Apparatus for coating on printing clinders

Abstract

A non-impact process and apparatus for coating printing cylinders with layers of a coating liquid, especially for coating flexographic printing sleeves with infrared sensitive layers.

1 . A process for coating a printing cylinder with a layer of a liquid, comprising the steps of: 
 (a) forming a fluid film of the liquid on a surface of a coating roll;    (b) positioning the surface of the coating roll a predetermined distance from an outer surface of the printing cylinder such that the fluid film contacts the outer surface and a coating gap between the outer surface of the printing cylinder and the surface of the coating roll is formed;    (c) simultaneously rotating and moving the coating roll relative to the printing cylinder in such a manner that the printing cylinder is coated with the liquid layer; and    (d) drying the liquid layer to form the coated printing cylinder.    
     
     
         2 . The process according to  claim 1 , characterized in that the printing cylinder is rotationally supported at both ends.  
     
     
         3 . The process according to  claim 1 , characterized in that the fluid film on the top of the coating roll is split into two parts to adjust coating thickness.  
     
     
         4 . The process according to  claim 3 , characterized in that the fluid film split into two parts is adjusted by varying the coating gap between printing cylinder and coating roll.  
     
     
         5 . The process according to  claim 1 , characterized in that the width of the predetermined distance between printing cylinder and coating roll is about 30-800 μm.  
     
     
         6 . The process according to  claim 1 , characterized in that the coating roll is rotated and moved from one end of the printing cylinder toward the other end of the printing cylinder in such a manner that a uniform overlapping spiral of the fluid film is formed on the printing cylinder.  
     
     
         7 . The process according to  claim 6 , characterized in that the trails of the overlapping spiral of the fluid film have an overlap of 20-80%.  
     
     
         8 . The process according to  claim 1 , characterized in that the printing cylinder comprises a photopolymerizable elastomeric printing layer.  
     
     
         9 . The process according to  claim 8 , characterized in that the photopolymerizable elastomeric printing layer is cylindrically disposed on a sleeve.  
     
     
         10 . The process according to  claim 1 , characterized in that the coating roll comprises a material having a predetermined hardness.  
     
     
         11 . The process according to  claim 10 , characterized in that the material of the coating roll has a Shore D hardness measured according to ASTM D 2240 of at least 60.  
     
     
         12 . The process according to  claim 10 , characterized in that the coating roll material is selected from the group consisting of thermoplastic or thermosetting non-elastomeric polymers, metals, and ceramic materials.  
     
     
         13 . The process according to  claim 10 , characterized in that the coating roll material is selected from the group consisting of polyamides and polyesters.  
     
     
         14 . The process according to  claim 1 , characterized in that the coating roll has a roll diameter of 90-150 mm.  
     
     
         15 . The process according to  claim 14 , characterized in that the coating roll has a roll width of 10-40 mm.  
     
     
         16 . The process according to  claim 1 , characterized in that the liquid is an infrared-sensitive composition.  
     
     
         17 . The process according to  claim 16 , characterized in that the liquid is an infrared-ablatable composition.  
     
     
         18 . The process according to  claim 17 , characterized in that the infrared-ablatable composition comprises carbon black.  
     
     
         19 . The process according to  claim 1 , characterized in that the process steps (a) to (d) are repeated at least once.  
     
     
         20 . The process according to  claim 19 , characterized in that for each repeat of the process steps (a) to (d) a different liquid is used.  
     
     
         21 . An apparatus to perform the process according to  claim 1  comprising: 
 (A) means to support and rotate the printing cylinder,  
 (B) means to support, rotate, and drive the coating roll at a predetermined distance from the printing cylinder,  
 (C) means to control the predetermined distance between the printing cylinder and the coating roll,  
 (D) a container to provide the liquid, and  
 (E) means to control drying conditions.  
 
     
     
         22 . The apparatus according to  claim 21 , characterized in that the container is installed on a vertically and horizontally moveable table.  
     
     
         23 . The apparatus according to  claim 21 , characterized in that the means to control drying conditions comprises fibre optic sensors.  
     
     
         24 . The apparatus according to  claim 21 , characterized in that the means to control the predetermined distance between the printing cylinder and the coating roll comprises a software-controlled motor.  
     
     
         25 . The apparatus according to  claim 21 , characterized in that the means to control the predetermined distance between the printing cylinder and the coating roll comprises mechanical means.  
     
     
         26 . The apparatus according to  claim 25 , characterized in that the mechanical means to control the predetermined distance comprises a micrometer.  
     
     
         27 . A photopolymerizable flexographic printing sleeve comprising an outermost layer coated by the process according to  claim 1.