Patent Publication Number: US-6655288-B2

Title: Method for spot coating on printing substrates in large size printing machines

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for spot coating on printing substrates in large size printing machines producing printed images by application of an ink layer on the printing substrates. 
     BACKGROUND OF THE INVENTION 
     Spot coating on surfaces of printing substrates is usually made by printing plates, which are especially made for this purpose. These printing plates have partial recesses. This solution is described in the 9 th  edition of the book “Offsetdrucktechnik” (Offset printing) by Helmut Teschner on pages 11 to 43. This solution is not applicable for large size printing presses because the coating plates can not be manufactured in sufficient quality at such plate dimensions. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method and apparatus for spot coating of printing substrates also applicable in large size printing presses. 
     “The present invention solves this and other problems by using a universally applicable offset plate to coat substantially the entire area of a printed image, wherein the coating reacts with ink layers of at least two ink systems thereby changing the printed image so that areas of varying gloss degrees are created. A printed offset plate may be used. The present invention uses a conventional printing press comprising at least two printing units for printing at least two ink systems, an optional dryer allocated to the printing units, and a coating unit for application of the final coating layer succeeding the printing units.” 
     An advantage of the present invention is that varying degrees of gloss can be produced using only a single coating plate without partial recesses. The manufacturing cost for the coating plates decreased. The coating plate can now be used for several printing jobs so that the make ready time is reduced. Furthermore, only one coating unit or coating tower is required. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is described below in greater detail by an exemplary embodiment of the invention and by reference to the drawing, wherein: 
     The figure is a schematic drawing of a sheet fed offset press in unitized design. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The sheet fed offset press in the figure has multiple printing units  31  to  34  arranged in unitized design. The embodiment shows four printing units  31  to  34  as an example. At least two printing units are used in the method according to the present invention. 
     A feeder  1  precedes the printing units  31  to  34 . The structure and function of the feeder  1  are known and, thus, will not be described herein. Each of the printing units  31  to  34  has an impression cylinder  21  to  24 , a plate cylinder  5  and a blanket cylinder  6 . For illustrative purpose, the plate cylinder  5  and the blanket cylinder  6  are only denoted in the printing unit  31 . The sheet travel direction is marked with an arrow. The figure also shows transfer drums  71  to  74  located between two impression cylinders  21  to  25 . The transfer drums  71  to  74  can also be embodied as perfecting drums. The impression cylinders  21  to  24  and the transfer drums  71  to  74  may be sheet guiding cylinders of double diameter. Inking and dampening units allocated to each printing unit  31  to  34  are not shown in the figure. 
     The shown printing units  31  and  32  print with an ink system including ink constituents that dry under radiation, such as ultraviolet radiation. The printing units  33  and  34  print with typical offset ink. 
     In the exemplary embodiment, a dryer  111  is allocated to the printing unit  32 . The dryer  111  dries the ink system, which is in this case an ultraviolet (UV) dryer. 
     A coating tower  4  follows the printing units  31  to  34  in the direction of the sheet travel. It has a coating form cylinder  8  allocated to the impression cylinder  25 . The coating form cylinder  8  carries a coating plate  81 . The coating tower  8  coats the printed image with a coating layer, which also dries under radiation. 
     A screened roller  9  is allocated to the coating form cylinder  8  and the coating plate  81 . The screened roller  9  is equipped with a chamber doctor blade  10  to supply the coating. A dryer  112  is allocated to the coating tower  4 . 
     The coating tower  4  is followed by a delivery unit  12 . The structure and function of the delivery unit  12  are known and, thus, will not be described herein. 
     The above-described apparatus can operate according to the following method: 
     The printing sheet is supplied by the feeder  1  and forwarded by an unshown means for sheet travel. The ink of an ink system is applied in the printing units  31  to  32  through the blanket cylinder  6 . The ink system includes proportional ink hardening under radiation, and in an exemplary embodiment, under ultraviolet radiation. These inks are denoted as hybrid ink. 
     Inks with similar processing characteristics are summarized herein as ink systems. 
     The ink layer is dried with the dryer  111  before the sheet is transferred to subsequent printing units  33  and  34 . The printing sheet is here printed with an ink of an ink system comprising other inks, for instance, inks typically used for offset printing. 
     The coating is applied next over substantially the entire sheet by the coating plate  81  in the coating tower  4 . The coating has the characteristics to react with ink systems differently, physically and/or chemically and to influence the degree of gloss in the ink layer variably. A colorless s coating that hardens like the hybrid ink hardens under ultraviolet light is us ed in the present embodiment. The coating layer is then dried in a dryer  112 . 
     An additional feature for the above-mentioned effect is that the ink systems m ay differ from each other in their capacity of coating resorption. The degree of gloss is reciprocally proportional to the capacity for resorption of the ink system to the coating, whereby for ink layers of ink systems with lower capacity for resorption, more coating retains at their surfaces; for ink layers of ink systems with higher capacity for resorption, less coating retains a t their surfaces. The gloss-determining constituents of the coating are picked up by the ink layers. 
     The present invention is not limited to the above mentioned difference in the capacity for resorption of a coating layer. Rather, the present invention includes all ink systems that change their gloss degree or gloss effect in combination with the coating layer. Nevertheless, drying and/or hardening of the sheet or the printing substrate after printing with additional energy is not necessary. Other process treatments of the ink layers and/or coating layers by physical and/or chemical reactions are possible in order to obtain varying degrees of gloss on the final coating layer. 
     In another embodiment of the present invention, the process treatment can be eliminated totally or partially. The above mentioned effects are obtained by selection of suitable ink systems and a corresponding coating.