JPH08304624A - Polarizing plate and its production - Google Patents

Abstract

PURPOSE: To provide a polarizing plate having high contrast and high transmission for blue light, improved in the reproducibility for a blue color when the plate is used for a reflection type color liquid crystal display device, and capable of obtaining the liquid crystal display device very easy to see. CONSTITUTION: This polarizing plate is obtd. by adsorbing and orienting iodine to a polyvinyl alcohol film and dipping the film in an aq. soln. containing boric acid and <2 pts.wt. potassium iodide to 100 pts.wt. of water. The obtd. plate shows >=35% transmittance in 500-700nm wavelength range in the spectrum of polarized light parallel to the orientation, and in the spectrum of polarized light perpendicular to that, it shows >=4% transmittance at 420nm wavelength, <=2% transmittance at 500nm wavelength and <=0.01% in 570-700nm wavelength range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in notebook type word processors, personal computers,
It is used in various fields such as electronic notebooks, personal digital assistants, amusement machines, stationery, mobile phones, etc., and along with this, the demand for polarizing plates is increasing, and the requirements for optical characteristics of polarizing plates are also diversifying. There is.

As a polarizing plate, an iodine polarizing plate in which iodine is adsorbed and oriented on a polyvinyl alcohol film is most often used. When the iodine-based polarizing plate is attached to a liquid crystal cell of a small reflective color liquid crystal display device used in recent portable devices or the like, the matching with the liquid crystal cell may be poor and the color reproducibility may be poor. In particular, the amount of transmitted blue light is poor, and it is required to increase the amount of transmitted blue light in the light transmission characteristics of the polarizing plate.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a polyvinyl alcohol film is adsorbed and oriented with iodine, and then subjected to a dipping treatment in a boric acid-containing aqueous solution. At this time, it was found that a polarizing plate having a large blue transmitted light amount can be obtained by using a boric acid-containing aqueous solution containing no potassium iodide, and the present invention has been completed.

That is, the present invention is as follows. (1) Wavelength in parallel light transmission spectrum 500 to 70
The light transmittance at 0 nm is 35% or more, the light transmittance at a wavelength of 420 nm in the orthogonal light transmission spectrum is 4% or more, and the wavelength is 5
Light transmittance at 00 nm is 2% or less, wavelength 570 to 700n
A polarizing plate in which iodine is adsorbed and oriented on a polyvinyl alcohol-based film having a light transmittance of m of 0.01% or less. (2) After the iodine is adsorbed and oriented on the polyvinyl alcohol-based film, it is immersed in a boric acid-containing aqueous solution having a potassium iodide content of less than 2 parts with respect to 100 parts by weight of water. The method for producing a polarizing plate according to the item 1). (3) The method for producing a polarizing plate according to the item (2), wherein a protective film is attached to at least one surface of the film after the immersion treatment in a boric acid-containing aqueous solution.

The present invention will be described in detail below. The polyvinyl alcohol-based film is not particularly limited, and a polyvinyl alcohol-based film that is normally used can be used. The polyvinyl alcohol, for example, is obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, and in some cases, a copolymerizable component such as a small amount of unsaturated carboxylic acid, olefins, What copolymerized vinyl ethers, unsaturated sulfonic acids, etc. may be used. Moreover, the polyvinyl formal film, the polyvinyl acetal film, etc. which modified these can be mentioned.

The thickness of the polyvinyl alcohol film is not particularly limited. For example, 50 to 150 μ
m. The degree of polymerization of the polyvinyl alcohol film is, for example, about 1000 to 10000, preferably 1500 to 5000, and more preferably 2000 to 5
000. The saponification degree is, for example, 80 to 100 mol%.
It is a degree, preferably 98 to 100 mol%.

The method for adsorbing iodine is not particularly limited, and a known method can be used. For example, a method of immersing a polyvinyl alcohol film in an aqueous solution of iodine and potassium iodide can be mentioned. The amounts of iodine and potassium iodide are, for example, 0.01 to 0.5 parts by weight of iodine and 0.
It is about 5 to 10 parts by weight. The processing temperature is, for example, 20 ° C.
˜40 ° C., and the processing time is, for example, 30 seconds to 300 seconds.

As a method for orienting iodine, the polyvinyl alcohol film may be uniaxially stretched before, after, or while adsorbing iodine. The method of uniaxially stretching the polyvinyl alcohol film is not particularly limited, but any method such as a wet method or a dry method may be used. The draw ratio is preferably 4 to 6 times.

After the iodine is adsorbed and oriented, it is immersed in a boric acid-containing aqueous solution. The amount of boric acid in the boric acid-containing aqueous solution is not particularly limited. For example, the amount of boric acid is about 2 to 15 parts by weight with respect to 100 parts by weight of water, and preferably about 7 to 12 parts by weight with respect to 100 parts by weight of water. Conventionally, the dipping treatment with a boric acid-containing aqueous solution has used a boric acid-containing aqueous solution containing potassium iodide, but in the present invention, the content of potassium iodide is 2 per 100 parts by weight of water.
It is necessary to use less than part of a boric acid-containing aqueous solution, preferably a boric acid-containing aqueous solution that does not contain potassium iodide. The temperature of the dipping treatment with the boric acid-containing aqueous solution is 60 ° C to 8 ° C.
The temperature is 0 ° C, preferably 68 ° C to 73 ° C. Processing time is 1
It is 00 seconds to 1200 seconds.

The protective film is attached to at least one surface of the film in which iodine is absorbed and oriented by being dipped in a boric acid-containing aqueous solution. The type of protective film is not particularly limited, and for example, a cellulose acetate film, an acrylic film, a polyester film, a polyolefin film, a polycarbonate film, a polyarylate film, a polyether sulfone film, or the like can be used. . Examples of the cellulose acetate film include triacetyl cellulose film and diacetyl cellulose film.

The thickness of the protective film is not particularly limited, but is, for example, about 50 to 200 μm. As such a protective film, for example, a triacetyl cellulose film (Fuji TAC-UV50: Fuji Photo Film Co., Ltd.)
Manufactured).

A polarizing plate is prepared by laminating such a protective film on one side or both sides of a film in which iodine is adsorbed and oriented by being dipped in a boric acid-containing aqueous solution. The protective film may contain an ultraviolet absorber, and the protective film containing the ultraviolet absorber may be soaked in a boric acid-containing aqueous solution to be bonded to one side or both sides of a film in which iodine is adsorbed and oriented. .

The polarizing plate thus obtained has a light transmittance of 35% or more at a wavelength of 500 to 700 nm in the parallel light transmission spectrum, a light transmittance of 2% or less at a wavelength of 500 nm in the orthogonal light transmission spectrum, and a wavelength of 570 to 570. 700
The light transmittance of nm is 0.01% or less, which is high contrast. In addition, the wavelength 42 in the orthogonal light transmission spectrum
The light transmittance at 0 nm is 4% or more, and the amount of blue transmitted light is large.

[0015]

The polarizing plate of the present invention has a high contrast, a large amount of blue transmitted light, and when used in a reflective color liquid crystal display device, blue color reproducibility is improved, and a very easy-to-see liquid crystal display device can be obtained. .

[0016]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples.
The parallel light transmittance referred to in the present invention is the light transmittance when two polarizing films are stacked so that their orientation directions are the same,
The orthogonal light transmittance is the light transmittance when two polarizing films are stacked so that their orientation directions are orthogonal to each other. The light transmittance was measured using a spectrophotometer UV2200 manufactured by Shimadzu Corporation.

Example 1 A polyvinyl alcohol film (Kuraray Co., Ltd .: Kuraray Vinylon VFX750RS) was uniaxially stretched 5 times at 110 ° C. This uniaxially stretched polyvinyl alcohol film was placed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.075 / 5/100 while maintaining the tension.
It was immersed for 60 seconds. Next, the weight ratio of boric acid / water is 7.5.
It was immersed in a 70 ° C. aqueous solution of 100/100 for 15 minutes.
This was washed with pure water at 15 ° C for 15 seconds and then dried under hot air at 50 ° C for 300 seconds. A triacetylcellulose film was attached to both surfaces of the thus obtained polarizing film to form a polarizing plate. Wavelength of the obtained polarizing plate 500-70
Parallel light transmittance of 0 nm is 37% to 38%, wavelength is 420n
The orthogonal light transmittance of m is 5.2%, the orthogonal light transmittance of a wavelength of 500 nm is 1.4%, the orthogonal light transmittance of a wavelength of 570 to 700 nm is 0.00%, and the amount of blue transmitted light is large. is there. FIG. 1 shows the light transmission spectrum of this polarizing plate.

Comparative Example 1 A polyvinyl alcohol film (Kuraray Co., Ltd .: Kuraray Vinylon VFX750RS) was uniaxially stretched 5 times at 110 ° C. This uniaxially stretched polyvinyl alcohol film was placed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.075 / 5/100 while maintaining the tension.
It was immersed for 60 seconds. Next, it was immersed in an aqueous solution of boric acid / potassium iodide / water at a weight ratio of 7.5 / 6.0 / 100 at 70 ° C. for 15 minutes. This was washed with pure water at 15 ° C for 15 seconds and then dried under hot air at 50 ° C for 300 seconds.
A triacetylcellulose film was attached to both surfaces of the thus obtained polarizing film to form a polarizing plate. The parallel light transmittance of the obtained polarizing plate at a wavelength of 500 to 700 nm is 37.
% -38%, orthogonal light transmittance of wavelength 420 nm is 0.01
%, The orthogonal light transmittance at a wavelength of 500 nm is 0.01%, the orthogonal light transmittance at a wavelength of 570 to 700 nm is 0.00%, and the amount of blue transmitted light is very small. FIG. 2 shows the light transmission spectrum of this polarizing plate.

[Brief description of drawings]

FIG. 1 is a diagram showing a light transmission spectrum of a polarizing plate obtained in Example 1.

2 is a diagram showing a light transmission spectrum of a polarizing plate obtained in Comparative Example 1. FIG.

[Explanation of symbols]

 Tp: parallel light transmittance Tc: orthogonal light transmittance

Claims (3)

[Claims] 1. A wavelength 50 in a parallel light transmission spectrum.
The light transmittance of 0 to 700 nm is 35% or more, the light transmittance of the wavelength 420 nm in the orthogonal light transmission spectrum is 4% or more, the light transmittance of the wavelength 500 nm is 2% or less, and the wavelength 570.
A polarizing plate in which iodine is adsorbed and aligned on a polyvinyl alcohol-based film having a light transmittance of 0.01% or less at a wavelength of 700 nm. 2. A polyvinyl alcohol-based film having a potassium iodide content of water 1 after iodine is adsorbed and oriented.
The method for producing a polarizing plate according to claim 1, wherein the dipping treatment is performed in a boric acid-containing aqueous solution which is less than 2 parts by weight with respect to 00 parts by weight. 3. The method for producing a polarizing plate according to claim 2, wherein a protective film is attached to at least one surface of the film after the immersion treatment in a boric acid-containing aqueous solution.