Compositions – Dust suppressants for bulk materials – or processes of...
Patent
1997-02-06
1998-08-04
Howard, Jacqueline V.
Compositions
Dust suppressants for bulk materials, or processes of...
427212, 427221, 44602, C09K 322
Patent
active
057888795
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/JP95/01324 filed Jul. 3, 1995.
TECHNICAL FIELD
The present invention relates to a method for preventing dust of a powdery material by use of a highly dust-preventive polytetrafluoroethylene (hereinafter referred to as PTFE).
BACKGROUND ART
Japanese Patent Publication No.52-32877 discloses a method for preventing dust of a powdery material by mixing the powdery material with PTFE and subjecting the mixture to compression-shearing at a temperature from about 20.degree. to 200.degree. C., thereby fibrillating the PTFE to prevent dusting of the powdery material. The PTFE disclosed therein includes fine powder or emulsion form of homopolymer of tetrafluoroethylene denoted by TEFLON.RTM. 6 or TEFLON.RTM. 30, and also fine powder or emulsion form of modified polymer of tetrafluoroethylene denoted by TEFLON.RTM. 6C or TEFLON.RTM. 64. Thereafter, "TEFLON.RTM. K-10" (PTFE fine powder) and "TEFLON.RTM. K-20" (PTFE emulsion) were developed and have being marketed for dust-preventing usages.
With regard to the above PTFE, however, there occur fluctuation in the dust-preventing effect due to insufficient fibrillation, unsatisfactory strength of fibrils and uneven distribution of PTFE in the powdery material. Especially for the dust preventing agent in an emulsion type, there are problems related to the emulsion itself such as separation and coagulation of PTFE colloidal particulates caused by mechanical actions during transportation, weighing and dilution thereof, which bring about clogging of pipes, pumps, orifices, etc., and further decrease concentration of PTFE in the emulsion to cause erroneous mixing rate of PTFE to a powdery material. Moreover, as the result of using a large amount of emulsion type dust preventing agents for such powdery materials as fertilizers, soil stabilizers and reclamation materials like coal ash, surfactants employed as the emulsion stabilizer have become possible contaminants of underground water, lakes, rivers, etc.
The present invention aims at providing a method for preventing efficiently dust of powdery materials by use of an aqueous emulsion of tetrafluoroethylene homopolymer, which emulsion being highly stable and a less possible contaminant of underground water.
DISCLOSURE OF THE INVENTION
According to the present invention of a method for preventing dust of a powdery material by mixing the powdery material with PTFE and subjecting the mixture to a compression-shearing action taken at temperatures from about 20.degree. to 200.degree. C. thereby the PTFE is fibrillated to prevent dusting of the powdery material, the method is characterized by that the PTFE used is an aqueous emulsion of tetrafluoroethylene homopolymer, the homopolymer has a specific gravity of not larger than 2.20 and an average particle size of 0.10-0.50.mu., and the emulsion contains a hydrocarbon-based anionic surfactant of not less than 1.0 wt % of PTFE as a emulsion stabilizer.
BEST MODE FOR CARRYING OUT THE INVENTION
The PTFE usable for the present invention is a homopolymer, though PTFE includes a so-called homopolymer of tetrafluoroethylene and a so-called modified polymer being a copolymer of tetrafluoroethylene and a comonomer of not more than 1%. A dust preventing agent using an aqueous emulsion of the modified PTFE polymer exhibits a dust preventing effect inferior to that of the present invention, and frequently requires over 50% excessive amounts of the agent to show the same effect.
The PTFE suitable for the present invention has an average particle size range of 0.10-0.50.mu., preferably 0.10-0.30.mu., and a specific gravity of not larger than 2.20, preferably not larger than 2.18. Colloidal particles having an average particle size of smaller than 0.10.mu. result inferior dust preventing effect, and those of larger than 0.50.mu. brings about unstable emulsions. PTFE having a specific gravity of larger than 2.20 results an inferior dust preventing effect. The average particle size of PTFE particles can be determined by a cen
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Chiba Shizuo
Gocho Tomohiro
Miyaji Hiroshi
Ogura Masatsune
Shimoda Tetsuya
Howard Jacqueline V.
Toomer Cephia D.
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