JPS6250802A - Polarizing film and its production - Google Patents

Abstract

PURPOSE:To permit the free setting of the dispositions of regions where light transmittances are different and the adjustment of the degree of the difference in the light transmittances as well as the continuous production of a polarizing film by dyeing and stretching a hydrophilic high-polymer film whose the dyeability is modified by a heating treatment. CONSTITUTION:The hydrophilic high-polymer film is subjected to the heating treatment to form the regions where the dyeability is modified, then the film is subjected to a dyeing treatment. The hydrophilic high-polymer film is subjected to a stretching treatment before or after or simultaneously with the above-mentioned heating treatment or dying treatment to obtain the polarizing film formed with the regions where the light transmittances are different (the hatching part in the figure shows the part subjected to the modification treatment for the dyeability and spots indicate the degrees of the light transmittance inversely proportional to the density thereof). The polarizing film obtd. in such a manner is cut to a prescribed size and can be used as, for example, a polarizer. The disposition of the regions where the light transmittances are different, the degree of the difference in the light transmittance, etc. can be set freely and the polarizing plates having the difference in the light transmittances suitable for various applications are efficiently formed. The polarizing plate is thereby made usable widely for the front and rear windshield glasses of automobiles, sunglasses and others.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a novel polarizing film that is made of a hydrophilic polymer film that has been subjected to dyeability modification treatment and that is preferably applied to polarizers that have regions with different light transmittances. Regarding.

Conventional technology Diversification of display purposes and clarification of display categories in fields such as liquid crystal display devices, front and rear glass of automobiles, and sunglasses;
Due to demands for decoration, etc., it has become an issue to provide a polarizing plate having regions with different light transmittances, and essentially to provide a polarizer for use in the polarizing plate.

Conventionally, polarizing plates or polarized light having regions with different light transmittances have been used, or polarizing plates with different light transmittances have been used in combination, or by changing the dyeing conditions, differences in the dyeing state have been created. It has been proposed that the polarizing film is made of a polarizing film with a change in light transmittance.

Problems to be Solved by the Invention However, until now, the method of changing the light transmittance of a polarizing film was to change the dyeing conditions such as the temperature of the dye bath during dyeing, the dye concentration, and the dyeing time. This method also has problems with material supply, such as the fact that it is difficult to adopt a continuous production method and a patch method is used, and that it is difficult to obtain products whose transmittance changes continuously or partially or locally. However, with the conventional combination method mentioned in 11, the problem is that the combination process is complicated and the production efficiency is low, whereas with the polarizing film obtained by changing the dyeing conditions, continuous production is difficult. In addition to poor performance and fabrication efficiency, the degree of freedom in arranging regions with different light transmittances and the degree of freedom in the degree of difference in light transmittance was small, making it unsatisfactory in practical terms. □ Solve the problems. Means and Effects The present invention overcomes the above-mentioned problems by a novel method using a hydrophilic polymer film whose dyeability has been modified.

That is, the present invention provides a polarizing film having regions with different light transmittances, which is made of a dyed and stretched product of a hydrophilic polymer film whose dyeability has been modified, and (A) a hydrophilic polymer film that has been heat-treated to improve its dyeability. Step of forming a modified region, ■) A step of dyeing the hydrophilic polymer film that has undergone the above-mentioned dyeing step, and a step of dyeing the hydrophilic polymer film before or at the same time as the above-mentioned (2) step or step. The present invention provides a method for producing a polarizing film having regions with different light transmittances, which comprises a step of stretching a polymer film.

Typical examples of the hydrophilic polymer film used in the present invention include a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, and a film made of an ethylene-vinyl acetate copolymer. .

In the present invention, a hydrophilic polymer film whose dyeability has been modified is used. As a result, even if the denatured part and the dangerous part are dyed under exactly the same conditions, the degree of staining can be different, and the light transmittance can be different.

The modification treatment can be carried out, for example, by heat treatment.

In other words, heat treatment changes the degree of crystallinity of the hydrophilic polymer film and modifies the degree of swelling of the film with respect to the dye solution.As a result, even when dyeing is carried out under the same conditions, the degree of dyeing can vary. The degree of the difference in light transmittance between the heat-treated portion and the non-heat-treated portion can be controlled by the treatment conditions such as the temperature and time of the heat treatment. The portion to be heat-treated is determined depending on the purpose, that is, it can be appropriately determined depending on the use of the polarizing film to be obtained. Examples of the heat treatment method include passing through a heated roll or drying tower, pressing with a heated medium made of metal or the like, and irradiating with heat rays such as infrared rays, but there are no particular limitations. A heating roll passing method, a heated object pressing method, and the like are preferable in terms of heating conditions and controllability of the heat-treated portion. The heat treatment conditions are appropriately determined depending on the desired degree of staining denaturation.

Typical processing conditions include, but are not limited to, 40 DEG C. to the melting point of the film and 10 seconds to 10 minutes.

The polarizing film of the present invention is made of a dyed and stretched product of a hydrophilic polymer film whose dyeability has been modified as described above. In other words, it is a hydrophilic polymer film subjected to dyeing treatment and stretching treatment.The dyeing treatment is performed on the hydrophilic polymer film that has been treated to modify the dyeability, but there are no restrictions on the order of the stretching treatment. . That is, the stretching treatment may be performed as a dyeing modification treatment step, a step before or after the dyeing treatment step, or a simultaneous step of stretching while performing the dyeing treatment. There are no particular limitations on the dyeing treatment conditions and stretching treatment conditions, and known conditions may be applied. General conditions include dye concentration of 0.3° to 15% by weight,
The bath temperature is 15 to 80°C, the dyeing time is 5 seconds to 30 minutes, and the stretching ratio is 1.05 times or more, especially 1.5 to 10 times.

The dye used is generally iodine, dichroic dye, etc., but any dye can be used as long as it can impart polarizing ability to the hydrophilic polymer film.

In this way, the polarizing film of the present invention having regions with different light transmittances is obtained. The thickness of the polarizing film is 10-1
007m is common, but is not limited to this. Further, the arrangement and shape of the regions having different light transmittances, the difference in light transmittance between adjacent regions, etc. may be determined as appropriate depending on the intended use of the polarizing film. Examples of the arrangement, shape, etc. of regions having different light transmittances are shown in FIGS. 1 to 6. In the figure, the hatched area is the stainable modified area, and the density of the dots indicates the degree of light transmittance in inverse proportion to the density. The film shown in Figure 3 is obtained by heat-treating the film using a heat roll that gradually heats up the temperature from the center to both ends. This is a polarizing film that is continuously raised.

Effects of the Invention According to the polarizing film of the present invention, it can be cut to a predetermined size and used as it is as a polarizer having regions with different light transmittances, resulting in a light transmittance suitable for various uses. A polarizing plate having a difference can be easily and efficiently produced.

Further, according to the method of the present invention, it is possible to continuously produce a polarizing film having regions with different light transmittances.
It also has the advantage of being able to obtain the polarizing film with high production efficiency, having a high degree of freedom in arranging regions with different light transmittances, and having a large degree of freedom in adjusting the degree of difference in light transmittance.

Examples Example 1 A polyvinyl alcohol film (saponification degree 99%) with a thickness of 757 m was heated at 80°C, 100°C or 1°C using a hot roll.
After heat treatment at 20 °C and stepwise for 20 m (4 m/min x 5 min contact time), the powder was treated with I in a 1 wt % aqueous solution (40 °C) of the direct dye Direct Sky Blue 5B.
/c for 10 minutes and then stretched 4 times at room temperature to obtain a polarizing film having the light transmittance shown in the table.

Margin Example 2 A polyvinyl alcohol film (saponification degree of 99%) with a thickness of 75 m is stretched 4 times at room temperature, and the width of the central part of the stretched film in the width direction is 5 cm! Continuous heat treatment was performed using a R heat press. This partial heat treatment was performed at 140° C. over a length of 50 m. Next, this heat-treated film was immersed in a 1% by weight aqueous solution of Direct Sky Blue 5B (40°C) for 10 minutes to obtain a polarizing film. The light transmittance of this polarizing film was 93% in the heat-treated part and 43% in the untreated part. From the above example, the degree of difference in light transmittance was different depending on the method of the present invention, and regions with different light transmittances were found. It can be seen that a polarizing film having appropriately arranged polarizing films can be efficiently obtained.

It can also be seen that the method of the present invention can be applied as a method for changing the light transmittance of a polarizing film.

[Brief explanation of the drawing]

1 to 6 show embodiments of the present invention. In the figure, the hatched area is dyed denaturation treatment (heat treatment)
In each section, the dots indicate a degree of light transmission that is inversely proportional to its density.

Claims (1)

[Scope of Claims] 1. A polarizing film having regions with different light transmittances, which is made of a dyed and stretched product of a hydrophilic polymer film that has been subjected to a modification treatment for dyeability. 2. The polarizing film according to claim 1, wherein the hydrophilic polymer film is a polyvinyl alcohol film. 3. (A) a step of heat-treating the hydrophilic polymer film to form a region with modified dyeability; (B) a step of dyeing the hydrophilic polymer film that has undergone the step (A); and (C) Production of a polarizing film having regions with different light transmittances, which comprises a step of stretching a hydrophilic polymer film before, after, or simultaneously with step (A) or step (B). Method.