オーバル形混練機における高分子材料の不規則流動の解析

抄録

The flow of polymeric material in an oval-type mixer was investigated by focusing on the initial period of mixing, during which the material near the rotor surface tends to keep its original high viscosity, and additive particles do not disperse effectively. The streamlines during mixing of low-density polyethylene in a mixer with a single oval rotor were observed by adding carbon black to the mixture as a tracer. Two phases of flow were observed in this initial mixing period. In the first phase, a closed circulating flow occurred on the front surface of the rotor. In the second phase, some of the material in the closed area began to gradually flow out and pass through the tip region of the rotor, then the remaining material suddenly broke and flowed out all at once. This has been previously referred to as“breaking phenomenon”.The velocity distribution for the second phase was calculated by solving a differential equation in which the velocity was evaluated under an assumption that the inverse absolute temperature varies linearly with the distance from the chamber surface. The estimated streamline in the boundary area between the flow of remaining material and the passing flow was in close agreement with experimental result. These analyses made clear the behavior that all material passes through the tip region of the rotor at least once, thereby clarified the behavior of irregular flow which affects the dispersion of additives.