US3826712A

US3826712A - Acrylic synthetic paper and method for producing the same acrylic fibers wet spun from a blend of hydrolyzed and unhydrolyzed acrylic polymers having at least 60 % acrylonitriles by weight and paper made from such fibers

Info

Publication number: US3826712A
Application number: US00320763A
Authority: US
Inventors: T Kobayashi; Y Terada; Y Masuda; H Sato
Original assignee: Asahi Chemical Industry Co Ltd
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 1972-01-18
Filing date: 1973-01-03
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30
Also published as: DE2302077A1; FR2168504A1; GB1408465A; DE2302077B2; FR2168504B1; IT981955B

Abstract

ACRYLIC SYNTHETIC PAPER HAVING AN IMPROVED STRENGTH IS PROVIDED. ACRYLIC POLYMER WAS DISSOLVED AND HYDROLYZED IN A CONCENTRATION NITRIC ACIID TO OBTAIN A POLYMER WITH A SWELLING WATER CONTENT BEING NO MORE THAN 200%; THE THUS HYDROLYZED POLYMER WAS BLENDED WITH UP TO 95% BY WEIGHT OF AN UNHYDROLYZED ACRYLIC POLYMER HAVING AN ACRYLONITRILE CONTENT OF AT LEAST 30% SUCH THAT THE TOTAL ACRYLONITRILE CONTENT IS AT LEAST 60% BY WEIGHT, THEN THE RESULTING BLEND WAS WET SPUN BY NITRILE ACID TO OBTAIN ACRYLIC FIBER; AND FURTHER THE RESULTANT ACRYLIC FIBER WAS BEATEN, COVERTED INTO A PAPER SHEET AND THEN DRIED TO OBTAIN THE ACRYLIC SYNTHETIC PAPER WITH AN IMPROVED STRENGTH.

Description

y 1974 YOSHHNORI MASUDA ETAL 3,826,712 ACRYLIC SYNTHETIC PAPER AND METHOD FOR PRODUCING THE SAME, ACRYLIC FIBERS WET SPUN FROM A BLEND OF HYDROLYZED AND UNHYDROLYZED ACRYLIC POLYMERS HAVING AT LEAST 60% ACRYLONITRILE BY WEIGHT AND PAPER MADE FROM SUCH FIBERS Filed Jan. 5, 1973 K 4 Sheets-Sheet 1 Fig..!

0 300-- 2 E z |OC O O 0: 200- E g 30C 3 3 '00 50 C LU ACRYLONITRILE POLYMER HNOs CONC 65% HNOs DISSOLVING TIME (Hr) July 30, 1974 YosHlNoRl MASUDA ETAL ACRYLIC SYNTHETIC PAPER AND METHOD FOR PRODUCING THE SAME ACRYLIC FIBERS WET SPUN FROM A BLEND OF HYDROLYZED AND UNHYDROLYZED ACRYLIC POLYMERS HAVING AT LEAST 60% ACRYLONITRILE BY WEIGHT AND PAPER MADE FROM SUCH FIBERS Filed Jan. 5, 1973 SWELLING WATER CONTENT(%) Fig.2

4 Sheets-Sheet 2 ACRYLONITRILE POLYMER HNOa Temp 30C 60% HNOa 70% HNOa 80% HNO3 DISSOLVING TIME (Hr) 3,826,712 PER AND METHOD FOR PRODUCING THE SAME ACRYLIC FIBERS WET SPUN FROM A BLEND OF HYDROLYZED AND July 30, 1974 YOSHINORI MASUDA ET AL ACRYLIC SYNTHETIC PA UNHYDROLY ZED ACRYLIC POLYMERS HAVING AT LEAST 60% ACRYLONITRILE BY WEIGHT AND PAPER MADE FROM SUCH FIBERS 4 Sheets-$heet :5

Filed Jan. 3, 1973 ATE; mmmsBz w w m 8Q 3Q 2 2 0 0 8 8 8 3 mm 82 HQNVliIWSNVHi YOSHINORI MASUDA ETAL 3,8 ACRYLIC SYNTHETIC PAPER AND METHOD FOR PRODUCING THE SAME; ACRYLIC FIBERS WET SPUN FROM A BLEND 0F HYDROLYZED AND UNHYDROLYZED ACRYLIC POLYMERS HAVING AT LEAST 60% ACRYLONITRILE BY WEIGHT AND PAPER MADE FROM SUCH FIBERS 4 Sheets-Sheet 4.

Filed Jan. 3, 1973 ATEQV mMmEDZ w 2 6 00m 89 00 8 8 9 8 9 8 8 8 8 8 00mm ooov v hk (%) HONVLLIWSNVHJ.

United" States Patent 3,826,712 ACRYLIC SYNTHETIC PAPER AND METHOD FOR PRODUCING THE SAME ACRYLIC FIBERS WET SPUN FROM A BLEND OF HYDROLYZED AND UNHYDROLYZED ACRYLIC POLYMERS HAV- ING AT LEAST 60% ACRYLON'ITRILES BY WEIGHT AND PAPER MADE FROM SUCH FIBERS Yoshinori Masuda, Hideo Sato, Tadahiro Kobayashi, and Yoshiaki Terada, Fuji, Japan, assignors to Asahi Kasei Kogyo Kabushiki Kaisha Filed Jan 3, 1973, Ser. No. 320,763 Claims priority, application Japan, Jan. 18, 1972, 47/ 6,616; July 27, 1972, 47/74,663 Int. Cl. D21h 5/12 US. Cl. 162-157 R 6 Claims ABSTRACT OF THE DISCLOSURE Acrylic synthetic paper having an improved strength is provided. Acrylic polymer was dissolved and hydrolyzed in a concentrated nitric acid to obtain a polymer with a swelling water content being not more than 200%; the thus hydrolyzed polymer was blended with up to 95% by weight of an unhydrolyzed acrylic polymer having an acrylonitrile content of at least 30% such that the total acrylonitrile content is at least 60% by weight, then the resulting blend was wet spun by nitric acid to obtain acrylic fiber; and further the resultant acrylic fiber was beaten, converted into a paper sheet and then dried to obtain the acrylic synthetic paper with an improved strength.

BACKGROUND OF THE INVENTION It has been considered that strength of natural pulp paper is exhibited due to friction power between fibrils, van der Waals force, hydrogen bonding power which are developed between fibrils when natural pulp is beaten.

From this point of view, some methods for improving the strength of acrylic synthetic paper by imparting a fibrillating ability to acrylic synthetic fibers. For example, Japanese Patent Publication No. 20757/61 has proposed a method which uses un-collapsed fibers. Japanese Patent Publication No. 2302/64 has proposed a method which uses gelled filaments stretched to reach the first breaking point and Japanese Patent Publication No. 19602/63 has proposed a method which comprises treating acrylic synthetic fibers with a strong mineral acid. By these methods, strength of acrylic synthetic paper has been improved to some extent. However, since the fibrillating ability of the conventional acrylic synthetic fibers has been insutficient in comparison with that of natural pulp, the strength of the obtained acrylic synthetic paper is inferior to that of natural pulp paper. In order to overcome these defects, use of paper strength increasing agents or heat press method have been employed for reinforcing adhesive ability. However, these methods have not been satisfactory from economical and operational viewpoints.

THE INVENTION As a result of the inventors intensive researches it has been discovered that acrylic synthetic fibers having highly fibrillating ability can be produced by wet spinning polymer blend consisting of (i) acrylic polymer having not more than 200 weight percent of swelling water content which polymer is obtained by copolymerizing acrylonitrile and hydrophilic ethylene series monomer and (ii) acrylic polymer other than the acrylic polymer mentioned in (i). By this method acrylic synthetic paper having sufficient properties for commercial and practical use can be obtained.

Further, after the extensive researches by the present 3,826,712 Patented July 30, 1974 ice inventors, it has been found that acrylic polymer having not more than 200 weight percent of swelling water content can be produced by dissolving and hydrolyzing the acrylic polymer in a concentrated nitric acid, and that acrylic synthetic paper for practical use can be obtained by wet spinning the hydrolyzed polymer and thereafter by mechanically treating, for example beating, the obtained acrylic fiber, thereby easily to produce acrylic synthetic paper having improved strength.

Furthermore, according to the invention, the swelling water content of the polymer can be controlled by selecting the hydrolysis condition such as the temperature of nitric acid, the concentration of nitric acid, the dissolving time, etc. Accordingly, the strength of the acrylic syn thetic paper can be optionally controlled.

BRIEF SUMMARY OF THE INVENTION The present invention relates an acrylic synthetic paper and method for producing the same, which method cornprises beating acrylic fiber, converting the beaten fibers into a paper sheet and drying thus obtained sheet.

More specifically, the present invention is characterized by using, as the aforesaid acrylic fiber:

(l) acrylic fiber which is obtained by dissolving and hydrolyzing acrylic polymer in a concentrated nitric acid to give acrylic polymer (hereinafter referred to as A polymer) having not more than 200 weight percent of swelling water content; or

(2) acrylic fiber obtained by wet spinning by nitric acid the polymer blend of:

acrylic polymer (hereinafter referred to as B polymer) having not more than 200 weight percent of swelling water content obtained by dissolving and hydrolyzing acrylic polymer in a concentrated nitric acid, and

acrylic polymer (hereinafter referred to as C polymer) other than B polymer; wherein the amount of B based on the total polymers (B+C) being not less than 5 weight percent.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows the correlation between the temperature of nitric acid and swelling water content of the polymer, when the acrylonitrile polymer (a polymer in Example 1) was dissolved and hydrolyzed in 65% nitric acid. The abscissa shows polymer dissolving time and the ordinate shows swelling water content of the polymer. FIG. 2 shows the correlation between the concentration of nitric acid and the swelling water content of the polymer, when the said acrylonitrile polymer was dissolved and hydrolyzed at 30 C. in a concentrated nitric acid. The abscissa shows polymer dissolving time and the ordinate shows the swelling water content of the polymer. FIG. 3 shows the infrared absorption spectrum of the acrylonitrile polymer (a polymer). FIG. 4 shows infrared absorption spectrum of the said a polymer after being dissolved and hydrolyzed in 65% nitric acid at 30 C. for 20 hours.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the swelling water content of the acrylic polymer is an important key factor. The fibrillating ability of acrylic fiber obtained by wet spinning by nitric acid the acrylic polymer having not more than 200 weight percent of swelling water content is superior, and by using the said fiber there can be obtained acrylic synthetic paper having improved strength for practical and commercial use.

Unless otherwise described, percent in the present invention means weight percent.

Swelling water content according to the invention means the ratio of the amount of the water to the weight of the Swelling Water Content (percent) the amount of swelling water in eoagulated product the Weight of dried coagulated product The amount of the swelling water content in coagulated product was measured by the following procedure. The coagulated product was obtained and washed by water. About 1 g. of the sample was taken from thus obtained product containing ample 'Water, dehydrated by Kokusan Superior 1005 Type centrifuge at a rotation of 3500 -r.p.m. for .10 minutes and then the weight (A g.) was carefully measured. Thereafter, the sample was dried for 2 hours by a hot drier maintained at a temperature of 105 C., and the weight (B g.) was measured. Finally, the amount of swelling water is calculated as (A-B) g. The value of B is used also for the dried weight of the coagulated product.

In the present invention, the acrylic polymer having not more than 200 weight percent of swelling water content is called as low swelling acrylic polymer and the acrylic polymer having not less than 200 weight percent of swelling water content is called as now-low swelling acrylic polymer.

For the preparation of low swelling acrylic polymer by introducing hydrophilic radical group, two methods were known heretofore. The one is to copolymerize acrylonitrile with hydrophilic ethylene series monomer having a group for example sulphonic acid group, carboxylic acid group, amide group, polyethylene glycol group, etc. The other is to introduce amide group and/or carboxylic acid group into the polymer by hydrolyzing in the nitric acid the nitrile group in the acrylic polymer.

The latter method on which many researches were reported wherein the hydrolyzed polymer is used for the production of the fiber has the disadvantage of giving nonuniform product possessing poor dyeing ability, thermoshrinkability etc. In the latter method, since concentrated nitric acid is used as a solvent, hydrolysis reaction of the polymer was purposely prevented by removing nitrogen peroxide and using cooled nitric acid.

But, according to the present invention, acrylic polymer is hydrolyzed so that the swelling water content of the polymer becomes less than 200 weight percent. And the superior acrylic synthetic paper having an improved strength was obtained from the polymer. The hydrolysis of acrylic polymer 'is influenced by the compositon of polymer, the temperature of nitric acid, the concentration of nitric acid, etc.

PIG. 1 shows the change of the swelling water content of acrylonitrile polymer (a polymer in Example 1) being dissolved in 65 nitric acid. The abscissa shows the dissolving time of the polymer and the ordinate shows the swelling water content of the polymer. Since the polymer is hydrolyzed in 65% concentrated nitric acid, the swelling water content of the polymer decreases to below 200%, with the increase of dissolving time.

As shown in FIG. 3 and FIG. 4, the polymer after being hydrolyzed in a concentrated nitric acid gives absorption at 1 680 cmf The absorption is concurrent with the characteristic absorption of amide group. This will indicate the hydrolysis of nitrile group of the polymer to amide group.

However, the strength of the paper prepared by wet spinning acrylonitrile-acryl amide copolymer by dimethyl sulfoxide as a solvent is inferior (Confer Control 2). This difference construed to be due to the difference of acryl amide arrangement after hydrolysis in the polymer.

In fact, the acrylic polymer copolymerized merely with acryl amide without hydrolysis gives no improved properties.

As shown in FIG. 1, the hydrolysis rate of the polymer increases, with the increase of the temperature of nitric acid. The time needed to make the swelling water content of the polymer below 200% is approximately 30, 15, and 5 hours at 10, 30, and 50 C., respectively, of the temperature of nitric acid.

The temperature of nitric acid can be widely varied, according to the polymer composition and the concentration of nitric acid. Usually a temperature from 0 C. to 70 0, preferably 5 C. to 50 C. is suitable. If a too high temperature above 70 C. is employed, the hydrolysis reaction of acrylic polymer becomes vigorous and control of the reaction becomes difficult, thereby giving acrylic synthetic polymer having poor strength. On the other hand, if a temperature below 0 C. is employed, the hydrolysis reaction rate becomes too small.

FIG. 2 shows the increase of the hydrolysis rate of the polymer with the increase of the concentration of nitric acid. However, the influence of the nitric acid concentration upon hydrolysis rate is smaller than that of the temperature of nitric acid. The concentration of nitric acid to be employed is preferably from 55 to The concentration of nitric acid employed below 55%, is not desirable, since the solubility of acrylic polymer becomes insufiicient.

The acrylic polymer to be hydrolyzed in the present invention can be either non-low swelling polymer or low swelling polymer. Of these two, low swelling polymer is more easily hydrolyzed in a concentrated nitric acid and the swelling water content is further lowered, thereby giving acrylic "synthetic paper having an improved strength.

Especialy, in the hydrolysis of the low swelling polymer, the strength of acrylic synthetic paper is markedly improved, when 1680 cm." A O.D. R. is not less than 011. Here, 1680 cm. A O.D.R. means the difference, before and after the hydrolysis, of O.D.R. (Optical Density Ratio) of the absorption of the acrylic polymer measured at 1680 GIL-'1 based on methylene absorption at 1460 cmr In other words, O.D.R. (Optical Density Ratio) means 1680 cm.- O. D./l460 cm? OD.

The production of acrylic synthetic fibers used in the present invention will be explained below.

l(.l) Only a low swelling acrylic polymer obtained by dissolving and hydrolyzing acrylic polymer in a concentrated nitric acid (The hydrolyzed polymer is referred to as A polymer hereinafter) is wet spun by nitric acid.

(2) Preferably, low swelling acrylic polymer (B polymer) obtained by dissolving and hydrolyzing acrylic polymer in a concentrated nitric acid, and acrylic polymer C polymer) other than said acrylic polymer is blended to obtain a polymer blend, with B polymer being 5 weight percent of the total polymer; and then thus obtamed polymer blend is wet spun by nitric acid. According to the preference, in the sense of modified method of (2), only the low swelling polymers having different polymer compositions and/or hydrolysis rates can be used. The fibrillating ability of the acrylic fibers obtained in accordance with said method (2) (blend spinning) is particularly superior. Therefore, acrylic synthetic paper having an excellent strength can be obtained from said fibers.

Acrylic fiber according to the present invention should contain at least 60% of polymerized acrylonitrile. Acrylic synthetic paper obtained from acrylic fiber with less than 60% of acrylonitrile is poor in properties, such as hand touch, weather resistance, chemical resistance, electric resistance, etc.

Accordingly, in method (1), polymer having at least 60% of acrylonitrile should be used for A polymer. In method (2), B polymer and C polymer should be selected so as to make acrylonitrile content in the fiber not less than 60%.

Polymerized acrylonitrile content in B polymer should be at least Below 30%, compatibility of B polymer and C polymer is poor and the obtained acrylic fiber is poor in physical properties. Similarly, blending ratio of B polymer to the total polymer should be at least 5%. Below 5%, fibrillating ability of the obtained acrylic fiber is insulficient. Further, acrylonitrilc content of C polymer is preferably at least 60%.

In the present invention, the known technique may be applied for producing the starting acrylic polymers. The polymerization reaction is conducted with or without the catalyst in the presence of heat, light or radioactive rays. Either one of solution polymerization, emulsion polymerization, or suspension polymerization can be employed. The starting acrylic polymer can be random polymer, block type polymer or graft type polymer. Among these, solution polymerization in a concentrated nitric acid is especially preferable, wherein polymerization and hydrolysis can be carried out simultaneously.

Acrylic fiber according to the invention can optionally contain ethylene series monomer as far as the specified condition of the composition, is satisfied.

Examples of the ethylene series monomers are alphasubstituted acrylonitrile such as methacrylonitrile and alpha-chloroacrylonitrile; alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate; vinyl esters of unsaturated ketones such as vinyl acetate, methyl vinyl ketone and ethyl vinyl ketone; vinyl ethers such as vinyl methyl ethers; styrene and alkyl derivatives thereof such as methyl styrene; carboxylic acids and salts thereof such as acrylic acid, alpha-chloroacrylic acid, methacrylic acid, itaconic acid and maleic acid; halogenated vinyl such as vinyl chloride, vinyl bromide and vinylidene chloride; vinyl pyridines such as 2-vinyl pyridine and Z-methyl-S-vinyl pyridine; sulphonic acids and salts thereof such as allyl sulphonic acid, methallyl sulphonic acid, vinyl sulphonic acid, styrene sulphonic acid; polyethylene glycol esters such as (meth)acrylic acid polyethylene glycol ester and itaconic acid polyethylene glycol ester; and amides such as (meth)acrylamide, N-methyl (meth)- acryl amide, N-ethyl (meth)acryl amide, N-hydroxy methyl (meth)acryl amide, N,N*dirnethyl (meth)acryl amide, N,N-diethyl (meth)acryl amide, N,N-dihydroxymethyl (meth)acryl amide. Among these, hydrophilic ethylene series monomers having sulphonic group, carboxyl group, amine group, polyethylene glycol, etc. are especially preferred.

Acrylic polymer in the invention means the polymer which has acrylonitrile as a polymerization ingredient.

The method for obtaining acrylic fiber from acrylic polymer is wet spinning by nitric acid and the known technique is applied for the present invention. Namely, a viscous solution obtained by dissolving the polymer in a concentrated nitric acid is coagulated in an aqueous coagulation bath normally containing less than 40% of nitric acid; and then the coagulated filaments are washed with water and thereafter are stretched usually to more than 3 times in hot water, steam, heated air, etc.

Thus obtained acrylic fibers which have been dried or undried are subjected to mechanical treatment, such as beating, and then to sheet making treatment and dried to obtain an acrylic synthetic paper.

The production of acrylic synthetic paper from acrylic fibers according to the present invention may be carried out in the same manner as that of the conventional nat ural pulp paper. That is, the apparatus and technique for production of paper from natural pulp may also be used as it is in the present invention. For example, as the degree of fibrillation of natural pulp can be controlled by the degree of beating, the degree of fibrillation of the acrylic fibers used in the present invention can also be controlled by changing the beating conditions such as beating time, beating load, dispersion concentration of fibers, etc. by a beater for paper making.

Acrylic synthetic paper of high strength and good quality can be produced from solely acrylic fibers according to the present invention. But sizing agents, fillers and other known additives may be added at the step of heating or sheet making in the present invention as in the production of the conventional natural pulp paper.

Furthermore, the fibrillated fibers obtained by beating the acrylic fibers in the present invention can be used as a reinforcing agent by mixing with natural pulp, fibrous organic or inorganic material or nonfibrous organic or inorganic material and making the mixture into a sheet. Especially when the organic or inorganic material is non-self-bonding material, the strength is conspicuously improved. The content of the acrylic fibers in the obtained sheet-like material can be optionally determined depending upon the desired strength of the sheet-like material, but preferably is l50%.. This is because when the content is less than 1%, the improvement in the strength of the sheet-like material is insuificient and when more than 50%, since the content of organic material or inorganic material other than the acrylic fibers is decreased, the characteristics as the sheet-like material comprising the organic or inorganic material are lost.

By using the acrylic fibers of the present invention as a bonding agent, not only the strength of sheet-like material can be improved by its excellent bonding ability, but also the loss of the bonding agent on the paper making wire can be decreased at paper making.

That is, in the conventional paper making process in which a high molecular resin bonding agent which is dissolved in water is added to raw materials for paper making, most of the high molecular resin bonding agent is extracted from paper making wire together with water and so much loss of the bonding agent is caused. On the other hand, sai-d defects in the conventional method have also been overcome by using the acrylic fibers of the present invention.

In the present invention, the acrylic fibers are dried to cause firm bonding between the fibers or between fibers and other organic or inorganic material, thereby to impart a high strength to the resultant sheet-like material.

Furthermore, said sheet-like material is improved in tensile strength and tearing strength. The improvement in tearing strength seems to be attained by resistance caused at cutting of the acrylic fibers by tearing.

Examples of the natural pulp, fibrous organic or inorganic materials, non-fibrous organic or inorganic materials used in the present invention are as follows: Natural pulps such as softwood pulp, hardwood pulp, hemp, etc.; regenerated cellulose fibers such as viscose rayon fibers,

cuprammonium rayon fibers, acetate fibers, etc.; synthetic fibers such as polyvinyl alcohol fibers, polyamide fibers, polyester fibers, polyester ether fibers, polyethylene fibers, polypropylene fibers, non-self bonding acrylic fibers, etc.; polyethylene and polypropylene synthetic pulps; inorganic fibers such as glass fibers, rock fibers, etc.; solid chips having a maximum diameter of 0.5-50 mm., preferably 1-25 mm., e.g., woody chips such as wood powders, wood chips, etc., powdery, granular and flaky resin chips obtained by crushing high molecular resins, mineral chips obtained by crushing natural minerals such as rocks, ores, micas, etc., glass chips obtained by shaping and crushing glass and other metallic chips, carbonaceous chips, etc.

The acrylic synthetic paper of the present invention can be obtained by the known shaping method. That is, heating can be carried out by beating machines such as beater, refiner, etc. and paper making can he carried out by paper making machines such as cylinder machine, Fourdrinier machine, etc. or wet non-woven fabric making machines such as hydroformer, jet former.

The present invention will be further illustrated by, but not limited to, the following Examples.

Example 1 Acrylonitrile polymer (a polymer; swelling water content 350%) was dissolved in nitric acid at the temperature and the concentration as shown in Table 1 to obtain viscous solution and then hydrolyzed for a time as shown in the Table 1. Swelling water content of the hydrolyzed polymer was shown in the Table 1. The viscous solution was cooled at C. On the other hand a polymer was dissolved in 65% nitric acid solution at 5 C., thereby substantially avoiding being hydrolyzed, to give unhydrolyzed a polymer.

Thus obtained hydrolyzed polymer and unhydrolyzed polymer were blended in a blending weight ratio being 50/50. Then the polymer blend was extruded into 30% aqueous nitric acid solution kept at 5 C., through spinneret. The resultant filaments were washed with water and then were stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

Then thus obtained fibers were dried at 100 C. and 'cut with a length of mm. The fibers were mixed with water so that the concentration became 1% and then beaten with a plumb of 2.5 kg. of TAPPI Niagara B type testing beater for 30 minutes to obtain dispersions. Those dispersions were formed into a sheet by T APPI standard sheet machine, which was dried at 100 C. to obtain paper having a basis weight of 40 g./m. Tensile strength of thus obtained papers were measured by Schopper tensile machine.

For reference, breaking lengths of paper obtained from softwood bleached kraft pulp (NBKP) in the same manner as mentioned above were measured.

TABLE 1 Concentration Tempera- Swelling of nitric ture of Dissolvwater Breaking acid, nitric ing time, content, length,

percent acid, 0. hrs. percent km. Note 60 30 20 185 5.4 This example.

65.. 5 20 340 0.2 Comparative example.

65 10 30 195 4.0 This example.

65 30 5 300 0.4 Oomparative example.

65 30 10 250 0.7 Comparative example.

65 30 20 165 8.0 This example.

NBKP 6. 8 Refcrential example.

Example 2 Acrylic polymer (b polymer; swelling water content 280%) containing 98% of acrylonitrile and 2% of N,N- dimethyl acryl amide was dissolved in 70% nitric acid kept at 30 C. to obtain viscous solution and the viscous solution was hydrolyzed in nitric acid for hours. The swelling water content was 130% Then the viscous solution was cooled to 5 C.

On the other hand b polymer was dissolved in 70% nitric acid at -5 C., avoiding thereby hydrolysis.

Then the said hydrolyzed b polymer and unhydrolyzed b polymer were blended with a blending ratio as shown in Table 2. Thereafter, the polymer blend was extruded into 30% aqueous nitric acid solution at 5 C. through spinneret. The resultant filaments were washed with water and then were stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

Thus obtained fibers were dried at 100 C.; and then heated, converted into a paper sheet and dried as in Example 1 to obtain paper having basis weight of 40 g./m. Physical properties were measured and the result were shown in Table 2.

Example 3 Acrylic polymer (c polymer; swelling water content 160%) containing of acrylonitrile and 15% of acrylic acid was dissolved in 60% aqueous nitric acid solution at 40 C. to obtain viscous solution.

The viscous solution was hydrolyzed in nitric acid at 40 C. for 10 hours. The swelling water content was and 1680 cmt- A O.D.R. was 0.83.

Then, the viscous solution was cooled to 5 C. On the other hand, acrylic polymer containing 65 weight percent of acrylonitrile and 35 weight percent of methacryl0 nitrile (d polymer; swelling water content 380%) was dissolved in 60% aqueous nitric acid solution at 5 C. to obtain viscous solution, thereby substantially avoiding the hydrolysis of d polymer.

The said hydrolyzed viscous c polymer solution and unhydrolyzed viscous d polymer solution were blended in a blending ratio being 50/50.

Thereafter, the spinning solution of the polymer blend was extruded into 30% aqueous nitric acid solution at -5 C. The resultant filaments were washed with water and then were stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers in undried state were beaten, formed into paper and dried to obtain paper having basis weight of 40 g./m. Breaking length of the paper was 9.2 km.

Control.c polymer in Example 3 was dissolved in 60% aqueous nitric acid solution at -2 C. to obtain the viscous solution. The viscous solution was kept at 2 C. for 10 hours. The swelling water content of the hydrolyzed polymer was and 1680 crnr' A O.D.R. was 0.05. Then, the viscous solution was further cooled at -5 C.

d polymer in Example 3 was dissolved in 60% aqueous nitric acid solution at 5 C., thereby avoiding hydrolysis.

Thus obtained c polymer and d polymer were blended in a blending weight ratio of 50/50, extruded into 30% aqueous nitric acid solution at 5 C. and stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers in undried state was beaten, formed into paper and dried to obtain paper having basis weight of 40 g./m. Breaking length of the paper was 6.4 km.

Example 4 Acrylic polymer (e polymer; swelling water content 140%) containing 40% of acrylonitrile and 60% of methoxy polyethylene glycol acrylate (CH CHCO OCH CH OCH was dissolved in 65 aqueous nitric acid solution at 5 C. to obtain viscous solution. The viscous solution was kept at 5 C. for 50 hours for hydrolysis. The swelling water content of the hydrolyzed polymer was 80% and 1680 cm.- A O.D.R. was 1.10.

On the other hand, acrylic polymer (f polymer; swelling water content being 350%) containing 95% of acrylonitrile and 5% of vinyl chloride was dissolved in 65% aqueous nitric acid solution at 5 C. The resultant viscous solution was kept at 5 C. for 50 hours for hydrolysis. The swelling water content of the hydrolyzed polymer was Thus obtained viscous solution were blended in a ratio of e/ being 20/80, extruded into 30% aqueou nitric acid solution at 5 C. and stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers were dried at 100 C. Then, the dried fibers were beaten, formed into paper and dried to obtain paper having basis weight of about 40 g./m. Breaking length of the paper was 8.4 km.

Example 5 Acrylic polymer (g polymer; swelling water content being 370%) containing 90% of acrylonitrile and 10% of methyl acrylate was dissolved in 70% aqueous nitric acid solution at 30 C. to obtain viscous solution. The viscous solutions were kept at 30 C. for 15 hours and 30 hours for hydrolysis and the swelling water content of thus obtained hydrolyzed polymers were 150% and 110%, respectively.

The thus obtained two kinds of viscous solution were blended in a blending weight ratio being 50/50, extruded into 30% of nitric acid solution at C. and stretched 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers in undried state was beaten, formed into paper and dried to obtain paper having basis weight of 40 g./m. Breaking length of the paper was 7.5 km.

Example 6 Acrylic polymer (h polymer) was prepared by polymerizing acrylonitrile and acryl amide (with ratio being 80/20) in the presence as catalyst of ammonium persulfate, acetyl acetone and ferric nitrate in 65% aqueous nitric acid solution at 25 C. for 25 hours. The swelling water content of the obtained polymer was 110% and O.D.R. at 1680 cm. was 2.20. The polymer was cooled to 5" C.

a polymer was dissolved in 65% aqueous nitric acid solution at 5 C. to obtain the viscous solution avoiding thereby hydrolysis.

Thus obtained viscous solutions of h polymer and a polymer was blended in a blending ratio being 50/50, extruded into 30% aqueous nitric acid solution at 5 C. and stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers in undried state was beaten, formed into paper and dried to obtain paper basis weight of approximately 40 g./m. Breaking length of the paper was 6.8 km.

Control 2.-Polymer (i polymer) was prepared by polymerizing acrylonitrile and acryl amide (with ratio being 75/25) in the presence as catalyst azobis-isobutyronitrile in dimethyl sulfoxide at 50 C. for 20 hours. The swelling water content of the obtained polymer was 130% and O.D.R. at 1680 cm? was 2.15.

On the other hand a polymer was dissolved in dimethyl sulfoxide to obtain the viscous solution.

Thus obtained viscous solutions of i polymer and a polymer were blended in a blending ratio being 50/50, extruded into 65% aqueous dimethyl sulfoxide solution at 25 C. and stretched to 5 times in boiling water to obtain filaments with approximately 3 denier.

The resultant fibers in undried state was beaten, formed into paper and dried to obtain paper having basis weight of about 40 g./m. Breaking length of the paper was 3.6 km.

What is claimed is:

1. An acrylic fiber of improved fibrillating characteristics prepared by the steps comprising (a) subjecting an acrylic polymer containing up to 60% by weight acrylonitrile to hydrolysis in nitric acid having a concentration weight unhydrolyzed acrylic polymer having an acrylonitrile content of at least 30%; said amount being such that the total acrylonitrile content is at least by weight; and (0) wet spinning the resultant polymer by nitric acid to form a fiber.

2. An acrylic fiber according to Claim 1, wherein acrylic polymer to be hydrolyzed is a low swelling polymer.

3. An acrylic synthetic paper prepared by the steps comprising (a)' subjecting an acrylic polymer containing up to 60% by weight acrylonitrile to hydrolysis in nitric acid having a concentration of at least 55 by weight at a temperature of O C. for a period of time suflicient to reduce the swelling water content to less than 200% by weight; (b) blending the hydrolyzed polymer with an amount of up to by weight unhydrolyzed acrylic polymer having an acrylonitrile content of at least 30%, said amount being such that the total acrylonitrile content is at least 60% by Weight; and (c) wet spinning the resultant polymer by nitric acid to form fibers; (d) beating the thus obtained acrylic fibers; (e) converting the beaten acrylic fibers into a paper sheet and (f) drying the thus obtained sheet.

4. A sheet-like material comprising acrylic synthetic fibers of Claim 3 further comprising at least one additional fibrous or non-fibrous material, the acrylic fiber content being 1-50% by weight.

5. A sheet-like material of Claim 4, wherein the additional material is fibrous and is selected from the group consisting of polyethylene fibers, polypropylene fibers, polyester fibers, acrylic fibers, polyamide fibers, glass fibers or rock fibers.

6. A sheet-like material of Claim 4, wherein the additional material is non-fibrous and is selected from the group consisting of glass flakes or mica flakes.

References Cited UNITED STATES PATENTS 3,047,455 7/1962 Holmes et al 162146 X 3,168,434 2/1965 Heyman l62-l46 X 3,047,456 7/1962 Ucci et al 162146 X 2,812,317 11/1957 Barrett 26029.6 AN X 3,410,837 ll/1968 Shibukawa 260-29.6 AN X 3,636,187 1/1972 Ohfuka et a1. 264182 FOREIGN PATENTS 721,947 1/1955 Great Britain 260--29.6 AN

ROBERT L. LINDSAY, JR., Primary Examiner W. F. SMITH, Assistant Examiner US. Cl. X.R.