Electrostatic inkjet ink composition

An electrostatic inkjet ink composition comprising:

• a non-aqueous solvent having a dielectric constant of from 1.5 to 20 and a surface tension at 25° C. of from 15 to 60 mN/m;
• a color material that is insoluble in the non-aqueous solvent;
• and
• a charge control agent that is soluble in the non-aqueous solvent,
• wherein the charge control agent contains a half-amide maleic acid copolymer containing repeating units represented by the following formulae (Ia′) and (Ib):
• 18
• wherein X2 is a group connecting a main chain and an atomic group L and represents —O—, —CH2OCO—, —OCO—, or —COO—;
• L represents an aliphatic group, provided that a total sum of carbon atoms contained in X2 and L is 12 or more;
• Y, and Y2 may be the same as or different from each other and each represents a hydrogen atom or an alkyl group:
• R1 and R2 may be the same as or different from each other and each represents a hydrogen atom, an aliphatic group, an alicyclic hydrocarbon group, an aromatic group, or a heterocyclic group;
• R1 and R2 may be cyclized with a carbon atom, and the ring containing R1 and R2 may contain a hetero atm;
• and M represents a hydrogen atom, a metal atom, or an ammonium salt or quaternary salt of an organic base.

An electrostatic inkjet ink composition comprising:

• a non-aqueous solvent having a dielectric constant of from 1.5 to 20 and a surface tension at 25° C. of from 15 to 60 mN/m;
• a color material that is insoluble in the non-aqueous solvent;
• and
• a charge control agent that is soluble in the non-aqueous solvent,
• wherein the charge control agent contains a polymer capable of being solubilized in the non-aqueous solvent, which is obtained by reacting a copolymer containing at least one monomer and maleic anhydride as constitutional units with a primary amino compound or a primary amino compound and a secondary amino group which is a polymer containing a half-amide maleic acid component and a maleinimide component as repeating units.

A method for forming an electrostatic inkjet image comprising:

• introducing an ink composition containing a non-aqueous solvent having a dielectric constant of from 1.5 to 20 and a surface tension at 25° C. of from 15 to 60 mN/m, a color material that is insoluble in the non-aqueous solvent, and a charge control agent that is soluble in the non-aqueous solvent and contains a half-amide maleic acid copolymer containing repeating units represented by the following formulae (Ia) and (Ib):
• 19
• wherein X1 represents a hydrocarbon group having 10 or more carbon atoms in total;
• Y1 and Y2 may be the same as or different from each other and each presents a hydrogen atom or an alkyl group;
• R1 and R2 may be the same as or different from each other and each represents a hydrogen atom, an aliphatic group, an alicyclic hydrocarbon group, an aromatic group, or a heterocyclic group;
• R1 and R2 may be cyclized with a carbon atom, and the ring containing R1 and R2 may contain a hetero atom, provided that a total sum of carbon atoms contained in X1, R1, and R2 is 14 or more;
• and M represents a hydrogen atom, a metal atom, or an ammonium salt or quaternary salt of an organic base,
• into a recording head having a plurality of recording electrodes disposed therein;
• applying a voltage to the recording electrodes to allow an electrostatic force to act on the ink, thereby ejecting ink droplets in a state that particles of the color material are concentrated;
• and
• forming print dots on a recording medium disposed opposite thereto.

A method for forming an electrostatic inkjet image comprising:

• introducing an ink composition containing a non-aqueous solvent having a dielectric constant of from 1.5 to 20 and a surface tension at 25° C. of from 15 to 60 mN/m, a color material that is insoluble in the non-aqueous solvent, and a charge control agent which is soluble in the non-aqueous solvent and contains a half-amide maleic acid copolymer containing repeating units represented by the following formulae (Ia′) and (Ib):
• 20
• wherein X2 is a group connecting a main chain and an atomic group L and represents —O—, —CH2OCO—, —OCO—, or —COO—;
• L represents an aliphatic group, provided that a total sum of carbon atoms contained in X2 and L is 12 or more;
• Y1 and Y2 may be the same as or different from each other and each represents a hydrogen atom or an alkyl group;
• R1 and R2 may be the same as or different from each other and each represents a hydrogen atom, an aliphatic group, an alicyclic hydrocarbon group, an aromatic group, or a heterocyclic group;
• R1 and R2 may be cyclized with a carbon atom, and the ring containing R1 and R2 may contain a hetero atom;
• and M represents a hydrogen atom, a metal atom, or an ammonium salt or quaternary salt of an organic base,
• into a recording head having a plurality of recording electrodes disposed therein;
• applying a voltage to the recording electrodes to allow an electrostatic force to act on the ink, thereby ejecting ink droplets in a state that particles of the color material are concentrated;
• and
• forming print dots on a recording medium disposed opposite thereto.

A method for forming an electrostatic inkjet image comprising;

• introducing an ink composition containing a non-aqueous solvent having a dielectric constant of from 1.5 to 20 and a surface tension at 25° C. of from 15 to 60 mN/m, a color material that is insoluble in the non-aqueous solvent, and a charge control agent that is soluble in the non-aqueous solvent, the charge control agent containing a polymer capable of being solubilized in the non-aqueous solvent, which is obtained by reacting a copolymer containing at least one monomer and maleic anhydride as constitutional units with a primary amino compound or a primary amino compound and a secondary amino group and which is a polymer containing a half-amide maleic acid component and a maleinimide component as repeating units, into a recording head having a plurality of recording electrodes disposed therein;
• applying a voltage to the recording electrodes to allow an electrostatic force to act on the ink, thereby ejecting ink droplets in a state that particles of the color material are concentrated;
• and
• forming print dots on a recording medium disposed opposite thereto.