Crosslinked core/shell polymer particles

Abstract

The present invention relates to crosslinked core/shell polymer particles containing a pigment which are usable in a water-based ink for ink-jet printing and exhibit excellent optical density and gloss and are prevented from suffering from occurrence of bronzing, wherein the polymer particles each include a core portion and a shell portion which are respectively made of a crosslinked polymer, and a weight ratio of the pigment to the pigment-containing crosslinked core/shell polymer particles [(weight of the pigment/weight of the pigment-containing crosslinked core/shell polymer particles)×100] is from 25 to 75. The present invention further relates to a water dispersion and a water-based ink for ink-jet printing which contain the crosslinked core/shell polymer particles and a process for producing crosslinked polymer particles.

1 . Crosslinked core/shell polymer particles containing a pigment, wherein the polymer particles each comprise a core portion and a shell portion which are respectively made of a crosslinked polymer, and a weight ratio of the pigment to the pigment-containing crosslinked core/shell polymer particles [(weight of the pigment/weight of the pigment-containing crosslinked core/shell polymer particles)×100] is from 25 to 75.  
     
     
         2 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the shell portion of the crosslinked core/shell polymer particles has a crosslinking degree of from 0.5 to 15% by weight.  
     
     
         3 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the core portion of the crosslinked core/shell polymer particles has a crosslinking degree of from 0.5 to 15% by weight.  
     
     
         4 . The crosslinked core/shell polymer particles according to  claim 1 , wherein a weight ratio of the core portion to the shell portion of the crosslinked core/shell polymer particles (core portion/shell portion) is from 0.3 to 3.  
     
     
         5 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the pigment is a cyan pigment.  
     
     
         6 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the core portion of the crosslinked core/shell polymer particles is made of a polymer obtained by polymerizing a crosslinkable monomer containing at least two reactive unsaturated groups in a molecule thereof with a hydrophobic monomer.  
     
     
         7 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the shell portion of the crosslinked core/shell polymer particles is made of a polymer obtained by crosslinking a polymer produced by copolymerizing a monomer mixture containing (a) a salt-forming group-containing monomer and (b) a macromer, and/or (c) a hydrophobic monomer, with a crosslinking agent containing at least two reactive functional groups in a molecule thereof.  
     
     
         8 . The crosslinked core/shell polymer particles according to  claim 1 , wherein the crosslinked core/shell polymer particles are produced through the following steps (1) to (3): 
 Step (1): mixing pigment-containing polymer particles, a crosslinkable monomer containing at least two reactive unsaturated groups in a molecule thereof, and a hydrophobic monomer with each other to incorporate at least a part of the crosslinkable monomer and the hydrophobic monomer into the pigment-containing polymer particles;    Step (2): polymerizing the crosslinkable monomer with the hydrophobic monomer to obtain core/shell polymer particles having a crosslinked core portion; and    Step (3): reacting the core/shell polymer particles having the crosslinked core portion which is obtained in the step (2), with a crosslinking agent containing at least two reactive functional groups in a molecule thereof.    
     
     
         9 . A water dispersion comprising the crosslinked core/shell polymer particles as defined in  claim 1  or  8 .  
     
     
         10 . The water dispersion according to  claim 9 , further comprising a water-insoluble organic compound.  
     
     
         11 . A water-based ink for ink-jet printing comprising the water dispersion as defined in  claim 9  or  10 .  
     
     
         12 . A process for producing crosslinked polymer particles containing a pigment, wherein a weight ratio of the pigment to the pigment-containing crosslinked polymer particles [(weight of the pigment/weight of the pigment-containing crosslinked polymer particles)×100] is from 25 to 75, comprising the following steps (1) to (3): 
 Step (1): mixing pigment-containing polymer particles, a crosslinkable monomer containing at least two reactive unsaturated groups in a molecule thereof, and a hydrophobic monomer with each other to incorporate at least a part of the crosslinkable monomer and the hydrophobic monomer into the pigment-containing polymer particles;    Step (2): polymerizing the crosslinkable monomer with the hydrophobic monomer to obtain polymer particles; and    Step (3): reacting the polymer particles which are obtained in the step (2), with a crosslinking agent containing at least two reactive functional groups in a molecule thereof.