Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1997-08-06
1999-03-30
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521142, 521143, 521146, 521917, C08J 900
Patent
active
058890645
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and an extrusion apparatus for producing a foamed polymer.
U.S. Pat. No. 5,158,986 discloses a process and an extrusion apparatus comprising the features of the preamble of claim 1 and claim 13, respectively. Foamed polymers which have a microcellular or submicrocellular structure are to be produced thereby. Such a structure is obtained by forming small bubbles or cells in the polymer by way of foaming, with the bubbles or cells having a size of at least 10 .mu.m and a cell density of more than 10.sup.9 cells/cm.sup.3 in the microcellular structure, and a cell size of less than 1 .mu.m and a cell density of more than 10.sup.12 cells/cm.sup.3 in the submicrocellular structure.
In the known process for producing foamed polymer by means of an extrusion apparatus, the polymer is fed to the extrusion apparatus and subsequently molten. A pressurized foaming agent, such as Co.sub.2, N.sub.2 or the like, is fed to the polymer melt. As much foaming agent as is soluble in the polymer melt at a given pressure and temperature is to be supplied to the melt. Polymer melt and foaming agent are subsequently mixed to produce a single-phase mixture or solution.
To make the polymer foam, a pressure drop or rise in temperature is subsequently produced, as a result of which the foaming agent, which has been added to the polymer, starts to expand and the polymer is foamed. In the known process and in the known apparatus, a pressure drop is produced by a throttle, which results in a thermodynamic instability in the mixture of polymer and foaming agent. The solubility of the foaming agent in the polymer is suddenly changed thereby and a nucleation for small gas bubbles or gas cells starts in the polymer. These bubbles or cell will grow until the pressure is reduced to ambient pressure and the temperature falls below a so-called glass transition or melt temperature of the polymer. In a preceding step, or at the same time, the foamed polymer is molded in a molding tool to obtain a final product.
In the method and apparatus of the prior art, a pressure drop is produced in a nozzle-like throttle. The throttle comprises an inlet port with a cross-section that is greater than the cross-section of the outlet port of the throttle. As a result of this reduced cross-section, the throttle has the additional function to build up pressure in the extrusion apparatus, with the pressure drop as required for foaming being produced by friction inside the throttle between inlet port and outlet port. Furthermore, a flow rate for the mixture of polymer and foaming agent flowing through the nozzle is predetermined by the inner structure of the throttle and the pressure drop produced. It has been found that, when such a nozzle-like throttle is used, it is only a filament-like or sheet-like discharge of the foamed polymer that can take place if the final product is to be of a sufficiently good quality. A good quality of the final product will be achieved if the cell size is, for instance, small, the cell density very high, and the cells are homogeneously distributed in the foamed polymer. Another quality improvement is obtained at a small degree of orientation of the polymer molecules.
JP 6-91725 A also discloses a process and an apparatus wherein a gear pump increases the pressure in the mixture of polymer and foaming agent. The pressure is adjusted by an additional pressure control valve and it is only after that valve that a foamed sheet is produced through a molding tool.
DE 38 33 777 C2 describes an extruder/gear pump combination for high-speed extrusion. A pressure build-up along the screw axis of the single-screw extruder is to be as low as possible and only a gear pump is to permit a substantial pressure build-up in the melt. The throughput is to be easily adjustable by adjusting the speed of the gear pump and the extruder speed which is adapted thereto in a controlled manner. Furthermore, a measuring probe is provided by which the screw speed is controlled such that a predetermined setpoint value is ob
REFERENCES:
patent: 5158986 (1992-10-01), Cha et al.
LandOfFree
Process and apparatus for producing a foamed polymer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for producing a foamed polymer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for producing a foamed polymer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1215701