US2838793A - Method and apparatus for melt spinning - Google Patents

Description

June 17, 1958 A. G. SCOTT ETAL 2,833,793

METHOD AND APPARATUS FOR MELT SPINNING Filed March 26, 1953 2 Sheets-Sheet 1 J INVENTORS.

ALEXANDER G.SCQTT HAROLD WEBER June 17, 1958 A. G. scoTT ET AL METHOD AND APPARATUS FOR MELT SPINNING Filed March 26, 1953 2 Sheets-Sheet 2 INVENTORS. ALEXANDER G. SCOTT HAROLD WEBER i 2 TATTORNEY United States 2,838,793 METHOD AND APPARATUS FORMELT SPINNING Alexander G. Scott," Ridgefield, and -Harold Weber, BloomfieltLN. J., assignors to Celanese '(Iorporation of America, New York, N. Y., a corporation of Delaware Application March 26, 1953, Serial No. 344,786

claims. or. 188) tentO the spinning orifices, supplying fresh powdered material to the plate, and drawing away the fused material passing through said orifices in the form of filaments. Although satisfactory filaments have been spun in this manner, the uniformity of the filaments has not been ashigh as desired.

It is an object of this invention to provide a novel process and apparatus for the production of artificial filaments from comminuted fusible filament-forming materials.

A further objectof this inventionis the provision of a new and improved process and apparatus of this character for producing filaments of greater uniformity than has heretofore been obtainable with similar processes and apparatus.

Other objects of this invention will appear from the following description and claims.

According to this invention the particles of fusible filament-forming material, contained within a vessel having a heated spinning jet, are urged against said jet by means of a plurality of alternately operating rams located within the vessel and having working faces which apply mechanical pressure to the particles adjacent to said jet.

More particularly, the spinning jet is in the form of an elongated electrically heated plate having a plurality of spinning orifices and is situated below a long tapered aperture at the bottom of the vessel. Powdered filamentforming material is urged against this plate by a pair of ramshaving working faces extending the lengthof said aperture. The rams are mounted in the form of a V, with the apex of the V adjacent to the jet plate,

so that they apply their mechanical pressure from different directions. During the reciprocation of the rams a force is applied to the particles by the downward movement of one -ram,-then this ram is raised-and a force is applied to the particles, from a different angle, by the downward movement of the other ram, and the sequence of operations is repeated. -The powdered material in contact with the jet plate is fused by the heat supplied to said plate and is drawn off through the orifices of said plate, while the upper particles of the layer of material adjacent to the plate, i. e. the particles in contact with the rams, remain unfused until they are forced closer to the plate by repeated downward movements of the rams against fresh powdered material which is intermittently supplied to the top of said layer. Just above the apex of the V there is provided a divider bar,

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whose lower surfaces are arranged to make sliding contact with the rams during the movement of said rams. When a ram is raised, a small quantity of powdered material flows by gravity around the divider bar on the side of said bar adjacent to that ram and then flows under said ram to make up for the material forced through the jet plate by the rams during their downward strokes.

The means for operating the rams comprises pistons attached to the rams and operating in cylinders. Compressed air is supplied alternately above and below each piston through a solenoid-operated 4-way valve. The electrical circuits of the solenoid for operating this valve include microswitches which are actuated by movement of the pistons, the circuits being so arranged that when one ram reaches its lowest desired position the valve is operated to cause that ram to be lifted and to cause the other ram to be moved downward towards the jet plate. By the use of the compressed air cylinders it is possible to maintain a substantially constant pressure on each ram during its downward stroke.

The drawing away of the fused material can be effected by simply allowing the products emerging from the orifices in the heated plate to fall away by their own weight. Except in the production of bristles and like heavy filamentary products, however, it is desirable to draw the fused material away at a greater linear rate, as by passing the filaments around a draw-roller or between nip rollers driven at the appropriate peripheral speed and disposed at a suflicient distance from the heated plate for the filaments to harden by cooling.

The filamentary products made in accordance with the invention can thus be in the form of a bundle of fine filaments, e. g. of 10 denier down to 1 denier or less,

associated together to form a. thread which can be twisted other such threads, can be converted into staple fibers for use in staple fiber yarns. Alternatively, however, filaments of heavy denier (e. g. of 10-200 denier) can be made, suitable for employment-singly or in small groups in the manner of yarns for textile purposes, or, by the use of a single orifice in the plate, still heavier filaments of up to 4,000 denier or more can be produced for such purposes as bristles. Or again, by providing an orifice in the plate in the form of a slit, narrow bands or ribbons, or straw-like products can be made, of a'width of the order 1 to 5 mm. or more. Such products can be drawn down from the orifices so as to reduce their denier without losing the width/thickness ratio of their original cross-section.

The degree of draw-down employed for the production of fine filaments, i. e. the ratio between the area of cross-section of the orifices in the plate and the area of cross-section of the filaments, is preferably of the order of 500 to 1,000 or more. For heavy filaments, however, a lower degree of draw-down can be employed, ranging from unity upwards according to the denier of the products required. The possibility of using a high degree of draw-down makes it unnecessary to use very fine orifices in the plate, and enables the same orifices to be used for filaments of very different deniers. orifices of the order of 0.02 or more in diameter, which offer no special difficulty in production, can be used, and the denier of the resulting filaments determined by the degree of draw-down. However, the properties of the filaments vary with the degree of draw-down; for example, when a lower degree of draw-down is employed the resulting filaments may exhibit a higher elongation at break.

From the draw roller or nip rollers by which the draw-down is effected, the filaments proceed to a collecting device, e. g. to a simple reel or, in the case of filament yarn, to a centrifugal pot or other twisting and winding device. On their way from the heated plate to the collecting device, the filaments may be treated with an anti-static lubricant or other finish.

The method and apparaus described above can be successfully operated in air at atmospheric pressure. Certain advantages can be obtained, however, by maintaining an atmosphere of an inert gas (e. g. of nitrogen) about the powdered material that has been supplied to the plate, particularly as regards the range of temperatures to which the plate may be heated without damage to the resulting filaments by charring, excessive bubble formation or other defects. For this purpose the vessel into which the powdered material is fed for delivery to the heated plate may be provided with a closure and with a supply pipe for feeding the inert gas. It is not desirable, in general, to maintain the powdered material supplied under a super-atmospheric gaseous pressure, whether of air or of insert gas, since it has been found thatthe use of such pressure greatly increases a tendency to the formation of numerous small bubbles of gas in the resulting filaments, giving them an opaque appearance and a much reduced specific gravity. In so far, however, as filamentary products of this character may be desirable for certain purposes, e. g. for thermal or electrical insulation, the use of pressure afiords a convenient means of obtaining them.

It has ben found that by maintaining a sub-atmospheric pressure about the powdered material that has been supplied to the heated plate certain further advantages can be obtained, particularly as regards the range of temperatures to which the plate may be heated without damagedue to charring or other decomposition of the material and without excessive formation of bubbles or other defects, and as regards the range of properties obtainable in the resulting filaments. Thus, when the powdered material is cellulose acetate and is maintained at sub-atmospheric pressure the temperature may range upwards from the lowest temperature at which the production of satisfactory filaments is possible to a temperature which is higher by 80-100 C. The use of higher temperatures increases the rate (in weight per unit time) at which the filaments are produced and the ease with which they can be drawn away from the orifices in the heated plate, while the availability of a wide range of practicable temperatures enables filaments of widely different characters to be obtained, from filaments of high tenacity and relatively low extensibility produced at low temperatures, to filaments of lower tenacity but greater extensibility produced at hi her temperatures. Moreover, the use of sub-atmospheric pressure in this way enables a still wider range of materials to be spun into filaments from the molten condition. If desired, an inert gas at sub-atmospheric pressure may be used.

By the use of this invention substantially uniform filamentary products can be successfully produced from a number of fusible filament-forming substances, including not only substances which are stable at and above their melting points, but also many which are liable to slow decomposition and discoloration if maintained for a substantial period at about the temperature at which they first become flowable. The method of the present invention does not require the material to be in a flowable state for more than a very short period of time. The time during which the filament-forming material is being urged by therams towards the jet face, in the form of apparatus described above, is itself of the order of 4 minutes or less, and the material is subjected to a temperature approaching that or" the heated jet plate for only a fraction of that time. The very short period of heating enables melt-spinning of materials of the type mentioned above to be effected, even with the use of substantially higher plate temperatures than those at which the materials become flowable, without substantial charring or discoloration of the resulting products. The invention is particularly applicable to fusible filament-forming substances which do not have a sharp melting point but are softened and gradually increase in flowability over a range of temperatures. When using materials with sharp melting points it is often preferable to employ a substantial degree of draw-down. The materials which do not have a sharp melting point, however, can in general be spun quite readily without substantial draw-down, (i. e. with no more than that caused by the weight of the extruded product) to form heavy bristles.

As has already been mentioned, cellulose acetate is an example of the materials to which the invention can be applied. The cellulose acetate used may be a full acetylated or a partially deacetylated (e. g. acetone-soluble) product. Although, as pointed out above, the material is subjected to a high temperature for only a very short time, it is desirable to take reasonable steps to stabilize the material against heat-decomposition. Accordingly, when using a partially deacetylated cellulose acetate, it is preferred to use a hot-ripened material, i. e. one deacetylated by ripening at a temperature substantially above room temperature, preferably after neutralizing part or all of the sulfuric acid employed as a catalyst in the acetylation process. Further, the material used is preferably one which, after ripening, has been stabilized by heating under pressure with water or very dilute acid to a temperature substantially above the boiling point at normal pressure of the mixture. A further measure, which is applicable to a number of different materials and which makes easier the production of filamentary products in accordance with the invention, is to heat the air-dry powdered material in the air or in vacuum, e. g. in the case of cellulose acetate to a temperature of ISO-200 C. for a period of /2 to /1 hour. The cellulose acetate may be employed with or without a content of plasticizer such as tricresyl phosphate or diethylhexyl phthalate.

The materials employed are supplied for the purpose of the invention in powder form. The size of the powder is not critical so long as it is not too coarse to pass into the layer of material in contact with the heated plate, nor so fine as to clog the apparatus or to give rise to difiiculties in handling through blowing about or being drawn away through the vacuum pipe which is used to place the particles under sub-atmospheric pressure. It has been found satisfactory to use a powder, the particle diameters of which are of the same order as, and range well below, the diameter of the spinning orifices in the heated plate. Thus with orifices of a diameter of 0.025 inch it has ben found practicable to use a powder which will pass through a gauze having openings per lineal inch but is retained on one having openings per lineal inch.

Other materials from which filaments may be produced according to the present invention include other cellulose esters such as cellulose propionate, cellulose acetate-propionate and cellulose acetate-butyrate; cellulose ethers, such as ethyl cellulose and benzyl cellulose; addition polymers such as polyethylene and polystyrene; other polymers such as polyhexamethylene-heptamethyleue urea obtained from hexamethylene diisocyanate and heptamethylene diamine, 4,4-polyurethane from tetramethylene diamine and 1,4-butanediol bis-(chloroformate), polyhexamethylene adipamide, polyaminocaproic acid and other polyamides, polyethylene terephthalate and other polyesters, and polyaminotriazoles, such as those from sebacic dihydrazide and hydrazine.

The powdered form in which the materials are supplied makes it possible to use mixtures of different materials by mixing together the separately powdered materials or to use mixtures of the powdered filament-forming materials with other materials, such as pigments, for example. Thus, a mixture of acetone-soluble cellulose acetate with 5% of the polyaminotriazone' mentioned, and -a mixture of 50% of cellulose acetate with 50% of 66 nylon,

and 'a mixture of 90% of cellulose acetate and of cellulose propionate of propionyl value 63.4%, have been successfully formed into bristles and drawn down into fine filaments; Further, filamentary products exhibiting colored or otherdesirable effects can be produced by mixing with the powdered or granular filament-forming material powdered or granular'dyestuffs, or white or colored pigments, or other effect materials, the added materials being incorporated'in the filamentary products as a consequence of the process of their production.

A preferred embodiment of this invention is shown in the accompanying drawing wherein,

Fig. 1 is a side elevational view, partly in section and with'parts broken away, of the apparatus of this invention;

Fig. 2 is a front elevational'view of the apparatus of this invention, with parts broken away, and

Fig. 3 is a diagrammatic view of the means for Operating the rams in the apparatus of this invention.

Referring now to the drawing, reference numeral 10 designates a vessel having side walls 12, end walls 13 and a cover 14 tightly fitting over said side and end walls and adapted to be secured-to said side walls by means of latches 16 carried by said side walls. Within the vessel 10 there is provided a central V-shaped hopper 17 formed by a pair of upper plates 18 and a pair of lower plates 19, 1 the plates 18 being joined to the plates 19 by any suitable meanssuchas screws (not shown). The plates 18 and 19 extend across the housing from one side wall 12 to the other and are secured to said side walls in any desired manner. At their lower ends the lower plates 19 are provided with tips 21 forming a central channel 22 extending across the entire bottom of the hopper 17.

Comminuted thermoplastic filament-forming material,

in flake or powder form, is placed in the hopper 1'7 passes down by gravity through the channel 22 and over the tapered upper surfaces 23 of a central divider bar 24, and then is forced by tampers or rams 26, 26a, having working faces 27, 27a, through an aperture 28 formed-in a strip cover 29,- and through spinning orifices located along the length of an electrically heated jet plate 31, which is in the form of a strip mounted between the strip cover 29 and a strip support 32. In order to cause the material to flow smoothlyand evenly through the channel 22,

there is provided a long vibrating comb 33 having teeth 34,"the comb being oscillated endwise by a vibrator 36 mounted on a side wall 12 (Fig. 2). The comb 33, divider bar 24, rams 26, 26a, aperture 28, strip cover 29 and strip support 32 extend substantially the entire width of the hopper 17, the divider bar being secured to the side walls E2 of the vessel, the strip cover 29 being mounted in a long slot 37 in the bottom 11 of the Vessel, and the strip support 32 being fixed to said bottom 11 in any suitable manner.

The jet plate 31 is adapted to be heated by the passage of an electric current therethrough, the current being suitably regulated so that the plate is maintained at a controlled temperature sufficient to melt the thermoplastic material forced against said plate by the action of the rams 26, 26a. The strip cover'29 is made of an electrically insulating material and the strip support 32 is faced with such insulating material, at 38, to prevent short circuits through said cover and support. 7

The rams 26, 26a are arranged in V-form and are adapted to be reciprocated in sliding contact with, and guided by, the smooth back surfaces 39 of the lower plates 19 and the smooth outer surfaces 41 of ram guides 42.

lower sides 44 of the divider bar 24 are suitably tapered so that the rains 26, 26a may fit against these sides during the'sliding movement of said rams; The sides of the passageway 28 in strip cover 29 are also tapered in alignment with the outer surfaces 41 of the ram guides 42, the bottom of said passageway providing an exposed area of the jet plate 31 of such size that, when the areas of the working faces 27, 27a of the rams 26, 26a are projected onto said plate along the lines of downward movement of said rams, said projected areas are substantially congruent and equal to the exposed area of said jet plate.

The 'rams 26, 26a are adapted to be reciprocated by means of compressed air. Thus, the rams 26, 26a are secured, by means of blocks 46, 46ato reciprocating rods 47, 47a (see also Fig. 2) moving in sleeves 48, 48a

and attached to yokes 49, 49a joined to piston rods 51, 51a at the end of which are pistons 52, 52a mounted in through a valve mechanism illustrated in Fig. 3, in which reference numeral 57 indicates a four-way air valve. The valve'57, of conventional construction, is of the type having a double solenoid, operating on momentary electrical impulses, for controlling the position of a valve rod (not shown). In thise type of valve, the valve rod remains in its last operating position after the solenoid is deenergized.

The valve 57 is provided with four ports: port 58 communicating with pipe 59 leading to a source of compressed air, port 61 which is open to the atmosphere, and ports 62 and63 communicating with pipes 64 and 66, respectively. The valve 5'7 is so constructed that when its rod is in one position the port 62 is connected with the port 58, and therefore with the source of compressed air, and

the port 63 is connected with the port 61, and therefore with the atmosphere, while when said rod is in its other position theseconnections are reversed. Pipe 64 is connected by means of branches 67 and 6% to the lower port 56a of the right cylinder 53a, as shown in. Figs. 1 and 2,

and to the upper port 54 of the left cylinder "3, while pipe 66 is connected, by means of branches 69 and 72, to V the upper port 54a of the cylinder 53a and to the lower port 56 of the cylinder 53. Thus, when the valve rod is in one position compressed air is admitted above the piston 52 and below the piston 52a, while the opposite sides of these pistons are subjected to atmospheric pressure, thereby causing the piston 52 to be driven in a downward direction and the piston 52a to be driven in an upward direction. When the valve rod is moved to its other position, the connections are reversed so that piston 52a is forced downwards and piston 52 is forced upwards.

As stated, the movement of the valve rod is controlled by a double solenoid. This solenoid has two portions 72 and '73, electrically connected to power lines 74, 76 through microswitches 77, 77a respectively, mounted on flanges 73 (Fig. l) of the lower hopper plates 19 and provided with operating plungers 79, 79a. During the movement of the rams 26, 2612, the pistons 52-, 52a and the yolqes 49, 49a, these plungers 7), 7% are engaged and moved, so as to close the microswitches 77, 77a, by

ends of bolts 81, 31a threaded adjustably in openings 82,

adjusted that when a ram 26 or 26:: reaches the lowest desired position of its travel, i. e., the position of ram 26 shown in Fig. l, the corresponding microswitch '77 or 77a, respectively, will be closed, thus energizing the corresponding portion 72 or 73 of the solenoid and causing the valve rod to move to reverse the valve connections. The speed of movement of the pistons 52, 52a and rams 26, 26a is controlled by means'of speed control valves 34, 84a, 86 and 86a located in the branches 67, 69, 71 and 68 respectively. These valves, which are of conventional construction, are preset so that the down-- strokes of the pistons 52, 52a are relatively rapid While the upstrokes of said pistons are effected slowly. More particularly, none of the valves 84, 84a, 86 and 86a presents any appreciable impediment to the flow of compressed air into the upper and lower portions of the cylinders 53, 53a, but these valves act to throttle the flow of air leaving said cylinders. Valves 84 and 84a are preset to impede the flow of air from the upper portions of the cylinders 53, 53a to a large extent, causing the pistons 52, 52a to move slowly during their upstrokes. Valves 86 and 86a are set to slow down the flow of air from the lower portions of the cylinders 53, 53a to only a slight extent, so that the downstrokes of the pistons 52, 52a take place quite rapidly but not so fast as to cause the rams 26, 26a to exert a sharp, sudden impact on the powdered material below said rams.

Assuming the parts to be initially in the position shown in Fig. 1, the closing of the left microswitch 77 causes the rod of the valve 57 to shift its position, so that compressed air is admitted above the piston 52:: and below the piston 52. As a result, the piston 52a descends rapidly into contact with the powdered filament-forming material which has flowed, from above, into the space below said piston. The powder at this point is in a state in which the application of a small force is sufficient to densify said powder considerably, say by about 30% of its bulk, so that the right ram 26a travels downward rather quickly for some distance. At the same time the left ram 26 moves upward slowly, so that it is still quite close to its initial position and prevents any of the powdered material from being forced upwardly around the left side of the bottom of the separator bar 24 by the downward motion of the right ram 26a. The material below the ram 26a is now tightly packed so that further downward movement of said ram is necessarily slower and depends on the rate at which the material is forced through the orifices in the jet plate 31. During this further downward movement the ram 26a exerts a constant pressure on the material below it, due to the constant pressure of the compressed air above the piston 52a, until after a considerable time, c. g. 3 minutes, the ram reaches its lowest desired position with its working face 27a adjacent to the lower edge of the divider bar 24. At this point the right microswitch 77a is actuated, thus causing a shift in the position of the rod of valve 57, and the operation is repeated with the right piston 52a ascending and the left piston 52 descending. In this manner a substantially constant pressure is exerted on the material below the rams and above the jet plate, the

intervals in which no pressure is exerted on said material being a minor fraction, e. g. on the order of about 0.1%, of the total time. For example, each such interval may be about Ms second or less.

The material within the vessel 10 is placed under a reduced pressure by means of a vacuum pump (not shown) connected to the hopper 17 through a vacuum pipe 87, shown near the top of said hopper in Figs. 1 and 2. The hopper is, of course, suitably sealed against leakage of air, particularly around the rams 26, 26a, back plates 88 having gaskets 39 being provided for this purpose. After the comminuted material has been placed in the hopper 17 and the cover 14 has been tightly closed, the vacuum is applied until the pressure in said hopper has been reduced to,- for example, 20 inches of mercury. Following this, the rams 26, 26a are placed in operation and the pressure in .the hopper is further reduced until it is at the desired operating value, e. g. about 1 pound per square inch absolute.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Apparatus for the production of artificial filamentary products from particles of fusible filament-forming material, said apparatus comprising a vessel for receiving particles of fusible filament-forming material, a heated spinning jet operatively connected to said vessel, a plurality of rams within said vessel and having working faces acting against said jet, said rams being movable in paths which are along intersecting lines, means for moving said rams to apply substantially constant mechanical pressure to the particles of material adjacent to said jet and dividing means in the path of the particles flowing through said vessel to said jet for directing said particles to positions in the path of one or the other of said rams.

2. Apparatus for the production of artificial filamentary products from particles of fusible filament-forming material, said apparatus comprising a vessel for receiving particles of fusible filament-forming material, said vessel having an aperture, a heated spinning jet adjacent to said aperture, said aperture being tapered inwardly toward said jet, a plurality of rams within said vessel and having working faces acting in intersecting directions against the material in said aperture, and means for moving said rams in intersecting directions to apply mechanical pressure to the particles of material in said aperture.

3. Apparatus for the production of artificial filamentary products from particles of fusible filament-forming material, said apparatus comprising a vessel for receiving particles of fusible filament-forming material, said vessel having an aperture at the bottom thereof and a heated spinning jet adjacent to and below said aperture, said aperture being tapered inwardly toward said jet, a pair of rams within said vessel and having working faces acting downwardly in intersecting directions against the material in said aperture, a divider having an upper surface in the path of the material flowing down said vessel to said jet, said divider having lower surfaces slidably engaged by said rams during their movements toward said jet, and means for moving said rams alternately to apply substantially constant mechanical pressure to the particles of material in said aperture, said means comprising cylinders, pistons in said cylinders and connected with said rams, means, including a valve, for admitting compressed gas to said cylinders to drive said pistons so as to move said rams toward said jet, the construction and arrangement being such that movement of said valve effects alternate movement of said rams with a rapid movement of one ram towards said jet and a slow movement of the other ram away from said jet, and electrical means, including switches actuated by the movement of said pistons, for moving said valve.

4. A process for the production of artificial filamentary products from comminuted fusible filament-forming materials, said process comprising applying mechanical pressure to the particles of material on one side of a layer of filament-forming material in contact with a heated jet having a spinning orifice therein so as to urge said particles toward said jet whereby said particles are fused by heat supplied from said jet, said pressure being applied toward said orifice alternately to different areas of said layer and from different directions, continually supplying fresh powdered material to said areas between successive applications of said pressure thereto and continuously drawing away the fused material through said orifice in the form of filaments.

5. Apparatus for the production of artificial filamentary products from particles of fusible filament forming material, said apparatus comprising a vessel for receiving particles of fusible filament-forming material, a heatedspinning jet operatively connected to said vessel, said spinning jet having a spinning orifice, means for applying mechanical pressure to particles of said filament-forming material supported on said spinning jet, said means including a plurality of rams within said vessel, each of said rams having a working face for applying the mechanical pressure to urge said particles of said filamentforming material toward said orifice, said working faces 9 of said rams operating against different areas of the mass of said particles at said jet, said rams being arranged to apply said mechanical pressure alternately from difierent directions toward said spinning orifice, and means for reciprocating said rams to move said working faces alternately.

Smith Dec. 4, 1869 '10 Schuh Apr. 20, 1926 Urschel Mar. 23, 1943 Billman Feb. 8, 1944 Weibel Feb. 13, 1945 Upton Nov. 3, 1953 Upton Nov. 3, 1953 Lipscomb et al. Apr. 10, 1956

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