| 摘要 |
<p>Spherical particles having a diameter between .007" and .040" are formed from melt extruded thermoplastic material suitable for casting on a heated mold surface and melting thereon to form a thin layer of material having a nominal thickness of .040" that is cooled and removed from the mold surface as a part having a porosity less than a visually observable threshold. The process includes the steps of providing microspheres formed of blended and melt extruded thermoplastic, plasticizers (if necessary) and pigment additives that constitute less than 5% by weight of the blend and shaped as a smooth round spherical particle; providing a heated casting surface and distributing a predetermined charge of such microspheres against the heated casting surface; melting the microspheres as a layer of thermoplastic material having a porosity less than .003 inches and thereafter cooling and removing the non-porous layer from the casting surface; in one embodiment of the process the microspheres are provided as a fixed charge having a weight substantially the same as the finished part and wherein the fixed charge is comprised of such microspheres; centrifugally casting the microspheres onto a heated mold surface where they are melt flowed into a thin layer, cooled and removed from the mold; in another embodiment of the process the microspheres are provided in greater weight quantities than the weight of the finished part and are placed on a heated mold surface to maintain a static pressure of the microspheres material against the heated mold surface as they are melt flowed into a thin layer. <MATH></p> |
