Photo-curable adhesive film and method for preparing the same

Abstract

The present invention relates to a photocurable adhesive film and a method for preparing the same, and provides an adhesive film having excellent peeling adhesion and creep resistance at both room temperature and high temperature and low modulus at a low temperature of -20°C by using an acrylic monomer having a specific structure within a specific content range. Furthermore, since the adhesive film of the present invention can provide folding reliability and stability of a display device, the adhesive film can be effectively used as an adhesive for a display device, particularly, in the field of foldable display devices.

Description

Background Technology

[0001] This disclosure relates to a photocurable adhesive film and a method for preparing the same.

[0002] Display-related technologies have evolved from smartphones to touchscreens in vehicles and control devices. Recently, there has been increased interest in foldable displays that can be bent freely without cracking or breaking.

[0003] For example, with the emergence of such foldable displays, the demand for adhesives, specifically optically clear adhesives (OCA), has increased. These adhesives are used as assembly layers or gap-filling layers between the exterior, cover glass, or sheet of electronic display components based on glass, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polyimide (PI), polyethylene naphthalate (PEN), cyclic olefin copolymers, etc., and the lower display module.

[0004] For example, in addition to conventional properties such as optical transparency, adhesion and durability, depending on the diverse properties of the display, adhesives with the following adhesive functions and physical properties are also required.

[0005] First, the adhesive needs to have excellent peel adhesion at high temperatures; second, it needs to have excellent creep resistance at high temperatures; and third, it needs to have low modulus at low temperatures.

[0006] To meet these requirements, adhesive compositions using acrylic monomers such as acrylic acid have been studied. However, while peel adhesion is improved, there are problems such as low creep resistance or increased modulus at low temperatures. As a result, there are limitations in applying the adhesive to a variety of displays.

[0007] Existing technical documents

[0008] Patent documents

[0009] (Patent Document 1) Korean Patent Registration No. 0476798 Summary of the Invention

[0010] Therefore, one object of the present invention is to provide an adhesive film and a method for preparing the same, which, when applied to foldable displays, provides folding reliability and stability of the display device through excellent peel adhesion and creep resistance at both room temperature and high temperature, and low modulus at low temperature.

[0011] To achieve this objective, according to one aspect of the invention, a photocurable adhesive film is provided, comprising an adhesive layer and at least one release layer, wherein the adhesive layer is induced by a photocurable adhesive composition comprising: a prepolymer; an acrylic monomer having the following structural formula; an initiator; and a crosslinking agent, and based on 100 parts by weight of the prepolymer, the photocurable adhesive composition comprises 0.5 parts by weight to 10 parts by weight of the acrylic monomer:

[0012] [Structured Formula]

[0013]

[0014] Where n is an integer from 1 to 3.

[0015] According to another aspect of the present invention, a method for preparing a photocurable adhesive film is provided, the method comprising preparing at least one release layer; and forming an adhesive layer by coating the at least one release layer with a photocurable adhesive composition, wherein the photocurable adhesive composition comprises a prepolymer; an acrylic monomer having the following structural formula; an initiator; and a crosslinking agent, and the photocurable adhesive composition comprises 0.5 parts by weight to 10 parts by weight of the acrylic monomer based on 100 parts by weight of the prepolymer.

[0016] The photocurable adhesive film of the present invention maintains excellent peel adhesion at both room temperature and high temperature, excellent creep resistance at high temperature, and low modulus at a low temperature of -20°C.

[0017] Furthermore, since the adhesive film of the present invention provides folding reliability and stability for the display device, the adhesive film can be effectively used as an adhesive for the display device, specifically an adhesive in the field of foldable displays. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of an adhesive film according to one embodiment of the present invention.

[0019] Figure 2 The illustration schematically shows a method for preparing an adhesive film according to one embodiment of the present invention.

[0020] Figure 3 The illustration schematically shows a method for preparing a photocurable adhesive composition according to one embodiment of the present invention. Detailed Implementation

[0021] The advantages and features of the present invention, as well as the methods for implementing them, will become apparent from the embodiments described in detail below with reference to the accompanying drawings. However, the invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. That is, these embodiments are provided for the sake of completeness of the disclosure and to fully inform those skilled in the art of the scope of the invention, and the invention is limited only by the scope of the appended claims.

[0022] The shapes, dimensions, ratios, angles, quantities, etc., shown in the accompanying drawings to illustrate the invention are merely exemplary, and the invention is not limited to the details shown in the drawings. Furthermore, in describing the invention, detailed descriptions of known related technologies will be omitted where it is determined that this unnecessarily obscures the subject matter.

[0023] Terms such as “comprising,” “having,” and “including” used herein are generally intended to allow for the addition of components other than those described in the details, unless the terms are used with “only.” When a component is referred to in the singular, it may include the plural form unless otherwise expressly stated.

[0024] Unless otherwise expressly stated, components should be interpreted as including tolerance ranges.

[0025] When terms such as “above,” “below,” “above,” “under,” and “between” are used to describe the positional relationship between two parts, one or more other parts may be positioned between them, unless they are used with the expression “immediately” or “directly.”

[0026] The features of the embodiments of the present invention may be connected or combined with each other in part or in whole, and may be interlocked or driven in various technical ways.

[0027] Embodiments of the present invention will be described in detail below. The following embodiments are provided as examples to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the embodiments described below and may be implemented in different forms.

[0028] Photocurable adhesive film

[0029] A photocurable adhesive film according to an exemplary embodiment of the present invention comprises an adhesive layer and at least one release layer, wherein the adhesive layer is induced by a photocurable adhesive composition comprising: a prepolymer; an acrylic monomer having the following structural formula; an initiator; and a crosslinking agent, and the photocurable adhesive composition comprises, based on 100 parts by weight of the prepolymer, 0.5 parts by weight to 10 parts by weight of the acrylic monomer.

[0030] [Structured Formula]

[0031]

[0032] Where n is an integer from 1 to 3.

[0033] Because the adhesive layer is induced by a photocurable adhesive composition comprising a prepolymer, an acrylic monomer having a specific structure, an initiator, and a crosslinking agent, and specifically, the acrylic monomer having a specific structure has a specific content, the photocurable adhesive film according to an exemplary embodiment of the present invention maintains excellent peel adhesion at both room temperature and high temperature, excellent creep resistance at high temperature, and low modulus at a low temperature of -20°C. Therefore, since the photocurable adhesive film provides folding reliability and stability for display devices when applied to displays, it can be effectively used as a pressure-sensitive adhesive (PSA) in display devices (e.g., foldable displays).

[0034] In this application, the term "foldable display" may refer to a flexible display designed to be repeatedly folded and unfolded like paper, and having folded portions with a curvature radius within 5 mm.

[0035] Each building layer in the photocurable adhesive film will be described in detail below.

[0036] Adhesive layer

[0037] A photocurable adhesive film according to an exemplary embodiment of the present invention includes an adhesive layer.

[0038] For example, when applied to displays, the adhesive layer can serve as an assembly layer or gap-filling layer between the cover glass or sheet of an electronic display assembly based on glass, PET, PC, PMMA, polyimide, PEN, cyclic olefin copolymers, etc., and the underlying display module. Furthermore, the adhesive layer can increase brightness and contrast to improve display performance, and can serve as a structural support for the assembly, protecting components by absorbing stresses applied by folding to prevent damage or destruction to the display panel components.

[0039] In a photocurable adhesive film according to an exemplary embodiment of the present invention, the adhesive layer is induced by a photocurable adhesive composition comprising a prepolymer, an acrylic monomer having a structural formula, an initiator, and a crosslinking agent.

[0040] Specifically, the adhesive layer can be formed by coating and curing the photocurable adhesive composition onto one surface of at least one release layer. For example, the adhesive layer can be formed by a photocurable photocurable adhesive composition.

[0041] According to an exemplary embodiment of the present invention, the photocurable adhesive composition for forming an adhesive layer comprises an acrylic monomer having a specific structural formula to achieve the desired effect of the present invention.

[0042] Typically, using polar monomers with carboxyl groups in the adhesive layer, such as acrylic acid (AA), can increase peel adhesion. However, to meet the required peel adhesion within a specific or broader range, the amount of monomer used needs to be increased. However, increasing the amount of monomer can significantly increase the modulus at low temperatures. Specifically, to absorb the additional stress in the adhesive layer, it is necessary to reduce the modulus of the adhesive layer at low temperatures, and increasing the modulus is not preferred because it may cause deformation or defects (such as cracks and delamination).

[0043] According to an exemplary embodiment of the present invention, the acrylic monomer is a polar monomer comprising a carboxyl group and a carbonyl group, and containing an ethyl group between the carboxyl group and the carbonyl group. Such structural features can benefit improved creep resistance while increasing peel adhesion at both room temperature and high temperature.

[0044] Furthermore, although the amount of acrylic monomers is increased within the range of exemplary embodiments of the present invention, low modulus at low temperatures and excellent creep resistance at high temperatures can be maintained, while improved peel adhesion is achieved.

[0045] In this structural formula, when n is 0, the modulus may increase, leading to deformation or defects (such as cracks and delamination). Furthermore, when n is 4 or higher, there may be issues with reduced creep resistance or decreased peel adhesion.

[0046] In addition, acrylic monomers may have a glass transition temperature (Tg) of 10°C to 50°C, for example, 20°C to 45°C, or 25°C to 43°C. When acrylic monomers have a glass transition temperature (Tg) within this range, an adhesive layer with low modulus at low temperatures of -20°C can be provided.

[0047] Acrylic monomers may include, for example, β-carboxyethyl acrylate (β-CEA).

[0048] Compared to other functional monomers with n=0, such as acrylic acid (AA) (referred to as β-CEA oligomers when n=1 to 3), β-CEA is a very flexible monomer with a glass transition temperature of approximately 37°C. These structural and physical characteristics of β-CEA specifically play a crucial role in improving peel adhesion and creep resistance at room and high temperatures, as well as reducing modulus at low temperatures. Furthermore, when the adhesive layer is applied to foldable displays, it exhibits excellent durability when repeatedly folded and unfolded hundreds of thousands or more times, for example, at room temperature, -20°C, and 60°C or higher.

[0049] Based on 100 parts by weight of prepolymer, acrylic monomers may be included in an amount of 0.5 parts by weight to 10 parts by weight. Specifically, based on 100 parts by weight of prepolymer, acrylic monomers may be included in an amount of 1 to 10 parts by weight, 1 to 8 parts by weight, 3 to 8 parts by weight, 3 to 6.5 parts by weight, 5 to 10 parts by weight, 5 to 8 parts by weight, or 5 to 7 parts by weight.

[0050] When acrylic monomers fall within this range, the desired effects of the exemplary embodiments of the invention can be advantageously achieved, namely, excellent peel adhesion and creep resistance at room and high temperatures, and the full desired effect of low modulus at low temperatures. If acrylic monomers are not used, or if they are smaller than this range, peel adhesion and creep resistance may decrease, and when acrylic monomers are larger than this range, the modulus at low temperatures may increase.

[0051] Meanwhile, according to an exemplary embodiment of the present invention, the photocurable adhesive composition comprises a prepolymer.

[0052] Prepolymers can exhibit adhesive properties as a major component of photocurable adhesive compositions. Furthermore, prepolymers can react with crosslinking agents (i.e., crosslink) to form films, etc.

[0053] The prepolymer may contain functional groups that react with the crosslinking agent. For example, the prepolymer may have at least one functional group selected from carboxyl groups, hydroxyl groups, acryloyl groups, methacryloyl groups, acetate groups, amide groups, amine groups, and glycidyl groups.

[0054] For example, the prepolymer can be an acrylic resin.

[0055] Specifically, the prepolymer can be an acrylic copolymer resin.

[0056] The prepolymer can be formed from a prepolymer composition comprising a first monomer and a second monomer.

[0057] The first monomer may include an acrylate monomer based on an aliphatic or aromatic hydrocarbon having 1 to 30 carbon atoms.

[0058] The first monomer may include at least one monomer selected from the following: for example, methyl acrylate, methyl (meth)acrylate, ethyl acrylate, ethyl (meth)acrylate, benzyl (meth)acrylate, n-butyl acrylate, n-butyl (meth)acrylate, sec-butyl acrylate, sec-butyl (meth)acrylate, tert-butyl acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, isodecyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl acrylate, n-hexyl acrylate, isooctyl acrylate, n-octyl acrylate, n-octyl (meth)acrylate, and isobornyl acrylate. The first monomer may include at least one monomer selected from the following: for example, benzyl (meth)acrylate, n-butyl acrylate, n-butyl (meth)acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, n-nonyl acrylate, n-hexyl acrylate, n-octyl acrylate, and n-octyl (meth)acrylate.

[0059] The second monomer may include a functional monomer containing at least one heteroatom. In this case, in addition to C and H, the heteroatom may also include at least one heteroatom selected from N, O, S and P.

[0060] The second monomer may include at least one monomer selected from the following: acrylic acid, vinyl acetate, 2,3-glycidyl (meth)acrylate, dimethacrylamide, acryloylmorpholine, 2-hydroxyethyl acrylate, and 2-hydroxyethyl (meth)acrylate.

[0061] For example, a combination of the first monomer and the second monomer may include 2-ethylhexyl acrylate and acrylic acid; 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate; n-butyl acrylate and acrylic acid; or n-butyl acrylate and 2-hydroxyethyl acrylate.

[0062] Based on the sum of the first monomer and the second monomer (the sum of the monomer mixture), the first monomer may be included in an amount of 90 to 99 parts by weight, preferably 94 to 98 parts by weight. When the content of the first monomer is greater than this range, there may be problems with reduced peel adhesion and creep resistance, and when the content of the first monomer is less than this range, the modulus at low temperature may increase.

[0063] Based on the sum of the first and second monomers, the second monomer may be included in an amount of 1 to 10 parts by weight, preferably 2 to 6 parts by weight. When the content of the second monomer is greater than this range, the modulus at low temperatures may increase. When the content of the second monomer is less than this range, there may be problems with reduced peel adhesion and creep resistance.

[0064] The weight ratio of the first monomer to the second monomer can be from 1:0.01 to 0.1. Specifically, the weight ratio of the first monomer to the second monomer can be from 1:0.01 to 0.09, 1:0.01 to 0.08, 1:0.02 to 0.06, or 1:0.02 to 0.05. When the weight ratio of the first monomer to the second monomer meets the requirements within a specific range, excellent creep resistance at high temperatures and low modulus at low temperatures can be achieved.

[0065] In addition to the first monomer and the second monomer, the prepolymer composition may also contain a first initiator.

[0066] The content of the first initiator may be from 0.001 parts by weight to 1 part by weight, based on 100 parts by weight of the prepolymer composition. Specifically, the content of the first initiator may be from 0.01 parts by weight to 1 part by weight or from 0.1 parts by weight to 0.5 parts by weight, based on 100 parts by weight of the prepolymer composition.

[0067] As the first initiator, a general photoinitiator can be used, and for example, at least one selected from ketones (benzophenone, acetophenone, etc.), benzoin, benzoin ether, benzyl compounds and benzyl ketals can be used as the photoinitiator.

[0068] For example, the photoinitiator may be benzoin ether (e.g., benzoin methyl ether or benzoin isopropyl ether) or a substituted benzoin ether.

[0069] For example, the photoinitiator can be a substituted acetophenone, such as 2,2-diethoxyacetophenone or 2,2-dimethoxy-2-phenylacetophenone.

[0070] For example, photoinitiators can be substituted α-ketones (e.g., 2-methyl-2-hydroxyphenylacetone), aromatic sulfonyl chlorides (e.g., 2-naphthalenesulfonyl chloride), or photooximes (e.g., 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime).

[0071] For example, photoinitiators can be 1-hydroxycyclohexylphenyl ketone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylpropane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, etc.

[0072] Examples of commercially available photoinitiators may include the Ciba IRGACURE series from Ciba Specialty Chemicals Co., Ltd., and the Esacure KIP series from IGM Resins Co., Ltd.

[0073] Depending on the polymerization method to be used, water-soluble or water-insoluble (i.e., oil-soluble) thermal initiators can be selectively used as thermal initiators.

[0074] As water-soluble initiators, the following can be used: persulfates, such as potassium persulfate, ammonium persulfate, sodium persulfate, and mixtures thereof; redox initiators, such as the reaction product of a reducing agent and a persulfate, such as a metabisulfite (e.g., sodium metabisulfite) or a bisulfate (e.g., sodium bisulfate); or 4,4'-azobis(4-cyanopentanoic acid) and its soluble salts (e.g., sodium salts, potassium salts), etc.

[0075] As oil-soluble initiators, azo dyes such as 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile), and 2,2'-azobis(2,4-dimethylpentanonitrile) can be used; or peroxides such as benzoyl peroxide, cyclohexane peroxide, and lauroyl peroxide can be used.

[0076] The viscosity of the prepolymer can be from 1,000 cP to 5,000 cP, preferably from 1,500 cP to 4,500 cP, and more preferably from 2,000 cP to 4,000 cP. When the viscosity of the prepolymer meets the above range, the adhesive properties and physical properties of the adhesive layer can be further improved.

[0077] The weight-average molecular weight (Mw) of the prepolymer can be from 10,000 to 2,000,000. Alternatively, the weight-average molecular weight of the prepolymer can be from 100,000 to 2,000,000. When the weight-average molecular weight of the prepolymer meets the above range, the adhesive properties and physical properties of the adhesive layer can be further improved.

[0078] Furthermore, according to an exemplary embodiment of the present invention, the photocurable adhesive composition includes a second initiator. For example, the photocurable adhesive composition may include a second initiator, specifically a photoinitiator for curing the photocurable adhesive composition.

[0079] Furthermore, the second initiator included in the photocurable adhesive composition may include a class of first initiators used in the prepolymer composition that forms the prepolymer.

[0080] Based on 100 parts by weight of prepolymer, the content of the second initiator can be from 0.05 parts by weight to 0.3 parts by weight. Based on 100 parts by weight of prepolymer, the content of the second initiator can be from 0.05 parts by weight to 0.25 parts by weight, 0.07 parts by weight to 0.2 parts by weight, 0.07 parts by weight to 0.18 parts by weight, or 0.07 parts by weight to 0.14 parts by weight. When the content of the second initiator is less than the above range, the content of residual monomers after the photocurable reaction is high, thus reducing the peel adhesion. And when the content of the second initiator is equal to or greater than the above range, the molecular weight of the polymer produced after the photocurable reaction is small, thus resulting in low creep resistance. When the content of the second initiator meets the above range, it is advantageous to form a photocurable adhesive with a high molecular weight.

[0081] Furthermore, according to an exemplary embodiment of the present invention, the photocurable adhesive composition comprises a crosslinking agent.

[0082] Crosslinking agents can react with prepolymers to form films, etc.

[0083] Based on 100 parts by weight of the prepolymer, the content of the crosslinking agent in the composition can be from 0.01 parts by weight to 0.5 parts by weight. Specifically, based on 100 parts by weight of the prepolymer, the content of the crosslinking agent in the composition can be from 0.05 parts by weight to 0.25 parts by weight, preferably from 0.07 parts by weight to 0.2 parts by weight, more preferably from 0.08 parts by weight to 0.2 parts by weight or from 0.08 parts by weight to 0.15 parts by weight.

[0084] The crosslinking agent may contain functional groups that react with the functional groups of the prepolymer.

[0085] For example, the crosslinking agent may have one or at least two functional groups selected from epoxy groups, isocyanate groups, carboxyl groups, hydroxyl groups, acryloyl groups, methacryloyl groups, acetate groups, and vinyl groups.

[0086] As a specific example, the crosslinking agent may have an epoxy group or an isocyanate group.

[0087] Crosslinking agents can be photocrosslinking agents, thermal crosslinking agents, or combinations thereof.

[0088] As a photocrosslinking agent, common multifunctional acrylic compounds can be used.

[0089] For example, the photocrosslinker may be at least one selected from diacrylates and triacrylates. Specific examples of photocrosslinkers may include 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate (HDDA), 1,9-nonanediol diacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

[0090] The thermal crosslinking agent can be an isocyanate-based compound, an epoxy resin-based compound, or a metal chelate-based compound.

[0091] Isocyanate-based compounds can be polyfunctional aromatic or aliphatic isocyanate compounds. For example, isocyanate-based compounds can be triisocyanates, such as toluene diisocyanate-trimethylolpropane (TDI-TMP) adducts.

[0092] Epoxy resin-based compounds may have one or at least two epoxy groups and may have functional groups that react with the prepolymer.

[0093] Metal chelate-based compounds can be chelate-based compounds containing metals such as Zn, Ni, Mn, Fe, Co, Cr, Al, Ti, or Zr.

[0094] Examples of commercially available thermal crosslinking agents may include the Saivinol curing agent series from Saiden Chemical Industry Co., Ltd.

[0095] The light-curable adhesive composition according to the exemplary embodiment may also contain other additives as needed.

[0096] Specific examples of additives include tackifiers (such as rosin esters, terpenes, phenols and aliphatic synthetic hydrocarbon resins, aromatic synthetic hydrocarbon resins, or mixtures of aliphatic and aromatic synthetic hydrocarbon resins), surfactants, plasticizers (other than physical foaming agents), nucleating agents (such as talc, silica, or TiO2), fillers (such as inorganic and organic fillers), fibers, aging inhibitors, antioxidants, UV absorbers, antistatic agents, lubricants, pigments, dyes, reinforcing agents, hydrophobic or hydrophilic silica, calcium carbonate, toughening agents, flame retardants, finely ground polymer particles (such as polyester, nylon, or polypropylene), stabilizers (such as UV stabilizers), and combinations thereof.

[0097] The amount of additive is not specifically limited to an appropriate amount that can achieve the desired properties of the composition, but may be, for example, 0.1 to 10 parts by weight or 0.1 to 5 parts by weight based on 100 parts by weight of prepolymer.

[0098] The photocurable adhesive composition according to the exemplary embodiments can be configured such that the various components illustrated above have specific amounts.

[0099] According to one example, the photocurable adhesive composition may comprise 100 parts by weight of a prepolymer, 0.5 to 10 parts by weight of an acrylic monomer, 0.01 to 0.5 parts by weight of a crosslinking agent, and 0.05 to 0.3 parts by weight of a second initiator.

[0100] According to another example, the photocurable adhesive composition may comprise 100 parts by weight of a prepolymer, 1 to 8 parts by weight of an acrylic monomer, 0.05 to 0.25 parts by weight of a crosslinking agent, and 0.05 to 0.25 parts by weight of a second initiator.

[0101] According to yet another example, the photocurable adhesive composition may comprise 100 parts by weight of a prepolymer, 3 to 8 parts by weight of an acrylic monomer, 0.07 to 0.2 parts by weight of a crosslinking agent, and 0.07 to 0.2 parts by weight of a second initiator.

[0102] The photocurable adhesive composition may comprise 100 parts by weight of a prepolymer, 3 to 6.5 parts by weight of an acrylic monomer, 0.08 to 0.2 parts by weight of a crosslinking agent, and 0.07 to 0.18 parts by weight of a second initiator.

[0103] In this case, the content of the components in the adhesive composition can be based on the solid content.

[0104] Also see Figure 3 The method for preparing a photocurable adhesive composition according to an exemplary embodiment of the present invention (S200) may include preparing a prepolymer composition by mixing a first monomer, a second monomer and a first initiator (S210); preparing a prepolymer by prepolymerizing the prepolymer composition (S220); and mixing the prepolymer, an acrylic monomer, a second initiator and a crosslinking agent (S230).

[0105] Furthermore, the photocurable adhesive composition can also be prepared by further mixing in other additives as needed.

[0106] In addition, the viscosity can be adjusted by using a solvent in each mixing step.

[0107] The content of each component is as described above.

[0108] However, the preparation method of the adhesive composition is not specifically limited, and the process conditions can be appropriately changed as needed.

[0109] peeling layer

[0110] A photocurable adhesive film according to an exemplary embodiment of the present invention includes at least one release layer.

[0111] The release layer is coated with the liquid component and serves as a carrier to facilitate the process through the drying oven and as a support for the adhesive layer before use. Furthermore, the release layer protects the adhesive surface after the coating liquid of the adhesive composition has dried until final use.

[0112] The at least one peeling layer may include multiple peeling layers.

[0113] The plurality of peeling layers may include a first peeling layer and a second peeling layer.

[0114] The first and second release layers may include at least one selected from the following: polyester (PET) film, polyethylene (PE) film, polypropylene (PP) film, and paper.

[0115] Furthermore, the first release layer may also include a fluorine-based release layer. Specifically, the first release layer may comprise fluorine-containing PET. More specifically, the first release layer may comprise PET treated with a fluorine-based release agent. By utilizing the excellent non-adhesive properties of fluorine compounds to impart lubricity, the fluorine-based release layer can exhibit excellent peelability.

[0116] The second release layer may comprise a silicone-based release layer. Specifically, the second release layer may comprise silicone-containing PET. More specifically, the second release layer may comprise PET treated with a silicone-based release agent. The silicone-based release agent may be used as a polysiloxane polymer having reactive groups in its molecule that are responsive to Si-H bond groups. The reactive groups that are responsive to Si-H bond groups may include at least one selected from alkenyl groups, such as vinyl groups and hexenyl groups. Silicon-based release layers exhibit excellent lubricity and good peelability.

[0117] The first and second release layers comprise either a silicon-based release layer or a fluorine-based release layer, respectively, so that the adhesive layer is not damaged and can be naturally peeled off.

[0118] Structure of photocurable adhesive film

[0119] See Figure 1 The photocurable adhesive film 1 includes an adhesive layer 12 and release layers 11 and 13. Specifically, the adhesive layer 12 may be disposed between the first release layer 11 and the second release layer 13. In this case, the adhesive layer 12 and the first release layer 11 can be bonded to each other. In addition, the adhesive layer 12 and the second release layer 13 can be bonded to each other. Furthermore, the adhesive layer 12 can be bonded to both the first release layer 11 and the second release layer 13.

[0120] When prepared as a film, the photocurable adhesive film according to an exemplary embodiment of the present invention may have a thickness in the range of 5 μm to 1000 μm or 10 μm to 100 μm.

[0121] Alternatively, when prepared as a thick film, the thickness of the adhesive film can be in the range of 0.1 mm to 5 mm or 1 mm to 3 mm.

[0122] The adhesive layer may have a thickness ranging from 5 μm to 1000 μm or from 10 μm to 100 μm.

[0123] The first and second release layers may have a thickness in the range of 5 μm to 100 μm or 10 μm to 100 μm.

[0124] When the thickness of the first and second release layers is too thin, it is difficult to support and preserve the adhesive layer. When the thickness is too thick, the winding may be interrupted and the shape of the adhesive film used may be modified.

[0125] However, the thickness of the first and second release layers can be thinner or thicker as needed, unless the effects of the invention are suppressed.

[0126] Physical properties of photocurable adhesive films

[0127] According to an exemplary embodiment of the present invention, the photocurable adhesive film has a 180° peel adhesion force of 550 g / in to 800 g / in at 70°. Specifically, the photocurable adhesive film has a 180° peel adhesion force of 570 g / in to 800 g / in at 70°. More specifically, the photocurable adhesive film has a 180° peel adhesion force of 570 g / in to 790 g / in or 575 g / in to 660 g / in at 70°.

[0128] In a photocurable adhesive film according to an exemplary embodiment of the present invention, the adhesive layer has a 180° peel adhesion force of 900 g / in to 1300 g / in at room temperature. Specifically, the adhesive layer has a 180° peel adhesion force of 900 g / in to 1200 g / in at room temperature. More specifically, the adhesive layer has a 180° peel adhesion force of 900 g / in to 1150 g / in or 930 g / in to 1150 g / in at room temperature.

[0129] 180° peel adhesion can be measured by cutting the photocurable adhesive film 1 inch wide, removing the release film, attaching the photocurable adhesive film to a stainless steel (SUS) substrate at room temperature for 1 hour, and then peeling the photocurable adhesive film at a peel rate of 305 mm / min at a 180° angle at room temperature or 70°C.

[0130] According to an exemplary embodiment of the present invention, the photocurable adhesive film may have a creep strain of 38% or less at 60°C after photocuring. Specifically, the photocurable adhesive film may have a creep strain of 35% or less, 30% or less, 28% or less, 26% or less, 25% or less, or 24% or less at 60°C after photocuring. More specifically, the photocurable adhesive film may have a creep strain of 20% to 38%, 20% to 35%, 20% to 30%, 20% to 38%, or 20% to 25% at 60°C after photocuring.

[0131] Creep strain refers to the deformation of a material over time under a constant load. Therefore, a lower creep strain indicates better creep resistance. In other words, a lower creep strain may reduce the occurrence of defects such as deformation, cracks, and delamination.

[0132] In creep strain testing, a 25 μm thick adhesive layer is folded 32 times to form a thickness of 800 μm, and then tested at 60°C using a DHR-2 rheometer TA instrument under the following conditions: static stress of 2000 Pa, creep time of 600 seconds, and recovery time of 600 seconds.

[0133] Furthermore, the photocurable adhesive film according to an exemplary embodiment of the present invention can have a shear modulus of 0.35 MPa to 0.50 MPa at -20°C after photocuring. Specifically, the photocurable adhesive film can have a shear modulus of 0.35 MPa to 0.49 MPa, 0.35 MPa to 0.46 MPa, 0.35 MPa to 0.45 MPa, 0.35 MPa to 0.43 MPa, 0.35 MPa to 0.42 MPa, or 0.35 MPa to 0.40 MPa at -20°C after photocuring.

[0134] The shear modulus was evaluated using the modulus value at -20°C, which was measured using an ARES-G2 rheometer TA instrument after the temperature was raised from -50°C to 150°C at a rate of 5°C / min, under conditions of strain from 0.02% to 15%, axial force of 1N, and vibration frequency of 10rad / sec.

[0135] In the photocurable adhesive film according to an exemplary embodiment of the present invention, the adhesive layer may have a tanδ of 0.2 to 0.4, 0.22 to 0.38, 0.2 to 0.35, or 0.25 to 0.35 at a temperature of 150°C. tanδ refers to the ratio of shear loss modulus to shear storage modulus, and a small tanδ value indicates a large shear storage modulus and strong elasticity.

[0136] The adhesive film can meet the requirements of being optically transparent before UV curing. For example, the adhesive film may have a haze of 5% or less, 2% or less, or 1% or less before UV curing. In addition, the adhesive film may have a light transmittance of 80% or more, 90% or more, or 95% or more before UV curing.

[0137] The adhesive film can meet the requirements of being optically transparent after UV curing. For example, the adhesive film can have a haze of 5% or less, 2% or less, or 1% or less after UV curing. In addition, the adhesive film can also have a light transmittance of 80% or more, 90% or more, or 95% or more after UV curing.

[0138] The photocurable adhesive film according to an exemplary embodiment of the present invention has physical properties suitable for use in display devices, specifically foldable displays.

[0139] Preparation method of photocurable adhesive film

[0140] A method for preparing a photocurable adhesive film according to an exemplary embodiment of the present invention includes preparing at least one release layer; and forming an adhesive layer by coating the at least one release layer with a photocurable adhesive composition, wherein the photocurable adhesive composition comprises a prepolymer; an acrylic monomer having a structural formula; an initiator; and a crosslinking agent, and the photocurable adhesive composition comprises 0.5 parts by weight to 10 parts by weight of the acrylic monomer based on 100 parts by weight of the prepolymer.

[0141] See Figure 2 The method for preparing a photocurable adhesive film (S100) may include preparing at least one release layer (S110).

[0142] At least one peeling layer includes a first peeling layer and a second peeling layer, and the type and thickness of the first peeling layer and the second peeling layer are as described above.

[0143] A method for preparing a photocurable adhesive film may include forming an adhesive layer by coating a photocurable adhesive composition onto at least one release layer (S120). Alternatively, the photocurable adhesive film may include forming an adhesive layer by coating a photocurable adhesive composition between two release layers (i.e., a first release layer and a second release layer).

[0144] The preparation of the photocurable adhesive composition can be carried out according to the conditions and methods described above.

[0145] Specifically, according to an exemplary embodiment of the present invention, a photocurable adhesive film can be prepared by coating and photocuring a photocurable adhesive composition between a first release layer and a second release layer to form an adhesive layer.

[0146] Alternatively, a photocurable adhesive film according to another exemplary embodiment of the invention may be prepared by coating and photocuring a photocurable adhesive composition on one surface of a first release layer or a second release layer to form an adhesive layer, and then bonding another release layer to one surface of the adhesive layer.

[0147] The photocuring process can be carried out by applying an adhesive composition to at least one release layer. Specifically, the photocurable adhesive composition can be applied to at least one release layer at a suitable thickness, and the application can be performed by methods such as slit-stick coating, blade coating, gravure coating, or mold coating. Furthermore, the coating rate can be in the range of about 1 m / min to 40 m / min or 5 m / min to 30 m / min.

[0148] The preparation method of the photocurable adhesive film may also include photocuring (S130).

[0149] Photocuring conditions may include two-stage photocuring.

[0150] Specifically, photocuring conditions may include a UV intensity of 2.1 W / cm². 2 The first photocuring cycle has a dwell time of 50 to 100 seconds; and the UV intensity is 9.0 W / cm². 2 The second photocuring process involves a dwell time of 100 to 150 seconds.

[0151] The physical properties of the photocurable adhesive film according to an exemplary embodiment of the present invention, specifically the physical properties of the adhesive layer, can be the physical properties evaluated after two-stage photocuring conditions.

[0152] The photocurable adhesive film according to an exemplary embodiment of the present invention can be used in display devices, and more specifically, can be effectively used as an adhesive film in the manufacturing process of display panels in the field of foldable display devices.

[0153] The display panel can be, for example, an organic light-emitting diode (OLED) display panel or a liquid crystal display (LCD) panel.

[0154] Example

[0155] The invention will be described in more detail below by way of examples. However, these examples are merely illustrative and the invention is not limited thereto.

[0156] Example 1

[0157] <Preparation of Photocurable Adhesive Compositions>

[0158] 2-Ethylhexyl acrylate (2-EHA) as the first monomer and acrylic acid (AA) as the second monomer were mixed at a weight ratio of 95.5:4.5 to prepare 100 parts by weight of monomer mixture. 0.04 parts by weight of IRG651 as the first initiator was added to this monomer mixture, and it was thoroughly mixed for about 5 minutes to obtain a prepolymer composition (S210).

[0159] The prepolymer composition was prepolymerized using a DTP UV curing machine (ΔT = 7°C) to obtain a prepolymer (S220) with a viscosity of about 2,000 cP.

[0160] Next, IRG651 as a second initiator, 1,6-hexanediol diacrylate (HDDA) as a crosslinking agent, and β-carboxyethyl acrylate (β-CEA) as an acrylic monomer are added to the prepolymer in the amounts shown in Table 1, and the mixture is mixed using a roller mixer for about 8 to 12 hours (S230) to obtain a light-curable adhesive composition with transparent viscosity (S200).

[0161] <Preparation of Photocurable Adhesive Films>

[0162] Using a KCD1 pilot-scale coating machine, a photocurable adhesive composition was coated onto a release layer under the following conditions to form an adhesive layer and prepare a photocurable adhesive film.

[0163] Structure of photocurable adhesive film

[0164] Adhesive layer thickness: 25μm

[0165] First release layer (top): Fluorine-based PET (92500RZASD, Kern Chemical)

[0166] Second release layer (bottom): Silicon-based PET (RF12ASW75, SK Hightech)

[0167] Curing conditions

[0168] Step 1: UV intensity is 2.1 W / cm 2 Dwell time = 50 seconds

[0169] Step 2: UV intensity is 9.0 W / cm 2 Dwell time = 150 seconds

[0170] Maximum linear velocity: 2.1 MPa

[0171] Example 2 and Example 3

[0172] Except for changing the amount of β-CEA to the content shown in Table 1 below, the photocurable adhesive composition and the photocurable adhesive film were obtained in the same manner as in Example 1.

[0173] Examples 4 to 6

[0174] Except for using a prepolymer composition in the same manner as in Example 1, where the amounts of 2-EHA and AA were changed to those shown in Table 1 below and the amounts of IRG651 (DAEHAN Chemicals) and β-CEA were changed to 0.1 parts by weight and 5 parts by weight respectively based on 100 parts by weight of prepolymer, a photocurable adhesive composition and a photocurable adhesive film were obtained.

[0175] Example 7

[0176] Except for changing the amount of β-CEA to the content shown in Table 1 below, the photocurable adhesive composition and the photocurable adhesive film were obtained in the same manner as in Example 6.

[0177] Comparative Example 1

[0178] 2-Ethylhexyl acrylate (2-EHA, LG Chemicals) as the first monomer and acrylic acid (AA, LG Chemicals) as the second monomer were mixed at a weight ratio of 95.5:4.5 to prepare 100 parts by weight of monomer mixture. Based on 100 parts by weight of monomer mixture, 0.15 parts by weight of IRG651 (DAEHAN Chemicals) as an initiator and 0.15 parts by weight of HDDA as a crosslinking agent were added to monomer mixture, and the mixture was mixed using a roller mixer for about 8 to 12 hours to obtain a photocurable adhesive composition and a photocurable adhesive film.

[0179] Comparative Example 2

[0180] Except that the amount of HDDA used as a crosslinking agent was changed to 0.12 parts by weight, a photocurable adhesive composition and a photocurable adhesive film were obtained in the same manner as in Comparative Example 1.

[0181] The composition and content of the corresponding materials are shown in Table 1 below:

[0182] [Table 1]

[0183]

[0184] -2-EHA: 2-Ethylhexyl acrylate

[0185] -AA: Acrylic acid (LG Chemicals)

[0186] -β-CEA: β-Carboxyethyl Acrylate (DSW Chemicals)

[0187] -IRG651 (DEAHAN Chemicals)

[0188] -HDDA: 1,6-Hexanediol diacrylate (SK Cytec)

[0189] Test case

[0190] Test Example 1: Shear Storage Modulus (G')

[0191] A 25 μm thick adhesive layer was folded 32 times to achieve a thickness of 800 μm, and then the shear storage modulus was measured using an ARES-G2 rheometer (TA instrument). The measurement conditions for the shear storage modulus are as follows, and the modulus values ​​measured at -20°C are shown in Table 2.

[0192] Temperature variation: -50℃ to 150℃

[0193] Heating rate: 5℃ / min

[0194] Strain: 0.02% to 15%

[0195] Axial force: 1N

[0196] Vibration frequency: 10 rad / sec

[0197] Test Example 2: Shear Loss Modulus (G)

[0198] A 25 μm thick adhesive layer was folded 32 times to achieve a thickness of 800 μm, and then the shear loss modulus was measured using an ARES-G2 rheometer (TA instrument). The measurement conditions for the shear loss modulus were the same as those for the shear storage modulus to obtain the data.

[0199] Test Example 3: tanδ (tan del)

[0200] A 25 μm thick adhesive layer was folded 32 times to achieve a thickness of 800 μm, and the tanδ value was then measured using an ARES-G2 rheometer TA instrument. The tanδ measurement conditions were the same as those for the shear storage modulus.

[0201] tanδ refers to the ratio of shear loss modulus to shear storage modulus.

[0202] Test Example 4: Creep Strain (%)

[0203] A 25 μm thick adhesive layer was folded 32 times to achieve a thickness of 800 μm, and then creep strain was tested using a DHR-2 rheometer (TA instrument). The creep strain measurement conditions are as follows.

[0204] Test temperature: 60℃

[0205] Static stress: 2000 Pa

[0206] Creep time: 600 seconds

[0207] Recovery time: 600 seconds

[0208] Test Example 5: 180° Peel Adhesion

[0209] The measurement conditions for 180° peel adhesion are as follows.

[0210] Test substrate: SUS

[0211] Flexible strip: 25μm PET (1 inch wide)

[0212] Aging: 1 hour at room temperature

[0213] Test temperature: room temperature, 70℃

[0214] Peeling rate: 305 mm / min

[0215] Repeat each sample 3 times.

[0216] The evaluation results of the test cases are shown in Table 2 below.

[0217] [Table 2]

[0218]

[0219] As can be seen in Table 2, compared with the photocurable adhesive films prepared in Comparative Examples 1 and 2, the photocurable adhesive films prepared in Examples 1 to 7 show significantly superior physical properties.

[0220] Specifically, firstly, when comparing Examples 1 to 3 and Comparative Example 2, which use the same amount of monomer mixture, second initiator and curing agent, it can be seen that, compared with the photocurable adhesive film of Comparative Example 2, the photocurable adhesive films of Examples 1 to 3 using β-CEA have increased 180° peel adhesion at room temperature and 70°C and reduced creep strain.

[0221] Specifically, it can be seen that in Examples 1 to 3, as the β-CEA content increases, the 180° peel adhesion increases, and the photocurable adhesive film of Example 3 using 5 parts by weight of β-CEA has a 180° peel adhesion at 70°C that increases to 790 gf / inch, which is significantly higher than that of the photocurable adhesive film of Comparative Example 2, which has a 180° peel adhesion of 530 gf / inch.

[0222] Meanwhile, even with a 5-fold increase in the β-CEA content, G' did not increase significantly at a low temperature of -20°C, given the shear storage modulus (G').

[0223] In particular, compared with the photocurable adhesive films of Comparative Examples 1 and 2, the creep strain of the photocurable adhesive films of Examples 1 to 3 was reduced, and compared with the creep strain of the photocurable adhesive film of Comparative Example 2 being 39.87%, the creep strain of the photocurable adhesive film of Example 3 using 5 parts by weight of β-CEA was significantly reduced to 29.8%.

[0224] Meanwhile, in the case of the photocurable adhesive films of Examples 3 to 6, which used 5 parts by weight of β-CEA, reduced the content of the second initiator to 0.1 parts by weight, and gradually reduced the content of acrylic acid to 4.5 parts by weight, 4 parts by weight, 3.5 parts by weight, and 3 parts by weight, it can be seen that, compared with the photocurable adhesive films of Examples 1 and 2 and Comparative Examples 1 and 2, the creep strain was significantly reduced to 22.6% to 29.8%, and G' at a low temperature of -20°C was reduced to 0.35 MPa.

[0225] Furthermore, when using the photocurable adhesive film of Example 7 with a β-CEA content of 6.5 parts by weight, it was confirmed that the creep strain was significantly reduced to 22.85%, and the 180° peel adhesion at room temperature and 70°C was 1030 gf / inch and 660 gf / inch, respectively, which were significantly improved compared with the photocurable adhesive films of Comparative Examples 1 and 2.

[0226] Therefore, according to an exemplary embodiment of the present invention, it has been confirmed that using β-CEA and adjusting the monomer content can provide an adhesive film with excellent physical properties, such as reduced peel adhesion at room temperature and high temperature of 70°C, creep resistance at high temperature of 60°C and shear storage modulus at low temperature of -20°C.

[0227] Explanation of the icons and symbols in the attached diagram.

[0228] 1: Photocurable adhesive film

[0229] 11: First peeling layer

[0230] 12: Adhesive layer

[0231] 13: Second peeling layer

Claims

1. A photocurable adhesive film, comprising: Adhesive layer and at least one release layer, The adhesive layer is induced by a photocurable adhesive composition comprising: a prepolymer; An acrylic monomer having the following structural formula; an initiator; and a crosslinking agent, and Based on 100 parts by weight of the prepolymer, the photocurable adhesive composition comprises 0.5 to 10 parts by weight of the acrylic monomer: Where n is an integer from 1 to 3, and The prepolymer is formed from a prepolymer composition comprising a first monomer and a second monomer, and the prepolymer has a viscosity of 1,000 cP to 5,000 cP, wherein the first monomer comprises an acrylate monomer based on an aliphatic or aromatic hydrocarbon having 1 to 30 carbon atoms, and the second monomer comprises a functional monomer containing at least one heteroatom, and wherein the weight ratio of the first monomer to the second monomer is 1:0.01 to 0.

1.

2. The photocurable adhesive film according to claim 1, wherein the acrylic monomer has a glass transition temperature (Tg) of 10°C to 50°C.

3. The photocurable adhesive film according to claim 2, wherein the acrylic monomer includes β-carboxyethyl acrylate (β-CEA).

4. The photocurable adhesive film according to claim 1, wherein, relative to the photocured adhesive layer, the adhesive layer has a 180° peel adhesion force of 550 g / in to 800 g / in at 70°C and a 180° peel adhesion force of 900 g / in to 1300 g / in at room temperature.

5. The photocurable adhesive film according to claim 1, wherein the photocurable adhesive film has a creep strain of 38% or less at 60°C after photocuring, and has a shear modulus of 0.35 MPa to 0.50 MPa at -20°C after photocuring.

6. The photocurable adhesive film according to claim 1, wherein the initiator and the crosslinking agent are present in amounts of 0.05 to 0.3 parts by weight and 0.01 to 0.5 parts by weight, respectively, based on 100 parts by weight of the prepolymer.

7. The photocurable adhesive film according to claim 1, wherein the at least one release layer comprises a plurality of release layers. The plurality of peeling layers includes a first peeling layer and a second peeling layer. The adhesive layer is disposed between the first release layer and the second release layer. The first release layer is a fluorine-based release layer, and The second release layer is a silicon-based release layer.

8. A method for preparing a photocurable adhesive film, the method comprising: Prepare at least one release layer; as well as An adhesive layer is formed by coating the at least one release layer with a photocurable adhesive composition. The photocurable adhesive composition comprises a prepolymer; The acrylic monomer having the following structural formula; an initiator; and a crosslinking agent, and the photocurable adhesive composition comprises, based on 100 parts by weight of the prepolymer, 0.5 to 10 parts by weight of the acrylic monomer: Where n is an integer from 1 to 3, and The prepolymer is formed from a prepolymer composition comprising a first monomer and a second monomer, and the prepolymer has a viscosity of 1,000 cP to 5,000 cP, wherein the first monomer comprises an acrylate monomer based on an aliphatic or aromatic hydrocarbon having 1 to 30 carbon atoms, and the second monomer comprises a functional monomer containing at least one heteroatom, and wherein the weight ratio of the first monomer to the second monomer is 1:0.01 to 0.1.

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