecyl acrylate (12 carbon numbers in the alkyl group) IBXA: Isobornyl acrylate (10 carbon numbers in the alkyl group (ring structure)) TDA: Tridecyl acrylate (13 carbon numbers in the alkyl group) IBXMA: Isobornyl methacrylate (10 carbon numbers in the alkyl group (ring structure)) nHA: n-heptyl acrylate (7 carbon numbers in the alkyl group) IAA: Isoamyl acrylate (5 carbon numbers in the alkyl group (branched)) 4HBA: 4-hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate AA: Acrylic acid DMAEA: 2-dimethylaminoethyl acrylate ACMO: Acryloylmorpholine MDEA: Methoxydiethylene glycol acrylate a1: (Meth) alkyl acrylate monomers with 1 to 3 carbon atoms in the alkyl group a2: (Meth) alkyl acrylate monomers with 4 or more carbon atoms in the alkyl group a3: Monomers containing hydroxyl groups a4: Monomers containing acid groups a5: Monomers containing amino groups a6: Monomers containing amide groups a7: Monomers containing oxygenated alkylene groups

(Example 1) <Preparation of adhesive> To 100 parts of the non-volatile components of the acrylic copolymer (R9), 0.14 parts of D-160N, a trihydroxymethylpropane adduct of hexamethylene diisocyanate, as a hardener, and 0.1 parts of KBM-403, as a low-polarity additive, were added, and ethyl acetate was further prepared so that the non-volatile components became 20%, and the mixture was stirred to obtain an adhesive.

<Preparation of adhesive sheet> The adhesive was applied to a 75 μm thick polyethylene terephthalate separator (peel film 1) in such a manner that the thickness after drying was 50 μm, and hot air dried at 100°C for 2 minutes to form an adhesive layer. Then, a 50 μm thick polyethylene terephthalate separator (peel film 2) was bonded to the adhesive layer to obtain a first adhesive sheet.

<Production of laminated body> One of the diaphragms was peeled off from the adhesive sheet, and the exposed adhesive layer was attached to CPI (colorless polyimide, manufactured by KOLON, 50 μm, polarity component 4.5 mN/m) as a light-transmitting flexible substrate using a laminating press at 25°C and a relative humidity of 50%. The other diaphragm was peeled off and attached to a PET film with a thickness of 188 μm using a laminating press, thereby obtaining a laminated body of PET film/adhesive layer/light-transmitting flexible substrate.

(Example 2 to Example 40, Comparative Example 1 to Comparative Example 12) As shown in Tables 4 to 7, the types and blending amounts (parts by mass) of acrylic copolymers, hardeners, and additives were changed, and an adhesive sheet was obtained in the same manner as in Example 1. Thereafter, an 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 properties of the adhesive layer and the laminate were measured and evaluated using the following method. The results are shown in Tables 4 to 7.

<Measurement of the mass per unit area of the adhesive layer (coating amount)> The obtained adhesive sheet was cut into a size of 100 mm × 100 mm, and the mass (mass W (g)) was measured. In addition, a polyethylene terephthalate separator with a thickness of 75 μm (peel film 1) and a polyethylene terephthalate separator with a thickness of 50 μm (peel film 2) used for the adhesive sheet were cut into a size of 100 mm × 100 mm, and the masses were 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 × 100 mm, and the adhesive layer exposed by peeling off the polyethylene terephthalate separator (peel film 2) with a thickness of 50 μm was attached to a weighed 300-mesh stainless steel metal mesh (mass W0), and the polyethylene terephthalate separator (peel film 1) with a thickness of 75 μm was peeled off to prepare a sample. The mass after weighing the sample was set as W1, and the mass after the sample was left to stand in ethyl acetate for 24 hours and then dried at 100°C for 1 hour and weighed was set as W2, and the following formula was used to calculate. Gel fraction (%) = {(W2-W0)/(W1-W0)}×100

<Measurement of polar term component of surface free energy> A 50 μm thick polyethylene terephthalate separator (peel film 2) was peeled off from the obtained adhesive sheet to expose the adhesive layer for measurement. The measurement was performed using MSA manufactured by KRUSS, and the polar term was calculated using the OWRK method based on the contact angle after 1 μl of water and diiodomethane were landed on the adhesive layer or the light-transmitting flexible substrate for 1 second.

<Evaluation of whitening of the bent part, deviation of the end, and exposure of the end according to the standard bending test> Using the obtained laminate, as a normal test, a bending tester (manufactured by Yuasa System Machinery Co., Ltd.) was used in an environment of 25°C and 50% relative humidity. The inner diameter (diameter) during bending was set to 3 mm, and one cycle was set for bending and opening 180°. 30 cycles were repeated at a speed of 30 round trips per minute. The appearance after the test was evaluated for whitening of the bent part and deviation of the end of the adherend using the following criteria. The higher the value of the evaluation criteria, the better, and it is practical as long as it is 3 or above. Appearance: Visually evaluate the presence of bubbles in the test laminate, the offset of the ends of the adherends, and the exposure of the ends of the adhesive layer under the following conditions.

[Whitening of the bend] 5: No bubbles were found within the range of 5 mm to the left and right of the bend. 4: There were 1 or more and 10 or less bubbles within the range of 5 mm to the left and right of the bend. 3: There were 11 or more and 50 or less bubbles within the range of 5 mm to the left and right of the bend. 2: There were 51 or more and 100 or less bubbles within the range of 5 mm to the left and right of the bend. 1: There were 100 or more bubbles within the range of 5 mm to the left and right of the bend.

[Offset of end portions] 5: The offset between the PET film and the light-transmitting flexible substrate is less than 1 mm. 4: The offset between the PET film and the light-transmitting flexible substrate is 1 mm or more and less than 2 mm. 3: The offset between the PET film and the light-transmitting flexible substrate is 2 mm or more and less than 3 mm. 2: The offset between the PET film and the light-transmitting flexible substrate is 3 mm or more and less than 4 mm. 1: The offset between the PET film and the light-transmitting flexible substrate is 4 mm or more.

[Exposure of the end] 5: The exposure of the end of the self-adhesive layer is less than 100 μm. 4: The exposure of the end of the self-adhesive layer is 100 μm or more and less than 200 μm. 3: The exposure of the end of the self-adhesive layer is 200 μm or more and less than 300 μm. 2: The exposure of the end of the self-adhesive layer is 300 μm or more and less than 400 μm. 1: The exposure of the end of the self-adhesive layer is 400 μm or more.

<Evaluation based on whitening of the curved part, deviation of the end, and exposure of the end in the high-speed bending test> The test was conducted at a reciprocating speed of 120 times per minute and a cycle number of 100,000 cycles in the standard bending test, and the evaluation was conducted based on the same evaluation criteria as the standard bending test.

[Table 4] Table 4 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Comparison Example 1 Comparison Example 2 Comparison Example 3 Adhesive layer Acrylic copolymer Type R9 R9 R10 R10 R11 R11 R9 R10 R11 Dispensing amount 100 100 100 100 100 100 100 100 100 Hardener Type D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-110N EX-313 Dispensing amount 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.4 0.18 Additives Type KBM-403 KBE-403 KBM-303 BYK325N 390S BX Dispensing amount 0.1 0.1 0.1 0.1 0.2 0.2 Mass per unit area of adhesive layer (g/m ² ) 44 47 44 45 46 42 56 53 52 Gel fraction (%) 67 65 66 64 65 63 64 65 66 Polar component (mN/m) 0.19 0.18 0.18 0.17 0.15 0.18 1.05 0.83 1.2 Translucent flexible substrate CPI CPI CPI CPI CPI CPI CPI CPI CPI Standard bending test Whitening of the bend 5 5 5 5 5 5 3 2 2 End offset 5 5 5 5 5 5 2 2 3 End exposed 5 5 5 5 5 5 4 3 4 High speed bending test Whitening of the bend 5 5 5 5 5 5 1 1 1 End offset 5 5 5 5 5 5 1 1 1 End exposed 5 5 5 5 5 5 1 1 1

[table 5] table 5 Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 Embodiment 13 Embodiment 14 Embodiment 15 Embodiment 16 Embodiment 17 Embodiment 18 Embodiment 19 Embodiment 20 Embodiment 21 Embodiment 22 Embodiment 23 Adhesive layer Acrylic copolymer Type R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R45 R46 R47 R48 R38 R38 R38 Dispensing amount 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Hardener Type D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N DID D-370N DID Dispensing amount 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 1.1 0.015 4.1 Additives Type KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 Dispensing amount 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Mass per unit area of adhesive layer (g/m ² ) 37 51 54 45 38 51 36 48 46 39 41 44 38 40 42 46 36 Gel fraction (%) 74 62 71 75 70 70 77 68 64 67 75 68 61 60 82 52 92 Polar component (mN/m) 0.25 0.24 0.24 0.12 0.39 0.28 0.13 0.36 0.28 0.17 0.04 0.25 0.07 0.26 0.11 0.1 0.11 Translucent flexible substrate PET PET PET PET PET PET PET PET PET PET PET PET PET PET PET PET PET Standard bending test Whitening of the bend 4 4 4 5 4 4 5 4 4 5 5 4 5 4 4 4 4 End offset 4 4 4 5 4 4 5 4 4 5 5 4 5 4 3 4 3 End exposed 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 3 4 High speed bending test Whitening of the bend 4 4 4 5 3 4 5 4 4 5 5 4 5 4 4 4 4 End offset 4 4 4 5 4 4 5 3 4 5 5 4 5 4 3 4 3 End exposed 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 3 4

[Table 6] Table 6 Embodiment 24 Embodiment 25 Embodiment 26 Embodiment 27 Embodiment 28 Embodiment 29 Embodiment 30 Embodiment 31 Embodiment 32 Embodiment 33 Embodiment 34 Embodiment 35 Embodiment 36 Embodiment 37 Embodiment 38 Embodiment 39 Embodiment 40 Embodiment 41 Adhesive layer Acrylic copolymer Type R38 R38 R38 R38 R38 R38 R38 R38 R38 R38 R52 R53 R54 R55 R56 R57 R58 R59 Dispensing amount 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Hardener Type D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-370N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N Dispensing amount 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.03 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 Additives Type KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 Dispensing amount 0.08 0.04 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Mass per unit area of adhesive layer (g/m ² ) 56 43 35 47 48 42 40 58 twenty two 76 54 44 49 42 41 50 57 52 Gel fraction (%) 80 76 67 70 75 61 71 58 73 62 64 71 69 69 71 60 65 66 Polar component (mN/m) 0.28 0.42 0.11 0.13 0.12 0.11 0.11 0.12 0 0 0 0 0 0 0 0 0 0 Translucent flexible substrate PET PET CPI P-CPI PMMA C-HDPE C-OPP PET PET PET PET PET PET PET PET PET PET PET Standard bending test Whitening of the bend 4 4 5 5 5 5 5 5 4 5 5 5 5 5 5 5 5 5 End offset 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 End exposed 5 5 5 5 5 5 5 4 5 4 5 5 5 5 5 5 5 5 High speed bending test Whitening of the bend 4 3 5 5 5 5 5 5 4 5 5 5 5 5 5 5 5 5 End offset 4 3 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 End exposed 5 5 5 5 5 5 5 4 5 4 5 5 5 5 5 5 5 5

[Table 7] Table 7 Comparison Example 4 Comparison Example 5 Comparative Example 6 Comparison Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Adhesive layer Acrylic copolymer Type R38 R38 R49 R50 R51 R60 R61 R62 Dispensing amount 100 100 100 100 100 100 100 100 Hardener Type D-160N D-160N D-160N D-160N D-160N D-160N D-160N D-160N Dispensing amount 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 Additives Type KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 KBM-403 Dispensing amount 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Mass per unit area of adhesive layer (g/m ² ) 9 110 49 50 55 42 46 36 Gel fraction (%) 73 62 72 67 65 82 52 92 Polar component (mN/m) 0.12 0.12 0.53 0.54 0.58 0.64 0.71 0.69 Translucent flexible substrate PET PET PET PET PET PET PET PET Standard bending test Whitening of the bend 3 4 3 2 2 2 2 3 End offset 4 4 2 3 2 2 3 2 End exposed 4 3 2 2 3 3 2 2 High speed bending test Whitening of the bend 2 3 2 1 1 1 1 2 End offset 3 3 1 1 2 2 1 1 End exposed 3 2 1 2 1 1 2 1

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

<Transparent flexible substrate> CPI: Colorless polyimide (manufactured by KOLON, 50 μm, polar component 4.5 mN/m) P-CPI: Colorless polyimide treated with plasma (treated with the above CPI, 50 μm, polar component 7.6 mN/m) PET: Polyethylene terephthalate (manufactured by Toyobo, 50 μm, polar component 5.8 mN/m) PMMA: Polymethyl methacrylate (manufactured by Mitsubishi Chemical, 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 component 4.8 mN/m) C-OPP: Corona-treated product of stretched polypropylene (manufactured by Toyobo Co., Ltd., 40 μm) (polarity component 4.6 mN/m)

In the corona treatment when manufacturing C-HDPE and C-OPP, a corona treatment device plasma dyne manufactured by Navitas was used, the speed was set to 100 mm/s, the distance between the corona discharge nozzle and the substrate was set to 20 mm, and the corona discharge nozzle was scanned once from one end of the substrate to the other end.

According to the results of Tables 4 to 7, the adhesive layer disclosed in the present invention does not cause the adherends to shift after bonding even if it is bent repeatedly, and the adhesive layer does not expose from the end. In addition, it is confirmed that even when colorless polyimide is used as a light-transmitting flexible substrate, the bent portion does not whiten due to foaming. Thus, the display including the laminate having the adhesive layer disclosed in the present invention has excellent bendability, thereby obtaining a display with excellent visibility. On the other hand, the adhesive layers of Comparative Examples 1 to 12 cannot satisfy all the above characteristics.

1: First adhesive layer (adhesive layer) 3: Translucent flexible substrate (cover plate) 4: Polarizing plate 5: Second adhesive layer 6: Barrier layer 7: Organic EL layer 8: Support body 9: Organic EL unit

FIG1 is a schematic cross-sectional view partially showing a laminated body of an embodiment of the present disclosure. FIG2 is a schematic cross-sectional view partially showing a flexible display as an example of use of the laminated body of an embodiment of the present disclosure.

1: Adhesive layer

3: Translucent flexible substrate (cover plate)

4: Polarizing plate

Claims (6)

A multilayer for a flexible display includes an adhesive layer on a light-transmitting flexible substrate. The multilayer for a flexible display is characterized in that the polar component of the surface free energy of the light-transmitting flexible substrate calculated based on the contact angle of water and the contact angle of diiodomethane and the Eutherian Laquey method is 3.0 mN/m or more, the polar component of the surface free energy of the adhesive layer calculated based on the contact angle of water and the contact angle of diiodomethane and the Eutherian Laquey method is 0.5 mN/m or less, the mass per unit area of the adhesive layer is 10 g/ ^m2 to 100 g/ ^m2 , The adhesive layer is formed of an acrylic adhesive, which comprises: an acrylic copolymer, wherein in 100% by mass of the acrylic copolymer, 25% by mass or less of repeating units derived from hydroxyl-containing monomers, 10% by mass or less of repeating units derived from acid-containing monomers, 15% by mass or less of repeating units derived from amide-containing monomers, 15% by mass or less of repeating units derived from amine-containing monomers, and 75% to 90% by mass of repeating units derived from alkyl (meth)acrylates having an alkyl group with 4 or more carbon atoms are contained; and a low-polarity additive. The laminate for a flexible display as described in claim 1, wherein the polar term component of the surface free energy of the adhesive layer calculated based on the contact angle of water and the contact angle of diiodomethane and the Eutherian-Laquet method is less than 0.2 mN/m. The laminate for a flexible display as claimed in claim 1, wherein the mass per unit area of the adhesive layer is 25 g/m ² to 70 g/m ² , and the gel fraction of the adhesive layer is 60 mass % to 80 mass %. The laminate for a flexible display as claimed in claim 1 comprises 0.02 to 4.0 parts by mass of a curing agent relative to 100 parts by mass of the acrylic copolymer. The multilayer body for a flexible display as described in any one of claims 1 to 4 further includes a polarizing plate on the adhesive layer. A flexible display comprises the multilayer body as described in claim 5, and an optical element.