US3929946A

US3929946A - Process for producing hygroscopic acrylic fibers

Info

Publication number: US3929946A
Application number: US394502A
Authority: US
Inventors: Zen-Ichi Orito; Minoru Uchida; Noriaki Mori
Original assignee: Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Rayon Co Ltd
Priority date: 1970-05-15
Filing date: 1973-09-05
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30

Abstract

Hygroscopic acrylic fibers having high moisture regain and excellent sweat absorbing property together with the excellent characteristics of the acrylic fibers are disclosed. The fibers contain open capillary voids in a content (X) of 4.0 to 63.2 % and have a free surface area (S) of 1.0 X 104 to 1.7 X 106 cm2/g and a contact angle of the surface of the fiber with water of at most 45*.

Description

' United States Patent Orito et al.

[ Dec. 30, 1975 PROCESS FOR PRODUCING HYGROSCOPIC ACRYLIC FIBERS Inventors: Zen-Ichi Orito; Minoru Uchida;

Noriaki Mori, all of Nagoya, Japan Assignee: Mitsubishi Rayon Co., Ltd., Japan Filed: Sept. 5, 1973 Appl. No.2 394,502

Related US. Application Data Division of Ser. No. 143,571, May 14, 1971, now abandoned.

Foreign Application Priority Data May 15, 1970 Japan 45-40910 US. Cl. 264/41; 8/130.l; 264/182; 264/343; 264/341 Int. Cl. B29C 25/00 Field of Search 8/1 15.5, 130.1; 264/343, 264 341, 182, 210 G References Cited UNITED STATES PATENTS 3/1952 Hall et al. 8/1 15.5 6/1959 Bedell 8/ll5.5

Primary ExaminerJay H. Woo Attorney, Agent, or Firm-Ctlshman, Darby & Cushman 57 ABSTRACT Hygroscopic acrylic fibers having high moisture regain and excellent sweat absorbing property together with the excellent characteristics of the acrylic fibers are disclosed. The fibers contain open capillary voids in a content (X) of 4.0 to 63.2 and have a free surface area (S) of 1.0 X 10 to 1.7 X 10 cm /g and a contact angle of the surface of the fiber with water of at most 45.

6 Claims, 3 Drawing Figures PROCESS FOR PRODUCING I-IYGROSCOPIC ACRYLIC FIBERS This is a division of application Ser. No. 143,571, filed May 14, 1971, and now abandoned.

The present invention relates to novel hygroscopic acrylic fibers and a process for producing the same. More particularly, it concerns hygroscopic acrylic fibers whose moisture regain is improved by subjecting l0 the human body under the clothes are normally about v 32C and about 40 to 60 RH, respectively. However,

sweating causes increase of humidity under clothes and when the relative humidity exceeds about 80 one feels uncomfortable. When one wears clothes of nonhygroscopic fibers, sweats in hot environment or when one takes exercises wearing clothes of non-hygroscopic fibers, humidity under the cloth rapidly increases and one feels uncomfortable in short timeIOn the contrary, in case of wearing clothes of hygroscopic natural fibers such as cotton, increase of humidity under the clothes is slow and uncomfortableness is not rapidly caused. This is because cotton has an excellent hygroscopicity and water absorbing property. For example, moisture regain of cotton at 65 RH at C is 7.2 and that of at 93 RI-l at 20C is 16.0 Thus, the difference (A H) in the moisture regains is 8.8 That is, the comfortableness in wearing clothes of cotton is attributed to the fact that the clothes of cotton have the function of controlling the increase of humidity under the clothes due to the great difference in moisture regains between at medium humidity and high humidity. Many attempts have been made to impart hygroscopicity to hydrophobic synthetic fibers such as polyesters, polyamides and acrylic fibers. For example, chemical methods such as copolymerization, graft copolymerization or blending of hydrophilic materials have been attempted as means for imparting hygroscopicity. However, according to these methods, a large amount of hydrophilic materials is required for attaining satisfactory hygroscopicity and hence, there is the defect that when a large amount of hydrophilic materials is incorporated into the polymer the properties of the fibers are degraded. Furthermore, British Pat. No. 812,460 and Japanese Patent Publication No. 538/68 mention a method for imparting hygroscopicity of hydrophobic synthetic fibers by treating them with aqueous sodium hydroxide solution and Japanese Patent Publication No. 4046/61 mentions a method for making fibers porous with foaming agent, etc. after forming of fibers. However, none of these methods can provide satisfactory hygroscopity and furthermore, these methods have defects such as deterioration of fiber properties. Recently, researches have been made on graft polymerization of hydrophilic materials with electron rays. However, there have been problems with apparatus for attaining said purpose. Such being the 2 case, acrylic fibers having hygroscopicity have not yet been industrially obtained by s'aidmethod.

It is an Object of the present invention to provide acrylic fibers having hygroscopicity and sweat absorbing properties comparable to cellulose fibers without damaging the excellent characteristics of acrylic fibers and a process for producing such fibers on an industrial scale.

During the course of investigation, it has been found that use of mechanism of the moisture absorption with capillary condensation is very effective and the hygroscopic fibers of the present invention have been obtained by forming open capillary voids in fibers in a fiber forming step and in accelerating the capillary condensation of moisture into the voids.

That is, the hygroscopic fibers of the present invention comprise acrylonitrile copolymer, contain open capillary voids in a content (X) of 4.0 to 63.2 and have a free surface area (S) of 1.0 X 10" to 1.7 X 10 (cm /g), a contact angle of the.surface of the fiber with water of at most 45. The present fibers preferably have a difference (AH) in moisture regainsbetween at 20C,

93 RH and 20C, 65 RH of higher than 5 and an usual fiber diameter (about 10 p. to 50 1.).

The capillary voids are formed at the stage of removal of solvent and permeating of coagulation liquid when acrylonitrile polymer solution is extruded into coagulation liquid in wet spinning and voids thus formed are maintained in stable state in the fibers without being collapsed. The voids are fine capillaries having a distribution of diameters and different from the macroscopic and uniform hollows as in the hollow fibers. The content of voids is measured as follows:

Firstly, the density of the fibers excluding the open voids is measured by immersing a small amount of fibers in n-heptane, completely permeating n-heptane into the open voids by vacuum suction to 5 mmHg and then placing the fibers into the density-gradient tube. On the other hand, the apparent density of the fibers including the open voids is measured by placing a small amount of fibers in a picnometer, effecting between suction to a high vacuum of about lO mmHG and then enclosing mercury thereinto. Since according to this measuring method, mercury does not enter the voids having a radius of less than 7 u, the apparent density can be measured. The content of voids is calculated in accordance with the following formula.

The fibers which contain capillary voids have generally greater inner free surface as compared with those having no voids. The inner free surface means free surface which takes part in absorption of moisture in fiber structure. The free surface area was measured in accordance with the report of F. M. Nelson by keeping a small amount of sample at a low temperature, adsorbing nitrogen gas in the sample under a certain pressure, estimating the amount of adsorbed nitrogen by gas chromatography and calculating the free surface area in accordance with BET theory (F. M. Nelson, E. T. Eggertsen, Anal Chem, 30 1387 (1958).

It has been found that absorption of moisture into open capillary voids increases with increase of hydrophilic degree of free surface of the voids and that it is necessary for acrylic fibers to make the surface hydrophilic in order to provide fibers of excellent hygroscopicity with the lowest possible voids content. The degree of the hydrophilic property of the surface is indicated by the contact angle of the surface of the fiber with water and is measured by keeping a single fiber perpendicular to the water surface after making it hydrophilic and reading the angle of water surface with the fiber with a microscope.

The hydroscopicity of the fibers is expressed by moisture regain and is measured by weighing the fibers in the absolutely dry state, allowing the fibers to absorb moisture in a desiccator where the humidity is adjusted to a certain relative humidity until the weight of the fibers reaches equilibrium and then weighing the fibers to calculate the moisture regain in accordance with the following formula.

in absolute dry state The difference (A H) in moisture regain is obtained by subtracting moisture regain at 65 RH at 20C from the moisture regain at 93 RH at 20C.

The difference (A H) in the moisture regain of usual acrylic fibers having no voids is about 1 to 2 As the result of various researches on void content, free surface area and contact angle of the surface of the fibers with water for providing desired fiber properties and excellent hygroscopicity in acrylic fibers having usual fiber density, it has been found that a void content (x) of 4.0 x 63.2 a free surface area (s) of 1.0 X 10 cm /g g S 1.7 X l cm /g and a contact angle of the surface of fibers with water of at most 45 are effective for the above mentioned purpose. That is, when the void contact and the surface area exceed said ranges, the balance of fiber properties cannot be kept, mechanical properties decrease and dyeing brightness is lowered. Furthermore, relation between the void content and the free surface area, namely, average size of voids also has an effect on the fiber properties. For example, when the void content is high and the surface area is small, voids of large size are present and hence improvement of hygroscopicity due to capillary condensation is poor and the mechanical properties are also not satisfactory. Improvement of hygroscopicity can be attained when a great number of voids of small size are present and in such case, the fiber properties also tend to be satisfactory.

Referring to FIG. 1, when the void content is lower than straight line AB (void content 4.0 or the free surface area is less than the straight line AD (free surface area l.0 X 10 cm /g), sufficient hygroscopicity cannot be attained under usual conditions. For example, if hygroscopicity is to be increased in the above case, it is necessary to carry out the treatment for making the fibers hydrophilic under severe conditions. However, such treatment results in coloration of fibers, deterioration of mechanical properties. Furthermore, the fibers whose void content is higher than the straight line CD (void content 63.2 or those whose free 4 surface area is greater than the straight line BC (the surface area 1.7 X 10 cm lg) can be produced with difficulty under the usual spinning conditions. Even if such fibers are produced employing special spinning conditions, the mechanical properties are deteriorated and the balance of the fiber properties cannot be kept.

Therefore, the hygroscopic acrylic fibers intended by the present invention can be obtained when the void content and the free surface area of the fibers are within the area surrounded by ABCD and the contact angle of the surface of the fibers with water is at most 45. Furthermore, when the void content is higher than the straight line KJ (X 14.5 within the area ABCD, such high hygroscopicity that A H is more than 8 can be easily obtained. Especially when X and S satisfy the requirements 14.5 g X 63.2 10 g S 10 (cm /g) and log S 2 114/(100 X) 2.90, namely, they are within the area of PQRS, the hygroscopicity, especially the value of A H attained is equal to or more than that of cellulosic fibers such as cotton and rayon and mechanical properties and dyeability are not lowered so much. Furthermore, the acrylic fibers above described can be easily produced on an industrial scale. When X and S have the relation log S 114/(100 X) 2.90, namely, they are in the range of below the curve RS, a hygroscopicity expressed by A H of more than 8 can be attained, but since the average size of voids become larger, the hygroscopicity attained is not so high for the void content and mechanical properties of the fibers are somewhat deteriorated. When the void content is lower than the straight line KJ (X= 14.5 it is difficult to obtain a hygroscopicity expressed by A H of more than 8 under usual conditions. However such hygroscopicity can be obtained by adopting somewhat severe treating conditions for making the surface of the fibers hydrophilic or by employing a copolymer of acrylonitrile with a hydrophilic monomer or blended polymer of such copolymer and acrylonitrile copolymer as a fiber forming polymer. That is, when the void content and the surface area satisfy the relation 8.0 X 5 14.5 and 1.! X 10 S E 1.7 X 10 (cm /g), namely, they are within LGJM, A H of more than 8 can be obtained by treating the fibers comprising conventional acrylonitrile copolymer with modifier under such condition that A H of control fibers having the same compositions and containing no voids becomes more than 2 Alternatively, when the void content and surface area satisfy the relations 6.0 X 2 14.5 and 1.0 X 10 S 1.7 X 10 (cm /g), namely, they are within EFJK, A H of more than 8 can be obtained by treating the fibers comprising the copolymer of blended polymer described above with modifier under such condition that A H of control fibers having the same compositions and containing no voids becomes more than 3 FIG. 2 shows insothermal absorption curves of the fibers of the present invention, cotton fibers and conventional non-hygroscopic acrylic fibers.

In FIG. 2, curve (1) indicates scoured cotton fibers, curve (2) indicates the hydrophilic fibers of the present invention which corresponds to the fibers of Sample No. 43 in Table 3 shown hereinafter, curve (3) indicates the hydroscopic fibers of the present invention which the correspond to the fibers of Sample No. 42 in Table 3 and curve (4) indicates the conventional acrylic fibers obtained by spinning a-copolymer comprising 93 of acrylonitrile and 7 of vinyl acetate by the usual wet spinning method. Curve (1) was obtained using values in the literature [A. R. Urquhart, A. M. Williams, J. Text. Inst. 15, T138 (1924)].

FIG. 3 illustrates the course of moisture absorption and moisture desorption of the fibers according to the present invention and the cotton fibers. The moisture absorption course is obtained by measuring the increment of weight of fibers immediately after introducing the fibers in absolute dry state into a cell in which the humidity is adjusted to C, 93 RH with a saturated aqueous solution of Glaubers salt. The moisture desorption course is obtained by measuring reduction of weight immediately after introducing the fibers in absorption equilibrium at 20C 93 RI-I into a cell which is rendered to the nearly absolute dry state with 95 sulfuric acid. Curve's (a) and (c) in FIG. 3 show the moisture absorption and desorption courses of the cotton'fibers, respectively and curves (b) and (d) indicates the moisture absorption and desorption courses of the fibers of the present invention which corresponds to Sample No. 43 respectively. As is seen from FIGS. 2 and 3, the hygroscopic acrylic fibers of the present invention are comparable to natural fibers having cotton-like properties in both moisture regain and the moisture absorption and desorption rate.

Since the hygroscopic fibers of the present invention are those in which hygroscopicity is given by open capillary voids and by making the surface of the fibers hydrophilic, there are provided characteristics that the hygroscopic effect is durably kept and moisture regain is higher than that of the fibers obtained by other methods.

Further characteristic of the present invention is that the acrylic fibers having said characteristics have water absorbability because they have a great number of open voids. This water absorption amount has a value similar to the voids content in the present invention.

The acrylic fibers in the present invention are those made of an acrylonitrile homopolymer, an acrylonitrile copolymer containing more than 50 by weight of acrylonitrile or a blend thereof. Copolymer components other than acrylonitrile which are copolymerizable with acrylonitrile include; however monoolefinic unsaturated compounds such as acrylic acid or esters thereof, a-chloroacrylic acid or esters thereof, methacrylic acid or esters thereof, e.g., methyl methacrylate, ethyl methacrylate, butyl methacrylate, methoxymethyl methacrylate and B-chloroethyl methacrylate, vinyl chloride, vinyl fluoride, vinyl bromide, vinyllidene chloride, l-chloro-l -bromoethylene, methacrylonitrile, acrylamide, methacrylamide, 2-chloroacrylamide or monoalkyl substituted product of these amides, methyl vinyl ketone, vinyl carboxylic ester, e.g., vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl stearate, N-vinyl imides, e.g. N-vinyl phthalimide and N-vinyl succimide, methylene malonic esters, itaconic acid or esters thereof, N-vinyl carbazole, vinyl furan, alkyl vinyl ethers, vinyl sulfonic acid, ethylene a,B-dicarboxylic acid or anhydrides or derivatives thereof, e.g., diethyl furmaric acid, diethyl maleic acid, diethyl citraconate and diethyl mesconate, styrene, vinyl naphthalene, vinyl substituted heterocyclic amines, e.g., vinyl pyridines, alkyl substituted vinyl pyridines, e.g., 2-vinyl pyridine, 4-vinyl pyridine, 5-methyl-2-vinyl pyridine, l-vinyl imidazole or alkyl substituted l-vinyl imidazoles, e.g., 2-, 4, or S-methyl-l-vinyl imidazole and other polymerizable materials having the C C structure.

6 Higher hygroscopicity can be obtained by using monomers having a hydrophilic property as high as possible line those to be copolymerized with acrylonitrile. The hydrophilic monomers suitable in the present invention are as follows:

The monomers having the gene'ral formula (wherein R is hydrogen or lower alkyl having not more than 4 carbon" atoms, R is R O R R N, R COO, R S, or R,-CONR (wherein R and R are alkyl, aryl or aralkyl groups which may or may not be substituted with substituents having no active hydrogen), A and B are alkylene, arylene or aralkylene groups which may or may not be substituted with substituents having no active hydrogen, Y is and n is an integer of 5 to Illustrative of these monomers are lauroxy polyethylene glycol acrylate [CI-I =CHCO(OCH CH OC l-l nonyl phenoxy polyethylene glycol methacrylate The hygroscopic acrylic fibers of the present invention can be obtained using a wet spinning apparatus used for producing conventional acrylic fibers and can be produced by wet spinning a polymer solution containing acrylonitrile copolymer to produce coagulated fibers having a large number of open capillary voids, stretching the fibers to fix the voids'without collapsing them and subjecting the fibers to a treatment with a modifier. That is, acrylic fibers before being subjected to dry heat treatment generally contain a large number of voids. These voids are collapsed by drying the fibers at a high temperature under tension. On the other hand, according to the process of the present invention, a large number of voids can be maintained in the fibers without collapsing.

It has been found that said fibers having a large num'- ber of open capillary voids exhibit excellent hygroscopicity as compared with the fibers in which voids have been collapsed. However, the hygroscopicity of such fibers is still unsatisfactory and the articles made of these fibers have poor utility because they tend to 7 cause fibrillation and pilling. As the results of intensive researches on production of fibers having further improved hygroscopicity and causing no fibrillation and pilling, it has been found that when the surface of the acrylic fibers having open capillary voids is made hydrophilic with a modifier, capillary condensation of moisture in the voids is accelerated to highly increase hygroscopicity and to obtain useful fibers having low fibrillation and pilling tendency. Furthermore, as the result of researches on relations between properties of the fibers and the ranges of void content (X) and surface area (S) of the fibers whose surfaces are made hydrophilic, it has been found that when X and S are within the range of 4.0 X g 63.2 and 1.0 X 10 S 1.7 X 10 cm /g, namely, within the area of ABCD in FIG. 1, hygroscopic fibers having excellent properties can be obtained.

In more detail, the hygroscopic acrylic fibers of the present invention can be produced by combination of the following steps,

a. preparing a spinning solution by dissolving an acrylonitrile copolymer in a solvent thereof,

b. extruding said spinning solution into aqueous coagulation liquid containing said solvent to form fibers,

0. stretching the thus formed fibers,

d. drying the stretched fibers, and

e. treating the fibers with a modifier.

In said steps, the capillary voids are mostly produced in the step (b) and the content and the size of the voids depend upon compositions of copolymer, compositions of spinning solution, compositions and temperature of coagulation liquid and spinning speed. In general, with rapid coagulation, the number of voids formed is increased. That is, the voids tend to be more easily formed with lower concentration of polymer in the spinning solution and of the solvent in the coagulation liquid, higher temperature of the coagulation liquid and higher spinning speed.

For example, when spinning is carried out employing a polymer concentration of to in a spinning solution containing dimethyl acetamide as a solvent, a spinning speed of 0.5 to 2.5 in terms of jet stretch which is the ratio of take up speed of the first roller to extruding speed from spinneret, a concentration of dimethyl acetamide in dimethyl acetamidewater coagulation liquid of less than 80 and a temperature of the coagulation liquid of higher than 20C, coagulated fibers having a void content of 10 to 70 and a free surface area of 10 to 2 X 10 cm /g are obtained. The fibers having such characteristics can be produced with any commonly used solvents by suitably choosing the spinning conditions. When thus obtained coagulated fibers are stretched while washing them in a boiling water, the void content and the surface area are kept unchanged or somewhat decreased, but most of the voids are maintained without collapsing. If said stretched fibers are subjected to the usual drying treatment, most of the voids therein are collapsed and only a low hygroscopicity is obtained. Therefore, attempts have been made to keep the void content and the surface area as they are in the fibers after stretched. As the results, it has been found that this is accomplished by drying the stretched fibers at a low temperature of lower than 60C or by subjecting them in wet state by annealing with saturated steam at a pressure of less than 2.8 kg/cm gauge and then drying them at a temperature of lower than 110C. The coagulated acrylic fibers in water swollen state are sensitive to heat and therefore, drying of said fibers at a high temperature causes collapse of most of the voids. However, when the coagulated acrylic fibers are dried at a low temperature as mentioned above, open capillary voids are maintained. These drying conditions are applicable to coagulated acrylic fibers obtained by wet spinning with any solvent. Thus, the hygroscopic fibers of the present invention can be obtained by producing coagulated fibers having a void content of more than 4 and a free surface area of more than 10 cm /g by choosing suitable spinning conditions and drying the coagulated fibers under the drying conditions as mentioned above to fix the voids in a content of 4.0 to 63.2 and a free surface area of 10 to 1.7 X 10 cm lg.

Furthermore, it has been found that the treatment with modiifer may be made before or after the drying of the fibers and the contact angle of the surface of the fibers with water or at most 45 is the most effective.

Said treatment with modifier for making the surface of the fibers hydrophilic can be accomplished by forming a hydrophilic layer on the free surface of the fibers by hydrolysis of the fibers with an aqueous solution of alkali metal hydroxide or carbonate, sulfuric acid, hydrochloric acid, or nitric acid, or amidoxime reaction with hydroxylamine aqueous solution of hydroxylamine salts such as hydroxylamine sulfate, hydroxylamine hydrochloride and hydroxylamine phosphate.

If the fibers are colored in said treatment with a modifier, the fibers can be bleached with the usual bleaching agent.

The conditions for the treatment with the above modifiers vary depending upon whether it is carried out before or after drying, and the latter generally requires severe conditions.

As mentioned above, the hygroscopic acrylic fibers of the present invention are produced by any one of the following four methods each of which comprises said steps (a) to (e).

1. Spinning conditions is extruded and the resultant fibers are coagulated and stretched. Thereafter, drying step (d) is carried out at a temperature of lower than 60C and then the fibers are subjected to the treatment with modifiers of the step (e).

2. Spinning solution is extruded and the resultant fibers are coagulated and stretched. Thereafter, the fibers are subjected to the treatment with the modifier of the step (e) and then are subjected to drying step (d) at a temperature of lower than 60C.

3. Spinning solution is extruded and the resultant fibers are coagulated and stretched. Thereafter, the fibers in wet state are annealed with saturated steam at a pressure of lower than 2.8 kg/cm and then are subjected to drying step (d) at a temperature of lower than 1 10C.

4. Spinning solution is extruded and the resultant fibers are coagulated and stretched. Thereafter, the fibers are subjected to the treatment with modifiers of the step (e) and then the fibers in wet state are annealed with saturated steam at a pressure of lower than 2.8 kg/cm Thereafter, they are subjected to the drying step (d) at a temperature of lower than C.

There are no differences in the void content and the surface area attained by the above four methods. However, the methods (3) and (4) have advantages over methods (1) and (2) in that according to the former, dyeability and fibrillation resistance of the resultant 9 fibers are improved in higher degree than according to the latter.

The present invention is illustrated more particularly by way of the following Examples, but as will be more apparent, is not limited to the details thereof.

EXAMPLE 1 contact angle, hygroscopicity of the fibers and other fiber properties are shown in Table 1.

in Table 1, Samples No.1- 8,11,l3,16,17and 19 were within the area PQRS in FIG. 1 and had a A H of more than 8 and good fiber properties. Samples No. 9 and 10 were within the area ABJK and had a A H of less than 8 Samples No. 12, 14 and 15 were in the area below the curve RSP and had somewhat low mechanical properties. Sample No. 18 had a surface area of larger than 10 cm /g and large A H, but somewhat lower dyeing brightness. Samples No. 20, 21 and 23 were comparative samples and had a A H of less than 5 The fibers of Sample No. 22 had a low dyeing brightness and low fibrillation resistance.

Table 1 Coagulation liquid Drying Sample Jet tempera- Void con No. Concentration Temperature Stretch ture tent (X) l 55 60 0.9 40 17.7 2 1.5 27.4 3 2.4 38.4 4 1.3 19.7 5 1.7 22.2 6 80 0.9 17.9 7 65 6O 16.2 8 80 23.1 9 55 40 4.3 10 60 53 8.6 11 50 40 15.7 12 1.3 20.1 13 1.7 28.5 14 2.0 37.4 15 2.0 60 34.1 16 65 40 0.9 40 17.5 17 1.3 26.0 18 1.7 29.5 19 2.0 40.0 20 55 0.9 70 5.0 21 60 1.7 70 24.0 22 70 3O .9 40 33.8 23 80 2.3 Difference Free surface Contact in moisture Denier Dry Dry area (S) angle regain (d) strength elongation x 10" /g) AH (g/ resultant fibers were stretched to 4.5 times the ori inal g 60 EXAMPLE 2 length in boiling water to obtain fiber tows. Then, crimps were mechanically imparted to said tows in the wet state and thetows were cut, into staples and the staples were dried at a temperature of lower than 60C. These staples were immersed in 15 g/l of aqueous sodium hydroxide solution at 70C for 30 minutes to make them hydrophilic and then they were washed with water and dried to produce hygroscopic fibers. Production conditions, void content, free surface area,

1 1 stretched to 5 times the original length in boiling water to obtain tows. Then, the tows were treated in g/l of aqueous solution of sodium hydroxide at 70C for 5 minutes and thereafter were washed with boiling water.

The resultant fibers were mechanically crimped in the wet state and then were cut into staples and dried at a temperature of lower than 60C. Production conditions, void content, free surface area, contact angle, hygroscopicity and other fiber properties of the thus obtained fibers are shown in Table 2.

In Table 2, samples No. 25 31 and 34 were within the area PQRS and had a A H of more than 8 Sample No. 24 had a surface area (S) of greater than 10 cm /g and exhibited somewhat low dyeing brightness. Samples No. 32 35 were in the area below the curve RSP and had somewhat poor mechanical properties. Samples No. 36 to 40 were comparative samples and Samples No. 36, 37 and 40 had a void content of higher than 63.2 and poor mechanical properties. Samples No. 38 and 39 had S of smaller than 10 cm lg and A H 20 of less than 5 12 state. These crimped tows in the wet state were annealed with saturated steam at a pressure of 0.8 to 2.8 kg/cm gauge and were cut into staples and dried at a temperature of lower than 110C. Then, these staples were subjected to treatment with aqueous solutions of sodium hydroxide, sodium carbonate, sulfuric acid and hydroxylamine sulfate, respectively. Production conditions, void content, free surface area, contact angle, hygroscopicity and other fiber properties of the thus obtained fibers are shown in Table 3. In Table 3, Samples No. 41 43, 56 and 56 were within the area PQRS and had a A H of more than 8 Samples No. 44 47 were within the area LGJM, but had a AH of more than 8 because the conditions for treatment with modifier were the somewhat severe condition that the fibers were treated with 15 g/l of NaOH at 100C for 30 minutes. It was found that when control fibers having no voids were subjected to the same treatment, A H of 2.2 was obtained. The control fibers were obtained by the same method as in this Example except that the fibers were dried on a heated roller at 130C to collapse Table 2 Coagulation liquid Drying Sample Jet tempera- Void con- No. Concentration Temperature Stretch ture tent (X) 24 40 0.9 40 20.3 25 0 34.2 26 60 55.0 27 50 20 50 23.7 28 40 32.5 29 60 40.8 30 40 1.3 35.0 31 6O 42.3 32 55 20 1.5 50 41.5 33 40 52.0 34 60 40 61.0 35 80 60 58.6 36 60 40 64.2 37 65.0 38 50 65 45.3 39 H I. H I, 532 40 65 80 69.0 Difference Free surface Contact in moisture Denier Dry Dry area (S) angle regain Strength Elongation x 10 m lg) AH (g/ them. Sam 1e No. 10 in Exam 1e 1 was within the same EXAMPLE 3 p p area as in the above, but since it was treated with 15 g/l of NaOH at C for 30 minutes, A H thereof was 5.1 When fibers having no voids were subjected to the same treatment, A H of 1.8 was obtained. Sample No. 48 was within the area HLMK and in this case A H of more than 8 cannot be attained even by a treatment with 15 g/l of NaOH at C for 30 minutes. Samples No. 49 to 53,58 and 5 9 and in the area below the curve RSP and had somewhat lower strength. Sample No. 60 was within the area ABFE and A H thereof was more than 5 which was less than 8 Samples No. 54 and 55 were comparative samples and it was found that A H thereof was less than 14 the wet state with saturated steam at a pressure of 0.3 to 2.8 kg/cm gauge and dried at a temperature of Table 3 Sample Coagulation liquid Jet Steam pressure Drying Condition for No Concentration Temperature Stretch at wet annealing temperature treatment with (C (kg/cm) (C) modifier 41 55 60 0.9 0.8 110 NaOl-l 15 g/l 70C X min. 42 I! II II 1.7 II I! 43 2.5 NaOl-l 10 g/l 100C X 30 min. 44 0.8 100 NaOl-l 15 'g/l 100C X 30 min. 45 n I, I, n H 46 60 2.8 110 47 I, 50 2'5 1, 48 I! I! 1'2 II II I! 49 1.4 NaOH 10 g/l 70C X 30 min. 50 1.0 100 51 1.5 0.8

Difference Void con- Free surface Contact in moisture Denier Dry strength Dry elongation tent (X) area (S) angle regain (d) (g/d) X /g) AH 39.2 41.4 40 17.9 3.26 2.06 34.0 32.4 36.1 41 12.3 3.68 1.77 41.3 20.5 25.5 40 11.0 4.42 1.43 42.5 12.0 120.0 38 9.1 3.34 1.90 40.6 8.2 30.6 8.5 3.29 1.85 41.0 14.4 30.0 8.3 4.10 1.50 38.9 10.0 1.1 8.1 3.86 1.53 39.0 14.0 1.0 7.5 3.65 1.67 40.0 43.2 2.2 40 9.6 4.30 1.26 35.0 52.1 5.5 10.1 3.72 1.20 34.1 54.0 19.1 10.3 3.89 1.31 38.3 52 65 1.2 2.5 110 NaOH 10 g/l 70C X 30 min. 53 55 H H ,1 H I. 54 65 I, n n 130 I, 55 40 0.9 110 56 55 6O 1.7 H 7.5 N

100C X 30 min. 57 NH Ol-LH SO 1 100C X min. 58 65 70 1.2 1.2 Na C0 20 g/l 70C X 30 min. 59 IV I! I! 1.5 I! I! 60 40 40 0.9 0.8 63.0 6.0 40 9.7 3.96 1.19 33.9 50.1 1.1 6.9 4.12 1.15 30.9 61.2 0.9 4.9 3.98 0.98 29.9 65.0 2.5 4.7 4.11 1.09 28.6 30.1 34.1 41 15.1 3.72 1.75 39.0 28.3 32.6 38 16.1 3.78 1.70 38.6 62.1 1.2 41 5.9 3.67 1.26 32.8 55.5 1.9 6.3 3.98 1.30 30.6 5.0 5.1 4.10 1.76 41.3

lower than 110C. EXAMPLE 4 A copolymer ([1;] 1.6) consisting of 93 of acrylonitrile and 7 of vinyl acetate was dissolved in dimethyl acetamide to prepare a spinning solution having a concentration of 25 by weight. This spinning solution was extruded into an aqueous solution of dimethyl acetamide with various concentrations and temperatures and at various jet stretches. The thus obtained coagulated fibers were stretched to 4.5 times the original length in boiling water to obtain fiber tows. Then, crimps were mechanically imparted to the tows in the wet state and then the tows were cut into staples. These staples were treated with 15 g/l of aqueous sodium hydroxide solution at 70C for 30 minutes. Thereafter, the staples were washed with boiling water, annealed in The production conditions, void content, free surface area, contact angle, hygroscopicity and other properties of the obtained fibers are shown in Table 4.

In Table 4, Samples No.61 to 75, 79, 80 and 82 were within the area PQRS and had a A H of more than 8 and good fiber properties. Sample No. 76 was within the area LGJM and had a A H of more than 8 Sam ples No. 78 and 82 had a surface area of greater than 10 cm /g and large A H, but had somewhat lower strength. Samples No. 81 and 83 were in the area below the curve RSP and also had somewhat lower strength. Samples No. 77, 85, 86 and 87 were comparative samples and among them, No. 77, 85 and 86 had a large A H, but their strength were considerably low. Sample No. 87 had a A H of less than 5 Table 4 Sample Coagulation liquid Steam pressure Drying No. Concentration Temperature Jet Stretch at wet annealing temperature g/cm) (C) Table 4-continued Sample Coagulation liquid Steam pressure Drying No. Concentration Temperature Jet Stretch at wet annealing temperature 62 I, H H 07 ,1 63 H n H 12 H 64 H V, U n 60 65 1| ,1 H I, 80 66 H H H I, 100 67 55 40 68 H 40 H H n 69 n 60 I, H I, 70 I, 1: L5 I, 71 n 24 I, I, 72 80 0.9 73 65 60 74 50 H ,1 H

Difference Void con Free surface Contact in moisture Denier Dry strength Dry elongation tent (X) area (S) angle regain (d) (g/d) X /g) AH 52.6 34.0 40 14.5 2.88 2.52 27.3 52.6 45.8 40 16.3 2.89 2.45 33.7 52.6 55.4 44 16.2 3.23 2.44 39.2 46.6 36.6 41 15.3 3.26 2.48 43.2 43.0 34.9 40 15.2 3.28 2.45 40.3 43.0 29.5 41 14.9 3.23 2.44 42.1 28.7 20.1 43 10.4 3.00 2.50 42.2 34.4 37.8 38 18.5 3.14 2.30 36.5 39.0 45.9 40 18.2 3.16 2.48 35.4 55.0 46.3 40 19.3 3.15 1.93 33.8 57.3 47.9 39 19.3 3.13 1.72 38.9 52.6 34.6 38 18.8 3.24 1.98 41.6 52.6 37.3 39 18.2 3.20 1.85 38.0 22.4 7.1 13.4 2.38 2.98 14.4 75 80 20 1.5 1.2 76 60 0.9 0.3 60 77 2.4 40 78 H 20 n 0] 79 50 40 0.9 2.5 110 80 1.0 81 55 20 2.0 40 82 I! 1: 03 H 83 6O 2.5 60 84 40 0.3 40 85 II If 2'4 I! II 86 H 70 I, n 87 40 2.0 1.2 34.4 6.0 50 5.0 3.01 2.93 44.0 8.5 1.2 40 8.2 2.50 3.20 22.7 68.3 76.5 40 23.0 2.96 1.28 30.9 62.5 108.0 41 25.7 2.79 1.12 27.3 49.0 18.0 15.2 2.73 2.54 39.6 51.2 99.0 41 19.1 2.86 2.40 35.3 62.0 71.2 40 18.7 3.10 1.63 30.2 60.1 91.7 19.0 3.23 2.30 32.8 57.5 34.0 39 15.0 3.13 1.54 32.1 57.8 160.0 22.7 3.24 1.41 33.0 61.2 171.0 40 26.9 3.30 1.20 27.0 64.2 148.0 24.3 3.26 1.30 29.6 3.8 80.2 4.0 2.98 3.10 30.4

EXAMPLE 5 50 The above copolymers were dissolved in dimethyl Acrylonitrile, vinyl acetate and lauroxy polyethylene glycol acrylate (CH CHCO(OCH Cl-l OC l-l were polymerized at 50C using a redox catalyst to obtain a copolymer having the following compositions. 55

Specific viscosity was measured at 0.1 g polymer/100 g DMF at 25C.

formamide (DMF) to prepare spinning solutions having a concentration of 24.0 by weight. Furthermore, polymer B having the same proportion of components as the polymer B was prepared by mixing polymers A and D at the ratio of 75 25 and 24.0 spinning solution thereof was prepared in the same manner as mentioned above. These spinning solutions were extruded into an aqueous solution of dimethyl formamide with various concentrations and temperatures and at various jet stretches. The thus obtained coagulated fibers were stretched to 4.5 times the original length in boiling water and then crimps were mechanically imparted to the tows in the wet state. The thus crimped tows in the wet state were annealed with saturated steam at a pres sure of 0.8 2.8 kg/cm gauge and cut into staples and dried at a temperature of lower than 1 10C. Thereafter, said fibers were treated with 5 g/l of aqueous sodium hydroxide solution at C for 30 minutes. The production conditions, void content, free surface area, contact 17 angle, hygroscopicity and other fiber properties are shown in Table 5.

In Table 5, Samples No. 89 to 94 were fibers obtained by copolymerization of acrylonitrile and hydrob. extruding said spinning solution into an aqueous coagulation liquid containing said solvent to form fibers, containing open capillary voids,

c. stretching the thus formed fibers,

philic monomer. The void content and the surface area d. annealing the stretched fibers in the wet state with were within the area EJFK. The void content was low, saturated steam at a pressure of 0.3 to 2.8 kg/cm but A H was more than 8 e. drying the annealed fibers at a temperature of A H obtained by subjecting the fibers containing no lower than 110C, and voids to the same treatment are also shown in Table 5. 10 f. treating the fibers with an aqueous solution con- Table 5 Steam Coagulation liquid pressure Drying Void con- Sample Polymer Jet at wet temperature tent (X) No. Concentration Temperature Stretch annealing (C) g/ 88 A 55 60 0.9 0.8 110 37.8 89 B H 61 90 B 65 1.2 1.7 14.0 91 B 55 0.9 0.8 8.0 92 C H H H 85 93 D II I! II I! 7.8 94 D 65 1.2 1.7 14.3

Difference Free Surface Contact in moisture Denier Dry Dry AH of control area angle regain (d) strength elongation fibers x 10 (cmlg) AH (g/d) The control fibers were obtained by the same method as in the present Example except that the fibers were dried on a heated roller at 130C to collapse the voids.

REFERENCE EXAMPLE For comparison, the void content, surface area and A 1-1 of the commercially available acrylic fibers are shown in Table 6. These fibers have substantially no capillary voids and their hygroscopicity was extremely Bayer A. G.)

What is claimed is: V

l. A process for producing hygroscopic acrylic fibers which includes the steps of a. preparing a spinning solution by dissolving an acrylonitrile copolymer containing more than 50% by weight of acrylonitrile with at least one other polymerizable monomer having the C=C structure and copolymerizable therewith in a solvent thereof,

taining a compound as a modifier selected from the group consisting of alkali metal hydroxide, alkali metal carbonate sulfuric acid, hydrochloric acid and hydroxylamine salt to render the surface of the fibers hydrophilic and accelerate condensation of moisture in the voids.

2. A process according to claim 1 wherein the solvent in dimethyl acetamide.

3. A process according to claim 1, wherein the drying step (d) is carried out at a temperature of lower than C.

4. A process according to claim 1, wherein the stretched fibers are subjected to the annealing step (d), the drying step (e), and then the treating step with a modifier (f).

5. A process according to claim 1, wherein the stretched fibers are subjected to the annealing step (d), the treating step with a modifier (f), and then the drying step (e).

6. A process according to claim 1, wherein after the stretching step (c), the treating step with a solution of modifier (f) is carried out and then annealing of the fibers is carried out and thereafter, the drying step (e) is carried out.

Claims

1. A PROCESS FOR PRODUCING HYGROSCOPIC ACRYLIC FIBERS WHICH INCLUDES THE STEPS OF A. PREPARING A SPINNING SOLUTION BY DISSOLVING AN ACRYLONITRILE COPOLYMER CONTAINING MORE THAN 50% BY WEIGHT OF ACRYLONITRILE WITH AT LEAST ONE OTHER POLYMERIZABLE MONOMER HAVING THE $C=C$ STRUCTURE AND COPOLYMERIZABLE THEREWITH IN A SOLVENT THEREOF, B. EXTRUDING SAID SPINNING SOLUTION INTO AN AQUEOUS COAGULATION LIQUID CONTAINING SAID SOLVENT TO FORM FIBERS, CONTAINING OPEN CAPILLARY VOIDS, C. STRETCHING THE THUS FORMED FIBERS, D. ANNEALING THE STRETCHED FIBERS IN THE WET STATE WITH SATURATED STEAM AT A PRESSURE OF 0.3 TO 2.8 KG/CM2, E. DRYING THE ANNEALED FIBERS AT A TEMPERATURE OF LOWER THAN 110*C, AND F. TREATING THE FIBERS WITH AN AQUEOUS SOLUTION CONTAINING A COMPOUND AS A MODIFIER SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HYDROXIDE, ALKALI METAL CARBONATE SULFURIC ACID, HYDROCHLORIC ACID AND HYDROXYLAMINE SALT TO RENDER THE SURFACE OF THE FIBERS HYDROPHILIC AND ACCELERATE CONDENSATION OF MOISTURE IN THE VOIDS.

2. A process according to claim 1 wherein the solvent in dimethyl acetamide.

3. A process according to claim 1, wherein the drying step (d) is carried out at a temperature of lower than 60*C.