JP3505968B2 - Manufacturing method of polarizing film - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 in which a polyvinyl alcohol-based resin film in which iodine or a dichroic dye is adsorbed and oriented is dipped in an aqueous solution of boric acid is known. However, it is difficult for such a polarizing film to satisfy the higher contrast required for a liquid crystal display device used outdoors or a liquid crystal display device with low power consumption.

[0003]

Therefore, the present inventors have found that
As a result of diligent studies to develop a method capable of producing a polarizing film having a higher contrast, it was found that a polarizing film having a high contrast can be obtained by stretching at a specific ratio in an aqueous solution of boric acid, and the present invention was achieved. It was

[0004]

[Means for Solving the Problems] That is, the present invention provides a film in which a polyvinyl alcohol resin film is uniaxially stretched and then iodine or a dichroic dye is adsorbed and oriented, while immersing the film in a boric acid aqueous solution. The present invention provides a method for producing a polarizing film by stretching it 8 times.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polyvinyl alcohol-based resin is a polyvinyl alcohol homopolymer or a copolymer with another monomer containing vinyl alcohol as a main copolymerization unit. The degree of polymerization is usually in the range of 1000 to 10000, preferably 1500 to 10000. The saponification degree of the polyvinyl alcohol resin is usually 85 to 1
It is about 100 mol%, preferably about 98 to 100 mol%. A polyvinyl alcohol-based resin film is obtained by forming a polyvinyl alcohol-based resin into a film by a usual method, and the thickness thereof is usually about 50 to 150 μm.

The uniaxial stretching of the polyvinyl alcohol resin film is usually performed by a dry method. In particular,
Examples include a method of uniaxially stretching using a heated roll, and a uniaxial stretching method between rolls in which stretching is performed while applying tensile force between rolls installed in a heating oven. The draw ratio is usually about 4 to 8 times.

The method itself for adsorbing and orienting iodine or a dichroic dye after uniaxial stretching is not particularly limited. For example, a method of immersing the dye in an aqueous solution of iodine and potassium iodide while keeping a tension state, a dichroic dye and Examples include a method of immersing in an aqueous solution of Glauber's salt. When immersed in an aqueous solution of iodine and potassium iodide, its composition is usually
0.01 to 0.5 parts by weight of iodine per 100 parts by weight of water,
The amount of potassium iodide is 0.5 to 10 parts by weight, and the temperature of the aqueous solution is usually in the range of 20 to 50 ° C. On the other hand, when an aqueous solution of a dichroic dye and mirabilite is used, the composition is usually 0.001 to 1 part by weight of dichroic dye and 1 to 10 parts by weight of mirabilite per 100 parts by weight of water. Usually 3
It is about 0 to 80 ° C. The uniaxially stretched polyvinyl alcohol-based resin film may be subjected to a dipping treatment in water before adsorbing and orienting iodine or a dichroic dye.

Thus, the polyvinyl alcohol resin film in which iodine or a dichroic dye is adsorbed and oriented is stretched while being immersed in an aqueous boric acid solution according to the present invention.
As the boric acid aqueous solution, an aqueous solution containing 2 to 18 parts by weight of boric acid, preferably 5 to 12 parts by weight, is used per 100 parts by weight of water. When iodine is adsorbed and oriented, the aqueous boric acid solution may further contain potassium iodide, and when potassium iodide is used, the amount thereof is usually 2 to 20 parts by weight per 100 parts by weight of water. is there. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher and is within a range that does not cause film breakage, and preferably 50 to 90.
It is about ℃. The immersion time in the aqueous boric acid solution is not particularly limited, but is usually 100 to 1200 seconds, preferably 150 to 600 seconds, and more preferably about 200 to 500 seconds.

In order to stretch the polyvinyl alcohol resin film in which iodine or a dichroic dye is adsorbed and oriented while being immersed in a boric acid aqueous solution, for example, the film may be stretched in a boric acid aqueous solution. The stretching method is not particularly limited, and for example, 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 in the aqueous boric acid solution is important, and the draw ratio is 1.1 to 1.8.
Double the range. If the stretching ratio at this time is less than 1.1 times or more than 1.8 times, the improvement in contrast is not sufficient, and if it exceeds 1.8 times, film breakage tends to occur, which is not preferable. After being stretched in an aqueous solution of boric acid, the desired polarizing film can be obtained by a method of washing with water and drying as usual.

The polarizing film thus obtained can be used as a polarizing plate by laminating a protective layer on one side or both sides of the polarizing film, as in a normal polarizing film.
Examples of the protective layer include a plate, sheet or film of cellulose acetate resin, acrylic resin, polyester resin, polyolefin resin, polycarbonate resin, polyether sulfone resin, etc., respectively.

[0012]

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

[0013]

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 index C _r representing the contrast of the polarizing film was obtained by the following method. (1) Parallel transmittance (T _p ) and orthogonal transmittance (T _c ).
The transmittance when two polarizing films thus obtained were stacked so that their absorption axes were parallel to each other was measured.
_p ), and the transmittance in the case where they are superposed so that their absorption axes are orthogonal to each other, is _defined as the orthogonal transmittance (T _c ). The transmittance T was measured using a spectrophotometer (Shimadzu UV-2200) in the wavelength region 4
Spectral transmittance measured at 10 nm intervals from 00 to 700 nm [τ
(Λ), where λ represents the wavelength. ] From the calculation formula (1) [Where P (λ) is the spectral distribution of standard light (C light source), y
(Λ) represents the 2-degree visual field color matching function. ] Was calculated. (2) Calculation of contrast index C _{r From} parallel transmittance (T _p ) and orthogonal transmittance (T _c ),
The calculation formula (2) was calculated by C _r = T _p / T _c (2).

Example 1 A polyvinyl alcohol film (thickness: 75 μm, degree of polymerization: 2,400, degree of saponification: 99.9% or more) was dry-axially uniaxially stretched (stretching ratio: 5 times), and iodine and iodinated while maintaining tension. 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. Then, 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 at a draw ratio of 1.3 times while being immersed in the film at 76 ° C. for 300 seconds. Then, rinse with pure water at 15 ° C for 10 seconds, and
It was dried at 0 ° C. to obtain a polarizing film (C _r = 1800).

Example 2 Except that the draw ratio in a boric acid aqueous solution was 1.7 times,
Operating in the same manner as in Example 1, the polarizing film (C _r = 20)
00) was obtained.

Comparative Example 1 A polarizing film (C _r = C _r) , which was prepared in the same manner as in Example 1, except that the draw ratio in the aqueous boric acid solution was 1.05.
1000) was obtained.

Comparative Example 2 An attempt was made to increase the draw ratio in a boric acid aqueous solution to 2.0, but the film was broken and the drawing could not be carried out.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-64-84203 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08J 7/00 C08J 7/12-7 / 14

Claims (2)

(57) [Claims] 1. A film in which a polyvinyl alcohol resin film is uniaxially stretched 4 to 8 times by a dry hot roll and then iodine or a dichroic dye is adsorbed and oriented, and 5 to 12 parts by weight of boric acid are added per 100 parts by weight of water. More than 50 ℃
The method for producing a polarizing film, wherein the polarizing film is stretched 1.1 to 1.8 times while being dipped in the boric acid aqueous solution for 100 to 1200 seconds . 2. The degree of polymerization of polyvinyl alcohol resin is 1
The method for producing a polarizing film according to claim 1, wherein the polarizing film is 000 to 10,000 .