US3918402A

US3918402A - Apparatus for developing an electrostatic latent image in electrophotography with a dry developing agent

Info

Publication number: US3918402A
Application number: US398548A
Authority: US
Inventors: Wasaburo Ohta
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1972-09-25
Filing date: 1973-09-18
Publication date: 1975-11-11
Anticipated expiration: 1992-11-11
Also published as: DE2345827A1; JPS5330329B2; JPS4953836A; DE2345827C2

Abstract

A powder cloud developing section and a brush developing section are disposed along the path of movement of an outer periphery of a drum on which an electrostatic latent image is supported, so that the electrostatic latent image is subjected to powder cloud developing and brush developing consecutively and developed into a visible image.

Description

United States Patent Ohta Nov. 11, 1975 [5 APPARATUS FOR DEVELOPING AN 3.040.704 6/1962 B1155 118/637 ELECTROSTATIC LATENT IMAGE IN 3.363.555 1/1968 Olden 101/426 3.375.807 4/1968 Eiehom 118/637 X ELECTROPHOTOGRAPHY WITH A DRY 3.543.720 12/1970 Drexler .1 18/637 DEVELOPING AGENT 3.670.701 6/1972 Weiler 118/637 [75] Inventor; wasabum Ohm, Yokohama, Japan 3.682.678 8/1972 Moradzadch ctul 117/175 3.707.390 12/1972 Sullivan, Jr. 118/637 [73] Assigneez Ricoh (10., Ltd., Tokyo, Japan [22] Filed: Sept. 18, 1973 Primary E.\'aminerMervin Stein Assistant lirc1n11'nerDouglas A. Salser [21] Appl' 398548 Attorney, Agent, 01' Fir/71Cooper, Dunham, Clark.

Griffin & Moran [30] Foreign Application Priority Data Sept. 25. 1972 Japan 47-95892 57 ABSTRACT 52 U.S. c1. 118/637; 427/18; ll8/D1G. 5 A Powder Cloud developing Section and brush devel- [51] Int. Cl. G03G 15/08 oping Saction are disposed along the P of [58] Field of Search 117/175; 118/623, 637, mam Of an uter periphery of a drum on which an ug 5 electrostatic latent image is supported. so that the electrostatic latent image is subjected to powder cloud 5 References Cited developing and brush developing consecutively and UNITED STATES PATENTS developed into a visible image. 2.732.775 1/1956 Young et al. 9.5/1.7 8 Claims, 4 Drawing Figures U.S. Patent Nov. 11,1975 Sheet10f2 3,918,402

4 W W wllllllllrlllllkrfllflr U.S. Patent Nov. 11, 1975 Sheet2of2 3,918,402

FIG-.3

FIG.4

APPARATUS FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE IN ELECTROPHOTOGRAPHY WITH A DRY DEVELOPING AGENT BACKGROUND OF THE INVENTION This invention relates to a method of and an apparatus for developing an electrostatic latent image in electrophotography using a dry developing agent and which are adapted for high speed developing of the electrostatic latent image.

Brush developing methods have been known for developing an electrostatic latent image in electrophotography with a dry developing agent. In carrying out such brush developing methods, a bristle brush or a magnetic brush has been used. The bristle brush consists of animal fur, synthetic fiber or bird feathers, which is used to apply toner particles to the electrostatic latent image to develop the same into a visible toner image. The magnetic brush is formed by mixing toner particles with a carrier consisting of iron powder or other ferromagnetic material to produce a developing agent and by bringing the carrier in the developing agent to an upright position with a megnet like the bristles of a brush, and the magnetic brush formed in this way is moved over the surface of the electrostatic latent image so as to develop the same.

When the electrostatic latent image to be developed by the brush developing method is supported on the outer periphery of a drum, the brush used is formed in roller shape so that one electrostatic latent image after another may be developed. When this is the case, the surface area of the drum with which the brush is brought into contact is reduced. An increase in the peripheral velocity of the rotating drum would thus result in a reduction in the amount of toner particles supplied to the electrostatic latent image, thereby producing images which are low in quality.

On the other hand, a powder cloud developing method has also been in use as a means for developing an electrostatic latent image in electrophotography with a dry developing agent. This method consists of scattering toner particles to form a powder cloud of high density in the air and exposing the electrostatic latent image to the atmosphere of this cloud so that the toner particlesmay adhere to the image and develop the same. This method is known as being able to produce a developed image of high quality, particularly as having a high resolving power and being able to reproduce half-tones with a high degree of fidelity. However, some disadvantages are associated with this method. When this method is used, it is difficult to produce a developed image of sufficiently high darkness unless the developing section is large in area; difficulty is experienced in forming a powder cloud; and background density tends to be higher than in other developing methods.

SUMMARY OF THE INVENTION This invention provides a method of and an apparatus for developing electrostatic latent images in electrophotography with a dry developing agent which combine brush developing with powder cloud developing into a single device to thereby. make up for each others defects and produce a developed image of sufficiently high darkness even if the electrostatic image carrying drum is rotated at high speed while completely elimihigh darkness and the developed image is free from background density. The invention offers these advantages, even when the electrostatic image carrying drum is rotated at high speed, thereby permitting a great increase in the rate of production of copies in electrophotography.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an apparatus for developing an electrostatic latent image with a dry developing agent comprising one embodiment of the invention;

FIG. 2 is a sectional view of an apparatus comprising another embodiment of the invention;

FIG. 3 is a fragmentary sectional view of an alternate form of powder cloud forming section for the developing apparatus shown in FIG. 1', and

FIG. 4 is a front view of an air pipe having a plurality of nozzles.

DESCRIPTION OF EMBODIMENTS The invention will now be described in detail with reference to embodiments shown in the drawings wherein like reference characters designate similar parts.

In FIG. 1, a photoconductive material layer 2, formed of selenium, zinc oxide, poly-N-vinylcarbazole or other photoconductive material, is provided on the periphery of a drum 1 made of steel, aluminum or other suitable material. An electrostatic latent image is formed on the photoconductive material layer 2 by a suitable conventional charging device and exposing device (not shown) as the drum 1 rotates in the direction of an arrow a at a constant rate on a shaft 3.

The photoconductive material layer 2 may be replaced by a dielectric layer formed of a copolymer of vinyl chloride and vinyl acetate, an alkyd resin or other dielectric substance. If this is the case, an electrostatic latent image can be formed on the dielectric layer by transfer printing from a photoconductive material layer or by an electrostatic recording process. Accordingly, it is to be understood that the term photoconductive material layer on which an electrostatic latent image is formed includes such a dielectric layer in this specification.

A powder cloud developing section A and a brush developing section B are disposed in the indicated order in respective positions which are leftwardly downwardly of the drum 1 in FIG. 1. An electrostatic latent image formed on the photoconductive material layer 2 moves successively along the two developing sections A and B as the drum 1 rotates. While moving, the electrostatic latent image receives a supply of toner particles through a powder cloud 4 formed in the developing section A and by a brush 5 formed in the developing section B and is developed into a visible image.

The brush 5 shown in the developing section B results from a magnetic brush developing process, though a fur brush may be used as the brush 5. In FIG. 1, a cylinder 7 supported by a shaft 6 and rotating in the direction of an arrow 12 is mounted leftwardly downwardly of the drum 1 and disposed in the developing section B. A number of fins 8 are attached to the periphery of the cylinder 7. Loosely supported on the shaft 6 is a mount 9 which is prevented from rotating about the shaft 6 by suitable means. The mount 9 mounts thereon permanent magnets 10 and 11 extending radially of the shaft 6 and disposed within the cylinder 7. The magnet 10 is fixedly disposed substantially along a normal to the periphery of the drum 1 and the magnet 11 is fixedly disposed substantially along a normal to a bottom wall of a casing 12 of the developing apparatus.

The casing 12 in which the cylinder 7 and the permanent magnets 10 and 11 are disposed contains therein a developing agent 13 comprising carbon black or other pigment in powder form treated with a resin which is generally referred to as a toner, and a carrier comprising iron, cobalt, nickel or other ferromagnetic substance in powder form.

In operation, when the cylinder 7 rotates in the direction of the arrow b, the developing agent 13 adheres to the outer periphery of the cylinder 7 as it is attracted to the permanent magnet 11 and the fins 8 move. After being adjusted in amount by a doctor blade 14, the developing agent 13 adhering to the outer periphery of the cylinder 7 is formed into the brush under the influence of a magnetic field formed by the permanent magnet 10.

The developing agent 13 forming the brush 5 moves with the cylinder 7 and is replaced by another supply of developing agent as the cylinder 7 rotates, so that the brush 5 consists of fresh developing agent at all times. Thus, as the cylinder 7 rotates, a supply of developing agent moves to a zone in which it is out of the influence of the magnetic field formed by the magnet so that developing agent which no longer forms the brush 5 is thrown off from the outer periphery of the cylinder 7 substantially in the direction of an arrow 0 by centrifugal forces exerted by the rotating cylinder 7. i

A shield 15 mounted on one edge of the casing 12 has connected to its lower end a baffle plate 15a which is disposed in the path of movement of the developing agent released from the outer periphery of the cylinder 7 and moving in the direction of the arrow c. Thus, this developing agent impinges on the baffie plate 15a and scatters into the powder cloud developing section A where it forms the powder cloud 4.

Bias voltages of opposite polarities are impressed on the shield 15 and drum 1 respectively from a power source 16 so that an electric field is formed in the developing section A and tends to direct the toner particles in the powder cloud 4 toward the photoconductive material layer 2 on the outer periphery of the drum 1. The electrostatic latent image introduced into the developing section A receives a supply of these toner particles and is rendered into a visible image by the action of the electric field.

The electrostatic latent image which moves while receiving a supply of toner particles from the powder cloud 4 reaches the developing section B in which it is brushed by the brush 5 and receives a supply of toner particles. This ensures that the electrostatic latent image is positively developed into a visible image and that excess toner particles adhering to the background of the image during powder cloud developing are removed by the brushing action of the brush 5. The supply of toner particles to the electrostatic latent image and the removal of excess toner particles from the background of the electrostatic image by the action of the brush 5 can be controlled to an optimum degree by controlling with a suitable control agent the degree to 5 which the toner particles are charged.

After the developing agent is released from the outer periphery of the cylinder 7, any residual developing agent remaining thereon is removed by a brush roller 17 disposed leftwardly of the cylinder 7 in FIG. 1, so

ing agent supply operation. The brush roller 17 which may be rotated in any direction as desired may be replaced by a scraper 18 as shown in dash-and-dot lines in the figure.

In FIG. 1, a toner supply bottle 19 is arranged in an inverted position and detachably mounted in an opening 12a formed at a left shoulder of the casing 12. A lid 20 adapted to close the mouth of the bottle 19 is slidably mounted in the casing 12 and moved into an operative position in which it opens the bottle 19 and permits the toner particles therein to be supplied to the casing 12 any time as desired. The bottle 19 is formed at its bottom with an opening 19a to facilitate moving of the toner particles downwardly. A seal member 21 consisting of soft fur or sponge is mounted on the shield 15 to close the gap between the shield 15 and the outer periphery of the drum 1 so that the powder cloud 4 is enclosed in the casing 12.

Preferably, the cylinder 7 is made of aluminum, plastics or other non-magnetic material. However, the cylinder 7 may be made of a magnetic material. The fins 8 may be made of any known material in any known shape and configuration and attached to the cylinder 7 in any known manner. When it is possible, the fins may be done without. In this embodiment, the developing agent is released from the cylinder 7 by centrifugal forces exerted on the cylinder and this makes it necessary to rotate the cylinder at a relatively high peripheral velocity. When the developing agent is released from the cylinder and scattered in the developing section A by other means than centrifugal forces, the cylinder may be rotated at any peripheral velocity as desired. Also, in place of rotating the cylinder, the permanent magnets may be moved while holding the cylinder stationary. In the embodiment shown and described, two permanent magnets are used, but the number of permanent magnets may be varied as desired.

In FIG. 2, there is shown another embodiment of the invention in which the developing agent on the outer periphery of the cylinder 7 is scooped up by a brush roller 22 rotating in a predetermined direction and scattered by bristles 22a and a number of wires 23, arranged adjacent the roller 22 to form a powder cloud 4 between the roller 22 and the drum 1. The brush roller 22 disposed leftwardly upwardly of the cylinder 7 in FIG. 2 has planted thereon bristles 22a of a relatively resilient material, such as pigs fur or wire, and is supported on a shaft 22b. The wires 23 for stripping the de veloping agent off the bristles 22a are arranged on the side of the periphery of the roller 22 near to the outer periphery of the drum 1. The developing agent scooped by the brush 22a from the outer periphery of the cylinder 7 is scattered in the direction of the periphery of the drum 1 by being stripped off the brush roller 22 by the wires 23, thereby forming the powder cloud 4 between the brush roller 22 and the drum 1.

that the cylinder surface is ready for the next develop- A shield 24 corresponding to the shield of the embodiment described with reference to FIG. 1 is curved in this embodiment. A wire netting 26 made of stainless steel, copper or other electrically conducting material and serving as an opposite electrode is mounted between an upper edge of the shield 24 and a support wire 25 supported between the two developing sections A and B and disposed along the outer periphery of the drum 1. Bias voltages are impressed on the wire netting 26 and the drum 1 from the power source as aforementioned, so that the toner particles passing through the wire netting 26 are supplied to the electrostatic latent image on the outer periphery of the drum 1.

In the embodiment shown and described, the cylinder 7 has no fins, and a scraper 27 is maintained at one end of engagement with the outer periphery of the drum 7 for scraping the residual developing agent off the drum 7. It is to be understood that the cylinder 7 may be provided with fins and the developing agent may be removed from the cylinder 7 as described with reference to the first embodiment shown in FIG. 1.

In FIG. 2, a funnel-shaped toner container 28 is mounted on a left shoulder of the casing 12 and has at its lower portion an opening 28a in which a brush roller 29 is mounted and adapted to rotate in the direction of an arrow d as desired so as to deliver an additional supply of toner particles to the developing agent 13 any time as desired. The brush roller 29 may be replaced by a roller provided on its outer periphery with a rough material layer. Any other known toner supply means than those shown and described herein may be used as desired.

A roller 31 having a plurality of agitator blades 30 mounted on its outer periphery is disposed in a leftward downward portion of the casing 12 as shown in FIG. 2. The roller 31 may be rotated in any direction at any time as desired to agitate the developing agent 13 in the casing 12.

FIG. 3 shows an embodiment in which a stream of air is ejected through nozzles 32a against the developing agent on the outer periphery of the cylinder 7 to blow off the agent in the direction of the arrows to form the powder cloud 4. The nozzles 32a (See FIG. 4) are each mounted at a forward end portion of one of several tubular members 32 connected to an air supply line 34 supported by a left shoulder of the casing 12 and a shield 33. A valve 35 is mounted on the air supply line 34 which is connected to a blower (not shown) for supplying a blast of air to the nozzles 32a for ejection therethrough.

In the embodiments shown in FIG. 2 and FIG. 3, the provision of the wire netting 26 is not essential. When no wire netting 26 is provided, a bias voltage is impressed on the

shield

24 or 33. In the embodiments shown in FIG. 1 to FIG. 3, a permanent magnet 36 of opposite polarity to that of the permanent magnet 10 may be mounted on the mount 9 in a position shown in dash-and-dot lines in FIG. 3 which corresponds to the portion of the outer periphery of the cylinder 7 from which the developing agent is scooped or blown off to form the powder cloud 4. This arrangement is effective to facilitate dispersion of the carrier by magnetic repulsion between the opposite poles of the magnets. In-all the embodiments, the permanent magnets may be replaced by suitable electromagnets.

Also, in all the embodiments shown and described herein, the powder cloud 4 is formed by the developing agent removed from the outer periphery of the cylinder 7 after it has adhered thereto by magnetic attraction, however, it is to be understood that the powder cloud forming means may be mounted separately from the brush developing means, although a certain degree of reduction in efficiency results.

What is claimed is:

1. An electrophotographic apparatus for developing an electrostatic latent image with a dry developing agent comprising:

a. a movable member having an electrostatic latent image formed on the surface thereof;

b. a brush developing section containing a brush developing means comprising:

i. a supply of developing agent; and

ii. a rotatable brush roller disposed in said supply and adjacent the path of movement of the surface of said movable member for applying said developing agent from said supply to said electrostatic latent image; and

c. a powder cloud forming section disposed adjacent said brush developing section upstream along the path of movement of the surface of said movable member and comprising powder cloud forming means for removing the developing agent from said rotating brush roller and scattering it to form a powder cloud for developing said electrostatic latent image,

such that the electrostatic latent image is developed into a visible image by powder cloud developing and brush developing to which it is subjected consecutively.

2. An apparatus according to claim 1 wherein said rotatable brush roller comprises a cylinder and magnetic means mounted within said cylinder and relatively rotatable therewith for forming a magnetic brush on the surface of said cylinder from said developing agent and for causing the magnetic brush to rotate around said cylinder.

3. An apparatus according to claim 2 wherein said powder cloud forming means comprises a wire netting serving as an opposite electrode for promoting the supply of the developing agent to the electrostatic latent image.

4. An apparatus according to claim 2 wherein said powder cloud forming means comprises air-blast nozzles for scattering the developing agent.

5. An apparatus according to claim 2 wherein said powder cloud forming means comprises a second brush roller for scattering the developing agent, and wires for removing the developing agent from the brush of the second brush roller.

6. An apparatus according to claim 2 wherein said movable member comprises a rotating drum.

7. An apparatus according to claim 2 wherein said magnetic means is fixed with respect to said brush developing section and said cylinder is rotated relatively thereto.

8. An apparatus according to claim 7 wherein said powder cloud forming means comprises a number of fins mounted on the outer periphery of said cylinder for throwing the developing agent out of the outer periphery of the cylinder, and a baffle plate for scattering the developing agent thrown out of the cylinder toward the powder developing section.

Claims

1. An electrophotographic apparatus for developing an electrostatic latent image with a dry developing agent comprising: a. a movable member having an electrostatic latent image formed on the surface thereof; b. a brush developing section containing a brush developing means comprising: i. a supply of developing agent; and ii. a rotatable brush roller disposed in said supply and adjacent the path of movement of the surface of said movable member for applying said developing agent from said supply to said electrostatic latent image; and c. a powder cloud forming section disposed adjacent said brush developing section upstream along the path of movement of the surface of said movable member and comprising powder cloud forming means for removing the developing agent from said rotating brush roller and scattering it to form a powder cloud for developing said electrostatic latent image, such that the electrostatic latent image is developed into a visible image by powder cloud developing and brush developing to which it is subjected consecutively.