JP2631403B2 - Manufacturing method of polarized film with excellent durability - Google Patents

Description

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

[Related Art] In recent years, liquid crystal display devices have been used for desktop electronic calculators, electronic watches, word processors, instruments for automobiles and machinery, and the demand for polarizing plates has been increasing along with this. The surrounding home appliances are often used under severe conditions, so that a film having 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.The film is formed by forming an aqueous solution of polyvinyl alcohol into a uniaxial film. It is manufactured by stretching and dyeing, or by uniaxially stretching after dyeing, and then preferably performing a durability treatment with a boron compound.

[Problems to be Solved by the Invention] However, in the case of the above-mentioned polyvinyl alcohol-based polarizing film, the iodine-dyed product has good polarizing performance, but has poor moisture resistance and heat resistance, and is exposed to a high humidity atmosphere or a high heat atmosphere. However, when dyed, 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 having excellent polarization performance and durability can be developed, it can be said that it is extremely useful in industry including its use expansion.

[Means for Solving the Problems] The present inventors have conducted intensive studies to solve such problems, and as a result, formed a high-polymerization degree polyvinyl alcohol resin film having an average degree of polymerization of 2600 or more, and after iodine dyeing. After uniaxial stretching or simultaneous iodine dyeing and uniaxial stretching or uniaxial stretching and then iodine dyeing, and then producing a polarizing film by treating with a boron compound, the film width after stretching in the above stretching step is before stretching. It has been found that the object can be achieved when the film is uniaxially stretched so as to have a film width of 40 to 60% of the film width of the present invention, and the present invention has been completed.

Such effects of the present invention can be obtained by using a high degree of polymerization product as polyvinyl alcohol as described above and by adopting specific stretching conditions. Hereinafter, the present invention will be described specifically.

The polarizing film of the present invention is a uniaxially stretched film of a polyvinyl alcohol resin film. Polyvinyl alcohol is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (salt,
(Including esters, amides, nitriles, etc.), olefins, vinyl ethers, unsaturated sulfonates, and the like, and may contain components copolymerizable with vinyl acetate. Average degree of saponification of polyvinyl alcohol is 85-100 mol%
Preferably, 98 to 100 mol% is practical.

In order to obtain the effect of the present invention, the average degree of polymerization is 2600 or more,
Preferably 3500-5000 is advantageous. If it is less than 2600, a remarkable effect is hardly obtained. The polyvinyl alcohol is formed according to a known method. Generally, a method of dissolving polyvinyl alcohol in water, an organic solvent, a mixed solvent of water / organic solvent and the like and casting the solution is used. The practical concentration of the solution is about 5 to 20% by weight. In addition, a so-called gel film forming method 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 is 40-120μ as a raw film
Is appropriate.

The raw film is stretched, dyed, and treated with a boron compound to produce a polarizing film. That is, the raw polyvinyl alcohol film is stretched and dyed with iodine, or the stretching and the dyeing are performed simultaneously, or the film is stretched after dyeing with iodine and then treated with a boron compound.

Regardless of which means is implemented, in the present invention, the film width after stretching in the stretching process is 40 times the film width before stretching.
It must be uniaxially stretched to に な る 60%, preferably 40-55%. 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 the uniaxial stretching of a polyvinyl alcohol film, it is usual to try to prevent the shrinkage in the width direction of the film as much as possible from the viewpoint of productivity, but in the present invention, the shrinkage in the width direction is contrary to the conventional technique. There is a great feature in controlling the value to a specific range. Roll stretching or the like is arbitrarily performed for stretching to 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 40 to 60%, the distance between the stretching rolls is set to be considerably long. Stretching and dyeing may be performed separately or simultaneously. When performed separately, the order of stretching and dyeing is also arbitrary. Stretching is desirably performed 4 times or more, preferably 6 times or more in the uniaxial direction.
The temperature condition during stretching is usually selected from 50 to 130 ° C.

The iodine dyeing on the film, that is, the adsorption of the polarizing element, is performed by bringing the liquid containing the polarizing element into contact with the film. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 2 g / l, the concentration of potassium iodide is 10 to 50 g / l, and the weight ratio of iodine / potassium iodide is 20 to 100. is there. A practical dyeing time of about 30 to 500 seconds is practical. 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.

The stretched and dyed film is then treated with a boron compound. 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 to coexist a small amount of potassium iodide 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,
The processing time is preferably about 5 to 20 minutes, and if necessary, the stretching operation may be performed during or after the processing. In this case, the film width after stretching in the last stretching step may be set to be 60% or less of the film width before stretching in the first stretching step.

The polarizing film thus obtained is laminated with a protective film having excellent optical clarity and mechanical strength on both surfaces or one surface thereof, dried and used as a polarizing plate. Examples of the protective film include conventionally known cellulose acetate-based films, acrylic films, polyester-based resin films, polyolefin-based resin films, polycarbonate-based films, polyetheretherkenton-based films, and polysulfone-based films.

[Operation] The polarizing film of the present invention has improved durability in a high temperature and high humidity state, and its 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.

EXAMPLES Next, the polarizing film of the present invention will be described in more detail with reference to examples.

In the present invention, the degree of polarization is In indicated, H ₁₁ at the time of superposition of two polarizing film sample, the value orientation direction was measured using a spectrophotometer in a state superimposed so as to become the same direction of the polarizing film, H ₁ 2 This is a value measured in a state where the polarizing films are overlapped so that the orientation directions of the polarizing films are orthogonal to each other when the two samples are overlapped.

Example 1 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 a 5.0% by weight aqueous solution. 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 to a width of 10 cm and mounted on a chuck.

The film was immersed in an aqueous solution consisting of 0.2 g / l of iodine and 50 g / l of potassium iodide at 30 ° C. for 120 seconds, and then 60 g / l of boric acid.
It was immersed in an aqueous solution having a composition of potassium iodide of 30 g / l, and simultaneously treated with boric acid 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 was 25 μm, the width was 5 cm, and the reduction rate of the film width (hereinafter simply referred to as reduction rate) was 50%. Using a polyvinyl alcohol aqueous solution as an adhesive, 80 μm-thick triacetyl cellulose was attached to both sides of the film and dried at 50 ° C. to obtain a polarizing plate. The single transmittance of this polarizing plate is 43.0
5% and the degree of polarization was 99.89%. Add this film to 60
After standing for 20 days in an atmosphere at 90 ° C. and a relative humidity of 90%, the same measurement was performed. As a result, the single transmittance was 43.08% and the degree of polarization was 99.
43%.

In addition, when subjected to a heat resistance test at 80 ° C. in a dry atmosphere for 20 days, the single transmittance was 43.05% and the degree of polarization was 99.87.
%Met.

Comparative Example 1 The same experiment as in Example 1 was performed using polyvinyl alcohol having an average degree of polymerization of 1700 and an average degree of saponification of 99.8 mol%.

The polarizing plate immediately after production has a single transmittance of 43.19% and a degree of polarization of 99.
It was 14%, had a single transmittance of 44.83% and a degree of polarization of 95.89% after standing for 20 days at 60 ° C. and a relative humidity of 90%.

Single transmittance after heat resistance test is 44.82%, polarization degree is 95.87%
Met.

Comparative Example 2 Example 1 except that the reduction rate of the film width was changed to 70%.
Did the same experiment. 43.26% single transmittance immediately after production,
The degree of polarization was 99.36%, the temperature was 60 ° C., the relative humidity was 90%, the single transmittance after several days of standing was 44.88%, and the degree of polarization was 97.66%. The unit transmittance after the heat test is 44.87% and the degree of polarization is 97.
67%.

Example 2 The same experiment as in Example 1 was conducted 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 polarizing plate immediately after production has a single transmittance of 44.05% and a degree of polarization of 9
The light transmittance was 9.78%, the relative transmittance was 60.degree. C., the relative humidity was 90%, the single transmittance after several days of standing was 44.88%, and the degree of polarization was 97.45%. The single transmittance after the heat test was 44.05%, and the degree of polarization was 99.76%.

Example 3 A film having a film thickness of 60 μm obtained by casting in Example 1 was stretched uniaxially four times at 110 ° C. The reduction rate of the film width was 70%. The stretched film was mounted on a chuck, and treated again in an iodine solution and a boric acid solution having the same composition as in Example 1 for 240 seconds and 5 minutes, respectively, and further re-stretched 1.5 times. The reduction rate of the width of the obtained polarizing film is 52
%Met. Thereafter, a polarizing plate was manufactured in the same manner as in Example 1. Immediately after the production of the polarizing plate, the single transmittance was 44.17%, the degree of polarization was 99.35%, the temperature was 60 ° C., the relative humidity was 90%, the single transmittance after several days of standing was 45.50%, and the degree of polarization was 96.04%. After the heat resistance test, the single transmittance was 44.17% and the degree of polarization was 99.34%.

Examples 4 and 5 In Example 1, the reduction rate of the film width was 46% (6.5%).
Double stretching) [Example 4] and 53% (5.4 times stretching) [Example 5] The same experiment was performed except for changing to [Example 5]. The results were as follows:

[Effect] In the present invention, a highly durable polarizing film is used by using a polyvinyl alcohol-based resin having a high degree of polymerization and defining the rate of decrease in the width of the film when the resin film is stretched in a specific range. Is obtained.

Claims (1)

(57) [Claims] 1. A polyvinyl alcohol-based resin film having an average degree of polymerization of 2600 or more is formed and is uniaxially stretched after iodine dyeing, or simultaneously with iodine dyeing and uniaxial stretching, or uniaxially stretched and then dyed with iodine, and then treated with a boron compound. In producing a polarizing film, a film having excellent durability characterized by being uniaxially stretched so that the film width after stretching in the stretching step is 40 to 60% of the film width before stretching. Manufacturing method.