JP2000206303A - Polarizing plate protective film and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in optical characteristics and a polarizing plate protective film causing no irregular display and contrast degradation even under a high-temperature or high-temperature humid environment when used for the polarizing plate. SOLUTION: This polarizing plate protective film is laminated with a resin layer having a smaller hygroscopicity than tri-acetyl cellulose and a positive photoelasticity constant, and with a resin layer having a smaller hygroscopicity than tri-acetyl cellulose and a negative photoelasticity constant, so that the photoelasticity constant of the polarizing plate protective film is not more than 10.0×10-7 cm2/kgf.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate protective film excellent in heat resistance and wet heat resistance, and a polarizing plate using the same.

[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 means for adapting a polarizing plate to a high-temperature or high-temperature and high-humidity environment, a protective film using a film made of a polycarbonate resin or a polymethyl methacrylate resin has been disclosed (Japanese Patent Application Laid-Open No. 7-56017). In addition, the average molecular weight is 30,000 or more, and the glass transition temperature is 1
It is also disclosed that a polycarbonate film having a temperature of 50 ° C. or higher is used as a protective film (JP-A-8-6).
2419).

[0005] Although all of the publications described in the above publications are improved in terms of moisture resistance, there is still room for improvement with respect to display unevenness and a decrease in contrast due to a change in phase difference under a high temperature environment. I have.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and, when used in a polarizing plate, does not cause display unevenness or a decrease in contrast even in a high-temperature or high-temperature and high-humidity environment. It is an object to provide a plate protective film and a polarizing plate having excellent optical characteristics.

[0007]

Means for Solving the Problems The polarizing plate protective film of the present invention is provided.
Lum is less hygroscopic than triacetyl cellulose
A resin layer having a positive photoelastic constant;
Resin with a lower hygroscopicity than base and a negative photoelastic constant
And a photoelastic constant of 10.0 × 10 ^-7cm^Two
/ Kgf or less.

Further, the polarizing plate of the present invention is characterized in that the polarizing plate protective film according to claim 1 is bonded to at least the surface of the polarizer on the liquid crystal cell side.

The photoelastic constant referred to in the present invention refers to a photoelastic effect in which when an elastic body receives an external force, it temporarily becomes an optically anisotropic body, generates birefringence, and returns to its original state after removing the external force. It is a constant representing the stress dependence of the birefringence difference in a substance. That is, the relationship between the birefringence difference (Δn) and the photoelastic constant is represented by the following equation. Δn = C · σ (C is photoelastic constant, σ is stress)

A resin having a positive photoelastic constant is a resin having a positive photoelastic constant, and a resin having a negative photoelastic constant is a resin having a negative photoelastic constant.
Each of the resins having the positive and negative photoelastic constants is required to be excellent in transparency and to be less hygroscopic than TAC. As long as these conditions are satisfied, either a homopolymer or a copolymer may be used.

The polarizing plate protective film of the present invention is a laminate of the resin layer having a positive photoelastic constant and the resin layer having a negative photoelastic constant, wherein the laminate has a photoelastic constant of 1
0.0 × 10 ⁻⁷ cm ² / kgf or less. If the photoelastic constant is higher than the above, the phase difference changes sharply at high temperature, and LC
As D, display unevenness and a decrease in contrast remarkably appear.

Examples of the resin having a positive photoelastic constant include polycarbonate (PC) and polysulfone (PS).
u), polyarylate, polyether sulfone, polyethylene terephthalate (PET), polystyrene, norbornene ring-opening polymerization hydrogenated product, and a copolymer containing these monomer units.

Examples of the resin having a negative photoelastic constant include homopolymers such as methyl methacrylate (MMA) and α-methylstyrene, copolymers containing these monomer units, and ethylene-tetracyclododecene copolymer. Coalescence and the like.

As a method of laminating a resin layer having a positive photoelastic constant and a resin layer having a negative photoelastic constant, besides co-extrusion molding and extrusion lamination, respective resin films are separately prepared, Dry lamination using known means, such as a polyurethane-based, polyester-based, or polyacryl-based adhesive, or an acrylic, silicone-, or rubber-based adhesive, can be employed.

In the case of dry lamination, it is preferable to apply a surface treatment such as a corona discharge treatment to the bonding surface in order to improve the adhesive strength. The polarizing plate protective film of the present invention requires at least the two resin layers described above, but other resin layers may be laminated as necessary. However, in order to minimize the loss of transmitted light, the number of layers is preferably three or less.

The total thickness of the polarizing plate protective film is 10 to 1
000 μm is preferable, and more preferably 30 to 500 μm
m. If the thickness is less than 10 μm, it is difficult to handle, the moisture permeability increases, and the durability deteriorates. 1000 μm
When the ratio exceeds, the transparency is deteriorated, and it is impossible to achieve the thin and light weight which is a feature of the LCD.

The thickness ratio of the resin layer having a positive photoelastic constant to the resin layer having a negative photoelastic constant is such that the total thickness is within the above range and the photoelastic constant is 10.0 × 10 ⁻⁷ cm ² / kgf
It can be appropriately selected within the following range.

In the polarizing plate according to the second aspect, the protective film for the polarizing plate according to the first aspect is laminated on at least one side of the polarizer, but the protective film is always used on the liquid crystal cell side of the polarizer. Otherwise, a change in the phase difference at a high temperature cannot be suppressed. Since the surface opposite to the liquid crystal cell is not affected by birefringence, the protective film of the present invention does not necessarily need to be used, and a resin can be selected regardless of the positive or negative photoelastic constant as long as it is transparent and has a low water absorption. Examples of such a resin include polycarbonate, polysulfone, polyarylate, polyethersulfone, polyethylene terephthalate, polystyrene, norbornene-based resin, PM
MA, poly-α-methylstyrene, copolymers containing these monomer units, and the like.

(Function) The protective film for polarizing plate of the present invention comprises:
Since the resin layer having lower hygroscopicity than TAC is laminated, the polarizer is protected from moisture even in a high-temperature and high-humidity environment, and a decrease in the degree of polarization and generation of discoloration are suppressed. Further, since the photoelastic constant is set to 10.0 × 10 ⁻⁷ cm ² / kgf or less, birefringence hardly occurs even when stress is generated due to shrinkage of PVA even in a high temperature environment, and the The occurrence of display unevenness and a decrease in contrast are suppressed. The polarizing plate using the polarizing plate protective film can maintain good optical characteristics even in a high-temperature and high-humidity environment.

[0020]

Embodiments of the present invention will be described below. Preparation of Polarizer An unstretched PVA film having a saponification degree of 99% and a thickness of 75 μm was washed with water at room temperature and stretched 5 times uniaxially. The dichroic dye was adsorbed by immersing the film in an aqueous solution containing 0.5% by weight of iodine and 5% by weight of potassium iodide while maintaining the tension of the film. Further, a cross-linking treatment was carried out 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 polarizer.

Preparation of acrylic pressure-sensitive adhesive and pressure-sensitive adhesive layer 94.8 parts by weight of butyl acrylate, 5 parts by weight of acrylic acid, 0.2 parts by weight of 2-hydroxyethyl methacrylate in the presence of 0.3 parts by weight of benzoyl peroxide With ethyl acetate as a solvent at a weight average molecular weight (Mw) of 120.
An ethyl acetate solution of an acrylic polymer having a ratio (Mw / Mn) of Mw to the number average molecular weight (Mn) of 3.9 was obtained. Toluene was added to the obtained ethyl acetate solution of the acrylic polymer to dilute it to obtain a toluene solution of 13% by weight of the acrylic polymer. An isocyanate crosslinking agent (manufactured by Nippon Polyurethane Co., trade name "Coronate L")
The solution obtained by adding 2.0 parts by weight and stirring was applied to a release film, and then left at 60 ° C. for 5 minutes and further at 100 ° C. so as not to foam.
And dried in two stages for 5 minutes to form an adhesive layer. A light-releasable release film was bonded to the surface of the pressure-sensitive adhesive layer. By this method, the average thickness of 10 μm and 25 μm
Various kinds of pressure-sensitive adhesive layers were produced.

(Example 1) Polycarbonate (PC) resin (trade name: Panlite L-1225Z, manufactured by Teijin Chemicals Limited)
E ") A 30% by weight methylene chloride solution is prepared and cast on a polyethylene terephthalate (PET) substrate.
5 minutes at 100 ° C, 5 minutes at 100 ° C, and 5 minutes at 130 ° C.
2 types of PC resin films were produced. Polymerization was carried out at 80 ° C. using 80% by weight of MMA, 15% by weight of maleic anhydride and 5% by weight of butyl acrylate, with 3% by weight of benzoyl peroxide as an initiator. 30% by weight of the obtained polymer
Cast on a PET substrate as a methylene chloride solution of
It dried at 100 degreeC for 5 minutes at 100 degreeC, peeled from the base material, and obtained the 75-micrometer-thick PMMA-type film after drying.

Each of the PC resin film (thickness: 10 μm) and the PMMA-based film has a surface of 40 W / m ² /
A corona discharge treatment was performed at a strength of min. Face the corona-discharge treated surfaces of these films, and
Then, a laminated film having a structure of PC resin film / adhesive layer / PMMA-based film was produced by laminating through the above-mentioned adhesive layer. Further, both surfaces of the laminated film were subjected to corona discharge treatment at 40 W / m ² / min, respectively, to obtain a protective film on the liquid crystal cell surface side.

On the other hand, a PC resin film (50 μm thick)
Was subjected to a corona discharge treatment at 40 W / m ² / min to obtain a protective film for the back surface of the liquid crystal cell surface.
On the PMMA-based film layer surface of the liquid crystal cell surface side protective film and the corona discharge treated surface of the air surface side protective film,
Polyester adhesive (trade name “T” manufactured by Toyo Morton Co., Ltd.
M-593 ") was applied so as to have a thickness of 2 μm after drying, and dried at 90 ° C.
The adhesive surface was bonded to both surfaces of the polarizer to form a polarizing plate.

(Example 2) Polysulfone (PSu) resin (trade name "U" manufactured by Teijin Amoko Engineer Plastics Co., Ltd.)
DEL, P-3500 ") in a 30% by weight anisole solution, and cast on a PET substrate at 60 ° C. for 5 minutes for 12 minutes.
Dried at 0 ° C for 5 minutes and further at 170 ° C for 5 minutes.
Two types of PSu films of μm and 50 μm were produced.
Ethylene-tetracyclododecene copolymer (trade name “APEL6015”, manufactured by Mitsui Petrochemical Co., Ltd .; hereinafter “APE
L)), cast on a PET substrate, dried at 60 ° C. for 5 minutes and at 120 ° C. for 5 minutes, and then peeled off from the substrate to obtain a 70 μm-thick AP.
An EL film was produced.

The above-mentioned PSu film (thickness 10 μm) and A
A corona discharge treatment is performed on each side of the PEL film at 40 W / m ² / min, and the corona discharge treatment surfaces are faced to each other, and bonded via the pressure-sensitive adhesive layer (thickness: 10 μm).
A laminated film of a PSu film / APEL film, and 40 W / m ² / m on both sides of the laminated film
In was subjected to a corona discharge treatment to obtain a protective film on the liquid crystal cell side.

On the other hand, a PC resin film (50 μm thick)
Was subjected to a corona discharge treatment at 40 W / m ² / min to obtain a back surface protective film. A polyester adhesive (trade name “TM-593”, manufactured by Toyo Morton Co., Ltd.) is applied to the APEL resin layer surface of the liquid crystal cell surface side protective film and the corona discharge treated surface of the back surface protective film.
A weight% ethyl acetate solution was applied so that the thickness after drying became 2 μm, and dried at 90 ° C. The adhesive surface was bonded to both surfaces of the polarizer to form a polarizing plate.

(Comparative Example 1) A 3% by weight aqueous solution of a polyvinyl alcohol-based adhesive (trade name “Gohsenol NH17”, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was applied to an alkali saponified film of TAC at a thickness of 1 μm and dried at 90 ° C. Thus, an adhesive layer was formed. The polarizer was bonded to the adhesive layer to form a polarizing plate.

Comparative Example 2 The same TAC alkali saponified film as used in Comparative Example 1 was used as a protective film on the liquid crystal cell side. The PC resin film obtained in Example 1 (thickness 5
(0 μm) was subjected to a corona discharge treatment at 400 W / m ² / min to obtain a back surface protective film. The same adhesive layer as in the comparative example was formed on the corona discharge treated surface of the back protective film and the TAC film, and bonded to each other with the polarizer interposed therebetween to obtain a polarizing plate.

[Evaluation of Performance] (1) Measurement of Photoelastic Constant of Protective Film on Liquid Crystal Cell Side: The protective film was cut into a rectangle,
The phase difference (incident light at 550 nm) with respect to the load was measured, and the inclination was determined. For the measurement of the phase difference, a birefringence meter (trade name “RETS-2000” manufactured by Otsuka Electronics Co., Ltd.) was used. (2) Polarizing plate: The acrylic pressure-sensitive adhesive layer (thickness: 25 μm) was formed on the protective film on the liquid crystal cell side obtained in Examples and Comparative Examples.
m) was peeled off from the release film and bonded to obtain a polarizing plate adhesive sheet. The polarizing sheet pressure-sensitive adhesive sheet was punched out into a 12.1 inch rectangle by a Thomson punching machine so that the angle of the absorption axis of the polarizer made an angle of 45 degrees with the side to obtain a test piece.

The release film left on the test piece was peeled off,
The adhesive surface was attached to soda glass having a thickness of 1.2 mm using a desktop laminator. After the glass plate was stuck the pressure-sensitive adhesive layer was left at room temperature for 1 hour, at 5 kgf / cm ² 20
After an autoclave treatment for one minute, it was left at room temperature for one hour to perform a durability test, and display characteristics were evaluated before and after the test based on the following degree of polarization and color difference. There are four measurement positions at the center of each side, 10 mm from the end.

Degree of polarization = [(H1-H2) / (H1 + H)
2)] ^1/2 (where, H1 parallel transmittance, H2 is orthogonal transmittance) Color difference: shown in Table 1 ΔE _H L, a, a calculation above results b value as an average value.

[0033]

[Table 1]

[0034]

The polarizing plate protective film of the present invention has a TAC
Has a lower hygroscopicity and a photoelastic constant of 10.0 × 10 ⁻⁷ c
Since m ² / kgf or less, when used for a polarizing plate, a decrease in the degree of polarization and discoloration are suppressed even in a high-temperature and high-humidity environment, and good optical characteristics can be maintained.
Further, the polarizing plate using the polarizing plate protective film does not deteriorate its optical characteristics even in a high-temperature and high-humidity environment, and can be suitably used for a portable device or an LCD mounted on a vehicle.

Continued on the front page F term (reference) 2H049 BB62 BC14 2H091 FA08X FA08Z FD15 GA16 GA17 LA04 LA06 MA03 MA10 2K009 CC24 CC34 DD01 DD07 EE00 FF02

Claims (2)

[Claims] 1. A resin layer having a smaller hygroscopic property than triacetyl cellulose and having a positive photoelastic constant and a resin layer having a smaller hygroscopic property than triacetyl cellulose and having a negative photoelastic constant are laminated. Constant is 10.0 × 10 ^-7
polarizing plate protective film, wherein the at cm ² / kgf or less. 2. The polarizing plate protective film according to claim 1,
A polarizing plate, which is bonded to at least a surface of a polarizer on a liquid crystal cell side.