Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2003-01-10
2004-09-14
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108200, C430S137150, C524S105000, C540S129000
Reexamination Certificate
active
06790576
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention and Related Background Art
The present invention relates to a dispersing agent for a pigment (hereinafter often “pigment-dispersing agent”) which is to improve dispersibility of pigments, and a pigment-dispersion composition incorporating the same. The present invention also relates to a toner for developing electrostatic images for image-forming methods, e.g., electrophotography and electrostatic printing, or for forming toner images in a toner-jet type image-forming method, and to a process for producing the same. In particular, the present invention relates to a toner for fixing images formed by the toner on a transfer medium under heating and pressure, and to a process for producing the same.
In processes for producing products, e.g., coating material, ink, toner and formed resin article, a pigment-dispersing agent has been effectively utilized as an additive for finely dividing a pigment and thereby sufficiently realizing its colorant performances (e.g., coloring capacity, transparency and gloss).
A pigment-dispersing agent should satisfy various requirements to fully exhibit its functions, e.g., chemical structure which fast adsorbs a pigment in the molecule, affinity for a solvent and resin which are used to disperse the pigment, and chemical structure which provides steric hindrance to prevent re-agglomeration of the pigment. A phthalocyanine-based pigment and carbon black incorporate a phthalocyanine-based colorant derivative. One type of known pigment-dispersing agents is prepared by mixing a material which can adsorb a pigment with a resin which has affinity for the solvent and resin and can provide steric hindrance, and bonding them to each other by acid-base interactions, in order to make the pigment commonly applicable to a variety of solvents and resins (disclosed in, e.g., Japanese Patent Application Laid-Open No. 06-122835, Japanese Patent Application No. 09-5989 and National Publication No. 2002-514263).
However, when such a two-component pigment-dispersing agent is used, it is necessary to prepare it under conditions which cause no scission of the bond of acidic and basic groups bonding them to each other, and to keep these conditions. When a pigment is dispersed in an aqueous solvent, in particular, sufficient care must be taken for a solvent pH level and a functional group of the resin to be incorporated. Even when they are dissociated from each other, dispersed conditions can be kept to some extent by the actions of a polar group of the phthalocyanine derivative. However, this may cause problems, e.g., re-agglomeration of the pigment or floating of the pigment in the presence of the polar group in the subsequent steps, e.g., drying, molding and polymerization.
Toners for printers and copying machines are composed of toner particles with a binder resin, colorant (e.g., magnetic particles, carbon black, dye or pigment) and wax as the main ingredients, and the toner particles generally have a weight-average particle diameter of 4 to 20 &mgr;m. In general, the toner particles are prepared by melting a mixture of a thermoplastic resin and a colorant to uniformly disperse the colorant in the resin, finely dividing the mixture after it is cooled, and classifying the resultant particles to produce particles of a desired particle diameter. The colorant is uniformly dispersed in the thermoplastic resin by, e.g., kneading or flushing, where a pigment-dispersing agent is expected to increase dispersibility of the pigment, when mixed with the colorant and the thermoplastic resin. However, the pigment-dispersing agent may adversely affect electrification characteristics of the toner particles, because it must be incorporated at 20 to 50% by weight based on the pigment.
Suspension polymerization, which involves no crushing of particles, is proposed for production of toner particles (disclosed in, e.g., Japanese Patent Application Laid-Open No. 05-197193). This process comprises the steps of dissolving or dispersing a colorant, charge control agent and wax in a polymerizable monomer to prepare a polymerizable monomer composition; dispersing the composition in an aqueous solvent containing a dispersion stabilizer with a dispersion apparatus to form polymerizable monomer composition particles in the aqueous solvent; and polymerizing and solidifying the polymerizable monomer in the polymerizable monomer composition to produce toner particles of intended particle diameter and composition. This process, involving no particle crushing step, is expected to bring favorable effects, e.g., energy saving, improved process yield and reduced cost. However, the pigment particles, even when finely dispersed in the polymerizable monomer, may re-agglomerate with each other in the polymerization step, to possibly deteriorate colorant capacity and transparency of the fixed images. Use of a pigment-dispersing agent for the process is considered. However, it tends to adversely affect electrification characteristics of the toner particles, because it must be incorporated at 20 to 50% by weight based on the pigment.
One of the pigment-dispersing agents proposed to solve the above problems has a pigment-adsorbing segment covalently bonded, to a resin material segment which has affinity for the solvent and resin and provides steric hindrance (disclosed in, e.g., Japanese Patent Application Laid-Open No. 2002-226727). When a compound in which a Cu-phthalocyanine skeleton is grafted in a polymer is employed as a dispersing agent, it can exhibit the dispersion effect even in a trace quantity in the pigment, and successfully prevents re-agglomeration of the pigment particles in the polymerization step and keeps electrification characteristics of the toner. However, production of such a pigment-dispersing agent needs a multi-staged synthesis route. Therefore, there are great demands for pigment-dispersing agents which can be produced in high productivity.
Incorporation of Zn-phthalocyanine is also proposed to control a color tone of a cyan pigment (disclosed in, e.g., Japanese Patent Application Laid-Open No. 2000-302993). However, Zn-phthalocyanine, when present alone, can neither prevent re-agglomeration of pigment particles nor improve their affinity for a dispersion medium, even when it is adsorbed on the pigment particle surface. Accordingly, it will bring no effect of dispersing the pigment. Japanese Patent Application Laid-Open No. 2000-302993 also describes that a dispersing agent is incorporated preferably at 5 to 80% by weight based on a pigment. However, pigment-dispersing agents exhibiting the effect in a smaller quantity are in demand.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a dispersing agent for a pigment free of the above problems.
It is another object of the present invention to provide a dispersing agent for a pigment capable of finely dispersing, in a smaller quantity, pigment particles in a dispersion medium.
It is another object of the present invention to provide an inexpensive dispersing agent for a pigment not involving a multi-staged synthesis route.
It is still another object of the present invention to provide a pigment-dispersion composition capable of keeping pigment particles stably dispersed in various production steps after the pigment is incorporated in the raw material.
It is still another object of the present invention to provide a toner in which a pigment can be finely dispersed in the toner particles and which is excellent in coloring capacity and transparency, and a process for producing the same.
It is still another object of the present invention to provide a toner free of colorant floating on a toner particle surface and excellent in electrification characteristics and environmental stability, and a process for producing the same.
The present invention relates to a dispersing agent for a pigment comprising at least
a metallic compound having a structure represented by the general formula (I):
(wherein, X
1
to X
4
are each independently a nitrogen atom or C—R (R is a hy
Fujimoto Norikazu
Itabashi Hitoshi
Canon Kabushiki Kaisha
Chapman Mark A.
Fitzpatrick ,Cella, Harper & Scinto
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