Effect of crystallization and interface formation mechanism on mechanical properties of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate

Abstract

ABSTRACT:A previous study has shown that the adhesion between the film and substrate of film-insert injectionmolded poly(propylene) (PP) film/PP substrate was evident with the increases in barrel temperature and injection holding pressure. In this second part of the research work, the crystallinity at the interfacial region (i.e., region between the film and the injected substrate) was extensively studied using FTIR imaging, polarized light microscopy, and DSC in an attempt to determine the level of influence that crystallinity has on the interface and bulk mechanical properties. Consequently, a more thorough and clearer picture of the influence of the inserted film on the interfacial crystallinity and subsequently the substrate mechanical properties, such as peel strength and impact strength, has been revealed. The initial proposition that crystallinity could enhance film-substrate interfacial bonding has been confirmed, judging from the higher peel strength with increasing crystallinity at the interfacial region. Nevertheless, the change in crystallinity was not only confined to the interfacial region. With the film acting as heat-transfer inhibitor between the injected resin and the mold wall, the total crystal structure of the substrate was substantially altered, which subsequently affected the bulk mechanical properties. The lower impact strength of film-insert injection-molded samples compared to that of samples without film inserts provided evidence of how the film could impart inferior properties to the substrate. The difference in cooling rate between the substrate and film might also cause other defects such as warpage and/or residual stress build-up within the product.

Effect of processing conditions on warpage of film insert molded parts

“…The FIM process is one of the most important polymer processing methods because surface quality of plastic parts can be improved with the inserted decorating film during the injection molding process. Since it can improve surface quality of the molded parts without any post-processing such as screen printing or spray painting, the FIM is a highly advanced method compared with the conventional injection molding [1][2][3][4].…”

Single-polymer composites (SPCs): Status and future trends

“…This kind of injection molding may be considered as a peculiar version of the LCM techniques. Earlier this technique, termed film insertion injection molding was used to prepare "laminated" SPCs [149]. LCM techniques, focusing on in situ copolymerization possibilities, round up the processing methods of two-constituent SPCs.…”

Relationship between the crystallization behavior and the warpage of film‐insert‐molded parts

“…On the other hand, a relatively imperfect crystalline skin layer developed in the top region because of the retarded heat transfer between the injected polymer resin and the film. Yamaguchi et al 20 reported that the heat transfer was retarded in the FIM specimen, and an amorphous skin layer approximately 1 lm thick was generated between the injected PP resin and metal mold. 20 WAXD profiles of the FIM specimen in the thickness direction are shown in Figure 5.…”

“…Yamaguchi et al 20 reported that the heat transfer was retarded in the FIM specimen, and an amorphous skin layer approximately 1 lm thick was generated between the injected PP resin and metal mold. 20 WAXD profiles of the FIM specimen in the thickness direction are shown in Figure 5. Nine characteristic crystalline peaks were observed at 2y values of 13.6, 15.7, 17, 20.3, 23.08, 24.85, 27.3, 31.98, and 34.86 , which corresponded to the (001), (0À11), (010), (À111), (100), (1À11), (101), (11À1), and (120) reflections, respectively.…”