JPH0565544B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a resin composite material reinforced with SiC whiskers, and particularly to a method for producing a SiC whisker-reinforced resin composite material using surface-modified SiC whiskers as a reinforcing material. [Prior Art] SiC whiskers have excellent specific strength, specific modulus, etc., and are thermally and chemically stable, so they are useful as composite reinforcing substances for various resin materials. In general, in order to use a fibrous reinforcing material to impart the expected composite performance to a resin, the reinforcing material must have good wettability with the matrix resin, and also undergo an interfacial chemical reaction with the matrix resin component to become strong. An important element is to combine them with each other. However, SiC whiskers inherently have poor wettability with resins and are chemically extremely stable, so they do not bond well with matrix resins. For this reason, attempts have been made to improve the bonding properties with matrix resin by modifying the surface properties of SiC whiskers. For example, methods of treating SiC whiskers with silane-based coupling agents,
SiC whiskers are oxidized in advance and the surface
A surface modification method has been proposed (Japanese Unexamined Patent Publication No. 113800/1983) in which a thin film of SiO ₂ is formed and then treated with a silane coupling agent. [Means to be solved by the invention] However, since the surface of SiC whiskers is chemically inert, even if the silane coupling treatment is applied as is, it is difficult to chemically bond with the reactive groups.
It is not possible to obtain a sufficient coupling effect. In this regard, the method of pre-oxidizing the surface of SiC whiskers and then silane coupling treatment significantly improves the bonding properties because the -OH groups formed on the surface increase the affinity with the reactive groups of the silane coupling agent. However, since the reactivity of the -OH group is not very high, it is still difficult to provide sufficient chemical bonds. The present invention was made in order to solve the problems of the conventional technology described above, and its purpose is to significantly increase the chemical bonding property with the matrix resin by using SiC whiskers that have been subjected to a novel surface modification treatment as a reinforcing material. The present invention provides a method for producing a SiC whisker-reinforced resin composite material. [Means for solving the problem] SiC according to the present invention to achieve the above object
The manufacturing method for whisker-reinforced resin composites consists of two steps: forming a carbonizable resin film on the surface of SiC whiskers and then carbonizing them; and after oxidizing the carbon film formed on the surface in the previous step, chemical surface treatment is performed. The structural feature is that the SiC whiskers processed through the process are combined with the matrix resin as a reinforcing material. First, the process of forming a carbonizable resin film on the surface layer of SiC whiskers and then carbonizing them is performed as follows. A resin solution is prepared by dissolving a carbonizable resin such as a phenolic resin, a furan resin, or divinylbenzene in an organic solvent. The concentration of resin solution is 0.1
It is desirable to set the amount in the range of ~20% by weight and leave it standing until the polymer chains of the resin are dispersed as a homogeneous phase in the organic solvent. Next, SiC whiskers are added to this resin solution and thoroughly stirred and mixed, and the dispersion is filtered under suction or pressure to separate it from the organic solvent.Then, the SiC whiskers are air-dried to remove the resin film attached to the surface layer. Heat and harden. The SiC whiskers with a carbonizable resin coating formed on the surface layer in this manner are placed in a firing furnace and carbonized in an inert gas at a temperature in the range of 800 to 1200°C. This carbonization process forms a carbon thin film with a thickness of 5 to 100 Å that is tightly adhered to the surface layer of the SiC whiskers. The process of oxidizing the carbon film formed on the surface layer surface in the above-mentioned pre-process and then subjecting it to surface treatment with a chemical agent is carried out as follows. Methods for oxidizing carbon films include, for example, immersing SiC whiskers in hot concentrated _HNO3 solution or _oxidizing them with _H3PO4 .
Wet method of electropolishing in a mixed acid of H ₂ SO ₄ or an alkaline solution such as NaOH, or in air.
A dry method of heating to a temperature of 300-400°C can be used. This oxidation treatment makes the surface of the carbon film -
Functional groups such as COOH and -OH are also generated. The oxidized carbon film is then surface-treated with a chemical that has good reactive bonding properties with -COOH and -OH groups and has excellent reactivity or compatibility with the matrix resin. Therefore, the type of agent used as a surface treatment agent must be selected depending on the matrix resin. For example, when using an epoxy resin as a matrix, diisocyanate and epoxy resin may be used together, diamine etc., polyamide resin or polyimide resin, etc. Surface treatment agents such as diamines and their compounds are preferably used when the matrix is made of polyurethane resin, and urethane prepolymers, polyethylene resins, polyolefin resins, etc. are used as the matrix, such as polyethylene grafted methyl acrylate. The SiC whiskers treated through the above steps are composited into a matrix resin using a conventional method such as a kneading method or a preform impregnation method. [Function] According to the process of the present invention, it can be used as a reinforcing material.
The surface layer of the SiC whisker is first oxidized and activated while being tightly coated with an extremely thin carbon film to generate functional groups such as -COOH and -OH.
Then, the surface is treated with a drug that is highly reactive with these functional groups and has excellent chemical bonding or compatibility with the matrix resin. This unique surface modification effect effectively increases the bonding between the SiC whisker reinforcement and the matrix resin and functions to improve composite performance. [Example] Phenol resin [Manufactured by Gunei Chemical Co., Ltd., Retop]
PGA-4508〕14.4g in ethyl alcohol 4780ml
(concentration: 0.3%) and allowed to stand for 7 days to prepare a solution in which the polymer chains of the phenolic resin were dispersed in a homogeneous phase. Diameter 0.3-0.6μm, length 30-60μm in resin solution
480 g of SiC whiskers were added, stirred and mixed to sufficiently disperse the mixture, and then filtered and air-dried to remove the solvent component. The amount of phenol resin that adhered to the surface layer of the SiC whiskers by this treatment was 2.4 g. Next, the treated product was held at 170°C for 2 hours to harden the resin layer, and then heated in a firing furnace (high-frequency induction heating furnace).
The carbonization treatment was carried out at a temperature of 1000° C. for 4 hours in an argon stream. The thickness of the formed carbon film was 15 μm on average, and the surface layer of the SiC whisker was integrally covered. The SiC whiskers with the carbon film formed are then heated to 70°C.
The surface was oxidized by immersion in a 60% HNO ₃ solution heated to 2 hours for 2 hours. In this state, the absorption spectrum was measured by Farier transform infrared absorption spectroscopy (FT-IR), and the chart from wave numbers 700 to 3500 cm ^-1 is shown in the figure. As can be seen from the figure, at the wave number position C=O at 1700 cm ^-1 , and at the wave number position C=O at 3200 cm ^-1 ,
A H peak was present, indicating that these functional groups were produced by oxidation. The oxidized product was placed in toluene, and 5% of tolylene 2,4 diisocyanate was added to the SiC whiskers.
After adding 10% epoxy resin as a surface treatment agent and stirring at room temperature for 1 hour, excess surface treatment agent components were removed and the mixture was dried. SiC whiskers surface-modified by the above process are added to a matrix resin made of epoxy resin (Epicoat 828 + DDM) with a volume content (Vf) of 2%.
The mixture was mixed and kneaded with three rolls to form the following. The molded product was cured in two stages: 4 hours at 130°C and 2 hours at 180°C to form a SiC whisker-reinforced resin composite. The strength characteristics of the obtained composite material were measured and the results are shown in the table below. For comparison, a similar composite was made using SiC whiskers as a reinforcing material without any surface treatment (Comparative Example 1), and a film of SiO ₂ was formed on the surface layer by heating at a temperature of 600°C in the air for 4 hours. The strength characteristics measured for a similar composite (Comparative Example 2) using SiC whiskers treated with aminosilane (Chitsuso Co., Ltd., S-330) as a reinforcing material are also listed in the table below.

〔Effect of the invention〕

As described above, according to the present invention, a method of forming a composite by forming a unique carbon film on the surface of the SiC whisker that brings about effective chemical bonding with the matrix resin is adopted, so that excellent composite performance is always achieved. It is possible to stably produce SiC whisker-reinforced resin composites.

[Brief explanation of drawings]

The figure is an absorption spectrum chart obtained by measuring the oxidation state of a carbon film formed in an example of the present invention by FT-IR.

Claims (1)

[Claims] 1 SiC treated through the steps of forming a carbonizable resin film on the surface layer of SiC whiskers and then carbonizing them, and oxidizing the carbon film formed on the surface layer in the previous step and then subjecting them to chemical surface treatment. A method for producing a SiC whisker-reinforced resin composite material, which is characterized by combining whiskers with a matrix resin as a reinforcing material.