Plate for offset printing and method for manufacturing said plate

Abstract

The plate includes an electrochemically anodisable metallic support of a thickness of 0.1-0.6 mm, carrying on one of its side a ceramic film of multilayer structure. The plate has greater hydrophillicity, resistance to chemical oxidation and to mechanical abrasion, and a lower surface tension that those of the prior art. The method comprises a first step in a bath containing sodium, potassium, ammonium or calcium borates, chlorides, carbonates and/or nitrates or forming mixed salts with elements of groups IIIB, IVB and VB, in a proportion of 5-40% by weight in relation to the total of the solution, at 20-60° C., 5-20 kC/m 2 and 50-250 V; and a second step in a bath containing sodium, potassium or lithium phosphates, silicates and/or carbonates, in a proportion of 1-35% by weight in relation to the total of the solution, at 20-70° C., 5-25 kC/m 2 and 150-400 V.

1 . Plate for wet-process offset printing characterized in that it comprises an electrochemically anodisable metallic support with a thickness of between 0.1 mm and 0.6 mm, with at least one of its sides supporting a ceramic film of multi-layer structure which includes: 
 (i) a first layer formed by a chemical structure derived from one or more of the following refractory oxides: SiO 2 , Al 2 O 3 , TiO 2 , HfO 2 , BeO and ZrO 2 , said first layer having a thickness of between 20 nm and  2 μm;      (ii) a second layer formed by the combination of at least one of the refractory oxides described in (i) with carbonates and/or nitrides of elements of groups IIIB, IVB and IIIA of the periodic table, said second layer having a thickness of between 0.1 μm and 3 μm;    (iii) a third layer formed by the combination of one or more silicates of the elements of groups IA, IIA, IIIA and IVB of the periodic table, said third layer having a thickness of between 0.5 μm and 10 μm;    (iv) a fourth layer formed by oxides and/or carbonates of groups IVB and VB of the periodic table, said fourth layer having a thickness of between 50 and 600 nm; and    (v) a fifth layer formed by sulphates, carbonates, nitrates, phosphates and/or silicates of groups IA and IIA of the periodic table, said fifth layer having a thickness of between 10 and 500 nm.    
     
     
         2 . Plate for printing according to  claim 1 , characterised in that said electrochemically anodisable metallic support is selected from a sheet or strip of aluminium, zirconium, aluminised steel, titanium or other electrochemically anodisable surface.  
     
     
         3 . Plate for printing according to  claim 2 , characterised in that said electrochemically anodisable support is a sheet or strip of aluminium with a degree of purity not less than 80%.  
     
     
         4 . Plate for printing according to  claim 1 , characterised in that said multilayer structure has the following limits of thicknesses and composition: 
 (i) from 100 to 500 nm basically composed of aluminium oxide;    (ii) from 1 to 3 μm which comprises at least 5% zirconium;    (iii) from 1 to 4 μm composed of silicon oxide and silicates of the elements of groups IA, IIA, IIIA or IVB of the periodic table;    iv) from 200 to 600 nm composed of zirconium oxide and/or carbonate;    (v) from 100 to 300 nm composed of acid phosphates of alkaline elements.    
     
     
         5 . Method for manufacturing a plate for wet-process offset printing characterised in that the ceramicisation of an electrochemically anodisable metallic support is carried out in an electrolytic treatment in two steps: 
 (i) a first step in a bath which comprises sodium, potassium, ammonium or calcium borates, chlorides, carbonates and/or nitrates or forming mixed salts with elements of groups IIIB, IVB and VB of the periodic table, in a proportion of between 5 and 40% by weight in relation to the total of the solution, at a temperature of between 20 and 60° C. with a surface density of charge between 5 and 20 KC/m 2  and at a maximum voltage of between 50 and 250 V; and    (ii) a second step in a bath which comprises sodium, potassium or lithium phosphates, silicates and/or carbonates in a proportion of between 1 and 35% by weight in relation to the total of the solution, at a temperature of between 20 and 70° C. with a surface density of charge between 5 and 25 KC/m 2  and at a maximum voltage of between 150 and 400 V.    
     
     
         6 . Method according to  claim 5 , characterised in that in said first step the compounds are in a proportion of between 10 and 30% by weight in relation to the total of the solution.  
     
     
         7 . Method according to  claim 5 , characterised in that in said second step the compounds are in a proportion of between 3 and 30% by weight in relation to the total of the solution.  
     
     
         8 . Method according to  claim 5 , characterised in that said first step is carried out in direct current at a maximum voltage of between 80 and 150 V.  
     
     
         9 . Method according to  claim 5 , characterised in that said second step is carried out in direct current at a maximum voltage of between 180 and 400 V.  
     
     
         10 . Method according to  claim 5 , characterised in that a sealing treatment is then carried out in a bath formed by dissolution of sodium, potassium, ammonium phosphates, silicates and/or carbonates of elements of groups IIIA, IVB and/or VB of the periodic table at a concentration of between 1 and 50% by weight in relation to the total of the solution and at temperature between 10 and 50° C.  
     
     
         11 . Method according to  claim 10 , characterised in that said compounds are present in a concentration between 5 and 30% by weight in relation to the total of the solution.  
     
     
         12 . Method according to  claim 10 , characterised in that said sealing treatment is carried out at temperature between 20 and 40° C.  
     
     
         13 . Method according to claims  5  and  10 , characterised in that a neutralising treatment is then carried out which comprises washing the plate with an aqueous solution of an acid or mixture of several acids selected from among the following: acetic acid, oxalic acid, phosphoric acid, citric acid and/or lactic acid, preferably phosphoric acid and/or citric acid in a concentration of between 1 and 40% by weight in relation to the total of the solution and at a temperature between 10 and 50° C.  
     
     
         14 . Method according to  claim 13 , characterised in that said acid or mixture of acids is selected from between acetic acid, oxalic acid, phosphoric acid, citric acid and/or lactic acid at a concentration between 5 and 30% by weight in relation to the total weight of the solution.  
     
     
         15 . Method according to  claim 14 , characterised in that said acid is selected from between phosphoric acid and/or citric acid.  
     
     
         16 . Method according to  claim 13 , characterised in that said neutralization treatment is carried out at a temperature between 20 and 40° C.  
     
     
         17 . Method according to  claim 5 , characterised in that organic or inorganic salts are added in each of the steps, preferably sulphates and/or acid phosphates of alkaline elements in order to reduce the maximum operating voltage.  
     
     
         18 . Method according to  claim 5 , characterised in that the method of ceramicisation is carried out using pulsing direct current.  
     
     
         19 . Method as claimed in any of  claims 5  to  18 , characterised in that said electrochemically anodisable support to be ceramicised is submitted to rising electrical voltages when said support travels though the treatment tank.