Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1994-03-08
1996-02-27
Nakarani, D. S.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428421, 428422, 523201, 525276, 525902, B32B 516, C08L 8300
Patent
active
054947529
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a composite microparticle of fluorine containing resins. More particularly, the present invention relates to a composite microparticle of fluorine containing resins having a multilayer or gradient structure which is excellent in blending property with synthetic resins, synthetic rubbers or coating materials, and dispersibility therein.
DESCRIPTION OF THE PRIOR ART
Perfluororesins such as polytetrafluoroethylene (referred to as "PTFE" hereinafter), tetrafluoroethylene (TFE)/perfluoro (alkyl vinyl ether) copolymer (referred to as "PFA" hereinafter), TFE/hexafluoropropylene (HFP) copolymer (referred to as "FEP" hereinafter) are usually commercially available in the form of microparticles, powder, pellets, etc. They are used in various fields as a molding raw material for a molded product which has excellent performance and function characteristics such as high and low temperature resistance, flame retardance, slidability, nontackiness, stain resistance, chemical resistance, weathering resistance and electrical characteristics, etc. They are also used as a modifying agent by dispersing in or blending with other materials. Perfluororesins are used in the form of powder or pellet for blending with a structural material such as a synthetic resin or synthetic rubber, and in the form of microparticles or powder for dispersing in a liquid or semisolid material such as a coating material, paint, oil, grease, ink and the like.
In the case of PTFE which is a typical perfluororesin, the microparticles are prepared by so-called emulsion polymerization in the presence of a surfactant in an aqueous medium and obtained in a colloidal form having an average particle size of from 0.05 to 1.0 .mu.m in an aqueous dispersion (latex).
Powdery PTFE includes aggregated powder of PTFE microparticles (fine powder) having an average particle size of from 100 to 1000 .mu.m which is prepared by aggregating and drying the above aqueous dispersion, and a granular particle (granular or molding powder) which is prepared by so-called suspension polymerization in the presence or absence of a small amount of a surfactant. They are used as molding powder in many fields. The PTFE powder of the type once subjected to heat-treatment at a temperature above the melting point of PTFE is also commercially available.
The fine powder or molding powder as a raw material for molding has a considerably high molecular weight and a melt viscosity of 10.sup.8 poise or more at 380.degree. C., hence having no melt processability. Therefore, they are seldom used as a modifying agent for other material by dispersing in or blending with it except in special cases. The main reason why the powder is unsuitable for dispersing or blending is that they undergo fibrillation during the dispersing or the blending procedure. Accordingly, the microparticle or powder of a low molecular weight PTFE, which is emulsion or suspension polymerized under such a condition that a low molecular weight PTFE can be obtained, is commercially available hitherto for dispersing or blending. The fibrillation characteristics of PTFE depends generally on its molecular weight and blending conditions. When the molecular weight of PTFE is below a certain level, the fibrillation characteristics is lost
On the other hand, when a high molecular weight PTFE is once subjected to heat-treatment (usually at a temperature above the melting point of the PTFE), it almost loses the fibrillation characteristics below the melting point. This is considered to be because the crystalline form of PTFE before the heat-treatment (virgin PTFE) is considerably different from that after the heat-treatment (sintered PTFE). However, when the high molecular weight PTFE which is once subjected to the heat treatment is blended with other material at a temperature above the melting point, it is also fibrillated during the melting and kneading procedure of the blend. Generally speaking, a polymer material has more preferred mechanical properties when it has higher m
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Shimizu Tetsuo
Yamaguchi Seitaro
Yamamoto Yoshihisa
Daikin Industries Ltd.
Le H. Thi
Nakarani D. S.
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