Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-05-18
2003-09-09
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111100, C430S111320, C430S111350, C430S124300, C430S045320
Reexamination Certificate
active
06617088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developer used in a trickle developing method in which an electrostatic latent image formed by an electrophotographic method or an electrostatic recording method is developed with a two-component developer while replenishment the developer to a developing device intermittently or continuously and discharging a part of the developer from the developing device intermittently or continuously, and an image forming method using the developer.
2. Description of the Related Art
A method in which an image information is visualized through an electrostatic latent image, such as an electrophotographic method, has been currently utilized in various fields. In the electrophotographic method, an image information is visualized such that an electrostatic latent image is formed on a photoreceptor by charging and exposure, developed with a toner-containing developer, transferred and fixed. The developer used here includes a two-component developer made of a toner and a carrier and a one-component developer made only of a toner such as a magnetic toner. The two-component developer is advantageous in that a controlling property is good because the carrier has functions of stirring, transporting and charging the developer and is functionally separated in the developer. Thus, it has been widely used at present. Especially, a developer using a carrier coated with a resin is excellent in a charge controlling property, and improves an environmental dependence relatively easily.
A method of fixing a toner image includes a heat-fixing method using a heating roller or a hot film. The method using the heating roller has been widely used because a thermal efficiency is good and high-speed fixing is enabled.
This fixing method is problematic in that a so-called offset phenomenon sometimes occurs. The offset phenomenon is that since a molten toner image is contacted with the surface of the heating roller under pressure, a part of the toner image is adhered to the heating roller, and the toner adhered is retransferred to stain a copied image.
In order to prevent the offset phenomenon, a method is employed in which a silicon rubber or a fluororesin having an excellent releasing property to a toner is coated on a surface of a heating roller and a releasing liquid such as silicon oil is further supplied to the surface thereof. This method is quite effective for preventing the offset phenomenon of the toner, but a device of feeding the offset preventing liquid is required. This is contrary to downsizing or weight reduction of a copier. Further, when the offset preventing liquid is heated and evaporated, an unpleasant smell is given or contamination inside the device occurs.
In order to solve these problems, a method in which a viscosity of a toner is limited (Japanese Patent Laid-Open Nos. 133,065/1989, 161,466/1990, 100,059/1990 and 229,265/1991), a method in which a wax such as a releasing resin is incorporated in a toner (Japanese Patent Publication No. 3,304/1977), a method in which a melt viscosity of a wax is limited (Japanese Patent Laid-Open Nos. 260,659/1991 and 122,660/1991), a method in which a diameter of a wax domain and a ratio of a wax present on a surface of a toner are limited (Japanese Patent Laid-Open No. 84,398/1995), and a method in which a shape of a wax domain is limited (Japanese Patent Laid-Open No. 161,145/1994) have been proposed.
Further, as a developing method, a cascade method was used in the past, but at present a magnetic brush method in which a magnet roll is used as a developer transporting unit is mainly used.
In the two-component developing method which is currently widespread, a circumferential speed of a developing sleeve is generally determined to be higher than a circumferential speed of a photoreceptor for securing a satisfactory image density, namely for feeding a sufficient developer to a developing region.
However, in this method, development defects caused by a relative difference in speed between the developing sleeve and the photoreceptor, for example, trail edge deletion of a solid image and trail edge deletion of a halftone image in an interface between a lead edge of the solid image and the halftone image when the halftone image and the solid image are present occur. With respect to these image deletions, it is considered that the amount of change in a potential of a developer layer owing to the movement of the toner in a developing nip region of a developing process depends on a latent image structure and an image is developed at different speeds with a developer that has experienced a history of an electric field just before the latent image to be developed in a region where the development is actually conducted, so that these defects notably occur in discontinuous spots of the latent image structure, for example, in the interface between the solid image and the non-image portion or the interface between the halftone image and the solid image.
For inhibiting these defects, it is proposed that trail edge deletion of a solid image is improved by decreasing a resistance of a carrier (Japanese Patent Publication No. 31,422/1995). Meanwhile, when a resistance of a developer or a carrier is decreased for improving the defects, a developing effective electrode extremely approaches to a photoreceptor by the excessive decrease in the resistance to reduce an ability to feed the toner to the photoreceptor or to cause so-called brush mark in which latent image leak is generated. Accordingly, in order to prevent the excessive decrease in the resistance of the developer or the carrier, it is proposed that a lower limit of the resistance of the carrier layer is regulated (Japanese Patent Publication Nos. 40,309/1993, 29,992/1994 and 31,422/1995).
The resistance of the developer layer is generally almost determined by a resistance of a carrier and a coating rate of a toner on the carrier. Further, the resistance of the developer depends on an electric field. Therefore, in a full color image in which various latent image levels are continuously present, there is a need to control the resistance of the carrier and the coating rate of the toner on the carrier especially for avoiding the developing defects.
Nevertheless, when the development is repeated over a long period of time, the resin coating layer on the surface of the carrier in the developer is worn out and peeled off, or the toner component is adhered to the surface of the carrier to decrease a chargeability of the carrier. However, since a developing potential is fixed, the coating rate of the toner on the carrier of the developer is gradually decreased for making an image density constant. Consequently, in the full color image, the developing defects are generated before the image density is changed or fogging occurs. Thus, the problem has not yet been improved satisfactorily.
Thus, a developing method in which a carrier is added together when a toner is supplemented for a toner consumed by the development and a carrier in a developing device is replaced little by little to control a change in a charging amount and stabilize an image density (so-called a trickle developing method) is proposed in Japanese Patent Publication No. 21,591/1990.
On the other hand, to meet the requirement for a high-image quality in recent years, the size of the toner is further decreased, and a non-electrostatic adhesion between a toner and a photoreceptor is enhanced. Thus, the transfer becomes difficult. Accordingly, a method is proposed in which the shape of the toner is controlled or an external additive as a spacer is added to the outer surface of the toner to suppress a contact force between the toner and the surface of the photoreceptor (Japanese Patent Laid-Open Nos. 337,738/1992 and 337,742/1992).
However, the external additive on the surface of the toner is embedded in the toner by the long-term stirring in the developing device, and the function as the spacer is not satisfactorily exhibited. Further, in the trickle developing method in which
Iizuka Akihiro
Taguchi Tetsuya
Yoshihara Koutarou
Yoshino Susumu
Dote Janis L.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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