Liquid developing agent and process for producing the same

Abstract

A liquid developing agent for electrophotography or electrostatic recording that can realize a high solid content and has excellent developing properties is characterized in that colored chips produced by heat kneading a pigment with a thermoplastic resin are dispersed by wet pulverization in an electrically insulating hydrocarbon solvent containing at least one pigment dispersant selected from the group consisting of specific modified novolak resins (A) having an aromatic ring and a ring opened structure of an epoxy group by a hydroxycarboxylic acid-derived carboxyl group, and copolymers (B).

1 . A liquid developing agent where a colored chip obtained by heat kneading a pigment with a thermoplastic resin is dispersed by wet pulverization in an electrically insulating hydrocarbon solvent dissolving at least one pigment dispersant selected from the group consisting of the following modified novolak resin (A) and copolymer (B) having an aromatic ring and a ring-opened structure of an epoxy group by a hydroxycarboxylic acid-derived carboxyl group:
 Modified novolak resin (A): a modified novolak resin having a novolak resin-derived aromatic ring and at least one group shown by a general formula (1) by ring-opening of an epoxy group by a hydroxycarboxylic acid-derived carboxyl group:   
     
       
         
         
             
             
         
       
       wherein an oxygen atom at the far left is derived from an oxygen atom contained in an aromatic hydroxyl group of a novolak resin, W 1  and X 1  each independently represent a divalent hydrocarbon group with carbon numbers of 1 to 19, i and j each independently represent an integer of i=1 to 30 and j=0 to 30, and R 1  represents a hydrogen atom or a methyl group. 
       Copolymer (B): a copolymer with a weight-average molecular weight of 3000 to 100000, having, in said copolymer, the amount corresponding to at least 10 mol % of the recurring unit shown by a general formula (2), and the amount corresponding to at least 10 mol % of at least one kind selected from the recurring units shown by a general formula (3) and a general formula (4): 
     
     
       
         
         
             
             
         
       
       wherein W 2  and X 2  each independently represent a divalent hydrocarbon group with carbon numbers of 1 to 19, p and q each independently represent an integer of p=1 to 30, and q=0 to 30, R 2 , R 3  and R 4  each independently represent a hydrogen atom or a methyl group, R 5  represents a hydrogen atom or a halogen atom, R 6  and R 7  each independently represent a hydrogen atom, a hydrocarbon group with carbon numbers of 1 to 5, an alkoxy group with carbon numbers of 1 to 5, an aryloxy group with carbon numbers of 6 to 10, or a halogen atom, R 8  represents a hydrogen atom or a methyl group, and R 9  represents a direct bond or a methylene group. 
     
   
   
       2 . The liquid developing agent of  claim 1 , wherein the concentration of the total solid content in a liquid developing agent was 13 to 50% by mass. 
   
   
       3 . The liquid developing agent of  claim 1 , wherein the composition of the pigment dispersant is 2 to 100 parts by mass relative to 100 parts by mass of the colored chip. 
   
   
       4 . The liquid developing agent of  claim 1 , wherein said electrically insulating hydrocarbon solvent is a high boiling point paraffin solvent. 
   
   
       5 . A process for producing the liquid developing agent of  claim 1 , wherein the colored chip obtained by heat kneading a pigment with a thermoplastic resin is subjected to dry pulverization into a coarse pulverized powder beforehand, further, said coarse pulverized powder is subjected to wet pulverization in an electrically insulating hydrocarbon solvent dissolving at least one pigment dispersant selected from the group consisting of said modified novolak resin (A) and said copolymer (B). 
   
   
       6 . The liquid developing agent of  claim 1 , wherein the concentration of the total solid content in a liquid developing agent has 13 to 50% by mass, and wherein the composition of the pigment dispersant is 2 to 100 parts by mass relative to 100 parts of mass of the colored chip. 
   
   
       7 . The liquid developing agent of  claim 6 , wherein said electrically insulating hydrocarbon solvent is a high boiling point paraffin solvent. 
   
   
       8 . The liquid developing agent of  claim 1 , wherein the composition of the pigment dispersant is 2 to 100 parts by mass relative to 100 parts by mass of the colored chip, and wherein said electrically insulating hydrocarbon solvent is a high boiling point paraffin solvent.