US3542466A - Development apparatus - Google Patents

Description

United States Patent [72] lnventors Carol A. Fox

Rochester; Merton R. Spear, Jr., Penfield; Armistead Wharton, Henrietta, New York [21] Appl. No. 692,335 [22] Filed Dec. 21, 1967 [45] Patented Nov. 24, 1970 [73] Assignee Xerox Corporation Rochester, New York a corporation of New York [54] DEVELOPMENT APPARATUS 5 Claims, 3 Drawing Figs. [52] US Cl 355/3; 1 18/637 [51] Int. Cl G03g 15/08 [50] FieldofSearch 355/3,14, 17; 118/637: 117/17.5 (Consulted) [56] References Cited UNITED STATES PATENTS 2,624,652 l/1953 Carlson 118/637 3,103,445 9/1963 Bogdonoff 117/17.5 3,160,091 12/1964 Schwertz 117/17.5X 3,318,284 5/1967 Hojo ll7/17.5X 3,374,768 3/1968 Lawes l17/17.5X

Primary Examiner.lohn M. Horan Attorneys-Norman E. Schrader, James .1. Ralabate and Ronald Zibelli ABSTRACT: Apparatus for the development of an electrostatic latent image which includes a housing having a sump area for containing a supply of electroscopic toner powder and a brush member for receiving the electroscopic toner powder charged to a polarity opposite that of an electrostatic latent image to be developed and delivering the electroscopic marking particles into contact with the surface of the electrostatic latent image. To affect the loading ofthe brush member. the electroscopic toner particles are scooped from the sump area and propelled in the direction of the brush member by a rotating plate member having finger elements which finger elements have a cup portion arranged at their extremity for scooping out a predetermined amount of toner powder from the sump portion ofthe housing. Each of the finger elements is formed with an arcuate shape from a resilient material in contact with interference member in the path of the fingers causing the fingers to flex and then return to an original position thereby propelling the toner powder toward the brush member. To affect proper charging of the toner particles. a screen member is positioned intermediate the brush member and the finger elements and is made out ofa material characterized by an electrostatic property removed in triboelectric series from the toner particles thereby causing the particles to be properly charged when passed through the screen and before being received onto the brush member.

Patented Nov. 24, 1970 Sheet INVENTORS MERTON R SPEAR JR. CAROL A. FOX BY ARM |STEAD WHARTON ATTORNEYS background.

. 1 DEVELOPMENT APPARA US This invention relates in general to electrostatic copying and in particular to apparatus for developing electrostatic latent images.

In one form of electrostatic printing, referred to as xerography and described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to aconductive backing is used to support electrostatic images. Usually the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of document information to be reproduced to discharge the charge inv the areas where light strikes the layer. The undischarge'd areasof the layer thus form an electrostatic latent image in conformity with the light pattern. The electrostatic latent image is developed by contacting it with a finely divided electrostatically attractable material such as an electroscopic resinous powder which is held in image areas by the electrostatic charges on the layer. The powder image is subsequently transferred to a sheet of paper or other support surface to which it is affixed to form a permanent print.

One ofthe more common methods of presenting developing material to the image is by cascading a two-component developer made up of electroscopic'marking particles referred to as toner" and coarse granular material called "carrier" over the image. The carrier is removed from thetoner inthe triboelectric series so that a triboelectric charge is generated between the toner and the carrier. Such charge causes the toner to adhere to the carrier which also provides mechanical control of the toner'so that the toner can be readily handled and brought into contact with the image to be developed. The toner is then attracted to the electrostatic latent image to produce a visible powder image. One drawback of the twocomponent developer used in cascade-type development is that the bouncing'action of the carrier granular material has an adverse effect on certain photoconductive layers. Also cascade-type development requires a great deal of physical space relative to the photoconductor surface and-for these as well as other reasons has imposed certain limitations on the development ofelectro static latent images.

As an alternative there is. brush development in which a brush in the form of a cylinder or the like frictionally electrifies toner particles which it contacts and presents the particles to the electrostatic latent image as described, for example, in U. 5. Pat. No. 3,251,706. In brush development it is common to use brushes which are made from synthetic or vegetable fibers oranimal fur. The developing material usually consists of the carrier and toner mentioned above or toner used alone. Also the brush fibers can be magnetic carrier granules formed into a brushlike formation through the use of a magnetic field as described, for example, in US. Pat. Nos. 2,832,311 and 2,874,063. r f I Although brush development has proved commercially successful, it has been noted that under certain atmospheric con-' ditions, there has been a tendency'to produce undesirable development characteristics. More specifically, at low relative humidities, images are developed at a decreased density and at high relative humidities toner is deposited in the background or nonimage areas. While it isnot completely understood, it is believed that at low relative humidity conditions the brush frictionally contacting toner develops a net .bias potential to suppress the image charges to limit the attraction of toner to the image. On the other hand with increasing relative humidity less charge is imparted triboele ctrically by the brush to the toner thereby increasing background deposition due to loosely adhering toner being easily attracted to the image channels or scooped out areas in the toner.

Attempts to overcome the above-noted disadvantages have come in air-conditioning which is unduly burdensome and expensive or by electrically biasing the brush which has not proven entirely successful. I

In accordance with the present invention the development of electrostatic latent images by brush action is greatly enhanced notwithstanding varying relative humidities enabling higher quality prints to be produced. Furthermore, due to the unique manner in which the toner particles are dispensed onto the brush, no channels or scooped out areas are formed in the toner sump.

It is therefore an object of the invention to improve the development ofelectrostatic latent images.

It is another object ofthe invention to minimize background in the development-of images notwithstanding the fact that development is effected in an atmosphere of variable relative humidity.

It is another object of the invention to increase the density of developed images without any corresponding increase in background. a

It is a further object of the invention to enhance the overall quality ofprints attainable by brushdeveloping techniques.

It is still a further object of the invention to dispense toner onto a brush to be used for developing images more simply than heretofore.

These and other objects of the invention are obtained, generally speaking, by imparting an electrostatic charge to the toner particles before they are received onto the developing brush and by loading them uniformly thereby insuring optimumly charged toner for development irrespective of relative humidity conditions.

For a better understanding'of the invention as well as other objects and further features thereof. reference is bad to the following detailed description of the invention to be read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of xerographic reproduction apparatus utilizing developing apparatus according to the invention;

FIG. 2 is an isometric view ofa brush developing assembly according to the present invention with its housing partially broken away to better illustrate its parts; and

. FIG. 3 is a diagrammatic view ofan alternative embodiment of apparatus according to the present invention.

I Referring now to FIG. 1 there is shown a xerographic copying system adapted for continuous and automatic operation employing a brush development assembly generally designated 10 constructed in accordance with the present invention. As in all xerographic systems based on the concept disclosed in the above-cited Carlson patent. a light or radiation image ofa document to be reproduced is projected on the sensitized surface ofa xerographic plate to form an electrostatic latent image which is developed with an oppositely charged developing material. The material in image configuration isthen transferred to a support surface to which it is permanently affixed.

As illustrated a document 19 to be reproduced is fed from a support tray 20 over a conveyor made up of guide rollers 21 driven by motor M-l for movement past an exposure station 31. During exposure illumination from a lamp 32 is reflected from the face of the document through an objective lens 33 and an exposure slit 34 onto the surface of a xerographic plate 35 in the form of a drum. Thereafter, document 19 is transported to an output tray 36.

Xerographic drum 35 comprises a cylindrical member mounted-in suitable bearings in a frame and driven in a counterclockwise direction by a motor M-2 at a constant rate such that the peripheral rate of the drum surface is identical to the rate of movement of the light image. The drum surface comprises a layer of photoconductive material, such as vitreous selenium, on a conductive backing.

Prior to exposure the drum surface is uniformly sensitized by means of a corona generating device 37 that is energized from a suitable high potential source. During exposure the light or radiation image discharges the photoconductive layer ,in the areas struck member 66 is electrostatically 3 light leaving on the drum an electrostatic latent'image corresponding to document 19.

In accordance with the present invention, as the drum surface continues its movement, the electrostatic latent image passes development assembly at which toner particlesor powder electrostatically charged opposite in polarity to the latent image are presented to the drum surface as will be explained more fully hereinafter.

After development, the powder image passes through an image transfer station at which the powder image is electro statically transferred'to a support surface web 40 by means of a second corona generating device 41 similar to corona generating device 37 mentioned above.

The support surface to which the ,powder image is transferred may be of any convenient type and is obtained from a supply roll 42 and is rolls and'directed into surface contact with the drum. After transfer the support surface is separated from the drum'surface and guided through'a suitable fusing apparatus 45 which may be of a type disclosed in US. Pat. No. 2,852,651. In this manner, the powder image is permanently affixed to its supportsurface which is fed over a system rolls and onto a takeuproll 48 that is driven by motor M-3.

After transfer the xerographic drum surface is brushed by a cleaning brush assembly 50 rotated by a motor M-4 to remove fed over suitable guide and tensioning' of guideand tensioning any residual developing material remaining on'the'drum surface. Alsothe drum surface is illuminated by a lamp 51 to' remove any electrostatic'charge that may remain thereon. The drum is now ready to receive charge from corona generating device 37 and undergo another reproduction cycle similar to that just described.

Referring now to brush development assembly charged tonerto the electrostatic FIG. 2 there isshown in greater detail 10 which presents optimumly Brush development assembly 10 comprises a' housing 60 formed by contiguous walls 62 which form an enclosure exceptfor an opening adjacent to xerographic drum '35 where development of the electrostatic latent image is effected. The lower or sump portion of housing 6.0 is filled with developer material 63 which isin the form of t'onermarking particles. Any suitable electrosco'pic toner composition may be used. Typical compositions for these toners are described in US. Pat. Nos. 2,618,551 tto Walkup, 2,618,552 to Wise, 2,638,416 to- Walkup and Wise, 2,788,288 to Rheinfrank, 2,753,308 to Landrigan, 2,891,011 and 3,079,342 to lnsalaco and Re 25,135 to Carlson. The size and color of the toner partieles depend upon the purpose intended as for example the size of xerographic toner in U .S. Pat. No. 3,079,342 is about 1' to about micronsIUsually these toners consist of an eleccolorant such as any suitable organic or I .64'rnovably mounted onhousing 60..

In the upper portion ofthe housing is a brush member 66 which is continuously rotated and receives charged .toner par,- ticles at a polarity opposite to that of the latent image in a manner to be described. The charged toner carried by brush deposited to the electrostatic latent image on the surface of drum due to a greater attraction betweenthe latent image normally chargedposi'tive and the toner particles which are charged negatively as will become more apparent. Brush member 66 is rotatable in a counterclockwise direction'or direction opposite to that of xerographic drum 35 to effect a gentle wiping action on the surface of the drum. Any suitable speed of rotation can be used for brush member 66. Typical surface speeds range from about one to about three times that of drum 35. It should be understood that the drum and brush member can rotate in the same as well as opposite directions as illustrated and that they can run at the same or at relative speeds.

ample,

relationship with the toner. lt should latent image accordingto 3 the present inventionto achieve high quality development.

Any suitable material 'can be used for brush member 66 but certain materials have-clearer preferences over others. For exsupported at one end, they can be brushed against the image without undue abrasion. Thus either easy flexibility or softness is essential and'both are desirable. Another characteristic of the brush material is that it have thecorrect triboelectrical v be noted, however, that the toner is primarily-charged prior to its being received onto the brush member as will become more apparent. Other properties of the brushmember are absence of film forming or scum forming ingredients and particularly electrically conductive ingredientsfsuitable durability. availability. In view of thebalance of the many desirable properties and characteristics several animal furs'and synthetic brush materials have proven satisfactory. Typical materials are New Zeala'nd rabbit, domestic rabbit. Russian fox, Camel hair, 'E l80 alpaca. CE740 nylon-acryla. CF622 Dynel (a synthetic fiber of percent acrylonitrile and percent vinyl chloride) and any. combination of them.

Brush member 66 is secured as by an adhesive to'a rotatable cylinder 71 which is in turn secured to a shaft 73 that is journaled in a yoke 75. Yoke 75 is pivotally mounted on housing 60-on a pair of studs 76, one of which is shown, to enable movement of the brush member 66 toward and away from the surface of the xerographic drum 35; To fix the yoke and hence the brush member in relation to the drum a bolt member 77 received through an arcuate slot 78 formed in the sides of the yoke isthreadingly received in side walls 62 of housing 60. In this manner the desired degree of contact between the bristles ofthe brush member and the drum can be achieved.

In accordance with the invention toner from the sump portion'of housing 60 is dispensed onto brush member 66 and is simultaneously charged optimumly to effect high quality development. To accomplish this, the toner is thrown or propelled through an apertured network or screen 80 to form Flicker assembly 81 comprises a cloud adjacent-tobru'sh member 66. Apertured network 80 is formed with openings large enough so that toner particles can readily pass throughand is preferably made from a material having triboelectric characteristics such that proper charging can be effected, Any suitable material may be used for screen 80 such as silk and coated or uncoated carrier materials. Typical carrier materials include methyl methacrylate, glass, iron, steel, ferrite, nickel, and mixtures thereof. Many of the fore-going and other typical carriers are described by U.S. Pat. No. 2,618,551 to Walkup, US. Pat. No. 2,638,416 to Walkup et al. and US. Pat. No. 2,61 8,552 to Wise.

To propel the toner' upwardly withsufflcient force to reach brush member 66, there is provided a flicker assembly 81. a rotatable shaft 82 to which is secured by screws 83'an array of finger elements 84 formed in a plate member 85.

shaft82 is rotated through the sump portion of housing 60. la

' thepath'of finger-elements 84 there is positioned a flicker rod 87 which contacts cupli ke recesses 86 causing the finger elements to flex and spring upwardly with great force thus propelling the toner through screen 80 andonto brush I member 66. It should be noted that each finger element is formed'with an urcuate portion 88 extending from the midsection outwardly toward cuplike recess enables each finger element to be displaced from its normal 86. Arcuate portion 88 path of rotation'by flicker rod 87 without excessive strain or stress being imparted to the finger element. Flicker rod 87 is formed with a flat surface portion 89 which serves to strike finger elements and is journaled forrotation in housing 60 to vary the surface contacted by the finger elements to achieve the desired striking force. a

It should be noted that plate member 85 terminates in vane elements 90 which upon rotation serve as augers and caUse the toner material to be moved inwardly toward the center of the housing to insure that the toner material is continuously and uniformly available to cuplike recesses 86 of flicker asbrush fibers should be soft and flexible so that while chemical and economical Arranged on the ends of finger elements i 84 are cuplike recesses 86 to facilitate the scooping of toneras v sembly 81. Plate member 85 may be formed of suitable material. Typical'ma't'erials are metal foil and plastic with thicknesses ranging from .002 inches to about .0l5 inches.

Flicker assembly 81 and brush member 66 are driven in any suitable manner as from a motor M-S drivingly connected to shaft 82. Shaft 82 rotates finger elements 84 and carries a gear 91 which meshes with an idler gear 93. ldler gear 92journal'cd on stud 93 meshes with gear 94 which is arranged integral with another gear 96 on stud 76. Gear 96 drives gear 97 which is secured to shaft 73 thereby causing brush member 66 to rotate. Any combination of gear ratios to obtain a desired rate vention in which charging of the toner is accomplished in the sump ofthe housing. The flicker assembly 101 for loading toner onto brush member 103 issimilar to that illustrated in the embodiment of H6. 2. lt is to be noted. however. that in place of a screen. toner triboelectrification is by vigorous rubbing of the toner by vane elements 105 which are secured to the same shaft 107 which drives flicker elements 109. Vane elements 105 are similar in shape to vane elements 90 above,

but are made froma carrier type material. such as those previ ously mentioned. In this manner, the toner is properly charged prior to being loaded'onto the member. It should be understood. however, that the apertured network or screen shown in FIG. 2 can be used in addition to the charge imparted in the sump area ifdesired,

By the present invention there is provided a brush development apparatus capable of developing high. quality images irrespective of ambient conditions. Heretofore brush development has not been altogether satisfactory because of its general unreliability in developing electrostatic images with a consistency of quality. The reason for this lack of reliability has been found to have a relationship with ambient humidity conditions. More specifically, developed images of decreasing density resulted with extremely low relative humidities. On the other hand athigh relative humidities developer is deposited in the background or nonimage areas. It is believed that this is. due to a breakdown in the triboelectrification between the brush and toner particles permitting toner weakly retained on the brush to be easily attracted from it to the relatively stronger field in the background or nonimage areas. With the present invention. the toner particles are charged prior to being loaded onto thefur brush which is rotated'in a path past what isin effect a cloud of charged particles so as to achieve the .proper triboelectrification necessary notwithstanding a variable relative humidity. Thus. the toner particles are precharged and do not necessarily require triboelectrification by frictional action'ofthe brushbristles on the toner. Also, the toner particles are not overcharged because they are deposited onto the brush bristles when formed in a cloud rather than by immersing the brush into a toner sump as was previously the case. V Y

comprising:

a housing havlng an opening formed therein; brush means positioned in said housing adjacent said opening and adapted for rotation; a supply of electroscopic toner powder contained in a sump portion of said housing; an actuator disposed in the sump portion of said housing comprising a rotatable plate member having finger elements formed the'rein;each of said finger elements having a cupped portion arranged at its extremity for scooping out a predetermined amount of toner powder from the sump portion of the housing, each of said finger elements being formed with an arcuate'shape and from resilient material to propel toner powder toward said brush means; and I an apertured member positioned intermediate said brush means and said supply of toner powder characterized by an electrostatic property removed in triboeleetric series from said toner powder for causing said toner powder to beelectrostatically charged prior to being received onto said brush means'whereby upon said brush means contacting a latentelectrostatic image, said charged toner powder is attracted thereto. 2. Apparatus according to claim 1 wherein an interference member is positioned in the path of said finger elements adjacent the outer extremity thereof thereby causing said finger elements to flex and then return to original form.

3. Apparatus according to claim 1 wherein said plate member is arranged'with vane elements for causing continuous flow oftoner'powder across the sump portion ofsaid housing.

4. Apparatus according to claim 1 including means for rotating saidbrush means and said plate member such that the rateof said brush means ranges from about one to about ten times that of said plate member.

5. An electrostatic copying machine of the type wherein a photoeonductive member sensitive to electromagnetic radiastations are disposed. the combination comprising:

Although the above description has particularly emphasized I the use of development when producing .positive copy from positive originals, it should be understood that the principles of the invention apply as well to reversal or negative development. 7

While the present invention as to its objects and advantages has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the scope of the appended claims. 1

We claim:

1. Apparatus for developing latent electrostatic images a charging station for providing a substantially uniform electrostaticcharge upon the surface of said photoconductive member;

anexposure station for exposing the charged surface to an electromagnetic radiation image to form a electrostatic latent image thereon; a development station for developing the latent image said developing station comprising; a housing having-an opening formed therein adjacent to the path ofsaid photoconductive member. brush means positioned in said housing adjacent said opening to contact the surface of said photoconductive member, a supply of electroscopic toner particles contained in a sump portion'ofsaid housing, an actuator disposed in the sump portion of said housing comprising a rotatable plate member having finger elements formed. therein. each ofsaid finger elements having a cupped portion arranged at its extremity for scooping outa predetermined amount of toner particles-from the sump portion of the housing, each of said finger elements being formed with an arcuate shape and from resilient material to propel toner powder toward said brush means; and

an apertured member positioned intermediate said brush means and said supply of tonerpow'der characterized by an electrostatic property removed in triboelectric series from said toner powder for causing said toner powder to be electrostatically charged prior to being received onto said brush means.

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