US3632722A - Rayon process - Google Patents

Abstract

THE APPLICATION DISCLOSES A PROCESS FOR PRODUCING HIGHLY POLYMERIZED VISCOSE RAYON FILAMENTS HAVING HIGH LOOP AND KNOT TENACITY. FIBERS OF HIGH VISCOSITY ARE SPUN INTO A LOW ACID CONCENTRATION BATH AND BEFORE FIXING IN A HOT ACID BATH ARE STRETCHED EITHER IN AIR OR IN A SEPARATE BATH. AFTER STRETCHING THE FIBERS ARE INTRODUCED INTO A SEPARATE BATH WHICH IS SUBSTANTIALLY NEUTRAL AND HAS A TEMPERATURE OF FROM 10* TO 40*C. AS A MODIFICATION, A SECOND SEPARATE BATH IS EMPLOYED INTO WHICH THE FIBERS ARE INTRODUCED AFTER THE FIRST MENTIONED SEPARAT BATH AND HIS BATH HAS A TEMPERATURE OF FROM 30* TO 80*C. AND HAS A PH OF 8 TO 10.5.

Description

"United States Patent 61 hce Patented Jan. 4, 1972 3,632,722 RAYON PROCESS Takashi Asaeda, Kuse-gun, Japan, assignor to Tachikawa Research Institute, Higashiyama-ku, Kyoto, Japan No Drawing. Original application Oct. 22, 1965, Ser. No. 502,564. Divided and this application Jan. 31, 1969, Ser. No. 795,681

Claims priority, application Japan, Nov. 2, 1964, 3 61,841 Int. Cl. D01f 3/12 US. Cl. 264196 1 Claim ABSTRACT OF THE DISCLOSURE The application discloses a process for producing highly polymerized viscose rayon filaments having high loop and knot tenacity. Fibers of high viscosity are spun into a low acid concentration bath and before fixing in a hot acid bath are stretched either in air or in a separate bath. After stretching the fibers are introduced into a separate bath which is substantially neutral and has a temperature of from to 40 C. As a modification, a second separate bath is employed into which the fibers are introduced after the first mentioned separate bath and his bath has a temperature of from 30 to 80 C. and has a pH of 8 to 10.5.

This application is a divisional application of application SN 502,564, filed Oct. 22, 1965 and now abandoned.

It is known that, in the process where a highly-polymerized cellulose viscose is spun into a low acid concentration bath (hereinafter referred to as high polymerizationlow acid process), the transversal properties, i.e. knot and loop tenacities, etc. are apt to decrease, while the axial properties, i.e. dry and wet tensile tenacities, etc., are substantially improved when some stretching is applied to the spun filaments.

Such a fact may depend on the fact that in the high polymerization-low acid process strain is apt to result within the fibers and the strain is more easily fixed in the fibres in comparison with that which occurs in conventional viscose processes.

Our applied process is characterized by the fact that the spun thread is treated, between its stretching stage and heat-setting stage, by water, a diluted solution of acid or weak alkaline neutral-salt or weak alkaline acidsalt whose pH is in the range from 1.4 to 10.5, being selected in conformity with the degree of development of the inner structure of the thread. The object of our invention is to provide improved fiber of highly polymerized rayon filament having high loop and knot tenacity without any deterioration of its so-called polynosic characteristics (hereinafter referred to as improving-effect).

In the viscose process, the following three fundamental reactions occur from the time of extrusion of viscose into a spinning bath to the regeneration of cellulose filaments: (a) neutralization of free alkalis in viscose, (b) regeneration of cellulose by the decomposition of cellulose xanthate, and (c) crystallization of cellulose molecules due to hydrogen bond formation in the molecules.

In the high polymerization-low acid process, only the first reaction and a part of the second reaction occurs in the spinning bath because of the low acid concentration of the spinning bath, and the remaining reactions are advanced mainly by the spinning liquor attached to the filaments after their leaving the spinning bath. That is to say, the spun threads immediately after leaving the spinning bath have a double layer structure whose inner layer consists of non-decomposed cellulose xanthate, the outer one consisting of regenerated cellulose with extremely low degree of coagulation. Therefore, the development of fiber structure is attained mainly outside the spinning bath, and yet its progress is very slow because the acid content of the liquor attached to the filaments is very low.

Generally, the spun thread is stretched immediately after leaving the spinning bath in order to increase the tenacity of the fibers. Therefore, in the high polymerization-low acid process, the stretching is applied at a relatively early stage of fiber formation, and the development of the fiber structure, that is, the hydrogen bonding, occurs mainly after the stretching stage.

It will be clear from the above fact that in the high polymerization-low acid process not only is the development of the crystal regions an outstanding feature of the process, but also the formation of hydrogen bonds in low ordered regions in quite remarkable. This is the reason why, in the high polymerization-low acid process, it is very difiicult to obtain fibers having high loop or knot tenacity while it is very easy to achieve high tensile tenacity both dry and wet.

Now, if a relaxation treatment which restrains the strain in the inner structure of the fibers originated by the stretching is applied to the threads during the stretching stage, or if a relaxation treatment by which the strain can be eliminated from the fibers is applied to the threads after the stretching, then we will be able to obtain the non-strained fibers.

The essential points of our process exist in that, firstly the spun threads must be relaxed before the heat-setting stage and, secondly, the condition of the relaxing liquor should be determined in conformity with the degree of development of the fiber structure during the treatment.

As mentioned above, in the high polymerization-low acid process, the fiber structure changes from the stretching stage to the heat-setting stage. Therefore, the suitable conditions of the relaxing liquor must be chosen corresponding to its stage of the treatment. Practically speaking, the relaxing liquor must have such an intensity that it can relax the amorphous regions only but has no influence upon the crystal regions.

If the relaxing intensity is too low for the fiber structure, then the desired improvement will not occur and, if it is too high, then although the improvement is sufficient, the crystal regions may be disturbed, and various defects, for instance, the decreasing of the polynosic characteristics or the formation of sticky fibers will result.

Now, there exists one proposal for the improvement of the polynosic fibers in which the fibers are treated when their inner structure has already been fixed and that is the use of a solution of caustic alkali such as caustic soda. By such a treatment, the loop tenacity is increased, but there are apt to occur certain dangers, for instance, the increasing of the elongation of fibers, the decreasing of the Wet tenacity, or the increasing of the second swelling value, etc. Because, in the completely fixed fibers even the amorphous regions are in high degree of coagulation, we ought to use a solution having a higher relaxing force in order to remove the strains from those amorphous regions. As the result, even the crystal regions are disturbed.

In our process the said danger does not exist, because the treatment resulting in the desired improvements is applied to the fibers before the heat-setting stage.

The stages of fiber developments after the spinning bath and prior to the heat-setting stage are threefold, viz fiber condition during the stretching stage and immediately after the stretching and after travelling a certain distance in the air after stretching.

At a time when the development of the fiber structure is just beginning to occur, for instance, at the stretching stage, the threads must be treated by a diluted acid liquor whose pH-value is more than 1.27 in order to obtain the desired improvement. The acid concentration of the treating liquor should be lower than that of the liquor previously attached to the fibers. Then the acid concentration in the surrounding liquor of the fibers is lowered, and the fiber structure which have already developed corresponding to the liquor attached to the fibers shall be relaxed, and accordingly the strain which is to occur at the stretching is limited. The treating-liquor in this case must be acidic, and water or an alkaline liquor is too strong for the relaxation of the fiber structure, and accordingly the formation of the sticky-fibers or the deterioration of the polynosic characteristics may be caused. Moreover, as shown in Table 2, a treating liquor that will not change the y-value of the threads should be used. This case is shown in Example 1.

At a time when the cellulose molecules have a parallel orientation and the hydrogen bonds formation in the amorphous regions has been advanced to a certain extent, for instance, at a period immediately after the stretching, the threads must be treated by using water or a solution whose pH-value is 7 or thereabouts containing extremely small quantity of acids, alkalis, or salts. By the said treatment only the amorphous regions are relaxed and the desired improvement will be obtained.

At this period, acid liquors have no improving effect. On the other hand, the relaxing-action of alkali liquors is still too strong for the threads, and accordingly the formation of the sticky-fibers as well as the deterioration of the polynosic characteristics will result. The actual treatment at this period is shown in Example 2.

At the stage where the fiber structure in the crystal regions as well as in the amorphous regions has been so advanced that heat-setting may be started, the desired improving-effect is obtained by treating the threads using an alkaline solution whose pH-value is 8 to 10.5. In this case, the neutral salts or acid salts, whose aqueous solutions are alkaline, are suitable as treating agents. Especially, such acid salts as sodium bicarbonate or disodium hydrogen phosphate exhibit an excellent improving-effect in a certein concentration range Without causing any damage to the polynosic characteristics of the fibers. The pH- value of the solutions of such acid salts is nearly constant irrespective of their concentration, as shown in Table 4. That is to say, in those salts the relaxing-ability has no relation to their concentration, because the relaxingability depends mainly on the concentration of the hydroxyl ions (pH-value). On the other hand, the presence of the salts is antagonistic to the relaxing action of the relaxing action of the hydroxyl ions hereinafter referred to as the salt-effect.

Therefore, where there is a suitable concentration of these salts, the range of relaxing effect is rather limited up to in the relatively lower-ordered regions where the strains are accumulated. The formation of the sticky fibers is also restrained in proportion to the salt concentration.

Now, caustic soda solution or ammonia water indicates a high pH-value even in low concentration, and with these agents the suitable pH-value for the relaxing treating can be attained at extremely low concentration, so that the salt-eifect can not be expected from such caustic alkalis. Therefore, damage to the polynosic characteristics occur under conditions where strain is eliminated from the fibers. For that reason, caustic alkalis are not desirable in the process.

On the other hand, sodium carbonate or sodium silicate presents some danger on account of their fairly strong alkali content although they are neutral salts. But it is not so unfavorable as caustic alkalis.

The actual procedures at this period are shown in Examples 3, 4 and 5.

The process employing the multi-step treatments at succeeding time periods is also possible. The process using the two-step treatment is shown in Example 6, and that of the three-step treatment is shown in Example 7.

4 In Table I there is shown a comparison of the improving-effect during or at the end of the several stages of operation.

TABLE I Condition of treatment: Relative loop tenacity Blank Treatment during stretching (A) l40 Treatment immediately after stretching (B) -150 Treatment just before heat-setting (C) -200 Treatment by A and B 200250 Treatments by A, B and C 230-280 As for the temperature of the treatment, the lower the temperature, the higher is the improving-effect, but use of lower temperatures will damage the polynosic properties as well as create a risk of forming sticky-fibers. The temperature during the treatments should be also selected corresponding to the fiber structure, i.e. to the stage of the treatment. At the stretching stage, the threads must be treated at the temperature of less than 30 C. Immediately after the stretching, a suitable temperature lies between 10 and 40 C., and just before the heat-setting, it lies between 30 and 80 C.

As mentioned above, at the relaxing condition where the high improving-effect can be obtained, there exists a fear that sticky fibers may be formed. To prevent such defect, it is efiective to add an alkyl quaternary ammonium salt,

to the relaxing liquor, where R is an alkyl radical having more than twelve carbon atoms, R R and R are one of the following radicals, i.e. methyl, ethyl, hydroxymethyl, and hydroxyethyl radicals, and X is halogen or sulphate radical. For instance, the addition of from 0.3 g. to 1.0 g. of dimethyl stearyl hydroxyethyl ammonium chloride to 1 litre of the relaxing liquor is distinctly effective.

One of the remarkable advantages of our present inven tion is that the fibers which have been treated by an alkaline medium have a distinct curl-appearance. Hitherto, it has been known that it is very difiicult to obtain the highly polymerized fibers having the curl-appearance. In our process it is quite easy to obtain the fibers having a curl number of more than 10 per 2.5 cm.

Generally speaking, if the spun threads are stretched at the period where the undecomposed cellulose xanthate still remains in the inner layer of the fibers, and are treated at the same time or immediately after the stretching by hot water or a hot acid bath, then a curl appears. By this treatment, while the regenerated cellulose of outer layer shows little microscopic change, the inner layer of the cellulose xanthate contracts strongly owing to its fairly loose structure. As the result, there appear curls in proportion to the dilference in the degree of contraction existing between the inner and outer layers.

Nevertheless, in the case of the high polymerizationlow acid process, it is impossible to obtain the curled fibers by the above-mentioned treatment. This is true for the following reasons. In the fibers of the high polymerization-low acid process, the outer layer of regenerated cellulose makes a harder structure due to stretching in comparison with the corresponding structure of the conven tional viscose process. This hard structure of the outer layer completely overcomes the contraction force of the inner layer which occurs as a result of the hot bath treatment. As a consequence, the contraction force of the inner layer produces a strain within the fibers.

If such fibers are treated before the heat-setting by an alkaline liquor Whose pH is below 10.5, then the hard outer layer of regenerated cellulose turns to a soft mantel owing to the vanishing of the hydrogen bonds existing in that layer. As the result, the anti-contraction force of the outer layer decreases to the same order as that of the contraction force of the inner layer, and the curl appearance is obtained.

EXAMPLE 4 A viscose having a high viscosity and a high 'y-value is EXAMPLE 1 spun in a low acid concentration bath. After the stretch- Viscose having a ball-falling viscosity of 420 sec. and 5 ing, the tow is cut t the r d length- T u fi s r -yalue of 63 is spun at 30 in a spinning bath cOntreated at various temperatures by a liquor containing 3 taining 17 g./l. of sulphurlc acid, 60 g./l. of sodium sulof NaHCOB, and am successively treated at phate, and 0.5 g./1. of zinc sulphate. The spun threads are assin thm h h t b th t 3 /l f 1 led to the stretching device after passing through guides p g ug a f a con ammg Suand a drawing roller. The concentration of sulphuric acid 10 P mud to fix the Inner structure of the fibersin a. liquor attached to the fibers at the entrance of the The results are shown in Table in comparison with stfetchlng dtfvlce 1S 11 (P the non-treated fibers. In this experiment, the influence Whlle bemg Stretched. on i f" the of the temperature upon the treatment is also examined threads are treated by various 11qu1ds having the acid conr h d th tent shown in the 1st column of Table 2 and a temperam a mon to t e Stu y of e lmprovmg'efiect of ture shown in the 4th column of Table 2. The results are a- Y these treatments the curled fibers are shown in Table 2 in comparison with the non-treated tained whose curl number is 9 to 10 per 2.5 cm. fibers.

TABLE 2 Wet 'y-value of threads Treating liquor Wet clonga- Loop tenactlon tenac- Before After H2804 NazSO4 Temp. Denier ity (perity stretchstretch- (g./l.) (g./l.) pH C.) (d.) (g.ld.) cent) (KM) ing ing 1 N on-treated.

EXAMPLE 2 TABLE 5 A viscose having a ball-falling viscosity of 440 sec. and Wet a 'y-value of 70 is spun at 32 C. in a spinning bath con- D 1 t q taining 17.6 g./l. of sulphuric acid, 60 g./l. of sodium sul- 35 Temperature C 8;; 7 5333 $3 3 3 i k i phate, and 0.4 g./l. of Zinc sulphate. After stretching on 1 52 3 89 11 8 5 1 the stretching device, the threads are treated by passing 1 them through an aqueous solution containing 0.85 g./l. g2 2-3 of dimethyl stearyl ,G-hydroxyethyl ammonium chloride. 3193 121 810 Finally, the fiber structure is fixed at 90 C. passing through a hot acid bath containing 3 g./l. of sulphuric EXAMPLE 5 acid. The result is shown in Table 3 in comparison with the non-treated fibers.

A viscose same as Example 2 is spun at 30 C. in a spinning bath containing 18.5 g./l. of sulphuric acid, 60 g./l. of sodium sulphate, and 0.45 g./l. of zinc sulphate. After the stretching on the stretching device the threads are cut to desired length. The cut fibers are treated at 55 C. for 5 minutes by liquids containing various quantities of Na HPO and are successively treated at 85 C. passing through a hot acid containing 3 g./l. of sulphuric acid to fix the inner structure of the fibers.

The results are shown in Table 4 in comparison with the non-treated fibers. By these treatments, the curled fibers are obtained. The curl number of the fibers treated by 5 g./l. of Na HPO is 9.6 per 2.5 cm.

TABLE 4 Wet Loop NazHPO4 Denier Tenacity Elongation tenacity (g-l (g-/ (p D A viscose and a spinning bath same as Example 3 are used. After the stretching, the threads are cut in desired length. The cut fibers are treated at 65 C. for 1 minute by liquors containing various quantities of Na CO and are successively treated at 90 C. passing through a hot acid bath to fix the inner structure of the fibers.

The results are shown in Table 6 in comparison with the non-treated fibers. By these treatments the curled taining 2.8 g./1. of sulphuric acid during the stretching. After cutting in desired length, the out fibers are treated at 55 C. by a liquor containing 5 g./l. of Na HPO and are then treated at C. by passing them through a hot acid bath containing 3 g./l. of sulphuric acid to fix the inner structure of the fibers.

The results are shown in Table 7 in comparison with the non-treated fibers and those fibers obtained from acidliquor-treatment only. In this experiment, the curled fibers are obtained from the combined treatments.

TABLE 7 Wet Loop Denier Tenacity Elongation tenacity Method of treatment (d.) (g./d.) (percent) (KM) Blank 1. 67 3. 59 13. 6 4. 9 One step treatment by acid liquor 1. 63 3. 66 12. 7. 2 Two-step-treatment by acid liquor and NazHOlh- 1.69 3. 54 14. 9 l3. 1

EXAMPLE 7 A viscose having a ball-falling viscosity of 450 sec. and a y-value of 72 is spun at 31 C. in a spinning bath containing 18.4 g./l. of sulphuric acid, 60 g./l. of sodium sulphate, and 0.4 g./l. of zinc sulphate. The tow is treated on the stretching device at 16 C. by a liquor containing 3.1 g./l. sulphuric acid and 0.3 g./l. of dimethyl stearyl B-hydroxyethyl ammonium chloride, and are successively treated by an aqueous liquor containing 0.5 g./l. of the above-mentioned surface active agent. After cutting the tow, the cut fibers are treated at 40 C. for 2 minutes by a liquor containing 3 g./l. of Na HOP and are immediately treated at 90 C. on passing through a hot acid bath to fix the inner structure of the fibers.

The result is shown in Table 8 in comparison with the non-treated fibers. Curled fibers are also obtained by this three-step-treatment.

What is claimed is:

1. In a process for the production of cellulose fibers by spinning a viscose of DR above 450, 'y-value of from 50 to 80, salt index of from 15 to 20 and a viscosity of above 300 into a spinning bath containing from 5 to 50 g./l. H 80 from 20 to 80 g./1. sodium sulphate and from 0.2 to 1.0 g./l. zinc sulphate at a temperature of from 20 to C., stretching the filaments in air to a draw ratio of from 1.5 to 3.0, treating the filaments in a bath which is substantially neutral and having a temperature of from 10 to C., further treating the fibers thus obtained in a bath of from 30 to C. With an alkaline solution of a salt having a pH of from 8 to 10.5 and fixing the fibers in a hot acid bath containing from 2 to 10 g./l. H 80 having a temperature of from 50 C. to C., the finished fibers having a curl of 9 to 10 per 2.5 cm.

References Cited UNITED STATES PATENTS 2,208,965 7/1940 Dousma 8137.5 3,340,340 9/1967 Mytum 264188 3,352,957 11/1967 Dorsch et al. -264196 3,364,290 1/1968 Dufena et al. 264-495 3,419,652 12/1968 KulOta 264168 3,084,021 4/1963 Morimoto 264-197 3,324,216 6/1967 Inoshita et al. 264-197 3,341,645 9/1967 Horiuchi et al. 264-496 3,320,117 5/1967 Aoki et al. 264-488 JAY H. WOO, Primary Examiner US. Cl. X.R.