EP0551864A1 - Method for surface treatment of carbon fibers - Google Patents

Method for surface treatment of carbon fibers Download PDF

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Publication number
EP0551864A1
EP0551864A1 EP93100330A EP93100330A EP0551864A1 EP 0551864 A1 EP0551864 A1 EP 0551864A1 EP 93100330 A EP93100330 A EP 93100330A EP 93100330 A EP93100330 A EP 93100330A EP 0551864 A1 EP0551864 A1 EP 0551864A1
Authority
EP
European Patent Office
Prior art keywords
carbon fibers
alkali metal
nitrate
oxidation
chopped strands
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93100330A
Other languages
German (de)
English (en)
French (fr)
Inventor
Eiji Fujisawa
Minoru Takeuchi
Hiroaki Shono
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Mitsubishi Gas Chemical Co Inc
Nitto Boseki Co Ltd
Original Assignee
Mitsubishi Gas Chemical Co Inc
Nitto Boseki Co Ltd
Kawasaki Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mitsubishi Gas Chemical Co Inc, Nitto Boseki Co Ltd, Kawasaki Steel Corp filed Critical Mitsubishi Gas Chemical Co Inc
Publication of EP0551864A1 publication Critical patent/EP0551864A1/en
Withdrawn legal-status Critical Current

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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
    • D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
    • D01F11/10—Chemical after-treatment of artificial filaments or the like during manufacture of carbon
    • D01F11/12—Chemical after-treatment of artificial filaments or the like during manufacture of carbon with inorganic substances ; Intercalation
    • D01F11/122—Oxygen, oxygen-generating compounds

Definitions

  • the present invention relates to a method for surface treating carbon fibers and in particular, to a method for surface treating carbon fibers by thermal oxidation which are used for improving strength of moldings made from carbon fiber-reinforced composite materials.
  • carbon fibers are used as reinforcing materials for fiber-reinforced composite materials, especially, fiber-reinforced resins because of their many excellent properties as industrial materials such as heat resistance, endurance, chemical resistance, lightness in weight, high modulus and small thermal expansion coefficient.
  • carbon fibers have the characteristic that compatibility with resins decreases with increase in the modulus. Therefore, there appears the defect that when fiber-reinforced resins are made by using carbon fibers of high modulus as they are, the resins decrease in shearing force.
  • the main surface treatments are oxidation treatments and at present there are chemical oxidation, electrolytic oxidation and vapor phase oxidation.
  • the electrolytic oxidation is sometimes employed for surface treatment of long carbon fibers.
  • introduction of acidic group into the surface of carbon fibers is not sufficient and moreover, there is the problem that a large amount of waste liquors containing graphitic acid remain after electrolysis.
  • this method which is effective for long fibers cannot substantially be applied to the surface treatment of short fibers because the short carbon fibers are difficult to use as an electrode.
  • the air oxidation is a representative of the vapor phase oxidation.
  • the air oxidation is the simplest and is easy for industrial employment.
  • the oxidation temperature reaches about 500°C for treatment of carbon fibers of high modulus made from mesophase pitches prepared from petroleum asphalt or coal tar or mesophase pitches obtained by polymerization of condensed polycyclic hydrocarbons produced by the processes described in Japanese Patent Kokai (Laid-Open) Nos.1-139621 and 1-254796 or substances containing the condensed polycyclic hydrocarbons, namely, so-called aromatic resins (AR). Accordingly, this method is also not suitable for practical use. Furthermore, when the temperature reaches the above range, oxidative destruction of carbon fibers progresses in the air and strength per se of the fibers reduces.
  • the oxidizing efficiency does not increase so much and when ozone is added to the oxidizing gas or the oxidizing gas is irradiated with ultraviolet rays for enhancing oxidizing efficiency, the working atmosphere is endangered and these means cannot be industrially employed.
  • the object of the present invention is to provide a method for thermal oxidation of carbon fibers according to which the carbon fibers can be efficiently surface treated to a proper extent with lowering the treating temperature and shortening the treating time irrespective of the kind of starting materials (polyacrylonitriles, pitches or any other materials) and the shape (long fibers and short fibers).
  • the present invention is a method for surface treatment of carbon fibers, characterized by allowing an alkali metal nitrate to adhere to carbon fibers in an amount of 0.01-5% by weight based on the weight of the carbon fibers and then heat treating the carbon fibers in the air at a temperature of the melting point or higher of the alkali metal nitrate and lower than 500°C.
  • the present invention is a method for surface treatment of carbon fibers, characterized by allowing an alkali metal nitrate to adhere to carbon fibers in an amount of 0.01-5% by weight based on the weight of the carbon fibers and then heat treating the carbon fibers in the air at a temperature of the decomposition temperature or higher of the alkali metal nitrate and lower than 500°C.
  • the carbon fibers to be treated have no special limitation.
  • the carbon fibers may be any of those which are prepared from polyacrylonitriles, pitches, rayons and other starting materials. Further, they may be of any shapes such as long fibers, short fibers, milled fibers and others and besides, they may have rising whiskers on the surface.
  • the method of the present invention can be applied to carbon fibers having any mechanical characteristics, namely, any of general-purpose carbon fibers, high-strength carbon fibers, high-modulus carbon fibers and others. However, since this method is high in treating efficiency, it is preferably applied to the high-modulus carbon fibers which are generally difficult to oxidize the surface, for example, mesophase carbon fibers and aromatic pitch carbon fibers.
  • the alkali metal nitrate used in the present invention includes sodium nitrate, potassium nitrate and rubidium nitrate. Of these nitrates, preferred is potassium nitrate which has no deliquescence and is easily available as industrial materials.
  • alkali metal nitrates are used preferably as an aqueous solution of 0.05-10% by weight in concentration or as fine powders of 0.1-5 ⁇ m in particle size.
  • the method of allowing the alkali metal nitrate to adhere to carbon fibers include, for example, impregnating the carbon fibers with an aqueous solution of the nitrate, spraying an aqueous solution of the nitrate or fine powders of the nitrate onto the carbon fibers, sprinkling fine powders of the nitrate on the carbon fibers or dusting the carbon fibers with fine powders of the nitrate.
  • the adhering amount of the alkali metal nitrate to carbon fibers is calculated from amount of the aqueous solution retained by the carbon fibers (pickup) and concentration of the aqueous solution when the alkali metal nitrate is used as an aqueous solution.
  • the alkali metal nitrate is allowed to adhere to carbon fibers in an amount of 0.01-5% by weight, preferably 0.03-3% by weight based on the weight of the carbon fibers by the above-exemplified method and then, the carbon fibers are heated in the air to carry out oxidation. If the adhering amount of the alkali metal nitrate is less than 0.01% by weight, the effect of using the alkali metal nitrate in the oxidation treatment cannot be obtained and if it is more than 5% by weight, a long time is required for removal of the alkali metal nitrate by washing after the oxidation treatment or the remaining alkali metal nitrate causes deterioration of resins which become a matrix for carbon fibers.
  • predrying is not necessarily essential even in the case of impregnation with aqueous solution and the oxidation can be started for the wet carbon fibers as they are.
  • the heating temperature is at lowest the melting point, preferably at lowest the decomposition temperature of the alkali metal nitrate and lower than 500°C.
  • the heating temperature is set in the above range because the surface treating method of the present invention utilizes oxygen generated when the alkali metal nitrate is subjected to heat decomposition.
  • oxygen and an alkali metal nitrite are produced.
  • the oxygen which is locally generated on the surface of carbon fibers makes it possible to perform rapid oxidation at a temperature lower than in conventional methods. Therefore, if the heating temperature for the oxidation treatment is higher than 500°C as in the usual air oxidation, the carbon fibers are excessively oxidized and the modulus is damaged or the use of the alkali metal nitrate becomes meaningless.
  • Melting points and decomposition temperatures of the alkali metal nitrates used in the present invention are shown below.
  • Melting point Decomposition temperature (a) Sodium nitrate (NaNO3) 306.8°C 380°C (b) Potassium nitrate (KNO3) 333°C about 400°C (c) Rubidium nitrate (RbNO3) 310°C at least 310°C
  • the treating time varies depending on various conditions of the kind and the amount of the alkali metal nitrates used and whether the carbon fibers to be treated are polyacrylonitrile type or pitch type, whether long fibers or short fibers and whether general-purpose carbon fibers, high-strength carbon fibers or high-modulus carbon fibers.
  • suitable range is 10-120 minutes.
  • a range of 10-60 minutes is especially suitable when pitch type short fibers are treated with potassium nitrate.
  • the carbon fibers are washed with water.
  • the nitrates used in Japanese Patent Kokai (Laid-Open) No.52-25199 are salts of copper, silver, zinc, cadmium, tin, lead, vanadium, antimony, bismuth, chromium, molybdenum, tungsten and the like and the treating temperature is low, namely, 80-120°C and thus, the technique of this publication is utterly different from the present invention.
  • U.S. Patent No.3876444 also discloses a surface treating method for carbon fibers with formates, acetates or nitrates of copper, lead, cobalt or cadmium and vanadium pentoxide in combination by vapor phase oxidation.
  • this method also utilizes the catalytic action possessed by nitrates of heavy metals and is different in action and mechanism from the surface treating method of the present invention which uses alkali metal nitrates.
  • the excellent oxidizing ability is due to the fact that when an alkali metal nitrate is placed in an atmosphere of at least the melting point, preferably at least the decomposition temperature of the alkali metal nitrate, the nitrate decomposes into oxygen and a nitrite.
  • the oxygen generated at the decomposition is in nascent state and rapidly oxidizes the carbon fibers at a treating temperature of 310-5007°C. Therefore, oxidative surface treatment of carbon fibers can be performed at a lower temperature and a higher speed than utilizing the catalytic action of activating the oxygen in the air (oxidizing gas) with nitrate ion as in the above prior art.
  • a precursor pitch containing 90% of mesophase which was prepared from coal pitches was melt spun at 340°C to obtain pitch fiber strands.
  • the strands of the pitch fibers were cut to 3 mm in length and heated to 310°C at a rate of 1°C/min in the air atmosphere to infusibilize them.
  • the infusibilized strands were further heated to 1000°C at a rate of 5°C/min in the nitrogen atmosphere and kept at that temperature for 10 minutes to make carbon fiber chopped strands.
  • AR aromatic resin manufactured by Mitsubishi Gas Chemical Company, Inc.
  • AR aromatic resin manufactured by Mitsubishi Gas Chemical Company, Inc.
  • the strands of the pitch fibers were cut to 3 mm in length and heated to 270°C at a rate of 1°C/min in the air atmosphere to infusibilize them.
  • the infusibilized strands were further heated to 1000°C at a rate of 5°C/min in the nitrogen atmosphere and kept at that temperature for 10 minutes to make carbon fiber chopped strands.
  • the carbon fiber chopped strands obtained in Preparation Example 1 were dipped in a 0.1% aqueous potassium nitrate solution and then taken out. In this case, pickup of the 0.1% aqueous potassium nitrate solution retained by the chopped strands was 30%.
  • the chopped strands were dried at 120°C to allow potassium nitrate to adhere to the surface of the carbon fibers. In this case, adhering amount of potassium nitrate was 0.03%.
  • the chopped strands containing potassium nitrate adhering to the surface of the carbon fibers were heat treated at 425°C for 30 minutes.
  • Reference Example 1 Measurement of flexural strength of composite material made of mesophase pitch carbon fibers subjected to oxidation treatment and nylon 6
  • the carbon fiber chopped strands obtained by heat treatment in Examples 1-3 were dipped in a polyether type urethane resin emulsion (solid content 1% by weight) to sufficiently impregnate the chopped strands with the emulsion and then dried at 120°C to size the chopped strands.
  • a polyether type urethane resin emulsion solid content 1% by weight
  • a composite molding was made of a thermoplastic resin and the above chopped strands and flexural strength thereof was measured.
  • nylon 6 manufactured by Toyobo Co., Ltd.
  • 30 parts of the chopped strands of the above Examples 1-3 were blended and made into a compound using a single-screw extruder at 265°C.
  • This compound was molded into a test piece of 126 mm in length, 12 mm in width and 6 mm in thickness by an injection molding machine under the conditions of cylinder temperature: 270°C and mold temperature: 90°C.
  • Comparative Reference Example 1 Measurement of flexural strength of composite material made of mesophase pitch carbon fibers subjected to no oxidation treatment and nylon 6
  • a molding was made in the same manner as in Reference Example 1 except that the unoxidized carbon fiber chopped strands prepared in Preparation Example 1 were used and flexural modulus of the molding was measured in the same manner as in Reference Example 1 to obtain 2295 kg/cm2.
  • the carbon fiber chopped strands obtained in Preparation Example 2 were dipped in a 0.05% aqueous potassium nitrate solution and then taken out. In this case, pickup of the 0.05% aqueous potassium nitrate solution retained by the chopped strands was 30%.
  • the chopped strands were dried at 120°C to allow potassium nitrate to adhere to the surface of the carbon fibers. In this case, adhering amount of potassium nitrate was 0.015%.
  • the chopped strands containing potassium nitrate adhering to the surface of the carbon fibers were heat treated at 425°C for 30 minutes in a muffle furnace.
  • the carbon fiber chopped strands obtained in Preparation Example 2 were dipped in a 10% aqueous potassium nitrate solution and then taken out. In this case, pickup of the 10% aqueous potassium nitrate solution retained by the chopped strands was 28%.
  • the chopped strands were dried at 120°C to allow potassium nitrate to adhere to the surface of the carbon fibers. In this case, adhering amount of potassium nitrate was 2.8%.
  • the chopped strands containing potassium nitrate adhering to the surface of the carbon fibers were heat treated at 425°C for 10 minutes.
  • the carbon fiber chopped strands obtained in Preparation Example 2 were heat treated in the air at 530°C for 60 minutes to perform surface oxidation of the carbon fibers.
  • Reference Example 2 Measurement of flexural strength of composite material made of aromatic resin carbon fibers subjected to oxidation treatment and polycarbonate resin
  • the carbon fiber chopped strands obtained by heat treatment in Examples 4-10 were dipped in a bisphenol type epoxy resin emulsion (solid content 1% by weight) to sufficiently impregnate the chopped strands with the emulsion and then sufficiently dried to size the chopped strands.
  • a composite molding was made of a thermoplastic resin and the above chopped strands and flexural strength thereof was measured.
  • EUPYRON S-2000 polycarbonate resin manufactured by Mitsubishi Gas Chemical Company, Inc.
  • 20 parts of the chopped strands of the above Examples 4-9 were blended and made into a compound using a single-screw extruder at 300°C.
  • This compound was molded into a test piece of 126 mm in length, 12 mm in width and 6 mm in thickness by an injection molding machine under the conditions of cylinder temperature: 300°C and mold temperature: 120°C.
  • Comparative Reference Example 2 Measurement of flexural strength of composite material made of aromatic resin carbon fibers subjected to no oxidation treatment and aromatic resin carbon fibers subjected to air oxidation and polycarbonate
  • the carbon fiber chopped strands obtained in Preparation Example 1 were dipped in a 0.5% aqueous potassium nitrate solution and then taken out. In this case, pickup of the 0.5% aqueous potassium nitrate solution retained by the chopped strands was 30%.
  • the chopped strands were dried at 120°C to allow potassium nitrate to adhere to the surface of the carbon fibers. In this case, adhering amount of potassium nitrate was 0.15%.
  • the chopped strands containing potassium nitrate adhering to the surface of the carbon fibers were heat treated at 400°C for 60 minutes.
  • the carbon fiber chopped strands obtained in Preparation Example 1 were heat treated in the air at 470°C for 60 minutes to perform surface oxidation of the carbon fibers.
  • Reference Example 3 Measurement of flexural strength of composite material made of mesophase pitch carbon fibers subjected to oxidation treatment and polyacetal resin
  • the carbon fiber chopped strands obtained by heat treatment in Example 11 were dipped in a polyether type urethane resin emulsion (solid content 1% by weight) to sufficiently impregnate the chopped strands with the emulsion and then sufficiently dried to size the chopped strands.
  • a polyether type urethane resin emulsion solid content 1% by weight
  • a composite molding was made of a thermoplastic resin and the above chopped strands and flexural strength thereof was measured.
  • DURACON polyacetal resin manufactured by Polyplastics Co., Ltd.
  • 20 parts by weight of the chopped strands of the above Examples 11 were blended and made into a compound using a single-screw extruder at 200°C.
  • This compound was molded into a test piece of 126 mm in length, 12 mm in width and 6 mm in thickness by an injection molding machine under the conditions of cylinder temperature: 200°C and mold temperature: 90°C.
  • Comparative Reference Example 3 Measurement of flexural strength of composite material made of mesophase pitch carbon fibers subjected to no oxidation treatment and mesophase pitch carbon fibers subjected to air oxidation and polyacetal resin
  • all sorts of carbon fibers including high-modulus carbon fibers the oxidization of the surface of which have been difficult can be properly surface treated at a lower treating temperature and in a shorter treating time than in conventional methods without damaging the modulus of carbon fibers.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Chemical Or Physical Treatment Of Fibers (AREA)
  • Inorganic Fibers (AREA)
  • Pigments, Carbon Blacks, Or Wood Stains (AREA)
EP93100330A 1992-01-14 1993-01-12 Method for surface treatment of carbon fibers Withdrawn EP0551864A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP4549/92 1992-01-14
JP4004549A JPH05195429A (ja) 1992-01-14 1992-01-14 炭素繊維の表面処理方法

Publications (1)

Publication Number Publication Date
EP0551864A1 true EP0551864A1 (en) 1993-07-21

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EP93100330A Withdrawn EP0551864A1 (en) 1992-01-14 1993-01-12 Method for surface treatment of carbon fibers

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EP (1) EP0551864A1 (ja)
JP (1) JPH05195429A (ja)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7712613B2 (en) 2001-08-23 2010-05-11 Pur Water Purification Products, Inc. Water filter materials and water filters containing a mixture of microporous and mesoporous carbon particles
US7740766B2 (en) 2001-08-23 2010-06-22 The Procter & Gamble Company Methods for treating water
US7740765B2 (en) 2001-08-23 2010-06-22 The Procter & Gamble Company Methods for treating water
US7749394B2 (en) 2001-08-23 2010-07-06 The Procter & Gamble Company Methods of treating water
US7850859B2 (en) 2001-08-23 2010-12-14 The Procter & Gamble Company Water treating methods
DE102015220145A1 (de) * 2015-10-16 2017-04-20 Bayerische Motoren Werke Aktiengesellschaft Kohlenstofffasermaterial, Verfahren zu dessen Herstellung, Faserverbundbauteil enthaltend das Kohlenstofffasermaterial

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115380080A (zh) * 2020-05-12 2022-11-22 三菱工程塑料株式会社 组合物、粒料、成型品和组合物的制造方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3627570A (en) * 1970-05-28 1971-12-14 Monsanto Res Corp Heat treatment of graphite fibers
EP0267995A1 (en) * 1985-08-20 1988-05-25 Toa Nenryo Kogyo Kabushiki Kaisha Process for surface treatment of carbon fibers

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS53111193A (en) * 1977-03-10 1978-09-28 Showa Denko Kk Surface treating of carbon fiber
US4374114A (en) * 1981-01-05 1983-02-15 Celanese Corporation Process for the surface modification of carbon fibers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3627570A (en) * 1970-05-28 1971-12-14 Monsanto Res Corp Heat treatment of graphite fibers
EP0267995A1 (en) * 1985-08-20 1988-05-25 Toa Nenryo Kogyo Kabushiki Kaisha Process for surface treatment of carbon fibers

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7712613B2 (en) 2001-08-23 2010-05-11 Pur Water Purification Products, Inc. Water filter materials and water filters containing a mixture of microporous and mesoporous carbon particles
US7740766B2 (en) 2001-08-23 2010-06-22 The Procter & Gamble Company Methods for treating water
US7740765B2 (en) 2001-08-23 2010-06-22 The Procter & Gamble Company Methods for treating water
US7749394B2 (en) 2001-08-23 2010-07-06 The Procter & Gamble Company Methods of treating water
US7850859B2 (en) 2001-08-23 2010-12-14 The Procter & Gamble Company Water treating methods
US7922008B2 (en) 2001-08-23 2011-04-12 The Procter & Gamble Company Water filter materials and water filters containing a mixture of microporous and mesoporous carbon particles
US8119012B2 (en) 2001-08-23 2012-02-21 The Procter & Gamble Company Water filter materials and water filters containing a mixture of microporous and mesoporous carbon particles
DE102015220145A1 (de) * 2015-10-16 2017-04-20 Bayerische Motoren Werke Aktiengesellschaft Kohlenstofffasermaterial, Verfahren zu dessen Herstellung, Faserverbundbauteil enthaltend das Kohlenstofffasermaterial

Also Published As

Publication number Publication date
JPH05195429A (ja) 1993-08-03

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