JP2001281452A - Optical film, polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a high performance polarizing plate at a low cost with a simple method by improving the yield in the polarizing plate punching process. SOLUTION: In the polarizing plate comprising a polarizing layer held between two transparent substrates, the polarizing plate has a polarizing layer comprising a polyvinyl alcohol type film 10-80 deg. obliquely stretched to which a polarizing element is adsorbed with alignment. Simultaneously, in the polarizing plate, at least one out of the transparent substrates satisfies the following inequalities at both of 380 and 780 nm wavelengths. Inequality 1 -10<=(nx-ny)×d<=10 (d: thickness of the transparent substrate) Inequality 2 0<= (nx+ny)/2-nz)×d<=20 (d: thickness of the transparent substrate) In the inequalities 1, 2, n expresses the refractive index, x expresses the MD direction of the transparent substrate, y expresses its TD direction, and z expresses its thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an obliquely stretched polyvinyl alcohol film, a polarizing plate, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art A polarizing plate is a liquid crystal display (hereinafter, LCD).
With the spread of the demand, the demand is increasing rapidly. Generally, a polarizing plate is obtained by laminating a protective film on both sides or one side of a polarizing layer having a polarizing ability via an adhesive layer. Polyvinyl alcohol (hereinafter, referred to as PVA) is mainly used for the polarizing layer, and the PVA film is stretched uniaxially and then dyed with iodine or a dichroic dye, or dyed in the opposite direction and stretched. A polarizing layer is formed by cross-linking. As a protective film, triacetyl cellulose is mainly used because it is optically transparent and has low birefringence.

In a conventional LCD, the transmission axis of a polarizing plate is arranged at an angle of 45 degrees with respect to the vertical or horizontal direction of the screen. I had to punch out. However, when punching in the 45 degree direction,
Eventually, an unusable part occurs near the end of the roll,
As a result, there was a problem that the yield was reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the yield in the polarizing plate punching step and to produce a high-performance polarizing plate at a low cost by a simple method.

[0005]

The object of the present invention has been attained as follows. (1) A film containing polyvinyl alcohol or modified polyvinyl alcohol is placed in the MD direction (longitudinal direction).
A film stretched obliquely in a direction of 10 to 80 degrees with respect to the film. (2) In a polarizing plate having a polarizing layer sandwiched between two transparent supports, the polarizing layer is characterized in that a polarizing element is adsorbed and oriented on a polyvinyl alcohol-based film obliquely stretched at 10 to 80 degrees. Polarizing plate. (3) The polarizing plate according to (2), wherein at least one of the transparent supports satisfies the following formulas 1 and 2 at any wavelength of 380 to 780 nm. (Formula 1) −10 ≦ (nx−ny) × d ≦ 10 (d: Transparent Support Thickness) (Formula 2) 0 ≦ {(nx + ny) / 2−nz} × d ≦ 20 (d: Transparent Support Thickness) ) In the formulas 1 and 2, n represents a refractive index, and x represents MD of the transparent support.
Represents the direction, y represents the TD direction (width direction) of the transparent support, and z represents the thickness direction of the transparent support. (4) A liquid crystal display device, wherein the polarizing plate according to (2) or (3) is used for at least one of two polarizing plates arranged on both sides of a liquid crystal cell.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As in the present invention, when an obliquely stretched polarizing layer is adhered to a transparent support by a roll, as shown in FIG. Since the direction (long direction of the roll) 13 (x-axis) is shifted, the linearly polarized light becomes elliptically polarized light due to the birefringence of the transparent support. Therefore, it is particularly preferable that the refractive indexes nx, ny, and nz of the transparent support in the x, y, and z directions satisfy the above expressions. Examples of such a transparent support include ZEONEX, ZEONOR (both manufactured by Nippon Zeon Co., Ltd.) and ARTON (JS
R (manufactured by Fuji Photo Film Co., Ltd .: triacetyl cellulose), as well as commercially available products such as JP-A-8-110402 and JP-A-1-110402.
Non-birefringent optical resin materials as described in Japanese Patent Application No. 1-293116 are exemplified. The transparent support has a surface treatment such as chemical treatment (such as saponification), mechanical treatment, corona treatment, and glow discharge treatment, and hydrophilicity with respect to water-soluble polyvinyl alcohol in order to improve adhesion to the polarizing layer. An undercoat layer (such as a gelatin layer) may be provided.

[0007] PVA is used as the polarizing layer. PV
A is usually a saponified polyvinyl acetate,
For example, it may contain a component copolymerizable with vinyl acetate, such as unsaturated carboxylic acid, unsaturated sulfonic acid, olefins and vinyl ethers. Further, a modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group, or the like can also be used. PV
The saponification degree of A is not particularly limited, but is preferably from 80 to 100 mol% from the viewpoint of solubility and the like, and is preferably from 90 to 100 mol%.
mol% is particularly preferred. The degree of polymerization of PVA is not particularly limited, but is preferably from 1,000 to 10,000,
500 to 5000 are particularly preferred.

[0008] The polarizing layer of the present invention is formed by casting a solution obtained by dissolving PVA in water or an organic solvent, stretching the PVA film and then dyeing it with iodine or a dichroic dye, or dyeing it. Stretch. As the solvent, in addition to water, alcohols (methanol, ethanol, propanol, butanol, etc.), polyhydric alcohols (glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc.), Amines (e.g., ethylenediamine, diethylenetriamine), dimethylsulfoxide, N-methylpyrrolidone, and the like, and mixtures thereof are used.

[0009] The stretching direction of the PVA film is inclined by 10 to 80 degrees with respect to the MD direction of the film at the time of casting.
This tilt angle extends so as to match the angle between the transmission axis of the two polarizing plates attached to both sides of the liquid crystal cell constituting the LCD and the vertical or horizontal direction of the liquid crystal cell. Usually, this angle is 45 degrees, but recently, in a new transmissive LCD mode, a reflective LCD, a transflective LCD, etc., it is not necessarily 4 degrees.
It is preferable that the stretching direction can be arbitrarily adjusted according to the design of the LCD.

FIG. 2 shows an example of 45 ° oblique stretching. Reference numeral 21 denotes a PVA film, 22 denotes a tenter, and 23 denotes a transport direction of the film. The width change of the film in the stretching direction is indicated by a dotted line. At a certain time, the PVA film chucked at the positions 24L and 24R in the figure moves to the position 25L at a speed of 26L on the left and moves to the position 25R at a speed of 26R on the right. Thereby, oblique stretching is performed. The stretching ratio is preferably 2.5 to 30.0 times, and 3.0 to 10.0.
Double is more preferred. Stretching can be dry stretching in air,
It may be wet stretching immersed in water, about 2.5 to 5.0 times for dry stretching and about 3.0 to 10.0 times for wet stretching. This oblique stretching step may be performed in several times, and by dividing into several times, it is possible to perform more uniform stretching even in high-magnification stretching. Before the oblique stretching, a slight stretching in the horizontal or vertical direction (to the extent that shrinkage in the width direction is prevented) may be performed. Stretching is achieved, for example, by performing tenter stretching in biaxial stretching as performed in normal film formation in the left and right different steps as described above. It is necessary to make the thickness of the PVA film different between left and right. In the case of casting film formation, there is a method in which the flow rate of the PVA solution is made left and right by, for example, tapering the die. By this step, the PVA of the present invention which is obliquely stretched by 10 to 80 degrees with respect to the MD direction.
A film is produced.

The dyeing step is performed by gas or liquid phase adsorption. As an example of the case where the iodine is used in the liquid phase, the iodine-potassium iodide aqueous solution is used to immerse the PVA film in the use of iodine. 0.1 to 2.0 g of iodine
/ L, potassium iodide is preferably 10 to 50 g / l, and the weight ratio of iodine to potassium iodide is preferably 20 to 100.
The dyeing time is preferably 30 to 5000 seconds, and the liquid temperature is 5 seconds.
To 50 ° C is preferred. As a dyeing method, not only immersion but also any means such as application or spraying of iodine or a dye solution is possible.

The dichroic dyes include azo, stilbene, quinone, anthraquinone, methine, azomethine, cyanine, merocyanine, quinophthalone,
Tetrazine and the like can be mentioned. Among them, azo and anthraquinone dichroic dyes are particularly preferred.

The dyed PVA film is then cross-linked with a boron compound, aldehyde or the like. Among them, a boron compound is particularly preferred. Examples of boron compounds include boric acid, borax, and the like. For example, the boron compound is used in a solution of 0.5 to 2.0 mol / l using an aqueous solution or a mixed solution of water and an organic solvent as a solvent, and the dyed PVA film is treated by dipping, spraying, coating or the like. It is preferable to add a small amount of potassium iodide to the boron compound solution. The processing temperature is preferably from 40 to 70 ° C., and the processing time is preferably from 5 to 20 minutes. In addition, oblique stretching may be performed during the treatment by the above method.

Further, the PVA film may be heat-treated. The water content of the film during the treatment is preferably 10 to 30%. The processing temperature is preferably 40 to 100 ° C.,
To 90 ° C is more preferable. Processing time is 0.5 to 1
Five minutes is preferred.

The PV for forming the polarizing layer thus prepared
The transparent support is bonded to both sides of the A film as a protective film via an adhesive. The adhesive is not particularly limited, and examples thereof include a PVA-based resin (including modified PVA such as an acetoacetyl group, a sulfonic acid group, a carboxyl group, and an oxyalkylene group) and a boron compound aqueous solution. Among them, the PVA-based resin is preferable. The thickness of the adhesive layer after drying is preferably 0.01 to 10 μm, and 0.05 to 5 μm.
Is particularly preferred.

On the side opposite to the polarizing layer of the protective film of the polarizing plate of the present invention, JP-A-4-229828 and JP-A-6-7511.
No. 5, JP-A-8-50206, etc., an optically anisotropic layer for LCD viewing angle compensation, an antiglare layer or an antireflection layer for improving the visibility of a display, or an LCD for improving the LCD brightness. A layer having a PS wave separation function by anisotropic scattering or anisotropic optical interference (polymer dispersed liquid crystal layer, cholesteric liquid crystal layer, or the like) can be provided.

FIG. 3 shows an example of punching a conventional polarizing plate, and FIG.
An example of punching a polarizing plate of the present invention is shown in FIG. In the conventional polarizing plate, the absorption axis 31 of the polarized light, that is, the stretching axis coincides with the MD direction 32, whereas in the polarizing plate of the present invention, the absorption axis 41 of the polarized light, that is, the stretching axis is inclined with respect to the MD direction. Since the angle 43 coincides with the angle formed between the absorption axis of the polarizing plate and the vertical or horizontal direction of the liquid crystal cell itself when the liquid crystal cell is bonded to the liquid crystal cell in the LCD, oblique punching in the punching process is not performed. It becomes unnecessary. Moreover, as can be seen from FIG. 4, the polarizing plate of the present invention can be manufactured by slitting along 43 without punching because the cut is straight along 43, and the productivity is remarkably excellent. .

[0018]

EXAMPLES The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples. [Example 1] Average polymerization degree 4000, saponification degree 99.8 m
ol% of PVA was dissolved in water to obtain a 4.0% aqueous solution. This solution was band-cast using a tapered die and dried. The width before stretching was 110 mm, and the thickness was 12 at the left end.
0 μm and 135 μm at the right end. The film was peeled off from the band, stretched obliquely at 45 ° in a dry state, and as it was, 0.5 g / l of iodine and 50 g of potassium iodide
/ L aqueous solution at 30 ° C for 1 minute, then dipped in an aqueous solution of boric acid 100g / l and potassium iodide 60g / l at 70 ° C for 5 minutes.
After washing with water for 0 second and further drying at 80 ° C. for 5 minutes, an iodine-based polarizing film of Example 1 was obtained. Film width 660
mm and thickness were 20 μm on both sides.

Example 2 PVA having an average polymerization degree of 1700 and a saponification degree of 99.5 mol% was dissolved in water to obtain a 5.0% aqueous solution. This solution was band-cast using a tapered die and dried, so that the width before stretching was 110 mm, the thickness was 180 μm at the left end, and 195 μm at the right end. The film was peeled off from the band and immersed in an aqueous solution of 0.2 g / l of iodine and 60 g / l of potassium iodide at 30 ° C. for 5 minutes, and then 100 g of boric acid.
l, immersed in an aqueous solution of potassium iodide 30 g / l,
The treatment was performed at 60 ° C. for 10 minutes while the film was obliquely stretched by 5 degrees. At this time, the film width was 660 mm, and the thickness was 30 μm on both sides.
Met. Further, this film is washed at 20 ° C.
After immersion for 0 seconds, immersion in an aqueous solution of 0.1 g / l of iodine and 20 g / l of potassium iodide at 30 ° C. for 15 seconds,
This film was dried at room temperature for 24 hours to obtain an iodine-based polarizing film. An 80 μm-thick triacetyl cellulose (manufactured by Fuji Photo Film Co., Ltd.) was bonded to both surfaces of this film using a PVA-based adhesive, and dried at 50 ° C. for 5 minutes to prepare a polarizing plate of Example 2. . The optical characteristics of the used triacetyl cellulose are (n) at 380 to 780 nm.
The maximum value of (x-ny) × d is 10 nm, ｛(nx + ny)
The maximum value of / 2-nz｝ × d was 40 nm.

Example 3 A protective film having a thickness of 50
A polarizing plate of Example 3 was prepared in the same manner as in Example 2, except that Zeonor having a thickness of μm (manufactured by Zeon Corporation) was used. The optical properties of the Zeonoa used were (n) at 380 to 780 nm.
The maximum value of x-ny) × d is 3.3 nm, ｛(nx + n)
y) / 2-nz｝ × d had a maximum value of 8.2 nm.

Comparative Example 1 A commercially available iodine-based polarizing plate (HL
C2-5518, width 650 mm, manufactured by Sanritz Co., Ltd.)
Was used as the polarizing plate of Comparative Example 1.

Comparative Example 2 A protective film having a thickness of 60
Example 2 except that a uniaxially stretched polycarbonate of μm was used.
In the same manner as in the above, a polarizing plate of Comparative Example 2 was prepared. The optical characteristics of the polycarbonate used were such that the maximum value of (nx−ny) × d at 380 to 780 nm was 170 nm, and Δ (nx +
ny) / 2-nz｝ × d was 100 nm.

(Evaluation of Polarizing Plate) With respect to the obtained polarizing plate, the following items were evaluated. (1) Transmittance The transmittance of the obtained polarizing plate was measured using a haze meter MODEL.
It measured using 1001DP (made by Nippon Denshoku Industries Co., Ltd.). (2) Degree of Polarization A polarizer was set on the light source side of a haze meter MODEL 1001DP (manufactured by Nippon Denshoku Industries Co., Ltd.), and the transmission axis of the obtained polarizing plate (in the stretching direction) was set with respect to the transmission axis of the polarizer. The transmittance T1 when the axes (the axes perpendicular to each other) were made parallel and the transmittance T2 when the axes were made perpendicular to each other were measured, and the degree of polarization was obtained by the following equation 3. (Equation 3) Degree of polarization [%] = {(T1−T2) / (T1 + T2)} ^1/2 × 100 (3) Number of punched sheets As a polarizing plate for a 14.3-inch LCD, 219.0 ×
The number of sheets that can pass through a size of 291.4 mm was obtained. The size of the polarizing plate was 650 mm in width and 1 in length according to Comparative Example 1.
000 mm was used.

Table 1 shows the results of Examples and Comparative Examples. The iodine-based polarizing film of Example 1 showed excellent transmittance and degree of polarization. The polarizing plate of Example 2 has almost the same transmittance as the commercial polarizing plate of Comparative Example 1 and slightly inferior in the degree of polarization, and the polarizing plate of Example 3 has substantially the same transmittance and polarizing degree as the commercial polarizing plate of Comparative Example 1. there were. Moreover, as shown in FIG.
Nine sheets can be punched for 4.1 inch LCD,
The yield was much higher than the six sheets of Comparative Example 1. The difference in the degree of polarization between Examples 2 and 3 is due to a slight difference in the birefringence of the support. Further, the polarizing plate of Comparative Example 2 did not function as a polarizing plate at all because of the large birefringence of the support.

[0025]

[Table 1]

Example 4 (Preparation of Viewing Angle Compensation Film) Linear alkyl-modified polyvinyl alcohol (MP-203, manufactured by Kuraray Co., Ltd.) 30
After adding 130 g of water and 40 g of methanol to the resulting mixture and stirring and dissolving, the mixture was filtered through a polypropylene filter having a pore diameter of 30 μm to prepare a coating solution for an alignment layer. The above-mentioned coating solution for an alignment layer is applied to a 100 μm-thick triacetyl cellulose film (manufactured by Fuji Photo Film Co., Ltd.) having an undercoat layer of a gelatin thin film (0.1 μm) using a bar coater, After drying, 4
Rubbing treatment was performed in the direction of 5 ° to form an alignment layer having a thickness of 0.5 μm. Next, 1.6 g of a compound LC-1 having the following structure as a liquid crystalline discotic compound, phenoxydiethylene glycol acrylate (M-10)
1, 0.4 g of Toa Gosei Co., Ltd., 0.05 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Company), and a photopolymerization initiator (Irgacure-
907 (manufactured by Ciba-Geigy) (0.01 g) was dissolved in 3.65 g of methyl ethyl ketone, and filtered through a polypropylene filter having a pore size of 1 μm to prepare a coating solution for an optically anisotropic layer. On the alignment layer, the coating liquid for an optically anisotropic layer was applied using a bar coater, dried at 120 ° C., further heated for 3 minutes, and aged with liquid crystal to align the discotic compound. 160W / cm at ℃
UV light with an irradiance of 400 mW / cm ² and an irradiation amount of 300 mJ / cm ² was cured using an air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) to cure the coating layer, and an optical anisotropic material having a thickness of 1.8 μm was used. By forming the layer, a viewing angle compensation film was formed.

[0027]

Embedded image

Next, as shown in FIG. 6, a polarizing plate 62 using a viewing angle compensation film 64 formed on one side of two protective films of an iodine-based polarizing film 61 of Example 2, and A polarizing plate 63 was prepared using a viewing angle compensation film on one side and a commercially available antiglare antireflection film (manufactured by Sanritz) 65 on the other side. At this time, the viewing angle compensation film was bonded so that the rubbing direction of the alignment layer coincided with the stretching direction of the polarizing layer. And 62 is L
Of the two polarizing plates sandwiching the liquid crystal cell 66 of the CD, the backlight 67 is used as the polarizing plate on the backlight 67, and the display 63 is used as the display-side polarizing plate. An LCD was prepared by pasting to the cell. The LCD thus produced exhibited excellent luminance, viewing angle characteristics, and visibility, and no deterioration in display quality was observed even after use at 40 ° C. and 30% RH for one month.

[0029]

The obliquely stretched polyvinyl alcohol film system of the present invention and the polarizing plate using the same exhibit optical characteristics equivalent to those of a commercially available polarizing plate, and can be supplied at a low cost by a large yield in stamping and a simple process. Can be. Thus, a liquid crystal display device having excellent display quality can be provided at low cost.

[Brief description of the drawings]

FIG. 1 illustrates an example in which a polarizing layer that is obliquely stretched is bonded to a transparent support by a roll.

FIG. 2 shows an example of 45 ° oblique stretching.

FIG. 3 shows an example of punching a conventional polarizing plate.

FIG. 4 shows an example of punching a polarizing plate of the present invention.

FIG. 5 shows an example of punching in Examples 2 and 3.

FIG. 6 shows an LC using the viewing angle compensation film of Example 4.
The example of D is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transparent support 12 PVA film 13 MD direction 14 Absorption axis 21 PVA film 22 Tenter 23 Film conveyance direction (MD direction) 24R Different speed drawing start position (right) 24L Different speed drawing start position (left) 25R Different speed drawing end position (Right) 25L Different speed stretching end position (Left) 26R Right stretching speed 26L Left stretching speed 31 Absorption axis (stretching axis) 32 MD direction 41 Absorption axis (stretching axis) 42 MD direction 43 Cutting surface (slit position) 61 Iodine-based Polarizing film (polarizing layer) 62 Lower polarizing plate 63 Upper polarizing plate 64 Wide view A 65 Anti-glare antireflection film 66 Liquid crystal cell 67 Backlight

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // B29K 29:00 B29K 29:00 B29L 7:00 B29L 7:00 11:00 11:00 F term ( Reference) 2H049 BA02 BA27 BB43 BC03 BC09 BC22 2H091 FA08X FA08Z FB02 FC07 FD15 KA10 LA16 LA30 4F100 AJ06 AK21B AK21G AT00A AT00C BA03 BA06 BA10A BA10C CB00 EJ37B GB41 JN10B 4F210 AA19AG01 Q73

Claims (4)

[Claims] 1. An optical film, wherein a film comprising polyvinyl alcohol or modified polyvinyl alcohol is obliquely stretched in a direction of 10 to 80 degrees with respect to the MD. 2. A polarizing plate comprising a polarizing layer sandwiched between two transparent supports, wherein the polarizing layer is formed by adsorbing and orienting a polarizing element on a polyvinyl alcohol film stretched obliquely at 10 to 80 degrees. Characteristic polarizing plate. 3. The polarizing plate according to claim 2, wherein at least one of the transparent supports satisfies Formulas 1 and 2 at any wavelength of 380 to 780 nm. (Formula 1) −10 ≦ (nx−ny) × d ≦ 10 (d: Transparent Support Thickness) (Formula 2) 0 ≦ {(nx + ny) / 2−nz} × d ≦ 20 (d: Transparent Support Thickness) ) In the formulas 1 and 2, n represents a refractive index, and x represents MD of the transparent support.
Represents the direction, y represents the TD direction of the transparent support, and z represents the thickness direction of the transparent support. 4. A liquid crystal display device, wherein the polarizing plate according to claim 2 is used for at least one of two polarizing plates arranged on both sides of a liquid crystal cell.