CN107033647B

CN107033647B - Polarizing plate comprising water-based primer composition and method for preparing optical film comprising primer layer

Info

Publication number: CN107033647B
Application number: CN201611263857.8A
Authority: CN
Inventors: 沈花燮; 徐银美; 金范锡; 李南贞
Original assignee: Anhui Hemei Material Technology Co ltd
Current assignee: Anhui Hemei Material Technology Co., Ltd
Priority date: 2010-09-20
Filing date: 2011-09-20
Publication date: 2022-02-18
Anticipated expiration: 2031-09-20
Also published as: JP2012063773A; CN107033647A; JP5553362B2; CN102417807A

Abstract

The present invention relates to a polarizing plate comprising a water-based primer composition, and a method of preparing an optical film comprising a primer layer. The primer composition includes, per 100 parts by weight of the primer composition, 1 to 30 parts by weight of the polyurethane polymer, 0.1 to 10 parts by weight of the water dispersible particles, and the balance water. The polarizing plate is positioned between the optical film and the primer layer formed from the primer composition. The method includes coating at least one side of an optical film with a primer composition; and drying the optical film coated with the primer composition. The primer composition has good adhesion properties and can be included in a polarizing plate without reducing the transparency of the polarizing plate and without requiring additional processes or equipment.

Description

Polarizing plate comprising water-based primer composition and method for preparing optical film comprising primer layer

The application is a divisional application of the chinese invention patent application entitled "water-borne primer composition, polarizing plate comprising the same, and method of producing optical film comprising primer layer", having application date of 2011, 9 and 20, and application number of 201110289760.5.

Cross Reference to Related Applications

The present invention claims priority from korean patent application No. 10-2010-0092685, filed on 20/2010 to the korean intellectual property office, and No. 10-2011-0083998, filed on 23/2011, and the disclosure of which is incorporated herein by reference.

Technical Field

The present invention relates to a water-based primer composition, a polarizing plate comprising the same, and a method of preparing an optical film comprising a primer layer. In particular, the present invention relates to a water-based primer composition for an optical film having good adhesion and transparency, a polarizing plate including the same, and a method of preparing an optical film including a primer layer.

Background

Generally, the polarizer has a stacked structure as shown in fig. 1. Referring to fig. 1, the polarizing plate includes a polarizer 1 and triacetyl cellulose (TAC) films 3 attached to both sides of the polarizer 1 using an aqueous adhesive 2 prepared from a polyvinyl alcohol (PVA) aqueous solution. If such a polarizing plate is used for an in-plane switching (IPS) type liquid crystal display without an additional compensation film, the viewing angle of the IPS type liquid crystal display is narrow. In this case, in order to increase the viewing angle of the IPS type liquid crystal display, one of the two polarizing plate TAC films may be replaced with a zero retardation TAC (Z-TAC) film having substantially no phase difference in thickness and surface directions.

However, since TAC films are substantially vulnerable to moisture erosion, Z-TAC films have poor durability due to dimensional change thereof when used for a long time. For this reason, attempts have been made to use a film formed of a cycloolefin resin or an acrylic resin, which is resistant to moisture and has a low phase difference. In particular, acrylic films are known to have advantages in terms of cost as well as optical performance and durability.

In the case of manufacturing a polarizing plate using a TAC film as a protective film, an aqueous PVA adhesive is generally used to bond the TAC film to the PVA polarizing plate. In this case, an alkali treatment or a corona treatment is performed on the surface of the TAC film to increase the adhesive strength. However, in the case of manufacturing a polarizing plate using an acrylic film and a PVA adhesive, it is difficult to obtain desired adhesive strength by alkali treatment or corona treatment. If a general TAC film is treated with alkali or corona, hydrophilic groups such as hydroxyl groups are introduced to the surface of the TAC film, and the bonding strength between the TAC film and the PVA adhesive can be easily ensured due to hydrogen bonds between the hydrophilic groups and the PVA adhesive. On the other hand, in the case where the acrylic film is treated with corona treatment or plasma treatment, sufficient bonding strength between the acrylic film and the PVA polarizing plate cannot be ensured.

The acrylic film may be bonded to the polarizer using an Ultraviolet (UV) curable acrylic adhesive. However, in this case, an additional curing step is required, and since volatile flammable monomers are used, an explosion-proof device may also be required. In addition, a general aqueous PVA adhesive can be formed into a thin layer having a thickness of about 100nm by controlling solid content and process, but it is difficult to form a UV curable acrylic adhesive into a layer having a thickness of about 1mm or less. Therefore, the polarizing plate including the acrylic adhesive layer may be broken due to the increase in brittleness of the acrylic adhesive layer. Further, even in the case where the acrylic adhesive may be strongly bonded to the acrylic film, the acrylic adhesive may not be strongly bonded to the polarizing plate. An adhesive including a large amount of acid functional groups can be firmly bonded to the polarizer. However, this may lead to corrosion and damage to the working environment.

Accordingly, there is a need for an acrylic film comprising a primer layer for improving process efficiency without changing existing adhesives. In addition, there is a need to develop a transparent primer composition having strong adhesive properties.

Disclosure of Invention

One embodiment of the present invention provides a primer composition for enhancing the bonding strength between a base material and an adhesive layer, while not affecting the transparency of an optical film.

Another embodiment of the present invention provides a polarizing plate, wherein a primer layer formed of the primer composition is positioned between a polarizer and an optical film.

Another embodiment of the present invention provides a method of preparing an optical film including a primer layer.

According to an embodiment of the present invention, there is provided a primer composition including: for every 100 weight parts of the primer composition, 1 to 30 weight parts of polyurethane polymer, 0.1 to 10 weight parts of water dispersible particles, and the balance of water.

The polyurethane polymer may have a weight average molecular weight between 30,000 and 100,000.

The primer composition may include 3 to 20 parts by weight of a polyurethane polymer.

The polyurethane polymer may comprise carboxylic acid groups.

The polyurethane polymer may be obtained by reacting a polyol and an isocyanate.

The polyol may be at least one selected from the group consisting of polyester polyol, polyether polyol and polycarbonate diol.

The isocyanate may be at least one selected from the group consisting of Toluene Diisocyanate (TDI), 4-diphenylmethane diisocyanate (MDI), 1, 5-Naphthalene Diisocyanate (NDI), tolidine diisocyanate (TODI), Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate, trans-cyclohexane-1, 4-diisocyanate, and Xylene Diisocyanate (XDI).

The water dispersible particles may include at least one inorganic oxide selected from the group consisting of silica, titania, alumina, zirconia, and antimony oxide.

The water-dispersible particles may include at least one selected from the group consisting of a silicone resin, a fluororesin, a (meth) acrylic resin, a crosslinked polyvinyl alcohol (PVA), and a melamine resin.

The water dispersible particles may have an average particle size between 10nm and 200 nm.

According to another embodiment of the present invention, there is provided an optical film comprising a primer layer formed on at least one side thereof, wherein the primer layer is formed from the primer composition according to any one of claims 1 to 10.

The primer layer may have a surface water contact angle between 40 ° and 100 °.

The optical film may be an acrylic film.

The acrylic film may include: a copolymer comprising alkyl (meth) acrylate units and styrene units; and an aromatic resin comprising a carbonate moiety in its main chain.

The acrylic film may include: alkyl (meth) acrylate units; a styrene unit; a 3-to 6-membered heterocyclic unit substituted with at least one carbonyl group; and an acrylonitrile unit.

The primer layer may have a thickness between 50nm and 1000 nm.

According to another embodiment of the present invention, there is provided a polarizing plate including: a polarizing plate; and an optical film attached to one side or both sides of the polarizer, wherein a primer layer formed from the primer composition according to any one of claims 1 to 10 is located on at least one side of the optical film.

The adhesive layer may be formed on one side or both sides of the polarizer, and the adhesive layer may be formed of PVA resin.

According to another embodiment of the present invention, there is provided a method of preparing an optical film including a primer layer, the method including: coating at least one side of an optical film with the primer composition according to any one of claims 1 to 10; and drying the optical film coated with the primer composition.

The method further comprises treating at least one side of the optical film with a surface treatment method selected from the group consisting of alkali treatment, corona treatment, and plasma treatment.

Drawings

The above and other aspects, features and other advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings, in which:

fig. 1 is a diagram illustrating a polarizing plate of the related art;

fig. 2 is a diagram illustrating a polarizing plate according to an embodiment of the present invention; and

fig. 3 is a diagram illustrating a polarizing plate according to another embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

The present invention provides a primer composition for improving the bonding strength between an optical film and an adhesive layer and preparing a polarizing plate having good water resistance.

The primer composition of the present invention may be water-soluble, and in this case, an explosion-proof device may not be used. The primer composition of the present invention comprises: 1 to 30 parts by weight of a polyurethane polymer per 100 parts by weight of the primer composition; 0.1 to 10 parts by weight of water dispersible particles; and the balance water. For example, the primer composition can include 3 to 20 parts by weight of the polyurethane polymer per 100 parts by weight of the primer composition. In another embodiment, the primer composition can include 5 to 15 parts by weight of the polyurethane polymer per 100 parts by weight of the primer composition.

The term "balance water" is used to describe: the primer composition comprises a polyurethane polymer and water-dispersible particles within the above ranges, with water making up the remainder of the primer composition to make up 100 wt% of the primer composition.

If the concentration of the polyurethane polymer is less than 1 part by weight per 100 parts by weight of the primer composition, the adhesion of the primer composition may be low. If the concentration of the polyurethane polymer is more than 30 parts by weight per 100 parts by weight of the primer composition, the viscosity of the primer composition may be high, resulting in difficulty in leveling the primer composition during the coating process, and it may take a long time to dry the primer composition.

If the concentration of the water dispersible particles is less than 0.1 parts by weight per 100 parts by weight of the primer composition, films including the primer composition may not slip against each other when the films are rolled, and thus the films may be torn. If the concentration of the water-dispersible particles is more than 10 parts by weight per 100 parts by weight of the primer composition, it is difficult to manufacture a transparent film having a haze of 0.3 or less by using the primer composition because the haze of the transparent film increases if the average particle diameter of the water-dispersible particles is 50nm or more.

The weight average molecular weight of the polyurethane polymer may be between 10,000 and 100,000. If the weight average molecular weight of the polyurethane polymer is less than 10,000, the adhesive strength of the primer composition is low, and if the weight average molecular weight of the polyurethane polymer is more than 100,000, it is difficult to prepare a water-dispersed urethane.

The polyurethane polymer may comprise carboxylic acid groups. In this case, when the polyurethane polymer is prepared, anions are generated to facilitate dispersion of the polyurethane polymer in water, thereby bringing the polyurethane polymer into closer contact with the polarizer.

The polyurethane polymer containing carboxyl groups can be obtained by a reaction between a polyol, a polyisocyanate and a chain extender having free carboxyl groups. Examples of the chain extender having a carboxyl group include dihydroxycarboxylic acids and dihydroxysuccinic acids. The dihydroxy carboxylic acid may be a dialkyl alcohol alkyl acid including dimethylol alkyl acids such as dimethylol acetic acid, dimethylol butyric acid, dimethylol propionic acid, dimethylol butyric acid and dimethylol valeric acid. The listed examples of dihydroxycarboxylic acids can be used individually or in mixtures.

The polyurethane polymer is obtained by a reaction between a polyol and a polyisocyanate. The polyol may be any polyol containing two or more hydroxyl groups per molecule. Examples of the polyol include polyester polyol, polyether polyol and polycarbonate diol. The polyol may be at least one selected from the listed materials. That is, the polyol may be one of the listed materials or a combination of two or more thereof.

The polyhydric alcohol may be at least one selected from the group consisting of ethylene glycol, 1, 2-acetone diol, 1, 3-propylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, neopentyl glycol, pentanediol, 1, 6-hexanediol, 1, 8-octanediol, 1, 10-decanediol, 4' -dihydroxyphenyl propane, 4' -dihydroxymethyl methane (4,4' -dihydroxymethyl ethane), diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1, 4-cyclohexanedimethanol, 1, 4-cyclohexanediol, bisphenol a, bisphenol F, glycerol, 1,1, 1-trimethylolpropane, 1,2, 5-hexanetriol, pentaerythritol, glucose, sucrose and sorbitol.

Polyester polyols can be obtained by reaction between a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include: aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1, 4-naphthalenedicarboxylic acid, 2, 5-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid and tetrahydrophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, and itaconic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1, 3-cyclohexanedicarboxylic acid and 1, 4-cyclohexanedicarboxylic acid; and reactive derivatives such as anhydrides, alkyl ethers and acid halides thereof. The listed examples of polyacids can be used individually or in mixtures. Alternatively, the polybasic acid may be at least one selected from the group consisting of polytetramethylene glycol (PTMG), polypropylene glycol (PPG), and polyethylene glycol (PEG).

The polycarbonate polyol may be at least one selected from the group consisting of poly (hexamethylene carbonate) diol and poly (cyclohexane carbonate) diol.

For example, polyether polyols can be obtained by ring-opening polymerization by adding alkylene oxides to polyhydric alcohols. For example, examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, and trimethylolpropane. The examples listed for the polyhydric alcohols can be used individually or in mixtures.

The polyisocyanate may be any compound containing two or more NCO groups. For example, the polyisocyanate may be selected from Toluene Diisocyanate (TDI), 4-diphenylmethane diisocyanate (MDI), 1, 5-Naphthalene Diisocyanate (NDI), tolidine diisocyanate (TODI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate, trans-cyclohexane-1, 4-diisocyanate, Xylene Diisocyanate (XDI), and combinations thereof.

The polyurethane polymer may be prepared by any method known in the art. For example, the polyurethane polymer may be prepared by a one-step process, in which the components are reacted with each other simultaneously, or by a multi-step process, in which the components are reacted with each other stepwise. If the polyurethane polymer includes carboxyl groups, the polyurethane polymer can be prepared by a multi-step process because the carboxyl groups can be easily introduced. In preparing the polyurethane polymer, a suitable urethane reaction catalyst may be used.

In addition to the above components, other polyols and/or other chain extenders may be used in the preparation of the polyurethane polymer.

For example, the other polyol may be a polyol having three or more hydroxyl groups, such as sorbitol, glycerol, trimethylolethane, trimethylolpropane, and pentaerythritol.

Examples of other chain extenders include: diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, neopentyl glycol, pentanediol, 1, 6-hexanediol, and propylene glycol; aliphatic diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, 1, 4-butanediamine and aminoethylethanolamine; alicyclic diamines such as isophorone diamine and 4, 4-dicyclohexylmethane diamine; and aromatic diamines such as xylylenediamine and toluenediamine.

In addition, a neutralizing agent may be used in the preparation of the polyurethane polymer. The neutralizing agent can improve the stability of the polyurethane polymer in water. Examples of the neutralizing agent include ammonia, N-methylmorpholine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolylen, morpholine, tripropylamine, ethanolamine and triisopropanolamine. The examples listed for neutralizing agents can be used individually or in mixtures.

The polyurethane polymer can be prepared by using an organic solvent which does not react with the polyisocyanate but is soluble in water. Examples of the organic solvent include: ester solvents such as ethyl acetate and ethylene glycol monobutyl ether acetate; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; and ethereal solvents such as dioxane tetrahydrofuran. The listed examples of organic solvents can be used alone or in admixture.

Any suitable dispersible particle may be used as the water dispersible particle in the present invention. For example, particles dispersible in water may be used as the water-dispersible particles. For example, inorganic particles or organic particles may be used as the water-dispersible particles. Examples of the inorganic particles include inorganic oxides such as silica, titania, alumina, zirconia, and antimony oxide. Examples of the organic particles include silicone resins, fluorine resins, (meth) acrylic resins, crosslinked polyvinyl alcohols, and melamine resins.

For example, silica may be used as the water dispersible particles due to its suitable anti-blocking property, high transparency, anti-fogging property, coloring resistance, and low influence on the optical properties of the polarizing plate. In addition, the use of silica can effectively form a primer layer due to good dispersion of silica in the primer composition and stability in a dispersed state.

The water dispersible particles may have an average particle diameter (primary average particle diameter) between 10nm and 200 nm. For example, the water dispersible particles may have an average particle size between 20nm and 70 nm. If the average particle diameter of the water-dispersible particles is less than 10nm, solution stability is deteriorated due to high surface energy, and thus the water-dispersible particles may be precipitated in the primer solution. On the other hand, if the average particle diameter of the water-dispersible particles is greater than 200nm, the water-dispersible particles may be unevenly dispersed and local agglomeration may occur in the primer solution, and thus, light having a wavelength of 400nm or more may be scattered due to the agglomeration greater than the wavelength of visible light (400nm to 800nm), thereby increasing haze. If the water-dispersible particles have an average particle diameter within the above range, it is possible to appropriately form an uneven structure on the primer layer, thereby effectively reducing the frictional force between the primer layer and the acrylic film and/or between the primer layers. The result is improved anti-blocking performance.

Since the primer composition of the present invention is an aqueous composition, the water-dispersible particles are mixed as an aqueous dispersion. For example, in the case of using silica as the water-dispersible particles, colloidal silica may be used as the water-dispersible particles. Commercially available colloidal silica products can be used: SNOWTEX series (Nissan chemical industries), AEROSIL series (Airproducts), EPOSTAR series (Nihon catalyst), SOLIOSTAR RA series, and LSH series (Ranco).

The present invention also provides an optical film in which at least one side thereof is covered with a primer layer formed of the primer composition.

The surface of the primer layer has a water contact angle between 40 ° and 100 °. For example, the water contact angle may be between 50 ° and 90 °. In another embodiment, the water contact angle may be between 60 ° and 80 °. If the water contact angle is less than 40 deg., the primer layer may react with iodine of the polarizer to destroy the arrangement of iodine since the primer layer is highly hydrophilic. This may result in deterioration of color properties and reduction of polarization degree. On the other hand, if the water contact angle is greater than 100 °, it may be difficult to contact the primer layer to the polarizer since the primer layer is hydrophobic.

The optical film may have a single layer structure or a multilayer structure including two or more layers. In the latter case, the layers may be stacked by using the same material or different materials. In the present invention, the term "optical film" is used to indicate that the film is used for optical purposes. For example, the term "optical film" includes: a transparent film having an optical transparency of 80% or more. In addition, the term "optical film" also includes films having an optical transparency of 50% or less if the film is suitable for a specific optical element, such as a polarizing plate.

Specifically, the optical film may be an acrylic film including a (meth) acrylate resin. For example, a film including a (meth) acrylate resin may be formed by extruding a molding material containing a (meth) acrylate resin as a main component.

The acrylic film may include: a copolymer having an alkyl (meth) acrylate unit and a styrene unit; and an aromatic resin comprising a carbonate moiety in its main chain. Alternatively, the acrylic film may include: alkyl (meth) acrylate units; a styrene unit; a 3-to 6-membered heterocyclic unit substituted with at least one carbonyl group; and an acrylonitrile unit. Alternatively, the acrylic film may be formed of an acrylic resin having a lactone structure.

Examples of the (meth) acrylate resin having a lactone ring structure are the (meth) acrylate resins having a lactone ring structure disclosed in Japanese laid-open patent application Nos. 2000-230016, 2001-151814 and 2002-120326.

The resin composition disclosed in korean patent laid-open publication No. 10-2009-0115040 is an example of a (meth) acrylate resin having an aromatic ring. The disclosed resin composition includes: (a) (meth) acrylate units comprising at least one (meth) acrylate derivative; (b) an aromatic unit comprising a chain having a hydroxyl-containing moiety and an aromatic moiety; and (c) a styrene unit comprising at least one styrene derivative. The units (a) to (c) may be contained in the resin composition as a single copolymer, or two or more of the units (a) to (c) may be contained in the resin composition as a copolymer.

The method for forming the (meth) acrylate resin film is not particularly limited. For example, materials such as a (meth) acrylate resin, a polymer, and additives may be sufficiently mixed by a suitable method to form a thermoplastic resin composition, and then a film of the thermoplastic resin composition may be formed. In another embodiment, solutions such as a (meth) acrylate resin solution, a polymer solution, and an additive solution may be separately prepared and mixed with each other to form a film using the mixed solutions.

The thermoplastic resin composition can be obtained by the following steps: premixing the above raw materials using a suitable stirrer such as a mixing homogenizer; the mixture was kneaded and extruded. The mixture may be kneaded by any mixer and extruded. For example, a single-screw extruder, a twin-screw extruder, or a pressure kneader may be used.

Examples of the film forming method include: solution casting, melt extrusion, calendering, and compression methods may be used. A solution casting method or a melt extrusion method may be desirably used to form a film.

Examples of the solvent that can be used in the solution casting method include: aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as cyclohexane and decalin; esters, such as ethyl acetate and butyl acetate; ketones such as acetone, butanone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, isopropanol, butanol, isobutanol, methyl cellulose, ethyl cellulose and butyl cellulose; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride; dimethylformamide; and dimethylsulfoxide. The solvents listed may be used alone or in admixture.

For example, a drum casting machine, a belt casting machine, or a spin coater can be used as an apparatus for performing the solution casting method. Examples of the melt extrusion method include a T-die method and an inflation method. The film may be formed at a temperature in the range of 150 ℃ to 350 ℃. For example, the film may be formed at a temperature in the range of 200 ℃ to 300 ℃.

In the case of forming a film using the T-die method, the T-die may be installed on the front end of a single-or twin-shaft extruder to roll the extruded film. In this case, when the film is extruded or rolled, the film may be uniaxially stretched (oriented) in the direction of extrusion by adjusting the temperature of the rolled portion of the film. Alternatively, the film may be simultaneously or sequentially biaxially stretched (oriented) in a direction perpendicular to the extrusion direction (biaxial orientation).

The acrylic film may be a non-oriented film or an oriented film. In the latter case, the acrylic film may be a uniaxially oriented film or a biaxially oriented film. If the acrylic film is a biaxially oriented film, the acrylic film may be simultaneously biaxially oriented or sequentially biaxially oriented. If the acrylic film is a biaxially oriented film, the quality of the acrylic film may be improved due to the improvement of mechanical strength. The oriented acrylic film may include another thermoplastic resin to prevent an increase in phase difference and maintain optical isotropy.

When the acrylic film is formed of the thermoplastic resin composition, the acrylic film may be stretched at a temperature close to the glass transition temperature of the thermoplastic resin composition. For example, an acrylic film may be stretched in a temperature range between (glass transition temperature-30 ℃) and (glass transition temperature +100 ℃). In another embodiment, the acrylic film may be stretched in a temperature range between (glass transition temperature-20 ℃) and (glass transition temperature +80 ℃). If the stretching temperature of the acrylic film is lower than (glass transition temperature-30 ℃), the acrylic may not be stretched sufficiently. On the other hand, if the stretching temperature of the acrylic film is higher than (glass transition temperature +100 ℃), the acrylic film may not be stably stretched due to the flow of the resin composition.

The stretch ratio is determined based on the area ratio, and the acrylic film may have a stretch ratio of between 1.1 and 25. For example, the draw ratio may be between 1.3 and 10. If the stretch ratio of the acrylic film is less than 1.1, the durability of the acrylic film may not be improved due to insufficient stretching. Further, if the stretch ratio of the acrylic film exceeds 25, the effect of stretching may not be increased as expected.

The acrylic film may be stretched at a stretch rate of 10%/min to 20,000%/min. For example, the acrylic film may be stretched at a stretch rate of 100%/min to 10,000%/min. If the stretching rate is less than 10%/min, it may take too much time to sufficiently stretch the acrylic film, resulting in an increase in the manufacturing cost of the acrylic film. On the other hand, if the stretching rate is more than 20,000%/min, the acrylic film may be torn.

After the acrylic film is stretched, the acrylic film may be heat-treated (annealed), thereby stabilizing the optical anisotropy and mechanical properties of the acrylic film. The conditions of the heat treatment are not particularly limited. For example, the heat treatment may be performed under conditions known in the art.

The optical film may be surface-treated to improve adhesive properties. For example, at least one of an alkali treatment, a corona treatment, and a plasma treatment may be performed on at least one side of the optical film.

The present invention also provides a polarizing plate comprising the polarizer and the optical film. Here, a primer layer formed of the above primer composition is formed on at least one side of the optical film, and the optical film is attached to one side or both sides of the polarizer. For example, the present invention provides the polarizing plate as shown in fig. 2 and 3. Referring to fig. 2 and 3, a polarizer is positioned between the

optical films

3 and 4, and a primer layer 5 formed of a primer composition is positioned between the polarizer 1 and at least one of the

optical films

3 and 4. Primer compositions and optical films that can be coated with primer compositions have been described above.

The adhesive layer may be formed on one side or both sides of the polarizer. In the present invention, the adhesive layer may be formed of PVA resin. If the adhesive layer is formed of a denatured PVA resin including an acetoacetyl group, the adhesive property of the adhesive layer may be further enhanced. For example, the adhesive layer may be formed of Gohsefimer Z-100, Z-200H, Z-210, Z-220, and Z-320 manufactured by Nippon synthetic chemical industries, Ltd. However, the material that can be used to form the adhesive layer is not limited thereto.

In the present invention, the primer layer may be formed between: a highly hydrophobic acrylic film having a water contact angle of about 90 °; and an aqueous adhesive or a highly hydrophilic polarizer having a water contact angle of 50 ° or less, thereby improving adhesive properties by a buffer function between two polar films having different surface properties and the polarizer.

The polarizing plate of the present invention may have an optical transparency of between 35% and 45% and a degree of polarization of 98 or more.

The invention also provides a method for preparing the optical film containing the primer layer. The method comprises the following steps: applying a primer composition on at least one side of the optical film; and drying the optical film. The optical film has been described in the above specification.

The optical film may be coated with the primer composition by using a bar coating method or a gravure printing method, and/or a discontinuous coater, thereby forming a primer layer. The primer layer may have a thickness between 50nm and 1,000 nm. For example, the primer layer may have a thickness between 100nm and 800 nm. In another embodiment, the primer layer may have a thickness between 200nm and 500 nm. If the thickness of the primer layer is less than 50nm, sufficient adhesive properties cannot be obtained. On the other hand, if the thickness of the primer layer is more than 1,000nm, the primer layer may not be sufficiently dried, or the sliding property of the water-dispersible particles may not be appropriate because the water-dispersible particles are buried in the primer layer.

For example, the drying of the optical film may be performed using a convection oven at a temperature range between 100 ℃ and 120 ℃ for one to five minutes, but is not limited thereto. The drying temperature may vary within the above range depending on the coating process of the primer composition. If the optical film is an oriented film, the drying temperature may be maintained at or below the glass transition temperature (Tg) of the optical film. If the drying of the optical film is performed while the optical film is stretched, the drying temperature may be set to a stretching temperature, which is equal to or lower than the decomposition temperature (Td) of the optical film.

In addition, the optical film may be surface-treated to improve adhesive properties. In this case, the method may further include performing at least one of alkali treatment, corona treatment, and plasma treatment on at least one side of the optical film. In particular, if the optical film is an acrylic film containing no lactone ring, it is necessary to perform such surface treatment on the optical film.

According to the present invention, the polarizing plate including the primer composition does not decrease optical transparency due to suitable optical transparency of the primer composition, and durability of the polarizing plate is improved due to suitable adhesive properties provided by the primer composition. In particular, even in the case where the primer composition is applied to the polarizing plate, the optical transparency, the degree of polarization, and the color properties of the polarizing plate are all changed in substantially the same manner as in the case where the PVA adhesive without the primer composition is used. Thus, the primer composition can be used in a mass production line without changing process conditions.

Various electronic devices, such as liquid crystal displays, can be manufactured using the primer composition and the polarizing plate of the present invention. That is, the use of the primer composition and the polarizing plate of the present invention is not limited thereto. That is, the primer layer formed from the primer composition can be used in electronic devices known in the art.

The present invention will now be described in detail with reference to examples. However, the following examples are only for describing the present invention, and the present invention is not limited to the following examples.

Example 1

The primer-treated acrylic film was prepared as follows: a10 wt% primer composition was prepared by the following steps: mixing 33.3g of CK-PUD-F (Chokwang-polyurethane dispersion: aqueous solution having a solid content of 30%), 1.4g of colloidal silica (aqueous solution having a solid content of 20%) and 65.3g of pure water; coating the primer composition onto the corona treated acrylic film to a thickness of about 300nm using a #3 rod; and the acrylic film was dried at 100 c for five minutes.

As the acrylic film, an AX film product (manufactured by Nippon Shokubai) having a thickness of 50 μm was used, and the acrylic film was at 50W/m²Corona treatment was performed at/min to produce a corona treated acrylic film. The polarizing plate was prepared as follows. PVA adhesive was coated on both sides of the polarizer. A primer-treated acrylic film was located on one side of the polarizer, and an alkali-treated TAC film was located on the other side of the polarizer. Then, the primer-treated acrylic film, polarizer and TAC film were pressed using a pressure roller and treated with hot air at 80 ℃ for five minutes.

Example 2

Except that 10 wt% of the primer composition was prepared by mixing 33.3g of CK-PUD-F (Chokwang-polyurethane dispersion: aqueous solution having a solid content of 30%), 1.4g of colloidal silica (aqueous solution having a solid content of 20%) and 65.3g of pure water; and a polarizing plate was prepared in the same manner as in example 1, except that the primer composition was coated on the corona-treated acrylic film to a thickness of about 500nm using a #5 rod.

Example 3

Except that 10 wt% of the primer composition was prepared by mixing 33.3g of SUPERFLEX210(Nippon Shokubai-polyurethane dispersion: aqueous solution having a solid content of 30%), 1.4g of colloidal silica (aqueous solution having a solid content of 20%) and 65.3g of pure water; and a polarizing plate was prepared in the same manner as in example 1, except that the primer composition was coated on the corona-treated acrylic film to a thickness of about 500nm using a #5 rod.

Comparative example 1

Except that the 4.5% by weight aqueous PVA solution was prepared by dissolving a PVA resin in pure water (average degree of polymerization: 2400, and degree of saponification: 99.9%); and an aqueous PVA solution was coated on the corona-treated acrylic film to a thickness of 500nm using a #5 rod, a polarizing plate was prepared in the same manner as in example 1.

Comparative example 2

A polarizing plate was prepared in the same manner as in example 1, except that 10 wt% of the primer composition (WLS 202: DIC-urethane dispersion) was coated on the corona-treated acrylic film to a thickness of 500nm using a #5 bar.

Comparative example 3

A polarizing plate was prepared in the same manner as in example 1, except that it was not treated with the primer composition.

Experimental example 1: evaluation of adhesion and Water resistance of polarizing plate

1. Adhesive performance

The adhesion performance of the polarizing plate was evaluated in the following manner. After fixing a 2cm wide section of the acrylic film, 90 degree peeling of the acrylic film 5 cm long was observed using a ta.xt. plus texture analyzer (manufactured by Stable Micro Systems). The results are shown in table 1 below.

In the case where 3.0N/2cm or more is required to peel the acrylic film from the polarizing plate, the polarizing plate can be safely detached from the panel in a reworking process.

2. Water resistance

The water resistance of the polarizing plate was evaluated in the following manner. One side of the polarizing plate was attached to a glass plate using an adhesive, and the polarizing plate attached to the glass plate was immersed in a hot water bath at 60 ℃ for eight hours. Then, shrinkage of the polarizing plate and peeling of the acrylic film (acrylic protective film) were observed. The results are shown in table 1 below.

[ Table 1]

EXAMPLES

Comparative examples c.e

Acrylic film

TAC triacetyl cellulose film

＊P1:CK-PUD-F 10％

＊P2:SF210 10％

P3 polyvinyl alcohol 4.5%

＊P4:WLS 202 10％

Referring to Table 1, in the case of using the primer composition of the present invention, the adhesion property was 3.0N/2cm or more. Therefore, according to the present invention, the rework process can be stably performed, and a polarizing plate having improved water resistance can be manufactured.

As described above, according to the present invention, the primer composition has good adhesion properties and can be used in the lamination process of the existing polarizing plate without lowering the transparency of the polarizing plate and without additional processes or equipment. In particular, in the case where an acrylic film is used as a protective film of a polarizer, the primer composition enhances the bonding between the acrylic film and the polarizer without deteriorating the optical properties and durability of the polarizing plate.

While the invention has been shown and described with respect to the actual embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A polarizing plate, comprising:

a polarizing plate; and

an optical film attached to one or both sides of the polarizer,

wherein the optical film comprises a primer layer,

wherein the primer layer is formed from a primer composition, and

wherein the primer composition consists of: 1 to 30 parts by weight of a polyurethane polymer, 0.1 to 10 parts by weight of a water dispersible particle, and the balance water, per 100 parts by weight of the primer composition,

wherein the polyurethane polymer is obtained by reacting a polycarbonate diol with an isocyanate, and

wherein the surface water contact angle of the primer layer is between 60 degrees and 80 degrees,

wherein the polycarbonate diol is at least one selected from the group consisting of poly (hexamethylene carbonate) diol and poly (cyclohexane carbonate) diol,

wherein the isocyanate is at least one selected from the group consisting of Toluene Diisocyanate (TDI), 4-diphenylmethane diisocyanate (MDI), 1, 5-Naphthalene Diisocyanate (NDI), tolidine diisocyanate (TODI), Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate, trans-cyclohexane-1, 4-diisocyanate, and Xylene Diisocyanate (XDI).

2. The polarizing plate of claim 1, wherein the polyurethane polymer has a weight average molecular weight of between 30,000 and 100,000.

3. The polarizing plate of claim 1, wherein the primer composition comprises 3 to 20 parts by weight of the polyurethane polymer per 100 parts by weight of the primer composition.

4. The polarizing plate of claim 1, wherein the polyurethane polymer comprises carboxylic acid groups.

5. The polarizing plate of claim 1, wherein the water dispersible particles have an average particle size between 10nm and 200 nm.

6. The polarizing plate of claim 1, wherein the optical film comprises a primer layer formed on at least one side of an acrylic film, and the acrylic film comprises:

a copolymer comprising alkyl (meth) acrylate units and styrene units; and

an aromatic resin comprising carbonate moieties in its backbone.

7. The polarizing plate of claim 1, wherein the optical film comprises a primer layer formed on at least one side of an acrylic film, and the acrylic film comprises: alkyl (meth) acrylate units; a styrene unit; a 3-to 6-membered heterocyclic unit substituted with at least one carbonyl group; and an acrylonitrile unit.

8. The polarizing plate of claim 1, wherein the primer layer has a thickness between 50nm and 1,000 nm.

9. The polarizing plate of claim 1, wherein an adhesive layer is formed on one or both sides of the polarizer.

10. The polarizing plate of claim 9, wherein the adhesive layer is formed of a polyvinyl alcohol (PVA) resin.