Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-10-19
2003-11-25
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S111350, C430S097000, C430S120400
Reexamination Certificate
active
06653040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic carriers used for charging toners contained in a two component-type electrophotographic developer comprising the carrier and the toner, the electrophotographic developers containing the same carrier, and to a developing method.
2. Description of the Related Art
One of the important properties required for a magnetic carrier used as one component of an electrophotographic developer is a quick charging property of a toner, which is another component of the electrographic developer. The magnetic carrier is required to charge the toner rapidly. In other words, the carrier is required to have a high charge build-up rate. If a portion of the toner supplied into the developing machine while printing does not charge rapidly, this portion of the toner will have too low an electrostatic charge for developing the image, and the toner may be scattered on printed sheets including on the background portion. As a result, the insufficiently charged toner will contaminate the prints, causing a phenomenon called “photographic foggingging” or “chemical foggingging”. In order to eliminate the insufficient charging and the photographic foggingging, various countermeasures have been proposed conventionally. In particular, extensive studies have been carried out in order to obtain superior magnetic core materials in terms of properties of materials, particle size, the surface coating, and further research was carried out to find suitable resin materials and the effects of heat treatments on the properties of the resin coated carriers. In order to reduce the photographic fogging, several measures were conventionally proposed such as improving the charging property of the carrier for the toner and improving the electric resistance of the developer composed of the carrier and the toner.
Examples of conventionally proposed techniques follow. Japanese Patent Application, First Publication No. Sho 47-17435 proposes to employ a fluororesin. Japanese Patent Application, First Publication No. Sho 60-19156 discloses that coating of a silane-coupling agent makes it possible to improve image density to a satisfactory level and to decrease the photographic fogging of images. Japanese Patent Application, First Publication No. Sho 61-20464 proposes to incorporate a conductive material in a silicone resin.
Japanese Patent Application, First Publication No. Sho 64-91144 discloses that a preferable image quality having no photographic fogging, no uneven density, and no blurring can be obtained by application of a mechanochemical treatment to silicone resin coated carrier particles, wherein the mechanochemical treatment is carried out by stirring the coated carrier particles mechanically until the carrier particles can charge the toner approximately 1.2 to 2.5 times. Japanese Examined Patent Application, Second Publication No. Hei 6-73030 discloses that carrier particles coated with a coating layer formed by a fluororesin, in which fluororesin particles are dispersed, shows a high image quality having no photographic fogging and a high stability over time in maintaining the charge. Japanese Patent Application, First Publication No. Hei 11-125934 discloses that a sufficient amount of charge can be obtained for the toner from the beginning of the printing by applying an impact force on the carrier particles coated with a silicone resin so as to accumulate a 1.5 times larger amount of electrostatic charge in the developer, which results in obtaining a high quality image having no photographic fogging over a long term.
However, photographic fogging is a complicated phenomenon and a complete solution to this problem is not yet obtained. The carrier is required to have characteristics such that the carrier not only charges the toner quickly to a predetermined level, but also the predetermined level of electrostatic charge must be maintained constant while printing. This is because the image density must be maintained constant while printing. A technique compatible with the quick charging and the long-term charge maintenance property is still a problem to be solved, because the quick charging is related to preventing the photographic fogging and the long-term charge maintenance property is related to the time-dependent reliability of the image density.
Recently, the charging or electrification mechanism between the carrier and the toner has been extensively studied. It is assumed that one possible mechanism is that the toner is charged as a result of an electron exchange process between the toner and the carrier due to the difference of surface energy levels of the toner and the carrier when the carrier is in contact with the toner. The surface energy level is related to a property which is called a work function. In general, when two substances having different work functions are in contact, the substance having a lower work function has a tendency to donate electrons (i.e., is likely to be positively electrified).
Various methods are proposed for measuring the work function of a substance, and, in general, the work function is obtained by measuring photoelectrons emitted from an object when light beams of various wavelengths are irradiated onto the object. Since the photoelectrons will not be emitted if the irradiated light does not exceed a certain energy level, an observation of the relationship between the light wavelength (photon energy) and the photoelectron emission makes it possible to obtain the minimum energy at which the photoelectron emission starts. Not only light beams but also X-rays or electron beams may be employed as the radiation, and the measurement is performed in a vacuum chamber in order to carry out an accurate observation of photoelectron emission.
Recently, however, a low energy electron counting apparatus has been developed which carries out the measurement of the work function by irradiation of ultraviolet light on an object in air. The above-described apparatus is becoming widely used in the fields of developers including toners and carriers for measuring their work functions. Japanese Patent Application, First Publication No.9-10610 defines the relationship between work functions of the toner and the carrier. Japanese Patent (Granted) Publication No. 2954786 discloses that a toner having superior color reproducibility can be obtained by identifying the differences of work functions of three primary color toners.
However, merely the work function is not sufficient for clarifying the electrostatic charging behaviors of the carrier and the toner, although the work function is one of the measures with respect to the charging performance. In the conventional carriers and toners developed employing the work function as a measure of electrification behaviors, a superior carrier is not yet available, which has performances of both quick charging and the charge maintenance properties, both of which are respectively required for eliminating the photographic fogging of an image and for maintaining the image density.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of developing electrostatic images by using a carrier for electrophotography, which is compatible not only for the quickly charging the toner but also for maintaining the necessary charge during printing.
The first aspect of the present invention provides an electrophotographic carrier by coating magnetic particles with a resin, wherein the carrier satisfies the following equation (B)>(−19.4)×(A)+31, wherein, (A) represents the carbon content in weight percent, and (B) represents the ratio of a square root ((CPS)
½
) of a number of emitted photoelectrons (CPS) to a excitation energy (eV).
The second aspect of the present invention is related to an electrophotographic developer, provided with a toner comprising at least a colorant and a binder resin and the above-described carrier.
The third aspect of the present invention provide a method for developing electrostatic images using the above
Amaya Shinji
Isonaka Takeshi
Kogawara Toshiro
Ohba Katsunori
Armstrong Westerman & Hattori, LLP
Dainippon Ink and Chemicals Inc.
Rodee Christopher
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