US2888711A - Production of filamentary materials - Google Patents

Description

June'2, 1959 D. FINLAYSON EI'AL 2,888,711

PRODUCTION OF 'FILAMENTARY MATERIALS Filed June 10, 1952 s Sheets-Sheet 1 A'Hurm s 5 I wussmsm H June 2, 1959 D. FINLAYSON ETAL 2,888,711

PRODUCTION OF FILAMENTARY MATERIALS Filed June 10, 1952 5 Sheets-Sheet 2 3 FIG. 5. 6 2 I26 87 I Q I27 88 :34 I33 7 i I36 89 2a 128 June 2, 1959 n. FlNLAYsoN ETAI; 2,888,711

PRODUCTIYLON OF FILAMENTARY MATERIALS Filed June 10, 1952 3 Sheets-Sheet 3 I nl/ 86 IOI I55 FIG. 8

PRODUCTION OF FRAMENTARY MATERIALS Donald Finlayson, Antoni Harcolinski, and Bolesiaw Krzesinslti, Spondon, near Derby, England, assignors to British Celanese Limited, a corporation of Great Britain Application June 10, 1952, Serial No. 292,772

Claims priority, application Great Britain June 15, 1051 11 Claims. (Cl. 18-8) This invention relates to the production of textile fibres and other filamentary products such as bristles, straws, ribbons and the like, and particularly to a method and to apparatus for the production of artificial filamentary products from fusible filament-forming materials (for example cellulose acetate) in powdered form.

US. application Ser. No. 243,994, filed August 28, 1951, describes a method of producing artificial filamentary products from powdered fusible filament-forming material which comprises, in its broadest aspect, urging the filament-forming material in powdered form against one side of a heated plate having spinning orifices therein so that the powdered material is fused by heat supplied from said plate, continually supplying fresh material to the plate, and drawing away the fused material through said orifices in the form of filaments. In this way it was found practicable to produce satisfactory filaments from a wide variety of fusible filament-forming materials in powdered form, including many materials the spinning of which into filaments from the molten condition had not previously been found practicable. The material drawn away in the form of filaments through the orifices in the heated plate is replaced by the supply of fresh powdered material, so that a thin layer of filament-forming material in contact with the plate is constantly maintained. The urging of the powdered material against the plate can be efiected by intermittently applying a mechanical pressure to the particles of material on the side of this layer remote from the plate. Such intermittency permits fresh powdered material to be supplied in very small quantities in the intervals between the successive applications of the pressure to make up for the molten material drawn away through the spinning orifices.

According to the present invention a method of producing artificial filamentary products from powdered fusible filament-forming material comprises urging the filament-forming material in powdered form against one side of a heated plate having spinning orifices therein so that the powdered material is fused by heat supplied from said plate, continually supplying fresh material to said plate, continuously maintaining a sub-atmospheric pressure about the powdered material that has been so supplied, and drawing away the fused material through said orifices in the form of filaments.

It has been found that by maintaining a sub-atmospheric pressure about the powdered material that has been supplied to the heated plate certain advantages can be obtained, particularly as regards the range of temperatures to which the plate may be heated without damage to the resulting filaments by 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 Patented June 2, 1959 temperature which is higher by -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 diiferent 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 higher 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.

An apparatus according to the present invention suitable for carrying out the method defined above comprises a substantially closed vessel, a plate in one wall of said vessel having one or more spinning orifices therein, a gas duct communicating with said vessel for the exhaustion of said vesselso as to maintain in said vessel a pressure substantially below atmospheric pressure, means for heating said plate to a temperature higher than that of any other part of the apparatus in contact with the filament-forming material, means for urging the filament-forming material in powdered form against said plate within said vessel, and means for supplying fresh powdered material from said vessel to said plate to replace material continuously drawn away from said orifices in the form of filaments. If it is desired that the atmosphere within the vessel should be an inert gas as well as being at sub-atmospheric pressure, a second gas duct may be provided to allow the supply of an inert gas to the vessel, the inert gas being continually drawn away through the first duct so as to maintain its pressure below atmospheric pressure. For the purpose of maintaining the sub-atmospheric pressure, a vacuum pump is provided, in communication with the first duct either directly or through a vacuum main serving a series of units of apparatus. It will be seen that, except for the provision of the vacuum pump, the apparatus defined is suitable for carrying out the process of US. application Ser. No. 243,994, filed August 28, 1951, in the case where, as described in that application, an atmosphere of an inert gas is to be maintained about the powdered material that has been supplied to the plate.

The degree of vacuum required for the purposes of the invention need not be so high as to require complicated and expensive pumps, glands and pressure locks in order to maintain it. A degree of vacuum giving a subatmospheric pressure of 10 lb./sq. in. absolute is believed to be sufficient for most practical purposes, and some advantage may be gained from an even smaller degree of vacuum. Nevertheless, it is preferred to use a sub-atmospheric pressure of the order of 4-5 lb./sq. in. absolute.

As in US. application Ser. No. 243,994, filed August 28, 1951, the urging of the powdered material against provided with a ram having a working face acting against the plate, and means for longitudinally reciprocating said ram at a frequency of say 3-50 strokes per second. The ram may either extend into the vessel through a suitable gland, to be longitudinally reciprocated by means outside the vessel, or the reciprocating means may be Wholly or partly contained within the vessel. Where such a gland is employed, and a second duct is required for the supply of an inert gas, said duct may communicate with the vessel through said gland.

The powdered material can be supplied to the vessel by hand or by any convenient feedrneans such as a lock chamber, and reaches the layer of material in contact with the plate in small quantities during the intervals bu tween the successive applications of the mechanical pressure. The tip or Working face of 'therarn acts in a well at the bottom of which is the heated plate. A small quantity of fresh powdered material passes under gravity beneath the tip of the ram each time the ram is raised. The ram may be raised just clear of the well, or a clear ance between the sides of the well and the ram may be relied on to give access for the material in the vessel to pass beneath the tip.

The drawing away of the fused material can be effected by simply allowing the products-emergingfrom the ori fices in the heated plate to fall away by their own weight. Except in the production or 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 round a draw-roller driven at the appropriate peripheral speed and disposed at a suflicient dis tance from the heated plate for the filaments to harden by cooling.

The filamentary products made in accordance with the invention can thus be made in the form of a bundle of fine filaments, eg of denier down to l denier or less, associated together to form a thread which can be twisted to any desired degree or, alone or in association with other such threads, can be converted into staple fibres for use in staple fibre yarns. Alternatively, however, fila' ments 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 4000 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 like flat filaments can be made, of a width of the order of 1-5 mm. or more. Such filaments can be drawn down from the orifices so as to reduce their denier without losing the width/ thickness ratio of their original crosssection.

The degree of draw-down employed for the production of fine filaments, i.e. the ratio between the area of crosssection of the orifices in the plate and the area of crosssection of the filaments, is preferably of the order of 500 to 1000 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 drawdown 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. Thus, orifices of the order of 0.02" or morein diameter, which ofier no special difiiculty in production, can be used, and the denier of the resulting filaments determined by the degree of draw-down. From the draw-roller by which the drawdown is efliected, the filaments proceed to a collecting device, e.g. to a simple reel or, in the case of a bundle of filaments to be formed into a continuous filament yarn, to a centrifugal pot or other twisting and winding device. On their way from the heated plate to the col lecting device, the filaments may be treated with an antistatic lubricant or other finish.

The invention will now be described in greater detail, particularly with reference to the form ofapparatus shown in the accompanying drawings, after which specific examples will be given of materials that can be employed and the conditions in which they can be converted into filaments by the invention. In the drawings:

Figure 1 is a side elevation of a unit of apparatus ac-- cording to the invention,

Figure 2 is a detail shown in cross-section of the apparatus shown in Figure l,

Figure 3 is a circuit diagram of the electrical heating arrangements of the apparatus shown in Figure 1,

Figure 4 is a front elevation of a further form of the apparatus according to the invention,

Figures 5 and 6 show two forms of gland arrangement alternative to those shown in Figures 1-4,

Figures'7 and 8 are a sectional side elevation and a part-sectional front elevation respectively of a third form of apparatus according to the invention, and

Figure 9 is a plan view of insulating slab 101.

Referring to Figures 1 and 2 of the drawings, the unit of apparatus there shown comprises a base plate 10, two rear pillars ii, a front pillar 12 and top plate 13. The top plate 13 carries the driving motor 14- of the unit "which is connected by a flexible coupling 15 to an eccentric 16, the crank 17 of which isadjustable in radius along a slot 18 and is secured in the desired position by means of a screw 19. The motor 14 and crank 17 rotate at about 1200 revolutions per minute. Through a connecting rod 21 the eccentricld drives a vertically acting tamper rod 21 slidably mounted in a guide bracket 22 fixed to the front pillar 12 of the unit. Beneath the bracket 22 is fixed an aligning tube 23, which is shown in section in Figure 2. The lower end of the tamper rod 21 within the aligning tube 23 is forked at 2 4 and carries a pin 25 passing through a vertical slot 26 in the upper end of a tamper holder 27. The tamper holder is a running fit inside the aligning tube 2.3 and is urged downwards by means of a strong compression spring 28. At the reduced lower end of the tamper holder 27 is mounted the tamper 29 proper.

The tamper 29 works in a jet assembly 31 carried on a bracket 32 slidably mounted on the front pillar l2 and vertically adjustable by means of a screw 33, so thatthe assembly 31 can be adjusted for height relatively, to the tamper 2? or lowered clear of the tamper when required. The jet assembly comprises a jet plate 35 secured between two slabs 36, 37 of heat-resisting electrically insulating material, the upper slab 36 eing bored at 33 to constitute a well which takes the tip of the tamper 2b with a clearance of about The lower slab 37 is similarly bored at 39, and the jet plate 35 is formed with a circle of nine spinning orifices 41, each of 0.025" diameter, at the bottom of the well '38. The ends of the jet plate 35 are connected by means of heavy copper leads 42 to a low-voltage source of electric current, as described in greater detail with reference to Figure 3. The lower slab 37 rests on an angle girder 43 carried by the bracket 32. The slabs 36, 37 and jet plate 35 are clamped together between the girder 4,3 and a fitment 46 by means of screws 47. To the fitment 46 is fixed a sheet metal cone 50 constituting a powder trough.

The trough 50 is covered by a closure 51 having a central gland 52 through which passes the tamper 29. Through the closure 51 pass a vacuum tapping 53 leading to a vacuum pump (not shown), and a gauge tapping 54 leading to a vacuum gauge (not shown). The vacuum pump is of such power asto be able to maintain a subatmospheric pressure within the powder trough 50 of the order of 4 lb./sq. in. absolute. For the feeding of powdered filament-forming material into the'trough 50, the closure is provided with a lock-chamber 55 fitted with an upper valve 56 and a lower valve 57, and with ahopper 58 above the upper valve. A window 59 in the closure 51 enables the quantity of powdered material in the trough 50 to be seen. When the supply in the trough 50 is running low, fresh powdered material can be fed into the trough from the hopper 58 by first opening the upper valve 56 to allow a charge of powder to enter the lockchamber 55 and then, after closing the valve 56, opening the valve 57 so as to allow the charge to pass into the trough 50. In this way, the supply of powdered material in the trough can be replenished without breaking the vacuum maintained by suction through the vacuum tapping 53: The vacuumtappingSll-and the gauge tapping F5 54 are fitted wtih gauze filters 60 to prevent the passage of powdered material.

The jet plate 35 is heated by an electric current supplied through the leads 42, the supply of current being controlled by the circuit shown in Figure 3. The circuit 1 of Figure 3 is supplied with alternating current at 200 volts from the mains terminals 62, to which are connected in series the primary coils 63, 64 of a principal transformer 65 and an auxiliary transformer 66 respectively. A variable resistance 67 is included in the circuit containing the primary coils 63, 64. The secondary coil 68 of the principal transformer 65 is directly connected through the leads 42 to the jet plate 35, and gives a voltage drop in the ratio of 200:1. The secondary coil 70 of the auxiliary transformer 66 is a high resistance coil giving a voltage rise of 1:3. It is connected to a variable resistance 71 and also to a pair of contacts 72, 73, arranged in parallel with the resistance 71 and controlled by means of a temperature recorder/ control instrument 7 4 of known type.

The instrument 74 is actuated by a thermocouple 75 fixed to the jet plate 35 within the lower slab 37, so as to record a temperature as near as possible to that of the spinning orifices 41. The upper contact 72 follows the movement of the recording pen 76 of the instrument 74, being driven by a suitable electronic servo-mechanism of known type. The lower contact 73 is a fixed but adjustable contact, its position being varied in accordance with the temperature desired of the jet plate 35. When the temperature of the jet plane, as recorded by the thermocouple 75 and the recording pen 76, exceeds a predetermined value, the contacts 72, 73 are opened and the reflected impedance of the primary 64 of the auxiliary transformer 66 increases. This reduces the voltage across the primary of the principal transformer 65,

so reducing the current through its secondary 68, i.e. the current supplied to the jet plate 35. When the temperature of the jet plate falls in consequence, the contacts 72, 73 are again engaged and the current is restored. In this way the temperature of the jet plate 35 can be maintained at a desired value with a high degree of accuracy. The variable resistance 71 enables the reflected impedance of the primary 64 to be adjusted to give the desired variation in the power supplied from the secondary 68; a variation of the order of has been found suitable. By adjusting the variable resistance 67 with contacts 72, 73 closed, the current from the secondary 68 can be adjusted so as to be slightly in excess of what is necessary to maintain the desired jet temperature.

In the operation of the device, powdered material is supplied to the powder trough 50, the trough is exhausted of air through the vacuum tapping 53, and the current through the jet plate 35 is turned on. When the desired temperature as indicated by the controller 74 is reached, the motor 14 is started. The material passes down the side of the tamper 29 into the bore of the upper slab 36, and the flat tip of the tamper 29, reciprocating vertically, tamps it into contact with the upper surface of the jet plate 35. The powder thus urged into contact with the jet face is melted and the pressure, though intermittently applied, is enough to cause the fused material to pass through the orifices 41 from which it is drawn away in the form of heavy bristles by its own weight. Once they have emerged, however, the bristles can be more rapidly drawn away from the orifices 41 in the form of fine filaments 78 by being passed round the feed roller 79 of a ring spinning device 80, by means of which they are collected and wound in the form of a package 81 of twisted filament yarn. On their way from the feed roller 79 to the ring spinning device 80, the filaments pass over a wick 82 for the application of an anti-static finish or lubricant.

The rate at which the powdered material is fed below the tip of the tamper 29 is self-adjusting so as to be equal to the rate at which the material is drawn away from the orifices 41 in the form of filaments 78. This is brought about by the form of connection between the tamper rod 21 and the tamper holder 27. By reason of the pin and slot connection 25, 26 the tip of the tamper is raised always to a constant height upon each revolution of the eccentric 16. This height is adjustable relative to the jet assembly 31, by means of the screws 33; a suitable height is /3" above the upper surface of the slab 36. The tamper 20 descends, however, only so far as the thickness of the layer of material lying over the jet plate 35 will permit, the pin 25 in the slot 26 allowing the residual movement of the tamper rod 21 under the influence of the eccentric 16 to take place independently of the tamper holder. The quantity of fresh material entering beneath the tip of the tamper 29 each time the tamper is raised depends upon the space created between the tip of the tamper in its uppermost position and the upper surface of the layer of material over the jet plate 35. If the material should enter beneath the tip of the tamper at a greater rate than that at which it was being drawn away in the form of the filaments 78, the thickness of the layer of material would increase, the clearance created beneath the tip of the tamper would diminish, and the rate of supply of fresh material would correspondingly diminish. Consequently a balance is arrived at between the rate of withdrawal in the form of filaments 78 and the rate of supply in the form of fresh powdered material from the powder trough 50.

The unit of apparatus shown in Figure 4 is one of a series of units arranged in line. The units are driven from a common shaft 86 carrying a series of eccentrics 87 each provided with a connecting rod 88 for the driving of a tamper rod 89 and tamper holder 90 which are united by a pin and slot connection 91, 02 similar to those shown in Figure 2. The tamper rod 89 and the tamper holder 90 are guided by bushes 93 in two rails 94, 95 respectively, extending the length of the series of units. A spring 96 similar to the spring 28 of Figure 2 acts between the upper rail 94 and a plate 9'7 carried by the tamper holder 90. The principal difierence between the unit of apparatus shown in Figure 4 and that shown in Figs. 1 and 2 lies in the form of the tamper and jet assembly.

The jet assembly comprises a jet plate 99 in the form of a long continuous strip extending the length of the whole series of units, and clamped along each edge by pairs of blocks 101, 102 of heat-resisting electrically insulating material. Along the middle of strip 99 are two continuous lines of spinning orifices 100. The blocks 101, 102 are clamped together by means of screws 103 passing through a retaining plate 104, through the blocks 101, 102 and an angle iron girder 105, and into bars 106. The bars 106 carry the side walls 107 of a powder trough provided with a closure 109 secured to flanges 110 at the upper edges of the side walls 107.

The tamper is in the form of a metal stem 111 secured to the lower end of the tamper holder 90 by means of an adjustable connection 112, and carrying at its lower end a tamper foot 113 in the form of a bar of a horizontal length equal to the spacing between the units of the series. The foot 113 works in the middle of a channel between the vertical edges of the blocks 101, having a clearance therefrom of the order of The stem 111 passes through a guide block 115 fixed t0 the closure 109, the passage being sealed by means of a rubber sleeve 116 secured to the guide block 115 and to the connection 112. The sleeve 116 is secured by means of wires 117. The closure 109 is provided with a vacuum pipe 118 leading to a vacuum pump (not shown). The pipe 118 leads into a tubular gauze filter 119 extending along the length of the trough formed by the walls 107.

The operation of the device is similar to that of the device described with reference to Figures 1 and 2, the jet plate 99 being heated by passing a current along its length from end to end under the control of temperaturecontrol means similar to that shown in Figure 3. The filaments 12d emerging as a sheet from the line of orifices 100' in the jet 99 can pass downwards to a collecting guide 121 where they turn through a right-angle to join the filaments produced by other units in the form of a heavy tow 122 of continuous filaments for collection at the end. of the series of units in any suitable manner. The tow 122 is suitable for conversion into staple fibres. In the form of apparatus shown, the trough 107' is fed by hand by removing the closure 109, and the apparatus is run until the charge so fed is exhausted.

Figures and 6 show two forms of gland arrangement, alternative to those shown in Figures 2 and 4, for actuating the tamper while maintaining the vacuum in the trough 50. In Figure 5 a tamper rod 125 is used which passes through a gland 126 in a bracket 127 corresponding to the bracket 22 of Figure l (or the rail 94 of Figure 4), and is provided at its lower end with a piston 128 working in a cylindrical space 129 in a fitment 130 to which the tamper 29 is secured. The tamper passes through a guide block 131 screwed into the closure 132 of the powder trough 50. The spring 23 acts betweenthe fitment 130 and a nut 133, which is screwed. below the gland 126 and is adjustable so as to vary the force-of the spring. A telescopic sleeve 134, 135 extends from the bracket 127 to the guide block 131, the upper sleeve 134 being secured by a gas-tight joint to the bracket- 127. The joint between the lower sleeve. 135 and the block 131, and the joint between the two sleeves 134, 135 are likewise rendered gas-tight, by means of rubber sleeves 136 which, however, enable the sleeve 135 to be raised when desired. A connection 137, communicating through the guide block 131 to the bore thereof through which the tamper 29 passes, enables a slow leak ofinert gas such as nitrogen to be supplied to the trough 50 if desired. The connection 137 may alternatively be used instead of the gauge tapping 54 shown in Figures 1 and 2 for connection to a vacuum gauge. The arrangement of Figure 5 has the advantage that the tamper rod 125-w0rks in the gland 126 with a constant stroke irrespective of variations in the stroke executed by the tamper 29 itself.

Figure 6 shows a form of connection between the tamper rod 21 and the tamper 29 which possesses the same advantage. In this arrangement the tamper rod 21 carries at its lower end a cylinder 140 in which works a piston 141 secured to the upper end of the tamper 29. The tamper 29 extends through a sleeve 142 formingan extension of the cylinder 140. The spring 28 is contained in the cylinder 1413 and works between the top of the cylinder and the piston 141. The gland 52, which in Figures l and 2 accommodates the tamper 29, accommodates in Figure 6 the sleeve 142. The stroke of the sleeve 142 through the gland 52 is thus a constant stroke irrespective of he variations in the stroke of the tamper 29. The interior of the cylinder 140, being subjected to vacuum, is sealed by means of a sealing ring 143.

Figures '7, 8 and 9 show diagrammatically a modification of the general arrangement described in Figure 4, in which the entire apparatus works in an evacuated chest. The chest 145 is provided with a front closurev 146, and the driving shaft 86 passes through a rotary vacuum seal 147 in one of the side walls of the chest. The eccentrics 143 on the shaft 86 differ from the eccentrics 37 of Figure 4 in being provided with ball bearings. The connections between the eccentrics and the tamper ems 111 are similar to that described with reference to Figure 5. Each comprises a piston 128 on the lower end of the tamper rod 125, a cylinder 129, fitment 130, and spring 28, all disposed between the rails 94, 95 which extend from one side to the other of the chest 145 and are supported on angle-iron brackets'149. A connection 150 provided with a tubular filter 151 communicates with a vacuum pump for evacuating the chest 145, A vacuum gauge 152 is provided at the top of the chest.

Since the entire apparatus is enclosedwithin the chest it is unnecessary to provide a powder trough with a closure like the closure 109 of Figure 4. Accordingly, a simple sheet metal trough 153 is employed, secured to the base of the chest 145 over a slot 154 into which the tamper feet 113'extend. The insulating slabs 101, 102, the jet plate 99 and the retaining plate 104 are secured to the face of the chest below the slot 154 by means of the screws 103. The modification shown in Figures 7 and 8 differs further from that shown in Figure 4 in that the tamper feet 113 are spaced from one another at their ends and work in separate slots 155 (Figure 9) in the upper insulating slab '101. This facilitates the sealingof the chest 145 against leakage of air inwards through the orifices at the points of junction of the tamper feet 113. The apparatus maybe fed with powder by chargingthe trough 153'by hand before fixing the front closure 146. Alternatively, however, a feed hopper may be employed as shown in dotted lines at 156, supported 'on the angle irons 149. The hopper 156 is open at the top and is formed with a long outlet slit at the bottom extending into and along the whole length of the trough 153. Powder fed into the hopper 156 discharges freely from the slit until'the level of powder in the trough 153 reaches the level of the slit, whereupon the discharge is checked until the level of powder fall's again. By these means a much larger charge of powder can be converted into filaments without opening the chest 145.

By the use of the method and apparatus described above 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 discolouration 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. The time during'which the filament-forming material is being urged towards the jet face, in the form of apparatus described above, is itself of the order of l minutev or less, andthe material can be subjected to a temperature approaching that of the heated jet plate for'only afraction of that time; The very short period of heatingienables 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'discolour-' ationof the resulting products. The invention is'particularly applicable to fusible filament-forming substances whichhave'not a sharp melting point but aresoftened andlgradually increase in fiowability over a range of temperatures. points it is often preferable to employ'a substantial degree of draw-down. The materials which have not 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 fully acetylated or 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 reasonablesteps to stabilise 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 neutralising part or all of the sulphuric acid employed as a catalyst in the acetylation process. Further, the material used is preferably one which, after ripening, has been stabilised by heating under pressure with water or very dilute acid When using materials with sharp melting 9. 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 aiI- dry powdered material in the air or in vacuum, e.g. in the case of cellulose acetate to a temperature of 150- 200 for a period of /z to hour. The cellulose acetate may be employed with or without a content of plasticiser 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. 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 been found practicable to use a powder which will pass through a gauze having 30 openings per lineal inch but is retained by one having 60 openings per lineal inch.

The following are given as examples of the applicaticn of the invention to the production of filaments from powdered cellulose acetate. The temperatures given are those indicated by the thermocouple in the control circuit of Figure 3; the temperature of the material immediately above the jet plate, however, is estimated to be about 20 higher. The tenacities given are in grams per denier:

EXAMPLE I A hot-ripened pressure-stabilized cellulose acetate of 53% acetyl value (calculated as acetic acid) was ground and screened to give a powder which would pass through a gauge of 30 openings per lineal inch but was retained by one of 60 openings per lineal inch. The powder was heated for 15 minutes at 200 C. and, after cooling, was fed to the apparatus described with reference to Figures 1 and 2. The jet plate temperature was set at 235 C. and a vacuum of 4 lb./sq. inch absolute pressure was applied. Heavy filaments emerged from the nine orifices in the jet plate and were drawn away by the feed roller at a speed of 16 metres per minute and collected as a ring-twisted yarn of 85 denier and 2.5 turns per inch. The twisted yarn had a tenacity of 2.5 and an extension (elongation at break) of 5%.

EXAMPLE II In carrying out Example I the temperature was raised to 250 C. to give a product of 10.7 denier per filament, 2.33 tenacity and 7.4% extension.

EXAMPLE III In carrying out Example I, the temperature was raised to 340 C. to give a product with a denier per filament of 21.1, a tenacity of 1.35 and an extension of 30.7%.

EXAMPLE IV In carrying out Example III, the rate of drawdown was increased to 50 metres/min. to give a product with a denier per filament of 8.7, a tenacity of 2.41 and an extension of 17.6%.

EXAMPLE V 10 of filamentary products from suitable filament-forming materials other than cellulose acetate. Examples of such other materials from which filamentary products have been successfully produced, together with the ranges of thermocouple temperatures employed for their production, are given below:

A.0ther organic acid esters or mixed esters of cellulose Cellulose propionate, both of 63.4% propionyl value and of 66.7% propionyl value (tripropionate), was formed into bristles and into filaments at temperatures ranging from 215290 C.

Cellulose acetopropionate of 26.7% acetyl value and 30.4% propionyl value was formed into bristles and fine filaments at 225-300" C.

Cellulose acetobutyrate of 40.0% acetyl value and 18.1% butyryl value was formed into bristles and fine filaments at 230 300 C.

B.Cellul0se ethers Ethyl cellulose of 45.1% ethoxy content was formed into bristles at 190-220 C., the bristles falling away under their own weight, having a denier ranging from 1300-600 according to the temperature.

Benzyl cellulose of about 63% benzoxy content was formed into bristles and into fine filaments at temperatures ranging from -190 C.

C.-Additi0n polymers Polyethylene was formed into bristles at temperatures of 230 C. and was formed into fine filaments at -230 C.

Polystyrene was formed into bristles and into fine filaments at 132160 C.

D.-C0ndensation products Polyhexamethylene-heptamethylene urea (from hexamethylene di-isocyanate and heptamethylene diamine) was formed into fine filaments at temperatures of 220- 270 C.

4.4-polyurethane (from tetramethylene diamine and the dichloroformic ester of 1.4-butanediol) was formed into bristles and into fine filaments at -220 C.

Polyhexamethylene adipamide (66 nylon) was formed into fine filaments at temperatures of 245-280 C.

Polyaminocaproic acid was formed into fine filaments at temperatures of 210-280 C.

Polyethylene terephthalate was formed into bristles and into fine filaments at temperatures of 230-270" C., the powder being heated to 200 C. under vacuum for 15 minutes before use.

The polyaminotriazole formed from sebacic dihydrazide and hydrazine (see U.S. Patent No. 2,512,667, Example 111) was formed into fine filaments at temperatures of 235-265 C. the material being heated under vacuum to 200 C. for 15 minutes before use.

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. Thus, a mixture of 95% acetonesoluble cellulose acetate with 5% of the polyaminotriazole mentioned, and a mixture of 50% of cellulose acetate with 50% of 66 nylon, and a mixture of 90% of cellulose acetate and 10% of cellulose propionate of propionyl value 63.4%, have been successfully formed into bristles and drawn down into fine filaments. Further, as is described in U.S. application S. No. 292,771 filed June 10, 1952 corresponding to U.K. application No. 13905/51, filed 12th June 1951, filamentary products exhibiting coloured or other desirable effects can be produced by mixing with the powdered or granular filament-forming material powdered or granular dyestuffs, or white or coloured pigments, or other eifect materials, the added materials being incorporated in the filamentary product as a consequence of the process of their production.

Having described our invention; what we desire to se cure by Letters Patent is l. A method of producing artificial filamentary prod ucts from powdered fusible filament-forming materials, said method comprising intermittently applying a mechanical pressure to particles of the powdered material on one side of a layer of filament-forming material in contact with a plate having at least one spinning orifice therein so as to urge said powdered material towards said plate, generating heat in the portion of said plate extending across the area of said layer whereby the powdered material in said layer is fused by heat originating in and supplied from said plate, continually supplying fresh powdered material to said layer in the intervals between uccessive applications of said pressure, continuously maintaining a sub-atmospheric pressure of at most 10 pounds per'square inch absolute about the powdered material that has been so supplied, and, both during the application of said pressure and in the intervals between successive-applications, continuously drawing away the fused material through said orifices in the form of filaments.

2. Method according to claim 1 wherein said mechanical pressure is applied at a frequency at at least 3 cycles per second.

a 3. Method according to claim 1 comprising applying the intermittent mechanical pressure simultaneously over substantially the whole area of the layer.

4. A method of producing artificial filamentary products from powdered fusible filament-forming materials, said method comprising intermittently applying a mechanical pressure to particles of the powdered material on one side of a layer of the filament-forming material in contact with a plate having at least one spinning orifice therein so as to urge said powdered material towards said plate, passing an electric heating current through the portion of said plate extending across the area of said layer whereby the powdered material in said layer is fused by heat generated in and supplied from said plate, continually supplying fresh powdered material to said layer in the intervals between successive applications of said pressure, continuously maintaining about the powdered material that has been so supplied a gaseous pressure below 10 lb/sq. inch absolute, and, both during the application of said pressure and in the intervals between successive applications continuously drawing away the fused material through said orifices in the form of filaments.

5. A method of producing artificial filamentary prod ucts from powdered cellulose acetate free from plasticizer, said method comprising intermittently applying a mechanical pressure to particles of the powdered material on one side of a layer of filament-forming material in contact with a plate having at least one spinning orifice therein so as to urge said powdered material towards said plate, passing an electric heating current through the portion of said plate extending acros the area of said layer whereby the powdered material in said layer is fused by heat generated in and supplied from said plate, continually supplying to said layer, in the intervals between successive applications of said pressure fresh powdered cellulose acetate of a particle diameter of the same order as and ranging below the diameter of the spinning orifices in the plate, continuously maintaining about the powdered material that has been so supplied an atmosphere of inert gas at a pressure less than 5 lb./sq. inch absolute, and, both during the application of said pressure and in the intervals between successive applications, continuously drawing away the fused material through said orifices in the form of filaments at a speed faster than said filaments would fall away under their own weight.

6. Apparatus for the production of artificial filamentary products from powdered fusible filament-forming materials, said apparatus comprising a substantially closed vessel, aplate in one wall of said vessel having at least one spinning orifice therein, a gas duct communicating with saidwessel, a vacuum pump connected to said gas duct for the exhaustion of said vessel so as to maintain therein a pressuresubstantially below atmospheric pressure, means for passing an electric heating current through the portion of the area of said plate at which said orifices are formed so as to heat said plate to a temperature higher than that of any other part of the apparatus in contact with the filament-forming material, and means for intermittently applying a mechanical pressure at a frequency of at least 3 cycles per second to the particles otxmaterial on that side of a layer of filament-forming material on said plate which is further from said plate, the construction and arrangement being such that fresh powdered material is admitted to said layer, from a portion of said vessel outside of said layer, in the intervals between successive applications of said pressure, to replace material continuously drawn away from said orifices in the form of filaments.

7. Apparatus according to claim 6 in which said means for applying mechanical pressure comprises a ram having a working face acting against the plate and means for longitudinally reciprocating said ram so as to apply the intermittent mechanical pressure.

8. Apparatus according to claim 7 comprising a gland in the wall of the vessel through which the ram passes, said means for reciprocating the ram being outside said vessel.

9. Apparatus according to claim 8 comprising a second ga duct communicating with the vessel through the gland for supplying inert gas to the vessel.

10. Apparatus according to claim 6 in which said means for applying mechanical pressure comprises a ram having a working face acting against the plate and means within the vessel for longitudinally reciprocating said ram so as to apply the intermittent mechanical pressure.

11. Apparatus for the production of artificial filamentary products from powdered fusible filament-forming materials, said apparatus comprising a substantially closed vessel, an elongated plate in one wall of said vessel having a row of spinning orifice along its length, a gas duct communicating with said vessel, a vacuum pump connected to said gas duct for the exhaustion of said vessel so as to maintain therein a pressure below 5 lb./' sq. inch absolute, means for passing an electric heating current along the length of said plate so as to heat said plate to a temperature higher than that of any other part of the apparatus in contact with the filament-forming material, a ram within said vessel, a gland in the wall of said vessel through which said ram passes, a second gas duct communicating with said vessel through said gland for the supply of an inert gas to said vessel, and means outside said vessel for longitudinally reciprocating said ram, said ram having a tip in the form of a foot with a long working edge extending over said row of orifices for intermittently applying a mechanical pressure to the particles of material on that side of a layer of filament-forming material on said plate which is further from said plate, the construction and arrangement being such that fresh powdered material i admitted to said layer, from a portion of said vessel outside of said layer, in the intervals between successive applications of said pressure, to replace material continuously drawn away from said orifices in the form of filaments.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,735 Pack Mar. 10, 1936 2,217,743 Greenewalt Oct. 15, 1940 2,234,986 Slayter Mar. 18, 1941 2,253,176 Graves Aug. 19, 1941 2,273,138 Graves Feb. 17, 1942 2,294,266 Barnard Aug. 25, 1942 2,309,496 Bird et al Jan. 26, 1943 2,336,159 Bent Dec. 7, 1943 2,369,506 Wcioel Feb. 13, 1945' 2,445,035 Munger et'al. July 13, 1948

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