JPH0122601B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polarizing film made of vinyl alcohol polymer. A polyvinyl alcohol-based polarizing film is produced by adsorbing a polarizing element such as iodine or a dichroic dye onto a polyvinyl alcohol film and stretching the film. However, the method of adsorbing a polarizing element after film formation has the following problems, which significantly limits mass productivity. (1) Since the polarizing element is adsorbed in an aqueous system, the strength of the polyvinyl alcohol film, which originally has poor water resistance, decreases, and the film may break or lose dimensional stability during the adsorption operation. (2) Since it is difficult to remove water after the adsorption treatment of the polarizing element, the dyeing in the areas where water droplets remain becomes lighter, which tends to cause uneven dyeing. (3) Since the polarizing element is adsorbed only to the surface layer of the film, imparting polarizing ability is not necessarily sufficient. However, as a result of intensive research by the present inventors,
By skillfully combining "undiluted solution dyeing" in which a polarizing element is added to the stock solution used for film formation, and "film dyeing" in which the polarizing element is adsorbed to the film after film formation, the above problems can be completely resolved. I found out what I can do. That is, the present invention provides vinyl alcohol polymer 100
A process of stretching a film formed from a vinyl alcohol polymer solution containing a polarizing element in an amount of 0.1 to 2.5 parts by weight, and containing a polarizing element before, after, or simultaneously with the stretching of the film. It is characterized in that it is combined with a step of bringing it into contact with a liquid. Now, if you try to achieve the desired polarizing ability only by "undiluted solution dyeing", you will have to increase the amount of polarizing element added to the undiluted solution, but this will increase the viscosity of the undiluted solution and cause it to lose its ductility. In addition to significantly inhibiting film formability, the film strength is reduced, causing troubles such as the film being more likely to break during take-off or stretching. On the other hand, according to the present invention, the amount of the polarizing element added to the stock solution can be adjusted appropriately within the range of 0.1 to 2.5 parts by weight per 100 parts by weight of the vinyl alcohol polymer. Neither film formability nor stretchability is particularly impaired. In addition, the film produced from the stock solution containing an appropriate amount of polarizing element has improved water resistance, so there will be no wrinkles or sagging during the next "film dyeing" process, and the dimensional stability will be reduced. It won't happen. As a result, in the present invention, polarizing films can be produced stably in large quantities, and the amount of polarizing elements contained in the film includes the amount of undiluted dyeing in addition to the amount of conventional film dyeing.
A polarizing film with extremely good polarizing ability can be obtained. Examples of the vinyl alcohol polymer in the present invention include ordinary polyvinyl alcohol, unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, α-olefins having 2 to 30 carbon atoms, and less than about 15 mol%. Copolymerized modified polyvinyl alcohol, polyvinyl formal, polyvinyl acetoacetal, polyvinyl acetal such as polyvinyl butyral, ethylene content 15~
Examples include saponified 55 mol% ethylene-vinyl acetate copolymer. Polarizing elements include iodine and various dichroic dyes, and potassium iodide, boric acid, and other auxiliaries are often used. A mixture of two or more types of polarizing elements can also be used. The polarizing element for "undiluted solution staining" and the polarizing element for "film staining" may be of the same type or different types. Further, the appropriate amount of the polarizing element to be used is 0.1 to 2.5 parts by weight per 100 parts by weight of the vinyl alcohol polymer. If the amount is less than 0.1 part by weight, no practical effect will be exhibited in the formed film. If it exceeds 2.5 parts by weight, it becomes difficult to form a film and is not practical. The vinyl alcohol polymer solution refers to a solution in which the vinyl alcohol polymer as described above is dissolved in a solvent such as water, an organic solvent, or a water-alcohol mixed solvent. When the vinyl alcohol polymer is polyvinyl alcohol, water is usually used as the solvent, and when the saponified ethylene-vinyl acetate copolymer is used, an alcohol-water mixed solvent is usually used as the solvent. Film formation is performed after adding a polarizing element to this solution. Film formation is performed by a casting method, a solution coating method, an extrusion method, or the like. The film thus obtained is subjected to "stretching" and "adsorption of a polarizing element". It is desirable that the stretching be carried out by a factor of two or more in the uniaxial direction. In particular, it is often set to 2.5 to 6 times. At this time, there is no problem in carrying out a slight stretching in the direction perpendicular to the above direction (stretching to an extent that prevents shrinkage in the width direction or more). Temperature conditions during stretching are room temperature to 180℃
It is common to choose from a range of degrees Celsius. Adsorption of the polarizing element onto the film is performed by contacting the film with a liquid containing the polarizing element. Although water is usually used as the liquid, other organic solvents or a mixed solvent of water and an organic solvent can also be used. Any means such as dipping, coating, and spraying can be used as the contacting means. The polarizing element suction operation described above is performed before or after the film is stretched, or simultaneously with the film stretching. "Simultaneous with stretching" refers to a case where stretching is performed in a polarizing element-containing liquid. Next, the method of the present invention will be further explained with reference to Examples. Hereinafter, "parts" refer to parts by weight. Example 1 Polyvinyl alcohol (degree of polymerization 1700, degree of saponification
99.5 mol%) in 1000 parts of a 15% aqueous solution of 3.6 iodine
%, potassium iodide 8.5%, and boric acid 1.75% are added and mixed, and this stock solution is cast onto an endless belt to form a film at a temperature of 80°C to form a film with a thickness of 65μ and a volatile content of 5.3%. I got the film. After passing this film through an aqueous solution (temperature 45°C) containing iodine 1.3g/, potassium iodide 3.0g/, and boric acid 0.62g/, the adhering water was squeezed out with a roll, and then air was blown at a temperature of 80°C. It was passed through a dryer to dry to a moisture content of 4.8%, then stretched 3.5 times in the longitudinal direction at a temperature of 85°C using a roll-type stretching machine, and heat-set at a temperature of 185°C. The results are shown in Table 1. Control example 1 Polyvinyl alcohol (polymerization degree 1700, saponification degree
99.5 mol%) in 100 parts of a 20% aqueous solution of 3.6 iodine
%, potassium iodide 8.5% and boric acid 1.75%.
Endless belt casting was difficult, but it was possible to form a film on a glass plate using a hand applicator. It was also difficult to stretch this film, and only a few products stretched 2.5 times were obtained. Control Example 2 In Control Example 1, the amount of dyeing liquid added was reduced to 10 parts and 40 parts of water was added to perform endless belt casting film formation. The obtained film was stretched 3.5 times in the longitudinal direction at a temperature of 85°C using a roll-type stretching machine, and was heat-set at a temperature of 185°C. Control Example 3 A film was formed in Example 1 without adding the dyeing solution, and the film was dyed and stretched in the same manner as in Example 1. The results of Control Examples 1 to 3 are shown in Table 1.

[Table] Example 2 The film formed in Example 1 was first stretched 3.5 times in the longitudinal direction, and then the stretched film was passed through a dyeing bath. Other conditions were the same as in Example 1. Stretchability and water resistance during film dyeing were both good, and there was no uneven dyeing of the polarizing film. The total light transmittance was 48.3% for the two parallel sheets and 2.8% for the two sheets orthogonal, which was slightly lower than in Example 1, but since this was dyeing after orientation, the amount of iodine adsorbed was slightly higher. This is probably because there are fewer of them. Example 3 Saponified ethylene-vinyl acetate copolymer (ethylene content 30 mol%, degree of saponification of vinyl acetate component 99)
Dissolve 115 parts (mol%) in 300 parts of a 50:50 mixed solvent of n-propanol and water, and add 2.2 parts of iodine, 5.2 parts of potassium iodide, and boric acid to this solution.
A staining solution prepared by dissolving 1.10 parts in 85 parts of the above mixed solvent was added. A coating device equipped with a doctor coater and a blow dryer was prepared, a polyester film was supplied to the device, and the room temperature stock solution prepared above was charged into the liquid reservoir to start film formation. The time from the coater to the dryer entrance is 47 seconds, air is blown at 10m/sec inside the dryer, the temperature is set to 70℃ at the dryer entrance and 120℃ at the exit, and the residence time in the dryer is 65 seconds. I made it so that The film that came out of the dryer was peeled off from the polyester film and wound up on a winder. Through the above operations, a film with a thickness of 30 μm and a volatile content of 4.8% was obtained. Next, this film was dyed in an aqueous solution containing 1.3 g of iodine, 3.0 g of potassium iodide, and 0.62 g of boric acid at a temperature of 45 DEG C., and simultaneously stretched four times in the longitudinal direction. After stretching, the adhered water was squeezed out using rolls, and the film was dried by passing it through a blow dryer at a temperature of 80°C. The results are shown in Table 2. Control Example 4 The amounts added to the solution in Example 3 were 3.3 parts of iodine, 7.8 parts of potassium iodide, and 1.65 parts of boric acid. Note that if the amount of dyeing solution added is larger than this, film formation becomes difficult. Using this stock solution, film formation was carried out in the same manner as in Example 3, and then the obtained film was stretched 4 times in the longitudinal direction in water at a temperature of 45° C. and dried. Comparative Example 5 A film was formed in Example 3 without adding a dyeing solution, and then stretched in a dyeing bath in the same manner as in Example 3. The results of Control Examples 3 and 4 are also shown in Table 2.

[Table] Note that the saponified ethylene-vinyl acetate copolymer film is less colored by a dyeing bath and has a lighter tone than a polyvinyl alcohol film, so the combined method of stock solution dyeing and film dyeing of the present invention is particularly effective. Example 4 Saponified ethylene-vinyl acetate copolymer (ethylene content 40 mol%, degree of saponification of vinyl acetate component
98.5 mol%) was dissolved in 300 parts of a mixed solvent of 55:45 by weight of isopropanol and water, and 2.2 parts of iodine, 5.2 parts of potassium iodide, and CI
A solution of 5 parts of Direct Yellow 11 dissolved in 85 parts of the above mixed solvent was added. This stock solution was cast onto an endless belt to form a film to obtain a film having a thickness of 29.5 μm and a volatile content of 5.8%. This film was heated to 45℃ containing 1.33g of iodine, 3.0g of potassium iodide, and 0.62g of boric acid.
After passing through an aqueous solution at a temperature of Heat-fixed at 115°C. Both film formability and stretchability were good, and there was no uneven dyeing. The polarization ability was 46.2% for two parallel lenses and 1.3% for two orthogonal lenses, which were favorable. On the other hand, when the film was formed without adding a dyeing solution and the film was dyed and stretched in the same manner as in Example 4, the polarizing ability was only 51.3% when the two films were parallel and 6.3% when the films were orthogonal. .

Claims (1)

[Claims] 1 per 100 parts by weight of vinyl alcohol polymer
Stretching a film produced from a vinyl alcohol polymer solution containing 0.1 to 2.5 parts by weight of a polarizing element, and contacting the film with a liquid containing a polarizing element before, after, or simultaneously with the stretching. A method for producing a polarizing film characterized by combining with.