JP3497903B2 - Polyvinyl alcohol film for raw material of polarizing film - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material of a polarizing film which is excellent in processing characteristics such as stretch / alignment processability and dichroic substance adsorption (dyeing) processability. It relates to a polyvinyl alcohol film. Conventionally, a liquid crystal display device has been used as a display device having a relatively small screen such as a clock, a calculator, a word processor, and instruments of a machine, and the demand for display quality has not been particularly severe. However, in recent years, liquid crystal display devices have been widely used as displays for laptop word processors, laptop personal computers, notebook personal computers, displays for instrument panels of automobiles and aircraft, liquid crystal projectors, and the like. There is a demand for improvement in durability and durability. Therefore, in order to achieve the above-mentioned objects, the polarizing film, which is a component of the liquid crystal display device, has an improved optical characteristic such as a large screen, a high degree of polarization and a high transmittance, and has water resistance, heat resistance, wet heat resistance and durability. In addition to the improvement of the properties, it is required to improve the processing characteristics as a raw film of the polarizing film from the viewpoint of further improving the productivity and securing the quality. Conventionally, as a polarizing film, polyvinyl alcohol (hereinafter referred to as PVA) adsorbing an iodine compound or a dichroic dye has been used.
Is abbreviated as a uniaxially stretched film.
Improvements in polarization performance and durability are required. On the other hand, a proposal using a highly polymerized PVA or a highly syndiotactic PVA as a raw material (see, for example,
No. 105204, JP-A-3-206402), the effects of high polymerization degree and high syndiotacticity are recognized in terms of polarization characteristics and durability. It is necessary to perform the orientation treatment at a high temperature, and the high temperature treatment causes problems such as desorption of the iodine compound and deterioration of the dyeability due to decolorization. Also,
A conventional raw film using PVA has poor dyeing properties with a dichroic dye, and has problems such as high temperature dyeing, a long dyeing time, and spots in the dyeing. SUMMARY OF THE INVENTION An object of the present invention is to provide an alignment treatment at a lower temperature as compared with a conventional high-performance polyvinyl alcohol film used as a raw material for a polarizing film. An object of the present invention is to provide a polyvinyl alcohol film for use as a raw material of a polarizing film, which is excellent in processing characteristics such as a high dyeing property with a hydrophilic substance. The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that syndiotacticity is 55% or more, and that ω-hydroxy-α-olefin
A film made of a polyvinyl alcohol-based polymer containing 0.01 to 1 mol% of at least one hydrophilic functional group selected from a hydroxyl group and an oxyalkylene group ;
The present invention has been completed by finding a polyvinyl alcohol film for a raw material of a polarizing film, which is uniaxially stretched 5 times or more at 0 ° C. Hereinafter, the present invention will be described in detail. [0007] The degree of polymerization of the PVA polymer in the present invention is not particularly limited.
It is preferably at least 00, and more preferably at least 1,000, more preferably at least 1500, from the viewpoint of the polarizing performance of the obtained polarizing film. The upper limit of the degree of polymerization of the PVA-based polymer is not particularly limited, but is preferably 20,000 or less from the viewpoints of film formability and processability into a polarizing film. The preferred range of the degree of polymerization is from 1500 to 10,000. [0008] The syndiotacticity of the PVA-based polymer in the present invention must be 55% or more, and preferably 58% or more. The upper limit of the syndiotacticity is not limited, but is preferably 75% or less from the viewpoint of film formability and processability such as stretching.
The preferred range of syndiotacticity is 60-68%
Is most preferred. If the syndiotacticity is lower than 55%, the polarization characteristics and durability are reduced. Incidentally, the “syndiotacticity” of the PVA polymer referred to in the present invention is:
It is a value based on a dyad display measured by the NMR method, and specifically, measured by the method described in JP-A-3-121102. In the present invention, the PVA-based polymer is ω-
Hydroxy-α-olefin group and oxyalkylene
One or more hydrophilic functional groups selected from among the group 0.0
It is necessary to contain 1 to 1 mol% (preferably 0.05 to 0.9 mol%, more preferably 0.08 to 0.8 mol%) . Functional group is preferably chemically bonded to the PVA polymer, allyl alcohol For example, 1-butene-4-ol, 7-octen-1-ol etc. ω- hydroxy -α- olefin, Oxyalkylene groups such as polyethylene oxide monoallyl ether and their lower alkyl ethers. There is no limitation on the method of introducing these functional groups, and examples thereof include a method by copolymerization described later and a method of introducing them into a polymer by a post-reaction. The method for producing the PVA polymer of the present invention is not limited, and is generally produced by the following method. That is, vinyl pivalate, vinyl trifluoroacetate,
It is obtained by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester such as vinyl trichloroacetate. The method for polymerizing the polyvinyl ester polymer of the present invention includes a solution polymerization method, a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method and the like. Particularly, in order to obtain PVA having a high degree of polymerization, these polymerization methods are used. A low-temperature polymerization method can be used in combination with the polymerization method. The PVA-based polymer having a hydrophilic functional group, which is a feature of the present invention, can also be obtained by copolymerizing a vinyl ester with a monomer having the functional group or a derivative (or precursor) thereof during polymerization. There is no particular limitation on these monomers, and the monomers may have a hydrophilic functional group, or may be hydrophilic by a chemical reaction such as hydrolysis, esterification, or ketalization after polymer production. It may be a precursor which is converted into a functional group having a property. [0012] As the monomer which can be used in this, allyl alcohol, 1-butene-4-ol, 7-octen-1-ol etc. ω- hydroxy -α- olefin, polyoxyethylene monoallyl ether, poly And oxyalkylene groups such as oxypropylene monoallyl ether and their lower alkyl ethers. The PVA polymer is obtained by saponifying the polyvinyl ester polymer thus obtained. In general, a transesterification process called alcoholysis using an alcohol solution of polyvinyl ester and an alkali catalyst such as caustic soda is used. Done by The degree of saponification, which is a conversion rate at which the vinyl ester unit is converted into a vinyl alcohol unit, is not particularly limited. However, a low degree of saponification has an adverse effect such as a decrease in durability as a polarizing film. Is preferable, and 95 mol% or more is more preferable. The amount of 1,2-glycol bond of the PVA polymer of the present invention is not particularly limited, and is generally 1.6 to 1.5.
Although 1.8 mol% of PVA is used, it is preferably 1.6 mol% or less from the viewpoint of high polarization degree and high durability. The method for producing a raw film for a polarizing film of the present invention and the method for producing a polarizing film using the raw film are not limited, and examples thereof include the following methods. As an example,
First, there is a method in which a PVA-based polymer film to be used as a film for a raw film for a polarizing film is prepared, and an alignment treatment such as adsorption and stretching of a dichroic substance such as iodine or a dye is performed. The order of the adsorption of the volatile substance and the stretching operation is arbitrary. In the present invention, the method for producing the raw film of the polarizing film is not limited, and a method of forming a liquid film from an aqueous PVA solution and drying the liquid film to obtain a film is generally employed. PVA
Film formation from a system copolymer solution includes cast film formation and dry film formation (extrusion into an inert gas such as air or nitrogen), wet film formation (extrusion of a PVA-based polymer into a poor solvent), and dry / wet. The film formation is performed by formula film formation or gel film formation (a method of once gelling a PVA-based polymer solution to obtain a film), and the solvent used at this time is dimethylsulfoxide, dimethylformamide, dimethylacetamide, ethylene glycol. , Glycerin and water are used alone or in combination. In addition, an aqueous solution of an inorganic salt such as lithium chloride and calcium chloride can be used alone or as a mixture with the organic solvent. Among them, water, dimethyl sulfoxide or a mixed solvent of dimethyl sulfoxide and water is preferably used. Further, a dichroic substance may be mixed with the solution to form a film, or a polyhydric alcohol such as glycerin or diglycerin or ethylene glycol and a derivative thereof may be contained in order to impart flexibility or the like to the film. . The film made of the PVA-based polymer obtained by the above film forming method is subjected to an orientation treatment by adsorption of a dichroic substance and uniaxial stretching, or a film to which a dichroic substance is added during film formation. Only uniaxial stretching is performed. It does not matter if the adsorption treatment and the orientation treatment are performed simultaneously or separately, and the order is arbitrary. The adsorption of the dichroic substance to the substrate film is usually performed by immersing the film in a liquid containing the dichroic substance, but the treatment conditions and methods are not particularly limited. When used, an aqueous solution of iodine-potassium iodide is used, and in the case of a dye, an aqueous dye solution is used.
In addition, boron compounds such as boric acid and borax may be added to these aqueous solutions. As the dichroic substance used in the polarizing film of the present invention, in addition to an iodine compound, a so-called dichroic dye is used alone or in combination. Representative examples include Direct black 17, 19, 1
54, Direct brown 44, 106, 19
5, 210, 223, Direct red 2, 23,
28, 31, 37, 39, 79, 81, 240, 24
2,247, Direct blue1,15,22,
78, 90, 98, 151, 168, 202, 236,
249, 270, Direct violet 9, 1
2, 51, 98, Direct green 1, 85,
Direct yellow 8, 12, 44, 86, 8
7, Direct orange 26, 39, 106,
107 and the like. Orientation treatment by stretching the film is performed by dry thermal drawing performed by a wet stretching or dry state performed while water or swell, subjected to the stretching of 5 times or more in a uniaxial direction. The stretching temperature varies depending on the stretching method and other conditions, but is usually between 20 ° C and 40 ° C. Further, at the time of dry heat stretching, it is preferable to carry out the treatment in an inert gas. The stretching in water is generally performed in an aqueous solution such as boric acid or borax. The adsorbed and stretched film is dried in air or an inert gas at a constant length. The dried film may be further subjected to a heat treatment at a temperature of 80 ° C. to 230 ° C. in order to impart water resistance, wet heat resistance and the like. In addition, a boron compound such as boric acid or borax may be added for the purpose of strengthening the adsorption of the dichroic substance to the base film and for imparting water resistance and wet heat resistance. It may be performed at the same time as before or after the stretching or at any time before or after these treatments. A feature of the present invention is that these orientation / adsorption treatments can be performed more easily than conventional PVA films. In order to obtain high polarization performance with conventional PVA, it is necessary to perform an alignment treatment at a high temperature. In particular, when a high polymerization degree PVA or a high syndiotacticity PVA is used, an alignment treatment at a higher temperature is required. When a film on which an iodine compound is adsorbed is treated at such a high temperature, desorption of the iodine compound,
Bleaching and spotting occur. By using the PVA of the present invention, high polarization performance can be obtained by stretching / orienting at a temperature lower by 3 ° C. or more than conventional PVA. Therefore, desorption of the adsorbed iodine compound can be reduced,
As a result, the dyeability is improved. In addition, the dyeability of the dichroic dye is improved by using the PVA of the present invention, and dyeing can be performed without requiring a high temperature or a long dyeing time. The polarizing film thus obtained is used as a polarizing plate by laminating a protective film (support) having optical transparency and mechanical strength on both surfaces or one surface. As the protective film, a cellulose acetate film, an acrylic film, a polyester film, or the like is usually used. Among them, a cellulose acetate film such as cellulose triacetate is generally used from the viewpoint of optical characteristics and the like. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples. The measurement of the transmittance (T), the degree of polarization (V), and the hue is based on the standard of the Electronic Industries Association of Japan (EIAJ) LD-201-.
Based on 1983, calculation was performed using a spectrophotometer with a C light source and twice viewing. The dichroic ratio (Rd) is a value indicating the polarization performance obtained by the following equation. Rd = log (T (1-V)) / log (T (1 + V)) Reference Examples 1 to 6 and Comparative Examples 1 to 6 (high polymerization degree PVA) 5% of the PVA polymer shown in Table 1 An aqueous solution was cast on a polyethylene terephthalate film, and the liquid film was dried at 60 ° C. and heat-treated at 120 ° C. for 3 minutes to obtain PVA.
A polymer film was obtained. Next, a polarizing film was manufactured using the obtained PVA-based polymer film as a raw material. (When the dichroic substance is an iodine-based compound) The PVA-based polymer film is immersed in water at 30 ° C. for 10 minutes, and is immersed in an iodine-potassium iodide solution (iodine concentration 0.0
After adsorbing the iodine compound at 25% by weight and a potassium iodide concentration of 0.03% by weight), the solution is adsorbed in a boric acid-potassium iodide solution (boric acid concentration of 4% by weight, potassium iodide concentration of 1.5%).
% By weight) and dried at 50 ° C. to produce a polarizing film. (When the dichroic substance is an organic dye) The PVA-based polymer film is immersed in water at 30 ° C. for 10 minutes, immersed in a DirectBlue 1 aqueous solution (concentration: 2% by weight), and then in a boric acid aqueous solution (boric acid concentration: 4% by weight) %) And dried at 50 ° C. to produce a polarizing film.
The above results are shown in Table 1 together with the dyeing conditions and the stretching conditions. [Table 1] Reference Examples 7 to 10, Examples 1 and 2, and Comparative Examples 7 to 11 (High Syndiotacticity PVA) The PVA polymers shown in Table 2 were used in the same manner as in Reference Examples 1 to 6, A PVA-based polymer film was obtained. Next, a polarizing film was manufactured using the obtained PVA-based polymer film as a raw material. The above results are shown in Table 2 together with the dyeing conditions and the stretching conditions. [Table 2] According to the present invention, a PVA film used as a raw material for a polarizing film is stretchable and orientable and adsorbs (dyes) a dichroic substance.
It has excellent processing characteristics such as processability. The polarizing film obtained from the raw film has excellent optical characteristics such as high polarization and high transmittance. The polarizing film obtained by the present invention is a high-performance and highly durable liquid crystal display, such as a liquid crystal television, a liquid crystal projector, a display for a word processor, a display for a personal computer, a display for an OA equipment terminal, and an instrument panel for an aircraft or a car, by utilizing the above characteristics. It is used for displays, filters, sunglasses, window glasses, anti-glare of various lights, various sensors, and the like.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-265727 (JP, A) JP-A-5-245857 (JP, A) JP-A-60-230606 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02B 5/30 C08F 16/06 C08L 29/04

Claims (1)

(57) [Claim 1] Syndiotacticity of 55% or more, ω-hydroxy-α-olefin group and oxo group
A film made of a polyvinyl alcohol-based polymer containing 0.01 to 1 mol% of one or more hydrophilic functional groups selected from silalkylene groups is uniaxially stretched 5 times or more at 20 to 40 ° C. Polyvinyl alcohol film for raw material of polarizing film.