KR0141406B1 - Manufacturing method of carbon fiber composite containing heat / oxidation resistance and abrasion resistance - Google Patents

Abstract

The surface of the PAN-based carbon fiber is coated using phosphoric acid content of 0.01 to 10 wt.% Or less to produce carbon fiber having heat / oxidation resistance improving effect and heat / resistant using the phosphate-coated carbon fiber and phenolic resin. Produces oxidized carbon fiber / phenolic resin toepreg and carbon fiber / phenolic resin composite material, thereby preventing damage to the fiber surface, minimizing the reduction of fiber diameter, and consequently contributing to improved abrasion properties Phosphoric acid coated carbon fiber composites are used for induced weapons and aerospace.

Description

Method for producing carbon fiber composites with improved heat / oxidation resistance and abrasion resistance.

1 is an enlarged photograph of a carbon fiber surface showing excellent oxidation resistance when the carbon fiber according to the present invention is exposed to various high temperatures with a scanning electron microscope. (10,000 magnification) (A: unheated process, B: 656 degreeC, C: 770 degreeC, D: 821 degreeC).

2 is a scanning electron micrograph (10,000 magnification) showing a similar improvement effect on the carbon fiber / phenolic resin toepreg prepared on the basis of the results of the heat / oxidation resistance to the carbon fiber according to the present invention (A: 500 ℃, B: 700 ° C., C: 800 ° C.).

Figure 3 is a scanning electron micrograph (10,000 magnification) showing a similar effect for the carbon fiber / phenolic resin composite material prepared on the basis of the results of the heat / oxidation resistance to the carbon fiber and tow preg according to the present invention (A: 620 C, B: 715 ° C, C: 785 ° C).

FIG. 4 is a photograph (10,000 magnification) of an enlarged observation of a severe damage and diameter change of the carbon fiber surface by scanning electron microscopy when the existing carbon fiber product is treated under the same conditions as the heat treatment temperatures in FIG. Treatment, B: 656 ° C, C: 770 ° C, D: 821 ° C).

FIG. 5 shows the extent of damage and diameter change of the surface of carbon fiber by scanning electron microscope when the composite material using existing carbon fiber and phenol resin without surface treatment is treated at the same condition as each heat treatment temperature in FIG. One photograph (10,000 magnification) (A: 590 degreeC, B: 715 degreeC, C: 785 degreeC).

The present invention uses phosphoric acid to improve the high temperature resistance, oxidation resistance and abrasion resistance that dominate the performance of carbon fiber reinforced composites, which are widely used in advanced induction weapon systems and various aerospace materials used at very high temperatures in air atmospheres. The present invention relates to a method of manufacturing a carbon fiber composite material using a polymer resin after coating carbon fiber with an optimal amount of phosphoric acid, which plays an important role as a reinforcing material in the manufacture of these composite materials. In more detail, phosphoric acid (H3PO4) is added to the surface of the filament in order to enhance oxidation resistance to rovings made of PAN (polyacrylonitrile) carbon fiber filaments. Coating to a range of 10 wt.%, To improve the heat / oxidation and abrasion resistance of the prepared carbon fiber, tow preg and related composite materials. In the prior art, the coating on the surface of the carbon fiber is simply different from the present invention because it is coated with epoxy resin or the like so as to improve the interfacial properties or to be easy to handle when weaving the fiber. When carbon fiber reinforced composites are exposed to air at high temperatures near or above 1,000 ° C, their surfaces, structures and their physical properties will be protected to a minimum extent from degradation and thermal oxidation. If you can, it is most desirable. In general, however, the carbon materials constituting these materials are oxidized when exposed to oxygen at high temperatures, which deteriorates their physical properties, which is a factor that significantly limits the use temperature limit in various applications. Furthermore, if the fiber surface and the matrix itself, as well as the strong interfacial bonding therebetween, are damaged by oxidation, serious degradation in the various physical properties of the composite is unavoidable. In the carbon fiber used in the carbon fiber reinforced composite material, the rayon system was mainly used in the initial stage of development, and since the 1970s, the PAN system used in the present invention has been widely used until now, and recently, the pitch system Carbon fibers are also emerging. Although surface treatment of carbon fibers is widely performed, reports on the surface treatment of carbon fibers for improving oxidation resistance and heat resistance of carbon fiber composite materials are not well known. Furthermore, some of the thermosetting or thermoplastic polymer resins used as matrices, which have excellent heat resistance, require relatively high molding temperatures and are difficult to process. It is easy to process and uses phenolic resin to form dense three-dimensional network structure after molding. Moreover, the phenolic resin used in the present invention has a higher char yield of about 70% with respect to heat / oxidation and abrasion resistance particularly required in the present invention than other thermosetting resins such as epoxy, and is formed after decomposition. The carbonized layer, which plays an important role in absorbing heat generated during ablation, is widely known as the most representative matrix resin used in a heat / abrasion composite material together with a carbon fiber as a reinforcing material. In addition, the interfacial adhesion between the carbon fiber and the phenolic resin after molding is very excellent and the thermal stability is also excellent. In addition, the phosphoric acid used for the surface coating in the present invention is known as one of the substances that function to inhibit the oxidation of carbon, especially when the carbon fiber / phenol resin composite is exposed to air at a high temperature of 550 ℃ or more, Reacts very sensitively to oxygen When oxygen penetrates into the composite material through the pores which increase during the pyrolysis process, phosphoric acid reacts with oxygen preferentially over carbon in carbon fiber and matrix to form a stable complex at active sites. In addition, it acts to effectively inhibit the oxidation of carbon fibers exposed to oxygen. Phosphoric acid (H3P04), also called orthophosphoric acid, is pyrophosphoric acid at about 200 ° C. through pyrolysis. (h4p2o7), metaphosphoric acid (HPO3) n at about 300 ° C, gradually changing to solid phosphorus at higher temperatures, forming a three-dimensional network and forming a protective layer to oxidize Since the present invention contributes to resistance, the present invention uses phosphoric acid to coat the surface to produce an improved heat / oxidation resistant and abrasion carbon fiber composite material. The purpose is to. Therefore, the present inventors can minimize the serious fiber surface damage caused by oxidation at high temperature by coating the surface of the PAN-based carbon fiber with phosphoric acid in order to improve the heat / oxidation resistance of the carbon fiber composite material. It has been found to complete the present invention. Hereinafter, the present invention will be described in detail. As the carbon fiber (trade name: Taekwang Industry, Acelan TZ-307), a high-strength PAN system composed of 3,000 filaments having physical properties shown in Table 1 was used.

High purity phosphoric acid was used for the purpose of oxidation inhibition, and the amount used for the coating treatment on the surface of the carbon fiber was investigated by varying the phosphoric acid content in the range of 0.01 to 10 wt.% For methanol in order to compare the result with the untreated fiber.

Example 1

Improved high temperature and oxidation resistance of carbon fiber

The preparation of the specimen coated with phosphoric acid on carbon fiber is as follows. First, the carbon fiber is cut to about 20 to 40 cm in length, and both ends of the tow are fixed to prevent short fibers from coming out. Hook one end of the toe to facilitate drying. After the optimum amount of phosphoric acid is added to methanol to form a mixed solution, hold one end of the tow and soak it in the mixed solution for several minutes to allow the solution to soak into the short fibers. The prepared carbon fibers are dried at 110 ° C. to 200 ° C. for about 5 hours. Carbon fiber tows not coated with phosphoric acid were used as is. Heat treatment of the coated carbon fiber was carried out stepwise in the air in the range of 300 to 900 ℃ using a thermogravimetric analyzer. Carbon fiber surface state change observed by scanning electron microscope after heat treatment at each temperature is shown in FIG. Even after high temperature heat treatment above 800 ℃, the surface of phosphate-coated carbon fiber was hardly found at the site of damage due to oxidation (scratching or chipping), and no significant change in carbon fiber diameter was observed even above 700 ℃. It was found that 70% or more of the original average diameter (6.8 µm) was maintained even at 800 ° C or higher. This proves that carbon fiber surface treatment by phosphate coating is very effective.

Example 2

Improved high temperature and oxidation resistance of carbon fiber / phenolic resin towrap coated with phosphoric acid

The carbon fiber tow surface-coated with phosphoric acid was sufficiently immersed in a mixed solution of phenol resin and methanol for several minutes, and then cured at about 90 ° C. to 120 ° C. for 30 minutes to 1 hour, in order to completely remove evaporated or unreacted materials. Curing for several hours at 160 ℃ to 200 ℃. Carbon fiber / phenolic resin towpreg surface-treated with phosphoric acid thus prepared is heat-treated at various temperatures as in Example 1. As shown in FIG. 2, the heat / oxidation resistance improvement effect of the phosphoric acid coating on the surface of the carbon fiber mentioned in FIG. 1 is obtained even in the topreg state of the carbon fiber surface-coated with the phenol resin. Similarly appeared. That is, the damage on the fiber surface due to thermal oxidation was not serious, and the change in fiber diameter was maintained at 700 ° C. up to about 95% or more of the original diameter. It has been found that 70% or more of diameters are conserved.

Example 3

Improved high temperature and oxidation resistance of carbon fiber / phenolic resin composites coated with phosphoric acid

In the composite material used in the present invention, after the phenolic resin was manually applied to a PAN-based carbon fiber woven fabric composed of eight runner-like tissues having the same fiber properties as those of the aforementioned carbon fiber, a solvent was volatilized to prepare a prepreg. After lamination, an autoclave was prepared. The carbon fiber woven fabric was coated on the fiber surface using phosphoric acid in the same manner as in Example 1 before the preparation of the prepreg, and then the fiber condition of the woven fabric prepared by drying was good and easy to handle. The weight ratio of the woven fabric and the resin used in preparing the prepreg was about 1: 1. The density of the carbon fiber / phenolic resin composite surface-treated with the obtained phosphoric acid was about 1.40 to 1.45 g / cm 3. The molding was preheated at 80 ° C. for 30 minutes, held at 110 ° C. for 90 minutes, and maintained at 160 ° C. for 90 minutes under 180 psi pressure, followed by a natural cooling path. When this surface-coated composite was exposed to temperatures above 500 ° C, as shown in Figure 3, the matrix area was totally decomposed and lost, and oxidation sites on the surface of the carbon fiber exposed above this temperature I could hardly find it. However, fiber diameter decreased slightly around 800 ℃. In this similar heat treatment region, the fiber surface and diameter retention effects were found to be superior to that of the composite material than that of the carbon fiber (Example 1) or the tow preg (Example 2). This may be due to the relative slowness of thermal resistance due to decomposition of the matrix region.

Example 4

Ablation Resistance Test

A torch test was conducted in the air according to ASTM-285 to investigate the abrasion resistance performance of the surface-coated carbon fiber / phenolic resin composite according to the present invention. In Example 3, a flat specimen having a width of 100 mm and a thickness of 6 to 9 mm, respectively, obtained from the composite material manufactured using the autoclave was used. During the test, the specimen is exposed to an atmosphere in which a high temperature, high velocity, high pressure gas flame of approximately 1800 ° C, emitted from an oxyacetylene torch, is uniformly dispersed in the center of the specimen. The distance between the tip of the torch and the specimen was 20 mm, the angle between the flame and the specimen was 90 °, and the ratio of oxygen and acetylene mixed gas, namely O / CH, was 4: 1. The abrasion rate calculated from the thickness of each specimen and the time it takes for the flame to penetrate from the front to the back of the specimen is 0.063 mm / sec on average for the phosphate-coated composites, while 0.054 mm / sec for the phosphate-coated composites. It showed a reduction effect of about 15% or more. This is because the phosphoric acid coating treatment on carbon fiber, mentioned in Examples 1, 2 and 3, very effectively increased the heat / oxidation resistance of the fiber, thereby preventing damage to the fiber surface and minimizing the reduction in fiber diameter, As a result, it can be judged that it contributed to the improvement of abrasion characteristics.

Comparative Example 1

Comparison with carbon fibers not surface-coated with phosphoric acid

When the carbon fiber surface treated with phosphoric acid was not treated at all in the air at the same heat treatment temperature as in FIG. 1, the carbon fiber surface was damaged by high temperature oxidation or the fiber diameter was reduced. It was. This result can be observed and compared with the photographs shown in FIG. 1 in Example 1. FIG. It is easy to prove that the phosphoric acid treatment on the fiber surface has a noticeable effect on heat / oxidation enhancement. In the case of FIG. 4, especially when the untreated carbon fiber is exposed to about 800 DEG C or more, the fiber surface is greatly damaged as the temperature increases, and the decrease in fiber diameter is reduced to 50% or more of the initial diameter before heat treatment. This reduction tends to be twice as large as in FIG. 1, and this antioxidant effect is more pronounced at high temperatures.

Comparative Example 2

Comparison with carbon fiber / phenolic resin toepreg without surface coating with phosphoric acid

Table 2 compares the change in fiber diameter with the results of Example 2 when a tow preg prepared using carbon fiber and phenol resin, which is used without surface treatment with phosphoric acid, is exposed to various heat treatment temperatures in air. The fiber diameter reduction rate at each temperature was about 2 times greater than that of the untreated one, and the degree of surface damage was much more severe than that shown in FIG.

Comparative Example 3

Comparison with carbon fiber / phenolic resin composites not surface-coated with phosphoric acid

FIG. 5 shows the same heat treatment temperature as used in FIG. 3 for composite materials prepared using an autoclave under the same conditions as in Example 3, using carbon fibers and phenolic resins not surface-coated with phosphoric acid. The results of scanning electron microscopy are compared when exposed to conditions. It can be seen that at about 600 ° C., the crystalline layers of the fiber surface began to be damaged and peeled off, large scratches occurred at about 700 ° C., and the damage was extremely severe throughout the fiber from about 800 ° C. The fiber diameter was also significantly reduced. This oxidation phenomenon was not observed in FIG. 3, and it can be easily proved that the composite material exhibits relatively good heat / oxidation resistance.

Claims (4)

A method for producing carbon fibers having improved heat / oxidation resistance and abrasion resistance, wherein the surface of the carbon fibers is coated with phosphoric acid. The method for producing carbon fibers having improved heat / oxidation resistance and abrasion resistance according to claim 1, wherein the carbon fibers are PAN-based carbon fibers. The method of producing carbon fiber with improved heat / oxidation resistance and abrasion resistance according to claim 1, wherein the phosphoric acid content is in the range of 0.01 to 10 wt.%. A method for producing prepreg and composite material having improved heat / oxidation resistance and abrasion resistance by treating polymer fibers with carbon fibers prepared according to the method of claim 1.