Comparison of large and small tow carbon fiber processes and a list of producers' scale

1. Definition of large and small tows of carbon fiber

PAN-based carbon fiber can be classified according to the size of the fiber tow, which can be divided into two categories: small tow and large tow, and the specific classification method is divided according to the number of K. Carbon fiber is a combination of many parallel filaments, so it is also called carbon fiber tow, and the number of tows refers to the number of monofilaments in each bundle of carbon fiber. That 1K means that a bundle of carbon fiber contains 1000 precursors. In the same way, 3K represents 3000K roots. At present, the number of carbon fibers per bundle ≥48K is usually called large tow carbon fiber in the carbon fiber industry. That is, the number of tows of 1k, 3K, 6K, 12K, and 24K is called small tow carbon fiber, and the number of tows exceeds 48K, which is a large tow or industrial-grade carbon fiber.

2. The difference between the size of the tow manufacturing process

(1) Precursor

The key to the preparation of carbon fiber is the carbon fiber precursor. The performance of the precursor directly determines the performance of the prepared carbon fiber. Japan's Toray, Toho and the United States' Hexel Company not only do not transfer the technology of preparing small tow carbon fiber precursors, but also do not sell products to the outside world. However, large tow carbon fiber precursor belongs to the category of civil polyacrylonitrile (i.e., acrylic yarn), which can be freely bought and sold in foreign commodity markets without any restrictions. The price of precursor for the preparation of small tow carbon fiber is 4 times that of civilian polyacrylonitrile precursor.

(2) Process differences

There are many technical problems in the application of large tow carbon fiber, mainly the process and effect of yarn spreading. Compared with small tows, large tow fibers accumulate and the yarn spreading effect is not good, which will cause the yarn to be difficult to evenly infiltrate, and the thickness and quality of the yarn are difficult to meet the requirements of product structure design.

The stability of large tow carbon fiber is not as good as that of small tow carbon fiber, and the interfacial shear strength of large tow carbon fiber resin is lower than that of small tow carbon fiber. Compared with large tow carbon fiber materials, small tow carbon fiber carbonization equipment is good, the production process is strictly controlled, and its performance is generally better than that of large tow fiber. Since the development of small tow carbon fiber, it has been mostly used in high-end applications such as aerospace, military industry and defense.

3. The difference in the cost of large and small tows

In the early days, because the research of carbon fiber was mainly focused on the application of military industry at that time, it was difficult for large tows to meet the needs (the performance was not satisfied, and the stability was not as good as small tows, etc.), so the domestic research on small tows was concentrated at that time. With the development of the industry and the release of the huge potential of the civilian market, high-quality, cost-effective large tow carbon fiber is about to come out.

Civil polyacrylonitrile precursor is the precursor for the preparation of large tow carbon fiber, and the price of precursor is usually about 60% of the cost of preparing carbon fiber. Due to the relatively low price of large tow precursor, the price of large tow carbon fiber can be controlled to about 50%-60% of small tow carbon fiber. At present, the main performance of some large tow carbon fibers on the market has approached or even exceeded that of some small tow carbon fibers. For example, the tensile strength and modulus of the large tow carbon fiber PAN-EX35 of the United States Zoltech Company are higher than that of the small tow T300 of Toray Company of Japan, and the price is relatively low. At present, the tensile strength of large tow carbon fiber can reach 3.5-5.0Gpa, and the tensile modulus is 230-290Gpa. The tensile modulus of T300 and T700 is 230Gpa, the tensile strength of T300 is 3.4Mpa, and the tensile strength of T700 is about 4.8Gpa.

4. List of large tow manufacturers

(1) Foreign large tow manufacturers

a. Zoltek of the United States, which was acquired by Toray Corporation of Japan. One of the most representative large tow carbon fiber products is ZOLTEK PX35, which is a typical low-cost commercial carbon fiber. Applications: Automotive (polyurethane systems for structural and semi-structural applications), wind power beam caps, civil engineering (bridges), high-pressure gas storage cylinders, offshore drilling pultrusion rods, etc.

b. SGL (SGL): At present, there is no 24k carbon fiber in the latest products, all of which are 50K large tow carbon fiber, and the mechanical properties have also been optimized. Areas of application: carbon-fibre battery-based housings for automobiles, door frames for aerospace airliners, as well as small aircraft, helicopters and air taxis, as well as in the industrial sector.

c. Mitsubishi of Japan: Mitsubishi of Japan has developed 50K and 60K specifications of large tow carbon fiber TRW40 (50K) and TRH50 (60K).

(2) Domestic large tow manufacturers

At present, there are few domestic manufacturers that have broken through the large tow carbon fiber technology, typical representatives are Shanghai Petrochemical, Jilin Chemical Fiber and Lanzhou Bluestar. In addition to the above three, Jilin Carbon Valley is currently building a 50K large tow precursor production line, and Xinjiang Longju 48K carbon fiber production line has also been successfully commissioned. In terms of technical routes, Shanghai Petrochemical and Bluestar both use NaSCN (sodium hydrosulfide) wet process, and Jilin Carbon Valley precursor technology is similar to SGL.

a. Shanghai Petrochemical: In 2018, it successfully trial-produced 48K large tow carbon fiber. In January 2021, Shanghai Petrochemical's 12,000 tons/year 48K large tow carbon fiber project officially started construction, with a total investment of 3.5 billion yuan. In August 2022, Shanghai Petrochemical's first large tow carbon fiber production line was CCCC.

b. Jilin Chemical Fiber: In 2017, it began to research 48K large tow carbon fiber precursor, successfully developed 48K carbon fiber precursor polymerization and spinning process technology in 2018, and obtained the first batch of 120 tons of 48K large tow carbon fiber precursor export orders in 2019. In August 2022, the high-yield and high-performance 50K large tow carbonization line was put into operation, marking the completion of the carbon fiber project with an annual output of 15,000 tons in two years. It is mainly used for wind power generation blades, etc. At present, the total production capacity of Jilin chemical fiber carbon fiber has been increased to 35,000 tons.

c. Lanzhou Bluestar: In 2018, Bluestar Group invested hundreds of millions of yuan to carry out technical transformation of the existing precursor production line, and the product was upgraded from the original 24K to 50K. In the second half of 2019, its 50K carbon fiber production line passed through the whole line. In 2022, the company plans to invest 370 million yuan to build a new precursor spinning production line with an annual production capacity of 5,000 tons and a carbon fiber production line of 2,500 tons per year, and Lanzhou Fiber will have an annual output of 3,500-4,000 tons of carbon fiber after completion. At present, the production capacity of carbon fiber large tow is 1,500 tons, and the production capacity of carbon fiber precursor is 4,000 tons.

As of 2018, Japanese companies led by Toray, Mitsubishi, and Toho accounted for 49% of the entire small tow market. In particular, Toray recently announced that it will invest in a plant in Spartanburg, South Carolina, and a plant in Gumi, South Korea, and increase production lines to an annual production capacity of 35,000 tons of conventional carbon fiber (small tows) from 2025, an increase of more than 20%. China's Zhongfu Shenying will have an annual production capacity of 28,500 tons per year by the end of 2023, ranking second in the world due to the full operation of the 25,000-ton-per-year Xining project.

Hatch of the United States, SGL of Germany, and Mitsubishi of Japan basically monopolize the entire large tow carbon fiber market, accounting for 58%, 31%, and 9% respectively. Due to the influence of the aviation field and the demand for wind power resources in recent years, large tow carbon fiber materials have been applied from automotive materials to wind turbine blades, hydrogen storage cylinders, etc. The market for carbon fiber has shifted to a dual-drive landscape for aerospace and industry.