Synthetic fiber forming apparatus for spinning synthetic fibers

Details Synthetic fiber forming apparatus for spinning synthetic fibers Synthetic fiber forming apparatus for spinning synthetic fibers

1998-08-20

2002-03-26

Nguyen, Nam (Department: 1722)

Plastic and nonmetallic article shaping or treating: processes

Outside of mold sintering or vitrifying of shaped inorganic...

Including plural heating steps

C264S176100, C425S463000, C425S464000, C425S131500

Reexamination Certificate

active

06361736

ABSTRACT:

FIELD OF INVENTION
The present invention relates to an apparatus and method for the production of synthetic fibers. In particular, the invention relates to an apparatus and method for the production of spun synthetic fibers having improved uniformity and production efficiencies.
BACKGROUND OF THE INVENTION
The expanding use of synthetic fibers has had a significant impact on the textile industry. Synthetic fibers are now used in many textile applications where natural fibers were traditionally used. This movement to the use of synthetic fibers mainly has been facilitated by their typically superior physical properties and relatively low manufacturing costs. In addition, synthetic fibers can be tailor-made to have a variety of different properties in order to enhance their applicability in numerous types of applications such as clothing, roping, industrial materials, and many other applications. For example, the material used, the fiber cross-sectional shape, the fiber size, etc. can be pre-selected to form a fiber which has the requisite features preferred for its intended end use. Further, where varieties of features or properties are required, multi-component synthetic fibers can be produced and utilized, with the individual fiber components being selected to provide specific features. In the production of such multi-component fibers, the manufacturer can control the cross-sectional shape of each of the various components as well as their relative proportions in the fiber structure. In this way, multi-component fibers enable a user to capitalize on the particular features of multiple different synthetic materials simultaneously, often with synergistic results.
The most common methods for producing synthetic filaments are spinning processes. Relatedly, such spinning processes also form intermediate stages in the production of nonwoven fabrics such as during spunbonding and meltblowing nonwoven fabric production processes. In these spinning processes, a flowable material (e.g., a solution-dissolved or molten polymer) is fed in a selected manner to a spinneret. The liquified material passes through the spinneret where it emerges in a plurality of thin material streams which are quenched (e.g., by a gaseous or liquid medium) in order to solidify the flowable material streams, thereby forming spun filaments.
Typically, when a plurality of synthetic fibers are produced, it is desirable for the individual fibers of the plurality to have relatively uniform cross-sectional dimensions, in order that uniform properties are consistently provided by each fiber. In commercial manufacturing environments, however, irregularities in fiber structures are commonly and undesirably introduced during fiber production, and variations can occur between the individual fibers relative to each other as well as along the length of each individual fiber.
One example of synthetic fiber production is described in U.S. Pat. Nos. 5,162,074 and 5,344,297 to Hills. In the manufacturing processes described in those patents, flowable polymer material is passed under pressure to etched distribution plates containing horizontal flow paths. The polymer material flows from an inlet point through these flow paths on the etched plate, where it is directed into the backholes of a spinneret. These horizontal flow paths can present several problems in the manufacturing process.
First, because the etched plate is designed to receive the flowable polymer material and to distribute it to the spaced backholes of the spinneret, the individual flow paths of the etched plate would thus, absent any intentional modification to their design, generally have different lengths and/or dimensions. This difference in the path lengths can cause the flowable polymer material in the longer flow paths to experience a larger drop in pressure than the polymer material in the shorter flow paths. This pressure differential between the materials in the different flow paths can thus cause the feed rate of the flowable polymer material to the spinneret backholes to vary, which can adversely affect the shape of the polymer streams exiting the spinneret. These pressure differentials can represent an even greater problem in the production of multi-component fibers, since the feeding of the flowable materials to form particular multi-component fibers typically needs to be very precise.
Because in the prior art methods the pressure irregularities are introduced downstream of the pressure regulating means (i.e., generally a metering plate proximate the material supply point), the pressure irregularities tend to manifest themselves directly in the form of irregularities in the spun fibers. To combat this problem, prior art methods have employed distribution plates where the shorter path lengths are intentionally lengthened so as to equalize the lengths for all of the flow paths. In other words, some channels are made longer than necessary, to achieve a particular fiber construction. This lengthening of the channel increases the dwell time of the flowable material, which can lead to undesirable and otherwise unnecessary polymer degradation. In addition, the extended length channels consume plate area which might be otherwise beneficially used. As a result of this loss of space, cross-sectional design complexity of the fibers can be limited, since more complex designs typically require more channels (and thus more plate space). In addition, the hole density in the spinneret must be correspondingly reduced, since the holes must be located farther apart when the channels take up a greater proportion of plate space. As a result, the through-put rate (and thus productivity) can be undesirably reduced.
Another problem can be experienced when the flow paths of a distribution plate are connected to exit holes with large cross-sectional dimensions. As the polymer material flows from the flow path into the distribution plate exit hole, more of the polymer material is distributed to the area of the exit hole nearest to the flow path outlet than to the opposite sides of the exit hole. This causes an uneven distribution of flowable polymer material to be fed to the spinneret, and as a result, generally precludes the use of the shape and size of the exit hole of the distribution plate in helping to determine the cross-sectional distribution of the respective polymers in the resulting fiber. Consequently, distribution plate designers generally must avoid the use of large and shaped exit holes. Instead, the cited art allows only the positioning of exit holes relative to each other to determine the multi-component cross-section, which is a less certain method than the one of the instant invention, which allows the use of the size and shape of the exit holes to determine the fiber configuration as well.
Accordingly, there exists a need for a method and apparatus for producing synthetic fibers having improved uniformity and for providing improved control over fiber cross-sectional shape.
SUMMARY OF THE INVENTION
In light of the above, it would be advantageous to provide a method and apparatus for improving the uniformity of synthetic fibers, while increasing the ease of achieving complexity of the design of a multi-component fiber cross-section. The present invention provides such consistent uniform fiber spinning by generally restoring and/or initiating a pressure equilibrium to the flowable material streams as they are delivered to the spinneret. This in turn allows the spinneret to produce synthetic fibers with more uniform structures and properties. Because the apparatus in one embodiment of the present invention can be used to actually create the requisite pressure for the spinning process, in that embodiment the pressure equipment located upstream of the distribution plate, such as the pressure and metering plates often utilized to provide pressure in conventional spin pack arrangements, can essentially be eliminated.
These and other advantages are provided according to the present invention by an apparatus for forming synthetic fibers which includes a distribution

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