JP4936588B2 - Carbon fiber for metal oxide coating and method for producing the same - Google Patents

Description

【００８７】
【表２】

【００８８】
【発明の効果】
本発明の金属酸化物コーティング用炭素繊維は、上記のように構成したので、各種金属酸化物を均一、強固、かつ多量にコーティングすることができる。
【００８９】
また、本発明の金属酸化物コーティング用炭素繊維を用いて製造する金属酸化物をコーティングした炭素繊維は、炭素繊維が本来有している高強度・高弾性率等の好ましい性能を損なうことなく、金属酸化物の特性を具備することができる。
【００９０】
特に、金属酸化物として磁性、透磁率性、超伝導性等を示すものを用いる場合は、得られる金属酸化物をコーティングした炭素繊維は、高強度・高弾性率と、磁性等の優れた性質とを兼備するものとなる。従って、本発明の金属酸化物コーティング用炭素繊維を用いて金属酸化物をコーティングした炭素繊維組織構造体を製造する場合は、このものは機械的性質の改善効果と電磁波吸収効果等とを効率良く発揮させることができる。
【図面の簡単な説明】
【図１】実施例１で得られた金属酸化物のコーティング前の炭素繊維の図面代用走査型電子顕微鏡（ＳＥＭ）写真である。Ａ、Ｂ及びＣは、炭素繊維断面の、それぞれ、倍率×５０００、×８０００及び×３００００のＳＥＭ写真である。Ｄ、Ｅ、Ｆ及びＧは、炭素繊維側面の、それぞれ、倍率×１０００、×３５００、×１００００及び×３００００のＳＥＭ写真である。
【図２】実施例１で得られた金属酸化物のコーティング後の炭素繊維の図面代用走査型電子顕微鏡（ＳＥＭ）写真である。Ａ、Ｂ及びＣは、炭素繊維断面の、それぞれ、倍率×５０００、×８０００及び×３００００のＳＥＭ写真である。Ｄ、Ｅ、Ｆ及びＧは、炭素繊維側面の、それぞれ、倍率×１０００、×３５００、×１００００及び×３００００のＳＥＭ写真である。
【図３】比較例１で得られた金属酸化物のコーティング前の炭素繊維の図面代用走査型電子顕微鏡（ＳＥＭ）写真である。Ａ、Ｂ及びＣは、炭素繊維断面の、それぞれ、倍率×５０００、×８０００及び×３００００のＳＥＭ写真である。Ｄ、Ｅ、Ｆ及びＧは、炭素繊維側面の、それぞれ、倍率×１０００、×３５００、×１００００及び×３００００のＳＥＭ写真である。
【図４】比較例１で得られた金属酸化物のコーティング後の炭素繊維の図面代用走査型電子顕微鏡（ＳＥＭ）写真である。Ａ、Ｂ及びＣは、炭素繊維断面の、それぞれ、倍率×５０００、×８０００及び×３００００のＳＥＭ写真である。Ｄ、Ｅ、Ｆ及びＧは、炭素繊維側面の、それぞれ、倍率×１０００、×３５００、×１００００及び×３００００のＳＥＭ写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon fiber suitable for coating a metal fiber surface with a metal oxide by a physical or chemical reaction, the same strand, a carbon fiber tissue structure, and a method for producing them.
[0002]
[Prior art]
The technology of simply manufacturing a composite material by simply coating different materials such as plastics, ceramics, and metals on carbon fibers is a relatively basic technology, and carbon fibers coated with these using the above technology are also well known in the art. Is.
[0003]
In recent years, with the advancement of functions of composite materials such as carbon fiber reinforced plastics, it is not only a matter of demanding improvement in strength, but a high-functionality that combines the characteristics of both by coating materials with different functions on the fiber substrate surface Alternatively, attempts have been made to develop multifunctional fibers, and various composite carbon fibers have actually been developed.
[0004]
Such composite carbon fibers not only have applications that make use of the high strength and elastic modulus of the carbon fibers themselves used in composite carbon fibers, but also combine the physical properties and functionality of different types of coated materials. is there.
[0005]
On the other hand, metal oxides are widely used in various industrial fields because they are excellent in magnetism, magnetic permeability and superconductivity, and also have catalytic action. Among these, magnetic oxides are not only put into practical use for magnetic recording media such as magnetic tapes, but also have conductivity, surface adsorption ability, and electromagnetic wave absorption ability, and are expected to be used in a wide range of applications.
[0006]
In particular, due to the recent development of information communication equipment, a wide variety of electromagnetic waves are flying around in the outside world, and electromagnetic interference that causes a computer or a control device to malfunction is a major social problem. In order to prevent such electromagnetic interference, various composite materials in which a magnetic oxide is combined as an electromagnetic wave absorber are being developed.
[0007]
Since the magnetic oxide has a function of absorbing electromagnetic waves in a wide frequency range, it is expected that a molded body having both mechanical strength and electromagnetic wave absorption characteristics can be realized by combining with carbon fibers.
[0008]
A technique for coating a carbon material with a metal oxide is known from Japanese Patent Laid-Open No. 10-208541. However, according to the prior art, it is difficult to coat a large amount of metal oxide firmly and uniformly on the surface of the carbon fiber, and it is possible to coat the metal oxide with a uniform and constant adhesion amount on each fiber. There is no carbon fiber whose surface condition is controlled.
[0009]
[Problems to be solved by the invention]
As a result of various studies to produce carbon fibers that can be coated uniformly and in large quantities with metal oxides, the present inventors have found that carbon fibers having a high carbon content are measured by the ESCA method._1S/ C_1SThe peak ratio, the equivalent of carboxyl groups or hydroxyl groups that are functional groups formed on the carbon fiber surface, and the ratio of carboxyl group / hydroxyl group has an important effect on the coating properties of metal oxides on the carbon fiber surface. As a result, the present invention has been completed.
[0010]
Therefore, the object of the present invention is to control the surface state of the carbon fiber so that the metal oxide can be uniformly coated on the carbon fiber surface uniformly and with an arbitrary amount of adhesion, and the carbon fiber for coating the metal oxide. It is to provide a manufacturing method.
[0011]
[Means for Solving the Problems]
The present invention for achieving the above object is described below.
[0012]
[1] Peak ratio O measured by ESCA method with a carbon content of 90% or more_1S/ C_1SIs a carbon fiber for metal oxide coating, having a carboxyl group and hydroxyl group on the fiber surface of 0.5 μeq / g or more and a carboxyl group / hydroxyl group of 1 or more.
[0013]
[2] The carbon fiber for metal oxide coating according to [1], which is formed in a filament shape.
[0014]
[3] The carbon fiber for metal oxide coating according to [1], which is formed in a fiber shape having a length of 1 to 100 mm.
[0015]
[4] The metal oxide coating according to [1], having a diameter of 3 to 10 μm, a tensile load of 1.5 g or more, a tensile elongation of 0.5% or more, and a volume resistivity of 0.1 Ω · cm or less. Carbon fiber for use.
[0016]
[5] The carbon fiber for metal oxide coating according to [1], which is produced by carbonization treatment of polyacrylonitrile fiber.
[0017]
[6] The carbon fiber for metal oxide coating according to [1], which is sized by a viscous material containing water.
[0018]
[7] A strand formed by concentrating 100 to 100,000 filaments according to [2], wherein the strand has a tensile strength of 200 kgf / mm.²As described above, the tensile elastic modulus is 20 tonf / mm²This is the carbon fiber strand for metal oxide coating.
[0019]
[8] A metal oxide comprising the carbon fiber for coating a fiber-like metal oxide according to [3] or the carbon fiber strand for coating a metal oxide according to [7]. Carbon fiber structure for coating.
[0020]
[9] The carbon fiber structure for metal oxide coating according to [8], wherein the carbon fiber structure for metal oxide coating is a woven fabric, a nonwoven fabric, synthetic paper, or felt.
[0021]
[10] In the method for producing a metal oxide coating carbon fiber for oxidizing a carbon fiber, the oxidation treatment allows the carbon fiber to pass through an aqueous solution of sulfate while passing an electric current through the carbon fiber. 90% or more, peak ratio O measured by ESCA method_1S/ C_1SIs 0.1 to 0.5, the carboxyl group and hydroxyl group on the fiber surface is 0.5 μeq / g or more, and the method for producing carbon fiber for metal oxide coating having carboxyl group / hydroxyl group of 1 or more.
[0022]
[11] A method for producing carbon fiber chopped fiber for metal oxide coating, wherein the strand according to [7] is cut into a length of 1 to 100 mm.
[0023]
Hereinafter, the present invention will be described in detail.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The carbon fiber for metal oxide coating of the present invention is produced by oxidizing the surface of the carbon fiber. Examples of the carbon fiber used as the raw material for producing the carbon fiber for metal oxide coating of the present invention include polymer fibers such as phenol resin, rayon, polyacrylonitrile, and pitch fibers such as petroleum pitch, carbon pitch, and liquid crystal pitch. Any of the carbon fibers that are used as a raw material can be used, and is not particularly limited. However, from the viewpoints of ease of production, stability of the quality to be obtained, and the like, acrylic carbon fibers that are mainly made by baking polyacrylonitrile fibers at 1000 to 3000 ° C. in an inert gas atmosphere are preferable.
[0025]
(Precursor)
The precursor used as a raw material for the acrylic carbon fiber is polyacrylonitrile fiber (polyacrylonitrile and polyacrylonitrile obtained by copolymerizing a monomer having a polar group). As this precursor, a precursor prepared by using a concentrated solution of polyacrylonitrile by a normal wet, dry, or dry / wet spinning method and under normal spinning conditions can be used. These polyacrylonitrile fibers themselves are known.
[0026]
As the polyacrylonitrile solvent used for spinning, organic solvents such as dimethylformamide, dimethyl sulfoxide, dimethylacetamide, and ethylene carbonate, and aqueous solutions such as nitric acid, rhodan salts, and zinc chloride are mainly used.
[0027]
In particular, a precursor spun from a polymer solution using an aqueous solution of zinc chloride is preferable because the orientation of polymer molecules is high, and a carbon fiber having good quality and high elongation can be obtained. This spinning method itself is known.
[0028]
It has been confirmed by means of metal analysis or the like that 10 to 100 ppm of the zinc component remains in the precursor made of polyacrylonitrile fiber spun using a zinc chloride aqueous solution as a solvent. The zinc component remaining at 10 to 100 ppm in the precursor promotes the growth of the carbon network surface without disturbing the orientation of the carbon network surface in the carbon fiber produced in the process of producing the carbon fiber by firing the precursor. To produce high performance carbon fiber.
[0029]
The carbon fiber obtained after firing contains about 20 to 200 ppm of zinc as a specific component. This zinc component does not deteriorate the performance of the carbon fiber even after the surface treatment process or the drying process of the carbon fiber, which will be described later. give.
[0030]
The precursor is preferably 0.5 to 3 denier and has an orientation degree of 90% or more by wide-angle X-ray diffraction.
[0031]
In order to impart stretchability and convergence to the precursor and improve workability, it is preferable to attach 0.01 to 1% of an oil agent to the precursor surface. As the oil agent, amino silicone, phosphate ester, polyethylene glycol modified silicone, aliphatic ester, glycidyl ether, aromatic ester, composite ester, fluorophosphate ester, etc. alone or in combination Can be used.
[0032]
(Flame resistant fiber)
The acrylonitrile fiber, which is a precursor prepared as described above, is heat-treated in air at 200 to 300 ° C. under tension, thereby obtaining a flame resistant fiber having a specific gravity of 1.3 to 1.4 that does not burn in air.
[0033]
(Raw carbon fiber)
Thereafter, the flame resistant fiber is heated at 1,000 ° C. to 3,000 ° C. in an inert gas atmosphere under a certain tension to be carbonized, thereby obtaining a raw carbon fiber.
[0034]
In particular, in order to obtain high-strength raw material carbon fibers, it is necessary to pay attention to the tension balance of the carbon fiber strands and the temperature gradient during passage through the carbonization furnace in the carbonization process at 1,000 to 3,000 ° C. These conditions are known to those skilled in the art. Since carbon fiber having high graphitic properties is not suitable as a raw material for carbon fiber for metal oxide coating in terms of performance and cost, the carbonization temperature is preferably 1,000 to 2,000 ° C.
[0035]
The raw carbon fiber thus obtained has a single fiber diameter of 3 to 10 μm, a tensile load of the single fiber filament of 1.5 g or more, a tensile elongation of 0.5% or more, and a volume resistivity of 0.1 Ω · cm. Hereinafter, those having a fiber specific gravity of 1.6 to 2.0 are preferred.
[0036]
Further, the carbon fiber strand obtained by bundling 100 to 100,000 raw carbon fibers (single fiber filaments) has a tensile strength of 200 kgf / mm.²As described above, tensile elastic modulus 20 ton / mm²The above is preferable.
[0037]
(surface treatment)
In the present invention, the raw carbon fiber is then subjected to a surface treatment to oxidize the surface of the carbon fiber. That is, as described above, the precursor carbon fiber obtained by firing the precursor at 1000 to 3000 ° C. and cooling it to a temperature of 400 ° C. or less in an inert gas atmosphere, or the precursor carbon fiber prepared and prepared in advance. Is sent to the surface treatment step, and in this step, functional groups such as carboxyl groups and hydroxyl groups are generated on the carbon fiber surface by an oxidation reaction.
[0038]
Surface treatment methods include strong acids such as sulfuric acid and nitric acid, salts of strong acids, salts of weak acids such as acetic acid and hypochlorous acid, alkalis such as sodium hydroxide and potassium hydroxide, or solutions of alkali salts. The method of immersing raw material carbon fiber or a carbon fiber bundle can be illustrated. In this case, it is also effective to apply an electric current to the carbon fiber to perform electrolytic oxidation. In particular, a method of passing a carbon fiber through an aqueous solution of sulfate while passing an electric current is a preferable surface treatment method.
[0039]
In this case, the carbon fiber obtained by passing an aqueous solution of sulfate while flowing electricity to the raw material carbon fiber at an electric quantity of 100 c / g or less, in particular 5 to 50 c / g, is mild in surface treatment conditions._1S/ C_1SThis is particularly preferable for controlling the peak ratio and the amount of functional groups.
[0040]
Examples of the sulfate include sodium sulfate, sodium hydrogen sulfate, ammonium sulfate, and ammonium hydrogen sulfate. The sulfate concentration is preferably 1 to 15% by mass.
[0041]
Or the method of making carbon fiber or a carbon fiber bundle contact oxidizing gases, such as ozone and halogen, and performing an oxidation process can also be illustrated.
[0042]
Further, when high-temperature air having a temperature exceeding 400 ° C. is brought into contact with the carbon fiber in the carbonization process, the carbon fiber causes an oxidation reaction with oxygen in the air.
[0043]
In the present invention, the carbon fiber for metal oxide coating is produced by introducing the functional group to the surface of the raw carbon fiber by subjecting the raw carbon fiber to the above oxidation treatment. It is within the range shown.
[0044]
a. O measured by ESCA method_1S/ C_1SThe peak ratio is 0.1 to 0.5, preferably 0.2 to 0.4.
b. The equivalents of carboxyl groups and hydroxyl groups (acidic functional groups) generated on the carbon fiber surface determined by neutralization titration are both 0.5 μeq / g or more, preferably 1 to 25 μeq / g.
c. The equivalent ratio of carboxyl group / hydroxyl group is 1 or more, preferably 1-10.
The introduction amount is adjusted by appropriately setting the concentration, temperature, amount of electricity, or gas concentration, treatment time, etc. of the treatment solution.
[0045]
In the surface treatment of carbon fiber, by setting the equivalent ratio of carboxyl group / hydroxyl to 1 or more, the coating property of the metal oxide on the fiber surface is increased and uniform coating is possible.
[0046]
The equivalent of the carboxyl group and phenolic hydroxyl group (acidic functional group) generated on the surface of the carbon fiber is obtained by immersing the carbon fiber in an excess alkaline solution to react the alkali with the acidic functional group, and then back titrating the alkaline solution with an acid. This can be calculated. It is considered that a carboxyl group and a phenolic hydroxyl group exist as the acidic functional group. Sodium hydroxide reacts with both carboxyl groups and phenolic hydroxyl groups. However, sodium bicarbonate reacts only with carboxyl groups. The equivalent of both functional groups can be quantified by back titrating with a sodium hydroxide solution and a sodium carbonate solution.
[0047]
As described later, when a metal oxide is coated on the surface of the carbon fiber, the precursor material of the metal oxide or the metal oxide itself is coordinated on the surface of the carbon fiber in proportion to the degree of the surface treatment of the carbon fiber surface. Or it tends to adhere easily. Therefore, O measured by the ESCA method of carbon fiber._1S/ C_1SIf the peak ratio is less than 0.1, the amount of metal oxide coating formed on the carbon fiber is small and tends to easily fall off, which is not preferable.
[0048]
O_1S/ C_1SWhen the peak ratio of is larger than 0.5, it is in a state where the surface treatment is excessively performed, in this case, the basic mechanical properties of the carbon fiber itself are impaired, and when the metal oxide is coated, This is not preferable because the adhesive strength between the metal oxide and the carbon fiber is low.
[0049]
Conversely, O_1S/ C_1SBy controlling the peak ratio, the coating amount of the metal oxide can also be controlled.
[0050]
(Cleaning process)
The surface-treated carbon fiber is then subjected to a cleaning treatment if necessary. Thereby, it is possible to remove residual components such as acid, alkali, and ions attached to the carbon fiber surface during the surface treatment. Washing is preferably water washing. As the washing water, ion-exchanged water is preferable, and water having a total metal ion component in water of 50 ppm or less is particularly preferable. By using water with a small amount of all metal ion components, it is possible to prevent a decrease in the activity of functional groups generated on the surface of the carbon fiber during washing.
[0051]
After washing, the carbon fiber is preferably dried. The drying is preferably performed so that the moisture content of the carbon fiber is 0.5% by mass or less.
[0052]
Thereby, the carbon fiber for metal oxide coating of this invention is obtained.
[0053]
The form of the carbon fiber for metal oxide coating of the present invention may be a single fiber of various forms such as a short fiber or a filament, or a strand formed by converging the single fibers. Moreover, the chopped fiber which cut the carbon fiber into 1-100 mm in length may be sufficient. Chopped fibers can be easily manufactured by cutting the strands.
[0054]
Carbon fiber bundles in which 100 to 100,000 dried filaments are bundled are inherently poorly organized in strands and easily spread by wind or the like, and are difficult to handle. Therefore, by attaching 1 to 10% by mass of water or oils such as higher alcohol, or a viscous substance such as epoxy resin as a sizing agent to the carbon fiber, the strands can be easily bundled and handled. Improved.
[0055]
Depending on the application, a water-soluble polymer substance such as polyvinyl alcohol (PVA) or polyethylene glycol (PEG) may be used as a hydrophilic sizing agent. These sizing agents are preferably removed prior to coating the metal oxide.
[0056]
(Metal oxide coating)
As a method of coating a metal oxide on the surface of the carbon fiber for metal oxide coating of the present invention produced as described above, a method of sizing by mixing a metal oxide into a paste-like substance such as a sizing agent, There are a method of plating with a precursor solution of a metal oxide, a method of chemical vapor deposition such as CVD, and the like.
[0057]
Furthermore, when considering cost reduction due to optimization of the coating state or continuation, the carbon fiber of the present invention is immersed in a metal oxide precursor solution, and metal ions are attached to the surface of the carbon fiber, followed by heat treatment. Thus, a method of generating a metal oxide on the carbon fiber surface is preferable. It is preferable to perform heat processing by hold | maintaining at 200-2000 degreeC for 30 to 300 minutes in the air.
[0058]
The carbon fiber of the present invention can be coated with a metal oxide on the surface by any of the above methods.
[0059]
As the metal oxide to be coated by sizing, iron oxide, titanium oxide, silicon oxide and the like are preferable.
[0060]
As the metal oxide precursor to be coated by plating, iron chloride, nickel chloride, cobalt chloride, titanium sulfate and the like are preferable.
[0061]
As the metal oxide or precursor thereof coated by chemical vapor deposition, magnesium oxide, beryllium oxide, aluminum oxide or the like is preferable.
[0062]
As the metal ions to be attached to the carbon fibers, ions such as Fe, Cr, Mn, Zn, Ni, and Si are preferable.
[0063]
The coating amount of the metal oxide is preferably 1 to 100% by mass, particularly preferably 10 to 50% by mass, based on the fiber mass (100%).
[0064]
In addition, carbon fiber structure structures, such as a textile fabric, a nonwoven fabric, a synthetic paper, and a felt, can be produced using the carbon fiber of this invention. The metal oxide can be attached to the carbon fiber structure by the above method.
[0065]
Further, the carbon fiber of the present invention has a strand tensile modulus of 15 tonf / mm.²Low elastic modulus carbon fiber of less than or a tensile elastic modulus of 40 ton / mm²The above high strength and high modulus carbon fibers can be used in combination. In addition to carbon fibers, the following reinforcing fibers can be used in combination with high elongation carbon fibers. Reinforcing fibers may be either inorganic or organic fibers. For example, in addition to natural and synthetic polymer fibers, glass fibers, aromatic aramid fibers, aromatic polyamide fibers, boron fibers, alumina fibers, and silicon carbide fibers are used in combination. can do. In any case, those having a tensile elongation of 2.0% or more are preferred.
[0066]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0067]
The equivalent of the carboxyl group on the carbon fiber surface and the phenolic hydroxyl group was determined by the following method.
[0068]
The carbon fiber is cut into about 5 cm and about 3 g of the carbon fiber is immersed in 0.1N hydrochloric acid and left overnight to liberate acidic functional groups present in the form of salts and rings. Thereafter, the carbon fiber is washed with pure water until neutral. Put neutral carbon fiber in Erlenmeyer flask, add 80 ml of pure water, perform deaeration for 30 minutes, add 1 ml of 0.05N sodium hydroxide solution or sodium hydrogen carbonate solution, and replace the Erlenmeyer flask with nitrogen. Then leave it in a sealed state for a whole day and night.
[0069]
Thereafter, the carbon fibers in the Erlenmeyer flask are sufficiently washed with pure water, and the wash water is subjected to back titration (potentiometric titration) with 0.01N hydrochloric acid standard solution.
[0070]
On the other hand, the same operation is performed to obtain a blank value.
[0071]
The amount of carboxyl group and phenolic hydroxyl group is calculated from the following formula.
[0072]
[Expression 1]
Amount of carboxyl groups (μeq / g) = 1000 (V₀-V₁) ・ T / p (1)
Total amount of acidic groups (μeq / g) = 1000 (V₀-V₂) ・ T / p (2)
Phenolic hydroxyl group content (μeq / g) = (2)-(1) (3)
V₀: Blank titration (ml)
V₁: Titration volume of washing water with sodium bicarbonate (ml)
V₂: Titration volume of washing water with sodium hydroxide added (ml)
t: Titration hydrochloric acid concentration (0.01N)
p: Mass of collected carbon fiber (g)
Example 1
An acrylonitrile fiber strand constituted by collecting 12,000 single fiber filaments having a thread thickness of 1.0 denier was flame-resistant in air at 280 ° C. and then carbonized at 1,400 ° C. Subsequently, the strand was continuously immersed in a 5% by mass ammonium sulfate aqueous solution, and the carbon fiber was subjected to a surface treatment with a residence time of 2 minutes while being energized with an electric amount of 15 c / g.
[0073]
Subsequently, after washing with ion-exchanged water having a total metal ion component of 10 ppm or less and drying, a carbon fiber for metal oxide coating having a water content of 0.1% by mass was obtained.
[0074]
Table 1 shows the performance of the obtained carbon fibers.
[0075]
1 g of this carbon fiber was sampled, immersed in 100 cc of a 0.02M / 0.01M / 0.1M solution of iron chloride / nickel chloride / urea, and heated to 200 ° C. by irradiation with microwaves in a nitrogen atmosphere at 50 atm. And kept in that state for 30 minutes. The fiber obtained by cooling, washing with water and drying was discolored brown and magnetism was observed.
[0076]
Wide-angle X-ray diffraction confirmed that Ni ferrite was coated on the fiber surface. The coating amount calculated from the mass change before and after the treatment was 5% by mass.
[0077]
When the surface state of the fiber was observed with a scanning electron microscope (SEM), as shown in the SEM photograph of FIG. 2, a state in which a substance considered to be Ni ferrite was uniformly coated on the fiber surface was observed. From these results, as shown in Table 1, it was confirmed that the carbon fiber produced under the conditions of Example 1 was a carbon fiber suitable for coating with a metal oxide.
[0078]
In addition, the SEM photograph of the carbon fiber before a coating process is shown in FIG.
[0079]
  Example 23
  As shown in Table 1, the carbon fiber production conditions and the surface treatment conditions were changed, and the surface of the carbon fiber was coated with a metal oxide in the same manner as in Example 1, and the coating amount and state of the metal oxide were examined. As a result, these carbon fibers were confirmed to be carbon fibers suitable for metal oxide coating.
[0080]
  Example4
  An acrylonitrile fiber strand composed of 6,000 single fiber filaments having a thread thickness of 1.0 denier was flame-resistant at 260 ° C. in air and then carbonized at 1,350 ° C. Subsequently, the strand was continuously immersed in a 5% by mass ammonium sulfate aqueous solution, and the carbon fiber was subjected to a surface treatment with a residence time of 2 minutes while being energized with an electric amount of 10 c / g.
[0081]
Subsequently, after washing with ion-exchanged water having a total metal ion component of 10 ppm or less and drying, a carbon fiber for metal oxide coating having a water content of 0.1% by mass was obtained. Table 1 shows the performance of the obtained carbon fibers.
[0082]
1 g of this carbon fiber was sampled and immersed in 50 ml of 50 mass% titanium sulfate aqueous solution, and then 50% ammonia water was gradually added until pH 7 was reached. Carbon fiber was taken out from the solution in the form of a bowl, washed with water, dried, and dried at 540 ° C. for 3 hours. The color of the fiber was almost unchanged and black. Wide-angle X-ray diffraction confirmed that the fiber surface was coated with titanium oxide. The coating amount calculated from the mass change before and after the treatment was 5% by mass.
[0083]
Comparative Example 1
Although it was the carbon fiber manufactured on the same conditions as Example 1, the carbon fiber which does not give surface treatment was produced. This fiber is O_1S/ C_1SThe value was 0.05, and it was confirmed that the relative equivalent number of functional groups such as carboxyl groups on the carbon fiber surface was small (Table 2).
[0084]
This carbon fiber was coated with a metal oxide under the same conditions as in Example 1. The coating amount of the metal oxide on the fiber is as small as 0.5% by mass, and it is confirmed that the coating state is sparse as shown in the SEM photograph of FIG. 4, and the carbon fiber is suitable for coating of the metal oxide. It was confirmed that there was no carbon fiber.
[0085]
In addition, the SEM photograph of the carbon fiber before a coating process is shown in FIG.
[0086]
[Table 1]

[0087]
[Table 2]

[0088]
【The invention's effect】
Since the carbon fiber for metal oxide coating of the present invention is configured as described above, various metal oxides can be coated uniformly, firmly and in large quantities.
[0089]
Further, the carbon fiber coated with the metal oxide produced using the carbon fiber for metal oxide coating of the present invention, without impairing the preferable performance such as high strength and high elastic modulus inherent in the carbon fiber, It can have the characteristics of a metal oxide.
[0090]
In particular, when using metal oxides that exhibit magnetism, magnetic permeability, superconductivity, etc., the carbon fiber coated with the resulting metal oxide has excellent properties such as high strength and high elastic modulus and magnetism. And will be combined. Therefore, when producing a carbon fiber textured structure coated with a metal oxide using the carbon fiber for metal oxide coating of the present invention, this effectively improves the mechanical properties and the electromagnetic wave absorption effect. It can be demonstrated.
[Brief description of the drawings]
1 is a scanning electron microscope (SEM) photograph substituting for a drawing of a carbon fiber before coating with a metal oxide obtained in Example 1. FIG. A, B, and C are SEM photographs of carbon fiber cross-sections at magnifications of × 5000, × 8000, and × 30000, respectively. D, E, F, and G are SEM photographs of the magnification of x1000, x3500, x10000, and x30000, respectively, on the carbon fiber side surface.
2 is a scanning electron microscope (SEM) photograph substituting for a drawing of the carbon fiber after coating with the metal oxide obtained in Example 1. FIG. A, B, and C are SEM photographs of carbon fiber cross-sections at magnifications of × 5000, × 8000, and × 30000, respectively. D, E, F, and G are SEM photographs of the magnification of x1000, x3500, x10000, and x30000, respectively, on the carbon fiber side surface.
FIG. 3 is a scanning electron microscope (SEM) photograph substituting for a drawing of the carbon fiber obtained in Comparative Example 1 before coating with the metal oxide. A, B, and C are SEM photographs of carbon fiber cross-sections at magnifications of × 5000, × 8000, and × 30000, respectively. D, E, F, and G are SEM photographs of the magnification of x1000, x3500, x10000, and x30000, respectively, on the carbon fiber side surface.
4 is a scanning electron microscope (SEM) photograph substituting for a drawing of a carbon fiber coated with a metal oxide obtained in Comparative Example 1. FIG. A, B, and C are SEM photographs of carbon fiber cross-sections at magnifications of × 5000, × 8000, and × 30000, respectively. D, E, F, and G are SEM photographs of the magnification of x1000, x3500, x10000, and x30000, respectively, on the carbon fiber side surface.

Claims (11)

Carbon content is 90% or more, peak ratio O _1S / C _1S measured by ESCA method is 0.25 to 0.4, carboxyl group and hydroxyl group on the fiber surface is 0.5 μeq / g or more, and carboxyl group / hydroxyl group Is a carbon fiber for metal oxide coating.  The carbon fiber for metal oxide coating according to claim 1, wherein the carbon fiber is formed into a filament shape.   The carbon fiber for metal oxide coating according to claim 1, wherein the carbon fiber is formed into a fiber having a length of 1 to 100 mm.  The carbon fiber for metal oxide coating according to claim 1, having a diameter of 3 to 10 µm, a tensile load of 1.5 g or more, a tensile elongation of 0.5% or more, and a volume resistivity of 0.1 Ω · cm or less.  The carbon fiber for metal oxide coating according to claim 1, wherein the carbon fiber is produced by carbonization treatment of polyacrylonitrile fiber.  The carbon fiber for metal oxide coating according to claim 1, which is sized by a viscous material containing water. A strand formed by concentrating 100 to 100,000 filaments according to claim 2, wherein the strand has a tensile strength of 200 kgf / mm ² or more and a tensile elastic modulus of 20 tof / mm ² or more. Carbon fiber strand.  A carbon fiber structure for metal oxide coating comprising the carbon fiber for fiber-like metal oxide coating according to claim 3 or the carbon fiber strand for metal oxide coating according to claim 7. Structure.  The carbon fiber structure for a metal oxide coating according to claim 8, wherein the carbon fiber structure for a metal oxide coating is a woven fabric, a nonwoven fabric, a synthetic paper, or a felt. In the manufacturing method of carbon fiber for metal oxide coating which oxidizes carbon fiber, the oxidation treatment passes an electric current of 5 to 100 c / g to the carbon fiber, and the sulfuric acid or sulfate aqueous solution having a concentration of 1 to 15% by mass. after passing, the carbon content of 90%, which is a shall be washed with deionized water, the peak ratio O _1S / C _1S measured by ESCA technique is 0.25 to 0.4, A method for producing a carbon fiber for metal oxide coating, wherein the carboxyl group and hydroxyl group on the fiber surface are 0.5 μeq / g or more and the carboxyl group / hydroxyl group is 1 or more.  A method for producing a carbon fiber chopped fiber for metal oxide coating, wherein the strand according to claim 7 is cut into a length of 1 to 100 mm.

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