JP2000275433A - Polarizing plate protection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate protection film varying little in double refractive index, avoiding formation of carbonized degraded materials during melt molding, preventing color unevenness of a liquid crystal display when used as a protective film for a polarizing film, and being excellent in contrast. SOLUTION: This polarizing plate protection film is deposited on at least one side of a polarizing film and is composed of polymethylpentene. The polymethylpentene is a single polymer of 4-methyl-1-pentene or a copolymer of 4-methyl-1-pentene with other α-olefin, e.g. α-olefin with 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 10-decene, 1-tetradecene, 1-octadecene, etc. Since the polymethylpentene has a melting point of 210 to 260 deg.C, it is excellent in heat resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polarizing plate protective film laminated as a protective film for a polarizing plate used in a liquid crystal display or the like.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays (LCDs) are often used for on-board equipment and portable information equipment, and there is a strong demand for the reliability of LCDs under high-temperature and high-temperature and high-humidity environments. Conventionally, polarizing plates used for LCDs are stretched and oriented polyvinyl alcohol (PV).
A film having optical isotropy is used as a protective film on both surfaces of a polarizer having iodine or a dichroic dye adsorbed on A). As a protective film, triacetyl cellulose (TAC) having a small birefringence is generally used.

However, since TAC has a high water absorption, the degree of polarization decreases and the transmittance decreases due to discoloration in a high-temperature and high-humidity environment. In addition, under the high temperature environment, the orientation of PVA is relaxed, and when a stress is applied to the TAC of the protective film, a large birefringence is caused to cause a decrease in the degree of polarization. Become.

As a means for making a polarizing plate compatible with a high-temperature or high-temperature and high-humidity environment, it is disclosed that a polycarbonate film having an average molecular weight of 30,000 or more and a glass transition temperature of 150 ° C. or more is used as a protective film. JP-A-8-62419). The polycarbonate film described in the above publication has excellent moisture resistance and heat resistance as compared with TAC, and the polarizing plate using this as a protective film has high reliability and reliability.
Excellent durability.

However, during actual use, an external force is applied to the polarizing plate protective film due to a dimensional change of the polarizing element or the like. Due to this external force, the birefringence of the polarizing plate protective film changes. For this reason, especially when incorporated in a liquid crystal display, it may appear as color unevenness or a reduced contrast due to a phase difference.

Japanese Patent Application Laid-Open No. Hei 5-212828 discloses a composite sheet for reducing the change in birefringence by using a norbornene-based resin sheet as a polarizing plate protective film in order to solve the above problems. ing. However, when this composite sheet is manufactured by a solvent casting method, poor appearance due to foaming and reduction in heat resistance due to poor drying are likely to occur. In order to solve this problem, it is necessary to gradually perform drying, which leads to an increase in size of the equipment, a decrease in production efficiency, and difficulty in manufacturing at low cost.

When a melt molding method is employed as another effective means, decomposition of the norbornene-based resin starts at the melt molding temperature, and carbonization degradation products are produced during the production. This causes a defect in appearance and makes it unusable as a protective film for a polarizing plate.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, has a small change in birefringence, hardly causes carbonized deterioration in melt molding, and uses this as a protective film for a polarizing film to form a liquid crystal. It is an object of the present invention to provide a polarizing plate protective film that does not have color unevenness on a display and has excellent contrast.

[0009]

The polarizing plate protective film of the present invention is characterized in that a protective film laminated on at least one side of a polarizing film, wherein the protective film is polymethylpentene.

[0010] The polarizing film refers to a polyvinyl alcohol (PVA) film or sheet having the function of a polarizer. For example, after adsorbing iodine on a PVA film,
PVA / iodine polarizer uniaxially stretched in a boric acid bath, P
After diffusing and adsorbing a highly dichroic direct dye onto a VA film, a uniaxially stretched PVA / dye-based polarizing film, a PVA / polyvinylene-based polarizing film having a polyvinylene structure formed by adsorbing iodine on a PVA film and stretching, and the like are listed. Can be

Polymethylpentene is 4-methyl-1
A homopolymer of pentene, or 4-methyl-1-pentene and another α-olefin, for example, ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-tetradecene, 1- A copolymer with an α-olefin having 2 to 20 carbon atoms such as octadecene,
Since the melting point is 210-260 ° C., the heat resistance is excellent. Usually, it is a crystalline polymer containing 85 mol% or more of 4-methyl-1-pentene.

The above 4-methyl-1-pentene polymer has a structure in which the unit represented by the following formula is repeated.

[0013]

Embedded image

The above 4-methyl-1-pentene polymer is
Density 0.82 to 0.86 g / cc, melting point 243 ° C,
A melt flow index (measured according to ASTM 1238-57T at 260 ° C. with a weight of 5 kg) of 0.01-100.
0, ash content 0.1% or less, transition metal content 5
Those having 0 ppm or less are preferred.

The above polymethylpentene film is manufactured by JI
The light transmittance by S K 7150 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Further, in order to obtain excellent moisture resistance without causing hydrolysis, the water absorption after impregnation for 24 hours according to JIS K 7209 is preferably 0.03% or less, more preferably 0.01% or less.

The thickness of the polymethylpentene film is usually from 5 to 500 μm, preferably from 10 to 150 μm.
m. If the thickness of the film is less than 10 μm, it becomes difficult to handle such as a decrease in handling properties, resulting in insufficient strength. Conversely, if the thickness is more than 150 μm, the transparency is reduced, and
This is inconvenient for use in a liquid crystal display or the like that requires thinning.

If the photoelastic coefficient of the protective film is large, the birefringence increases due to external force and residual stress during molding. There is a relationship between birefringence and photoelastic coefficient as shown in the following equation. That is, Δn = C × σ (Δn is a birefringence index, C is a photoelastic coefficient,
(σ represents stress) Therefore, in order to reduce the birefringence (Δn), it is necessary to reduce the photoelastic coefficient (C).

The photoelastic coefficient (C) is actually obtained from the applied external force (σ) and the phase difference (Re) of the film. That is, when Re = d × Δn = d × C × σ (d is the thickness of the film) and both sides are multiplied by the film width W, Re × W = C × σ × d × W = C × P (P represents a load. Here, the photoelastic coefficient C of polymethylpentene is (3-1).
0) × 10 ⁻⁷ cm ² / kgf, the amount of change in birefringence (Δn) is small even under load P,
It can be seen that the amount of change in the phase difference (Re) is also small.

As a means for forming the polymethylpentene film, a usual forming method such as a solution casting method and a melt forming method is used, but from the viewpoint of productivity, the melt forming method is preferable. As the melt molding method, a method using a T-die, a melt extrusion method such as an inflation method, a calender method, a hot press method, and an injection molding method are used. Among them, the T-die molding method is preferable in terms of excellent productivity and thickness accuracy.

It is necessary to laminate a polymethylpentene film as a protective film on at least one side of the polarizing film, and it is more preferable to laminate on both sides. For the lamination of the polarizing film and the polymethylpentene film, for example, polyester-based, acrylic-based, silicone-based, rubber-based adhesives,
A known technique using an adhesive such as a polyurethane-based, polyester-based, or polyacryl-based adhesive is employed.

Further, as a pretreatment for bonding and laminating, it is preferable to perform a surface modification treatment in order to secure adhesiveness with a pressure-sensitive adhesive or an adhesive. An ordinary method can be used as a means for surface modification. That is, as a chemical treatment method, a surface grafting method in which a monomer or polymer having a functional group capable of reacting with an adhesive molecule is fixed to the film surface, a method of coating another polymer or monomer on the surface, a coupling agent treatment , Treatment with strong oxidizing agent, Chemical treatment to remove surface layer, CA to strengthen surface layer
There are SING processing and chemical processing as a surface roughening method.

Examples of the physical treatment method include a glow discharge treatment, a corona discharge treatment, a plasma jet treatment, and an asputter treatment as a surface roughening method.

(Function) In the present invention, since polymethylpentene is used as a protective film for a polarizing plate, its birefringence does not change because its photoelastic coefficient is smaller than that of TAC or PC conventionally used. When a polarizing plate obtained by laminating them is incorporated in a liquid crystal display, a display having excellent color unevenness and contrast can be obtained. Further, a polarizing plate having more excellent moisture resistance and heat resistance than TAC can be provided.

Further, as compared with norbornene-based resins, the formation of carbonized deterioration products during melt molding is suppressed, and even when molded by an extrusion molding method, a product having excellent appearance quality can be obtained.

[0025]

Next, examples of the polarizing plate protective film of the present invention will be described. (Example 1) Production of polarizing plate protective film Resin used: Polymethylpentene resin (trade name "TPX RT18" manufactured by Mitsui Chemicals, Inc., density 0.833 g / c)
m ³ , melting point 240 ° C, melt flow rate 26g / 10
Min (260 ° C., 5 kg ASTM D 1238) Extruder: single screw extruder 50φ, L / D = 28, extrusion temperature 2
70-300 ° C T-die: coat hanger type, width 500mm Discharge rate: 12kg / hr Forming: 6m / roll at 60 ° C with a three-roll take-off machine
min speed, average thickness 60μm, width 430m
m of polymethylpentene film was obtained. Then, a corona discharge treatment was performed on one surface as a surface treatment at 50 W / m ² / min to obtain a polarizing plate protective film.

Preparation of Polarizing Film An unstretched PVA film having a saponification degree of 99% and a thickness of 75 μm was washed with water at room temperature, and then stretched 5 times uniaxially. While maintaining the tension of the film, the film was immersed in an aqueous solution containing 0.5% by weight of iodine and 5% by weight of potassium iodide to adsorb the dichroic dye. Further, a cross-linking treatment was performed for 5 minutes with an aqueous solution of 10% by weight of boric acid and 10% by weight of potassium iodide at 50 ° C. to obtain a polarizing film.

Preparation of Polarizer Aqueous polyester solution (trade name “TM”, manufactured by Toyo Morton Co., Ltd.)
-593 ") 100 parts by weight, isocyanate-based curing agent solution (manufactured by Toyo Morton Co., Ltd., trade name" CAT-56 ") 18
After blending parts by weight, the solid content concentration is 30% with ethyl acetate
Diluted so as to be applied to the polarizing film with a bar coater,
This was dried at 80 ° C. for 1 minute. 3μm thickness after drying
Met. This was thermally laminated on a corona discharge treated surface of a polymethylpentene film using a roll heated to 80 ° C. The adhesive solution was applied to the corona discharge treated surface of another polymethylpentene film under the same conditions as above and dried, and the adhesive layer having a thickness of 3 μm was obtained.
The polarizing film surface of the polymethylpentene film laminate was thermally laminated under the same conditions as described above to obtain a polarizing plate having protective films on both surfaces. This was further cured at 40 ° C. for 2 days.

Comparative Example 1 Thermoplastic saturated norbornene resin (trade name "ZEONOR 1600" manufactured by Zeon Corporation)
R "), and a protective film was obtained in the same manner as in Example 1 except that the extrusion temperature was changed to 275 to 300 ° C.

(Comparative Example 2) A polyvinyl alcohol-based adhesive (trade name "GOHSENOL NH" manufactured by Nippon Synthetic Chemical Co., Ltd.) was placed on one side of an alkali saponified TAC film (thickness: 75 μm).
17)) was applied so as to have a thickness of 1 μm after drying, and dried at 90 ° C. The same polarizing film as that used in Example 1 was attached to the adhesive-coated surface to form a polarizing plate.

Performance Evaluation (1) Measurement of Photoelastic Coefficient (Protective Film Only) A protective film was cut into a width of 20 mm and a length of 100 mm, and a phase difference was measured while applying a load in the long side direction. Calculation. Measurement of load: Force gauge DPS-5 (IMADA
Level 0, 0.5, 1.0, 1.5 kg Measurement of phase difference: Senarmont method (manufactured by Asuka Electronics Co., Ltd.) Measurement wavelength 633 nm FIG. The phase difference was measured in a state where a load was applied. Both ends of the sample 1 are fixed by the chucks 2 and 3, and a 633 nm laser beam emitted from below the sample 1 is received while measuring the load received by the sample 1 by the load measuring device 4 connected to one of the chucks 3. The signal is received by the unit 5 and the phase difference is measured. 6 is a rail of the chuck 2 and 7 is a screw.

(2) Appearance quality The protective film alone was visually inspected for foreign substances, and expressed by the following criteria.・ ・ ・: Foreign matter having a size of 50 μm or more was 10 / m ² or less. ×: Foreign substances having a size of 50 μm or more were 11 / m ² or more. (3) Adhesion The polarizing film and the protective film were peeled off, and the appearance was visually observed.・ ・ ・: No problem. 剥: Peeled when bent or peeled by hand. ×: Peeled as it is.

(4) Degree of polarization Equation {(Y0−Y90) / (Y0 + Y90)} ^1/2 × 1
The degree of polarization was determined by 00. Y0: Total light transmittance of two sheets whose polarizing axes are aligned parallel to each other Y90: Total light transmittance of two sheets whose polarizing axes are aligned orthogonally Total light transmittance is measured based on JIS K 7150 did. (5) Durability test Degree of polarization after high temperature: 7 in a dryer heated to 80 ° C
After the elapse of 00 hours, the degree of polarization was measured. Adhesion after passage of high temperature and high humidity: The adhesion after passage of 700 hours in a high temperature and high humidity bath at 60 ° C. and 90% RH was examined. Degree of polarization after passage of high temperature and high humidity: The degree of polarization after 700 hours in a high temperature and high humidity bath at 60 ° C. and 90% RH is the above (4).
The measurement was performed in the same manner as described above. Table 1 shows the above results.

[0033]

[Table 1]

According to Table 1, the protective film of the polarizing plate of the example has a photoelastic coefficient 1/2 that of TAC, a small change in birefringence, and excellent durability after high temperature and high humidity. It is clear that. On the other hand, Comparative Example 1 was inferior in appearance due to generation of carbonized deterioration during melt molding.
Those having very low durability after passage of high temperature and high humidity.

[0035]

The polarizing plate protective film of the present invention has a small photoelastic coefficient. Therefore, when a polarizing plate obtained by laminating the polarizing film on a polarizing film is incorporated in a liquid crystal display, a display with excellent color contrast and excellent contrast can be obtained. Further, a polarizing plate having excellent moisture resistance and heat resistance can be obtained. Furthermore, since there is little decomposition or deterioration occurring at the melt molding temperature, the protective film has less foreign matter and excellent appearance, and the extrusion molding method is suitable for production, and it can be produced at low cost with good productivity.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a phase difference measurement state.

[Explanation of symbols]

 1: Sample 2, 3: Chuck 4: Load measuring device 5: Light receiving section 6: Rail 7: Screw

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA27 BB22 BB43 BB51 BC22 4F006 AA19 AB13 BA00 BA09 CA05

Claims (1)

[Claims] 1. A protective film laminated on at least one surface of a polarizing plate, wherein the protective film is polymethylpentene.