Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-03-30
2003-12-02
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108400, C430S109300, C430S109400, C430S110300
Reexamination Certificate
active
06656654
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner and a two-component developer for use with an image forming process such as an electrophotographic process or electrostatic printing process. The present invention also relates to a container filled with the above-mentioned toner or two-component developer, and an image forming apparatus equipped with the aforementioned container.
2. Discussion of Background
Various electrophotographic image forming methods are described, for instance, in U.S. Pat. No. 2,297,691 and Japanese Patent Publications No. 49-23910 and No. 43-24748. Generally, in such image forming methods, latent electrostatic images are formed on the surface of a photoconductor by making use of the characteristics of a photoconductive material employed in the photoconductor. The latent electrostatic images are then developed with a toner to obtain visible toner images, which are transferred to a transfer sheet such as a sheet of paper when necessary and fixed thereon by the application of heat and/or pressure, or a vapor of a solvent. Image-bearing copies are thus made.
The methods of developing the latent electrostatic images can be roughly classified into two methods.
One method is a liquid development method which uses a liquid developer prepared by finely dispersing various kinds of pigments or dyes in an electrical insulating organic solvent.
The other method is a dry development method in which a dry toner comprising a natural or synthetic resin and a coloring agent such as carbon black dispersed in the resin is employed. More specifically, the dry development method includes cascade development, magnetic brush development, powder cloud development, and the like. The dry development method has been widely adapted in recent years.
For fixing the toner images on the transfer sheet, a heat roller image fixing method is in general use because of its excellent energy efficiency. By this image fixing method, a heat roller is directly brought into pressure contact with a toner image deposited on the transfer sheet.
In consideration of the environmental protection from the viewpoint of energy saving, there is a demand for reduction in the electric consumption necessary for the heat roller to complete the image fixing operation. Various improvements in an image fixing unit have been made to satisfy the above-mentioned demand. For instance, it is proposed to reduce the thickness of a heat roller which comes in contact with the toner image. This proposal shows a noticeable improvement in heat energy efficiency and a drastic curtailment of time required to raise the temperature of the heat roller to a predetermined temperature. However, in this case, the specific heat capacity of the heat roller becomes so small that the temperature on the surface of the heat roller largely varies depending on whether a portion of the heat roller passes through a transfer sheet or not. Thus, a toner image on the transfer sheet is melted by the contact with a heated portion of the roller and the melted toner readily adheres to the surface of the image fixing roller. The melted toner adhering to the heat roller is again transferred back to a non-image portion of the transfer sheet while the heat roller is rotating over the transfer sheet. The so-called hot-offset phenomenon occurs in this manner. The requirements for toner have become more severe in order to prevent the occurrence of the above-mentioned hot-offset phenomenon.
In recent years, there is a tendency that the thermal energy applied to the toner images at the image fixing step becomes smaller to achieve image fixing at lower temperatures in light of energy saving or to accomplish high-speed copying operation. To cope with the image fixing at lower temperatures, various resins and waxes with low softening points have been adapted in the preparation of toner compositions.
The addition of a wax as a release agent to the toner composition or the use of a polyester resin which can be fixed at lower temperatures has been investigated to satisfy both the low-temperature image fixing and anti-hot-offset performance. For example, a toner comprising two kinds of linear polyester resins is disclosed in Japanese Laid-Open Patent Applications 63-225244, 63-225245, and 63-225246. However, this toner cannot apply to a wide-range of image forming process speeds, that is, from a low speed to a high speed. Further, toner compositions disclosed in Japanese Laid-Open Patent Applications 3-188468 and 9-204071 comprise polyester resins, of which the acid value, hydroxyl number, molecular weight distribution, or tetrahydrofuran-insoluble content is specified. However, further improvement is required in order to satisfy all the requirements, that is, the low-temperature image fixing performance, anti-hot-offset performance, and blocking resistance.
To solve the above-mentioned problems, it is proposed that a chelate compound having salicylic acid or oxysalicylic acid as a ligand be used as a charge control agent for use in a toner composition. Japanese Laid-Open Patent Application 62-145255 and Japanese Patent Publication 55-42752 disclose metal complex salts of salicylic acid derivatives as the charge control agents. However, those metal complexes may produce environmental problems because they have heavy metals such as chromium (Cr) and cobalt (Co).
In consideration of environment, investigation of a salicylic acid derivative having as a central metal iron (Fe) instead of the above-mentioned heavy metal such as chromium (Cr) has been proceeding. Japanese Laid-Open Patent Application 1-309072 describes that the effect can be obtained only when a metal complex of a salicylic acid derivative having carboxyl group or sulfoxyl group as a substituent is used as the charge control agent.
A toner composition disclosed in Japanese Laid-Open Patent Application 9-325520, of which thermal characteristics are specified, comprises a resin with a specific structure and an organic metallic compound. In this application, the valence number of the employed metal for use in the metallic compound is not particularly limited. Even though this toner is employed for image formation, the effect of preventing the hot-offset phenomenon is still unsatisfactory.
Japanese Laid-Open Patent Applications 7-230188 and 10-10785 exhibit an effect obtained only by the combination of a specific resin and an iron complex compound having an oxycarboxylic acid as a ligand.
According to the above-mentioned applications, an effect can be exhibited only when an iron complex compound of salicylic acid having a specific structure is employed in a toner composition, or the combination of a particular resin and an iron complex of salicylic acid is used in a toner composition. According to the above-mentioned applications, it is unclear whether such an effect can be obtained or not unless the substituent for the iron complex compound of salicylic acid is limited to carboxyl group or sulfoxyl group, or unless the structure of the resin to be used together with the iron complex of salicylic acid is specifically limited. It is impossible to expect the dispersion properties in a resin and the charging characteristics of a charge control agent in the form of a metal complex compound so long as the ligand of the metal complex is different.
In recent years, there is a tendency for the toner particle size to decrease in line with the demand for high quality copy image. A decrease in particle size of toner causes various problems although the toner image quality is improved. In the image fixing step, the fixing properties of toner particles become poor, in particular, at a halftone portion. This is because the deposition amount of toner is small at the halftone portion, and some fine toner particles deposited on the halftone portion, lying on a depression of a transfer sheet, tends to cause an offset phenomenon. Namely, the heat energy provided by an image fixing roller is extremely small.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invent
Higuchi Hiroto
Matsuda Hiroaki
Sugiyama Akemi
Suzuki Masanori
Dote Janis L.
Ricoh & Company, Ltd.
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