Abstract
The low strength of the Integrated Thermocouple Sensor has been already reported was improved, furthermore, a new Integrated Thermocouple Sensor with improved pattern shape which can prevent errors due to thermal conduction was fabricated, and the melt temperature distribution along the cavity thickness direction was measured in a broad range of injection rates and for high viscosity materials such as short glass fiber reinforced thermoplastics which were difficult to measure with the previous sensor. The following conclusions were obtained.
(1) When the crystalline polymer with high viscosity is injected at high injection rates, a protruding type of temperature peak caused by shear heating is generated at the vicinity of the cavity wall. On the other hand, the resins with low viscosity and amorphous polymers, this peak does not occur easily.
(2) The reinforced polypropylene with short glass fiber, it was confirmed that when the base resin is high viscosity polypropylene, though the generation of the temperature peak is marked except for high injection rate, the temperature distribution including the temperature peak generation area does not change considerably even if the glass fiber content changes sharply regardless of the change in the base resin viscosity and injection rate.
(3) The above temperature distribution did not change considerably even if glass fibers are mixed with the base resin, because of the following two opposite effects offset each other. (a) the viscosity increases, promoting shear heating which raises the temperature, (b) the thermal conductivity in the molten state increases, promoting cooling at the vicinity of the cavity wall, which lowers the temperature.
(4) These results (1) (2) indicate that the temperature peak generation is affected by the viscosity characteristics of resins near the crystallization temperature “Tc” or the glass transition point “Tg, ” latent heat, and thermal conductivity. Furthermore, the heat resistance between the resin surface and cavity surface may also be an important factor which influences temperature peak generation.
