Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-01-28
2002-11-05
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S199000, C525S276000, C526S247000, C524S544000, C524S545000, C524S546000
Reexamination Certificate
active
06476144
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an agent which minimizes a size of spherulites in a melt-processable crystalline fluorine-containing resin and can make a surface of a molded article smooth, a crystalline fluorine-containing resin composition containing the agent for minimizing spherulite size and a molded article obtained from the composition. The molded article of the present invention has a smooth surface and can be used suitably for various products, parts and containers in the field of semi-conductor manufacturing equipment.
BACKGROUND ART
Melt-processable crystalline fluorine-containing resins are excellent, in heat resistance, chemical resistance and the like, and are used widely as a molding material in various fields. Particularly crystalline tetrafluoroethylene/perfluoro (alkyl vinyl ether) copolymer (PFA) is from the viewpoint of its excellent chemical and thermal stability and moldability, used as a material for a sheet, tube, joint, container, carrier, bellows, seal, etc. in the field of production of semi-conductors which is required to be free from contamination. In such a field of production of semi-conductors, as mentioned above, contamination by impurities and foreign matters (particles) is extremely required to be avoided, and it is required to make inside of equipment and inner surfaces of pipe and container as smooth as possible because particles are easily accumulated there.
However since PFA is a crystalline melt-processable resin, relatively large spherulites exist in a molded article obtained by melt-molding the resin. If many of such relatively large spherulites exist, it prevents a surface of the molded article from becoming smooth.
It is known that spherulites of PFA can be made smaller by increasing the number of nucleuses of spherulites, and basically the following two methods for minimizing a size of spherulite have been studied.
One is a method for blending polytetrafluoroethylene (PTFE) as an agent for forming a nucleus of spherulite into a PFA composition (JP-A-7-70397, JP-A-7-237257, JP-A-7-292200, JP-A-9-316266). There are two proposals of blending, as an additive, PTFE having a crystallization temperature of not less than 305° C. and a crystallization calorie of not less than 50 J/g or PTFE crosslinked with ionizing radiation.
Another one is a method for blending, as a nucleus-forming agent, PFA having a low molecular weight or PFA having a low copolymerizing ratio of a perfluoro(alkyl vinyl ether) (PAVE) unit (JP-A-8-41267, JP-A-8-73689, JP-A-8-109225).
However in those methods, since crystallization temperatures of PFA having a low copolymerizing ratio of a PAVE unit and PFA having a low molecular weight are lower than that of PTFE, sufficient number of spherulite nucleuses are not formed and a spherulite size is not minimized sufficiently.
According to the method for blending PTFE as an agent for minimizing spherulite size into a PFA composition, though a spherulite size is minimized and through sight of an obtained molded article is improved, the molded article is wholly whity and transparency is not enough.
An object of the present invention is to provide the agent for minimizing size of spherulite in a melt-processable crystalline fluorine-containing resin such as PFA. The agent can not only minimize the size of spherulite in the resin and make highly smooth a surface of molded article obtained by melt-molding the resin but also decrease generation of particles.
While the conventional approaches are based on the use of highly crystalline agents for minimizing spherulite size such as PTFE and PFA having a high content of tetrafluoroethylene (TFE), the present inventors have made intensive studies as to converse approach, that is, use of an amorphous fluorine-containing polymer which has been considered not to be able to become a crystalline nucleus from a commonsense point of view. As a result, the present inventors have found that unexpectedly an amorphous fluorine-containing polymer has an excellent function of minimizing a spherulite size. Thus the present invention was completed. Though the reason for that is not clear, it is assumed that an amorphous fluorine-containing polymer decreases a growing speed of spherulite of a crystalline fluorine-containing resin and even in case of slow cooling, crystallization completes without growing the spherulite, and thus a size of produced spherulite is minimized.
DISCLOSURE OF THE INVENTION
Namely the agent of the present invention for minimizing spherulite size of a melt-processable crystalline fluorine-containing resin comprises an amorphous fluorine-containing polymer, preferably an amorphous fluorine-containing polymer having a glass transition temperature of not more than 25° C.
As such an amorphous fluorine-containing polymer, there can be used selectively one having a compatibility with a crystalline fluorine-containing resin.
In case of minimizing spherulite size of a crystalline PFA as a crystalline fluorine-containing resin, a preferred amorphous fluorine-containing polymer to be used is an amorphous tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer.
Also as the agent for minimizing spherulite size of the present invention, there can be used one which contains a fluorine-containing multi-segment polymer comprising (A) an amorphous fluorine-containing polymer chain segment and (B) a crystalline fluorine-containing polymer chain segment comprising 80 to 100% by mole of tetrafluoroethylene (TFE) recurring unit and 0 to 20% by mole of a recurring unit represented by the formula (I):
CF
2
=CF−RF
f
1
(I)
wherein R
f
1
is CF
3
or OR
f
2
, in which R
f
2
is a perfluoroalkyl group having 1 to 5 carbon atoms.
In that case, the crystalline fluorine-containing polymer chain segment (B) may be a polymer chain segment consisting of TFE recurring unit or a polymer chain segment comprising TFE recurring unit and perfluoro(alkyl vinyl ether) (PAVE) recurring unit and containing PAVE in an amount of not more than 20% by mole.
In case where a crystalline PFA is used as a crystalline fluorine-containing resin, a preferred minimizing agent of spherulite size is an amorphous tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer or a fluorine-containing multi-segment polymer consisting of TFE recurring unit as the segment (B).
Thermal stability is improved by fluorinating those amorphous fluorine-containing polymer and fluorine-containing multi-segment polymer.
In case of minimizing spherulite size of vinylidene fluoride polymer (PvdF), examples of the amorphous fluorine-containing polymer to be used are, for instance, fluorine-containing elastomers having hydrogen atom such as vinylidene fluoride/hexafluoropropylene copolymer, vinylidene fluoride/hexafluoropropylene/tetrafluoroethylene copolymer, vinylidene fluoride/chlorotrifluoroethylene copolymer and vinylidene fluoride/chlorotrifluoroethylene/tetrafluoroethylene copolymer. Also there can be used the agent for minimizing spherulite size which contains a fluorine-containing multi-segment polymer having such an amorphous fluorine-containing polymer in its segment.
In case of a chlorotrifluoroethylene polymer (PCTFE), examples of the amorphous fluorine-containing polymer to be used are, for instance, vinylidene fluoride/chlorotrifluoroethylene copolymer, vinylidene fluoride/chlorotrifluoroethylene/tetrafluoroethylene copolymer, and the like. Also there can be used the agent for minimizing spherulite size which contains a fluorine-containing multi-segment polymer having such an amorphous fluorine-containing polymer in its segment.
The present invention also relates to the crystalline fluorine-containing resin composition prepared by blending those minimizing agents of spherulite size into a melt-processable crystalline fluorine-containing resin.
It is preferable that the minimizing agent is blended in an amount of 0.1 to 50 parts (part by weight, hereinafter the same) on the basis of 100 parts of the crystalline fluorine-containing resin.
Examples of the preferred melt-processable crystalline fluo
Aoyama Takahisa
Okanishi Ken
Shimizu Tetsuo
Suzuki Tatsuo
Yoshida Minoru
Armstrong Westerman & Hattori, LLP
Daikin Industries Ltd.
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