Pre-expanded polypropylene resin beads and process for producing molded object therefrom by in-mold foaming

A process for preparing cellular moldings of a polypropylene resin from pre-expanded particles comprising the steps of filling polypropylene resin pre-expanded particles having an expandability of 1.0 to 1.5 in a mold capable of being closed but incapable of being hermetically sealed in the state of being compressed at a compression rate of 10 to 60%, and heating said particles to fuse together, said expandability being represented by the equation:

• Expandability = Expansion ratio of polypropylene resin pre- expanded particle after steam heating Expansion ratio of polypropylene resin pre- expanded particle before steam heating
• wherein the expandability is measured by subjecting the pre-expanded particle to the steam heating without imparting an inner pressure thereto, said steam has a temperature equal to the melting point peak temperature of said polypropylene resin measured by differential scanning calorimetry under the conditions that 1 to 10 mg of the pre-expanded particles is heated to 210° C. at a rate of 10° C./minute, then cooled to 40° C. at a rate of 10° C./minute and heated again to 210° C. at a rate of 10° C./minute, and said expansion ratio of polypropylene resin pre-expanded particle after steam heating denotes the value measured after the restoration from shrinking by impregnating the pre-expanded particle with air.

A process for preparing cellular moldings of a polypropylene resin comprising the steps of filling polypropylene resin pre-expanded particles having an expandability of 1.5 to 1.8 in a mold capable of being closed but incapable of being hermetically sealed, without applying an inner pressure-imparting procedure to said pre-expanded particles, and heating said particles to fuse together, said expandability being represented by the equation:

• Expandability = Expansion ratio of polypropylene resin pre- expanded particle after steam heating Expansion ratio of polypropylene resin pre- expanded particle before steam heating
• wherein the expandability is measured by subjecting the pre-expanded particle to the steam heating without imparting an inner pressure thereto, said steam has a temperature equal to the melting point peak temperature of said polypropylene resin measured by differential scanning calorimetry under the conditions that 1 to 10 mg of the pre-expanded particles is heated to 210° C. at a rate of 10° minute, then cooled to 40° C. at a rate of 10° C./minute and heated again to 210° C. at a rate of 10° C./minute, and said expansion ratio of polypropylene resin pre-expanded particle after steam heating denotes the value measured after the restoration from shrinking by impregnating the pre-expanded particle with air.

A process for preparing cellular moldings of a polypropylene resin comprising the steps of filling polypropylene resin pre-expanded particles having an expandability of 1.0 to 1.8 in a mold capable of being closed but incapable of being hermetically sealed, and heating said particles to fuse together, said expandability being represented by the equation:

• Expandability = Expansion ratio of polypropylene resin pre- expanded particle after steam heating Expansion ratio of polypropylene resin pre- expanded particle before steam heating
• wherein the expandability is measured by subjecting said pre-expanded particle to said steam heating without imparting an inner pressure thereto, said steam has a temperature equal to the melting point peak temperature of said polypropylene resin measured by differential scanning calorimetry under the conditions that 1 to 10 mg of the pre-expanded particles is heated to 210° C. at a rate of 10° C./minute, then cooled to 40° C. at a rate of 10° C./minute and heated again to 210° C. at a rate of 10° C./minute, and said expansion ratio of polypropylene resin pre-expanded particle after steam heating denotes the value measured after the restoration from shrinking by impregnating the pre-expanded particle with air.