JPH05681B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a polarizing plate. [Conventional technology] In recent years, desktop electronic computers, electronic clocks, word processors,
2. Description of the Related Art Liquid crystal display devices are used in instruments such as automobiles and machinery, and the demand for polarizing plates is increasing accordingly. A polarizing plate is generally made by forming protective films on both sides of a polarizing film having polarizing ability via an adhesive layer. Typical polarizing films used include polyvinyl alcohol resins, saponified ethylene-vinyl acetate copolymers, and other vinyl alcohol uniaxially stretched films dyed with iodine, and protective films include cellulose acetate. These films are widely used as surface protective films because of their excellent optical transparency and non-orientation properties. Since vinyl alcohol films and cellulose acetate films are both hydrophilic, they are generally bonded together using a hydrophilic adhesive. For this reason, the obtained polarizing plate has a high water absorption rate when left in a high humidity atmosphere for a long time, and as water is absorbed, the adhesive strength decreases and the polarizing properties deteriorate, causing problems in so-called moisture resistance and dimensional stability. There may be cases where In order to solve this problem, for example,
Publication No. 50301 proposes saponifying the surface of the cellulose acetate film of the protective film to strengthen the adhesive force between the adhesive and cellulose acetate, and improve moisture resistance, heat resistance, and dimensional stability. There is. Furthermore, in JP-A No. 61-245107, the surface of the polarizing film is treated once with an aqueous solution of a hydrophilic polymer such as polyvinyl alcohol, carboxymethyl cellulose, urethane, acrylic, or epoxy, or with an adhesive, and then treated again. It has been proposed to provide a polarizing plate with improved adhesive strength by bonding a protective film with an adhesive. [Problems to be Solved by the Invention] However, although the method described in JP-A-56-50301 improves the adhesive strength between the protective film and the adhesive layer, it does not improve the adhesive strength between the polarizing film and the adhesive layer. There was no improvement in this point, and it is important to improve this point at the same time in order to improve the moisture resistance and dimensional stability of the polarizing plate. Compared to this method, the method described in JP-A-61-245107 aims to improve the adhesion between the polarizing film and the adhesive layer, and between the adhesive layer and the protective film at the same time, so it is somewhat more practical. Although the product is obtained,
Moisture resistance and dimensional stability are still not fully satisfactory, and further improvement is desired. [Means for Solving the Problems] Therefore, as a result of intensive research in order to solve the problems, the inventors of the present invention have developed a method of attaching a cellulose acetate-based protective film to at least one surface of a vinyl alcohol-based polarizing film using an adhesive material. It was discovered that a polarizing plate with excellent moisture resistance and dimensional stability can be obtained by heat treating the bonded polarizing plate at a temperature of 90 to 110°C, and the present invention I was able to complete it. The vinyl alcohol polarizing film of the present invention is generally a uniaxially stretched polyvinyl alcohol film or a saponified ethylene-vinyl acetate copolymer film on which iodine or dichroic dye is adsorbed and oriented. Polyvinyl alcohol and saponified ethylene-vinyl acetate copolymers are not necessarily limited to these, but include small amounts of unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins, vinyl ethers, unsaturated It may contain a component copolymerizable with vinyl acetate or further with ethylene, such as a sulfonate. The polarizing film of the present invention can be manufactured by any known method, for example, the following methods may be employed.
The present invention is not limited to this. An aqueous solution of iodine or dichroic dye, or an aqueous solution prepared by adding potassium iodide and/or boric acid to this aqueous solution, is kept at room temperature or heated (30 to 60°C), and a polyvinyl alcohol film or ethylene is added to the aqueous solution. - A saponified vinyl acetate copolymer film is impregnated and dyed and stretched 3 to 5 times, or the stretched film is immersed in the above-mentioned impregnating liquid in advance and dyed. The surface of the obtained film is washed with alcohol or water while maintaining tension, and dried to obtain a polarizing film. The cellulose acetate-based protective film of the present invention includes films such as cellulose diacetate and cellulose triacetate. Further, it is more effective to subject the surface of the protective film to saponification treatment with an alkali, plasma treatment, glow discharge treatment, corona discharge treatment, high frequency treatment, electron beam treatment, etc. The adhesive used in the present invention is not particularly limited, and any known adhesive may be used, such as polyvinyl alcohol and its derivatives, starches, water-soluble polymers such as carboxymethyl cellulose, acrylic resins, urethane resins, and epoxy resins. Hydrophilic polymers such as Adhesives are practically used in aqueous solutions with a concentration of 0.5 to 40% by weight, preferably 1 to 10% by weight. Above, the amount of adhesive applied is 0.1 to 5 g/m ² ,
Preferably, 1 to 3 g/m ² is appropriate. 0.1g/
If it is less than ^m2 , the adhesive strength is insufficient;
If it exceeds 5 g/m ² , the effect will not increase in proportion to the amount used, and it is not practical. Usually, it is advantageous to apply the adhesive so as to form a uniform film on the polarizing film or cellulose acetate protective film. The coating operation is not necessarily limited to a coating method using a roll or the like, but also includes methods such as a spraying method and a dipping method. Apply the adhesive to the cellulose acetate-based protective film (or polarizing film), and bond it to at least one side of the polarizing film (or cellulose acetate-based protective film) at 30 to 90°C, preferably 60 to 80°C. for 0.5 to 5 minutes,
Preferably dry for 1 to 2 minutes, followed by 90 to
The polarizing plate of the present invention can be obtained by performing heat treatment at 110°C for about 0.5 to 5 minutes. It is difficult to obtain the effect of the present invention at a heat treatment temperature of 90°C or lower, whereas at a heat treatment temperature of 110°C
If the temperature is exceeded, the film will yellow and cause problems. The polarizing plate thus obtained has better moisture resistance and dimensional stability than conventional ones, and is extremely important industrially. [Function] In the production method of the present invention, after adhering the vinyl alcohol polarizing film and the cellulose acetate protective film,
Heat treatment at ~110°C significantly improves the heat resistance, moisture resistance, and dimensional stability of the resulting polarizing plate. [Examples and Comparative Examples] The present invention will be described in more detail below with reference to Examples and Comparative Examples. The degree of polarization in the present invention is a value determined from the following formula. H|; Transmittance was measured by overlapping two samples so that the orientation directions of the polarizing films were in the same direction (parallel transmittance). H⊥; Transmittance was measured by overlapping two samples in a direction in which the orientation directions of the polarizing films were orthogonal to each other (orthogonal transmittance). Nippon Denshoku Kogyo Z-1001DP was used to measure transmittance.
A spectrophotometer was used. Example 1 A polyvinyl alcohol film with a degree of polymerization of 3800, a degree of saponification of 99.9 mol%, a water content of 10% by weight, and a thickness of 50μ was mixed with 5.0 g of iodine, 250 g of potassium iodide, 10 g of boric acid,
While immersed in a 40℃ bath consisting of 1000g of water,
It was uniaxially stretched up to 4 times in minutes. The surface of the obtained film was washed with alcohol while maintaining tension, and then air-dried to obtain a polarizing film. A 4% aqueous solution of polyvinyl alcohol with a degree of polymerization of 1700 and a degree of saponification of 99.9 mol% was applied to a thickness of 5μ on a cellulose triacetate film whose surface had been surface-treated with alkali.
It was pasted on both sides of the polarizing film, dried at 80°C for 2 minutes in a hot air dryer, and then heat-treated at 95°C to obtain a polarizing plate. Moisture resistance test was performed on the obtained polarizing plate at 60℃ - 90%
After being left in a constant temperature and humidity chamber at RH for 10 days, the single transmittance,
Changes in polarization degree and dimensional changes were measured. The test results are shown in Table 1. Example 2 An experiment was conducted in the same manner as in Example 1 except that the heat treatment temperature was changed to 105°C. The results are shown in Table 1. Example 3 An experiment was conducted in the same manner as in Example 1 except that the stretching ratio of the polyvinyl alcohol film was changed to 5 times. Example 4 In place of the polyvinyl alcohol film in Example 1, ethylene content was 40 mol%, saponification degree of vinyl acetate component was 99.9 mol%, volatile content was 5% by weight,
An experiment was carried out in accordance with Example 1, except that a saponified ethylene-vinyl acetate copolymer film having a thickness of 70 μm was used. The results are shown in Table 1. Control Examples 1 and 2 An experiment was conducted according to Example 1, except that the heat treatment temperature was 85° C. (Control Example 1) and 120° C. (Control Example 2). The results are shown in Table 1.

[Table] [Effects] As mentioned above, the method of the present invention involves bonding a vinyl alcohol polarizing film and a cellulose acetate film,
By subsequently heat-treating at a temperature of 90-110℃,
The moisture resistance and dimensional stability of the resulting polarizing plate are significantly improved, providing an industrially excellent method.

Claims (1)

[Claims] 1. A method for producing a polarizing plate, which comprises adhering a cellulose acetate-based protective film to at least one surface of a vinyl alcohol-based polarizing film using an adhesive material, and then heat-treating the film at a temperature of 90 to 110°C.