摘要
胶合板的生产工艺中,陈化是一个必不可少的工序。在一定的生产工艺中,陈化时间将直接影响产品的胶粘质量。高温固化的酚醛树脂要形成比较理想的胶粘层,首先要保证(1)在热压过程中,树脂固化之前具有一定的流动性,以便树脂能湿润所有的接触面。所谓的接触面应包括胶层两侧木材表面和胶粘剂渗入一定深度所接触的表面;(2)胶粘剂经热压后必须充分固化。木材用水溶性酚醛树脂胶粘时不可避免地要有相当数量的水分带入木材(约为施胶量的50％)。胶粘剂中的水对胶粘层形成的质量有很大的影响,例如胶在基材中的流动性。水分过多胶的流动性便大,渗透性也随之增加,造成胶层过薄或缺胶,降低了胶粘质量。水分不足,胶的流动性差,不能很好地湿润材面,而且渗透性不够。另一方面如果胶层中的水没有充分排出,酚醛胶就不能彻底固化,也不能得到很高的胶粘强度。陈化就是为了调节胶层中的水分,使胶对某种木材具有适当的湿润性和渗透性。
The length of assembly-time in the process of plywood manufacturing is usually determined by the qualities of adhesive used,among which the molecular weight distribution in the resin might be the major factor.The molecular wecular weight distribution in water-soluble PF resins of various formulation were determined by means of GPC spectroscopy and the length of assembly-time were arbitrarily fixed at 10,20,30,45,60,and 90 minutes.The gluing quality was determined in terms of both dry and wet tension strengths developing in the birch plywood glue-lines.Experimental results revealed that the larger the amount of high molecular weight portion exists in the resin,the shorter the assembly-time should be.On the contrary,the less the amount of high molecular weight portion exists in the resin,the longer the assembly-time should be.Generally,better bonding strength can be achieved with a resin having a large portion of high molecular weight portion but there seems no significant effect on wet bonding strength.During assembly-time,the spread adhesive will undergo various changes with the formation of water in excess of the neccessary amount,which may affect the gluing quality adversely and should be eliminated by prolonging the assembly-time The molecular weight distribution in PF resin which determines the water formation in its curing process,thus has an important bearing on assembly-time.It should be mentioned here a PF resin with large amunt of low molecular weight portion is likely to be more water resistant in the created glue-lines.
