US2370721A

US2370721A - Method of extruding fused thermoplastic compositions

Info

Publication number: US2370721A
Application number: US375761A
Authority: US
Inventors: Dreyfus Henry
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1940-02-27
Filing date: 1941-01-24
Publication date: 1945-03-06
Anticipated expiration: 1962-03-06
Also published as: GB599668A

Description

H. DREYFUS 2,370,721

METHOD OF EXTRUDING FUSED THERMOPLASTIC COMPOSITIONS March 6, 1945.

-F'iled Jan. 24, 1941 Patented Mar. 6, 1945 METHOD OF EXTRUDING FUSED THERMO- PLASTIC COMPOSITIONS Henry Dreyfus, London, England, assignor to Celanese Corporation of America, a corporation of Delaware Application January 24, 1941, Serial No. 375,761 In Great Britain February 27, 1940 Claims.

This invention relates to the production of thermoplastic products and more particularly to the production of artificial filaments, films, foils and like shaped articles having a basis of thermoplastic compositions.

Various processes are known for forming shaped articles by extruding fused thermoplastic compositions, but when working at the high temperatures generally necessary for these processes, difiiculties have been encountered in securing uniform feed of the compositions to the extrusion orifices.

I have now found that very satisfactory feed may be secured if a pump, especially a gear pump, is introduced into the feed pipe for the fused material, preferably at a point close to the extrusion orifices, and at least the gland or glands of the pump is maintained in a non-solvent medium at a temperature higher than the fusion point of the composition. Preferably the whole pump is immersed in the hot non-solvent medium.

If it is desired to immerse only the gland or glands of the pump in the non-solvent medium, a suitable casing may be built round each or all of the glands to be immersed and provision made for heating the medium to the desired degree, especially by electrical heating coils. If desired the medium may be circulated through the casing, being heated outside the casing. Preferably, means are provided for drawing off liquid from the lower part of the casing so that any thermoplastic composition which escapes through the glands may be readily recovered for return to the process.

.As indicated, however, it is preferably to immerse the whole pump in the hot non-solvent medium, and in such case the medium may be the same as that into which the thermoplastic composition is to be extruded, for example according to the process described in U. S. application S. No. 369,405, filed December 10, 1940. In this event, provision is made not only for withdrawing from the medium thermoplastic composition which escapes through the glands, but also to ensure that such composition is prevented from interfering with the smooth passage of the extruded materials through the medium.

Whether the whole pump or only the glands thereof are maintained at the elevated temperature, it is advantageous to reduce the tendency for the fused thermoplastic composition to escape through the glands by introducing non-solvent medium into the glands themselves at a point along their length under a pressure lower than the minimum pressure within the pump so that the medium has no tendency to enter the pump chamber.

The invention will now be described in greater detail with reference to the accompanying drawing, in which Fig. 1 is a diagrammatic side elevation of apparatus in which an immersed pump delivers fused material to a spinning nozzle immersed in the same fiuid as the pump; and

Fig. 2 is a side elevation of a pump fitted with means for heating the pump gland only.

In Fig. 1, a pump 23 supplied with fused material from a jacketed pipe 24 is immersed in nonsolvent liquid in a casing 25 which also serves as a setting bath for the filaments 26 extruded from the nozzle 21 directly connected to the pump 23. The liquid is heated by pipes 28 at the bottom of the casing 25. Spent or contaminated liquid may be removed from the casing through the drain 29 and fresh liquid may be supplied from the pipe 30. The

pipes

29, 30 may also be used for continuous circulation of fluid through the casing 25.

In Fig. 2, the gland 20 of the pump 1 is surrounded by a casing 3| containing non-solvent liquid. This liquid may be circulated through the casing by means of

pipes

32, 33. An electric element 34 surrounding the casing 3| provides for the heating of the liquid in the casing. Nonsolvent liquid at lower pressure than that of the fused material supplied through the pipe 8 to the pump may be admitted to the glands 20 by a pipe 2|.

Pumps for use according to the invention may be made of or lined with any suitable material, due regard being paid to the temperature to which they are to be subjected and to the nature of any thermoplastic composition which is to contact with them. Examples of suitable materials, particularly for the surfaces which are exposed to contact with the compositions, are iron, tin, silver, tantalum, aluminium, copper, and chromium. It will be understood that suitable alloys, e. g., stainless steel, may also be employed.

For securing uniformity in the extruded materials it is of considerable importance to ensure good temperature control of the thermoplastic compositions. Feeding the compositions through narrow tubes is advantageous for this purpose. Further, strict control must be exercised over the heating means, whether the composition is heated directly, e. g. by electrical winding round such a narrow tube, or indirectly through a hot fluid medium. Preferably electrical means are employed for heating, either directly or indirectly,

and the electric circuit may include an element of which the resistance automatically varies to reduce current as its temperature increases. Such a resistance element, present, for example, in the heated fluid medium, will operate as a thermostat, and permits the temperature to which the thermoplastic compositions are subjected to be controlled in a particularly simple manner. This type of temperature control may be employed in conjunction with apparatus in which a pump is employed for forwarding the compositions or in which any other method of forwarding is employed.

The temperature to which the glands must be heated will depend largely upon the nature of the thermoplastic composition which is to be forwarded by the pump. In general, however, temperatures of the order 01 ZOO-250 up to 290 or 300 C. are desirable, particularly when employing compositions which have a basis of superpolymers formed by the self-condensation of aminocarboxylic acids, or by the condensation of diamines with dicarboxylic acids.

The present invention may be applied to the extrusion of other thermoplastic compositions than those referred to in the preceding paragraph, for example, compositions comprising thermoplastic cellulose derivatives, e. g., cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetopropionate, cellulose acetobutyrate, ethyl cellulose and benzyl cellulose and ether esters of cellulose, polyvinyl ethers and esters, e. g., polyvinyl acetate and polyvinyl chloracetate, and polymerized esters of unsaturated acids, e. g., those of the acrylic and methacrylic acid series.

The non-solvent medium in which the glands are immersed according to the present invention may comprise any substance which is liquid and substantially stable at the desired temperature of operation, which is advantageously the extrusion temperature of the composition. For example, it may comprise a hydrocarbon e. g. a paramn or arylated paramn, acenaphthene, anthracene or an alkyl or aryl derivative of anthracene, benzene, diphenyl, toluene, a diphenyl-methane or diphenyl-ethane or an alkyl derivative thereof, naphthalene or an alkyl or aryl derivative of naphthalene, including dinaphthyl, phenanthrene, or a compound containing partially or fully hydrogenated aromatic nuclei, e. g., tetralin; an ether, e. g., isoamyl ether, the dimethyl ether of triethylene glycol, anisol, ethyl benzyl ether, a dinaphthyl ether, an alkyl naphthyl ether or diphenyl ether; or. a halogen-substitution derivative of a hydrocarbon or an ether.

While it is preferable to employ liquid media, vaporous or gaseous media may also be employed if desired, e. g. the vapours of the above-mentioned and similar compounds, nitrogen, hydrogen and carbon dioxide.

Having described my invention, what I desire to secure by Letters Patent is: e

1. Method of extruding fused thermoplastic compositions, comprising delivering a thermoplastic composition to an extruding point by means of a. feed pump the whole of which, including the gland, is immersed in a, liquid which is a non-solvent for the thermoplastic material of the composition, maintaining said liquid at a temperature higher than the fusion point at the composition and extruding said composition by means of said hot pump into said non-solvent liquid.

2. Method of extruding fused thermoplastic compositions, comprising delivering a thermoplastic composition to an extruding point by means of a feed pump, at least the gland of which is surrounded by a liquid which is a nonsolvent for the thermoplastic material of the composition, maintaining said liquid at a. tem perature higher than the fusion point of the composition, introducing said liquid into the gland of the pump at a superatmospheric pressure lower than the minimum pressure within the pump chamber but sufliciently high to minimize leakage into the gland and extruding said composition by means of said pump into said hot non-solvent liquid.

3. Method of extruding fused thermoplastic compositions, comprising delivering a thermoplastic composition to an extruding point by means of a feed pump the whole of which, in cluding the gland, is immersed in a liquid which is a non-solvent for the thermoplastic material of the composition, extruding said composition by means of said pump into said body of nonsolvent liquid, circulating said liquid, and electrically heating said liquid to a temperature higher than the fusion point of the composition.

4. Method of extruding fused thermoplastic compositions, comprising delivering a thermoplastic composition to an extruding point by means of a feed pump the whole of which, including the gland, is immersed in a liquid which is a non-solvent for the thermoplastic material of the composition, maintaining said liquid at a temperature higher than the fusion point of the composition, introducing said liquid into the gland of the pump at a superatmospheric pressure lower than the minimum pressure within the pump chamber but sufiiciently high to minimize leakage into the gland and extruding said composition by means of said pump into said hot non-solvent liquid.

5. Method of extruding fused thermoplastic compositions, comprising delivering a thermoplatic composition to an extruding point by means of a feed pump, at least the gland of which is surrounded by a liquid which is a nonsolvent for the thermoplastic material of the composition, electrically heating said non-solvent liquid so as to maintain it at a temperature higher than the fusion point of the composition, circulating said liquid, introducing said liquid into the gland of the pump at a superatmospheric pressure lower than the minimum pressure within the pump chamber but sufflciently high to minimize leakage into the gland and extruding said composition by means of said pump into said hot non-solvent liquid.

HENRY DREYFUS.