Injection-molded plastic container with improved stacking strength

Abstract

A thermoplastic, injection-molded container provides stacking strength with reduced thickness walls by the addition of a series of shallow, spaced vertical buttresses integrally molded into the container sidewalls.

1 . A thermoplastic, injection molded container comprising: 
 a base;    sidewalls extending upward from the base;    a lid releasably sealing to an upper edge of the sidewalls to enclose a container volume; and    wherein the sidewalls have integrally molded variations in wall thickness forming a plurality of vertical buttresses providing resistance to stacking loads.    
   
   
       2 . The thermoplastic, injection molded container of  claim 1  wherein the vertical buttresses extend inward from an inside of the container.  
   
   
       3 . The thermoplastic, injection molded container of  claim 1  wherein the vertical buttresses are separated by arcuate wall sections of substantially constant thickness.  
   
   
       4 . The thermoplastic, injection molded container of  claim 3  wherein the arcuate wall sections have a width at least five times a width of the vertical buttresses.  
   
   
       5 . The thermoplastic, injection molded container of  claim 1  wherein the vertical buttresses have a cross section providing a continuous curved inner circumference to the container.  
   
   
       6 . The thermoplastic, injection molded container of  claim 1  wherein the vertical buttresses have a first thickness greater than a second thickness of the sidewalls away from the vertical buttresses, wherein the first thickness is selected to provide a substantially smooth and circular outer circumference of the container without depressions caused by shrinkage.  
   
   
       7 . The thermoplastic, injection molded container of  claim 1  wherein the vertical buttresses are separated by varying distances such that at least two vertical buttresses are adjacent to each other within a first distance and separated from at least two other vertical buttresses by a second distance greater than the first distance.  
   
   
       8 . The thermoplastic, injection molded container of  claim 1  wherein the sidewalls taper outward toward a top of the container allowing the container to be stacked in nested configurations, and wherein the thickness of the buttresses in excess of the thickness of the sidewalls away from the vertical buttresses is less than a taper of the sidewall from a bottom to a top of the vertical buttresses, whereby the buttresses do not interfere with stacking.  
   
   
       9 . The thermoplastic, injection molded container of  claim 8  wherein the thickness of the buttresses in excess of the thickness of the sidewalls away from the buttresses is substantially constant along a vertical extent of the buttress.  
   
   
       10 . The thermoplastic, injection molded container of  claim 1  wherein the thickness of the buttresses in excess of the thickness of the sidewalls away from the vertical buttresses is greater than 2% and less that 30% of the thickness of the sidewalls away from the vertical buttresses.  
   
   
       11 . The thermoplastic, injection molded container of  claim 1  wherein the container volume is substantially five gallons and wherein wall thickness away from the buttresses is less than  85  thousands of an inch.  
   
   
       12 . The thermoplastic, injection molded container of  claim 1  wherein the buttresses extend less than an entire height of the sidewalls.  
   
   
       13 . The thermoplastic, injection molded container of  claim 1  wherein a top end of the buttresses is tapered into the sidewalls.  
   
   
       14 . The thermoplastic, injection-molded container of  claim 1  wherein the container meets standard ASTM D4504-94 for stacking strength.  
   
   
       15 . The thermoplastic, injection molded container of  claim 1  further including horizontal buttresses extending across the base.  
   
   
       16 . The thermoplastic, injection molded container of  claim 15  wherein the horizontal buttresses extend radially from a center of the base.  
   
   
       17 . The thermoplastic, injection molded container of  claim 15  wherein the horizontal buttresses extend circumferentially in a set of concentric loops about a center of the base.  
   
   
       18 . The thermoplastic, injection-molded container of  claim 1  wherein the base is substantially circular and the upward extending sidewalls form a cylinder.  
   
   
       19 . A method of fabricating a container comprising: 
 (1) molding a base and integral sidewalls extending upward from the base to define a container volume wherein the sidewalls have integrally molded variations in wall thickness forming a plurality of vertical buttresses; and    (2) contact printing an outer surface of the container.    
   
   
       20 . A mold for a thermoplastic container comprising: 
 a core body defining a container volume opening along a container axis and having therein a series of constant depth shallow grooves parallel to the container axis and extending substantially a height of the core body;    a mold shell fitting about the core body to define therebetween a container having a base and sidewalls extending upward from the base to surround the container volume; and    whereby the depth of the shallow grooves is such as to allow removal of a formed container from the core body by flexure of the formed container.    
   
   
       21 . The mold of  claim 20  wherein the shallow grooves run parallel to a dominant direction of flow of thermoplastic into a mold formed by the core body and the mold shell and wherein the grooves run less than an entire length of the mold core.