US 3285696 A
Description (OCR text may contain errors)
United States Patent '0.
3,285,696 METHOD FOR THE PREPARATION OF FLEXIBLE CARBON FIBRE Yasugoro Tsunoda, Kumamoto-ken, Japan, assignor to Tokai Denkyoku Seizo Kabushiki Kaisha, Tokyo, Japan No Drawing. Filed Apr. 5, 1963,'Ser. N0.270,807 Claims priority, application Japan, Aug. 25,1960, 35/ 36,145 3 Claims. (Cl. 23-209.1)
This application is a continuation-in-part of my earlier previously copending application, Ser. No. 97,461 filed March 22, 1961, now abandoned.
This invention relates to methods for the preparation of flexible heat resisting and corrosion resistant fibre.
The corrosion resistance of carbon and graphite against various chemicals and the heat resistance of carbon and graphite are substantially perfect excepting when these materials are placed in an oxidizing atmosphere. It has therefore been considered desirable to produce woven fabric made of carbon or graphite but which also has satisfactory mechanical strength It is known that if a fibre (for example, cotton or Orlon) containing carbon is heated at high temperatures (700-3,000 C.) in an inert gas atmosphere such as nitrogen or argon, the fibre retains the shape it had before-the heat treatment. Fibre obtained in this way is, however, so brittle that yarn and woven fabric made of such fibre are of no practical use.
It is an object of this invention to prepare fibrous carbon and graphite having improved properties.
Other objects and advantages of this invention will be apparent from the following description of some preferred embodiments.
The invention provides a method for the preparation of heat resisting and corrosion resistant fibre, characterized in that fibre, made of a material selected from the group consisting of acrylonitrile polymer and acrylonitrile copolymer prepared from less than 85 mol percent of acrylonitrile and not more than 15 mol percent of a monovinyl compound, is heated at a temperature from 180 to 550 C. in an oxygen-containing atmos phere for a time sufficient to blacken the fibre. Then the blackened material is carbonized and if necessary graphitized by a conventional method.
The fibrous carbon and graphite prepared by the methd mentioned. above are mechanically stronger and more flexible than those made by direct carbonization or graphitization without the pretreatment according to the invention.
According to the invention, a product such as -a filament, staple, or batting is made of the fibre which is made from acrylonitrile homopolymer or copolymer produced by copolymerizing not less than 85 mol percent of acrylonitrile with not more than 15 mol percent of a monovinyl compound such as methyl acrylate, methyl methacrylate, vinyl, acetate, vinyl chloride, vinylidine chloride, 2-methyl-5-vinyl pyridine or the like. This product is heated for 5-60 minutes at 180-230 C. in an oxygen containing atmosphere such as air. The temperature and time necessary for heating depend on the thickness of the fibre or woven fabric but, for convenience, it is determined by the degree of blackening of the fibre. Polyacrylonitrile becomes yellowish, brown and black successively by heating in air, but yellowish and brown fibres are not suit-able for the purpose of this invention since their carbonized or graphitized products are brittle.
Then the blackened. fibre is carbonized at a temperature between 700-1200 C. for not less than 1 hour in an inert atmosphere to form a carbonized fibre. If a more heat resistant and corrosion resistant fibre is required, the carbonized fibre is graphitized at a temperature bep .JCC
tween 1200-3000 C. in an inert atmosphere to form a graphitized fibre. Said inert atmosphere may be an inert gas or a packing material such as graphite, carbon black and silica. 1
Example I 'Staple of acrylonitrile copolymer containing 4 mol percent of methyl acrylate (yarn countings #48, two-ply) was heated in air at 220 C. for 3 hrs. in order to blacken it completely. Then the blackened fibre was heated in a nitrogen atmosphere at 1,000 C. for 1 hr. The product was not broken by bending, its tensile strength being above 60 g./yarn. The same staple was heated in air at 220 C. for 20 minutes and. a dark brown fibre was obtained. Then the fibre was heated in a nitrogen atmosphere at 1,000 C. for 1 hour. A carbonized fibre resulted which was so brittle that it was easily broken by bending and its tensile strength was 20 g./yarn. On the other hand, the tensile strength of the product which was made merely by direct heating of the same fibre of polyacrylonitrile in a nitrogen atmosphere at 1,000 C. for 1 hr. was as small as about 6-11 g./yarn. The latter product was relatively'inflexible so that it too was readily broken by bending.
Example 2 Batting of acrylonitrile polymer mol percent) was blackened by heating in air at 230 C. for 15 minutes. The blackened cotton obtained in this way was then heated in a nitrogen atmosphere at 1,000 C. for 1 hr. The product retained its original form and was flexible. On the other hand, the product which was made merely by heating the same batting in a nitrogen atmosphere at 1,000 C. for 1 hr. formed a conglomerate which was easily broken by a small force.
Example 3 A fibre made of copolymer of acrylonitrile 92 mol percent and 2-methyl-5-vinylpyridine 8 mol percent was treated in the manner mentioned in Examples 1 and 2. Substantially the same results were obtained.
Example 4 Woven fabric (plain weave; warp and woof yarn countings No. 48, two-ply) made of yarns of acrylonitrile copolymer containing 4 mol percent of methyl acrylate was heated in air at 220 C. for 1 hr. and then the blackened fibre was heated in nitrogen at 1,000 C. for 1 hr. The product was flexible and not broken even by bending to an angle of 180 degrees. The woven fabric heated solely at 1,000 C. for 1 hr. was broken by bending to angle of 15.
Example 5 The same yarn as that used in Example 1 was blackened by being heated in air at 220 C. for 30 minutes. Then it was buried in graphic powder and graphitized at 3,000 C. The product was flexible, its tensile strength being above 40 g./yarn. The same yarn was buried in graphite and graphitized at 3,000 C. The product obtained in this way was very brittle, its tensile strength being below 6 g./yarn.
What is claimed is:
1. A method for the preparation of flexible heat resistant and corrosion resistant fibre, comprising pretreating a fibre, which is to be carbonized and which is selected from the group consisting of acrylonitrile homopolymer and acrylonitrile copolymer prepared from not less than 85 mol percent of acrylonitrile and not more than 15 mol percent of a monovinyl compound, by heating the fibre at a temperature of from 180 to 550 C. in an oxygen containing atmosphere for a time sufficient to blacken the fibre',and then carbonizing the blackened fibre at a temperature between 700 and 1200 C. for not less than one hour in an inert atmosphere to form a carbonized fibre. Y
2. A method according to claim 1 wherein said carbonized fibre is then graphitized at a temperature between 1200 to 3000 C. in an inert atmosphere to form a graphitized fibre.
3. A method as claimed in claim 1, wherein the pretreatment heating is effected for 5-60 minutes..
7 4' References Cited by the Examiner UNiTED "STATES PATENTS 2,799,915 7/1957 Barnett et al. 8-115.5 X 3,011,981 12/1961 Soltes 252S02 3,027,222 3/ 1962 Wilkinson 8115.5 3,107,152, 10/1963 Ford et al. 23209'.2 X
-, MILTON WEISSMAN, Primary Examiner.
OSCAR R. VERTIZ, Examiner.
E. J. MEROS, Assistant Examiner.