JPH07151912A - Production of polarized film - Google Patents

Abstract

PURPOSE:To improve polarizing performance, dyeability and film appearance by forming a polyvinylalcohol resin film, specifying the water content of the film, uniaxially orienting the film at specified temp. and then dying. CONSTITUTION:After a polyvinylalcohol resin film is formed, its water content is controlled to >=10wt.%. The film is uniaxially oriented at 60-150 deg.C and dyed. The polyvinylalcohol resin is produced by saponification of polyvinylacetate obtd. by polynm. of vinyl acetate. The average saponification degree is 85-100mol%, preferably 98-100 mol% for practical use. The water content is the proportion (wt.%) calculated as the whole water content (weight) in the raw film/polyvinylalcohol resin (weight). The water content is preferably 10-200 wt.%, and more preferably 20-150wt.%. The raw film with controlled water content is simultaneously subjected to heat treatment such as floating drying and to uniaxially orientation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyvinyl alcohol-based resin polarizing film, and more particularly to a method for producing a polyvinyl alcohol-based resin polarizing film excellent in dyeability, film appearance and optical durability.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in desk-top electronic computers, electronic timepieces, word processors, measuring instruments such as automobiles and machines, and the demand for polarizing plates has increased accordingly. In particular,
Highly polarized films are required for accurate instruments.

At present, one of the known typical polarizing films is a polyvinyl alcohol type polarizing film.
The polarizing film includes a polyvinyl alcohol resin film dyed with iodine and a dichroic dye dyed film, which is prepared by forming an aqueous solution of a polyvinyl alcohol resin film and uniaxially stretching it. It is manufactured by dyeing or dyeing and then uniaxially stretching, and then preferably subjecting to a durability treatment with a boron compound. Therefore,
In the stretching process as described above, the applicant of the present invention for producing a film having a higher polarization performance is uniaxially stretched by 4.5 times or less during the boron compound treatment process, and then the film is subjected to
A two-stage stretching method has been proposed in which uniaxial stretching is performed at less than double. (Japanese Patent Application No. 2-417681)

[0004]

However, in the case of the polyvinyl alcohol-based resin polarizing film obtained by the above method, although the polarizing performance is sufficiently good, the film before dyeing is sufficiently examined. However, there was still room for improvement in dyeability and film appearance.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that after forming a polyvinyl alcohol resin film into a film, the water content is 10% by weight.
Based on the above, it was found that when the film uniaxially stretched at 60 to 150 ° C. is subjected to a dyeing treatment step, a polarizing film having excellent polarization performance and excellent dyeability and film appearance can be obtained, and the present invention has been completed. It was.

As described above, the effect of the present invention is that the film-forming film of polyvinyl alcohol resin is uniaxially stretched at a water content of 10% by weight or more and at a temperature of 60 to 150 ° C. before the dyeing treatment step. It is obtained by adopting the processing conditions of. Hereinafter, the present invention will be specifically described.

The polarizing film of the present invention is a uniaxially stretched film of polyvinyl alcohol resin film. Polyvinyl alcohol resin is generally 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, ester, amide, (Including nitrile), olefins, vinyl ethers, unsaturated sulfonates, and the like, and may contain a component copolymerizable with vinyl acetate. The polyvinyl alcohol-based resin has an average saponification degree of 85 to 100 mol%, preferably 98 to 100.
Molar% is practical.

In order to obtain the effects of the present invention, the average degree of polymerization may be any of 500 to 5000, but normally 1000 to 4700 is advantageous. The polyvinyl alcohol resin is formed into a film by a known method. A general method is to dissolve a polyvinyl alcohol-based resin in water, an organic solvent, a water / organic solvent mixed solvent or the like and cast the solution. It is practical that the 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 a polyvinyl alcohol resin is introduced into a coagulation bath to form a film can also be carried out.
A suitable thickness of the original film is 40 to 120 μm.

Usually, the above original film is dyed, optionally treated with a boron compound, and uniaxially stretched in the dyeing process or the boron compound treatment process to obtain a polarizing film. As described above, it is characterized in that it is uniaxially stretched under specific conditions before the dyeing treatment step. That is, the formed raw fabric film is uniaxially stretched under the temperature condition of 60 to 150 ° C. after the moisture content is adjusted to 10% by weight or more. The water content in the present invention means the weight% calculated from the total water content (weight) in the raw film / polyvinyl alcohol resin content (weight).

The method of conditioning the humidity is not particularly limited. For example, when a polarizing film is continuously produced in a raw film production line, the water content of the raw film immediately before the production of the polarizing film is 0.5 to 0.5. Since the content is less than 10% by weight, a method of humidifying with a known humidifier for a film line, a method of heating and drying after soaking in water and a method of adjusting to the above-mentioned water content can be mentioned.

At this time, if the water content of the raw film is less than 10% by weight, the flexibility of the film is lowered, which is unsuitable, and preferably 10 to 200% by weight, more preferably 2%.
It is 0 to 150% by weight. If the water content is too high, the solubility and flexibility of the film surface will tend to be too high, and the film strength will decrease, which is not preferable. Further, the moisture-conditioned raw film is subjected to heat treatment at a temperature condition of 60 to 150 ° C. by a known method such as floating drying or longitudinal uniaxial stretching, and at the same time uniaxially stretched.

At this time, if the heat treatment temperature is lower than 60 ° C., the workability is poor and sufficient stretching cannot be carried out. On the contrary, if it exceeds 150 ° C., the film is curled, which is not suitable. It is preferably 90 to 120 ° C. Further, the uniaxial stretching, roll stretching, any method such as tenter stretching is carried out, in the roll stretching can be carried out one-stage type, multistage type, the stretching ratio, the presence or absence of the stretching in the post-process and the post-process Although it cannot be absolutely stated depending on the stretching ratio, the stretching ratio is usually 2.0 to 10 times, preferably 3.0 to 8 times. The uniaxially stretched film thus obtained is subjected to a dyeing treatment step to be a polarizing film. Hereinafter, steps after the dyeing processing step will be described.

Iodine dyeing of the uniaxially stretched film, that is, adsorption of the polarizing element is carried out by bringing a liquid containing the polarizing element into contact with the film. Usually iodine-
An aqueous solution of potassium iodide is used, and the concentration of iodine is 0.1.
˜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. Practical dyeing time is about 30 to 500 seconds. In addition to water solvent, it is acceptable to include a small amount of water-compatible organic solvent.

As the contact means, immersion is preferable, but any means such as coating and spraying can be applied.

In the dyeing treatment step, the uniaxially stretched film can be further stretched within a range not departing from the effects of the present invention. In the stretching treatment, the stretching temperature is preferably about 30 to 70 ° C., and the treatment time is preferably about 60 to 600 seconds.

In order to draw in such a range, any method such as roll drawing and tenter drawing is carried out, but the former is usually carried out. Roll stretching can be performed in either a single-stage type or a multi-stage type.

The film thus dyed is then treated with a boron compound. Boric acid and borax are practical as the boron compound. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.5 to 2 mol / l, and potassium iodide coexists in the solution for practical use. The treatment method is preferably a dipping method, but of course, a coating method and a spraying method can also be carried out. In addition, it is possible to perform uniaxial stretching during the treatment with the boron compound as in the dyeing treatment step, and the conditions at that time are in accordance with the stretching conditions during the dyeing treatment step.

The polarizing film thus obtained is appropriately washed, dried and heat treated according to a conventional method, and a protective film excellent in optical transparency and mechanical strength is attached to both surfaces or one surface thereof, and dried to be used as a polarizing plate. It Examples of the protective film include conventionally known cellulose acetate film, acrylic film, polyester resin film, polyolefin resin film, polycarbonate film, polyether ether ketone film, and polysulfone film. .

[0019]

[Operation] Since the polarizing film of the present invention is subjected to a special stretching treatment before the dyeing treatment step, it is excellent in polarizing performance and is excellent in dyeability and film appearance. Used for display applications, especially for vehicles,
It is useful for displaying various industrial instruments and household appliances.

[0020]

EXAMPLES 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 expressed by the following equation.

[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2
× 100 (%) where H ₁₁ is the transmittance measured by using a spectrophotometer in a state where the two polarizing film samples are superposed so that the orientation directions of the polarizing films are the same. %) And H ₁ are the transmittances (%) measured when the two samples were superposed so that the polarizing films were aligned so that the orientation directions thereof were orthogonal to each other.

Example 1 A polyvinyl alcohol resin having an average degree of polymerization of 3800 and an average degree of saponification of 99.7 mol% was dissolved in water to give 5.0% by weight.
A concentrated aqueous solution was obtained. The solution was cast on a polyethylene terephthalate film and dried to obtain a film having a water content of 70% by weight and a film thickness of 60 μm. The film was cut into a width of 10 cm, mounted on a chuck, and uniaxially stretched 5.0 times in an atmosphere of 110 ° C. for 5 minutes. The uniaxially stretched film was uniaxially stretched twice at 30 ° C. in an aqueous solution containing 0.2 g / l iodine and 50 g / l potassium iodide, and then boric acid 60 g / l and potassium iodide 30 g / l were used. While being immersed in the aqueous solution, it was uniaxially stretched at a temperature of 40 to 60 ° C. by a factor of 2. Finally, it was dried at room temperature for 24 hours to obtain a polarizing film.

A spectrophotometer (RETS-2000, manufactured by Otsuka Electronics Co., Ltd.) was used to measure in-plane variation in transmittance of the polarizing film.
The difference between the maximum value and the minimum value of the in-plane transmittance was 1.0 (%), and the film thickness of the film was examined with a continuous film thickness meter to find that there was no film thickness variation. The surface condition was good and smooth. Further, in order to measure the durability of the polarizing film, a triacetyl cellulose film having a film thickness of 80 μ was attached to both sides of the film via an acrylic adhesive and dried at 70 ° C. to obtain a polarizing plate. This polarizing plate had a single transmittance of 41.3% and a polarization degree of 97.7%. Further, when the polarization degree was similarly measured after leaving the polarizing plate under a dry condition of 90 ° C. for 20 days, the polarization degree was 97.2%.

Examples 2 to 5 and Comparative Examples 1 to 3 Polyvinyl alcohol resin (PV
The resin, the water content and the stretching treatment conditions of the raw film of A) were changed as shown in Table 1, and a polarizing film was prepared according to Example 1 and evaluated in the same manner. The evaluation results are shown in Table 2.

[0025]

[Table 1] Raw material PVA moisture content Stretching temperature Stretching time Stretching ratio Average degree of polymerization Saponification degree (wt%) (° C) (min) (times) Example 1 3800 99.7 100 110 110 5 5.0 〃 2 1700 99 .7 60 90 5 5 5.0 〃 3 2600 99.7 80 100 5 5 5.0 〃 4 3800 99.7 90 110 110 5 5.0 〃 5 4500 99.3 100 110 110 5 4.7 Comparative Example 1 3800 99. Cut at 7 5 110 5 5.0 〃 2 3800 99.7 100 30 5 5 5.0 〃 3 3800 99.7 100 180 5 5.0 5.0 Note) The degree of saponification represents mol%.

[0026]

[Table 2] Initial performance Endurance performance Polarization degree (%) Transmission rate (%) In-plane variation (%) Polarization degree change (%) * Smoothness Example 1 97.7 41.3 1.0 -0. 5 Good 〃 2 98.1 41.3 1.0 -0.5 Good 〃 3 98.3 41.1 1.0 -0.3 Good 〃 4 98.7 41.2 0.9 -0.3 Good 〃 5 98.7 41.2 1.1-0.3 Good Comparative Example 1 Measurement not possible due to cutting during stretching 〃 2 96.9 41.0 1.3 -2.2 Good 〃 3 91.3 41.5 1 .1-0.5 Good * Indicates the difference (%) between the measured value (%) after heat treatment and the measured value (%) before treatment.

[0027]

EFFECT OF THE INVENTION The polarizing film of the present invention, which has been subjected to a special stretching treatment before the dyeing treatment step, is excellent in polarizing performance and is excellent in dyeability and film appearance. It is used for liquid crystal displays and is particularly useful for vehicles, displays of various industrial instruments and household appliances.

Claims (1)

[Claims] 1. A polyvinyl alcohol-based resin film is formed into a film, and then the water content is set to 10% by weight or more, and 60 to 150.
A process for producing a polarizing film, which comprises subjecting the film uniaxially stretched at 0 ° C. to a dyeing treatment step.