JP2895435B2 - Manufacturing method of polarizing film with excellent durability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polarizing film having excellent durability and a high degree of polarization.

[0002]

2. Description of the Related Art In recent years, desktop electronic calculators, electronic timepieces, and word clocks
Liquid crystal display devices are used for professionals, automobiles, and instruments of machinery and the like, and accordingly, the demand for polarizing plates is increasing. In particular,
Meters and household appliances around the kitchen are often used under severe conditions, so that a film with high durability and a high degree of polarization is required. At present, one of the known polarizing films is one in which a polyvinyl alcohol-based film is dyed with iodine and one in which a dye is dyed. This film is formed by forming an aqueous solution of polyvinyl alcohol. It is produced by uniaxially stretching and dyeing this, or by dyeing and then uniaxially stretching, and then preferably performing a durability treatment with a boron compound.

[0003]

However, in the case of the above-mentioned polyvinyl alcohol-based polarizing film, the iodine-dyed product has good polarizing performance, but is inferior in moisture resistance and heat resistance, and is not suitable for use in a high humidity atmosphere or a high heat. When exposed to an atmosphere, there is a problem that the degree of polarization is reduced, that is, the durability is inferior. On the other hand, the dyed product has the advantage that the polarization performance is inferior but the durability is excellent. As described above, the polyvinyl alcohol-based polarizing film has advantages and disadvantages, and in fact, it is inevitable to properly use it according to the required performance of the end use. Therefore, if a polyvinyl alcohol-based polarizing film excellent in both polarizing performance and durability can be developed, it can be said that it is extremely industrially useful, including expansion of its use.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such a problem, and as a result, the average degree of polymerization was found to be 260.
After forming a polyvinyl alcohol-based resin film of 0 or more, upon producing a polarizing film by uniaxially stretching,
It has been found that the object can be achieved when the film is uniaxially stretched at least during the treatment with a boron compound so that the film width after stretching is 60% or less of the film width before stretching. Was. In the case where the uniaxial stretching is performed twice or more during the production of the polarizing film, the film width after the stretching in the last stretching step is 60% or less of the film width before stretching (raw material) in the first stretching step. To do so. Such effects of the present invention can be obtained by using a product having a high degree of polymerization as the polyvinyl alcohol and employing specific stretching conditions as described above.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below.
The polarizing film of the present invention is a uniaxially stretched film of a polyvinyl alcohol-based resin film. Polyvinyl alcohol is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. However, the present invention is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (salt, ester, amide, Including nitriles), olefins,
It may contain components copolymerizable with vinyl acetate, such as vinyl ethers and unsaturated sulfonates. The average degree of saponification of polyvinyl alcohol is practically 85 to 100 mol%, preferably 98 to 100 mol%.

In order to obtain the effect of the present invention, the average degree of polymerization is 2600 or more, preferably 3500 to 5000. If it is less than 2,600, a remarkable effect is hardly obtained. The polyvinyl alcohol is formed according to a known method. As such a method, polyvinyl alcohol is converted to water, an organic solvent,
A method of dissolving in a mixed solvent of water / organic solvent or the like and casting is common. The practical concentration of the solution is about 5 to 20% by weight. In addition, a so-called gel film forming method or the like, in which a solution of polyvinyl alcohol is introduced into a coagulation bath to form a film, and the like can be performed. The film thickness of the raw film is 40-120.
μ is appropriate.

The above-mentioned raw film is dyed, stretched and treated with a boron compound to produce a polarizing film. That is, after the polyvinyl alcohol raw film is dyed with iodine, it is stretched and treated with a boron compound at the same time. In the present invention,
It may be stretched at least during the boron compound treatment, and if necessary, stretched before iodine dyeing, stretched simultaneously with dyeing, stretched after iodine dyeing,
Stretching can be performed two or more times (multi-stage stretching).

Regardless of which means such as one-stage stretching or multi-stage stretching is performed, in the present invention, in the stretching process,
The film must be uniaxially stretched so that the film width after stretching is 60% or less, preferably 40 to 55% of the film width before stretching. In the case of multi-stage stretching, as described above, the film width after stretching in the last stretching step is set to be 60% or less of the film width before stretching in the first stretching step. By limiting the rate of decrease in the length of the film in the width direction to such a specific range, the polarization performance and the durability can be simultaneously improved. Conventionally, in uniaxial stretching of a polyvinyl alcohol film, it is usual to try to prevent the film from shrinking in the width direction as much as possible from the viewpoint of productivity. Control shrinkage to a specific range
There is a big feature in the point that it does. Roll stretching or the like is arbitrarily performed for stretching in such a range. Roll stretching can be performed in either a single-stage system or a multi-stage system.
In order to reduce the shrinkage to 60% or less, the distance between the stretching rolls is set to be considerably long. The stretching is desirably performed in a uniaxial direction at least four times, preferably at least six times. The temperature condition during stretching is usually selected from 50 to 130 ° C.

The iodine dyeing of the film, that is, the adsorption of the polarizing element, is carried out by bringing the liquid containing the polarizing element into contact with the film. Usually, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is 0.1 to 2 g / l,
The concentration of potassium iodide is suitably 10 to 50 g / l, and the weight ratio of iodine / potassium iodide is suitably 20 to 100. The dyeing time is practically about 30 to 500 seconds. A small amount of an organic solvent compatible with water other than the water solvent may be contained. The contact means is preferably immersion, but any means such as coating and spraying can be applied.

[0010] The dyed film is then treated with a boron compound while being stretched as described above. Boric acid and borax are practical as boron compounds. The boron compound is used in the form of an aqueous solution or a mixed solution of water and an organic solvent at a concentration of about 0.5 to 2 mol / l, and it is practically desirable that a small amount of potassium iodide coexist in the liquid. The treatment method is preferably an immersion method, but of course, a coating method and a spraying method can also be performed. The temperature during processing is about 50-70 ° C, and the processing time is 5
It is preferably about 20 minutes, and if necessary, a stretching operation may be performed after the treatment.

[0011] The polarizing film thus obtained is
A protective film having excellent optical transparency and mechanical strength is bonded to both sides or one side thereof, and dried to be used as a polarizing plate.
Examples of the protective film include conventionally known cellulose acetate films, acrylic films, polyester resin films, polyolefin resin films, polycarbonate films, polyetheretherketone films, and polysulfone films.

Thus, the durability of the polarizing film of the present invention in a high-temperature, high-humidity state is improved, and the degree of polarization does not decrease even after being left for a long time. Utilizing such characteristics, it is used for a liquid crystal display, and is particularly useful for a vehicle, various industrial instruments, display of household electric appliances, and the like.

[0013]

Next, the polarizing film of the present invention will be described in more detail by way of examples. The degree of polarization referred to in the present invention is [(H ₁₁
−H ₁ ) / (H ₁₁ + H ₁ )] ^1/2 , where H ₁₁ is a state in which two polarizing film samples are superimposed so that the polarizing films are oriented in the same direction when they are superposed. value measured using a spectrophotometer in, H ₁ at the time of superposition of the two samples is a value measured in a state superimposed so as to be a direction in which alignment directions are perpendicular to each other of the polarizing film.

Example 1 A polyvinyl alcohol having an average degree of polymerization of 3800 and an average degree of saponification of 99.5 mol% was dissolved in water to obtain an aqueous solution having a concentration of 5.0% by weight. The solution was cast on a polyethylene terephthalate film and dried to obtain a film having a thickness of 60 μm. This film was cut into a width of 10 cm and mounted on a chuck. The film was washed with 0.2 g / l iodine and 50 potassium iodide.
g / l in an aqueous solution at 30 ° C. for 120 seconds,
Then, the substrate was immersed in an aqueous solution having a composition of boric acid 60 g / l and potassium iodide 30 g / l, and simultaneously subjected to boric acid treatment for 5 minutes while being uniaxially stretched 6 times. Finally, it was dried at room temperature for 24 hours. The film thickness of the obtained film is 25 μ,
The width was 5 cm, and the reduction rate of the film width (hereinafter simply referred to as reduction rate) was 50%. An 80 μm-thick triacetyl cellulose was adhered to both sides of the film using an aqueous solution of polyvinyl alcohol as an adhesive, and dried at 50 ° C. to obtain a polarizing plate. The single transmittance of this polarizing plate is 43.05%,
The degree of polarization was 99.89%. Then add this film to
When the same measurement was performed after leaving it in an atmosphere of 0 ° C. and a relative humidity of 90% for 20 days, the single transmittance was 43.08.
% And the degree of polarization were 99.43%. Further, a heat resistance test was conducted by leaving the substrate at 80 ° C. in a dry atmosphere for 20 days.
Met.

Comparative Example 1 The same experiment as in Example 1 was carried out using polyvinyl alcohol having an average degree of polymerization of 1700 and an average degree of saponification of 99.8 mol%. The single transmittance of the polarizing plate immediately after production is 43.19%,
The degree of polarization is 99.14%, 60 ° C., 90% relative humidity.
%, The single transmittance after 20 days of standing is 44.83%,
The degree of polarization was 95.89%. After the heat test, the single transmittance was 44.82% and the degree of polarization was 95.87%.

Comparative Example 2 Example 1 except that the reduction rate of the film width was changed to 70%.
Did the same experiment. The single transmittance immediately after production is 43.26.
%, Degree of polarization is 99.36%, 60 ° C, relative humidity 90%,
The simplex transmittance after several 20 days of standing was 44.88%, and the degree of polarization was 97.66%. After the heat resistance test, the single transmittance was 44.87% and the degree of polarization was 97.64%.

Example 2 The same experiment as in Example 1 was carried out except that polyvinyl alcohol having an average degree of polymerization of 4500 and an average degree of saponification of 99.3 mol% was used. The single transmittance of the polarizing plate immediately after production is 44.05.
%, Degree of polarization 99.78%, 60 ° C., relative humidity 90
%, The single transmittance after 20 days of standing is 44.88%,
The degree of polarization was 97.45%. The single transmittance after the heat resistance test was 44.05%, and the degree of polarization was 99.76%.

Example 3 The same experiment as in Example 1 was carried out except that polyvinyl alcohol having an average degree of polymerization of 3000 and an average degree of saponification of 99.5 mol% was used. The single transmittance of the polarizing plate immediately after production is 42.78.
%, Degree of polarization 99.88%, 60 ° C., relative humidity 90
%, The single transmittance after 20 days of standing days is 43.08%,
The degree of polarization was 99.78%. After the heat test, the single transmittance was 42.68% and the degree of polarization was 99.82%.

Embodiments 4 and 5 In the embodiment 1, the reduction rate of the film width was 46% (6.
[Example 4] and 53% (5.4 times stretching)
The same experiment was performed except that the example was changed to [Example 5]. The results were as follows. Example 4 Example 5 Single Transmittance Polarization Degree Single Transmittance Polarization Degree 43.14% 99.89% 43.24% 99.23% After endurance test 43.74% 99.45% 44.53% 98 .74% After heat test 43.14% 99.87% 43.24% 99.22%

[0020]

According to the present invention, excellent durability can be obtained by using a polyvinyl alcohol resin having a high degree of polymerization and by regulating the reduction rate of the film width in a specific range when the resin film is stretched. A polarizing film is obtained.

Continuation of the front page (56) References JP-A-1-105204 (JP, A) JP-A-60-248333 (JP, A) JP-A-60-218603 (JP, A) European Patent Application Publication 297927 (EP, A1) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/30

Claims (1)

(57) [Claims] 1. After forming a polyvinyl alcohol-based resin film having an average degree of polymerization of 2600 or more, the film is uniaxially stretched to produce a polarizing film. At least during the treatment with a boron compound, the film is uniaxially stretched. A method for producing a polarizing film having excellent durability, characterized in that the film is uniaxially stretched so that the film width is 60% or less of the film width before stretching.