JP2779413B2 - Manufacturing method of polarizing plate - Google Patents

Description

The present invention relates to a method for producing a polarizing plate.

[Related Art] In recent years, liquid crystal display devices have been used in desktop electronic calculators, electronic watches, word processors, instruments of automobiles and machinery, and the demand for polarizing plates has been increasing.

Generally, a polarizing plate is obtained by forming a protective film on both sides of a polarizing film having a polarizing ability via an adhesive layer.

As the polarizing film, for example, those obtained by dyeing iodine on a vinyl alcohol-based uniaxially stretched film such as a polyvinyl alcohol-based resin or a saponified ethylene-vinyl acetate copolymer are typically used.As the protective film, cellulose acetate is used. A system film is widely used because it has excellent optical transparency and non-orientation as a surface protective film.

Since both the vinyl alcohol-based film and the cellulose acetate-based film are hydrophilic, they are generally bonded using a hydrophilic adhesive. For this reason, the obtained polarizing plate has a large water absorption rate in a high-humidity atmosphere for a long time, and as it absorbs water, the adhesive strength is reduced, and the physical properties of polarized light are reduced, which causes a problem in so-called moisture resistance and dimensional stability. ,
In addition, if the temperature is high, the degree of polarization may be reduced and heat resistance may be impaired.

In order to solve this problem, for example, Japanese Unexamined Patent Publication No.
In Japanese Patent Application Laid-Open Publication No. H11-163, it is proposed that the surface of a cellulose acetate-based film of a protective film is saponified to strengthen the adhesive force between an adhesive and cellulose acetate, and to improve moisture resistance, heat resistance and dimensional stability. .

In JP-A-61-245107, the surface of the polarizing film is once treated with an aqueous solution or an adhesive of a hydrophilic polymer such as polyvinyl alcohol, carboxymethylcellulose, urethane, acrylic, or epoxy, and then again. It has been proposed to provide a polarizing plate with improved adhesive strength by bonding a protective film via an adhesive.

[Problems to be Solved by the Invention] However, in the method described in Japanese Patent Application Laid-Open No. 56-50301,
The adhesive strength between the protective film and the adhesive layer is improved, but the adhesive strength between the polarizing film and the adhesive layer is not improved at all. It is important in improving stability.

Compared with this method, the method described in JP-A-61-245107 aims to improve the adhesion between the polarizing film and the adhesive layer, and the adhesive layer and the protective film at the same time, so that it is somewhat more practical. Although the product can be obtained, the moisture resistance, heat resistance, and dimensional stability are not yet sufficiently satisfactory, and further improvement is desired.

[Means for Solving the Problems] Accordingly, the present inventors have conducted intensive studies in order to solve such problems, and as a result, a cellulose acetate-based protective film was formed on at least one surface of a vinyl alcohol-based polarizing film using an adhesive material. In producing a polarizing plate bonded by bonding, it was found that a polarizing plate excellent in heat resistance, moisture resistance and dimensional stability can be obtained by using an aqueous solution of a boron compound as an adhesive material, and completed the present invention. I came to.

The feature of the production method of the present invention is that an aqueous solution of a boron compound is used as the adhesive material as described above. Therefore, a vinyl alcohol-based polarizing film layer and a boron compound adhesive layer, and a boron compound-based adhesive layer and a cellulose acetate-based adhesive layer are used. Since any of the protective film layers can be firmly bonded, heat resistance, moisture resistance and dimensional stability are remarkably improved.

As the vinyl alcohol-based polarizing film of the present invention, a film obtained by adsorbing and orienting iodine or a dichroic dye on a uniaxially stretched polyvinyl alcohol-based film or a saponified ethylene-vinyl acetate copolymer film is generally used.

The saponified product of polyvinyl alcohol and ethylene-vinyl acetate copolymer is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (salt, ester, amide,
Nitrile, etc.), olefins, vinyl ethers, unsaturated sulfonic acid salts, and the like, and may contain components copolymerizable with vinyl acetate or ethylene.

The polarizing film of the present invention is manufactured by any known method, and for example, the following means is employed, but the present invention is not limited thereto.

An aqueous solution of iodine or a dichroic dye, or an aqueous solution obtained by adding potassium iodide and / or boric acid to the aqueous solution at room temperature or heated (30 to 60 ° C.), is added to a polyvinyl alcohol-based film or ethylene. -Impregnation dyeing of a saponified vinyl acetate copolymer film and stretching it 3 to 5 times, or immersing the stretched film in the above impregnating solution in advance and dyeing. The surface of the obtained film is washed with alcohol or water while keeping the tension, and dried to obtain a polarizing film.

As the cellulose acetate-based protective film of the present invention, there are films such as cellulose diacetate and cellulose triacetate. Further, the surface of the protective film may be saponified with alkali, plasma treatment, glow discharge treatment, corona discharge treatment, high-frequency treatment,
It is more effective to perform electron beam processing or the like.

The boron compound of the present invention, specifically, boric acid, borate,
It means borax and the like, and as the borate, salts such as sodium, potassium and lithium are used. The boron compound is practically used in a 0.5 to 40% by weight, preferably 1 to 10% by weight aqueous solution.

The amount of the boron compound aqueous solution is 0.1 to 5 g /
m ² , preferably 1-3 g / m ² is suitable. When the amount is less than 0.1 g / m ² , the adhesive strength is insufficient. On the other hand, when the amount exceeds 5 g / m ² , the effect does not increase for the amount used and is not practical.

Usually, it is advantageous that the adhesive is applied so as to form a uniform film on the polarizing film or the cellulose acetate protective film. In that case, the coating film thickness of the boron compound aqueous solution is 0.1 to
5μ, preferably 2-5μ is practical. The coating operation is not necessarily limited to a coating unit using a roll or the like, and includes a spraying method, a dipping method, and the like.

Further, a water-soluble polymer such as polyvinyl alcohol may be used in combination with the adhesive.

The above-mentioned aqueous solution of the boron compound is applied to the cellulose acetate-based protective film (or the polarizing film), and is bonded to at least one surface of the polarizing film (or the cellulose acetate-based protective film);
The polarizing plate of the present invention can be obtained by performing a heat treatment at 30 to 90 ° C, preferably 60 to 80 ° C, for 0.5 to 5 minutes, preferably 1 to 2 minutes. The polarizing plate thus obtained is excellent in heat resistance, moisture resistance and dimensional stability as compared with those using other conventional adhesives, and is extremely important in industry.

[Function] In the production method of the present invention, when the vinyl alcohol-based polarizing film and the cellulose acetate-based protective film are bonded to each other, an aqueous solution of a boron compound is used, so that the obtained polarizing plate has heat resistance, moisture resistance, and dimensional stability. The properties are significantly improved.

[Examples and Comparative Examples] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

The polarization degree in the present invention is a value obtained from the following equation.

H ₁₁ ; Two samples were superimposed so that the orientation directions of the polarizing films were the same, and the transmittance was measured. (Parallel transmittance) H ₂ ; Two samples were superposed on each other in a direction in which the orientation directions of the polarizing films were orthogonal to each other, and the transmittance was measured. (Orthogonal transmittance) The transmittance was measured using a Z-1001DP spectrophotometer manufactured by Nippon Denshoku Industries.

Example 1 Degree of polymerization 1700, degree of saponification 99.9 mol%, water content 10% by weight,
50 μm thick polyvinyl alcohol film
g, potassium iodide 250g, boric acid 10g, water 1000g 40 ℃
The film was uniaxially stretched to 4 times in about 5 minutes while being immersed in the bath.

The obtained film was washed with alcohol while keeping the tension, and then air-dried to obtain a polarizing film. A 4% by weight aqueous solution of boric acid is applied to a thickness of 5 μ on a triacetylated cellulose film surface-treated with an alkali, and attached to both surfaces of a polarizing film.
Heat treatment was performed in a hot air drier for 2 minutes to obtain a polarizing plate.

In the moisture resistance test, the obtained polarizing plate was allowed to stand in a thermo-hygrostat at 60 ° C.-90% RH for 500 hours, and then the single transmittance, the change in the degree of polarization, and the dimensional change were measured.

The heat resistance test is performed after leaving in an 80 ° C hot air dryer for 500 hours.
The single transmittance, the change in the degree of polarization, and the dimensional change were measured. The results of these tests are shown in Table 1.

Example 2 Instead of the 4 wt% boric acid aqueous solution in Example 1, 1
An experiment was conducted in the same manner except that an aqueous solution of borax by weight was used.

 The results are shown in Table 1.

Example 3 Instead of the 4% by weight boric acid aqueous solution in Example 1, 6.
The same experiment was conducted except that a 5% by weight aqueous solution of potassium borate was used.

Example 4 A saponified ethylene-vinyl acetate copolymer having an ethylene content of 40 mol%, a saponification degree of a vinyl acetate component of 99.9 mol%, a volatile content of 5 wt%, and a thickness of 70 μm in place of the polyvinyl alcohol film in Example 1. 4% by weight of film
The experiment was carried out in the same manner as in Example 1 except that a 5% by weight aqueous solution of sodium borate was used instead of the boric acid aqueous solution. The results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated except that an aqueous 1% by weight aqueous solution of polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.9 mol% was applied as an adhesive to a thickness of 2 μ instead of the 4% by weight aqueous boric acid solution in Example 1. The experiment was performed according to the procedure.

 The results are shown in Table 1.

Control Example 2 A urethane-based adhesive was applied to both surfaces of the polarizing film obtained in Example 1 (only the solid content was 1 μm in thickness), dried sufficiently, and then the same urethane-based adhesive was applied to an alkali-treated triacetylated cellulose film. And applied to both surfaces of the polarizing film. The polarizing plate thus obtained was subjected to a moisture resistance and heat resistance test in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3 A saponified ethylene-vinyl acetate copolymer having an ethylene content of 40 mol%, a degree of saponification of a vinyl acetate component of 99.9 mol%, a volatile content of 5% by weight, and a thickness of 70 μm in place of the polyvinyl alcohol film in Comparative Example 1. The experiment was performed according to Control Example 1 except that a film was used.

[Effects] As described above, in the production method of the present invention, when a vinyl alcohol-based polarizing film and a cellulose acetate-based film are bonded to each other, an aqueous solution of a boron compound is used as a bonding material, so that the obtained polarizing plate has heat resistance and moisture resistance. The properties and dimensional stability are significantly improved, and an industrially superior method is provided.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-226104 (JP, A) JP-A-62-240905 (JP, A) JP-A-62-138578 (JP, A) 33547 (JP, A) JP-A-57-212276 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 5/30

Claims (1)

(57) [Claims] 1. A polarizing plate comprising a cellulose acetate-based protective film adhered to at least one surface of a vinyl alcohol-based polarizing film by using an adhesive material, wherein an aqueous solution of a boron compound is used as the adhesive material. Method for manufacturing a polarizing plate.