PROCESS FOR THE PREPARATION OF FLEXIBLE CARBON YARN AND CARBON PRODUCTS MADE THEREFROM

Abstract: A process for the preparation of a carbon yarn product includes the steps of pyrolizing raw carbonaceous yarn comprising a plurality of carbon fibers, at a temperature above about 650 DEG F; flexing the pyrolized yarn to substantially break fiber-to-fiber bonding between the fibers; and, exposing the yarn to a temperature sufficient to carbonize the pre-carbonized yarn to a final and higher carbon assay. A flexible yarn element (10) includes a plurality of carbon filaments (11) wherein each filament (11) is in contact with at least one other filament (11). A sizing material at least partially coats the plurality of filaments (11), wherein the sizing material of each filament (11) is substantially separated from the sizing material of the at least one other filament (11) in contact therewith.

Description: PROCESS FOR THE PREPARATION OF FLEXIBLE CARBON YARN AND CARBON PRODUCTS MADE THEREFROM TECHNICAL FIELD The present invention generally relates to a carbon yam and carbon yam products. More particularly, the invention relates to a carbon yam which is flexible after being carbonized. Specifically, the present invention relates to a carbon yam product which is flexed after pre-carbonizing to break fiber-to-fiber bonds between the yam filaments. BACKGROUND OF THE INVENTION Carbon yam products are used in many applications such as in the preparation of carbonized fabrics for composite reinforcement and the like. An example of a carbonized fabric is found in U.S. Patent No. 972,110. Often, a number of carbon-based filaments are bound together such as by twisting, to form a yam element. Individual yam elements are then further processed such as by twisting a number of elements to form a cord, or weaving the elements to form a cloth or fabric. In industries using carbonizable ya , such as carbonized fabric industries or the like, the first step in manufacturing the carbon yam is to remove any sizing materials such as starch, mineral oil, wetting agents or "surfactants" or the like, from the raw yam. This procedure is known as "scouring" and usually includes cleaning the yam with a dry cleaning solvent such as perchloroethylene or another similar scouring agent. Sizing materials are often applied to carbonizable filaments during the formation of the yam products to prevent damage during subsequent processing to prepare the yam. Such subsequent processing may include twisting, spooling, weaving or the like. The sizing material is applied to the yam product to help prevent damage during such processing. However, if the sizing is not removed from the carbonizable yam prior to carbonizing, the resulting carbon yam product is stiff, brittle, weak and is generally not useable or further processible. This has been determined to be caused, it is believed, by bonding between the individual filaments of the yam. The bonding is likely caused by the reaction of the sizing material between the filaments during carbonization procedures. The sizing material is present on the raw filaments, and it might be intentionally not removed from the filaments or its removal might be non- uniform. In either case, the resulting carbon yam product is deficient for the reasons as stated hereinabove. Unfortunately, perchloroethylene and other scouring solvents have come under scrutiny and regulation, and their use has become increasingly undesirable. A need exists therefore, for a flexible and strong carbon yam which is prepared without a solvent scouring step. SUMMARY OF INVENTION It is therefore, an object of the present invention to provide a strong and flexible carbon yam and products thereof. It is another object of the present invention to provide a strong and flexible, rayon-based carbon yam and yam products. It is still another object to provide a process for the preparation of a strong flexible carbon yam. At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to carbon yam, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed. In general the present invention provides a process for the preparation of a carbon yam product which comprises the steps of pyrolizing raw carbonaceous yam comprising a plurality of carbon fibers, at a temperature above about 650°F; flexing the pyrolized yam to substantially break fiber-to-fiber bonding between the fibers; and, exposing the yam to a temperature sufficient to carbonize the carbon. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevational, fragmentary view of a yam element made from a plurality of filaments twisted together; Fig. 2 is a perspective, fragmentary view of a fabric formed by weaving a number of elements as in Fig. 1; Fig. 3 is a side elevational view of a portion of a flexing apparatus according to the present invention; Fig. 4 is a partially schematic front elevational view of the flexing apparatus as in Fig. 3; and, Fig. 5 is a close up view of a portion of the flexing apparatus of Fig. 3. PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION The present invention is directed toward a carbon yam product. More particularly, the present invention provides a flexible, non-scoured, preferably rayon- based carbon yam. Heretofore, it has been necessary to scour rayon yams prior to carbonization in order to remove the sizing materials applied prior to processing. Otherwise, the resulting carbonized yam is stiff and brittle and essentially useless for further processing. It is not an acceptable solution to merely not size the yam, because sizing is necessary for handling the raw yam for further processing thereof. The present invention provides a flexible carbon yam from which the sizing material has not necessarily been removed. Because many scouring solvents have been or will be regulated, it is desirable to provide a yam product which is flexible and yet which has not been scoured. As used herein, the term "carbon yam" shall be used to connote an element which is made up of a plurality of individual carbon-based filaments. A "yam product" is an article or the like formed from the yam, such as a fabric or other article. A filament is simply a strand of the carbon material, and a plurality of filaments may be brought together such as by twisting, or the like, to form a larger element. Each filament in an element therefore, is in contact with at least one other filament in the element and may be in contact with a plurality of other filaments. A number of elements may themselves be brought together to form a cord and so on. Although the terms filament, element, cord and the like are arbitrarily chosen, they have accepted meanings in the industry, allowing relative size determinations to be made and conveyed. No other limitations are to be imputed to the present invention as a result of the use of these terms. For purposes of illustration, Fig. 1 shows a yam element 10 which is made up of a number of individual filaments or fibers 11. Filaments 11 are twisted together to form element 10. A plurality of elements 10 may be used for example, to weave a fabric 12 (Fig. 2) having warp elements 13 and fill elements 14. Each filament 10 according to the present invention, is formed from a carbonaceous material, such as rayon, polyacrylonitrile, pitch, phenolic resins, and the like. Such carbonaceous materials may be readily carbonized by exposure to elevated temperatures. It has been found that during carbonization procedures, the sizing materials which have been at least partially coated onto the filaments 11 prior to twisting to form element 10, or prior to other similar processing, bonds with the sizing on adjacent filaments 10. The resulting yam is stiff and brittle due to this inter-filament bonding. In order to provide a strong and flexible carbon yam, the present invention employs conventionally sized, raw, i.e. , non-carbonized, non-scoured ya , and subjects the yam to a pre-carbonization process by exposing the yam to elevated temperatures sufficient to cause bonding of the sizing material. For example, a rayon-based carbonaceous yam such as carbonizable bright rayon having 720 filaments/ 1650 denier, such as is commercially available from North American Rayon Corp. and Gmpo Cydsa and others, and sized with mineral oils, may be subjected to a temperature cycle reaching above about 650°F, such as from about 650°F to about 750°F, for a period of time sufficient to cause the inter-filament bonding. The time period will of course vary, such as from about 5 to about 14 days. This pre-carbonization pyrolysis may be accomplished by conventional heating techniques. After the pre-carbonization pyrolysis is completed, the stiff and brittle yam is subjected to a flexing operation to now be described. The pre-carbonized yam is subjected to a mechanical working, kneading or flexing procedure whereby the yam is flexed, thereby mechanically and substantially separating or breaking the bonds between the sizing of adjacent filaments. The flexed yam is then fully carbonized at a temperature sufficient to carbonize the yam, such as by exposure to temperatures above about 2000°F and as high as 4500°F or higher, depending upon the desired properties of the carbon yam, and the desired carbon assay. One preferred range for the final carbon content or "assay" is from about 90 to 100 percent, which will of course, vary depending upon the expected end use of the material. Flexing of the yam according to the present invention is preferably accomplished by applying an equal and opposite force upon opposing sides of the yam or yam product. This is preferably accomplished by employing a flexing apparatus 20 (Fig. 3) having a pair of rotatable opposed rolls 21 and 22 which are placed in peripheral contact with for example, element 10. The center of roll 21, axis A in Fig. 4, is preferably parallel to axis B of roll 22, and rolls 21 and 22 are rotatable on their respective axis A and B. Furthermore, at least one roll, such as roll 21, is moveable in a direction indicated by arrow 23 (Fig. 3), substantially perpendicular to the direction of travel of element 10 which is shown by arrow 24 in Fig. 3. As will be appreciated, the relationship as described with respect to the movement of roll 21 and the direction of travel of element 10 may be of an angle other than 90 degrees representing a perpendicular arrangement, and still be within the scope of the invention. Movement of a roll such as roll 21 may be accomplished by any conventional method, either by being manually or automatically controlled. Because the means of accomplishing such movement is not a limitation of the invention, drive unit means 30 for accomplishing such movement is schematically represented in the drawings. It will be appreciated then, that roll 21 is selectively moveable transversely to its axis of rotation A, such that the force exerted upon the element 10 is selectively adjusted by moving roll 21. Further, drive unit 30 may also be employed to rotate roll 21 on its axis A, or another means of accomplishing rotation of roll 21 (not shown) may be employed without limitation. A similar drive unit 31 may be operatively connected to roll 22. As shown in Fig. 5, yam element 10 may be compressed between rollers 21 and 22, thus breaking inter-fiber and inter-filament bonding. The size of rollers 21 and 22 will vary with respect to each other, the means of rotating one or both, and the yam element to be flexed. The rollers 21 and 22 are shown in the drawings as being of different sizes, all of which are within the scope of the invention. The distance of movement of roll 21 and hence the flexural pressure exerted upon the yam being processed is, of course, dependent upon the nature of the yam, the thickness of the yam, the amount of sizing and the strength of inter- element bonding, and the like. By way of example, for a rayon-based carbon yam fabric, such as is commercially available from for example, Highland Industries, having about 720 filaments per element and a denier of 1650 sized with mineral oil and having been pre-carbonized by exposure to 700°F for 12 hours, the required equal and opposite force exerted upon the fabric would be about 3 pounds/inch for 10 times. By "for 10 times" it is meant that the yam is flexed by 10 pair of rollers 21 and 22 at the given force. By way of example only, the equal and opposite force exerted upon an average rayon-based carbon yam or carbon yam product may vary from about 2 to about 5 pounds/inch for from about 5 to about 12 times. It has been found that passing the yam through a series of sinuous path rollers, that is, with no equal opposing force being applied to the yam, will not be sufficient to break the inter-filament sizing bonds. Sinuous path rollers work for yams which are only mildly fiber bonded. Severely fiber bonded yams are brittle and will break in a sinuous path. For a sinuous path to work effectively requires a small roller diameter and acute angles for its path. Furthermore, sinuous paths will have virtually no effect on the fill yam in the fabric. Because the fill yams are parallel to the length of the rollers in a sinuous path roller, they experience no bending action as they pass through the path. Therefore, sinuous path mechanisms are not useful for woven fabrics. That is, when an element such as element 10 is passed over a single roller (not shown), the filaments 11 proximate to the roller will experience compression forces; the middle filaments 11 will be relatively neutral in applied force; and, the distal filaments 11 will undergo tension forces. According to the present invention however, as illustrated in Fig. 3, when fabric 12 is passed through flexing apparatus 20, all of the filaments 11 are subjected to the equal and opposite compression forces, and both fill elements 13 and warp elements 14 of a fabric 12 will be flexed and substantially debonded. The material may then be subjected to standard carbonization procedures, and the resulting product will remain flexible and strong, as will be exemplified hereinbelow. It will be appreciated that even slight amounts of breaking of inter- filament bonds will provide an improvement in the flexibility in the resulting yam or yam product and would be within the scope of the invention. It is preferred however, that substantially all of the inter-filament bonds be broken. Furthermore, it will also be appreciated that inter-element bonding may also occur between yam elements and yam products, which may also be broken and which would be within the scope of the present invention. General Experimental In order to demonstrate the effectiveness of the present invention in providing a flexible, non-scoured carbon yam, a number of flexible yam elements and products were prepared according to the invention. For comparison, a number of comparative examples were also prepared and tested, as will be more fully discussed hereinbelow. Example No. 1 In this example, a GRUPO CYDSA rayon-based yam element was sized with "99" or CYDSA Std., which are proprietary sizings available from GRUPO CYDSA. None of the samples were scoured and equivalent samples of each were tested with flexing according to the present invention and without such flexing. Each sample was pre-carbonized by exposure to 700°F for 12 hours, flexed or not flexed as required, and then carbonized by exposure to temperatures above about 2000°F. Heating was achieved by use of a conventional furnace. Furthermore, ten identical samples of each were tested for Break Strength after carbonizing, unit weight in grams per meter (g/m) and Tenacity in grams/denier (g/d). The average break strength was also determined between the ten samples of each yam. The results of these tests are reported in TABLE I hereinbelow. a) Rayon-based carbon yarn; 1 ply; 1650 denier; 750 filaments/element b) Mixture of starch and mineral oil c) CYDSA std. sizing from GRUPO CYDSA The results of the tests reported in TABLE I indicate that the unscoured and mechanically worked materials, i.e., flexed according to the present invention, were about twice as strong as the unscoured but not mechanically worked materials. Example No. 2 In this example, samples were prepared as in Example No. 1, however, a number of the samples were flexed twice and a number of the control samples were scoured with perchloroethylene. The results of the tests of these samples is reported in TABLE π hereinbelow. 10 0 I 15 - 20 a) Rayon-based carbon yarn; 1 ply; 1650 denier; 750 filaments/element 25 b) Mixture of starch and mineral oil c) CYDSA std. sizing from GRUPO CYDSA d) Heating element from The Carborundum Company The results reported in TABLE π provide further evidence that the unscoured and mechanically worked materials were about twice as strong as the unscoured but not mechanically worked materials. It is also shown that the unscoured and mechanically worked materials have comparable strengths to the standard scoured materials. Example No. 3 In order to demonstrate the application of the invention to other carbon yams, NARC-23, a 5-ply rayon cordage from North American Rayon was tested as above, with five samples each of six yams, A-F, being tested. Three of the six yam elements, A-C, were mechanically worked and three, D-F, were not, in order to provide a comparison. The results of this example are reported in TABLE m hereinbelow. 10 Average 9.70 10.40 11.32 3.50 2.70 3.10 15 a) North American Rayon; 5 ply rayon cordage made from 1650 denier; 720 filaments/element; 2 twists per inch The results of Example No. 3 again show that the samples according to the present invention A-C, were two to three times stronger than the unflexed comparison examples, D-F. Example No. 4 In order to demonstrate the effectiveness of the present invention in providing a flexible yam product, a carbon cloth having conventional warp and fill elements was prepared. Certain samples of the cloth were scoured or unscoured, and certain samples were mechanically worked or unworked, as indicated in TABLE IV hereinbelow. TABLE IV also indicates the test results of these samples. TABLE IV Unscoured vs. Scoured - Flexed vs. As is Carbon Cloth 10 15 Average, lbs./in. 20.0 25.2 30.9 35.7 36.9 42.6 20 Break Strength - Fill, lbβ./in. TABLE IV CONTINUED 14 14 19 24 21 19 14 12 18 27 19 25 10 15 24 26 18 20 13 15 21 24 22 18 12 14 22 24 17 20 l H 10 Average, lbs./in. 12.9 14.3 21.6 26.0 19.3 20.7 a) GRUPO CYDSA rayon woven into an 8 harness satin cloth b) North American Rayon rayon woven into an 8 harness satin cloth 15 c) North American Rayon rayon woven into an 8 harness satin cloth The results in TABLE IV again show that the unscoured and mechanically worked materials are stronger than the comparable comparison unscoured and/or not mechanically worked materials. Thus it should be evident that the carbon yams, yam products and methods of the present invention are highly effective in providing a flexible, non- scoured material. The invention is particularly suited for rayon-based carbon yams, but is not necessarily limited thereto. Based upon the foregoing disclosure, it should now be apparent that the use of the carbon yam and methods described herein will carry out the objects set forth hereinabove. It is, therefore, to be understood that any variations evident fall within the scope of the claimed invention and thus, the selection of specific component elements can be determined without departing from the spirit of the invention herein disclosed and described. Thus, the scope of the invention shall include all modifications and variations that may fall within the scope of the attached claims.

Claims: CLAIMS What is claimed is: 1. A process for the preparation of a carbon yam product comprising the steps of: pyrolizing sized raw carbonaceous yam comprising a plurality of carbon fibers, at a temperature above about 650°F; flexing said pyrolized yam to substantially break fiber-to-fiber sizing bonding between the fibers; and, exposing said yam to a temperature sufficient to carbonize the carbon yam. 2. A process, as set forth in claim 1 , wherein said step of flexing includes passing said yam between at least two opposing rollers, such that an equal and opposite force is exerted upon said yam sufficient to substantially break fiber-to-fiber bonding in said yam. 3. A process, as set forth in claim 2, wherein said force is from about 2 to about 5 pounds per inch. 4. A process, as set forth in claim 1, wherein said carbonaceous fibers are rayon- based. 5. A process, as set forth in claim 1, wherein said fibers are at least partially coated with a sizing material, and wherein said step of flexing said pyrolized ya breaks bonds formed by said sizing material between at least two of said fibers. 6. A flexible yam formed by the process of claim 1. 7. A process, as set forth in claim 2, wherein at least one of said rollers is selectively moveable transversely to its axis of rotation, such that the force exerted upon said yam is selectively adjusted by moving said at least one of said rollers. 8. A flexible yam element comprising: a plurality of carbon filaments wherein each said filament is in contact with at least one other said filament; a sizing material at least partially coating said plurality of filaments; wherein said sizing material of each said filament is substantially separated from the sizing material of said at least one other said filament in contact therewith. 9. A yam element, as set forth in claim 8, wherein said sizing material is selected from the group consisting of starch, mineral oil, wetting agents and mixtures thereof. 10. A yam element, as set forth in claim 8, wherein said carbonaceous filaments are rayon-based. 11. A flexible, pre-carbonization pyrolized, carbonizable yam product containing a plurality of yam elements, wherein the yam elements are comprised of a plurality of individual filaments in contact with adjacent filaments and the filaments are at least partially coated with at least one sizing material, and wherein the yam elements are substantially free from inter-filament bonding of said sizing material. 12. The flexible, pre-carbonization pyrolized, carbonizable yam product as in claim 11 wherein the filaments are derived from a carbonaceous material selected from the group consisting of rayon, acrylonitrile, pitch, phenolic resins, and mixtures thereof. 13. The flexible, pre-carbonization pyrolized, carbonizable yam product as in claim 11 wherein the filaments are derived from rayon. 14. The flexible, pre-carbonization pyrolized, carbonizable yam product as in claim 11 wherein the sizing material is selected from the group consisting of starch, mineral oil, wetting agents and mixtures thereof. 15. The flexible, pre-carbonization pyrolized, carbonizable yam product as in claim 11 comprising a woven fabric. 16. A carbonized yam product derived from the flexible, pre-carbonization pyrolized, carbonizable yam product of claim 11.

Inventors: DEVANE KENNETH A, FERNANDEZ RAMON B, DEVANE, KENNETH, A., FERNANDEZ, RAMON, B.
Applicants: BP CHEMICALS HITCO INC, BP CHEMICALS (HITCO) INC.
Application year: 1995
Main classification: D02G3
IPC codes: D01F9