Radiation curable ink and preparation method and image forming method using the same

Abstract

A radiation-curable ink including, (a) a colorant dispersion containing a pigment and a diluent, the pigment being present in an amount of 20 to 95 weight % based on the total weight of the colorant dispersion; (b) a polymerizable compound; and (c) a polymerization initiator, wherein the radiation-curable ink has a viscosity of 6 to 500 mPa·s measured at 25° C. and comprises water in an amount of not more than 2.5 weight % based on the total weight of the radiation-curable ink measured with Karl Fisher method.

What is claimed is:  
     
         1 . A radiation-curable ink comprising: 
 (a) a colorant dispersion containing a pigment and a diluent, the pigment being present in an amount of 20 to 95 weight % based on the total weight of the colorant dispersion;    (b) a polymerizable compound; and    (c) a polymerization initiator, 
 wherein the radiation-curable ink has a viscosity of 6 to 500 mpa·s measured at 25° C. and comprises water in an amount of not more than 2.5 weight % based on the total weight of the radiation-curable ink measured with Karl Fisher method.  
   
     
     
         2 . The radiation-curable ink of  claim 1 , comprising water in an amount of not more than 1.5 weight % based on the total weight of the radiation-curable ink measured with Karl Fisher method.  
     
     
         3 . The radiation-curable ink of  claim 1 , further comprising a polymerization inhibitor capable of preventing the polymerizable compound from photo-polymerizing or thermo-polymerizing.  
     
     
         4 . The radiation-curable ink of  claim 1 , wherein an acid value of each of the diluent, the polymerizable compound and the polymerization initiator is at most 10.  
     
     
         5 . The radiation-curable ink of  claim 1 , further comprising an amino compound as a polymerization accelerator.  
     
     
         6 . The radiation-curable ink of  claim 3 , wherein the polymerization inhibitor is contained in the colorant dispersion.  
     
     
         7 . A method for producing a radiation-curable ink, comprising the steps of: 
 (a) adding a pigment to a diluent containing at least one component selected from the group consisting of a resin, a dispersant and a first polymerizable compound in a vessel to obtain a pigment mixture, a weight ratio of the pigment being 20 to 95 weight % based on the total weight of the pigment mixture;    (b) dispersing the pigment mixture to obtain a colorant dispersion;    (c) adding a second polymerizable compound and a polymerization initiator to the colorant dispersion to obtain a radiation-curable ink precursor, provided that the first polymerizable compound and the second polymerizable compound may be the same or different with each other;    (d) adjusting a content of water in the radiation-curable ink precursor to be not more than 2.5 weight % based on the total weight of the radiation-curable ink precursor; and    (e) dispersing the radiation-curable ink precursor to obtain a radiation-curable ink having a viscosity of 6 to 500 mPa·s measured at 25° C.    
     
     
         8 . The method for producing a radiation-curable ink of  claim 7 , wherein the diluent used in the step (a) comprises a polymerizable monomer or a polymerizable oligomer.  
     
     
         9 . The method for producing a radiation-curable ink of  claim 7 , wherein a polymerization inhibitor is further added in the step (a).  
     
     
         10 . The method for producing a radiation-curable ink of  claim 9 , wherein the polymerization inhibitor is a phenol derivative comprising a carbon-carbon double bond derived from an acrylic acid.  
     
     
         11 . The method for producing a radiation-curable ink of  claim 7 , wherein the step (d) is carried out by applying heat to the radiation-curable ink precursor or by subjecting the radiation-curable ink precursor under a reduced pressure so as to reduce water.  
     
     
         12 . A method for forming a cured image, comprising the steps of: 
 (a) jetting droplets of the radiation-curable ink of  claim 1  on an ink-jet printing sheet with an ink-jet printer so as to form an image; and    (c) irradiating an actinic ray on a surface of the ink- jet sheet to such an extent that the image formed with the radiation-curable ink is cured to form the cured image.