JPH0792321A - Polarizing plate - Google Patents

Abstract

PURPOSE:To provide a polarizing plate excellent in durability in an environment at a high temp. and humidity. CONSTITUTION:The durability of a polarizing plate is improved by using a multilayered film consisting of an amorphous polymer film, a boric acid (precursor)-contg. layer and an amorphous polymer film as a protective film. The total amt. of elemental boron forming boric acid (precursor) in the boric acid (precursor)-contg. layer is 0.4-10wt.% of the amt. of the polarizer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polarizing plate.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for liquid crystal display devices such as liquid crystal televisions, personal computers and word processors, or liquid crystal display devices for automobile panels. For this reason, the polarizing plates used for these are required to be able to maintain stable performance for a long period of time in various environments, especially in a hot and humid environment. The polarizing plate is a uniaxially oriented vinyl alcohol-based film in which a dichroic dye is adsorbed and oriented, and a polarizing plate using a polarizer obtained by applying a boric acid treatment is generally used. At least one surface of the child, for example, the side opposite to the liquid crystal display panel, is provided with a protective film for the purpose of protecting the polarizer from the external environment.

However, such a polarizing plate has a problem that it is inferior in durability under high temperature and high humidity environment, and in order to solve this problem, a polarizing plate using a protective film laminated with an acrylic resin as a water vapor barrier layer (JP 61-2
31502), a polarizing plate coated with a vinylidene chloride resin as a barrier layer (JP-A-61-69029).
(Japanese Unexamined Patent Publication (Kokai) No. Hei.
No. 02) has been proposed, but it is still not enough.

[0004]

Means for Solving the Problems As a result of investigations for solving the above problems, the present inventors have found that it is composed of an amorphous polymer film / boric acid (precursor) -containing layer / amorphous polymer film. It was found that such problems can be solved by using such a multilayer film as a protective film, and the present invention has been reached. That is, the present invention is a polarizing plate in which a protective film is laminated on at least one side of a polarizer made of a polyvinyl alcohol film and subjected to a boric acid treatment, and an amorphous polymer film / boric acid (precursor) is used as the protective film. ) Containing layer / amorphous polymer film is a multilayer film, and the total amount of boron element constituting boric acid (precursor) in the boric acid (precursor) containing layer is 0. The present invention relates to a polarizing plate characterized by using a multilayer film in the range of 4 wt% to 10 wt%.

The present invention will be described in detail below. As the polarizer, a uniaxially oriented vinyl alcohol-based film in which a dichroic dye is adsorbed and oriented, and a boric acid-treated one can be used. As a vinyl alcohol film, a polyvinyl alcohol film (hereinafter P
VA film), polyvinyl formal film, polyvinyl acetal film, poly (ethylene-vinyl acetate) copolymer film, partially polyene film of PVA film, and the like.

Examples of the method for uniaxially orienting the vinyl alcohol film include a uniaxial stretching method, and for example, a dry stretching method (compression stretching method) or a wet stretching method can be used.

Examples of dichroic dyes include iodine and dichroic dyes, and dichroic dyes, such as azo direct dyes, whose performance is less deteriorated in a high temperature and high humidity environment can be preferably used.

Examples of the method of adsorbing and orienting the dichroic dye on the vinyl alcohol film include a method of dipping and adsorbing the vinyl alcohol film in an aqueous solution of the dichroic dye.

As the boric acid treatment, for example, 30 ° C. to 80 ° C.
A method of immersing in a boric acid (concentration of about 1 wt% to 15 wt%) aqueous solution at about ° C can be used.

The thickness of the polarizer is not particularly limited, but usually 1
It is about 0 to 50 μm. As for the content of boric acid in the polarizer, the total amount of boron elements constituting boric acid is 3 wt% to 7 wt%.
It is preferable to adjust so as to be in the range (total amount of boron elements constituting boric acid / weight of polarizer).

The amorphous polymer film is not particularly limited, and examples thereof include cellulose triacetate film (hereinafter referred to as TA
C film), cellulose diacetate film, etc.
Film, polyester film represented by polyethylene terephthalate film, acrylic film represented by polymethylmethacrylate film,
An amorphous polymer film having excellent transparency such as a styrene film represented by a polystyrene film or a polycarbonate film can be used. Preferably,
It is a TAC film obtained by a solvent casting method.

As the boric acid (precursor) used in the boric acid (precursor) -containing layer, boric acid or a compound [boric acid precursor] capable of liberating boric acid can be used. Examples of the boric acid precursor include boric acid. Examples thereof include acids, metal salts such as metaboric acid, and boroxine derivatives that release boric acid in the presence of water.

The amount of boric acid (precursor) in the boric acid (precursor) -containing layer is such that the total amount of boron elements constituting boric acid (precursor) is in the range of 0.4 wt% to 10 wt% with respect to the weight of the polarizer. Is adjusted. Preferably 0.8 wt% to 4
wt%. In forming the boric acid (precursor) -containing layer, a polymer having compatibility with boric acid (precursor) and transparency can be mixed with boric acid (precursor).

Examples of such polymers include acrylic resins represented by polymethylmethacrylate, styrene resins represented by polystyrene, polyester resins represented by polyethylene terephthalate, and polycarbonate. Hydrophobic polymers such as bonnet resin, cellulose-based resins such as TAC and cellulose acetate, polyvinyl alcohol
And a polymer having hydrophilicity such as vinyl alcohol resin such as ethylene-vinyl alcohol copolymer. When using hydrophobic boric acid (precursor) (trialkylboroxine etc.), a polymer having hydrophobicity is preferable,
Hydrophilic boric acid (precursor) (boric acid, sodium borate, etc.)
In this case, it is preferable to use a polymer having hydrophilicity.

The method for forming the boric acid (precursor) -containing layer on the amorphous polymer film is not particularly limited.
For example, a method in which a solution of boric acid (precursor) and a polymer dissolved in water or an organic solvent is applied onto an amorphous polymer film, or a boric acid (precursor) and a polymer are melt-kneaded to form an amorphous polymer film. It is possible to use a method in which the film is cast on the surface to form a film.

The proportion of the polymer and boric acid (precursor) is, for example, 1 to 100 boric acid (precursor) per 100 parts by weight of the polymer.
The amount is about 3 parts by weight, preferably about 3 to 40 parts by weight of boric acid (precursor) per 100 parts by weight of the polymer. The thickness of the boric acid (precursor) -containing layer is, for example, about 1 μm to 50 μm, preferably about 5 μm to 20 μm.

Next, an amorphous polymer film is laminated on the boric acid (precursor) -containing layer by a known method, for example, by laminating with an adhesive or the like as necessary, the amorphous polymer film is highly amorphous. A protective film having a structure of molecular film / boric acid (precursor) -containing layer / amorphous polymer film is obtained. The amorphous polymer film has a thickness of, for example, about 2 μm to 200 μm. It should be noted that an antioxidant, an ultraviolet absorber, a light stabilizer, etc. may be added to the boric acid (precursor) -containing layer to the extent that the effects of the present invention are not impaired.

The protective film is on at least one side of the polarizer,
That is, it is provided on the surface in contact with the high temperature and high humidity atmosphere. As a method for adhering the polarizer and the protective film, a conventionally known method can be used. For example, a method of bonding the protective film and the polarizer with a vinyl alcohol-based or cyanoacrylic-based adhesive may be used.

[0019]

The polarizing plate of the present invention has excellent durability in a high temperature and high humidity environment, and thus can be used in various environments without any practical problems.

[0020]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The optical characteristics were evaluated by the following methods.・ Measurement equipment: Spectrophotometer (TC-1, Tokyo Denshoku Co., Ltd.)
800M type spectrophotometer) is used.・ Transmittance: The light transmittance of the polarizing film is measured, and the JIS
Z8701 (XYZ color system, and X ₁₀ Y ₁₀ Z ₁₀ color system by the color display method) the value of Y obtained in accordance with. Degree of polarization P (%) = {(Y //-Y | ) / (Y // + Y
│ )} ^0.5 × 100 Y //: light transmittance (measured every 10 nm in the wavelength region of 400 to 700 nm in a state where two polarizers are superposed so that the alignment directions of the polarizers are the same). Y value obtained from parallel transmittance). Y | : Calculated from the light transmittance (orthogonal transmittance) measured every 10 nm in the wavelength region of 400 to 700 nm in a state where two polarizers were superposed so that the orientation directions of the polarizers were orthogonal to each other. Value of Y. Hue L, a, b: JIS Z 8729 (L ^* a ^* b
^* Display method of object color by color system and L ^* u ^* v ^* color system). -ΔT, ΔP, ΔE: Calculated by the following formula. Transmittance: (ΔT) _{i, 0} = (Y) _i- (Y) ₀ Polarization degree: (ΔP) _{i, 0} = (P) _i- (P) ₀ Hue: (ΔE) _{i, 0} = {(ΔL ^* ) _{I, 0} ² + (Δ
a ^* ) _{i, 0} ² + (Δb ^* ) _{i, 0} ² } ^0.5 (ΔL ^* ) _{i, 0} = (L ^* ) _i- (L ^* )
₀ (Δa ^* ) _{i, 0} = (a ^* ) _i- (a ^* ) ₀ (Δb ^* ) _{i, 0} = (b ^* ) _i- (b ^* ) ₀ 0 = initial state. i shows the state after aging for 280 hours in an atmosphere of 80 ° C. and 90% RH.

Example 1 A PVA film (Kuraray vinylon # 75) having a thickness of 75 μm
00; Kuraray Co., Ltd. longitudinally uniaxially stretched (stretching ratio 4
Times) to obtain a polarizer base material. While keeping the polarizer base material in a tensioned state, an azo dye (C-I Direct Yellow 12: concentration 0.032 wt%, C-I Direct Red 81: concentration 0.085 wt%, and C-I・ Direct Violet 9: Concentration 0.20w
t%) and sodium mirabilite (concentration: 2 wt%), and immersed in an aqueous solution at 60 ° C. for 10 minutes. Next, boric acid at 65 ° C (concentration 7.5w
t%) aqueous solution for 10 minutes, and then 3 times with water at 20 ° C.
It was washed for 0 seconds to obtain a polarizer (size: 5 cm × 10 c
m, weight of polarizer: 0.12 g, total amount of boron element / weight of polarizer = 5 wt%). Same size as polarizer but 50μ thick
m TAC film (Fujitac CLEAR; made by Fuji Photo Film Co., Ltd.), boric acid (concentration 0.25 wt
%) And polyvinyl alcohol (Kuraray Poval PVA
A boric acid (precursor) -containing layer was formed by applying and drying an aqueous solution containing -117; degree of polymerization 1700, degree of saponification 98.5%; Kuraray Co., Ltd. (concentration 1 wt%) at room temperature. (Dry thickness 5 μm) On the boric acid (precursor) -containing layer, a TAC film (Fujitac CLEAR; manufactured by Fuji Photo Film Co., Ltd.) having the same size and thickness as described above was wetted with water, laminated, and dried.
Protective film (Structure: TAC film / Boric acid (precursor)
Content layer / TAC film, boric acid (precursor) The total amount of boron elements constituting boric acid (precursor) in the content layer / weight of polarizer = 0.8 wt%) was obtained. Similarly, another protective film was prepared. PV protective film of 2 sheets
A polarizing plate was obtained by bonding the upper and lower surfaces of the polarizer with an A-based adhesive. Table 1 shows the results of the heat and moisture resistance evaluation of the polarizing plate.

Example 2 A polarizing plate was produced in the same manner as in Example 1 except that the concentration of boric acid was 0.33 wt% (boron forming the boric acid (precursor) in the layer containing boric acid (precursor)). Total amount of elements / weight of polarizer = 1.1 wt%). The results of moist heat resistance evaluation are shown in Table 1.

Example 3 A polarizing plate was obtained in the same manner as in Example 1 except that sodium borate (Na ₂ B ₄ O ₇ ) was used in place of boric acid and the concentration thereof was 1.39 wt%. (Precursor) total amount of boron element constituting boric acid (precursor) in the containing layer / weight of polarizer = 1.1 wt%). The results of moist heat resistance evaluation are shown in Table 1.

Comparative Example 1 A polarizing plate was obtained in the same manner as in Example 1 except that the concentration of boric acid was 0.066 wt% (boron forming the boric acid (precursor) in the boric acid (precursor) -containing layer). Total amount of elements /
Weight of polarizer = 0.1 wt%). The moist heat resistance evaluation result is No. 1
Shown in the table.

Comparative Example 2 A polarizing plate was obtained in the same manner as in Example 1 except that boric acid was not used. The results of moist heat resistance evaluation are shown in Table 1.

Comparative Example 3 A polarizing plate was obtained in the same manner as in Example 1 except that two TAC films each having a thickness of 50 μm were stuck together and used as a protective film. The results of moist heat resistance evaluation are shown in Table 1.

Comparative Example 4 The same experiment as in Example 1 except that the TAC film located on the polarizer side was not provided and the boric acid (precursor) containing layer side was bonded to the polarizer using a PVA adhesive. However, only a polarizing plate with low initial performance was obtained.

<Table 1> Initial performance 80 ° C x 90% RH x 280 hours Transmittance Polarization degree Performance change after initial hue Experiment number Y (%) P (%) L ₀ a ₀ b ₀ ΔT (% ) ΔP (%) ΔE Example 1 39.0 98.4 68.8-2.0 2.7-4.6-0.50 6.5 Example 2 40.2 98.7 69.7-2.1 2.8-4.4-0.64 6.2 Example 3 39.6 98.8 69.7-2.1 2.7-5.0-0.43 5.8 Comparative Example 1 41.0 98.1 70.1-2.2 3.0-7.6-0.76 10.6 Comparative Example 2 40.1 98.5 69.6-2.1 2.7-8.5-0.93 9.2 Comparative Example 3 40.7 98.8 70.0-2.1 2.8-9.2-0.91 9.4

Claims (1)

[Claims] 1. A polarizing plate comprising a polyvinyl alcohol-based film and a boric acid-treated polarizer having a protective film laminated on at least one side thereof. The protective film comprises an amorphous polymer film / boric acid (precursor). It is a multi-layer film having a structure of containing layer / amorphous polymer film, and the total amount of the boron element constituting boric acid (precursor) in the boric acid (precursor) containing layer is 0.4 wt with respect to the weight of the polarizer. % ~ 1
A polarizing plate comprising a multi-layer film in the range of 0 wt%.