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- Technology to increase durability of the photoconductor
Research and Development
About
Environmental Technologies
Technology to increase durability of the photoconductor
Durability of the photoconductor is an important subject with regard to decreasing customer service costs as well as reducing environmental load, such as resource saving and waste reduction. Konica Minolta has focused on the protective overcoat layer of the photoconductor to increase its durability.
Factors that deteriorate the photoconductor and the functions required for the photoconductor
The organic photoconductor (hereafter, referred to as "OPC") is subject to various mechanical, electrical, and chemical stresses during the electrophotographic processes of charging, exposing, developing, and cleaning. Wear and scratches that occur during the process of repetitive creation of images are critical deterioration factors that determine the service life of the OPC. Specifically, during the color processing of recent years, mechanical stress caused by the intermediate transfer belt is added to the stress applied by the blade and the brush used as cleaning members, and the environment where the OPC is used is more severe than ever. Therefore, it is strongly required that the OPC's resistance to wear and flaws be further improved. As the result of further studies, we found that a highly durable OPC can be obtained by providing a protective overcoat layer which includes dispersed nanosize fillers on the electrical-charge transportation layer.
Design of the highly-durable protective layer
Selection of fillers
In selecting fillers, we focused on nanosize metal-oxide particulates which can give the protective layer a hard surface and ensure optical transparency. Furthermore, from the view point of electrostatic characteristics, low relative permittivity of the filler is desirable to ensure a good charging ability. Therefore, we have selected silica particulates. Moreover, from the view point of production stability, it is desirable that fillers in the coating liquid are not deposited. To achieve this, we have chosen silica particulates to be used as metal-oxide particulates because silica particulates with low specific gravity are advantageous.
Control of mechanical strength
Fig.1: Dependence of filler content on scratch resistance
Fig.1 plots the relationship between the amount of silica particulates contained in the protective overcoat layer and the film strength. When the amount of silica added is small, filler effect is low, resulting in small and deep scratches on the protective layer, and when there is an excess of silica particulates added, it makes the film vulnerable to partial breakage. Therefore, it is important to control the amount of silica particulates added so that the amount is within a range that can improve film strength.
Fig.2 shows wear resistance of the OPC in which OCL that contains 20wt% of silica particulates has been provided. In comparison with the conventional OPC, the amount of wear has been significantly reduced. Since different processes create different mechanical stress, an appropriate additive amount needs to be determined.
As shown in Fig.3, during the testing that actually uses bizhub PRO C6500, we confirmed that the OPC which has had OCL provided can sustain good potential stability and image characteristics for about 400 kilo prints.
Fig.2: Wear loss: conventional OPC vs. overcoated OPC
Fig.3: Cyclic stability of an overcoated OPC