The purpose of this study is to investigate the effects of insertion of controlled composition gradient layer on mechanical characteristics of composite specimens made by Fused Deposition Modeling (FDM) type 3D printer equipped with co-axial extruder. The tensile characteristics of composite filaments made from Poly-Lactic Acid (PLA) and Glycol-modified PolyEthylene Terephthalate (PETG), in which compositions were varied from each other, were investigated. Test results showed that the tensile characteristics of composite filament could be controlled by changing the volume fraction of PLA/PETG. Sandwiched composite specimens having different numbers of composition gradient layers were fabricated to investigate the bending characteristics. Bending test results showed that when composition gradient layer was introduced to a sandwiched composite specimen, the energy absorption until failure increased while bending strength and modulus were almost same. The effects of inserting controlled composition gradient layer on interlayer adhesion strength under shear and tensile load were also investigated. Interlayer adhesion test revealed that the observed interlayer shear／tensile strength was improved by inserting the composition gradient layer to avert the adhesion between different polymers.

The formation of wrinkles on decorative PP sheets is a typical problem of in-mold injection molding. In a previous paper, through visualization analysis, we showed that the decorative sheet slips on the mold surface and deforms along the flow direction during in-mold injection molding. In simulation of the amount of this deformation, the interfacial thermal resistance (ITR) of each mold surface during in-mold injection molding should be considered in order to calculate changes in the sheet temperature. Therefore, in this study, we developed a method to measure the temperature inside the decorative PP sheet and the temperature of the flow front resin contacting the sheet using an infrared temperature sensor. We conducted experiments using a visualization mold model to compare (a) the results of changing the temperature inside the measured sheet and the temperature of injected resin with (b) the results of calculating the temperature distribution along the sheet thickness by virtually changing the ITR on each sheet interface. As a result, we successfully identified the heat transfer coefficients of the injected resin-sheet and sheet-cavity surface interface, which were 2800 W/m²・K on the injected resin-sheet interface and 1000 W/m²・K on the sheet-cavity surface interface.