Patent ID: 11858182
Assignee: FITS HOLDING B.V.
Field: Other special machines (Mechanical engineering)
Classification: CPC B | IPC B

Claim 9:
10. Method for manufacturing a sandwich panel in a press having press plates, which sandwich panel comprises at least one foam layer of a first thermoplastic and cover layers, the method comprising the steps of:
a) providing a starting structure comprising at least one layer of a first thermoplastic and two cover layers; wherein said at least one layer of said first thermoplastic comprises a chemical blowing agent having a decomposition temperature above the melting temperature or melting range of the first thermoplastic;
b) contact heating said starting structure between the press plates of the press to a temperature above the decomposition temperature of the chemical blowing agent so that decomposition of the chemical blowing agent occurs, thereby obtaining an intermediate structure wherein the decomposed chemical blowing agent is present in the at least one layer of the first thermoplastic while maintaining pressure on the starting structure by the press plates;
c) subsequent to the decomposition of the chemical blowing agent cooling of the intermediate structure thus obtained to a foaming temperature by conversion of hot pressurized water in the press plates into steam by means of a controlled expansion valve, while maintaining pressure on the intermediate structure by the press plates;
d) at said foaming temperature, foaming of said at least one layer of said first thermoplastic comprising the decomposed chemical blowing agent by moving the press plates a predetermined distance apart, while exerting a pressure on the structure being foamed, wherein the volume is made to increase to a final volume and then kept constant, thereby obtaining said sandwich panel;
e) further cooling of said sandwich panel at a constant final volume while pressurized in contact with the press plates to a temperature below the glass transition temperature or melting temperature or range of the first thermoplastic by conversion of hot pressurized water in the press plates into steam by means of a controlled expansion valve;
f) final cooling of the sandwich panel of step e); and
g) opening of the press and removing sandwich panel cooled in step f) from the press.