Patent Publication Number: US-2011048260-A1

Title: Roller body having a roller coating for improved ink-water-emulsion formation in printing units of wet offset machines and method for the manufacturing thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to roller bodies made of steel, aluminium or carbon fibre reinforced plastic material in printing units of wet offset machines, having a roller coating, the objective of which is to guarantee the formation of a stable ink-water-emulsion. The invention further relates to a method for the manufacturing of such coated roller bodies. 
     2. Description of Related Art 
     According to the prior art such roller bodies are provided with matted chromium coatings (see roller assembly according to  FIG. 1 ) or with RILSAN® coatings (usual product name in offset machines for coatings from the group of polyamides, see roller assembly according to  FIG. 2 ). The latter coatings are regarded as lipophilic and wear-resistant and very often show a very smooth surface, in particular if the printing unit operates with highly-pigmented ink or even zinc white including titanium dioxide pigments. Already after a short operation, highly pigmented inks very often have the effect, that even layers of matted chromium are heavily smoothened and lose the desired surface roughness. Neither a smoothened coating of matted chromium nor a smooth RILSAN® coating are able to form in a sufficient quantity the stable ink-water-emulsion which is necessary for the printing process, with the consequence, that according to the prior art emulsification aids in the form of isopropyl alcohol and/or tenside-containing additive are added to the fountain solution. These additional measures are as such undesirable, because they are cost-increasing and damaging to the environment (isopropyl alcohol is regarded as damaging the atmosphere and is a volatile organic compound). Moreover, in the practice of low-isopropyl or isopropyl-free printing it turned out that partly not before weeks of operation of the printing unit, an increase in the concentration of the tenside-containing additives leads to an overturning of the printing process, because there is no longer a “water-in-ink-emulsion”, but rather an “ink-in-water-emulsion”; the latter, of course, wets not only the ink-containing zones on the printing plate, but also the water-containing zones, so that not print pattern is produced on the paper to be printed, but only an uncontrolled inking. 
     Therefore, the invention aims at providing coated roller bodies of steel, aluminium or fibre reinforced plastic material, which in wet offset machines are in close contact to the dampening form roller and which serve the formation of a stable ink-water-emulsion, which coated roller bodies have a wear-resistant surface the topography of which does not change during the printing machine operation even if inks with many pigments which may have very abrasive effects are processed, and which coated roller bodies permanently maintain a sufficiently high roughness. Furthermore, the invention is intended to provide for a relatively simple and cost-effective method for the manufacturing of such coated roller bodies. 
     SUMMARY OF THE INVENTION 
     The objective of the invention is solved according to claim  1  as well as by the method according to claim  6 . 
     A roller body is made of steel, aluminium or carbon fibre reinforced plastic material, which roller body is in direct contact with a dampening form roller in printing units of wet offset machines for improved ink-water-emulsion formation. A coating is provided made of highly wear-resistant oxide ceramics or of wear-resistant hard metal, wherein pores which are open towards the circumferential surface of the roller body, are provided in a layer matrix of the coating 
     In particular, the roller bodies of steel, aluminium or fibre reinforced plastic materials to be coated, which in wet offset machines are in direct contact with the dampening form roller, are provided with a porous coating made of highly wear-resistant oxide ceramics such as, for example, Al2O3, Cr2O3, TiO2, SiO2 or ZrO2 or mixtures thereof, or made of wear-resistant hard metal such as for example, WC/Co, Cr3C2/NiCr, NiCrBSi, WC/Ni, TiC/Ni, molybdenum, chromium etc., which coating preferably is applied by means of a thermal spraying method and is subsequently ground to size, so that pores in the matrix of the layer are opened. 
     The surfaces produced in this process preferably show roughnesses of 1.0 μm&lt;Rz&lt;500 μm, in particular Rz=5 μm to 25 μm. The thicknesses of the porous coatings according to the invention preferably range from 25 μm to 2000 μm, preferably at about 150 μm. The porous coating according to the present invention made of oxide ceramics or hard metal does not have to be applied by thermal spraying, but may also be applied by means of coating methods such as PVD (Physical Vapour Deposition), CVD (Chemical Vapour Deposition), sintering, enamelling, hot isostatic pressing, electroplating, explosion cladding, build up welding, build up brazing, adhesion methods or reactive processes. If the roller body to be coated is made of fibre reinforced plastic material and the coating process involves a thermal spraying process, it preferably has to be taken into account that a circumferential velocity of at least 0.2 m/s is observed and cooling processes are applied, which keep the fibre reinforced plastic material below 200° C., because otherwise a delamination may occur. 
     These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an emulsification aid in the form of a distributor cylinder. 
         FIG. 2  shows an emulsification aid in the form of a porously coated tandem roller. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  an emulsification aid in the form of a distributor cylinder R designed in the above-described manner is shown, which is positioned below a dampening form roller  1  of a wet offset machine. As is known, an ink-water-emulsion is applied onto a plate cylinder by the dampening form roller  1 . 
       FIG. 2  shows an emulsification aid in the form of a porously coated tandem roller T on the dampening form roller  1 . 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.