JP2002221619A - Polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a polarizing plate having a low water content even in a conventional production process using an aqueous PVA solution as an adhesive and to provide a polarizing plate free of the lowering of performance such as the lowering of the degree of polarization and a hue change and excellent in durability even when used in a highly humid hot environment. SOLUTION: The polarizing plate is obtained by sticking a plastic film having about 200-3,000 g/m2.24 hr steam permeability (at 40 deg.C and 90% RH) as a protective film (a) on one face of a polarizer and a cycloolefin resin film as a protective film (b) on the other face with an aqueous polyvinyl alcohol solution as an adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly durable polarizing plate which is excellent in productivity and does not lower the degree of polarization even when used in a high humidity and heat environment.

[0002]

2. Description of the Related Art A conventional polarizing plate is composed of a polyvinyl alcohol (hereinafter, referred to as PVA) -based film and a polarizer having iodine or a dichroic dye adsorbed and aligned thereon, and a cellulose triacetate-based film (hereinafter, referred to as a protective film). TAC), PVA
What laminated | stacked the aqueous solution of resin as an adhesive was common.

[0003] However, since TAC has a large water absorption and moisture permeability, the degree of polarization of a polarizing plate using TAC as a protective film in a high-temperature and high-humidity environment is drastically reduced.

For this reason, a polarizing plate using a film having a small water absorption or water vapor transmission rate as a protective film has been proposed. For example, in JP-A-7-77608, a film made of a thermoplastic saturated norbornene-based resin is used as a protective film and bonded to a polarizer, and the degree of polarization after leaving at 80 ° C. and 90% RH for 500 hours is 95%. As described above, a polarizing plate having a single transmittance of 38% or more is disclosed. However, using a film with low water absorption and water vapor transmission rate as a protective film,
To technically mass-produce the polarizing plate, a great technical problem remains. In other words, when laminating the protective film on the polarizer,
If a film having a small water absorption or water vapor transmission rate is used as the protective film, the moisture contained in the polarizer and the adhesive is less likely to evaporate through the protective film in the drying step of the adhesive, and as a result, the moisture content of the manufactured polarizing plate is reduced. However, there is a problem that the adhesive strength is insufficient, and the degree of polarization is easily reduced.

[0005]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is that a polarizing plate having a low water content can be stably manufactured in the conventional manufacturing process, and the polarizing plate is used even when used in a high humidity and heat environment. An object of the present invention is to provide a polarizing plate which is excellent in durability without a decrease in performance such as a decrease in degree and a change in hue.

[0006]

According to the present invention, as a protective film (a) on one side of a polarizer, the water vapor transmission rate is (40 ° C. × 90%).
RH in) from about 200 to about 3000g / m ² · 24h
The present invention relates to a polarizing plate formed by laminating a plastic film of r and a cyclic olefin resin film as a protective film (b) on the surface on the opposite side.

It is preferable to laminate the protective film (a) and the protective film (b) using a polyvinyl alcohol-based aqueous solution as an adhesive.

Furthermore, the water vapor transmission rate is (40 ° C. × 90%
RH in) from about 200 to about 3000g / m ² · 24h
Preferably, the plastic film of r is a cellulose acetate-based film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As the polarizer of the present invention, conventionally known polarizers can be used. In a preferred embodiment, a film made of PVA or a derivative thereof is uniaxially stretched and oriented.
A polarizer produced by adsorbing iodine, treating with boric acid water, and drying under tension can be used. Or,
A film made of PVA or a derivative thereof is immersed in an aqueous solution of iodine to adsorb iodine, then uniaxially stretched in boric acid water, and dried under tension to obtain a polarizer. Instead of iodine, a polarizer using a dichroic dye such as an azo type, anthraquinone type or tetrazine type is similarly produced.

[0010] The degree of polarization of the polarizer is preferably about 95.0.
% Or more, more preferably about 99.0% or more, and still more preferably about 99.7% or more. The thickness of the polarizer is not particularly limited, but is usually about 10 to 40 μm.

Next, the protective film (a) laminated on the polarizer will be specifically described.

The protective film (a) laminated on one side of the polarizer has a water vapor transmission rate of about 200 to about 3000 g / m ² ···
A plastic film in the range of 24 hours (at. 40 ° C. × 90% RH) can be used. The water vapor transmission rate is preferably from about 300 to about 2000 g / m ² · 24 h
r, more preferably from about 400 to about 1800 g / m ² · 2
4 hr, more preferably about 500 to about 1500 g / m
A ² · 24hr.

[0013] The material of the plastic film is not particularly limited as long as the water vapor permeability is within the above range. For example, polyester films, polyolefin films, cellulose acetate films, polycarbonate films, polyvinyl alcohol films, polyethersulfone films, polyarylate films, polyimide films, polyamide imide films, polyamide films, etc. Can be illustrated. In order to make the most of the performance of the polarizer, among them, a film with excellent appearance, good surface smoothness, and a small optical in-plane retardation is preferable. A cellulose acetate-based film that can be easily controlled within the above range is preferable. Specific examples of the cellulose acetate-based film include TAC and cellulose diacetate. Note that the cyclic olefin-based resin is not included in the material of the plastic film.

The method for obtaining the protective film (a) from the material is not particularly limited, and examples thereof include a solution casting method, an extrusion method, and a calendering method.

Examples of the solvent used in the solution casting method include alicyclic hydrocarbons such as cyclohexane and cyclohexene and derivatives thereof, and aromatic hydrocarbons such as toluene, xylene and ethylbenzene and derivatives thereof.

When a cellulose acetate film is used for the protective film (a) of the present invention, the water vapor transmission rate is (40 ° C. ×
From about 200 to about 3000 g / m ^2.
It needs to be between 24 hours and its thickness is preferably about 30 to about 100 μm.

When the water vapor permeability of the protective film (a) is (40 ° C.)
About 200 g / m at × 90% RH)^Two・ 24hr not yet
If it is full, the moisture in the polarizer and the adhesive during the adhesive drying process
Does not evaporate sufficiently through the protective film.
High fraction, resulting in poor adhesion strength
Polarization performance and durability of the polarizing plate
No. On the other hand, when the water vapor transmission rate is (40 ° C. × 90% RH)
About) 3000g / m ^Two・ If it exceeds 24 hours,
Of the polarizing plate under 80 ° C × 90% RH environment
Becomes worse, which is not preferable.

Next, the protective film (b) laminated on the polarizer will be specifically described.

The protective film (b) laminated on the opposite surface of the polarizer of the present invention refers to a cyclic olefin resin film.

The cyclic olefin-based resin of the present invention is a general generic name. Specifically, (1) a polymer obtained by hydrogenating a ring-opening (co) polymer of a cyclic olefin as required;
(2) an addition (co) polymer of a cyclic olefin, (3) a random copolymer of a cyclic olefin and an α-olefin such as ethylene or propylene, (4) an unsaturated carboxylic acid or Examples thereof include a graft-modified product modified with a derivative thereof. The cyclic olefin is not particularly limited, and examples thereof include norbornene, tetracyclododecene, and derivatives thereof (for example, those having a carboxyl group or an ester group).

An ultraviolet absorber,
Various known additives such as inorganic or organic anti-blocking agents, lubricants, antistatic agents and stabilizers may be added for the purpose.

The method for obtaining the protective film (b) from the cyclic olefin resin is not particularly limited, and examples thereof include a solution casting method, an extrusion method, and a calendering method.

Examples of the solvent used in the solution casting method include alicyclic hydrocarbons such as cyclohexane and cyclohexene and derivatives thereof, and aromatic hydrocarbons such as toluene, xylene and ethylbenzene and derivatives thereof.

The cyclic polyolefin-based film of the present invention has a water vapor transmission rate of 1 to 40 ° C. × 90% RH.
500 g / m ² · 24 hr, preferably 1 to 200 g
/ M ² · 24 hr, more preferably 1 to 100 g /
m ² · 24 hr. The water vapor transmission rate is (40 ° C. × 9
If it is less than 1 g / m ² · 24 hr (at 0% RH), the water content in the polarizing plate is high because the water in the polarizer and the adhesive does not sufficiently evaporate through the protective film in the adhesive drying step. As a result, adhesive strength is hardly obtained, and the polarizing performance and durability of the obtained polarizing plate tend to deteriorate. The water vapor transmission rate is 500 g / (at 40 ° C. × 90% RH)
If it exceeds m ² · 24 hr, 8
The durability in a 0 ° C. × 90% RH environment tends to be significantly deteriorated.

The thickness of the cyclic olefin-based film may be appropriately designed, but is preferably about 30 to about 100 μm.

Next, the adhesive for lamination will be specifically described. The adhesive used for laminating the polarizer and the protective film (a) and the protective film (b) is, for example, an ultraviolet-curable adhesive, a solvent-based adhesive, a water-based adhesive, a thermosetting adhesive, or the like. Any one can be used as long as it can obtain an appropriate adhesive strength with the film (a) and the protective film (b). Emulsions and polyvinyl alcohol-based aqueous solutions are examples of those having good adhesion strength to a polarizer and relatively suppressing discoloration of a polarizing plate. In particular, a polyvinyl alcohol-based aqueous solution is preferable because it can suppress discoloration of the polarizing plate and increase the adhesion strength.

The bonding may be performed only with an adhesive, or may be performed via an anchor coat material or the like.

The polyvinyl alcohol-based resin is mainly composed of a resin obtained by saponifying a vinyl acetate resin, and preferably has a degree of polymerization of about 1,000 to about 3,000 and a saponification degree of about 94% or more. Preferably, the degree of polymerization is about 15
Those having a saponification degree of from about 98% to about 3000% are desirable. For the purpose, it may be a copolymer obtained by copolymerizing a small amount of another monomer, for example, acrylic acid, crotonic acid, itaconic acid, or the like, or a monomer modified with, for example, an alkyl group or an epoxy group.

The coating amount of the adhesive solution is preferably about 0.01 to about 10 μm, more preferably about 0.02 to about 5 μm, and still more preferably about 0.05 to about 3 μm in thickness after drying. . If the applied amount of the adhesive is too small, the adhesive strength tends not to be obtained as expected, and if the applied amount is too large, water tends to remain.

It is to be noted that a substance which is cured by reacting with polyvinyl alcohol, for example, polyisocyanate, boric acid, alkylenediamine, epoxy resin and the like may be added. In particular, a polyisocyanate gives a preferable result.

The method of laminating the protective film (a) and the protective film (b) on the polarizer is not particularly limited as long as an appropriate adhesive strength can be obtained between each protective film and the polarizer. Any of the above methods may be used.

[0032]

Next, typical examples of the present invention will be described together with comparative examples. The methods for measuring and evaluating the physical properties used in the present invention are as follows.

The moisture permeability is determined by the Mocon method (PERM manufactured by Mocon Corporation).
ARTRAN-W600 type moisture permeability measuring device)
It measured at 90 degreeC * 90% RH.

The water content of the polarizing plate was calculated from the weight loss rate after drying a polarizing plate having a size of 10 cm × 10 cm at 150 ° C. for 3 hours.

The adhesive strength was determined as the minimum value by sampling a polarizing plate to a width of 10 mm and performing a 180 ° peel test between the protective film (a) and the polarizer and between the protective film (b) and the polarizer. The peeling speed was 200 mm / min.

The degree of polarization of the polarizing plate was calculated by the following method. That is, two polarizing plates are overlapped so that the polarization axes are in the same direction, and 400 nm is measured using a spectrophotometer.
The average value of the light transmittance values continuously measured from to 700 nm is defined as T1. Next, two polarizing plates are overlapped so that the polarizing axes are orthogonal to each other, and the average value of the light transmittance values measured in the same manner is defined as T2. Then, the degree of polarization was calculated from the following equation (1). [Equation 1] Degree of polarization (%) = {(T ₁ −T ₂ ) / (T ₁ + T ₂ )} ^1/2 ×
100 The single transmittance of a polarizing plate is an average value of light transmittance values (in the direction of the transmission axis and the absorption axis) of one polarizing plate continuously measured from 400 nm to 700 nm using a spectrophotometer. . The moist heat test of the degree of polarization of the polarizing plate was performed by the following method.
That is, the polarizing plate was left in an atmosphere of 80 ° C. × 90% RH for 48 hours. The degree of polarization retention is a value obtained by dividing the degree of polarization after the test by the degree of polarization before the test. The higher the value, the better the resistance to moist heat.

Example 1 30 parts by weight of a cyclic olefin resin (ZEONEX 490 manufactured by Nippon Zeon Co., Ltd.) was mixed with a mixed solvent of xylene and cyclohexane (weight mixing ratio 2:
1) It was dissolved in 70 parts by weight, and a film was formed by a casting method to obtain a protective film (b) having a thickness of 50 μm. Further, on one side surface, a polyvinyl alcohol resin was formed as an easy-adhesion layer with a thickness of about 0.5 μm via an acrylic anchor coat material.

The water vapor permeability of the protective film thus obtained is 3.
0 g / m ² · 24 hr (at. 40 ° C. × 90% RH).

PVA film (Kuraray Co., Ltd. Kuraray vinylon film VF-9X75R, thickness 75 μm)
Was immersed in an aqueous solution consisting of 5000 parts by weight of water, 35 parts by weight of iodine and 525 parts by weight of potassium iodide for 5 minutes to adsorb iodine. The film is then dried at 45 ° C. at 4% by weight.
The film was stretched 4.4 times in the machine direction in a boric acid aqueous solution, and then dried under tension to obtain a polarizer.

Next, a 5% aqueous solution of PVA having an average degree of polymerization of 1800 and a saponification degree of 99% is laminated as an adhesive so that the surface of the easily adherent layer of the protective film (b) obtained above is on one side of the polarizer. And as a protective film (a) on the opposite surface,
80 μm thick, moisture permeability 600 g / m ² · 24 hr (40 ° C.
× 90% RH), and PVA having an average degree of polymerization of 1800 and a saponification degree of 99% was used as an adhesive.
% Aqueous solution, so that the adhesive is formed in an undried state on both sides of the interface so that the thickness after drying is 0.5 μm, and a rubber roll / metal roll (rubber roll diameter 200 m
m, metal roll diameter 350mm, linear pressure 10kg / cm)
After passing through a drying zone at 70 ° C. for 3 minutes, the film was wound up. The structure of the obtained polarizing plate is as follows:
PVA aqueous solution 0.5 μm / polarizer / PVA aqueous solution 0.5 μm / adhesive treatment layer 0.5 μm / anchor coat / (b) layer. Table 1 shows the evaluation results of the polarizing plates thus obtained. Moreover, the obtained polarizing plate did not change the hue in the environmental test.

(Example 2) As a casting solution, 30 parts by weight of a cyclic olefin resin (ARTON manufactured by JSR Corporation) was dissolved in 70 parts by weight of xylene, and a film was formed by a casting method. A film (b) was obtained. Further, on one side surface, via an acrylic anchor coating material, polyvinyl alcohol resin as an easy adhesion layer of about 0.5 μm
Formed.

The protective film (b) thus obtained has a water vapor transmission rate of 90 g / m ² · 24 hr (at. 40 ° C. × 90% R
H).

A polarizing plate was obtained in the same manner as in Example 1 except that this protective film (b) was used. Table 1 shows the evaluation results of the polarizing plates thus obtained.

Comparative Example 1 Protective Films (a) and (b)
Then, a polarizing plate was prepared in the same manner as in Example 1 except that the cyclic olefin-based film of Example 1 was used. Table 1 shows the evaluation results of the polarizing plates thus obtained.

Comparative Example 2 Protective Films (a) and (b)
Instead of the TAC of Example 1, the thickness was 80 μm and the moisture permeability was 9
A polarizing plate was prepared in the same manner as in Example 1, except that TAC of 00 g / m 2 · 24 hr was used. Table 1 shows the evaluation results of the polarizing plates thus obtained.

Comparative Example 3 In place of the TAC of Example 1, the thickness was 250 μm and the moisture permeability was 150 g / m ² · 24 hr.
A polarizing plate was prepared in the same manner as in Example 1 except that TAC of (at. 40 ° C. × 90% RH) was used. Table 1 shows the evaluation results of the polarizing plates thus obtained.

[0047]

[Table 1]

[0048]

According to the present invention, the productivity is excellent, and
Even when used in a high-humidity / heat environment, a polarizing plate excellent in durability without deterioration in the degree of polarization or a change in hue or the like can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ken Yamamoto R & D Dept., 163 Morikawaramachi, Moriyama-shi, Shiga Prefecture R72. (72) Inventor Takao Uesugi 98-1 Minami-Tanaka, Kiyosato-mura, Niigata Pref., Niigata Prefecture 2H091 FA08X FA08Z FB02 FD15 GA16 GA17 LA04 LA06 LA12

Claims (3)

[Claims] 1. A plastic film having a water vapor transmission rate (at 40 ° C. × 90% RH) of about 200 to about 3000 g / m ² · 24 hr as a protective film (a) on one surface of a polarizer, and the other surface thereof A polarizing plate comprising a protective film (b) and a cyclic olefin resin film laminated thereon. 2. The polarizing plate according to claim 1, wherein the protective film (a) and the protective film (b) are laminated using a polyvinyl alcohol aqueous solution as an adhesive. 3. A plastic film having a water vapor transmission rate (at 40 ° C. × 90% RH) of about 200 to about 3000 g / m ² · 24 hr is a cellulose acetate film. The polarizing plate according to claim 1.