JPH04173125A - Manufacture of polarizing film - Google Patents

Abstract

PURPOSE:To contrive to improve the polarizing performance and durability of the film concerned by a method wherein uniaxial stretching of highly polymerized polyvinyl alcohol-based film having specified thickness and complete fusion temperature is performed during at least either one of dyeing process or boron compound treating process. CONSTITUTION:Polyvinyl alcohol stock film having a mean degree of polymerization of 2,600 or more, preferably 3, 500-5,000 has film thickness of 30-100mum, preferably 50-90mum. The complete fusion temperature of the shock film in hot water is 65-90 deg.C, preferably 71-80 deg.C. When the stock film is uniaxially stretched during at least either one of dyeing process on boron compound-treating process, the durability at high temperature and humid state of the obtained polarizing film is improved and its degree of polymerization does not lower even after being left as it is over a long period of time. Consequently, when uniaxial stretching during the boron compound-treating process is intended, the stock film is immersed in water solution consisting of 0.2g/l of iodine and 60g/l of potassium iodide at 30 deg.C for 240 sec and, at the same time, uniaxially stretched at a draw ratio of 120% and, after that, immersed in water solution having the composition of 60g/l of boric acid and 30g/l of potassium iodide and, at the same time, uniaxially stretched at a draw ratio of 600% and then subjected to boric acid treatment over 5min and finally dried at room temperature for 24hr.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polarizing film that is highly durable and has a high degree of polarization.

[Prior Art] In recent years, liquid crystal display devices have been used in electronic calculators, electronic clocks, word processors, instruments for automobiles and machinery, and the demand for polarizing plates has increased accordingly. In particular, since instruments and home appliances used in the kitchen are often used under harsh conditions, films with high durability and a high degree of polarization are required.

One of the typical polarizing films currently known is a polyvinyl alcohol film dyed with iodine and a film dyed with a dye. 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 polyvinyl alcohol-based polarizing film described in 2., the iodine-dyed product has good polarizing performance, but has poor moisture resistance and heat resistance, and cannot be used in high-humidity or high-temperature environments. On the other hand, dye-dyed products have the disadvantage of poor polarization performance due to a decrease in the degree of polarization of the surface exposed to the surface, which is called poor durability.On the other hand, dye-dyed products have the advantage of having poor polarization performance but excellent durability.

As described above, polyvinyl alcohol-based polarizing films have advantages and disadvantages, and the reality is that it is necessary to use them appropriately depending on the performance required for their final use.

Therefore, if a polyvinyl alcohol-based polarizing film with excellent polarizing performance and durability could be developed, it would be extremely useful in industry, including expanding its uses.

[Means for Solving the Problems J] As a result of intensive research in order to solve such problems, the inventors of the present invention have conducted uniaxial stretching of polyvinyl alcohol-based raw films in at least one of the dyeing process and the boron compound treatment process. When producing a polarizing film, a polyvinyl alcohol film having a thickness of 30 to 100 μ as an original film and a complete dissolution temperature of 65 to 90 °C in hot water, especially a polyvinyl alcohol film with an average degree of polymerization of 2600 or more is used. The inventors have discovered that the object can be achieved by using a polyvinyl alcohol film, and have completed the present invention.

As mentioned above, such effects of the present invention can be obtained by using a polyvinyl alcohol film having a specific thickness and complete dissolution temperature, preferably a product with a high degree of polymerization, and by adopting specific stretching conditions. . The present invention will be specifically explained below.

The polarizing film of the present invention is a uniaxially stretched 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. ), olefins,
It may contain components copolymerizable with hinyl acetate, such as vinyl ethers and unsaturated sulfonates. The average degree of saponification in polyvinyl alcohol is 85 to 100 mol%
Preferably 98 to 100 mol% is practical.

In order to obtain the effects of the present invention, it is advantageous that the average degree of polymerization is 2,600 or more, preferably 3,500 to 5,000. 260
If it is less than 0, it is difficult to obtain significant effects. The polyvinyl alcohol is formed into a film according to a known method. A common method is to dissolve polyvinyl alcohol in water, an organic solvent, a mixed solvent of water/organic solvent, etc., and then cast the solution. A practical concentration of the solution is about 5 to 20% by weight. In addition, a so-called gel film forming method in which a polyvinyl alcohol solution is introduced into a coagulation bath to form a film can also be implemented. The raw film needs to have a thickness of 30 to 100 microns, preferably 50 to 90 microns. If it is less than 30μ, it will not be possible to stretch, and if it is more than 100μ, the film thickness accuracy will decrease, making it unsuitable. And the film has a complete dissolution temperature in hot water of 65 to 90°C, preferably 71 to 8°C.
Must be 0°C.

Such a specific film can be easily prepared by heat-treating a polyvinyl alcohol film, but in any case, only by using a film with such properties can uniaxial stretching be carried out during the dyeing process or the boron compound treatment process. It becomes possible to implement it. In other words, a film with a complete dissolution temperature of 65°C or lower is not practical due to partial melting or deterioration during stretching;
If the temperature is above ℃, sufficient stretching may not be carried out,
Troubles tend to occur during stretching, making it difficult to obtain the desired polarizing film.

In addition, the complete melting temperature in the present invention is 2000 m in a 2a beaker.
After adding 1 liter of water and raising the temperature to 30℃, 2 cm x 2 c
The water temperature is defined as the temperature at which the film is completely dissolved by adding m film pieces and increasing the water temperature at a rate of 3° C./min while stirring.

A polarizing film is produced by stretching, dyeing, and treating the above raw film with a boron compound. In the present invention, uniaxial stretching is carried out during at least one of the dyeing process and the boron compound treatment process, preferably during the reprocessing. Implementation is essential. - It is difficult to obtain a durable polarizing film even if a stretched film is dyed or treated with boron, or even if the film is uniaxially stretched after dyeing or boron compound treatment.

Iodine dyeing, that is, adsorption of the polarizing element onto the film, is carried out by bringing the film into contact with a liquid containing the polarizing element. Usually, an aqueous solution of iodine-potassium iodide is used, and the appropriate concentration of iodine is 01-29/a, the concentration of potassium iodide is 10-509/ρ, and the weight ratio of iodine/potassium iodide is 20-100. be. A practical dyeing time is about 30 to 500 seconds. The temperature of the treatment bath is preferably 30 to 80°C. In addition to the water solvent, a small amount of an organic solvent compatible with water may be included.

As the contact means, dipping is preferred, but any means such as coating or spraying can also be applied.

The dyed film is then treated with a boron compound. Practical boron compounds include boric acid and borax. 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 2,
It is practically desirable that a small amount of potassium iodide coexist in the liquid. As the treatment method, a dipping method is preferable, but a coating method and a spraying method are also possible. The temperature during processing is about 50-70℃,
The treatment time is preferably about 5 to 20 minutes.

In the present invention, as described above, uniaxial stretching must be carried out during at least one of the dyeing process and the boron compound treatment process.

The polarizing film of the present invention is finally uniaxially stretched 2 to 8 times, preferably 3 to 6 times, but it is practical to carry out this stretching in both steps. When stretching in both steps, the dyeing step is 12 to 2 times, preferably 1
．． 2 to 1.5 times, preferably 2 to 6 times, preferably 2 to 4 times in the boron compound treatment step.

To stretch within this range, roll stretching, tenter stretching, etc. may be optionally carried out, but the former is usually carried out. Roll stretching can be carried out either in a single stage or in a multistage manner.

The polarizing film thus obtained is used as a polarizing plate by laminating a protective film with excellent optical transparency and mechanical strength on both or one side thereof and drying it. Examples of the protective film include conventionally known cellulose acetate films, acrylic films, polyester resin films, polyolefin resin films, polycarbonate films, polyether ether ketone films, and polysulfone films.

[Function] The polarizing film of the present invention has improved durability under high temperature and high humidity conditions, and its degree of polarization does not decrease even if left for a long period of time. Taking advantage of these properties, it is used in liquid crystal display applications, and is particularly useful for vehicle applications, various industrial instruments, displays for household electrical appliances, and the like.

[Example] Next, the polarizing film of the present invention will be explained in more detail by giving examples.

In addition, the polarization degree referred to in the present invention is Hll when two polarizing film samples are stacked together so that the polarizing films are oriented in the same direction, and measured using a spectrophotometer. Transmittance (%), H, measured using H is the transmittance (%) measured when two samples are stacked so that the orientation directions of the polarizing films are perpendicular to each other. It is.

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 an aqueous solution having a concentration of 8.0% by weight. The vaginal fluid was cast onto a polyethylene terephthalate film and dried to obtain a film with a thickness of 80 μm. This film was heat-treated at 150°C for 2 minutes to obtain a film having a complete dissolution temperature of 72°C. The film was cut to a width of 10 cm and attached to a chuck.

Iodine 0,2 g/(1, potassium iodide 60
240 seconds at 30°C in an aqueous solution consisting of
At the same time, it was uniaxially stretched 1°2 times, and then 60g/ρ of poric acid,
It was immersed in an aqueous solution having a composition of 30 g of potassium iodide and Q, and at the same time was subjected to a poric acid treatment for 5 minutes while being uniaxially stretched 6 times.

Finally, it was dried at room temperature for 24 hours. A polyvinyl alcohol aqueous solution was used as an adhesive on both sides of the film to give a film thickness of 8.
A polarizing plate was obtained by pasting 0μ triacetylcellulose and drying at 50°C. The single transmittance of this polarizing plate is 445%,
The degree of polarization was 99.5%. 60 more copies of this film
When the same measurement was performed after leaving it in an atmosphere of 90% relative humidity at 1°C for 40 days, the single transmittance was 44.8% and the degree of polarization was 99.3%.

Further, when a heat resistance test was carried out by leaving it in a dry atmosphere at 80° C. for 40 days, the single transmittance was 44.4% and the degree of polarization was 99.5%.

Control Example I The same experiment as in Example 1 was conducted using polyvinyl alcohol with an average degree of polymerization of 3800 and an average degree of saponification of 995 mol % (no heat treatment, complete dissolution temperature 65° C.).

Immediately after manufacturing, the single transmittance of the polarizing plate is 440%, and the degree of polarization is 9.
8.7%, 60℃, relative humidity 90%, number of days left 4
Single transmittance after 0 days is 454%, polarization degree is 97.5%
Met.

Single transmittance after heat resistance test is 45.1%, degree of polarization is 97
It was 8%.

Comparative Example 2 The same experiment as in Example 2 was carried out except that a film having a complete dissolution temperature of 100° C. was used, but dyeing was not possible.

Example 2 Polyvinyl alcohol film with an average degree of polymerization of 4500 and an average strength of 99.3 mol% (complete dissolution temperature 72 ° C., film thickness 75
The same experiment as in Example 1 was conducted except that μ) was used.

The single transmittance of the polarizing plate immediately after manufacture is 44.5%, and the degree of polarization is 9.
9.8%, 60℃, relative humidity 90%, number of days left 4
Single transmittance after 0 days is 446%, polarization degree is 99.7%
Met. After the heat resistance test, the single transmittance was 44.5% and the degree of polarization was 99.8%.

Comparative Examples 3 to 4 The original film used in Example 1 was stretched 5 times at 60°C, and then dyed and treated with a boron compound in the same manner as in the same example. (Comparative Example 3) Further, the raw film used in Example 1 was subjected to only dyeing and boron compound treatment under the same conditions as in Example 1, and then stretched five times.

The results were as follows.

Control example 3 Control example 4 Single transmittance Degree of polarization Single transmittance Degree of polarization Immediately after manufacture 44,0 98.7 45,
0 98.6 After durability test 45,4 9
7,5 45.3 97.4 After heat resistance test 45,1 97.8 45,2
97.6 [Effect] In the present invention, a polarized film with excellent durability is obtained by using a specific polyvinyl alcohol film and stretching the resin film during at least one of the dyeing process and the boron compound process. is obtained.

Patent applicant Nippon Gosei Kagaku Kogyo Co., Ltd. February 4, 1992

Claims (1)

[Claims] 1. When manufacturing a polarizing film by uniaxially stretching a polyvinyl alcohol-based raw film in at least one of the dyeing process and the boron compound treatment process, the raw film has a thickness of 30 to 100 μm. 1. A method for producing a polarizing film, characterized by using a polyvinyl alcohol film having a polyvinyl alcohol film having a complete dissolution temperature of 65 to 90°C in hot water. 2. Claim 1, characterized in that a polyvinyl alcohol film having a complete dissolution temperature in hot water of 71 to 80°C is used.
Manufacturing method described. 3. The manufacturing method according to claim 1, characterized in that a polyvinyl alcohol base film having an average degree of polymerization of 2,600 or more is used.