US3492691A

US3492691A - Spinning of fibres

Info

Publication number: US3492691A
Application number: US573532A
Authority: US
Inventors: Paul Lambton Inwood Carr
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1965-08-20
Filing date: 1966-08-19
Publication date: 1970-02-03
Anticipated expiration: 1987-02-03
Also published as: GB1088240A; NL6611719A

Description

Feb. 3, 1970 P. L. l. CARR 3,492,591

- SPINNING 0F FIBRES I Filed Aug. 19. 1966 2 Sheets-Sheet 1 v mun /raw? PQWZQMBm/YZYWMoCZ/W yzumwwg /wzw United States Patent 3,492,691 SPINNING 0F FIBRES Paul Lambton Inwood Carr, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Aug. 19, 1966, Ser. No. 573,532 Claims priority, application Great Britain, Aug. 20,1965, 35,785/ 65 Int. Cl. D01d 5/08, 11/00 US. Cl. 18-8 1 Claim ABSTRACT OF THE DISCLOSURE The uniformity of melt spun polymer filaments is improved by surrounding the molten filaments with series of axially spaced-apart collars which together with the effect of the moving filaments induce a laminar flow to the ambient air which flows inwardly toward the filaments and then along the path of the filaments.

The present invention relates to the melt-spinning of fibre-forming polymers.

According to the present invention we provide a process for the spinning of a fibre-forming polymer wherein the said polymer in the liquid state is forced through one or a plurality of holes in a spinneret plate, the stream or streams of polymer formed thereby travelling substantially vertically downwards from the spinneret plate and solidifying as it, or they, pass through the ambient fluid, a flow of ambient fluid being induced by the movement of the stream or streams of polymer initially towards the stream or group of streams of polymer and then following the path of the, or of each, polymer stream, deflecting means being disposed at intervals along the length of the path of the stream or streams of polymer whereby the flow of the ambient fluid towards the stream or each stream, of polymer and thereafter following the path of the, or of each, stream of polymer, is a stable laminar flow, the said conditions of stable laminar flow persisting until the temperature of the, or of each, stream of polymer falls to the solidification point.

By the term ambient fluid, we mean gases and vapours which are chemically inert towards the polymer; the most convenient gas to use is air.

In the formation of a filament by melt-spinning, a polymer at a temperature above its melting point is forced through a hole to form a narrow stream of molten polymer. This stream of polymer normally travels vertically downwards and is acted upon by a force in a downwards direction along the length of the stream in such a manner as to attenuate the stream as it cools and eventually solidifies. Thus the speed of movement of the polymer stream along its length increases with distance from the spinneret and becomes quite high at a moderate distance from the exit of the spinneret hole.

As the stream of polymer moves away from the exit of the spinneret hole, it loses heat to the surrounding air, resulting in a local zone of air of temperature higher than the surroundings. The air immediately adjacent to the polymer stream will be carried along with the polymer stream and more distant layers will be carried along to a diminishing extent. The air which is carried along with the polymer stream, is replaced by inward flow of air towards the polymer stream.

The uses to which filaments are put demand a high degree of uniformity in the filaments; this in turn demands a high degree of uniformity of the thermal history of all parts of the filament. That is any particular point in the final filament must have been subice jected to substantially the same profile of temperature change as any other point at the same distance from the long axis of the filament.

The system of moving polymer stream and layers of air, under such circumstances is, however, inherently unstable, partly in view of the onset of turbulent flow conditions at sufficiently high velocity of the polymer stream and partly due to interaction of the moving layers with the incoming flow of air towards the polymer stream.

We have found that when it is ensured that the flow of air towards the stream of polymer is a laminar flow, and therefore contains no eddies, then gerater stability is conferred on the system, and the air temperature gradient from the surface of the polymer stream outwards at any given distance from the exit of the spinneret hole tends to remain much more constant than it otherwise would.

Normally in the manufacture of filaments by meltspinning, a spinneret plate is used in which are bored a series of holes in some regular geometrical pattern, for example a circle or oval. In such a case, the flow of air induced towards the polymer streams must come from essentially one side of each polymer stream, that is the side away from the volume which is substantially enclosed by the polymer streams. It is therefore the inflow of air from this side which must be controlled.

The need for controlling the flow of air towards the polymer stream arises from the presence of adverse movement in the surrounding air, which may arise from locally moving bodies or from convection currents. Convection currents may, for example, be induced by the heated air leaving the vicinity of the polymer stream at points more distant from the exit from the spinneret hole and where the polymer stream has solidified.

We have found that the desired conditions of laminar flow of air towards the polymer streams can be ensured by, for example, a series of members so constructed and disposed that, while they permit the free flow of air towards and finally into the direction of motion of the polymer stream, they do not permit the interference with such flow by non-laminar flows.

The members may suitably form a series of control surfaces, of which there should be at least two. The control surfaces may be in the form of complete collars surrounding the group of polymer streams or of more than one member substantially delineating a collar. The collars may, for example, be in the form of annular discs, but are preferably of such shape that the parts further away from the polymer streams are at progressively higher levels with a smooth graduation in order to minimize the entry of rising currents of air between successive control surfaces. Such a formation of the control surfaces also minimizes the breaking away of the zone of air adjacent to the polymer streams and moving with them. The collars may advantageously be in the form of the surface of a conical frustum with the wider part uppermost, or of the surface generated by the rotation of a portion of an exponential curve about the abscissa.

The plurality of control surfaces may comprise a single member; such member may, for example be a suitably offset Archimedean screw with a least two complete turns.

A greater number than two control surfaces produces an improvement, albeit with diminishing magnitude of improvement with number. Below a separation of about 5 mm., the effect of air drag impairs the necessary free flow of air. At separation greater than about mm., the requisite effect in producing a stable laminar flow is not observed, and the results produced are inferior to those for a lesser separation.

. to arrange a series of closely spaced obstructions, for

example a gauze, across the threshold delineated by the adjacent outer edges of the control surfaces. Such an arrangement has the effect of smoothing out turbulence in the air stream as it starts to flow between the adjacent control surfaces, and thus facilitates the establishment of laminar flow.

The mmeber or members comprising each control surface may be of continuous laminar form or may be pierced by a number of apertures. The number and disposition of such apertures should not be such as to permit the passage freely through them of the ambient fluid in more than a minor amount compared to the total flow.

The construction and disposition of the control surfaces should be such that the edge of each control surface nearer to the polymer stream is distant by a predetermined amount.

The predetermined amount is controlled mainly by the nature of the ambient fluid and to only a minor extent by the linear speed of the polymer stream and should be such that no part of the member is appreciably nearer to the polymer stream than the point at which the induced air-flow in the direction of motion of the polymer stream is from about 1% to about of the value of the linear rate of motion of the polymer stream. This value may be calculated on the basis of normal physical principles. Using air as the ambient fluid, a suitable distance between a control surface and the polymer stream may be as small as about 4 mm. but should not exceed about 30 mm. In order to produce a useful effect, a control surface should extend radially for a distance of at least about mm. The inner edge of the control surface may advantageously be conformed so that the distance from it of each of the outermost of the polymer streams is approximately equal.

The disposition ,of the control surfaces along the length of the polymer streams should be such as will ensure the closest approximation to laminar flow in the fluid flow induced towards the polymer streams. The effectiveness of the disposition can be checked by the observation of the movement of smoke trails introduced into the vicinity of the control surfaces.

When melt-spinning is carried out according to the process of our invention, that is with laminar flow of the ambient fluid towards the polymer streams and thereafter along with the polymer streams, the conditions are such that the rate of heat transfer from the polymer streams to the ambient fluid is minimized. Thus for a given size of polymer stream, the use of the process of our invention results in the minimum degree of orientation, other things being equal. This is manifested in the spun fibre by its possessing a relatively low birefringence. In normal use of melt-spin fibres a predetermined degree of orientation has to be arrived at in order that the fibre shall have the desired useful properties. In order to achieve the predetermined degree of orientation, cold drawing is resorted to, that is drawing of a temperature below the melting point of the polymer of which the fibre is composed. In this cold drawing step it is found that fibres as spun having a low degree of orientation can successfully be drawn to a higher draw ratio than fibres having a high degree of orientation as spun. Thus, to obtain a particular final drawn denier, a fibre of low degree of orientation as spun may be of higher denier than when the as-pun orientation is higher. Thus if one considers the combined process of spinning a fibre followed by drawing it to produce a particular final drawn denier in the fibre, the process of our invention permits the spinning of a higher denier fibre. Or alternatively our invention permits an increase in the windup speed and increase in the throughput per spinneret hole for the same degree of orientation.

In order that the process of our invention may be the more fully comprehended, we give hereinafter a descrip tion of a specific embodiment by Way of example and with reference to the accompanying drawings in which:

FIGURE 1 shows a cross-section in a vertical plane through the centre of a spinneret plate, of a series of deflecting members. A multiplicity of polymer streams is shown for clarity, although such a section would not show more than two;

FIGURE 2 shows a plan view 0 fthe uppermost deflecting member;

FIGURE 3 is a representation of a threadline being formed under the conditions of our invention;

FIGURE 4 is one representation of a threadline being formed under conditions outside our invention.

Referring to FIGURES 1 and 2, a series of six identical members 5, constructed from inch thick tinned steel and each consisting of a portion 6 in the form of the curved surface of a right conical frustum of conical angle base 7 cm. diameter and top 1.75 cm. diameter, integral with an annular disc 7 of outside diameter 10 cm. and internal diameter 7 cm., are held in fixed juxtaposition, with the annular discs 5 being in parallel planes and the bases of the conical frustal portions 6 facing all in the same direction, by means of rods 7, 8 and 9 which are threaded and pass through holes of which there are three equidistant bored through each annular disc 5 with centres 0.5 cm. from the outer edge of the disc 5. The members are held in their relative positions (1 /2 inches separation between adjacent annular parts) by means of nuts 10 screwed on to the threaded rods 7, 8 and 9.

In use the assembly of members is disposed with the rods 7, 8 and 9 vertical and the bases of the conical frustal portions 6 uppermost. The uppermost member has its annular part at 2.5 cm. from the spinneret plate. The assembly hereinbefore described was for use with a spinneret plate in which were bored 15 spinning holes of .009 inch diameter with centres on a circle of 1 cm. diameter. The assembly was so positioned with respect to the streams of polymer issuing from the spinning holes that each polymer stream was approximately 4 mm. from the nearest point of each of the conical frustal portions 6.

EXAMPLE 1 (A) Using the described apparatus, poly(ethylene terephthalate) of viscosity ratio 1.7 as measured in orthochlorophenol solution at 1% concentration at 25 C., and containing 0.5% of titanium dioxide delustrant, was melt-spun at a temperature of 290 C. at a throughput per hole of 0.4 g. per minute through 15 circular holes of 0.009 inch diameter on a circle of radius 0.25 inch (0.635 cm.). The fibre was wound up at 1,500 cm. per second. The coefiicient of variation of the resultant yarn was determined by weighing 25 lengths of yarn of 10 metres length and calculating the coeflicient in the usual manner. The coeflicient of variation was found to be 0.66%.

(B) For comparison, spinning of exactly similar polymer was carried out under exactly the same conditions omitting only the assembly of members as hereinbefore described. Measurement of the coefficient of variation of the resultant yarn by the same method gave a value for the coefficient of 1.2%.

EXAMPLE 2 Example 1A was repeated exactly with the single distinction that a cylinder of gauze was fitted around the assembly of members. The gauze was of 32 meshes per inch and made of 30 gauge wire (British Standard Wire Gauge). The gauze cylinder was in contact with the outer edge of each member of the assembly of members and extended from the spinneret plate to the lowest of the members. Thus the induced flow of ambient air had to flow through the meshes of the gauze.

The yarn produced had a coeflicient of variation, measured as described in Example 1A, of 0.4%.

EXAMPLE 3 (A) Poly(ethylene terephthalate) of viscosity ratio the same as that used in Example 1, was spun through a single circular hole of 0.009 inch diameter at a throughput per hole of 1.6 g. per minute. The stream of molten polymer was led through the centre points of 1 cm. holes in the centre of a series of 7 cm. discs each disposed horizontally in similar relation to that described for the members for Example 1. The resultant monofil was wound up at 1,500 cm. per second. The monofil was of 16 denier. This is product I.

(B) By Way of comparison, spinning was carried out exactly as described in Example 3A with the exception that the series of discs was omitted. The monofil was of 16 denier. This is product II.

Comparison of the coefiicient of variation of the diameter of products I and II showed an improvement of product I as compared with product II. Product I had coefficient of variation 2%, while product II had coeflicient of variation 5%.

EXAMPLE 4 (A) Using the apparatus of Example 1A, isotactic polypropylene of viscosity ratio 2.8, as measured on a 1% solution in deccehydro-naphthalene at 135 (3., at a temperature of 285 C., at a throughput of 0.25 gm./min./hole through circular holes of diameter 0.015 in. diameter (0.0381 cm.) with centres on a circle of radius 0.635 cm. The yarn was wound up at 10 metres/sec. Using the assembly of members as described in Example 1, the coeificient of variation of the spun yarn was 2.6%.

(B) By Way of comparison, Example 4A was repeated exactly with the only distinction that the assembly of members was omitted. The coefiicient of variation of the spun yarn was 4.3%.

EXAMPLE 5 (A) In this example the assembly of members employed was as follows:

The number of members was 8 and all were of identical shape and dimensions similarly oriented and similarly disposed with relation to each other and to the spinneret plate as shown in FIGURE 1. Each member was of the form described in connection with Example 1 with conical angle 100, and base of conical frustum 12 cm. diameter. The top of the conical frustum being of 5.8 cm. diameter for the uppermost member reducing by uniform stages to 5.2 cm. for the lowermost member. This variation was in conformity with the convergence of the filaments to a guide 1.5 metres below the spinneret. The various members were spaced from adjacent members by 2.5 cm. A gauze cylinder was fitted round the device as described in Example 2. The uppermost member was 2.5 cm. from the spinneret plate. The device was fitted below a spinneret plate in which were bored spinneret holes of 0.009 inch diameter in a scatter pattern such that the overall diameter of the set of filaments was initially 5 cm. and the hole spacing was approximately 1 cm. The assembly was positioned so that the clearance between the filaments and the inner edge of each member was approximately 4 mms.

Poly(ethylene terephthalate) of viscosity ratio, as measured as described in Example 1, 1.7 and containing 0.5% by weight of titanium dioxide was spun under the following conditions:

Spinning temperatures C-.. 290 Throughput gms./mm./hole 1.14 20 hole scatter spinneret as described.

Wind up speed ..-cms./sec 2100 The coeflicient of variation of the resultant yarn as measured by the Uster Evenness Tester was 1.3%.

(B) For comparison, the yarn was spun under exactly the same conditions omitting the stabilization device. The coefiicient of variation was 2.3%.

A further improvement in the stability of the air can be effected by incorporating vertical fins in the space between adjacent control surfaces. This is because disturbances in the flow are three dimensional disturbances.

EXAMPLE 6 The apparatus was as used in Example 5 with the single exception that vertically and radially disposed laminar members were placed symmetrically between, and forming a bridge between, each adjacent pair of members (5 of FIGURE 1) and between the uppermost member 5 and the spinneret plate.

The coefficient of variation of the spun yarn using the stabilization device with this modification was 1.1% measured as before in Example 5.

Our invention is applicable not only to an array of spinneret holes with radial symmetry but also to other configurations, for example, a rectangular configuration.

EXAMPLE 7 (A) The apparatus used was as described in Example 6 with the distinctions that the spinneret holes were 24 in number and that the spinneret holes were arranged in 6 straight rows of 4 forming a rectangular pattern of overall dimensions 5 cm. x 2.2 cms. The coefficient of variation of the yarn spun using this apparatus was 1.75%.

(B) By comparison using the same spinning apparatus as in 7A but omitting the apparatus to control the flow of ambient air the coefficient of variation of the yarn spun was 2.6%.

By way of further explanation of the conditions pertaining in the use of our invention, reference is made to FIG- URES 1 and 2. Referring to FIGURE 1, the threadline 1 moving away from the spinneret 2, under the conditions of our invention induces a flow of air inward as shown by the streamlines and thence in stable laminar flow in the direction of motion of the threadline. The velocity profile of the induced air flow is shown at 4. The transition to turbulence, shown at 5, occurs beyond the point where the threadline has solidified. Under these conditions the heat transfer at a point at a particular distance from the spinneret is constant with time. Referring to FIGURE 2, under conditions outside of our invention there is an unstable laminar region 6 which exhibits large lowfrequency fluctuations. This is partly due to natural convection effects resulting in the presence of warm air currents and partly due to vibration of the threadline itself, the fluctuations are also to some extent inherent in the geometry of the system. Early separation of the boundary layer, spiralling, and in fact any departure from axial symmetry leads to a momentary increase in the local rate of cooling, leading to deviation from the desired steady conditions.

What I claim is:

1. Apparatus for melt spinning a fibre-forming polymer comprising: a spinneret for forming at least one stream of polymer travelling substantially vertically downwardly from said spinneret through the ambient fluid in the vicinity of the stream; and ambient fluid control means for inducing the ambient fluid to flow laminarly toward the polymer stream and thereafter laminarly along the path of the polymer stream until the temperature of the stream falls to the solidification point, said means including ambient fluid deflecting elements disposed at spaced-apart intervals along the length of the path of the stream, said deflecting elements being out of contact with and at least partially surrounding the polymer stream, said deflecting elements being collar-shaped annular discs having a central portion shaped as a depending converging conical frustum so as to define at least two annular control surfaces each of which is shaped such that a point moving radially along the surface from the iner to the outer edge has at no time any downward component of motion, the inner edge of each control surface being spaced from the polymer stream not less than about 4 mm. and not more than about 30 mm., and each control surface extending at least about 10 mm. from its inner to the outer edge has at no time any downward surface by at least about 5 mm. and at most about 100 mm.

References Cited UNITED STATES PATENTS 9/1966 Massey et al. 4/1967 Finzel et a1. 12/1967 Nommensen et a1.

JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner us. 01. X.R.