Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-10-26
2002-01-08
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C252S585000, C264S001310, C264S001340, C264S001350, C359S490020, C524S557000, C525S057000
Reexamination Certificate
active
06337369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarizing film comprising a polyvinyl alcohol derivative with a polyvinylene structure.
2. Description of the Background
A Polarizing sheet having a light-transmitting and shielding function laminated with protective films is a basic constituent element for a liquid crystal display (LCD), along with a liquid crystal having a light-switching function. The applications of the LCD include small-sized instruments such as pocket calculators, watches, etc. in the early years, as well as lap-top personal computers, word processors, liquid-crystal color projectors, on-vehicle navigation systems, liquid-crystal TV, indoor and outdoor measuring instruments, etc. The LCD has been used in heavy temperature and humidity fluctuations of from low temperature to high temperature and from low humidity to high humidity. Accordingly, there has been desired a polarizing sheet which has excellent durability such as wet heat resistance, etc. and excellent polarizing properties.
A polarizing sheet has a structure that both sides of a polarizing film as obtained from a polyvinyl alcohol (hereinafter referred to as PVA) film are laminated with supporting films of cellulose triacetate or the like. As a polarizing film, there have been known an iodine-containing polarizing film as prepared by dyeing a PVA film with iodine, a dye-containing polarizing film as prepared by dyeing a PVA film with a dichroic dye, and a polarizing film of a PVA derivative with a polyvinylene structure as prepared by dehydrating a PVA film (U.S. Pat. No. 2,173,304).
The iodine-containing polarizing film and the dye-containing polarizing film have good polarizing properties, while they have a problem that their durability is poor. The polarizing film of a polyvinyl alcohol derivative with a polyvinylene structure has excellent durability, while it has a problem that its polarizing property is poor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a polarizing film which has excellent durability and excellent polarizing properties.
Having intensively studied to solve the above object, the present inventor has found out a polarizing film having a dichroic ratio of at least 20 and comprising a polyvinyl alcohol derivative with a polyvinylene structure as obtained from a polyvinyl alcohol material having a degree of polymerization of at least 2000, and has completed the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is described in more detail hereinunder.
The degree of polymerization of the PVA material to be used for producing the polarizing film of the present invention is at least 2000, but preferably at least 2800, more preferably at least 3000, even more preferably at least 3500. The higher the degree of polymerization, the better the durability and the polarizing properties. In view of the film-forming properties, the upper limit of the degree of polymerization is preferably 30000. The degree of polymerization of the PVA is measured according to JIS-K-6726.
In view of the polarizing properties and the durability, the degree of hydrolysis of the PVA is preferably at least 90 mol %, more preferably at least 98 mol %, even more preferably at least 99 mol %, still more preferably at least 99.5 mol %.
The dichroic ratio of the polarizing film is at least 20, preferably at least 25, more preferably at least 30. To increase its dichroic ratio, it is desirable that a PVA film having a high degree of polymerization and containing a dehydrating promoter is stretched under dry-heat at a high stretch ratio in an oxygen-poor atmosphere.
The wavelength of maximal absorption in the range of the visible ray absorption spectrum (wavelength: 380 to 780 nm) of the polarizing film is preferably at least 500 nm, more preferably at least 520 nm, even more preferably at least 540 nm. The upper limit of the wavelength of maximal absorption is preferably 650 nm, more preferably 620 nm. As the degree of polymerization of the PVA to be used as a material becomes higher, the wavelength of maximal absorption tends to shift to a higher wavelength side.
In the case where the wavelength of maximal absorption is in the above-described range, it is estimated that the number of vinylene units of conjugated double bonds which constitute the polyvinylene structure be approximately from 15 to 30.
As a method for producing PVA, for example, there are a method of hydrolyzing a polyvinyl ester polymer as obtained through radical polymerization of a vinyl ester monomer such as vinyl acetate and the like, with an alkali catalyst or an acid catalyst.
As a method for polymerizing a vinyl ester monomer, for example, there are bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like. Bulk polymerization or emulsion polymerization is preferable to obtain PVA having a degree of polymerization of at least 4000. As a polymerization catalyst, for example, there are azo catalyst, peroxide catalyst, redox catalyst, etc.
As a vinyl ester monomer, for example, there are vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl trifluoroacetate, vinyl versatate, etc. Of those, vinyl acetate is preferable.
The vinyl ester monomer may be copolymerized with a copolymerizable comonomer.
As a comonomer, for example, thare are olefins such as ethylene, propylene, 1-butene, isobutene, etc.; acrylic acid and its salts; acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc.; methacrylic acid and its salts; methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc.; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetonacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts and quaternary salts, N-methylolacrylamide and its derivatives, etc.; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts and quaternary salt, N-methylolmethacrylamide and its derivatives, etc.; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.; nitrites such as acrylonitrile, methacrylonitrile, etc.; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.; allyl compounds such as allyl acetate, allyl chloride, etc.; maleic acid and its salts and esters; vinylsilyl compounds such as vinyltrimethoxysilane, etc.; isopropenyl acetate, etc.
As another method for producing PVA, there may be a method of hydrolyzing a polyvinyl ether polymer from t-butyl vinyl ether, benzyl vinyl ether, trimethylsilyl vinyl ether and the like.
A PVA film as prepared by film-forming a PVA having a degree of polymerization of at least 2000 is used for producing the polarizing film of the present invention. As a method of film-forming a PVA film, for example, there is a casting method or a die-casting method that comprises casting a PVA solution onto a resin film, a drying drum or a drying belt. As a solvent for the PVA, for example, there are water, an organic solvent, and a mixed solvent of water and an organic solvent. The organic solvent includes dimethylsulfoxide, phenol, methanol, ethanol, etc. The PVA solution may optionally contain any of plasticizers, surfactants, dichroic dyes, inorganic salts, etc. The PVA film may be heat-treated, if desired. The thicknes
Kuraray Co. Ltd.
Reddick Judy M.
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