Corrugated sheet fed printing process with uv curable inks

Abstract

A flexographic printing system for printing flat corrugated sheets using radiation curable inks. An ultraviolet curing unit is positioned after each of the printing stations. The ink applied at each station is partially cured before a different color ink is applied at the next printing station.

1 . An in-line flexographic printing press for printing corrugated paperboard sheets using radiation curable inks, the printing press comprising:
 a transport system for transporting corrugated paperboard sheets along a linear path;   a series of printing stations positioned along the linear path for successively applying layers of radiation curable ink to the corrugated paperboard sheets;   a series of interstation UV radiation sources, each UV radiation source associated with one of the printing stations for only partially curing the layer of radiation curable ink applied by that printing station before the layer reaches a next printing station;   a final printing station for applying a final layer of radiation curable ink;   a final UV radiation source following a last printing station of the series for curing the final layer all preceding partially cured layers of radiation curable ink to produce printed corrugated paperboard sheets; and   a cutting station at which the printed corrugated paperboard sheets are die cut.   
     
     
         2 . The system of  claim 1 , wherein the printing stations are positioned to apply ink to a bottom surface of the sheets, and the interstation UV radiation sources and the final UV radiation source are positioned to direct UV radiation at the bottom surface of the sheets. 
     
     
         3 . The system of  claim 1  wherein the interstation UV radiation sources each include at least one elongated UV lamp. 
     
     
         4 . The system of  claim 3 , wherein the UV lamp comprises a medium pressure mercury vapor lamp. 
     
     
         5 . The system of  claim 3 , wherein the UV lamp has a rating of about 150 watts per inch or less. 
     
     
         6 . The system of  claim 5 , wherein the UV lamp has a rating of about 100 watts per inch or less. 
     
     
         7 . The system of  claim 3 , wherein the interstation UV radiation sources each include at least two UV lamps. 
     
     
         8 . The system of  claim 1 , wherein each of the interstation UV radiation sources includes a fan duct assembly and a UV curing head assembly mounted on the fan duct assembly. 
     
     
         9 . The system of  claim 8 , wherein the fan duct assembly directs air flow through the UV curing head. 
     
     
         10 . The system of  claim 9 , wherein the UV curing head includes at least one elongated UV lamp having a rating of about 150 watts per inch or less. 
     
     
         11 . The system of  claim 10 , wherein the UV lamp has a rating of about 100 watts per inch or less. 
     
     
         12 . The system of  claim 1 , wherein the transport system is capable of transporting sheets at surface speeds of up to at least 1,000 feet per minute. 
     
     
         13 . A method comprising:
 transporting the flat corrugated paperboard sheet through an in-line flexographic printing press;   applying a first layer of radiation curable ink to the sheet at a first print station of the printing press;   partially curing the first layer with UV radiation immediately following the first print station;   applying a second layer of radiation curable ink to the sheet at a second print station of the printing press;   partially curing the second layer with UV radiation immediately following the second print station;   applying a final layer of radiation curable ink at a final printing station of the printing press;   fully curing the final layer and the partially cured first and second layers immediately following the final printing station to produce a printed flat corrugated paperboard sheet; and   die cutting the printed flat corrugated paperboard sheet.   
     
     
         14 . The method of  claim 13 , wherein the first and second layers are applied to a bottom surface of the flat sheet, and wherein partially curing the first layer comprises directing UV radiation onto the first layer of radiation curable ink on the bottom surface. 
     
     
         15 . The method of  claim 13 , wherein the UV radiation for partially curing is produced by one or more UV lamps having a rating of about 150 watts per inch or less. 
     
     
         16 . The method of  claim 15 , wherein the UV lamps have a rating of about 100 watts per inch or less. 
     
     
         17 . A method comprising:
 transporting a flat corrugated paperboard sheet along a linear path past a plurality of printing stations of a flexographic printing press;   applying a layer of UV curable ink to the sheet at each printing station;   partially curing each layer of UV curable ink applied before it reaches a next one of the printing stations;   applying the final layer of UV curable ink over the partially cured layers;   fully curing the final layer and the partially cured layers to produce a printed flat corrugated paperboard sheet; and   die cutting the printed flat corrugated paperboard sheet.   
     
     
         18 . The method of  claim 17 , wherein the UV radiation for partially curing is supplied by a UV source having a rating of about 150 watts per inch or less. 
     
     
         19 . The method of  claim 18 , wherein the UV source has a rating of about 100 watts per inch or less.