US3106763A - Production of crimped filaments - Google Patents

Description

Oct. 15, 1963 F. REEDER ETAL 3,106,763

PRODUCTION OF CRIMPED FILAMENTS-- Filed July 19, 1961 Fran/r Ree dez 50/ 5/01 Krzesms/n By fheir af/omeys United States Patent 3,106,763 PRUDUCTION 0F CRIMPED FILAMENTS Frank Reader and Boleslaw Krzesiuski, Coventry, England, assignors to Courtaulds Limited, London, England,

a company of Great Britain Filed July 19, 1961, Ser. No. 125,093 Claims priority, application Great Britain July 27, 1960 13 Claims. (Cl. 28-72) This invention concerns the production of crimped polyacrylonitrile filaments. By polyacrylonitrile we mean both homopolymers of acrylonitrile and also copolyrners containing at least 80 percent by weight of acrylonitrile. Such copolymers may be the product of copolymerisation with acrylonitrile of such other monomers as styrene, methyl acrylate, itaconic acid, methallyl sulphonic acid and its salts, vinyl acetate and vinyl pyridine. The invention is particularly applicable to copolymers containing 90 to 95 percent by weight of acrylonitrile.

To assist in the conversion of polyacrylonitrile staple fibre to spun yarn, it is usual to crimp the continuous filament tow before it is cut into staple fibre. The crimping technique most commonly employed for this purpose involves the use of a stufling box. However, the crimp inserted in the fibre by normal stuffing box techniques may be unstable to subsequent fibre treatment, in particular to boiling, unless specific steps are taken to impart stability to the crimp.

In order to ensure uniform drying and other early processing of filaments in tow form, it is desirable that some method be provided for imparting a crimp to polyacrylonitrile filaments which have not been subjected to the first drying after they have been wet-spun. Moreover, if the filaments are crimped at this early stage in their production, it may be possible to impart a more stable, built-in crimp. However, the use of a stufling box on filaments still in aquagel form may result in the filaments being bruised.

Even if it were possible to provide a stuffing-box crimping method which did not damage filaments treated while still wet from spinning, it is an inherent disadvantage of stuffing-box methods that the crimp obtained is substantially two-dimensional. It would be possible to produce filaments having better bulk if a crimping method could be invented, which could be applied to never-dried polyacrylonitrile filaments to give a three-dimensional crimp. By never-dried filaments we mean filaments which have been wet-spun and not subsequently dried.

It is an object of this invention to provide such a process. 0

According to this invention, amethod of producing crimped polyacrylonitrile filaments comprises passing never-dried polyacrylonitrile filaments at an elevated temerature and under stretching tension over an edge and ubsequently immersing the stretched filaments, under conitions allowing them to shrink, in an aqueous bath at temperature of 70 to 100 C.

The crimped filaments obtained according to the invenshould be dried under conditions of minimum tenin order to avoid reducing or destroying the crimp. erably the tension during drying does not exceed rams/denier. ing from room temperature to the highest temperdepending upon the water content of the wet fibres e nature of the drying, at which no substantial uration of the filaments occurs. The lower drying tures give the higher degrees of crimp in terms of of crimps per unit length of crimped filament. other hand, since drying is much slower at lower res, for practical reasons the drying is preferied out at 70 to 150 C.

The temperature of drying may be ice The temperature of the filaments while they are being stretched over an edge may also vary, within certain rather narrower limits. The lower limit is determined by the temperature below which no substantial stretching is possible, which is about 50 C., while the upper limit is that above which the filaments are dry, viz. about 100 C. A convenient Way of heating the filaments is to immerse them during stretching in steam or hot or boiling water (i.e. water above about 80 C.), in which case the filaments temperature will be about 80 to 90 C., depending upon the linear speed of the filaments through the heating zone.

While the filaments are being passed over the edge, they are subjected to a stretching tension. It is difiicult to collect the never-dried filaments Without incidentally imparting some stretch, say of the order of a 2-fold stretch. However, we prefer to stretch the filaments to 8 to 14 or more times their original length. Within reasonable limits, the higher tensions give higher degrees of crimp.

The heating of the filaments to the temperature at which they are to be stretched over an edge may, if desired, be carried out in stages, by passing the filaments through a bath at a relatively lower temperature of at least 30 (3.,

by immersing the filaments batchwise in the bath.

for example 60 C., before the hot-stretching operation according to the invention. In these circumstances, it is also possible to split up the stretching into two stages. For example a 2- or 3-fold stretch in the bath may be followed by a 4-fold stretch over an edge in steam.

The edge may be formed in a body made, for example, of stainless steel, of a ceramic material, or of compressed asbestos. The dimensional nature of the edge is an important factor controlling the crimp produced. If the edge is too blunt, little or no crimp may be obtained. On the other hand, too sharp an edge may, in combination with a sufficiently high tension or a suificiently small angle between the filaments leading towards and away from the edge, result in the filaments, or one or more of them being severed. In general, the radius of curvature of the edge may usefully lie in the range of 2 to 40 thousandths of an inch, preferably 4 to 30 thousandths of an inch. The angle of the edge may lie below 140 degrees of arc and may advantageously lie above 30 degrees. A -degree angle, which is-most readily available, gives wholly satisfactory results. If desired, the member carrying, the edge may be mounted so as to be able to rotate or swing against an appropriate resistance about an axis transversely at right angles to the path of the filaments, so that irregularities in the filament bundle which might otherwise foul the edge are able to release themselves (or be released by an operator) by turning the edge.

The angle between the filaments approaching the edge and those leaving it is preferably about 60-150 degrees and in general angles between 80 degrees and degrees are most useful.

The degree of crimp obtainable by the process according to this invention may be improved by subjecting the filaments to cooling immediately after they have passed over the edge. The cooling may be brought about by blowing cool air or spraying cool water on to the filaments or by passing the filaments through a bath of cool water. The air or water may, for example, be at a temperature of 20 C. or less. A-cooling treatment may thus be combined with a washing of the tow interposed'between the edge-stretching and relaxation stages.

The filaments are next allowed to shrink and crimp in a suitable aqueous bath. The shrinkage may be permitted It is more practicable, however, to pass the filaments con- -.tinuously through the bath, while withdrawing the filaments at a speed sufficiently slower than the feedspeed to allow the shrinkage to occur. The shrinkage occurring in the bath is usually much less than the stretch originally imparted and may be of the order of 20 percent, for example.

We have already stated that the temperature of the relaxing bath should be 70 to 100 C. Within this range, the higher degrees of crimp occur at the higher temperatures, but a disadvantage of higher temperatures which must be weighed against their advantage is that they tend to have a delustering eifect on the filaments. Preferably, the bath temperature is 80 to 92 C.

The bath in which the filaments are relaxed may contain only water or may also contain compounds which it is desired to apply to the filaments, such as finishing agents. The presence of a wetting agent may prove advantageous. It is therefore possible to combine the relaxing treatment with other treatments to which the filaments are normally subjected in the course of manufacture. In particular, by appropriate choice of bath characteristics and drying conditions, it is possible to combine the crimping according to this invention with the treatment to improve fibre properties described in the specification of the abandoned co-pending United States patent application Krzesinski and Hyam, Serial No. 121,- 354, filed July 3, 1961, and assigned to the same assignee as the present application.

The denier of the filaments treated is dictated more by the proposed end-use of the filaments or staple fibres than by the requirements of the present process. However, filaments of lower denier, say 3 or 6, are in general more easily crimped and give a higher degree of crimp under given conditions than do filaments of higher denier, say 9 or 15.

The invention and its advantages are not limited solely to filaments which are subsequently to be converted to staple fibre. The production of a crimp at an early stage in the preparation of the filaments leads to more easy and uniform processing during, for example, the drying stage. It is very important that the preparation of filaments or fibres using heavy tows should result in filaments of uniform properties and it is often in the drying stage that irregularities occur.

The process according to the invention is more simple than stufiing-box methods and involves no complicated equipment. The crimp obtained after drying is more stable than that produced by most stuffing box methods. Immersion in hot or boiling water for short periods thereafter has little adverse effect, while if the crimp is removed by stretching it can frequently be restored by subjecting the filaments to a further assisted relaxation treatment, e.g. immersion in a free-to-shrink state in steam.

In an experiment to test the stability of the crimp, filaments crimped by the method hereinafter described in Example 1 were immersed in boiling water for minutes and then dried at a temperature in the range 80 to 90 C. There was no visible loss of crimp. Another sample of the same filaments was then stretched by about 12 percent to remove the crimp and then exposed for one minute to steam at atmospheric pressure and dried at 80 to 90. The crimp in the tow was restored to a considerable extent.

The invention will now be further described by means of the following examples and by reference to the accompanying drawing, which illustrates the production of crimped fibres by the method according to the present invention. Referring to the drawing, the sequence of operations illustrated and as used in each of the examples consisted of spinning a polyacrylonitrile dope into a spin bath 1 from which the filaments were withdrawn over take-up rollers 2 and passed, first through a preheat bath 3 of water at 60 C. and then through a steam box 4. At the end of the steam box at which the filaments were withdrawn they passed over a sharp-edged guide 5 and thence, over output rollers 6 by which the stretching force was applied, and sprayed with cold Water from a spray 7, to a number of washing troughs 8 of water at room temperature. The washed filaments were then introduced by a pair of nip rollers 9 into the relaxing bath 11, from which they were taken by a second pair of nip rollers 10 to be collected and subsequently dried. In Examples 1-4, batch drying was employed; in Examples 5-7, the filaments were dried continuously in fcstoons.

The dope in each case comprised a polymer containing acrylonitrile and methyl acrylate residues in the weight proportion-s of 94:6 dissolved in a sodium thiocyanate solution of about 51. percent concentration by weight, the polymer concentration being 12.2 percent by weight. The spinning bath was a 10 percent by weight solution of sodium thiocyanate.

In Examples 1-4, the edge used was of compressed asbestos and had an angle of 120 degrees and a radius of curvature of 7 thousandths of an inch. The two yarn paths formed an angle of 122 degrees.

upon which they were Example 1 The dope, containing polymer of intrinsic viscosity about 1.5, was spun through a jet having 200 holes of 3 thousandths of an inch each and the filaments were withdrawn from the bath at 2.5 metres/min. After preheating and stretching over the edge, the filaments were passed at 20 metres/min. into the first wash trough, the overall stretch therefore being 8 X.

The temperature of the relaxation bath was 90 C. and the shrinkage occurring therein, compensated by running the withdrawing rolls more slowly than the feed rolls, was about 20 percent. The time of immersion was 20 seconds.

The 200/3 den. tow obtained after drying at to C. had an attractive, bulky, wool-like appearance. The individual filaments possessed a mainly helical crimp of varying amplitude and of frequency varying between 5 and 8 crimps per inch.

Example 2 The dope employed in Example 1 was spun under identical conditions and the filaments were taken up at 2.5 metres/min. After preheating, the tow was given an 8-fold stretch over the edge and then washed.

By immersion for 60 seconds in an aqueous bath at 0., followed by drying at 80 to 90 C., a tow was obtained in which the attractive, bulk filaments had a helical crimp varying between 14 and 25 crimps pe inch.

Example 3 The conditions were similar to Example 2, b take-up speed was 1.9 metres/min, giving an stretch of 10.5 before the stretched tow was co at 20 metres/min.

The relaxing treatment consisted of immersio seconds in a bath at 90 C., and following dry to 90 C. a tow of filaments having 6 to 12 inch was obtained.

Example 4 Under spinning conditions otherwise sin of the preceding three examples, the dope to give a 200/3 den. tow, which was ta. metres/min. The stretch was again 10.5

By immersion for 60 seconds in we of attractive wool-like filaments was 0 ments had a helical crimp varying 4 to 9 per inch.

Under spinning conditions s' in Examples 1-4, a 600-denier t was taken up at 2.5 metres/min. a stainless steel edge of 90 deg ture of 13 thousandths of an K at the edge made an angle of 92 degrees with the yarn leaving the edge. The following table gives the relaxation and drying conditions in three separate runs and the crimp results obtained.

Relaxation D 1m rying r ps temp. inch Temp. Time 0.)

( 0.) (seconds) Example 6 Relaxation Drying Orimps/ temp. inch Tern Time 0.)

( 0. (seconds) Example 7 Using the spinning and stretch conditions of Example 6 but a different jet, an 1800-denier tow of 9-denier filaments was stretched 8-fold over the same 90-degree stainless steel edge. The following table gives relaxation and drying conditions and results.

Relaxation Drying Crlmps/ temp. inch Temp. Time 0.)

( 0.) (seconds) Whatwe claim is:

1. A method of producing crimped polyacrylonitrile filaments comprising passing aquagel polyacrylonitrile filaments at an elevated temperature and under stretching tension over an edge and subsequently immersing the stretched filaments, under conditions allowing them to shrink, in an aqueous bath at a temperature of 70 to 100 C.

2. A method as claimed in claim 1, in which the temperature of the filaments during stretching is 50 to 100 C.

3. A method of producing crimped polyacrylonitrile filaments comprising immersing aquagel polyacrylonitrile filaments in an aqueous medium which is at at least 80 C. and simultaneously stretching the filaments between 8-fold and 14-fold over an edge, and subsequently immersing the filaments, under conditions allowing them to shrink, in an aqueous bath which is at 70 to 100 C. I

6 4. A method of producing crimped polyacrylonitrile filaments, comprising immersing aquagel polyacrylonitrile laments in water at at least 30 C. and simultaneously stretching the filaments, immersing the filaments in an aqueous medium at at least C. and simultaneously stretching the filaments further over an edge, the total stretch being suflicient to i-ncrease the length of the filaments to between 8 and 14 times their original length and thereafter immersing the filaments, under conditions allowing shrinkage, in an aqueous bath which is at 70 to C.

5. A method of producing crimped polyacrylonitrile filaments comprising stretching the aquagel filaments, while immersed in an aqueous medium selected from steam and water at at least 80 C., to between 8 and '14 times their original length, over an edge which encloses an angle of 30 to degrees and which has a radius of curvature between 2 and 40 thousandths of an inch, and subsequently immersing the filaments, under conditions allowing shrinkage, in an aqueous bath having a temperature of 70 to 100 C.

6. A method as claimed in claim 5, in which the radius of curvature of the edge is from 4 to 30 thousandths of an inch.

7. A method as claimed in claim 6, in which the filaments enclose an angle at the edge of between 60 and degrees.

8. A method of producing crimped polyacrylonitrile filaments, comprising stretching the aquagel filaments, while immersed in an aqueous medium selected from steam and water at at least 80 C., to between 8 and 14 times their original length, over an edge which has a radius of curvature of 4 to 30 thousandths of an inch, feeding the filaments continuously into an aqueous bath having a temperature of 70 to 100 C., withdrawing the filaments continuously from the bath at a slower rate, and drying the filaments at a temperature of 70 to 150 C.

9. A method as claimed in claim 8, in which the aqueous bath is at 80 to 92 C.

10. A method as claimed in claim 8, in which the filaments are cooled between the stretching and the immersion in the aqueous bath.

11. A method as claimed in claim 10, in which the filaments are cooled by contact with a fluid medium below 20 C.

12. A method of producing crimped polyacrylonitrile filaments, comprising immersing the aquagel filaments in steam, simultaneously stretching the filaments to between 8 and 14 times their original length over an edge which has a radius of curvature of 4 to 30 thousandths of an inch, feeding the filaments continuously into an aqueous bath which is at 70 to 100 C., withdrawing the filaments continuously from the bath at a slower rate, and drying the filaments, under a tension not exceeding 10 milligrams/denier, at a temperature of 70 to 150 C.

13. A method as claimed in claim .12, in which the aqueous bath contains a wetting agent.

FOREIGN PATENTS Great Britain Oct. 8, 1958

Claims (1)

1. A METHOD OF PRODUCING CRIMPED POLYACRYLONITRILE FILAMENTS COMPRISING PASSING AQUAGEL POLYACRYLONITRILE FILAMENTS AT AN ELEVATED TEMPERATURE AND UNDER STRETCHING TENSION OVER AN EDGE AND SUBSEQUENTLY IMMERSING THE STRECTCHED FILAMENTS, UNDER CONDITIONS ALLOWING THEM TO SHRINK, IN AN AQUEOUS BATH AT A TEMPERATURE OF 70* TO 100*C.

Images