Research On Interface Strength Of IMD Injection Molding

As a new type of technology,in-mold decoration(IMD)can form the products with the advantages of smooth surface,wear-resistance,and patterns protection,IMD is widely used in automobiles,home appliances,electronics and other fields.However,this process is complicated and there are many defects,especially poor interface bonding,which will greatly affect the performance and life of the product.The forming mechanism of the interface in the forming process and the interface strengthening method are hot topics in the current in-mold decorative forming technology.Therefore,this dissertation studies the interfacial strength of IMD products in depth and systematically explores the influence of molding process parameters and the influence of the film on the interfacial strength.In this dissertation,the injection molds were designed firstly and the in-mold injection molding process experiments were carried out.The variable control experiments were carried out for different parameters.The injection molding process products were obtained under different parameters.The peel strength test was used to obtain the bonding strength of the interface.Based on cohesion model,zigzag fluctuations of the stripping curve were explained with ABAQUS.The thermal history of the interface during the forming process has a very important influence on the interface formation.This paper established the heat transfer model of the mold,melt and thin film in the cooling process,simulation of the temperature field at the interface was carried out based on the ANSYS thermal analysis module.The results showed that the film significantly hinders the heat transfer.Increasing the mold temperature and the thickness of the film were favorable for the increase of the interface temperature.The interface temperature difference caused by different mold temperatures and film thickness can reach 20°C-40°C.Crystallization played a key role in the formation of interface strength.In this paper,the influence of process parameters on the interfacial crystallinity was analyzed based on the flow-induced crystallization kinetics model,and the crystallinity was used as a measure of the influence of process parameters on the interfacial strength.Studies shown that the interface bonding strength is positively correlated with the crystallinity,raising the temperature favors the crystallization,the crystallinity increased by 4.7%,and the interface strength increased by 2119 N/m.Melt equilibrium melting point increased with improved injection speed,the crystallization induction time reduced,thus promoting crystallization.The crystallinity increased by 3.4%,and the interface strength increased by 1305 N/m.The increase in film thickness favors crystallization,the interface crystallinity increased by 5.9%,and the interface strength increased by 2247 N/m.Surface modification is an effective way to increase the interface activity.In this paper,corona treatment was used to destroy the molecular structure of the film surface and introduce oxygen-containing groups,as a result,the surface roughness increased from 9.7nm to 56.8nm,the wetting angle reduced from 96° to 80°,the surface wettability raised dramatically.The IMD article interface strength obtained by corona treatment was increased by 648 N/m.