US 3139467 A
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June 30, 1964 N. DRISCH ETAL 3,139,467
METHOD FOR SPINNING VISCOSE Filed Nov. 14, 1962 A TTORNE Y United States Patent ice 3,139,467 METHGD FUR SPHJNING VISCOSE Nicolas Drisclr, Paul Heirbach, and Henri Rodier, Paris,
France, assiguors to Chimiotex S.A., Geneva, Switzerland, a corporation of Switzerland Filed Nov. 14, 1962, Ser. No. 237,527 Claims. (Cl. 264-198) This invention relates to a viscose spinning process and has for an object the manufacture of fibers, filaments, etc., having high mechanical characteristics and with stable microfibrillar structure, belonging notably to the group of polynosics.
it is known that in order to obtain fibers having all of these properties, it is necessary to spin a viscose of high viscosity and containing a high-DP cellulose under conditions such that there is coagulation without regeneration, the filaments formed then being drawn at a relatively high gamma index and regenerated in a second hot dilute deacidified bath.
A number of processes for achieving this objective have been proposed. For example, spinning in hi hly diluted acid bath, spinning in concentrated acid bath, spinning in saline or organic baths, etc.
In the case of dilute baths, it should also be mentioned that the addition of formaldehyde makes it possible to stabilize the gelled viscose and to spin at high gammas while maintaining a substantial acidity of the bath. Filaments are then produced with very high characteristics, as specified in French Patent No. 1,266,492 of April 22, 1960, with stretchings in the order of 300% and even more. In the case of the cold dilute bath and in the absence of formaldehyde, very high gammas could be obtained by further reducing the acid content of the bath, but the limit of spinning capacity is then very quickly reached. In accordance with the present invention fibers and filaments of the type in question are spun through use of hi bly dilute baths and through stretching at exceptionally high gamma indices. In order to stretch in this range of gamma indices, it is important to take out of the first bath not only filaments actually possessing a high gamma index, but also to retard as much as possible subsequent lowering of this index so as to beable to apply very advanced stretching. This involves working on a gel which is brought to the neutral state at the shortest possible distance from the spinneret.
More specifically this is accomplished by using a special vertical spinning device, wherein the filaments on coming out of the bath are supported on a partially immersed roll. The chemistry of the viscose and of the bath, notably the degree of sulfocarbona'tion of the viscose and the acid concentration must be suitably controlled. Under these conditions, the filaments, barely coagulated'by a cold bath with very low acid concentration and incapable of continuing by themselves, are supported on coming out of the bath by a partially immersed roll having the same peripheral speed as the feed speed of the filaments, the point of tangency of the filaments with the roll being approximately at the level of the bath. When they have covered a certain distance on the outer part of the roll, coagulation has sufficiently progressed and the filaments then have sufilcient strength to be able to continue by themselves in the air and to be subjected to stretching operations. Consequently, the bath adhering to the filaments continues to be neutralized on the course over the outer part of the roll and when the filaments have acquired enough strength to undergo stretching, they are impregnated in a weaker acid bath. As a result, at that time the pH of the gel may be neutral, or even alkaline. The quantity of bath still adhering to the filaments can moreover 3,139,467 Patented June 30., 1964 also be controlled, by submitting the gel on the roll to slight drying by means of a force pump the pressure of which is regulated.
On the other hand, in conventional horizontal or vertical spinnings, filaments which necessarily have sutficient strength on coming out of the bath to be able to continue in the air are not only in a more advanced state of regeneration, but, moreover, are still impregnated with the bath which is relatively more concentrated and, consequently causes regeneration to continue.
Referring to the drawing, the viscose is brought through swan neck 4- to spinneret 1 and the filaments 5 formed in spinning bath 2 are directed over partially immersed roll 3 so that point of tangency A is situated on level N of the spinning bath. The filaments are supported by roll 3 up to point B where the pressure of a roll 6 is exerted and the filaments then pass in succession over rolls 7, 8, 9, 10, 11 between which they are subjected to gradually increasing stretching. They are then picked up by rolls 12, pass into second bath 13, over rolls 14 and 15 and, finally, are wound on spool 16.
The roll 3 may be finely perforated on its cylindrical surface and provided with an inner screen 17 on its immersed part, so as to be able to eliminate through suction part of the liquid impregnating the filaments which are in gel state. The degree of immersion of roll 3 and the angle of contact of filaments 5 on this roll are not critical and can be varied. It is, however, important that the point of tangency A not be situated above the level N of the bath so that the filaments are brought into contact and are supported by the roll 3 before they leave the bath.
With the device described, gammas in the order of 50 can be attained at point B, i.e., at the start of stretching, and stretching can be easily completed at a gamma ranging between 10 and 20. This process makes it possible to spin at very low acidities (15 g./liter and less), with spinnerets having a large number of holes (8,000 to 15,000, for example). It is suitable for the manufacture of polynosic fibers. The process is also usable, however, for the spinning of textile rayon and tire rayon. In the latter case, primary stretching is markedly reduced in order to provide for greater stretch in the second bath.
For evaluation of this process, the concept of pH of the gel is used, which is determined as follows:
The gel is picked up in the desired place and is imme diately centrifuged at 300 G. for 5 minutes at low temperature. A quantity of 25 g. of this centrifuged gel is then introduced into 750 cc. of distilled ice water and, after stirring, the pH of the extraction water is measured. A conventional figure is obtained which is a measure of the state of decomposition of the gel.
Table 1 gives, for example: For a 5.2/3.8 viscose and 3 different baths, the pH of gels which have been obtained after roll 3 (point B), as a function of vertical travel in Bath, HZSOl/SOJNEZ, 15-35 g./l., Temperature 20 C 2 1. 3 l. 1 Bath, H2SOi/SO4Na2, 15-35 g./l., Temperature 10 C 7. 1 6 5. 1 Bath, HZSOl/SO-lNflz, 15-75 g./l., Temperature Table 2 gives for the same viscose and same baths the gamma indices determined at the outlet of the first bath (point B) and, at the end of primary stretching (point D), also as a function of vertical travel in the first bath.
The pH and gamma index of the gel can be further controlled. For the same viscose and a 1535 g./l. H SO /SO Na bath at 10 C., the following figures were obtained, as indicated in Table 3:
TABLE 3 Without drying With drying Point Point Point Point B D B D pH value 7.1 7. 5 9. 7 9. 9 Gamma Index 51 15 53 21 The figures of Tables 1, 2 and 3 clearly reveal that this process makes it possible to take out of the bath an acid, neutral or alkaline gel, the gamma index of which at roll 6 varies between 38 and 61, while it still ranges between 10 and 26 after the last drawing roll 11. The process, regarded as a whole, is therefore extremely flexible and makes it possible, in practice, to spin a gel in a considerable pH and gamma index range.
In the process, according to this invention, a viscose containing at least 3% cellulose and from 1.5 to 10% soda the sulforcarbonation rate of which is at least in relation to the alpha-cellulose can be used. The gamma index of the viscose used in spinning should have a range between and 100 and the cellulose contained in the viscose should have a DP of at least 500 and preferably above 600. The viscosity of the viscose at time of spinning should range between 150 and 1000 poises and is preferably above 400 poises. The viscose is spun in a bath containing less than 60 g./l., preferably, 8 to 40 g./l., sulfuric acid, 10 to 120 g./l., sodium sulfate and no or little (less than 1%) zinc sulfate. The bath can further contain small quantities of formal or a modifying agent such as polyalkylene oxide. The temperature of the bath ranges between 0 and 40 C., preferably between 5 and 30 C. The filaments obtained are stretched at least 100% and preferably at least 160%, which stretching can be imparted during travel in the air between the two baths and/or in a second hot dilute acid bath.
If rayon is spun, the yarn is preferably collected on spools. If staple fiber is spun, the roving is passed in slack state to a third degassing bath and is then placed in cans.
Filaments manufactured according to the present process have a high strength exceeding 4.5 g./den. in conditioned state and 4 g./den. in wet state and also a high modulus of elasticity in wet state, having an elongation in wet state of less than 3% under a load of 0.5 g./d. They are circular in section and their swelling is less than Through suitable treatment in nitric acid, it can be verified that the filaments in question possess a highly characteristic fibrillar structure far closer to that of cotton than to that of other regenerated cellulose yarns. Physical testing, as, for example, X-ray diagram and double refraction determination, reveal the existence of an extremely oriented structure. Structural char- Example 1 Linters pulp is soaked for 35 minutes in 230 g./l. soda at 20 C. and the alkali cellulose obtained is pressed at the rate of 3.2 in relation to alpha-cellulose. This alkali cellulose undergoes no ripening and is directly sulfocarbonated with 55% carbon disulfide in relation to alphacellulose. The xanthate formed is dissolved in dilute soda to produce a viscose containing 5.25% cellulose and 3.80% soda, to which are added surface-active products facilitating filtration and preventing clogging of the spinnerets. This viscose has a viscosity of 600 poises and the DP of the cellulose it contains is 600.
It is then spun by means of a spinneret of 8,000 holes of .06 mm. and into a first bath at 10 0, containing 15 g./l. of sulfuric acid and 35 g./l. of sodium sulfate. Vertical travel in the bath is 20 cm. and the diameter of the semi-immersed roll is 30 cm. The viscose is spun at the rate of 7 meters per minute without squeezing, which yields at point B a gamma index of 51 and a substantially neutral gel (pH:7.1). It is then gradually stretched 191% in air by means of a set of several rolls, which yelds at point D a gamma index of 16, and then the bundle of filaments is passed into a second hot dilute acid bath where it again undergoes 4.1% stretches. Finally, the bundle passes into a third degassing bath with a slight slack and is received in the can. Total stretching is 201%. After the usual washing deacidification, desulfurization and oiling treatments, filaments are obtained with the following characteristics:
Unit titer "den.-- 1.5 Strength in conditioned state g./den 5.3 Strength in wet state g./den 4.7 Elongation in conditioned state percent 10 Elongation in wet state do 12 Modulus in wet state (elongat. percent under 0.5
g./den.) 1.5 Loop strength g./den 0.7
After treatment with 5% soda, the filaments just described still have a strength of wet state of 4 g./den. and a modulus in wet state (elongation percent under 0.5 g./den. of 3.
Example 2 Wood pulp having a high alpha-cellulose content is converted into alkali cellulose and the latter is immediately sulfocarbonated without any intermediate ripening with 57% carbon disulfide in relation to alpha-cellulose; the xanthate formed is then dissolved in dilute soda to yield a 6.5 :5 viscose to which suitable surface-active products are added. The DP of the cellulose contained in the viscose is 550 and the viscosity is 500 poises. Viscose is spun in a vertical spinning device as described above by means of a spinneret with 40 holes of .07 mm. in a bath containing 15 g./l. sulfuric acid and 75 g./l. sodium sulfate at a temperature of 10 C. Vertical travel is 10 cm. and the diameter of the semi-immersed roll is 30 cm. It is spun at the rate of 10 m./min. with slight squeezing, which yields at point B a gamma index of 53 for an almost neutral gel (pl-i=8). It is then gradually stretched in the air over a set of rolls which yields at point D a residual gamma index of 15. Finally, the yarn is fixed in a second hot dilute acid bath and is then wound on a spool. After the usual finishing treatments, the filamerits constituting this yarn show the following characteristics:
Unit titer den 1.25
Strength in conditioned state g./den 5.1
:Strength in Wet state g./den 4.2 Elongation in conditioned state percent 11 Elongation in wet state do- 11 Modulus in Wet state (elongation percent under 0.5 g./den.) 1.7 Loop strength g./den 0.75
After treatrnent with soda, and the filaments just described have a strength in wet state of 3.4 g./den. and a modulus in wet state of 3.5.
What is claimed is:
1. A process for the manufacture of fibers or filaments having high mechanical characteristics, a stable microfibrillar structure and good dimensional stability, which comprises spinning a viscose containing a cellulose having a DP of at least 500 and a viscosity of at least 150 poises and a gamma index of at least with a cold acid bath containing not over grams of sulfuric acid per liter and from 10 to g./l. sodium sulfate and sub- "staritially no zinc sulfate; the spinning taking place in an upward vertical direction, andwhile the filaments=are still incapable of supporting then1selves,-;conveying said filaments at the exit of said bath't'angentiallypn a partially immersed hollow rotating surface fersai distance to allow partial extraction "of the-said bathby vacuum through the surface and simultaneously coagulating to a point at which said filaments become self-supporting and then stretching said filaments in air.
2. The process set forth in claim 1 in which the filaments are stretched by at least 100%.
3. The process set forth in claim 1 in which the filaments are stretched by at least 4. A process according to claim 1 wherein the viscosity of the viscose is at least 400 poises.
5. A process according to claim 1 wherein the gamma index of the viscose is at least 50.
References Citetl in the file of this patent UNITED STATES PATENTS 2,705,184 Drisch et a1. Mar. 29, 1955 3,024,493 Kornpass Mar. 13, 1962