Mold for hot-forming a thermoplastic lens

Abstract

The mold comprises two dies mounted in a sheath to slide along the axis of the sheath and each presenting a forming face facing the other. The two dies and the sheath are provided with intrinsic heat transfer means. A parison or preform of said thermoplastic material is placed between the two dies and the assembly is enclosed in the sheath; the dies and the sheath are heated by their intrinsic heat transfer means up to a forming temperature. The dies are moved towards each other to shape the material by plastic deformation until a predetermined relative position is reached corresponding to the thickness desired for the lens; the dies and the sheath are cooled by their intrinsic heat transfer means down to an unmolding temperature; and the finished lens is extracted from the mold.

1 . A mold for hot-forming a thermoplastic lens, the mold comprising two dies mounted in a sheath to slide along an axis of the sheath, and each presenting a transverse forming face facing the other, wherein the two dies and the sheath are provided with intrinsic and both-way heat transfer means, wherein said heat transfer means is adapted to a thermoplastic material lens.  
   
   
       2 . A mold according to  claim 1 , in which each die comprises: 
 a base containing at least a fraction of the heat transfer means of said die, and means for connecting them to a heat transfer source; and    a removable insert fitted to the base and carrying the forming face.    
   
   
       3 . A mold according to  claim 2 , in which the base of each die receives all of the heat transfer means of said die, the insert having no such means, being temperature regulated solely by heat transfer with the base.  
   
   
       4 . A mold according to  claim 1 , in which the sheath possesses an annular recess open to the inside and communicating with the interstitial gap defined by the forming faces of the two dies.  
   
   
       5 . A mold according to  claim 4 , in which the interstitial gap defined by the forming faces of the two dies co-operates with the annular recess to form a sealed inside volume which is connected to the outside via at least one suction channel passing through the sheath.  
   
   
       6 . A mold according to  claim 5 , in which the suction channel opens out into the annular recess.  
   
   
       7 . A mold according to  claim 4 , including a trimming ring slidably mounted in the sheath.  
   
   
       8 . A mold according to  claim 7 , in which the trimming ring co-operates with a lip bordering the annular recess.  
   
   
       9 . A mold according to  claim 4 , in which the sheath has two portions mounted to slide relative to each other along the same sliding axis as the dies between firstly an open configuration giving direct access to the interstitial gap defined by the forming faces of the two dies and secondly a closed configuration in which the two portions are in contact via junction faces in a transverse join plane.  
   
   
       10 . A mold according to  claim 9 , in which the annular recess of the sheath is implemented in the form of a groove formed as a setback in the junction face of at least one of the two portions of the sheath.  
   
   
       11 . A mold according to  claim 10 , in which the groove possesses draft taper.  
   
   
       12 . A mold according to  claim 1 , in which the heat transfer means comprise an internal circuit for circulating a heat-conveying fluid.