Research and Development

Before the developing unit had been improved, spent toner on the carrier occurred and the ability to electrically charge the toner was low due to stress in the developing unit. This caused the toner to scatter and fogging to become worse, thereby limiting the unit's service life. To solve this problem, we made an effort to reduce stress inside the developing unit.

The developer circulates vertically along two axes by means of the mixing screw and the feed screw in the developing unit. However, the weight of the developer located near the feed screw installed on the upper side applied stress on the developer located near the mixing screw installed on the lower side. To solve this problem, a dividing member has been inserted between the feed screw and the mixing screw and the shape of the screws has been modified. As a result, the developer circulates smoothly along the two vertical axes. By doing so, the developer near the mixing screw receives less stress from the developer near the feed screw, and torque reduction of the mixing screw has been achieved. In addition, the entire torque of the developing unit has been reduced by approximately 30% as the result of using a small-diameter particle toner and carriers.

The charger of the full-color multifunction printer made by Konica Minolta uses pin-array electrodes. An electric discharge is generated from sharp-pointed pins of the pin-array electrode located on the photoconductor drum side and electrically charges the photoconductor drum. The electric discharge contaminates the pin points of the pin-array electrode due to discharge products, which increases uneven charging. Since the amount of generated discharge products depends on the charging current, by using about twice as many pins as the previous model and decreasing the current running through each pin, contamination on the pin array due to discharge products has been reduced. Thus, the progression of uneven charging has been inhibited.

To extend the service life of the photoconductor drum, it was necessary to solve the problem that made it difficult to obtain the required charging performance due to the progressive wear of the photosensitive layer. Therefore, we have used a mechanically-strong overcoat layer (hereafter, referred to as "OCL") to reduce wear and extend the service life of the photoconductor drum.

With regard to the technology to extend the service life of the cleaning blade, there was a problem in that wear of the blade edge progresses as it is used longer, resulting in insufficient cleaning. To reduce the wear of the blade edge, we have used a lubricating agent for the toner's external additive. By applying the lubricating agent onto the photoconductor drum via the toner, it is possible to decrease the surface energy of the photoconductor drum, thereby decreasing friction between the photoconductor drum and the cleaning blade and reducing the wear of the blade edge. Furthermore, in order to reduce the amount of wear, we have employed the new cleaning blade, which is not so easily worn as the conventional blades used to be.

Fig.3 shows the comparison of the abrasion width of the cleaning blades after printing about 40,000 copies. The bar graph on the left represents the use of the conventional toner and conventional cleaning blade, the bar graph in the middle represents the use of the above-mentioned new toner and the conventional cleaning blade, and the bar graph on the right represents the use of the new toner and the new cleaning blade. The right bar graph indicates that the abrasion width of the new cleaning blade is less than 50% of that of the conventional models.