JP2014101605A - Method of manufacturing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a carbon fiber, conducting a surface treatment of the carbon fiber efficiently and safely, at low cost and without applying a burden on the environment.SOLUTION: The method of manufacturing a carbon fiber is a manufacturing method of the carbon fiber including heat treating the carbon fiber having an untreated surface at 200 to 600°C under a super heated steam atmosphere containing an oxygen concentration of 1 to 1000 ppm. The oxidizing gas is preferably oxygen. The atmosphere used in the invention may contain an inactive gas of 0 to 80 vol% other than the super heated steam. Preferably it is heat treated under an atmosphere containing 1 to 1000 ppm of oxidizing gas and having a percentage of super heated steam of 20 to 99.9 vol%.

Description

  The present invention relates to a method for producing a carbon fiber in which carbon fiber is efficiently surface oxidized.

  Carbon fiber has excellent specific strength and specific elastic modulus, and is excellent in lightness. Therefore, as a reinforcing fiber for thermosetting and thermoplastic resin, not only conventional sports and general industrial applications, but also aerospace applications, Widely used for automotive applications. As usage applications expand, higher performance is required for carbon fiber reinforced resin composite materials (hereinafter referred to as composites).

The performance of the composite differs depending not only on the difference in mechanical properties between the carbon fiber used and the matrix resin, but also on the difference in interface properties such as adhesion between the carbon fiber and the resin. However, since the surface of the carbon fiber having a graphite structure has low wettability with respect to the resin, the adhesion with the resin is low. For this reason, functional groups such as hydroxyl groups and carboxyl groups are introduced into the surface of the carbon fiber by surface treatment to improve the adhesion with the resin.

As methods for surface treatment of carbon fiber, liquid phase oxidation treatment such as electrolytic oxidation treatment and chemical liquid oxidation treatment and gas phase oxidation treatment are known. However, electrolytic oxidation treatment is industrially easy to perform. Has been widely implemented. However, in the method of surface treatment of carbon fiber by liquid phase oxidation treatment such as electrolytic oxidation treatment or chemical solution oxidation treatment, it is necessary to wash the chemical solution such as electrolyte attached to the carbon fiber after the surface treatment with pure water, etc. The apparatus may become large and the manufacturing cost may increase. In addition, there is a problem in that it is necessary to dispose of the chemical solution remaining after the treatment and the waste solution generated by the washing of the fibers, which causes a large environmental load.
On the other hand, in the gas phase oxidation treatment, the chemical solution does not remain in the fiber after the treatment, and the disposal of the chemical solution and the waste solution is not necessary, so that the environmental load is small and the cost is advantageous.

As a surface treatment method by gas phase oxidation, heating in a gas containing an oxidizing gas, a method using plasma or electromagnetic waves, and the like are known.
For example, Patent Document 1 proposes a surface treatment method using ozone which is an oxidizing gas. However, ozone is very easily decomposed, and the decomposition is particularly severe at higher temperatures, so that it is generally performed at a low temperature. In this case, the oxidation reaction is extremely slow. In order to promote the reaction, it is necessary to increase the ozone concentration. To that end, excess ozone must be supplied, and ozone reaction efficiency deteriorates. In addition, ozone has a danger of being harmful to the human body. Therefore, the oxidation reaction by ozone is not currently industrially used as a method for surface treatment of carbon fibers.

Patent Document 2 proposes a surface treatment method in an atmosphere irradiated with electromagnetic waves. However, such a process generates a powerful electromagnetic wave and requires a complicated device, which is not cost effective industrially.
Patent Document 3 proposes a method of performing heat treatment at 600 to 800 ° C. in an oxidizing atmosphere having a carbon concentration of 15 to 30% by mass. However, under such conditions, the oxidizing action on carbon fibers is insufficient, and electrolysis is performed. Repeated oxidation treatment by oxidation treatment is required.
Therefore, there is a need for a carbon fiber surface treatment method that is safe, does not burden the environment, and is advantageous in terms of cost and quality.

JP 2000-154460 A JP 2004-238777 A JP 2009-544863 A

  The objective of this invention is providing the manufacturing method of the carbon fiber which can perform the surface treatment of carbon fiber efficiently, with a safe and low environmental load.

The carbon fiber production method of the present invention is a carbon fiber production method in which a carbon fiber is subjected to a surface treatment by a gas phase oxidation treatment method, and the carbon fiber is introduced with a gas containing at least an oxidizing gas and superheated steam. It is the manufacturing method of the carbon fiber heated at 200-600 degreeC in a process chamber.
The oxidizing gas contained in the gas introduced into the processing chamber is preferably oxygen, and the abundance of the oxidizing gas is preferably 1 to 1000 ppm with respect to the total volume of the gas introduced into the processing chamber. . More preferably, the carbon fiber is heat-treated in a treatment chamber into which a gas containing at least 1-1000 ppm of oxidizing gas and 20-99.9 vol% of superheated steam is introduced.

  Since the carbon fiber manufacturing method of the present invention performs surface treatment of carbon fiber using an oxidizing gas and superheated steam, the surface treatment of carbon fiber can be efficiently performed with low environmental load.

The present invention relates to a method for producing carbon fiber in which a surface treatment of carbon fiber is performed by a vapor phase oxidation method.
The carbon fiber manufacturing method of the present invention is a carbon fiber manufacturing method in which the carbon fiber is heated at 200 to 600 ° C. in a treatment chamber into which a gas containing at least an oxidizing gas and superheated steam is introduced.
The production method of the present invention can surface-treat known carbon fibers such as PAN-based and pitch-based without limitation. As the carbon fiber used in the present invention, a PAN-based carbon fiber is preferably used from the viewpoint of the obtained composite physical properties.

  The fineness of the carbon fiber used in the present invention is not particularly limited, but the single fiber fineness is preferably 0.1 to 50 dtex, more preferably 0.5 to 2.0 dtex, and the total fineness of the fiber bundle is It is preferable that it is 10-500000 tex, More preferably, it is 150-10000 tex. The number of filaments in the precursor fiber bundle used in the present invention is preferably 1000 to 100,000, more preferably 3000 to 50000. Moreover, 12000 or more are more preferable from the surface of manufacturing efficiency, and 24000 or more are further more preferable.

In the method for producing carbon fiber of the present invention, the carbon fiber is heated at 200 to 600 ° C. in a treatment chamber into which a gas containing at least an oxidizing gas and superheated steam is introduced.
Superheated steam is steam that is superheated to a temperature higher than the boiling point of water at any pressure. The superheated steam used in the present invention is preferably superheated steam having a dryness of 1.0 or more. If the dryness of water vapor is 1.0 or more, the efficiency of the surface treatment reaction can be sufficiently increased.

Superheated steam causes a water gasification reaction to carbon at a high temperature, and can oxidize the carbon fiber surface by side reaction with an oxidizing gas in a mild reaction field of 200 to 600 ° C. The heat treatment temperature is more preferably 300 to 500 ° C. If the treatment temperature is 200 ° C. or higher, the oxidation reaction proceeds sufficiently. On the other hand, when the treatment temperature exceeds 600 ° C., carbon in the carbon fiber is extracted by the water gasification reaction of superheated steam, and the strength of the carbon fiber is lowered.
The treatment time is not particularly limited, but is preferably 1 to 60 minutes from the viewpoint of reaction uniformity and productivity.

  In the present invention, the gas introduced into the treatment chamber may contain an inert gas in order to adjust the surface treatment reaction. In the present invention, the amount of superheated steam contained in the gas introduced into the processing chamber is preferably 20 to 99.9 vol% with respect to the total gas volume. On the other hand, the inert gas contained in the gas introduced into the processing chamber is preferably 0 to 80 vol%, more preferably 0 to 30 vol%, and more preferably 0.1 to 20 vol% with respect to the total gas volume. More preferably.

If the amount of superheated steam contained in the gas introduced into the treatment chamber is 20 vol% or more, the water gasification reaction efficiency is good and the surface oxidation treatment time can be easily shortened.
Examples of the inert gas include inert gases such as argon, helium, and neon, and nitrogen. Of these, argon or nitrogen is preferably used.

  The oxidizing gas contained in the gas introduced into the processing chamber is preferably 1 to 1000 ppm, more preferably 1 to 100 ppm, based on the total gas volume. If the amount of the oxidizing gas contained exceeds 1000 ppm, the carbon fiber tends to be decomposed into carbon dioxide, and the strength of the carbon fiber tends to decrease.

  Examples of the oxidizing gas include oxygen, ozone, nitric oxide, nitrogen dioxide, nitrous oxide, dinitrogen oxide, dinitrogen tetroxide, dinitrogen pentoxide, sulfur monoxide, sulfur dioxide, and sulfur trioxide. Can be mentioned. Preferably, it is oxygen that has a low environmental impact and is safe.

  For mixing the superheated steam and the oxidizing gas, a method of dissolving the oxidizing gas in water as a superheated steam source in advance or a method of separately introducing it into the processing chamber may be used. In the case of introducing an extremely small amount of oxidizing gas with high accuracy, a method of dissolving the oxidizing gas in water as a heating water vapor source in advance is preferable.

  The treatment chamber used in the present invention may use a closed superheated steam treatment apparatus or an open superheated steam treatment apparatus. The open type is preferable because it allows easy continuous production. When using an open type processing apparatus, it is preferable that the open part of the processing apparatus is sealed by a known means such as a water seal or a labyrinth structure in order to prevent gas from entering from the outside. In addition, by adjusting the opening area of the open part of the processing apparatus or the amount of gas containing superheated steam introduced into the processing apparatus, the amount of gas containing superheated steam introduced into the processing apparatus and the opening of the processing apparatus are adjusted. It is preferable to balance the outflow amount of the gas ejected from the section.

  The amount of the gas containing superheated steam introduced into the processing apparatus is preferably 0.0001 to 1000 times per minute with respect to the processing chamber volume of the processing apparatus. More preferably, the amount is 0.001 to 100 times per minute. If the amount of gas containing water vapor is 0.0001 times the amount of the processing chamber volume per minute, sufficient superheated water vapor can be present in the processing chamber, and the carbon fiber surface can be processed. . On the other hand, if the amount is 1000 times or less per minute, damage to the fiber due to the wind pressure of the introduced gas can be suppressed.

  In addition, the amount of gas containing superheated steam introduced into the processing chamber is adjusted so that the atmosphere gas in the processing chamber contains 20 vol% or more of superheated steam, and the atmosphere gas in the processing chamber is sufficiently replaced with the introduced gas. Is preferred. The amount of water vapor contained in the gas introduced into the processing chamber and the atmospheric gas in the processing chamber can be measured, for example, by a method of obtaining absolute humidity from the wet bulb temperature using a humidity chart. (For example, Ikeda et al., Simple measurement of mixing ratio of superheated steam and air by measuring the temperature of spherical wet material, Transactions of the Japan Society of Mechanical Engineers (B) 78, 790, 1267 to 1278, 2012)

  In the present invention, it is preferable that the heat treatment is performed by applying a tension at which the carbon fiber is not bent in a treatment chamber into which a gas containing an oxidizing gas and superheated steam is introduced. If the tension is low, the yarn will run wild and take damage such as yarn breakage. The tension during the surface treatment is not particularly limited, but it is preferably 9 to 60 N for 1 dtex carbon fiber in order to suppress yarn damage.

In the present invention, the surface untreated carbon fiber may be pretreated using a known technique before performing the heat treatment in the treatment chamber into which the gas containing superheated steam and oxidizing gas is introduced.
The carbon fiber production method of the present invention as described above is safe because most of the gaseous components used are water and inert gas. In addition, since no chemical solution such as an electrolytic solution is used, the chemical solution does not remain in the treated fiber, and it is not necessary to dispose of the chemical solution or the waste solution. Therefore, the surface treatment of the carbon fiber can be performed at a low cost with a low environmental load.

  In the production method of the present invention, known carbon fibers such as PAN-based and pitch-based can be surface-treated without limitation, but as the carbon fibers used in the present invention, PAN-based carbon is used from the viewpoint of the obtained composite physical properties It is preferable to use fibers. The PAN-based carbon fiber can be produced, for example, by the following method.

A PAN fiber obtained by spinning a spinning solution obtained by polymerizing a monomer containing 90% by mass or more, preferably 95% by mass or more of acrylonitrile, and then washing, drying and stretching is used as a precursor fiber. . The number of filaments of the precursor fiber is preferably 1000 filaments or more, more preferably 12000 filaments or more in terms of production efficiency.
Such a precursor fiber is subjected to a flameproofing treatment at 200 to 300 ° C. in heated air for 10 to 100 minutes to obtain a flameproofing fiber. In the flameproofing treatment, it is preferable to stretch the precursor fiber in a range of a draw ratio of 0.90 to 1.20.

  Further, after the obtained flame-resistant fiber is carbonized at a low temperature of 300 ° C. to 1000 ° C., a carbon fiber having a dense internal structure is obtained through a two-stage carbonization step of carbonizing at a high temperature of 1000 to 2000 ° C. . When a higher elastic modulus is required, the graphitization treatment may be further performed at a high temperature of 2000 to 3000 ° C.

  The carbon fiber is subjected to the above-described surface treatment and then subjected to sizing treatment as necessary. The sizing method can be carried out by a conventionally known method, and the sizing agent is preferably used after changing its composition as appropriate according to the application, and after adhering to the carbon fiber. The adhesion amount of the sizing agent is preferably 0.1 to 3.0%, more preferably 0.1 to 1.5%. When the adhesion amount of the sizing agent exceeds 3.0%, the openability of the carbon fiber is lowered, and the impregnation into the fiber bundle inside the matrix resin tends to occur.

In general, when the amount of sizing agent attached is small, there is a problem that a portion where no sizing agent is attached is formed and it is difficult to maintain uniformity. However, the carbon fiber produced according to the present invention has uniform surface functional groups, and the wettability of the fiber surface is improved uniformly, so even with a small amount of adhesion, the sizing agent can be evenly distributed. Can be attached.
The carbon fiber thus obtained can be widely used as a reinforcing fiber such as a thermoplastic resin and a thermosetting resin for sports use, leisure use, general industrial use, aerospace use, automobile use and the like.

The carbon fiber obtained by the carbon fiber production method of the present invention is used and combined with a matrix resin, and a composite material can be obtained by a known means / method such as autoclave molding, press molding, resin transfer molding, filament winding molding, etc. .
Carbon fiber is usually used as a sheet-like reinforcing fiber material. Examples of the sheet-like material include those obtained by arranging fiber materials in a sheet shape in one direction, those obtained by forming a fiber material into a fabric such as a woven or knitted fabric and a nonwoven fabric, and multiaxial woven fabrics.

  As the matrix resin, a thermosetting resin or a thermoplastic resin is used. Specific examples of thermosetting matrix resins include epoxy resins, unsaturated polyester resins, phenol resins, vinyl ester resins, cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins and cyanate ester resins. And a prepolymerized resin, bismaleimide resin, polyimide resin and polyisoimide resin having acetylene terminal, and polyimide resin having nadic acid terminal. These can also be used as one type or a mixture of two or more types. Of these, epoxy resins and vinyl ester resins excellent in heat resistance, elastic modulus, and chemical resistance are particularly preferable. These thermosetting resins may contain commonly used colorants and various additives in addition to the curing agent and the curing accelerator.

Examples of the thermoplastic resin include polypropylene, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, aromatic polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamide , Polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyacrylonitrile, polyaramid, polybenzimidazole and the like.
The content of the resin composition in the composite material is 10 to 90% by weight, preferably 20 to 60% by weight, and more preferably 25 to 45% by weight.

  Hereinafter, the present invention will be specifically described by way of examples. The evaluation method of the physical property of each fiber in each Example and Comparative Example was based on the following method.

<Superheated steam generator>
The superheated steam was prepared by using a superheated steam generator and utility power steamer UPSS-W60 manufactured by Tokuden Corporation.

<Ultra pure water>
As water that is a superheated steam source, ultrapure water “Ultrapur” (product name) manufactured by Kanto Chemical Co., Ltd. was used.

<Gas flow rate and concentration adjustment>
The gas flow rate was monitored using a high-temperature gas flow meter and an oxygen concentration meter, and the atmosphere required by adjusting the flow rate of each gas was prepared.

<Processing chamber oxygen concentration>
The oxygen concentration in the treatment chamber was measured using an oxygen sensor XZR-500 and an oxygen concentration meter XCU-500 manufactured by Michel Japan. The average of the measured values every 1 minute of treatment time was defined as the oxygen concentration value.

<Oxygen content of pure water as a water vapor source>
The oxygen concentration contained in pure water as a water vapor source was measured using DO Master B1032 manufactured by Iijima Electronics Co., Ltd.

<Carbon fiber surface oxygen concentration O / C>
The surface oxygen concentration O / C of the carbon fiber was performed using ESCA JPS-9000MX manufactured by JEOL Ltd. After cutting out the carbon fibers and arranging them on a stainless steel sample support base, the photoelectron escape angle was set to 90 degrees. MgKα was used as the X-ray source, and the inside of the sample chamber was measured at a vacuum degree of 1 × 10 ⁻⁶ Pa. As the correction of the peak due to the measurement time of charging, first main peak of binding energy of C _1S B. E. Was adjusted to 284.6 ev. The O _1S peak area was determined by drawing a straight base line in the range of 528 to 540 eV. The C _1S peak area was determined by drawing a straight base line in the range of 282 to 292 eV. O / C was calculated from the obtained O _1S peak area and C _1S peak area ratio.

<Strand tensile strength>
The strand tensile strength of the carbon fiber was measured according to JIS R-7608 and the epoxy resin-impregnated strand was measured.

<Amount of sizing agent (solvent extraction method)>
The carbon fiber bundle 10g was taken out, acetone was used as a solvent, and the adhesion amount of the sizing agent was determined based on JIS R7604 A method (solvent extraction method).

<Example 1>
Precursor PAN fiber strands (single fiber fineness 0.7 dtex, filament number 24000) are flame-resistant in air until the fiber has a specific gravity of 1.35, then in a nitrogen gas atmosphere at a maximum temperature of 650 ° C. Low temperature carbonized. Thereafter, carbon fiber was produced by high-temperature carbonization at 1300 ° C. in a nitrogen atmosphere. When the carbon fiber surface oxygen concentration (O / C) of the obtained unsurface-treated carbon fiber was measured, it was 2.6%.
Subsequently, the non-surface-treated carbon fiber was passed through an open heating furnace (treatment chamber) filled with superheated steam to perform surface treatment. Oxygen was previously dissolved in ultrapure water as a superheated steam source, and the oxygen concentration in the treatment chamber was adjusted to 1 ppm. The ratio of superheated steam in the atmosphere in the processing furnace was 99.9 vol%. The temperature in the treatment chamber was 250 ° C., and the treatment chamber residence time of the fiber to be treated was 15 minutes. When the O / C of the obtained carbon fiber was measured, it was 7.9%, and it was confirmed that the surface treatment improved the O / C of the fiber surface, and the carbon fiber surface was oxidized.
Sizing treatment is performed on the carbon fiber after the treatment by adjusting the concentration of the sizing agent bath so that the sizing agent adhesion amount is 1.0 wt% with the sizing agent mainly composed of bisphenol A type epoxy resin. When the strand tensile strength was measured, it showed a good strength of 4980 MPa.

<Examples 2 to 4>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 1 except that the temperature in the treatment chamber was changed to the temperature shown in Table 1. Table 1 shows the O / C and strand strength of the obtained carbon fiber.
Also in Examples 2 to 4 in which the treatment temperature was changed, the carbon fiber surface was sufficiently oxidized. When Examples 1 to 4 were compared, as the processing temperature increased, O / C improved and the strand strength tended to improve.

<Comparative Example 1>
As in Example 1, PAN fiber strands (single fiber fineness 0.7 dtex, filament number 24000) as precursor fibers were flame-resistant in air until the fiber specific gravity reached 1.35, and then a nitrogen gas atmosphere Medium temperature carbonization was performed at a maximum temperature of 650 ° C. Thereafter, carbon fiber was produced by high-temperature carbonization at 1300 ° C. in a nitrogen atmosphere. When the carbon fiber surface oxygen concentration (O / C) of the obtained unsurface-treated carbon fiber was measured, it was 2.6%.
Sizing by adjusting the concentration of the sizing agent bath so that the sizing agent adhesion amount is 1.0 wt% with the sizing agent mainly composed of bisphenol A type epoxy resin, without performing surface treatment on the untreated carbon fiber. Processed. The strand tensile strength of the obtained carbon fiber bundle was 4240 MPa, which was lower than those of Examples 1 to 4.

<Comparative example 2>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 1 except that the temperature in the treatment chamber was changed to 150 ° C. When O / C of the obtained carbon fiber was measured, it was 2.9%, and the fiber surface was hardly oxidized.
The treated carbon fiber was subjected to sizing treatment in the same manner as in Example 1, and the strand tensile strength of the carbon fiber bundle was measured. As a result, it was 4310 MPa.

<Comparative Example 3>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 1 except that the temperature in the treatment chamber was changed to 750 ° C. When O / C of the obtained carbon fiber was measured, it was 16.5%, and the fiber surface was sufficiently oxidized.
The treated carbon fiber was subjected to sizing treatment in the same manner as in Example 1, and the strand tensile strength of the carbon fiber bundle was measured. As a result, it was as low as 1960 MPa. It is considered that the treatment temperature is too high, carbon in the carbon fiber is pulled out by the water gasification reaction, and the strength of the carbon fiber is lowered.

<Examples 5-9>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 3 except that the oxygen concentration in the treatment chamber was changed to the concentration shown in Table 2. Table 2 shows the O / C and strand strength of the obtained carbon fiber.
Also in Examples 5 to 9 in which the oxygen concentration in the treatment chamber was changed, the carbon fiber surface was sufficiently oxidized. When Examples 5 to 9 and Example 3 were compared, the O / C was improved and the strand strength was improved as the oxygen concentration was increased. In Example 9 in which the oxygen concentration in the treatment chamber exceeded 1000 ppm, a slight decrease in strand strength was observed.

<Examples 10 to 12>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 3 except that the residence time of the fiber to be treated was changed to the time shown in Table 3. Table 3 shows the O / C and strand strength of the obtained carbon fiber.
Also in Examples 10 to 12 in which the residence time was changed, the carbon fiber surface was sufficiently oxidized. When Examples 10-12 and Example 3 were compared, the tendency for O / C to improve was seen as residence time became long.

<Examples 13 to 17>
The surface oxidation treatment of the carbon fiber was performed in the same manner as in Example 3 except that the water vapor ratio in the processing chamber was changed to the ratio shown in Table 4. The water vapor ratio in the processing chamber was adjusted by introducing argon gas, which is an inert gas, from another line into the processing chamber while monitoring using a flow meter. Table 4 shows the O / C and strand strength of the obtained carbon fiber.
Also in Examples 13 to 17 in which the water vapor ratio in the treatment chamber was changed, the carbon fiber surface was sufficiently oxidized.

Claims (4)

  A carbon fiber manufacturing method for performing carbon fiber surface treatment by a gas phase oxidation method, wherein the carbon fiber is heated at 200 to 600 ° C. in a treatment chamber into which a gas containing at least an oxidizing gas and superheated steam is introduced. A method for producing carbon fiber, comprising:   The manufacturing method of the carbon fiber of Claim 1 whose oxidizing gas contained in the gas introduce | transduced into a process chamber is 1-1000 ppm.   The method for producing carbon fiber according to claim 1 or 2, wherein the oxidizing gas is oxygen.   The carbon fiber according to any one of claims 1 to 3, wherein the carbon fiber is heat-treated in a treatment chamber into which a gas containing at least 1-1000 ppm of oxidizing gas and 20-99.9 vol% of superheated steam is introduced. Manufacturing method.