US3696785A

US3696785A - Development apparatus

Info

Publication number: US3696785A
Application number: US99443A
Authority: US
Inventors: Paul G Andrus
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1970-12-18
Filing date: 1970-12-18
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10
Also published as: CA949824A

Abstract

Xerographic development apparatus employing a donor member adapted to retain toner on its periphery and a number of processing stations arranged around its periphery, including a loading station having means to load toner on the peripheral surface of the donor member, and a toner layer preparation station having means to prepare the toner layer on the donor member prior to presentation of the toner layer to the imaged region of a photoconductor.

Description

United States Patent [15] 3,696,785 Andrus 1 Oct. 10, 1972 [S4] DEVELOPMENT APPARATUS 3,203,394 8/1965 Hope et a1 ..l18/637 72 Inventor: Paul G. Andrus, Powell, Ohio 3,331,355 7/1967 1301181168 et a1 ..1 18/637 [73] Assignee: Xerox Corp., Stamford, Conn. p Emmmer Me1-vin Stein 22 Filed; 1 1970 Assistant Examiner-Leo Millstein Attorney-James J. Ralabate, James P. O'Sulhvan and [211 Appl. No.: 99,443 Donald Daley [52] US. Cl. ..118/637, l17/17.5, 355/3 ABSTRACT [51] int. Cl. 13/00 xerographic development apparatus employing a [58] Field of Search ..118/637; 1 17/ 17.5; 93/5151}; donor member adapted to retain. toner on its periphery and a number of processing stations arranged around its periphery, including a loading sta- [56] References Cited tion having means to load toner on the peripheral sur- UNITED STATES PATENTS face of the donor member, and a toner layer preparatron station having means to prepare the toner layer 2,820,716 1/ 1958 Harmon eta] ..1 17/ 17.5 on the donor member prior to presentation of the 3,152,012 10/ 1964 Schaffert ..1 18/637 toner layer 0 the imaged region ofa photoconducton 3,427,242 2/1969 Mihajlov ..96/1 3,405,682 10/1968 King et a1. ..118/637 14 Claims, 2 Drawing Figures VACUUM PATENTED B W 3.696.785

VACUUM INVENTOR. PAUL 6. AN DRUS ATTORNEY DEVELOPMENT APPARATUS BACKGROUND OF THE INVENTION This apparatus relates to xerography and more particularly to an improved method and apparatus for the development of electrostatic images by which a toner layer which is of controlled thickness and uniformity, and which is agglomerate-free, is presented to the latent image to develop it.

In the reproduction process of xerography, a photoconductive surface is charged and then exposed to a light pattern of the information to be reproduced, thereby fonning an electrostatic latent image on the photoconductive surface. Toner particles, which may be finely divided, pigmented, resinous material, are applied to the latent image where they are attracted to the photoconductive plate in imagewise configuration, thereby forming a toner image on the photoconductive surface. The toner image can be fixed and made permanent on the photoconductive surface or it can be transferred to another surface where it is fixed.

One known method of developing latent electrostatic images is by a process called transfer development. Transfer development broadly involves bringing a layer of toner to an imaged photoconductor where toner particles will be transferred from the layer to the imaged areas. In one transfer development technique, a layer of toner particles is applied to a donor member which is capable of retaining the particles on its surface and then the donor member is brought into close proximity to the surface of the photoconductor. In the closely spaced position, particles of toner in the toner layer on the donor member are attracted to the photoconductor by the electrostatic charge on the photoconductor so that development takes place.

In one embodiment of a transfer development system, a cylindrical donor member is rotated while closely spaced from the moving surface of a photoconductive drum bearing an electrostatic latent image thereon. As the donor member turns, its peripheral surface, which is adapted to retain toner particles thereon,

rotates through a reservoir of toner and a layer of toner particles is deposited on this surface. As rotation continues the toner layer is brought adjacent the photoconductive surface where the toner particles in the layer are attracted to the imaged areas. The donor member then continues to rotate so that the portion of its surface which gives up toner to the photoconductive surface recirculates, after development, through the toner reservoir and is retoned. In this manner, a continuous development process is carried out.

Although the toner layer formed on the surface of the donor member in the manner described above is normally adequate to develop the latent image on the photoconductive surface, the toner images produced are not always of the highest quality. A degradation in quality can occur for a number of reasons. For instance, the thickness of the toner layer on the donor member may not always be uniform and as a consequence when the toner layer is brought adjacent to the photoconductive surface, the toner in the greater regions of thickness will be compacted between the photoconductive surface and the donor member surface. This will result in a compaction of toner particles and the compacted mass may be transferred to the photoconductive surface or, no toner at all may be transferred. Also, those regions of the toner layer that have been compacted between the donor and the photoreceptor have a tendency to cause the toner to deposit in non-imaged areas. In regions of least thickness, the toner will be too far away from the photoconductive surface to afford effective development.

Another problem associated with touchdown development systems known heretofore, is that under certain conditions, toner particles have a tendency to agglomerate, i.e., several particles will cling together so that they act as one. Whatever the cause, it prevents each individual particle in the agglomerate from being effectively influenced by the attractive forces emanating from specific areas of the photoconductor.

In addition to the requirement of a toner layer of uniform thickness which is free of agglomerates, it has been found desirable to have the toner particles in the layer charged uniformly so that all that are needed can be efi'ectively transferred to the imaged areas of the photoconductor. Further, in the continuous process of development as described above, wherein a given point on the donor surface rotates through the toner reservoir to be loaded, is then brought adjacent the photoconductor to develop, and then back into the toner reservoir to be loaded, it is necessary to prepare the toner surface for reloading after development has taken place. This preparation is necessary so that an image history or ghost pattern is not retained in the toner layer after the donor surface has been reloaded with toner. If a ghost pattern is retained it can interfere with accurate development of the imaged portion of the photoconductive surface.

The art of xerographic development would be significantly advanced if all of the foregoing problems and disadvantages could be eliminated.

Accordingly, it is an object of the invention to improve apparatus for developing latent electrostatic images.

It is a further object of the invention to improve apparatus for accomplishing transfer development.

It is a still further object of the invention to eliminate ghost images in the toner layer of a donor member in the development of xerographic images.

It is yet a further object of the invention to remove toner agglomerates from the toner layer on a donor member in the development of xerographic images.

Another object of the invention is to improve transfer development apparatus to insure that the toner layer on the donor member is of uniform thickness prior to its presentation to the photoconductor.

SUMMARY OF THE INVENTION A This invention is directed to a transfer development apparatus having a donor member which is loaded with toner. The donor member is adapted to be brought into development relation with a photoconductor bearing a latent image thereon, whereby toner particles on the donor member are deposited in imagewise configuration on the photoconductor. The donor member has in association therewith, a means to condition the toner layer, prior to its presentation to the development region of the photoconductor, by removing agglomerates from the toner layer and making the toner layer of uniform thickness. This means is located between the loading means for the donor member and the zone where active development takes place. It broadly comprises a clean-up roll which is spaced a short distance from the surface of the donor roll. The spacing between the clean-up roll and the donor roll surface should be such that it comes into contact with the outermost region of the toner layer and removes all toner above a certain thickness without compacting the remainder of the toner layer on the donor member. At the same time, the action of the clean-up roll removes all toner agglomerates in the toner layer.

In an embodiment where the donor member is an endless surface, such as a cylinder, the invention includes a means, such as a cleaning means, to prepare the surface of the donor member for reloading with toner. This means is located adjacent the periphery of the donor member, between the region where active development takes place and the toner reservoir. To assist in removing the toner via this means, a neutralizing charging means is positioned at a point just after the active development zone and before the cleaning means, to neutralize the charge on the toner layer.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be used in conjunction with the accompanying drawing, wherein:

FIG. 1 is a sectional view of xerographic apparatus in accordance with the present invention.

FIG. 2 is an isometric view of a clean-up roll in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is a transfer development system in which toner is applied to an electrostatic latent image on a photoconductive plate to develop the image. Although the system is described herein as part of a xerographic copier, it can be utilized in conjunction with any reproduction system wherein a latent image is to be developed by applying toner thereto.

Referring to FIG. 1 of the drawing, there is shown a xerographic reproduction system employing the present invention. In this apparatus the xerographic plate is in the form of a drum which passes through stations A through E in the direction shown by the arrow. The drum has a suitable photosensitive surface, such as one including selenium overlying a layer of conductive material, on which a latent electrostatic image can be formed. The various stations about the periphery of the drum which carry out the reproduction process are: charging station A, exposing station B, developing station C, transfer station D, and cleaning station E. Stations A, B, D, and E represent more or less conventional means for carrying out the charging, exposing, transfer and cleaning. Apart from their association with the novel arrangement to be described with respect to station C, they form no part of the present invention.

At station A a suitable charging means 12, e.g., a corotron, places a uniform electrostatic charge on the photoconductive material. As the drum rotates, a light pattern, via a suitable exposing apparatus 14, e.g., a projector, is exposed onto the charged surface of the drum. The latent image formed on the surface of drum 10 is developed or made visible by the application of a finely divided, pigmented, resinous powder, called toner, at developing station C, which is described in greater detail infra. After the drum is developed at station C, it passes through transfer station D, comprising copy sheet 16, corona charging device 18 and fuser device 20. Following transfer and fixing of the developed image to the copy sheet, the drum rotates through cleaning station E, comprising cleaning device 22, e.g., a rotating brush.

At developing station C, the apparatus includes a donor roll 24, rotatably mounted adjacent a toner reservoir 26, containing a supply of toner 28. The donor roll 24 is positioned so that a portion of its periphery comes into contact with toner 28. The donor roll 24 is also located so as to provide a small gap between the surface of drum l0 and the outer surface of a toner layer carried by donor roll 24. This gap can conveniently be approximately 1 mil.

While donor roll 24 can be any device adapted to carry a layer of toner to the development region, a preferred type is that embodying the principles described in U. S. Pat. No. 3,203,394. In essence, a preferred donor roll can comprise, an electrically conductive support member in the form of a cylinder, a thin electrically insulating layer overlying the support member, and a continuous, electrically conductive screen pattern overlying the insulating layer. To effect toner loading of a donor roll of this type, a charging means adapted to apply a charge potential to the conductive screen with respect to the conducting support cylinder is employed. As the donor roll rotates into contact with toner particles in the toner reservoir, toner particles are deposited on the surface of the donor roll. Since the toner mass contains both positively and negatively charged particles, the entire donor surface becomes coated with toner. If the screen pattern is connected to a positive charging potential, negative toner will go to the screen itself and positive toner will go to the areas between the lines of the screen. In this manner the donor roll will continuously pick up a thin layer of toner particles.

As indicated above, because of conditions difficult to control, some of the toner particles tend to agglomerate and be deposited on the surface of the donor roll and protrude well above the mean thickness of the toner layer. In addition, if some provision is not made for controlling the thickness of the toner layer carried by the donor roll, thicker regions of the toner layer will be compacted between the donor roll surface and the surface of the photoconductive layer in the development zone, also producing agglomerates. In order to insure removal of agglomerates and also to control the thickness of the toner layer presented to the imaged photoconductive drum, a clean-up roll 32 is positioned in close proximity to the surface of the donor roll at a point located in advance of the active development region. Located between clean-up roll 32 and the toner reservoir is a charging means 30, such as a corona charging device, which places a uniform charge on the toner layer having a polarity opposite to the polarity of the latent image on the photoconductive drum.

The clean-up roll 32 is calculated to remove agglomerates from the toner layer carried by the donor and to reduce the thickness of the toner layer to a uniform thickness. At the same time the clean-up roll is calculated to remove loosely adhen'ng but non-agglomerated toner which would undesirably to to the background area of the copy.

The clean-up roll 32 may be either one of two types: it may be a roll, at ground potential, which removes agglomerates and smooths the surface of the toner layer by a purely mechanical action or it may be an electrically biased roll which removes agglomerates and loosely adhering toner by electrostatic attraction. When removing agglomerates and excess toner by strictly mechanical forces, the clean-up roll can be of a design having micro appendages on the surface thereof. FIG. 2 of the drawing shows a clean-up roll 44 of this type having micro appendages 46 disposed on the surface thereof. By micro appendages is meant small individual extensions from the surface of the roll or ridgelike extensions extending along the length of the roll. When this type of roll is brought into contact with the upper region of the toner layer and rotated at a faster rate than the rotation of the donor roll, the appendages will strike agglomerates, free them or break them up and, at the same time, reduce the overall level of the toner layer to a comparatively uniform thickness. For example, a roll of trihelicoid design, having a rotation rate of from 50 to 75 times that of the rate of rotation of the donor drum has been found satisfactory. It has been found desirable to rotate the clean-up roll in a direction counter to the direction of rotation of the donor roll.

When using an electrically biased roll, the roll 32 can be smooth-surfaced, as shown in FIG. 1 of the drawing, and need not rotate at a rate faster than the rate of rotation of the donor roll. The biased roll will remove agglomerates and loosely adhering toner and yield a toner layer of more or less uniform thickness With either type of roll, a cleaning mechanism is positioned adjacent the surface of the clean-up roll and is calculated to remove the particles which are dislodged or electrostatically attracted from the toner layer of the donor roll. This cleaning mechanism can be a brush 34, employed in association with a vacuum system 36, which draws the removed toner particles from the cleaning brush.

After passing by the clean-up roll 32, the agglomerate-free toner layer, of controlled thickness, is presented to the charged and exposed photoconductor and some of it is attracted to the-image areas of the photoconductor, whereupon transfer development, as described above, takes place. Because the toner layer is of uniform thickness, no toner compaction is experienced. This coupled with the absence of agglomerates, results in copy of excellent quality. Following development, the donor roll is prepared for reloading by exposing residual toner thereon to a neutralizing charge, via a charging means 38, to make easier the removal of the residual toner by way of a suitable cleaning means, e.g., a rotating brush 40 equipped with a vacuum means 42, The donor roll is thus freed of any image history from the development region and is prepared to pick up fresh toner.

It is to be understood that while for purposes of illustration the donor member has been described basically as a cylinder, it may be an endless belt or other planar surface adapted to deliver toner from the toner source to the development region, after subjecting the toner layer to the conditioning apparatus described herein. A vibrating means may be used in conjunction with the toner reservoir to keep the toner particles loose and to assist in loading the donor roll.

While the present invention has thus far been described with respect to a transfer development technique wherein the donor member and toner layer are spaced from the imaged surface, and toner particles must traverse an air gap to reach the imaged regions of the photoconductor, this has been only by way of illustration. It is to be understood that the present invention can be employed in association with other transfer development techniques where a toner laden donor actually contacts the imaged photoreceptor very lightly and no air gap is involved. In one such technique the toner-laden donor is rolled in a non-slip relationship into and out of contact with an electrostatic latent image to develop the image in a single rapid step. In another such technique the toner-laden donor is rolled in a non-slip relationship into and out of contact with an electrostatic latent image to develop the image in a single rapid step. In another such technique the tonerladen donor is skidded across the xerographic surface. Skidding the donor by as much as the width of the thinnest line will double the amount of toner available for development of a line which is perpendicular to the skid direction, and the amount of skidding can be increased to achieve greater density or greater area coverage.

It is to be noted, therefore, that the term transfer development is generic to development techniques where l) the toner layer is out of contact with the imaged photoconductor and the toner particles must traverse an air gap to effect development, (2) the toner layer is brought into light rolling contact with the imaged photoconductor to effect development, and (3) the toner layer is brought into contact with the imaged photoconductor and skidded across the imaged surface to effect development. Transfer development has also come to be known as touchdown development and includes the three techniques described above.

Conventional drive means, e.g., motors and belts, are employed to drive the several movable members all in a manner well within the skill of the art.

Since many changes can be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the drawing and specification should be interpreted illustratively and not in a limited sense.

What is claimed is:

1. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said developing means including in combination:

a. a donor member capable of retaining toner parti cles along a transportable surface thereof,

b. means to continuously advance said donor member past a plurality of treating stations, said treating stations comprising:

1. a toner loading station including a supply of toner particles, at which toner particles are contacted and retained by said donor member;

2. a clean-up station having a clean-up member operative to convert said toner particles retained on said donor member to a toner layer of uniform thickness and to remove toner agglomerates therefrom; and

2 a developing station at which the agglomeratefree toner layer of uniform thickness is presented in developing relation to said latent image on said xerographic plate.

2. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said means including a. an endless donor member capable of retaining a layer of toner particles along a transportable surface thereof;

. a clean-up station having a rotatable, cylindrical clean-up member located adjacent said donor member so as to contact the outermost region of said layer of toner particles, said clean-up member being so constructed and designed to convert the layer of retained toner particles to one of comparatively uniform thickness and remove toner agglomerates therefrom; and

3. a developing station at which the agglomeratefree toner layer of uniform thickness is presented in developing relation to said latent image on said xerographic plate.

3. The apparatus of claim 2 wherein said clean-up member has micro-appendages on the curved surface thereof and said clean-up member is adapted to rotate at a rate in excess of the rate of transport of the surface of said donor member.

4. The apparatus of claim 3 wherein said clean-up member is adapted to operate at ground potential.

5. The apparatus of claim 3 wherein said clean-up member is adapted to rotate in a direction counter to the direction of transport of the surface of said donor member.

6. The apparatus of claim 3 wherein a charging station is located between said toner loading station and said clean-up station and is adapted to place a uniform charge on said toner particles retained by said donor member of a polarity opposite to that of said latent image.

7. The apparatus of claim 3 wherein said donor member is located adjacent said xerographic plate so that said agglomerate-free toner layer of uniform thickness is presentable in closely spaced developing relation to said latent image.

8. The apparatus of claim 3 having a cleaning means located between said developing station and said toner loading station and adapted to remove at least the outermost region of said toner layer.

9. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said means including a. an endless donor member capable of retaining a layer of toner particles along a transportable surface thereof;

. a clean-up station having a rotatable, cylindrical clean-up member located adjacent said donor member so as to contact the outermost region of said layer of toner particles, said clean-up member being so constructed and designed to convert the layer of retained toner particles to one of comparatively uniform thickness and remove toner agglomerates therefrom wherein said clean-up member is an electrically biased, comparatively smooth-surfaced cylindrical member and is adapted to rotate at a rate substantially equal to the rate of transport of the toner layer; and

10. The apparatus of claim 9 wherein said clean-up member is adapted to rotate in a direction counter to the direction of transport of the toner layer.

11. The apparatus of claim 10 having a toner removal means in association with said clean-up member adapted to remove toner particles from the surface of said clean-up member.

12. The apparatus of claim 9 wherein a charging station is located between said toner loading station and said clean-up station and is adapted to place a uniform charge on said toner particles retained by said donor member of a polarity opposite to that of said latent image.

13. The apparatus of claim 9 wherein said donor member is located adjacent said xerographic plate so that said agglomerate-free toner layer of uniform thickness is presentable in closely spaced developing relation to said latent image.

14. The apparatus of claim 9 having a cleaning means located between said developing station and said toner loading station and adapted to remove at least the outermost region of said toner layer.

Claims

1. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said developing means including in combination: a. a donor member capable of retaining toner particles along a transportable surface thereof, b. means to continuously advance said donor member past a plurality of treating stations, said treating stations comprising: 1. a toner loading station including a supply of toner particles, at which toner particles are contacted and retained by said donor member; 2. a clean-up station having a clean-up member operative to convert said toner particles retained on said donor member to a toner layer of uniform thickness and to remove toner agglomerates therefrom; and 2 a developing station at which the agglomerate-free toner layer of uniform thickness is presented in developing relation to said latent image on said xerographic plate.

2. a clean-up station having a clean-up member operative to convert said toner particles retained on said donor member to a toner layer of uniform thickness and to remove toner agglomerates therefrom; and 2 a developing station at which the agglomerate-free toner layer of uniform thickness is presented in developing relation to said latent image on said xerographic plate.

2. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said means including a. an endless donor member capable of retaining a layer of toner particles along a transportable surface thereof; b. means to continuously advance said donor member past a plurality of treating stations, said treating stations comprising:

2. a clean-up station having a rotatable, cylindrical clean-up member located adjacent said donor member so as to contact the outermost region of said layer of toner particles, said clean-up member being so constructed and designed to convert the layer of retained toner particles to one of comparatively uniform thickness and remove toner agglomerates therefrom; and

2. a clean-up station having a rotatable, cylindrical clean-up member located adjacent said donor member so as to contact the outermost region of said layer of toner particles, said clean-up member being so constructed and designed to convert the layer of retained toner particles to one of comparatively uniform thickness and remove toner agglomerates therefrom wherein said clean-up member is an electrically biased, comparatively smooth-surfaced cylindrical member and is adapted to rotate at a rate substantially equal to the rate of transport of the toner layer; and

3. a developing station at which the agglomerate-free toner layer of uniform thickness is presented in developing relation to said latent image on said xerographic plate.

9. In an apparatus for developing an electrostatic latent image formed on the surface of a xerographic plate, means for developing said latent image, said means including a. an endless donor member capable of retaining a layer of toner particles along a transpoRtable surface thereof; b. means to continuously advance said donor member past a plurality of treating stations, said treating stations comprising: