Why use small tows for carbon fiber cloth?

When polyacrylonitrile-based carbon fiber is used, for important structures, small tows of 12k or less must be used; large tow fibers are strictly prohibited; such strict regulations are mainly due to the tensile strength of small tows. The strength is very stable, the dispersion is very small, its coefficient of variation is below 5%, and the glue is easy to infiltrate and penetrate, so its performance and quality can be effectively controlled in the production and use process; while the large tow Otherwise, the coefficient of variation is as high as 15% -18%, or even greater. The reliability shown in the test and trial is poor, so it cannot be used as a reinforcement material for load-bearing structures.