Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-09-29
2000-11-28
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524366, 524544, 524545, 524376, C08K 506, C08L 2718
Patent
active
061536881
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a composition which is an aqueous polytetrafluoroethylene dispersion as concentrated, and to the use thereof. The aqueous polytetrafluoroethylene dispersion composition of the invention is useful, for example, for coating base materials such as glass fibers, carbon fibers and aramide fibers (hereinafter referred to as "fibrous base materials") for preparing conveyor belts, roof materials (tent fabrics) for architectural fabric structure, packings, high-frequency printed boards, etc., and is also suited as it is for use as a battery binder and a material for coating compositions.
BACKGROUND ART
It is already known to concentrate an aqueous polytetrafluoroethylene dispersion by adding a surfactant to the dispersion, thereafter heating the dispersion to form a transparent aqueous solution as an upper layer and to concentrate polymer particles as contained in a lower aqueous layer, and removing the upper layer by decantation. The surfactant used is an ethylene oxide adduct of an alkylphenol (polyoxyethylene alkyl phenyl ether). However, the concentrated dispersion has many problems, such as those given below, for use in impregnating fibrous base materials.
(1) In the impregnating-baking step, the surfactant thermally decomposes, converting into a harmful organic aromatic compound (such as benzene, toluene or xylene) as an exhaust gas to cause air pollution.
(2) The surfactant partially undergoes thermal decomposition to produce a tarlike substance, which accumulates on the inner wall of the baking furnace of the impregnating-baking apparatus. The substance falls onto or adheres to the fibrous base material passing through the furnace to lower the yield from the viewpoint of quality.
(3) The surfactant, which is difficult to thermally decompose or dissipate, partly remains in the fibrous base material after baking, assuming a brown color to seriously impair the hand of the impregnated material.
(4) Because the remaining portion of the surfactant is carbonized, use of the impregnated material in preparing high-frequency printed boards entails impaired electric characteristics.
When the dispersion is used as a battery binder, the surfactant is left undissipated almost entirely under the drying condition (about 250 to about 300.degree. C.) for the electrode material, remaining in the electrode material and contributing to impaired performance.
To solve these problems, aqueous polytetrafluoroethylene dispersion compositions are known in which an ethoxylated aliphatic alcohol (polyoxyethylene alkyl ether) is used (see, for example, JP-B-21532/1977). It is known that polyoxyethylene alkyl ethers are lower than polyoxyethylene alkyl phenyl ethers in decomposition temperature, therefore readily dissipate on thermal decomposition in many cases, are less likely to remain in polymers, and form films which are apparently advantageous in yellow index of plastics (ASTM D-1925-63T) measured.
Polyoxyethylene alkyl ethers, which contain no benzene ring in the structure, do not convert into a harmful organic aromatic compound (such as benzene, toluene or xylene) on thermal decomposition, giving rise to no air pollution. Thus, the aqueous polytetrafluoroethylene dispersion comprising a polyoxyethylene alkyl ether has various advantages and yet is not in wide use because in the field of fibrous base materials impregnated with aqueous polytetrafluoroethylene dispersions wherein the dispersion is used most frequently, the following properties are required of the dispersion.
(1) For impregnation, the dispersion is relatively stabilized in viscosity and low in viscosity-temperature dependence.
(2) The dispersion has a relatively low viscosity of 10 to 30 cp at room temperature (25.degree. C.) and smoothly penetrates into fibrous base materials.
(3) When the dispersion is repeatedly applied in layers, the resulting coating still remains free of cissing or coagulation.
JP-B-21532/1977 mentions nothing about such impregnation.
We have conducted intensive research on the invention of JP
REFERENCES:
patent: 3705867 (1972-12-01), Holmes
patent: 5218031 (1993-06-01), Nayder et al.
English Abstract of JP-A-5-339,537--Kobayashi et al, 1993.
English Abstract of JP-A-4-168,170--Yamada et al, 1992.
English Abstract of JP-A-8-046,932--Tanaka et al, 1996.
English Abstract of JP-A-5-320,360--Tabata et al, 1993.
English Abstract of JP-A-3-001,442--Oda et al, 1991.
English Abstract of JP-A-3-147,254--Tsuchiya et al, 1991.
Hayashi Tadao
Miura Toshiro
Daikin Industries Ltd.
Kintner Arent Fox
Zitomer Fred
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