CO₂ injection foam molding ebnables us to add excellent properties e.g., cushioning and thermal insulation to conventional resins. However, in practice of injection foam molding, there was a problem about cell size distribution in a molded article in which an area was occupied with fine cells (area (1)) while other was with coarse cells (area (2)). In this study, we focused on the supply pressure of CO₂, which was one of the operating conditions to change cell generation to obtain uniform cell size distribution, and performed the direct observation of cell generation during injection foam molding in a molded article. When the supply pressure was high (supercritical, 15.0MPa), a large number of cells was generated by rapid pressure drop in resin after the resin was injected from nozzle. The cell growth was suppressed with high-viscosity by cooling down the molten resin and small cells were generated at the melt front. To achieve uniform cell size distribution, the operation strategies were proposed for both high and low supplying pressures of CO₂. At low supply pressure (subcritical, 7.0MPa), collapsing cells by resin-pressure at the end of mold improved to synchronize the onset of cell re-generation and eventually obtained fine cells in the area (2). At high pressure (15.0MPa), reducing the pressure difference between supplying and barrel pressures increased the amount of gas dissolved in resin and enhanced cell generation. Subsequently, cell size became uniform in the area (1).

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