JPS6012367B2 - Manufacturing method of polarizing film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new manufacturing method for providing a polarizing film that has excellent polarizing properties and good durability such as overflow resistance and heat resistance.

In recent years, liquid crystal display systems using polarizing plates with a surface protection film layer provided on at least one side of the polarizing film have expanded in use from small objects such as clocks and desktop computers to large objects such as automobile instruments. This shows a tendency to expand.

Along with this trend, polarizing films that constitute a part of polarizing plates are required to have increasingly high durability and polarizing properties. The following three types of polarizing films forming part of polarizing plates have been known so far.

One of them is the iodine-based type, which is most commonly used for liquid crystal display systems in the above-mentioned small items.L This type of polarizing film is made by, for example, adsorbing and aligning iodine on a polyvinyl alcohol-based film. Due to the release and diffusion of iodine, it is difficult to obtain sufficient moisture resistance and heat resistance, making it unsuitable for large articles requiring high durability. Dichroic dye-based polarizing films similar to such iodine-based types also have the same drawbacks. Another polarizing film is a polyene-based polarizing film obtained by partially dehydrochlorinating a polyvinyl chloride film and then stretching the film in one direction to generate polyene. It has improved green fastness compared to iodine-based or dichroic dye-based polarizing films, but it is not suitable for applications where the polarizing plate comprising the polarizing film is exposed to high temperatures, e.g. 60 qo. For example, when used in automobile display devices, there is a problem that the color tone changes or becomes darker due to the influence of temperature, and there is a need for further improvement in terms of heat resistance.

Yet another polarizing film is a polyene-based polarizing film obtained by partially dehydrating a polyvinyl alcohol film and then stretching the film in one direction to produce polyene. The film has the advantage that it can be used for a relatively long time because it is highly sensitive to the release and diffusion of adsorbed substances (iodine) and darkening at high temperatures, such as polarizing films. During the manufacturing process, because polyene is simply stretched in heated air or superheated steam before or after polyene is produced, the orientation of the segments in the film is not sufficient and the polarizing properties are not necessarily fully satisfactory. Therefore, the object of the present invention is to provide a polarizing film made of a polyvinyl alcohol film that has durability such as green resistance and heat resistance, and sufficient and good polarizing properties.
The present invention provides a method for manufacturing with simple operations.

That is, the present invention comprises a pre-treatment step which includes a step of impregnating a polyvinyl alcohol film with an acid catalyst and a step of stretching it in water; The present invention provides a method for producing a polarizing film characterized by performing a post-treatment step consisting of two steps.

The method of the present invention involves applying an underwater stretching step and a dry heat stretching step to the amorphous region having segments consisting of non-uniform lengths and entanglements that exist in a polyvinyl alcohol film before stretching. By forming an amorphous region having segments of uniform size and directionality, a highly oriented polarizing film is finally obtained.

As the polyvinyl alcohol film used in the present invention, a film made of polyvinyl alcohol alone or a copolymer of the alcohol and polyvinyl acetate is used.

Therefore, in a system made of a copolymer, a film made of a copolymer with a vinyl acetate content of 10 mol% or less, practically 5 mol% or less, is preferable, and if the vinyl acetate content exceeds the above value, Physical strength in an aqueous solution is insufficient, and the desired polarizing film cannot be obtained. Further, the average degree of polymerization of the polyvinyl alcohol or the copolymer of the alcohol and polyvinyl chloride is 1100 to 26
LIIO is preferably 1300 to 2200 for practical purposes.
If it is less than 0, it will swell too much in an aqueous solution or the orientation of the segments will be poor, and if it is more than 2,600, it will be difficult to form a film, which is not preferable. Such a polyvinyl alcohol film is first subjected to a pretreatment process that includes a step of impregnating it with an acid catalyst and a step of stretching it in water.

The step of impregnating the acid catalyst and the step of stretching in water are as follows:
If this order or the reverse order is used to treat polyvinyl alcohol film, and if the stretching process in water is followed by the step of impregnating the acid catalyst, there may be a gap between the two processes as necessary. A drying step for appropriately drying the polyvinyl alcohol film may be included. Next, a process of impregnating a polyvinyl alcohol film with an acid catalyst will be explained.

As the acid catalyst, inorganic acids such as hydrogen chloride, hydrogen bromide, hydrogen iodide, nitric acid, sulfuric acid, phosphoric acid, and shelf acid, and/or organic acids such as valatoluensulfonic acid and acetic acid are used. The acid concentration in the treated aqueous solution that is adjusted to impregnate the polyvinyl alcohol film with the acid catalyst depends on the treatment conditions during the stretching process in water that is performed before or after the impregnation process, and the heat treatment process during the post-treatment process. Although it varies depending on the temperature and time, it is 0.01 to 1% by weight, practically 0.01% by weight.
0.05 to 5% by weight is preferred. Therefore, by setting the acid concentration in the treatment aqueous solution and/or the stretching aqueous solution, the immersion time of the film, etc., the amount of acid catalyst impregnated in the film immediately before the heat treatment step is 10 × 10-4 to 200 ×
10-4 ta'ta polymer, preferably 20x10-4~
The adjustment to 100 x 10-4 ta' polymer is desirable for providing the film with good polyene-forming ability and for producing polarizing films on an industrial basis.

The temperature of the treated aqueous solution is 0 to 70 qo, practically 0
-30oo is preferable, and if it is outside this range, it is not preferable because it may not be possible to reliably impregnate the acid catalyst or uneven coloring may occur due to non-uniform impregnation. A process of stretching a polypynyl alcohol film impregnated with or not impregnated with an acid catalyst in water will be described.

The temperature in the aqueous solution for stretching is 0 to 40 qo, preferably 0 to 40 qo.
Set to 3000 cold water. The temperature of the aqueous solution is 000
If it is less than 4 pi, the desired uniform stretching cannot be achieved, and if it is more than 4 pi, the degree of swelling of the film becomes too large and good segment orientation cannot be obtained. The above-mentioned acid catalyst can be added to the aqueous solution as necessary, and when stretching a polyvinyl alcohol film impregnated with an acid catalyst in advance in an aqueous stretching solution, from the viewpoint of preventing desorption of the acid catalyst, Addition of a small amount of acid catalyst to the aqueous solution is preferred. The polyvinyl alcohol film introduced into the aqueous stretching solution set in this manner is heated to approximately 1.1
It is stretched to a magnification of ~6 times, preferably 1.5 to 4 times. The polyvinyl alcohol film, which has been impregnated with an acid catalyst and subjected to a pretreatment process of stretching to a predetermined ratio, is then subjected to post-treatment consisting of a first process of dry hot stretching and a second process of heat treatment. The process produces a polarizing film with good durability and polarizing properties, which are the objectives of the present invention. Therefore, if the stretched polyvinyl alcohol film that has been subjected to the pre-treatment process and is transferred to the post-treatment process contains 0.1 to 2% by weight, preferably 1 to 10% by weight of water, the following: This is desirable because it not only improves the workability of the post-processing process, but also contributes to improving the orientation of the segments.

Although it is not difficult for a skilled person to determine the moisture content of such a film empirically even if it is air-dried in the pretreatment process, it is possible to make it uniform by passing it through a drying process set under predetermined conditions. Setting the water content to a certain level is preferable in order to reduce variations in quality of the final product, the polarizing film. In the case where the drying step is used in the above, the drying method may be a general method such as contacting with a heated metal drum or passing through heated air. The stretched polyvinyl alcohol film that has been subjected to such a pretreatment step and a drying step if necessary is then introduced into a dry stretching step, and is further increased by 1.1 to 5 times, preferably 1.5 to 4 times. It is stretched to

Therefore, the product of the stretching ratio in water during the pretreatment step and the further stretching ratio under dry heat, the total stretching ratio is 3.
It is necessary to adjust it to ~8 times, or practically 4 to 7 times, and if it is outside this range, there will be problems such as not being able to obtain good polarization characteristics, which is not preferable. It should be noted that the temperature during dry heat stretching is preferably about 80 to 16 mm; outside this range, there are problems such as poor stretching workability and insufficient polarization properties. Dry heat stretching treatment does not require the use of any separate equipment; for example, one equipped with a heating device between a film supply roll and a take-off roll, or one consisting of a heated supply V-feed roll and a low-temperature take-off roll. is used. The dry-heat stretched film is heat-treated at 100 to 180 qo, practically 120 to 150° C., to produce polyethylene, thereby producing a polarizing film.

If the heat treatment temperature is less than 100 qo, it takes a long time and it is not possible to economically produce polyene, and if it is more than 180 qo, carbonyl groups are produced due to oxidation which deteriorates the polarizing properties in addition to polyene, which is undesirable. . A polarizing film produced by subjecting a polyvinyl alcohol film to the above-mentioned pre-treatment and post-treatment processes is free from uneven lengths and entanglements contained in the amorphous regions present in the polyvinyl alcohol film. Because the segments are converted into segments of uniform length and highly directional, they have excellent durability such as moisture resistance and heat resistance, and polarization properties.

The reason why the polarizing film obtained by the production method of the present invention has such good durability and polarizing properties is considered to be because the polyvinyl alcohol film is stretched in cold water in the pretreatment step.

In other words, in polyvinyl alcohol films, crystalline regions and amorphous regions are randomly oriented, and the amorphous regions are formed from segments of non-uniform length and entanglement. By immersing the film in the film and stretching it, the film undergoes appropriate swelling, destruction of some crystalline regions, and disentangling of segments in the amorphous region, and the length is made uniform by a limited stretching ratio. This is thought to be because an amorphous region having a moderate degree of directionality is formed, and the segments of the amorphous region become highly oriented due to further dry heat stretching. A good polarizing film produced by the production method of the present invention has a surface protection film layer formed on one or both sides of the film, and is used by being incorporated into a liquid crystal display device of various articles.

The surface protection film layer is made of optically transparent synthetic resins, and these resins can be applied to the polarizing film surface and cured to form a coating, or the resins can be preformed into a film. It is formed by pasting.

Examples of resins that can be applied and cured on the surface of a polarizing film to form a resin coating include polyacrylic polymer resins and polyurethane resins, and examples of resins that can be formed into a film and then attached are Cellulose acetate resin, polyacrylic resin, polycarbonate resin, etc. are used.

The polarized light plate, which has a surface protection film layer formed on one or both sides of the polarizing film, can be further bonded with a reflective plate such as an aluminum plate having a satin-like surface on one side, or it can be made to have light diffusion and transparency. For example, by bonding styrene vapor with an adhesive substance (added with an appropriate amount of titanium oxide, pearl pigment, etc.) that imparts light diffusing and transmitting ability, it becomes a light diffusing and transmitting and reflecting body.
It can be used in combination with articles having other functions. Examples of the present invention will be shown below.

Example 1 A polyvinyl alcohol-vinyl acetate copolymer (bonded acetate group 0.2 mol %) with an average degree of polymerization of 1300 and a thickness of 7
A film of 0.0 μm was immersed in a treated aqueous solution containing 1% by weight of hydrogen chloride (water temperature: 30°C) for 10 minutes.

Next, the film was stretched to 2.3 degrees in one direction in an aqueous stretching solution (water temperature 1.5 qo) containing 0.2% by weight of hydrogen chloride, and then dried for 15 minutes in a heating chamber maintained at 65 qo. do. Next, this stretched film was further stretched 2.4 times (total stretching ratio 6 times) in a heating furnace at 120°C, and then 13 times
000 for 10 minutes to obtain a polarizing film.

Comparative Example 1--The same film as in Example 1 was heated at 170o
After dry heat stretching to 6 times in a heating furnace of
% by weight aqueous solution (water temperature 30°C) for 3 minutes. Next, after wiping off the aqueous solution on the surface, it was dried at 8,000 for 5 minutes and further treated at 15,000 for 30 minutes to obtain a polarizing film. Comparative Example 1-B The same film as in Example 1 is immersed in an aqueous solution containing 1% by weight of hydrogen chloride (water temperature: 30 qo) for 1 minute.

Next, an aqueous solution of 0.5% by weight of hydrogen chloride (water temperature 1.5°C)
While immersed in water, it is stretched 5 times for 12 minutes. This is 65
00 for 15 minutes and heat treated at 130 qo for 18 minutes to obtain a polarizing film. Example 2 A powder of polyvinyl alcohol monovinyl acetate copolymer (2 mol% of bonded acetic acid groups) having an average degree of polymerization of 1700 was dissolved to obtain 1
After forming a 5% aqueous solution, it was cast onto a release liner so that the thickness after drying was 75 mm, and polyvinyl alcohol-
A pinyl acetate copolymer film is obtained.

Next, the film was coated in a treated aqueous solution containing 2% by weight of sulfuric acid (water temperature: 50% by weight).
0) for 5 minutes.

This was added to an aqueous stretching solution containing 0.1% by weight of sulfuric acid (water temperature: 0.5°C).
) and then dried at 65% for 15 minutes.

Next, it is stretched 2 times in a heating furnace at 110 oo (total stretching ratio 6 times)
This is heat-treated at 140:00 am for 15 minutes to obtain a polarizing film. Example 3 A polyvinyl alcohol-vinyl acetate copolymer (bonded acetic acid 1.4 mol%) with an average degree of polymerization of 1500 and a thickness of 70
The mountain film is soaked for 5 minutes in a treated aqueous solution of baratluensulfonic acid (water temperature 30°C).

The film was then treated with 0.0 valatluene sulfonic acid.
The film is stretched twice in one direction in a 2% by weight aqueous stretching solution (water temperature 1.5°C), and then dried at 65°C for 19 minutes.
Next, this stretched film is stretched twice between a 110 qC heating supply roll and a 15 qo take-off roll (total stretching ratio: 4 times), and is further heat-treated at 130 qC for 10 minutes to obtain a polarizing film.

Example 4 The same film as in Example 1 is soaked for 5 minutes in a treated aqueous solution (water temperature 15qC) containing 0.8 weight of hydrogen chloride.

Next, the film is stretched twice in one direction in an aqueous stretching solution (water temperature: 2°C) containing 0.1% by weight of hydrogen chloride, and then dried at 70°C for 10 minutes. Next, this stretched film is
The film was stretched 3 times (total stretching ratio: 6 times) in a heating furnace at 20:00, and further heat-treated at 135° C. for 7 minutes to obtain a polarizing film.

Next, the test results of Examples 1 to 4 and Comparative Examples 1 to 1 are shown in Table 1.

The polarization ratio as a measure of polarization characteristics shown in Table 1 was determined using the following formula.

Polarization rate (%) = No Kansan Ashi X,.

. However, Ho is the parallel average transmittance at 450 to 70 degrees (transmittance when two polarizing films are arranged so that their coaxes are parallel to each other), and Ho is the average transmittance at 450 to 70 degrees.
Orthogonal average transmittance at 0 touch (transmittance when two polarizing films are arranged so that their edges are perpendicular to each other)
It is.

Table 1 (number of units) The polarizing film obtained by the production method of the present invention is notable for having good polarizing properties, as is clear from the above examples.

Since polyvinyl alcohol film is used as the starting material for the polarizing film, it has excellent durability such as temperature resistance and heat resistance. Therefore, a polarizing plate using the polarizing film obtained by the manufacturing method of the present invention as a polarizer can be usefully used in liquid crystal display devices ranging from small items such as watches and desktop computers to large items such as automobiles and meters. It is.

Claims (1)

[Scope of Claims] 1. A pretreatment step that includes a step of impregnating a polyvinyl alcohol film with an acid catalyst and a step of stretching it in water, a first step of dry heat stretching, and a heat treatment to produce polyene. 1. A method for producing a polarizing film, comprising: a second step of producing a polarizing film; and a post-processing step of producing a polarizing film. 2. The method for producing a polarizing film according to claim 1, wherein the pretreatment step is performed in the order of impregnation with an acid catalyst and stretching in water. 3. The method for producing a polarizing film according to claim 1, wherein the pretreatment step is performed in the order of stretching in water and impregnation with an acid catalyst. 4. The method for producing a polarizing film according to claim 3, wherein a drying step is performed between the step of stretching in water and the step of impregnating with an acid catalyst. 5. The method for producing a polarizing film according to claim 1, wherein a drying step is performed between the pre-treatment step and the post-treatment step. 6 The average degree of polymerization of the polyvinyl alcohol film is 1
100 to 2600. The method for producing a polarizing film according to any one of claims 1 to 5. 7 The amount of acid catalyst impregnated into the polyvinyl alcohol film is 10 x 10^-^4 to 200 x 10^-^4 g
6. A method for producing a polarizing film according to any one of claims 1 to 5, which is a /g polymer. 8. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the temperature during stretching in water is 0 to 40°C. 9. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the stretching ratio in water is 1.1 to 6 times. 10. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the polyvinyl alcohol film has a water content of 0.1 to 20% by weight before dry heat stretching. 11
The method for producing a polarizing film according to any one of claims 1 to 5, wherein the temperature during dry heat stretching is 80 to 160°C. 12. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the stretching ratio during dry heat stretching is 1.1 to 5 times. 13. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the total stretching ratio of stretching in water and dry heat stretching is 3 to 8 times. 14. The method for producing a polarizing film according to any one of claims 1 to 5, wherein the heat treatment temperature is 100 to 180°C.