Fiber reinforced plastic flat plates

A process for continuously preparing a fiber reinforced plastic (FRP) flat plate having no warps, comprising:

• covering with film-like sheetings both the top and bottom surface of a continuous FRP flat plate molding material comprising a reinforcing fiber material impregnated with a liquid resin material curable by means of an ionizing radiation;
• continuously transporting the covered material in the lengthwise direction;
• irradiating the covered material as it is being transported by means of an ionizing radiation until said molding material is cured, said ionizing radiation being .alpha.-rays, .gamma.-rays, X-rays, neutron beam or mixtures thereof wherein the dose rate is about 10.sup.2 -10.sup.8 rad/hr with a total dose of about 10.sup.5 -10.sup.7 rad;
• and
• applying tensions to the film-like sheeting covering the FRP molding material in both the lengthwise and the widthwise directions before and in the course of the irradiation, said tensions being in a degree sufficient to press and hold the molding material so as to maintain the thickness thereof uniform and the surfaces thereof smooth before and in the course of radiation.