How to hot press composites?

Push the charging cart assembly into the middle of the hot plate of the multi-layer press, the hot plate rises slowly, and pressurizes to pass steam to suppress after closing.

The key to the pressing process is to determine the process parameters, among which the important parameters are temperature, pressure and time. The pressure system firstly depends on the variety and nature of the material, and secondly considers the product thickness, board area and equipment conditions.

Temperature

The first stage is the rise from room temperature to the significant reaction temperature of the material, that is, the preheating stage. At this time, the resin melts and discharges part of the volatiles, and the pressure is generally 1/3~1/2 of the full pressure.

The second stage is the intermediate insulation stage. At this time, the resin melts and penetrates, and the reaction speed is low. The heat preservation time depends on the ageing and tenderness of the tape and the thickness of the product board. When the outflow resin is close to gelation and the filament is stretched, the pressure should be increased and the temperature should be increased.

The third stage is the heating stage. This is to increase the degree of resin curing. At this time, the resin reaction speed increases.

The fourth stage is the heat preservation stage. The purpose is to fully cure the resin. The temperature depends on the curing characteristics of the resin, and the curing time depends on the thickness of the board.

The fifth stage is the cooling stage. When the end of the holding stage is reached, the heating can be stopped, and then slowly cooled, and the required high pressure is maintained. The cooling rate has an effect on the flatness of the surface of the product. The cooling rate should be controlled. It should not be too fast when starting to cool, and it will be demolded when it drops below 50°C.

Pressure

The function of pressure is to overcome the vapor pressure of the volatiles, to make the bonding resin flow, and to make the adhesive layer close contact, and to prevent the plate from being deformed when it is cooled.

The size of the molding pressure is determined according to the curing characteristics of the resin. If small molecules escape during curing, the pressure should be higher; when the curing temperature of the resin is high, the molding pressure should be increased accordingly. The size of the molding pressure also needs to consider factors such as the thickness of the product, the rubber content of the tape and the heating rate.

Time

The time from the start of preheating and pressing to the removal of the product is the pressing time. It is the sum of the pre-pressing, hot pressing and cooling time. The pressing time is related to the curing speed of the resin, the thickness of the laminate and the pressing temperature. Whether it is fully cured is the basis.

The pre-pressing time depends on the properties of the tape. If the tape has a high insoluble resin content and a low volatile content, the pre-pressing time will be short, otherwise it will be relatively prolonged. The hot pressing time is to ensure that the resin in the tape is fully cured. If it is too short, the resin will not be cured completely, and if it is too long, the product performance will decrease, which needs to be determined through repeated trials. Cooling time is a link to ensure product quality. If the cooling time is too short, it will easily cause the product to warp and crack; if it is too long, it will reduce production efficiency.

Cooling demoulding

After the heat preservation is over, the heat source can be turned off, and the temperature can be cooled naturally or by cold air, cold water, etc., but the pressure should not be reduced prematurely, otherwise it will cause the surface of the product to foam or warp. The demoulding temperature is generally lower than 60°C.

Post-processing

The purpose of post-treatment is to further cure the resin until it is completely cured, while partially eliminating the stress in the product and improving the performance of the product. The post-treatment of epoxy board and epoxy phenolic board is for 120-150 minutes in an environment with a temperature of 120-130℃, which can improve the mechanical and electrical properties of the product.