JPH07333425A - Production of polarizing plate - Google Patents

Abstract

PURPOSE:To produce a polarizing plate having an excellent dimensional stability against heat treatment and an excellent water resistance by heat-treating a polarizing raw film at a specified temp. or higher. CONSTITUTION:A polarizing raw film stretched in a wet state is heat treated at >95 deg.C. In this method, the polarizing raw film to be used is not limited, and for example, a polyvinylalcohol film or ethylene-vinylacetate copolymer saponified film is used as the base film, especially a polyvinylalcohol film as the base film is preferable. A dichromatic dye or iodine is adsorbed and oriented to the base film to give a polarizing function. The dichromatic dye used is, for example, a water-base dye such as acid dye and direct dye is preferable. As for the structure of the dye, azo dye, stilbene dye, anthraquinone dye, methine dye, cyanine dye and the like can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method for producing a polarizing plate excellent in dimensional change due to heat and humidity and water resistance.

[0002]

2. Description of the Related Art In recent years, when a liquid crystal display device is used in a vehicle or outdoors, further improvement in durability is demanded. By the way, in a normal polarizing plate, a cellulose acetate film excellent in optical transparency and non-orientation is used as a support through an adhesive layer on both sides of a polarizing element film having a polarizing ability. As the polarizing element film, a polyvinyl alcohol film dyed (iodine or dichroic dye) and uniaxially stretched is typically used. However, it is general that both the polyvinyl alcohol film and the cellulose acetate film are bonded by a hydrophilic and rewetting adhesive. Therefore, the obtained polarizing plate has a large water absorbency in a high humidity atmosphere for a long time, which causes problems such as dimensional stability and generation of microcracks. For example, in the production of a dye-based polarizing plate, a polarizer film obtained by wet stretching a polyvinyl alcohol-based film is usually dried at a temperature of 60 ° C to 70 ° C. However, the polarizing plate produced at this drying temperature has insufficient water resistance because it undergoes dimensional changes under wet heat and dry heat, microcracking occurs in a heat cycle test and the like. In order to solve this problem, for example, Japanese Patent Publication No. 5-68
In JP-A No. 1, a cellulose acetate-based protective film is adhered to at least one surface of a vinyl alcohol-based polarizing element film using an adhesive material, and then heat-treated at a temperature of 90 to 110 ° C. to improve moisture resistance and dimensionality. It is proposed to improve.

[0003]

[Problems to be Solved by the Invention] However, Japanese Patent Publication No. 5-6
In the method described in Japanese Patent Publication No. 81, moisture resistance, dimensional stability, suppression of microcrack generation due to lack of water resistance, etc. are not yet sufficiently satisfactory in the field where high durability is required such as for in-vehicle use. Improvement is required.

[0004]

Means for Solving the Problems As a result of various investigations by the present inventors on a method of manufacturing a polarizing plate having the above-mentioned problems improved, the wet-stretched polarizing film was heat-treated at a temperature of 95 ° C. or higher. The inventors have found that a polarizing plate having good dimensional stability and water resistance due to heat can be obtained, and completed the present invention. That is, the present invention provides (1) a method of manufacturing a polarizing plate, which comprises heat-treating a polarizing element film at a temperature of 95 ° C. or higher,
(2) A method for producing a polarizing plate, which comprises heat-treating a polarizing element film at a temperature of 95 ° C. or higher and then pasting it on a support,
(3) The method for producing a polarizing plate according to the above (1) or (2), wherein the polarizing element film is a dye-based polarizing element film which is wet-stretched using polyvinyl alcohol as a base material, and (4) the heat treatment temperature is 95.
The method for producing a polarizing plate according to (1) or (2) above, wherein (4) the heat treatment is performed by a dry heating method under tension of the polarizing film. Production method,
(5) The method for producing a polarizing plate according to (4) above, wherein the dry heat method is a hot air drying method.

The polarizing film used in the present invention is not particularly limited, but may be a polyvinyl alcohol film or ethylene-based film.
Those having a saponified vinyl acetate copolymer film as a substrate, particularly those having a polyvinyl alcohol film as a substrate are preferable, and a dichroic dye or iodine is adsorbed and oriented on this substrate to impart a polarizing ability. Is commonly used. The substrate preferably has a film thickness of about 25 to 50 μm after stretching and drying, and the film thickness before stretching is, for example, about 60 to 70 μm.
It is about m. The adsorption orientation method is not particularly limited,
For example, a polyvinyl alcohol film or a saponified film of an ethylene-vinyl acetate copolymer is immersed in an aqueous solution of a dichroic dye, dyed, and uniaxially stretched in the machine direction 3 to 5 times in the longitudinal direction, or a film previously uniaxially stretched in the machine direction. There is a method of immersing the dye in the above aqueous solution and dyeing. As a preferable method, for example, a dyed film is prepared with a concentration of about 2 to 5%.
The method of stretching in a boric acid aqueous solution at about 30 to 60 ° C. can be mentioned. Details thereof are described in, for example, JP-A-59-14525.
No. 5 and JP-A No. 60-156759. The surface of the obtained stretched film is washed with water or alcohol under tension, if necessary. When using a base material that is colored by adding a dichroic dye in advance, the base material may be uniaxially stretched in the machine direction.

The dichroic dye used here is preferably a water-soluble dye such as an acid dye or a direct dye, and its structure is, for example, an azo dye, a stilbene dye,
Anthraquinone dyes, methine dyes, cyanine dyes and the like can be used. As a concrete example, for example, JP-A-5
9-145255 and JP-A-60-156759, disazo compounds, trisazo compounds described in JP-A-3-78703, and CI Direct Yellow 12 and CI Dire represented by color index general name.
ct Yellow 44, CI Direct Orange 26, CI Direct Ora
nge 39, CI Direct Red 2, CI Direct Red 23, CI Di
rect Red 31, CI Direct Red 79, CI Direct Red 81, C
I Direct Vilet 9, CI Direct Vilet 35, CI Direct V
ilet 51, CI Direct Blue 15, CI Direct Blue 78, C
I Direct Blue 90, CI DirectBlue 168, CI Direct Bl
ue 202, CI Direct Blue 203, CI Direct Brown 2, CI
Direct Black 17, CI Direct Black 19, CI Direct Bla
ck 118, CI Direct Black 132, etc. still,
These water-soluble dyes preferably have a content of a pigment component capable of imparting a polarizing ability of 95%, more preferably 99% or more (both are by weight), and a desired pigment component such as an inorganic salt or an unreacted product. Impurities other than are removed by a method such as an ion exchange membrane method or a recrystallization method. In actual use, since a single dye has a polarization characteristic only in a specific wavelength range, a polarizing element film having excellent polarization characteristics over the entire wavelength range of visible light of 400 to 700 nm which is most commonly used is used. In order to obtain it, it is preferable to appropriately mix and use two or more kinds of water-soluble dyes having absorption characteristics in different ranges within this wavelength range. As an example of a specific combination,
CI Direct Orange 39, CI Direct Red 81, JP 59
-145255, Green described in Example 23;
There are four types of blue compounds described in JP-A-3-78703.

[0007] The polarizing film obtained by the above method is preferably heat-treated under tension (in a tensioned state).
The heat treatment is performed at a temperature of 95 ° C. or higher, more preferably 95 ° C. to 135 ° C., and further preferably 100 ° C. to 130 ° C. from the viewpoint of optical characteristics. The treatment time is about 1 to 10 minutes, preferably about 2 to 5 minutes. The treatment method may be either wet heat treatment or dry heat treatment, but dry heat treatment is preferable, and various drying methods such as hot air drying and electrothermal drying can be adopted.

A polarizing plate of the present invention can be obtained by attaching a support to one or both sides of the polarizing film that has been heat-treated by the above method using an adhesive, if necessary, and then drying if necessary. To be Examples of the support used here include cellulose triacetate film (FT-80, manufactured by Fuji Photo Film Co., Ltd.) surface-treated with alkali, cellulose diacetate film and the like. Examples of the adhesive include polyvinyl alcohol and the like. The film thickness is preferably about 50 to 80 μm. When polyvinyl alcohol is used, an aqueous solution having a polymerization degree of about 1700 to 2400 and a saponification degree of about 98 to 99 mol% and a concentration of about 2 to 5% is preferable.

The polarizing element film heat-treated by the above method has a refractive index of about 1.006 to 1.008 times that of the polarizing element film obtained by the conventional method (drying at about 60 ° C.). It turned out. This means that the crystallinity of the base material of the polarizer film obtained by the method of the present invention is higher than the crystallinity of the polarizer film obtained by the conventional method, and It is considered that the polarizing plate of the present invention is superior in heat-resistant dimensional stability to the polarizing plate obtained by the conventional method, and the generation of microcracks is suppressed.

[0010]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Example 1 A polyvinyl alcohol film was swollen in warm water at 40 ° C., and then CI Direct Orange 39, CI Direct Red 8
1. A dichroic dye obtained by blending green described in Example 23 of JP-A-59-145255 and blue described in JP-A-3-78703 in a weight ratio of 4: 3: 2: 2. After dyeing with a 0.1% aqueous solution at 40 ° C. for 2 minutes, the concentration is 2.
It was uniaxially stretched 4 times in the longitudinal direction at 40 ° C. in a 5% aqueous solution of boric acid. The obtained polarizing film was heat-treated at 100 ° C. for 3 minutes under tension (drying with hot air). Both surfaces of this heat-treated polarizing film were coated with a 4% aqueous solution of polyvinyl alcohol having a degree of polymerization of 1700 and a degree of saponification of 99.9 mol%, and a surface-treated cellulose triacetate film with an alkali was stuck to the both sides, and the temperature was kept at 80 ° C.
And dried for 6 minutes to obtain a polarizing plate of the present invention. The resulting polarizing plate was measured for dimensional changes after 200 hours of testing under the respective reliability test conditions of 80 ° C./90% RH, 100 ° C., and −40 ° C., and the presence or absence of microcracks was observed. The results are shown in Table 1.
It was shown to. Also, measure the refractive index of the heat-treated polarizing film,
The results are shown in Table 2.

Example 2 A polarizing plate of the present invention was obtained in the same manner as in Example 1 except that the heat treatment temperature of the polarizing element film was changed to 110 ° C. The reliability test was also performed under the same conditions as in Example 1. The results are shown in Table 1. The refractive index of the heat-treated polarizing film was measured and is shown in Table 2.

Example 3 A polarizing plate of the present invention was obtained in the same manner as in Example 1 except that the heat treatment temperature of the polarizing element film was changed to 120 ° C. The reliability test was also performed under the same conditions as in Example 1. The results are shown in Table 1. The refractive index of the heat-treated polarizing film was measured and is shown in Table 2.

Example 4 A polarizing plate of the present invention was obtained in the same manner as in Example 1 except that the heat treatment temperature of the polarizing element film was changed to 130 ° C. The reliability test was also performed under the same conditions as in Example 1. The results are shown in Table 1. The refractive index of the heat-treated polarizing film was measured and is shown in Table 2.

Comparative Example 1 A polyvinyl alcohol film was swollen in warm water at 40 ° C., then dyed with a dichroic dye and then uniaxially stretched 4 times in a 40 ° C. bath having a boric acid concentration of 2.5%. The obtained polarizing element film was dried under tension at 60 ° C., and the cellulose triacetate film surface-treated with alkali had a polymerization degree of 1700 and a saponification degree of 99.9.
A 4% aqueous solution of polyvinyl alcohol (mol%) was applied, laminated on both surfaces of the polarizing film, and dried at 80 ° C. to obtain a polarizing plate. The obtained polarizing plate is 80 ° C / 90% RH, 100 ° C,
The presence or absence of dimensional change and occurrence of microcracks after a 200-hour test was measured under each reliability test condition of -40 ° C, and the results are shown in Table 1. The refractive index of the heat-treated polarizing film was measured and is shown in Table 2.

[0015]

[Table 1] Table 1 Presence or absence of dimensional change and occurrence of microcracks after reliability test Example 80 ° C / 90% RH 100 ° C-40 ° C 1-1.46% -1.65% None 2-1.53% -1.58% None 3-1.46% -1.43% None 4-1.48% -1.35% None Comparative Example 1 -1.88% -2.20% Yes

[0016]

Table 2 Relationship between heat treatment temperature and refractive index of polarizing element film Example Example Heat treatment temperature of polarizing element film (° C.) Refractive index Ratio of refractive index 1 100 1.5148 1.0064 2 110 1.5160 1.0072 3 120 1.5168 1.0077 4 130 1.5170 1.0078 Comparative Example 1 60 1.5052 1.0000

The refractive index was measured by using the Abbe refractometer after cutting the polarizing element films obtained in Examples and Comparative Examples into a size of 20 mm * 10 mm.

[0018]

According to the method of the present invention, the refractive index of the polarizing element film can be made about 1.006 to 1.008 times that of the conventional one, the dimensional change due to heat is small, and the generation of microcracks is suppressed. A highly durable polarizing plate can be obtained.

Claims (6)

[Claims] 1. A method of manufacturing a polarizing plate, which comprises heat-treating a polarizing element film at a temperature of 95 ° C. or higher. 2. A method for producing a polarizing plate, which comprises heat-treating a polarizing element film at a temperature of 95 ° C. or higher and then attaching the film to a support. 3. The method for producing a polarizing plate according to claim 1, wherein the polarizing element film is a dye-based polarizing element film obtained by wet stretching using polyvinyl alcohol as a base material. 4. The method for producing a polarizing plate according to claim 1, wherein the heat treatment temperature is 95 ° C. to 135 ° C. 5. The method for producing a polarizing plate according to claim 1, wherein the heat treatment is performed by a dry heating method under tension of the polarizing element film. 6. The method of manufacturing a polarizing plate according to claim 5, wherein the dry heating method is a hot air drying method.