US3682595A - Method of preparing carbonaceous non-woven fabric - Google Patents

Abstract

A METHOD OF PREPARING A CARBONACEOUS NON-WOVEN FABRIC COMPRISING BINDING CARBONACEOUS FIBERS USING AS A BINDER A HIGH MOLECULAR WEIGHT MATERIAL WHICH DOES NOT PASS THROUGH A PITCH-LIKE MOLTEN STATE DURING CARBONIZING AND THEN CARBONIZING THE SYSTEM. THE BINDER MATERIALS INCLUDE POLYMERS OF VINYLIDENE CHLORIDE, VINYLIDENE FLUORIDE, VINYL CHLORIDE, ACRYLONITRILE AND COPOLYMERS THEREOF, POLYVINYL ALCOHOL, PHENOL RESIN, EPOXY RESIN, UNSATURATED POLYESTER RESIN, FURAN RESIN AND POLYDIVINYL BENZENE RESIN.

Description

United States Patent 'O 3,682,595 METHOD OF PREPARING CARBONACEOUS NON-WOVEN FABRIC Kensuke Okuda, 8, Ichigayadai-machi, Slunjuku-ku; Tadaaki Yoshida, 10-13, 3-chome, Nerima, Nerima-ku; and Kastuyuki Sugawara, 13-7, l-chome, Higaslnyulngaya Ota-ku, all of Tokyo, Japan No Drawing. Filed May 28, 1970, Ser. No. 41,545

Claims priority, application Japan, May 28, 1969, 44/ 40,879 Int. Cl. C01b 31/02, 31/07 US. Cl. 423-447 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a non-woven fabric composed of almost only carbonaceous material prepared by binding carbonaceous fibers with a binder and then burning them.

More particularly, the present invention relates to unwoven fabrics composed almost entirely of carbonaceous material prepared by binding so-called carbonaceous fibers, such as blackened fibers, carbon fibers, or graphite fibers, having a length of longer than 1 mm, with a binder in a desired amount; although the method of forming a web of fibers may be varied according to the length of the fibers and the thickness of the unwoven fabrics of this invention, and then burning them in an atmosphere which can be obtained industrially.

(2) Description of the prior art In general, carbonaceous fibers are prepared by carbonizing fibers such as rayon fibers or acrylonitrile fibers by burning them at a proper temperature, and hence in the case of preparing fabricated articles of carbonaceous fibers, such as spinning yarns, fabrics, and non-Woven fabrics, it is necessary to fabricate the raw fibers, such as rayon fibers r polyacrylonitrile fibers, into a fabricated article and then carbonize the article. However, in such as conventional method, the efficiency of carbonization is very low (20-40%) and the weight loss and the change in diameter of the fibers are remarkable. Therefore, even if a binder is used for making such fabricated carbonaceous articles, the binding power of the binder is lost during the carbonization and the preparation of carbonaceous non-woven fabrics having a sufl'icient strength is impossible.

The present inventors have investigated methods of making non-woven carbonaceous fabrics by directly fabricating carbonaceous fibers without being accompanied with the aforesaid drawbacks but encountered various difiiculties since the materials to be fabricated are carbonaceous fibers.

That is, since carbonaceous fibers are high in rigidity and hence readily broken, it is diificult to form a Web of such carbonaceous fibers. When the web of carbonaceous fibers is formed by a dry method or a wet method, the fundamental point is in the manner of opening the "ice fibers and this difliculty has been overcome by providing a novel fiber opening method using a high speed gas stream fiber opening cylinder (Japanese patent application No. 2933/69).

Furthermore, in order to make non-woven fabrics, it is necessary to first fabricate the carbonaceous fibers (opened by the aforesaid manner) into a web having the desired thickness and a suitable shape, by either a dry or wet method, and after binding them with a binder, to carbonize the binder.

In the case of binding carbonaceous fibers with a binder by an immersion method, a method may be employed in which the binder is dissolved or dispersed in an aqueous dispersion of slurry of the carbonaceous fibers to bind the fibers with the binder. The carbonization following the binding procedure is generally conducted by heattreating the fibers bound by the binder at a high temperature in an inert gas but in this case it is desirable to conduct the heat treatment at a temperature as low as possible and in an industrially profitable atmosphere, for example, for a short period of time in air.

Requirements for a binder used to prepare carbonaceous non-woven fabrics are that the binder have a definite extent of affinity to the carbonaceous fibers when the binder is in a solid, molten or solution state; that the binder have a sufficient action as a carbonaceous binder, as well as that it have a definite binding strength after it is carbonized or during the carbonization of it. Furthermore, in the case of easily carbonizing the binder at a comparatively low temperature, there are two kinds of binders, that is, a binder which is carbonized through a state of pitch having a comparatively low viscosity and a binder which is directly carbonized without passing through such a pitch-like state, it is ditficult to sufliciently bind the carbonaceous fibers and maintain the shape of the bound fibers, which makes it difiicult to obtain sufficfiient dimensional strength of the final product. Therefore, a binder which is carbonized without passing through a pitch-state is more preferable with respect to car-bonaceous fibers.

Also, the nature of carbonaceous fibers depends upon the conditions used to prepare them; for example, they begin to have a reduction in weight or denaturation by oxidation in air, and hence a binder which can be completely carbonized in air at a comparatively low temperature of 400 to 500 C. is used with a more economical effect. Of course, if a graphitization is required, the binder may be heat-treated at a sufiiciently high temperature.

SUMMARY OF THE INVENTION As the result of detailed experiments, the present inventors have discovered that a polymer of vinylidene chloride, vinylidene fluoride, vinyl chloride or acrylonitrile or copolymers thereof; a thermoplastic resin such as polyvinyl alcohol or a derivative thereof; or a heat-curing resin such as a phenol resin, an epoxy resin, an unsaturated polyester resin, a furan resin, and a polydivinyl benzene resin satisfy the aforesaid conditions as a binder for carbonaceous fibers. The present inventors have succeeded in producing carbonaceous non-woven fabrics by impregnating the carbonaceous fibers with such a binder by an immersion method or a spraying method using the aforesaid high molecular weight materials as the binder, either as a solution thereof having a suitable concentration or as a latex thereof, and thereafter carbonizing the system in such a manner that the binder maintains a sufficient binding power during the carbonization process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The concentration of the binder in the solution or latex may vary from 1 to 50 weight percent.

The amount of binder impregnated into the carbonaceous fibers is below- 10 weight-percent,-based on the weight of the fibers.

Any suitable solvent may be employed to dissolve the binder into solution or to form a latex therewith. The only requirement for the solvent is that it be compatible with the binder.

The binder-fiber system is carbonized by heating the system from a temperature of room temperature (ca. 20 C.)--200 C. to 3501000 C. at a rate of about 0.5- C. per minute.

The carbonization process is carried out in air, nitrogen, argon or hydrogen, or a like atmosphere.

The molecular weight of the binder is not critical to an understanding of the present invention, as long as the molecular weight is such that the binder satisfy the abovedescribed requirements.

The carbonaceous non-woven fabrics thus prepared can be used not only as a heat insulating material, packing materials, and filters but also as electric heating elements, electrodes and coating materials for antistatic purposes utilizing their conductive property.

The present invention will be further illustrated by the following on-limiting examples.

EXAMPLE I A bundle of about 10,000 carbonaceous fibers each having a diameter of 8 microns and a length of about 7 cm. was opened into fibers by an opening method using the aforesaid high-speed gas stream fiber opening cylinder and thereafter the fibers were fabricated into a random web having a weight of about 200 g./cm. by means of a cyclone system. The web was immersed in a 4% solution of a binder (polyvinylidene fluoride) in dimethyl acetone to impregnate the fiber web to a proportion of about 3% by weight of binder and then the thus-impregnated web was burned at a temperature of 550 C. in anitrogen atmosphere. By the above procedure, a quite excellent carbonaceous fabric was obtained. It was confirmed by chemical analysis that about 99% of the binder was carbonized.

EXAMPLE II A bundle of carbonaceous fibers as in Example I was cut into a length of about 3 cm. and after being opened by the same procedure as in Example I, the fibers were fabricated into a web having weight of about 50 g./cm. by means of a condenser-cylinder system. A copolymer of vinylidene chloride and vinyl chloride (70/30 Weight ratio) was dissolved in tetrahydrofuran in a proportion of 2%. The thus-prepared solution was applied to the web by a spraying method so that the resulting proportion of copolymer applied to the Web was about 4% based on the weight of the web, and then the web containing the binder was heat-treated at a temperature of about 700 C. in a nitrogen atmosphere to carbonize the binder, whereby a carbonaceous non-woven fabric, in which the binder had almost completely been carbonized, was obtained.

EXAMPLE III A bundle of carbonaceous fibers each having a diameter of 7 microns was cut into a length of about 3 mm. and was opened by means of the fiber opening machine as used in Example'I and the fibers were then fabricated into a non-woven fabric by a so-called wet method using an aqueous latex dispersion of about 10% by weight of a copolymer of vinylidene chloride and vinyl chloride 20 weight ratio). The product was a paper-like non-woven material having a high uniformity and a weight of about 10 g./cm. By heat-treating the non-woven fabric at a temperature 0f380 C. in air, a carbonaceous non-woven fabric having a high uniformity and a high density was obtained.

What is claimed is: I

1. A method of preparing a carbonaceous non-woven fabric which comprises binding a .web of carbonaceous fibers with less than 10 weight percent, based on the weight of said fibers, of a high molecular weight material which does not pass through a pitch-like molten state during carbonizing selected from the group consisting of polyvinylidene fluoride and copolymers of vinylidene chloride and vinyl chloride, and thereafter carbonizing the binder by heating to a temperature of from 350 C. to 1000 C.

2. The method of claim 1, wherein said high molecular weight material is a copolymer of vinylidene chloride and 3. The method of claim 1, wherein said high molecular weight material is a copolymer of vinylidene chloride and vinyl chloride.

4. The method of claim 2, wherein said binder is carbonized by heating to a temperature of from 350 to 1000 C. at a rate of from 0.5 to 5 C. per minute.

5. The method of claim 3, wherein said binder is carbonized by heating to a temperature of from 350 to 1000 C. at a rate of from 0.5 to 5 C. per minute.

6. The method of claim 1 wherein said binder material is applied as a 1 to 50 weight percent solution or latex.

References Cited oTHER REFERENCES Kirk-Othmer' Encyclopedia of Chemical Technology, 2nd ed., vol. 9, 1966, pp. 840-845.

Okuda JpPolymer Science, Part A, vol. 2, 1964, pp. 17491750.

EDWARD J. MEROS, Examiner.

. US. Cl. X.R. 117-46; 204 29 V