A new method for manufacturing carbon fiber: 10 times the production efficiency, and the sintering process is reduced to 5 minutes.-Tofore Carbon Fiber with Hanyan Indstrial

A new method for manufacturing carbon fiber: 10 times the production efficiency, and the sintering process is reduced to 5 minutes.

Japan's New Energy and Industrial Technology Development Agency (NEDO), Tokyo University, Japan's Institute of Industrial Technology, Toray, etc. through joint research, developed a production efficiency of 10 times the current production process carbon fiber (CF) manufacturing methods. The characteristic is to shorten the sintering time to 30~60 minutes in the past 5 minutes.

In order to meet the increasingly stringent global fuel efficiency requirements, the use of CFRP (Carbon Fiber Reinforced Resin Matrix Composites) in automotive bodies, such as high-end vehicles, is increasing. However, the global supply of PAN-like carbon fibers for this material was only about 50,000 tons in 2014. In order to use CFRP in mass production vehicles in the future, it is necessary to increase the production of PAN carbon fibers and reduce manufacturing costs.

At present, the PAN type carbon fiber manufacturers in the world use the manufacturing method called "entering the rattan way". It was invented in 1959, and Japanese manufacturers such as Toray, Diren and Mitsubishi Liyang are also using the technology to make carbon fibers (Fig. 1).

Fig. 1: current manufacturing method of PAN type carbon fiber

After spinning, PAN is treated by refractory treatment, I. e. it is oxidized by heating in air to 200-300 degrees Celsius, giving it heat resistance. The process takes 30~60 minutes.

The rattan feeding method is first to mix solvents and catalysts in PAN copolymers, and then to spin and roll them up. The next thing to do is to "refractory treatment," that is, rolled up PAN filaments into the furnace to oxidize it, giving it heat resistance. The heating temperature is 200~300 degrees, and the heating time takes 30~60 minutes. After refractory treatment, PAN fibers will be put into another heating furnace to be heated to 1000~2000 C to make carbon fibers. Carbonization takes only a few minutes.

Although global carbon fiber manufacturers have long used the rattan method, this method of refractory treatment time-consuming, in terms of "small tows" (from 12,000 fiber twisted carbon fiber) for each production line, the annual output limit is about 2,000 tons. And from the cost of equipment, each production line needs 10 billion to 20 billion yen. This is the biggest reason for the high cost of carbon fiber. The current price of carbon fiber per kilogram is around 3000 yen. In order to use CFRP in mass production vehicles, it is necessary to improve the efficiency of carbon fiber production, reduce manufacturing costs, so that the price is below 1000 yen.

Save fire treatment

To this end, NEDO launched the National Innovative New Structural Materials Research and Development Program in 2011 with the goal of eliminating fire-resistant treatments that impede productivity improvements. The University of Tokyo, CIRC, Toray, Diren, Torbonne Knicks and Mitsubishi Liyang participated in the project and worked on the development of new manufacturing methods under the five-year plan up to 2015 (Figure 2).

Fig. 2: manufacturing technology developed by University of Tokyo

The spinning process can be shortened to about 5 minutes by oxidation in the liquid instead of the original refractory treatment.

In a manufacturing process led by the University of Tokyo, a new polymer (precursor polymer) was developed to remove the refractory treatment. The main point is that the polymer is not fireproof but oxidized in solvent after spinning.

Then the microwave heating device was heated to more than 1000 C for carbonization. The heating time takes only 2~3 minutes. After carbonization, plasma is also used for surface treatment to form carbon fibers. Plasma treatment takes less than 2 minutes. In this way, the sintering time needed 30~60 minutes can be shortened to about 5 minutes. In the new manufacturing method, plasma treatment is used to improve the bonding between carbon fiber and thermoplastic resin as the base material of CFRP.

Use low cost clothing PAN

Polymers used as raw materials are not PAN copolymers currently used in carbon fibers, but low-cost PAN materials for clothing. In clothing PAN, oxidants are added and dissolved in solvents to oxidize them in a short time. Because it is oxidized in liquid, it is necessary to add a dissolution enhancer. The preceding step to microwave carbonization is the same as the usual propylene fiber manufacturing process (Fig. 3).

Figure 3: making carbon fibers with new technology

(a) precursor polymers made from low price PAN for clothing. (B) adding dissolved promoter and oxidant in the spinning of PAN to oxidize the liquid. (c) carbon fiber produced by new process.

The tensile modulus, tensile strength and elongation of carbon fiber prepared by the new method are 240GPa, 3.5 GPa and 1.5% respectively. These values are the same as those of Dongli general class carbon fiber "T-300" used for sporting goods.

The future task is to shorten the whole manufacturing process time of production level, including the previous process. In order to improve the production efficiency and increase the amount of PAN fiber (increase the "fineness"), the difficulty of controlling the oxidation reaction will be increased and the sintering rate will not be increased. Denier refers to the thickness of silk thread, expressed as the weight of fiber length per meter.

However, the new method can easily increase the size of PAN fibers and can be treated in large quantities because of the oxidation treatment in the liquid rather than the refractory treatment. Moreover, the new method is to use microwave heating device to carry out carbonization, so the sintering time is greatly shortened.

"With the increase in size and the shortening of sintering time, even at the mass production level, the production efficiency can be increased by 10 times as much as it is today," said Hiroshiro Yingshan, a professor at the University of Tokyo who led the development.

He also said that the relevant fiber manufacturers plan to build in a few years a few tons of annual production of empirical factories to supply samples to automobile manufacturers and other manufacturers. In addition, we plan to achieve mass production of more than 20 thousand tons per year in 10 years. The price target for mass production is "less than half of the current ".

A new method for manufacturing carbon fiber: 10 times the production efficiency, and the sintering process is reduced to 5 minutes.