US3244275A - Crimped staple fibres - Google Patents

Description

April 5, 1966 JJ R. MURLEY CRIMPED STAPLE FIBRES Filed April 2, 1963 GST/EHPs Het-cw- 25A/.577% 'aF 84H5, ss/,Cri

INVENT OR BY @@54/m ATTORNEYS' United States Patent M 3,244,275 CRHMPED STAPLE FIBRES John Reginald Murley, Harrogate, England, assigner to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Apr. 2, 1963, Ser. No. 259,892 lf2 Claims. (Cl. 2015-835) This invention relates to `a `process for making crimped staple fibres from synthetic fibre forming polymers, particularly those made from polyethylene tereplithalate.

I have found unexpectedly that a 3 dimensional crimp and deformations in cross-section can be obtained in staple fibres made from synthetic nbre forming polymers by submitting a bulk quantity of randomly arranged vfibres to mechanical compression for example :be-tween the platens of a .baling press. Undirectional compression of a bulk quantity of substantially randomly laid fibres has been found to give the desired result but it will be appreciated that compression in more than one direction simultaneously or in succession will give the desired result e.g, by compressing a bale first in one direction and then at right angles thereto, under suitable conditions. These conditions are quite critical but we have determined by research and experiment that they can be expressed very simply by reference to the ultimate density or true density of the fibres which are being so compressed.

I have found that the fibres after suitable compression in the baie,'have a lesser tendency to recover with the result that retaining straps which are used for balng such 'fibres do not snap open with a great force when cut. Moreover and more importantly the fibres are deformed beyond the elastic limit and also a plastic deformation occurs in the cross-section of the fibre. Unexpectedly .these deformations are of such a kind that contrary to expectations the textile processing of such fibres although it requires certain modifications is not only possi-ble but in some cases facilitated. Uncrimped fibres of uniform cross-section cannot be processed on normal textile processing machinery including carding and spinning but when compressed according to my invention are found to have sufficient retentivity and cohesion with each other to allow lap formation and subsequently to make the spinning lof such initially uncrimped fibres into yarns possible.

According to my'invention, therefore I provide a process for making crimped staple fibres from synthetic fibre forming polymers, particularly those made from polyethylene terephthalate, comprising compressing a bale of substantially randomly arranged fibres to a density which is at least 50% of the density of a single fibre in the bale and maintaining this pressure for a time sufficient for deformation of the fibres in their longitudinal direction beyond the elastic limit and also of their cross-section involving a plastic deformation to take place so that the fibres when released from pressure upon examination 4show a 3 dimensional crimp and deforma-tions and at least 20 deformations of the cross-section of the bres per linear cm. of the fibre, without any fusing between individual fibres. The deformations are caused by compressing the fibres in contact with one another until a deforma-tion beyond the elastic limit takes place at their contacting surfaces. In the case of staple fibres of about 1 to l0 inches in length and of deniers between l and l0, the length of the fibre is of course many times greater then the diameter and accordingly the deformations in a random array of fibres will be approximately l or 2 fibre diameters along the length. It will be appreciated that the deforming effect of one fibre from another with which it is in contact will depend on the angle between 3,244,275 Patented Apr. 5, 1966 ICC the axis of the fibres at the point of contact and upon the inclination of the line Which is perpendicular to the axis of both fibres and which passes through their mutual point of contact to the direction of external pressure application that is to say the line 4of travel of the platens of a baling press.

Generally I have found a compression of a multitude of randomly laid fibres in a bale of 50% to 80% of the density of the single fibre is required to yachieve crimping and the deformation of the cross-section beyond the elastic limit. The timing of the compression has an effect on the recovery of the fibres. The bale should therefore be maintained in a highly compressed state at a density greater than that of the final bale for a period of at least 1A, preferably about 1/2--1 minute, in order to appreciably reduce the tendency of the bale to recover from its compressed state. By this meansvit has been found possible to restrain a polyethylene terephthalate fibre ybale of 46 lbs. per cu. ft. density after ultimate compression with the same number and size of steel straps as are necessary on a bale of the same weight but only of ll lbs. per cu. ft. density. This lack of recovery has a further advantage inasmuch las the high density bale when released from its straps expands slowly and by only a smal.'l amount, compared with the immediate and extensive recovery of the low density bale which expands to about twice its bale length. I have found that the initial openness or lay of the fibres has a considerable effect on the pressures which are required to compress a bulk quantity to within ythe specified limit, in order to g-et the required amount of deformation.

If e.g. as occurs in practice, a large tow of crimped filaments is cut, the cut tuftsof fibres tend to cohete due to the presence of finish composition on the fibres and due to the mechanical compression during any previous crimping. Such tufts have a density of about 4 lbs. per cu. ft. in the case of polyethylene terephthalate fibres. If such fibre tufts are separated after cutting by a fiuid stream a much looser and desirably random distribution of bres is obtained.

Compression is commercially conveniently carried out in a baling press capable of exerting the required compression of the fibres. The fibres may be crimped by known methods, or uncrimped fibres may be used. In the former case additional crimp in 3 dimensions is super-imposed on the existing sinusoidal or saw-tooth crimp; in the latter case a random 3 dimensional non-uniformal crimp results provided of course the fibres are substantially randomly distributed during.` compression. Conveniently the fibres are compressed to the required high density already in the form of a bale but in this context it will be appreciated that by a bale We mean a bulk quantity of fibres exceeding at least 10 lbs. in Weight, preferably 10G-200 lbs. in weight.

The invention will be further understoodfrom the following detailed description in conjunction with the drawings in which:

FIGURE 1 is a block diagram illustrating the process steps for producing crimped fibres in accordance with the principles of the present invention;

FIGURE 2 is a perspective view of a strapped bale of compressed fibres crimped by the process of the present invention; and

FIGURE 3 is a graph in which the density of the compressed fibers is plotted against applied pressure.

Iny my British Patent 777,113 an apparatus for baling resilient staple fibers is described using rams having a clearance of at least 1.5 mm. all around in the compression chamber. Bales of fibres can be compressed to a density of about 20 lbs. cu. `ft. i.e. bales with a residual density of 11-15 lbs. per cu. ft. can be obtained with such a baler. This is insufficient for the production of fibers of my invention having a three dimensional crimp and other deformations. However, by modifying the design of the baler, we can produce the required high density bales, e.g. by using the ram for feeding the fibers into the chamber, as the high compression ram, withdrawing the ram after that compression, until sufficient fibre has been compressed in a first direction until the prescribed density has been achieved and then continuing the operation as described, by compressing a number of layers using said ram for feeding the fibers, as part of one side of the compression chamber, before compressing the fibers in a direction at right angles with a second ram against a quantity of previously compressed fiber and forming the side of said chamber, thereby also achieving continuous operation.

It will be appreciated that other baling machines may be used which are capable of compressing fibres to the required density A bale formed according to the present invention is illustrated in FIGURE 2. It has been found, unexpectedly, that even these high compression bales when strapped are quite safe to handle and that the bale is quite dead, that is to say, the straps do not snap open when cut, as happens with live bales which endanger the operator when the straps are cut. I have found ythat such live bales are obtained when compressing, for example, polyethylene terephthalate fibres to a density up to 40 lbs. per cu. ft.

Although my description and the examples refer particularly to polyethylene terephthalate fibres, I believe that my invention is applicable to other synthetic linear polymer fibres such as those made from copolyesters based on terephthalic acid, polyamides, polyacrylonitrile, ethylene polymers particularly stereospecic polypropylene, and other fibre forming vinyl type polymers and polyoxymethylene.

It should be appreciated that the bulk quantity of super compressed fibres should not be subjected to ya heat setting treatment in this compressed form because of the poor heat transfer properties of the fibres and therefore a resultant uneven heat treatment.

As seen in FIGURE 3 when the density, in lb./1cu. ft. of a bulk quantity of fibres is plotted against the applied pressure, in tons per sq. inch a curve is obtained which at first rises slowly but then turns steeply and continues in a substantially straight line with a clearly definable break before continuing in the steep rise in a line displaced substantially parallel with the line before the break, below. The break in the line is believed to coincide with the formation of the crimps and the deformations in the fibres, beyond their elastic limit.

The following examples illustrate but do not limit my invention.

Example 1 A 225,000 denier tow of 11/2 denier polyethylene terephthalate filaments which have been drawn, crimped and heat set to give 12 to 2O sinusoidal crimps, substantially in one plane, were cut into cotton type staple lengths of 11/2. The cut staple fibres Were fed into a baling machine, in principle as described in British Patent 777,113, but in .addition to the slight compression and instead of the light ram, a heavy ram was used, capable of compressing each pre-weighed lot of fibres to give a resulting bale density of 64.1 lbs. per cu. ft., when the ram formed the top of the compression chamber. At this stage, the second ram was brought into operation and the bale was compressed Iat right angles against a previously compressed bale, ejected and strapped as described in British Patent 777,113.

This bale Which had been compressed to a density of 64.1 lbs/cu. ft. was inert, dead and safe to handle when the straps were cut or opened accidentally. The fibres had non-uniform three dimensional Icrimp and they could be peeled off in leather-like layers and on working by hand quickly assumed a desirable bulk and soft handle. Satisfactory laps of fibres weighing 131/2 ozs. per sq. yard were prepared.

Although it is not stated in the example, I have found that the distribution of finish which had been applied to the filaments is improved in my bales.

Example 2 A bale containing 11/2 denier crimped and heat-set polyethylene terephthalate fibers 11/2 long and prepared on a baling machine as described in principle in British Patent 777,113 of dimensions 20 x 18 X 42" with 4 straps passing across the 20 edge and encompassing the bale longitudinally is placed in a vertical hydraulic baling press. The direction of travel of the platens is vertical and is parallel to the longest dimensions of the bale. The bale density is 11 lb./ cu. ft. In the top and bottom platens of the press there are groves to accommodate the straps. The straps are tightened when the platens, originally a distance of 42 apart at the beginning of the compression stroke, are closed to 8". The force required to effect this compression is 320 tons. Those four sides of the bale which are not in contact with the platens are not supported in any way. The bale is then compressed further by a force of 560 tons. This pressure is maintained for 30 seconds. The separation of the platens is now 7 the density about 66 lbs. per cu. ft. When the pressure is released the bale bulges between the straps. The approximate height of the bale is 14 inches. Surprisingly' the bale expands in height but there is little change in the other dimensions. The bale density is 45 lbs/cu. ft. This bale is inert, dead and safe to handle when the straps are cut or opened accidentally. The fibres have a nonuniform, three dimensional crimp and 60 deformations of cross-sections per inch. Only the usual amount of disturbance of the bres as used with bales of a density of 11-20 lbs. per cu. ft. is required when transferring the fibres to the aprons of an opening line, to restore the usual bulk. Satisfactory laps of fibres weighing 13`1/z oz. per sq. yard have been prepared.

Example 3 Three slabs of high density bales prepared as described in Example 2 are pressed lightly together and strapped, the straps are removed before combining the three slabs. With each of the slabs weighing lbs., a bale weighing 360 lbs. is obtained occupying a volume of only 3A of a 120 lb. -bale having a density of only l1 lbs. per cu. ft. This illustrates the saving which can be obtained in warehouse space and in shipping costs with my bales.

Example 4 A 120 lb. bale of randomly laid polyethylene terephthalate staple fibers 11/2" long and of 11/2 denier the fibres having an ultimate density of 86 lbs. per cu. ft. is compressed in a superdensity hydraulic baling press. The initial bale has an overall height of 40 inches and 36 inches across the straps and having .a bulk density of 17.9% of the ultimate density. This bale is further compressed t0 an overall height of l5" and measuring 11" across the straps when released from pressure and having -a bulk density of 52% of the ultimate density in its strapped condition. The bale is placed axially between the platens of the high density hydraulic press which are slotted to accommodate the straps, the load is raised to 40,000 tons bale weight (lbs.)

the length of the bale in inches is then equal to bale weight (lbs.)

The density is 68% of the ultimate density. The bale is then strapped with four straps to give a strap tension of 50 l-bs. per sq. inch on a power tool and the straps are sealed. The load on the platens of the press is then increased to 600 tons and held at this pressure for 1 minute until yielding of the libres is complete. The density is 77% of the ultimate density of the libres in this condition. The load is then released and the bale expands to an effective length in inches of bale weight divided .by 10.5. This resutls in the density of the bale of 52% of the ultimate density.

Example 5 Three high density bales .are combined in the same press and using the procedure as in the previous example, but the original straps are retained and the combination of -bales is secured by a separate set of four straps.

Example 6 A bale of polypropylene is prepared using an apparatus as described in British Patent 777,113, a load of 350 tons is used to compress a bale so obtained, the bulk density of the polypropylene libres was 38 lbs. per cu. ft., compared with 58 lbs. per cu. ft. for the polyethylene terephthalate libres. Both these densities are equivalent to about 67% of the ultimate density of the libre. The individual libres when examined under the microscope were found to be similarly deformed as the polyethylene terephthalate libres.

Example 7 A bale of polyethylene terephthalate staple libres 11/2 denier 11/2 which had not been crimped but which were coated with a spin linish solution of polyethylene glycol monolaurate and a corrosion inhibitor were compressed into a high density bale as described in Example 4. On examination the libres showed permanent deformations on the long and short libre axes. The libres were subjected to normal processing conditions at a temperature of 76 F. Iand 38% relative humidity resulting in a satisfactory 1A() S cotton count yarn.

Two weights of opener lap were made, lirstly, one of 13 oz. per yard and secondly one of 17 oz. per yard. The lighter lap licked at unrolling but the heavier lap did not. There was 4a deposit of loose libres thrown out at the drawing stages. This example illustrates that the libres can be processed on the cotton system without previous crimping.

What I claim is:

1. A process for imparting three-dimensional crimp to a mass of short lengths of libres of synthetic libre forming polymer comprising: compressing as a unit the whole mass of said fibres which are randomly arranged in contact with each other to a density which is at least as great as 50% of the density of a single libre; and maintaining this compressive pressure for a period of time to cause deformation of a majority of the libres in their longitudinal direction beyond their elastic limit and to cause plastic deformation in the cross section of a majority of the libres thereby producing a three-dimensional crimp and .at least 20 deformations of each libre per linear centimeter thereof without any fusing between individual libres.

2. A process according to claim 1 in which the deformations are caused by compressing the fibres in contact with one another until a deformation beyond the elastic limit takes place on their contacting surfaces and in which the libres are l to inches in length and of a denier between 1 and 10. l

3. A process according to claim 1 in which a multitude of randomly laid libres in said mass are compressed 50% to 80% of the density of a single libre.

4. A process according to claim 1 in which said mass is maintained in a highly compressed state at a density greater than that of the final mass for a period of at least 1A minute.

S. A process according to claim 1 in which the libres are separated and opened after cutting by a liuid stream to obtain a looser desirably random distribution of libres 4before compressing in .a bale.

6. A process according claim 1 in which the quantity of libres -being compressed exceeds 10 lbs. in weight.

7. A process according to claim 1 in which the libres are synthetic linear polymer libres of a libre forming polymer selected from the group consisting of polyethylene terephthalate, copolyesters based on terephthalic acid, polyamides, polyacrylonitrile ethylene polymers particularly stereo-specilic polypropylene and libre formed vinyl type polymers and polyoxymethylene polymer.

8. A process of imparting three-dimensionl crimp to short lengths of libres of synthetic libre-forming polymer comprising: mechanically compressing into the form of a self-supporting bale at least a ten pound mass of said libres which are randomly arranged in contact with each other, said compressing step being effected by a pressure such that, when compression pressure is plotted against the density of the mass of libres there is obtained a curve which at lirst rises slowly but then turns steeply and continues in a substantially straight line with a clearly definable break before continuing in the steep rise in a line displaced substantially parallel with the line before the break; and maintaining this compressive pressure for a period of time to cause deformation of a lmajority of the libres in their longitudinal direction beyond their elastic limit and to cause plastic deformation in the cross section of a majority of the fibres thereby producing a threedimensional crimp and at least 20 deformations of each libre per linear centimeter thereof without any fusing between individual libres.

9. A strapped compressed bale of randomly arranged unfused staple libres of polyethylene terephthalate, said libres being of substantially uniform density and having a three-dimensional crimp and .at least 20 deformations of each libre per linear centimeter thereof, said bale having a mass of at least ten pounds and a density which is at least as great as 50% of the density of a single fibre, said bale having a reduced tendency to expand after having been compressed and thereby having a reduced tendency to cause baling straps to snap open when the straps are cut.

10. A compressed -bale as in claim 9 wherein said libres are between 1 and 10 inches in length and of deniers between 1 and l0, said deformations in the random array of fibres being about l to 2 libre diameters along the lengths of said libres and occ-urring at the contacting surfaces of said libres.

11. A compressed bale as in claim 9 wherein said polyethylene terephthalate libres are about one and one-half inches in length.

12. A compressed bale as in cla-im 11 wherein said polyethylene terephthalate libres have la spin linish uniformly distributed thereon.

References Cited by the Examiner UNITED sTATEs PATENTS 2,311,174 2/1943 Hitt i 19-66 2,539,725 1/1951 carahei 2o6 83.5 2,647,285 8/1953 Piau 28-72 2,707,806 5/1955 Wilkie. 2,780,838 2/1957 Wilkie 20s- 83.5 X

FOREIGN PATENTS 338,269 6/1921 Germany.

THERON E. CONDON, Primary Examiner. DONALD w. PARKER, Examiner.

L. K. RIMRODT, I. M. CASKIE,

Assistant Examiners.

Claims (1)

1. 9. A STRAPPED COMPRESSED BALE OF RANDOMLY ARRANGED UNFUSED STAPLE FIBRES OF POLYETHYLENE TEREPHTHALATE, SAID FIBRES BEING OF SUBSTANTIALLY UNIFORM DENSITY AND HAVING A THREE-DIMENSIONAL CRIMP AND AT LEAST 20 DEFORMATIONS OF EACH FIBRE PER LINEAR CENTIMETER THEREOF, SAID BALE HAVING A MASS OF AT LEAST TEN POUNDS AND A DENSITY WHICH IS AT LEAST AS GREAT AS 50% OF THE DENSITY OF A SINGLE FIBRE, SAID BALE HAVING A REDUCED TENDENCY TO EXPAND AFTER HAVING BEEN COMPRESSED AND THEREBY HAVING A REDUCED TENDENCY TO CAUSE BALING STRAPS TO SNAP OPEN WHEN THE STRAPS ARE CUT.

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