Adhesive film for polarizing plate, polarizing plate, and display device

Abstract

Disclosed are an adhesive film for a polarizing plate, a polarizing plate, and a display device. The adhesive film includes a cured product of a composition including: a (meth) acrylic copolymer; a cross-linking agent; an adhesion enhancer; and cellulose nanocrystals subjected to surface modification by an amino group-containing silane coupling agent, in which the cellulose nanocrystals are present in an amount of 0.05 parts by weight to 0.3 parts by weight with respect to 100 parts by weight of the (meth) acrylic acid copolymer.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0052584, filed on April 19, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0003] The present application relates to an adhesive film for a polarizing plate, a polarizing plate, and a display device. BACKGROUND

[0004] An image display panel, for example, a liquid crystal panel used in a liquid crystal display, generally includes a polarizing plate on opposite sides of a liquid crystal cell formed of a liquid crystal layer between a pair of transparent substrates, with an adhesive layer interposed between the liquid crystal cell and the polarizing plate. The adhesive layer needs to have, for example, high durability to prevent problems such as peeling and warping during durability tests such as heating and humidification and generally performed as an environmental accelerated test. In particular, optical films for automotive panels need to have high durability so as to prevent defects such as peeling or warping caused by the adhesive layer even in durability tests under higher temperature / humidity conditions.

[0005] Background art of the present application is disclosed in Korean Patent Laid-open Publication No. 2015-0010567, etc. SUMMARY

[0006] An object of the present application is to provide an adhesive film for a polarizing plate that ensures high post-heating adhesive strength without deteriorating cohesion.

[0007] One aspect of the present application relates to an adhesive film for a polarizing plate.

[0008] The adhesive film for a polarizing plate includes a cured product of a composition including: a (meth)acrylic copolymer; a crosslinking agent; an adhesion enhancer; and cellulose nanocrystals subjected to surface modification with an amino group-containing silane coupling agent, wherein the cellulose nanocrystals are present in an amount of 0.05 parts by weight to 0.3 parts by weight with respect to 100 parts by weight of the (meth)acrylic copolymer.

[0009] Another aspect of the present application relates to a polarizing plate.

[0010] The polarizing plate includes the adhesive film for a polarizing plate.

[0011] A further aspect of the present application relates to a display device.

[0012] The display device includes the polarizing plate.

[0013] Embodiments of the present application provide an adhesive film for a polarizing plate, which can improve durability under high temperature, high temperature / humidity, and thermal shock conditions by securing a high post-heating adhesive strength without deteriorating cohesion. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present application.

[0015] Figure 2 is a schematic view of a test sample for measuring cohesion.

[0016] REFERENCE NUMERALS

[0017] 20: soda lime glass plate

[0018] 21: stack

[0019] 22, 400: adhesive film

[0020] 23: test sample

[0021] 100: polarizer

[0022] 200: upper protective layer

[0023] 300: lower protective layer

[0024] a: length

[0025] b: width

[0026] W: load DETAILED DESCRIPTION

[0027] Hereinafter, exemplary embodiments of the present application will be described in detail so as to be easily practiced by those having ordinary knowledge in the art. It should be understood that the present application can be implemented in various ways and is not limited to the following embodiments. In the accompanying drawings, parts irrelevant to the description of the present application are omitted for the sake of clarity, and the same components will be denoted by the same reference numerals throughout the specification.

[0028] The terms used herein are used to describe the exemplary embodiments and are not intended to limit the present application. Herein, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms.

[0029] Herein, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0030] Herein, "X to Y" used to indicate a specific numerical range means "greater than or equal to X and less than or equal to Y (X≤ and ≤Y)".

[0031] Generally, there is a trade-off between cohesion and adhesion, in that higher cohesion results in lower adhesion, and vice versa. An adhesive film applied to a display device for a vehicle, such as a car navigation system, is typically exposed to high temperatures for a long time, and thus needs to have both high adhesion and cohesion at high temperatures.

[0032] An adhesive film for a polarizing plate according to one embodiment can provide high post-heating adhesion strength without deteriorating cohesion. As a result, the adhesive film for a polarizing plate can improve durability under high temperature, high temperature / high humidity, and thermal shock conditions.

[0033] Cohesion can be evaluated by a creep test. A lower creep value indicates higher cohesion. The adhesive film for a polarizing plate can have a creep value of 100 micrometers to 250 micrometers, for example, 100 micrometers, 110 micrometers, 120 micrometers, 130 micrometers, 140 micrometers, 150 micrometers, 160 micrometers, 170 micrometers, 180 micrometers, 190 micrometers, 200 micrometers, 210 micrometers, 220 micrometers, 230 micrometers, 240 micrometers, 250 micrometers, 110 micrometers to 250 micrometers. Within this range, the adhesive film can easily ensure high post-heating adhesion strength, thereby improving durability of the polarizing plate.

[0034] The adhesive film for a polarizing plate can have a post-heating adhesion strength of 700 grams / 25 millimeters or more, for example, 700 grams / 25 millimeters, 750 grams / 25 millimeters, 800 grams / 25 millimeters, 850 grams / 25 millimeters, 900 grams / 25 millimeters, 950 grams / 25 millimeters, 1000 grams / 25 millimeters, 700 grams / 25 millimeters to 1,000 grams / 25 millimeters. Within this range, the adhesive film can easily improve durability of the polarizing plate.

[0035] The "post-heating adhesion strength" indicates an adhesion strength measured after the adhesive film is attached to a glass plate and the adhesive film is left at 50°C for 48 hours. Here, the "adhesion strength" is measured on a test sample prepared by adhering the adhesive film to a glass plate, when the adhesive film is peeled from the glass plate at a peeling angle of 180° and a peeling rate of 300 millimeters / minute at 25°C and 50% RH (relative humidity).

[0036] The adhesive film for a polarizing plate according to the embodiment can have a high change rate in post-heating adhesion strength with respect to initial adhesion strength. As a result, when the adhesive film is exposed to a severe environment, such as high temperature, the adhesion strength of the adhesive film rapidly increases, and the adhesive film can facilitate improvement in durability of the polarizing plate under high temperature, high temperature / high humidity, and thermal shock conditions. In particular, when the polarizing plate is applied to a display device for a vehicle, such as a car navigation system, the adhesive film can further improve durability of the polarizing plate.

[0037] In one embodiment, the adhesive film for a polarizing plate can have an adhesive strength variation rate of 130% or more than 130% according to Formula 1 calculation. Within this range, the adhesive film can easily improve the durability of the polarizing plate under high temperature, high temperature / high humidity, and thermal shock conditions.

[0038] Adhesive strength variation rate = (PS1- PS0) / PS0 x 100%,--- (1)

[0039] where PS0 denotes the initial adhesive strength of the adhesive film, and PS1 denotes the adhesive strength of the adhesive film after heating.

[0040] In one embodiment, the adhesive film can have an adhesive strength variation rate of 130% to 400%, for example, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 140% to 300% according to Formula 1 calculation.

[0041] In Formula 1, PS0 can range from 100 grams force / 25 millimeters to 400 grams force / 25 millimeters, for example, 200 grams force / 25 millimeters to 400 grams force / 25 millimeters. In Formula 1, PS1 can be 700 grams force / 25 millimeters or more than 700 grams force / 25 millimeters, for example, 700 grams force / 25 millimeters to 1000 grams force / 25 millimeters.

[0042] The adhesive film can have a haze of 1% or less than 1%, specifically 0% to 1%, in the visible light range (for example, at a wavelength of 550 nanometers). Within this range, the adhesive film can be used for a display device.

[0043] The adhesive film can have a thickness of 5 micrometers to 50 micrometers, more specifically 5 micrometers to 35 micrometers. Within this range, the adhesive film can be used for a polarizing plate.

[0044] Next, an adhesive film for a polarizing plate according to one embodiment will be described.

[0045] The adhesive film for a polarizing plate according to the embodiment includes a cured product of a composition including: a (meth)acrylic copolymer; a crosslinking agent; an adhesion enhancer; and a cellulose nanocrystal subjected to surface modification with an amino group-containing silane coupling agent, wherein the cellulose nanocrystal is present in an amount of 0.05 parts by weight to 0.3 parts by weight with respect to 100 parts by weight of the (meth)acrylic copolymer.

[0046] In one embodiment, the adhesive film for a polarizing plate can be a thermally cured product of the composition.

[0047] In one embodiment, the adhesive film for a polarizing plate can include a (meth)acrylic copolymer, a crosslinking agent, an adhesion enhancer, and cellulose nanocrystals subjected to surface modification with an amino group-containing silane coupling agent. These components can be derived from the composition.

[0048] Hereinafter, the composition will be described in detail.

[0049] (meth)acrylic copolymer

[0050] The (meth)acrylic copolymer includes a copolymer of a monomer mixture of an alkyl group-containing unsaturated monomer and a carboxylic acid group-containing unsaturated monomer.

[0051] In one embodiment, the total amount of the alkyl group-containing unsaturated monomer and the carboxylic acid group-containing unsaturated monomer in the monomer mixture can be 95% by weight or more, for example, 99% to 100% by weight, or 100% by weight. Within this range, the effect of the adhesive film can be easily achieved.

[0052] The alkyl group-containing unsaturated monomer can include a (meth)acrylic monomer having an alkyl group.

[0053] The (meth)acrylic monomer having an alkyl group can include a (meth)acrylic monomer having an alkyl group at an ester site thereof. Here, the "alkyl group" can be a linear or branched C1 to C 10 alkyl group. Specifically, the (meth)acrylic monomer containing an alkyl group can include at least one selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate, but is not limited thereto.

[0054] The (meth)acrylic ester monomer having an alkyl group can have a homopolymer glass transition temperature of less than 0℃, for example, -80℃ to -10℃, or -70℃ to -10℃. Within this range, the composition can easily ensure improvement in processability and reliability of a polarizing plate.

[0055] The unsaturated monomer containing an alkyl group can be present in the monomer mixture in an amount of 60 to 99% by weight, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 80% to 99%, or 85% to 95% by weight. Within this range, the composition can easily ensure improvement in the peeling strength and reliability of the polarizing plate.

[0056] The unsaturated monomer containing a carboxylic acid group can include a (meth)acrylic monomer having a carboxylic acid group.

[0057] For example, the (meth)acrylic monomer having a carboxylic acid group can be represented by Formula 1:

[0058]

[0059] wherein L 11 is a substituted or unsubstituted C1 to C5 alkylene group, n is 0 or 1, m is 0 or 1, and R1 is hydrogen or methyl.

[0060] For example, the (meth)acrylic monomer having a carboxylic acid group can include at least one of (meth)acrylic acid or (meth)acrylic carboxyethyl ester (including 2-carboxyethyl (meth)acrylate), etc.

[0061] The unsaturated monomer containing a carboxylic acid group can be present in the monomer mixture in an amount of 1 to 40% 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%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 1% to 20%, or 5% to 15% by weight. Within this range, the composition can easily ensure improvement in the peeling strength and reliability of the polarizing plate.

[0062] The (meth)acrylic copolymer can have a weight average molecular weight (Mw) of 1,000,000 to 2,000,000 g / mol, for example, 1,500,000 to 2,000,000 g / mol. Within this range, the composition can easily ensure the effects of the present application. Here, the "weight average molecular weight" can be measured by gel permeation chromatography based on a polystyrene standard.

[0063] The (meth)acrylic copolymer can have a glass transition temperature (Tg) of -35°C or less than -35°C, for example, -50°C to -35°C. Within this range, the composition can easily ensure the effect of the present application. Here, the "glass transition temperature" can be measured using a differential scanning calorimeter (DSC).

[0064] In one embodiment, the (meth)acrylic copolymer can be prepared by polymerizing a monomer mixture through a typical polymerization method. The polymerization method can include any typical method known to those skilled in the art. For example, the (meth)acrylic copolymer can be prepared by adding an initiator to the monomer mixture, followed by typical copolymer polymerization, for example, suspension polymerization, emulsion polymerization, solution polymerization, etc. The polymerization can be performed at a polymerization temperature of 65°C to 70°C for 6 hours to 8 hours. The initiator can be a typical initiator, including azo-based polymerization initiators and / or peroxides, such as benzoyl peroxide or acetyl peroxide.

[0065] Crosslinking agent

[0066] The crosslinking agent is a thermosetting crosslinking agent and can include at least one selected from the group consisting of isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, metal chelate crosslinking agents, and azidoethane crosslinking agents. Preferably, the crosslinking agent includes an isocyanate crosslinking agent.

[0067] The isocyanate crosslinking agent can include a di- to hexa-functional isocyanate curing agent. Specifically, the isocyanate curing agent can include at least one aromatic isocyanate curing agent selected from the group consisting of toluene diisocyanate, xylene diisocyanate, halogenated toluene diisocyanate, phenylene diisocyanate (including m-phenylene diisocyanate, etc.), and tetramethyl-xylene diisocyanate; at least one aliphatic isocyanate curing agent selected from the group consisting of hexamethylene diisocyanate and pentamethylene diisocyanate; alicyclic isocyanate curing agents (e.g., cyclohexylmethylene diisocyanate, etc.); or adducts thereof, for example, at least one of polyols such as trimethylolpropane (TMP); and adducts of the above curing agents.

[0068] The crosslinking agent (e.g., isocyanate crosslinking agent) can be present in an amount of 0.1 parts by weight to 5 parts by weight, for example, 0.1 parts by weight, 0.5 parts by weight, 1 parts by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, 5 parts by weight, 1 parts by weight to 5 parts by weight, with respect to 100 parts by weight of the (meth)acrylic copolymer. Within this range, the composition can ensure an increase in the peel strength of the adhesive film.

[0069] Adhesion enhancer

[0070] The adhesion enhancer includes an aromatic-modified terpene resin having a softening point of 100°C or more (e.g., 120°C to 150°C). The adhesion enhancer, when combined with the cellulose nanocrystals that are surface-modified with an amino-containing silane coupling agent, can easily obtain the above-mentioned effects of the adhesive film.

[0071] The aromatic-modified terpene resin can have a weight average molecular weight of 900 g / mol or more, specifically 900 g / mol, 1000 g / mol, 1100 g / mol, 1200 g / mol, 1300 g / mol, 1400 g / mol, 1500 g / mol, 1600 g / mol, 1700 g / mol, 1800 g / mol, 1900 g / mol, 2000 g / mol, 900 g / mol to 2000 g / mol, more specifically 900 g / mol to 1,500 g / mol. Within this range, the terpene resin can ensure the adhesion enhancement effect at a thin film thickness.

[0072] The adhesion enhancer (e.g., the aromatic-modified terpene resin) can be present in an amount of 0.01 parts by weight to 1 part by weight, specifically 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight, 0.1 parts by weight to 0.8 parts by weight, more specifically 0.1 parts by weight to 0.5 parts by weight, with respect to 100 parts by weight of the (meth)acrylic acid copolymer. Within this range, the adhesion enhancer can ensure the increase in the peeling strength of the adhesive film while reducing its haze.

[0073] Cellulose nanocrystals

[0074] The adhesive film includes cellulose nanocrystals, specifically cellulose nanocrystals that are surface-modified with an amino-containing silane coupling agent. Since the cellulose nanocrystals have hydrophilicity due to the abundance of hydroxyl groups on their surface before the surface modification, the cellulose nanocrystals generally exhibit poor dispersibility in typical polymers.

[0075] The cellulose nanocrystals that are surface-modified with the amino-containing silane coupling agent have high compatibility with the cured product including the (meth)acrylic acid copolymer and the crosslinking agent, thereby facilitating the increase in the post-heating adhesion strength of the adhesive film without causing the deterioration of its cohesion. In particular, the amino-containing silane coupling agent can improve the compatibility with the copolymer including a monomer mixture of an alkyl-containing unsaturated monomer and a carboxylic acid group-containing unsaturated monomer.

[0076] Amino group-containing silane coupling agents can include alkoxysilanes having at least one amino group. For example, the amino group-containing silane coupling agent can include at least one selected from the group consisting of aminopropyl trialkoxysilane such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and the like; phenyl aminopropyl trialkoxysilane such as N-phenyl-3-aminopropyl trimethoxysilane, and the like; N-2-(aminoethyl)-3-aminopropyl trialkoxysilane such as N-2-(aminoethyl)-3-aminopropyl methyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyl trimethoxysilane, and the like; N-2-(aminoethyl)-3-aminopropyl alkyl dialkyl dialkoxysilane; 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine; and N-(vinylbenzyl) 2-aminoethyl-3-aminopropyl trimethoxysilane hydrochloride.

[0077] The cellulose nanocrystals subjected to the surface modification with the amino group-containing silane coupling agent can have an aspect ratio of 1 to 50, for example, 2 to 40, or 5 to 30. Within this range, the cellulose nanocrystals can have better mechanical properties than cellulose resins or cellulose nanofibers. The aspect ratio refers to the ratio of the length to the average diameter of the cellulose nanocrystals.

[0078] In one embodiment, the cellulose nanocrystals subjected to the surface modification with the amino group-containing silane coupling agent can have an average diameter of 1 nanometer to 30 nanometers, 2 nanometers to 25 nanometers, or 2 nanometers to 20 nanometers, and a length of 10 nanometers to 1,000 nanometers, 100 nanometers to 900 nanometers, or 200 nanometers to 800 nanometers. Within these ranges, the cellulose nanocrystals can have better mechanical properties than cellulose resins or cellulose nanofibers.

[0079] The cellulose nanocrystals subjected to the surface modification with the amino group-containing silane coupling agent can have a crystallinity of 50% or greater than 50%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 50% to 95%, or 60% to 80%. Within this range, the cellulose nanocrystals can have better mechanical properties than cellulose resins or cellulose nanofibers.

[0080] The surface modification of the cellulose nanocrystals with the amino group-containing silane coupling agent can be performed by typical cellulose surface modification methods.

[0081] In one embodiment, the amino group-containing silane coupling agent surface-modifies at least a portion of the surface area of the cellulose nanocrystals.

[0082] The cellulose nanocrystals subjected to the surface modification with the amino group-containing silane coupling agent are present in an amount of 0.05 parts by weight to 0.3 parts by weight with respect to 100 parts by weight of the (meth)acrylic acid copolymer.

[0083] The adhesive film allows to increase the post-heating adhesive strength of the adhesive film while preventing the deterioration of the cohesive force of the adhesive film when the cellulose nanocrystal is present in an amount of 0.05 parts by weight or more relative to 100 parts by weight of the (meth)acrylic copolymer. The adhesive film allows to increase the post-heating adhesive strength of the adhesive film without excessively increasing the cohesive force of the adhesive film when the cellulose nanocrystal is present in an amount of 0.3 parts by weight or less relative to 100 parts by weight of the (meth)acrylic copolymer. For example, the cellulose nanocrystal can be present in an amount of 0.05 parts by weight to 0.3 parts by weight (e.g., 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight) relative to 100 parts by weight of the (meth)acrylic copolymer.

[0084] The cellulose nanocrystal surface-modified with the amino group-containing silane coupling agent can be combined with an adhesive enhancer to increase the post-heating adhesive strength of the adhesive film while preventing the deterioration of the cohesive force of the adhesive film. Here, the adhesive enhancer and the nanocrystal can be present in a weight ratio of 1:0.1 to 1:5, for example, 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:0.5 to 1:3, in the composition. Within this range, the composition can facilitate the increase in the post-heating adhesive strength of the adhesive film without causing the deterioration of the cohesive force of the adhesive film.

[0085] In one embodiment, the amino group-containing silane coupling agent can be present in an amount of 95% by weight or more, for example, 99% by weight to 100% by weight, 100% by weight, in the compound used for the surface modification of the cellulose nanocrystal. Within this range, the effect of the adhesive film can be easily achieved.

[0086] The adhesive film can further include a silane coupling agent. The silane coupling agent can further increase the peeling strength of the adhesive film.

[0087] The silane coupling agent can be present in an amount of 0.001 parts by weight to 5 parts by weight relative to 100 parts by weight of the (meth)acrylic copolymer. Within this range, the silane coupling agent can increase the peeling strength of the adhesive film. Preferably, the silane coupling agent is present in an amount of 0.01 parts by weight to 1 parts by weight.

[0088] The silane coupling agent can include at least one selected from an epoxy group-containing silane coupling agent, a mercapto group-containing silane coupling agent, an amino group-containing silane coupling agent, an alkyl group-containing silane coupling agent, and an isocyanate group-containing silane coupling agent.

[0089] Preferably, the silane coupling agent includes an amino group-containing silane coupling agent. An epoxy group-containing silane coupling agent can help achieve the effects of the present application. Specifically, the amino group-containing silane coupling agent can include an aminopropyl trialkoxysilane, an aminoethyl trialkoxysilane, or the like.

[0090] The composition can further include typical additives known to those skilled in the art. The additives can include a UV absorber, an antioxidant, a surfactant, a pigment, a dye, a heat stabilizer, a dispersant, an inorganic particle, or the like, but are not limited thereto.

[0091] Although the composition can be a solvent-free type, the composition can include a solvent to increase the applicability of the composition.

[0092] The adhesive film can be prepared from the composition by any typical method known to those skilled in the art.

[0093] The polarizing plate according to one embodiment includes an adhesive film for a polarizing plate.

[0094] The polarizing plate includes a polarizer; and an adhesive film for a polarizing plate formed on at least one surface of the polarizer.

[0095] The adhesive film for a polarizing plate is the same as described above, and the description thereof will be omitted.

[0096] Polarizer

[0097] The polarizer is used to polarize external light or internal light.

[0098] The polarizer can include a polyvinyl alcohol-based polarizer in which a polyvinyl alcohol film is dyed with iodine or the like. For example, the polyvinyl alcohol-based polarizer is manufactured by dyeing a polyvinyl alcohol film with iodine or a dichroic dye, and then stretching the dyed film in a certain direction. Specifically, the polarizer is manufactured by a stretching process, a dyeing process, and a stretching process. The method of performing each process is known to those skilled in the art.

[0099] The polarizer can have a thickness of 1 micrometer to 50 micrometers. Within this range, the polarizer can be used in a display device.

[0100] The polarizing plate can further include at least one protective layer or a retardation layer on at least one surface of the polarizer.

[0101] Retardation layer

[0102] The retardation layer is a layer that prevents reflection of external light by realizing circular polarization of light emitted in a linear polarization manner in the polarizer, thereby improving appearance and screen quality.

[0103] In one embodiment, the retardation layer can have an in-plane retardation of 100 nm to 220 nm, specifically 100 nm to 180 nm, for example, λ / 4 retardation (first retardation layer) at a wavelength of 550 nm. In this range, the retardation layer can ensure improvement in screen quality by reducing reflectance of external light.

[0104] In another embodiment, the retardation layer can have an in-plane retardation of 225 nm to 350 nm, specifically 225 nm to 300 nm, for example, λ / 2 retardation (second retardation layer) at a wavelength of 550 nm. In this range, the retardation layer can ensure improvement in screen quality by reducing reflectance of external light.

[0105] In another embodiment, the retardation layer can be implemented by a stack of the first retardation layer and the second retardation layer.

[0106] In one embodiment, the retardation layer can exhibit negative wavelength dispersion.

[0107] In one embodiment, the retardation layer can have a thickness of 0.1 μm to 10 μm, for example, 1 μm to 5 μm. In this range, the polarizing plate can have a reduced thickness and can achieve a desired retardation.

[0108] In one embodiment, the retardation layer can be a non-liquid crystal layer or a liquid crystal layer. Preferably, the retardation layer is a liquid crystal layer, thereby making a reduction in thickness of the polarizing plate possible.

[0109] For example, the liquid crystal layer can be formed of a composition including a liquid crystal compound having at least one of an aromatic functional group or an alicyclic functional group. In one embodiment, the liquid crystal compound can be a polymer, oligomer, or monomer including a unit consisting of an aromatic ring and a polymerizable functional group capable of imparting liquid crystallinity. The polymerizable functional group can include a (meth)acryl group, an epoxy group, a vinyl ether group, etc., which can be cured by heat or light to increase the strength of the liquid crystal retardation layer.

[0110] The composition can be formed of a composition including an aromatic group-containing liquid crystal compound as described above. The composition can further include typical additives well known to those skilled in the art, such as a leveling agent, a polymerization initiator, an alignment aid, a heat stabilizer, a lubricant, a plasticizer, an antistatic agent, etc.

[0111] Protective Layer

[0112] The protective layer can be formed on at least one surface of the polarizer to protect the polarizer or to provide an additional function to the polarizing plate.

[0113] The protective layer can include an optically transparent protective film and / or an optically transparent protective coating layer.

[0114] When the protective layer is of the protective film type, the protective layer can include a protective film formed of an optically transparent resin. The protective film can be formed by melting and extruding an optically transparent resin. A stretching process can be added as necessary. The resin can include at least one selected from the group consisting of a cellulose ester resin including triacetyl cellulose and the like, a cyclic polyolefin resin including a cyclic olefin polymer (COP) and the like, a polycarbonate resin, a polyester resin including polyethylene terephthalate (PET) and the like, a polyether sulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, a non-cyclic polyolefin resin, a polyacrylate resin including a poly(methyl methacrylate) resin, a polyvinyl alcohol resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, and the like. Preferably, the protective film includes a film formed of a cyclic polyolefin resin including a cyclic polyolefin and the like.

[0115] When the protective layer is of the protective coating type, the protective layer can improve adhesion to the polarizing plate, transparency, mechanical strength, thermal stability, moisture resistance, and durability. In one embodiment, the protective coating for the protective layer can be formed of a photoactive radiation curable resin composition including a photoactive radiation curable compound and a polymerization initiator.

[0116] The photoactive radiation curable compound can include at least one selected from the group consisting of a cationically polymerizable curing compound, a radically polymerizable curing compound, a polyurethane resin, and a silicone resin. The cationically polymerizable curing compound can be an epoxy-based compound having at least one epoxy group or an oxetane-based compound having at least one oxetane ring. The radically polymerizable curing compound can be a (meth)acrylic compound having at least one (meth)acryloyloxy group therein.

[0117] The protective layer can have a thickness of 5 micrometers to 200 micrometers, specifically, 30 micrometers to 120 micrometers for the protective film type or 50 micrometers to 100 micrometers for the protective coating type. Within this range, the protective layer can be used in an optical display device.

[0118] The protective layer can include a functional coating formed on at least one surface thereof or can be subjected to a surface treatment. The functional coating can include a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, a low reflectance layer, an ultra-low reflectance layer, an anti-glare layer, and the like, but is not limited thereto. The surface treatment can include a corona treatment and the like, but is not limited thereto.

[0119] The protective layer can be adhered to the polarizer or to a bonding object other than the polarizer through an adhesive layer. The adhesive layer can be formed of a water-based adhesive or a light-curable adhesive, but is not limited thereto. Both the water-based adhesive and the light-curable adhesive can be appropriately used with reference to details known to those skilled in the art.

[0120] Figure 1is a sectional view of a polarizing plate according to an embodiment.

[0121] Reference Figure 1 According to the present embodiment, the polarizing plate can include a polarizer 100, an upper protective layer 200 formed on an upper surface of the polarizer 100, and a lower protective layer 300 and an adhesive film 400 for the polarizing plate, which are sequentially stacked on a lower surface of the polarizer.

[0122] Although not shown in Figure 1 , the polarizing plate can further include at least one selected from the group consisting of a polarizer protective film, an anti-reflection film, a retardation film (a liquid crystal layer or a non-liquid crystal layer), and an adhesive film commonly used in a polarizing plate.

[0123] An optical display device according to an embodiment of the present application includes a polarizing plate according to the present application. For example, the optical display device can include a light emitting device display having a light emitting device, a liquid crystal display, etc.

[0124] Next, the present application will be described in more detail with reference to some examples. However, it should be noted that these examples are provided for illustrative purposes only and should not be construed in any way as limiting the present application.

[0125] Preparation Example 1

[0126] In a 1 liter reactor equipped with a cooling device for temperature control under a nitrogen atmosphere, a monomer mixture containing 95 parts by weight of n-butyl acrylate and 5 parts by weight of acrylic acid and 100 parts by weight of ethyl acetate as a solvent were put in, and nitrogen was supplied to the reactor so as to replace oxygen while stirring the reactor for 1 hour, and then the reactor was maintained at 55°C. 0.2 parts by weight of 2,2-azobisisobutyronitrile was added as an initiator, and reacted with the resulting mixture for 5 hours to prepare a solution containing an acrylic acid copolymer. The acrylic acid copolymer had a weight average molecular weight of 1,500,000 g / mol, a glass transition temperature of -42°C, and a molecular weight distribution (Mw / Mn) of 2.3. By adding ethyl acetate to the resulting solution, a solution containing 17% by weight of the acrylic acid copolymer in terms of solid content was prepared.

[0127] Preparation Example 2

[0128] To 500 ml of an aqueous solution of pH 3.0 prepared using acetic acid, 30 g of 3-aminopropyltriethoxysilane was added and dispersed at room temperature using a magnetic stirrer for 20 minutes. To the 3-aminopropyltriethoxysilane sufficiently dispersed solution, 10 g of cellulose nanocrystals was added and stirred at room temperature for 4 hours. The mixture obtained after completion of the reaction was filtered to obtain a solid product, then washed several times with distilled water, and finally washed with ethanol. The finally washed reaction product was dried at 120°C under reduced pressure for 12 hours to prepare cellulose nanocrystals subjected to surface modification with 3-aminopropyltriethoxysilane and having a light yellow solid phase.

[0129] Example 1

[0130] A pressure-sensitive adhesive film composition was prepared by mixing, as a crosslinking agent, 2 parts by weight of Coronate L (isocyanate crosslinking agent, Polyurethane Co., Ltd.), as an adhesion enhancer, 0.1 part by weight of an aromatic group-modified terpene resin (softening point: 120 to 150°C, Tamanol 901, Arakawa Co., Ltd.), 0.1 part by weight of the surface-modified cellulose nanocrystals prepared in Preparation Example 2, and, as a solvent, 25 parts by weight of methyl ethyl ketone, with respect to 100 parts by weight of the acrylic copolymer prepared in Preparation Example 1.

[0131] A pressure-sensitive adhesive film for a polarizing plate was prepared by depositing the prepared pressure-sensitive adhesive film composition to a predetermined thickness on one surface of a polyethylene terephthalate release film, followed by drying at 90°C for 4 minutes (thickness: 23 micrometers).

[0132] A polyvinyl alcohol film (degree of polymerization: 2800, thickness: 20 micrometers, Mitsubishi Chemical Co., Ltd.) was dyed by immersion in an aqueous solution containing 0.3% by weight of potassium iodide, and then stretched to 5.0 times the original length in the machine direction (MD). The stretched polyvinyl alcohol film was color corrected by immersion in an aqueous solution containing 3% by weight of boric acid and an aqueous solution containing 2% by weight of potassium iodide, and dried at 50°C for 4 minutes, thereby preparing a polarizer (light transmittance: 45%, thickness: 7 micrometers).

[0133] A polyvinyl alcohol water-based adhesive was deposited to a predetermined thickness on the upper and lower surfaces of the prepared polarizer, and a triacetyl cellulose film was stacked on the upper and lower surfaces thereof, followed by heat treatment, thereby preparing a triacetyl cellulose film / polarizer / triacetyl cellulose film stack.

[0134] A polarizing plate was prepared by adhering the prepared pressure-sensitive adhesive film for a polarizing plate to one surface of a triacetyl cellulose film.

[0135] Example 2 and Example 3 and Comparative Examples 1 to 3

[0136] A polarizing plate was prepared in the same manner as in Example 1, except that the composition for the adhesive film was changed as listed in Table 1.

[0137] The adhesive film for the polarizing plate and the polarizing plate prepared in the examples and comparative examples were subjected to the performance evaluation in Table 1, and the results are shown in Table 1.

[0138] (1) Adhesive strength (unit: gram force / 25 mm)

[0139] The polarizing plate prepared in each of the examples and comparative examples was cut to a size of 150 mm x 25 mm (MD x TD of the polarizer) and attached to an alkali-free glass plate through the adhesive film for the polarizing plate, and then a 2-kg roller was reciprocally rolled on the cut polarizing plate once, thereby preparing a test sample. The prepared test sample was left to stand at room temperature for 1 hour, and then the initial peeling strength was measured. Then, using a peeling strength measuring instrument (Texture Analyzer), the peeling strength when the polarizing plate was peeled from the alkali-free glass plate was measured at a peeling angle of 180° and a peeling rate of 300 mm / min at 23°C and 50% RH.

[0140] A test sample was prepared in the same manner as described above. The prepared test sample was heated in an oven at 50°C for 48 hours and left to stand at 23°C and 50% RH for 1 hour, and then the peeling strength was measured. The peeling strength was measured by the same method as described above.

[0141] (2) Cohesive force (unit: μm)

[0142] The polarizing plate prepared in each of the examples and comparative examples was cut to a size of 150 mm x 25 mm (MD x TD of the polarizer) and attached to a soda-lime glass plate through the adhesive film for the polarizing plate, and then a 2-kg roller was reciprocally rolled on the cut polarizing plate once, thereby preparing a test sample. The prepared test sample was placed in a high-pressure autoclave at 50°C and 3.5 atm, treated for 1,000 seconds, and left to stand at 23°C and 50% RH for 24 hours. Then, the prepared test sample was left to stand at 25°C and 65% RH under a load of 2,250 gram force at an angle of 180° for 1,000 seconds, and then the extension length of the test sample was measured using a Texture Analyzer. Figure 2 is a plan view and a sectional view of a test sample for measuring cohesive force. With reference to Figure 2 , a test sample 23 including a stack 21 and an adhesive film for the polarizing plate 22 was prepared and attached to a soda-lime glass plate 20 so that the attached area was 15 mm x 15 mm (length x width, a x b), and then a load W was applied.

[0143] (3) Durability

[0144] The polarizing plates manufactured in Examples and Comparative Examples were cut to a size of 100 mm x 80 mm (MD x TD of the polarizer) and attached to a glass plate through an adhesive film for a polarizing plate, and then a pressure of 4 to 5 kg / cm2was applied to the cut polarizing plate, thereby preparing a test sample.

[0145] The prepared test sample was left at 95°C for 500 hours to evaluate high temperature durability. The prepared test sample was left at 60°C and 95% RH for 500 hours to evaluate high temperature and high humidity durability. The heat shock durability was evaluated by performing 100 cycles, each cycle including leaving the test sample at -40°C for 30 minutes and leaving the test sample at 80°C for 30 minutes. The durability evaluation was performed by visually checking the air bubble generation or peeling between the inside of the adhesive film, the adhesive film and the glass plate, or the adhesive film and the triacetyl cellulose film. No air bubble generation or peeling was rated as OK, and any air bubble generation or peeling was rated as NG.

[0146] Table 1

[0147]

[0148] As shown in Table 1, the adhesive film for a polarizing plate in the Examples can improve the durability of the polarizing plate under high temperature, high temperature / high humidity, and heat shock conditions by providing a high post-heating adhesive strength without reducing cohesive force.

[0149] It should be understood that various modifications, alterations, changes and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the present application.

Claims

1. An adhesive film for a polarizing plate, comprising a cured product of a composition, said composition comprising: a (meth)acrylic acid copolymer; a crosslinking agent; an adhesive enhancer; and cellulose nanocrystals surface-modified with an amino-containing silane coupling agent. The cellulose nanocrystals are present in an amount of 0.05 to 0.3 parts by weight relative to 100 parts by weight of the (meth)acrylic acid copolymer.

2. The adhesive film according to claim 1, wherein the cured product is a thermosetting product.

3. The adhesive film according to claim 1, wherein the adhesive film has a creep value of 100 micrometers to 250 micrometers.

4. The adhesive film according to claim 1, wherein the adhesive film has a heat-bonded adhesive strength of 700 g / 25 mm or greater than 700 g / 25 mm.

5. The adhesive film according to claim 1, wherein, According to Formula 1, the adhesive film has a rate of change of adhesive strength of 130% or greater: Bond strength change rate = (PS1 - PS0) / PS0 x 100%, --- (1) Where PS0 represents the initial adhesive strength of the adhesive film, and PS1 represents the adhesive strength of the adhesive film after heating.

6. The adhesive film according to claim 1, wherein, In Formula 1, PS0 ranges from 100 gf / 25 mm to 400 gf / 25 mm.

7. The adhesive film of claim 1, wherein the amino-containing silane coupling agent comprises at least one selected from: aminopropyltrialkoxysilane; phenylaminopropyltrialkoxysilane; N-2-(aminoethyl)-3-aminopropyltrialkoxysilane; N-2-(aminoethyl)-3-aminopropylalkyldialkyldialkoxysilane; 3-triethoxysilyl-N-(1,3-dimethylbutylene)propylamine; and N-(vinylbenzyl)2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride.

8. The adhesive film according to claim 1, wherein the cellulose nanocrystals have an aspect ratio of 1 to 50.

9. The adhesive film according to claim 1, wherein the cellulose nanocrystals have a crystallinity of 50% or greater than 50%.

10. The adhesive film according to claim 1, wherein the adhesive enhancer and the cellulose nanocrystals surface-modified by the amino-containing silane coupling agent are present in the composition in a weight ratio of 1:0.1 to 1:

5.

11. The adhesive film according to claim 1, wherein the amino-containing silane coupling agent is present in the surface-modifying compound of the cellulose nanocrystals in an amount of 95% by weight or greater than 95% by weight.

12. The adhesive film of claim 1, wherein the adhesive enhancer comprises an aromatic-modified terpene resin.

13. The adhesive film according to claim 12, wherein the aromatic-modified terpene resin has a softening point of 100°C or greater.

14. The adhesive film of claim 1, wherein the (meth)acrylic acid copolymer comprises a copolymer of monomer mixtures, the monomer mixture comprising alkyl-containing unsaturated monomers and carboxylic acid-containing unsaturated monomers.

15. The adhesive film according to claim 14, wherein in the monomer mixture, the alkyl-containing unsaturated monomer and the carboxylic acid-containing unsaturated monomer are present in a total amount of 95% by weight or greater than 95% by weight.

16. A polarizing plate comprising an adhesive film as claimed in any one of claims 1 to 15.

17. A display device comprising a polarizing plate as claimed in claim 16.

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