1. Field of the Invention
The invention relates to a toner supply roller which is used for forming a toner image onto an electrostatic image bearing member, its manufacturing method, and a developing apparatus having such a roller. More particularly, the invention relates to a method of processing a toner supply roller suitable for forming a stable image.
2. Related Background Art
Hitherto, an image forming apparatus for developing by a non-magnetic one-component toner has been known.
In a developing apparatus using the non-magnetic one-component toner, a toner supply roller comes into contact with a developing roller and the toner supply roller is rotated, thereby supplying toner onto the developing roller.
Further, the toner supplied onto the developing roller is conveyed to a developing section which faces a photosensitive drum by the rotation of the developing roller. On the way of the conveyance, the toner is restricted by an elastic blade which is in contact with the developing roller, is coated onto a toner layer having a predetermined thickness, and is used for development in the developing section.
The toner supply roller is constructed in a manner such that an elastic sponge such as urethane foam, silicon foam, or the like is held on the surface of a core and an external surface of the held sponge is processed, thereby forming a cylindrical shape, namely, a roller-like shape. The roller-like processing, namely, an outer-diameter processing of the sponge is generally performed by a machine processing such as polishing by a bite or a melt cutting processing such as cutting by a nichrome wire which generated heat.
In case of using a sponge whose density is relatively high, when the outer-diameter processing by the melt cutting of the nichrome wire is performed, a melting degree of the surface of the sponge is large and a thin film is formed on the surface. Consequently, a conveying performance of the toner by the supply roller is deteriorated or a melted substance is entangled with the nichrome wire, thereby deteriorating a cutting ability of the nichrome wire or increasing a cutting resistance, so that an inconvenience such that a dimensional precision of the outer diameter remarkably deteriorates. Therefore, in the case of a material whose density is relatively high, the outer-diameter processing by polishing is generally performed.
A conventional processing method of the toner supply roller will now be described in detail hereinbelow. The toner supply roller made of urethane foam has been processed by the following five steps and has been put into practical use.
(1) Sectioning Process
First slab stock (sponge) is cut into a rectangular parallelepiped using a centrifugal peeling machine and horizontal table splitter.
(2) Boring
A hole to insert a core is bored into the urethane rectangular parallelepiped.
(3) Attaching the Core
A hot melt adhesive agent is coated onto the core, the coated core is inserted into the hole of the urethane rectangular parallelepiped, and the adhesive agent is heated and hardened at a temperature in a range from 180.degree. C. to 200.degree. C., thereby adhering the core to the urethane rectangular parallelepiped.
(4) Outer-diameter Processing
An external surface of the urethane rectangular parallelepiped made of the foaming material is polished by a bite or is melted and cut by a nichrome wire, thereby forming a cylinder. The polishing processing by the bite and the melt cutting processing by the nichrome wire will now be described in detail hereinbelow.
(4a) Polishing Processing
By pressing the bite of the polishing machine onto the urethane rectangular parallelepiped fixed in the horizontal direction and scanning the bite in the horizontal direction while rotating the rectangular parallelepiped around a horizontal axis, the external surface of the rectangular parallelepiped is polished, thereby obtaining a cylinder.
(4b) Melt Cutting Processing by a Nichrome Wire
A current is supplied to the nichrome wire fixed in the horizontal direction so as to generate heat, the nichrome wire which generates the heat is pressed onto the urethane rectangular parallelepiped, and the rectangular parallelepiped is rotated around the horizontal axis, thereby melting and cutting the external surface of the rectangular parallelepiped and obtaining a cylinder.
(5) Side Cutting
In order to set a length in the longitudinal direction of the cylinder to a predetermined length, both edge surfaces of the cylinder are cut to a desired length.
However, the toner supply roller obtained by the conventional processing method has the following problems.
(1) In Case of the Polishing Processing
After completion of the processing by polishing, a step of removing polishing powder by sucking or blowing the air or the like for the surface of the roller is needed. The polishing powder is likely to enter the sponge and it is difficult to completely eliminate the powder by the sucking or blowing of the air or the like. When the toner supply roller on which the polishing powder remains is used for development, the polishing powder is mixed into the toner. The toner containing the polishing powder is supplied to the developing sleeve and is sandwiched in a nip portion between the developing sleeve and the elastic blade, thereby obstructing a toner coating onto the developing sleeve. There is, consequently, a problem that a white stripe appears in the longitudinal direction on a developed image.
In case of processing by polishing, remaining portions of cells produced by cutting on the sponge surface remain in an inverted fuzzy state. The fuzz cannot be removed by air or the like. When the toner supply roller is used for development, the fuzz is torn off by the slide abrasion with the developing sleeve and becomes a cause of occurrence of the white stripe in the longitudinal direction on the image in a manner similar to the case of the polishing powder. Since there is a fear such that an outer diameter of the roller is largely fluctuated due to the influence by the fuzz, unless the outer diameter to be managed is set to a coarse value, a yield of the toner supply roller deteriorates. Further, since the polishing processing is executed while the bite is moving on the surface of the roller little by little, there is also a disadvantage such that it takes a long time for processing.
(2) In Case of Melt Cutting Processing by a Nichrome Wire
In case of a sponge in which a foaming density is high and a hardness is high and, further, in case of a sponge in which a diameter of foamed cell is small, since a load to be applied to the nichrome wire is large, the nichrome wire is easily deformed or torn off, so that a working precision deteriorates. On the other hand, when a processing speed is decreased so as not to apply a load onto the nichrome wire, the nichrome wire is not cut but a productivity of the toner supply roller deteriorates. When a current supply amount to the nichrome wire is increased and a heat generating temperature is raised, there is a problem such that a melting margin of the sponge is increased and a processing surface is deformed wavy and is not flattened.