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A method and mold design for forming a molded chair seat portion and chair back support portion using air counterpressure and two different materials in an injection molding procedure. The two different materials comprise a first material having a low flexural modulus and the other material having a

A method and mold design for forming a molded chair seat portion and chair back support portion using air counterpressure and two different materials in an injection molding procedure. The two different materials comprise a first material having a low flexural modulus and the other material having a high flexural modulus. Other additives for tailoring the physical properties of the molded product are added to the mixture of the two materials. The air counterpressure is achieved using shop air pressure. The mold may be used to form the seat portion and the back support portion with a single stroke. An endothermic foaming agent is added to the mixture of the two materials to reduce the weight of the finished part, to reduce cycle time, and to assist in the uniform distribution of the materials that are injected into the mold cavity by the injection nozzle.

대표청구항 ▼

[ What is claimed is:] [1.] A method for injection molding a chair part in an injection mold having a mold cavity, said mold having an injection nozzle communicating with said cavity, said method comprising:mixing polymer particles of low density, low flexural modulus polymer with high density parti

[ What is claimed is:] [1.] A method for injection molding a chair part in an injection mold having a mold cavity, said mold having an injection nozzle communicating with said cavity, said method comprising:mixing polymer particles of low density, low flexural modulus polymer with high density particles of high flexural modulus comprising acrylic, butadiene and styrene;mixing with said polymer particles and said high density particles additives comprising an endothermic foaming agent and a color agent;delivering said particles and said additives in a mix in a linear path toward said mold;heating said mix at multiple locations along said path whereby said mix is in the form of a melt at said injection nozzle;applying air under pressure to said cavity for establishing a counterpressure that controls the distribution of said melt throughout said cavity;circulating coolant through said mold whereby temperatures at selected locations of said cavity can be controlled;said Low modulus polymer, upon reaching the walls of said cavity, solidifying to form a skin;said foaming agent, when its decomposition temperature is reached, forming cells of gas throughout said melt thereby creating an internal pressure in said melt that acts on said skin to create a smooth surface finish for the chair parts; andcontrolling the temperature of said melt during a cool-down phase of the injection cycle whereby the high modulus material solidifies before the low modulus polymer, the high modulus material thereby being centered in the finished chair part.