Core for hollow product manufacture including multilayer filling material and method of manufacturing hollow product using the core

A method of manufacturing a hollow product using a core, the method comprising:

• a core input step in which a core filled with a filling material is input into a cavity of a mold that is openable and closeable;
• a molding step in which a melt is injected into the cavity to surround the core so that a molded product is molded;
• and
• a filling material removing step in which the filling material is removed from the core embedded in the molded product,
• wherein the core includes a pipe having a hollow formed in the pipe,
• wherein the filling material includes:
• a support member being configured to support the pipe;
• and
• a melting bar passing through the support member in a longitudinal direction of the melting bar,
• wherein the support member includes:
• a first support member, being disposed inside the hollow of the pipe and having a space formed in the first support member;
• a second support member, being disposed in the space;
• and
• a third support member, being disposed in the hollow of the pipe to close both ends of the pipe to prevent the first support member and the second support member from flowing to an outside,
• wherein the first support member is made of a water-soluble material,
• wherein the second support member is made of a water-insoluble material,
• wherein the third support member is made of an air-permeable material,
• wherein the melting bar passes through the second support member in a longitudinal direction of the second support member,
• wherein the filling material removing step includes:
• removing the third support member so that a first space portion is formed in a space occupied by the third support member, and
• heating the molded product so that the melting bar melts and a second space portion is formed in the second support member, and
• wherein a melting point of the melting bar is about 200° C., and melting points of the first support member and the second support member are higher than the melting point of the melting bar.