JP2001174634A - Method of producing polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method pf producing a polarizing film which makes it possible to produce a liquid crystal display device where so-called white voids are hardly generated. SOLUTION: In the production method of a polarizing film, a uniaxially stretched polyvinylalcohol resin film dyed with a dichroic dye and treated with boric acid is washed with water and then dried while applying tension. The tension (A) (N/m) per unit width of the film and the temperature (B) ( deg.C) satisfy the inequality (1): A<=0.1225B2-9.947B+376.32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a polarizing film.

[0002]

2. Description of the Related Art A polarizing film is useful as one of optical parts constituting a liquid crystal display. 2. Description of the Related Art Conventionally, as a method for manufacturing a polarizing film, a method in which a uniaxially stretched polyvinyl alcohol resin film dyed with a dichroic dye is subjected to boric acid treatment, washed with water, and then dried is widely known. The polarizing film thus obtained is used by being incorporated in a liquid crystal display device as a polarizing plate having a protective film laminated on both surfaces or one surface thereof.

[0003] However, when such a liquid crystal display device is used at a high temperature, a phenomenon called so-called "white loss" may occur in which the vicinity of the center of the four sides of the display screen looks white. When such white drop occurs, the contrast near the midpoint of the four sides of the display screen decreases, and the display quality decreases.

[0004]

The inventors of the present invention have conducted intensive studies to develop a method for manufacturing a polarizing film capable of producing a liquid crystal display device in which so-called white spotting is unlikely to occur. When the tension (A) and the temperature (B) in the drying treatment of the uniaxially stretched polyvinyl alcohol resin film dyed with a dye satisfy a predetermined relational expression, it has been found that the occurrence of white spots is small, and the present invention Reached.

[0005]

That is, the present invention provides a uniaxially stretched polyvinyl alcohol resin film which has been dyed with a dichroic dye and has been treated with boric acid, washed with water, and dried under tension to obtain polarized light. This is a method for producing a film, and the tension per unit width in the drying treatment (A)
A polarizing film characterized in that (unit: N / m) and temperature (B) (unit: ° C.) satisfy the inequality (1) A ≦ 0.1225B ² −9.947B + 376.32 (1) Is provided.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The uniaxially stretched polyvinyl alcohol resin film applied to the production method of the present invention is a film obtained by uniaxially stretching a polyvinyl alcohol resin film. Examples of the polyvinyl alcohol resin in the polyvinyl alcohol resin film include a resin obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, vinyl acetate, and copolymers of other monomers copolymerizable therewith. Other monomers include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like. The degree of saponification is usually 85 mol% to 100 mol%, preferably 98 mol%.
１００100 mol%. The polyvinyl alcohol resin may be further modified, and examples of the modified polyvinyl alcohol resin include polyvinyl formal and polyvinyl acetal. The polymerization degree of the polyvinyl alcohol resin is usually 1000 to 10
000, preferably 1500-10000.

The polyvinyl alcohol resin film is uniaxially stretched and dyed with a dichroic dye.
Boric acid treated. For uniaxial stretching, the film may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. The stretching may be dry stretching in the air or wet stretching in which the film is swollen with a solvent. The stretching ratio is usually about 4 to 8 times.

In order to dye a polyvinyl alcohol resin film with a dichroic dye, for example, the polyvinyl alcohol resin film may be immersed in an aqueous solution containing a dichroic dye.

When iodine is used as the dichroic dye, for example, a polyvinyl alcohol resin film may be immersed in an aqueous solution containing iodine and potassium iodide. The content of iodine in such an aqueous solution is usually 10
It is about 0.01 to 0.5 parts by weight per 0 parts by weight, and the content of potassium iodide is usually 0.1 to 100 parts by weight of water.
It is about 5 to 10 parts by weight. The temperature of such an aqueous solution is usually about 20 to 40 ° C, and the immersion time is usually 30 to 300.
On the order of seconds.

When a dichroic dye is used as the dichroic dye
For example, two colors of polyvinyl alcohol resin film
What is necessary is just to immerse in the aqueous solution of the coloring dye. In such an aqueous solution
The dichroic dye content is usually 1 × per 100 parts by weight of water.
10 ー^Three~ 1 × 10 ー^TwoIt is on the order of parts by weight. Such an aqueous solution
May contain inorganic salts such as sodium sulfate.
No. The temperature of such an aqueous solution is usually about 20 to 80 ° C.
The immersion time is usually about 30 to 300 seconds.

The boric acid treatment is performed, for example, by immersing a uniaxially stretched polyvinyl alcohol resin film dyed with a dichroic dye in an aqueous boric acid solution. The content of boric acid in the boric acid aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. The temperature of the boric acid aqueous solution is usually 50 ° C or higher, and preferably 50 ° C to 85 ° C. The immersion time is usually about 100 to 1200 seconds, preferably 150 to 600 seconds.
It is on the order of seconds, more preferably on the order of 200 to 500 seconds.

When the dichroic dye is iodine, the aqueous boric acid solution may contain potassium iodide. When potassium iodide is contained, the content is usually 100 parts of water.
About 2 to 20 parts by weight, preferably 5 to 15 parts by weight
Parts by weight.

The uniaxial stretching may be performed before dyeing,
It may be performed simultaneously with the dyeing, or may be performed after the dyeing.
When the uniaxial stretching is performed after the dyeing, the uniaxial stretching may be performed before the boric acid treatment or may be performed during the boric acid treatment.

The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of the water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually 2 to 120 seconds.

Next, a drying treatment is performed while applying tension to the polyvinyl alcohol resin film. The tension and the drying temperature applied to the polyvinyl alcohol resin film in the drying process satisfy the above inequality (1). The method for applying the tension is not particularly limited, and the tension may be applied in the same manner as in the case where the tension is applied so that the film is not loosened in the ordinary drying treatment.

The value of the tension (A) is not particularly limited as long as the above inequality (1) is satisfied. However, when the tension (A) is small, the polarizing film obtained tends to be wrinkled, and has a value of 800 N. / M, the polyvinyl alcohol resin film tends to be easily broken.
It is in the range of about 0 N / m to 800 N / m. The direction of the tension is usually the stretching direction of the polyvinyl alcohol resin film.

Although the width of the polyvinyl alcohol resin film may be reduced by the drying treatment,
The tension per unit width (A) in the present invention is a value based on the width of the polyvinyl alcohol resin film before the drying treatment.

The temperature (B) in the drying treatment is usually 41
° C or higher. Moreover, since the degree of polarization of the obtained polarizing film tends to decrease when the temperature is high, it is usually 100 ° C.
Less than or equal. The processing time in the drying process is usually 12
It is about 0 to 600 seconds.

It is preferable that the shrinkage in the stretching direction of the polyvinyl alcohol resin film in the drying treatment is 2% or more, since white spots can be further prevented. Here, the shrinkage ratio (R) is calculated from the length (L0) of the polyvinyl alcohol resin film before the drying treatment and the length (L1) of the polyvinyl alcohol resin film after drying (2) R = (L0−L1) / L0. It is a value calculated by (2).

A polarizing film is obtained by a drying treatment.
The polarizing film is heated to 90 ° C. without tension.
Equation (3) E = 1− (W1 / W0) (3) where E is the weight change rate, and W0 is the weight of the polarizing film before being left for a while. , W1 indicate the weight of the polarizing film after standing.), And the weight change rate (E) calculated by the method is 8%.
It is preferable to be as follows. Therefore, the temperature and time in the drying process are adjusted so that the weight change rate (E) becomes 8% or less.

The polarizing film thus obtained can be used as a polarizing plate by laminating a protective film on one or both sides thereof in the same manner as a normal polarizing film. As the protective film, for example, triacetyl cellulose, cellulose acetate resin film such as diacetyl cellulose, acrylic resin film, polyester resin film, polyarylate resin film, polyether sulfone resin film, cyclic polyolefin resin film such as polynorbornene film and the like. The thickness is usually about 30 to 200 μm. Usually, a transparent and optically isotropic adhesive is used for lamination, and as the adhesive, for example, a polyvinyl alcohol-based adhesive is used.

Such a polarizing plate may have a hard coat layer, an antireflection layer, an antiglare layer and the like on the surface.

[0023]

According to the manufacturing method of the present invention, it is possible to manufacture a polarizing film which enables a liquid crystal display device with less so-called dropping even when used at a high temperature.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 A polyvinyl alcohol film (thickness: 75 μm, degree of polymerization: 2400, degree of saponification: 99.9% or more) was monoaxially stretched in a dry system [stretching ratio: 5 times], and iodine and potassium iodide were kept in a tensioned state. Was immersed for 60 seconds in an aqueous solution (containing 0.05 parts by weight of iodine and 5 parts by weight of potassium iodide per 100 parts by weight of water, 28 ° C.). Then, while maintaining the tension, an aqueous solution of boric acid (an aqueous solution containing boric acid and potassium iodide, containing 7.5 parts by weight of boric acid and 6 parts by weight of potassium iodide per 100 parts by weight of water, temperature, 73 ° C.] for 300 seconds. Thereafter, the substrate was washed with pure water (15 ° C.) for 10 seconds. Tension on the washed film (tension per unit width is 206N /
Drying was performed at 90 ° C. for 300 seconds while applying m) to obtain a polarizing film. The shrinkage ratio (R) in the stretching direction of the film before and after the drying treatment was 6%.

A polyvinyl alcohol-based adhesive is applied to both sides of the polarizing film, and a protective film (a triacetyl cellulose film having a saponified surface, "Fujitack UV80", manufactured by Fuji Photo Film Co., Ltd.), 80 μm thick ] On both sides and dried at 50 ° C. for 5 minutes to obtain a polarizing plate.

An acrylic pressure-sensitive adhesive was applied to one surface of the polarizing plate, and cut into a rectangle (250 mm × 180 mm) such that the absorption axis was at 45 ° to the long side. The two polarizing plates were adhered to both sides of a transparent glass plate so as to form a cross Nicol, and observed visually. The portion where the polarizing plates were bonded to both sides of the glass plate appeared uniformly black, and no light leakage was observed. After the glass plate to which the polarizing plate was bonded was allowed to stand for 500 hours under a dry heat condition of 80 ° C., and visually observed, light leakage (white drop) near the center of each side of the polarizing plate was relatively small. Was.

Example 2 The tension (A) per unit width in the drying treatment was 304 N.
/ M and the temperature (B) were changed to 80 ° C. to obtain a polarizing plate. The shrinkage ratio (R) in the stretching direction of the polyvinyl alcohol resin film in the drying treatment was 2.5%.

When this polarizing plate was bonded to both surfaces of the glass plate in the same manner as in Example 1, and visually observed, the portion where the polarizing plate was bonded to both surfaces of the glass plate appeared uniformly black, and light leakage was observed. Was not done. After the glass plate to which the polarizing plate was bonded was allowed to stand for 500 hours under a dry heat condition of 80 ° C., and visually observed, light leakage (white drop) near the center of each side of the polarizing plate was relatively small. Was.

Example 3 The tension (A) per unit width in the drying treatment was 108 N
/ M and the temperature (B) were changed to 70 ° C., and a polarizing plate was obtained in the same manner as in Example 1. The shrinkage ratio (R) in the stretching direction of the polyvinyl alcohol resin film in the drying treatment was 5%.

When this polarizing plate was bonded to both surfaces of the glass plate in the same manner as in Example 1, and visually observed, the portion where the polarizing plate was bonded to both surfaces of the glass plate appeared uniformly black, and light leakage was observed. Was not done. After the glass plate to which the polarizing plate was bonded was allowed to stand for 500 hours under a dry heat condition of 80 ° C., and visually observed, light leakage (white drop) near the center of each side of the polarizing plate was relatively small. Was.

Comparative Example 1 The tension per unit width (A) in the drying treatment was 304 N.
/ M and the temperature (B) were changed to 50 ° C., and a polarizing plate was obtained in the same manner as in Example 1. The shrinkage (R) in the stretching direction of the polyvinyl alcohol resin film in the drying treatment was 1%.

When this polarizing plate was bonded to both surfaces of the glass plate in the same manner as in Example 1, and visually observed, the portion where the polarizing plate was bonded to both surfaces of the glass plate appeared uniformly black, and light leakage was observed. Was not done. The glass plate to which the polarizing plate was bonded was left for 500 hours under a dry heat condition of 80 ° C., and was visually observed. As a result, light leakage (white drop) near the center of each side of the polarizing plate was relatively large. Was.

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Claims (3)

[Claims] 1. A method for producing a polarizing film, comprising washing a uniaxially stretched polyvinyl alcohol resin film dyed with a dichroic dye and treated with boric acid, followed by drying while applying tension to produce a polarizing film. The tension (A) (unit: N / m) and temperature (B) (unit: ° C.) per unit width in Equation (1) are given by the following inequality (1): A ≦ 0.1225B ² −9.947B + 376.32 (1) A method for producing a polarizing film, characterized by satisfying. 2. The method according to claim 1, wherein the uniaxially stretched polyvinyl alcohol resin film is shrunk in the stretching direction by 2% or more in the drying treatment. 3. The method according to claim 1, wherein the temperature (B) in the drying treatment is 41 ° C. or higher.