Coating processes – Application to opposite sides of sheet – web – or strip
Reexamination Certificate
1999-08-13
2001-05-29
Beck, Shrive (Department: 1762)
Coating processes
Application to opposite sides of sheet, web, or strip
C427S293000, C156S180000
Reexamination Certificate
active
06238733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for producing fiber-reinforced polymer compositions using a plasticating extruder and a plasticating extruder for carrying out the method.
2. Description of Related Art
A method and a plasticating extruder are disclosed in DE-C 40 16 784, in which the fiber strand enters the impregnating device and the strand exits after impregnation in a planar form. There is, however, little possibility that there will be good wetting of the fiber and the scattered material. The main problem, though, is that the individual fibers of the widely spread-apart fiber strand cannot be kept apart by the spreading lugs. The individual fibers are tied together in a compact strand by the 90° deflection from the guide transversely to the screw axis at the feed nozzle, up to the end of the impregnating channel and to the screw element of the extruder axis. This means that this compact strand, which comprises many endless individual fibers, is of a great thickness, thus leading to rapid pinching off or cutting off between the screw flights and the barrel wall. The resultant fiber entanglements, which are still not completely impregnated, are then very difficult to break up again with the mixing and kneading to be mixed with the remaining melt, or the mixing and kneading/shearing zone must be made so intensive and/or long that a very high proportion of very short fibers/fines are produced in the product as a result.
Furthermore, this results in more rapid pinching off of the compact fiber strand and uncontrolled slipping of the individual fibers. Different slipping rates of the glass fiber strands occur, which makes it extremely difficult or impossible for the machine to be in a state capable of carrying out the process, that is, undefined drive ratios and uncontrollable process states occur. Moreover, the pre-impregnated fiber strand has to be distributed homogeneously in the melt with the individual fibers while still in the mixing-in zone. The individual fibers pre-impregnated with liquid polymer are drawn in by the respective screw element and thereby cut or pinched off. As a result, the drive force that can be exerted on the fiber strand is relatively small, because it is not possible for an adequately large angle of wrap around the extruder shafts to occur. This also produces a great undefined slippage of the fibers in the feeding region, for which reason the fiber content in the polymer is subject to strong fluctuations. Measuring the changes in rate at the fed-in fiber strand and using the rotational-speed control on the extruder shafts to compensate for this error leads to a strong harmful pulsation in the molten polymer fed in the impregnating region and to pulsation in the mixing region and consequently in the product discharge. The envisaged melt control by the meter through the displaceable screw barrel does not solve this problem either, because when individual fibers slip considerably the rotational speed at the extruder shaft would have to be increased and more matrix melt would inevitably be conveyed from the melt located in the region of the screw. That is, the mixing ratio of fiber to matrix in this case changes disadvantageously. Furthermore, apart from the exact weight distribution of the glass fiber content, a pulsation-free even product discharge is required for product processing and material reproducibility.
The difficulties suggested in the preceding are not intended to be exhaustive but are among many tending to reduce the desirability of the known methods and the known plasticating extruders. Other noteworthy problems may exist; however, those presented above should be sufficient to demonstrate that those known methods and apparatuses are amenable to worthwhile improvements.
SUMMARY OF THE INVENTION
Accordingly, it is therefore a general object of the invention to provide a method and a plasticating extruder for producing fiber-reinforced polymer compositions that will obviate or minimize the above described difficulties.
It is a specific object of the invention is to provide a method and a plasticating extruder for producing fiber-reinforced polymer compositions with a good degree of mixing.
It is another object of the invention is to provide a method and a plasticating extruder for producing fiber-reinforced polymer compositions having good fiber impregnation.
It is still another object of the invention is to provide a method and a plasticating extruder for producing fiber-reinforced polymer compositions in which the long fibers make up as large a proportion as possible and the smallest or short fibers make up as small a proportion as possible of the product.
It is a further object of the invention is to provide a method and a plasticating extruder for producing fiber-reinforced polymer compositions in which the product discharge takes place steadily without pulsation.
A preferred embodiment of the method according to the invention intended to accomplish at least some of the foregoing objects includes passing the fiber strand along at least one coating nozzle into a feed opening of the plasticating extruder; winding the fiber strand onto and around at least one extruder shaft in a driving-forward manner; drawing the fiber strand into barrel bores of a screw barrel, wherein a diameter of the barrel bores is at least four times a thickness of the fiber strand; applying a liquid polymer onto a first flat side of the fiber strand from the at least one coating nozzle; pressing a second side of the fiber strand into a liquid polymer film that was already applied on the screw shaft; and feeding the polymer impregnated fiber strand from a feeding-in and impregnating zone into screw barrels having a reduced diameter in a discharge and conveying zone.
A preferred embodiment of the plasticating extruder according to the invention that is intended to accomplish at least some of the foregoing objects includes a plasticating extruder for producing fiber-reinforced polymer compositions having a drawing-in and impregnating zone and a discharge and conveying zone, comprising a heater that heats a fiber strand; a first barrel in the drawing-in and impregnating zone; a polymer feed on the first barrel and including at least one coating nozzle; first barrel bores in the first barrel, each first barrel bore having a diameter that is at least four times a thickness of the fiber strand; rotationally driven first extruder shafts in the first barrel bores; a feed opening in the first barrel for introducing a fiber strand into the first barrel bores; a second barrel in the discharge and conveying zone; a cutting edge at an entrance to the second barrel; second barrel bores in the second barrel, each having a diameter that is less than the diameter of the first barrel bores; and rotationally driven second extruder shafts in the second barrel bores.
Additional objects and advantages of the invention will be set forth in the following detailed description, or may be learned by practicing the invention. The objects and advantages of the invention may be realized and obtained with the instrumentalities and combinations particularly described herein.
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Beck Shrive
Crockford Kirsten A.
Foley & Lardner
Maschinenfabrik J. Dieffenbacher GmbH & Co.
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