The press load is heated with hot water that circulates through the heat exchange plates between the stacks. It takes time to get the heat to the center of the stack. The time-temperature system is designed to allow the laminate in the center of the stack to be fully cured without excessively curing the outer layer. When the curing or polymerization of the resin is completed, the press load is passed through the heat exchange plate before the pressure is released. The circulating cold water is cooled. Moisture is present in the uncured impregnated paper and is mostly produced as a by-product of polymerization. The moisture will instead be vaporized and bubbled, or the platen will be destroyed if the panel is depressurized at over 100 °C.
In order to rapidly heat and cool the press, a very large energy flow is required. In order to minimize the actual energy costs, people have designed a complex and often complicated valve and water storage system to save energy. It is most desirable to heat the recycled water to the maximum required temperature only with high pressure steam. There is also a cooling tower that cools the cooling water. 40% to 60% of the heat used in each press cycle can be recycled and reused.
Press pressures for high pressure laminates range from 5.5 to 10.3 kPa. The purpose of the pressurization is to compress the laminate to no voids. This greatly increases the strength properties of the laminate. The secondary requirement for pressurization is to hold any moisture or other volatiles under sufficient pressure to prevent flash evaporation. The pressure of the press is also to compensate (equalize) any unsaturated paper in the press load. Saturated paper is most likely caused by accidental factors such as hard spots in the sheet forming or foreign matter inclusions. On the other hand, it may also be caused by regular factors such as back-impregnated backsheet coated paper or unimpregnated paper associated with various core paper configurations. The hydraulic pressure provides the driving force for the resin to flow. This resin flow is like what happens when a saturated impregnation is performed on an impregnator, ie most of the resin is transported in the larger orifice of the area. The greater resistance and smaller cross-section of smaller orifices limits their ability to transport resin.
The hydraulic pressure provides the driving force for the resin to flow. The viscosity of this resin flowing fat solution is much higher than that in the impregnator, so the influence of capillary force is small in the distribution of the resin from the macropores to the small pores.
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