US3195430A - Electrostatic printing apparatus - Google Patents

Description

y 1965 c. J. YOUNG 3,195,430

ELECTROSTATIC PRINTING APPARATUS Filed Dec. 28, 1960 2 Sheets-Sheet 1 [I 22 z; 5 ll /4 I ll I 1' L 191 \C INV EN TOR.

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ITMAWEY July 20, 1965 c. J. YOUNG 3,195,430

ELECTROSTATIC PRINTING APPARATUS Filed Dec. 28, 1960 2 Sheets-Sheet 2 4! Fg if 10 INVEN TOR.

United States Patent O 3,195,430 ELECTROSTATIC PRINTING APPARATUS Charles J. Young, Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Dec. 28, 1960, Ser. No. 78,930 6 Claims. (Cl. 9'51.7)

This invention relates generally to improved electrostatic printing apparatus and more particularly to such apparatus including improved means for applying liquid developer compositions t electrostatic images.

In the art of electrostatic printing, electrostatic images are produced on the surface of an insulating material. Such images comprise a pattern of electrostatic charges on the surface. Visible images are commonly produced therefrom by applying across the surface a dry mixture of finely-divided developer particles and substantially larger carrier particles. The developer particles deposit in charged areas to produce a visible image in substantial configuration with the pattern of charges. Several methods of producing Visible images are described in Electrofax Direct Electrophotographic Printing on Paper, by C. J. Young and H. G. Greig, RCA Review, December 1954, vol. XV, No. 4.

The recording element may comprise almost any insulating surface but, preferably, the recording surface is also photoconductive to enable the recording of light images. Recording elements comprising photconductive selenium coated plates are described in US. Patent 2,297,691, issued October 6, 1942, to C. F. Carlson. Re-

cording elements comprising photoconductive coatings on paper are described in the aforementioned Young and Greig publication.

A so-called liquid process for developing electrostatic images has been proposed in which the solid developer particles are suspended in an insulating carrier liquid. Liquid development methods provide many distinct advantages over the use of dry developer mixtures and other methods of developing electrostatic images for some applications. Basically, the liquid developer consists of finely-divided developer particles dispersed in an insulating liquid. This developer can be flowed over a surface bearing an electrostatic image or the surface can be immersed in a tray of liquid developer. It can also be sprayed or rolled onto the surface. A liquid developer process for charge images is described in greater detail by K. A. Metcalf and R. J. Wright in a paper entitled Xerography, published in the Journal of the Oil and Colour Chemists Association, November 1956, vol. 39, No. 11, London England and in another paper entitled Liquid Developers for Xerography published in the Journal of Scientific Instruments, February 1955, vol. 32.

Although the above-rnentioned liquid development processes are suitable for many purposes, it has been found that they have at least one serious deficiency. When producing a visible image by deposition of developer particles from a liquid onto a charged surface, particles adhere in the background areas as well as in the image areas on the surface. Background areas are those areas on the surface bearing little or no electrostatic charge and hence, are those areas in which deposition of developer particles is unwanted. Such spurious deposit in non-image areas results in a spotted or mottled background on the finished print which, in many applications, is unsatisfactory. This effect is even more pronounced when attempting to reproduce fine detail. The more finely-divided the developer particles are, the greater the spurious deposition in background areas.

In addition to the foregoing, it has been found that when images are developed with a liquid composition carried on a roller, second and subsequent rotational cycles ice of the roller cause ghost images to be offset printed on a recording medium by the roller.

It is a general object of this invention to provide improved electrostatic printing apparatus.

A further object of this invention is to provide improved appara-tus for applying liquid developer compositions to electrostatic images.

A still further object is to provide improved roller apparatus for developing electrostatic images on recording members with substantial reduction or elimination of undesirable offest printing of ghost images thereon.

These and other objects are accomplished in accordance with this invention which provides electrophotographic apparatus including means for charging the surface of an electrophotographic member, means for transporting the member through an exposure region, and a developer mechanism adjacent the exposure region comprising a developer roller adapted to have the electrophotographic member contact therewith and means for washing said roller with liquid developer composition in a manner to substantially reduce or eliminate offest printing or ghost images deriving from the previous development of the preceding electrostatic images.

Other objects and advantages will be apparent from the following detailed description to be read with reference to the accompanying drawings wherein:

FIG. 1 is a side elevational, cross-sectional view of the interior of an electrostatic printing apparatus made in accordance with this invention;

FIG. 2 is a rear elevational, cross-sectional view of the interior of the apparatus of FIG. 1 taken along the line 2-2 thereof;

FIG. 3 is a side elevational view, partly in section, of the developer mechanism of FIG. 2;

FIG. 4 is an enlarged side view partially in cross section of a portion of the developer mechanism of FIG. 3.

Similar reference characters are applied to similar elements throughout the drawings.

A compact photocopy apparatus in accordance with this invention is illustrated in FIG. 1. The apparatus is designed with a portion of the top of the housing thereof forming an inverted V-shaped roof. This V-shaped structure is adapted, as shown, to support a book 11 so that a page thereof which is to be copied is in contact with a transparent plate 13. A hinged plate 14 is provided to insure that the page to be copied is firmly held against the transparent plate 13. A single sheet, such as a letter, could be equally well held in place by the hinged plate 14. The page of the book is illuminated through the transparent plate 13 by means of a light source 15 and a reflector 17.

The light source 15 may comprise one or more pencil shaped horizontal lamps. Well suited for the purpose are lamps such as 500 watt tungsten filament quartz tubes which contain traces of iodine. The iodine in the lamp functions to catch tungsten particles which evaporate during operation and to return those particles to the filament. Such a lamp is produced by the General Electric Corporation, catalogue No. SOOTS'Q/CL. The reflector 17 conveniently comprises a segment of a 6" hollow cylinder, the inside of which is polished to a high degree. Since the distance from the light source 15 to the bottom edge of the plate 13 is much less than the distance of the light source 15 to the top edge of the plate 13, the refiector 17 is positioned to concentrate reflected light toward the upper portion of the transparent plate 13 so that the entire area under the plate is uniformly illuminated.

Light reflected from the page of the book 11 is concentrated through lens 19 to impinge upon the mirror 21. The light is then reflected from the mirror 21 upwardly and focused on an exposure plane 23. A shutter 25 is 3 provided in the light path between the mirror 21 and the exposure plane 23 in order to prevent any light from entering the right hand compartment 27 of the copier apparatus except when exposure is desired.

Further details of the internal structure of the compartment 27 are illustrated in FIGURE. 2. A supply roll of photo-sensitive webbing is mounted in the lower portion of the compartment 27. The webbing 3% on the supply roll may comprise, for examole, electrophotographic paper such as is described in the aforementioned Young and Greig publication. The paper 3% is fed from the supply roll 29 over an idler roller 31 through a double corona charging apparatus 53 and into the exposure plane 23. The paper is then carried partly around one roller of a pair of pressure rollers in a manner so that it reverses its direction and is then brought out from the copier apparatus under a heat fusing mechanism 25;;

in the apparatus as shown in FIGURE 2, the double corona charging unit 33 may comprise 2 opposed structures of very fine parallel wires as described in US. Patent 2,922,883, issued to E. C. Giaimo, Jr., and the heat fuser 28 one such as is described in U.S. Patent 2,857,682 to R. G. Olden et a1.

From the charging apparatus 33 the paper is transported into the exposure plane 23 with its photosensitive surface facing downward. While the paper is maintained stationary in the exposure plane 23, the light image refiected upward from the mirror 21 will substantially redues or eradicate the charges placed on the paper by the corona unit 33 in those areas on which light impinges. As the paper 36 passes over one of the pressure rollers 25, liquid developer composition from liquid developer unit is applied to the other pressure roller 26, which in turn applies the liquid developer composition to the paper 3b to produce, in those areas thereon which were not struck by light, a visible image of developer material. This visible image is then fixed to the surface of the paper as it passes under the fuser 28.

In FIGURE 3, the developing unit 35 of FIG. 2 is illustrated in greater detail. This developer unit includes the two pressure rollers 25 and 26 which engage the paper and which are driven to pull the paper from the supply roller 29 (FIG. 2) through the projection plane 23 shown in FIGURE 2. Liquid developer composition is applied to the upper pressure roller 26 by means of an applicator ll. The developer composition is supplied to the applicator 411 through a pipe 43 (FIG. 3) connected to a centrifugal pump 45. As liquid developer composition is carried by the upper pressure roller 26 into contact with the paper, a turbulent nip as of thedeveloper composition is formed where the roller 26 contacts the paper. This turbulent nip 46 of developing composition substantially enhances development of images on the paper and also enhances clean up of developer material which may adhere in unwanted areas on the paper 36. The liquid developer composition not only forms the nip 46 but also flows down the surface of the paper 3@ as it is carried over the pressureroller 25. The developer composition is thereby caused to be in contact with a substantial portion of the paper 30 as it is transported over the roller 25.

Developer composition in excess of that used to develop animage on the paper drops therefrom into a tray or sump 47 positionedbelow the two pressure rollers 25 and 26. The developer composition collected in the sump 47 is returned to the developer container 44 through a pip 49 which surrounds the feed pipe 43. 7

An important feature of the developer unit shown in FIG. 3 is that it comprises a substantially closed system for developing images on the paper 3%. Such a closed system makes it possible to use developer compositions which include a highly volatile liquid without resulting in excessive evaporation of that liquid. Excessive evaporation would ultimately result in wide variations in the concentration of the developer material in the developer composition.

An example of a suitable, highly volatile developer composition is one wherein finely-divided electroscopic developer particles are dispersed in a liquid carrier of tr1chlorotriliuoroethane.

Example A black pigment is prepared by making two solutions:

Solution one comprises:

6 grams Iosol Black (Cl. Solvent Black 13) 490 grams methanol Solution two comprises:

9 grams Spirit Nigrosine (CI. 50415) 406 to 600 grams methanol Solution one is poured into solution two with continuous stirring. Gnce the solutions have been thoroughly mixed and a black, relatively insoluble pigment is precipitated, the mixture is filtered and the filter cake allowed to dry. The dried filter cake is'broken up and dispersed in dimethyl polysiioxane liquid having a viscosity of about 2 centistokes. The proportions in this dispersion are about 1 to 10 parts black pigment to about 20 parts of liquid. It is preferred that the liquid content be kept as low as possible but sufiicient to provide a uniform dispersion. After ball milling the black pigment is classified as to particles size. Particles having a diameter of 74 microns or less are preferred.

7 Also prepared is a solution consisting of:

260 grams dimethyl polysiloxane 200 grams trichiorotriiluoroethane.

About one part by weight pigment dispersion per 10 parts solution is added to provide a final developer composition.

As images are developed on the paper with the apparatus, the concentration of developer particles in the container dd will become depleted at a greater rate than will the liquid carrier portion thereof. in order to maintain the proportions of components in the liquid developer at a substantially constant level, means are provided for injecting into the container 4d, metered amounts of a concentrated developer composition. The developer concentrate is contained in a jar 51. A reciprocating pump 53 is inserted in the jar 51 and is powered by a solenoid 54. At each stroke of the pump 53 in the jar 51 a small quantity of developer concentrate is forced through the pipe 55 and injected into the container 44. it is desirable that the reciprocating pump 53 be provided with an adjustable stroke whereby the quantity of developer concentrate injected each time into the container 44 can be regulated. It is also desirable that the solenoid be energized, if desired, each exposure cycle or if desired once each two cycles or once each five cycles or so.

A sutable developer concentrate may be prepared by dispersing developer material such as that described heretofore in a dimethyl polysiloxane in a proportion of about 20 parts by weight of developer material to parts by weight of a dimethyl polysiloxane having a viscosity from 0.6 to about 3 centistokes.

In FIG. 4 further details are provided of a suitable construction for the applicator member 41 of FIG. 3. The applicator member is here shown as comprising a metalhead til which will have a length equal to the length of the paper to be developed. One face 63 of the applicator member is bevelled so that it can be positioned in close proximity to the pressure roller 26. An elongated U-shaped slot 65 is provided in the head 61 and into this slot developer composition is supplied under pressure through the pipe 43. 'Near the top of the slot there is provided an elongated slide 66 having a multiplicity of apertures 67 therethrough. These apertures being, for example, holes .040 inch in diameter, counter sunk on one side, and spaced about inch apart along the length of the slide 66. By using such a slide, a con-' venient means is provided whereby, upon removal of the slide 66 from the head 61, both the slide 66 and the U- shaped slot 65 can be easily cleaned.

It has been found that, in normal operation, development of the image on the paper as it is carried over the lower pressure roller 25 will cause a ghost image to be off-set printed on the upper pressure roller 26 as the periphery thereof moves away from the paper 30. Unless some means are provided for removing this ghost image from the upper pressure roller 26, it would again contact the paper and off-set print thereon a ghost image which under most circumstances would be undesirable in a finished print. In the embodiment illustrated herein, developer composition is forced through the apertures 67 in the slide 66 under pressure so that the composition strikes the roller 26 with suflicient force to substantially obliterate any offset images previously formed on the surface thereof.

What is claimed is:

1. Reproduction apparatus comprising a camera housing having a bottom portion and a roof portion, said roof portion being formed in the shape of an inverted V, one leg of said inverted V including a transparent plate, said roof portion having an apex that is more distant from said bottom portion than the edges of said inverted V, whereby an opened 'book may be supported on said roof portion by only the legs of said inverted V, illumination means Within said housing for projecting light onto said transparent plate and material positioned thereon for copying purposes, means within said housing for focusing a light image reflected from said material to be copied onto a focal plane, said means including a mirror and a lens positioned in the light path between said mirror and said transparent plate, means for supporting a supply roll of photosensitive sheet material means for guiding said sheet material into said focal plane, means for moving said sheet material from said supply roll into said focal plane and out of said focal plane means for energizing said illumination means to produce a latent image on said photosensitive sheet material and means for applying liquid developer composition to said sheet material to develop said latent image.

2. The reproduction apparatus of claim 1 including a hinged plate adjacent said transparent plate for holding subject matter to be copied against said transparent plate.

3. Reproduction apparatus comprising a camera housing having a bottom portion, a partition in said housing dividing it into first and second compartments, said first compartment having a roof portion thereof formed in the shape of an inverted V, one leg of said inverted V including a transparent plate, said roof portion having an apex that is more distant from said bottom portion than the edges of said inverted V, whereby an opened book may be supported on said roof portion by the legs of said inverted V, illumination means within said first compartment for projecting light onto said transparent plate and material positioned thereon to be copied, means within said housing for focusing a light image reflected from said material to be copied onto a focal plane within said second compartment, said means including a mirror in said second compartment for reflecting light onto said focal plane and a lens mounted in an aperture in said partition in the light path between said mirror and said transparent plate, means for supporting a supply roll of photosensitive sheet material means for guiding said sheet material into said focal plane, means for moving said sheet material from said supply roll into said focal plane and out of said focal plane, means for energizing said illumination means to produce a latent image on said photosensitive sheet material and means for applying liquid developer composition to said sheet material to develop said latent image.

4. The reproduction apparatus of claim 3 including shutter means in said second compartment in the light path between said lens and said focal plane.

5. Electrophotographic apparatus comprising: a camera housing having a bottom portion and a roof portion, said roof portion being formed in the shape of an inverted V, one leg of said inverted V including a transparent plate; said roof portion having an apex that is more distant from said bottom portion than the edges of said inverted V, whereby an opened book may be supported on said roof portion by only the legs of said inverted V, illumination means within said housing for projecting light onto said transparent plate and material positioned thereon to be copied; means within said housing for focusing a light image reflected from said material to be copied onto a focal plane, said means including a mirror and a lens positioned in the light path between said mirror and said transparent plate; means for supporting a supply roll of electrophotographic sheet material means for guiding said sheet material into said focal plane, means for moving said sheet material from said supply roll into said focal plane and out of said focal plane, means adjacent said focal plane for producing a substantially uniform electrostatic charge on one surface of said sheet material; means for energizing said illumination means to produce a latent electrostatic image on said electrophotographic sheet material :and means for applying liquid developer composition to said sheet material to develop said latent image.

6. Electrophotographic apparatus comprising: a camera housing having a bottom portion, a partition in said camera housing dividing it into first and second compartments, said first compartment having a roof portion thereof formed in the shape of an inverted V, one leg of said inverted V including a transparent plate; said roof portion having an apex that is more distant from said bottom portion than the edges of said inverted V, whereby an opened book may be supported on said roof portion by only the legs of said inverted V, illumination means within said first compartment for projecting light onto said transparent plate and material positioned thereon to be copied; means within said housing for focusing a light image reflected from said material to be copied onto a focal plane within said second compartment, said means including a mirror in said second compartment for reflecting light onto said focal plane and a lens mounted in an aperture in said partition in the light path between said mirror and said transparent plate; means within said second compartment for supporting a supply roll of elec trophotographic sheet material; means for guiding said sheet material into said focal plane; means for moving said sheet material from said supply roll into said focal plane and out of said focal plane; means adjacent said focal plane for producing a substantially uniform electrostatic charge upon a surface of said sheet material; means for energizing said illumination means for producing a latent electrostatic image upon said sheet material; means for applying a finely-divided developer material to said latent electrostatic image to produce therefrom a visible image and means for fixing said visible image to said electrophotographic sheet material.

References Cited by the Examiner UNITED STATES PATENTS 1,313,098 8/19 Leumann 1l8-259 2,227,850 1/41 Steinlauf 73 2,914,996 12/59 Whitman 95-1.7 2,927,503 3/60 Zollinger 88-24 2,940,358 6/60 Rosenthal 95-1.7 2,950,661 8/60 Limberger 951.7 3,003,404 10/61 Metcalfe 95--1.7

EVON C. BLUNK, Primary Examiner.

JOHN M. HORAN, NORTON ANSHER, Examiners.

Claims (1)

1. REPRODUCTION APPARATUS COMPRISING A CAMERA HOUSING HAVING A BOTTOM PORTION AND A ROOF PORTION, SAID ROOF PORTION BEING FORMED IN THE SHAPE OF AN INVERTED V, ONE LEG OF SAID INVERTED V INCLUDING A TRANSPARENT PLATE, SAID ROOF PORTION HAVING AN APEX THAT IS MORE DISTANT FROM SAID BOTTOM PORTION THAN THE EDGES OF SAID INVERTED V, WHEREBY AN OPENED BOOK MAY BE SUPPORTED ON SAID ROOF PORTION BY ONLY THE LEGS OF SAID INVERTED V, ILLUMINATION MEANS WITHIN SAID HOUSING FOR PROJECTING LIGHT ONTO SAID COPYING PURPOSES, MEANS WITHIN SAID HOUSING FOR FOCUSING A LIGHT IMAGE REFLECTED FROM SAID MATERIAL TO BE COPIED ONTO A FOCAL PLANE, SAID MEANS INCLUDING A MIRROR AND A LENS POSITIONED IN THE LIGHT PATH BETWEEN SAID MIRROR AND SAID TRANSPARENT PLATE, MEANS FOR SUPPORTING A SUPPLY ROLL OF PHOTOSENSITIVE SHEET MATERIAL MEANS FOR GUIDING SAID SHEET MATERIAL INTO SAID FOCAL PLANE, MEANS FOR MOVING SAID SHEET MATERIAL FROM SAID SUPPLY ROLL INTO SAID FOCAL PLANE AND OUT OF SAID FOCAL PLANE MEANS FOR ENERGIZING SAID ILLUMINATION MEANS TO PRODUCE A LATENT IMAGE ON SAID PHOTOSENSITIVE SHEET MATERIAL AND MEANS FOR APPLYING LIQUID DEVELOPER COMPOSITION TO SAID SHEET MATERIAL TO DEVELOP SAID LATENT IMAGE.

Images