Fine powder of high molecular weight fluorine containing...

Details Fine powder of high molecular weight fluorine containing... Fine powder of high molecular weight fluorine containing...

1997-01-22

2002-04-02

Dye, Rena L. (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C428S036900, C428S036920, C526S247000, C526S250000, C526S252000, C526S254000, C526S255000

Reexamination Certificate

active

06365243

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to (a) the fine powder of high molecular weight fluorine containing fused resins (this fine powder is especially suitable in producing jigs, etc. used in the manufacturing processes of semiconductors), (b) mold goods obtained by molding this fine powder, and (c) these production methods.
BACKGROUND OF THE INVENTION
Inasmuch as fluorine containing fused resins are especially excellent in heat resistance, chemical resistance, electrical insulation, nonviscous property, lower friction property, etc. among many kinds of plastics, they are applied in fields ranging from the space development and aircraft industries to the household goods industry, chemical industry, the electric and electronic industries, and the machine industry.
It is comparatively difficult, however, to mold fluorine containing fused resins because they have higher melt viscosities and narrower ranges of proper mold processing conditions as compared with other general-purpose plastics. Such resins, moreover, may decompose slightly at high molding temperatures to produce corrosive gases. Especially, as high molecular weight resins having a melt viscosity of 10
6
or greater poise are excessively high in melt viscosity and very low in fluidity, it is very difficult to mold them by ordinary extrusion molding and injection molding. As a result, these resins have so far been without an application.
Conversely, as appreciated from the case of superhigh molecular weight polyethylene, plastics generally develop merits with increased molecular weight. It is thus possible to improve mechanical properties, including strength, modulus of elasticity, abrasion resistance and resistance to flex fatigue; and to improve chemical properties such as weatherability and chemical resistance. It is therefore naturally expected that valuable improvements of properties can be achieved also in fluorine containing fused resins by increasing their molecular weight. Such improvements, however, have not been utilized practically because of the above-mentioned molding difficulty. Rather, techniques of lowering the molecular weight of fluorine containing resins have been studied while maintaining their mechanical and chemical properties.
Furthermore, although fluorine containing fused resins are usually molded by extrusion and injection, the resins are supplied in the form of pellets, as with other general-purpose plastics. This is done to secure a good supply of raw materials for molding machines, including facile dropping through hoppers and feeding into the screws, and to make the handling of raw materials easy.
High molecular weight resins, however, having melt viscosities of 10
6
or greater poise are difficult to pelletize because of excessive melt viscosity.
Accordingly, there exists no alternative to their being supplied in the form of powder as they are. Powder, however, immediately following polymerization has low apparent density and inferior fluidity, making its supply unstable. This has also been a factor obstructing the practical use of high molecular weight fluorine containing fused resins.
Conversely, inasmuch as fluorine containing fused resins have the above-mentioned excellent properties, it is the ingredient of choice in the manufacturing processes of semiconductors as mold goods such as wafer carriers, tubes, joints, square brackets, etc. Because LSI is highly integrated and concentrated, minute amounts of impurities such as particles, metals, etc. have come into question. Concerning mold goods of fluorine containing fused resins used in these applications, the demand for high purity is also increasing.
Accordingly, the liquation of particles from mold goods of fluorine containing fused resins is a problem. Proposed to decrease the number of liquated particles have been a method for extracting these particles with a fluorine-containing solvent, and a method of washing mold goods with isopropyl alcohol, etc. Both methods, however, have problems in cost and productivity because they are after-treatments conducted by means of special equipment and chemical liquids.
SUMMARY OF THE INVENTION
The purposes of this invention are (a) to improve the properties of fine powder of high molecular weight fluorine containing fused resins that have not been utilized, (b) to offer mold goods that have diminished numbers of liquated particles and that are preferable to the manufacturing processes of semiconductors by molding the fine powder, and (c) to offer the production methods of these mold goods.
DETAILED DESCRIPTION OF THE INVENTION
This invention thus relates (a) to the fine powder of high molecular weight fluorine containing fused resins having melt viscosities of 10
6
to 10
10
poise, apparent densities of 0.4 to 1.5 g/cc, and specific surface areas of 2 m
2
/g or less; and (b) to mold goods obtained by molding the fine powder.
As the kinds of fluorine containing fused resins in this invention, at least one kind of resins are given that are selected from the resin group composed of copolymers of tetrafluoro ethylene and perfluoro alkylvinyl ether (hereinafter “PFA”), copolymers of tetrafluoroethylene and hexafluoropropene (hereinafter “FEP”), copolymers of tetrafluoro ethylene and ethylene (hereinafter “ETFE”), vinylidene fluoride homopolymers (hereinafter “PVDF”), copolymers of vinylidene fluoride and tetrafluoro ethylene, copolymers of vinylidene fluoride and hexafluoropropene, copolymers of vinylidene fluoride and chlorotrifluoroethylene, copolymers of chlorotrifluoroethylene and ethylene (hereinafter “ECTFE”), etc. Here, a copolymer PFA is preferable to be a copolymer of tetrafluoro ethylene and at least one kind of perfluoro alkylvinyl ethers as expressed by the formula CF
2
═CFO(CF
2
)mF (in this formula, m is an integral number of one to six), or a formula CF
2
═CF(O—CF
2
CF(CF
3
))nOC
3
F
7
(in this formula, n is an integral number of 1 to 4); and is especially preferable to be a copolymer of tetrafluoro ethylene of 92% to 99% and perfluoro alkylvinyl ether of 1% to 8% by weight. Further, FEP is preferable to be a copolymer of tetrafluoro ethylene of 72% to 96% and hexafluoropropene of 4% to 28% by weight. ETFE is preferable to be a copolymer of tetrafluoro ethylene of 74.5% to 89.3% and ethylene of 10.7% to 25.5% by weight. These fluororesins are allowed to be copolymerized with other monomers in an amount not adversely to affect the essential properties of each resin. As the other monomers, the following compounds are given as examples: (a) tetrafluoro ethylene, (b) chlorotrifluoroethylene, (c) hexafluoropropene, (c) perfluoro alkylvinyl ether, (d) fluoroalkyl (C1 to C10) ethylene, (e) perfluoroalkyl (C1 to C10) allyl ether, (f) compounds expressed by the formula CF
2
═CF[OCF
2
CFRf(CF
2
)p]qOCF
2
(CF
2
)rY (in this formula, Rf is fluorine atom or trifluoro methyl radical, Y is a halogen atom, p is 0 or 1, q is 0 or an integral number of 1 to 5, r is 0 or an integral number of 1 to 2. When, however, p is 1, Rf is fluorine atom), and (g) compounds expressed by the formula CH
2
=CF(CF
2
)nX (in this formula, n is an integral number of 0 to 8, and X is a hydrogen or fluorine atom).
The melt viscosity of fluorine containing fused resins in this invention must indispensably be 10
6
to 10
10
poise from the point of view of decreasing the number of liquated particles and improving the quality of mold goods,. Those resins having melt viscosity of less than 10
6
poise, which are collectively called fluorine containing fused resins and are usually commercially available for mold processing, are not preferable because they have lower mechanical properties and large numbers of liquated particles as will be mentioned later. Furthermore, in case of resins having melt viscosities of more than 10
10
poise, their mold processing temperatures cannot help being increased over the starting temperatures of their thermal decompositions to obtain favorable mold goods. Accordingly, these resins are not preferable because their mold goods are foamed and colored.
G

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