Adhesive composition for a foldable display and an adhesive film for a foldable display comprising a cured product thereof

Abstract

The present invention relates to an adhesive film and an adhesive composition that can provide the same, wherein the adhesive film has excellent folding characteristics even under sub-zero temperature conditions and can thus be easily applied to a foldable display.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2020-0116499, filed on September 11, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an adhesive composition for a foldable display and an adhesive film for a foldable display including an adhesive layer containing a cured product thereof. Background Art

[0003] In recent years, with the development of display-related technologies, display devices that can be deformed during use (e.g., folded, rolled into a roll, or stretched like a rubber band) have been researched and developed. These displays can be deformed into various shapes, thereby meeting the demand for both larger displays during use and smaller displays for portability.

[0004] The deformable display device can be deformed into various shapes according to user needs or the needs of the use of the display device, as well as into a predetermined shape. Therefore, it is necessary to identify the deformed shape of the display and control the display device according to the identified shape.

[0005] Deformable display devices also present the potential for damage to their components due to deformation. Therefore, these components must meet both folding reliability and stability requirements. In particular, the adhesive films used to secure these components must be sufficiently deformable to mitigate stress applied to the components when the display is deformed. Furthermore, there has been a recent demand for adhesive films with physical properties that enable folding properties even when used in sub-zero temperatures.

[0006] Therefore, there is a need for an adhesive film having physical properties that can be easily applied to foldable displays. Summary of the Invention

[0007] Technical issues

[0008] An object of the present invention is to provide an adhesive film having excellent folding characteristics even under sub-zero temperature conditions and thus being easily applicable to foldable displays, and an adhesive composition that can provide the same.

[0009] However, the objects to be achieved by the present invention are not limited to the above objects, and those skilled in the art will clearly understand other objects not mentioned herein from the following description.

[0010] Technical Solution

[0011] One embodiment of the present invention provides an adhesive composition for a foldable display, comprising a (meth)acrylate-based polymer that is a reaction product of a monomer mixture, the monomer mixture comprising: a first monomer, the first monomer including at least one of a first acrylate-based monomer including an alkyl group having 12 to 14 carbon atoms and a first methacrylate-based monomer including an alkyl group having 14 to 16 carbon atoms; a second monomer, the second monomer including at least one of a second acrylate-based monomer including an alkyl group having 3 to 10 carbon atoms and a second methacrylate-based monomer including an alkyl group having 8 to 12 carbon atoms; and a (meth)acrylate-based monomer containing a polar functional group.

[0012] Another embodiment of the present invention provides an adhesive film for a foldable display including an adhesive layer including a cured product of the adhesive composition for a foldable display.

[0013] Effects of the Invention

[0014] The adhesive composition for a foldable display according to one embodiment of the present invention may provide an adhesive layer having excellent folding characteristics under room temperature and sub-zero temperature conditions.

[0015] Furthermore, the adhesive film for a foldable display according to one embodiment of the present invention may have excellent folding reliability under room temperature and sub-zero temperature conditions.

[0016] The effects of the present invention are not limited to the above-mentioned effects, and effects not mentioned herein will be clearly understood by those skilled in the art based on this specification and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram showing samples used for folding evaluation.

[0018] Figure 2 Schematic diagram showing the folding test. DETAILED DESCRIPTION

[0019] Throughout the present specification, it should be understood that when any part is referred to as “comprising” any component, unless otherwise stated, it does not exclude other components but may further include other components.

[0020] Throughout this specification, when any member is referred to as being 'on' another member, it not only refers to a case where any member is in contact with another member but also refers to a case where a third member exists between the two members.

[0021] Throughout the present specification, the unit "parts by weight" may refer to a weight ratio between components.

[0022] Throughout this specification, the term "(meth)acrylate" is intended to include both acrylate and methacrylate.

[0023] Throughout this specification, terms including ordinal numbers such as "first" and "second" are used to distinguish one component from other components, and the components are not limited by the ordinal numbers. For example, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component without departing from the scope of this disclosure.

[0024] Throughout this specification, the "weight average molecular weight" and "number average molecular weight" of any compound can be calculated using the molecular weight and molecular weight distribution of the compound. Specifically, the molecular weight and molecular weight distribution of the compound can be obtained by placing tetrahydrofuran (THF) and the compound in a 1 ml glass vial to prepare a test sample in which the concentration of the compound is 1 wt %; filtering the standard sample (polystyrene) and the test sample through a filter (pore size: 0.45 μm); injecting each sample filtrate into a GPC syringe; and comparing the elution time of the test sample with the calibration curve of the standard sample. At this time, Infinity II 1260 (Agilent Technologies, Inc.) can be used as a measuring instrument, and the flow rate and column temperature can be set to 1.00 mL / min and 40.0°C, respectively.

[0025] Throughout this specification, the storage modulus of the adhesive layer can be measured using an Advanced Rheometric Expansion System (ARES)-G2 rheometer (TA Instruments).

[0026] Hereinafter, this specification will be described in more detail.

[0027] One embodiment of the present invention provides an adhesive composition for a foldable display, comprising a (meth)acrylate-based polymer that is a reaction product of a monomer mixture, the monomer mixture comprising: a first monomer, the first monomer including at least one of a first acrylate-based monomer including an alkyl group having 12 to 14 carbon atoms and a first methacrylate-based monomer including an alkyl group having 14 to 16 carbon atoms; a second monomer, the second monomer including at least one of a second acrylate-based monomer including an alkyl group having 3 to 10 carbon atoms and a second methacrylate-based monomer including an alkyl group having 8 to 12 carbon atoms; and a (meth)acrylate-based monomer containing a polar functional group.

[0028] The adhesive composition for a foldable display according to one embodiment of the present invention may provide an adhesive layer having excellent folding characteristics under room temperature and sub-zero temperature conditions.

[0029] According to one embodiment of the present invention, an adhesive composition for a foldable display can provide an adhesive layer having excellent folding reliability even at low temperatures by including a (meth)acrylate-based polymer produced by reacting a monomer mixture including a first monomer, a second monomer, and a (meth)acrylate-based monomer containing a polar functional group.

[0030] According to one embodiment of the present invention, the first monomer may include at least one of a first acrylate-based monomer including an alkyl group having 12 to 14 carbon atoms and a first methacrylate-based monomer including an alkyl group having 14 to 16 carbon atoms.

[0031] Specifically, the first acrylate-based monomer may include a linear or branched alkyl group having 12 to 14 carbon atoms. For example, the first acrylate-based monomer may include at least one of n-dodecyl acrylate (lauryl acrylate), isododecyl acrylate, n-tridecyl acrylate, isotridecyl acrylate, n-tetradecyl acrylate, and isotetradecyl acrylate.

[0032] In addition, the first methacrylate-based monomer may include a linear or branched alkyl group having 14 to 16 carbon atoms. For example, the first methacrylate-based monomer may include at least one of n-tetradecyl methacrylate, iso-tetradecyl methacrylate, n-pentadecyl methacrylate, iso-pentadecyl methacrylate, n-hexadecyl methacrylate, and iso-hexadecyl methacrylate.

[0033] When at least one of a first acrylate-based monomer and a first methacrylate-based monomer is used as the first monomer, low-temperature (eg, −20° C.) folding reliability of a cured product of the adhesive composition for a foldable display may be effectively improved.

[0034] According to one embodiment of the present invention, based on 100 parts by weight of the monomer mixture, the content of the first monomer may be 20 to 60 parts by weight. Specifically, based on 100 parts by weight of the monomer mixture, the content of the first monomer may be 25 to 55 parts by weight, 30 to 50 parts by weight, 35 to 45 parts by weight, 20 to 50 parts by weight, 22.5 to 47.5 parts by weight, 25 to 45 parts by weight, 27.5 to 42.5 parts by weight, 30 to 40 parts by weight, 32.5 to 47.5 parts by weight, 35 to 45 parts by weight, 37.5 to 42.5 parts by weight, 35 to 60 parts by weight, 38 to 57.5 parts by weight, 40 to 55 parts by weight, 43 to 52.5 parts by weight, or 45 to 50 parts by weight.

[0035] When the content of the first monomer in the monomer mixture is controlled within the above range, the low-temperature storage modulus of the cured product of the adhesive composition for a foldable display can be effectively reduced. Furthermore, when the content of the first monomer is within the above range, the crystallinity of the cured product can be suppressed, thereby improving the folding properties of the adhesive layer containing the cured product.

[0036] According to one embodiment of the present invention, the second monomer may include at least one of a second acrylate-based monomer including an alkyl group having 3 to 10 carbon atoms and a second methacrylate-based monomer including an alkyl group having 8 to 12 carbon atoms.

[0037] Specifically, the second acrylate-based monomer may include a linear or branched alkyl group having 3 to 10 carbon atoms. For example, the second acrylate-based monomer may include at least one of n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, isohexyl acrylate, n-heptyl acrylate, isoheptyl acrylate, n-octyl acrylate, isooctyl acrylate, ethylhexyl acrylate, n-nonyl acrylate, isononyl acrylate, n-decyl acrylate, and isodecyl acrylate.

[0038] In addition, the second methacrylate-based monomer may include a linear or branched alkyl group having 8 to 12 carbon atoms. For example, the second methacrylate-based monomer may include at least one of n-octyl methacrylate, isooctyl methacrylate, ethylhexyl methacrylate, n-nonyl methacrylate, isononyl methacrylate, n-decyl methacrylate, isodecyl methacrylate, n-undecyl methacrylate, isoundecyl methacrylate, n-dodecyl methacrylate, and isododecyl methacrylate.

[0039] When at least one of a second acrylate-based monomer and a second methacrylate-based monomer is used as the second monomer, low-temperature (eg, -20°C) folding reliability of a cured product of the adhesive composition for a foldable display may be effectively improved.

[0040] According to one embodiment of the present invention, the second monomer may be included in an amount of 35 to 80 parts by weight based on 100 parts by weight of the monomer mixture. Specifically, based on 100 parts by weight of the monomer mixture, the content of the second monomer may be greater than 35 parts by weight and less than 80 parts by weight, 36 parts by weight to 79 parts by weight, 40 parts by weight to 79 parts by weight, 45 parts by weight to 79 parts by weight, 50 parts by weight to 75 parts by weight, 55 parts by weight to 70 parts by weight, 60 parts by weight to 65 parts by weight, 35 parts by weight to 65 parts by weight, 37.5 parts by weight to 62.5 parts by weight, 40 parts by weight to 60 parts by weight, 42.5 parts by weight to 57.5 parts by weight, 45 parts by weight to 55 parts by weight, 47.5 parts by weight to 52.5 parts by weight, 50 parts by weight to 80 parts by weight, 52.5 parts by weight to 75 parts by weight, 55 parts by weight to 70 parts by weight, 57.5 parts by weight to 67.5 parts by weight, or 60 parts by weight to 65 parts by weight.

[0041] When the content of the second monomer in the monomer mixture is controlled within the above range, the low-temperature storage modulus of a cured product of the adhesive composition for a foldable display can be effectively reduced.

[0042] According to one embodiment of the present invention, the (meth) acrylate-based monomer containing a polar functional group may include a carboxylic acid group. That is, the (meth) acrylate-based monomer may include a carboxylic acid group as a polar functional group. When a (meth) acrylate-based monomer containing a carboxylic acid group is used, the (meth) acrylate-based polymer can be effectively cured by an epoxide-based cross-linking agent to be described later. In addition, when a (meth) acrylate-based monomer containing a carboxylic acid group is used, the adhesion of the cured product of the adhesive composition for a foldable display can be maintained, and therefore the adhesive film for a foldable display can be prevented from separating from the base film during folding.

[0043] The polar functional group-containing (meth)acrylate-based monomer may include, for example, at least one of (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropionic acid, 4-(meth)acryloyloxybutyric acid, and (meth)acrylic acid dimer.

[0044] According to one embodiment of the present invention, based on 100 parts by weight of the monomer mixture, the content of the (meth) acrylate-based monomer containing a polar functional group may be 1 part by weight to 4 parts by weight. Specifically, based on 100 parts by weight of the monomer mixture, the content of the (meth) acrylate-based monomer containing a polar functional group may be 1 part by weight to 3 parts by weight, 1 part by weight to 2 parts by weight, 2 parts by weight to 4 parts by weight, or 2 parts by weight to 3 parts by weight. When the content of the (meth) acrylate-based monomer containing a polar functional group is controlled within the above range, the adhesive properties of the cured product of the adhesive composition for a foldable display can be effectively improved.

[0045] According to one embodiment of the present invention, the weight ratio between the first monomer and the (meth) acrylate-based monomer containing a polar functional group may be 1: 0.025 to 1: 0.1. Specifically, the weight ratio between the first monomer contained in the monomer mixture and the (meth) acrylate-based monomer containing a polar functional group may be 1: 0.03 to 1: 0.08, 1: 0.04 to 1: 0.06, 1: 0.025 to 1: 0.07, 1: 0.035 to 1: 0.05, 1: 0.05 to 1: 0.1 or 1: 0.08 to 1: 0.1. When the weight ratio between the first monomer contained in the monomer mixture and the (meth) acrylate-based monomer containing a polar functional group is within the above range, the low-temperature storage modulus of the cured product of the adhesive composition for a foldable display can be effectively reduced. In addition, the cured product can be suppressed from having crystallinity, thereby improving the folding properties of the adhesive layer containing the cured product.

[0046] According to one embodiment of the present invention, the weight ratio between the first monomer and the second monomer may be 1:0.5 to 1:4. Specifically, the weight ratio between the first monomer and the second monomer contained in the monomer mixture may be 1:0.6 to 1:3.7, 1:0.7 to 1:3.5, 1:0.9 to 1:3, 1:1 to 1:2.7, 1:1.5 to 1:2.5, 1:0.5 to 1:3, 1:0.8 to 1:2.5, 1:1 to 1:2, 1:1.5 to 1:4, 1:2 to 1:4 or 1:3 to 1:4. When the weight ratio between the first monomer and the second monomer contained in the monomer mixture is controlled within the above range, the low temperature storage modulus of the cured product of the adhesive composition for foldable display can be effectively reduced. In addition, the cured product of the adhesive composition for foldable display can be suppressed to have crystallinity, thereby effectively improving the folding characteristics of the adhesive layer of the cured product of the adhesive composition for foldable display.

[0047] According to one embodiment of the present invention, the weight ratio of the polar functional group-containing (meth)acrylate-based monomer to the second monomer may be 1:10 to 1:85. Specifically, the weight ratio of the polar functional group-containing (meth)acrylate-based monomer to the second monomer included in the monomer mixture may be 1:15 to 1:80, 1:20 to 1:75, 1:25 to 1:70, 1:30 to 1:65, 1:30 to 1:50, 1:10 to 1:65, 1:15 to 1:60, 1:20 to 1:55, 1:25 to 1:50, 1:30 to 1:45, 1:30 to 1:85, 1:35 to 1:80, 1:40 to 1:75, 1:45 to 1:70, or 1:50 to 1:65. When the weight ratio between the polar functional group-containing (meth)acrylate-based monomer and the second monomer contained in the monomer mixture is within the above range, the low-temperature storage modulus of the cured product of the adhesive composition for a foldable display can be effectively reduced, and the adhesive performance of the cured product of the adhesive composition for a foldable display can be effectively improved.

[0048] According to one embodiment of the present invention, the (meth)acrylate-based polymer may be produced by thermal polymerization. Specifically, the (meth)acrylate-based polymer may be produced by adding a thermal initiator to a monomer mixture and performing thermal polymerization.

[0049] According to one embodiment of the present invention, the (meth)acrylate-based polymer may have a weight average molecular weight of about 1,500,000 g / mol to about 2,500,000 g / mol. Specifically, the weight average molecular weight of the (meth)acrylate-based polymer may be 1,500,000 g / mol to 2,500,000 g / mol, 1,650,000 g / mol to 2,300,000 g / mol, 1,800,000 g / mol to 2,200,000 g / mol, 1,500,000 g / mol to 2,000,000 g / mol, 1,700,000 g / mol to 2,000,000 g / mol, 1,850,000 g / mol to 2,000,000 g / mol, 2,000,000 g / mol to 2,500,000 g / mol, or 2,100,000 g / mol to 2,400,000 g / mol. When the weight average molecular weight of the (meth)acrylate-based polymer is within the above range, the cured product of the adhesive composition for a foldable display can have excellent folding reliability and adhesion. In addition, when the weight average molecular weight of the (meth)acrylate-based polymer is controlled within the above range, the low-temperature storage modulus of the cured product of the adhesive composition for a foldable display can be effectively reduced while maintaining the storage modulus of the cured product at room temperature.

[0050] According to one embodiment of the present invention, the adhesive composition for a foldable display may further include an epoxide-based crosslinking agent. As the epoxide-based crosslinking agent, any epoxide-based crosslinking agent used in the art may be used without limitation. Specifically, a multifunctional epoxy compound may be used as the epoxide-based crosslinking agent, and the multifunctional epoxy compound may include at least one of a diphenylmethane skeleton, a dinaphthalene skeleton, a triazine skeleton, and a biphenyl skeleton.

[0051] In addition, the epoxide-based crosslinking agent may include at least one of ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N,N,N',N'-tetraglycidylethylenediamine, and glycerol diglycidyl ether, but the type of the epoxide-based crosslinking agent is not limited thereto. For example, BXX-5240 may be used as the epoxide-based crosslinking agent.

[0052] According to one embodiment of the present invention, based on 100 parts by weight of the (meth) acrylate-based polymer, the content of the epoxide-based cross-linking agent may be 0.01 parts by weight to 0.1 parts by weight. Specifically, based on 100 parts by weight of the (meth) acrylate-based polymer, the content of the epoxide-based cross-linking agent may be 0.01 parts by weight to 0.07 parts by weight, 0.01 parts by weight to 0.05 parts by weight, or 0.01 parts by weight to 0.03 parts by weight. When the content of the epoxide-based cross-linking agent is controlled within the above range, the curing reaction of the (meth) acrylate-based polymer contained in the adhesive composition for a foldable display can be effectively carried out.

[0053] According to one embodiment of the present invention, the adhesive composition for a foldable display may further include a solvent. As the solvent, any solvent used in the art may be used without limitation. For example, the solvent may include at least one of methyl ethyl ketone, ethyl acetate, toluene, xylene, benzene, cyclohexane, and cycloheptane, but the type of solvent is not limited thereto.

[0054] According to one embodiment of the present invention, the adhesive composition for a foldable display may further include additives. For example, the additives may include at least one of a release control agent, an additional cross-linking agent, an antistatic agent, a tackifying resin, a curing agent, a UV stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, a defoaming agent, and a surfactant, but the type of additive is not limited thereto.

[0055] According to one embodiment of the present invention, the solid content of the adhesive composition for foldable display can be 10 wt % to 30 wt %. The term "solid content" may refer to the components included in the adhesive composition for foldable display except the solvent. For example, the solid content may include a (meth) acrylate-based polymer and an epoxide-based cross-linking agent included in the adhesive composition for foldable display. The adhesive composition for foldable display that meets the above-mentioned solid content can have a suitable viscosity and therefore can have excellent coating characteristics.

[0056] According to one embodiment of the present invention, the viscosity of the adhesive composition for a foldable display may be 500 cp to 2,500 cp. Specifically, the viscosity of the adhesive composition for a foldable display at 25°C may be 500 cp to 2,500 cp, 700 cp to 2,300 cp, or 850 cp to 2,200 cp. The adhesive composition for a foldable display having a viscosity within the above range may have excellent coating properties.

[0057] Another embodiment of the present invention provides an adhesive film for a foldable display including an adhesive layer including a cured product of the adhesive composition for a foldable display.

[0058] The adhesive film for a foldable display according to one embodiment of the present invention may have excellent folding reliability under room temperature and sub-zero temperature conditions.

[0059] According to one embodiment of the present invention, an adhesive film for a foldable display may include a release film and an adhesive layer comprising a cured product of an adhesive composition for a foldable display disposed on the release film. As the release film, any release film used in the art may be selected and used without limitation. For example, a polyester film treated with a silicone release agent may be used as the release film.

[0060] According to one embodiment of the present invention, the adhesive layer may include a thermally cured product of an adhesive composition for a foldable display. For example, the adhesive layer may be formed by applying the adhesive composition for a foldable display to a release film and thermally curing the applied adhesive composition at a temperature of 100° C. to 150° C. for 1 to 5 minutes.

[0061] According to one embodiment of the present invention, the thickness of the adhesive layer may be 10 μm to 100 μm. Specifically, the thickness of the adhesive layer may be 15 μm to 80 μm, 20 μm to 65 μm, or 25 μm to 50 μm. When the thickness of the adhesive layer is within the above range, the adhesive layer can exhibit excellent adhesion and folding properties when applied to a foldable display.

[0062] According to one embodiment of the present invention, the storage modulus of the adhesive layer as measured at -20°C may be 100,000 Pa or less. Specifically, the storage modulus of the adhesive layer as measured at a temperature of -20°C and a frequency of 1 Hz may be 30,000 Pa to 100,000 Pa. More specifically, the storage modulus of the adhesive layer as measured at a temperature of -20°C and a frequency of 1 Hz may be 35,000 Pa to 98,000 Pa, 40,000 Pa to 98,000 Pa, 43,000 Pa to 98,000 Pa, 45,000 Pa to 95,000 Pa, 50,000 Pa to 90,000 Pa, 55,000 Pa to 85,000 Pa, 60,000 Pa to 80,000 Pa, 65,000 Pa to 7 5,000 Pa, 30,000 Pa to 65,000 Pa, 35,000 Pa to 63,000 Pa, 40,000 Pa to 61,000 Pa, 45,000 Pa to 59,000 Pa, 60,000 Pa to 100,000 Pa, 61,000 Pa to 98,000 Pa, 63,000 Pa to 95,000 Pa, 65,000 Pa to 90,000 Pa, or 70,000 Pa to 85,000 Pa. When the storage modulus of the adhesive layer at -20°C is within the above range, the adhesive layer can exhibit excellent folding properties even at low temperatures.

[0063] According to one embodiment of the present invention, the storage modulus of the adhesive layer as measured at 25°C may be 10,000 Pa or higher. Specifically, the storage modulus of the adhesive layer as measured at a temperature of 25°C and a frequency of 1 Hz is 10,000 Pa to 40,000 Pa. More specifically, the storage modulus of the adhesive layer as measured at a temperature of 25°C and a frequency of 1 Hz may be 10,000 Pa to 37,000 Pa, 10,000 Pa to 36,000 Pa, 15,000 Pa to 35,000 Pa, 20,000 Pa to 30,000 Pa, 10,000 Pa to 30,000 Pa, 12,000 Pa to 28,000 Pa, 1 5,000 Pa to 26,000 Pa, 17,000 Pa to 25,000 Pa, 20,000 Pa to 24,000 Pa, 20,000 Pa to 40,000 Pa, 20,000 Pa to 36,000 Pa, 22,000 Pa to 34,000 Pa, 24,000 Pa to 31,000 Pa, or 25,000 Pa to 28,000 Pa. The adhesive layer having a storage modulus at 25° C. satisfying the above range may have excellent folding characteristics and thus may effectively relieve stress applied to components of a foldable display.

[0064] According to one embodiment of the present invention, the storage modulus of the adhesive layer at -20°C and the storage modulus at 25°C can be measured using the ARES-G2 rheometer as described above.

[0065] Therefore, the adhesive layer according to one embodiment of the present invention may have excellent folding characteristics and thus may be easily applied to a foldable display.

[0066] Embodiments of the invention

[0067] Hereinafter, the present invention will be described in detail with reference to examples.

[0068] Example 1

[0069] Production of (meth)acrylate-based polymers

[0070] Lauryl acrylate as a first monomer, 2-ethylhexyl acrylate as a second monomer, and acrylic acid as a polar functional group-containing (meth)acrylate-based monomer were prepared and mixed together to obtain a monomer mixture.

[0071] In this case, the first monomer was included in an amount of 20 parts by weight, the second monomer was included in an amount of 79 parts by weight, and the polar functional group-containing (meth)acrylate-based monomer was included in an amount of 1 part by weight, based on 100 parts by weight of the monomer mixture.

[0072] The monomer mixture was added to a 1-L reactor in which nitrogen was refluxed and equipped with a cooling device for easy temperature control, followed by the addition of ethyl acetate (EAc) as a solvent. The reactor was then purged with nitrogen for approximately 1 hour to remove oxygen, and the reactor temperature was maintained at 85° C. After homogenizing the monomer mixture, 5,000 ppm of benzoyl peroxide (BPO) was added as a reaction initiator, and the monomer mixture was allowed to react for 6 hours, thereby producing a (meth)acrylate-based polymer having a weight-average molecular weight of 1,850,000 g / mol. A (meth)acrylate-based polymer solution was prepared by diluting the (meth)acrylate-based polymer with ethyl acetate.

[0073] Preparation of adhesive composition for foldable displays

[0074] To the (meth)acrylate-based polymer solution prepared as described above, BXX-5240 as an epoxide-based crosslinking agent was added in an amount of 0.03 parts by weight based on 100 parts by weight of the (meth)acrylate-based polymer. The resulting mixture was diluted with methyl ethyl ketone and methyl isobutyl ketone and mixed using a mechanical stirrer for 15 minutes or longer. Thereafter, the mixture was allowed to stand at room temperature (25°C) to remove bubbles generated during mixing, thereby preparing an adhesive composition for a foldable display having a solid content of 22% by weight and a viscosity of about 1,500 cp at 25°C.

[0075] Production of adhesive films for foldable displays

[0076] A coating of the adhesive composition for foldable displays prepared above was formed on a silicone release-treated polyester film using a knife coater. The coating was then dried in a Mathis oven at 140°C for 3 minutes. This produced an adhesive film for foldable displays comprising a 25 μm thick adhesive layer.

[0077] Examples 2 to 17

[0078] A (meth)acrylate-based polymer, an adhesive composition for a foldable display, and an adhesive film for a foldable display were produced in the same manner as in Example 1, except that a monomer mixture was prepared as shown in Table 1 below.

[0079] The weight average molecular weight (Mw) of the produced (meth)acrylate-based polymer is shown in Table 1 below.

[0080] Comparative Examples 1 to 7

[0081] A (meth)acrylate-based polymer, an adhesive composition for a foldable display, and an adhesive film for a foldable display were produced in the same manner as in Example 1, except that a monomer mixture was prepared as shown in Table 1 below.

[0082] The weight average molecular weight (Mw) of the produced (meth)acrylate-based polymer is shown in Table 1 below.

[0083] Comparative Example 8

[0084] Production of (meth)acrylate-based polymers

[0085] Lauryl acrylate as a first monomer, 2-ethylhexyl acrylate as a second monomer, and acrylic acid as a polar functional group-containing (meth)acrylate-based monomer were prepared and mixed together to obtain a monomer mixture.

[0086] In this case, the first monomer was included in an amount of 20 parts by weight, the second monomer was included in an amount of 79 parts by weight, and the polar functional group-containing (meth)acrylate-based monomer was included in an amount of 1 part by weight, based on 100 parts by weight of the monomer mixture.

[0087] The monomer mixture was added to a 1-L reactor in which nitrogen was refluxed and equipped with a cooling device for easy temperature control, followed by the addition of ethyl acetate (EAc) as a solvent. The reactor was then purged with nitrogen for approximately 1 hour to remove oxygen, and the reactor temperature was maintained at 85° C. After homogenizing the monomer mixture, 5,000 ppm of benzoyl peroxide (BPO) was added as a reaction initiator, and the monomer mixture was allowed to react for 3 hours, thereby producing a (meth)acrylate-based polymer having a weight-average molecular weight of 500,000 g / mol. A (meth)acrylate-based polymer solution was prepared by diluting the (meth)acrylate-based polymer with ethyl acetate.

[0088] Preparation of adhesive composition for foldable displays

[0089] To the (meth)acrylate-based polymer solution prepared as described above, BXX-5240 as an epoxide-based crosslinking agent was added in an amount of 0.03 parts by weight based on 100 parts by weight of the (meth)acrylate-based polymer. The resulting mixture was diluted with methyl ethyl ketone and methyl isobutyl ketone and mixed using a mechanical stirrer for 15 minutes or longer. Thereafter, the mixture was allowed to stand at room temperature (25°C) to remove bubbles generated during mixing, thereby preparing an adhesive composition for a foldable display having a solid content of 22% by weight and a viscosity of about 200 cp at 25°C.

[0090] However, the weight average molecular weight of the (meth)acrylate-based polymer prepared in Comparative Example 8 was 500,000 g / mol, and the viscosity of the adhesive composition for a foldable display prepared in Comparative Example 8 was about 200 cp at 25° C. Therefore, in the process of forming a coating layer of the adhesive composition for a foldable display on the silicone release-treated polyester film by a knife coater, dewetting occurred due to the low viscosity of the composition, making coating impossible.

[0091] Comparative Example 9

[0092] Production of (meth)acrylate-based polymers

[0093] Lauryl acrylate as a first monomer, 2-ethylhexyl acrylate as a second monomer, and acrylic acid as a polar functional group-containing (meth)acrylate-based monomer were prepared and mixed together to obtain a monomer mixture.

[0094] In this case, the first monomer was included in an amount of 20 parts by weight, the second monomer was included in an amount of 79 parts by weight, and the polar functional group-containing (meth)acrylate-based monomer was included in an amount of 1 part by weight, based on 100 parts by weight of the monomer mixture.

[0095] The monomer mixture was added to a 1-L reactor with nitrogen reflux. The reactor was then purged with nitrogen for approximately 1 hour to remove oxygen. Next, after homogenizing the monomer mixture, approximately 500 ppm of a reaction initiator (Irgacure 184) was added. The monomer mixture was then subjected to bulk polymerization under UV light, thereby producing a (meth)acrylate-based polymer having a weight-average molecular weight of 3,000,000 g / mol. A (meth)acrylate-based polymer solution was prepared by diluting the (meth)acrylate-based polymer with ethyl acetate.

[0096] Preparation of adhesive composition for foldable displays

[0097] To the (meth)acrylate-based polymer solution prepared as described above, BXX-5240 as an epoxide-based crosslinking agent was added in an amount of 0.03 parts by weight based on 100 parts by weight of the (meth)acrylate-based polymer. The resulting mixture was diluted with methyl ethyl ketone and methyl isobutyl ketone and mixed using a mechanical stirrer for 15 minutes or longer. Thereafter, the mixture was allowed to stand at room temperature (25°C) to remove bubbles generated during mixing, thereby preparing an adhesive composition for a foldable display having a solid content of 22% by weight and a viscosity of about 20,000 cp at 25°C.

[0098] However, the weight average molecular weight of the (meth)acrylate-based polymer prepared in Comparative Example 9 was 3,000,000 g / mol, and the viscosity of the adhesive composition for a foldable display prepared in Comparative Example 9 was about 20,000 cp at 25° C. Therefore, in the process of forming a coating layer of the adhesive composition for a foldable display on the silicone release-treated polyester film by a doctor blade coater, a thickness unevenness phenomenon occurred significantly due to the high viscosity of the composition, making coating impossible.

[0099] [Table 1]

[0100]

[0101] In Table 1 above, "LA" represents lauryl acrylate, "TDMA" represents tetradecyl methacrylate, "2-EHA" represents 2-ethylhexyl acrylate, "BA" represents butyl acrylate, "AA" represents acrylic acid, and "HBA" represents hydroxybutyl acrylate.

[0102] Furthermore, in Table 1 above, each content of the first monomer, the second monomer, and the polar functional group-containing monomer is based on 100 parts by weight of the monomer mixture, and the content of the crosslinking agent is based on 100 parts by weight of the (meth)acrylate-based polymer.

[0103] Experimental example

[0104] Storage modulus measurement

[0105] The storage modulus of the adhesive layers produced in Examples 1 to 17 and Comparative Examples 1 to 4 at -20°C and 25°C was measured using an Advanced Rheometric Expansion System G2 rheometer (TA Instruments) as follows.

[0106] Specifically, a sample was prepared by laminating to a thickness of 1 mm the adhesive layer produced in Example 1. Then, using a parallel plate jig having a diameter of 8 mm, the storage modulus of the sample at each of -20°C and 25°C was measured.

[0107] <Measurement Conditions>

[0108] Strain: 5%

[0109] Frequency: 1Hz

[0110] Initial temperature: -40°C; final temperature: 90°C

[0111] Heating rate: 10°C / min

[0112] Furthermore, the storage moduli at -20°C and 25°C of the adhesive layers produced in Examples 2 to 17 and Comparative Examples 1 to 7 were measured in the same manner as above, and the results of the measurements are shown in Table 2 below.

[0113] Folding Evaluation

[0114] Folding evaluation of each of the adhesive layers produced in Examples 1 to 17 and Comparative Examples 1 to 7 was performed as follows.

[0115] Figure 1 is a schematic diagram showing samples used for folding evaluation.

[0116] like Figure 1As shown, using the adhesive layer (PSA) produced in each of Examples 1 to 17 and Comparative Examples 1 to 7, a colorless polyimide (CPI) having a thickness of 40 μm was bonded to a cover window (LG Chem Ltd.) including a 13 μm thick hard coating layer (HC) formed on one surface of a 50 μm thick PET, thereby producing a laminate.

[0117] Thereafter, a sample was prepared by cutting a laminate having a laminate structure of cover window (HC / PET) / adhesive layer (PSA) / CPI into a size of 140 mm×80 mm.

[0118] Figure 2 Schematic diagram showing the folding test.

[0119] like Figure 2 As shown, under the temperature condition of -20°C, the sample was clamped between the parallel plates of the folding test device and folded once per second at a curvature radius of 5 mm. In this way, a dynamic folding test consisting of a total of 200,000 folding cycles was performed.

[0120] After the test was completed, the sample was collected and visually observed for bubbling, lifting, and cracking of the hard coating. If there was no bubbling or lifting of the hard coating and no cracking of the hard coating, the sample was evaluated as "OK". If there was bubbling, lifting, or cracking of the hard coating, the sample was evaluated as "NG". The results of the evaluation are shown in Table 2 below.

[0121] [Table 2]

[0122]

[0123] With reference to Tables 1 and 2 above, it was determined that the adhesive layers produced in Examples 1 to 17 of the present invention all satisfied a storage modulus of 100,000 Pa or less as measured at -20°C, indicating that the results of the folding evaluation of the samples at -20°C were excellent. In addition, it was determined that the adhesive layers produced in Examples 1 to 17 all had a storage modulus of 10,000 Pa or more as measured at 25°C.

[0124] On the other hand, it was determined that both the adhesive layer of Comparative Example 1 produced without using the first monomer LA and the adhesive layer of Comparative Example 2 produced without using the second monomer 2-EHA had a storage modulus as measured at -20°C of higher than 100,000 Pa, indicating that the result of the folding evaluation performed at -20°C was poor.

[0125] In addition, it was determined that in the case of the adhesive layers produced in Comparative Examples 3 and 4 in which the contents of the first monomer and the second monomer did not satisfy the content range according to the embodiment of the present invention, the storage modulus as measured at -20°C was higher than 100,000 Pa, indicating that the result of the folding evaluation performed at -20°C was poor.

[0126] Meanwhile, it was confirmed that in the case of Comparative Example 5 in which a hydroxyl group-containing (meth)acrylate-based monomer was used as the polar functional group-containing (meth)acrylate-based monomer, the storage modulus at -20°C and 25°C was appropriate, but the result of the folding evaluation performed at -20°C was poor.

[0127] Furthermore, it was confirmed that in the case of Comparative Examples 6 and 7 in which the content of the polar functional group-containing (meth)acrylate-based monomer was too high or too low, the result of the folding evaluation performed at -20°C was poor.

[0128] Therefore, it can be seen that the adhesive composition for a foldable display according to one embodiment of the present invention can provide an adhesive layer having excellent folding characteristics even under low temperature conditions such as -20°C.

Claims

1. An adhesive composition for a foldable display, comprising a (meth)acrylate-based polymer that is a reaction product of a monomer mixture, the monomer mixture comprising, based on 100 parts by weight of the monomer mixture: 20 to 60 parts by weight of a first monomer including at least one of a first acrylate-based monomer including an alkyl group having 12 to 14 carbon atoms and a first methacrylate-based monomer including an alkyl group having 14 to 16 carbon atoms; 35 parts by weight to 80 parts by weight of a second monomer including at least one of a second acrylate-based monomer including an alkyl group having 3 to 10 carbon atoms and a second methacrylate-based monomer including an alkyl group having 8 to 12 carbon atoms; and 1 to 4 parts by weight of a polar functional group-containing (meth)acrylate-based monomer, the polar functional group-containing (meth)acrylate-based monomer including a carboxylic acid group. 2 . The adhesive composition according to claim 1 , wherein a weight ratio between the first monomer and the polar functional group-containing (meth)acrylate-based monomer is 1:0.025 to 1:0.

1. 3 . The adhesive composition according to claim 1 , wherein a weight ratio between the first monomer and the second monomer is 1:0.5 to 1:

4. 4 . The adhesive composition of claim 1 , wherein a weight ratio between the polar functional group-containing (meth)acrylate-based monomer and the second monomer is 1:10 to 1:

85.

5. The adhesive composition of claim 1, further comprising an epoxide-based crosslinking agent. 6 . The adhesive composition according to claim 5 , wherein the epoxide-based crosslinking agent is included in an amount of 0.01 to 0.1 parts by weight based on 100 parts by weight of the (meth)acrylate-based polymer. 7 . The adhesive composition of claim 1 , wherein the (meth)acrylate-based polymer has a weight average molecular weight of 1,500,000 g / mol to 2,500,000 g / mol. 8 . An adhesive film for a foldable display, comprising an adhesive layer comprising a cured product of the adhesive composition for a foldable display according to claim 1 . 9 . The adhesive film according to claim 8 , wherein the adhesive layer has a storage modulus as measured at −20° C. of 100,000 Pa or less. 10 . The adhesive film according to claim 8 , wherein the adhesive layer has a storage modulus as measured at 25° C. of 10,000 Pa or more.

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