Deep drawn microcellularly foamed polymeric containers made via solid-state gas impregnation thermoforming

A method for forming a thermoplastic material into a desired shape, the method comprising:

• increasing the degree of crystallinity of a thermoplastic material by infusing, for a period of time, the thermoplastic material with a gas,
• wherein the thermoplastic material:
• includes a core and a surface layer adjacent the core;
• and
• has a threshold degree of crystallinity above which bubbles will not nucleate when the gas-infused thermoplastic material is heated to its glass-transition-temperature, and
• wherein the increase in the degree of crystallinity of the thermoplastic material results in the degree of crystallinity of the surface layer being:
• greater than the degree of crystallinity of the core;
• and
• greater than the threshold degree of crystallinity of the thermoplastic material,
• nucleating bubbles in the gas-infused thermoplastic material from the infused gas by heating the gas infused thermoplastic material to a temperature that is at least the glass-transition-temperature of the gas-infused thermoplastic material;
• holding, for a period of time, the heating temperature to cause the bubbles to grow in size, thereby forming a mostly foamed thermoplastic material in which 70-98% of foaming has completed;
• and
• thermoforming the mostly foamed thermoplastic material into a shape by heating to above the glass-transition-temperature after a degas time during which the concentration of gas in the mostly foamed thermoplastic material decreases,
• wherein the degas time occurs at room temperature after the holding time and prior to the thermoforming, and
• wherein the thermoforming occurs when 40-95% of the infused gas remains in the mostly foamed thermoplastic material such that during the thermoforming, the remaining gas in the mostly foamed thermoplastic material acts as a lubricant between polymer chains of the mostly foamed thermoplastic material and increases formability of the mostly foamed thermoplastic material.