Patent ID: 7641842

Claim:
In a rotational molding method for fabrication of a molded, hollow form polyethylene product in a rotational molding cycle wherein polyethylene particles are charged to a rotational mold, the rotational mold is closed, heated to a molding temperature from about 350 to 650 degrees F. while being rotated about its major and minor axes for a time sufficient to form said molded product and the mold is cooled to a demolding temperature from 90 to 170 degrees F., opened and the molded product is ejected, including the in-mold incorporation of indicia in an indicia area within the exterior surface of said molded product which consists essentially of: a. applying to a selected indicia area of the interior surface of the rotational mold at a temperature from 90 to 170 degrees F. successive layers of: I. a top coat covering said indicia area and comprising a hydrocarbon resin pressure sensitive adhesive having a melting temperature less than said molding temperature and greater than said demolding temperature and being tacky at said demolding temperature; ii. an indicia coat of a mixture of colorant and hydrocarbon wax having a melting temperature greater than said demolding temperature and less than said molding temperature overlying said top coat in a preselected indicia array; iii. a backing coat covering said indicia coat and comprising a backing coat pressure sensitive adhesive which is adhesive at ambient temperatures and which has a melting temperature less than said demolding temperature of 90 to 170 degrees F., and iv. a carrier sheet; wherein said backing coat pressure sensitive adhesive bonds said indicia coat to said carrier sheet at ambient temperatures and permits said carrier sheet to separate from said backing and indicia coats at said demolding temperature and wherein said indicia, bottom and top coats are stable and resistant to decomposition at said molding temperature; b. pressing said carrier sheet against said coats to bond said coats to said inside surface of said mold; c. removing said carrier sheet and leaving said top, indicia and backing coats on said inside surface of said mold; d. continuing said rotational molding method by charging polyethylene molding resin into said mold, closing said mold, heating said mold to said molding temperature while rotating said mold about its major and minor axes for a time sufficient to form said molded product and cause said indicia, bottom and top coats to transfer to and become permanently incorporated into the surface of said product, cooling said mold to said demolding temperature, opening said mold and ejecting a molded product having said top, indicia and backing coats fused into its outside surface leaving no significant amount of residue on the mold surface.