1. Field of the Invention
The present invention relates to a developing apparatus, a developing method, and a developing agent or developer for such a developing apparatus, in which development is performed by using a first two-component developer of a first toner concentration and a second two-component developer of a second toner concentration that is higher than the first toner concentration.
2. Description of the Related Art
In a developing apparatus employed in an electrophotography machine such as a copying machine, a printer, a facsimile machine, etc., using a dry two-component developer (toner and carrier) as stated above, as development processing is repeated, a toner component is being consumed, whereas a carrier is being reduced in its electrification performance due to peeling off of a resin coating material on the surface of each carrier particle, adhesion of the toner component to the surfaces of toner particles, and so on. As the electrification performance is reduced, the quality of images that are developed by the developing apparatus is deteriorated. Thus, there has been proposed a technique in which a carrier is replenished together with a toner so as to decrease such reduction of the toner and the electrification performance, whereby the interior of the developing apparatus can be kept at a constant condition even if development processing is repeated. For example, in Japanese patent application laid-open No. S62-127874 (US (31) 801366)(FIGS. 2, 5, 6, 7, and page 9), a toner and a carrier are supplied together or separately from each other so as to keep constant the toner concentration that is changing in accordance with the progress of development processing. In such a case, for example in Japanese patent application laid-open No. H6-301289 (FIG. 1, page 7, and summary), a two-component developer is controlled to keep its bulk or volume constant.
However, in case where the toner and the carrier are simply replenished to the two-component developer as stated above, they are not electrified until after the replenishment thereof. As a result, sufficient electrification is not performed at appropriate timing, so it is difficult to satisfactorily produce an effect of replenishment. In this case, in particular, as the reduction in size of the developing apparatus progresses, the duration permitted for electrification in the developing apparatus is becoming shortened, thus lowering the effect of replenishment. In addition, even if the toner and the carrier have been beforehand mixed at the time of the replenishment thereof, electrification thereof is not carried out to a satisfactory extent, so the effect of replenishment is not satisfactorily exhibited.
Accordingly, consideration has been given to such a problem that electrification is not satisfactorily performed even when the toner and the carrier have been beforehand mixed with each other at the time of their replenishment. As shown in FIG. 10, in the past, a toner and a carrier, which together constitute a two-component developer, are provided in steps S11 and S12, respectively, and mixed with each other in step S13 as indicated by lines Y11, Y12, and then put into and stored in a developing apparatus as a two-component developer LT of a low toner concentration to be supplied to a developing roller in step S14 as indicated by line Y13. On the other hand, the toner and the carrier provided in steps S11, S12 are also put into and stored, as a replenishment two-component developer JT of a high toner concentration, in a cartridge detachably attached to the developing apparatus in step S15 as indicated by lines Y14, Y15.
The replenishment two-component developer JT prepared in the above-mentioned manner has a toner concentration higher than that of the two-component developer supplied to the developing roller (i.e., the amount of the carrier is smaller in comparison with the toner). As a consequence, it could be understood that even if the toner and the carrier were mixed with each other, there would be a small chance that particles of the toner are compressed between particles of the carrier, thus resulting in insufficient electrification. Accordingly, there was also another consideration that the amount of carrier to be mixed should be increased for the replenishment developer, but following such a consideration results in another problem that the consumption of the carrier increases to push up the cost and it becomes necessary to take a large discharge space for a degraded carrier.