| abstract |
This ball made of thermoplastic material has physical properties substantially akin of those of conventional leather balls, and comprises at least two layers of thermoplastic material molten successively in a same mold and adhering completely to each other; the external layer consists of a material selected from the group of polyamids, thermoplastic elastomers, plastisols and polyurethanes, and the internal layer consists of a material selected from the group comprising thermoplastic elastomers, polyurethanes, polyesters and polyester-polyethers. The ball is manufactured by rotational molding consisting in casting successively into a mold made of two detachable complementary portions and to which a planetary motion is imparted, thermoplastic materials constituting the ball-forming layers, from the external layer to the innermost layer, the material for forming one of the internal layers being introduced after opening the mold at a temperature such that the material forming the preceding layer or layers has not melted completely, thus permitting the breaking of said layer or layers at the level of the joint between the two mold portions. This ball is suitable for games such as football, soccer, rugby, volley-ball, hand-ball, and the like. |