Electrophotography – Image formation – Development
Reexamination Certificate
2000-03-01
2001-07-03
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S027000, C399S265000, C430S110100
Reexamination Certificate
active
06256471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a technology for forming a thin layer of toner on a developing roller that supplies toner to a photosensitive drum.
2. Description of Related Art
A typical laser printer that uses a non-magnetic single-component toner has a developing roller that carries thereon the toner, a layer thickness-regulating blade disposed at a side of the developing roller for forming a thin toner layer on the developing roller, and a photosensitive drum disposed facing the developing roller, on which drum an electrostatic latent image is formed.
The layer thickness-regulating blade is pressed against a surface of the developing roller. Toner supplied onto the developing roller is rubbed between the layer thickness-regulating blade and the developing roller, so that toner is sufficiently electrically charged and, at the same time, is placed as a thin layer of a predetermined thickness on the developing roller. An electrostatic latent image is formed on the photosensitive roller by uniformly electrically charging the surface of the photosensitive roller through the use of an electrical charging device and then irradiating the surface with a laser beam based on predetermined image data through the use of a laser emitting device. Thus-electrically charged toner is transferred selectively to the electrostatic latent image on the photosensitive roller, thereby developing the image.
However, to develop an image of a toner of a single non-magnetic component, the electrical charging of toner is carried out substantially entirely by friction contact between the layer thickness-regulating blade and the developing roller. Therefore, to uniformly charge the toner, it is necessary to quite strongly rub the toner by strongly pressing the layer thickness-regulating blade against the developing roller. In order to improve the flowability and the stability of the electrical charge, an external additive made of fine powder of silica, alumina, titanium oxide or the like is added to a toner. Therefore, if the toner is rubbed excessively strongly, particles of the external additive become sunk in toner matrix particles, so that the flowability decreases or the electrical charging characteristic of toner decreases.
SUMMARY OF THE INVENTION
To solve the aforementioned problems, the invention adopts a silicone rubber having a good electrical charging characteristic as a material of a pressing portion of a layer thickness-regulating member. At the silicone rubber-made pressing portion, the layer thickness-regulating member presses a developing agent on a developing agent carrier. The pressing force with which the pressing portion presses the developing agent is as weak as about 15-30 gf/cm, so that the abrasion of the silicone rubber-made pressing portion is reduced. Therefore, the electrical charging characteristic of the developing agent is prevented from deteriorating, so that high image quality can be maintained. Furthermore, the life span of a developing device is extended, so that the running cost will decrease.
The developing agent may be a polymerized toner. The polymerized toner achieves a very good flowability. Therefore, the friction resistance that occurs when the developing agent is rubbed between the pressing portion and the developing agent carrier is reduced. If a very weak pressing force is set for the pressing portion as in the invention, the pressing force is likely to fluctuate depending on various conditions. Fluctuation of the pressing force impedes stable friction electrical charging of the developing agent. However, if a polymerized toner having high flowability is adopted, the adverse effect of fluctuation of the pressing force can be ignored, so that stable development becomes possible.
Furthermore, the developing agent may contain at least two kinds of external additives that are different in particle size. In that case, relatively large external additive particles function as spacers. That is, relatively large particles and relatively small particles of the external additives simultaneously adhere to particles of the developing agent, and relatively large external additive particles prevent relatively small external additive particles from being sunk into particles of the developing agent when the developing agent particles collide. In particular, if the relatively large-particle external additive has a BET specific surface area less than 100 m
2
/g based on nitrogen adsorption, the sinking of relatively small external additive particles can be effectively prevented, so that good flowability of the developing agent can be ensured.
Such use of a large-particle external additive is not feasible according to the conventional art, because a toner containing such a large-particle external additive accelerates the abrasion of the silicone rubber. In the invention, however, the adoption of a polymerized toner curbs the abrasion of the silicone rubber, and therefore allows a large-particle external additive to be contained in the toner.
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Horinoe Mitsuru
Sato Shougo
Brother Kogyo Kabushiki Kaisha
Chen Sophia S.
Oliff & Berridg,e PLC
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