JPH1090517A - Iodine-based polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate having excellent durability under dry heat. SOLUTION: This iodine base polarizing plate consists of a polyvinylalcohol film formed by adsorption orientation of iodine. The high heat resistant index determined from the absorbance spectra when the polarizing plate is irradiated with UV visible linearly polarized light parallel with the absorption axis of the polarizing film constituting the polarizing plate is <=150. The absorbance of the absorption peak existing in a wavelength range from 200 to 230nm in the absorption spectra when the polarizing plate is irradiated with the UV visible linearly polarized light perpendicularly the absorption axis of the polarizing film is <=2.9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an iodine-based polarizing plate having high heat resistance.

[0002]

2. Description of the Related Art
Polarizing plates using, as a polarizer, an iodine-based polarizing film in which iodine is adsorbed and oriented on a polyvinyl alcohol (hereinafter referred to as PVA) film or a dye-based polarizing film in which a dichroic dye is adsorbed and oriented on PVA are generally known. I have. Among these polarizing plates, iodine-based polarizing plates are widely used as liquid crystal display members because they have higher contrast than dye-based polarizing plates. However, the demand for an iodine-based polarizing plate has become stricter due to the expansion of the application field of the liquid crystal display device, and the optical durability under dry heat, particularly the change in hue, has become a problem.

The inventors of the present invention have intensively studied a polarizing plate having excellent durability under dry heat in order to solve such a problem. As a result, it has been found that the ultraviolet-visible linear line is parallel to the absorption axis of a polarizing film constituting the polarizing plate. The high heat resistance index determined from the absorbance spectrum when irradiating polarized light is 150 or less, and 200 in the absorbance spectrum when irradiating ultraviolet-visible linear polarized light perpendicular to the absorption axis of the polarizing film.
A polarizing plate manufactured by using a polarizing film having an absorption peak at an absorption peak in the wavelength range of 2.9 nm to 230 nm of 2.9 or less and laminating a protective film on at least one surface thereof has durability under dry heat, that is, heat resistance. The inventors have found that they have excellent properties, and have reached the present invention.

[0004]

That is, the present invention relates to an iodine-based polarizing plate comprising a polyvinyl alcohol film on which iodine is adsorbed and oriented, wherein ultraviolet-visible linearly polarized light is parallel to an absorption axis of the polarizing film constituting the polarizing plate. The high heat resistance index determined from the absorbance spectrum upon irradiation is 150 or less, and the absorption in the wavelength range from 200 nm to 230 nm in the absorbance spectrum upon irradiation with ultraviolet-visible linearly polarized light perpendicular to the absorption axis of the polarizing film. An iodine-based polarizing plate having a peak absorbance of 2.9 or less.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The high heat resistance index in the present invention is a value determined from an absorbance spectrum when irradiating ultraviolet-visible linearly polarized light in parallel with the absorption axis of the polarizing film, that is, when irradiating ultraviolet-visible linearly polarized light at an angle at which the absorbance is maximized, As shown in FIG. 1, the absorbance at 325 nm and the wavelength from 290 nm to 310 n
a difference from the absorbance at the peak position in the wavelength range of m;
A horizontal line is drawn from the 325 nm position of the absorbance spectrum to the shorter wavelength side, and is defined by the following [Equation 1] from the wavelength difference b (unit: nm) until the horizontal line crosses the absorbance spectrum again.

[0006]

(High heat resistance index) = b / a

The PVA film has a degree of polymerization of 1000 to 10
000, preferably 1500-5000 PVA is used. The saponification degree is, for example, 85-1.
About 100 mol%, preferably 98 to 100 mol%
It is. The method of forming the PVA film is not particularly limited,
Usually, a known method can be used. The thickness of the PVA film is not particularly limited. For example, 50 μm to 15
It is about 0 μm.

A uniaxially stretched and iodine-adsorbed and oriented PV
As a method for preparing the A film, a commonly used method can be applied. For example, a method in which an unstretched PVA film is uniaxially stretched in water and then immersed in a solution of iodine and potassium iodide, the unstretched PVA film is immersed in a solution of iodine and potassium iodide, or uniaxially during immersion. A method of stretching, a method of dipping a uniaxially stretched PVA film in a solution of iodine and potassium iodide, and the like can be given. The composition of the aqueous solution of iodine and potassium iodide is, for example, a weight ratio of water: iodine: potassium iodide of 100: (0.01 to 0.5) :( 0.5 to 1).
0). The temperature of the aqueous solution at that time is, for example, 20 to
It is about 50 ° C.

P with uniaxial stretching and iodine adsorption and orientation
As a method of immersing the VA film in a boric acid-containing aqueous solution, for example, a method of immersing a uniaxially stretched and iodine-adsorbed PVA film in an aqueous solution containing boric acid and potassium iodide is used. The composition of this solution is such that the weight ratio of water: boric acid: potassium iodide is 100:
(2-15): about (2-20), preferably 10
0: (5 to 12): about (5 to 15). The temperature of the boric acid-containing aqueous solution is, for example, 50 ° C. or higher, preferably 5 ° C.
It is in the range of 0 ° C or higher and 85 ° C or lower. The time for treating with the boric acid-containing aqueous solution is not particularly limited, for example,
It is 100 to 1200 seconds, preferably 150 to 600 seconds, more preferably 200 to 500 seconds.

The stretched PVA film after boric acid treatment is subsequently washed with water and dried to form a polarizing film. Depending on the washing conditions, the absorbance of the absorption peak in the wavelength range of 200 nm to 230 nm when irradiating ultraviolet-visible linearly polarized light perpendicular to the absorption axis of the polarizing film changes. Therefore, control of the washing conditions is important in the present invention. . Although the absorbance changes depending on the washing method, water temperature, etc., for example, at a temperature of 3 ° C. to 50 ° C., for a time range of 5 seconds to 240 seconds, a relatively long time for low-temperature water and a relatively long time for high-temperature water By washing with water for a short time, 200 n of the absorbance spectrum when irradiating ultraviolet-visible linearly polarized light perpendicular to the absorption axis of the polarizing film
The absorbance of the absorption peak in the wavelength range from m to 230 nm can be 2.9 or less. However, the present invention is not limited to this, and it is important that the absorbance of the absorption peak in the wavelength range of 200 nm to 230 nm be 2.9 or less by variously combining the water temperature, the washing method, and the like.

In order to produce a polarizing film having a high heat resistance index of 150 or less, it is important to control drying conditions after washing with water. The drying conditions cannot be uniformly defined because factors such as the air volume in the drying oven, the temperature, and the drying time are involved. For example, the drying time is 10 seconds or more, the drying temperature is 70 ° C. or more, and the drying time is preferably 20 seconds. As described above, the drying temperature is 75 ° C. or higher. Usually, drying is performed for a relatively long time at a low temperature and for a relatively short time at a high temperature side, but drying may be performed for a long time at a high temperature side. However, the present invention is not limited to this, and it is important that the high heat resistance index be 150 or less by variously combining the conditions of the air volume, the temperature, and the drying time. As a drying method after washing with water, a far-infrared ray method or the like can be used in addition to the hot air drying method. In this case, the high heat resistance index is set to 150 or less by variously combining the output intensity and the distance from the lamp. Of course, the high heat resistance index may be set to 150 or less by using both the hot air drying method and the far infrared ray method.

A polarizing plate can be obtained by laminating a protective film on at least one side of the polarizing film. As the protective film, for example, a cellulose acetate-based film,
An acrylic film, a polyester resin film, a polyolefin resin film, a polycarbonate film, a polyarylate film, a polyethersulfone film and the like can be mentioned.

[0013]

The iodine-based polarizing plate of the present invention has better durability under dry heat than the conventional iodine-based polarizing plate.

[0014]

Hereinafter, the present invention will be described in detail with reference to Examples.
The present invention is not limited to this. The measurement of the absorbance spectrum of the polarizing film and the evaluation of durability under dry heat were performed as follows.

(1) Measurement of absorbance spectrum of polarizing film: UV-visible spectrophotometer (UV-220 manufactured by Shimadzu Corporation)
0). Attach a film holder with a polarizer made by Shimadzu Corporation to an ultraviolet-visible spectrophotometer to obtain an absorbance spectrum with ultraviolet-visible linearly polarized light as incident light,
A polarizing prism made of calcite was used as a polarizer of the film holder with a polarizer. The incident angle of the ultraviolet-visible linearly polarized light was adjusted by rotating the polarizing film sample. The angle of the sample at which the absorbance is highest is the angle at which the incident ultraviolet-visible linearly polarized light is incident parallel to the absorption axis of the polarizing film, and from the absorbance spectrum measured in this state,
The high heat resistance index was determined by the above [Equation 1]. The absorbance at the peak position in the wavelength range from 200 nm to 230 nm was read from the absorbance spectrum measured by rotating the sample by 90 degrees from the angle at which the UV-visible linearly polarized light was incident parallel to the absorption axis of the polarizing film.

(2) Evaluation of heat resistance: The transmission hue when two polarizing plates are stacked so that their absorption axis directions are 90 degrees is represented by L ^* , a ^* , b ^* color system. Those were designated as orthogonal hues. The orthogonal hues were calculated using the C light source spectral distribution. The test sample for which the orthogonal hue was measured was left in a drying oven at 90 ° C. for 500 hours, and the orthogonal hue was measured again.
From the orthogonal hues before and after the introduction of the oven, the color difference was determined by the following [Equation 2]. The smaller the color difference, the better the heat resistance.

[0017]

[Number 2] color difference = [(before the introduction L ^* - after the input L ^{*) 2} + (before put a ^* - of after turning a ^{*) 2} + (before the introduction b ^* - after the introduction b ^{*) 2} ] ^1/2

Example 1 A 75 μm-thick PVA film (degree of polymerization: 2400, degree of saponification: 99.9% or more) was subjected to dry uniaxial stretching (stretching ratio: 5 times), and while maintaining tension, iodine and iodine were applied. An aqueous solution containing potassium (iodine: potassium iodide: water =
0.05: 5: 100 (weight ratio)) for 60 seconds. Next, a 73 ° C. aqueous solution containing potassium iodide and boric acid (potassium iodide: boric acid: water = 6: 7.5: 10)
0 (weight ratio)) for 300 seconds. Further, after washing with pure water at 17 ° C. for 10 seconds, the film was dried at 95 ° C. for 5 minutes to obtain an iodine polarizing film. The high heat resistance index of this polarizing film was 79, and the absorbance at the absorbance peak in the wavelength range from 200 nm to 230 nm was 2.8. A PVA-based adhesive is applied to both surfaces of the polarizing film, and a protective film (a saponified surface-treated triacetyl cellulose film having a thickness of 80 μm (Fujitac UV80: manufactured by Fuji Photo Film Co., Ltd.)) is bonded. After drying at 50 ° C. for 5 minutes, a polarizing plate was obtained. A glass plate was adhered to one surface of the obtained polarizing plate via an adhesive, and the color difference after leaving in a drying oven at 90 ° C. for 500 hours was 1.0.

Example 2 A polarizing film was obtained in the same manner as in Example 1 except that the film was washed with pure water at 23 ° C. for 10 seconds. The high heat resistance index of this polarizing film was 114, and the value of the absorbance peak in the wavelength range of 200 nm to 230 nm was 2.5. After this polarizing film was formed into a polarizing plate by the same method as in Example 1, and then into a polarizing plate with a glass plate by the same method as in Example 1, 9
The color difference after standing in a drying oven at 0 ° C. for 500 hours was 0.8.

Comparative Example 1 A polarizing film was obtained in the same manner as in Example 1 except that the film was washed with pure water at 10 ° C. for 10 seconds. The high heat resistance index of this polarizing film was 95, and the value of the absorbance peak in the wavelength range of 200 nm to 230 nm was 3.0. After this polarizing film was formed into a polarizing plate by the same method as in Example 1, and then into a polarizing plate with a glass plate by the same method as in Example 1, 90
The color difference after being left in a drying oven at 500 ° C. for 500 hours is 2.
Nine.

Comparative Example 2 A polarizing film was obtained in the same manner as in Example 1 except that the film was washed with pure water at 17 ° C. for 10 seconds and then dried at 75 ° C. for 5 minutes. The high heat resistance index of this polarizing film is 304, 200
The value of the absorbance peak in the wavelength range from nm to 230 nm was 2.8. This polarizing film was formed into a polarizing plate in the same manner as in Example 1, then into a polarizing plate with a glass plate in the same manner as in Example 1, and then placed in a 90 ° C. drying oven.
The color difference after leaving for 0 hours was 3.5.

Comparative Example 3 A polarizing film was obtained in the same manner as in Example 1 except that the film was washed with pure water at 10 ° C. for 20 seconds and then dried at 80 ° C. for 5 minutes. The high heat resistance index of this polarizing film is 159, 200
The value of the absorbance peak in the wavelength range from nm to 230 nm was 2.7. This polarizing film was formed into a polarizing plate in the same manner as in Example 1, then into a polarizing plate with a glass plate in the same manner as in Example 1, and then placed in a 90 ° C. drying oven.
The color difference after standing for 0 hours was 5.6.

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[Procedure amendment]

[Submission date] November 22, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a diagram showing an absorbance spectrum when ultraviolet-visible linearly polarized light is irradiated perpendicularly to an absorption axis of a polarizing film.

[Explanation of symbols] a Absorbance difference b Wavelength difference

Claims (2)

[Claims] 1. An iodine-based polarizing plate comprising a polyvinyl alcohol film on which iodine is adsorbed and oriented, which is determined from an absorbance spectrum when ultraviolet-visible linearly polarized light is irradiated in parallel to an absorption axis of a polarizing film constituting the polarizing plate. High heat resistance index is 150 or less, and in the absorbance spectrum when irradiated with ultraviolet-visible linearly polarized light perpendicular to the absorption axis of the polarizing film, 200 nm to 230 nm.
The iodine-based polarizing plate, wherein the absorbance at an absorption peak in the wavelength range of 2.9 or less is 2.9 or less. 2. The high heat resistance index shows the absorbance at 325 nm and the absorbance at the peak position in the wavelength range from 290 nm to 310 nm in the absorbance spectrum when irradiating ultraviolet-visible linear polarized light parallel to the absorption axis of the polarizing film. 2. A ratio (b / a) of a wavelength difference b (unit: nm) until a horizontal line is drawn from the 325 nm position of the absorbance spectrum to the shorter wavelength side and intersects the absorbance spectrum again with respect to the difference a. The iodine-based polarizing plate described in the above.