Rigid-foam plastic mold and method of preparation

A method for the preparation of rigid composite polyolefin foam mold elements of a multi-part mold comprising male and female mold elements, each mold element having a rigid composite thermoplastic foam body, a back surface, and an interior mold facing surface contoured so as to form in a closed mold position a mold cavity to prepare a defined object by a molding process, which method comprises:

• (a) contacting under substantially continuous pressure with a heated die element one surface of a first rigid olefinic thermoplastic foam material to melt and deform the contacted foam portion of the rigid olefinic thermoplastic foam material;
• and
• (b) rapidly chilling the die element while maintaining the die element in substantially continuous contact with the olefinic thermoplastic foam material to form a thin, solid skin layer of the cooled olefinic thermoplastic foam material as a mold facing surface, which solid skin layer is integrally bonded to the underlying body of the rigid olefinic thermoplastic foam material thereby providing a male or female mold element;
• (c) repeating steps (a) and (b) with a second thermoplastic olefinic foam material to form a second mating mold element;
• (d) placing the male and female mold elements as prepared in a closed mold position and heating the male and female mold elements under pressure between heated platens, the back surfaces of the male and female mold elements heated to a temperature and for a time sufficient to melt a portion of the back surface of the male and female mold elements;
• and
• (e) and cooling the back surfaces of said male and female elements while under pressure between the platens to provide for correction of any bowing distortions in the male and female mold elements and to provide a relatively thick, solid, integrally bonded support layer of the solid thermoplastic cooled material on the back surface of the male and female mold elements.

The method for the preparation of a rigid composite thermoplastic foam mold element of a multi-part mold comprising male and female mold elements, each mold element having a thermoplastic rigid foam body, a back surface, and an interior mold facing surface contoured to form in a closed mold position a mold cavity to prepare a defined object by a molding process, which method comprises:

• (a) inserting between the surface of a heated die element and the surface of a rigid thermoplastic foam material a thin, solid, thermoplastic sheet material;
• (b) contacting one surface of the solid, thin, thermoplastic sheet material with the heated die element to thermoform the thin thermoplastic sheet material;
• (c) contacting under substantially continuously pressure one surface of the rigid thermoplastic foam material with the thermoformed thin thermoplastic material with the heated die element on the opposite side of the thermoformed material to melt and deform a portion of the foam of the rigid thermoplastic foam material in contact thermoformed material;
• and
• (d) rapidly chilling the die element while maintaining the die element in substantially continuous contact with the one side of the thermoformed thin thermoplastic sheet material to integrally bond one surface of the cooled thermoformed sheet material to the underlying body of the rigid thermoplastic foam material and to form a solid thermoformed skin layer as a facing surface of the mold element.