Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-02-06
2004-02-10
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137150
Reexamination Certificate
active
06689525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dispersing agent for a pigment (hereinafter often “pigment-dispersing agent”) which is to improve the dispersibility of a pigment in the process of producing coating materials, inks, toners or resin molded products, and a pigment-dispersion composition which contains the dispersing agent. This invention also relates to a toner for forming a toner image in an image-forming process such as electrophotography or electrostatic printing or a image-forming process carried out by a toner-jet method, and a process for producing such a toner.
2. Related Background Art
In the manufacture of coating materials, inks, toners or resin molded products, pigment-dispersing agents have effectively been utilized as additives for making pigments have small particle diameter so as to sufficiently bring out the performance required as coloring materials (such as coloring power, transparency and luster).
In order for a pigment-dispersing agent to exhibit its function, the agent is required to have a chemical structure that it is strongly adsorptive on the pigment in the molecule and a chemical structure that it has affinity for mediums, solvents and resins used in dispersing the pigment and can be a steric hindrance for preventing re-agglomeration of the pigment. As a dispersing agent for phthalocyanine pigments or carbon black, a derivative of phthalocyanine coloring matter is used. In order to make the pigment have general-purpose properties for various mediums, solvents and resins, it is common to separately add an agent having adsorptivity on the pigment and a resin material which has affinity for mediums, solvents and resins and can be a steric hindrance, and make these combine with each other by acid-base mutual action to bring out the function as the pigment-dispersing agent.
However, when such a two-component type dispersing agent is used, it is necessary to prepare a pigment-dispersion composition under such conditions that the bond attributable to the acid-base which keeps the both combined with each other does not break. Especially when the pigment is dispersed in an aqueous medium, attention must be paid also to the pH of water or mediums and the functional group of the resin to be added. Even when the pigment is dispersed in the state the both have dissociated, the state of dispersion to a certain extent can be achieved on account of the action of polar groups of a phthalocyanine derivative. It, however, may come into question that the pigment re-agglomerates in post steps of drying, shaping, polymerization reaction and so forth or that the pigment migrates to particle surfaces because of the presence of polar groups.
Meanwhile, toner particles used in printers and copying machines are fine particles formed chiefly of (i) a resin, (ii) a colorant such as a magnetic material, carbon black, a dye or a pigment and (iii) a wax, and have particle diameters usually ranging from 6 to 30 &mgr;m. Toner particles are commonly produced by mixing and melting a colorant comprised of a dye or pigment or a magnetic material in a thermoplastic resin to disperse the colorant uniformly in the thermoplastic resin, followed by fine pulverization and classification to obtain toner particles having a desired particle diameter. This method is relatively stable as a technique, and enables relatively easy management of materials and production steps. Since, however, the particle diameter of toner particles depends on the mechanical pulverization of resins, an attempt to make their particle diameter small to an average particle diameter of 6 &mgr;m or less results in a low yield. This is because, in view of an attribute that the charge quantity increases with a decrease in particle diameter when a toner having toner particles is electrostatically charged by means of a triboelectric charging member, its particle size distribution must be made sharp in order for the toner to be uniformly charged and this makes it necessary to remove finer power and coarse powder in a large quantity in the step of classification.
In recent years, as a method having overcome the above problem, a method of producing toner particles by polymerization (e.g., a method of producing toner particles by suspension polymerization) is proposed. Such a method is disclosed in, e.g., Japanese Patent Publication No. 36-10231 and No. 51-14895 and Japanese Patent Application Laid-open No. 53-17735, No. 53-17736 and No. 53-17737. This method is a method in which materials to be included into toner particles, such as a colorant (e.g., a magnetic material or carbon black), a charge control agent and a release agent (e.g., a wax) are dissolved or dispersed in a polymerizable monomer optionally together with a polymerization initiator and a dispersing agent to prepare a polymerizable composition, which is then dispersed in an aqueous medium containing a dispersion stabilizer, by means of a dispersion apparatus to form fine particles, and the polymerizable monomer in the fine particle is polymerized and then solidified to obtain toner particles having any desired particle diameter and composition. This method has not any pulverization step, and is expected to bring about the effect of energy saving, improvement in process yield and cost reduction. On the other hand, depending on production conditions such as the state of stirring and the size of production scale, toner particles whose particle size distribution has varied to have a relatively broad particle size distribution are obtained in many cases, and the step of classification must be carried out in many cases in order to regulate them to have a desired particle size distribution required to obtain high-quality and highly minute toner images.
As a method of producing toner particles by dispersion polymerization promising much sharper particle size distribution, a method is available which makes use of dispersion polymerization proposed in Japanese Patent Publication No. 6-17073 and Japanese Patent Application Laid-open No. 61-18965, No. 61-18966, No. 61-228458 and No. 62-73276. This is a method of producing toner particles with uniform particle size distribution by initiating polymerization reaction by heat or light, from a uniform system in which a polymeric dispersing agent, a polymerizable monomer, a polymerization initiator, a colorant, a charge control agent and so forth have been dissolved or dispersed, to form those which serve as nuclei of toner particles, and allowing the particles to grow individually. The dispersion polymerization is regarded as a reliable method of producing monodisperse particles of about 1 to 10 &mgr;m in particle diameter. Because of their very sharp particle size distribution, a toner having such toner particles can also have a sharp charge quantity distribution, and, compared with those produced by other methods, has superior dot reproducibility in development, fidelity of transfer and fixing performance. The dispersion polymerization, however, has a problem that, when used as a method of producing toner particles, the colorant such as a pigment, which tends to be insoluble in the reaction system, may enter the interiors of particles with difficulty.
In recent years, in order to overcome this problem, it is proposed in Japanese Patent No. 2,633,383 (corresponding to U.S. Pat. No. 5,124,226) to treat the surfaces of pigment particles so that the pigment can be incorporated into the toner particles with ease. According to this publication, it is disclosed that toner particles with uniform particle diameter which contain the pigment in the interiors of toner particles can be obtained using as a pigment-dispersing agent a compound having radical-polymerizable groups. In reality, however, the situation is that the pigment can slightly be incorporated into the toner particles. Accordingly, it is sought to further incorporate the pigment into toner particles to more improve coloring efficiency.
In addition, where toner particles are colored in the conventional method, the pigment is incorpo
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