Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/145—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from pitch or distillation residues

Definitions

• This invention relates to pitch-based high performance carbon fibers having superior workability and their production method. More particularly, it relates to pitch-based carbon fibers obtained by mitigating carbonization treatment to such an extent that silicone types spin finish oils coated at the time of spinning of pitch are remained, having a high cohesiveness of bundles and lubricity by the remaining silicone type spin finish oils and having a superior workability and to their producing method.
• the carbon fibers obtained from a pitch according to a method of the present invention is incomplete in crystallization and orientation structure of carbon hexagonal network and yet have capability of increasing their tensile strength and modulus of elasticity greatly by an additive heat treatment carried out under a relaxed state whereby the growth of graphitic crystalline and orientation structure proceed.
• the carbon fibers of the present invention are superior in adaptation to various kinds of processes such as taking up on bobbins, transportation to a higher grade of carbonization or graphitization step, weaving,knitting and working for the reinforcement of resin.
• the pitch-based carbon fibers of the present invention are easy in working because of their lower carbonization grade, and their cost is lower than those of a higher carbonization grade. Thus even when working loss is produced, they have an advantage because the influence upon the cost of product is small.
• the carbon fibers derived from a pitch according to the present invention are patient against bending of small radius of curvature compared with carbon fibers subjected to higher grade of carbonization and have superior characteristic properties because their bent portions receive stress relaxation by the carboni­zation treatment applied thereafter and show superior resistance to abrasion, flexion and scratching.
• a method for obtaining carbon fibers by subjecting a pitch having a high softening point to melt-spinning, oxidizing the resulting fibers to make them infusible, followed by carbonization carried out in an inert gas atmosphere is disclosed in Japanese official gazette of examined application (Tokuko) 15728 of 1966.
• This is certainly a superior production method of pitch-­based carbon fibers but according to the disclosed method, it is necessary to keep fibers in a stretched state during the carbonization to obtain fibers having high modulus of elasticity. Since thermoset pitch fibers are extremely brittle, it is difficult to hold them in a stretched state. It is considered actually to be impossible to obtain high modulus carbon fibers by this method.
• optically anisotropic pitch is easily graphitizable material and has superior properties as raw material for high strength, high modulus carbon fibers. Particularly, there is no need of being kept in a stretched state during the carboni­zation; it is considered to be an advantageous method in view of cost and quality.
• Carbon fibers from an optically anisotropic pitch can be easily made into a high strength and high modulus fibers but on the other hand, they have such weak points, that they are liable to be flawed, e.g. liable to be broken at the time of working. Such weak points exist more or less in case of brittle fibers.
• Glass fibers, PAN-based carbon fibers, etc. are coated by sizing agents to give lubricity and cohesiveness of bundles.
• repelling a sizing agent due to harmful effect of easily graphitizable property. Since uniform coating is difficult, shortages of lubricity and cohesiveness of bundles are also weak points.
• Japanese unexamined patent application (Tokukai) 21911 of 1985 discloses a method in which light grade of carboniza­tion is carried out at a temperature of 400 - 650°C after thermosetting. This method is effective to some-extent for keeping the modulus of elasticity of carbon fibers small and for preventing them from being flawed but since bundles of the fibers have no cohesive­ness and no lubricity, there are problems in insufficiency of workability.
• thermosetting which is a heat treatment carried out in the oxidative atmosphere.
• second oils after thermosetting process The problem of this method is the liability of being flawed at the time of imparting the second oils because the pitch fibers after thermo­setting are equally or more brittle than the pitch fibers after spinning.
• the carbonization of pitch-based fibers is carried out generally by the heat treatment in the atmosphere of an inert gas and its effect is considered, in general, to be depend on temperature and time.
• spin finish oils there is the effect of spin finish oils remained.
• the effect for lubricity and cohesiveness of bundles are notable. Further there seems to be a difference of effectiveness between apparatus for carbonization.
• the present invention comprises coating spun pitch fibers with silicone type spin finish oils, introducing said pitch fibers in the oxidative atmosphere at a maximum temper­ature of 200 - 400°C to effect the thermosetting and subsequently subjecting said pitch fibers to the carbonization treatment in the atmosphere of an inert gas at a temperature of 400 - 1000°C under the condition that the silicone type finish oils remained on said pitch fibers are in the range of 0.1% - 2.0% by weight of said fibers and transferring them to a next working step.
• a high softening point pitch referred to in the present invention is an easily graphitizing pitch such as an optically anisotropic pitch.
• the easily graphitiz­ing pitch forms needle cokes by dry distillation. Further, at the time of carbonization of pitch fibers, it produces high modulus carbon fibers even under a tensionless condition.
• the easily graphitizing pitches include, besides optically anisotropic pitches, dormant mesophase pitches, and premesophase carbonaceous materials which show similar graphitizing property.
• the silicone type oil used in the present invention is preferably a matter having a heat resistance of 500°C or more.
• the heat resistance of oils is defined as a temperature at which a reduction of the weight of oils measured by using a thermobalance (TG high temperature type CN 8068 AZ manufactured by Rigaku Denki was used; Sample size 10 mg, flow amount of nitrogen; 40 ml/min. cell diameter; 5mm, cell depth 2.5 mm) at a heating rate of 10°C/min. in the stream of nitrogen becomes practically zero. (It means that the change of the weight in a temperature range of 100°C becomes less than the sensitivity. The sensitivity is adjusted as 0.1% of the initial weight.)
• silicone type spin finish oils those which show smaller amount of decomposition sludge by heating is preferable.
• Polysiloxane type and polyaminosiloxane type are preferable.
• a solvent as a diluent those such as a sur­factant which is not a silicone type, a lubricant or an antioxidant.
• carbon fibers of the present invention were determined to contain 2.0 - 15.0% by weight of oxygen, 0.07 - 0.7% by weight of sulfur. If these contents are too little, those inferior in workability are resulted. On the contrary, if they are too much, there is a tendency that the properties of ultimate products which are carbonized at a temperature of 2000°C or more, are lowered.
• the remaining amount of the oils is preferably in the range of 0.2 - 1.0% by weight of fibers.
• the remaining amount of the oils being too small, the cohesiveness and lubricity of bundle of filament yarns become poor and are liable to produce trouble by static electricity.
• the remaining amount of the oils being too much, it is not preferable not only because of the increase of the amount of oils imparted at the time of spinning which is disadvantageous in view of the cost but also because of reduction of thermosetting velocity.
• the reason for reduction of thermosetting velocity is not clear completely but it seems to be caused by the prevention of diffusion of oxygen by the film of the oils and reduction of the effective oxygen concentration caused by the large amount of vapour due to the oils generated in the inside of a furnace which drives oxygen out of the furnace.
• Carbon fibers produced by the present invention have a tensile strength of 5 - 50 Kgf/mm2, an elongation of 0.3 - 8.0% and a capability of increasing its tensile strength to 150 Kgf/mm2 or more and its modulus of elasticity to 30,000 Kgf/mm2 or more by the additive heat treatment carried out in the relaxed state. If the tensile strength becomes smaller than this range, it is not preferable because fibers become liable to be flawed at the step of next working. If the tensile strength becomes greater than this range, it is not preferable because fibers become liable to be broken at the time of working and abrasion resistance is reduced.
• the tensile strength is preferably in the range of 10 - 45 Kgf/mm2.
• the elonga­tion is preferably in the range of 0.6 - 5.0%.
• Increase of tensile strength and increase of modulus of elasticity by the additive heat treatment carried out in the relaxed state are phenomena usually observable in case of easily graphitizing pitch but those having a tensile strength smaller than above-­mentioned range after an additive heat treatment is not preferable because resistance to fatique and resistance to oxidation are inferior.
• the tensile strength after the additive heat treatment is preferably in the range of 200 - 450 Kgf/mm2.
• Those having a modulus of elasticity smaller than above-­mentioned range are not preferable because resistance to fatique and resistance to oxidation is inferior and change of dimension at the time of working is greater.
• the modulus of elasticity after the additive heat treatment is preferably in the range of 40,000 - 100,000 Kgf/mm2.
• the carbon fibers produced according to the present invention have, preferably a specific gravity of 1.30 - ­1.70, a specific electric resistance of 5 ⁇ 108 - 5 ⁇ cm, a stack height of graphitic layers L c (002) of 8 - 32 ⁇ , a graphitic interlayer spacing distance d 002 of 3.46 - 3.49 ⁇ and after strength and modulus have been increased by the additive heat treatment, a stack height of graphitic layers L c (002) of 36 ⁇ or more, increase of a stack height L c (002) of 5 ⁇ or more, a graphitic interlayer spacing distance d 002 is 3.46 ⁇ or less and decrease of interlayer spacing distance d 002 is 0.03 ⁇ or more.
• a specific gravity is 1.35 - 1.60
• a specific electric resistance is 1 ⁇ 108 ⁇ 1 ⁇ 102 ⁇ cm and after strength and modulus have been increased by the additive heat treatment
• a stack height of graphitic layers Lc (002) of 70 -240 ⁇ and a graphitic interlayer spacing distance d 002 is 3.36 - 3.44 ⁇ .
• resulting pitch fibers are wound up on bobbins or without being wound up on bobbins and introduced con­tinuously into an oxidative atmosphere at a maximum temperature of 200 - 400°C while being placed on a transportation belt for thermosetting, subsequently the fibers are subjected to carbonizing treatment in the atmosphere of an inert gas at a temperature of 400 - 1000°C while being placed on a transportation belt, under the condition to make the silicone type oils remaining on the pitch fibers in the adhered state in the amount of 0.1% - 2.0% by weight of said fibers and said fibers are transferred to a next step.
• the spin finish oils and a sizing agent are imparted during the spinning step before the pitch fibers are placed on a transportation belt. The remaining of these chemical agents is effective in improving handling property at the time of winding up of fibers after carbonization or various kind of working.
• any way is allowable so long as reversal of order of fiber-bundles does not occur e.g. such a way where it does not occur that fibers placed afterwards get into the previously formed fiber layers and order of fibers is disturbed.
• a transportation belt is a net conveyer When the fiber-bundles are delivered from a direction close to the vertical to the transportation belt surface, it often happens that they get into the holes of belt or previously formed fiber layers.
• the fibers are subjected to thermosetting in the oxidative atmosphere at a maximum temperature of 200° - ­400°C preferably while being placed on a transportation belt after spinning.
• heating temperature it is preferable to select a temperature lower than 200°C at the inlet and to elevate the temperature slowly to give the highest temperature at the outlet, rather than to keep a fixed temperature throughout the whole process.
• Most preferably the maximum temperature is 250 - 350°C.
• the pitch fibers after thermosetting are extremely weak, they cannot be subjected to a treatment in which a force is applied to the fibers. It is preferable to send them into a carbonization apparatus as they are in the state placed on the transportation belt. During the treatment carried out in the state placed on the transportation belt, there is no need of imparting oils or sizing agents.
• the carbonization treatment is carried out at a temperature of 400 - 1000°C in an inert gas atmosphere under the condition in which silicone type oils are remaining in the state adhered on the pitch-based fibers in an amount of 0.1% - 2.0% by weight based upon said fibers.
• an inert gas it is preferable to start from the substitution of the oxidative atmosphere by an inert gas at a temperature close to about 400°C. If the substitution by the inert gas is insufficient, a problem such as a decrease of fiber diameter, insufficiency of an increase of strength or the like may occur.
• Treatment time varies according to the diameter of fibers but it is preferable to elevate the temperature slowly at a rate of 10 - 100°C/min at the beginning and carry out the substitution of the atmosphere sufficiently by an inert gas and to maintain at a constant temperature for several seconds or several hundred seconds in the final stage.
• Resulting fibers are subsequently taken up on bobbin or the like and subjected to a next processing. If necessary after subjecting to a further processing, such as weaving, knitting or the like, an additional carbonization can be applied to produce high strength, high modulus carbon fibers. Further it is possible to treat the fibers at higher temperature to graphitize the fibers. At the time of the additional carbonization, it is possible to stretch the fibers to increase a tensile strength and a modulus of elasticity.
• the carbon fibers obtained according to the present invention differently from the fibers highly carbonized, have a smaller modulus of elasticity, a superiority in cohesiveness of bundles and a superiority in workability to such works as those containing a step of bending at a small radius of curvature e.g. weaving and knitting. Further since the fibers of the present invention are of lower cost than fibers of advanced carbonization state, they are extremely advantageous in case of products which cause a large amount of working loss. Since relaxation of strain occurs at the time of carbonization, they are superior in abrasion resistance and fatique resistance of bent parts of small radium of curvature. Further they show a resistance against a fluff forming by abrasion and against a flexion and a scratching.
• the carbon fibers obtained according to the present invention are liable to be wetted by a resin prepolymer, an adhesive, an oiling agent and a sizing agent and have superior workability.
• the graphitic interlayer spacing distance of the pitch-based carbon fibers of the present invention was measured by using a X-ray diffraction apparatus. Fibers were ground to powder. About 10% by weight of high purity silicon powder for X-ray standard was admixed as a internal standard substance, and mixture was filled in a sample cell. By a X-ray diffractometer method, in which Cu K ⁇ ray was used as a source of ray, carbon 002 diffraction line and the standard. silicon 111 diffraction line were measured,then the diffraction angle of( ⁇ )of carbon 002 plane was calculated from 002 diffraction peak position to which correction relating to Lorentz polarization factor, atomic scattering factor and absorption factor have been made.
• a distillate fraction of a residual oil of a thermal catalytic cracking (FCC) having an initial fraction of 450°C and a final fraction of 560°C (converted to an atmospheric pressure) was subjected to heat treatment at a temperature of 400°C for 6 hours while sending methane gas therein and further heated at a temperature of 330°C for 8 hours to grow mesophase and the mesophase pitch was separated by sedimentation taking advantage of difference of specific gravities.
• This pitch had an optically anisotropic portion of 100%, a quinoline insoluble portion of 43% and a toluene insoluble portion of 82%.
• This pitch was spun through a spinning hole having an enlarged part at an outlet.
• spin finish oils were coated upon the spun fibers according to a common procedure, the pitch fibers were taken up at a rate of 270 m/min. and piled up on a transportation belt while giving waving motion so as to form spiral shape locus.
• the spin finish oils silicone type oils having a heat resistance of 630°C and a viscosity of 230 centi-Stokes was used.
• the amount of adhered spin finish oils was 3.0% based upon the weight of the pitch fibers.
• resulting fibers were subjected to thermosetting by an oxidation treatment with air while elevating a temperature at a rate of 3°C/min. in a furnace having a temperature of 160°C at an inlet and 320°C at an outlet.
• the fibers which came out of a furnace were sent into a carbonization furnace while being kept on the transportation belt.
• the temperature at the inlet was 420°C.
• elevating temperature at a rate of 5°C/min. till 500°C and at a rate of 20°C/min. till 580°C substitution of the atmosphere with an inert gas was carried out.
• the fibers were taken out of the furnace and after reversing the upper and lower layer while putting the fibers between the transportation belt and a second belt, the fibers were wound up on bobbins.
• the amount of the oils remaining on the resulting fibers was 0.25%.
• a tensile strength, a modulus of elasticity, an elongation, a specific gravity and a specific electric resistance were, 27 Kgf/mm2, 820 Kgf/mm2, 3.3%, 1.52 and 2 ⁇ 107 ⁇ cm, respectively.
• the properties of plain woven fabrics before and after the heat treatment in the atmosphere of argon were investigated.
• the woven fabrics of the fibers before the heat treatment were compared after an additive heat treatment carried out in the atmosphere of argon. Both did not show big difference in a tensile strength, an elongation and a modulus of elasticity but the woven fabrics made from the fibers after the heat treatment were slightly bulky, had a tendency of being fluffy by abrasion, and were slightly inferior in resistance to flexion and scratching and the resistance to abrasion of their selvage parts was inferior greatly.
• Example 1 The pitch fibers spun as in Example 1 were wound up on bobbins made of alumina porcelain and subjected to a thermosetting and a carbonization treatment under a condition for heating similar to Example 1. The amount of the oils remaining was 0.09%. It seems that a cooling rate after the carbonization treatment was slow and on this account decomposition loss was large.
• the tensile strength, the elongation, the modulus of elasticity and the crystalline state did not show much difference from Example 1 but the weaving property was greatly inferior, and weaving of the multiple axial fabrics and the three-dimensional fabrics were difficult.
• Example 1 Further when the amount of the spin finish oils after spinning was increased than in Example 1 and the remaining amount was 0.25%, the weaving property became close to Example 1, but the wound-up shape of filaments was worse, breakage of filaments occurred frequently and it was difficult to pass through the preparation step for weaving.
• Pitch fibers spun as Example 1 were taken in a cans made of a heat-proof alloy and subjected to a thermosetting and a carbonization treatment under a temperature-elevating condition similar to Example 1. The remaining amount of the oils was 0.08%. Since a cooling rate after the carbonization treatment was slow as in Comparative example 1, it seems that decomposition loss increased. The tensile strength, the elongation, the modulus of elasticity and the crystalline state of the fibers were not different greatly from these values of Example 1. But because taking out of the cans was difficult, the estimation of the weaving property was difficult.
• Example 1 By using the pitch same with Example 1, spinning was carried out under the same spinning condition with Example 1.
• the fibers after a thermosetting in the state piled up on a transportation belt were subjected to a carbonization treatment by changing the maximum temperature of a carbonization furnace. Then the fibers were wound up on bobbins and the remaining amount of the oils was measured and the working property was evaluated by weaving. The result thereof is shown in Table 1.
• the pitch-based carbon fibers produced according to the present invention are superior in cohesiveness and lubricity of bundles and in processability or workability even when second oils or the like are not imparted after the thermosetting or the carbonization.
• the pitch-based carbon fibers produced according to the present invention can be easily processed than conventional products with no remaining spin finish oils and having higher carbonization grade and are inexpensive in cost because there is no need of an additional imparting of second oils or the like.
• the carbon fibers produced according to the present invention are patient against a bending of small radius of curvature and are superior in resistance to abrasion, to flexion and to scratching of bent parts because the bent parts receive a stress relaxation by the carbonization treatment carried out in the later stage.
• the carbon fibers produced according to the present invention can be used in various kind of fiber reinforced composite materials as they are or after the carbonization treatment or the graphitization treatment. Further they can be used as raw materials for activated carbon fibers.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Inorganic Fibers (AREA)
• Chemical Treatment Of Fibers During Manufacturing Processes (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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• 1987
  • 1987-09-03 JP JP62219224A patent/JPH0651928B2/ja not_active Expired - Lifetime
• 1988
  • 1988-01-26 CA CA000557363A patent/CA1311883C/en not_active Expired - Fee Related
  • 1988-01-27 EP EP88101195A patent/EP0276840B1/de not_active Expired - Lifetime
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