JP2001066427A - Protective film for polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a protective film for a polarizer having excellent wear resistance and ray transmittance which does not influence the extinction state of a polarizer in a cross Nicol position, by forming a wear-resistant layer on one surface of a specified polyester film. SOLUTION: The protective film is made of a laminated film produced by forming a wear-resistant layer on one surface of a polyester film having 0 to 0.005 difference of the refractive index in the film plane. The polyester which constitutes the film is prepared by condensation polymerization of an aromatic dicarboxylic acid and an aliphatic glycol. As for the aromatic dicarboxylic acid, for example, telephthalic acid and 2,6-naphthalene dicarboxylic acid can be used. As for the aliphatic glycol, ethylene glycol, diethylene glycol and 1,4-cyclohexane dimethanol can be used. A typical polyester is polyethylene telephthalate(PET), polyethylene-2,6-naphthalene dicarboxylate (PEN) or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film for a polarizer, which is used by being adhered to the surface of a polarizer. Accordingly, the present invention relates to a polarizer protective film used for producing a polarizing plate.

[0002]

2. Description of the Related Art Generally, a polarizing plate used for a liquid crystal display panel or the like has a three-layer structure in which protective films are laminated on both surfaces of a polarizer. As the polarizer, one obtained by adsorbing iodine and / or a dichroic dye on uniaxially oriented polyvinyl alcohol is generally used, and as a protective film of the polarizer, a cellulose triacetate (TAC) film has flatness, It is generally used because it has excellent properties such as light transmittance and non-orientation.

[0003] As a method for producing a cellulose triacetate (TAC) film, a dope is cast on a band or a drum, peeled off, and then dried.
A solution casting method is generally used. However, this method is problematic in that the film forming speed is low. In U.S. Pat. Nos. 2,607,704 and 2739069, the dope is stripped off from the band or the drum as quickly as possible, and both sides of the stripped dope film are dried at a high temperature. To this end, it has been proposed to increase the dope concentration or to select a solvent to speed up the gelling of the dope on the band or drum.

[0004] However, in these methods, the viscosity of the dope is increased and the fluidity is deteriorated. When a high-concentration dope is extruded from a casting die at a high speed, the surface state of the film may be called sharkskin (shark skin), and the flatness may be extremely deteriorated due to the melt fracture phenomenon. Japanese Patent Application Laid-Open No. 56-1626 discloses a method for eliminating shark skin caused by the melt fracture phenomenon.
No. 17 proposes a method in which low-concentration dope is co-cast on both sides of the dope, and casting is performed while enclosing the high-concentration dope. However, although the co-casting method is preferable for preventing the melt fracture phenomenon, it requires a plurality of dope adjusting steps, dope transporting steps, and the like, which is troublesome in terms of equipment.

[0005] Further, as a means for solving this problem,
In Japanese Patent Application Laid-Open No. 7-32391, by controlling the doping temperature, the die temperature, and the die lip temperature, and setting the boiling point of the dope at normal pressure to a certain range,
A method for making a cellulose triacetate (TAC) film is described. On the other hand, polyester films are excellent in flatness, light transmittance, mechanical properties, thermal properties, etc., but in particular, biaxially oriented polyester films have birefringence, and the main orientation axis is within the film plane. At present, they are hardly used as protective films for polarizers because they do not exist in a certain direction.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polarizer that does not affect the extinction state in a crossed Nicol state and has a high abrasion resistance. An object of the present invention is to provide a polarizer protective film having excellent light transmittance.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by using a specific film, and have completed the present invention. That is, the gist of the present invention resides in a polarizer protective film characterized by having a wear-resistant layer on one surface of a polyester film having an in-plane refractive index difference of 0 to 0.005.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The protective film of the present invention has a refractive index difference within the film plane of 0.
It is composed of a laminated film in which a wear-resistant layer is provided on one surface of a polyester film having a thickness of up to 0.005, and is used by being adhered to the surface of a polarizer via an adhesive or the like. In a preferred embodiment of the present invention, an adhesive layer is provided on the other surface on which the wear-resistant layer is provided, and a release film is laminated on the surface of the adhesive layer.

If the refractive index difference in the plane of the film exceeds 0.005, when the polarizing plate is arranged in a crossed Nicols state, the extinction state is disturbed and light interference color is generated, which is not preferable. In the present invention, the polyester film is a film obtained by stretching and orienting a sheet melt-extruded from an extrusion die according to a so-called extrusion method.

The polyester constituting the film of the present invention refers to a polyester obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2,6-naphthalenedicarboxylic acid, and the like. As the aliphatic glycol,
Ethylene glycol, diethylene glycol, 1,4-
Cyclohexane dimethanol and the like. Typical polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

The above polyester may be a copolymer containing a third component. Examples of the dicarboxylic acid component of the copolymerized polyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, P-oxybenzoic acid and the like). As a glycol component,
Examples include ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like. Two or more of these dicarboxylic acid components and glycol components may be used in combination.

In the present invention, it is preferable that particles are contained in the film under conditions that do not impair transparency, in consideration of the handling properties. As the particles, for example, silicon dioxide,
Examples thereof include calcium carbonate, aluminum oxide, titanium dioxide, kaolin, talc, zeolite, lithium fluoride, barium sulfate, carbon black, and heat-resistant polymer fine powder as described in JP-B-59-5216. These particles may be used in combination of two or more kinds. The average particle size of the particles is generally 0.02 to 2 μm, preferably 0.05 to 1.5 μm, more preferably 0.05 to 1.5 μm.
１1 μm. The content of the particles is usually 0.01 to 2% by weight, preferably 0.02 to 1% by weight.

As a method for incorporating particles into the film, a known method can be employed. For example, particles can be added at any stage of the polyester production process. In particular, at the stage of esterification or the stage after the end of the transesterification reaction and before the start of the polycondensation reaction, it is preferable to add as a slurry dispersed in ethylene glycol or the like to advance the polycondensation reaction. Also, using a kneading extruder with a vent,
A method of blending a slurry in which particles are dispersed in ethylene glycol or water with a polyester raw material, a method of blending dried particles with a polyester raw material using a kneading extruder, and the like can also be adopted.

The production of the film is carried out by a method in which a sheet melt-extruded from an extrusion die according to an extrusion method is stretched and oriented in two longitudinal and transverse directions. In the extrusion method, polyester is melt-extruded from an extrusion die,
It is cooled and solidified by a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is necessary to increase the adhesion between the sheet and the rotary cooling drum, and the electrostatic application adhesion method or the liquid application adhesion method is preferably employed.

The method for stretching and orienting the film in the biaxial direction is not particularly limited, but a simultaneous biaxial stretching method, a sequential biaxial stretching method and the like are employed. In order to obtain in-plane refractive index isotropy, the simultaneous biaxial stretching method is preferable. The simultaneous biaxial stretching method is a method of simultaneously stretching the unstretched sheet in the machine direction and the width direction while controlling the temperature at 70 to 120 ° C., preferably 80 to 110 ° C. in a machine-controlled manner. 4 in area magnification
50 to 50 times, preferably 7 to 35 times, and more preferably 1 to 35 times.
It is 0 to 20 times. And, continuously, 170-250
A heat treatment is performed at a temperature of ° C. under tension or relaxation within 30% to obtain a stretched oriented film.

In the sequential biaxial stretching method, the unstretched sheet is stretched in one direction by a roll or tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C, preferably 80 to 110 ° C, and the stretching ratio is usually 2.5 to 7
Times, preferably 3.0 to 6 times. Next, stretching is performed in a direction orthogonal to the stretching direction of the first stage. The stretching temperature is usually 70 to 120 ° C, preferably 80 to 115 ° C,
The stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times.
It is twice. Subsequently, a heat treatment is performed at a temperature of 170 to 250 ° C. under tension or relaxation within 30% to obtain a stretched oriented film.

In the sequential biaxial stretching, a method in which unidirectional stretching is performed in two or more stages can be adopted. In that case, it is preferable that the stretching is performed so that the stretching ratios in the two directions finally fall within the above ranges. If necessary, the film may be stretched in the vertical and / or horizontal directions again before or after the heat treatment. Although the thickness of the film of the present invention is not particularly limited, it is generally 5 to 150 μm, preferably 1 to 150 μm.
It is 0 to 100 μm, and more preferably 25 to 75 μm. When the thickness of the film is less than 5 μm, the surface protection of the polarizer may be reduced, and the handleability in the abrasion resistant layer forming step and the adhesive layer forming step tends to deteriorate. Further, when the thickness of the film exceeds 150 μm, a decrease in flexibility and a decrease in the total light transmittance hinder a handling work as a protective film and a case where an inspection accompanied by optical evaluation is performed. There are cases.

Examples of the material constituting the abrasion-resistant layer of the film of the present invention include various crosslinkable resins, metal oxides, and hard carbon materials. Usually, crosslinkable resins are preferably used. Is done. Specific examples of the crosslinkable resin include an acrylic resin, a urethane resin, a melamine resin, an epoxy resin, an organic silicate resin, and a copolymer resin of a silicon-containing compound and a fluorine-containing compound.

In the present invention, an active energy ray-curable resin is preferably used from the viewpoint of productivity and the like. As the active energy ray-curable resin, unsaturated polyester resin, acrylic resin, addition polymerization resin, thiol
Acrylic hybrid resin, cationic polymerization resin,
Hybrid resins of cationic polymerization and radical polymerization are exemplified. Among these, acrylic resins are preferred in terms of curability, scratch resistance, surface hardness, flexibility, durability, and the like.

The above acrylic resin contains an acrylic oligomer as an active energy ray polymerization component and a reactive diluent. And, if necessary, a photopolymerization initiator, a photopolymerization initiation auxiliary agent, a modifier and the like are contained. A typical example of the acrylic oligomer is an oligomer in which a reactive acryloyl group or methacryloyl group is bonded to an acrylic resin skeleton. Other acrylic oligomers include polyester (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, polyether (meth) acrylate, silicone
(Meth) acrylate, polybutadiene (meth) acrylate, and the like. Further, melamine, acryloyl group or methacryloyl group that is a rigid skeleton,
An oligomer to which isocyanuric acid, cyclic phosphazene, or the like is bonded can be given.

Since the reactive diluent functions as a solvent in the coating process as a medium of the coating agent, and has a group which itself reacts with the polyfunctional or monofunctional acrylic oligomer, the reactive diluent is used as a medium for the coating film. It becomes a polymerization component. Specific examples of the reactive diluent include pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, and dipentaerythritol penta (meth) ) Acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene glycol (meth) acrylate, propylene glycol di (meth) acrylate, (meth) acryloyloxypropyltriethoxysilane, (meth) acryloyl Oxypropyltrimethoxysilane and the like can be mentioned.

Examples of the photopolymerization initiator include, for example, 2,2-
Ethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, p-chlorobenzophenone, p-methoxybenzophenone, Michler's ketone, acetophenone, 2-chlorothioxanthone, anthraquinone, phenyl disulfide, 2-methyl- [4- (methylthio) phenyl] -2-morpholino-1-propanone and the like.

Examples of the photopolymerization initiation aid include tertiary amines such as triethylamine, triethanolamine and 2-dimethylaminoethanol, alkylphosphines such as triphenylphosphine, and thioethers such as β-thiodiglycol. As the modifier, an antistatic agent, a coating improver, an antifoaming agent, a thickener, inorganic particles, organic particles,
Examples include a lubricant, an organic polymer, a dye, a pigment, and a stabilizer. These are used within a range that does not inhibit the reaction by the active energy ray, and can improve the properties of the active energy ray-curable resin layer according to the application. An organic solvent can be added to the composition of the active energy ray-curable resin layer for the purpose of improving workability during coating and controlling the coating thickness.

In the present invention, the abrasion-resistant layer preferably contains an ultraviolet absorber. The ultraviolet absorber is blended in order to prevent deterioration of the liquid crystal or the like of the liquid crystal display panel due to ultraviolet rays. Examples of the ultraviolet absorber contained in the wear-resistant layer include an organic ultraviolet absorber and an inorganic ultraviolet absorber.

Examples of the organic ultraviolet absorbers include salicylic acids, for example, phenylsalicylate, pt-butylphenylsalicylate, p-octylphenylsalicylate, and benzophenones, for example, 2-hydroxy-4.
-Benzyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone Benzotriazoles such as 2,2-2′-dihydroxy-4,4′-dimethoxybenzophenone,
-(2'-hydroxy-5'-t-octylphenyl)
-Benzotriazole, 2- (2'-hydroxy-5 '
-Methylphenyl) benzotriazole, 2- (2'-
Hydroxy-3'5'-di-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-
Butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3'5'-di-
Examples thereof include natural products such as t-butylphenyl) -5-chlorobenzotriazole, such as oryzanol, shea butter, and baicalin; and biological systems such as keratinocytes, melanin, and urocanic acid. These organic UV absorbers can be used alone or in combination of two or more. A hindered amine compound can be used in combination with these organic ultraviolet absorbers as an ultraviolet stabilizer.

Examples of the inorganic ultraviolet absorber include titanium oxide, zinc oxide, indium oxide, tin oxide, talc, kaolin, calcium carbonate, titanium oxide-based composite oxide, zinc oxide-based composite oxide, and ITO (tin-doped indium oxide). ), ATO (antimony-doped tin oxide) and the like. Examples of the titanium oxide-based composite oxide include silica, alumina-doped titanium oxide and the like,
Examples of the zinc oxide-based composite oxide include aluminum-doped zinc oxide. These inorganic ultraviolet absorbers can be used alone or in combination of two or more. Further, an organic ultraviolet absorber and an inorganic ultraviolet absorber may be used in combination.

In the present invention, the formation of the abrasion-resistant layer is performed by a method in which a curable resin composition is applied to one surface of a film and cured. As a coating method, a reverse roll coating method, a gravure roll coating method, a rod coating method, an air knife coating method, or the like can be employed. Curing of the applied curable resin composition is performed by, for example, active energy rays or heat. As the active energy rays, ultraviolet rays, visible rays, electron beams, X-rays, α-rays, β-rays, γ
Lines are used. As the heat source, infrared heater,
A heat oven or the like is used. Irradiation with active energy rays is usually performed from the side of the coating layer, but may be performed from the side opposite to the coating layer in order to increase the adhesion to the film. If necessary, a reflector that can reflect active energy rays may be used. The film cured by the active energy rays has particularly good abrasion resistance.

The coating amount of the wear-resistant layer is usually 0.1 to 10
g / m ^2, preferably in the range of 0.2-5 g / m ^2. When the coating amount is less than 0.1 g / m ² , the abrasion resistance tends to decrease, and when it exceeds 10 g / m ² , the shrinkage of the abrasion resistant layer upon curing increases, and the film becomes May curl to the side. In the present invention, the total light transmittance of the protective film is preferably 85% or more, more preferably 90% or more. When the total light transmittance is less than 85%, for example, when used as a constituent member of a liquid crystal display panel or the like, hue, luminance, brightness, contrast, and the like may be reduced.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the examples and comparative examples, “parts” means “parts by weight”. The measuring methods and evaluation criteria used in the present invention are as follows. (1) In-plane refractive index difference: 10 mm in width and 50 in length while shifting the angle by 10 degrees
mm sample was taken from the film, and the refractive index of each sample in the direction of the sampling angle was measured with an Abago refractometer manufactured by Atago Optical Co., Ltd. The measurement of the refractive index was performed at 23 ° C. using a sodium D line. The difference between the maximum value and the minimum value of the refractive index obtained in the measurement (the maximum value of the refractive index−the minimum value of the refractive index) was calculated, and the difference was taken as the refractive index difference. (2) Total light transmittance of the laminated film The total light transmittance was measured using an integrating sphere turbidimeter (“NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS-K7105. (3) Quenching state Two polarizing plates on which the sample films were attached were overlapped so that the polarizer was in a crossed Nicols state, and white light was irradiated from below, and the quenching state when viewed from above was evaluated. (4) Abrasion resistance Using "RUBING TESTER" manufactured by Ohira Rika Kogyo Co., Ltd., a long fiber cellulose nonwoven fabric was wound around a 65 mm x 50 mm metal flat plate indenter and rubbed 100 times. Thereafter, the surface was observed, and the case where the wear-resistant layer hardly changed was evaluated as good, and the case where the wear-resistant layer was dropped was evaluated as poor.

Production Example 1 (Polyester A) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor, heated and heated, and methanol was distilled off. The temperature was raised to 230 ° C. over 4 hours from the start of the reaction, and the transesterification was substantially completed. Next, an ethylene glycol slurry containing 0.1 part of silica particles having an average particle size of 1.54 μm was added to the reaction system, and ethyl acid phosphate was added to the slurry.
After adding 04 parts and 0.01 parts of germanium oxide, 1
In 00 minutes, the temperature reached 280 ° C and the pressure reached 15 mmHg. Thereafter, the pressure was gradually reduced to finally 0.3 mmHg.
And After 4 hours, the inside of the system was returned to normal pressure to obtain polyester A. The content of the silica particles of the polyester A was 0.1% by weight.

Production Example 2 (Polyester Film A1) Polyester A was dried at 180 ° C. for 4 hours in an inert gas atmosphere, melt-extruded at 290 ° C. by a melt extruder, and the surface temperature was adjusted by using an electrostatic contact method. It was cooled and solidified on a cooling roll set at 40 ° C. to obtain an unstretched sheet. The obtained sheet was treated with T.I. M. Simultaneous biaxial stretching was performed using a long stretching machine manufactured by Long Corporation at 95 ° C. so that the area ratio became 16 times. After that, it is heat-set at 230 ° C.
A polyester film A1 was obtained. The difference in the refractive index of the obtained film was 0.001.

Production Example 3 (Polyester Film A2) A polyester film A2 was obtained in the same manner as in Production Example 2 except that simultaneous biaxial stretching was performed so that the stretching ratio was 12 times the area magnification. The difference in the refractive index of the obtained film was 0.001. Production Example 4 (Polyester Film A3) A polyester film A3 was obtained in the same manner as in Production Example 2, except that simultaneous biaxial stretching was performed so that the stretching ratio was 20 times the area magnification. The difference in the refractive index of the obtained film was 0.001.

Production Example 5 (Polyester film A4) Polyester A was dried at 180 ° C for 4 hours in an inert gas atmosphere, melt-extruded at 290 ° C by a melt extruder, and the surface temperature was adjusted by using an electrostatic application adhesion method. It was cooled and solidified on a cooling roll set at 40 ° C. to obtain an unstretched sheet. After stretching the obtained sheet 3.5 times in the longitudinal direction at 85 ° C.,
The film was stretched 3.7 times in the transverse direction at 0 ° C., and further heat-set at 230 ° C. to obtain a 38 μm-thick polyester film A4. The refractive index difference of the film was 0.025.

Example 1 30 parts of dipentaerythritol hexaacrylate, 4 parts
In an active energy ray-curable resin composition comprising 40 parts of a functional urethane acrylate, 27 parts of a bisphenol A type epoxy acrylate and 3 parts of 1-hydroxycyclohexyl phenyl ketone, 0.6 part of ITO particles having a particle size of 0.02 μm and ATO particles are prepared. 0.4 part of the blended composition was applied to one surface of the polyester film A1 so that the thickness after curing was 1 g / m ^2, and a high-pressure mercury lamp having an energy of 120 W / cm was used. For 15 seconds to form a cured film. Then, an acrylic pressure-sensitive adhesive was applied on the surface opposite to the surface on which the cured film was applied, and a polarizer and a sample film were adhered to obtain a laminate.

Example 2 Example 1 was repeated except that an abrasion-resistant cured film was formed so that the thickness after curing was 0.5 g / m ^2.
To obtain a laminate. Example 3 Example 1 was repeated except that an abrasion-resistant cured film was formed so that the thickness after curing was 0.2 g / m ^2.
To obtain a laminate.

Example 4 A laminate was obtained in the same manner as in Example 1 except that the polyester film A1 was changed to the polyester film A2. Example 5 A laminate was obtained in the same manner as in Example 1 except that the polyester film A1 was changed to the polyester film A3.

Comparative Example 1 A laminate was obtained in the same manner as in Example 1 except that the polyester film A1 was changed to the polyester film A4. Comparative Example 2 In Example 1, except that a cured film was not formed,
A laminate was obtained in the same manner as in Example 1.

[0038]

[Table 1]

[0039]

According to the present invention, it is possible to provide a polarizer protective film having excellent abrasion resistance and light transmittance without affecting the extinction state of the polarizer in the crossed Nicols state. The industrial value of the invention is high.

Claims (3)

[Claims] 2. The method according to claim 1, wherein the difference in refractive index within the film plane is from 0 to 0.00.
5. A polarizer protective film having a wear-resistant layer on one surface of the polyester film of No. 5. 2. The polarizer surface protective film according to claim 1, wherein the wear-resistant layer mainly comprises an active energy ray-curable resin containing an ultraviolet absorber. 3. The polarizer protective film according to claim 1, wherein the total light transmittance is 85% or more.