Plastic and nonmetallic article shaping or treating: processes – Forming electrical articles by shaping electroconductive... – Conductive carbon containing
Reexamination Certificate
1997-07-14
2001-10-23
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming electrical articles by shaping electroconductive...
Conductive carbon containing
C264S210200, C264S040700, C425S145000, C425S149000
Reexamination Certificate
active
06306323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus and methods for extruding polymer compositions.
2. Introduction to the Invention
Polymeric compositions are often shaped by melt extrusion. A conveying means conveys the molten polymeric composition as a continuous stream under pressure to an extrusion orifice, and forces it through the orifice to form an extrudate of desired shape. In many cases, the composition is fed as a solid to a conveying means which melts the composition through a combination of shearing and external heating. Well known conveying means include single screw and twin screw extruders. Unfortunately, conventional conveying means often fail to deliver the molten composition to the extrusion orifice at a constant rate, as a result of pressure variations within the conveying means, particularly when the composition has high viscosity. This results in an extrudate of variable quality. It is well known to mitigate this problem by placing a gear pump (alternatively known as a melt pump) between the conveying means and the extrusion orifice. The gear pump helps to deliver a substantially constant volume of molten polymeric composition to the extrusion orifice, and in consequence to produce an extrudate of improved quality. However, the gear pump must be correctly sized and the pressure variations must be small enough to ensure that the gear pump is neither starved nor overfed.
SUMMARY OF THE INVENTION
We have found that the problems outlined above are particularly serious when conductive polymers are melt extruded. The term “conductive polymer” is used herein to denote a composition which comprises a polymeric component and, dispersed therein, a particulate conductive filler, e.g. carbon black, graphite, a metal, a conductive ceramic, or a metal carbide or nitride. Particularly when the conductive polymer contains a high concentration of particulate filler (which may be only the conductive filler or a mixture of conductive and non-conductive fillers), pressure variation s during the extrusion process can cause undesirable variation in the electrical properties of the extrudate, even when a gear pump is placed between the conveying means and the extrusion orifice.
We have discovered, in accordance with the present invention, that when a gear pump is used in combination with a conveying means and an extrusion orifice (as outlined above) greatly improved results can be obtained through the use of a polymer relief means, which, when the pressure in the gear pump exceeds a selected level, bleeds molten polymer from the system, and thus ensures that the gear pump is not overfed (and, therefore, continues to deliver a constant volume of molten polymeric composition to the extrusion orifice).
The present invention is particularly suitable for use in the extrusion of conductive polymer and will be chiefly described by reference to such use. However, it is to be understood that the invention can also be used in the extrusion of other polymeric compositions, and that the information given herein for conductive polymers is applicable to other polymeric compositions (with, if appropriate, modifications which will be apparent to those skilled in the extrusion of polymers having regard to their own knowledge and the information herein).
In one preferred aspect, the present invention provides a apparatus for producing a melt-extruded article composed of a polymeric composition, preferably a conductive polymer, the apparatus comprising
(1) conveying means for conveying a molten polymeric composition under pressure;
(2) a passageway;
(3) a first gear pump;
(4) an extrusion orifice; and
(5) a polymer relief means
the components (1), (2), (3) and (4) being arranged so that molten polymeric composition conveyed by the conveying means passes in a continuous stream sequentially through the conveying means, the passageway, the first gear pump and the extrusion orifice; and
the polymer relief means being associated with the first gear pump so that, if the pressure in the first gear pump exceeds a first selected level, the polymer relief means removes molten polymeric composition from the continuous stream thereof until the pressure in the first gear pump falls below a second selected level. The second selected level is equal to or lower than the first selected level, and is sufficiently high to ensure that the removal of the molten polymeric composition does not reduce the pressure to a level which results in the melt pump being starved.
As discussed below, the polymer relief means is preferably a gear pump, and for this reason the gear pump (
3
) is often referred to herein as the “first” gear pump, even though it is the only gear pump when the polymer relief means is a component other than a gear pump.
In a second preferred aspect, the present invention provides a method of making an article composed of a molten polymeric composition, preferably a conductive polymer, the method comprising the steps of
(A) conveying a continuous stream of a molten polymeric composition under pressure to a gear pump;
(B) operating the gear pump so that the molten polymeric composition conveyed to the gear pump in step (A) passes through the gear pump to an extrusion orifice and is extruded through the orifice; and
(C) when the pressure within the gear pump exceeds a selected level, removing molten polymeric composition from the continuous stream thereof
REFERENCES:
patent: 3078513 (1963-02-01), Levison et al.
patent: 4013745 (1977-03-01), Brinkmann et al.
patent: 4171193 (1979-10-01), Rahlfs
patent: 4213747 (1980-07-01), Friedrich
patent: 4237441 (1980-12-01), van Konynenburg et al.
patent: 4388607 (1983-06-01), Toy et al.
patent: 4534889 (1985-08-01), van Konynenburg et al.
patent: 4545926 (1995-10-01), Fouts, Jr. et al.
patent: 4560498 (1985-12-01), Horsma et al.
patent: 4591700 (1986-05-01), Sopory
patent: 4721589 (1988-01-01), Harris
patent: 4724417 (1988-02-01), Au et al.
patent: 4774024 (1988-09-01), Deep et al.
patent: 4858139 (1989-08-01), Wirtz
patent: 4885457 (1989-12-01), Au
patent: 4935156 (1990-06-01), van Konynenburg et al.
patent: 5049850 (1991-09-01), Evans et al.
patent: 5167894 (1992-12-01), Baumgarten
patent: 5179521 (1993-01-01), Edge
patent: 5250228 (1993-10-01), Baigrie et al.
patent: 5267847 (1993-12-01), Bohm et al.
patent: 5378407 (1995-01-01), Chandler et al.
patent: 5378415 (1995-01-01), Gohlisch et al.
patent: 5451919 (1995-09-01), Chu et al.
patent: 5582770 (1996-12-01), Chu et al.
patent: 5747147 (1998-05-01), Wartenberg et al.
patent: 5801612 (1998-09-01), Chandler et al.
patent: 5802709 (1998-09-01), Hogge et al.
patent: 5814264 (1998-09-01), Cai et al.
patent: WO 98/05503 (1998-02-01), None
Patent Abstracts of Japan, vol. 13, No. 189 (abstract of Japanese PublicationNo. 01016422).
Chu Edward F.
Jordan Susan M.
Lahlouh John
Eashoo Mark
Silbaugh Jan H.
Tyco Electronics Corporation
LandOfFree
Extrusion of polymers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Extrusion of polymers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Extrusion of polymers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2603849