Patent ID: 8721951

Claim:
A method to form a seamless hollow enclosure by rotomolding, including the following steps, in sequence: introducing a first charge of thermosetting polymer resin into an enclosing mold, the thermosetting polymer resin characterized by offgassing during thermal crosslinking; heating the mold, while rotating the mold about at least two axes, sufficiently to flow the first charge of thermosetting polymer resin but not sufficiently high to thermally crosslink the first charge of thermosetting polymer resin, the first charge of thermosetting polymer resin flowing onto an interior of the enclosing mold and forming a first layer defined by the interior of the enclosing mold; introducing a low permeation thermoplastic resin into the enclosing mold before the first layer has substantially thermally crosslinked; heating the mold sufficiently to flow the low permeation thermoplastic resin onto an internal surface of the first layer while rotating the mold about at least two axes, the low permeation thermoplastic resin forming a second layer; introducing a second charge of thermosetting polymer resin into the mold; heating the mold sufficiently to flow the second thermosetting polymer to form a third layer on an internal surface of the second layer while rotating the mold about at least two axes; continuing to rotate the mold about at least two axes while heating the mold sufficiently to cure each of the first layer and the third layer into crosslinked thermoset polymer layers; cooling the mold while rotating the enclosing mold about at least two axes.