KR102159485B1 - Pressure Sensitive Adhesive composition using foldable display - Google Patents

Abstract

The present application relates to a pressure-sensitive adhesive composition for a foldable display and a use thereof.
The pressure-sensitive adhesive composition of the present application has excellent bending reliability along with it, and is useful for forming a pressure-sensitive adhesive layer for a foldable display.

Description

Adhesive composition for foldable display {Pressure Sensitive Adhesive composition using foldable display}

The present application relates to a pressure-sensitive adhesive composition for a foldable display and a use thereof.

With the recent development of display-related technologies, research and development of display devices capable of being deformable at the stage of use, such as folding, rolling in a roll shape, or stretching like a rubber band, are being developed. Since these displays can be deformed into various forms, it is possible to satisfy both the demand for an increase in size of the display at the stage of use and the demand for miniaturization of the display for portability.

The deformable display device may not only be transformed into a pre-set form, but may be transformed into various forms in response to a user's request or a situation in which the display device is used. Accordingly, it is necessary to recognize a deformed shape of the display and control the display device in response to the recognized shape.

Meanwhile, since the deformable display device has a problem that each component of the display device is damaged according to the deformation, each component of the display device must satisfy folding reliability and stability.

Patent Document 1: Korean Patent Publication No. 2015-0011230 A

The present application provides an adhesive composition for a foldable display and a use thereof.

After curing, the pressure-sensitive adhesive composition for a foldable display of the present application satisfies a storage modulus within a predetermined range in a wide temperature range, for example, -40°C to 60°C, and has excellent bending reliability.

The present application relates to a pressure-sensitive adhesive composition for a foldable display and a use thereof.

After curing, the pressure-sensitive adhesive composition according to the present application has a storage elastic modulus in the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in a wide temperature range, for example, in a temperature range of -40°C to 60°C, so that it is foldable. ) It has physical properties suitable for use in displays.

The pressure-sensitive adhesive composition may be cured to form a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer may be included in a foldable display to be used for attaching a display panel and a cover glass.

In the present application, the term "foldable display" is designed to be repeatedly folded and unfolded like paper, and thus may refer to a flexible display in which the folded portion has a radius of curvature of 5 mm or less.

Unlike conventional adhesives, the adhesive applied to the foldable display must satisfy the bending reliability. In order to achieve this excellent bending reliability, the temperature range in which the actual foldable display can be used, such as For example, the storage modulus must be maintained within an appropriate range.

Accordingly, the applicant of the present invention controls the type and content of the monomer forming the acrylic polymer contained in the pressure-sensitive adhesive composition for a foldable display, and appropriately selects a crosslinking agent to crosslink it, and after curing -40℃ to 60℃ It has come to the invention of a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer suitable for a foldable display having a storage modulus of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in a wide temperature range of.

That is, the present application relates to a pressure-sensitive adhesive composition for a foldable display comprising an acrylic polymer composed of a polymerized unit of a (meth)acrylic acid ester monomer and a polymerizable monomer having a crosslinkable functional group. In addition, after curing, the pressure-sensitive adhesive composition has a storage modulus (G') of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa within a temperature range of -40°C to 60°C.

The pressure-sensitive adhesive composition of the present application includes an acrylic polymer made of polymerized units of specific monomers, and has a storage modulus in a temperature range in which a foldable display can be used, specifically, in a temperature range of -40°C to 60°C. It is maintained within the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa.

Accordingly, the pressure-sensitive adhesive composition of the present application can secure not only the adhesive properties, which are the intrinsic physical properties of the pressure-sensitive adhesive layer, but also the bending reliability required by the pressure-sensitive adhesive for foldable displays.

The storage modulus may be, for example, a value measured according to a manual using a rheological property meter (Advanced Rheometric Expansion System, Ta Instruments) under conditions of a frequency of 0.1 rad/s to 100 rad/s and a strain rate of 10% or less.

In one example, the storage modulus is derived by measuring according to the temperature while changing the temperature from -40°C to 60°C at a frequency of 6.2rad/s and a strain rate of 10% or less using a TA's G2 series rheometer. Can be.

The storage modulus after curing of the pressure-sensitive adhesive composition decreases linearly or non-linearly from -40°C to 60°C, so the pressure-sensitive adhesive composition has a storage elastic modulus that does not exceed 5.0 x 10 ⁶ Pa at -40°C, In the case of having a storage modulus of 1.0 x 10 ⁴ Pa or more at 60°C, the pressure-sensitive adhesive composition may have a storage elastic modulus within the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in the entire temperature range of -40°C to 60°C. have.

As described above, it is possible to secure excellent bending reliability suitable for a foldable display within the storage elastic modulus change rate range.

In another example, after curing of the pressure-sensitive adhesive composition, the storage modulus in the temperature range of -40°C to 60°C is 1.5 x 10 ⁴ Pa to 3.5 x 10 ⁶ Pa, 1.5 x 10 ⁴ Pa to 2.0 x 10 ⁶ Pa or 1.5 x 10 ⁴ Pa to 1.0 x 10 ⁶ Pa.

The pressure-sensitive adhesive composition of the present application includes an acrylic polymer. The acrylic polymer is composed of a polymerized unit of a (meth)acrylic acid ester monomer and a polymerizable monomer having a crosslinkable functional group.

In the present application, the term ``a polymer consists of a polymerized unit of a monomer'' means a state in which the monomer is polymerized in a skeleton such as a main chain or a side chain of a polymer formed by polymerization of the monomer, and a polymerization unit of any monomer other than the monomer It can mean that it doesn't contain. Accordingly, the acrylic polymer of the present application may not include polymerization units of other monomers other than the above-described (meth)acrylic acid ester monomer and the polymerizable monomer having a crosslinkable functional group.

In addition, the term "(meth)acrylic acid" means acrylic acid or methacrylic acid.

The type of the (meth)acrylic acid ester monomer is not particularly limited, and may be, for example, an alkyl (meth)acrylate. In the above, the term "(meth)acrylate" means acrylate or methacrylate.

Specifically, the alkyl (meth)acrylate may be an alkyl (meth)acrylate having an alkyl group having 5 to 20 carbon atoms. In the case of using an alkyl (meth)acrylate having an alkyl group having less than 5 carbon atoms, in the temperature range of -40°C to 60°C, the desired storage modulus range may not be achieved.

The alkyl (meth)acrylate having an alkyl group having 5 to 20 carbon atoms is, for example, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate. )Acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylic Rate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, octadecyl (meth)acrylate, or isobornyl (meth)acrylate may be exemplified, but are not limited thereto.

In addition, as long as the polymerizable monomer having a crosslinkable functional group included as a polymerization unit in the acrylic polymer is polymerized with the (meth)acrylic acid ester monomer forming the acrylic polymer to provide a crosslinkable functional group to the polymer, there is no particular limitation. Can be chosen.

In the above, the crosslinkable functional group may be selected without limitation, as long as it can cause a crosslinking reaction with a crosslinking agent described later at a temperature in the range of, for example, about 50 to 300.

In one example, the crosslinkable functional group may be at least one selected from the group consisting of a hydroxy group, an isocyanate group, a glycidyl group, an epoxy group, an amine group, and a carboxyl group.

In a specific example, the polymerizable monomer having a crosslinkable functional group may be a monomer having a hydroxy group, a monomer having a carboxyl group, or a monomer having an amine group, but is not limited thereto.

The monomer having a hydroxy group is, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth) ) Hydroxyalkyl (meth)acrylate such as acrylate or 8-hydroxyoxyl (meth)acrylate; Hydroxypolyalkylene glycol (meth)acrylate such as hydroxy polyethylene glycol (meth)acrylate or hydroxypolypropylene glycol (meth)acrylate; There may be such as, but is not limited thereto.

The monomer having a carboxy group is, for example, (meth)acrylic acid, 2-(meth)acryloyloxy acetic acid, 3-(meth)acryloyloxy propyl acid, 2-carboxyethyl acrylate, 4-(meth) There may be acryloyloxy butyric acid, acrylic acid duplex, itaconic acid, maleic acid or maleic anhydride, but is not limited thereto.

The monomer having an amine group is, for example, 2-aminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate or N,N-dimethylaminopropyl There may be (meth)acrylate, etc., but is not limited thereto.

Among the monomers having various crosslinkable functional groups, an appropriate type may be selected in consideration of a desired glass transition temperature of the acrylic polymer or reactivity with a crosslinking agent described below.

In a specific example, the crosslinkable functional group may be a carboxy group. When the acrylic polymer contains a monomer having a carboxyl group as a polymerized unit, the storage modulus of the pressure-sensitive adhesive composition may be achieved by sequential crosslinking reactions by two or more different crosslinking agents described below.

The acrylic polymer may contain a polymerized unit of a (meth)acrylic acid ester monomer and a polymerizable monomer having a crosslinkable functional group in a predetermined ratio.

In one example, the acrylic polymer may consist of 90 to 99.5 parts by weight of a (meth)acrylic acid ester monomer and 0.5 to 10 parts by weight of a polymerizable monomer having a crosslinkable functional group.

In another example, the acrylic polymer is 92 to 99.5 parts by weight of a (meth) acrylic acid ester monomer and 0.5 to 8 parts by weight of a polymerizable monomer having a crosslinkable functional group, or 94 to 99 parts by weight of a (meth) acrylic acid ester monomer and a crosslinkable functional group It may consist of 1 to 6 parts by weight of a polymerizable monomer having a polymerizable monomer. In the above, the term "parts by weight" means a weight ratio between each component unless otherwise defined.

A foldable display adhesive having a storage modulus within the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in a temperature range of -40°C to 60°C after curing within the above polymerization unit ratio range Compositions can be provided.

The acrylic polymer of the present application may have, for example, a glass transition temperature (Tg) in the range of -120 to -40. The glass transition temperature (Tg) range of the pressure-sensitive adhesive composition to be described later can be achieved within the range of this glass transition temperature (Tg), and the storage modulus in the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in a wide temperature range It is possible to provide a pressure-sensitive adhesive composition showing. In another example, the glass transition temperature (Tg) of the acrylic polymer may be in the range of -100°C to -45°C, or -80°C to -50°C.

The acrylic polymer of the present application may also have a weight average molecular weight in the range of 5,000 to 3,000,000. In the present application, the term weight average molecular weight may mean a value converted to standard polystyrene measured by GPC (Gel Permeation Chromatograph), and unless otherwise specified, the molecular weight of a polymer may mean the weight average molecular weight of the polymer. I can. In another example, the weight average molecular weight of the acrylic polymer may be in the range of 100,000 to 2,500,000 or 500,000 to 2,200,000.

The acrylic polymer of the present application can be prepared in various ways. For example, the polymer is a mixture of monomers in which a necessary monomer is selected from the above-described monomers, and the selected monomer is mixed in a desired ratio, solution polymerization, bulk polymerization, and suspension polymerization. polymerization) or emulsion polymerization, and appropriately, it can be prepared by solution polymerization. The method of preparing the polymer through solution polymerization is not particularly limited.

The solution polymerization method may be carried out for 6 to 15 hours at a polymerization temperature of 50 to 140 by mixing a radical polymerization initiator and a solvent, for example, in a state in which the above-described monomer components are mixed in an appropriate weight ratio.

Radical polymerization initiators used to produce acrylic polymers are known and include, for example, azo polymerization initiators such as azobis isobutyronitrile or azobiscyclohexane carbonitrile; Or oxides such as benzoyl peroxide or acetyl peroxide; And the like can be used.

The polymerization initiator may be used alone or in combination of two or more, and the content is preferably about 0.005 to 3 parts by weight.

In addition, a solvent used to prepare the acrylic polymer is known, and for example, ethyl acetate or toluene may be used, but is not limited thereto.

The pressure-sensitive adhesive composition of the present application may also include a crosslinking agent. The crosslinking agent can crosslink an acrylic polymer, for example.

The present application may provide a pressure-sensitive adhesive composition having physical properties suitable for application to a foldable display, including a crosslinking agent having a functional group capable of reacting with a crosslinkable functional group contained in an acrylic polymer.

The crosslinking agent is, for example, a bifunctional or higher polyfunctional compound containing two or more functional groups capable of reacting with the crosslinkable functional group of the acrylic polymer, for example, 2 to 6 functional groups in one molecule. It may mean a multifunctional compound to be included. In addition, two or more functional groups contained in one molecule may be functional groups of the same or different species.

Specifically, the crosslinking agent is at least one selected from the group consisting of an alkoxy silane group, a carboxyl group, an acid anhydride group, a vinyl ether group, an amine group, a carbonyl group, an isocyanate group, an epoxy group, an aziridinyl group, a carbodiimide group and an oxazoline group. It may be a multifunctional compound containing two or more functional groups in one molecule. The type of the functional group may vary depending on the type of the crosslinkable functional group included in the acrylic polymer or other mechanisms for implementing the crosslinked structure.

In one example, the crosslinking agent containing a carboxyl group, o-phthalic acid, isophthalic acid, terephthalic acid, 1,4-dimethylterephthalic acid, 1,3-dimethylisophthalic acid, 5-sulfo-1,3-dimethylisophthalic acid, 4 ,4-biphenyldicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, norbornenedicarboxylic acid, diphenylmethane-4,4'-dicarboxyl Aromatic dicarboxylic acids such as acids or phenylindanedicarboxylic acid; Aromatic dicarboxylic acid anhydrides such as phthalic anhydride, 1,8-naphthalenedicarboxylic anhydride or 2,3-naphthalenedicarboxylic anhydride; Alicyclic dicarboxylic acids such as hexahydrophthalic acid; Alicyclic dicarboxylic acid anhydrides such as hexahydro phthalic anhydride, 3-methyl-hexahydro phthalic anhydride, 4-methyl-hexahydro phthalic anhydride, or 1,2-cyclohexanedicarboxylic anhydride; Or oxalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, suberic acid, maleic acid, chloromaleic acid, fumaric acid, dodecanoic acid, pimelic acid, citraconic acid, glutaric acid, itaconic acid, etc. And aliphatic dicarboxylic acids.

In one example, the crosslinking agent including an acid anhydride group is pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, diphenylsulfone tetracarboxylic acid Dianhydride, diphenylsulfidetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, perylenetetracarboxylic dianhydride or naphthalenetetracarboxylic dianhydride, and the like.

In one example, the crosslinking agent containing a vinyl ether group is ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, pentaerythritol divinyl ether, propylene glycol di Vinyl ether, dipropylene glycol divinyl ether, tripropylene glycol divinyl ether, neopentyl glycol divinyl ether, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, glycerin divinyl ether, trimethyl Allpropanedivinyl ether, 1,4-dihydroxycyclohexanedivinyl ether, 1,4-dihydroxymethylcyclohexanedivinyl ether, hydroquinone divinyl ether, ethylene oxide modified hydroquinone divinyl ether, ethylene oxide Modified resorcin divinyl ether, ethylene oxide modified bisphenol A divinyl ether, ethylene oxide modified bisphenol S divinyl ether, glycerin trivinyl ether, sorbitol tetravinyl ether, trimethylolpropane trivinyl ether, pentaerythritol trivinyl ether, penta Erythritol tetravinyl ether, dipentaerythritol hexavinyl ether, dipentaerythritol polyvinyl ether, ditrimethylolpropane tetravinyl ether or ditrimethylolpropane polyvinyl ether.

In one example, the crosslinking agent including the amine group may include aliphatic diamines such as ethylenediamine or hexamethylenediamine; Alicyclic diamines such as 4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldicyclohexyl, diaminocyclohexane or isophoronediamine Ryu; Alternatively, there may be aromatic diamines such as xylenediamine.

In one example, the crosslinking agent containing an isocyanate group is 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2 ,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-toluidinediisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanatebenzene, dianicidindiisocyanate, 4 ,4'-diphenylether diisocyanate, 4,4',4''-triphenylmethane triisocyanate, ω,ω-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4 -Dimethylbenzene,ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylacrylylene diisocyanate, 1,3-tetramethylxylene diisocyanate, xylylene diisocyanate or xylylene diisocyanate Aromatic polyisocyanates such as; Trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butalene diisocyanate, dodecamethylene diisocyanate or 2 Aliphatic polyisocyanates such as ,4,4-tramethylhexamethylene diisocyanate; Or 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexanediisocyanate, 1,4-cyclohexanediisocyanate, methyl-2,4- Alicyclic polyisocyanates such as cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate, 4,4'-methylenebis(cyclohexylisocyanate) or 1,4-bis(isocyanatemethyl)cyclohexane, etc., or There may be a reaction product of one or more of the above polyisocyanates and polyols.

In one example, the crosslinking agent containing an epoxy group is ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N,N,N,N'-tetraglycidyl-1,3 -There may be xylenediamine, or glycerin diglycidyl ether.

In addition, the pressure-sensitive adhesive composition of the present application may include two different cross-linking agents among the cross-linking agents, and may perform a cross-linking reaction with a cross-linkable functional group included in the acrylic polymer.

In a more specific example, the two or more different crosslinking agents may be formed of a first crosslinking agent reacting with a crosslinkable functional group of an acrylic polymer and a second crosslinking agent reacting with a crosslinkable functional group formed by reaction of the first crosslinking agent.

That is, the pressure-sensitive adhesive composition of the present application includes two different crosslinking agents together with an acrylic polymer, and the two types of crosslinking agents are formed by the reaction of the first crosslinking agent reacting with the crosslinkable functional group of the acrylic polymer and the first crosslinking agent. It may be a second crosslinking agent reacting with a crosslinkable functional group.

According to the implementation mechanism of the crosslinking structure as described above, the storage modulus of the pressure-sensitive adhesive composition of the present application after curing can be adjusted within the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in the temperature range of -40°C to 60°C. .

In one example, the first crosslinking agent may be a crosslinking agent including an epoxy group, and the second crosslinking agent may be a crosslinking agent including an isocyanate group.

As described above, when the two different crosslinking agents of the present application are crosslinking agents each including an epoxy group and an isocyanate group, the carboxy group included in the acrylic polymer and the crosslinking agent may implement a sequential crosslinking reaction.

Specifically, when the crosslinkable functional group included in the acrylic polymer of the present application is a carboxyl group, the crosslinking agent including an epoxy group as the first crosslinking agent reacts with the carboxy group, and the crosslinking agent including an isocyanate group as the second crosslinking agent is A crosslinked structure of the acrylic polymer may be implemented by reacting with a hydroxyl group formed by reaction of an epoxy group with a carboxyl group contained in the acrylic polymer.

By such a sequential crosslinking reaction, a desired storage modulus change rate of the pressure-sensitive adhesive composition can be achieved.

The two or more different crosslinking agents may be included in the pressure-sensitive adhesive composition within a content range capable of achieving the above object.

In one example, two or more different crosslinking agents may be included in the composition in the range of 0.001 to 5 parts by weight based on 100 parts by weight of the acrylic polymer. In another example, the two or more different crosslinking agents may be included in the composition in the range of 0.001 to 3 parts by weight, 0.01 to 2 parts by weight or 0.02 to 2 parts by weight based on 100 parts by weight of the acrylic polymer. When the content of the crosslinking agent exceeds 5 parts by weight or less than 0.001 parts by weight, the desired storage modulus cannot be achieved within the temperature range of -40°C to 60°C.

In a specific example, when the two or more different crosslinking agents are made of the aforementioned first crosslinking agent and the second crosslinking agent, the first crosslinking agent is in the range of 0.0005 to 3.5 parts by weight based on 100 parts by weight of the acrylic polymer, and the second crosslinking agent is an acrylic polymer. It may be included in the pressure-sensitive adhesive composition within the range of 0.0005 to 1.5 parts by weight based on 100 parts by weight.

In another example, when the two or more different crosslinking agents are made of the aforementioned first crosslinking agent and the second crosslinking agent, the first crosslinking agent is in the range of 0.001 to 3.0 parts by weight based on 100 parts by weight of the acrylic polymer, and the second crosslinking agent is an acrylic polymer. It is included in the pressure-sensitive adhesive composition within the range of 0.001 to 2.0 parts by weight based on 100 parts by weight, or the first crosslinking agent is in the range of 0.01 to 2.0 parts by weight based on 100 parts by weight of the acrylic polymer, and the second crosslinking agent is 0.003 to 1.0 based on 100 parts by weight of the acrylic polymer. It may be included in the pressure-sensitive adhesive composition within the range of parts by weight.

The pressure-sensitive adhesive composition of the present application includes known additional components, such as antistatic agents, tackifier resins, curing agents, ultraviolet stabilizers, antioxidants, toning agents, reinforcing agents, fillers, defoaming agents, surfactants or plasticizers, in addition to the acrylic polymer and crosslinking agent described above. It may contain additionally.

The pressure-sensitive adhesive composition of the present application, after curing as described above, has a storage elastic modulus in the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa in a temperature range of -40°C to 60°C, so a foldable display It is useful to form a pressure-sensitive adhesive layer having bending reliability suitable for.

The pressure-sensitive adhesive composition of the present application also has a glass transition temperature (Tg) of the composition in order to prevent a radical change in the storage modulus value of the pressure-sensitive adhesive composition in the temperature range (-40°C to 60°C) in which the desired storage modulus is to be achieved. It may be kept lower than the lower limit (-40°C) of the temperature range (-40°C to 60°C).

In one example, the pressure-sensitive adhesive composition of the present application may have a glass transition temperature (Tg) of less than -40°C in a state in which an acrylic polymer and a crosslinking agent implement a crosslinking structure. Through the above conditions, in a temperature range of -40°C to 60°C, it may have a storage modulus within the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa.

In another example, the pressure-sensitive adhesive composition may have a glass transition temperature (Tg) of -45°C or less, -50°C or less, or -55°C or less while implementing a crosslinked structure. The lower limit of the glass transition temperature (Tg) of the pressure-sensitive adhesive composition may be, for example, -150°C or higher, -100°C or higher, or -80°C or higher.

The present application also relates to the use of an adhesive composition. Since the pressure-sensitive adhesive composition of the present application has bent reliability suitable for a foldable display, it can be used for applications such as attaching a panel and a cover glass to a foldable display.

In one example, the present application relates to a foldable display including an adhesive layer, which is a cured product of an adhesive composition. In addition, the pressure-sensitive adhesive composition includes an acrylic polymer composed of a polymerized unit of a (meth)acrylic acid ester monomer and a polymerizable monomer having a crosslinkable functional group, and the storage modulus after curing within a temperature range of -40°C to 60°C ( G') value is in the range of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa.

Other specific configurations of the foldable display are known by, for example, Korean Patent Application Publication No. 2015-0138450, and the present application may include the pressure-sensitive adhesive such as the configuration of a known foldable display without limitation. .

The present application may provide a pressure-sensitive adhesive composition having bending reliability suitable for application to a foldable display.

Hereinafter, the pressure-sensitive adhesive composition for a foldable display according to the present application will be described in more detail with reference to Examples and Comparative Examples, but the following examples are only examples according to the present application, and the technical idea of the present application is limited. Is not.

The physical properties of the pressure-sensitive adhesive composition of the present application were evaluated by the following method.

1. Molecular weight measurement

The weight average molecular weight (Mw) was measured under the following conditions using GPC, and the measurement result was converted using standard polystyrene of Agilent system for the production of the calibration curve.

< Measurement conditions>

Measuring instrument: Agilent GPC (Agilent 1200 series, U.S.)

Column: Connect 2 PL Mixed B

Column temperature: 40°C

Eluent: THF (Tetrahydrofuran)

Flow rate: 1.0 mL/min

Concentration: ~ 1 mg/mL (100μL injection)

2. Storage modulus measurement

The pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples were coated between the release films, and then cut into a size of 15 cm × 25 cm, the release film on one side was removed, and then laminated several times to make the thickness of about 1 mm. Subsequently, the laminate is cut into a circle having a diameter of 8 mm, compressed using a glass, and then left to stand overnight to improve wetting at the interface between each layer, thereby reducing air bubbles generated during lamination. Removed to prepare a sample. Subsequently, the sample was placed on a parallel plate, the gap was adjusted, the zero point of Normal & Torque was adjusted, and the stability of the normal force was confirmed, and the storage modulus was measured.

(1) Measurement equipment and measurement conditions

Measuring instrument: ARES-RDA with forced convection oven, TA Instruments Inc. (G2 series Rheometer)

(2) Measurement conditions:

geometry: 8 mm parallel plate

Thickness: approx. 1 mm

test type: dynamic strain frequency sweep

Strain = 0.1 [%]

Initial temperature: -40℃, Final temperature: 60℃

Frequency: 6.2rad/s

Example One

Preparation of pressure-sensitive adhesive composition (C1)

98 parts by weight of 2-ethylhexyl acrylate (EHA) and 2 parts by weight of beta-carboxyethyl acrylate (β-CEA) were added to a 1L reactor in which nitrogen gas was refluxed and a cooling device was installed to facilitate temperature control. . Then, 150 parts by weight of ethyl acetate (EAc) was added as a solvent, nitrogen gas was purged for 60 minutes to remove oxygen, and azobisisobutyronitrile (a reaction initiator) while maintaining the temperature at 60°C ( After the reaction was initiated by adding 0.02 parts by weight of AIBN), the reaction product, which was reacted for about 1 hour, was diluted with ethyl acetate (EAc) to prepare an acrylic polymer (A1) having a molecular weight of about 2 million. 0.03 parts by weight of a crosslinking agent, N,N,N',N'-tetraglycidyl-m-xylene diamine (BXX-5240, Samyoung Ink Co., Ltd.), based on 100 parts by weight of the acrylic polymer (A1), 0.005 parts by weight of xylene diisocyanate (BXX-5627, Samyoung Ink Co., Ltd. (manufactured by Samyoung Ink Co.)) were uniformly mixed to prepare a pressure-sensitive adhesive composition (C1).

Of the adhesive layer (E1) formation

After coating the pressure-sensitive adhesive composition (C1) to a thickness of about 25 μm on a silicone release film (RF12N) manufactured by SKC and drying, a light peeling release film (RF02N) was applied, and then cured at 40° C. for 2 days to form the pressure-sensitive adhesive layer (E1). Formed.

Example 2

By adding 2 parts by weight of acrylic acid instead of 2 parts by weight of beta-carboxyethyl acrylate (β-CEA) to prepare a pressure-sensitive adhesive composition (C2) containing an acrylic polymer (A2) having a molecular weight of about 2 million, and using this A pressure-sensitive adhesive layer (E2) was formed in the same manner as in Example 1, except that (E2) was formed.

Comparative example One

A pressure-sensitive adhesive composition (D1) comprising an acrylic polymer (B1) having a molecular weight of about 2 million manufactured using 98 parts by weight of butyl acrylate (BA) and 2 parts by weight of acrylic acid was prepared, and the pressure-sensitive adhesive layer (F1) was formed using this Except for one, to form the pressure-sensitive adhesive layer (F1) in the same manner as in Example 1.

Comparative Example 2

A pressure-sensitive adhesive composition (D2) containing 94 parts by weight of butyl acrylate (BA) and an acrylic polymer (B2) having a molecular weight of about 2 million prepared using 6 parts by weight of acrylic acid was prepared, and the pressure-sensitive adhesive layer (F2) was formed using this Except for one, to form the pressure-sensitive adhesive layer (F2) in the same manner as in Example 1.

The types and contents of the monomers forming the acrylic polymers (A1, A2, B1, B2) in the pressure-sensitive adhesive compositions (C1, C2, D1, D2) according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below. .

A1 A2 B1 B2 EHA 98 98 β-CEA 2 AA 2 2 6 BA 98 94 Mw 2,000,000 2,000,000 2,000,000 2,000,000 EHA: 2-Ethylhexyl acrylate
β-CEA: beta-carboxyl ethyl acrylate
AA: acrylic acid
BA: butyl acrylate

Experimental example 1-Measurement of storage modulus

After curing of the compositions according to Examples and Comparative Examples, in order to find out the rate of change in storage modulus according to temperature, -40°C and 60°C according to the measurement method described above using ARES-RDA, TA instruments equipped with a forced convection oven. The storage modulus at °C was measured and shown in Table 2.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Storage modulus at -40℃ (Pa) 7.0 x 10 ⁵ 8.5 x 10 ⁵ 6.5 x 10 ⁶ 9.4 x 10 ⁸ Storage modulus at 60℃ (Pa) 2.1 x 10 ⁴ 3.5 x 10 ⁴ 1.1 x 10 ⁵ 1.1 x 10 ⁵

Experimental example 2-dynamic folding test

PI film (SKC KOLONE PI, IF 70) having a thickness of 50 μm was used as a structure of PI film/adhesive layer/PI film/adhesive layer/PI film to form a PI film laminate, and prepared in Examples and Comparative Examples. One pressure-sensitive adhesive layer was laminated with the laminate, and then cut into a size of 140mm x 80mm. Then, at -40℃, room temperature and 60℃, using a bending test equipment, a radius of curvature of 2.5mm, repeated 2500 times per hour, and a total of 100,000 dynamic folding tests were performed, and then the PI film laminate and the adhesive If lifting occurs at the interface, it is evaluated as NG, and if lifting occurs, it is evaluated as OK and shown in Table 3 below.

Condition Example 1 Example 2 Comparative Example 1 Comparative Example 2 Dynamic folding test -40℃ OK OK NG NG Room temperature OK OK NG OK 60℃ OK OK NG OK

Experimental example 3-static folding test

PI film (SKC KOLONE PI, IF 70) having a thickness of 50 μm was used as a structure of PI film/adhesive layer/PI film/adhesive layer/PI film to form a PI film laminate, and prepared in Examples and Comparative Examples. One pressure-sensitive adhesive layer was laminated with the laminate and then cut into a size of 140mm x 80mm. Thereafter, the interface between the PI film laminate and the pressure-sensitive adhesive layer was observed after 24 hours in a folded state with a radius of curvature of 2.5 mm. The temperature conditions were measured at -40℃, room temperature, and 60℃, respectively, and the result of static folding test at each temperature was evaluated as NG if lifting occurs at the interface between the PI film laminate and the adhesive, and OK if lifting does not occur. It is shown in Table 4.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 -40℃ OK OK NG NG Room temperature OK OK NG OK 60℃ OK OK NG OK

Experimental example 4-Glass transition temperature measurement

The pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples were applied thinly between the two substrates on which the release film was laminated, and after irradiating with ultraviolet rays, the two substrates were removed. Thereafter, the release film cured with the pressure-sensitive adhesive composition is cut into a width of 0.5 cm and a length of 4 cm, and the temperature is raised from -30°C to 150°C by 5°C/min by a DMA measuring device, and the glass transition temperature (Tg ) Was derived, and the results are shown in Table 5 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Tg -60℃ -57℃ -37℃ -27℃

Claims (14)

A (meth)acrylic acid ester monomer, an acrylic polymer composed of a polymerization unit of a polymerizable monomer having a crosslinkable functional group, and a crosslinking agent for crosslinking the acrylic polymer,
The crosslinking agent is composed of a first crosslinking agent reacting with a crosslinkable functional group of an acrylic polymer and a second crosslinking agent reacting with a crosslinkable functional group formed by reaction of the first crosslinking agent,
A pressure-sensitive adhesive composition for a foldable display having a storage modulus (G') of 1.0 x 10 ⁴ Pa to 5.0 x 10 ⁶ Pa within a temperature range of -40°C to 60°C. The method of claim 1,
(Meth) acrylic acid ester monomer is an alkyl (meth) acrylate foldable (foldable) pressure-sensitive adhesive composition for display. The method of claim 1,
The (meth)acrylic acid ester monomer is 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n -Octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl ( Meta) acrylate, octadecyl (meth) acrylate and isobornyl (meth) acrylate, any one or more selected from the group consisting of a foldable pressure-sensitive adhesive composition for display. The method of claim 1,
The crosslinkable functional group is any one or more selected from the group consisting of a hydroxy group, an isocyanate group, a glycidyl group, an epoxy group, an amine group, and a carboxyl group. The method of claim 1,
The crosslinkable functional group is a carboxyl group, a foldable display adhesive composition. The method of claim 1,
The acrylic polymer is a foldable pressure-sensitive adhesive composition for a foldable display comprising 90 parts by weight to 99.5 parts by weight of a (meth)acrylic acid ester monomer and 0.5 to 10 parts by weight of a polymerizable monomer having a crosslinkable functional group. delete The method of claim 1,
The crosslinking agent is a molecule having one or more functional groups selected from the group consisting of alkoxy silane groups, carboxyl groups, acid anhydride groups, vinyl ether groups, amine groups, carbonyl groups, isocyanate groups, epoxy groups, aziridinyl groups, carbodiimide groups and oxazoline groups A pressure-sensitive adhesive composition for a foldable display that is a multifunctional compound containing two or more within. delete The method of claim 1,
The first crosslinking agent is a crosslinking agent containing an epoxy group, and the second crosslinking agent is a crosslinking agent containing an isocyanate group. The pressure-sensitive adhesive composition for a foldable display. The method of claim 1,
The content of the crosslinking agent is in the range of 0.001 to 5 parts by weight based on 100 parts by weight of the acrylic polymer. The method of claim 1,
The content of the first crosslinking agent is in the range of 0.0005 to 3.5 parts by weight based on 100 parts by weight of the acrylic polymer, and the content of the second crosslinking agent is in the range of 0.0005 to 1.5 parts by weight based on 100 parts by weight of the acrylic polymer. . The method of claim 1,
A pressure-sensitive adhesive composition for a foldable display having a glass transition temperature (Tg) of -50°C or less in a state in which the acrylic polymer and the crosslinking agent implement a crosslinking structure. A foldable display comprising an adhesive layer that is a cured product of the adhesive composition for a foldable display of claim 1.