CA1254167A - Electroplating cleaned graphite fibres with metal - Google Patents
Electroplating cleaned graphite fibres with metalInfo
- Publication number
- CA1254167A CA1254167A CA000457196A CA457196A CA1254167A CA 1254167 A CA1254167 A CA 1254167A CA 000457196 A CA000457196 A CA 000457196A CA 457196 A CA457196 A CA 457196A CA 1254167 A CA1254167 A CA 1254167A
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- organic compounds
- compounds
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Abstract
ABSTRACT OF THE DISCLOSURE
Metal coated fibers, the majority of which comprise a core of graphite and a thin, uniform firmly adherent electrically conductive layer of an electrodepositable metal, such as nickel or the like, are provided by electrodeposition from a solution onto the core. Uniformity and production speed are substantially improved if the surface of the core fibers is provided substantially free of adsorbed organic compounds. In the electrodeposition process the voltage is in excess of what is normally required for metal deposition.
Metal coated fibers, the majority of which comprise a core of graphite and a thin, uniform firmly adherent electrically conductive layer of an electrodepositable metal, such as nickel or the like, are provided by electrodeposition from a solution onto the core. Uniformity and production speed are substantially improved if the surface of the core fibers is provided substantially free of adsorbed organic compounds. In the electrodeposition process the voltage is in excess of what is normally required for metal deposition.
Description
~254~67 ELECTROPLATING CLEANED GRAPHITE
FIBERS WITH METAL
The present invention relates to an improved process for the production of bundles of fibers having conductive graphite cores coated with thin, uniform, adherent layers of electro-deposited metals. The process improvement comprises providing the cores free of adsorbed organic compounds prior to and during electrodeposition of the metal. Adsorbed organic compounds may interfere with the electrodeposition of uniform, adherent metal coatings.
~;~5~,7 BACKGROUND OF THE INVENTION
Bundles of high strength fibers Gf non-metals and semi-metals, such as carbon, boron, silicon carbide, and the like, in the form of filaments, mats, cloths and chopped strands are known to be useful in reinforc-ing metals and organic polymeric materials. Articles comprising metals or plastics reinforced with such fibers find wide-spread use in replacing heavier com-ponents made of lower strength conventional materialssuch as aluminum, steel, titanium, vinyl polymers, nylons, polyesters, etc., in aircraft, automobiles, office equipment, sporting goods, and in many other fields.
High strength carbon fibers are made by heating polymeric fiber, e.g., acrylonitrile polymers or copoly-mers, in two stages, one to remove volatiles and carbon-ize and other to convert amorphous carbon into crystal-line carbon. During such procedure, it is known thatcarbon changes from amorphous to single crystal then orients into fibrils. If the fibers are stretched during the graphitization, then high strength fibers are formed. This is critical to the formation of the boundary layer, because as the crystals grow, there are formed high surface energies, as e~emplified by incomplete bonds, edge-to-edge stresses, differences in morphology, and the like. It is also known that the new carbon fibrils in this form can scavenge organic compounds, because the surfaces behave like activated carbon, to produce non-carbon surface layers which are firmly adsorbed thereto.
~254~67 61109-7298 Numerous unsuccessful attempts have been reported to provide such filaments, especially carbon filaments, in a form uniquely suitable for reinforcing metals and plastics. Many have involved depositing layers of metals, especially nickel and copper, as thin surface layers on the filaments. Such a coated fiber was then to be used in a plastic or metal matrix. The metals in the prior art procedures have been vacuum deposited, electrolessly deposited, and electrolytically deposited, but the resulting coatings were poorly bonded resulting in poor translation of physical properties from the fiber to the matrix.
It is suggested in Canadian Application 457,193 (see also United States Patent 4,661,403) that if electroplating is selected, and if operating conditions are chosen to require a very high order of external voltage, then uniform, continuous adherent, thin metal coatings can be provided to fibers, especially carbon fibers.
High voltage is used in the present invention. Its use is believed to provide energy sufficient to transport metal ions through the boundary layer to provide uniform nucleation of the metal on the fibers directly. Yarns or tows comprising the thin metal coatings on the fibers, woven cloth, yarns, and the like, according to the present invention can be knotted and folded without the metal flaking off. The coated fibers are distinguish-able from any of the prior art because they can be sharply bent without disrupting the metal-carbon bond, as observed with electroless metal or vacuum deposited coated fibers. The fibers are characterized by bond strengths which provide that even if the `~25~67 coating cracks, it does not peel off. In other words, coated fibers of the present invention are distinguishable from those of the prior art because (i) they are con-- 3a -125~167 -4- 1109-72~8 tinuous; (iil the majority of the fibers are uniformly metal coated; and (Iii) the bond strength (metal~to-core) on the maj-ority of the fibers is very high. When scaling up production of the electoplated fiber bundles to higher production rates, and when using a variety of sources of graphite fibers, production rates are increased and fiber quality is improved with careful attention to the presence or absence of adsorbed organic compounds.
It was discovered that providing and maintaining the fibers free of organic materials produced uniform plating and increased pro-duction rates.
BRIEF DESCRIPTIOM OF THE DRAWINGS
The invention may be more readily understood by refer-ence to the accompanying drawings in which;
Figure 1 is a transverse cross sectional view of a metal coated fiber produced by the improved process of this invention.
Figure la is a longitudinal cross sectional view of a metal coated fiber produced by the improved process of this invention.
Figure 2 and 2a are transverse and longitudinal cross sect-ional views of, respectively, of a core fiber coated with metal not according to this invention, illustrating the non-uniform plating resulting from organic compound contamination.
Figure 3 is a view showing an apparatus for carrying out the process of the present invention.
Figure 4 is a magnified photographic view of a metal coated fiber according to this invention which has a uniform coating because a core fiber free of organic compound contamination was provided.
, ~1 `
i25~67 Figure 5 is a magnified coating of a fiber not according to this invention which has a non uniform coating because a core fiber contaminated with adsorbed organic compounds- was provided.
All the drawings repres-ent schematics of the articles des-cribed.
SUMMARY OF THE INVENTIO~
According to the present invention, in a process for the production of coated fibers, said process comprising:
(,a), providing a continuous length of a plurality of elect-rically conductive graphite core fibers, (b), continuously immersing at least a portion of the lengthof s~aid fibers in a solution capable of electrolytically depositing at least one metal, (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally re-quired to cause metal deposition, whereby (i) the metal is re-duced on the surface of the fibers, (,ii) the metal nucleates sub-stantially uniformly onto the surface of the fibers and (iii) there is provided a substantially uniform, firmly adherent layer of metal on said core, the improvement comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds lZ54167 which interfere with the electrodeposition of the metal, wherein said adsorbed organic compounds are removed by solvent cleaning, by chemical cleaning or by high temperature cleaning.
. .
~54~67 The term "substantially free" as used herein and in the appended claims means avery lowamount of adsorbed organic compounds, i.e., an amount which does not interfere with the plating, and contribute to a non-uniform coating. It is very difficult to remove or avoid all traces, but usually an amount covering up to about five percent of the surface area of a short length can be tolerated, without serious detriment.
In one preferred embodiment, a surface substantially free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting the graphite core fibers with a solvent for such compounds. A useful solvent is l,l,l-trichloroethane. This can be used in a conventional degreaser. Because of the high purity requirements of the cleaned fiber, the solvent must be changed or purified frequently.
In another preferred embodiment, the surface free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting the graphite fibers with an aqueous solution of an inorganic cleaning agent, preferably an inorganic phosphorus-containing compound including but not limited to phosphates and polyphosphates, and especially preferably trisodium phosphate. Typically a solution in water of 60 g./l. of trisodium phosphate can be used and heating to a temperature of about 140F. to boiling facilitates removal of any organic compounds when the bundles of fibers are passed through the solution. Because the inorganic cleaning agents are, in most cases, alkaline when dissolved in water, and the subsequent plating lZ~4~67 -7a- 61109-7298 solutions are generally acidic, it is a preferred feature to neutralize the pretreated yarns or tows with a dilute inorganic acid prior to immersion in the electroplating solution.
i25~fi7 ~ydrochloric acid or other mineral acids are suitable in aqueous solution.
In its other primary aspect, the present invention includes maintaining the graphite surface free of organic compounds by excluding them from the electro-plating solution, or permitting the presence therein of only organic compounds which are capable of reduction to free sulfur at the cathodic surface (the clean graphite fibers themselves). This improvement comprises in essence, rigorously excluding conventional electroplating additives which comprise or include organic compounds --such as wetting agents, like sodium lauryl sulfate, chelating agents, and brighteners which include organic components. Saccharin , for example, is suitable as an organic grain modifying agent Ibrightener) because, on the cathode, saccharin has the rather unique ability to reduce to elemental sulfur.
Other preferred features include carrying out the process in an electrolytic bath which is recycled into contact with the fibers immediately prior to immersion in the bath so as to provide increased current carrying capacity to the fibers and replenishment of the electrolyte on the surface of the fibers. In preferred embodiments, coating metals will be nickel, silver, zinc, copper, lead, cadmium, tin, cobalt, gold, indium, iron, palladium, platinum, tellurium, and alloys of the foregoing, without limitation.
~254i67 DETAILED DESCRIPTION OF THE INVENTION
Referring to Figs. 1 and la continous yarns and tows for use in the core 2 according to the present invention are available from a number of sources commercially. For example, suitable carbon fiber yarns are available from Hercules Company, Hitco, Great Lakes Carbon, Union Carbide Companyand similar sources in the United States, and overseas. All are made, in general, 10 by procedures described in U.S. 3,677,705. The fibers can be long and continuous or they can be short, e.g., 1 to 15 cm. in length. As mentioned above, all such carbon fibers may have a thin layer of adsorbed materials, such as organics, like oils, waxes, etc. that are on their surface. These layers may be continuous or non-continuous.
Referring to Figs. 2 and 2a, adsorbed organic compounds 3 are shown to be adsorbed to the surface of fiber 2- Plating occurs at bare spots on the carbon and grows upwardly and outwardly, somewhat like a mushroom, as shown, to produce non-uniform deposits.
Figs. 4 and 5 are electron photomicrographs showing, respectively, uniform and non-uniform plated coatings, the latter being bumpy, while the former is smooth.
Removing adsorbed organic compounds can be carried out in any known way. Preferably, it will be done either with solvents, in a degreaser, or in washing baths with aqueous inorganic cleaning agents and optional neutralization.
lZ54167 .
10 _ Referring to Fig. 3, shown schematically is an arrangement of elements in a continous yarn or tow plating processing apparatus in which yarns or tow 24 is removed from storage reel 40 and sent through hot solvent degreaser 36 (or hot inorganic cleaning agent solution bath 36). Rinsing conduits and baths (not shown) can be included and, if the yarn or tow retain alkaline inorganic cleaner residues, they can be neutralized in one more optionalneutralizers 34 which can contain an inorganic acid, such as 10 percent aqueous hydrochloric acid. The cleaned fibers can be held in protected storage, free of organic contaminants, or sent directly to electroplating.
Referring again to ~ig. 1, metal layer 4 will be of any electrodepositable metal, and it will be electrically continuous. Two layers, or even more, of metal can be applied and metal can be the same or differ-ent, as will be shown in the working examples. In any case, the innermost layer will be so firmly bonded to core 2 that sharp bending may cause the coating to fracture, but it will not peel off. The metal will sub-stantially not flake off when the fiber is twisted or knotted, which is a problem in fibers metal coated according to the prior art.
Formation of the metal coating layer by the electrodeposition process used in this invention can be carried out in a number of ways. For example, a plurality of core fibers can be immersed in an electrolytic bath and through suitable electrical connections the high external voltage used herein can be applied. The pro-cedure may be carried out in a continuous fashion on a moving tow of fibers.
~25~i67 ~ 1109-7298 To overcome the problem oE fiber burnout because of the high currents or power, to keep them cool enough outside the bath, one can pour water on the fibers, for example, but it is preferred to operate in an apparatus s~lown schematically in Figure 3. Electrolytic bath solution 8 is maintained in tank 10.
Also included are anode baskets 12 and idler rollers 14 near the ~ottom of tank 10. Two electrical contact rollers 16 are located above the tank. Stripped and cleaned tow 24 is pulled by means not shown off feed roll 26, over first contact roller 16 down into the bath under idler rollers 14, up through the bath, over second contact roller 16 and into take up roller 28. Optional, but very much preferred, is a simple loop comprising pump 18, conduit 20, and feed head 22. This permits recirculating the plating solution at a large enough flow rate to sufficiently cool the tow and pumping the solution onto contact rollers 16. Dis-charged just above the roller, the sections of tow 24 entering and leaving the solution are totally immersed and thus cooled. At the high current carried by the tow, the heat generated in some cases might destroy them before they reach or after they leave the bath surface without such cooling. The flow of the electrolyte fac-ilitates electrical contact between the rollers 16 and all filaments in the tow. More than one plating bath can be used in series, and is preferred, and 3 to 4 are used for reasons of economy, and the fibers can be rinsed free of electrolyte solution, dried, chopped, woven into fabric, all in accordance with conventional procedures .
4 ~i7 DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following Examples illustrate the present invention, but are not intended to limit it.
Four tows (fiber bundles) of 12,000 strands each of 7 micron graphite fibers were continuously drawn through a solution of 8 oz./gal. of trisodium phosphate heated at 180-200F., then through two rinse tanks. The effluent from the second rinse tank was returned to the first. The tows were then passed through a neutralizing tank containing 10% aqueous solution of C.P. hydrochloric acid (35%), then through two rinse tanks. The effluent from the second of these two rinse tanks was returned to the first, and the waste from all tanks was combined for self-neutralization.
In a continuous electroplating system, a plat-ing solution was provided having the following composi-tion:
INGREDIENTS AMOUNT
nickel sulfate (NiSO4.6H20) 40 oz. /gallon nickel chloride (NiCl2.6H2O) 12-20 oz./gallon boric acid (H3BO3)5-8 oz./gallon The bath was heated to 140-160F., and had a pH of 3.8-4.2 .
~25~67 O
The anode baskets were kept filled with el~ctro-lytic nickel pellets and four tows (fiber bundles) of 12,000 strands each of 7 micron carhon fibers stripped of organic contaminants as described above were continu-ously drawn through the bath at a tow speed of 5 feet/min. and with 120 amps. current, adjusted to give 5 ampere-minutes per 1,000 strands total. The voltage drop from anode to cathode was 30 volts. ~t the same time, electrolytic solution was recycled through a loop into contact with the entering and leaving paths of the tow. The tow was next passed continuously through an identical bath, at a tow speed of 5.0 ft./min. with 180 amps. current. The final product was a tow of high strength coated fibers according to this invention comprising a 7 micron fiber core and about 50% by weight of the coated fiber of crystalline electrodeposited nickel adhered firmly to the core. The metal coating was uniform and free from bare spots.
Whei~ a length of the fiber was sharply bent, then examined, there was no circumferential cracking on the metal coating in the tension side of the bend. The tow could be twisted and knotted without causing the coating to flake or come off as a powder.
E~AMPLE 2 When the procedure of Example 1 was repeated, substituting graphite tows which had been passed through hot li~uid and condensinq vapors of l,l,l-trichloroethane to strip them free from organics, uniform metal coatings were ultimately produced.
~5~ i7 To illustrate the adverse effects of organic compounds, when the concentration of organic impurities in the degreaser of Example 2 was allowed to build up, the organics recontaminated the graphite fibers and the nickel coating became non-uniform. When the trisodium phosphate cleaning bath in Example 1 was replaced with wetting agents containing organics (Wyandotte BN* cleaner, Oakite 190* cleaner of Ivory Liquid* detergent) ultimately the nickel plating was non-uniform.
Many variations of the present invention will suggest themselves to those skilled in this art in light of the above, detailed description. For example, instead of nickel plating solutions, those capable of depositing silver, zinc, copper, lead and gold can be substituted. All such variations are within the full intended scope of the invention as defined in the appended claims.
* Trade mark ~ ,t!
FIBERS WITH METAL
The present invention relates to an improved process for the production of bundles of fibers having conductive graphite cores coated with thin, uniform, adherent layers of electro-deposited metals. The process improvement comprises providing the cores free of adsorbed organic compounds prior to and during electrodeposition of the metal. Adsorbed organic compounds may interfere with the electrodeposition of uniform, adherent metal coatings.
~;~5~,7 BACKGROUND OF THE INVENTION
Bundles of high strength fibers Gf non-metals and semi-metals, such as carbon, boron, silicon carbide, and the like, in the form of filaments, mats, cloths and chopped strands are known to be useful in reinforc-ing metals and organic polymeric materials. Articles comprising metals or plastics reinforced with such fibers find wide-spread use in replacing heavier com-ponents made of lower strength conventional materialssuch as aluminum, steel, titanium, vinyl polymers, nylons, polyesters, etc., in aircraft, automobiles, office equipment, sporting goods, and in many other fields.
High strength carbon fibers are made by heating polymeric fiber, e.g., acrylonitrile polymers or copoly-mers, in two stages, one to remove volatiles and carbon-ize and other to convert amorphous carbon into crystal-line carbon. During such procedure, it is known thatcarbon changes from amorphous to single crystal then orients into fibrils. If the fibers are stretched during the graphitization, then high strength fibers are formed. This is critical to the formation of the boundary layer, because as the crystals grow, there are formed high surface energies, as e~emplified by incomplete bonds, edge-to-edge stresses, differences in morphology, and the like. It is also known that the new carbon fibrils in this form can scavenge organic compounds, because the surfaces behave like activated carbon, to produce non-carbon surface layers which are firmly adsorbed thereto.
~254~67 61109-7298 Numerous unsuccessful attempts have been reported to provide such filaments, especially carbon filaments, in a form uniquely suitable for reinforcing metals and plastics. Many have involved depositing layers of metals, especially nickel and copper, as thin surface layers on the filaments. Such a coated fiber was then to be used in a plastic or metal matrix. The metals in the prior art procedures have been vacuum deposited, electrolessly deposited, and electrolytically deposited, but the resulting coatings were poorly bonded resulting in poor translation of physical properties from the fiber to the matrix.
It is suggested in Canadian Application 457,193 (see also United States Patent 4,661,403) that if electroplating is selected, and if operating conditions are chosen to require a very high order of external voltage, then uniform, continuous adherent, thin metal coatings can be provided to fibers, especially carbon fibers.
High voltage is used in the present invention. Its use is believed to provide energy sufficient to transport metal ions through the boundary layer to provide uniform nucleation of the metal on the fibers directly. Yarns or tows comprising the thin metal coatings on the fibers, woven cloth, yarns, and the like, according to the present invention can be knotted and folded without the metal flaking off. The coated fibers are distinguish-able from any of the prior art because they can be sharply bent without disrupting the metal-carbon bond, as observed with electroless metal or vacuum deposited coated fibers. The fibers are characterized by bond strengths which provide that even if the `~25~67 coating cracks, it does not peel off. In other words, coated fibers of the present invention are distinguishable from those of the prior art because (i) they are con-- 3a -125~167 -4- 1109-72~8 tinuous; (iil the majority of the fibers are uniformly metal coated; and (Iii) the bond strength (metal~to-core) on the maj-ority of the fibers is very high. When scaling up production of the electoplated fiber bundles to higher production rates, and when using a variety of sources of graphite fibers, production rates are increased and fiber quality is improved with careful attention to the presence or absence of adsorbed organic compounds.
It was discovered that providing and maintaining the fibers free of organic materials produced uniform plating and increased pro-duction rates.
BRIEF DESCRIPTIOM OF THE DRAWINGS
The invention may be more readily understood by refer-ence to the accompanying drawings in which;
Figure 1 is a transverse cross sectional view of a metal coated fiber produced by the improved process of this invention.
Figure la is a longitudinal cross sectional view of a metal coated fiber produced by the improved process of this invention.
Figure 2 and 2a are transverse and longitudinal cross sect-ional views of, respectively, of a core fiber coated with metal not according to this invention, illustrating the non-uniform plating resulting from organic compound contamination.
Figure 3 is a view showing an apparatus for carrying out the process of the present invention.
Figure 4 is a magnified photographic view of a metal coated fiber according to this invention which has a uniform coating because a core fiber free of organic compound contamination was provided.
, ~1 `
i25~67 Figure 5 is a magnified coating of a fiber not according to this invention which has a non uniform coating because a core fiber contaminated with adsorbed organic compounds- was provided.
All the drawings repres-ent schematics of the articles des-cribed.
SUMMARY OF THE INVENTIO~
According to the present invention, in a process for the production of coated fibers, said process comprising:
(,a), providing a continuous length of a plurality of elect-rically conductive graphite core fibers, (b), continuously immersing at least a portion of the lengthof s~aid fibers in a solution capable of electrolytically depositing at least one metal, (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally re-quired to cause metal deposition, whereby (i) the metal is re-duced on the surface of the fibers, (,ii) the metal nucleates sub-stantially uniformly onto the surface of the fibers and (iii) there is provided a substantially uniform, firmly adherent layer of metal on said core, the improvement comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds lZ54167 which interfere with the electrodeposition of the metal, wherein said adsorbed organic compounds are removed by solvent cleaning, by chemical cleaning or by high temperature cleaning.
. .
~54~67 The term "substantially free" as used herein and in the appended claims means avery lowamount of adsorbed organic compounds, i.e., an amount which does not interfere with the plating, and contribute to a non-uniform coating. It is very difficult to remove or avoid all traces, but usually an amount covering up to about five percent of the surface area of a short length can be tolerated, without serious detriment.
In one preferred embodiment, a surface substantially free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting the graphite core fibers with a solvent for such compounds. A useful solvent is l,l,l-trichloroethane. This can be used in a conventional degreaser. Because of the high purity requirements of the cleaned fiber, the solvent must be changed or purified frequently.
In another preferred embodiment, the surface free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting the graphite fibers with an aqueous solution of an inorganic cleaning agent, preferably an inorganic phosphorus-containing compound including but not limited to phosphates and polyphosphates, and especially preferably trisodium phosphate. Typically a solution in water of 60 g./l. of trisodium phosphate can be used and heating to a temperature of about 140F. to boiling facilitates removal of any organic compounds when the bundles of fibers are passed through the solution. Because the inorganic cleaning agents are, in most cases, alkaline when dissolved in water, and the subsequent plating lZ~4~67 -7a- 61109-7298 solutions are generally acidic, it is a preferred feature to neutralize the pretreated yarns or tows with a dilute inorganic acid prior to immersion in the electroplating solution.
i25~fi7 ~ydrochloric acid or other mineral acids are suitable in aqueous solution.
In its other primary aspect, the present invention includes maintaining the graphite surface free of organic compounds by excluding them from the electro-plating solution, or permitting the presence therein of only organic compounds which are capable of reduction to free sulfur at the cathodic surface (the clean graphite fibers themselves). This improvement comprises in essence, rigorously excluding conventional electroplating additives which comprise or include organic compounds --such as wetting agents, like sodium lauryl sulfate, chelating agents, and brighteners which include organic components. Saccharin , for example, is suitable as an organic grain modifying agent Ibrightener) because, on the cathode, saccharin has the rather unique ability to reduce to elemental sulfur.
Other preferred features include carrying out the process in an electrolytic bath which is recycled into contact with the fibers immediately prior to immersion in the bath so as to provide increased current carrying capacity to the fibers and replenishment of the electrolyte on the surface of the fibers. In preferred embodiments, coating metals will be nickel, silver, zinc, copper, lead, cadmium, tin, cobalt, gold, indium, iron, palladium, platinum, tellurium, and alloys of the foregoing, without limitation.
~254i67 DETAILED DESCRIPTION OF THE INVENTION
Referring to Figs. 1 and la continous yarns and tows for use in the core 2 according to the present invention are available from a number of sources commercially. For example, suitable carbon fiber yarns are available from Hercules Company, Hitco, Great Lakes Carbon, Union Carbide Companyand similar sources in the United States, and overseas. All are made, in general, 10 by procedures described in U.S. 3,677,705. The fibers can be long and continuous or they can be short, e.g., 1 to 15 cm. in length. As mentioned above, all such carbon fibers may have a thin layer of adsorbed materials, such as organics, like oils, waxes, etc. that are on their surface. These layers may be continuous or non-continuous.
Referring to Figs. 2 and 2a, adsorbed organic compounds 3 are shown to be adsorbed to the surface of fiber 2- Plating occurs at bare spots on the carbon and grows upwardly and outwardly, somewhat like a mushroom, as shown, to produce non-uniform deposits.
Figs. 4 and 5 are electron photomicrographs showing, respectively, uniform and non-uniform plated coatings, the latter being bumpy, while the former is smooth.
Removing adsorbed organic compounds can be carried out in any known way. Preferably, it will be done either with solvents, in a degreaser, or in washing baths with aqueous inorganic cleaning agents and optional neutralization.
lZ54167 .
10 _ Referring to Fig. 3, shown schematically is an arrangement of elements in a continous yarn or tow plating processing apparatus in which yarns or tow 24 is removed from storage reel 40 and sent through hot solvent degreaser 36 (or hot inorganic cleaning agent solution bath 36). Rinsing conduits and baths (not shown) can be included and, if the yarn or tow retain alkaline inorganic cleaner residues, they can be neutralized in one more optionalneutralizers 34 which can contain an inorganic acid, such as 10 percent aqueous hydrochloric acid. The cleaned fibers can be held in protected storage, free of organic contaminants, or sent directly to electroplating.
Referring again to ~ig. 1, metal layer 4 will be of any electrodepositable metal, and it will be electrically continuous. Two layers, or even more, of metal can be applied and metal can be the same or differ-ent, as will be shown in the working examples. In any case, the innermost layer will be so firmly bonded to core 2 that sharp bending may cause the coating to fracture, but it will not peel off. The metal will sub-stantially not flake off when the fiber is twisted or knotted, which is a problem in fibers metal coated according to the prior art.
Formation of the metal coating layer by the electrodeposition process used in this invention can be carried out in a number of ways. For example, a plurality of core fibers can be immersed in an electrolytic bath and through suitable electrical connections the high external voltage used herein can be applied. The pro-cedure may be carried out in a continuous fashion on a moving tow of fibers.
~25~i67 ~ 1109-7298 To overcome the problem oE fiber burnout because of the high currents or power, to keep them cool enough outside the bath, one can pour water on the fibers, for example, but it is preferred to operate in an apparatus s~lown schematically in Figure 3. Electrolytic bath solution 8 is maintained in tank 10.
Also included are anode baskets 12 and idler rollers 14 near the ~ottom of tank 10. Two electrical contact rollers 16 are located above the tank. Stripped and cleaned tow 24 is pulled by means not shown off feed roll 26, over first contact roller 16 down into the bath under idler rollers 14, up through the bath, over second contact roller 16 and into take up roller 28. Optional, but very much preferred, is a simple loop comprising pump 18, conduit 20, and feed head 22. This permits recirculating the plating solution at a large enough flow rate to sufficiently cool the tow and pumping the solution onto contact rollers 16. Dis-charged just above the roller, the sections of tow 24 entering and leaving the solution are totally immersed and thus cooled. At the high current carried by the tow, the heat generated in some cases might destroy them before they reach or after they leave the bath surface without such cooling. The flow of the electrolyte fac-ilitates electrical contact between the rollers 16 and all filaments in the tow. More than one plating bath can be used in series, and is preferred, and 3 to 4 are used for reasons of economy, and the fibers can be rinsed free of electrolyte solution, dried, chopped, woven into fabric, all in accordance with conventional procedures .
4 ~i7 DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following Examples illustrate the present invention, but are not intended to limit it.
Four tows (fiber bundles) of 12,000 strands each of 7 micron graphite fibers were continuously drawn through a solution of 8 oz./gal. of trisodium phosphate heated at 180-200F., then through two rinse tanks. The effluent from the second rinse tank was returned to the first. The tows were then passed through a neutralizing tank containing 10% aqueous solution of C.P. hydrochloric acid (35%), then through two rinse tanks. The effluent from the second of these two rinse tanks was returned to the first, and the waste from all tanks was combined for self-neutralization.
In a continuous electroplating system, a plat-ing solution was provided having the following composi-tion:
INGREDIENTS AMOUNT
nickel sulfate (NiSO4.6H20) 40 oz. /gallon nickel chloride (NiCl2.6H2O) 12-20 oz./gallon boric acid (H3BO3)5-8 oz./gallon The bath was heated to 140-160F., and had a pH of 3.8-4.2 .
~25~67 O
The anode baskets were kept filled with el~ctro-lytic nickel pellets and four tows (fiber bundles) of 12,000 strands each of 7 micron carhon fibers stripped of organic contaminants as described above were continu-ously drawn through the bath at a tow speed of 5 feet/min. and with 120 amps. current, adjusted to give 5 ampere-minutes per 1,000 strands total. The voltage drop from anode to cathode was 30 volts. ~t the same time, electrolytic solution was recycled through a loop into contact with the entering and leaving paths of the tow. The tow was next passed continuously through an identical bath, at a tow speed of 5.0 ft./min. with 180 amps. current. The final product was a tow of high strength coated fibers according to this invention comprising a 7 micron fiber core and about 50% by weight of the coated fiber of crystalline electrodeposited nickel adhered firmly to the core. The metal coating was uniform and free from bare spots.
Whei~ a length of the fiber was sharply bent, then examined, there was no circumferential cracking on the metal coating in the tension side of the bend. The tow could be twisted and knotted without causing the coating to flake or come off as a powder.
E~AMPLE 2 When the procedure of Example 1 was repeated, substituting graphite tows which had been passed through hot li~uid and condensinq vapors of l,l,l-trichloroethane to strip them free from organics, uniform metal coatings were ultimately produced.
~5~ i7 To illustrate the adverse effects of organic compounds, when the concentration of organic impurities in the degreaser of Example 2 was allowed to build up, the organics recontaminated the graphite fibers and the nickel coating became non-uniform. When the trisodium phosphate cleaning bath in Example 1 was replaced with wetting agents containing organics (Wyandotte BN* cleaner, Oakite 190* cleaner of Ivory Liquid* detergent) ultimately the nickel plating was non-uniform.
Many variations of the present invention will suggest themselves to those skilled in this art in light of the above, detailed description. For example, instead of nickel plating solutions, those capable of depositing silver, zinc, copper, lead and gold can be substituted. All such variations are within the full intended scope of the invention as defined in the appended claims.
* Trade mark ~ ,t!
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the production of coated fibers, said process comprising:
(a) providing a continuous length of a plurality of electrically conductive graphite core fibers;
(b) continuously immersing at least a portion of the length of said fibers in a solution capable of electrolytically depositing at least one metal; and (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally required to cause metal deposition, whereby (i) the metal is reduced on the surface of the fibers, (ii) the metal nucleates substantially uniformly onto the surface of the fibers; and (iii) there is produced a substantially uniform, firmly adherent layer of metal on said core, the improvement which comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds which interfere with the electrodeposition of the metal wherein said adsorbed organic compounds are removed by solvent cleaning, chemical cleaning or high temperature cleaning.
(a) providing a continuous length of a plurality of electrically conductive graphite core fibers;
(b) continuously immersing at least a portion of the length of said fibers in a solution capable of electrolytically depositing at least one metal; and (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally required to cause metal deposition, whereby (i) the metal is reduced on the surface of the fibers, (ii) the metal nucleates substantially uniformly onto the surface of the fibers; and (iii) there is produced a substantially uniform, firmly adherent layer of metal on said core, the improvement which comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds which interfere with the electrodeposition of the metal wherein said adsorbed organic compounds are removed by solvent cleaning, chemical cleaning or high temperature cleaning.
2. A process as defined in claim 1 wherein the surface free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting said graphite core fibers with a solvent for such compounds.
3. A process as defined in claim 2 wherein the solvent is 1,1,1-trichloroethane.
4. A process as defined in claim 1 wherein the surface sub-stantially free of adsorbed organic compounds is provided by removing substantially all of any such compounds by contacting said graphite core fibers with an aqueous solution of an inorganic cleaning agent.
5. A process as defined in claim 4 wherein said inorganic cleaning agent is an inorganic phosphorus-containing compound.
6. A process as defined in claim 5 wherein said inorganic phosphorus-containing compound is trisodium phosphate.
7. A process as claimed in claim 5 wherein the solution of trisodium phosphate is alkaline and including the step of neutral-izing the surface of the stripped graphite fibers with a dilute inorganic acid prior to immersion of the fibers in the solution capable of electrolytically depositing said metal.
8. A process as defined in claim 1 wherein the surface is maintained substantially free of adsorbed organic compounds by excluding substantially all of such compounds from the solution capable of electrolytically depositing said metal, and by including in said solutions substantially only organic compounds which are capable of cathodic reduction to free sulfur.
9. A process as defined in claim 8 wherein the solution capable of electrolytically depositing said metal includes saccharin as an organic grain modifying agent.
10. A process as defined in claim 1 wherein the plurality of fibers is provided substantially free of adsorbed organic compounds by contacting with a hot aqueous solution of trisodium phosphate, neutralizing with a dilute aqueous solution of hydrochloric acid and electroplating in a solution in which the only organic compound is saccharin.
11. A process as defined in claim 1 including recycling the bath into contact with the plurality of fibers immediately prior to immersion therein so as to provide increased current capacity to the fibers and replenishment of the electrolyte on the surface of the fibers therein.
12. A process as defined in claim 1 wherein said metal com-prises nickel, silver, zinc, copper, lead, cadmium, tin, cobalt, gold, indium, iron, palladium, platinum, tellurium, or an alloy of the foregoing.
13. In the process for the production of coated fibers, said process comprising:
(a) providing a continuous length of a plurality of electrically conductive graphite core fibers;
(b) continuously immersing at least a portion of the length of said fibers in a solution capable of electrolytically depositing at least one metal; and (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally required to cause metal deposition, whereby (i) the metal is reduced on the surface of the fibers, (ii) the metal nucleates substantially uniformly onto the surface of the fibers, and (iii) there is provided a substantially uniform, firmly adherent layer of metal on said core fibers, the improvement which comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds which interfere with the electrodeposition of the metal by contacting non-plated core fibers with a hot aqueous solution of trisodium phosphate, neutralizing with a dilute aqueous solution of hydrochloric acid and electroplating in a solution in which the only organic compound is saccharin.
(a) providing a continuous length of a plurality of electrically conductive graphite core fibers;
(b) continuously immersing at least a portion of the length of said fibers in a solution capable of electrolytically depositing at least one metal; and (c) providing a quantity of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is in excess of what is normally required to cause metal deposition, whereby (i) the metal is reduced on the surface of the fibers, (ii) the metal nucleates substantially uniformly onto the surface of the fibers, and (iii) there is provided a substantially uniform, firmly adherent layer of metal on said core fibers, the improvement which comprises providing graphite core fibers whose surfaces are substantially free of adsorbed organic compounds which interfere with the electrodeposition of the metal by contacting non-plated core fibers with a hot aqueous solution of trisodium phosphate, neutralizing with a dilute aqueous solution of hydrochloric acid and electroplating in a solution in which the only organic compound is saccharin.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US50744283A | 1983-06-24 | 1983-06-24 | |
| US507,442 | 1983-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254167A true CA1254167A (en) | 1989-05-16 |
Family
ID=24018666
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000457196A Expired CA1254167A (en) | 1983-06-24 | 1984-06-22 | Electroplating cleaned graphite fibres with metal |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1254167A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108888862A (en) * | 2018-06-29 | 2018-11-27 | 成都三乙医疗科技有限公司 | A kind of physiotherapy electrode plate |
-
1984
- 1984-06-22 CA CA000457196A patent/CA1254167A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108888862A (en) * | 2018-06-29 | 2018-11-27 | 成都三乙医疗科技有限公司 | A kind of physiotherapy electrode plate |
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