Method and apparatus for enhanced minimal shear molding utilizing extrusional, pelletization, and melt rheological control of pellets and micropellets and molded objects made therefrom

Abstract

The present invention relates to a method for enhancement of the minimal shear molding process utilizing pellets and/or micropellets produced through controlled extrusional and pelletization processes in combination with nonpowder melt flow rheology that incorporates reduced molding temperature and/or reduced cure time, reduced rotation axis ratios and/or reduced rotation rates. Molding can be uniaxial, biaxial, or multiaxial rotational or oscillatory or both. The molded items produced can be single or multiple layers and can be produced in one or more molding sequences using similar or different chemical compositions.

What is claimed is: 
     
         1 . A method of minimal shear molding comprising:
 providing a minimal shear molding composition mixture in a mold for minimal shear molding, the mixture separating into two or more layers, at least one of the two or more layers comprising micropellets that are spherical to lenticular in geometric configuration and smaller than 0.7 mm in cross-section, wherein each layer is compositionally different; and   forming at least two layers of a molded article with the mixture.   
     
     
         2 . The method according to  claim 1 , wherein forming at least two layers of the molded article comprises forming an inner surface of the molded article that is smooth without flow irregularities. 
     
     
         3 . The method according to  claim 1 , wherein providing the minimal shear molding composition mixture in the mold further comprises providing at least one layer comprising pellets between 0.7 mm and 3.5 mm in cross-section. 
     
     
         4 . The method according to  claim 3 , wherein providing the minimal shear molding composition mixture in the mold further comprises providing at least one layer comprising pellets between 0.7 mm and 1.6 mm in cross-section. 
     
     
         5 . The method according to  claim 4 , wherein providing the minimal shear molding composition mixture in the mold further comprises providing at least one layer comprising pellets between 0.7 mm and 1.0 mm in cross-section. 
     
     
         6 . The method according to  claim 1 , wherein forming at least two layers of the molded article occurs at temperatures at least 25° C. below molding temperatures of a 35 mesh powder of comparable composition. 
     
     
         7 . The method according to  claim 6 , wherein forming at least one layer of the molded article occurs at temperatures at least 100° C. below molding temperatures of a 35 mesh powder of comparable composition. 
     
     
         8 . The method according to  claim 1 , wherein forming at least two layers comprises rotating the mold at a rate of approximately 1.75 rpm to 6 rpm. 
     
     
         9 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises rotating the mold in at least one axis, uniaxially. 
     
     
         10 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises rotating the mold in two or more axes, multiaxially. 
     
     
         11 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises rotating the mold continuously and circularly in at least one axis. 
     
     
         12 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises arcuately oscillating the mold in at least one axis. 
     
     
         13 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises rotating the mold continuously without stopping to add materials into the mold. 
     
     
         14 . The method according to  claim 1  further comprising forming at least one partial layer by arcuately oscillating the mold. 
     
     
         15 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises rotating the mold at different rotation rates in two or more axes. 
     
     
         16 . The method according to  claim 1  further comprising providing an additional minimal shear molding composition in the mold to form at least one additional layer of the molded article. 
     
     
         17 . The method according to  claim 16 , wherein forming at least two layers of the molded article further comprises forming a smooth surface between two or more of the at least two layers and the at least one additional layer of the molded article. 
     
     
         18 . The method according to  claim 16 , wherein providing the additional minimal shear molding composition in the mold further comprises sequentially providing the minimal shear molding composition in the mold manually by controlled release. 
     
     
         19 . The method according to  claim 16 , wherein providing the additional minimal shear molding composition in the mold further comprises sequentially providing the minimal shear molding composition in the mold thermally by controlled release. 
     
     
         20 . The method according to  claim 1  further comprising molding an adhesive layer between the two or more layers to limit separation of the two or more layers on cooling and storage. 
     
     
         21 . The method according to  claim 1 , wherein providing the minimal shear molding composition mixture in the mold further comprises providing at least one layer comprising micropellets having less than 1% of fines. 
     
     
         22 . The method according to  claim 1 , wherein providing the minimal shear molding composition mixture in the mold further comprises simultaneously providing all components for forming the at least two layers in the mold without sequential addition of components. 
     
     
         23 . The method according to  claim 1 , wherein the mold includes a vent, the method further comprising providing additional material in the mold through the vent. 
     
     
         24 . The method according to  claim 1 , wherein forming at least two layers of the molded article further comprises cross-linking at least one layer of the molded article. 
     
     
         25 . The method according to  claim 1 , wherein providing the minimal shear molding composition mixture in the mold further comprises including a foaming agent in the mold, and forming at least two layers of the molded article further comprises causing the foaming agent to expand. 
     
     
         26 . The method according to  claim 1  further comprising providing at least one non-melting composition in the mold, the at least one non-melting composition having a melting point higher than a maximum temperature within the mold. 
     
     
         27 . The method according to  claim 1 , wherein the mixture separates into two or more layers based on at least one of differential melt viscosity, melt density, pellet size, pellet density, softening temperature, melting temperature, polarity, component immiscibility, surface dynamics, and surface wetting. 
     
     
         28 . The method according to  claim 27 , wherein the mixture separates into two or more layers by varying at least one of rotation rate, rotation ratio, composition, molding process temperature, and molding process time. 
     
     
         29 . The method according to  claim 1 , further comprising selecting one or more compositions and molding conditions to enable variation of surface patterning and color. 
     
     
         30 . The method according to  claim 29 , wherein selecting one or more compositions and molding conditions further comprises selecting one or more of oversized pellets, low melt index pellets, and fractional melt pellets. 
     
     
         31 . A method of minimal shear molding comprising:
 placing a composition mixture into a mold for minimal shear molding, the mixture separating into two or more layers, at least one layer of the two or more layers comprising micropellets that are spherical to lenticular in geometric configuration and smaller than 0.7 mm in cross-section, and at least one layer of the two or more layers comprising pellets that are spherical to lenticular in geometric configuration and larger than 0.7 mm in cross-section, wherein each layer is compositionally different; and   rotating the mold to form at least two layers of a rotationally molded article with the mixture.   
     
     
         32 . A method of minimal shear molding comprising:
 delivering a composition mixture to a mold for minimal shear molding, the mixture comprising a first layer having micropellets that are smaller than 0.7 mm in cross-section and a second layer having comprising pellets that are larger than 0.7 mm in cross-section, the micropellets and pellets having different geometric configurations, wherein the first and second layers are compositionally different; and   making at least one layer of a rotationally molded part with the mixture.   
     
     
         33 . The method according to  claim 32 , wherein delivering the composition mixture to the mold further comprises delivering at least one layer comprising one or more of micropellets and pellets having a spherical to lenticular geometric configuration.