1.HPL material system
Today, HPL can be manufactured in multi-opening presses or in continuous presses. Both manufacturing processes permit the production of HPL that meets the visual and mechanical requirements of the EN 438 standard. Multi- opening presses are loaded at room temperature, closed, put under hydraulic pressure (> 5 MPa) and heated to temperatures above 120 °C. The heat achieves the flowing process of the melamine and phenolic resins. The liquified resins are pressed between and into the cellulose fibres under high pressure, which results in increased bulk density and a sealed surface. The surface texture (high gloss, matt, woodgrains, etc.) is determined by the pressure plates which are pressed against the melted and then hardening melamine resin layer. The subsequent completion of the chemical reaction (condensation) – the hardening – results in a fully cross-linked structure in the form of a sheet, giving it a high level of strength. The cellulose fibres strengthen the HPL. They are chemically bonded and fully integrated into the new structure. After hardening is completed, the pressed material is cooled down under pressure to release tensions. The complete pressing cycle takes around 100 minutes, depending on press loading and the maximum temperature.
If continuous presses are used, the impregnated paper webs (from rolls) are pressed between two steel belts. Depending on the thickness of the HPL (up to max. 1.2 mm) and the length of the production line, the feed rate varies between 8 and 30 m/min.
