Method and apparatus for embossing a precision pattern of micro-prismatic elements in a resinous sheet or laminate

Abstract

An improved method and apparatus is provided for continuously embossing a precision pattern of micro-prismatic elements on a surface of a resinous sheeting material with the aid of an endless metal embossing belt. The method includes the steps of moving the belt along a closed path through a heating station and a cooling station, conveying superimposed resinous film and sheeting material into proximity with the belt, passing the film and sheeting between the belt and a series of sonic welding heads to thereby begin to impress a pattern of micro-prismatic formations of the belt into one surface of the sheeting, pressing the film and sheeting against the heated belt until the one surface of the sheeting fully conforms to the embossing pattern, and stripping the film and embossed sheeting from the belt.

What is claimed is:  
     
         1 . A method for continuously embossing a precision pattern of micro-prismatic elements on one surface of a continuous resinous sheeting material, the method being performed with the aid of a generally cylindrical metal embossing element having an inner surface and an outer surface, the outer surface having a precision embossing pattern which is the reverse of the precision pattern to be formed on one surface of said sheeting, and wherein the method includes the steps of: 
 (a) continuously moving the embossing element through a heating station where said embossing element is heated to a predetermined temperature and then to a cooling station where said embossing element is cooled below said predetermined temperature;    (b) continuously conveying into proximity with said embossing element superimposed resinous film and at least one layer of sheeting material, said resinous materials of said film and said sheeting each having different glass transition temperatures;    (c) continuously passing said superimposed resinous film and sheeting between said embossing element and at least one sonic welding head with one surface of said sheeting confronting and engaging said precision pattern of said embossing element to thereby begin to impress said pattern into said sheeting;    (d) heating said embossing element to said predetermined temperature at said heating station, said temperature being greater than the glass transition temperature of said sheeting and less than the glass transition temperature of said resinous film;    (e) pressing said superimposed film and sheeting against said embossing element at a plurality of pressure points sequentially spaced along said heating station with said one surface of said sheeting confronting and engaging said precision pattern of said embossing element until said one surface of said sheeting fully conforms to said precision embossing pattern; and    (f) continuously stripping said superimposed layer of film and embossed sheeting from said embossing element.    
     
     
         2 . The method according to    claim 1   , including the step of preheating said resinous film prior to passing said film and sheeting between said embossing element and said at least one sonic welding head.  
     
     
         3 . The method according to    claim 1   , including the step of cooling said superimposed film and sheeting prior to stripping said film and sheeting from said embossing element.  
     
     
         4 . The method according to    claim 1    wherein said path is substantially cylindrical through said heating station and said pressure points are provided by at least three spaced pressure rollers.  
     
     
         5 . The method according to    claim 1    wherein said precision pattern is in the form of an array of female microcube corner type elements whereby the sheeting formed thereby has male microcube corner elements on one face thereof;  
     
     
         6 . The method according to    claim 1    wherein said at least one sonic welding head vibrates at approximately 20,000 cycles per second.  
     
     
         7 . The method according to    claim 1    wherein said at least one sonic welding head vibrates approximately 0.010 inch.  
     
     
         8 . The method according to    claim 1   , including providing multiple sonic welding heads arranged across a width of said metal embossing element.  
     
     
         9 . The method according to    claim 8   , wherein said sonic welding heads are arranged in staggered overlapping relation.  
     
     
         10 . Apparatus for continuously embossing a precision pattern of micro-prismatic elements on one surface of transparent resinous material, said apparatus comprising: 
 embossing means including an embossing tool in the form of a thin metal element having an inner surface and an outer surface, said outer surface having a precision embossing pattern thereon which is the reverse of the precision pattern to be formed in the resinous material;    means for continuously moving said embossing element along a closed path;    means for introducing superimposed film and sheeting of resinous materials onto said embossing element with one face of said sheeting in direct contact with said pattern on said embossing element;    means for applying sonic vibration to said superimposed film and sheeting with said one face of said sheeting in direct contact with said embossing element to thereby begin to heat an impress said pattern into said sheeting;    means for raising the temperature of said embossing element to the glass transition temperature of said sheeting and below the glass transition temperature of said film while said embossing element is in a first portion of its path;    pressure means sequentially spaced along said first portion of said path for pressing said superimposed film and sheeting against said embossing element until said one surface fully conforms to said embossing pattern; and    means for stripping said superimposed film and embossed sheeting from said embossing element.    
     
     
         11 . Apparatus according to    claim 10   , including means for preheating said resinous film prior to introducing said film and sheeting onto said embossing element.  
     
     
         12 . Apparatus according to    claim 10   , including means for cooling said superimposed film and sheeting prior to stripping said film and sheeting from said embossing element.  
     
     
         13 . Apparatus according to    claim 10    wherein said closed path is substantially cylindrical.  
     
     
         14 . Apparatus according to    claim 10    wherein said embossing tool is endless and seamless.  
     
     
         15 . Apparatus according to    claim 10    wherein said precision pattern is in the form of an array of female microcube corner type elements whereby the sheeting formed thereby has male microcube corner elements on one face thereof.  
     
     
         16 . Apparatus according to    claim 10    wherein said means for applying sonic vibration to said superimposed film and sheeting includes at least one sonic welding head vibrating at approximately 20,000 cycles per second.  
     
     
         17 . Apparatus according to    claim 10    wherein said means for applying sonic vibration to said superimposed film and sheeting includes a sonic welding head vibrating at approximately 0.010 inch.  
     
     
         18 . Apparatus according to    claim 12    wherein said means for cooling includes a shoe member having chilled fluid running therethrough.  
     
     
         19 . Apparatus according to    claim 18    wherein said embossing element passes over said shoe member.  
     
     
         20 . Apparatus according to    claim 12    wherein said means for cooling includes a cold air plenum.  
     
     
         21 . Apparatus according to    claim 10    wherein said means for applying sonic vibration includes a plurality of sonic welding heads arranged across a width of said embossing element.  
     
     
         22 . Apparatus according to    claim 20    wherein said sonic welding heads are arranged in staggered overlapping relation along the width of the embossing element.