US2736920A - Spinneret - Google Patents

Description

March 6, 1956 D. B. wlcKER 2,736,920

I SPINNERET Filed lbw. 34, 1951 INVENTOR .04 a. IV/CAI/P,

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ATTORNEY United States Patent SPINNERET Dan B. Wicker, Stamford, Conn, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine Application November 24, 1951, Serial No. 258,005

1 Claim. (c1. ls-s This invention relates to improved spinnerets for the production of artificial fibers and particularly for the wet spinning of tow which comprises a large number of comparatively fine filaments.

In the production of artificial fibers, a dope or solution of the coagulable material is extruded through a spinneret containing a number of minute orifices into a coagulating chamber where the fiber is coagulated or formed either by the vaporation of a volatile solvent in dry spinning or into a bath of a liquid coagulant in the case of wet spinning. With continuous filament yarn, little difliculty has been encountered in coagulating the comparatively small number of individual filaments or fibers (e. g. 30240 filaments) which make up the strand extruded by a single spinneret as the coagulating medium easily penetrates to all of the filaments in these small bundles. However, the problem is more troublesome in the case of tow which is chiefly used in the production of staple fibers. An extremely large number of comparatively thin fibers is desired for tow. Further, the more of these filaments that can be produced by a single spinneret, the greater is the manufacturing efficiency because fewer spinnerets and hence fewer spinning positions are required. While the number of filaments produced by a single spinneret can be increased by increasing the area of the spinneret face, other considerations limit the feasible size of spinneret faces to a maximum of a few inches. Additional problems arise in wet spinning when employing a coagulating bath at a considerably lower temperature, say 40 C. or more, than the temperature of the dope being extruded. Such a process is described in Patent No. 2,558,730 to Cresswell in which solutions of various acrylonitrile polymers and copolymers are extruded at about 100 C. into a coagulating solution maintained near 0 C. In using the spinnerets of the prior art for making tow by the Cresswell process, the concomitant transfer of heat in the zone of extrusion resulted in such a difference in the effective orifice temperatures among the various orifices in a single spinneret that unacceptable size divergencies of filament deniers occurred. Furthermore, the heating effect of the spinning solution was found to elevate the temperature of the coagulating liquid in the immediate zone of extrusion to a point where even with proper temperature control in the main bath, the ambient temperature conditions of some of the orifices and filaments extruded therefrom were above the maximum figure of C. This gave rise to improper gel characteristics in the acrylic fiber as evidenced by the milky, opaque cast of the filaments and by reduced susceptibility to the stretching necessary to orient the molecules for maximum strength. The spinnerets described herein are designed especially for the production of tow or staple fibers in the Cresswell process, but they may be used for other extrusion processes.

An object of the invention is to provide an improved spinneret for the shaping of artificial fibers.

Another object of the invention is to provide an improved spinneret for the wet spinning of artificial fiber "ice tow by the extrusion of a relatively hot dope into a relatively cold coagulating bath.

Var-iousother objects and advantages of the present invention will be apparent to those skilled in the art from the accompanying description.

The present invention concerns a multi-filament spinneret in which the spinning orifices are disposed in V- shaped perforate areas separated from one another by imperforate portions of the spinneret face. It accordingly comprises an article of manufacture possessing the features, properties and relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claim.

The invention is best understood in conjunction with the accompanying drawing in which:

Fig. 1 is a diagrammatic plan view of a spinneret.

Fig. 2 is a fragmentary diagrammatic plan View of another modification of the invention.

The spinneret is a shallow cup having a flat exterior face 12 and a flange 14 for reinforcement and convenience in mounting. Although the spinneret shown is of the circular configuration which is preferred for ease of manufacture, it should be understood that this device may also be of rectangular or even irregular shape as desired. The V-shaped areas 16 on the face of the spinneret denote those areas which are perforated with orifices through which the dope is extruded into the coagulating medium. Because of their small size and close spacing the individual orifices are not shown. For example, in one spinneret of this design with a 2 /2 diameter face, each of the V- or chevron-shaped perforate areas has 413 holes of microns diameter, thereby providing a spinneret capable of extruding 2478 individual filaments or fibers. These holes are located with an average distance or pitch between centers of 0.024" on 36 concentric circles having diameters ranging from 0.576" to 2.256"; thus the average pitch between circles is 0.024". Each arm 18 of each of the Vs contains 7 rows of orifices. No simple rule for the spacing of the perforate areas and of the orifices therein is known, but the figures set forth herein have produced good results in the Wet spinning of acrylic fiber tow by the Cresswell process mentioned earlier. It will be observed that the perforate V-shaped areas are arranged radially with their vertices 20 directed inwardly, that is adjoining the imperforate central section or area. With this arrangement three imperforate bands 22 extend diametrically across the face of the spinneret and provide channels for easy access of the coagulating fluid to the outer sides of the V. On the device mentioned these channels are about 0.266" wide and the width of the arms 18 of the V is about 0.187". It will be noted in the above description that the centers of all of the orifices are arranged on concentric circles. This greatly expedites the manufacture of spinnerets, particularly those having an orifice pattern as complex as that described here, since it permits the use of a circular pantograph in the initial steps of locating and starting to pierce these closely-spaced fine holes.

Another modification of the invention appears in Fig. 2 with each of the corners 120, 124 and 126 smoothed or rounded off by omission of one of a few holes at each of these corners on each V in contrast to the corresponding angular corners 20, 24 and 26 of the apertured areas in Fig. 1. This form of the invention is preferred for use under the most critical of operating conditions. Such conditions often lead to filament breakage and it is felt that removing the orifices at the sharp corners of the apertured areas Will reduce filament breakage during critical conditions.

The differences in the product obtained with the spinnerets of the present invention are much greater than would be expected from prior art spinnerets having perforate sectors (i. e. wedge-shaped sections) surrounding an imperforate center and separated by similar imperforate diametrical bands. 2478 substantially uniformly transparent strands of satisfactory filament diameter have been obtained with the former; yet with the old spinnerets of similar arrangement having six sectors of 167, 333 and 667 orifices per sector respectively or a total of about 1000, 2000 and 4000 holes per spinneret respectively of 90 microns diameter, the results were distinctly inferior as evidenced by the considerable number of unstretchable opaque and oversized filaments produced in extruding an acrylic polymer by the aforesaid Cresswell process. Thus, even if the number of orifices were reduced sufficiently in the prior art spinnerets to produce satisfactory filaments, at least several times as many spinnerets'would be required in comparison with the novel spinnerets.

While there are above disclosed but a limited number of embodiments of the structure of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claim as are stated therein, or required by the prior art.

What I claim as new and desire to secure by Letters Patent is:

A multi-filament spinneret which comprises an imperforate center area, a plurality of substantially V-shaped perforate areas of substantially the same size, branches of adjacent V-shaped areas being substantially parallel, with the branches of the V perforated with a plurality of spinning orifices in each of the plurality of rows, said V-shaped areas being disposed radially about the center area with the vertices of the Vs adjoining the center area and substantially equi-distant from the center of the spinneret, and imperforate areas of suflicient width to provide free access of a coagulating fluid between the perforate V-shaped areas, said spinneret having a minimum total of about 1,000 orifices.

References Cited in the file of this patent UNITED STATES PATENTS 2,447,994 Wicker Aug. 24, 1948 FOREIGN PATENTS 319,444 Germany Mar. 5, 1920 321,344 Germany May 21, 1920 395,524 Germany May 22, 1924 536,574 Germany Oct. 27, 1931 755,342 France Sept. 4, 1933

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