Method of manufacturing sandwich panel

Method of manufacturing a sandwich panel comprising the steps of:

• a) an assembling step of providing a plate-shaped assembly of a first cover part and a second cover part and between these cover parts a core part of a thermoplastic material containing a swelling agent, wherein the thermoplastic material of the core part is an amorphous polymer of polyetherimide (PEI), and the swelling agent is acetone;
• b) a heating step of heating the assembly resulting from step a) under pressure between heated press tools in a press to a foaming temperature below the glass transition temperature of the thermoplastic material in the core part;
• c) a foaming step of foaming the thermoplastic material in the core part under pressure and at the foaming temperature wherein the spacing between the press tools is increased;
• d) a cooling step of cooling the foamed sandwich panel resulting from step c), while the sandwich panel is maintained under pressure between the press tools;
• e) a discharging step of removing the thus cooled sandwich panel from the press;
• and
• f) a drying step of drying the sandwich panel thus obtained;
• wherein the cooling step d) is carried out in two substeps, comprising a first substep d1) of cooling the foamed assembly from the foaming temperature to an intermediate temperature in the range of 70-100° C. at a first cooling rate of at least 216° C./min and a second substep d2) of cooling the foamed assembly from the intermediate temperature to ambient temperature at a second cooling rate of 20° C./min or less, thereby effecting bonding of the foam core part to the first and second cover parts.