Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-22
2002-02-26
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S494000
Reexamination Certificate
active
06350801
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a filler-containing polytetrafluoroethylene granular powder and a preparation process thereof.
BACKGROUND ART
Hitherto, a process for preparing a filler-containing polytetrafluoroethylene (PTFE) granular powder by granulating a mixture of a filler and a PTFE powder with stirring in water was proposed, for example, in JP-B-43-8611, JP-B-44-22619, JP-B-48-37576, JP-B-49-17855, JP-B-56-8044, JP-B-57-18730, etc.
However, by the process for preparation disclosed in each of the above-mentioned patent publications, a filler-containing PTFE granular powder having a small particle size and a narrow particle size distribution could not be obtained.
For that reason, in case of preparing, for example, small articles such as seal rings in the form of a rubber band, thin moldings and molded products having a small surface roughness, there was a problem that complicated and uneconomical steps must be employed, such as step of sieving a filler-containing PTFE granular powder to take out only particles of small size and molding them, or step of cutting the obtained molding.
Also a granular powder having excellent powder flowability cannot be obtained only by pulverizing a filler-containing PTFE granular powder.
In JP-B-60-21694, there was proposed a process for preparing a filler-containing PTFE granular powder by granulating, with stirring in water, a PTFE powder and a filler which has been previously surface-treated with an aminosilane compound in coexistence with a water-insoluble organic liquid and an anionic surfactant. However, an apparent density of the filler-containing PTFE granular powder and tensile strength of molded products obtained therefrom are not fully satisfactory.
Further in the above-mentioned preparation process, there were problems that long steps are employed, a complicated step of pre-mixing the filler and the PTFE powder is necessary and cost is high.
The present inventors have made intensive studies in view of the above-mentioned problems, and as a result, have found that those problems can be solved by mixing the PTFE powder and the filler in water in the state of slurry in the presence of a surfactant and further granulating the mixture with stirring in the presence of an organic liquid which forms liquid-liquid interface with water.
The present inventors have made further studies in order to obtain a granular powder more excellent in powder characteristics and physical properties in the above-mentioned granulation process (hereinafter also referred to as “slurry granulation process”), and have found that when a specific nonionic surfactant is used, an obtained granular powder has a low electrostatic charge and can give molded articles having a high whiteness (Z value).
Namely an object of the present invention is to provide a filler-containing PTFE granular powder having a good processability and a process for preparation thereof. Particularly an object of the present invention is to provide a filler-containing PTFE granular powder which has a large apparent density, a small average particle size, a narrow particle size distribution, a small electrostatic charge and good physical properties such as powder flowability, and gives molded products having excellent physical properties such as elongation and a high whiteness, and a process for preparation thereof.
DISCLOSURE OF THE INVENTION
The present invention relates to a process for preparing a filler-containing polytetrafluoroethylene granular powder by granulation, in water with stirring, of a polytetrafluoroethylene powder prepared by suspension polymerization and a filler; characterized in that the powder and filler are poured in water separately without being pre-mixed, are mixed with stirring in the presence of a nonionic surfactant having a hydrophobic segment comprising a poly(oxyalkylene) unit having 3 or 4 carbon atoms and a hydrophilic segment comprising a poly(oxyethylene) unit to give a slurry, and then are granulated with stirring in the presence of an organic liquid which forms liquid-liquid interface with water.
The present invention also relates to a process for preparing a filler-containing polytetrafluoroethylene granular powder by granulation, in water with stirring, of a polytetrafluoroethylene powder prepared by suspension polymerization and a filler; characterized in that the powder is poured in water and stirred in the presence of a nonionic surfactant having a hydrophobic segment comprising a poly(oxyalkylene) unit having 3 or 4 carbon atoms and a hydrophilic segment comprising a poly(oxyethylene) unit to give a slurry, and then after the filler is added and mixed to the slurry, the mixture is granulated with stirring in the presence of an organic liquid which forms liquid-liquid interface with water.
Further the present invention relates to a process for preparing a filler-containing polytetrafluoroethylene granular powder by granulation, in water with stirring, of a polytetrafluoroethylene powder prepared by suspension polymerization and a filler; characterized in that a water-containing powder of polytetrafluoroethylene after suspension-polymerized is wet-pulverized without being subjected to drying, poured in water, and stirred in the presence of a nonionic surfactant having a hydrophobic segment comprising a poly(oxyalkylene) unit having 3 or 4 carbon atoms and a hydrophilic segment comprising a poly(oxyethylene) unit to give a slurry, and then after the filler is added and mixed to the slurry, the mixture is granulated with stirring in the presence of an organic liquid which forms liquid-liquid interface with water.
Further the present invention relates to a process for preparing a filler-containing polytetrafluoroethylene granular powder; characterized in that in each of the above-mentioned preparation processes, the granulation with stirring is carried out in combination use of stirring and deagglomeration by using means for deagglomerating a granular powder obtained by the granulation in addition to means for stirring.
The present invention also relates to a filler-containing PTFE granular powder prepared by any of the above-mentioned processes which is characterized in that an apparent density of the filler-containing PTFE granular powder is not less than 0.7 g/cm
3
, a flowability (defined hereinafter) of the granular powder is not less than 6 times and an electrostatic charge is not more than 50 V or that an angle of repose is not more than 40 degrees in case of an apparent density of not less than 0.7 g/cm
3
and less than 0.9 g/cm
3
, not more than 38 degrees in case of an apparent density of not less than 0.9 g/cm
3
and less than 1.0 g/cm
3
, and not more than 36 degrees in case of an apparent density of not less than 1.0 g/cm
3
, and an average particle size is not more than 500 &mgr;m and an electrostatic charge is not more than 50 V.
REFERENCES:
patent: 3674736 (1972-07-01), Lerman et al.
patent: 3766133 (1973-10-01), Roberts
patent: 3915916 (1975-10-01), Leverett
patent: 4370436 (1983-01-01), Nakamura et al.
patent: 54-17782 (1979-07-01), None
patent: 3-255133 (1991-11-01), None
patent: 4-309548 (1992-11-01), None
patent: 6-73189 (1994-03-01), None
patent: 8-208929 (1996-08-01), None
patent: WO97/11111 (1996-09-01), None
Asano Michio
Sukegawa Masamichi
Daikin Industries Ltd.
Henderson Christopher
LandOfFree
Filled granular polytetrafluoroethylene powder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Filled granular polytetrafluoroethylene powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Filled granular polytetrafluoroethylene powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2960959