US2971219A - Mixer distribution plate - Google Patents

Description

Feb. 14, 1961 B. E. HILL MIXER DISTRIBUTION PLATE Filed Aug. 14, 1956 INVENTOR BROA DUS E. HILL ATTORNEY MIXER DISTRIBUTION PLATE Broadus E. Hill, Kinston, N.C., assignor to E, L du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Aug. 14, 1956, Ser. No. 603,934

6 Claims. (Cl. 18--8) This invention relates to the preparation of fibers from synthetic linear polymers, and more particularly to an improved process and apparatus for spinning fibers from molten synthetic linear polymers.

The melt spinning of synthetic linear polymers through apparatus including a metering pump, a filter pack comprising a system of screens or a finely divided inert material supported by a screen assembly, and a spinneret plate is described in U.S. 2,266,368 to Hull et al., and

in U.S. 2,278,875 to Graves. Apparatus of this type is particularly useful in the melt spinning of polyamides and polyesters, such as polyhexamethylene adipamide and polyethylene terephthalate.

It has frequently been observed in melt spinning that the filaments are not entirely uniform in quality despite efforts to supply the polymer to the spinneret pack at a constant pressure, temperature, and rate. It has been found that a major reason for this lack of uniformity between filaments is that the molten polymer near the periphery of the spinneret plate is cooler than the polymer near the center of the plate owing to heat losses from the side of the chamber as the polymer passes slowly through the filter pack. The difference in temperature between. center and periphery may amount to C. or even more. Accordingly, the polymer extruded near the circumference of the spinneret plate is extruded more slowly and solidifies more rapidly into filaments than does the polymer extruded near the center of the plate, resulting in non-uniformities in yarn properties.

It is an object of this invention to provide a process for supplying molten polymer to a spinneret plate at a temperature which is substantially constant across the plate. Another object is to provide apparatus for accomplishing this process. Other objects will be apparent from thefollowing description and claims.

These objects are achieved by the present invention which, briefly described, comprises redistributing the flow of a stream of molten polymer being transmitted to a spinneret just prior to the arrival of the stream at the spinneret orifices such that the polymer initially at the periphery of the stream is supplied to the area about the center of the spinneret plate and the polymer initially near the center of the stream is supplied to the area about the circumference of the spinneret. Apparatus useful according to the present invention comprises a distribution plate having a plurality of channels leading from near the center of its upper face to near the edge of its lower face and from near the edge of its upper face to near the center of its lower face. Optionally, the plate may also have a plurality of vertical channels substantially midway between the center and the edge of the plate, said vertical channels preferably being smaller in diameter than the other channels. When used for the purposes of the present invention, the distribution plate is positioned above the spinneret plate a relatively short distance, with only a relatively small free space between the distribution plate and the spinneret plate, so that the molten polymer becomes substantially uniform in temperature through heat transfer and mixingand then is extruded before a new temperature differential can be established.

The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying illustrations. Referring now to the drawings:

Figure l is a view of the upper face of a distribution plate constructed in accordance with the present invention.

Figure 2 is a sectional view of a portion of a spinneret assembly, with the distribution plate in place and shown in section along the lines 22 of Figure 1..

Figure 3 is a top view of an optical distribution plate similar to that shown in Figure l, but in addition it is provided with vertical channels described more fully below.

Figure 4 is a section along the line 4-4 of Figure 3.

As shown in the drawings, the distribution plate 1 has channels 2 leading from near the center of its upper face to near the periphery of its lower face and channels 3 leading from near the periphery of its upper face to near the center of its lower face. The plate is mounted in pack holder 4, which has vertical channels 5 leading to the spinneret plate 6 provided with orifices 7, which may number up to several hundred, for spinning the polymer. Gasket 8 provides sufficient separation between the pack holder and the spinneret plate to allow even distribution of molten polymer to all the spinneret orifices. Suitable members 9 are provided for support of spinneret plate and pack holder. Supported in the pack holder above the distribution plate by screen 10 is filter medium 11, which is a finely-divided inert material, such as sand, useful in filtering out non-fusible material. The molten polymer is supplied to the filter by suitable means from a reservoir (not shown).

Optional modifications of the distribution plate are also shown in the figures. Vertical channels 12, shown in Figures 3 and 4, may be provided at locations intermediate between the center and the edge of the plate; however, if these channels are provided, they are preferably of smaller diameter than the diagonally disposed channels, usually about two-thirds the diameter of the diagonally disposed channels. Shallow annular recess 13 in the lower face of the distribution plate, connecting with a l the channels in the distribution plate, is desirable to provide a small reservoir for even distribution of the molten polymer to vertical channels 5 in the pack holder when the spinneret pack is assembled in the manner shown in Figure 2. Annular groove 14 around the edge of the upper face of the distribution plate may also be provided to accommodate gasket 15, which is useful in preventing molten polymer from by-passing the distribution plate as weli as in preventing leakage of the filter medium around the edges of the screen.

The distribution plate may also be modified in other ways, of course, to accommodate it for use with spinning apparatus of various other designs. For example, if the pack holder is designed such that the distribution plate contacts the spinneret plate directly, the recess 13 in the distribution plate should be sufficiently extensive to connect with all of the spinneret holes as well as all of the channels in the distribution plate. However, in its simplest form the distribution plate comprises a plate having channels leading from near the center of its upper face to near the edge of its lower face and from near the edge of its upper face to near the center of its lower face. The plate is preferably circular and of the same order of diameter as the spinneret plate with which it is used. It may be fabricated from stainless steel, or from other materials suitable for use in contact with molten polymers at elevated temperatures, by usual shaping procedures such as drilling.

The process of the present invention provides for redistribution of a stream of molten polymer in a manner highly conducive to the establishment of uniform temperature throughout the polymer just prior to spinning, thus making possible the production of yarn of quite high quality. Spinning'at such uniform temperatures has not been feasible previously; owing to the limited space about each spinneret, including the necessity that the face of the spinneret be open for spinning, the provision of insulation of the required thickness and auxiliary heating throughout the apparatus down to the level of the spinneret has not proved practicable.

.Use of the process of the present invention results in substantial improvement in product quality. One important criterion of yarn quality is the frequency of segments of undrawn filament in the drawn yarn, since these undrawn segments accept dye much more readily than the drawn filaments and hence show up in dyed fabrics as undesirable, deeply-dyed flecks. Such defects are readily detected by dyeing a representative sample of the drawn yarn, for example with a dye such as Celanthrene Brilliant Blue FFS (Cl. No. Pr. 228) in the case of polyethylene terephthalate yarn. It has been found that the frequency of undrawn segments is greatly reduced when the distribution plates of the present invention are employed in spinning the yarn.

The uniform spinning temperature providedvby the process of the present invention also results in increased control of the spinning process. One problem encountered in maintaining continuous spinning is the spontaneous cessation of spinning by one or more filaments, followed by resumption of spinning in such a way that the filament spins onto-the floor instead of reentering the thr'eadline. It has been found that use of the distribution plates of this invention materially reduces the occurrence of these trailing filament ends, thus reducing the amount of attention to each spinneret required of the operator.

The following example is illustrative of the improvement in temperature uniformity at the spinneret, together with the resultant improvements in control of spinning and product quality, which can be achieved with the process and apparatus of the present invention.

Example A stainless steel plate having a thickness of about inch and a diameter of about 4% inches was provided with 8 holes of 7 inch diameter sloping at a 25 angle from near the center of the upper face to near the edge of the lower face 8, additional holes of inch diameter sloping ata 25 angle from near the edge of the upper face to near the center of the lower face, and 16 vertical .holes of A; inch diameter equally spaced on a circle about 2 /2 inches in diameter. The plate was provided with a shallow annular recess on the lower face and an annular groove on the upper edge as shown in Figure 2 and mounted in a spinneret pack as shown in the figure. The spinneret contained 250 holes. In spinning molten polyethylene terephthalate with this apparatus at 1200 yards per minute to produce 10.8 denier-per-filament yarn (undrawn), it was observed that the temperature at the center of the spinneret was 290 C. and the temperature near the edge of the spinneret was 288 'C., a difference of only 2' C. In continuous spinning, discontinuities in spinning resulting in trailing ends averaged only 0.29 per spinneret per day. The yarn was warp-drawn at a draw ratio of 3.6X, cut into staple yarn, carded, and blended. A sample of the blended yarn was dyed with Celanthrene Brilliant Blue FFS dye. Dark-dyed filament defects amounts to only 6.5 defects per 100 grains of yarn.

-The experiment was repeated, using a pack of the same composition but omitting the distribution plate. It was observed that the temperature at the center of the spinneret was 292 C. and the temperature near the edge in trailing ends averaged 0.5 per spinneret per day. The yarn was warp-drawn at a draw ratio of 3.6X, cut into staple yarn, carded, and blended under the same conditions as in the previous experiment. .A sample of the blended yarn, when dyed with Celanthrene Brilliant Blue FF-S dye under the same conditions used in the previous experiment, exhibited 13.5 dark-dyed'filament defects per grains of yarn.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A spinneret assembly for spinning molten fiberforming material comprising a perforated spinneret plate,

a housing around the said plate in fluid-tight relationship therewith, means for delivering the molten material to the said housing, and a distribution plate within the said housing between the spinneretplate and the said means for delivering the molten material, the said distribution plate having diagonally disposed channels passing completely therethrough extending from near the center of each face of the plate to near the periphery of the opposite face.

2. In a spinneret head having a spinneret plate provided with a large number of orifices a distribution plate for diverting the flow of molten material within the spinneret head comprising a plate with diagonally disposed channels passing completel therethrough, said channels passing from near the center of each face of the plate to near the periphery of the opposite face.

3. The apparatus of claim 2 in which the distribution plate is also provided with a series of holes located about midway between the center and the periphery of the said distribution plate and passing completely through at right angles to the face of the plate.

4. The apparatus of claim 1 in which a filter is interposed between the source of supply and the distribution plate.

5. A spinneret assembly for spinning molten fiberforming material which comprises a spinneret plate provided with extrusion orifices, a housing around the said plate in fluid-tight relationship therewith, means for supplying a molten fiber-forming material to the said housing, a distribution plate in the said housing between the means for supplying the molten material and the spinneret plate, said distribution plate having diagonally disposed channels passing completely therethrough leading from the center of the housingoutwardly and from the periphery of the housing inwardly, a shallow chamber communicating with the extrusion orifices of the spinneret plate and the channels of the said distribution plate, whereby the temperature of the molten materials is maintained at a substantially uniforrn'temperature at all the extrusion orifices.

6. The apparatus of claim 5 in which a filter is interposed between the source of supply and the distribution plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,345,086 Becker Mar. 28, 1944 2,408,713 Webb Oct. 1, 1946 2,440,761 Sisson et a1. May 4, 1948 2,589,870 Sale Mar. 18, 1952 2,683,073 Pierce July 6, 1954 2,690,930 Corson Oct. 5, 1954 2,729,538 Hull -c Jan. 3, 1956 2,736,920 Wicker Mar. 6, 1956 2,742,667 Clouzeau Apr. 24, 1956 FOREIGN PATENTS 67,376 Denmark Aug. 9, 1948 435,384 Great Britain Sept. -19, 1935 735,788 Great Britain Aug 31,1955

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