US3419652A - Process for producing highly crimped fibers - Google Patents

Description

United States Patent ()fifice 3,419,652 PROCESS FOR PRODUCING HIGHLY CRIMPED FIBERS Masaichi Kubota, Atsushi Kawai, and Seiichi Omoto, Ohtake-shi, Japan, assignors to Mitsubishi Rayon Co., Ltd., Tokyo, Japan No Drawing. Filed Sept. 1, 1964, Ser. No. 393,784 Claims priority, application Japan, Sept. 10, 1963, 38/ 47,835 16 Claims. (Cl. 264--168) ABSTRACT OF THE DISCLOSURE A process for producing highly crimped viscose fibers which includes extruding a viscose containing at least 4% cellulose, and having a viscosity of from 100 to 1000 poises and a salt point of at least 16, into a coagulating bath containing zinc sulfate, formaldehyde and a small amount of sulfuric acid, stretching the thus formed fibers in an aqueous bath at a temperature of from 66 to 88 C. under substantially tensionless conditions, and relaxing the stretched fibers in an aqueous bath at a temperature of from 30 to 70 C.

This invention relates to highly crimped viscose fibers having good dimensional stability and nonuniform crosssectional structure and to a process for producing the fibers.

Conventional crimped viscose fibers have had a serious defect in that they have not been dimensionally stable. Moreover their crimp characteristics have not been satisfactory. Many attempts have been proposed to overcome these defects, but none of them have heretofore been successful, especially with regard to dimensional stability.

Recently there have been developed high-wet-modulus fibers (polynosic fibers) which have improved dimensional stability. These fibers are produced generally by extruding a viscose of high viscosity and of high gamma value into a coagulating bath of low acid and low salt content. Since coagulation of viscose is slow under these conditions, the cross section of the fibers is circular and the cross-sectional structure is uniform. As in the case of conventional crimped viscose fibers, it is possible to give polynosic fibers some extent of crimp by stretching the fibers as they emerge from a coagulating bath, cutting to staple length and then relaxing the fibers in an aqueous bath. However on account of uniform cross-sectional structure, the percentage crimp thus obtained is generally less than 5 percent and it is difficult to make it more than 6 percent. Moreover the crimp of these fibers is lost by applying only a small load and the crimp cannot be re covered by removing the load. Accordingly it is essentially impossible for polynosic fibers to be used as crimped fibers.

There is also another known process in which a viscose containing cellulose of a high degree of polymerization is extruded into a coagulating bath of low acid and low salt content, the extruded fibers are stretched progressively by passing several godet rolls and the stretched fibers are subjected to relaxation to develop crimp. Since the fibers obtained by this process have a uniform cross-sectional structure, they cannot develop satisfactory crimps. Moreover, these fibers have a low knot strength. On account of these drawbacks, they have never been commercialized.

3,419,652 Patented Dec. 31, 1968 An object of the present invention is, accordingly, to provide a process for producing highly crimped viscose fibers having good dimensional stability and non-uniform cross-sectional structure. Another object of the present invention is to provide a process for producing viscose fibers of superior crimp, i.e., high crimp number, high percentage crimp and high crimp elasticity. A further object of the present invention is to provide a process for producing viscose fibers having superior fiber properties.

These and other objects are attained in accordance with the present invention wherein a viscose which contains 4 weight percent of cellulose, and has a viscosity of from 100 to 1000 poises and a salt index (salt point) of more than 16, is extruded into a coagulating bath containing from 0.05 to 0.5 g./l. of zinc sulfate, from 10 to 250 g./l. of sodium sulfate and from 6 to 20 g./l. of formaldehyde and sulfuric acid having such a concentration as defined in the following formulas, the fibers thus formed are Withdrawn from said bath and stretched in a bath of water or diluted aqueous acid solution at a temperature from 60 C. to 88 C., under substantially tensionless conditions and to a percent stretch as defined in the following formulas and then, before or after cutting into staple length, subjected to relaxation in a bath of water or diluted aqueous acid solution at a temperature of from 30 C. to C. to develop crimps.

Minimum concentration of sulfuric bath (g./l.)=2A+4 Maximum concentration of sulfuric bath (g./1.)=7A+8 Minimum stretch percent=2T+3.3F96

Maximum stretch percent=4T+6.6F144 acid in coagulating acid in coagulating wherein (percent) by weight in The fibers produced by the present invention have remarkably superior crimp characteristics. For example, they can have more than 12 crimps per inch, more than 9 percent crimp and more than percent of crimp elasticity. Crimp stability is better than that of conventional crimped viscose staple fibers. Crimp recovery in Water is also superior. These superior properties are due to the nonuniform structure of fiber cross section. It is surprising that fibers produced at the extremely slow coagulating conditions of viscose as in the present invention show the same nonuniform cross-sectional structure as those produced by the so called conjugate spinning process. As hereinafter described, such advantages can only be gained by a specified combination of various conditions of the viscose, coagulating bath, stretching bath and crimping bath, all of which are significant points of the present invention.

Fibers produced according to the present invention not only have superior crimp characteristics but also have exceedingly superior mechanical properties. This is, tenacity, elongation and wet modulus of the fibers are about the same as those of the latest known polynosic fibers. Dry

tenacity is about 4 g./d., wet tenacity is about 3 g./d., their dry elongation is about from to percent and their wet modulus is 1 g./d. or more. Accordingly, the fibers produced by the present invention have good dimensional stablity and can stand repeated washing. Knot strength and abrasion resistance are also excellent. Water retention is about 70 percent. This value is about the same or slightly higher than that of latest polynosic fibers and it is a sufiicient value for water resistance and dimensional stability. The fact is that the fibers of the present invention are not low in water retention dyeing properties. It is a feature of the fibers of the present invention that the skin layer is biassed, the core is exposed to the outside and the fiber cross sectional structure is as nonuniform as that of the so-called conjugate spinning fibers. On account of their superior crimp characteristics and excellent mechanical properties, the present fibers have good spinability to yarn and can be used in a wide variety of fabrics with or without synthetic or cotton fibers. Fabrics converted from the present fibers have comfortable hand, high slip-resistance, high dimensional stability and superior mechanical properties.

A process having similarity to the present invention is I disclosed in Japanese Patent No. 452,141. This process relates to producing fibers having dry tenacity of more than 5 g./d., wet tenacity of more than 4 g./d., water retention of less than 55 percent and circular cross-sectional structure by extruding a viscose containing cellulose of a high degree of polymerization, having high viscosity and high gamma value into a coagulating bath of relatively low acid concentration containing formaldehyde and subsequently subjecting the extruded fibers to a high extent of stretch in a hot aqueous bath. However, since the crosssectional structure of the fibers produced by the abovementioned method is uniform, it is impossible to produce highly crimped fibers. Furthermore, fibers having a strength of more than 5 g./d., and water retention of less than 55 percent cannot be obtained when the fibers extruded by the above-mentioned method are stretched under substantially tensionless conditions. On the other hand, the present invention relates to a process for producing highly crimped fibers having nonuniform crosssectional structure using a specified viscose, coagulating bath and stretching conditions. It is impossible to produce the highly crimped fibers of the present invention by use of the method of the Japanese patent.

In the practice of the present invention, it is necessary that the cellulose concentration in the viscose is more than 4 percent by weight. When it is lower than 4 percent, development of crimps is not satisfactory. Preferable cellulose concentration is from 6 to 10 percent by weight. The alkali concentration in the viscose is preferably from 2 to 8 percent by weight and more preferably from 3 to 6 percent by Weight. The ratio of alkali to cellulose is particularly preferable when it is in the range of from 0.521 to 0.7: 1. The viscosity of the viscose must be in the range of from 100 to 1000 poises. Beyond this range, development of crimps is not satisfactory. Most preferably, the viscosity is from 200 to 700 poises. In the present invention it is possible to produce highly crimped viscose fibers having superior mechanical properties without employing cellulose of an especially high degree of polymerization. The salt index of the viscose to be used in spinning must be higher than 16. With a value less than 16, satisfactory crimp development cannot be obtained. Most preferably, the salt index is from to 23.

The coagulating bath must contain sulfuric acid, sodium sulfate, Zinc sulfate and formaldehyde.

The concentration of sulfuric acid is calculated in accordance with the concentration of alkali in the viscose. When the alkali concentration in the viscose is A (percent), the sulfuric acid concentration must be in the following range:

Minimum sulfuric acid concentration g./l. =2A +4 Maximum sulfuric acid concentration (g./l.) =7A+ 8 For fibers having deniers of 2 or less than 2, it is preferable to use the following range of sulfuric acid concentration:

Minimum sulfuric acid concentration (g./l.) =2A+4 Maximum sulfuric acid concentration (g./l.) =3A+8 and for fibers having deniers more than 2, it is preferable to use the following range of sulfuric acid concentration:

Minimum sulfuric acid concentration (g. /l.) =4A+4 Maximum sulfuric acid concentration (g./l.) =7A+8 At a concentration lower than the above-defined range, development of crimps is not satisfactory and spinning operations are difiicult. At a concentration higher than that range, deveolpment of crimps become impossible.

The concentration of sodium sulfate must be from 10 to 250 g./l., preferably from 50 to g./l. for fibers having deniers of 2 or less than 2 and preferably from to g./l. for fibers having deniers of more than 2. The concentration of zinc sulfate must be from 0.05 to 0.5 g./l. When the coagulating bath contains less than 0.0 5 g./l. of zinc sulfate or it does not contain zinc sulfate at all, the development of crimps becomes insufficient and When the bath contains higher than 0.5 g./l. of Zinc sulfate extruded fibers stick together and thus, crimps can not be developed. Most preferably, the concentration of zinc sulfate is from 0.1 to 0.3 g./l. It is possible to replace Zinc sulfate with cadmium, sulfate or nickel sulfate but ammonium sulfate or magnesium sulfate is not effective.

The formaldehyde concentration must be from 6 to 20 g./l. At concentrations lower than 6 g./ 1., develop- Inent of crimps is not sufficient and at concentrations higher than 20 g./l., crimp development becomes insufficient. Most preferably, the concentration of formaldehyde is from8 to 15 g./l.

The temperature of coagulating bath is preferably from 15 C. to 25 C. The length of immersion in the coagulating bath is suitably in the range of from 20 cm. to 60 cm. Fibers emerging from the coagulating bath can not develop sufficient crimps unless they are stretched under conditions of high gamma value. When the gamma value of the viscose to be spun is 78, the gamma value of fibers emerging from the coagulating bath is from 60 to 75 to be most suitable. The preferred gamma value of fibers emerging from the coagulating bath for the development of crimps is in the range of 60 to 80.

Fibers emerging from the coagulating bath are subjected to stretching in an aqueous stretching bath. The temperature of the stretching bath must 'be from 60 C. to 88 C. If it is outside this range, suflicient crimps cannot be developed. A particularly preferred temperature of the stretching bath is from 70 C. to 83 C. A water bath may be used but an aqueous bath containing a low concentration of sulfuric acid is preferably used as the stretching bath. An aqueous bath containing sulfuric acid salts may also be used. A stretching bath having a sulfuric acid content of about 10 g./l. is most preferable. The percent stretch in the stretching bath is dependent upon the temperature of the stretching bath and the formaldehyde concentration in the coagulating bath.

The upper and lower limits of the percent stretch are decided according to the following formulas, in which T C.) is the temperature of the stretching bath, and F (g./-l.) is the concentration of formaldehyde in the coagulating bath.

Minimum stretch (percent)=2T-]-3.3F-96 Maximum stretch (percent) =4T+6.6F 144 Maximum stretch (percent) is preferably 3T+6.6F-128 for fibers having deniers of 2 or less than 2.

The above two formulas have been empirically derived from many experimental results. When the percent stretch deviates from the upper and low limits defined in the above formulas, development of crimps becomes difficult. The tension applied to the fibers in the stretching bath is not more than 0.2 g./d. and preferably, it is from 0.05 to 0.02 g./d. This is a significant point of the present invention. When the stretching tension exceeds 0.2 g./d. it is impossible to produce fibers having non-uniform cross-sectional structure and accordingly it is impossible to develop crimps.

The fibers stretched as described above are subjected to relaxation in an aqueous bath to develop crimps. The temperature of the relaxation bath must be in the range of from 30 C. to 70 C. Outside this range, development of crimps becomes insufiicient and properties of resulting fibers are poor. Preferably, the temperature of the relaxation bath is from 40 C. to 60 C. The relaxation bath can be water for a diluted acidic aqueous bath. The fibers may be treated with a diluted acidic solution at a temperature higher than 70 C. to complete regeneration after development of crimps. The fibers may be cut to staple length after development of crimps but are preferably out before development of crimps.

If the crimped fibers obtained by the present invention are treated with from 2 to 4 percent by weight of a dilute aqueous sodium hydroxide solution at room temperature after completing regeneration, the crimp characteristics may be improved.

The invention is illustrated by the following examples.

EXAMPLE 1 Wood pulp sheets were steeped in 17.5 weight percent aqueous caustic soda solution at a temperature of 20 C. for 1 hour and squeezed out to a weight 2.8 times the original weight of pulp. Then the squeezed out pulp sheets were shredded at a temperature of 20 C. for 1 hour to obtain crumbs of alkali cellulose. After ageing, the alkali cellulose was added to 55 percent, based upon the weight of cellulose, of carbon disulfide. After xanthation at a temperature of 26 C. for 2 hours, the xanthated alkali cellulose was dissolved in aqueous caustic soda solution and water, whereby viscose containing 8 percent by weight of cellulose and 4 percent by weight of alkali was produced. The degree of polymerization of cellulose in the viscose was 360. a

After being filtered, this viscose was cooled, deaerated, ripened, and extruded through spinnerets at a viscosity of 250 poises, a salt index of 20 and a gamma value of 80 into a coagulating bath containing 14 -g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 14 g./l. of formaldehyde at a temperature of 20 C. The length of bath immersion was 33 cm. and the gamma value of fibers emerging from the coagulating bath was 64. The fibers were stretched to 150 percent of their original length, namely to a stretch ratio of 2.50:1, in a second bath containing 10 g./l. of sulfuric acid at a temperature of 80 C., cut to staple and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps. The crimped fibers were subjected to a convention-a1 refining process. The properties and characteristics of the resulting fibers were as follows.

Denier d 1.9 Dry tenacity g./d 4.2 Wet tenacity g./d 3.2 Dry elongation percent 12 Wet elongation do 16 Dry knot strength g./d 2.4 Water tension percent 73 Wet modulus g./d 1.8 Number of crimps per inch Percentage crimp 9 Crimp elasticity percent 90 EXAMPLE 2 After aging, alkali cellulose produced by a conventional method was added to 55 percent, based upon the weight of cellulose, of carbon disulfide and after xanthation at a temperature of 26 C. for 2 hours, the resulting xanthate was dissolved in aqueous caustic soda solution and water whereby viscose containing 8 percent of cellulose and 4 percent of alkali was obtained.

The resulting viscose was filtered, cooled, deaerated, ripened and extruded at a viscosity of 500 poises and a salt index of 20, into a coagulating bath containing 16 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 8 g./l. of formaldehyde at a temperature of 25 C. The length of bath immersion was 30 cm. and the gamma value of fibers emerging from the coagulating bath was 66. The fibers were cut to staple length and subjected to a stretching and relaxation treatment under the same conditions as in Example 1 to obtain crimped fibers. The properties and crimp characteristics of the resulting fibers were as follows.

Denier d 2 Dry tenacity g./d 4.3 Wet tenacity 'g./d 3.3 Dry elongation percent 10 Wet elongation do 14 Dry knot strength g./d 21 Water retention percent Number of crimps per inch 15 Percentage crimp 9 Crimp elasticity percent 83 EXAMPLE 3 Viscose produced by the method of Example 1 was extruded into a coagulating bath containing 14 g./l. of sulfuric acid, g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 8 g./l. of formaldehyde at a temperature of 25 C. Fibers emerging from the coagulating bath were stretched percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 70 C., cut to staple and subjected to relaxation in a crimping :bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps, and to a conventional refining process. The properties and crimp characteristics of resulting fibers were as follows.

Denier d 1.9 Dry tenacity g./d 3.5 Wet tenacity g./d 2.7 Dry elongation percent 11 Wet elongation do 15 Dry knot strength g./d 1.6 Water tension percent 72 Wet modulus g./d 1.6 Number of crimps per inch 17 Percentage crimp 15 Crimp elasticity percent 75 The fibers produced according to the method of Example 3 were cut into sections and the sections were skindyed. Some sections of the fibers were core-dyed.

Skin dyeing was conducted in an aqueous solution containing 1 percent by weight of J apanol Brilliant Blue 6 BKX (C.I. Direct Blue 1) and 10 percent by weight of sodium chloride at a temperature of 100 C. for 30 minutes, followed by decoloration of the core and dehydration.

Core dyeing was conducted in an aqueous solution containing 1 percent by weight of Solophenyl Fast Blue Green BL (C.I. Direct Green 27) and. 0.3 percent by Weight of sodium sulfate at room temperature for 5 hours, followed by washing with water.

EXAMPLE 4 Alkali cellulose produced by a conventional method was subjected to aging, added to 57 percent, based upon the weight of cellulose, of carbon disulfide, xanthated at a temperature of 26 C. for 2 hours and dissolved in an 1 aqueous caustic soda solution and water to obtain viscose containing 7 percent by weight of cellulose and 4 percent by weight of alkali.

EXAMPLE 5 Viscose produced by the same conditions as in Example 4 to give a salt index of 20, was extruded into a coagulating bath containing 15 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde. Fibers emerging from the coagulating bath were stretched 125 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 70 C., cut to staple length and subjected to relaxation to develop crimps in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. and to a conventional refining process. As controls, spinning was performed at the same conditions as in the present example except that coagulating bath containing 0.5 g./1. of zinc sulfate or no zinc sulfate was used. The properties of the resulting fibers were as follows. When the concentration of zinc sulfate became 1 g./l., fibers stuck together and no crimps were developed.

Concen- Dry Wet Dry tration of Denier tenacity tenacity elongation zinc sul- ((1.) (g./d.) (EL/ti.) (percent) fate (g./l.)

Present invention 0.2 2 3.8 2. 9 11 C ontrol 2 3. 3 2. 5 D0 0. 5 2 3. 6 2. 4 10 Wet Dry knot Number Percentage Crimp elongation strength of crimps crimp elasticity (percent) (g./d.) per inch (percent) (percent) Present invention-.. 13 1. 8 12 79 Control 13 1. 4 7 5 83 12 1. 3 9 6 80 EXAMPLE 6 This viscose was filtered, cooled, deaerated, ripened and extruded at a viscosity of 250 poises, salt index of and gamma value of 87, into a coagulating bath containing 15 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde, at a temperature of 20 C. Fibers emerging from the coagulating bath were stretched 125 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 70 C., out to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps and to a conventional refining process. Crimp characteristics of the resulting fibers were as follows. As a control, fibers were produced by the same conditions as in Example 4 except that viscose ripened at 14 C. and having a salt index of 15 was used. The properties of the resulting fibers were very much the same as in Example 4. Crimp characteristics in both the cases were as follows.

Viscose produced according to the same method as in Example 4 was extruded into a coagulating bath containing 18 g./l. of sulfuric acid, 125 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath were stretched 175 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 85 C., cut to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps and to a conventional refining process. The properties and crimp characteristics of the resulting fibers are shown in the following table. The properties and crimp characteristics of controls produced according to the same conditions except that the concentration of sodium sulfate was 280 g./l. are also shown in the same table. When the coagulating bath did not contain sodium sulfate, fibers stuck together and no crimps were developed.

Salt Number Percentage Crimp index of crimps crimp elasticity per inch (percent) (percent) Present invention- 20 15 11 79 Control 15 7 5 83 Sections of fibers produced according to the present example were dyed as in Example 3.

EXAMPLE 7 The same viscose as in Example 4 was extruded into a coagulating bath containing 18 g./l. of sulfuric acid, 50

g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath were stretched 150 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 80 C., out to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. and to a conventional refining process. The properties and crimp characteristics of resulting fibers are shown in the following table. The properties and crimp characteristics of a control produced by the same method as in the present example except that the concentration of formaldehyde was 5 g./l. are also shown in the same table.

1 0 EXAMPLE 9 The same viscose as in Example 4 was extruded into a coagulating bath containing 16 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 8 g./l. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath were stretched.150 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 80 C., out to staple length and subjected to relaxation in a crimping bath at a temperature of 50 C. to develop crimps and to a conventional refining process. In this instance there is a certain relation between the stretching conditions and tension of the fibers in the second bath. Tension is also 0 when stretching is Formal- When the concentration of formaldehyde became higher than g./l., fibers stuck together.

110 percent, 0.02 g./d. when stretching is 150 percent.

and 0.4 g./d. when stretching is 300 percent. The properties and crimp characteristics of these fibers are as follows Stretch Tension Denier Dry Wet Dry (percent) (g./tl.) (d.) tenacity tenacity elongation (g./d.) (g./d.) (percent) Present invention 110 0. 005 2 3. 5 2. 5 13 150 0.02 2 3. 9 3. 0 10 300 0. 6 2 5. 5 4. 6 8

Wet Dry knot Number Percentage Crimp elongation strength of crimps crimp elasticity (percent) (g./d.) per inch (percent) (percent) Present invention 15 1. 5 17 15 78 Do l3 1. 8 14 12 85 Control 9 2. 2 3 2 95 EXAMPLE 8 EXAMPLE 10 The same viscose as in Example 4 was extruded into a coagulating bath containing 18 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath :were stretched 150 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 80 C., cut to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of C. to develop crimps and to a conventional refining process. The properties and crimp characteristics of the resulting fibers together with those of controls produced by the same conditions as in the present example except that sulfuric acid concentrations were 11 g./l. and 38 g./l. respectively, are shown in the following table.

Viscose prepared under the same conditions as in Example 1 was extruded into a coagulating bath containing 16 g./l. of sulfuric acid, g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath, were stretched percent in a second bath containing 10 g./1. of sulfuric acid at a temperature of 70 C., cut to staple length and subjected. to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps and to a conventional refining process. The properties and crimp characteristics of resulting fibers are shown in the following table. The properties and crimp characteristics of fibers crimped at a temperature higher or lower than those in the present example are added to the table. When the temperatures of the crimping bath is higher than 70 C., fibers stick together.

temperature of 70 C., cut to staple length and subjected to relaxation in a crimping bath containing g./l. of sul- Temperature of Denier Dry Wet Dry Crimping (tl.) tenacity tenacity elongation bath (g./d.) (g./d.) (percent) Present invention 50 2 3.8 2. 9 10 20 2 2.6 1.9 9 70 2 2.4 1.6 11

Wet Dry knot Number Percentage Crimp elongation strength of crimps crimp elasticity (percent) (g./t1.) per inch (percent) (percent) Present invention 12 1. 7 14 12 85 11 1.5 12 11 87 12 1.3 14 15 83 EXAMPLE 11 furic acid at a temperature of 50 C. to develop crimps Viscose prepared under the same conditions as in Example 4 Was extruded into a coagulating bath containing 16 g./l. of sulfuric acid, 75 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 23 C. Fibers emerging from the coagulating bath were stretched 150 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 80 C. cut to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps and to a conventional refining process. Sections prepared from the resulting fibers were skindyed as in Example 3. As controls, nonstretched fibers and fibers stretched by 350 percent were likewise skindyed.

EXAMPLE 12 Viscose produced by the same conditions as in Example 4 to give a slat index of 20, a gamma value of 87 and a viscosity 300 poises was extruded into a coagulating bath containing 27 g./l. of sulfuric acid, 150 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 14 g./l. of formaldehyde at a temperature of C. The fibers emerging from the coagulating bath were stretched 150 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 70 C., cut to staple length and subjected to relaxation in a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. to develop crimps and to a conventional refining process. The properties and crimp characteristics of resulting fibers and conventional crimped fibers are as follows:

and a conventional refining process. The properties and crimp characteristics of the resulting fibers are shown as follows.

Denier d 5.2 Dry tenacity g./d 3.4 Wet tenacity g./d 2.5 Dry elongation percent 14 Wet elongation percent 15 Dry knot tenacity g./d 1.3 Number of crimps per inch 10 Percentage crimp percent 19 Crimp elasticity percent 84 As control, spinning was performed under the same conditions as in this example except that a coagulating bath contaninig 0.5 -g./l. of zinc sulfate or no zinc sulfate was used. In these cases, development of crimps was insufficient. When the coagulating bath contained more than 1 g./l. of zinc sulfate, resulting fibers stuck together and thus development of crimps was also insufficient.

EXAMPLE 14 Viscose produced by the same conditions as in Example 4 was extruded into a coagulating bath containing 30 g./l. of sulfuric acid, 150 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 10 g./l. of formaldehyde at a temperature of 20 C. The fibers emerged from the coagulating bath were stretched 175 percent in a second bath containing 10 g./l. of sulfuric acid at a temperature of 73 0, cut to staple and subjected to relaxation in a Alkali cellulose produced by the same method as in Example 4 was aged, added to percent, based upon the Weight of cellulose, of carbon disulfide, xanthated for 2 hours at a temperature of 26 C. and dissolved in an aqueous caustic soda solution and water to give a viscose containing 8 percent by weight of cellulose and 4 percent by weight of alkali. The viscose was filtered, cooled, deaerateld, ripened rand extruded through spinnerets at a viscosity of 400 poises and a salt index of 20 g. into a coagulating bath containing 30 g./l. of sulfuric acid, 150 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 12 g./1. of formaldehyde at a temperature of 20 C. Fibers emerging from the coagulating bath were stretched 150 percent in a second bath containing 10 g./l. of sulfuric acid at a crimping bath containing 10 g./l. of sulfuric acid at a temperature of 50 C. and conventional refining process. The properties and crimp characteristics of resulting fibers were as follows:

Denier d 5.0 Dry tenacity g./d- 3.8 Wet tenacity g./d 2.9 Dry elongation "percent" 11 Wet elongation percent 12 Dry knot tenacity g./d 1.5 Wet modulus g./d 1.6 Number of crimps per inch 10 Percentage crimp percent 15 Crimp elasticity "percent..- 89

As control, spinning was performed at the same conditions as in this example except that the coagulating bath containing 75 g./l. of sodium sulfate was used. In this case, resulting fibers of deniers stick together and thus development of crimps was insutficient. When the coagulating bath containing more than 250 g./l. of sodium sulfate, development of crimps was also insufficient.

We claim:

1. A process for producing highly crirnped viscose fibers which comprises extruding a viscose containing at least 4 percent cellulose, said viscose having a viscosity of from 100 to 1000 poises and a salt point of at least 16, into a coagulating bath containing from 0.05 to 0.5 g./l. zinc sulfate, from to 250 g./l. sodium sulfate, from 6 to g./l. formaldehyde and a concentration of sulfuric acid of from 2A+4 to 7A+8 wherein A is the alkali concentration in the viscose in percent by weight, withdrawing the fibers thus formed from the coagulating bath and stretching said fibers in an aqueous bath at a temperature of from 60 C. to 88 C. under substantially tensionless conditions to the extent defined in the following formulas:

Minimum stretch percent=2T+3.3F96 Maximum stretch percent=4T+ 6.6F- 144 wherein T is the temperature of the stretching bath C.), and

F is the concentration of formaldehyde (g./l.) in the cogulating bath,

and subsequently subjecting the stretched fibers to relaxation in an aqueous bath at a temeprature of from 30 C. to 70 C. to develop crimps.

2. The process according to claim 1 wherein the stretched filaments are cut to staple length before being subjected to relaxation.

3. The process according to claim 2 wherein the fibers are subjected to complete regeneration in an aqueous acidic solution at a temperature of at least 70 C. and then to treatment in an aqueous alkaline solution.

4. The process according to claim 1 wherein the relaxed fibers are subjected to complete regeneration in an aqueous acidic solution at a temperature of at least 70 C.

5. The process according to claim 1 wherein the cellulose concentration in the viscose is from 6 to 10 percent, the alkali concentration in the viscose is from 3 to 5 percent, the viscosity of the viscose is from 200 to 700 poises, the salt point of the viscose is from 20 to 23 and the de gree of polymerization of the cellulose in the viscose is from 300 to 600.

6. The process according to claim 1 wherein the coagulating bath contains from 0.05 to 0.4 g./l. of zinc sulfate, from 10 to 100 g./l. of sodium sulfate, from 6 to 15 g./l. of formaldehyde and a concentration of sulfuric acid of from 2A+4 to 3A+8.

14 7. The process according to claim 6 wherein the percent stretch is defined by the following formulas:

Minimum stretch percent=2T-|-3.3F96 Maximum stretch percent=3T+6.6F--l28 8. The process according to claim 1 wherein the coagulating bath contains from 0.1 to 0.3 g./l. of zinc sulfate, from 50 to g./l. of sodium sulfate, from 8 to 14 g./l. of formaldehyde and a concentration of sulfuric acid of from 2A+4 to 3A+ 8.

9. The process according to claim 1 wherein the coagulating bath contains from 0.05 to 0.5 g./l. of zinc sulfate, from to 250 g./l. of sodium sulfate, from 6 to 20 g./l. of formaldehyde and a concentration of sulfuric acid of from 4A+4 to 7A+8.

10. The process according to claim 9 wherein the percent stretch is defined by the following formulas:

Minimum stretch ratio percent=2T+3.3F-96 Maximum stretch ratio percent=4T+6.6F-144 11. The process according to claim 1 wherein the coagulating bath contains from 0.1 to 0.3 g./l. of zinc sulfate, from to g./l. of sodium sulfate, from 10 to 16 g./-l. of formaldehyde and a concentration of sulfuric acid of from 4A+4 to 7A+8.

12. The process according to claim 1 wherein the temperatuer of the coagulating is from 15 C. to 25 C.

13. The process according to claim 1 wherein the tension applied to the fibers in the stretching bath does not exceed 0.2 g./d.

14. The process according to claim 1 wherein the tension applied to the fibers in the stretching bath does not exceed 0.1 g./d.

15. The process according to claim 1 wherein the tension applied to the fibers in the stretching bath is from 0.005 to 0.02 g./d.

16. The process according to claim 1 wherein the temperature of stretching bath is from 70 C. to 83 C.

References Cited UNITED STATES PATENTS 3,046,083 7/1962 Bates et a1. 264-168 3,107,970 10/1963 Kusunose et a1. 264197 3,108,849 10/1963 Owash et a1. 264-198 3,109,698 11/1963 Klein et al. 3,226,461 12/1965 Wise et a1. 264-- X DONALD J. ARNOLD, Primary Examiner. J. H. WOO, Assistant Examiner.

US. Cl. X.R.