Patent ID: 8900505

Claim:
A method of making an inverted-hook groove in a pre-formed plant fiber-molded cup lid comprising: covering an outer side of a thermally compressed and shaped plant fiber molded cup lid with an outer mold converting a thermally compressed and shaped plant fiber-molded cup lid, said outer mold having a transversely annular slide groove at a place corresponding with a location where said molded lid is to be formed with an inverted-hook groove; said annular slide groove receiving a set of shaping slide blocks therein, each of said slide block formed with a protruding-out shaping ridge at an inner edge; said molded cup lid having a lower side receiving an inner mold that has a central portion receiving a material-propping block; said inner mold and said material-propping block matching a shape of said molded cup lid; said inner mold formed with an annularly inward-recessed receiving groove at a place corresponding with a location where said molded cup lid is to be formed with an inverted-hook groove, a shape of said receiving groove aligning with that of said shaping ridge; during making said inverted-hook groove, said outer mold and said inner mold together with said material-propping block closed together first; said slide blocks are pushed to move inward to let said shaping ridges resist the surface of said molded cup lid; said shaping ridges continuously moved forward to make the surface of said molded cup lid deformed together with the shape of said shaping ridge and contracted into said receiving groove of said inner mold, thus forming the annularly inverted-hook groove; and separating said inner and outer mold and removing said molded cup lid with an annularly inverted-hook groove.