Electrophotographic paper and method for manufacturing thereof

Abstract

Electrophotographic paper and a method for its production, according to which method a cellulose pulp is slushed, a filler is mixed with the slush, and the slush is formed in the paper machine into a web, which is dried. According to the invention, bivalent or trivalent cations in an amount of at least 0.1% of the dry weight of the pulp are attached to the acid groups of the cellulose pulp before the forming of the web. Thereby a paper web is obtained the surface charge of which is at least approximately 600 V when relative humidity is 40%. The surface charge of the paper according to the invention remains stable within a wide humidity range. For this reason, when the paper according to the invention is used, the need for drying the paper in the printing press is significantly reduced.

1 . An electrophotographic paper which comprises a fibrous paper web formed from a cellulose pulp, characterized in that it contains, in an amount of at least 0.1% of the dry weight of the pulp, bivalent or trivalent ions bonded to the acid groups of the cellulose pulp, in which case the surface charge of the paper web is at least approximately 600 V when relative humidity is 40%.  
     
     
         2 . The paper according to  claim 1 , characterized in that the ions bonded to the acid groups are calcium, magnesium or aluminum ions or a mixture thereof.  
     
     
         3 . The paper according to  claim 1  or  2 , characterized in that the amount of the calcium, magnesium or aluminum bonded to the acid groups is approximately 0.15-0.5% of the dry weight of the fibers.  
     
     
         4 . The paper according to any of claims  1 - 3 , characterized in that the surface charge of the paper is at least 610 V when relative humidity is 40%.  
     
     
         5 . The paper according to any of the preceding claims, which paper contains calcium as the counter-ion for acid groups, characterized in that the change in the surface charge of the paper is at maximum ±25% when relative humidity is 20-50%.  
     
     
         6 . The paper according to any of the preceding claims, characterized in that the cellulose pulp is a chemical hardwood pulp that contains hemicellulose compounds over 10% of the dry weight of the pulp.  
     
     
         7 . The paper according to  claim 6 , characterized in that the cellulose pulp is birch sulfate pulp.  
     
     
         8 . The paper according to any of the preceding claims, characterized in that the bivalent or trivalent ions are mainly bonded to methylglucuronic acid or hexenuronic acid groups.  
     
     
         9 . The paper according to any of the preceding claims, characterized in that the cellulose pulp contains, in an amount of approximately 0.1-20% of the weight of the pulp, a cellulose derivative having a bivalent or trivalent counter-ion.  
     
     
         10 . The paper according to  claim 9 , characterized in that the cellulose pulp contains a calcium-form carboxymethyl cellulose.  
     
     
         11 . The paper according to any of the preceding claims, characterized in that it contains a filler 1-40%, preferably approximately 5-30%, of the weight of the cellulose pulp.  
     
     
         12 . The paper according to  claim 11 , characterized in that the filler is kaolin or precipitated or ground calcium carbonate.  
     
     
         13 . The paper according to any of the preceding claims, characterized in that on the surface of the paper web there is a coating pigment layer.  
     
     
         14 . The paper according to  claim 13 , characterized in that the pigment is calcium carbonate, kaolin, gypsum, talc, chalk and/or a mixture thereof.  
     
     
         15 . The paper according to any of the preceding claims, characterized in that the grammage of the paper is 50-180 g/m 2  and it contains coating approximately 0-30 g/m 2  of surface.  
     
     
         16 . A method for the production of an electrophotographic paper from a cellulose pulp, according to which process 
 the cellulose pulp is slushed,    a filler is mixed with the slush, and    the slush is formed in the paper machine into a web, which is dried, characterized in that    bivalent or trivalent cations in an amount of at least 0.1% of the dry weight of the pulp are attached to the acid groups of the cellulose pulp before the forming of the web.    
     
     
         17 . The method according to  claim 16 , characterized in that the cellulose pulp used is a chemical pulp made from hardwood.  
     
     
         18 . The method according to  claim 16  or  17 , characterized in that the cellulose pulp used is birch sulfate pulp.  
     
     
         19 . The method according to any of claims  16 - 18 , characterized in that the bivalent or trivalent cations are attached to the acid groups of the cellulose pulp by ion exchange.  
     
     
         20 . The method according to  claim 19 , characterized in that the bivalent or trivalent cations are attached to the acid groups by contacting the cellulose pulp with an aqueous solution of a salt comprising bivalent or trivalent cations, in conditions wherein the salt is at least in part in a dissociated form.  
     
     
         21 . The method according to  claim 20 , characterized in that calcium ions are attached to the acid groups by adding to an aqueous suspension of the cellulose pulp a calcium salt so that the hardness of the water rises to 10 dH°.  
     
     
         22 . The method according to any of claims  16 - 21 , characterized in that the bivalent or trivalent ions are attached to the acid groups of the cellulose pulp before retention chemicals, cationic polymers and/or fillers are added to the cellulose pulp.  
     
     
         23 . The method according to any of claims  16 - 22 , characterized in that the cellulose pulp used is a recycled chemical pulp.  
     
     
         24 . The method according to any of claims  16 - 23 , characterized in that a cellulose derivative having a bivalent or trivalent counter-ion is applied to the paper web in an amount of 0.1-20% of the weight of the cellulose pulp.  
     
     
         25 . The method according to  claim 24 , characterized in that the cellulose derivative comprises a calcium-form carboxymethyl cellulose.  
     
     
         26 . The method according to any of claims  16 - 25 , characterized in that a filler is added to the slush in an amount of approximately 1-40%, preferably approximately 5-30%, of the weight of the cellulose pulp.  
     
     
         27 . The method according to  claim 26 , characterized in that the filler used is kaolin or precipitated or ground calcium carbonate.  
     
     
         28 . The use, as the print medium for printed matter to be produced by electrophotographic, a paper web made up of a cellulose pulp that contains, in an amount of at least 0.1% of the dry weight of the fibers of the cellulose pulp, bivalent or trivalent ions bonded to the acid groups of the cellulose pulp, in which case the surface charge of the paper web is at least approximately 600 V when relative humidity is 40%.  
     
     
         29 . The use according to  claim 28 , characterized in that the bivalent or trivalent ions are calcium, magnesium or aluminum, or a mixture thereof.