Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Patent
1997-01-30
1998-05-26
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
264205, 26421115, 26421116, 26421117, 264233, 264234, D01D 504, D01D 506, D01F 626, D01F 674
Patent
active
057560315
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of polybenzoxazole or polybenzothiazole filaments and fibers.
Fibers prepared from polybenzoxazole (PBO) and polybenzothiazole (PBT) (hereinafter referred to as PBZ or polybenzazole polymers) may be prepared by first extruding a solution of polybenzazole polymer in a mineral acid (a polymer "dope") through a die or spinneret to prepare a dope filament. The dope filament is then drawn across an air gap, washed in a bath comprising water or a mixture of water and a mineral acid, and then dried. If multiple filaments are extruded simultaneously, they may then be combined into a multifilament fiber before, during, or after the washing step.
As the filaments of polybenzazole dope are extruded, the high extensional viscosity of the dope, the rapid cooling of the filaments, and the differences in the cooling rates of the filaments extruded at the center of the spinneret as compared to those extruded at the edge of the spinneret, may cause frequent breaks in the filaments as they are drawn across the air gap. Although this spinning stability problem can be reduced to some extent by using a slower spinning speed, and/or having a lower hole density on the spinneret, these methods are often less than desirable from the standpoint of productivity or equipment design. Since smaller diameter filaments are more desirable than larger diameter filaments which would be normally obtained by the use of a spinneret having larger orifices, the spin-draw ratio may need to be increased significantly to draw the filaments sufficiently to produce smaller diameter filaments, which may also cause breaks in the filaments.
Further, although the stability of the spinning line may be improved by decreasing the number of holes per spinneret (referred to hereafter as hole density), it becomes necessary to increase the number of spinnerets per spinning head or to increase the spinneret size in order to continuously spin a large number of filaments from a single spinning head. However, such equipment configurations may be less than desirable.
U.S. Pat. Nos. 5,294,390 and 5,385,702 disclose processes for increasing the stability of a spinning line by extruding polybenzazole filaments through a partially enclosed air gap which has gas flowing through it to cool the filaments at a relatively uniform temperature. Although this method increases the stability of the spinning line, methods for further increasing the spinning stability and the number of filaments which can be extruded per spin head while maintaining a relatively stable spinning line are desirable.
SUMMARY OF THE INVENTION
In one aspect, this invention is a process for the preparation of polybenzazole filaments which comprises (a) extruding the filaments from a spinneret having at least 100 holes, which are arranged to form a annular pattern around the center of the spinneret, the center and at least two radial sections of the spinneret having no holes and an average width which is at least about 3 times the minimum pitch of the holes; and (b) drawing the filaments through a quench chamber while providing a substantially radial gas flow therein across the spinneret from at least two different directions.
In a second aspect, this invention is a process for the preparation of polybenzazole filaments which comprises (a) extruding the filaments from a spinneret having at least 100 holes, which are arranged to form an annular pattern around the center of the spinneret, the center having no holes and an average width which is at least about 3 times the minimum pitch of the holes; and (b) drawing the filaments through a quench chamber while providing a substantially radial gas flow therein through the filaments from at least two directions.
It has been discovered that the process of the invention provides a means to prepare polybenzazole filaments and fibers which permits their spinning from spin-dies having a relatively high orifice density, but while maintaining relatively stable spinning condit
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Faley Timothy L.
Iba Ihachiro
Mills Michael E.
Tani Katsuya
Thumma Ira M.
Tentoni Leo B.
Toyobo Co. Ltd.
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