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

Abstract

To provide an adhesive film for a polarizing plate, having high adhesive power after heating without decreasing in cohesion power.SOLUTION: An adhesive film for a polarizing plate includes a (meth)acrylic copolymer, a crosslinking agent, an adhesiveness enhancer, and a cured material of a composition containing cellulose nanocrystal whose surface is modified with an amino group containing silane coupling agent. The cellulose nanocrystal is contained by 0.05 parts by weight to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer. The cured material may be a thermally cured material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an adhesive film for a polarizing plate, a polarizing plate, and a display device. [Background technology]

[0002] In image display panels, such as liquid crystal panels used in liquid crystal display devices, polarizing plates are typically laminated on both sides of a liquid crystal cell formed of a liquid crystal layer disposed between a pair of transparent substrates, with a pressure-sensitive adhesive layer interposed therebetween. Such pressure-sensitive adhesive layers are required to have high durability, and are required to avoid problems such as peeling or lifting caused by the pressure-sensitive adhesive in, for example, durability tests that involve heating and humidification, which are typically performed as accelerated environmental tests. In particular, optical films used in in-vehicle panels are required to have durability that prevents defects such as peeling or lifting caused by the pressure-sensitive adhesive even in durability tests under high-temperature and high-humidity environments, compared to conventional methods.

[0003] The background art of the present invention is disclosed in Korean Patent Publication No. 2015-0010567 and the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 2015-0010567 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an adhesive film for polarizing plates that has high adhesive strength after heating without reducing cohesive strength. [Means for solving the problem]

[0006] According to one embodiment, an adhesive film for a polarizing plate is provided.

[0007] The adhesive film for polarizing plates comprises a cured product of a composition containing a (meth)acrylic copolymer, a crosslinking agent, an adhesion promoter, and cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent, and the cellulose nanocrystals are contained in an amount of 0.05 to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer.

[0008] According to one embodiment, a polarizer is provided.

[0009] The polarizing plate includes an adhesive film for polarizing plates.

[0010] According to one embodiment, a display device is provided.

[0011] The display device includes a polarizer. [Effects of the Invention]

[0012] The pressure-sensitive adhesive film for polarizing plates of the present invention has high adhesive strength even after heating without a decrease in cohesive strength, and therefore can improve durability against high temperatures, high temperature and high humidity, and thermal shock. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view of a polarizing plate according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram of a test piece for measuring cohesive strength. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, parts that are not relevant to the description are omitted in order to clearly explain the present invention, and the same reference numerals are used throughout the specification to refer to the same or similar components.

[0015] The terms used herein are merely for the purpose of describing exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly dictates otherwise.

[0016] In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0017] In this specification, when describing a range of values, "X to Y" means X or more and Y or less.

[0018] Generally, cohesion and adhesive strength have a trade-off relationship, so that as cohesion increases, adhesive strength decreases, and vice versa. Adhesive films used in vehicle-mounted display devices such as car navigation systems are often exposed to high temperatures for long periods of time, so they must simultaneously ensure high adhesive strength and cohesion at high temperatures.

[0019] The adhesive film for polarizing plates according to one embodiment can provide high adhesive strength after heating without reducing cohesive strength, thereby improving durability under high temperature, high temperature and high humidity, and thermal shock.

[0020] Cohesive strength can be evaluated by creep, with lower creep indicating higher cohesive strength. The creep of the pressure-sensitive adhesive film for polarizing plates may be 100 μm to 250 μm, for example, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250 μm, or 110 μm to 250 μm. By adopting the above range, it becomes easier to ensure high adhesive strength after heating, and the durability of the polarizing plate can be improved.

[0021] The adhesive strength of the polarizing plate adhesive film after heating may be 700 gf / 25 mm or more, for example, 700, 750, 800, 850, 900, 950, 1000 gf / 25 mm, or 700 gf / 25 mm to 1000 gf / 25 mm. By adjusting the adhesive strength within the above range, the durability of the polarizing plate can be easily improved.

[0022] "Adhesive strength after heating" refers to the adhesive strength measured after the adhesive film for polarizing plates is attached to a glass plate and left to stand for 48 hours at 50°C. Here, the "adhesive strength" is the value measured when a test piece in which the adhesive film is attached to a glass plate is peeled from the glass plate at a peel angle of 180° and a peel rate of 300 mm / min at 25°C and 50% relative humidity.

[0023] The adhesive film for polarizing plates according to one embodiment may exhibit a higher rate of change in adhesive strength after heating compared to the initial adhesive strength. Accordingly, when exposed to a harsh environment such as high temperature, the adhesive strength rapidly increases, thereby easily improving the durability of the polarizing plate under high temperature, high temperature and humidity, and thermal shock. In particular, when the polarizing plate is used in an in-vehicle display device such as a car navigation system, the durability of the polarizing plate can be further improved.

[0024] In one embodiment, the pressure-sensitive adhesive film for polarizing plates may have a rate of change of 130% or more as determined by the following formula 1. By adjusting the rate of change to fall within the above range, the durability of the polarizing plate at high temperatures, high temperature and high humidity, and under thermal shock can be easily improved.

[0025] [Formula 1] Adhesive strength change rate = (PS1-PS0) / PS0 x 100 In Equation 1, PS0 is the initial adhesive strength of the adhesive film for polarizing plates, and PS1 is the adhesive strength of the adhesive film for polarizing plates after heating.

[0026] In one embodiment, the adhesive film may have a rate of change of Formula 1 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%.

[0027] In Equation 1, PS0 may be 100 gf / 25 mm to 400 gf / 25 mm, for example, 200 gf / 25 mm to 400 gf / 25 mm. In Equation 1, PS1 may be 700 gf / 25 mm or more, for example, 700 gf / 25 mm to 1000 gf / 25 mm.

[0028] The adhesive film may have a haze of 1% or less, specifically 0% to 1%, in the visible light region, for example, at a wavelength of 550 nm. By adjusting the haze to fall within the above range, the adhesive film can be used in display devices.

[0029] The thickness of the adhesive film may be 5 μm to 50 μm, specifically 5 μm to 35 μm. By adjusting the thickness within this range, the adhesive film can be used for a polarizing plate.

[0030] Hereinafter, an adhesive film for polarizing plates according to one embodiment will be described.

[0031] The adhesive film for polarizing plates comprises a cured product of a composition containing a (meth)acrylic copolymer, a crosslinking agent, an adhesion promoter, and cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent, and the cellulose nanocrystals are contained in an amount of 0.05 to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer.

[0032] In one embodiment, the pressure-sensitive adhesive film for polarizing plates may be a thermosetting material.

[0033] In one embodiment, the adhesive film for polarizing plates may include a (meth)acrylic copolymer, a crosslinking agent, an adhesion promoter, and cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent. These may be derived from a composition.

[0034] The composition will be described in detail below.

[0035] (Meth)acrylic copolymer (Meth)copolymers include copolymers of a monomer mixture containing an alkyl group-containing unsaturated monomer and a carboxylic acid-containing unsaturated monomer.

[0036] In one embodiment, the total amount of the alkyl group-containing unsaturated monomer and the carboxylic acid-containing monomer in the monomer mixture may be 95% by weight or more, for example, 99% by weight to 100% by weight, or even 100% by weight. By adopting this range, the effects of the PSA film can be easily achieved.

[0037] The alkyl group-containing unsaturated monomer may include a (meth)acrylic monomer having an alkyl group.

[0038] The (meth)acrylic monomer having an alkyl group may be a (meth)acrylic monomer having an alkyl group at the ester moiety. Here, the "alkyl group" may be a linear or branched alkyl group having 1 to 10 carbon atoms. Specifically, the alkyl group-containing (meth)acrylic monomer may include, but is not limited to, one or more of methyl (meth)acrylate, ethyl acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, iso-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate.

[0039] The (meth)acrylic monomer having an alkyl group can be selected so that the glass transition temperature of its homopolymer is less than 0° C., for example, −80° C. to −10° C., or −70° C. to −10° C. By selecting a (meth)acrylic monomer having an alkyl group so that the glass transition temperature falls within the above range, the processability and reliability of the polarizing plate of the present application can be easily improved.

[0040] The alkyl group-containing unsaturated monomer may be contained in the monomer mixture in an amount of 60 to 99% by weight, for example, 60, 65, 70, 75, 80, 85, 90, 95, 99% by weight, 80 to 99% by weight, or 85 to 95% by weight. By adopting this range, it is possible to easily provide an improved peel strength and improved reliability of the polarizing plate.

[0041] The carboxylic acid-containing unsaturated monomer may include a (meth)acrylic monomer having a carboxylic acid. For example, the (meth)acrylic monomer having a carboxylic acid may be represented by the following Chemical Formula 1:

[0042] [ka]

[0043] In Chemical Formula 1, L 11 is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, n is 0 or 1, m is 0 or 1; R 1 is hydrogen or a methyl group.

[0044] For example, the (meth)acrylic monomer having a carboxylic acid may include one or more of (meth)acrylic acid, carboxyethyl (meth)acrylate, including 2-carboxyethyl (meth)acrylate, and the like.

[0045] The carboxylic acid-containing unsaturated monomer may be included in the monomer mixture in an amount of 1 to 40 wt%, 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 wt%, 1 to 20 wt%, or 5 to 15 wt%. By using the above ranges, the peel strength and reliability of the polarizing plate can be improved.

[0046] The (meth)acrylic copolymer may 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. By adopting this range, the effects of the present application can be easily achieved. Here, the "weight-average molecular weight" can be measured using gel permeation chromatography in terms of polystyrene.

[0047] The (meth)acrylic copolymer may have a glass transition temperature (Tg) of −35° C. or lower, for example, −50° C. to −35° C. By using a (meth)acrylic copolymer having a glass transition temperature in the above range, the effects of the present application can be easily achieved. Here, the “glass transition temperature” may be measured using a differential scanning calorimeter (DSC).

[0048] In one embodiment, the (meth)acrylic copolymer may be produced by polymerizing a monomer mixture using a conventional polymerization method. The polymerization method may include conventional methods known to those skilled in the art. For example, the (meth)acrylic copolymer may be produced by adding an initiator to the monomer mixture and then performing conventional copolymerization, such as suspension copolymerization, emulsion copolymerization, or solution copolymerization. The polymerization temperature may be 65°C to 70°C, and the polymerization time may be 6 to 8 hours. As the initiator, conventional initiators including azo polymerization initiators and / or peroxides such as benzoyl peroxide or acetyl peroxide may be used.

[0049] Crosslinking agent The crosslinking agent is a thermosetting crosslinking agent and may include one or more of an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an amine-based crosslinking agent, a metal chelate-based crosslinking agent, and an aziridine-based crosslinking agent, and preferably includes an isocyanate-based crosslinking agent.

[0050] The isocyanate crosslinking agent may be a bifunctional to hexafunctional isocyanate crosslinking agent. Specifically, the isocyanate crosslinking agent may be one or more aromatic isocyanate crosslinking agents selected from toluene diisocyanate, xylylene diisocyanate, halogen-substituted toluene diisocyanate, phenylene diisocyanate (e.g., m-phenylene diisocyanate), and tetramethyl-xylylene diisocyanate; one or more aliphatic isocyanate crosslinking agents selected from hexamethylene diisocyanate and pentamethylene diisocyanate; alicyclic isocyanate crosslinking agents such as cyclohexamethylene diisocyanate, or adducts thereof, for example, polyols such as trimethylolpropane (TMP), and adducts of the above-mentioned crosslinking agents.

[0051] The crosslinking agent, for example, an isocyanate-based crosslinking agent, may be contained in an amount of 0.1 to 5 parts by weight, for example, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts by weight, or 1 to 5 parts by weight, relative to 100 parts by weight of the (meth)acrylic copolymer. By adopting the above range, the effect of improving the peel strength of the adhesive film can be obtained.

[0052] Adhesion promoter The adhesion promoter is an aromatic modified terpene resin having a softening point of 100° C. or higher, for example, 120° C. to 150° C. This makes it possible to easily obtain the effects of the adhesive film described above when combined with cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent.

[0053] The weight-average molecular weight of the aromatic modified terpene resin may be 900 g / mol or more, specifically 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000 g / mol, 900 g / mol to 2000 g / mol, and more specifically 900 g / mol to 1500 g / mol. By adopting the above range, the effect of increasing adhesive strength can be achieved even in a thin film.

[0054] The adhesive promoter, for example, an aromatic-modified terpene resin, may be contained in an amount of 0.01 to 1 part by weight, specifically 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 part by weight, 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight, per 100 parts by weight of the (meth)acrylic copolymer. By adopting the above ranges, the effects of increasing the peel strength of the adhesive film and reducing haze can be obtained.

[0055] cellulose nanocrystals

[0056] The adhesive film contains cellulose nanocrystals that have been surface-modified with an amino group-containing silane coupling agent. Before surface modification, cellulose nanocrystals have abundant hydroxyl groups on their surfaces, making them hydrophilic, and therefore generally have low dispersibility in common polymers.

[0057] Cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent exhibit excellent compatibility with cured products containing (meth)acrylic copolymers and crosslinkers, and therefore can easily increase the adhesive strength after heating without reducing the cohesive strength of the adhesive film. In particular, the amino group-containing silane coupling agent can improve compatibility with the copolymer of the monomer mixture containing the above-mentioned alkyl group-containing unsaturated monomer and carboxylic acid-containing unsaturated monomer.

[0058] The amino group-containing silane coupling agent can comprise one or more alkoxysilanes having one or more amino groups.For example, the amino group-containing silane coupling agent can comprise one or more of the following: aminopropyltrialkoxysilanes, including 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, etc.; phenylaminopropyltrialkoxysilanes, such as N-phenyl-3-aminopropyltrimethoxysilane; N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrialkoxysilanes, such as N-2-(aminoethyl)-3-aminopropylalkyldialkoxysilanes; 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine; and N-(vinylbenzyl)2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride.

[0059] The cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent may have an aspect ratio of 1 to 50, for example, 2 to 40, or 5 to 30. By adopting this range, the nanocrystals can exhibit superior mechanical properties compared to cellulose resins or cellulose nanofibers. The aspect ratio refers to the ratio of the length to the average diameter of the cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent.

[0060] In one embodiment, the cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent may have an average diameter of 1 to 30 nm, 2 to 25 nm, or 2 to 20 nm, and a length of 10 to 1000 nm, 100 to 900 nm, or 200 to 800 nm. By adopting these ranges, the cellulose nanocrystals can exhibit superior mechanical properties compared to cellulose resins or cellulose nanofibers.

[0061] The cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent may have a crystallinity of 50% or more, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95%, 50% to 95%, or 60% to 80%. Having a crystallinity within this range allows the cellulose nanocrystals to provide superior mechanical properties compared to cellulose resins or cellulose nanofibers.

[0062] The surface modification of the cellulose nanocrystals with an amino group-containing silane coupling agent may be carried out using a conventional method for modifying the surface of cellulose.

[0063] In one embodiment, the amino group-containing silane coupling agent can modify at least a portion of the surface of the cellulose nanocrystals.

[0064] The cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent are contained in an amount of 0.05 to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer.

[0065] When the cellulose nanocrystals are contained in an amount of 0.05 parts by weight or more per 100 parts by weight of the (meth)acrylic copolymer, the adhesive strength after heating can be increased, and the cohesive strength can also be increased. When the cellulose nanocrystals are contained in an amount of 0.3 parts by weight or less per 100 parts by weight of the (meth)acrylic copolymer, the cohesive strength of the adhesive film does not become excessively high, and therefore the adhesive strength after heating can also be increased. For example, the cellulose nanocrystals may be contained in an amount of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.05 to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer.

[0066] The cellulose nanocrystals surface-modified with an amino-group-containing silane coupling agent can be combined with an adhesion promoter to increase the adhesive strength of the adhesive film after heating while preventing a decrease in the cohesive strength. In this regard, the adhesive promoter:nanocrystals surface-modified with an amino-group-containing silane coupling agent may be included in the composition in a weight ratio of 1:0.1 to 1:5, e.g., 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, or 1:0.5 to 1:3. By adopting this range, the adhesive strength of the adhesive film after heating can be easily increased while preventing a decrease in the cohesive strength.

[0067] In one embodiment, the amino group-containing silane coupling agent may be contained in the surface modification compound of the cellulose nanocrystal at 95% by weight or more, for example, 99% by weight to 100% by weight, or 100% by weight. By adopting this range, the effects of the adhesive film for polarizing plates described above can be easily achieved.

[0068] The pressure-sensitive adhesive film may further contain a silane coupling agent, which can further increase the peel strength of the pressure-sensitive adhesive film.

[0069] The silane coupling agent may be contained in an amount of 0.001 to 5 parts by weight per 100 parts by weight of the (meth)acrylic copolymer. By adopting this range, the effect of improving the release force can be exhibited. Preferably, the silane coupling agent may be contained in an amount of 0.01 to 1 part by weight.

[0070] The silane coupling agent can include one or more of an epoxy group-containing silane coupling agent, a mercapto group-containing silane coupling agent, an amine group-containing silane coupling agent, an alkyl group-containing silane coupling agent, and an isocyanate group-containing silane coupling agent.

[0071] Preferably, the silane coupling agent may include an amino group-containing silane coupling agent. The epoxy group-containing silane coupling agent can enhance the effects of the present invention. Specifically, the amino group-containing silane coupling agent may be an amino group-containing silane coupling agent such as aminopropyltrialkoxysilane or aminoethyltrialkoxysilane.

[0072] The composition may further contain conventional additives known to those skilled in the art, including, but not limited to, ultraviolet absorbers, antioxidants, surfactants, pigments, dyes, heat stabilizers, dispersants, inorganic particles, etc.

[0073] The composition may be a solvent-free type that does not contain a solvent, but the composition may contain a solvent to improve its applicability.

[0074] The adhesive film can be produced using the composition by a conventional method known to those skilled in the art.

[0075] A polarizing plate according to one embodiment includes an adhesive film for polarizing plates.

[0076] The polarizing plate includes a polarizer and an adhesive film for polarizing plates laminated on at least one surface of the polarizer.

[0077] The adhesive film for polarizing plates has already been explained, so the explanation thereof will be omitted.

[0078] Polarizer A polarizer can polarize external or internal light.

[0079] The polarizer may include a polyvinyl alcohol-based polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine or the like. For example, a polyvinyl alcohol-based polarizer is manufactured by dyeing a polyvinyl alcohol film with iodine or a dichroic dye and stretching the dye in a specific direction. Specifically, the polarizer is manufactured through a swelling process, a dyeing step, and a stretching step. Methods for performing each step are generally known to those skilled in the art.

[0080] The thickness of the polarizer may be in the range of 1 μm to 50 μm, which allows the polarizer to be used in a display device.

[0081] The polarizing plate may further include at least one of a protective layer and a retardation layer on at least one surface of the polarizer.

[0082] retardation layer The retardation layer realizes an anti-reflection function by converting the emitted linearly polarized light into circularly polarized light after the external light passes through the polarizer, thereby preventing reflection of the external light, thereby improving the appearance and screen quality.

[0083] In one embodiment, the retardation of the retardation layer in the in-plane direction at a wavelength of 550 nm may be 100 nm to 220 nm, specifically 100 nm to 180 nm, for example, λ / 4 (first retardation layer). By adopting this range, the reflectance to external light can be reduced, and the screen quality can be improved.

[0084] In another embodiment, the retardation layer may have a retardation in the in-plane direction at a wavelength of 550 nm of 225 nm to 350 nm, specifically 225 nm to 300 nm, for example, λ / 2 (second retardation layer). By adopting this range, the reflectance to external light can be reduced, and the screen quality can be improved.

[0085] In still another embodiment, the retardation layer may be a laminate of a first retardation layer and a second retardation layer.

[0086] In one embodiment, the retardation layer can exhibit reverse wavelength dispersion.

[0087] In one embodiment, the retardation layer may have a thickness of 0.1 μm to 10 μm, for example, 1 μm to 5 μm. By adjusting the thickness within this range, the polarizing plate can be made thinner and a target retardation can be achieved.

[0088] In one embodiment, the retardation layer may be a non-liquid crystal layer or a liquid crystal layer. Preferably, the retardation layer is a liquid crystal layer, which allows the polarizing plate to be made thinner.

[0089] For example, the liquid crystal layer may be formed of a composition containing a liquid crystal compound having at least one of an aromatic functional group and an alicyclic functional group. In one embodiment, the liquid crystal compound may be a polymer, oligomer, or monomer containing a unit composed of an aromatic ring and a polymerizable functional group that can impart liquid crystallinity. The polymerizable functional group may include a (meth)acryloyl group, an epoxy group, a vinyl ether group, or the like, and may be cured by heat or light, thereby increasing the strength of the liquid crystal retardation layer.

[0090] The composition may be formed from a composition containing the aromatic-containing liquid crystal compound described above. The composition may further contain additives such as a leveling agent, a polymerization initiator, an alignment aid, a heat stabilizer, a lubricant, a plasticizer, and an antistatic agent, and the details thereof can be referred to knowledge of those skilled in the art.

[0091] protective layer

[0092] A protective layer is formed on at least one surface of the polarizer to protect the polarizer or to provide an additional function to the polarizing plate.

[0093] The protective layer may include one or more of an optically clear protective film and a protective coating layer.

[0094] When the protective layer is a protective film type, it may include a protective film formed of an optically transparent resin. The protective film may be formed by melting and extruding the resin. If necessary, a stretching process may be further added. The resin may include one or more of cellulose ester-based resins including triacetyl cellulose, cyclic polyolefin-based resins including cyclic olefin polymers (COP), polycarbonate-based resins, polyester-based resins including polyethylene terephthalate (PET), polyethersulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, acyclic polyolefin-based resins, polyacrylate-based resins including polymethyl methacrylate resin, polyvinyl alcohol-based resins, polyvinyl chloride-based resins, and polyvinylidene chloride-based resins. Preferably, the protective film may be a film formed of a cyclic polyolefin-based resin including a cyclic polyolefin.

[0095] When the protective layer is a protective coating layer type, it can have good adhesion to the polarizer, transparency, mechanical strength, thermal stability, moisture blocking properties, and durability. In one embodiment, the protective coating layer for the protective layer may be formed of an active energy ray-curable resin composition including an active energy ray-curable compound and a polymerization initiator.

[0096] The active energy ray-curable compound may include one or more of a cationically polymerizable curable compound, a radically polymerizable curable compound, a urethane resin, and a silicone resin. The cationically polymerizable curable compound may be an epoxy compound having at least one epoxy group in the molecule, or an oxetane compound having at least one oxetane ring in the molecule. The radically polymerizable curable compound may be a (meth)acrylic compound having at least one (meth)acryloyloxy group in the molecule.

[0097] The thickness of the protective layer is 5 μm to 200 μm, specifically 30 μm to 120 μm, and may be 50 μm to 100 μm in the case of a protective film type, or 5 μm to 50 μm in the case of a protective coating layer type. By adopting this range, the protective layer can be used in optical display devices.

[0098] The protective layer may include a functional coating layer formed on at least one surface thereof or may be surface-treated. The functional coating layer may be, but is not limited to, a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, a low-reflection layer, an ultra-low-reflection layer, an anti-glare layer, etc. The surface treatment may be, but is not limited to, a corona treatment.

[0099] The protective layer may be attached to a polarizer or an adherend other than a polarizer by an adhesive layer. The adhesive layer may be formed of, but is not limited to, a water-based adhesive or a photocurable adhesive. The water-based adhesive and the photocurable adhesive may be used as appropriate, taking into account the knowledge of those skilled in the art.

[0100] FIG. 1 is a cross-sectional view of a polarizing plate according to one embodiment.

[0101] Referring to FIG. 1, the polarizing plate may include a polarizer 100, an upper protective layer 200 laminated on an upper surface of the polarizer, a lower protective layer 300 sequentially laminated on a lower surface of the polarizer, and an adhesive film 400 for the polarizing plate.

[0102] Although not shown in FIG. 1, the polarizing plate may further include one or more of a polarizer protective film, an anti-reflection film, a retardation film (liquid crystal layer or non-liquid crystal layer), and an adhesive film, which are commonly used in polarizing plates.

[0103] An optical display device according to one embodiment of the present invention includes the polarizing plate of the present invention. For example, the optical display device may be a light-emitting element display device having a light-emitting element, a liquid crystal display device, or the like. [Example]

[0104] The present invention will be described in more detail with reference to the following examples, which are provided for the purpose of facilitating understanding of the present invention and are not intended to limit the scope of the present invention.

[0105] Preparation Example 1

[0106] A monomer mixture containing 95 parts by weight of n-butyl acrylate and 5 parts by weight of acrylic acid, along with 100 parts by weight of ethyl acetate as a solvent, was placed in a 1 L reactor equipped with a nitrogen gas reflux and a cooling device for easy temperature control. Nitrogen gas was introduced over 1 hour with stirring to replace the oxygen in the reactor with nitrogen, and the reactor temperature was maintained at 55°C. An acrylic copolymer-containing solution was prepared by adding 0.2 parts by weight of 2,2-azobisisobutyronitrile as an initiator and reacting for 5 hours. The resulting acrylic copolymer had a weight-average molecular weight of 1.5 million g / mol, a glass transition temperature of -42°C, and a molecular weight distribution (Mw / Mn) of 2.3. Ethyl acetate was added to prepare a solution with a solids content of 17% by weight of the acrylic copolymer.

[0107] Preparation Example 2:

[0108] 30 g of 3-aminopropyltriethoxysilane was added to 500 mL of an aqueous acetic acid solution at pH 3.0 and dispersed at room temperature for 20 minutes using a magnetic stirrer. 10 g of cellulose nanocrystals were added to the solution with the 3-aminopropyltriethoxysilane thoroughly dispersed, and the mixture was stirred at room temperature for 4 hours. After the reaction was complete, the resulting mixture was filtered, and the filtered material was washed multiple times with distilled water and then with ethanol. After washing, the reaction product was dried under reduced pressure at 120°C for 12 hours to produce pale yellow, solid-phase cellulose nanocrystals surface-modified with 3-aminopropyltriethoxysilane.

[0109] Example 1

[0110] A composition for adhesive films was prepared by mixing 100 parts by weight of the acrylic copolymer prepared in Preparation Example 1 (based on solid content), 2 parts by weight of Coronate L (an isocyanate-based crosslinking agent, Polyurethanes Co., Ltd.) as a crosslinking agent, 0.1 parts by weight of an aromatic-modified terpene resin (Tamanol 901, Arakawa, softening point 120°C to 150°C) as an adhesion promoter, and 0.1 parts by weight of the surface-modified cellulose nanocrystals prepared in Preparation Example 2, and mixing with 25 parts by weight of methyl ethyl ketone as a solvent.

[0111] The prepared adhesive film composition was applied to one side of a release polyethylene terephthalate film in a predetermined thickness and dried at 90° C. for 4 minutes to prepare an adhesive film for polarizing plates (thickness: 23 μm).

[0112] A polyvinyl alcohol film (Mitsubishi Chemical Corporation, degree of polymerization: 2800, thickness: 20 μm) was dyed by immersion in a 0.3 wt% aqueous potassium iodide solution, and then stretched in the machine direction (MD) at a uniaxial stretching ratio of 5.0. The stretched polyvinyl alcohol film was then immersed in a 3 wt% aqueous boric acid solution and a 2 wt% aqueous potassium iodide solution for hue correction, and dried at 50°C for 4 minutes to produce a polarizer (light transmittance: 45%, thickness: 7 μm).

[0113] A polyvinyl alcohol-based water-based adhesive was applied to each of the upper and lower surfaces of the prepared polarizer to a predetermined thickness, and triacetyl cellulose films were attached to each of the upper and lower surfaces, followed by heat treatment to prepare a triacetyl cellulose film-polarizer-triacetyl cellulose film laminate.

[0114] The prepared adhesive film for polarizing plates was attached to one side of the triacetyl cellulose film to produce a polarizing plate.

[0115] Examples 2 to 3 and Comparative Examples 1 to 3

[0116] The same method as in Example 1 was carried out, except that the composition of the composition forming the adhesive film for polarizing plate in Example 1 was changed as shown in Table 1 below.

[0117] The adhesive films for polarizing plates and the polarizing plates of the Examples and Comparative Examples were evaluated for the physical properties shown in Table 1 below, and the results are shown in Table 1 below.

[0118] (1) Adhesive strength (unit: gf / 25mm) The polarizing plates prepared in the Examples and Comparative Examples were cut to a polarizer MD x TD (150 mm x 25 mm), attached to an alkali-free glass plate via a polarizing plate adhesive film, and rolled back and forth once with a 2 kg roller to prepare test specimens. The initial peel strength was measured one hour after preparation at room temperature. The peel strength was measured using a Texture Analyzer, a peel strength measuring device, when the polarizing plate was peeled from the alkali-free glass plate at a peel angle of 180° and a peel speed of 300 mm / min at 23°C and 50% relative humidity.

[0119] Test pieces were prepared in the same manner as above. The prepared test pieces were heated in an oven at 50°C for 48 hours, and then left to stand at 23°C and 50% relative humidity for 1 hour, after which the peel strength was measured. The peel strength was measured in the same manner as above.

[0120] (2) Cohesive force (unit: μm) The polarizing plates prepared in the Examples and Comparative Examples were cut to a polarizer MD×TD (150 mm×25 mm) and attached to a soda-lime glass plate via a polarizing plate adhesive film. Test specimens were then prepared by rolling a 2 kg roller back and forth once. The prepared test specimens were placed in an autoclave at 50°C and 3.5 atm for 1000 seconds and then left to stand at 23°C and 50% relative humidity for 24 hours. Using a texture analyzer, the length of the polarizing plate adhesive film stretched after being held at an angle of 180° and a load of 2250 gf for 1000 seconds at 25°C and 65% relative humidity was measured. Figure 2 shows a plan view and a cross-sectional view of a test specimen used to measure cohesive strength. Referring to Figure 2, a test specimen 23 was prepared by laminating a laminate 21 and a polarizing plate adhesive film 22. The test specimen was attached to a soda-lime glass plate 20 so that the area was length × width (a × b, 15 mm × 15 mm), and a load W was applied.

[0121] (3)Durability The polarizing plates produced in the examples and comparative examples were cut into polarizer MD×TD (100 mm×80 mm), attached to a glass plate via an adhesive film for polarizing plates, and then subjected to a pressure of 4 kg / cm 2 ~5kg / cm 2 The test specimen was prepared by applying a pressure of 1000 kJ / cm.

[0122] The prepared test specimens were left to stand at 95°C for 500 hours, after which their durability was evaluated. The prepared test specimens were left to stand at 60°C and 95% relative humidity for 500 hours, after which their durability was evaluated. Each test specimen was left to stand at -40°C for 30 minutes and at 80°C for 30 minutes, and durability was evaluated after 100 cycles. Durability was evaluated by visual observation based on whether or not there were any bubbles or peeling within the adhesive film, between the adhesive film and the glass plate, or between the adhesive film and the triacetyl cellulose film. A sample with no bubbles or peeling was rated as OK, while a sample with any one of bubbles or peeling was rated as NG.

[0123] [Table 1]

[0124] As shown in Table 1, the adhesive films for polarizing plates of the examples exhibited excellent durability against high temperatures, high temperature and humidity, and thermal shock by providing high adhesive strength after heating without reducing cohesive strength.

[0125] Simple variations and modifications of the present invention can be easily implemented by those skilled in the art, and all such variations and modifications can be considered to be included within the scope of the present invention. [Explanation of symbols]

[0126] 100 Polarizer 200 Upper protective layer 300 Lower protective layer 400 Adhesive film for polarizing plates

Claims

1. The cured product includes a composition containing a (meth)acrylic copolymer, a crosslinking agent, an adhesion promoter, and cellulose nanocrystals surface-modified with an amino group-containing silane coupling agent, The adhesive film for polarizing plates contains the cellulose nanocrystals in an amount of 0.05 to 0.3 parts by weight per 100 parts by weight of the (meth)acrylic copolymer.

2. The pressure-sensitive adhesive film for polarizing plates according to claim 1 , wherein the cured product is a thermoset product.

3. 2. The pressure-sensitive adhesive film for polarizing plates according to claim 1, which has a creep of 100 μm to 250 μm.

4. 2. The pressure-sensitive adhesive film for polarizing plates according to claim 1, which has an adhesive strength after heating of 700 gf / 25 mm or more.

5. The rate of change represented by the following formula 1 is 130% or more, [Formula 1] Adhesive strength change rate = (PS1 - PS0) / PS0 x 100 In the above formula 1, PS0 is the initial adhesive strength of the adhesive film for polarizing plates, The pressure-sensitive adhesive film for polarizing plates according to claim 1 , wherein PS1 is the adhesive strength of the pressure-sensitive adhesive film for polarizing plates after heating.

6. The pressure-sensitive adhesive film for polarizing plates according to claim 5, wherein PS0 in the formula 1 is 100 gf / 25 mm to 400 gf / 25 mm.

7. The amino group-containing silane coupling agent is one or more of aminopropyltrialkoxysilane, phenylaminopropyltrialkoxysilane, N-2-(aminoethyl)-3-aminopropyltrialkoxysilane, N-2-(aminoethyl)-3-aminopropylalkyldialkoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-(vinylbenzyl)2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, the adhesive film for polarizing plates according to claim 1.

8. 2. The pressure-sensitive adhesive film for polarizing plates according to claim 1, wherein the cellulose nanocrystals surface-modified with the amino group-containing silane coupling agent have an aspect ratio of 1 to 50.

9. 2. The pressure-sensitive adhesive film for polarizing plates according to claim 1, wherein the cellulose nanocrystals surface-modified with the amino group-containing silane coupling agent have a crystallinity of 50% or more.

10. The adhesive film for polarizing plates according to claim 1 , wherein the adhesive promoter and the nanocrystals surface-modified with the amino group-containing silane coupling agent are contained in the composition in a weight ratio of 1:0.1 to 1:

5.

11. The adhesive film for polarizing plates according to claim 1 , wherein the amino group-containing silane coupling agent is contained in the surface modifying compound of the cellulose nanocrystal in an amount of 95% by weight or more.

12. The pressure-sensitive adhesive film for polarizing plates according to claim 1 , wherein the adhesion promoter comprises an aromatic modified terpene resin.

13. The pressure-sensitive adhesive film for polarizing plates according to claim 12 , wherein the aromatic modified terpene resin has a softening point of 100° C. or higher.

14. The pressure-sensitive adhesive film for polarizing plates according to claim 1 , wherein the (meth)acrylic copolymer comprises a copolymer of a monomer mixture containing an alkyl group-containing unsaturated monomer and a carboxylic acid-containing unsaturated monomer.

15. The pressure-sensitive adhesive film for polarizing plates according to claim 14 , wherein the total amount of the alkyl group-containing unsaturated monomer and the carboxylic acid-containing monomer is 95% by weight or more in the monomer mixture.

16. A polarizing plate comprising the pressure-sensitive adhesive film for polarizing plates according to any one of claims 1 to 15.

17. A display device comprising the polarizer of claim 16.

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