JPH04204802A - Manufacturing method of polarizing film - Google Patents

Abstract

PURPOSE:To obtain a polarizing film having high accuracy of thickness by uniaxially stretching a film of a mixture of PVA having a high polymn. degree with PVA having a low polymn. degree. CONSTITUTION:When a film of a mixture of two or more kinds of PVA's having different polymn. degrees is uniaxially stretched, PVA having >=2,600 average polymn. degree is blended with PVA having <2,6OO average polymn. degree. PVA is usually produced by saponifying polyvinyl acetate obtd. by polymerizing vinyl acetate, but in this case, the polymer may contain a small amt. of components copolymerizable with vinyl acetate, e.g. unsatd. carboxylic acid (salt, ester, amide or nitrile), olefins, vinyl ethers or unsatd. sulfonate. A polarizing film having high accuracy of thickness based on PVA having a high polymn. degree is obtd. in an industrially advantageous manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polarizing film having excellent film thickness accuracy and a high degree of polarization.

[Prior Art] In recent years, liquid crystal display devices have been used in desktop electronic computers, electronic clocks, word processors, instruments for automobiles and machinery, and the demand for polarizing plates has accordingly increased.

In particular, since instruments 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. , after staining - axis)
After stretching, it is manufactured by performing a durability treatment, preferably with a boron compound.

However, although polyvinyl alcohol films are generally stretched using a wet method, moisture breaks hydrogen bonds between molecules and increases molecular motion, which greatly affects the stretchability of the film. Stable processing may be quite difficult or uneven stretching may occur.

As a result, the durability decreases, that is, the degree of polarization decreases when left in a high humidity atmosphere for a long period of time, which may cause practical troubles.

5 Problems to be Solved by the Invention 1 As one of such countermeasures, it has been proposed to use polyvinyl alcohol with a high degree of polymerization, for example, polyvinyl alcohol with an average degree of polymerization of 2600 or more, as a raw film. In this case, it is not easy to maintain a uniform film thickness, and slight variations in film forming conditions will reduce the film thickness accuracy, resulting in a decrease in the yield of polarizing films. Problems remain.

"Means for Solving the Problems" The present inventors have worked diligently to obtain a highly polymerized polyvinyl alcohol-based polarizing film that is industrially advantageous and has high film thickness accuracy without setting very strict film-forming conditions. As a result of repeated research, the present invention was completed by discovering that the object can be achieved when polyvinyl alcohol having an average degree of polymerization of less than 2,600 is blended with polyvinyl alcohol having an average degree of polymerization of 2,600 or more.

The polarizing film of the present invention is a uniaxially stretched polyvinyl alcohol film made by mixing two or more types of polyvinyl alcohols having different degrees of polymerization. Polyvinyl alcohol is usually produced by saponifying polyvinyl acetate obtained by polymerizing hinyl acetate, or in the present invention, it is not necessarily limited to this. ), difines, vinyl ethers, unsaturated sulfonates, etc., which can be copolymerized with vinyl acetate.

Saponification degree in polyvinyl alcohol is 85-100
A mole %, preferably 98 to 100 mole % is practical.

Further, any average degree of polymerization can be used for the high polymerization degree polyvinyl alcohol of the present invention, but 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. be.

In addition, the average degree of polymerization of low polymerization degree polyvinyl alcohol is 26
Desirably less than 00, preferably 500 to 2000.

The mixing weight ratio of high polymerization degree polyvinyl alcohol and low polymerization degree polyvinyl alcohol is 4/6 to 8/2, preferably 5
15 to 8/2 is advantageous.

When the ratio is 8/2 or more, it is difficult to obtain the effects of the present invention, and when the ratio is 4/6 or less, durability and high polarization properties are deteriorated.

The polyvinyl alcohol film is uniaxially stretched, and the magnification is 3.5 to 10 times, preferably 4.5 to 7 times.
It's double.

The stretching ratio may be finally set within the above range, and the stretching operation may be carried out not only in one step but also in multiple steps at any stage of the manufacturing process.

It is indicated by. Hll is the transmittance (%) measured using a spectrophotometer when two polarizing film samples are stacked so that the orientation direction of the polarizing films is in the same direction, and H is the transmittance (%) of the two polarizing films. Transmittance (
%).

The above film is manufactured by casting a stock solution of polyvinyl alcohol dissolved in water or an organic solvent,
Examples of methods include stretching and dyeing with iodine, or stretching and dyeing simultaneously, but after dyeing with iodine, stretching, and then treating with a boron compound. Examples of solvents used in preparing the stock solution include water, dimethyl sulfokide (DMSO),
), polyhydric alcohols such as N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, amines such as ethylenediamine and diethylenetriamine, and mixtures thereof.

The organic solvent may contain a small amount of water, for example, 5 to 30% by weight. A practical concentration of polyvinyl alcohol in the stock solution is 4 to 10% by weight.

The polyvinyl alcohol film-forming stock solution obtained using the solvent is formed into a film by any method such as a casting method or an extrusion method.

The film forming method is a dry/wet film forming method, that is, the solution is once discharged from a slit in the mouth into the air or into an inert atmosphere such as nitrogen, helium, argon, etc., and then introduced into a coagulation bath and unstretched. Form a film. Alternatively, the film-forming solution discharged from the nozzle may be partially dried on a roller or belt conveyor and then introduced into the coagulation chamber.

The solvent used in the coagulation bath is one that is miscible with the solvent for the highly polymerized polyvinyl alcohol, such as alcohols such as methanol, ethanol, propatool, butanol, acetone, benzene, and toluene.

As a method for obtaining a polyvinyl alcohol film, in addition to the above methods, a method called a so-called gel stretching method can also be employed.

That is, a polyvinyl alcohol film forming stock solution is prepared by dissolving polyvinyl alcohol in a solvent such that the polymer concentration is 30% or less. The solution is discharged into air or an inert atmosphere through a slit-shaped mouthpiece and then introduced onto a surface-cooled roller or belt conveyor or into a coagulating liquid to form a gelled film. The gelled film is stretched after desolvation. The film forming method includes the drying and
It is almost the same as the wet film forming method, but the difference is that a gelled film is formed so that the polymer concentration does not change from the original solution.

In this case, examples of the solvent for the polyvinyl alcohol film-forming stock solution include polyhydric alcohols such as glycerin, ethylene glycol, Trie J-dinoglycol, tetraethylene glycol, and trimethynylpropane, benzenesulfonamide, and caprolactam.

The polyhinyl alcohol unstretched film obtained as described above is then stretched and dyed. Stretching and dyeing may be performed separately or at the same time. When carried out separately, the order of stretching and dyeing is also arbitrary. It is desirable that the film be stretched 3.5 times or more, preferably 4.5 times or more in the uniaxial direction. At this time, it is also possible to perform some stretching (stretching to an extent that prevents shrinkage in the width direction or more) in a direction perpendicular to the above direction. Temperature conditions during stretching are 50-1
It is common to choose from 30°C.

Staining, that is, adsorption of the polarizing element to 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.
The appropriate concentration of iodine is 0.1 to 2 g/(!, the concentration of potassium iodide is 10 to 50 g/ff, and the weight ratio of iodine/potassium iodide is 20 to 100. The dyeing time is about 30 to 480 seconds. It is also practical.In addition to the water solvent, there may be no problem in containing a small amount of a battering machine solvent that is compatible with water.

Any means such as dipping, coating, and spraying can be used as the contacting means.

The stretched and 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/Q, and it is practically desirable that a small amount of potassium iodide be present in the solution.

The treatment method is preferably a dipping method, but of course a coating method or a spraying method is also possible.

The temperature during processing is about 50-70℃, the processing time is 5-20℃.
The stretching time is preferably about 10 minutes, and if necessary, stretching may be performed during or after the treatment.

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. Examples of protective films include conventionally known cellulose acetate films, acrylic films, fluororesin films such as tetrafluoroethylene-hexafluoropropylene copolymers, polyester resin films, and polyolefin resin films. It will be done.

5. Effects] The polarizing film of the present invention has high film thickness accuracy and improved durability under high temperature and high humidity conditions, and its degree of polarization does not decrease even if it is left for a long time.

Taking advantage of these properties, it is used in liquid crystal display applications, and is particularly useful for vehicle applications and displays for various industrial instruments.

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

Example 1 70 parts of polyvinyl alcohol with an average degree of polymerization of 3800 and a saponification degree of 99.5 mol% and polyvinyl alcohol 301 with an average degree of polymerization of 1700 and a saponification degree of 99.7 mol% were dissolved in water to give 5.0% by weight. A concentrated solution was obtained. The liquid was cast onto a polyethylene terephthalate film and dried to obtain an original film. This film was attached to a chuck and immersed in an aqueous solution containing 0.2 g/Q of iodine and 60 g/ρ of potassium iodide for 240 seconds at 30°C, and then 70 g/Q of boric acid.
a. It was immersed in an aqueous solution having a composition of 30 g/'ρ of potassium iodide, and at the same time was subjected to boric acid treatment for 5 minutes while being uniaxially stretched 60 times. Finally, it was dried at room temperature for 24 hours.

Cellulose triacetate membranes having a thickness of 80 μm were laminated on both sides of the film using a 3% by weight aqueous polyvinyl alcohol solution.

The obtained f-co polarizing film had a single transmittance of 44% and a degree of polarization of 99.8%. Further, when this film was left in an atmosphere at 60° C. and 90% relative humidity for 10 days, the monomer transmittance was 45% and the degree of polarization was 985%. In addition, when the film thickness in the middle direction of the film was measured using an Anritsu Electric continuous film thickness meter, the average film thickness was 70μ, the maximum value was 71μ, and the minimum value was 6.
The film thickness accuracy was extremely good at 9μ.

Control Example 1 The same experiment as in Example 1 was conducted except that only polyvinyl alcohol with an average degree of polymerization of 3800 and a degree of saponification of 99.5 mol % was used.

The single transmittance was 44%, the polarization degree was 99.8%, the single transmittance after being left in high humidity was 45%, and the polarization degree was 98.5%, which was good, but the average film thickness was 72μ, the maximum value was 76μ, Minimum value 67
μ, and the film thickness accuracy was poor.

Example 2 50 parts of polyhinyl alcohol with a degree of polymerization of 4,500 and a degree of saponification of 99.3 mol%, and an average degree of polymerization of 1,100 and a degree of opacification of 9
The same experiment as in Example 1 was conducted except that 50 parts of 97 mol% polyvinyl alcohol was used. The results are shown in the table.

Examples 3-4 Average degree of polymerization 150 as low polymerization degree polyvinyl alcohol
The same experiment as in Example 1 was carried out except that one with an average degree of polymerization of 1100 and a saponification degree of 99.7 mol% (Example 4) was used. went.

The results are shown in the table.

Example 5 In Example 1, the raw film was dried at room temperature. Subsequently, the film was stretched 5.0 times in the uniaxial direction at 110°C. The stretched film was mounted on a chuck and treated in an iodine solution and a boric acid solution having the same composition as in Example 1 for 240 seconds and 5 minutes, respectively, and was further stretched 1.3 times. The results are shown in the table.

[Effects] In the present invention, by using polyvinyl alcohol with a low degree of polymerization, a product with high film thickness accuracy can be obtained while maintaining the durability of a polyvinyl alcohol polarizing film with a high degree of polymerization.

Patent applicant: Nippon Gosei Kagaku Kogyo Co., Ltd. Procedural amendment February 4, 1992 . Display of incidents 1990 Patent Application No. 338720 2. Name of the invention polarizing film 3. Person who makes corrections Relationship to the incident: Patent applicant

Claims (1)

[Scope of Claims] 1. A polarizing film obtained by uniaxially stretching a film made of a mixture of a high degree of polymerization polyvinyl alcohol having an average degree of polymerization of 2,600 or more and a low degree of polymerization polyvinyl alcohol having an average degree of polymerization of less than 2,600. 2. The polarizing film according to claim 1, wherein the mixing weight ratio of high polymerization degree polyvinyl alcohol and low polymerization degree polyvinyl alcohol is 4/6 to 8/2. 3. Average polymerization degree as low polymerization degree polyvinyl alcohol is 5.
The polarizing film according to claim 1, characterized in that polyvinyl alcohol of 00 to 2000 is used.