US2266363A - Apparatus for the production of filaments - Google Patents

Description

1941- G. D. GRAVES 2,266,363

APPARATUS FOR THE PRODUCTION OF FILAMENTS Filed Noir. 10, 1958 GEORGE GRAVES INVENTQR ATTOR Y Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE APPARATUS FOR THE PRODUCTION OF FILAMENTS George D. E. I. du

Graves, Wilmington, DeL, I Pont de Nemours and Company, Wilassignor to mington, a corporation of Delaware Application November 10, 1938, Serial No. 239,760

4 Claims.

described in United States Patents to Carothers Nos. 2,071,250 and 2,071,253. These synthetic linear polyamides are of two types: those obtained from monoamino-monocarboxylic acids and those obtained from the reaction of suitable .diamines and dibasic-carboxylic acids. These synthetic linear polyamides may be prepared, for example, by a process of condensation-polymerization such as described in United States Patent 2,130,948.

In the extrusion of these molten organic filament-forming compositions through spinneret orifices to form filaments, it is necessary that the molten composition be homogeneous and free from lumps and foreign material which would obstruct its passagethrough these orifices and thereby cause irregularities in diameter of the filaments or even cessation of flow. Further, it is important that the fiow of material into the spinneret'orifices be uniform and, particularly, that multiple spirmeret orifices in parallel be equally supplied as inequality of supply results in variation in diameter of filament.

In the production of filaments from molten compositions the molten material is fed into the filament-forming equipment, 1. e., the spinneret, under suitable pressure and at suitable temperature, from a supply duct communicating with a reservoir of the molten material. pose of preventing incompletely fused polymer, or foreign matter, from reaching the spinneret orifices, a spinneret pack is interposed between the supply duct and the spinneret orifices.

This spinneret pack may be composed of a large number of metal screens but such arrangement is cumbersome, the initial cost is high, and, if not constructed with extreme care, operating diificulties are encountered such as dripping from spinneret orifices, non-uniform fiow to the spineret orifices, irregularity in the diameter of the filament being extruded, and the like. In addition to such objections, the trouble and cost of cleaning the metal screens when they have become objectionably obstructed through one cause or another, which is not so infrequent even when the operation is running smoothly, is excessive.

For the pur- An object of the present invention is to provide an improved spinneret assembly for the melt extrusion of filaments. A further object is to provide an economical and practical'means oi suitably filtering a molten organic filamentforming composition. A still further object is to provide a relatively inexpensive spinneret assembly which will satisfactorily filter a molten organic filament-forming composition and permit its being equally supplied to multiple spinneret orifices in parallel. A further and particular object is to provide a spinneret pack which will overcome the objections heretofore mentioned to the multiple metal screen spinneret pack. Other objects will be apparent from the description of the invention given hereinafter.

The above objects are accomplished according to the present invention by the use of a spinneret assembly containing, in place of the multiple metal screen spinneret pack heretofore used, a mass of inert, finely divided material.

The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawing wherein:

The figure is a sectional view through a spinneret assembly designed according to one specific embodiment of the present invention.

With reference to the figure of the drawing, the base of a portion of a melt extrusion apparatus is represented by reference numeral I, the duct 2 therein communicating with any suitable source of molten material to be supplied under pressure. The internally threaded. spinneret packretaining tubular member 3 is screwed ,on to the externally threaded portion of the base I which is provided with a shoulder 4 against which the tubular member 3 is adapted to abut with an annular metal-covered asbestos gasket 5 interposed to give a tight joint between the base I and the spinneret assembly proper.

The lower end of the tubular member 3 is externally threaded and has screwed thereon the internally threaded annular spinneret-holder 6 which carries the plate-type spinneret 1 having spinneret holes 3, 8 through which the molten material'is adapted to be extruded to form filaments. Between the spinneret 'l and the bottom of the tubular member 3 are interposed one or more annular metal-covered asbestos gaskets a, a which ensure a tight joint between the tubular member 3 and the spinneret-holder 6 as well as insuring the firm seating of the spinneret I in the spinneret-holder 6.

The tubular member 3 defines a chamber which isfilled'with a spinneret pack comprising a v on one or more coarse metal screens l2, I: the

bottom one of which is supported by the spinneret-1. A coarse mesh metal screen I! is placed. I on top of the finely divided inert material. \a The spinneret pack is placed in the spinneret assembly when that assembly'is detached from the base I. Since'a tight contact is required to avoid leakage past the gasket 0, the total height of the layers of screens and finely divided inert material must not be so great as to prevent screwing the spinneret assembly and gasket 5 tightly up against the base I'. On the other hand, it is frequently desirable to have the finely divided v inert material III in the spinneret pack somewhat packed down rather than loose and the necessary compression to accomplish this may be conveniently achieved by making the depth of the bed of finely divided inert material such that, when the spinneret assembly is screwed tightly against the base i with gasket 5 interposed, the lower extending portion of the base-l will cdne into firm contact with the screen is, thus packing the finely divided inert material as desired. The screen i3, unless required to assist in compressing the filter pack, may optionally be omitted.

In the operation of the apparatus as described, the molten material is delivered under pressure of any suitable pumping device through the duct 2 and is forced downward through the spinneret pack" and out through the holes in the spinneret 1. 1

The molten material first encounters the coarse screen it which functionsphiefiy to hold the finely divided inert material in place and to distribute the molten polymer over the entire upper surface of the bed of finely divided inert material. The bed ll of finely divided inert material catches and retains the solid lumps 0t, polymer, foreign matter, dirt, and the like. The fine screen ll beneath the finely divided inert material is capable of filtering action but is not depended upon for this function and serves primarily to support and restrain the finely divided inert material resting on it. Actual examination of spinneret assemblies constructed according to the present invention and dismantled after use has shown that theremoval of particles from the molten polymer is accomplished entirely by the body of finely divided inert material and that the supporting screen II is not called upon to serve as a filter other than to retain the finely divided inert material itself.

The coarse screen or screens I 2, interposed between the supporting screen ii and the top of the spinneret I and which are preferably at least two in number, serve, or course, to support the screen H but their principal function is that of spacers-to create a relatively unimpeded passage for the molten material from the bottom of the bed ill of finely divided inert material to the orifices in the spinneret I.

Also, for the purpose of facilitating and equalizing the fiow of molten material into the orifices 8, 8, the entrance end of these latter are widened out as indicated at H in the drawing. Obviously, strict adherence to the proportions and details of design of the apparatus illustrated in the drawing is not essential. The drawing represents merely one specific embodiment which has been successful in prolonged actual use. The widening of the spinneret pack-retaining 75 .and thevlike, reduce the frictional resistance to the passageaasasssm I tubular member, 3 at the top is not essential.

but isdesirable as a means of providing anincreased area for filtering and, ofcourse, a relatively wide and shallow bed of sand 'interposes less frictional resistance to the passage'of the molten material than would the same volume of finely divided inert material in a bed of smaller diameter. In some instances, particularly in the spinning of very fine filaments for use in yarn, it is not always an advantage to or the molten material to a minimum as a substantial back pressure may be desirable. To take advantage of the enlarged area at the top of the bed of finely divided inert material, the discharge of the duct 2 is tapered out to practically the full diameter of the interior of the tubular member I.

The invention broadly contemplates the use of any finely divided inert material to form the assembly provided filter pack in the spinneret it is of a taining too large a proportion oi extremely fine particles will meet this requirement but material of a fibrous nature may not be useful under certain conditions due to a tendency to mat. the term inert material" as used herein, is meant a material that will not be affected by, or will not contaminate, the melt being extruded, that will remain solid at the temperature to which it will be exposed, and that possesses sufiicient mechanical strength not to break down 3:6 disintegrate rapidly under the conditions of Silica sand has been found stop up the o s the retaining screen. Other types or Z d- 1 1 3 8110 as zireonia sand may be used but are not so readily available. Finely divided iron filings, stainless steel filings, and similar inert metallic mmelfiioned as suitable for ven on me the n rous suitable materials that will eadily aim to those skilled in the art.

While wide variations of the design and proportions of the apparatus illustrated in the drawmg would normally be made by those skilled in the art to provide an apparatus best adapted for the particular conditions prevailing, the following example is given to illustrate a specific spinneret assembly in accordance with the present invention.

Example L-Reference will be made to the drawing, a spinneret assembly of the design there shown being used. A spinneret, provided with four holes adapted to form simultaneously four filaments each of 0.028" diameter, was employed. Resting on the spinneret were two 20 mesh metal screens, l2, l2 and an mesh metal 'screenll. P

'3 was 1.50" and that of the upper part was 2.00".

The total depth of the bed of sand was about 1.75". Placed on the bed of sand was a 20 mesh metal screen I l. The spinneret assembly as described was screwed on to the base of the melt extrusion apparatus as illustrated in the drawing.

Polyh'examethylene adipamide was melted and brought to a temperature of 280-295 C. in a vessel with the air displaced by commercially pure carbon dioxide. and pumped at the linear rate of 250 feet per minute through the spinneret assembly described above. During the course of the extrusion of the melt 300-500 pounds per square inch pressure developed back of the spinneret pack. The melted polymer was extruded at the rate of 150 grams per minute into filaments of excellent quality.

The above example is merely illustrative and is concerned with the extrusion of a relatively coarse filament at a moderate pressure. It is not essential that a multiple layer sand bed be used in the present invention as a bed of a single layer of sand of a suitable mesh size will serve satisfactorily, particularly in the extrusion of relatively coarse filaments for use as bristles in tooth brushes, and the like. A filter pack comprising a single layer of sand passing a mesh screen and retained on a 50 mesh screen may be used successfully in place of the two layer bed of sand described in the example.

As disclosed in United States patent application Serial No. 239,770, filed of even date herewith, in the names of Aifthan, Heckert, and Hull, and entitled Method and apparatus for the production of artificial structures, me use of a multiple layer of finely divided material in a spinneret pack has been found particularly advantageous in the melt spinning of relatively fine filaments for use in yarns, and the like. The preferred inert material is sand which has been carefully elutriated to remove dust or excessively fine particles, and the layers of sand are arranged in order of diminishing particle size in the direction of flow of'the molten composition, the sand having a particle size preferably falling between 20 mesh and 150 mesh.

A preferred arrangement of the sand spinneret pack in said application Serial No. 239,770 consists of four strata in the lowermost of which is used a fine sand having a particle size of about 60-150 mesh, predominantly 100-150 mesh. The sand in the next stratum is preferably about 45- 100 mesh, predominantly 45-65 mesh, and in the next stratum the sand should be about 35-65 mesh with the coarser size predominating. In.

the uppermost stratum it is preferred that all of the sand should be coarser than. 65 mesh although not coarser than 20 mesh. By defining the size of particles in mesh size is meant those particles which will just pass through a screen of the standard mesh indicated.

As disclosed in said application Serial No. 239,- 770, the melt spinning of a molten material through a spinneret assembly having a sand pack as described above builds up a substantial back pressure in the neighborhood of 800 pounds per square inch or more but tliis should not exceed 1500 pounds per square inch. An advantage in such an arrangement is that the molten polymer being spun is continuously kept under a very substantial pressure which practically eliminates bubble formation, a factor detrimental to the spinning of satisfactory fine filaments.

As those skilled in the art will appreciate, that portion of the apparatus of the present invention which comes in contact with the molten material to be extruded, must be made of some material which is inert toward the molten material.

Machine steel, chromium-vanadium, and 18-8 stainless steel are conveniently available and suitable for use in making both the massive parts and the screens of'the apparatus.

The temperature of the molten material should not appreciably diminish during its passage through the spinneret assembly as not only actual solidification of the material must be avoided but also any appreciable increase in viscosity. It has been found that the drop in temperature of the molten material in its passage through the spinneret assembly is not usually sufficient to necessitate the jacketing of the spinneret assem- 'bly but a heating jacket might be necessary under certain conditions.

The invention has been chiefly described in connection with its use in.the manufacture of filaments from synthetic linear polyamides such as polyhexamethylene adipamide. The invention is obviously applicable, however, to the melt extrusion of any organic filament-forming composition. As examples of such filament-forming compositions, the following may be mentioned: synthetic linear polyamides, that is, synthetic linear polymers containing CONH units in the linear chain, synthetic linear polymers such as polyesters, polyethers, polyacetals, and mixedpolyester-polyamides, such as may be prepared by condensation reactions as described in United States Patent No. 2,071,250 may also be employed. Other types of synthetic polymers, such as ethylene polymers, vinyl polymers, polystyrene and polyacrylic acid derivatives may also be spun with advantage in accordance with the present invention.

The filament-forming material used in accordance with the present invention may contain modifying agents, e. g., luster-modifying agents,

plasticizers, pigments, and dyes, antioxidants, resins, etc., such as will occur to those skilled in the art.

The use of a spinneret pack made in accordance with the present invention has many advantages over the spinneret packs heretofore used in the melt extrusion of filament-forming organic compounds. A pack of sufficient depth is easily possible so that a filter-can remain in operation for far longer periods of time before it becomes necessary to change it, than was possible with the multiple screen packs heretofore used. The relatively unobstructed space between the bottom of the spinneret pack proper and the spinneret orifices, comprising the space occupied by the spacing screens and the enlarged entrances to the orifices, insures uniformity of the rate of delivery of molten material to' the several orifices in parallel and thus protects against nonuniformity in the diameter of the filaments produced.

A great advantage of the present invention is that the use of inexpensive and readily available material, such as sand, as the principal component of the spinneret pack, in place of a multiplicity of permanent metal screens, simplifies and decreases materially the cost of cleaning the equipment when it has finally been run so long as to become objectionably obstructed or when it has, by design or otherwise, been allowed to cool below the melting point of the material being extruded. The used sand is merely discarded and replaced by new sand at negligible cost, while the metal screens used with it, only three or four in number, maybe either cleaned or discarded.

As many apparently widely different embodiments of this invention may be made without prising -a material, said spinneret pack being located imto be understood that the invention is not limited to the specific embodiments them! except as defined in the appended c Iclaim:

1. A spinneret assembly for the extrusion of molten organic filament-forming compositions T comprising a spinneret'and a spinneret pack combed 01 finely divided inert granular mediately adjacent the inner face of the spin- 2. A spinneret assembly for the extrusion of molten organic filament-forming compositions comprising a spinneret and a spinneret pack comprising a bed of sand, said spinneret pack being located immediately adjacent the inner face of the spinneret neret.

as de-cos departing from the spirit and scope thereof, it I a 01' said chamber, of said chamber,

3. A spinneret assembly for th extrusion oi molten organic filament-forming compositions comprising a spinneret and a spinncret pack comprising a bed of sand of particle size between 20 mesh and 50 mesh, said spinneret pack being 10- cafed immediately adjacent the inner face of the spinneret.

4. Apparatus for the extrusion of molten organic filament-torming compositions comprising a closed chamber, a supply duct entering the top granular material within said chamber, a fine mesh screen supporting said bed, and means for supporting said screen out 01' contact with said spinneret.

GEORGE D. GRAVES.

a spinneret forming the bottom

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