When conducting in-mold injection molding, wrinkle formation on decorative sheets is a problem faced during the resin filling process. In our previous papers, through visualization analysis, we showed that the sheet deforms elongationally in the flow direction. Moreover, we also identified the interfacial thermal resistance of each interface during in-mold injection molding using our developed method of measuring temperature inside the sheet and temperature of the flow front resin contacting the sheet. In this paper, we calculated the time at which sheet deformation stops by comparing the results of calculating frictional force derived from perpendicular force imposed on the sheet and elongation force in the flow direction derived from shear stress and thermal stress. The calculated and measured results showed good agreement with each other, confirming that the deformation of the sheet stops after some time from the passing of the flow front because the sheet is fixed to the cavity surface by the frictional force, which suppresses the elongation and deformation in the flow direction. Furthermore, we showed the sheet deformation model during in-mold injection molding by comparing the calculated and measured deformation amount of the sheet. While the perpendicular force did not increase to fix the sheet on the cavity surface, the sheet slipped on the mold surface and deformed due to thermal expansion and shear stress. After the frictional force derived from the perpendicular force increased enough to fix the sheet onto the cavity surface, the sheet deformation stopped. Based on the sheet deformation model, we proposed solutions to reduce wrinkling of the decorative sheet from the perspectives of thermal expansion, deformation stress, and frictional force.

The illumination of LED displays on highways has decreased throughout 25 years of use. The main cause is degradation of epoxy encapsulate due to long-term exposure to ultraviolet rays, and this is especially notable at the tip. Benzene rings in the epoxy resin photodissociate and weaken the encapsulate. This in turn leads to light scattering due to craze formation around the tip, where the degradation is most notable, ultimately leading to decreased luminance. In this study, the degraded epoxy encapsulate was repaired by applying clear acrylic coating with silicone on its surface. The acrylic paint completely filled the craze grooves, preventing diffused reflection and resulting in a complete recovery of luminance. Upon subjecting repaired LED to artificially accelerated degradation equivalent to approximately 30 years of outdoor exposure, the decline in luminance was held to 2％, and the post-repair durability was also sufficient. This repair method was applied to actual LED displays with notably poor visibility on highways and it was verified that the luminance could be sufficiently restored.