Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
1998-05-04
2001-03-27
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S210700, C264S177190, C264S288400, C264S292000, C264S331140, C264S173130, C264S165000
Reexamination Certificate
active
06207091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to processes for producing the drawn molded article of a fluoroplastic (a fluorine-contained resin), more particularly to a process for producing a drawn molded article of a fluoroplastic which is significantly improved in mechanical properties such as strength, tensile modulus and the like by drawing a fluoroplastic under the specified conditions.
2. Prior Art
Fluoroplastics have been widely used as engineering plastics because their remarkably high melting point, excellent resistance to chemicals and low friction coefficient of the surfaces. Since a fluoroplastic resembles in chemical structure closely a polyolefin, it has been attempted to produce a drawn article in the form of a film, tape and yarn of high strength and tensile modulus by stretching the molecular chains having been changed to be uniaxially oriented and highly crystallized morphology. Japanese Laid-Open Patent Publication Nos. 1-192812, 2-307907 and 5-78908 disclose the process of producing a fluoroplastic fiber by applying a technique of drawing polyethylene or polypropylene. One of these prior techniques involves a complicated processes in which after dissolving a fluoroplastic which is not dissolved with a general-purpose solvent, with a special solvent thereby obtaining the solution, the fluoroplastic is drawn by spinning, followed by extracting the solvent. In another technique, a fluoroplastic solution is melted by heating at a temperature higher than the melting point thereof and the resulting high viscosity melt is drawn by spinning. However, it is very difficult in technical view to spin the solution and the melt uniformly and since particularly the latter method is effected at a high temperature above the melting point, there are anxieties of the occurrence of gases which thermally decomposes the fluoroplastic and is harmful for a human body. Therefore, the fact is that the above-mentioned two methods are inadequate for practical use. Other than these prior methods, there are another methods of extruding polytetrafluoroethylene in the solid state as disclosed in J. Polym. Sci. Polym. Phys. Ed., 17 (1979) 73 and Polym. Eng. Sci., 26 (1986) 239. However, these methods fail to improve the strength of the drawn article to an extent that would be satisfactory.
Furthermore, although it is disclosed in Japanese Laid-Open Patent Publication No. 8-132521 that a drawn article is obtained by tensile stretching an article derived from solid-state extrusion, this method has been demanded to be further improved.
Generally speaking, a drawn article can be improved in strength and tensile modulus with respect to the drawing direction by using a starting fluoroplastic having a larger molecular weight if starting fluoroplastics are intended to be drawn at the same draw ratio or by increasing the draw ratio if starting fluoroplastics are the same in molecular weight. However, in the already mentioned methods the use of a starting fluoroplastic excessively increased in molecular weight leads to a reduction in solubility in a solvent or an increase in viscosity when melted, resulting in not only an inconvenience that spinning or drawing operation is hindered but also a risk that the breakage caused by drawing occurs frequently.
It has been found that there can be produced a drawn molded article of a fluoroplastic excelled in mechanical properties such as strength and tensile modulus by drawing in a specified manner.
SUMMARY OF THE INVENTION
According to the present invention, there is provided with a process for producing a drawn molded article of a fluoroplastic wherein a fluoroplastic molded article is brought into contact with a heating medium set at a temperature exceeding the static melting point of the molded article and drawn at a temperature at which the molded article does not substantially melt. The inventive process is characterized by the use of the heat medium in the form of a stretch pin. Furthermore, the inventive process is characterized in that the fluoroplastic molded article is obtained by solid-state extruding or solid-state rolling a fluoroplastic at temperatures within which the fluoroplastic does not substantially melt.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the present invention is intended to produce a drawn molded article by drawing the molded article of a fluoroplastic in a specified manner.
Fluoroplastic used as a starting material may be any type of fluoroplastic inclusive of a copolymer. Eligible fluoroplastic exemplarily includes polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), chlorotrifluoroethylene-ethylene copolymer (ECTFE), tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinylether copolymer (EPE), polyvinylidenefluoride (PVDF) and polyvinylfluoride (PVF), among which polyvinylidenefluoride is particularly preferred because it can be highly crystallized by drawing. A copolymer used as a starting fluoroplastic is not particularly restricted to its ratio of comonomers and may be those derived from alternating copolymerization, random copolymerization or block copolymerization. Copolymerization may be preferably done by a two or more-stage reaction. Such multi-stage copolymerization may be effected by repeating only homopolymerization under the condition of different molecular weight or by conducting homopolymerization and copolymerization in combination.
Bonding between monomers including comonomers may be head-to-head, head-to-tail or tail-to-tail bond. The above mentioned fluoroplastics may be used singularly or in combination. The combination of more than two fluoroplastics is not restricted to the blend ratio of each fluoroplastics as long as the accomplishment of the present invention is not bothered.
No particular restrictions are imposed upon the molecular weight of the starting fluoroplastic. However, fluoroplastics of too low molecular weight would result in difficulty in producing a drawn article increased in tensile strength because they cannot be drawn by tensile stretching at a higher drawn ratio, while those of too high molecular weight would result in difficulty in increasing a deformation ratio by extrusion or rolling because of their too long molecular chains. Therefore, a fluoroplastics suitable for the invention have a molecular weight in the range of preferably 5.0×10
3
to 5.0×10
9
, more preferably 5.0×10
4
to 5.0×10
8
and further preferably 5.0×10
5
to 1.0×10
8
. The method of measuring the molecular weight of a fluoroplastic has been reported in a variety of documents. For instance, the molecular weight of polytetrafluoroethylene can be measured by estimating from a relaxation time in the molten state as reported in Polymer Engineering Science 28, 538 (1988) or from the light scattering of the solution as reported in Macromol 22, 831 (1989). The molecular weight of tetrafluoroethylene-hexafluoropropylene copolymer can be measured by estimating from a relaxation time in the melted state as taught in Macromol., 18, 2023 (1985) while that of tetrafluoroethylene-ethylene copolymer can be measured by estimating from the condition of light scattering of the solution as taught in Macromol., 20, 98 (1987). The molecular weight of other fluoroplastics can be measured by applying the method of estimating from a relaxation time in the molten state as taught in Polymer Engineering Science 25, 122 (1985). The molecular weight distribution of a fluoroplastic can be derived from the measurement of molecular weight in accordance with the foregoing method. A fluoroplastic to be used in the present invention will preferably be narrow in molecular weight distribution to obtain a drawn article excelled in mechanical properties.
No limitations are imposed upon the method of producing a starting fluoroplastic used in the invention. Therefore, there may be e
Endo Ryoukei
Kanamoto Tetsuo
Uehara Hiroki
Akin Gump Strauss Hauer & Feld L.L.P.
Eashoo Mark
Nippon Mitsubishi Oil Corporation
Silbaugh Jan H.
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