US3500793A - Developer roller coating means and guide for electrostatic copying machine - Google Patents

Description

March 17, 1970 R. J. BARTUSEK 3,500,793

DEVELOPER ROLLER COATING MEANS AND GUIDE FOR ELECTROSTATIC COPYING MACHINE y Filed Oct. 50, 1967 3 Sheets-Sheet 1 Int/6771277" Robert J fiarzusek.

March 17, 1970 R. J. BARTUSEK DEVELOPER ROLLER COATING MEANS AND GUIDE FOR ELECTROSTATIC COPYING MACHINE 3 Sheets-Sheet 2 Filed Oct. 30, 1967 k T? w mm n5 1 I r m R 5512M WM q g March 17, 1970 R. J. BARTUSEK 3,500,793

DEVELOPER ROLLER COATING MEANS AND GUIDE FOR ELECTROSTATIC COPYING MACHINE Filed Oct. 50, 1967 3 Sheets-Sheet 5 fnzierdr- Foberz J Barzusek.

United States Patent Office 3,500,793 Patented Mar. 17, 1970 U.S. Cl. 118637 7 Claims ABSTRACT OF THE DISCLOSURE Apparatus for use in the development station of electrostatic copying machines using liquid developer compositions, to improve development of a copy sheet bearing a latent electrostatic image. In particular, this invention relates to improvements in apparatus for coating a developer roller with liquid developer for subsequent application to the image bearing copy sheet.

Conventional electrostatic copying, wherein a copy sheet bearing a latent electrostatic image is subjected to a developing medium, can be broadly divided into two categories based upon the characteristics of the d veloping medium. The first category utilizes a granular electroscopic powder which may be either cascaded over the latent image or applied by creating a powder cloud adjacent thereto. The second category, to which the invention relates, uses liquid developers or toners which comprise a liquid vehicle carrying a finely divided opaque powder.

The advantages of liquid developers over dry powder developers with respect to total development time and the degree of control of the developing process, are well known by those familiar with the art.

The development step is probably the most vexatious and critical step in the electrostatic copying process. It is during this step that the liquid developer is physically applied to the copy sheet by electrostatic attraction. The opaque particles in the liquid developer adhere to the sheet establishing a visible light and dark pattern corresponding to the latent electrostatic image. The development step takes place at a development station which may include a rotating drum or roller, called a developer roller. The surface of the developer roller is coated with liquid developer and the image bearing copy sheet is transported into developer application relationship with the coated surface.

The liquid coating over the surface of the developer roller directly affects the quality of. the reproduced image, thus its parameters must be accurately controlled for consistent high quality copying. The parameters involved include a copious supply of liquid developer forming a heavy coating over the roller surface for obtaining high contrast images. The coating should have a uniform thickness along the length of the roller to obviate streaking the image bearing sheet. Also, the coating should comprise fresh liquid developer to prevent repeatedly applying developer to the copy sheet which has been depleted of the image forming opaque powder.

In addition to the above parameters, care must be taken to prevent liquid developer from reaching the image bearing sheet in any other manner than by normal application from the developer roller. Splashing and fortuitously misdirected droplets of liquid developer must be held to a minimum and if such droplets occur, the image bearing sheet must be shielded from their path.

This invention obviates the above-mentioned problems and difliculties by utilizing a novel combination copy sheet guide and shield, and a novel liquid developer nozzle construction for evenly applying a heavy coating of fresh liquid developer to the surface of the developer roller. The roller surface carries the fresh coating to the image sheet for subsequent application to one surface thereof.

The nozzle is positioned closely adjacent the developer roller and substantially close to the area where liquid developer is transferred from the roller surface to the image bearing sheet. The peripheral surface of the roller is coated with liquid developer by rotating it through a longitudinal pool of liquid, the pool being formed by a cavity in the nozzle and by a segment of the roller surface. In addition, an arcuate shoe is disposed adjacent the roller surface and a gap therebetween assists in wetting the surface with liquid developer. Finally, a low velocity stream of liquid developer is directed toward the area of the roller surface where the liquid developer is applied to the copy sheet. This low velocity stream assists in purging a portion of the partially depleted liquid developer from the roller surface, allowing a fresh coating to be carried to the copy sheet.

Accordingly, the primary object of this invention is to provide means for improving the developing step in electrostatic copying machines.

Another object of this invention is to provide improved application of liquid developer from a developer roller of an electrostatic copying machine, to a copy sheet bearing a latent electrostatic image.

Another object of this invention is to provide means for maintaining a copious coating of liquid developer on the surface of a developer roller for subsequent transfer, upon demand, to a copy sheet bearing a latent electrostatic image.

A further object of this invention is to provide means for maintaining a uniformly heavy coating of liquid developer on a developer roller in an electrostatic copying machine, for subsequent transfer, upon demand, directly to a copy sheet bearing a latent electrostatic image.

It is also an object of this invention to provide means for maintaining a fresh coating of liquid developer on the developer roller of an electrostatic copying machine.

Other objects of this invention will become apparent from an understanding of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an elevational view of the invention including a copy sheet transport system therefor.

FIG. 2 is a top plan view of the invention and copy fsheet transport system taken along lines 2-2 of FIG. 1.

FIG. 3 is an enlarged three dimensional perspective view of the liquid developer nozzle and associated developer roller.

FIG. 4 is a greatly enlarged cross-sectional elevational view taken generally along line 44 of FIG. 3 showing the surface of the developer roller in detail.

With reference to FIGS. 1 and 2 there is shown a portion of a housing for a development station 8 of an electrostatic copying machine. The housing includes a top wall 10 having a sloping frontal portion 12, a rear wall 14, side walls 16 and 18, and a bottom wall 20. An opening 21 is provided through frontal portion 12 for exiting of a copy sheet, designated by reference numeral 22. As best seen in FIG. 1, the copy sheet enters the development station through an entrance guide 24 comprising upper and lower guide walls 26 and 28 respectively. The copy sheet is picked up by a nip 29 formed between a pair of rotating entrance rollers 30 and 32 which carry the sheet through a V-shaped combination sheet guide and shield 34 and across the top surface of a rotating developer roller 36. The orientation of the copy sheet with respect to the roller surface and the physical charcateristics of the developer roller will be discussed in detail below.

From the develop roller, movement of the copy sheet is assisted by frictional contact between the top surface thereof and a roller 38. This frictional contact directs the copy sheet over a drying roller 40 having a peripheral surface 41, which moves in a direction opposite to the direction of the copy sheet. Surface 41 removes superfluous liquid from the underside of the copy sheet. Operation of the drying roller and an associated doctoring blade 42 is more fully described in a copending application of Casimir S. Samczyk bearing Ser. No. 632,746, filed Apr. 21, 1967 and assigned to the same assignee as the subject application.

Further progress of the copy sheet through the development section includes a curved direction changing guide 44 which'deflects the horizontally moving paper upwardly and directs it to a nip 45 between a pair of combination pressure and transport rollers 46 and 48 which remove additional excess liquid. The copy sheet is subsequently fed through an exit guide 50 and is finally advanced by a pair of exit rollers 52 and 54 through the exit opening 21 provided in frontal portion 12.

The above description is of a transport system for feeding a copy sheet bearing a latent electrostatic image into the development station of an electrostatic copying machine, advancing the sheet through a guide, past a developer roller, over a drying roller, changing its direction of movement, and finally guiding the sheet through an exit opening to the exterior of the machine.

Referring now to FIGS. 3 and 4 in addition to FIG. 1, the developer roller 36 and the liquid developer nozzle will be described in detail.

The developer roller is fabricated of electrically conductive material such as steel. It is supported for rotation on a concentric shaft 51 having a center-line or axis 52, and is journalled to side walls 16 and 18 at 53 and 55 respectively. The peripheral surface of the developer roller comprises a plurality of closely spaced circular grooves 57 separated by circular ridges 57a which, when rotating, distribute the liquid developer along the roller length. The height and width of the grooves and ridges are extremely small, being measured in thousandths of an inch, although the exact dimensions do not appear to be critical. As best seen in FIG. 4, the crests or tops of ridges 57a are preferably flat to present a substantial area of liquid developer coating to the copy sheet.

The grooves and ridges of the developer roller are coated with liquid developer by a longitudinal nozzle assembly generally referred to by reference numeral 56. The nozzle assembly includes a shoe 58 having an accurate wall 60 complementary in shape to the curved surface of developer roller 36 and disposed closely adjacent thereto to define a space or a gap 62. Nozzle assembly 56 also includes an interior plenum chamber 64 extending its entire length and an inlet pipe 65 communicating with the chamber for admitting liquid developer. A liquid distribution baflle 67 is disposed in the plenum chamber directly above the junction of the inlet pipe to insure sideward dispersion of the liquid developer and to provide an even liquid flow across the length of the chamber.

An opening is provided through the top wall of the plenum chaber which leads to a serpentine path 66 terminating in a longitudinal nozzle restriction or orifice 68. From the orifice, liquid developer is discharged into a longitudinal cavity 70 defined by the surface of roller 36, a baflle 72 and a pair of supporting sidewalls 74 and 76. The cavity is disposed substantially above the shaft 51 of developer roller 36 and contains a longitudinal liquid pool 71 through which the grooved and ridged surface of the developer roller moves to capillarily pick up its coating. The copy sheet is subsequently directed over the top of the roller, a fraction of an inch above its surface. Ideally, the lower surface of the copy sheet floats over the roller, riding on the liquid developer coating.

Liquid developer is normally stored in a container 78 disposed directly beneath the nozzle and developer roller.

A supply of liquid developer 80 is maintained in the tank at an adequate level to supply a recriculating pump 82 having a pump inlet 83. The pump delivers liquid developer through a flexible walled conduit 84, having a throttling clamp 85 secured thereabout, to inlet pipe 65 of the nozzle. Regulation of the quantity of liquid developer delivered to the nozzle is effected by a throttle adjustment screw 85a. Interaction of plenum chamber 64 and the serpentine path function to convert the velocity of the liquid into a static pressure having a very small velocity component. The distribution bafile in combination with the plenum chamber and serpentine path establish a smooth, even liquid flow across the length of the orifice. This even flow maintains a uniform liquid pool across the length of longitudinal cavity 7 0.

The direction of rotation of the developer roller, as indicated by arrow 90, allows the roller surface to capillarily pick up liquid developer from pool 71 and carry it toward the top of the roller as a liquid coating thereover, for application to the underside of copy sheet 22. While rotation of the roller surface through the liquid pool is probably the most important method of coating the developer roller, two additional coating methods are also employed with the above nozzle construction.

In the first additional method, the small velocity component of the liquid developer flowing through longitudinal orifice 68 follows the underside of baffie 72 in a generally laminar flow and is directed toward the top of the developer roller. This laminar velocity component not only reaches out to coat the roller surface just before application to the copy sheet, but also conditions the surface by impinging upon it with sufficient force to wash out old liquid developer which has been partially depleted of toner particles during the last roller revolution. The conditioned roller is thus coated with fresh liquid developer for immediate application to the copy sheet.

The second additional technique utilizes the gap between arcuate wall 58 of shoe 60 and the surface of the developer roller. The gap communicates with liquid pool 71 and the liquid developer tends to flow therethrough under gravitational influence. The downward flow is counter influenced by the upward rotation of the roller surface and the capillary action between the surface and the liquid developer filling the gap. Movement of liquid through the gap in one direction and movement of the roller surface in the opposite direction functions to thoroughly wet the surface with developer.

In accordance with the invention, it should be noted that the proximity of the area at which the roller surface is coated with developer to the area at which the developer is applied to the copy sheet surface, aids the roller surface in retaining a heavy liquid developer film.

The combination V shaped copy sheet guide and shield 34 is disposed directly above the nozzle and is supported by sidewalls 74 and 76. The guide comprises an upper leg 96 and lower leg 98 defining a longitudinal slot 100 at the apex of the V. A copy sheet passing between rollers 30 and 32 is deflected by the appropriate guide leg and guided to and through the slot. As the sheet exits from the slot, proper alignment is established for wetting contact between the leading edge of the copy sheet and the roller surface. Subsequently, the roller carries the leading edge over the top surface so that the underside of the sheet is tangential to the roller surface and floats on the liquid coating over the flat crests of circular ridges 57a.

A pair of upper and lower overhangs 102 and 104, respectively, forming acute angles with legs 96 and 98, shield the copy sheet from fortuitously misdirected liquid developer droplets which may otherwise cause spotting. The lower overhang also shields the underside of the copy sheet from liquid developer which may migrate rearwardly over the nozzle. Excess liquid developer which may drip from the shield elements is collected in container 78 for recirculation by pump 82 back to the nozzle. In addition, container 78 collects overflow from the liquid pool and also collects liquid which trickles through the liquid gap 62.

The transport rollers, the developer roller, and the drying roller are all driven by a main driving gear 106 which in turn is driven by motor means, not shown. The main driving gear drives a gear 108 fastened to roller 32, a gear 110 secured to roller 38 and a gear 112 secured to roller 54 for movement of the entrance transport, friction, and exit transport rollers respectively. An intermediate gear 114 is driven by gear 110 to ultimately drive the drying roller 40 through a gear 116 secured thereto. Intermediate gear 114 also drives roller 48 through an integral gear 118.

It is obvious that upon study by those skilled in the art the disclosed invention may be altered or modified both in physical appearance and construction without departing from its inventive concept. Therefore, the scope of protection to be given this invention should not be limited by the embodiment described above, but should be determined by the essential descriptions thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for applying liquid developer composition to a copy sheet bearing a latent electrostatic image, comprising: a supply of liquid developer; a peripheral surface over which it is desired to uniformly distribute a coating of said liquid developer composition; developer retaining means adjacent said roller including a longitudinal shoe forming a longitudinal cavity partially defined by a segment of said roller peripheral surface substantially above said axis; means delivering a quantity of liquid developer from said supply to said cavity, forming a longitudinal pool of liquid developer therein; said roller surface moving through said pool and capillarily picking-up said liquid developer in a uniformly distributed coating; said longitudinal shoe having a shape complementary to the surface of the developer roller and extending through a substantial area of are beneath said cavity and closely adjacent but non-contiguous with a side segment of said roller surface thereby defining a narrow liquid-filled gap communicating with said cavity; said gap being maintained sufliciently narrow to prevent substantial loss of liquid from said pool during rotation of said roller, and means transporting said copy sheet into contact with said coating for application of liquid developer thereto.

2. The apparatus as set forth in claim 1 wherein the peripheral surface of said roller moves upwardly at said gap, capillarily picking-up said liquid developer and substantially overcoming the gravitationally influenced downward liquid flow therethrough.

3. Apparatus for applying liquid developer composition to a copy sheet bearing a latent electrostatic image, comprising: a supply of liquid developer; a rotating developer roller having a horizontal axis and a peripheral surface over which it is desired to uniformly distribute a coating of said liquid developer composition; developer retaining means adjacent'said roller forming a longitudinal cavity, partially defined by a segment of said roller peripheral surface, substantially above said axis; a pump having a liquid inlet communicating with nozzle means discharging said liquid developer into said cavity, forming a longitudinal pool of liquid developer therein; said roller surface moving through said pool and capillarily picking-up said liquid developer in a uniformly distributed coating; said nozzle means comprising a member having a length substantially equal to the length of said cavity; said member defining a longitudinal plenum chamber having an inlet at one location therealong receiving liquid developer from said pump outlet, and an outlet extending the length thereof; said member also defining a longitudinal discharge orifice communicating with said chamber outlet for discharging liquid developer into said cavity; liquid distribution means interior of said chamber for substantially equalizing liquid flow along said orifice; 'bafile means above said orifice extending partially over and comprising one wall of said cavity; said baffle means directing a portion of liquid discharged from said orifice toward the top surface of said developer roller in a generally laminar flow; and means transporting said copy sheet into contact with said coating for application of liquid developer thereto.

4. The apparatus as set forth in claim 3 wherein said transport means include copy sheeet guide means disposed behind and substantially level with the top surface of said roller; said guide means guiding a surface of said copy sheet into tangentially skimming relationship with the top of said developer roller.

5. The apparatus as set forth in claim 4 wherein said guide means comprise a longitudinal fabrication having a portion of V shaped cross-section defining a slot along the apex thereof; said V portion receiving said copy sheet and guiding it through said slot toward said developer roller; and wherein each end of said V portion carries shield means for shielding said copy sheet from rearwardly migrating and fortuitously dispersed.

6. Apparatus for applying liquid developer composition to a copy sheet bearing a latent electrostatic image, comprising: a supply of liquid developer; a rotating developer roller having a horizontal axis and a peripheral surface over which it is desired to uniformly distribute a coating of said liquid developer; unitary, substantially rigid developer retaining means adjacent said roller forming a longitudinal cavity partially defined by a segment of said roller peripheral surface substantially above said axis; means delivering a quantity of liquid developer from said supply to said cavity, forming a longitudinal pool of liquid developer therein; said roller surface moving through said pool-and capillarily picking up said liquid developer in a uniformly distributed coating; said liquid delivery means comprising a pump having a liquid inlet communicating with said supply of liquid developer and a liquid outlet; a nozzle coupled to said liquid outlet for discharging said liquid developer into said cavity and for directing at least a portion of said liquid at the roller surface generally in the direction of its movement for conditioning thereof, and means transporting said copy sheet into contact with said coating for application of liquid developer thereto.

7. The apparatus as set forth in claim 6, wherein said nozzle includes a longitudinal discharge orifice for dis charging said liquid developer along substantially the entire length of said cavity and for establishing a velocity component having a direction intercepting said roller surface.

References Cited UNITED STATES PATENTS 3,276,424 9/1966 Marx et al. 118-637 3,369,523 2/1968 Naumann 118-637 3,112,685 12/1963 Fluke 118410XR 3,113,884 12/1963 Kohler 118-410 XR 3,124,484 3/ 1964 Magnusson 118-637 3,245,381 4/1966 Brenneisen et al. 1l8637 3,307,466 3/1967 Fukuda 118-259 XR PETER FELDMAN, Primary Examiner US. Cl. X.R.

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