JPH0217670B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to carbon fibers for composite materials and methods for producing the same. Traditionally, carbon fibers have been used to improve surface inertness and improve compatibility with the matrix when mixed with other composite materials, such as synthetic resin or metal matrices, to create composite materials. Therefore, various surface activation methods have been studied, including directly adding active groups of various oxidizing agents to the surface of carbon fibers, sizing treatment with organic sizing agents, and surface treatment using metal vapor deposition. Previous improvement methods have had drawbacks such as complicated manufacturing processes that are difficult to control and poor work efficiency. Furthermore, there has been no improvement method that provides similar compatibility with matrices of synthetic resins, metals, and ceramics. The present invention has a new surface active coating, and when used in composite materials, the affinity can be adjusted according to the matrix to be reinforced, the interlaminar shear strength can be improved, and the manufacturing is easy and efficient. The present invention provides carbon fibers for composite materials, which are formed by forming a coating made of a hydrolyzate of alkoxyaluminum acetylate on the surface of carbon fibers. Furthermore, the present invention provides a method for producing the above-mentioned carbon fiber for composite materials, in which an alkoxy group formed by substituting a part of the alkoxy group of aluminum alcoholate with ethyl acetoacetate or methyl acetoacetate is added to the surface of the carbon fiber. The method is characterized in that a film of a solution of aluminum acetylate is formed, and the film is left to stand or heated to form a film made of a hydrolyzate of alkoxyaluminum acetylate. Next, examples of the present invention will be described in detail. As a raw material, a part of the alkoxy group of aluminum alcoholate is replaced with ethyl acetoacetate or methyl acetoacetate to create alkoxyaluminum acetylate, and a predetermined amount of this is dissolved in a dilute alcohol solution, or a small amount as necessary. A solution to which acetic acid is added as an auxiliary agent is prepared, and this is applied to the surface of the carbon fiber to be treated to form a film. Possible methods for forming the coating include immersion in the solution and spray coating of the solution, but it is preferable to allow the coating to pass through the solution continuously. For example, the above-mentioned processing solution is stored in a U-shaped glass container, and the carbon fibers are introduced from one open end of the container and taken out from the other open end to continuously flow through the solution at a predetermined speed. It is efficient to pass it through. The carbon fibers to which the solution coating has been attached are then air-dried, and the coating is dried to form a coating made of a hydrolyzate of alkoxyaluminum acetylate on the surface of the carbon fibers, thereby producing the carbon fibers for composite materials of the present invention. obtain. If necessary, the carbon fiber with the dried coating is placed in a heating furnace and heated to 100°C or higher to adjust the degree of hydrolysis and produce the desired product. In the above production method, by substituting a part of the alkoxy group of aluminum alcoholate with ethyl acetoacetate or methyl acetoacetate to obtain alkoxyaluminum acetylate, the hydrolysis rate of aluminum alcoholate is slowed down and a film is formed. Work can be done smoothly, and
It has been found that the coating has the effect of preventing drying, cracking due to shrinkage during heating, whitening, etc. In addition, during the above-mentioned air drying or drying treatment at a relatively low temperature, for example, around 50°C, the alkoxyaluminum acetylate film comes into contact with moisture in the atmosphere and undergoes partial hydrolysis, resulting in elimination of alkoxy groups and Detachment of ethyl acetoacetate occurs, resulting in a film in which hydrolysates such as aluminum hydroxide and aluminum acetylate coexist. Further, if necessary, by heating at a temperature of 100° C. or more, the film is partially or entirely made into an aluminum oxide film. in this case,
When heating in the range of 100° C. to 500° C., aluminum oxide is partially used to form a mixed film with the above-mentioned film having hydroxyl groups or acetyl groups.
Note that heating to 500°C or higher results in a film consisting only of aluminum oxide. Note that in the preparation of the alkoxyaluminum acetylate solution described above, the addition of acetic acid serves to further acetate a portion of the alcoholate. A more detailed example of the preparation of this solution is as follows: aluminum alcoholate is dissolved in 4 equivalents of alcohol, an equivalent amount of ethyl acetoacetate is added, and the mixture is thoroughly stirred to produce an equivalent amount of alkoxyaluminum acetylate. Adding a further equivalent of acetic acid further acetates a portion of the alcoholate. Alcohol is further added to this solution to prepare a diluted solution so that the amount of alkoxyaluminum acetylate is 0.4% by weight. The reason why it is preferable to keep the thickness of the film after drying or heat treatment to 1 μm or less is because when producing a transparent metal oxide thin film, if the film is made thicker than this, cracks and whitening may occur, and the bond with the carbon fibers may be broken and the coating may This is because it will not happen. The present invention also uses the carbon fiber for composite material obtained in this way and manufactures a composite material with improved shear strength by adding arbitrary materials such as synthetic resin, metal, and inorganic materials such as ceramics. In this case, by utilizing the properties of the film mentioned above, depending on the material of the material to be composited with carbon fiber, it is possible to
Adjust the degree of hydrolysis of alkoxyaluminum acetylate at temperatures up to 500℃, or 500℃
By heating above, the alkoxyaluminum acetylate is thermally decomposed into aluminum oxide, and a preferable composite material can be obtained. That is, when the matrix is plastic, the carbon fiber for composite materials of the present invention utilizes the affinity of acetylate groups with plastic, and when the matrix is metal or ceramic, it utilizes the affinity of aluminum oxide with metals and ceramics. It is something. In this case, the coating of the carbon fiber for composite material of the present invention may be treated in advance with a coupling agent such as silane, titanium, borane, etc., and then bonded with other desired materials for composite material. Next, more detailed examples will be described. Example 1 Isopropoxy aluminum Al (i-
0.7 mol of OC ₃ H ₇ ) ₃ was dissolved in isopropyl alcohol (i
-C ₃ H ₇ OH), further added 0.7 mol of ethyl acetoacetate (CH ₃ -COCH ₂ COOC ₂ H ₅ ) and stirred to create isopropoxyaluminum ethyl acetoacetate _. COOH)
Add 0.5mol and stir to make a prepolymer.
Furthermore, 8 mol of isopropyl alcohol is added to this to create a solution for carbon fiber treatment. Next, carbon fibers are immersed in this solution to form a coating on their surfaces. Next, this is dried at room temperature and further calcined at 200℃ for 10 minutes to form a coexistence of alkoxyaluminum ethyl acetylate, aluminum hydroxide produced by its hydrolysis, aluminum acetylate, and aluminum oxide on the surface of the carbon fiber. A film was formed. Next, the carbon fiber and hardening agent for composite materials of the present invention
The weight ratio of epoxy resin mixed with a small amount of BF ₃ is 1.
The mixture was mixed in a ratio of 1 to 1, and molded under heat and pressure to form a composite material. A test piece of 3 x 10 x 12 mm was prepared for this composite material, and the interlaminar shear strength was measured, as shown in Table 1 below.
The measurement results shown in are obtained. Example 2 A solution having the same composition as in Example 1 was applied to the surface of the same carbon fiber to form a film, and then
After drying, this was further passed through a silane coupling agent solution consisting of 0.2 wt% aminoethylaminopropylmethyldimethoxysilane, 89.8 wt% ethyl alcohol, and 10.0 wt% water to uniformly adhere it to the coating. After that, the carbon fibers for composite materials of the present invention were produced by drying and firing in the same manner as above. Using this, a composite molded material with epoxy resin was obtained in the same manner as in Example 1. The interlaminar shear strength was measured in the same manner, and the results shown in Table 1 below were obtained. Comparative Example A composite molded material with epoxy resin was made using the same carbon fibers to be surface-treated as used in Example 1, and the interlaminar shear strength was measured in the same manner as in Example 1. The results shown are obtained.

【table】

[Table] As is clear from Table 1 above, it can be seen that the interlaminar shear strength of the products using the present invention is significantly higher than that of the untreated products. In addition, in the treatment solution of the present invention, a solution of alkoxy acetylate in which aluminum is replaced with a metal such as titanium or zirconium is mixed with a solution of alkoxy aluminum acetylate, and a metal oxide such as titanium oxide or zirconium oxide is mixed. It is also possible to mix them into the coating. As described above, according to the present invention, a film of a solution of alkoxyaluminum acetylate obtained by substituting a part of the alkoxy group of aluminum alcoholate with ethyl acetoacetate or methyl acetoacetate is formed on the surface of the carbon fiber; By leaving it or heating it, it is possible to produce carbon fiber for composite materials in a simple process, which provides a strong bond to the composite material. Accordingly, it is possible to provide a composite material with improved interlaminar shear strength by heating the fiber coating to a predetermined temperature or without heating, and by using a coupling agent as necessary.

Claims (1)

[Claims] 1. A carbon fiber for composite material, which is formed by forming a coating made of a hydrolyzate of alkoxyaluminum acetylate on the surface of the carbon fiber. 2. The carbon fiber for composite material according to claim 1, wherein the thickness of the coating is 1 μm or less. 3. Forming a film of a solution of alkoxyaluminum acetylate, which is obtained by substituting a part of the alkoxy group of aluminum alcoholate with ethyl acetoacetate or methyl acetoacetate, on the surface of the carbon fiber,
A method for producing carbon fibers for composite materials, which comprises leaving the film to stand or heating it to form a film made of a hydrolyzate of alkoxyaluminum acetylate.