Masaharu, Shimamura (Iyo-gun, JP)
Hideharu Minakuchi (Iyo-gun, JP)
Hiroshi Sakai (Iyo-gun, JP)
Tsutomu Kuwabara (Iyo-gun, JP)
Kazuo Yuki (Iyo-gun, JP)
Takao Okawa (Iyo-gun, JP)
Tamio Abe (Iyo-gun, JP)

04/748821

11/16/1971

07/30/1968

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264/77

264/177.130, 425/465, 264/182

D01D5/253; D01F6/18; D01D5/00

264/177F,182 18/8SS

3169089	Filaments	February 1965	Miller et al.
3194002	Multifilament yarn of non-regular cross section	July 1965	Raynolds et al.
3187607	Spinneret production	June 1965	Krammede
3249669	Process for making composite polyester filaments	May 1966	Jamieson
3303530	Spinnerette	February 1967	Cobb
3447998	MONO-COMPONENT SELF-CRIMPING ACRYLIC FIBERS AND PROCESS FOR MAKING THE SAME	June 1969	Fitzgerald et al.
3306888	Azo compounds	February 1967	Mortimer
3412191	Method for producing artificial fibers	November 1968	Kotajima et al.

Jay, Woo H.

Sherman, And Shalloway

1. A process for the preparation of acrylic fibers with noncircular cross sections which comprises spinning through noncircular orifices, the perpendicular portions of which are from 0.08 mm. to 0.15 mm. in length, a spinning solution comprising an organic solvent solution of a polymer containing at least 85 mol percent of acrylonitrile, at an extrusion rate of no higher than 10 meters per minutes, said orifices having a shape factor of not less than 16, the shape factor being defined as into a spinning bath which consists of an aqueous solution of an organic solvent at a concentration of 30-60 percent and is maintained at a temperature not higher than 35° C., with a jet stretch of not less

2. The process of claim 1 wherein the organic solvent in the spinning

3. The process of claim 2 wherein the spinning solution is that obtained by polymerization of at least 85 mol percent of acrylonitrile and optionally at least one other monomer which is copolymerizable with acrylonitrile, in an organic solvent consisting substantially of dimethylsulfoxide, in the

4. The process of claim 10 wherein the spinning solution is a liquid mixture of a dimethylsulfoxide solution of polymer (A) consisting of at least 85 mol percent of acrylonitrile and up to 15 mol percent of at least one other monomer copolymerizable with acrylonitrile and having an intrinsic viscosity ranging from 1.0-1.4, with another dimethyl sulfoxide solution of polymer (B) consisting of at least 85 mol percent of acrylonitrile and up to 15 mol percent of at least one other monomer copolymerizable with acrylonitrile and having an intrinsic viscosity ranging from 1.6 to 2.0, the mixing ratio of the polymers (A) to (B) in

5. A process for the preparation of acrylic fibers with noncircular cross sections which comprises spinning through orifices, the perpendicular portion of which are from 0.08 mm. to 0.15 mm. in length, a solution obtained by polymerization of a monomer system consisting of 85 mol percent of acrylonitrile and up to 15 mol percent of at least one other monomer which is copolymerizable with acrylonitrile, in an organic solvent consisting essentially of dimethylsulfoxide, in the presence of azobis-dimethylvaleronitrile catalyst, at an extrusion rate of no higher than 10 meters per minute, said orifices being of the configuration having a shape factor of not less than 16, the shape factor being defined as into a spinning bath which consists of an aqueous solution of an organic solvent at a concentration of 30-60 percent and is maintained at a temperature not higher than 35° C., with a jet stretch of not less than 0.9.

The present invention relates to a process for the preparation of acrylic fibers with odd-shaped sections.

Many proposals have been made in the past concerning the preparation of fibers having cross sections of modified configurations, by wet-spinning of acrylic polymer solution through noncircular orifices. However, in all of those known methods it is difficult to impart to the fibers the cross sections of the configurations identical with those of the noncircular orifices. Furthermore, the methods are subject to numbers of troubles in respect of the preparation of special orifices and operational procedures.

The object of the invention is to provide a process for the preparation of acrylic fibers having cross sections of the configurations identical with, or closely resembling, those of the noncircular orifices, with ease and industrial advantages.

The above object can be accomplished by the present invention which will be explained in detail in the following descriptions.

The process for the preparation of acrylic fibers of odd-shaped sections in accordance with the invention comprises spinning an organic solvent solution of a polymer containing at least 85 mol percent of acrylonitrile, at an extrusion rate of not higher than 10 meters per minute, through odd-shaped orifices of the configuration having a shape factor of not less than 16, the shape factor being defined as into a spinning bath which consists of an aqueous solution of an organic solvent at a concentration of 30- 60 percent and is maintained at a temperature not higher than 35° C., with a jet stretch of not less than 0.9.

The acrylic fibers thus obtained in accordance with the invention possess the cross sections of the configurations identical with, or very similar to, those of the orifices employed. Textile products prepared from the fibers, such as woven or knit goods, exhibit very favorable harshness, hand and a feeling of cool touch, when compared with similar goods prepared from conventional acrylic fibers. Accordingly, the products of the invention are commercially very valuable, particularly as clothing in warm or hot seasons.

The invention now will be explained in further detail.

The polymers containing at least 85 mol percent of acrylonitrile used in the subject process are well known per se, since they have been conventionally used for the preparation of ordinary acrylic fibers. To wit, they include homopolymers of acrylonitrile as well as copolymers of at least 85 mol percent of acrylonitrile with any other component or components which are copolymerizable with acrylonitrile. The most typical of such copolymerizable components include, for example, vinyl monomers such as acrylates, methacrylates, acrylamides, methacrylamides, unsaturated ketones, and vinyl ethers; and also the vinyl monomers containing a sulfonic acid group, carboxyl group, phosphoric acid group, salts of the foregoing, or group of quaternary ammonium salt. Of course the copolymerizable components are not limited to the above examples. More than one of those components may be employed concurrently.

The organic solvent used for dissolving the above polymer to form the spinning solution may be any of those which are conventionally used for acrylic fiber preparation. For example, dimethylsulfoxide (DMSO), dimethylacetamide, and dimethylformamide may be named, among which DMSO being particularly preferred. The viscosity of the spinning solution again may be within the conventionally employed range, viz, 100- 400 poise/45° C. The preparation of the fibers of desired odd-shaped section is easier with the spinning solutions of higher viscosity, but when the viscosity is excessively high, the spinnability of the solution is impaired, and satisfactory commercial productivity cannot be obtained.

It is critical that the extrusion rate at which spinning solution is pumped through the spinneret holes, is not higher than 10 m./min. At a higher extrusion rate, fibers of the desired configuration cannot be obtained. The lower limit of the extrusion rate at the nozzle is determined in consideration of satisfactory productivity, which is normally in the order of 0.5 m./min.

Now the "odd-shaped cross section" will be explained with reference to the attached drawings.

In the drawings:

FIG. 1 is a magnified photograph (400X) showing cross sections of undrawn fibers obtained in one embodiment of the subject process;

FIG. 2 is a magnified photograph (600X) of cross sections of the fibers obtained by drawing and drying the undrawn fibers of FIG. 1;

FIG. 3 is a diagrammatical sketch of a fiber section, shown for explaining degree of modification of the fiber having an odd-shaped cross section; and

FIG. 4 is a rough sketch of an orifice portion of a spinneret employed in one embodiment of this invention, shown in vertical section.

The term, "fiber of odd-shaped section" is intended to cover the fibers having noncircular, normally polygonal cross sections. According to the invention, fibers of polygonal cross section in which no side is concave or depressed, i.e. cross section of convex-polygon, can be easily obtained. Whereas, it is known that normally fibers of convex-polygonal cross sections are hardly obtainable, since during the spinning, cross section of a fiber approaches to a circle due to the surface tension.

According to the invention, spinnerets with orifices of a shape factor not less than 16 are used, whereby the fibers having cross sections of the configurations identical with, or very similar to, those of the orifices can be obtained. The shape factor is defined as follows: While the shape factor of a circle is 12.5, that of an equilateral triangle is 20.8, and that of a regular square is 16. When the shape factor of the fiber cross section is less than 16, the product fibers exhibit little harshness in hand, and consequently have reduced commercial value. The upper limit of the shape factor is not critical, but the preferred value is 30 or less, inter alia, 25 or less.

Orifices of triangular cross section are advantageously used in the invention, since triangular orifices can be easily bored, and the fibers spun therethrough also exhibit excellent hand.

FIG. 1 is an enlarged photograph (400X) of the cross sections of undrawn acrylic fibers spun through orifices of equilateral triangular cross section. The cross sections of the same fibers which are subsequently drawn and dried are shown in the photograph of FIG. 2 with 600X magnification. In both photographs the fibers are recognized to have approximately equilateral triangular cross sections (cf. example 1).

FIG. 3 is a diagrammatical sketch for explaining the degree of modification of the cross section of spun fibers. "Degree of modification" refers to the norm or scale to indicate the degree of deviation of the cross sectional configuration of the fiber leaving the spinning bath, from shape of the orifice employed. FIG. 3 shows an example of using an orifice of equilateral triangular cross section.

In the same drawing, the cross section of the fiber is the area surrounded by the exterior, thick line. The area of the triangle formed by linking the points a, b, and c contacting with the exterior line, i.e., the area filled with diagonal lines, is identified as A ₂ and the areas outside the triangle, i.e., the blank areas within the fiber cross section are identified as A ₁ as a whole. The ares A ₁ and A ₂ are measured. If A ₁ equals zero, the fiber cross section is also an equilateral triangle, and the degree of modification is 100. When the fiber cross section is a perfect circle, the value of A ₁ /A ₂ corresponds to the degree of modification of zero. Based on the foregoing system, the degree of modification is determined from the numerical value of A ₁ /A ₂ . The degree of modification of the fiber shown in FIGS. 1 and 2 can be regarded as 100.

The cross sectional area of one orifice is in the order of 0.003- 0.03 mm. ² , similarly to the cases of conventional acrylic fiber preparation.

FIG. 4 shows, in vertical elevation, the cross section of an orifice portion of a spinneret within the scope of this invention. While a large number of orifices consisting of feed portion (2) of the spinning solution and perpendicular portion (3) for discharge are bored in the spinneret (1), only one orifice is shown in the drawing. We discovered that the preferred length of the perpendicular portion ("L" in the drawing) is not less than 0.08 mm. When it is less than 0.08 mm., the uniformity in the degree of modification of the spun fibers is impaired. Whereas, if the perpendicular portion is excessively extended, the resistance to the spinning solution discharge is markedly increased. Consequently, the appropriate upper limit in the length of the perpendicular portion is approximately 0.15 mm.

As the spinning bath, an aqueous solution of organic solvent is used. The organic solvents of the same group as described as to the preparation of spinning solution are usable. It is preferred that the organic solvent used in the spinning bath is of the identical type with that used for the preparation of spinning solution. The appropriate concentration of the organic solvent in the aqueous spinning bath ranges 30- 60 percent by weight. Satisfactory degree of modification can be imparted to the cross section of the spun fibers at the concentrations lower than 30 percent but such low concentrations tend to invite loss of transparency (opaque) of fibers. Whereas, the concentrations higher than the aforesaid upper limit are disadvantageous in that they invite decrease in the degree of modification of the fiber cross section. Thus the above concentration range is selected, the optimum range being 40- 55 percent.

Furthermore, it is preferred that the temperature of the spinning bath should be maintained at no higher than 35° C. At higher temperatures, the degree of modification in the resultant fiber cross section is decreased.

The jet stretch is required to be not less than 0.9. "Jet stretch" refers to the ratio of the rate at which protofibers are taken out of the coagulation bath, to the linear rate at which dope (spinning solution) is pumped through the spinneret holes. With a jet stretch of less than 0.9, the desired degree of modification cannot be obtained. The greater the jet stretch, the higher the degree of modification. At excessively great jet stretch, however, void formation in the spun fibers is increased, which causes loss of luster in the product as well as decrease in the maximum drawable ratio. Accordingly, drawn fibers of high strength cannot be obtained. From the foregoing considerations, preferably the maximum jet stretch is in the order of 1.5, the optimum range being 1.0- 1.2. While the jet stretch in conventional acrylic fiber preparation normally ranges 0.3- 0.8, considerably higher range of jet stretch is applied in the subject invention.

So far the various conditions to be applied in the practice of this invention have been explained in detail. From the foregoing it may be understood that the object of the invention is achieved only as the combined effect of adopting the above-described conditions. Thus it is possible to produce with ease, commercially valuable acrylic fibers of odd-shaped sections. The process of this invention is entirely novel, having never been practiced in the past. The process furthermore is industrially very advantageous.

In the preparation of the above-mentioned spinning solution a polymer prepared by the ordinary aqueous polymerization may be dissolved in a solvent, or a monomer may be polymerized in a solvent by the solution polymerization method. In the preparation of the acrylonitrile polymer, no specific limitation is given to the polymerization catalyst and initiator to be used and other polymerization conditions, but the conventional polymerization procedures may be applied. However, in case a jet stretch to be adopted is as extremely high as in the present invention, an occurrence of voids is frequently observed in the resulting filaments. Satisfactory results in respect of prevention of the occurrence of such void filaments can be obtained by the use of spinning solutions mentioned hereinbelow.

One of such spinning solutions is obtained by polymerizing acrylonitrile alone or at least 85 mol percent of acrylonitrile with other copolymerizable monomer or monomers, in an organic solvent consisting substantially of dimethylsulfoxide, in the presence of azobis-dimethylvaleronitrile catalyst. Generally, when a high jet stretch is applied, cracks are formed on the fiber surfaces, since the spinning solution discharged from the orifices is strongly drafted while its coagulation is incomplete. The solution of spinning bath tends to nonuniformly enter into the fiber through the cracks, to consequently form voids in the fiber or make the fiber nontransparent. Such objectionable tendency, furthermore, is particularly conspicuous when dimethylsulfoxide is used as the organic solvent, although dimethylsulfoxide has been most commonly employed in conventional acrylic fiber preparation. Again generally speaking, the fibers prepared under application of high jet stretch, particularly the fibers of odd-shaped section, tend to exhibit low tensile elongation and knot strength, and are brittle. Formation of voids in the fibers enhances such tendency. This deficiency is, however, eliminated by the use of the above-specified spinning solutions.

The reason why the use of azobis-dimethylvaleronitrile catalyst contributes to the preparation of favorable spinning solution has not yet been fully clear, but probably the narrow distribution in degree of polymerization of the product polymer and little residual quantity of the catalyst in the solution are closely correlated with the question.

Other preferred type of the spinning solution consists of liquid mixture of a dimethylsulfoxide solution of (A) a polymer containing at least 85 mol percent of acrylonitrile having an intrinsic viscosity of 1.0- 1.4, with another dimethylsulfoxide solution of (B) a polymer containing at least 85 mol percent of acrylonitrile having an intrinsic viscosity of 1.6- 2.0, the ratio of the polymers (A) to (B) in the liquid mixture being 95:5 to 70:30 percent by weight. In the above, the intrinsic viscosity of polymer is measured as to 0.1 N sodium thiocyanate solution in dimethylformamide at 25° C. (g./100 ml.). Using such spinning solutions, formation of voids in the fibers can be prevented even when high jet stretch is applied. It is indeed surprising that the blending of minor quantities of polymer (B) having a high intrinsic viscosity can easily prevent the void formation in the fibers. This effect is not obtained when the intrinsic viscosity of the polymer (B) is less than 1.6. Also when the viscosity exceeds 2.0, operations such as mixing, dissolving, and spinning become objectionably difficult. The above spinning solutions can be readily prepared, for example, by mixing a dimethylsulfoxide solution of the polymer (A) resulting from solution polymerization of acrylic monomer in dimethylsulfoxide, with a similar solution of polymer (B) obtained in the similar manner.

Hereinafter the invention will be more specifically explained with reference to the following examples.

EXAMPLE 1

A DMSO solution of a copolymer composed of 95.6 mol percent of acrylonitrile, 4 mol percent of methyl acrylate, and 0.4 mol percent of sodium allylsulfonate (polymer concentration: 20.3 percent, viscosity: 210 poise/45° C.) was used as the spinning solution, which was spun through a spinneret in which 3,000 orifices of equilateral triangular cross section were provided at random. Thus spun solution was discharged into a spinning bath containing an aqueous DMSO solution maintained at 30° C., at a rate of 80 g./min. The length of perpendicular portion of the orifices was 0.08 mm. In the experiments, DMSO concentration of the spinning bath, extrusion rate of the spinning solution, and the jet stretch were varied as indicated in table 1 below. The degrees of modifications in cross sections of the resultant fibers are also given in the same table. ##SPC2##

FIG. 1 shows the cross sections of the undrawn fibers obtained in the run wherein the spinning bath concentration was 40 percent and the jet stretch was 1.33 (cf. table 1), in 400X magnification. The photograph of FIG. 2 shows the cross sections of the same fibers after subsequent drafting and drying.

From table 1, it can be understood that generally the degree of modification increases concurrently with the increase in spinning draft. At the jet stretch of 0.90 and above, the modified cross-sectional configurations are generally satisfactory, but with the jet stretch of 1.69 and 2.14, the fibers were observed to become nontransparent. The maximum degrees of modification were obtained at the spinning bath concentrations ranging 20- 60 percent inter alia, 30- 50 percent. However, the fibers obtained with the use of spinning bath concentrations of 10 percent and 20 percent were found to be lose transparency (opaque).

The greater becomes the jet stretch, the degree of modification in the fiber section is more satisfactory, but the maximum drawable ratio in drawing the protofiber leaving the spinning bath is decreased. Therefore, the correlation between the jet stretch and maximum drawable ratio is tested the next. In the experiments, 50 percent aqueous DMSO solution was used as the spinning bath, and the jet stretch was varied for each run. Specific jet stretches and the maximum drawable ratios of the corresponding fibers were as indicated in table 2 below.------------------ ---------------------------------------------------------TAB LE 2 Jet stretch 0.45 0.90 1.50 1.69 2.14 Maximum drawable ratio 9.5 8.0 7.0 6.3 4.4 ____________________________________________________________ _____________ _

Considering the foregoing results collectively, the optimum spinning bath concentration ranges 30- 60 percent, and the preferred jet stretch is at least 0.9 , preferably up to 1.5.

EXAMPLE 2

Employing the identical spinning solution and spinneret with those used in example 1, spinning was performed while the spinning bath temperature was varied within the range of 20° - 50° C., in order to observe the corresponding variation in the fiber solution. The extrusion rate of the spinning solution was 2.5 m./min., the jet stretch was 1.20, and the spinning bath concentration was 50 percent. The results of the experiments are given in table 3. Spinnability was generally improved with the rise in the bath temperature, and consequently the productivity also is improved. However, lower temperature more favorably affected the formation of odd-shaped section. Thus, the results given in table 3 also clearly indicate that the suitable spinning bath temperature is not higher than 35° C.------------------------------------------------- --------------------------TABLE 3 Spinning bath temp. (°C.) 25 30 35 40 50 Degree of modification 94 90 83 56 32 ____________________________________________________________ _____________ _

EXAMPLE 3

Employing the identical spinning solution and spinneret with those used in example 1, spinning was performed, while the output and takeoff velocity were varied to change the spinning rate at the orifices in each run. As the result, an interesting fact was discovered that even under a same spinning draft, variation in output quantity, i.e., the extrusion rate, of the spinning solutions appreciably affects the formation of odd-shaped section. The results of the experiments are shown in table 4. The suitable extrusion rate of the spinning solution at the orifices for forming satisfactory fibers with odd-shaped section is 10 m./min. and below. This fact means that a certain limit exists in the productivity of fibers with odd-shaped section, and also that the section of appropriate spinning conditions is very important for the preparation of high quality fibers with odd-shaped section, with satisfactory productivity. ##SPC3##

In the above experiments, the spinning bath concentration was 50 percent and the bath temperature was 30° C.

EXAMPLE 4

A DMSO solution of a copolymer composed of 95.0 mol percent of acrylonitrile, 4.5 mol percent of methyl acrylate and 0.5 mol percent of sodium allylsulfonate (concentration: 21.4 percent, viscosity: 236 poise/45° C.) was diluted to provide a spinning solution with a viscosity of 80 poise/45° C. Both the first-mentioned solution and the diluted spinning solution were respectively fed through a spinneret in which 3,000 rectangular orifices were randomly disposed. In each orifice the ratio of the longer side to the shorter side was 1:3, and the shape factor was 21.3. The solutions were thus spun into a 45 percent aqueous dimethylacetamide solution of 30° C., with a extrusion rate at the orifices of 5.5 m./min. and the jet stretch of 1.1. The fibers resulted from the original solution of 236 poise/45° C. maintained uniform and very distinct odd-shaped section, but the diluted spinning solution gave only the fibers of unsatisfactory cross-sectional configurations.

EXAMPLE 5

A DMSO solution of an acrylic copolymer composed of 95.0 mol percent of acrylonitrile, 4.5 mol percent of methyl acrylate, and 0.5 mol percent of sodium allylsulfonate (concentration: 20 percent, viscosity: 210 poise/45° C.) was spun through a spinneret having 30,000 equilateral triangular orifices, at the extrusion rate of 6 m./min., into a 50 percent aqueous DMSO solution of 25° C. The jet stretch was 1.0. When the length of the perpendicular portion of the orifices was 0.08 mm., fibers of sufficiently uniform odd-shaped cross section were obtained, but when the length was shortened to 0.06 mm., approximately 5 percent of rejects resulted. Minute examinations proved that the rejects were mainly spun out from the central portion of the spinneret.

The above experiments were repeated under a jet stretch of 1.2. In that case, fibers of satisfactorily uniform odd-shaped cross section were obtained when the length of the perpendicular portion of the orifices was 0.12 mm. When the length was as short as 0.04 mm., however, approximately 6 percent of rejects were found to be present in the product.

EXAMPLE 6

22.7 parts of acrylonitrile, 1.45 parts of methyl acrylate, 0.30 part of sodium allylsulfonate, 0.05 part of azobis-dimethylvaleronitrile (ADVN), 0.02 part of sulfuric acid, and 0.08 part of dodecylmercaptan were dissolved in 74.5 parts of DMSO. Thus-formed liquid mixture was passed through three polymerization vessels which were maintained at 55° C. in succession, at a flow rate of 5 liters/hour. The degree of polymerization of the resultant polymeric solution (a) was 74 percent. In the solution (a), residual catalyst was substantially undetectable. The unreacted monomer was continuously removed from the solution by means of a vertical film evaporator. The property data of the resultant polymeric solution were as follows: polymer concentration: 19.5 percent; solution viscosity: 180 poise/45° C., and intrinsic viscosity [η]: 1.38. The ratio of Pw/Pn of this polymer was 1.24, where Pn is the number average degree of polymerization and Pw is the weight average degree of polymerization.

Separately, a spinning solution (b) was prepared by an ordinary solution polymerization procedure in DMSO, of acrylonitrile as the first component, methyl acrylate as the second component, and sodium allylsulfonate as the third component, in the presence of azobis-isobutyronitrile (AIBN) as the polymerization catalyst. The Pw/Pn of this second polymer was 2.20. The property data of this spinning solution were as follows: intrinsic viscosity [η]: 1.30; polymer concentration: 20.5 percent, and the solution viscosity: 192 poise/45° C. The above two solutions were each spun through a spinneret having equilateral triangular orifices at various supply rates, into a 50 percent aqueous DMSO solution of 23° C., with a jet stretch of 1.0. The take off velocity was 5 m./min. The resultant fibers were drawn by 6X in glycerin of 120° C., washed with water, and dried at 140° C. with 10 percent relaxation. After that crimping treatment, the fibers were cut to provide staple fibers of approximately 3, 5 and 7 deniers.

The cross sections of the fibers were of substantially identical configuration with that of the orifices. The physical properties of the products are given in table 5. ##SPC4##

As can be understood from the above results, the polymeric solution prepared with ADVN catalyst gave the better results compared with the solution from conventional polymerization with AIBN catalyst.

The void ratio percent was measured as follows: 200 strands of the filaments were evenly collected and passed through a small hole in a thin copper plate. The protruding ends from the two surfaces of the copper plate were cut off, and the number of fibers in which voids were found upon microscopic observation of their cross sections was counted. The void ratio was determined in accordance with the equation below:

Those fibrous materials were subject to a spinning quality test under ordinary spinning conditions. As the result, the fibers from the solution polymerized in the presence of ADVN catalyst exhibited better spinning quality in comparison with the fibers prepared with the use of AIBN catalyst. Occurrence of waste fibers was much less in case of spinning the former.

EXAMPLE 7

The polymeric solution (a) obtained from the polymerization with the use of ADVN catalyst as described in example 6 was spun through various spinnerets which are provided with equilateral triangular orifices, into a 50 percent aqueous solution of DMSO of 30° C., under various jet stretch as 1.0, 1.15, and 1.30. The as-spun fibers were drawn, washed with water, and dried under the same conditions as employed in example 6. All the products had triangular cross sections, and had the properties as given in table 6 below.--------------------------------------------------- ------------------------TABLE 6 Jet stretch 1.0 1.15 1.30 Denier (d.) 2.95 2.99 3.04 Dry strength (g./d.) 3.84 3.89 3.69 Dry elongation (%) 24.1 24.5 23.0 Knot strength (g./d.) 1.99 2.02 2.10 Void ratio (%) 1.0 2.0 3.5 ____________________________________________________________ _____________ _

The products exhibited favorable properties compared with those of the fibers from the spinning solution (b) of example 6, which was polymerized in the presence of AIBN catalyst.

The spinning quality test of those products also gave satisfactory results.

EXAMPLE 8

The polymeric solution (a) and (b) as obtained in example 6 were mixed under thorough stirring at various mixing ratios specified in table 7. The resultant mixtures were deairated, and used each as the spinning solution, which was spun through a spinneret with equilateral triangular orifices, into a 50 percent aqueous DMSO solution of 25° C., at a jet stretch of 1.05. The as-spun fibers were take off velocity of 6 m./min., drawn by 5.8X in a glycerin bath of 120° C., washed with water, and dried at 150° C. The void ratios of the resultant fibers of 8 deniers were determined as shown in table 7 below.------------------------------------------------------ -------------- -------TABLE 7 Mixing ratios of polymeric solutions (%) Void ratio (%) (a):(b) ____________________________________________________________ _____________ _ 100:0 2.9 75:25 2.8 50:50 11.1 25:75 14.5 0:100 14.9 ____________________________________________________________ _____________ _

From the above results, it can be understood that the higher mixing ratio of polymeric solution (a), in which ADVN was used as the polymerization catalyst, contributes to lessen the void ratio.

EXAMPLE 9

A solution A of a ternary copolymer compose of 97.70 mol percent of acrylonitrile, 2.0 mol percent of methyl acrylate, and 0.30 mol percent of sodium allylsulfonate was prepared by solution polymerization in DMSO in the presence of azobisisobutyronitrile (AIBN) as the polymerization catalyst. The copolymer concentration was 20.4 percent. The intrinsic viscosity of the product copolymer [η] was 1.230.

Separately, another copolymer solution B (concentration: 21.0 percent) was prepared in the similar manner to the above, the composition of the copolymer being 97.70 mol percent of acrylonitrile, 2.0 mol percent of methyl acrylate and 0.30 mol percent of sodium allylsulfonate. The intrinsic viscosity [η] of this copolymer was 1.80.

The solutions A and B were mixed at various ratios as indicated in table 8, and each liquid mixture was spun through a spinneret with equilateral triangular orifices into a 50 percent aqueous DMSO solution of 20° C. at various jet stretches as 1.08 and 1.33. The as-spun fibers were take off velocity of 5.5 m./min., drawn by 5.8X in a glycerin bath of 120° C., washed with water, and dried thoroughly in hot air current of 145° C. The cross sections of each 200 strands of thus-obtained filaments were examined through a microscope, and the number of filaments containing voids were counted to determine void ratio (percent). The results are given in table 8.

The results indicate that the void ratio can be remarkably decreased by the use of spinning solutions prepared by mixing conventional polymeric solution with a polymeric solution of high degree of polymerization, and that consequently the fiber properties can be conspicuously improved---------------------------------------------------- -------------- ---------TABLE 8 Mixing ratio (%) Void ratio (%) Run No. Polymer Polymer Jet stretch Jet stretch A B (1.08) (1.33) ____________________________________________________________ _____________ _ 1 100 0 11.9 21.7 2 95 5 9.7 16.1 3 90 10 5.1 10.6 4 85 115 4.3 7.2 5 80 20 2.1 5.0 ____________________________________________________________ _____________ _

example 10

a polymeric solution of identical polymer composition with that of the solution B of example 9 was prepared, however at a polymer concentration of 20.8 percent. The polymer had an intrinsic viscosity [η] of 1.60. This solution was mixed with the polymeric solution A of example 9, at a ratio of 30 percent based on the resultant mixture. The liquid mixture was spun under identical conditions with those employed in example 9. The void ratio in the resultant fibers was 1.8 percent under the jet stretch of 1.08, and 4.3 percent when the jet stretch was 1.33.