押出発泡における発泡剤溶解現象に関する研究
A Study of the Solubility of Blowing Agents in Foam Extrusion Systems
御林 毅・茂谷 茂・林 隆博・吉田博之
Mihayashi, Tsuyoshi / Motani, Shigeru / Hayashi, Takahiro / Yoshida, Hiroyuki
The solubility of fluorocarbon blowing agents in foam extrusion of thermoplastic resin was investigated by both experimental and theoretical approaches. The thermoplastic resin used was polystyrene, while CFC-12 and HFC-134a were the selected fluorocarbon blowing agents.
First of all, in our experimental approach, we developed a direct observation system using a fiberscope, and observed the shape and behavior of gas bubble in the extrusion system. In this experiment, we used CFC-12 as the blowing agent. It was noted that (1) the phenomena called gas dispersion in this field is the same as gas solubility in the resin, (2) huge voids generated in the plastic foam was mainly caused by poor solubility of the blowing agent. We considered the effects of pressure, temperature, and residence time in additional experiments.
Next, we constructed a quantitative theoretical model by applying the concept of absorption velocity that is defined for gas-liquid equilibrium for this phenomena. In a numerical simulation based on this model, the results showed good agreement with experimental results.
Finally experimental production parameters (pressure, temperature and residence time) were calculated for HFC-134a and polystyrene.
Key words: Foam extrusion / Blowing agent / Absorption velosity / Fiberscope / Theoretical model