Multi-functional peripherals (MFPs) and digital printing systems contain shiny tubular components called “photoconductor drums” that convert light into electrostatic charge. Color devices include four of these photoconductor drums, one for the transfer of each color of toner (cyan, magenta, yellow, and black).
In the printing process, different levels of electric potential are applied to different areas of the surface of the photoconductor drum by means of charge generation and exposure to light, creating an invisible “electrostatic latent image” composed of static electricity. This static electricity causes toner to adhere to the surface of the drum because of its electric potential. The toner adhering to the photoconductor drum is transferred to the paper either directly or via an intermediate transfer belt, after which it is heated and compressed in a process known as “fusion fixation.”
Finally, any remaining toner that has not been transferred from the surface of the photoconductor drum is removed with a cleaning blade.
Every time printing is performed, the photoconductor drum goes through the repeated process of charging, exposure, transfer, and cleaning. In this process it not only comes into contact with cleaning components such as a blade or a brush, but is also subject to mechanical stress from other components such as an intermediate transfer belt. This eventually results in wearing, scratching, or roughening of the surface, reducing the density of the printed material in places or generating streaky image noise.
One type of printing used in commercial printing is print on pre-print, which involves printing over paper on which images or other matter have already been printed. In this process, ink from the printed paper comes into contact with the photoconductor drum, attacking it chemically. Other chemical stresses within the device may cause chemical changes on the surface of the photoconductor drum, reducing its electrical resistance and gradually causing images to blur.
Photoconductor drums must be replaced before their condition deteriorates to this extent, but the frequency with which replacement is required can be reduced by improving their durability. The development of photoconductor drums capable of withstanding relentless mechanical and chemical stress will therefore both improve the efficiency of printing for customers and help cut service costs as well as effectively reducing the burden on the environment, particularly by conserving resources and reducing waste.
Konica Minolta has developed a hard, high-density overcoat layer with a universal hardness of 240 N/mm2, the top level in the industry, which greatly reduces the amount of wear and surface roughening, providing a major improvement in the stability of the surface condition.
The photographs below show the surface of a photoconductor drum after having printed 1 million A4 sheets. The conventional photoconductor drum (left) has scratches and wide scrapes, as indicated by the arrows, but no such scrapes or scratches are evident on the surface of the new photoconductor drum (right) even after having printed 1 million A4 sheets.
Surface comparison between a conventional photoconductor drum (left) and the new photoconductor drum (right) after printing 1 million A4 sheets
The new overcoat layer is also more resistant to the effect of oxidation.
The photographs below show a comparison of images experimentally printed from a slightly worn film (scraped by approximately 1.5 μm) in a high-temperature, high-humidity environment. The images produced by the conventional photoconductor drum (left) are faulty as a result of oxidation extending to the photoconductor layer inside the film, but the new overcoat layer uses a material with a high film density and excellent durability, meaning that stable images are still produced (right).
Konica Minolta has succeeded in maintaining high image quality over 1 million printings by setting the cleaning conditions for the photoconductor drum surface utilizing the strength of this new overcoat layer.
Comparison of images printed with a conventional photoconductor drum (left) and one using the new overcoat layer (right) after printing 1 million A4 sheets with the film scraped by approximately 1.5 μm at high temperature and humidity
Organic/inorganic hybrid The overcoat layer of Konica Minolta's photoconductor drums had previously been formed by dispersing nano-size particles of inorganic filler to increase its hardness. The new overcoat layer utilizes curable resin, an organic substance, as its main ingredient, and this is chemically bounded to inorganic filler to create an organic/inorganic hybrid film, a development that dramatically increases its hardness.
The surface of the inorganic filler is treated to enable it to react with the organic ingredient, and the filler is then reacted with the curable resin to create a hybrid substance. It is this hybridization between the inorganic filler and the organic ingredient that produces durable performance that combines the advantages of inorganic and organic materials.
The electrophotographic organic photoconductor technology used in photoconductor drums is the fruit of long years of research and development as one of Konica Minolta's core technologies, and we will continue to respond to new market needs as they arise.