To improve the releasability of a prepreg from a releasing paper or the like, its flexibility and its self-adhesion by a method wherein an intermediate prepreg consisting of predetermined constituent elements is produced and heat-treated at a certain fixed surface temperature and, at the same time, treated under the state that the difference between the surface temperature and a solid temperature is kept within a specified range.
In order to manufacture the prepreg, after an intermediate prepreg, which is obtained by impregnating a thermoplastic resin-containing water-based resol resin in reinforcing fibers, is produced, the intermediate prepreg is heat-treated at a certain fixed surface temperature and, at the same time, treated under the state that the difference between the surface temperature and a solid temperature is kept within 5°C. In this case, the surface temperature represents the temperature at the outermost layer of the intermediate prepreg. Further, the solid temperature represents the temperature at the middle portion of the intermediate prepreg. In addition, the heat treating temperature is set in the range of 25-60°C. The treating time of the heat treating is in the range of l2 hours - 30 days. Thus, a prepreg, the releasability existing between which and a releasing paper and/or a releasing film, a flexibility of which and the self-adhesion of which are favorable, is obtained.
NINOMIYA HIROAKI
NAGATA HIDEO
