Overview of prepreg

Prepreg refers to the composite of resin matrix and reinforcement that can be stored by impregnating the resin matrix with continuous fibers or fabrics under strictly controlled conditions. Prepreg is the intermediate material for manufacturing composites, and its quality directly affects the quality of composites. In application, the prepreg is cured by thermal polymerization. Once cured, the thermosetting resin will be fully crosslinked to form a composite material with corrosion resistance, heat resistance, light weight and high strength. The composite material prepared has been widely used in aerospace, wind power generation, high-speed rail, automobile, fishing gear, rowing and other fields

At present, the reinforcement fibers used in the classification of prepreg are mainly carbon fiber and glass fiber. The most commonly used classification methods are thermosetting prepreg and thermoplastic prepreg. Their properties are similar, for example. The matrix resin of thermosetting prepreg is mainly epoxy resin, phenolic resin, benzoxazine, bismaleimide, polyimide and other thermosetting resins, while the matrix resin of thermoplastic prepreg is mainly polysulfone, polyphenylene sulfide, polyethersulfone and other thermoplastic resins.

With mature technology and stable performance, thermosetting resin is the mainstream matrix resin of prepreg at present, and has been widely used in the aerospace field. However, thermoplastic prepreg is also developing rapidly, and relevant technologies have made breakthroughs in the main structural parts of Airbus aircraft.

Table 2 Application of different types of thermosetting prepregs in aerospace field

Prepreg has a wide range of applications, with aerospace as its main application, including civil aircraft, jet fighters, helicopters, aero-engines, satellites and rockets. Foreign aviation composite technology is relatively mature and has been widely used in aircraft and engines. At present, North America is the largest market for aviation composite materials, accounting for 58% of the market, followed by Europe, accounting for 38%. Hatch and Solvay respectively hold about 40% of the carbon fiber prepreg market, with the same market share. Together, the two companies occupy the leading position in the global prepreg market.

In China, AVIC Hi-Tech Corporation (600862. SH) occupies a leading position in the field of aviation prepreg, builds a first-entry barrier, has complete military-related qualification certification, and its products have been used in a variety of military aircraft models. Its prepreg production capacity is sufficient, with a dedicated production plant of 15000 square meters, and equipped with four sets of international large-scale hot-melt prepreg machines. At present, AVIC Composite Co., Ltd., a subsidiary of the company, undertakes the production and supply of prepregs for major military aircraft, plays a leading role in the military products of aviation composite materials, and has a strong customer resource advantage in the downstream market. AVIC Composite and Aviation Industry Group signed a related party transaction agreement to supply prepregs to its main engine plants such as Shenyang Aircraft and Chengdu Aircraft. Due to the increase in the number of military aircraft in the main engine plants and the higher proportion of composite materials used in new military aircraft, the amount of related party transactions of prepregs continued to grow, from 979 million yuan in 2015 to 2.296 billion yuan in 2020, with a compound growth rate of 18.58% during the period.

In addition to AVIC Hi-Tech, domestic suppliers in the field of military aviation prepreg also include Hengshen Co., Ltd. In 2018, AVIC Hi-Tech's prepreg sales reached 1.492 billion, and its business revenue far exceeded that of its peers; The prepreg business of Hengshen achieved revenue of 92 million yuan, up 37.31% year on year. Guangwei Composite also produces some prepregs, but it is mainly used in the non-military aviation field. In 2018, Guangwei Composite produced 7.46 million square meters of prepregs and sold 7.16 million square meters, realizing business income of 183 million yuan, up 12.88% year on year.

In terms of the price of prepreg, the military prepreg of AVIC Composite Materials Co., Ltd. exceeds 1200 yuan/square meter, 5 square meters per kilogram, and 6000 yuan per kilogram. The added value of prepreg products is extremely high.

Forecast of prepreg market

In 2018, the global aviation prepreg market size was about 32 billion yuan. According to the statistics and forecasts of market research institutions Marketsandmarket and Stratview Research, the global prepreg market in 2018 is about 6.4 billion dollars, and is expected to maintain a compound annual growth rate of 10.5% in the next few years, reaching 11.5 billion dollars by 2024. At present, the prepreg market in the aviation sector has accounted for more than 70% of the prepreg market for all purposes, and the proportion will continue to rise.

With the development of aviation composite materials, the application range of prepreg in military aircraft at home and abroad is expanding, and the proportion of its consumption will increase significantly. Guosheng Securities Research has calculated the market size of domestic military aircraft carbon fiber prepreg. It is estimated that the market size of China's military aircraft prepreg will be about 94.812 billion yuan in the next 10 years. Considering other equipment, the market size of China's military prepreg will be more than 100 billion yuan in the next 10 years.

Development trend of prepreg technology

With the rapid development of lightweight and high-speed aerospace, lightweight and flame-retardant rail transit, and highly integrated electronics and electrical appliances, the requirements for flame retardancy, mechanical properties, heat resistance, and dimensional stability of composite materials are becoming higher and higher, and the requirements for prepreg are also becoming more and more stringent. In the future, prepreg will develop in the following directions.

(1) Develop a new hot melt prepreg system. There are two main preparation methods of prepreg, namely solution impregnation method and hot-melt adhesive film method. At present, solution impregnation method is the main method. Solution impregnation is a process of impregnating fibers or fabrics with resin solution, volatilizing the solvent in the resin, and making the prepreg reach stage B; This method has less investment in production equipment, but its disadvantages are that the resin content of prepreg is difficult to accurately control, and a large amount of solvent volatilizes, resulting in environmental pollution. The hot-melt adhesive film method is to first make the molten resin into a uniform and flat adhesive film, and then make a composite impregnation of the adhesive film and fiber or fabric at a certain temperature and pressure to obtain a qualified prepreg; This process has the advantages of accurate resin content control, less volatile and no environmental pollution. Therefore, it is more and more urgent to develop new hot melt prepreg system.

(2) Long storage period at room temperature. In order to reduce the manufacturing cost of composite materials, in addition to adopting various new technologies, an important aspect is to vigorously develop low temperature and low pressure curing resin systems. If the service life of the resin and its prepreg at room temperature is extended without increasing the curing temperature, it is not necessary to build a large refrigeration equipment, but also not to reform the existing molding equipment. This will significantly reduce the storage and process costs of advanced composite materials in manufacturing and use.

(3) High performance. "Light weight, long life, high reliability, high efficiency, high stealth, high penetration and low cost" is the development goal of the new generation of aircraft, which puts forward higher and higher requirements for the lightweight, high strength, high temperature resistance, ablation resistance, high mechanical strength, high dielectric property, designability, etc. of prepreg. At the same time, electronic products continue to develop in the direction of high speed and high frequency. At the same time, the requirements for reliability are becoming higher and higher. For the prepreg used for copper clad plate, it has become increasingly important to have high heat resistance and excellent dielectric properties. At present, although phenolic prepreg has good temperature resistance, flame retardancy and high strength, its brittleness, poor toughness and low impact damage tolerance restrict the application of phenolic resin-based composites, and the toughening and modification of phenolic prepreg has become a major development trend. The toughness of epoxy prepreg is relatively good, but its heat resistance and flame retardancy are not good, so it is necessary to carry out modification research on heat resistance and flame retardancy. Shuangma prepreg has good heat resistance and high mechanical strength, but its curing temperature is high and its brittleness is large. Therefore, it needs to be modified. In addition, the lightweight of composite materials requires the introduction of modified fillers in the preparation process of prepreg, and the uniform dispersion of fillers is a recognized technical problem, which needs further study.