JPH1149878A - Production of polarized film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to obtain a polarized film having a high contrast and useful for outdoor liquid crystal display devices, low power consumption liquid crystal display devices, etc., by orienting a polyvinyl alcohol resin film in a specific ratio in an aqueous boric acid solution. SOLUTION: This method for producing a polarized film comprises monoaxially orienting (A) a polyvinyl alcohol resin film (e.g. the film having a resin polymerization degree of 1,000-10,000) in an orientation ratio of 4-8 times e.g. by a dry method, allowing the film to adsorb (B1 ) iodine or (B2 ) a dichroic dye, immersing the film in (C) an aqueous boric acid solution [e.g. a solution containing 2-18 pts.wt. of boric acid in 100 pts.wt. of water] e.g. in conditions comprising a temperature of >=50 deg.C and an immersion time of 100-1,200 sec and simultaneously again orienting the film in a ratio of 1.1-1.8 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a polarizing film.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a polarizing film, for example, a method is known in which a film in which iodine or a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin film is immersed in an aqueous boric acid solution. However, it has been difficult for such a polarizing film to satisfy a higher contrast required for a liquid crystal display device used outdoors or a low power consumption liquid crystal display device.

[0003]

The inventors of the present invention have made intensive studies to develop a method for producing a polarizing film having a higher contrast, and as a result, by stretching the film in a boric acid aqueous solution to a specific magnification. The present inventors have found that a high-contrast polarizing film can be obtained, and have reached the present invention.

[0004]

That is, the present invention provides a film obtained by uniaxially stretching a polyvinyl alcohol resin film and then adsorbing and orienting iodine or a dichroic dye.
An object of the present invention is to provide a method for producing a polarizing film, wherein the film is stretched 1.1 to 1.8 times while being immersed in an aqueous boric acid solution.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polyvinyl alcohol-based resin in the polyvinyl alcohol-based resin film used in the present invention is, for example, a copolymer of polyvinyl alcohol or another monomer having vinyl alcohol as a main copolymerization component. And the degree of polymerization is usually from 1,000 to 10,000,
Preferably it is in the range of 1500-10000. A polyvinyl alcohol-based resin film is obtained by forming the polyvinyl alcohol-based resin by a usual method, and the thickness is usually about 50 to 150 μm. Such a polyvinyl alcohol-based resin film is usually saponified after film formation, and the degree of saponification is usually about 85 to 100 mol%, preferably about 98 to 100 mol%.

[0006] Uniaxial stretching of such a polyvinyl alcohol-based resin film is usually performed in a dry manner. Specifically, a method of uniaxially stretching using a hot roll, a roll-to-roll uniaxial stretching method of stretching while applying a tensile force between rolls installed in a heating oven, and the like are included, but are not limited thereto. is not. The stretching ratio is usually about 4 to 8 times.

The method of adsorbing and orienting iodine or a dichroic dye after uniaxial stretching is not particularly limited. For example, a method of immersing in an aqueous solution of iodine and potassium iodide while maintaining a tension state, and a method of dichroic dye and sodium sulfate A method of dipping in an aqueous solution may be used. When immersed in an aqueous solution of iodine and potassium iodide, the composition is usually 0.01 to 0.5 parts by weight of iodine and 0.5 to 10 parts by weight of potassium iodide per 100 parts by weight of water. Usually 2
The range is from 0 to 50 ° C. When an aqueous solution of the dichroic dye and sodium sulfate is used, the composition is usually 0.001 to 1 part by weight of dichroic dye and 1 to 10 parts by weight of sodium sulfate per 100 parts by weight of water, and the temperature of the aqueous solution is usually 30 to 80 parts by weight. It is about ° C.
Polyvinyl alcohol-based resin film after uniaxial stretching,
Before iodine or a dichroic dye is adsorbed and oriented, it may be immersed in water.

Thus, the film on which iodine or the dichroic dye is adsorbed and oriented needs to be stretched while being immersed in an aqueous boric acid solution. As the boric acid aqueous solution, an aqueous solution containing about 2 to 18 parts by weight, preferably about 5 to 12 parts by weight of boric acid per 100 parts by weight of water is used. When iodine is adsorbed and oriented, it may further contain potassium iodide. When potassium iodide is used, its amount is usually 2 to 20 parts by weight per 100 parts by weight of water.
Parts by weight. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher and a range that does not cause film breakage, and preferably 50 ° C.
~ 90 ° C. Although the immersion time in the boric acid aqueous solution is not particularly limited, it is generally 100 to 1200 seconds, preferably 150 to 600 seconds, more preferably 200 to 50 seconds.
It is about 0 seconds.

In order to stretch a film on which iodine or a dichroic dye is adsorbed and oriented while dipping in a boric acid aqueous solution,
For example, the film may be stretched in an aqueous boric acid solution.
The stretching method is not particularly limited. For example, the stretching can be performed by appropriately adjusting the tension applied to the film. The tension is adjusted according to the temperature and concentration of the boric acid aqueous solution.

In the method of the present invention, the draw ratio is important, and it is necessary that the draw ratio is in the range of 1.1 to 1.8.
If the stretching ratio is less than 1.1 times or exceeds 1.8 times, the contrast is not sufficiently improved, and if it exceeds 1.8 times, the film tends to break, which is not preferable. After being stretched in an aqueous boric acid solution, the desired polarizing film can be obtained by a method of washing with water and drying in the same manner as usual.

The polarizing film thus obtained can be used as a polarizing plate by attaching a protective layer to one or both surfaces thereof in the same manner as a normal polarizing film. Examples of the protective layer include a plate, sheet or film of cellulose acetate, acrylic resin, polyester resin, polyolefin resin, polycarbonate resin, and polyethersulfone resin.

[0012]

According to the method of the present invention, a high-contrast polarizing film can be easily produced.

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The contrast ( _Cr ) of the polarizing film was determined by the following method. (1) Parallel transmittance (T _p ) and orthogonal transmittance (T _c )
The transmittance when two polarizing films obtained are superimposed so that their absorption axes are parallel to each other is referred to as the parallel transmittance (T
_p ), and the transmittance in the case where the absorption axes are overlapped so as to be orthogonal to each other is _defined as orthogonal transmittance (T _c ). The transmittance was measured in a wavelength range of 400 using a spectrophotometer (Shimadzu UV-2200).
The spectral transmittance [.tau.
(Λ), where λ indicates the wavelength. ], The calculation formula (1) [Where P (λ) is the spectral distribution of standard light (C light source), y
(Λ) indicates a two-degree visual field color matching function. ]. (2) Contrast calculated parallel position transmittance (C _r) (T _p) and the perpendicular position transmittance (T _c),
It was calculated by equation _{(2) C r = T p} / T c (2).

Example 1 A polyvinyl alcohol film (thickness: 75 μm, degree of polymerization: 2400, degree of saponification: 99.9% or more) was uniaxially stretched in a dry system (stretching ratio: 5 times), and iodine and iodine were kept in a tensioned state. It was immersed in an aqueous solution of potassium [iodine: potassium iodide: water = 0.05: 5: 100 (weight ratio)] at 28 ° C. for 60 seconds. Next, a boric acid aqueous solution (boric acid 7.
(5 parts by weight, potassium iodide 6 parts by weight, water 100 parts by weight)
The film was stretched to 1.3 times the draw ratio while being immersed at 76 ° C. for 300 seconds. Then, wash with pure water at 15 ° C for 10 seconds,
After drying at 0 ° C., a polarizing film (C _r = 1800) was obtained.

EXAMPLE 2 Except that the stretching ratio in an aqueous boric acid solution was 1.7 times,
By operating in the same manner as in Example 1, a polarizing film (C _r = 20)
00).

Comparative Example 1 The same procedure as in Example 1 was carried out except that the stretching ratio in an aqueous solution of boric acid was changed to 1.05, to obtain a polarizing film (C _r =
1000).

COMPARATIVE EXAMPLE 2 An attempt was made to increase the draw ratio in an aqueous boric acid solution to 2.0 times, but the film was cut and could not be drawn.

Claims (7)

[Claims] 1. A film obtained by uniaxially stretching a polyvinyl alcohol-based resin film and then adsorbing and orienting iodine or a dichroic dye in a boric acid aqueous solution.
A method for producing a polarizing film, comprising stretching the film 1.8 times. 2. The method for producing a polarizing film according to claim 1, wherein the uniaxial stretching of the polyvinyl alcohol-based resin film is performed in a dry manner. 3. The method for producing a polarizing film according to claim 1, wherein the stretching ratio in uniaxial stretching of the polyvinyl alcohol-based resin film is 4 to 8 times. 4. The method for producing a polarizing film according to claim 1, wherein the boric acid aqueous solution contains 2 to 18 parts by weight of boric acid per 100 parts by weight of water. 5. The method for producing a polarizing film according to claim 1, wherein the temperature of the boric acid aqueous solution is 50 ° C. or higher. 6. An immersion time in an aqueous solution of boric acid of 100 to 12 hours.
The method for producing a polarizing film according to claim 1, wherein the time is 00 seconds. 7. The polymerization degree of the polyvinyl alcohol resin is 1
The method for producing a polarizing film according to claim 1, wherein the number is from 000 to 10,000.