JPH079484B2 - Dye-based polarizing plate manufacturing method - Google Patents

Description

The present invention relates to a method for producing a highly efficient dye-based polarizing plate with excellent productivity.

More specifically, the mixture of a hydrophilic polymer and a dichroic dye is formed on a hydrophobic polymer film, and the hydrophobic polymer film is stretched and oriented in a uniaxial direction. The present invention relates to a method for producing a dye-based polarizing plate having a molecular film as a protective film, and an object thereof is to provide a method for producing an optically homogeneous dye-based polarizing plate with high productivity. .

Currently, a polarizing plate is a stretched and oriented polyvinyl alcohol or its derivative, or a polyene-based film in which polyene is generated and oriented by dehydrochlorination of a polyvinyl chloride film or dehydration of a polyvinyl alcohol-based film as a polarizing element. It is general that a color dye is adsorbed and a cellulose acetate-based film is laminated on both sides of the film as a protective film to manufacture.

Among them, a polarizing plate using iodine as a polarizing element is excellent in initial polarization performance, but it is weak against water and heat and has a problem in its durability when used for a long time in high temperature and high humidity conditions. There is. In order to improve durability, it is considered to strengthen treatment with an aqueous solution containing formalin or boric acid, or to use a polymer film with low moisture permeability as a protective film. In the state, durability is insufficient.

A polarizing plate using a dichroic dye as a polarizing element is more durable against water and heat than a polarizing plate using iodine, but has the following problems.

(1) The cost of the cellulose acetate-based protective film is high, and as a result, the cost of the dye-based polarizing plate is high.

(2) The manufacturing process is complicated, the yield is poor, and the processing of the waste liquid containing the used dye is troublesome, which causes the cost of the dye-based polarizing film to increase.

(3) Dyeing unevenness is large, and it is difficult to obtain a uniform polarizing film.

(4) It is difficult to obtain a long polarizing film having the same hue.

(5) It is difficult to control the concentration in the dyeing solution tank, and it is difficult to obtain a long polarizing film having the same function.

Various studies have been made to solve these problems.
In particular, in order to reduce the price with respect to the above items (1) and (2), various inexpensive protective films replacing cellulose acetate-based protective films have been proposed, but at present, they have not been put into practical use. The treatment of the waste liquid containing the used dye is inevitable as long as the existing dyeing method is applied to the film. Furthermore, in order to solve the problems (3) to (5),
Although a batch dyeing method is also used instead of the continuous dyeing method, it is difficult to obtain a completely optically homogeneous material, and productivity is deteriorated, which further increases the cost. Further, JP-A-56-158301 discloses a method for producing a polarizing film by stretching a film formed from a mixture of a polyvinyl alcohol polymer and a dichroic dye in at least uniaxial direction. . According to this method, the problems (3) to (5) may be solved, but as long as a cellulose acetate film is used as a protective film, significant cost reduction cannot be expected.

The present inventors, in view of these circumstances, as a result of intensive studies, a mixture containing a hydrophilic high molecular polymer and a dichroic dye,
By forming a film on a hydrophobic polymer film, stretching and orienting it in a uniaxial direction together with the hydrophobic polymer film, and using the hydrophobic polymer film as a protective film, it is optically homogeneous and highly transparent. It was found that a productive dye-based polarizing plate can be obtained, and the present invention has been completed.

That is, in the present invention, a hydrophilic polymer and a specific organic direct dye having a high dichroic ratio are dissolved in water or an organic solvent or a mixed solvent of water and an organic solvent, and then flown onto a hydrophobic polymer film. After stretching and film formation, (1) uniaxially stretching treatment with the hydrophobic polymer film or (2) two films prepared and mixed with a hydrophilic polymer and a dichroic dye Uniaxially stretched by a compression stretching method in a state where the layers are overlapped on the inner surface, based on either, the obtained polarizing plate is a uniaxially stretched hydrophobic polymer film as a protective film The present invention relates to a method for producing a dye-based polarizing plate that is low in cost, has no dyeing unevenness, has no hue change over a long length, that is, is optically homogeneous, and has no change in polarization performance over a long length.

The organic direct dye used in the present invention may be any one having a high dichroic ratio, but it is generally selected from azo dyes. The organic direct dye used in the present invention is represented by a color index generic name (CIGeneric Name) and a trade name,
The following is exemplified.

CI Direct Black 17 …… Product name example (the same applies below) Japanol First Black D Conc. CI Direct Yellow 12 …… CISO FENIN C. Eye Direct Blue 202 (CIDirect) Blue 202 …… Sumilite Supurablue 3GS) CI Direct Black 19 …… Sumilite Black G
Conc) CI Direct Red 31 (CIDirect Red 31 …… NIPPON FIRST RED BB CONC) CI Eye Violet 9 …… CI Direct Violet 9 …… NIPPON PRILIANT
Violet BK Conc) C-I Direct Red 2 (CIDirect Red 2 ... Benzopurpurin 4B) C-I Direct Red 81 (CIDirect Red 81-Sumilight Red 4B) C-I Direct Violet 51 (CIDirect Violet) 51 …… Sumilite Violet
BB) CI Direct Orange 26 (CIDirect Orange 26 …… Direct First)
Orange S) CI Direct Red 247 (JADirect First)
Red FA) C-I Direct Blue 168 (CIDirect Blue 168 ... Direct Copper Blue 2B) C-I Direct Green 85 (CIDirect Green 85 ... Direct Dark Green BA) C-I Direct Brown 223 (CIDirect Brown 223) ...... Direct Brown M
A) CI Direct Black 51 …… Direct First
Black Conc. C.I.Direct Black 154 (CIDirect Black 154 ... Direct Deep Black XA) C.I.Direct Yellow 44 (CIDirect Yellow 44 ... Direct First)
Yellow GC) CI Direct Black 32 ...... Direct First
Black AB) CI Direct Black 22 (Direct Direct 22)
Black B) C-I Direct Yellow 28 (CIDirect Yellow 28 ... Sumilite Supura Yellow BC Conc) C-I Direct Orange 107 (CIDirect Orange 107 ... Sumi-Lite Supura Orange GD Extra Conc) C-I Direct Red 79 ( CIDirect Red 79 …… Sumilite Supura Red
4BL 170%) CI Direct Blue 71 (Sumilight Blue BRR)
Conc) CI Direct Blue 78 (CIDirect Blue 78 ... Sumilite Supura Blue G Conc) C.I.Direct Brown 106 (CIDirect Brown 106 ... Sumilight Supra Brown G Conc) C.I.Direct Black 112 (CIDirect Black) 112 …… Sumilite Supura Gray CGL) C-I Direct Black 113 (CIDirect Black 113 …… Sumilight Supura Gray NGL Conc) C-I Direct Yellow 142 (CIDirect Yellow 142 …… Sumilight Yellow G)
R) CI Direct Blue 1 …… Direct Sky Blue
6B) These dichroic dyes can be used alone to form a color polarizing film, but to make them even better, two or more types of dyes should be mixed in the entire wavelength range of visible light of 400 to 700 nm. It can be used as a polarizing film having the same absorption characteristics (that is, having a neutral color) and having a high degree of polarization.

For example, in the entire wavelength range of visible light of 400 to 700 nm, if you show the combination of dyes to obtain a polarizing film with a neutral color and a high degree of polarization, C.I.Direct Black 17, C.I.
It is a mixture of 3 types of dyes: Eye Direct Yellow 12 and Sea Eye Direct Blue 202.

Furthermore, in the entire wavelength range of visible light from 400 to 700 nm, if you show another dye combination to obtain a polarizing film with a neutral color and a high degree of polarization, C-I Direct Black 17, C-I Direct It is a combination of 4 types of dyes: Yellow 12, C-I Direct Blue 202, and C-I Direct Orange 26.

Further, the objective can be achieved by combining four kinds of dyes, namely, C-I Direct Blue 1, C-I Direct Red 81, C-I Direct Orange 107, and C-I Direct Green 85.

Even more preferred are C-I Direct Red 31, C-I.
Direct Violet 9, Sea Eye Direct Red 2, Sea Eye Direct Red 81 and Sea
When one or more of the organic direct dyes of Eye Direct Violet 51 are mixed, the difference between the maximum light transmittance and the minimum light transmittance and the difference between the maximum polarization degree and the minimum polarization degree are smaller than those when not mixed. Becomes more neutral color,
In addition, the degree of polarization becomes high, which is preferable.

In addition, as a method for approaching the difference between the maximum light transmittance and the minimum light transmittance infinitely close to zero in the entire wavelength range of visible light of 400 to 700 nm to more completely approximate a neutral color, It is also possible to employ a method of appropriately mixing a dye having absorption ability and having no dichroism.

As the hydrophilic polymer used in the present invention, polyvinyl alcohol, polyvinyl formal, polyvinyl alcohol such as polyvinyl acetal and polyvinyl butyral and derivatives thereof are generally used, besides, ethylene, olefins such as propylene and crotonic acid, Unsaturated carboxylic acids such as acrylic acid, methacrylic acid and maleic acid, or their alkyl esters, those modified with acrylamide, saponified EVA resins, cellulosic resins and the like are generally used. Among them, a high-molecular polymer composed of polyvinyl alcohol and its derivative has good solubility in water or an organic solvent, good compatibility with an organic direct dye having good dichroism, and a film formed. Since the dichroic dye is easily oriented when stretched and oriented, it is a hydrophilic high molecular polymer which is particularly useful in the present invention. Further, a polyvinyl alcohol having a high saponification degree of 85% or more, preferably 95% or more is a hydrophilic high molecular polymer particularly useful in the present invention.

The solvent for dissolving the hydrophilic high molecular polymer and the dichroic dye may be any solvent as long as it can dissolve these and is not particularly limited. For example, when polyvinyl alcohol and its derivative are used, water, ethylene glycol, glycerin, dimethylformamide and a mixed solvent thereof, and a solvent in which a monohydric alcohol such as methanol and ethanol is used together can be used. Among them, warm water is a solvent often used because it dissolves polyvinyl alcohol having a large degree of saponification well.

As a method for dissolving the hydrophilic high molecular polymer and the dichroic dye in the solvent, any method may be used as long as they are uniformly dissolved and mixed, but first, the dichroic dye is dissolved in the solvent,
After that, a method of adding and dissolving the hydrophilic high molecular weight polymer can be adopted. Further, a method in which the hydrophilic polymer and the dichroic dye are dissolved in different solvents and then mixed and dissolved is also possible.

The concentration of the hydrophilic high molecular polymer dissolved in the solvent varies depending on the kind of the hydrophilic high molecular polymer, but is generally 5 to 30%, preferably 10 to 20%. The concentration of the dichroic dye dissolved in the solvent varies depending on the type of hydrophilic high molecular polymer, the type of dichroic dye, the film thickness when formed into a film, the required performance when formed into a polarizing film, etc. Generally, it is about 0.1 to 5%, preferably about 0.3 to 2.5% based on the hydrophilic high molecular weight polymer.

A mixture of a hydrophilic high molecular polymer and a dichroic dye is
A hydrophobic polymer film is cast and formed into a film. The thickness of the film is preferably about 5 to 50 μm.

As the hydrophobic polymer film used in the present invention, when uniaxially stretched, the light transmittance is improved, as long as it is 80% or more, basically any may be used, a cellulose acetate film, Acrylic films, olefin films such as polyethylene and polypropylene, polyamide films, polyester films, fluorine-based films such as tetrafluoroethylene-6-propylene fluoride-based copolymers, vinyl chloride films, etc. Resin film can be used.

When casting a mixture of a hydrophilic polymer and a dichroic dye on these polymer films, the surface of the polymer film is activated by means of corona treatment, plasma treatment, organic titanate treatment, etc. Needs to be improved. If necessary, the adhesive composition may be coated. Thus, a mixture of a hydrophilic polymer and a dichroic dye is cast on the polymer film having improved surface wettability to form a film, thereby forming a film. In order to improve the adhesiveness between the polymer film and the mixture film, it is also effective to carry out electron beam treatment, ultraviolet treatment or the like after forming the film.

A film composed of a hydrophobic polymer film, a hydrophilic polymer polymer formed thereon and a dichroic dye is integrally stretched in a uniaxial direction by a suitable method. By stretching and orienting the composite film, the dye molecules are oriented and the polarization performance is exhibited. As a method for uniaxially stretching, there are a method of performing tensile stretching with a tenter method, a method of performing tensile stretching between rolls, a method of performing compression stretching between rolls, and the like. However, since a composite of different polymers is stretched at the same time, the method of performing compression stretching between rolls is most effective. Since the stretching conditions differ depending on the type of polymer film, it is difficult to stretch uniformly by the tension stretching method, but the compression stretching method allows stretching with a wide allowable range. Even in the case of the compression stretching method, it is quite difficult to uniformly stretch a composite film composed of different types of polymer films, and a polymer film of the same type as the hydrophobic polymer film is placed on the hydrophilic polymer film. When the layers are overlapped and stretched into a so-called three-layer structure, the stretching is performed uniformly without unevenness in stretching, which is a more preferable method. Therefore, a method of preparing two composite films, uniaxially stretching by performing compression stretching in a state where the hydrophilic high molecular weight polymer films are overlapped on the inner surface, is an epoch-making method for manufacturing a dye-based polarizing plate at low cost. Has become a popular method. In order to bond the hydrophilic polymer films to each other more firmly, it is more effective to apply water, a water-soluble adhesive or the like before compression and stretching. Generally, the draw ratio in compression drawing is 2
It is about 9 to 9 times, but depending on the kind of the polymer forming the composite film, it can usually be stretched to about 2.5 to 6 times. When polyvinyl alcohol is used as the hydrophilic polymer and high-density polyethylene is used as the hydrophobic polymer film, the draw ratio is 3 to 8 times, preferably 3.5 to 6 times.

After stretching the composite film of the hydrophobic polymer film and the hydrophilic polymer film, boric acid treatment is carried out for the purpose of improving the water resistance and the polarization performance of the hydrophilic polymer film. The boric acid treatment improves the light transmittance and the degree of polarization of the polarizing film. The conditions of boric acid treatment vary depending on the type of hydrophilic high molecular polymer used and the type of organic dichroic dye, but generally, the boric acid concentration is 1 to 15
%, Preferably 5 to 10%, and the treatment temperature is 30 to 80
Desirably it is in the range of 50 ° C, preferably 50-75 ° C. When the boric acid concentration is 1% or less and the temperature is 30 ° C or less, the treatment effect is small, and the boric acid concentration is 15% or more and the temperature is 80%.
If the temperature is above ℃, the polarizing film becomes brittle, which is not preferable. Further, if necessary, a fixing treatment may be performed together with an aqueous solution containing a cationic polymer compound.

The dye-based polarizing plate having a protective film on one side thus obtained can be used not only as a polarizing plate but also as a polarizing plate having a protective film on both sides by adhering the inner surfaces together. It can be used as a board. Furthermore, an optically transparent polymer film, preferably a hydrophobic polymer film used for the polarizing plate is compressed and stretched to the same extent to form a protective film on the other side. It is also possible to use it as a polarizing plate by adhering or pasting it on.

Since the dye-based polarizing plate obtained in this manner can omit the step of dyeing a film as in the conventional case, the preparation of the dyeing liquid and the treatment of the waste liquid are unnecessary, and the manufacturing process is greatly simplified. Problems will be reduced and productivity and yield will be improved. Furthermore, since the process of bonding and laminating can be simplified, the cost can be significantly reduced as compared with the conventional dye-based polarizing plate. Furthermore, since it does not go through the step of dyeing as in the conventional case, the dichroic dye is uniformly dispersed in the hydrophilic polymer film and has no color unevenness, and there is no hue change over a long length,
The dye-based polarizing plate is extremely optically homogeneous. When combined with boric acid treatment, a dye-based polarizing plate with high performance, which has less color than conventional dye-based polarizing plates, can be obtained.

In particular, the polarizing plate produced according to the present invention by using three or more kinds of dichroic dyes is optically homogeneous over a long length as compared with the conventional dye-based polarizing plate, and moreover, it has a visible light of 400 to 700 nm. The difference between the maximum light transmittance and the minimum light transmittance in the entire wavelength range is very small, it shows a neutral color, and the difference between the maximum polarization degree and the minimum polarization degree in the same wavelength range is small, and iodine is used as a polarizing element. Since it has excellent polarization performance comparable to that of iodine-based polarizing plates, it can be used for liquid crystal display applications. It is particularly suitable for applications requiring high durability such as in-vehicle applications and display applications for various industrial instruments.

Hereinafter, the present invention will be described in more detail by way of examples, which are illustrative and not limiting.

In addition, the polarization degree in the present invention means that two polarizing films or polarizing plates are prepared and a light transmittance curve is measured in a state where these two polarizing plates are superposed (measurement device: Shimadzu UV-210 spectrophotometer). ), The value obtained by the following formula.

Here, H _‖ is a value (called parallel transmittance) measured in a state where the two polarizing plates are superposed so that the orientation directions of the polarizing films are the same, and H _⊥
Is a value (called orthogonal transmittance) measured in a state where the two samples are superposed so that the orientation directions of the polarizing films are orthogonal to each other.

Example 1 Polyvinyl alcohol having an average degree of polymerization of 1700 and a saponification degree of 99.5% was dissolved in water, and 1.2 wt% of CIA Direct Black 17 (C.
I.Direct Black 17, brand name ... Japanol Fast Black D) was added and completely and uniformly dissolved. This mixed solution was added to the high-density polyethylene film (thickness
400μ, corona treatment was applied to the surface so that the wetting tension would be 54 dyne / cm or more, and then surface treatment was also performed using organic titanate) and cast to a thickness of about 12μ It was formed into a film and dried. The same high-density polyethylene film as the above was used as an auxiliary film except that no surface treatment was performed, and the composite film was laminated on the polyvinyl alcohol film side, and compressed 4 times vertically in a uniaxial direction between a pair of rolls at 90 ° C. After stretching, the auxiliary film was peeled off to obtain a dye-based polarizing plate with a protective film on one side. The single transmittance at 590 nm at which the polarizing plate exhibits maximum absorption was 39%, and the polarization degree was 84%.

Example 2 A dye-based polarizing plate with a protective film on one side was produced in the same manner as in Example 1, and heat treatment was carried out by passing the polyvinyl alcohol film side through a heating roll heated to 160 ° C. This dye-based polarizing plate with a protective film on one side consists of 7.5 wt% boric acid.
After dipping in an aqueous solution at 0 ° C for 5 minutes, it was washed with water at 20 ° C for 1 minute and dried. A high-density polyethylene film (thickness 100 μm) compressed and stretched by 4 times was attached to the polarizing plate with a urethane adhesive to obtain a dye-based polarizing plate having protective films formed on both sides. The single transmittance at 590 nm at which the polarizing plate exhibits maximum absorption was 41%, and the polarization degree was 94%.

Example 3 Polyvinyl alcohol having an average degree of polymerization of 1700 and a degree of saponification of 96.5% was dissolved in water, and this solution was used to prepare CIDirect Black17.・ Direct Yellow 12 (CIDirect Yellow 12. product name …… kuxofenin), C-I Direct Blue 202 (CIDirec
t Blue202. Product name …… Sumilite Supura Blue 3GS)
0.8 wt% for polyvinyl alcohol,
0.4 wt% and 0.7 wt% were added and completely and uniformly dissolved. This mixed solution is used as a polypropylene film (thickness 300
μ, corona treatment is applied to the surface so that the wetting tension is 54 dyne / cm or more), and the film is cast to a thickness of about 12 μ on the surface, and the accelerating voltage is 200 KV in the undried state. Electron beam irradiation was performed at a dose of 10 Mrad to bond the polypropylene film and the polyvinyl alcohol film.

Two composite films were prepared, and water was added to polyvinyl alcohol, and the inner surface (polyvinyl alcohol film surface) was superposed on each other, and compressed and stretched 3.5 times in a longitudinal uniaxial direction between a pair of rolls at 100 ° C. Then, a neutral dye-based polarizing plate having protective films formed on both surfaces was obtained. The average single-piece transmittance of this polarizing plate in the visible light wavelength range of 400 to 700 nm was 37%, and the polarization degree was 84%.

Example 4 A composite film of a polypropylene film and a polyvinyl alcohol film was obtained in the same manner as in Example 3. Polypropylene film without surface treatment (thickness 30
(0 μ) as an auxiliary film, the composite film was superposed on the polyvinyl alcohol film side, and compressed and stretched 2.5 times uniaxially between a pair of rolls at 120 ° C., and then the auxiliary film was peeled off to give a single-sided protective film. A dye-based polarizing plate was obtained. Only the polyvinyl alcohol side of this polarizing plate was heat-treated by passing it through a hot roll heated to 160 ° C. This dye-based polarizing plate with a protective film on one side is boric acid 7.5 wt%
Was immersed in an aqueous solution of 60 ° C. for 5 minutes, washed with water of 20 ° C. for 1 minute and dried. Prepare two sheets of dye-based polarizing plates with a protective film on one side that have been treated with boric acid, and apply and bond a water-soluble adhesive on one surface of polyvinyl alcohol so that polyvinyl alcohol adheres to each other on the inner surface. A neutral dye-based polarizing plate having protective films on both sides was obtained. This polarizing plate had an average single-element transmittance of 40.5% and a polarization degree of 95% in the visible light wavelength region of 400 to 700 nm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kikui 2-10-1 Tsukahara, Takatsuki City, Osaka Sumitomo Kagaku Kogyo Co., Ltd. (56) Reference JP-A-56-158301 (JP, A) JP Sho 56-25419 (JP, A)

Claims (3)

[Claims] 1. A dye system characterized in that a mixture containing a hydrophilic polymer and a dichroic dye is formed on a hydrophobic polymer film and uniaxially stretched together with the hydrophobic polymer film. Method for manufacturing polarizing plate. 2. A mixture of a hydrophilic polymer and a dichroic dye is formed on a hydrophobic polymer film, and the resulting composite film is a mixture of the hydrophilic polymer and the dichroic dye. The method for producing a dye-based polarizing plate according to claim 1, wherein uniaxial stretching treatment is carried out by a compression stretching method in a state in which the layers made of are laminated inside. 3. The method for producing a dye-based polarizing plate according to claim 1 or 2, wherein the hydrophilic high molecular polymer is polyvinyl alcohol or a derivative thereof.