US2686709A - Process for producing heavy denier regenerated cellulose filaments - Google Patents

Description

Patented Aug. 17, 1954 PROCESS FOR PRODUCING HEAVY DENIER REGENERATED CELLULOSE FILAMENTS Rudolph Woodell, Richmond, Va., assignor to E. I. du Pont de Nemours and Company, Wil-.

mington, DeL,

a corporation of Delaware No Drawing. Application March 7, 1952, Serial No. 275,454

4 Claims. (CI, 18-54) This invention relates to the production of regenerated cellulose filaments, fibers, and the like, having a pronounced crimp or curl. More particularly, it relates to an improved method for producing such crimped fibers and filaments of heavy deniers at high spinning speeds.

U. S. Patent No. 2,515,834 to W. D. Nicoll discloses a process for the production from viscose, of crimped, wool-like fibers and filaments of regenerated cellulose. These fibers are unique in that the crimp, after being removed mechanically by stretching, combing, or the like, maybe substantially completely restored by suspending the fiber, free from all tension, in an aqueous liquid. The process. comprises spinning filaments into a bath while maintaining a critical balance between the compositions of the viscose and of the bath, imposing a high tension and stretch on the filaments during spinning, and relaxing the filaments in a liquid, free of all tension, after substantially complete regeneration. In accord ance with the first sub generic embodiment of invention disclosed in that patent, a viscose solution containing over 5% alkali and about 7% cellulose at a salt index of 1.5-6.0 is extruded into a bath containing 6.59.5% sulfuric acid, 15-30% sodium sulfate, and 0.l-3% zinc sulfate. The bath is maintained at a temperature of ie-75 G. The compositions of the viscose and of the bath are maintained according to the formula given in the patent. In addition to the above-mentioned ingredients of the coagulating bath, it is permissible to have present as much as 6% or 7% glucose or similar organic substances well known in the art. Bath travel distances of over 50 inches are operable. During the spinning of the filaments a stretch of at least 40% and a spinning tension of at least 0.5 gram per denier must be imposed. After substantially complete regeneration, the filaments are relaxed, free of all tension, in a liquid which will swell them. The patent states that this treatment will result in a wool-like yarn containing above 10 crimps per inch. It should be noted that spinning speedsoi only 2500 inches per minute or 69.5 yards per .minute are mentioned in the examples.

The high tension required for this process may be secured by the use of a suitable system of guides and rollers in the bath adapted to increase tension on the filaments gradually. One illustration of rollers which may be employed for this purpose are rollers, provided with means for developing a resistance to rotation in the bath. These are described in U. S. Patents 2,083,251, 2,083,252, and 1,878,455. Tension may also be applied between two feed wheels during the passage of the yarn through a secondary bath, if

l caused by broken filaments and the like.

Producing heavy denier yarns of 10 deniers per filament and higher, capable of withstanding the high spinning tensions necessary in this process, is very difficult. U. S. Patents No. 2,517,694 to H. D. Marion et a1. and No. 2572,9343 to M. P. Kulp et al. point out that above about 10 deniers per filament, the crimping is negligible. A preference for 1 to- 6 deniers per filament is mentioned in these patents Since lower spinning tensions are necessarily imposed on the heavy denier yarn, the resultant crimp is very unsatisfactory. This difiiculty is even greater at increased spinning speeds,-i. e., Y. P. M. and higher. Operating at increased spinning speeds is, of course, quite desirable from an economic standpoint, but it is very difficult to increase these speeds and still be able to attain high spinning tensions for even the fine denier filaments without excessive breaking of filaments. causing interruptions in the process. Attaining the required spinning tension for heavy denier filaments at increased spinning speeds under ordinary conditions is a practical impossibility. The crimpability of heavy denier yarn is further reduced by the very nature of the filament. It would not be expected that a relatively stiff, heavy material would crimp as well as a fine material.

It is an object of the present invention to produce yarn, filaments and fibers of heavy denier that are highly crimpable. A further object is the production of heavy denier filaments and fibers, characterized by increased breaking tensions. A further object is to provide heavy denier filaments and fibers capable of withstanding the spinning tensions necessary for the production of highly crimpable yarns at increased spinning speeds. A still further object is to provide a method by means of which crimpable artificial fibers and filaments can be produced during the usual course of production with a minimum disturbance to normal production and with a minimum investment in additional equipment. Other objects will become apparent from the following description and claims.

The above objects are accomplished in accordance with the present invention by spinning regenerated cellulose filaments of at least denier per filament at spinning speeds of at least 100 yards per minute, under tension, from a viscose solution into a coagulating and regenerating bath and, after substantially completely regenerating the filaments, freely suspending the filaments, in filamentous structure form, in an aqueous liquid bath in complete absence of tension to completely relax them. A high degree of crimp is obtained by observing the following critical conditions in carrying out the process:

(a) The viscose solution must have an alkali content (calculated as NaOH) of 4.0 to 7.5%,

(b) The viscose solution must have a salt index (as determined by Reinthaler-Rowe, Artificial Silk, 1928, page 69) of between 1.5 and 7,

(c) The coagulating and regenerating bath must have a sulfuric acid content of between 6.5% and 9.5%,

(d) The coagulating and regenerating bath must have a sodium sulfate content of between and (e) The coagulating and regenerating bath must have a zinc sulfate content of between 0.1% and 3%,

(f) The filaments must travel at least 50 inches in the coagulating and regenerating bath, (9) The temperature of the coagulating bath must be between C. and 75 'C.,

(h) The extrusion velocity must be adjusted relative to said spinning speed of at least 100 yards per minute to give a ratio of spinning speed to extrusion velocity of between 2.5:1 and 4:1,

(2') The temperature of the relaxing bath must be between 0 C. and 120 C., and not more than one of said critical conditions is outside of the following ranges for the indicated condition:

(7') Salt index of viscose 3.5 to 5.5.

(k) Sulfuric acid content of bath 7.5% to 8.5%. (Z) Sodium sulfate content of bath 1- 19% to 25%. (m) Zinc sulfate content of bath 0.85% to 2.0%. (11) Length of travel in bath Over 75 inches. (0) Temperature of coagulating bath to 60 C. (10) Temperature of relaxing bath 60 to 100 C.

It will be seen that the above process differs .from and is an improvement over the process of U. S. Patent No. 2,515,834 to Nicoll in that heavy denier filaments (greater than 10 denier per filament) are spun at high speed (spinning speeds of at least 100 yards per minute) by main taining a ratio of spinning speed to extrusion velocity of between 2.511 and 4:1. This latter condition does not apply to the spinning of ordinary deniers. For filament deniers below 10, at spinning speeds as high as 100 yards per minute, extrusion velocities which are about equal to or slightly lower than the feed-wheel or spinning speed have been satisfactory. Further lowering of the extrusion velocity to one-ha1f the spinning speed in the spinning of the fine denier filaments results in poor spinning performance characterized by filament breaks and filament wraps.

When spinning heavy denier material, the appropriate extrusion velocity to obtain satisfactory crimping is critically different. Unexpectedly, it has been found necessary to use a ratio of spinning speed to extrusion velocity of between about 2.5: 1

and 4:1 at spinning speeds of at least about yards per minute. Operating at higher extrusion velocities lowers the breaking tension of the filaments with an accompanying serious reduction in crimpability and, in addition, also results in poor spinning performance. Reducing the extrusion velocity below the range disclosed above likewise results in poor spinning performance, and there is no apparent increase in the crimpability of the filaments.

The table illustrates the important aspects of the invention. Yarn of 18 denier per filament was spun at a spinning speed of 100 yards per minute in accordance with the general procedure disclosed in U. S. Patent No. 2,515,834, except for the changes indicated. A viscose solution containing 7% cellulose and 6% alkali was spun at a sodium chloride index of 3.6 into a bath at a temperature of 56 C. containing 8.5% sulfuric acid, 24% sodium sulfate, 1.5% zinc sulfate, and

Table Extrusion i i fii Breaking 8 8:31 Orim Velocity, S peed t5 zggi Tiension? Waves get Yds./Min. Extrusion Grams per Inch Velocity Denier These data illustrate the necessity for reducing the extrusion velocity in order to obtain breaking tensions that will produce fibers that are capable of crimping to a commercially useful extent. sions, of the order necessary to produce heavy denier fibers of commercially acceptable crimpability, can only be obtained by substantially reducing the extrusion velocity. At this spinning speed of 100 yards per minute, satisfactory breaking tensions are obtained when extruding at velocities of 33 to 39 yards per minute.

Similarly when spinning yarn of 10 deniers per filament at spinning speeds of 100 yards per minute, optimum performance, based on a comparison of the breaking tensions obtained and the number of interruptions due to poor spinning, resulted atan extrusion velocity of 34.5 yards per minute. This extrusion velocity, which corresponds to a ratio of spinning speed to extrusion velocity ratio of 2.90, resulted in a breaking tension of 0.60 g. p. d. This permitted operation at a spinning tension of 0.50 g. p. d.

When this discovery was applied to the finer, lighter yarns, it was found that optimum performance was obtained at lowered extrusion velocities, but these velocities were at least 1.5 to 2 times the optimum extrusion velocities found in the case of the heavy denier yarns. Thus, when spinning yarn of 6 deniers per filament at 100 yards per minute optimum performance was achieved at an extrusion velocity of 54 yards per minute, corresponding to a spinning speed i to extrusion velocity ratio of 1.85. At this ratio Further, they illustrate that breaking tenbreaking tension of 0.87 g. p. d. and an operable spinning tension of 0.73 g. p. d.

It is apparent that the spinning of crimpable fibers of heavy denier filaments and higher) depends on spinning at high spinning tension. Imposing a high spinning tension on heavy denier filaments necessitates increasing th breaking tension of the filaments. Increasing this tension is, surprisingly, accomplished by substantially reducing the extrusion velocity to increase the ratio of spinning speed to extrusion velocity. When spinning at a speed of 100 yards per minute, it is necessary that the value of this ratio be above about 2.5 to 1 and preferably not over 3 to 1. If the spinning speed is increased, the range of this ratio may also be increased above 2.511 to values not in excess of about 4:1.

This invention provides an improved and an inexpensive method for producing the crimped filaments and fibers which find a wide demand in industry. This method requires no additional equipment and makes it possible to produce a satisfactory heavy denier, crimped fiber, which heretofore had not been possible. The method is applicable to fibers produced by the bucket, bobbin, or any of the continuous spinning processes. These fibers are useful, not only for new effects in textiles, but also for other industrial applications, e. g., as artificial down or hair substitutes. Further, these filaments are useful as a replacement for wool in carpets, rugs, and other floor coverings, and upholstery.

As many different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments disclosed except to the extent defined in the appended claims.

What is claimed is:

1. In the process for producing crimpable regenerated cellulose filaments and fibers wherein a viscose solution having an alkali content of 4% to 7.5% and a salt index between 1.5 and 7 is extruded in the form of filaments into a coagulating and regenerating bath having a sul- 6 yards per minute using an extrusion velocity which provides a ratio of spinning speed to extrusion velocity of between 2.521 and 4:1.

2. A process for producing 10 to 18 denier crimped regenerated cellulose filaments and fibers which comprises extruding a viscose, having an alkali content of 4% to 7.5% and a salt index of 8.5 to 5.5, in the form of filaments at an extrusion velocity of 33 to 39 yards per minute into a coagulating and regenerating bath having a sulfuric acid content of 7.5% to 8.5%,

furic acid content between 6.5% and 9.5%, a

sodium sulfate content between 15% and 30%, a zinc sulfate content between 0.1% and 3% and a temperature between 40 C. and 75 C., the resulting filaments are conducted through the bath for at least 50 inches, the filaments are stretched under a tension approaching the breaking tension and wherein not more than one of the above critical conditions is outside of the following range for the indicated condition:

Salt index of viscose 3.5 to 5.5. Sulfuric acid content of bath 7.5% to 8.5%. Sodium sulfate content of bath 19% to 25%. Zinc sulfate content of bath 0.85% to 2.0%. Length of travel in bath Over 75 inches. Temperature of coagulating bath50" to 60 C.

the improvement for obtaininga high degree of crimp when spinning heavy denier filaments which comprises spinning filaments of 10 to 18 deniers per filament at a speed of at least 100 a sodium sulfate content of 19% to 25%, a zinc sulfate content of 0.85% to 2.0% and a temperature of 50 to 60 C., conducting the resulting filaments through the bath for over inches and stretching them under a tension approaching the breaking tension, withdrawing the filaments from the bath at a spinning speed of about yards per minute and, after substantially complete regeneration, suspending the filaments in complete absence of tension in an aqueous liquid bath at a temperature of 0 to C. until completely relaxed.

3. A process for producing 10 to 18 denier crimped regenerated cellulose filaments and fibers which comprises extruding a viscose solution having an alkalioontent of 4 to 7.5% and a salt index of 3.5 to 5.5 through a spinneret into a coagulating and regenerating bath having a sulfuric acid content of 7.5% to 8.5%, a sodium sulfate content of 19 to 25%, a zinc sulfate content of 0.85 to 2.0% and a temperature of 50 to 60 0., through the bath for over 75 inches and stretching them under a tension approaching the breaking tension, withdrawing the stretched filaments at a spinning speed of at least 100 yards per minute the extrusion velocity and size of spinneret orifices being correlated with the spinning speed to give filaments of 10 to 18 deniers per filament and a ratio of spinning speed to ex trusion velocity of between 2.5:1 and 3:1 and, after substantially complete regeneration, suspending the filaments in complete absence of tension in an aqueous liquid bath at a temperature of 60 to 100 C. until completely relaxed.

4. A process for producing 10 to 18 denier crimpable regenerated cellulose filaments and fibers which comprises extruding a viscose solution having an alkali content of 4 to 7.5% and a salt index of 3.5 to 5.5 through a spinneret into a coagulating and regenerating bath having a sulfuric acid content of 7.5 to 8.5%, a sodium sulfate content of 19 to 25%, a zinc sulfate content of 0.85 to 2.0% and a temperature of 50 to 60 C., conducting the resulting filaments through the bath for over 75 inches and stretching them under tension approaching the breaking tension, withdrawing the stretched filaments at a spinning speed of at least 100 yards per minute and completing the regeneration, the extrusion veloity and size of spinneret orifices being cor- References Cited in the file of this patent UNITED STATES PATENTS Name Date Nicoll July 18, 1950 Number conducting the resulting filaments,

Claims (1)

1. IN THE PROCESS FOR PRODUCING CRIMPABLE REGENERATED CELLULOSE FILAMENTS AND FIBERS WHEREIN A VISCOSE SOLUTION HAVING AN ALKALI CONTENT OF 4% TO 7.5% AND A SALT INDEX BETWEEN 1.5 AND 7 IS EXTRUDED IN THE FORM OF FILAMENTS INTO A COAGULATING AND REGENERATING BATH HAVING A SULFURIC ACID CONTENT BETWEEN 6.5% AND 9.5%, A SODIUM SULFATE CONTENT BETWEEN 15% AND 30%, A ZJNC SULFATE CONTENT BETWEEN 0.1% AND 3% AND A TEMPERATURE BETWEEN 40* C. AND 75* C., THE RESULTING FILAMENTS ARE CONDUCTED THROUGH THE BATH FOR AT LEAST 50 INCHES, THE FILAMENTS ARE STRETCHED UNDER A TENSION APPROACHING THE BREAKING TENSION AND WHEREIN NOT MORE THAN ONE OF THE ABOVE CRITICAL CONDITIONS IS OUTSIDE OF THE FOLLOWING RANGE FOR THE INDICATED CONDITION: