Method for making a molded polymeric article

Abstract

This disclosure relates to a method for making a polymeric article mold, a method for making a polymeric article with that mold, and improved surface topography features for a polymeric article. A prototype article is formed and then coated with a thin conductive layer. The coated prototype article is then electroformed until nickel plated to a sufficient depth to define a nickel plating tool. After the prototype article has been removed from the mold face of the nickel tool, the tool can be used as a mold for forming finished polymeric articles which replicate the original prototype article. The use of fine topography features such as a dense upstanding stem array on the surface of the prototype article facilitates accurate and complete electroforming by increased surface area presentation. The disclosure also presents improvements to microreplicated surface structures such as stem arrays. The improvements include the formation on a stem array having separate zones of stems of differing heights, and the formation of directional microreplicated features (e.g., stems) which are oriented and shaped to promote or restrict frictional interaction in one or more particular directions.

1 . A method of making a molded polymeric article, the method comprising: 
 electroforming a plating onto a first surface of a prototype article, wherein the first surface is defined at least in part by a desired arrangement of fine topography features and is electrically conductive, so that the plating defines an article mold having, on a first portion thereof corresponding to the first surface of the prototype article, a reverse image arrangement of the fine topography features thereon;    separating the prototype article from the article mold;    introducing a polymeric material onto the article mold which flows into and over the reverse image arrangement of fine topography features;    curing the polymeric material; and    separating the cured polymeric material from the article mold to define a molded polymeric article having, on a finished surface corresponding to the first portion of the article mold, a desired arrangement of fine topography features thereon, wherein at least a portion of the desired arrangement of fine topography features on the finished surface includes an array of upstanding stems, and wherein the array of upstanding stems has a density of at least about 500 stems per square inch.    
     
     
         2 . The method of  claim 1 , wherein the array of upstanding stems has a density of at least about 1000 stems per square inch.  
     
     
         3 . The method of  claim 1 , wherein the array of upstanding stems has a density of at least about 1500 stems per square inch.  
     
     
         4 . The method of  claim 1 , wherein the array has a plurality of zones of upstanding stems, and wherein the stems in adjacent zones differ in height.  
     
     
         5 . The method of  claim 4 , wherein the stem height change from one zone to the next is gradual.  
     
     
         6 . The method of  claim 4 , wherein the array has a plurality of zones of upstanding stems, and wherein the stems in adjacent zones differ in configuration.  
     
     
         7 . The method of  claim 1 , and further comprising: 
 verifying the electrical conductivity of the coated portions of the prototype article prior to the electroforming step.    
     
     
         8 . The method of  claim 1 , and further comprising: 
 defining the first surface of the prototype article to include at least one area having no topography features.    
     
     
         9 . The method of  claim 8 , wherein the one area is generally planar.  
     
     
         10 . The method of  claim 1 , wherein the article mold is defined as two or more separable mold sections, and wherein the separating step includes moving the mold sections apart from each other.  
     
     
         11 . The method of  claim 1 , and further comprising: 
 forming the prototype article; and    coating portions of the prototype article, including at least the first surface there, with a thin layer of conductive material.