Ricoh Company, Ltd.

Kazuhiro Yuasa

Eisaku Murakami

Hiroshi Saitoh

Tetsuo Yamanaka

Toshihiro Sugiyama

Satoru Komatsubara

Hiroshi Hosokawa

Yoshiaki Tanaka

Eiji Takenaka

Iwao Matsumae

Shuichi Endoh

Mugijiroh Uno

Yozo Matsuura

Shiroh Kondoh

Mitsuru Kondo

Shuichi Takahashi

Kenya Komada

Mugijirou Uno

Kazumasa Koike

Yoshiya Itoh

Hiroyuki Kiyoi

Noboru Furukawa

Masanori Yoshimura

Masahiro Kawabe

Mugijiro Uno

Eizi Takenaka

Mugiziroh Uno

In an image forming apparatus, a developing device operable with toner or single component type developer has a hard first developing roller and a soft second developing roller. Fine magnetic N-S poles are formed on the periphery of the first roller. The second roller conveys the toner, electrostatically transferred thereto from the first roller, to an image carrier. The device frees a toner image from deterioration due to toner particles charged to a polarity opposite to an expected polarity. The toner forms a uniform thin layer on the first roller and is uniformly charged. Toner for use with this type of developing device is also disclosed.

Developing device for an image forming apparatus

In an electrophotographic image recording apparatus of the type using a single-ingredient type developer, i.e., toner, a latent image is electrostatically formed on a photoconductive drum or similar image carrier. A developing unit has a developing roller for conveying the toner deposited thereon, and an intermediate roller for conveying the toner transferred thereto from the developing roller and depositing it on the latent image to thereby produce a corresponding toner image. An image transfer unit transfers the toner image to a cut sheet. During the development of an area of the image carrier other than a latent image area, at least one of biases assigned to the developing roller and intermediate roller, respectively, is switched over to thereby form an electric field different in direction from an electric field assigned to the formation of the toner image between the two rollers. As a result, the toner existing on the intermediate roller is collected by the developing roller. This successfully prevents the toner from depositing on the intermediate roller except when required, and frees the image transfer unit from the deposition of the toner.

Electrophotographic recording apparatus configured to switch a bias

In an electrophotographic image forming apparatus of the type using single-ingredient type high resistance toner, a developing roller or similar toner conveyor roller is covered with a dielectric layer which is comparatively thick at opposite end portions than at an intermediate portion. A conductive or semiconductive elastic layer underlies the dielectric layer. With the above configuration, the dielectric layer is prevented from coming off the roller. This, coupled with the fact that the elastic layer does not contact a photoconductive element, eliminates current leaks and thereby extends the life of the roller and photoconductive element.

Method of coating a toner conveyor roller

In an electrophotographic recording apparatus of the type using a single-ingredient type developer, i.e., toner, a developing device has a developing roller for conveying the toner deposited thereon, and an intermediate roller for conveying the toner transferred theretofrom the developing roller and depositing it on a latent image electrostatically formed on an image carrier to thereby produce a corresponding toner image. During the development of an area of the image carrier other than a latent image area, a bias assigned to the developing roller is switched over to thereby form an electric field different in direction from an electric field assigned to the formation of the toner image between the two rollers. Further, before the rotation of the image carrier is stopped, the bias assigned to the developing roller is again switched in order to form the electric field for the formation of the toner image between the rollers. As a result, a toner layer is formed on the intermediate roller. Subsequently, the rotation of the image carrier is stopped. The device obviates defective images ascribable to the adhesion of the image carrier and intermediate roller while eliminating background contamination and wasteful toner consumption.

Developing device for an electrophotographic recording apparatus

In an image forming apparatus using a corona discharge type charging device and a contact type image transferring device, a toner deposited on a photoconductive element in the form of a black stripe is prevented from being transferred to the image transferring device; otherwise, the toner would be transferred from the image transferring device to the rear of the following recording medium. Because the toner forming the black stripe is limited to the toner charged to a polarity opposite to an expected polarity, toner consumption ascribable to the stripe is reduced.

Image forming apparatus with bias control to prevent undesirable toner

An image forming apparatus including a developing device having various components with specific relationships between their lengths. There is an image bearing member such as a photoconductive drum or belt having a photosensitive layer. The photosensitive layer has a length A. A first toner transporting roller has two ends, the length between the two ends being defined as B. Additionally, there is a second toner transporting roller, disposed between and contacting both the image bearing member and the first toner transporting roller. The length of the second toner transporting roller being defined as C. The components of the image forming apparatus are constructed such the length of the second toner transporting roller is less than or equal to the lengths of both the first toner transporting roller and the photosensitive layer of the image bearing member. This means that the relationships A&gt;C and B&gt;C may exist. As an alternative, B is approximately equal to C with A being greater than both B and C. As a further alternative, A, B and C are each approximately equal to each other.

Developing device having the lengths of two toner transporting rollers

A developing apparatus is capable of providing stable charging ability for a developer and stable transfer ability for transferring the developer to a photoreceptor for electronic photography to prevent residual positive images and stain of texture which appear on a toner image. A first toner transfer roller 23 has a core supported to be rotatable and a sheet type insulation layer wound around the outer periphery of the core. The insulation layer is made of elastic rubber in which magnetic material having a specified particle size is uniformly dispersed and the magnetic material is formed with ferromagnetic substance such as magnet and magnetized in advance. The first toner transfer roller 23 attracts toner T by actuating magnetism on the insulation layer since the magnetic material added to the insulation layer is magnetized.

Developing apparatus for electronic photographic recording equipment,

In an image forming apparatus, a developing device has a first developer carrier for depositing a developer thereon, a regulating member for regulating the amount of the developer deposited on the first developer carrier, and a second developer carrier having an elastic surface, and contacting the first developer carrier while biting into it by a predetermined amount. The developer is provided with a preselected degree of fluidity. Hence, even when the same portion of the surface of the second developer carrier runs a plurality of times past a position where the two developer carriers contact each other without any developer being fed from the second developer carrier to an image carrier, the first developer carrier can surely strip the developer from the second developer carrier. As a result, a developer on which a predetermined amount of charge is deposited is transferred from the first developer carrier to the second developer carrier. This successfully protects images from defects. Particularly, when the developer has a zinc stearate content of greater than 0.1 wt %, it is possible to prevent the developer from melting and adhering to a member which regulates the developer.

Device for electrostatically developing a latent image on an image

A developing device which includes a first toner transporting roller, a second toner transporting roller to which toner is transported from the first toner transporting roller and an image bearing member such as a photoconductive drum or belt. Seals are located between the circumferential ends of one of the toner transporting rollers and a bottom portion of a toner hopper. When the seals are between the bottom of toner hopper and the first toner transporting roller, the first toner transporting roller is longer than the second toner transporting roller and the circumferential portions of the first toner transporting roller which contact the seals do not contact the second toner transporting roller. Alternatively, when the seals are between the bottom of toner hopper and the second toner transporting roller, the second toner transporting roller is longer than the first toner transporting roller and the circumferential portions of the second toner transporting roller which contact the seals do not contact the first toner transporting roller. Additionally, when the seals contact the second toner transporting roller, side seals may be placed against the ends of the first toner transporting roller. In both of these arrangements, the length of the second toner transporting roller is shorter than a length of an effective area of a photoconductive layer on the image bearing member.

Developing device having seals between a toner transport roller and the

Toner, and devices for electrostatically depositing a uniform

In an electrophotographic image forming apparatus of the type using single-ingredient type high resistance toner, a developing roller or similar toner conveyor roller is covered with a dielectric layer which is comparatively thick at opposite end portions than at an intermediate portion. A conductive or semiconductive elastic layer underlies the dielectric layer. With the above configuration, the dielectric layer is prevented from coming off the roller. This, coupled with the tact that the elastic layer does not contact a photoconductive element, eliminates current leaks and thereby extends the life of the roller and photoconductive element.

Toner conveyor roller and image forming apparatus having the same

In an image forming apparatus, a developing device of the type developing an electrostatic latent image formed on an image carrier by using single-component type toner has a regulating member for regulating the amount of the toner fed thereto, a first conveying member for conveying the toner regulated by the regulating member and deposited thereon, and a second conveying member for conveying the toner transferred from the first conveying member thereto to the image carrier. The first and second conveying members are each movable at a particular speed in a particular direction. The device is free from problems attributable to oppositely charged toner particles despite the use of the single-component type toner and, in addition, insures attractive images.

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Zama, Japan

Kazuhiro Yuasa