US3212251A - Process for making synthetic paper yarn - Google Patents

Description

United States Patent 01 ice 3,212,251 Patented Oct. 19, 1965 3,212,251 PROCESS FOR MAKING SYNTHETIC PAPER YARN William Finan Linke and Walter Florus Reynolds, Stamford, Conn, assignors to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Original application Nov. 27, 1962, Ser. No. 240,428, now Patent No. 3,168,802, dated Feb. 9, 1965. Divided andthis application Apr. 7, 1964, Ser. No. 358,106

5 Claims. (Cl. 57-157) This is a division of application Serial No. 240,428, filed by us on November 27, 1962, now Patent No. 3,- 168,802, issued February 9, 1965.

The present invention relates to a process for the manufacture of textile yarn substantially composed of fibrillated polyacrylonitrile papermaking fibers.

It is known that synthetic paper of unique properties can be prepared by refining an aqueous suspension of said spun polyacrylonitrile filaments, sheeting the resulting suspension of fibrillated filaments to form a waterlaid web, and drying the web at elevated temperature thereby also heat-bonding the fibrils cf. Wooding et al. US. Patent No. 2,810,646 (1957). The fibers may be composed of substantially pure polyacrylonitrile, or of a copolymer of acrylonitrile with a minor amount of monomeric material copolymerizable therewith, or of a blend of a major amount of such polymer or copolymers and a minor amount of a different polymer which is COIl'lpatible therewith (of. Belgian Patent No. 588,577).

At the present time, textile yarn is commercially manufactured by a'method which involves continuously twisting a ribbon of cellulose paper to the extent of 5 to or more times per inch so as to form a yarn having a diameter A or less of the width of the ribbon. The number of twists per inch is at least sufficient to form the ribbon into a closed helix but is insuflicient to cause the closed helix to kink. The resulting yarn is necessarily smooth. A twisting rate of 300 twists per minute is currently regarded as slow, and modern high-speed machines produce more than 3,000 twists per minute. Even slow twisting subjects the paper to deformation which is sufficiently sudden and sharp to cause the paper to crack. It is necessary, therefore, for the paper to be in limp state during the twisting step, and this is etfected by pre-wetting the paper with water.

Water is seriously detrimental to the tensile strength of cellulose paper, and therefore only wet strength paper (paper which contains a wet strength resin) is adapted to the twisting process.

Up to the present it has not proved practical to produce yarn from water-laid polyacrylonitrile paper because polyacrylonitrile paper possesses the snap and rattle of crisp bond cellulose paper, and no means has been found for rendering the paper limp'without also rendering it tacky, as for example when the paper is sprayed with a solvent. Polyacrylonitrile paper can be wet with water, but the water does not render the paper sufliciently limp to permit it to be twisted as described.

In the past, it has proved possible to form yarn from polyacrylonitrile paper ribbon without cracking the ribbon, by twisting the ribbon at very slow speeds, i.e., at speeds less than about 150 twists per minute. However, the resulting yarn has not proved satisfactory because polyacrylonitrile paper is springy, and the resulting yarn possesses a strong intrinsic tendency to untwist. This tendency becomes evident when the yarn breaks or is cut, in which event it instantly reverts back to paper ribbon form.

The discovery has now been made that a continuous twisted yarn which has no inherent tendency to revert to ribbon form can be manufactured at commercial speed, i.e. at speeds in excess of 300 twists per minute, from a paper ribbon substantially composed of heat-bonded, fibrillated water-laid polyacrylonitrile papermaking fibers, without cracking provided that the twisting is performed while the ribbon is at a temperature in excess of its rattle point. A feature of the invention is that the resulting yarn, at room temperature, is heat-set, and possesses no tendency to revert back to ribbon form even when broken or cut, and a further feature is that the process can be performed at high speeds. We have successfully produced yarn from polyacrylonitrile paper ribbon at the rate of 3960 twists per minute, which indicates that the process can be successfully performed at the maximum rate which modern twisting machines are capable of.

The product is a continuous smooth, unkinked helical textile yarn consisting essentially of a heat-set twisted paper ribbon of heat-bonded fibrillated water-laid polyacrylonitrile papermaking fibers.

The invention results from the discovery that when polyacrylonitrile paper is heated momentarily above its rattle point, the fiber-to-fiber bonds of the paper remain sufiiciently strong to permit the paper to withstand the tensions involved in the twisting operation, and that this heating does not cause significant permanent detriment to the paper.

As stated, polyacrylonitrile paper normally (i.e., when dry and at room temperature) exhibits the rattle and snap characteristic of good quality bond paper. We have found that when heated, however, the paper passes through a transition point above which the paper is substantially as limp as untreated cloth or wet chamoi-s leather and does not rattle when shaken. This transition temperature (hereinafter termed the rattle point) can be determined by'placirig a sheet of the paper in contact with an electric hot plate having a known surface temperature, allowing the sheet to come to thermo-equilibrium, and then rapidly removing the sheet with tongs applied to one corner or end and causing the paper sheet to undergo wave-like shakes by rapidly moving the tongs to and fro horizontally while the .paper is suspended vertically. When the test is repeated over a series of temperatures, the approximate transition temperature or rattle point can be readily determined.

The rattle point of most polyacrylonitrile papers appears to be in the range of about -250 F. The paper may be satisfactorily twisted between that temperature and the temperature at which it starts to yellow or become tacky, which is generally about 400-550 F. In practice, we prefer that the paper be twisted at a temperature close to but safely above its rattle point as this temperature (e.g. 50100 F. above the rattle point) does not harm the ribbon and avoid-s the danger of the ribbon breaking while it is twisted or of yellowing or becoming tacky.

During yarn manufacture this is most conveniently determined by shaking the ribbon by hand as it emerges from the heating means. The limpness which the paper possesses above its rattle point is readily perceived with a little practice.

We have noticed that a comparatively soft yarn is generally produced when the paper is twisted at low temperature (e.g. 150250 F.) and that a stronger but harsher yarn is generally obtained when the paper is twisted at a higher temperature, e.g. 300-400 F. The two ranges thus produce distinct types of yarn.

The invention does not depend on the method employed for heating the paper ribbon to bring it above its rattle point, and any convenient method may be employed. One suitable method is to subject the ribbon to direct infra-red radiation. Another method is to employ a gas flame as the direct source of heat. Still another means is to heat the ribbon by direct contact with steam.

In practice, we have found it most convenient to employ a smooth electrically-heated quartz tube as the heating means, a thermocouple being used to determine the temperature within, and a transformer being provided so that the temperature may be varied as desired. The ribbon is passed through the tube, and the temperature of the tube is correlated with the speed of travel of the ribbon so that the temperature of the ribbon is sufficiently high to ensure that it arrives at the twisting point at a temperature safely above its rattle point.

The resulting yarn or thread may be wound at once, and special cooling has not been found necessary. Thus the yarn may be spooled at a temperature between its rattle point and its tack point.

The yarn produced by the process may contain some or all of the components normally found in synthetic polyaerylonitrile paper as, for example, wet-strength resins, sizing agents, and pigments and dyes, together with minor amounts of other fibers which may be cellulose pa-permaking fibers.

The yarn has the open, porous, fibrous structure characteristic of cotton yarn. It may be woven or knitted in normal manner to form textile fabrics. These textile fabrics, being substantially composed of polyaerylonitrile fibers, possess particular utility for applications where resistance to water, most organic solvents, ultraviolet light, and acids are desired. These textiles are therefore particularly suited for the manufacture of chemical filter cloth and outdoor apparatus coverings.

The invention does not depend upon the number of turns given the ribbon during the twisting operation. In general the ribbon is twisted so as to provide a yarn having a diameter or less of the width of the ribbon employed.

The invention will be more particularly illustrated by the examples which follow. These examples represent embodiments of the invention and are not to be construed as limitations thereof.

Example 1 The paper used was a water-laid web substantially composed of heat-bonded fibrillated polyaerylonitrile papermaking fibers composed of approximately 90% by weight acrylonitrile-10% methylmethacrylate copolymer. The paper had a basis weight of 35 lbs. per in. per 24" x 36"/500 ream, and was supplied as rolls of ribbon in. wide. This ribbon consistently broke when twisted to the extent of 3 twists per inch at the rate of 180 twists per minute (ribbon speed 5 feet per minute), but could be twisted without breaking at 120 twists per minute.

The twisting machine used was a Meadows full-scale 12spindle paper ribbon twister, but only one spindle was used.

The machine was modified by installing two quartz heating tubes each 6" long and in diameter for heating the paper ribbon before twisting. One tube extended upstream from the last steel roller yarn guide located approximately 8 inches from the twisting point, and the other extended downstream from this roller guide to the pigtail yarn guide, so that most of the twisting occurred while the paper was passing through the latter tube. Both tubes were wound with nichrome electrical resistance tape and were covered with asbestos paper for thermal insulation. An infra-red lamp was positioned above the steel roller guide, over the space between the tubes, to prevent the ribbon from cooling as it passed this point.

Electric current was supplied to each of the heating tubes through a variable transformer, and the -trans-- formers were gradually turned up to develop an air temperature estimated at 300 F. within the tubes. The ribbon was run through the heated tubes without being threaded through the traveller of a ring and traveller twister, so that no twisting occurred. As the temperature of the heating tubes increased, a temperature was reached at which the ribbon left the second or downstream tube in limp state, showing that it was above its rattle point. At this point the ribbon was threaded through the traveller and onto the collecting spool. Additional heat was then supplied to ensure a twisting temperature safely in excess of the rattle point of the ribbon, and the twisting machine was placed in full operation at the rate of 3,600 twists per minute (ribbon speed 30 feet per minute; 10 twists per inch).

Yarn formation took place smoothly and without difficulty. The paper ribbon showed no tendency to break. The temperature of the ribbon at the point of twisting was estimated to be approximately 250 F.

The temperature of the heating tubes was varied on either side of the starting temperature. The ribbon developed a tendency to crack when twisted at a temperature below approximately 200 F. and the ribbon tended to yellow and become tacky when heated above about 500-600 F. The range 200 F. to 400 F. appeared to be preferable, because very satisfactory results were obtained without any noticeable change in the color or other properties of the fibers.

Example 2 The foregoing procedure was repeated, except that the upstream heating tube and infra-red lamp were removed, and the downstream heating tube was replaced by a heating tube 3" in length so as to provide flash heating at a point directly adjacent to the point of twisting. The resulting yarn had a softer hand than the yarn of Example 1.

Example 3 The procedure of Example 1 was repeated except that the heating tubes and the infra-red lamp were removed, and the ribbon was passed between two elongated orifices which supplied steam over a 6" length of the ribbon as close to the twisting point as possible, "and an infra-red lamp was positioned to shine on the ribbon as it advanced to the twisting point, so as to prevent the ribbon from cooling prior to being twisted. Substantially the same results were obtained.

The paper produced by the process of the present application is claimed in the parent application identified above.

We claim:

1. A process for the manufacture of continuous yarn from a paper ribbon substantially composed of heatbonded fibrillated water-laid polyaerylonitrile papermaking fibers, which ribbon cracks when twisted into a continuous smooth unkinked helical warn at a rate in excess of about twists per minute, which comprises continuously twisting said ribbon at a rate in excess of 300 twists per minute to form a continuous smooth, unkinked helical yarn having a diameter less than about the width of said ribbon while said ribbon has a temperature between its rattle and tack points thereby preventing cracking of said ribbon during said twisting.

2. A process according to claim 1 wherein the ribbon is twisted at a temperature in the range of 50-100 F. above its rattle point.

3. A process according to claim 1 wherein the ribbon is twisted while at a temperature in the range of 300 F. 400 F.

4. A process for the high-speed manufacture of continuous yarn from a paper ribbon substantially composed of fibrillated water-laid polyaerylonitrile papermaking fibers, which ribbon cracks when twisted into a continuous smooth unkinked helical yarn at a rate in excess of about 150 twists per minute, which comprises continuously twisting said ribbon at a rate in excess of 3,500 twists per minute to form a continuous smooth, unkinked helical yarn having "a diameter less than about the width of said ribbon and flash-heating said ribbon immediately prior to said twisting whereby said ribbon is twisted while at a temperature between its rattle and tack points thereby preventing cracking of said ribbon during said twisting 5. A process for the high-speed manufacture of continuous yarn from a paper ribbon substantially composed of fibrillated water-laid polyacrylonitrile papermaking fibers, which ribbon cracks when twisted into a continuous smooth unkinked helical yarn at a rate in excess of about 150 twists per minute, which comprises continuously twisting said ribbon 'at a rate in excess of 3,500 twists per minute to form a continuous smooth, unkinked helical yarn having a diameter less than about the width of said ribbon, flash-heating said ribbon immediately prior to said twisting whereby said ribbon is twisted while at a temperature between its rattle and tack points, thereby preventing cracking of said ribbon during said twisting and spooling said yarn while said yarn has a temperature between the rattle point and tack point of said paper.

References Cited by the Examiner UNITED STATES PATENTS 1/55 Keeler 19-150 4/57 Crouzet 571 14 X 10/57 Wooding .923 12/57 Strang 57-5889 12/59 Faircloth 57167 2/ 61 Wilke et 'al 57-164 X 7/62 Holmes et al 162157 FOREIGN PATENTS 9/20 Germany.

MERVIN STEIN, Primary Examiner.

Claims (1)

1. A PROCESS FOR THE MANUFACTURE OF CONTINUOUS YARN FROM A PAPER RIBBON SUBSTANTIALLY COMPOSED OF HEATBONDED FIBRILLATED WATER-LAID POLYACRYLONITRILE PAPERMAKING FIBERS, WHICH RIBBON CRACKS WHEN TWISTED INTO A CONTINUOUS SMOOTH UNKINKED HELICAL WARN AT A RATE IN EXCESS OF ABOUT 150 TWISTS PER MINUTE, WHICH COMPRISES CONTINUOUSLY TWISTING SAID RIBBON AT A RATE IN EXCESS OF 300 TWISTS PER MINUTE TO FORM A CONTINUOUS SMOOTH, UNKINKED HELICAL YARN HAVING A DIAMETER LESS THAN ABOUT 1/10 THE WIDTH OF SAID RIBBON WHILE SAID RIBBON HAS A TEMPERATURE BETWEEN ITS RATTLE AND TACK POINTS THEREBY PREVENTING CRACKING OF SAID RIBBON DURING SAID TWISTING.