Title of Invention	A PROCESS FOR THE PREPARATION OF A FREE-FLOWING MOLDING POWDER
Abstract	The present invention relates to a process for the preparation of a free-flowing molding Powder, which comprises agglomerating a finely divided non free-flowing powder of at least one polytetrafluoroethylene or modified polytetrafluoroethylene with an aqueous medium which contains at least one surface active trialkylamine oxide, and drying the agglomerates. PRICE: THIRTY RUPEES

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Description a process for the preparation of a The invention relates to/ free-flowing molding powders comprising at least one optionally modified suspension polytetrafluoroethylene, an active amount of at least one trialkylamine oxide and if appropriate one or more fillers, to a process for their manufacture and their use for making sintered articles. A distinction is made between two types of polymers of tetrafluoroethylene (TFE), namely between thermoplastics which can be processed from the melt and types which are not processable from the melt, primarily the photopolymers, i.e. polytetrafluoroethylene (PTFE) itself, but in addition also the so-called "modified" TFE polymers which comprise (one) other co monomer(s) in such a small amount - usually Those TFE polymers which are not processable from the melt and are obtained by the suspension polymerization process are used for molding powders. At most, small amounts of dispersing agents are employed in this pro- cuss, and the polymerization is carried out with inten¬sive thorough mixing. The polymer obtained by this process, which has an average particle size of about 800 to 1200 μm or more as the crude polymer is subjected to one of the known comminuting processes for PTFE - for example grinding in a hammer mill or wet cutting - and is thereby finely divided down to an average particle size of 20 to 100μm. The fillers employed should likewise be in finely divided form, i.e. should have approximately the average particle size of the ground polymer. The mixture thus obtained has poor processing properties and is therefore agglomerated. The customary agglomera¬tion process is known to the expert, for example from US-A 3 527 857 and 3 781 258. In this process, the polymer powder, which has been premixed with the fillers, is suspended in a liquid agglomerating medium comprising water and an organic liquid, and this organic liquid must be capable of wetting the polymer powder and furthermore is soluble in water at most up to the extent of 15 % by weight, preferably up to the extent of 3 % by weight. A great problem in the production of shaped articles from such agglomerates lies in discoloration. Since TFE polymers are expensive, high requirements are also imposed on the quality of the shaped articles produced there from. US-A 3 882 217 thus relates to a process for the preparation of a free-flowing PTFE molding powder, provided with fillers if appropriate, by agitation of a finely divided PTFE powder, which comprises a filler if appropriate, with a water-containing medium for the purpose of agglomeration, and drying of the mixture containing agglomerated particles, which comprises wetting the finely divided PTFE powder with an aqueous solution of a volatile nonionic surface-active agent, the concentration of the surface-active agent being at least 40 times the critical micelle concentration at 20°C. These volatile nonionic surface-active agents - conden¬sates of ethylene oxide and alkyl phenols or long-chain alcohols are mentioned as being particularly suitable -have the effect of a considerable improvement in the discoloration. It has now been found that the discoloration can be suppressed considerably more with certain volatile surface-active agents having a swatter-ionic character, that is to say trialkylamine oxides, than with the known oxyethylates. Trialkylamine oxides are known surface-active agents. They are usually prepared by oxidation of the correspond¬ing tertiary amines in aqueous hydrogen peroxide solu¬tions (US-A 3 215 741 and 3 283 007) . They are employed, for example, as an emulsifier for aqueous dispersions for textile treatment (EP-A 471 416), as a fiber processing agent (EP-A 229 340) or as a dispersing agent for impreg¬nation of yarns and textile sheet-like structures, and also as a dispersing agent for concentration of fluorine polymer dispersions (US-A 5 219 910). Preferred amine oxides are those of the formula RXR2R3N -* 0 in which R1 is an alkyl radical having 6 to 22 carbon atoms or a mixture of such alkyl radicals, R2 has the meaning of R1 or is an alkyl radical having 1 to 4 carbon atoms and R3 is an alkyl radical having 1 to 4 carbon atoms. R2 and R3 are preferably methyl groups. The amine oxides employed according to the invention are much more volatile than the oxyethylates employed to date, which decompose when heated in air to form undesir¬able volatile and solid degradation products, it being possible for the volatile products to be deposited on the cooler surfaces of the waste air passages. In contrast, the amine oxides give only highly volatile, non-toxic decomposition products. Another advantage of the use of the amine oxides is the lower use concentration, which is from 0.1 to 2 % by weight, based on the polymer and, if appropriate, filler. In general, up to 1 % by weight of amine oxide, prefer¬ably 0.2 to 0.5 % by weight, is sufficient. A particular advantage of the invention is that because of the higher volatility of the amine oxides, they can be removed from the shaped articles even during drying at temperatures of up to about 150 °C. The removal of the volatile constituents at this lower temperature is very much less expensive in terms of apparatus than the corresponding removal in the course of sintering. The removal of the amine oxides at low temperatures is advantageous above all if a softer grain of the molding powder and improved mechanical properties of the sintered compacts are required. A decisive advantage of the invention is that the discol¬oration of the shaped articles during sintering is further considerably improved compared with the prior art. If the molding powder according to the invention comp¬rises fillers, possible fillers are the customary products, above all carbon black, graphite, carbon powder, mica, talc, glass in the form of powder, fibers, beads or hollow beads, silicon dioxide, for example in the form of quartz, silicates, metal oxides and double oxides, such as iron oxide, cobalt oxide, chromium oxide, aluminum oxide, titanium oxide, antimony trioxide, lead oxide, cobalt blue, ultramarine, organic pigments, such as benzidine dyestuffs or phthalocyanine dyestuffs, salt¬like substances, such as potassium titanate or barium titanate, and furthermore also metals in the form of floes, flakes or powders, such as bronze, copper, aluminum or brass, as well as synthetic fibers of plas¬tics of high heat stability, such as, for example, polyimide fibers or agamid fibers. The weight content of filler, based on the sum of polymer and filler, is up to 75 % by weight, preferably 5 to 70 % by weight, in particular 15 to 60 % by weight. The molding powders according to the invention can be prepared by methods which are known per se, for example by the process of US-A 3 882 217. Preferred is a process for the preparation of a free-flowing molding powder, which comprises agglomerating a finely divided non free-flowing powder of at least one optionally modified polytetrafluoroethylene in an aqueous medium which contains at least one trialkylamine oxide, and drying the agglomerates. Accordingly, the present invention provides a process for the preparation of a iree-rlowing molding powder, which comprises agglomerating a finely divided non Jree-flovving powder of at least one polytetrafluoroethylene or modified polytetrafluoroethylene with an aqueous medium which contains at least one surface active trialkylamine oxide, and drying the agglomerates. The invention is illustrated in more detail in the following examples. Example 1 1.5 kg of finely divided suspension PTFE (d50 20 to 30 /xm) are mixed with 500 g of finely divided coal (d50 20 to 30 μ m) in a fluid mixer. 900 g of a 0.5 % strength by weight solution of lauryldimethylamine oxide are added to the homogeneous mixture formed, which is not free-flowing, and the components are mixed intensively. The resulting moist powder is subjected to a rolling treatment and dried at 180°C for 12 hours. The cooled product is then freed from coarse and fine material by sieving. The resulting agglomerates have an average particle diameter of 700 μ m, a bulk density of 600 g/1 and good free-flowing properties. The properties of the molding powder can be varied within certain limits by the nature and duration of the rolling treatment. Example 2 1.5 kg of finely divided suspension PTFE (d50 20 to 30μm) are mixed with 500 g of ground glass fibers (d50 30 to 50 μm) in a fluid mixer. 800 g of a 0.5 % strength by weight solution of lauryldimethylamine oxide are added to the mixture formed, which is not free-flowing, and the components are mixed intensively. The resulting moist powder is subjected to a rolling treatment and dried at 280"C for 12 hours. The cooled product is then freed from coarse and fine material by sieving. The resulting agglomerates have an average particle diameter of 750 μ m, a bulk density of 650 g/1 and good free-flowing proper¬ties. Example 3 1.7 kg of finely divided suspension PTFE (d50 20 to 30μm) are mixed with 300 g of finely divided graphite (d50 30 μm) in a fluid mixer. 900 g of a 0.5 % strength by weight solution of cetyl-dimethylamine oxide are added to the mixture formed, which is not free-flowing, and the components are mixed intensively. The resulting moist powder is subjected to a rolling treatment and dried at 280°C for 12 hours. The cooled product is then freed from coarse and fine material by sieving. The resulting agglomerates have an average particle diameter of 790 /im, a bulk density of 600 g/1 and good free-flowing proper¬ties. Example 4 0.8 kg of finely divided suspension PTFE (d50 20 to 30 /xm) are mixed with 1.2 kg of fine bronze powder (d50 30 to 50 μ m) in a fluid mixer. 800 g of a 0.5 % strength by weight solution of cetyl-dimethylamine oxide are added to the mixture formed, which is not free-flowing, and the components are mixed intensively. The resulting moist powder is subjected to a rolling treatment and dried at 280°C for 12 hours. The cooled product is then freed from coarse and fine material by sieving. The resulting agglomerates have an average particle diameter of 750μm, a bulk density of 1100 g/1 and good free-flowing proper¬ties. VVE CLAIM: 1. A process for the preparation of a free-flowing molding powder, which comprises agglomerating a finely divided non free-flowing powder of at least one polytetrafluoroethylene or modified polytetra- fluoroethylene with an aqueous medium which contains at least one surface active trialkylamine oxide, and drying the agglomerates. 2. The Process as claimed in claim 1, in which up to 75 % by weight of filler (s) and, to make up to 100 % by weight, optionally modified polytetra-f luoroethylene is used and if appropriate other customary constituents. 3. The process as claimed in claim 2, in which 0.2 to 1 % by weight of amine oxide and 5 to 70 % by weight of filler (s) are used. 4.The process as claimed in one or more of the preceding claims, in which the amine oxide corre¬sponds to the formula R1R2R3N -> 0 in which R1 is an alkyl radical having 6 to 22 car¬bon atoms or a mixture of such alkyl radicals, R2 has the meaning of R1 or is an alkyl radical having 1 to 4 carbon acoms and Rs is an alkyl radical having 1 to 4 carbon atoms. 5. A process for the preparation of a free-flowing molding powd substantially as herein described with reference to the accompanying drawing

Documents:

1177-mas-1995 abstract.pdf

1177-mas-1995 assignment.pdf

1177-mas-1995 claims.pdf

1177-mas-1995 correspondence -others.pdf

1177-mas-1995 correspondence -po.pdf

1177-mas-1995 description (complete).pdf

1177-mas-1995 form-1.pdf

1177-mas-1995 form-10.pdf

1177-mas-1995 form-26.pdf

1177-mas-1995 form-4.pdf

1177-mas-1995 others.pdf

1177-mas-1995 petition.pdf