热塑性树脂胶合板板坯热压过程中影响温度变化的主要因素

以聚乙烯薄膜为胶黏剂、桉树单板为原料制作多层热塑性树脂胶合板,并对影响制作过程中板坯温度变化的主要因素进行研究,以便更好地控制产品质量,提高生产效率,减少能源消耗。研究结果表明:板坯含水率对热塑性树脂胶合板热压所需时间有显著影响,降低板坯的含水率,能明显缩短板坯热压至要求温度所需时间; 当板坯含水率较高时,通过提高热压温度能明显缩短热塑性树脂胶合板的热压时间,当板坯含水率较低时,对热压时间的缩短则不如板坯含水率较高时明显; 所使用的厚度0.08 mm以下的聚乙烯薄膜不会阻碍热量在板坯中的传递,对板坯温度的变化没有明显影响; 板坯从热压机推移至冷压机的过程中,板坯与外部环境接触,表面温度会快速下降,如果下降过大会使板材表层的胶合强度明显降低,因此在确定热压温度参数时,应考虑板坯从热压机推移至冷压机过程中可能产生的温度损耗,才能保证板材的强度。
In the manufacturing of thermoplastic resin plywood, the thermoplastic resin film in the mat must be heated to a temperature above its melting point during the hot-pressing process. It is required that the thermoplastic resin could be in the molten state, so that it could contact fully with the veneer surface. After that, the mat should be cooled to a temperature below the melting point during the cold-pressing process under a certain pressure, gluing the veneers together. It is different from the traditional wood-based panel adhesives, such as phenol formaldehyde resin and urea formaldehyde resin, that can be cured at various temperatures. Therefore, the control of mat temperature is crucial to ensure the bonding strength of the thermoplastic resin plywood. To control product quality, increase the production capacity, and reduce energy consumption, we studied the main factors affecting the mat temperature change in the production process of thermoplastic resin plywood made of polyethylene film and eucalyptus veneers. Results showed that the moisture content of mat had a significant influence on the time for heating mat to the required temperature. It would shorten the hot-pressing time obviously by reducing the moisture content of the mat. When the moisture content of the mat was high, the increase in hot-pressing temperature would significantly reduce the hot-pressing time, while the moisture content of the mat was low, the reduction in the hot-pressing time was not obvious. The polyethylene film would not affect the heat transfer and temperature change in the mat when the film thickness was lower than 0.08 mm. If the surface temperature of the mat decreased too fast during the hot-pressing to cold-pressing process, the bonding strength of the mat outer layer could decreased obviously. When designing the hot-pressing temperature, it was necessary to take into account the temperature loss that may occur during the hot-pressing to cold-pressing process according to the environmental conditions, to ensure the performance of the plywood