Adhesive film, optical component containing the same, and optical display device containing the same

Abstract

The present invention provides an adhesive film formed from a composition for an adhesive film comprising a (meth)acrylic binder, a (meth)acrylic oligomer and a curing agent, the adhesive film having a peak temperature of tan δ value of about -40°C or less and a storage modulus at -20°C of about 0.3 MPa or less, an optical member including the same and an optical display device including the same.

Description

Technical Field

[0001] The present invention relates to an adhesive film, an optical member including the same, and an optical display device including the same.

Background Art

[0002] In recent years, while the technical interest in foldable display devices has been rapidly increasing, the development of adhesive films included in foldable display devices has also been continued. The adhesive film must be excellent in optical transparency and peel strength against an adherend, and must also be excellent in folding properties.

[0003] In order to obtain the above-described adhesive film, a method of forming a coating layer by applying a composition containing a (meth)acrylic monomer, a crosslinking agent, and a photopolymerization initiator to a release film or an adherend and curing it by light such as UV irradiation is known.

[0004] However, in the above-described method, since the composition is a composition that does not contain a solvent (solvent-free composition) in consideration of UV irradiation or the like, it has been difficult to make the thickness of the finally produced adhesive film 20 μm or less. In addition, the solvent-free composition has a high viscosity and poor coating properties, so it has a limit in being thinly and uniformly coated, and it is difficult to reduce the thickness of the finally produced adhesive film and to have a uniform surface.

[0005] On the other hand, in recent years, as the external UV irradiation amount increases, light-emitting elements and the like in an optical display device may be damaged by external UV irradiation, and the reliability and lifespan of the optical display device may be reduced. Therefore, a method of including a UV absorber in the adhesive film can be considered. However, when the adhesive film is formed by UV curing by UV irradiation, the curing rate is decreased by the UV absorber, and there is a limit to the content of the UV absorber that can be added, and it has been difficult to obtain the desired adhesive film.

[0006] The background technology of this invention is disclosed in Korean Published Patent No. 10-2017-0070753, among others. [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide an adhesive film having a thin profile and a uniform surface, high peel strength, and excellent folding properties at low temperatures.

[0008] Another object of the present invention is to provide an adhesive film formed from a thermosetting composition, which has high peel strength and excellent folding properties at low temperatures.

[0009] Another object of the present invention is to provide an adhesive film that reduces external UV transmission and has an effect of improving the lifespan and reliability of elements within the panel. [Means for solving the problem]

[0010] One aspect of the present invention is an adhesive film.

[0011] 1. The adhesive film is formed from an adhesive film composition comprising a (meth)acrylic binder, a (meth)acrylic oligomer, and a curing agent, wherein the adhesive film has a peak temperature of tanδ value of approximately -40°C or lower and a storage modulus of approximately 0.3 MPa or lower at -20°C.

[0012] 2. The adhesive film has a peak temperature of tanδ value of approximately -40°C or lower, a storage modulus of approximately 0.3 MPa or lower at -20°C, and a peel strength of approximately 600 gf / 25 mm or higher on a glass plate or SUS.

[0013] In 3.1-2, the adhesive film may have a thickness of approximately 20 μm or less.

[0014] In 4.1, the adhesive film may have a peel strength of approximately 600 gf / 25 mm or more on a glass plate or SUS.

[0015] In 5.1-4, the adhesive film may have a shear deformation rate of approximately 18% or more.

[0016] In 6.1-5, the adhesive film may have a change rate of approximately 10% or less in the shear deformation rate shown in the following formula 1.

[0017]

number

[0018] (In the above formula 1, A is the initial shear deformation rate of the adhesive film (unit: %), B is the shear deformation rate after high temperature and high humidity, which is the shear deformation rate (in %) of the adhesive film after it has been left at 60°C and 95% relative humidity for 10 days and then left at 25°C for 2 hours. In 7.2, the adhesive film may be formed from an adhesive film composition comprising a (meth)acrylic binder, a (meth)acrylic oligomer, and a curing agent.

[0019] In 8.1-7, the (meth)acrylic binder may have a glass transition temperature of approximately -55°C or lower.

[0020] In 9.1-8, the (meth)acrylic binder may include a (meth)acrylic copolymer of a monomer mixture containing a (meth)acrylic monomer whose homopolymer glass transition temperature is approximately -50°C or lower.

[0021] In section 10.1-9, (meth)acrylic monomers having a glass transition temperature of about -50°C or lower may be included in the monomer mixture in an amount of about 90% to 100% by weight.

[0022] 11. In 1-10, the monomer mixture can include from about 40% to less than 100% by weight of a (meth)acrylic monomer having a branched-chain alkyl group with 3 to 10 carbon atoms and a glass transition temperature of the homopolymer of about -50°C or lower, and from more than 0% to 60% by weight or less of a (meth)acrylic monomer having a linear alkyl group with 1 to 10 carbon atoms and a glass transition temperature of the homopolymer of about -50°C or lower.

[0023] 12. In 1-11, the (meth)acrylic oligomer may have a glass transition temperature of about 50°C or higher.

[0024] 13. In 1-12, the (meth)acrylic oligomer can include an oligomer of a monomer mixture containing a (meth)acrylic monomer having a hydroxyl group.

[0025] 14. In 1-13, the (meth)acrylic oligomer may have a weight average molecular weight of about 3,000 to 50,000.

[0026] 15. In 1-14, the curing agent includes an isocyanate-based curing agent, and the composition for the adhesive film can include 100 parts by weight of the (meth)acrylic binder, about 3 parts by weight or less of the (meth)acrylic oligomer, and about 1 part by weight or less of the isocyanate-based curing agent.

[0027] 16. In 1-15, the composition for the adhesive film can further include one or more curing agents selected from a metal chelate-based curing agent, a carbodiimide-based curing agent, an aziridine-based curing agent, and an epoxy-based curing agent.

[0028] 17. In 1-16, the adhesive film can further include a UV absorber.

[0029] The optical member of the present invention includes an optical element and the adhesive film of the present invention formed on at least one surface of the optical element.

[0030] The optical display device of the present invention includes the adhesive film of the present invention. [Effects of the Invention]

[0031] The present invention can provide an adhesive film having a thin profile and a uniform surface, high peel strength, and excellent folding properties at low temperatures.

[0032] This invention provides an adhesive film formed from a thermosetting composition, exhibiting high peel strength and excellent folding properties at low temperatures.

[0033] The present invention can provide an adhesive film that reduces external UV transmission and has the effect of improving the lifespan and reliability of elements within the panel. [Brief explanation of the drawing]

[0034] [Figure 1] This figure shows an example of measuring the shear deformation rate of an adhesive film according to one embodiment of the present invention. [Modes for carrying out the invention]

[0035] [Best mode for carrying out the invention] The invention will be described in detail with reference to the attached examples so that it can be easily implemented by a person with ordinary skill in the art to which the invention pertains. The invention can be embodied in a variety of different forms and is not limited to the examples described herein.

[0036] In this specification, "acrylic" may mean acrylic and / or methacrylic.

[0037] In this specification, "copolymer" may include polymers or resins.

[0038] In this specification, the "peak temperature of the tanδ value" is a value measured by using a rheometer to measure the storage modulus and loss modulus by temperature, and reading the temperature at which the tanδ value, calculated as the ratio of the loss modulus to the storage modulus, is highest.

[0039] In this specification, "shear strain" is a value measured using the creep evaluation method at 60°C, and represents the degree to which a test specimen formed of an adhesive film deforms when a constant shear force is applied to the specimen. Referring to Figure 1, the maximum strain when the strain applied to a test specimen formed of an adhesive film by a constant force and time corresponds to the shear strain, and is the value that corresponds to the initial shear strain when the rate of change of the shear strain is measured.

[0040] In this specification, "glass transition temperature of homopolymer" may mean the glass transition temperature (Tg) measured for the homopolymer of the monomer under test using TA Instrument's DSC Discovery. Specifically, the endothermic transition curve obtained when the homopolymer of the monomer under test is heated to 180°C at a rate of 20°C / min, then gradually cooled to -100°C, and then heated to 100°C at a rate of 10°C / min can be used to determine the glass transition temperature by finding the inflection point of the endothermic transition curve.

[0041] In this specification, when a numerical range is described, "X to Y" means X or greater and Y or less (X ≤ and ≤ Y).

[0042] The adhesive film of the present invention is formed from a thermosetting composition, and while having a thin profile, it exhibits excellent folding properties at low temperatures and high peel strength. The adhesive film of the present invention reduces external UV transmission, thereby improving the lifespan and reliability of elements within the panel.

[0043] The following describes an adhesive film according to one embodiment of the present invention.

[0044] The adhesive film according to this embodiment (hereinafter referred to as "adhesive film") has a peak temperature of tanδ value of approximately -40°C or lower and a storage modulus of approximately 0.3 MPa or lower at -20°C. By having the above-mentioned peak temperature of tanδ value and storage modulus range at -20°C, the adhesive film can have excellent folding properties at low temperatures.

[0045] Specifically, the adhesive film may have a peak temperature of tanδ value of, for example, -70°C, -69°C, -68°C, -67°C, -66°C, -65°C, -64°C, -63°C, -62°C, -61°C, -60°C, -59°C, -58°C, -57°C, -56°C, -55°C, -54°C, -53°C, -52°C, -51°C, -50°C, -49°C, -48°C, -47°C, -46°C, -45°C, -44°C, -43°C, -42°C, -41°C, -40°C, -70°C to -40°C, and more specifically, -50°C to -40°C. Within this range, the adhesive film has excellent folding properties at low temperatures and can have the effect of relieving stress applied to the foldable panel at low temperatures.

[0046] Specifically, the adhesive film may have a storage modulus at -20°C of, for example, 0.001 MPa, 0.005 MPa, 0.01 MPa, 0.015 MPa, 0.02 MPa, 0.025 MPa, 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.045 MPa, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, more specifically 0.001 MPa to 0.3 MPa, and more specifically 0.05 MPa to 0.25 MPa. Within this range, the adhesive film has excellent folding properties at low temperatures and can have the effect of easing the stress applied to the foldable panel at low temperatures.

[0047] The adhesive film has a peel strength of approximately 600 gf / 25 mm or more against the adherend. Within this range, the high peel strength against the adherend allows for excellent reliability even when folding at room temperature. The "adherend" may be a glass plate (including alkali-free glass plates or soda-lime glass) or SUS (steel-use stainless). The "peel strength" is a value measured against the adherend with an adhesive film of 15 μm thickness or less at 25°C. The adhesive film can ensure the above peel strength against both glass plates and SUS, which are the adherends. The adhesive film of the present invention simultaneously possesses excellent folding properties and peel strength at low temperatures. For example, the peel strengths are 600gf / 25mm, 650gf / 25mm, 700gf / 25mm, 750gf / 25mm, 800gf / 25mm, 850gf / 25mm, 900gf / 25mm, 950gf / 25mm, 1000gf / 25mm, 1050gf / 25mm, 1100gf / 25mm, 1150gf / 25mm, 1200gf / 25mm, 1250gf / 25mm, 1300gf / 25mm, 1350gf / 25mm, 1400gf / 25mm, 14 50gf / 25mm, 1500gf / 25mm, 1550gf / 25mm, 1600gf / 25mm, 1650gf / 25mm, 1700gf / 25mm, 1750gf / 25mm, 1800gf / 25mm, 1850gf / 25mm, 1900gf / 25mm, 1950gf / 25mm, 2000gf / 25mm, specifically 600gf / 25mm to 2000gf / 25mm, and more specifically 700gf / 25mm to 1500gf / 25mm.

[0048] The adhesive film may have a storage modulus of approximately 0.02 MPa or higher at 60°C, for example, 0.02 MPa, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, specifically 0.02 MPa to 0.5 MPa, and more specifically 0.02 MPa to 0.1 MPa. Within this range, the reliability of the adhesive film at high temperatures can be excellent.

[0049] The adhesive film may have a storage modulus ratio at 60°C to storage modulus at -20°C of approximately 1:1 to approximately 1:20, for example, approximately 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, specifically 1:2 to 1:10. Within this range, excellent folding properties can be achieved over a wide range of temperatures, including high and low temperatures.

[0050] The adhesive film may have a shear deformation rate of approximately 18% or more, for example, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, specifically 18% to 40%, and more specifically 20% to 35%. Within the above range, reliability can be ensured during folding at low temperatures.

[0051] The adhesive film may have a change rate of shear deformation of approximately 10% or less, as shown in Formula 1 below, for example, 0%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, specifically 0.1% to 10%, and more specifically 0.1% to 5%. Within this range, excellent folding properties at low temperatures can be ensured even after being left in high temperature and high humidity conditions for a long period of time.

[0052]

number

[0053] (In the above formula 1, A is the initial shear deformation rate of the adhesive film (unit: %), B is the shear deformation rate after high temperature and high humidity, which is the shear deformation rate (in %) of the adhesive film after it has been left at 60°C and 95% relative humidity for 10 days and then left at 25°C for 2 hours. In the above formula 1, A and B may each be approximately 18% or more, for example, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, specifically 18% to 40%, and more specifically 20% to 35%. Within this range, reliability can be ensured in folding at low temperatures.

[0054] The adhesive film may have a thickness of approximately 20 μm or less, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or more specifically, more than 0 μm and 15 μm or less. Within this range, thin optical components and optical display devices can be easily manufactured.

[0055] The adhesive film having the peak temperature of the tanδ value, storage modulus at -20°C, peel strength to the adherend, shear deformation rate, and rate of change of shear deformation rate described above was formed from a thermosetting adhesive film composition. The present invention forms an adhesive film having the above-described physical properties from a thermosetting composition. Through this, in addition to the effects mentioned above, since there is no limit to the amount of UV absorber, improvements in the lifespan and reliability of elements in the panel due to external UV transmission can also be obtained.

[0056] The following description will apply to the aforementioned thermosetting composition (hereinafter also referred to as "the composition").

[0057] The composition comprises a (meth)acrylic binder, a (meth)acrylic oligomer, and a curing agent. The (meth)acrylic binder has a higher weight-average molecular weight than the (meth)acrylic oligomer.

[0058] (Meth)acrylic binders, when cured by a hardening agent, form a matrix for adhesive films and can help improve folding properties at low temperatures.

[0059] The (meth)acrylic binder may have a glass transition temperature of approximately -55°C or lower, for example, -70°C, -69°C, -68°C, -67°C, -66°C, -65°C, -64°C, -63°C, -62°C, -61°C, -60°C, -59°C, -58°C, -57°C, -56°C, -55°C, specifically -70°C to -55°C. Within this range, even when a curing agent is included, the peak temperature of the tanδ value and the storage modulus at -20°C can be reached, improving folding properties at low temperatures.

[0060] The (meth)acrylic binder may include a (meth)acrylic copolymer of monomer mixtures containing (meth)acrylic monomers in which the glass transition temperature of the homopolymer is approximately -50°C or lower, for example, -80°C, -79°C, -78°C, -77°C, -76°C, -75°C, -74°C, -73°C, -72°C, -71°C, -70°C, -69°C, -68°C, -67°C, -66°C, -65°C, -64°C, -63°C, -62°C, -61°C, -60°C, -59°C, -58°C, -57°C, -56°C, -55°C, -54°C, -53°C, -52°C, -51°C, -50°C, specifically -80°C to -50°C. Within the aforementioned range, the glass transition temperature of the binder can be easily reached, and the peak temperature of the tanδ value and the storage modulus at -20°C can be reached.

[0061] (Meth)acrylic monomers having a homopolymer glass transition temperature of approximately -50°C or lower, specifically -80°C to -50°C, are not subject to any special restrictions on their type, as long as they have the aforementioned glass transition temperature range. The glass transition temperature can be measured by referring to a catalog of the relevant (meth)acrylic monomer or by a method commonly known to those skilled in the art.

[0062] In one specific example, as the monomer having a glass transition temperature of approximately -50°C or lower, one or more (meth)acrylic monomers having linear or branched alkyl groups with 1 to 10 carbon atoms, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 carbon atoms, may be selected and used. For example, the (meth)acrylic monomers having linear or branched alkyl groups with 1 to 10 carbon atoms may include, but are not limited to, one or more of N-butyl acrylate, 2-ethylhexyl acrylate, isodecyl acrylate, and isononyl acrylate.

[0063] In one specific example, a (meth)acrylic monomer having a homopolymer glass transition temperature of about -50°C or lower may be included in the monomer mixture in an amount of 90% by weight or more, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, specifically 90% to 100% by weight. Within this range, the glass transition temperature range of the binder can be easily reached.

[0064] In one specific example, the monomer mixture consists of approximately 40% by weight or more and less than approximately 100% by weight of (meth)acrylic monomers having a homopolymer glass transition temperature of approximately -50°C or lower and branched-chain alkyl groups having 3 to 10 carbon atoms, for example, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61% by weight, 62% by weight Amount%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 8 2% by weight, 83% by weight, 84% by weight, 85% by weight, 86% by weight, 87% by weight, 88% by weight, 89% by weight, 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight, 98% by weight, 99% by weight, 99.9% by weight, specific This includes 40% to 90% by weight of a homopolymer and a (meth)acrylic monomer having a linear alkyl group with 1 to 10 carbon atoms and a glass transition temperature of the homopolymer of approximately -50°C or lower, with a content of 0% to 60% by weight, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26% This can include amounts of 10% to 60% by weight, specifically 27% by weight, 28% by weight, 29% by weight, 30% by weight, 31% by weight, 32% by weight, 33% by weight, 34% by weight, 35% by weight, 36% by weight, 37% by weight, 38% by weight, 39% by weight, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, and 60% by weight, specifically 10% to 60% by weight. Within this range, the glass transition temperature range of the binder can be easily reached.

[0065] The monomer mixture may further contain (meth)acrylic monomers having a homopolymer glass transition temperature greater than approximately -50°C. However, the content of monomers having a homopolymer glass transition temperature greater than approximately -50°C in the monomer mixture should not affect the range of the binder's glass transition temperature. For example, (meth)acrylic monomers having a homopolymer glass transition temperature greater than approximately -50°C may be included in the monomer mixture in amounts of less than 10% by weight, for example, 0.01% by weight, 0.05% by weight, 0.1% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 9.5% by weight, 9.9% by weight, specifically between 0.01% by weight and less than 10% by weight.

[0066] For example, a (meth)acrylic monomer whose homopolymer glass transition temperature is above approximately -50°C may have a homopolymer glass transition temperature of approximately -50°C to approximately 150°C, for example, -49°C, -45°C, -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C. The (meth)acrylic monomer having a glass transition temperature of approximately -50°C may be selected from one or more of the following: (meth)acrylic monomers having hydroxyl groups, (meth)acrylic monomers having aromatic groups, (meth)acrylic monomers having alicyclic groups, (meth)acrylic monomers having heteroalicyclic groups, and (meth)acrylic monomers having amino groups.

[0067] The (meth)acrylic binder may have a weight-average molecular weight (Mw) of approximately 1.5 million or less, for example, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, 1,150,000, 1,200,000, 1,250,000, 1,300,000, 1,350,000, 1,400,000, 1,450,000, or 1,500,000, specifically between approximately 900,000 and approximately 1,500,000. Within this range, the formation of the matrix of the adhesive film becomes easier, and the peel strength and reliability can be improved.

[0068] The (meth)acrylic binder may have a polydispersity index (PDI) of about 10 or less, specifically about 3 to about 10. Within this range, the formation of the matrix of the adhesive film becomes easier, and the peel strength and reliability can be improved.

[0069] (Meth)acrylic binders can be produced by polymerizing the monomer mixture using a conventional polymerization method. The polymerization method may include conventional methods known to those skilled in the art. For example, (meth)acrylic binders may be produced by conventional copolymer polymerization, such as suspension polymerization, emulsion polymerization, or solution polymerization, after adding an initiator to the monomer mixture. The polymerization temperature may be about 60°C to 70°C, and the polymerization time may be about 6 to 8 hours. Conventional initiators can be used, including azo polymerization initiators and / or peroxides such as benzoyl peroxide or acetyl peroxide.

[0070] (Meth)acrylic oligomers can increase the peel strength of adhesive films. The adhesive films described above are formed from thermosetting compositions and may have a thin thickness, but their peel strength may be reduced. (Meth)acrylic oligomers can increase the cohesive force of adhesive films and thus increase their peel strength.

[0071] The (meth)acrylic oligomer may have a glass transition temperature of approximately 50°C or higher. Within this range, the peel strength of the adhesive film can be increased. Specifically, the (meth)acrylic oligomer may have a glass transition temperature of, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, more specifically 50°C to 90°C, and more specifically 50°C to 80°C. Within the aforementioned range, the peel strength of the adhesive film can be increased, and its folding properties at low temperatures can be improved.

[0072] The (meth)acrylic oligomer has a weight-average molecular weight of approximately 3,000 to 50,000, for example, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000, 19,000, 20,000, 3,000, 40,000, 50,000, specifically 5,000 to 50,000. Within this range, the cohesive strength of the adhesive film can be increased.

[0073] The (meth)acrylic oligomer may include an oligomer of a monomer mixture containing a (meth)acrylic monomer having a hydroxyl group. The hydroxyl group contained in the (meth)acrylic oligomer can provide the effect of improving high temperature and high humidity durability. Among the (meth)acrylic oligomers, the (meth)acrylic monomer having a hydroxyl group can help improve the peel strength of the adhesive film and ensure folding properties at low temperatures when the (meth)acrylic binder is a (meth)acrylic binder that does not have crosslinkable functional groups, such as a hydroxyl group or a carboxylic acid group. The (meth)acrylic monomer having a hydroxyl group may include, but is not limited to, 4-hydroxybutyl (meth)acrylate and hydroxyethyl (meth)acrylate. The (meth)acrylic monomer having a hydroxyl group may be included in the monomer mixture in an amount of about 0.1% to about 99.9% by weight.

[0074] The (meth)acrylic oligomer may contain (meth)acrylic monomers as its main constituent units, the homopolymer having a glass transition temperature of approximately 90°C or higher, for example, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, specifically 100°C to 120°C. Within this range, it is possible to prevent the storage modulus of the adhesive film at high temperatures from becoming excessively high and to ensure the glass transition temperature range. For example, the (meth)acrylic monomer is a monofunctional (meth)acrylic monomer, and may specifically be methyl acrylate, hydroxyethyl methacrylate, etc., but is not limited thereto. The "main constituent unit" means that the monomer in question is contained in the total units of the (meth)acrylic oligomer in an amount of approximately 50% by weight or more, 60% by weight or more, and 100% or less.

[0075] (Meth)acrylic oligomers may also further contain (meth)acrylic monomers as constituent units, the homopolymer having a glass transition temperature of approximately 50°C or less, for example, -80°C to 0°C, specifically -80°C, -75°C, -70°C, -65°C, -60°C, -55°C, -50°C, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C.

[0076] In one specific example, the (meth)acrylic oligomer may include an oligomer of a monomer mixture containing 4-hydroxybutyl (meth)acrylate and methyl methacrylate. The monomer mixture may further contain one or more of methacrylic acid and N-butyl (meth)acrylate.

[0077] The (meth)acrylic oligomer may be included in amounts of approximately 3 parts by weight or less per 100 parts by weight of the (meth)acrylic binder, for example, 0.001 parts by weight, 0.5 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, specifically 0.001 parts by weight to 3 parts by weight, and more specifically 0.01 parts by weight to 1 part by weight. Within this range, it is possible to increase the peel strength of the adhesive film while preventing an increase in the storage modulus at low temperatures.

[0078] The hardening agent can enhance the reliability of the adhesive film by forming a matrix for the adhesive film through thermal curing of the (meth)acrylic binder.

[0079] The curing agent may include an isocyanate-based curing agent.

[0080] In one specific example, the isocyanate-based curing agent does not need to contain urethane bonds.

[0081] The isocyanate curing agent may include two or more functional isocyanate curing agents, specifically two- to six-functional isocyanate curing agents. In one specific example, the isocyanate curing agent may include one or more aromatic isocyanate curing agents or aliphatic isocyanate curing agents from among xylene diisocyanate (XDI) containing m-xylene diisocyanate, methylenebis(phenyl isocyanate) (MDI) containing 4,4'-methylenebis(phenyl isocyanate), naphthalene diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate, or adducts thereof. For example, the adduct may be a trimethylolpropane adduct of tolylene diisocyanate, a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, a trimethylolpropane adduct of xylene diisocyanate, an isocyanurate of tolylene diisocyanate, an isocyanurate of hexamethylene diisocyanate, and an isocyanurate of isophorone diisocyanate. The isocyanate-based curing agent may contain one or more of the above compositions.

[0082] The isocyanate-based curing agent may be included in an amount of about 1 part by weight or less per 100 parts by weight of the (meth)acrylic binder, specifically 0.01 to 1 part by weight, and more specifically 0.01 to 0.5 parts by weight. Within this range, it is possible to prevent an increase in the storage modulus of the adhesive film at low temperatures while improving the reliability of the adhesive film.

[0083] The above composition may further contain a curing agent that does not have an isocyanate group (hereinafter also referred to as a "non-isocyanate curing agent").

[0084] The non-isocyanate curing agent may contain one or more of the following: metal chelating curing agents, carbodiimide curing agents, aziridine curing agents, and epoxy curing agents, and preferably contains a metal chelating curing agent. The metal chelating curing agent can increase the curing rate of the (meth)acrylic binder.

[0085] As a metal chelating curing agent, conventional curing agents can be used, but curing agents containing metals such as aluminum, titanium, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium can also be used. For example, a metal chelating curing agent may contain one or more of the following: aluminum ethyl acetacetate diisopropylate, aluminum tris(ethyl acetate), alkyl acetacetate aluminum diisopropylate, aluminum isopropylate, mono-sec-butoxyaluminum diisopropylate, aluminum-sec-butyrate, aluminum ethylacetate, tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, titanium acetylacetonate, titanium octylene glycolate, titanium tetraacetylacetonate, titanium ethyl acetate, polyhydroxytitanium stearate, and aluminum acetylacetonate.

[0086] The non-isocyanate curing agent may be included in an amount of approximately 5 parts by weight or less, specifically 0.01 to 2 parts by weight, per 100 parts by weight of the (meth)acrylic binder. Within this range, the effect of the adhesive film of the present invention will not be affected, and additional effects can be obtained.

[0087] The above composition may further contain a silane coupling agent.

[0088] Silane coupling agents can enhance the adhesive strength of adhesive films. Silane coupling agents may include conventional silane coupling agents known to those skilled in the art. For example, silane coupling agents may include, but are not limited to, epoxy group-containing silane coupling agents such as glycidoxypropyltrimethoxysilane and glycidoxypropylmethyldimethoxysilane.

[0089] The silane coupling agent may be included in an amount of about 0.01 to 5 parts by weight per 100 parts by weight of the (meth)acrylic binder. Within this range, an improvement in peel strength can be further achieved.

[0090] The composition may further contain a UV absorber. The UV absorber is contained in the adhesive film and can prevent damage to light-emitting elements and other components within the panel by reducing the amount of UV light incident from the outside. In one specific example, the adhesive film may have a light transmittance of about 20% or less at wavelengths of about 390 nm or less, for example, 0% to 10%.

[0091] The UV absorber may have a maximum absorption wavelength of approximately 390 nm or more, specifically 390 nm to 400 nm, or more specifically, between 390 nm and 400 nm. Within this range, it is possible to sufficiently absorb ambient light with wavelengths of 420 nm or less, 400 nm to 420 nm, and 405 nm or less, thereby reducing UV transmittance and preventing damage to the light-emitting element.

[0092] The aforementioned "maximum absorption wavelength" means the wavelength that exhibits the maximum absorption peak, that is, the wavelength that produces the maximum absorbance in the wavelength-dependent absorbance curve. The aforementioned "absorbance" can be measured by a conventional method known to those skilled in the art.

[0093] The UV absorber may be included in the adhesive film in an amount of approximately 0.1% to 1.5% by weight, specifically 0.5% to 1% by weight. Within this range, a UV blocking effect can be achieved, and problems such as the leaching of the UV absorber from the adhesive film can be eliminated.

[0094] The UV absorber may include, but is not limited to, one or more indole-based absorbers and triazine-based absorbers having the maximum absorption wavelength.

[0095] The composition may further contain additives. These additives may include those found in adhesive films and may be common additives known to those skilled in the art. For example, the additives may include, but are not limited to, one or more of pigments, ultraviolet absorbers, leveling agents, and antistatic agents.

[0096] The composition may further contain a solvent. The solvent enhances the coatability of the composition, enabling the provision of an adhesive film having a uniform surface while maintaining a thin thickness. The solvent may include common types known to those skilled in the art. For example, the solvent may include, but is not limited to, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, etc. In one specific example, the composition may contain about 20% to 30% by weight, specifically 20% to 25% by weight, of the solids content of the adhesive film. Within this range, the coatability of the composition can be excellent.

[0097] The adhesive film may have a haze of approximately 2% or less in the visible light region (e.g., wavelengths of 380 nm to 780 nm), specifically 0.1% to 1%, and a total light transmittance of approximately 90% or more, specifically 95% to 99%. Within this range, optical transparency is improved, and the adhesive film can be used in optical display devices.

[0098] An optical member according to one embodiment of the present invention includes an optical element and an adhesive film formed on at least one surface of the optical element, wherein the adhesive film includes the adhesive films according to each embodiment of the present invention. Thus, the optical member has good bending and / or good folding characteristics and can be used in a flexible display device.

[0099] In one embodiment, the optical element provides certain optical functions in a display device, such as light emission, polarization, optical compensation, improvement of display image quality, and / or conductivity. Examples of optical films include display panels including OLED panels, window films, windows, polarizing films, polarizing plates, color filters, phase difference films, elliptic polarizing films, reflective polarizing films, anti-reflective films, compensation films, brightness-enhancing films, alignment films, light-diffusing films, glass shatterproof films, surface protection films, OLED element barrier layers, plastic LCD substrates, transparent electrode films containing ITO (indium tin oxide), FTO (fluorinated tin oxide), AZO (aluminum dopped zinc oxide), CNT (carbon nanotube), Ag nanowires, graphene, etc. The optical element can be easily manufactured by a person with ordinary skill in the art to which the present invention belongs.

[0100] For example, a touch panel can be formed by attaching a window or optical film to a touchpad using an adhesive film. Alternatively, an adhesive film can be applied to a conventional polarizing film, as in the past.

[0101] The optical display device of the present invention includes the adhesive film of the present invention.

[0102] Optical display devices may include organic light-emitting element display devices, liquid crystal display devices, and the like. Optical display devices may include flexible display devices. However, optical display devices may also include non-flexible display devices.

[0103] [Modes for carrying out the invention] The structure and operation of the present invention will be described in more detail below through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any way.

[0104] Example 1 A (meth)acrylic binder was prepared by polymerizing 100 parts by weight of a monomer mixture containing 70 parts by weight of 2-ethylhexyl acrylate (2-EHA) and 30 parts by weight of n-butyl acrylate (n-BA).

[0105] Based on the solid content, a composition for adhesive films with a solid content of 20% by weight was prepared by mixing 0.04 parts by weight of (meth)acrylic oligomer 1, 0.2 parts by weight of isocyanate curing agent 2, and 0.06 parts by weight of silane coupling agent (S-1, Saiden Chemical Co., Ltd.) with 100 parts by weight of the (meth)acrylic binder prepared as described above, and then mixing in methyl ethyl ketone as a solvent.

[0106] The adhesive film composition produced above was applied to a polyethylene terephthalate film, which was the first release film, to a thickness of 15 μm, cured at 100°C for 3 minutes, and then combined with a polyethylene terephthalate film, which was the second release film, to produce an adhesive sheet consisting of the first release film, adhesive film, and second release film.

[0107] Examples 2 to 4 An adhesive sheet was manufactured by following the same method as in Example 1, except that the type and / or content of each component in Example 1 was changed as shown in Table 1 below.

[0108] Comparative Examples 1 to 3 An adhesive sheet was manufactured by following the same method as in Example 1, except that the type and / or content of each component in Example 1 was changed as shown in Table 1 below.

[0109] Adhesive films were manufactured by peeling PET films from the adhesive sheets produced in the examples and comparative examples. The physical properties of the adhesive films were evaluated as shown in Table 1 below, and the results are shown in Table 1 below.

[0110] (1) Peel strength (unit: gf / 25mm): The adhesive sheets of the examples and comparative examples were cut to a size of length × width (25mm × 25mm), and the first release film was peeled off. One side of a PET film (length × width × thickness: 150mm × 25mm × 75μm) was corona treated twice using a corona treatment machine, discharging at a dose of 78 doses per treatment (total dose: 156 doses). One side of the adhesive film was placed against the corona-treated surface of the corona-treated PET film, and after the second release film of the adhesive sheet was released, the other side of the adhesive film was placed against a glass plate (soda-lime glass), and a test specimen was manufactured by pressing it with a 2kg hand roller.

[0111] The manufactured test specimens were fixed to a TA.XT-Plus Texture Analyzer (manufactured by Stable Micro System), a peel strength measuring instrument. Using the TA.XT-Plus Texture Analyzer, the adhesive film and PET film were pulled 180° from a glass plate at a speed of 300 mm / min at 25°C, and the peel strength was measured in the region where the peel force was maintained at a constant level while the adhesive film and PET film were peeled from the glass plate.

[0112] Instead of glass plates (soda-lime glass), SUS (steel-use stainless, SUS306 plate) was used, and the peel strength was measured using the same method.

[0113] (2) Storage Modulus (Unit: MPa): After peeling off two release films from the adhesive sheets manufactured in the examples and comparative examples, multiple adhesive films were laminated together to create a sample with a thickness of 500 μm. The laminate of the adhesive film sample was perforated using an 8 mm diameter perforator, and this was used as a test specimen. Using a rheometer (TA Corporation, DHR3), a dynamic viscoelasticity measuring device, the modulus was measured in temperature sweep test mode at a temperature rise rate of 5 °C / min in the temperature range of -50 °C to 100 °C under conditions of 1% strain and 1 Hz. The storage modulus was measured at -20 °C and 60 °C, respectively.

[0114] (3) Shear deformation rate (unit: %) and rate of change of shear deformation rate (unit: %): The release films on both sides were removed from the adhesive sheets of the examples and comparative examples to obtain adhesive films (length × width: 100 mm × 25 mm). Multiple adhesive films were stacked, and the stack was perforated using a perforating machine with a diameter of 8 mm to produce cylindrical test specimens (thickness: 400 μm, diameter: 8 mm) having an upper surface and a lower surface.

[0115] The upper and lower surfaces of the manufactured cylindrical test specimens were mounted so that they engaged with the upper and lower jigs of a rheometer (TA Corporation, DHR3), a dynamic viscoelasticity measuring device. The chamber temperature was set to 60°C, the axial force to 1N, and the torque to 2000Pa. The time was set to 600s, and the shear deformation rate at this time was defined as the initial shear deformation rate.

[0116] The adhesive films obtained by releasing the release films from both sides of the adhesive sheets manufactured in the examples and comparative examples were placed in a chamber at 60°C and 95% relative humidity for 10 days. After placing the adhesive films at 25°C for 2 hours, the shear deformation rate was measured using the same method as the initial shear deformation rate measurement, and this value was defined as the "shear deformation rate after high temperature and high humidity." The rate of change was calculated using Equation 1.

[0117]

number

[0118] (In the above formula 1, A is the initial shear deformation rate of the adhesive film (unit: %), B is the shear deformation rate after high temperature and high humidity, which is the shear deformation rate (in %) of the adhesive film after it has been left at 60°C and 95% relative humidity for 10 days and then left at 25°C for 2 hours. (4) Peak temperature of tanδ (unit: °C): This was the same as the modulus measurement method described above. The storage modulus and loss modulus were measured for the prepared stacked test specimens according to temperature, and the temperature at which the tanδ value, determined by the ratio of these (loss modulus / storage modulus), was highest was confirmed.

[0119] (5) Folding at low temperature: The release films on both sides were separated from the adhesive sheets produced in the examples and comparative examples to obtain adhesive films. The adhesive films were placed between corona-treated polyethylene terephthalate (PET) films with a thickness of 50 μm, so that the corona-treated side of the PET film was in contact with the adhesive film, and after being attached with a roller, they were aged at room temperature for 12 hours and then cut into pieces measuring 70 mm x 140 mm to produce test specimens. The cut test specimens were fixed to a flexibility evaluation device (CFT-200, Covotech) using adhesive (4965, Tesa Tape Co., Ltd.), and bending was repeated at a rate of 30 cycles per minute at -20°C so that the radius of curvature of the test specimen in the vertical direction (140 mm) was 3 mm (one cycle is defined as bending and unbending the adhesive film in half once). When bending was repeated as one cycle, the number of cycles at which cracks first occurred in the polyethylene terephthalate film was measured visually. Adhesive films with a high initial cycle count are those that can easily relieve (relax) the stress on polyethylene terephthalate film caused by bending. A first cycle count of 100,000 or more is considered acceptable, while a first cycle count of less than 100,000 is considered unacceptable.

[0120] [Table 1]

[0121] *(Meth)acrylic oligomer 1: Oligomer formed from NCI, 4-hydroxybutyl acrylate and methyl methacrylate *(Meth)acrylic oligomer 2: Oligomer formed from NCI, 4-hydroxybutyl acrylate, methyl methacrylate, and methacrylic acid. *(Meth)acrylic oligomer 3: Oligomer formed from Saiden, 4-hydroxybutyl acrylate, methyl methacrylate, methacrylic acid, and n-butyl acrylate. *(Meth)acrylic oligomer 4: Oligomer formed from Saiden, 4-hydroxybutyl acrylate, methyl methacrylate, methacrylic acid, and tert-butyl methacrylate. *Hardening agent 1: Saiden, toluene diisocyanate-based hardening agent *Hardening agent 2: NCI, hexamethylene diisocyanate-based hardening agent *Hardening agent 3: Saiden, metal chelate-based hardening agent As shown in Table 1 above, the adhesive film of the present invention has a thin thickness and a uniform surface, high peel strength, and excellent folding properties at low temperatures. The adhesive film of the present invention is formed from a thermosetting composition and provides an adhesive film with high peel strength and excellent folding properties at low temperatures. Although not shown in Table 1 above, the adhesive film of the present invention reduces external UV transmission and has the effect of improving the lifespan and reliability of elements in the panel.

[0122] However, as shown in Table 1 above, the comparative adhesive films that deviated from the configuration of the present invention could not satisfy all of the effects of the present invention described above.

[0123] Simple modifications and alterations of the present invention can be readily implemented by those with ordinary skill in the art, and any such modifications and alterations can be considered to fall within the scope of the present invention.

Claims

1. An adhesive film formed from an adhesive film composition comprising a (meth)acrylic binder, a (meth)acrylic oligomer, and a curing agent, The (meth)acrylic binder has a glass transition temperature of -55°C or lower. The (meth)acrylic binder has a weight-average molecular weight of 900,000 to 1,500,000. The (meth)acrylic binder is a monomer mixture (meth)acrylic copolymer consisting only of 40% by weight or more and less than 100% by weight of (meth)acrylic monomers having branched-chain alkyl groups with 3 to 10 carbon atoms and a homopolymer glass transition temperature of -50°C or lower, and more than 0% by weight and up to 60% by weight of (meth)acrylic monomers having linear-chain alkyl groups with 1 to 10 carbon atoms and a homopolymer glass transition temperature of -50°C or lower. The (meth)acrylic oligomer has a glass transition temperature of 50°C or higher. The (meth)acrylic oligomer consists of an oligomer of a monomer mixture containing a (meth)acrylic monomer having a hydroxyl group. The (meth)acrylic oligomer has a weight-average molecular weight of 3,000 to 50,000. The curing agent includes an isocyanate-based curing agent. The adhesive film is an adhesive film in which the peak temperature of the tanδ value is -40°C or lower, and the storage modulus at -20°C is 0.3 MPa or lower.

2. The adhesive film according to claim 1, wherein the adhesive film has a thickness of 20 μm or less.

3. The adhesive film according to claim 1 or claim 2, wherein the adhesive film has a peel strength of 600 gf / 25 mm or more on a glass plate or SUS.

4. The adhesive film according to claim 1 or claim 2, wherein the adhesive film has a shear deformation rate of 18% or more.

5. The adhesive film described above is the adhesive film according to claim 1 or claim 2, wherein the rate of change of the shear deformation rate in the following formula 1 is 10% or less: [Math 1] (In the above formula 1, A is the initial shear deformation rate of the adhesive film (unit: %), B is the shear deformation rate after high temperature and high humidity, which is the shear deformation rate (in %) of the adhesive film after it has been left at 60°C and 95% relative humidity for 10 days and then left at 25°C for 2 hours.

6. The homopolymer has a glass transition temperature of -50°C or lower, and the (meth)acrylic monomer having a branched-chain alkyl group having 3 to 10 carbon atoms is 2-ethylhexyl acrylate. The adhesive film according to claim 1 or claim 2, wherein the glass transition temperature of the homopolymer is -50°C or lower, and the (meth)acrylic monomer having a linear alkyl group having 1 to 10 carbon atoms is n-butyl acrylate.

7. The adhesive film according to claim 1 or claim 2, wherein the (meth)acrylic monomer having a hydroxyl group is 4-hydroxybutyl acrylate.

8. The adhesive film according to claim 1 or claim 2, wherein the composition for the adhesive film comprises 100 parts by weight of the (meth)acrylic binder, 3 parts by weight or less of the (meth)acrylic oligomer, and 1 part by weight or less of the isocyanate curing agent.

9. The adhesive film according to claim 1 or claim 2, wherein the composition for the adhesive film further comprises one or more curing agents selected from a metal chelating curing agent, a carbodiimide curing agent, an aziridine curing agent, and an epoxy curing agent.

10. The adhesive film according to claim 1 or claim 2, further comprising a UV absorber.

11. The optical element and an adhesive film formed on at least one surface of the optical element, The adhesive film includes the adhesive film described in claim 1 or claim 2, wherein the optical member comprises the adhesive film described in claim 1 or claim 2.

12. An optical display device comprising the optical member described in claim 11.

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