US3124484A

US3124484A - magnusson

Info

Publication number: US3124484A
Authority: US
Publication date: 1964-03-10
Anticipated expiration: 1981-03-10

Description

March 10, 964 K. J. MAGNUSSON 3,124,434

' ELECTROSTATIC PRINTING APPARATUS Filed March 27, 1962 3 Sheets-Sheet 1 11 11 II 1111 I 1 I I I I I I I l I I 1 I I I I I 1 I 1 I I I I I 11 INVQNEOR. Mar 1 Maw/11a March 10, 1964 K. J. MAGNUSSON ELECTROSTATIC PRINTING APPARATUS 3 Sheets-Sheet 2 Filed March 27, 1962 I N VEN TOR. Kw J Mil/M10 9 2 lt/l/fl/V March 1964 K. J. MAGNUSSON ELECTROSTATIC PRINTING APPARATUS 3 Sheets-Sheet 3 Filed March 2'7, 1962 INVENTOR. 7' j MIA V 1 Immu/ 3,124,484 Patented Mar. 10, 19 64 ELECTROSTATIC PRINTING APPARATUS Knot J. Magnusson, Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Mar. 27, 1962, Ser. No. 182,881 6 Claims. (Cl. 118-637) This invention relates generally to improved electrostatic printing apparatus and particularly to such apparatus including improved means for applying liquid developer compositions to an image bearing web or the like.

In the art of electrostatic printing, electrostatic images are produced on the surface of an insulating materiah 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. charged areas to produce a visible image in substantial configuration with the pattern of charges. Several meth ods 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'maycomprise almost any insulating surface but, preferably, the recording surface is also photoconductive to enable the recording of light images. Recording elements comprising.photoconductive selenium coated plates are described in U.S. Patent 2,297,691, issued October 6, 1942, to C. F. Carlson. Recording 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 finelydivided 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. Metcalfe and R. J. Wright in a paper entitled I 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-mentioned 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 areasas 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 deposition in nonimage areas results in a spotted or mottled background on the finished print which, in many applications, is unsatisfactory. This efi'ect is even more pronounced when attempting to reproduce fine detail. The more finely-divided the developer particles are, the greater the spurious deposi:

tion in background areas.

-In addition to the foregoing deficiency, it has been found that when images are developed with a liquid composition carried on a roller, second and subsequent rota- United States Patent Office The developer particles deposit in A tional cycles of the roller cause ghost images to be offset printed on a recording medium by the roller. Considerable care must be exercised in applying the liquid developer dispersion to the developer roller to provide a uniform distribution of developer thereon to obviate streaking of the developed image, which may occur when a plurality of jets are employed to apply developer to 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 apparatus for applying liquid developer compositions to electrostatic images.

Another object is to provide improved means for more uniformly applying liquid developer to roller apparatus members with substantial reduction or elimination of undesirable offset 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, a developer mechanism adjacent the exposure region comprising a developer roller adapted to have the electrophotographic member contact therewith and means for uniform- 1y applying liquid developer composition to said roller in a manner to substantially reduce or eliminate offset printing or ghost images deriving from the previous development of the preceding electrostatic images, and to minimize streaking or non-uniformity in the density of the developed image. The desired uniformity in the application of the developer to the roller is insured by means of a continuous fountain or fan jet of developer extending continuously across substantially the entire width of the developer roller.

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

FIGURE 1 is a front, cross-sectional view taken along the section line 1-1 of FIG. 2 of the interior of an electrostatic printing apparatus made in accordance with this invention;

FIGURE 2 is a side, cross-sectional view of the interior of the apparatus of FIG. 1 taken along the line 22 thereof;

FIGURE 3 is a side cross-sectional view of the developer mechanism of FIG. 2;

FIGURE 4 is a perspective partially cut-away View of I paratus 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 Witha transparent plate '13. A hinged platel4 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 1-7.

suggest The light source 15 may comprise one or more pencil shaped horizontal lamps. Well suited for the purpose are la'rnps 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 Company, catalogue No. 500T3Q/ 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 reflector 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. In addition, if required, a properly shaped screen 16 or absorber 18, in the direct or reflected paths respectively of the illumination, may be used to improve illumination uniformity on the page to be copied.

Light reflected from the page of the book 11 is concentrated through a lens system 19 to impinge upon the mirror 21. The light is then reflected from the mirror 21 upwardly and focused on an exposure plane 23. If desired, a shutter 24 is provided in the light path between the mirror 21 and the exposure plane 23 in order to prevent any ambient light from reaching the exposure plane except when exposure is desired.

Further details of the internal structure of the compartment 27 are illustrated in FIGURE 2. A supply roll 29 of photosensitive webbing is mounted in the lower portion of the compartment 27. The webbing 30 on the supply roll may comprise, for example, electrophotographic paper such as is described in the aforementioned Young and Greig Publication. The paper 30 is fed from the supply roll 29 over an idler roller 31 through a double corona charging apparatus 33 and into the exposure plane 23. The paper is then carried partly around one flexible surface roller 25 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 28.

In the apparatus as shown in FIGURE 2, the double corona charging unit 33 may comprise two opposed structures of very fine parallel wires as described in US. Patent 2,922,883, issued to E. C. Giaimo, Jr., on January 26, 1960, and the heat fuser 28 one such as is described in US. Patent 2,857,682 to R. G. Olden et al. on October 28, 1958.

From the charging apparatus 33 the paper 30 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 charging unit is energized and traverses the paper forwards and back to the position shown. After charging is completed, the light source is energized for desired exposure time, and the light image reflected upward from the mirror 21 to substantially reduce or eradicate the charges placed on the paper by the corona unit 33 in those areas on which light impinges. As the paper 30 subsequently passes over one of the pressure rollers 25, liquid developer composition from liquid developer unit 35 is applied to the other pressure roller 26, which in turn applies the liquid developer composition to the paper 30 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 FIGURES 3 and 4, 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 the applicator 41, described in detail hereinafter. The developer composition is supplied to the applicator 41 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 46 of the developer 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 30. The liquid developer composition not only forms the nip 46 but also flows down the surface of the paper 30 as it is carried over the pressure roller 25. The developer composition is thereby caused to be in contact with a substantial portion of the paper 3% as it is transported over the roller 25.

Developer composition in excess of that used to develop an image on the paper drops therefrom into a tray or sump 47 positioned below the two

pressure rollers

25 and 26. The developer composition collected in the sump 47 is returned to the developer container 4-4 through a pipe 49, which preferably surrounds the feed pipe 43.

A preferred form of the applicator 41 includes a metallic head having its upper surface and ends curved to conform to the surface of the upper pressure roller 26 to provide a seal for the liquid developer dispersion. The applicator 41 has a length slightly shorter than the length of the pressure roller 26. An elongated U-shaped slot 42 extending almost the full length of the applicator 41, and centered therein, opens at the lowest point 42' thereof into the developer supply pipe 43. The applicator 41 is supported in the developer assembly 35 by flat pressure springs, 51 and 53, which press the applicator firmly against the surface of the roller 26. The face 55 of the applicator 41 adjacent the lower edge of the pressure roller 26 is undercut about .005 inch as shown in the detailed illustrations thereof in FIGURES 6, 7 and 8. The precise depth of undercut required is dependent upon developer pump capacity in order to insure that developer continuously fills the slot and undercut openings. Thus, while the upper surface 57 and the ends 59 of the lower adjacent surface are in close proximity to the face of the roller 26, the developer is applied extremely uniformly and with the desired pressure to the lower face of the pressure roller 26 along substantially its entire length.

After the developer has been carried by the upper roller 26 to develop the electrostatic image on the paper 30, the developer runs down the surface of the paper, as indicated by the stippling in FIG. 3, until it reaches the wiper seal 61. The wiper seal 61 comprises a member, for example, of Teflon, bevelled to conform to the surface of the paper carried by the lower pressure roller 25. It is pressed against the lower surface of the paper by one or more flat or coiled springs 63 supported in a bracket 65 attached to the side of the sump 47. Excess developer collected in the bottom of the sump 47 is returned to the developer reservoir 44- through the return pipe 49.

FIGURE 5 shows a modification of the developer applicator element 41 wherein the applicator 4.1 is shaped to conform to the curvatures of both

pressure rollers

25 and 26 to provide end seals therewith for the developer solution after it is first applied to the upper roller 26 and after it cascades down the surface of the paper around the roller 25. As an alternative, the return pipe 49 for the excess developer is separate from and not coaxial with the supply pipe 43.

An important feature of the developer units described by reference to FIGS. 3 to 8 is that they comprise substantially closed systems for developing images on the paper 30. Such closed systems make 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 parts solution 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 trichlorotri'fluoroethane.

Example A black pigment is prepared bymaking two solutions.

Solution 1 comprises: Grams Iosol Black (Cl. Solvent Black 13) 6 Methanol 400 Solution 2 comprises:

Spirit Nigrosine (CI. 50415) 9 Methanol 400 to 600 Solution 1 is poured into solution 2 with continuous stirring. Once 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 polysiloxane liquid having a viscosity of about 2 centistokes. The proportions in this dispersion are about 1 to 10 parts black pigment to about parts of liquid. It is preferred that the liquid content be kept as low as possible but sufi'icient'to provide ,a uniform dispersion. After ball milling the black pigment is classified as to particle size. Particles having a diameterof 74 microns or less are preferred.

Also prepared is a solution consisting of:

Grams Dimethyl polysiloxane (silicone) 200 Trichlorotrifiuoroethane (Fre0n). 200

About one part by weight pigment dispersion per 10 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 44 may 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 44, metered amounts of a concentrated developer composition. The developer concentrate is contained in a jar 67. A reciprocating pump 69 is inserted in the jar 67 andis powered by a solenoid 71. At each stroke of the pump 69 in the jar 67 a small quantity of developer concentrate is forced through the pipe 73 and injected into the container 44. It is desirable that the reciprocating pump 69 be provided with an adjustable stroke whereby the quantity of developer concentrate injected each time into thecontainer 44can be regulated. It is also desirable that the solenoid be energized, ifdesired, each exposure cycle or'if desired once each two cycles or one each five cycles or so.

A suitable 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 80 parts by weight of a dimethyl polysiloxane having a viscosity from 0.6 to about 3 Centisto kes.

What is claimed'is: I

1. Apparatus for applying liquid developer composition to a continuous web bearing a latent electrostatic image, said apparatus comprising:

(a) liquid developer supplying means,

(12) a pair of pressure rollers adapted to contact op posite surfaces of said web, one of said rollers being adapted to have said web contact a substantial por- 6 and providing means for bringing liquid developer composition into contact with said Web, (0) means providing a continuous column of said liquid developer extending transversely substantially across said other roller for applying said liquid developer composition to said other roller to develop said latent image on said web and to substantially obliterate offset images formed on saidother roller as a result of previous development of electrostatic images on said web with said other roller,

(d) said liquid applying means comprising an element having one edge surface and adjacent end surfaces contacting said other roller and shaped to conform to the curvature thereof, and having another undercut edge surface between said end surfaces closely spaced from said other roller along a substantial portion of its length, and a longitudinal slotted portion between each of said surfaces, said slotted portion communicating with the developer supply means, f

and (e) means for rotating said rollers and moving said web therebetween.

2. Apparatus for applying liquid developer composition to a continuous web bearing a latent electrostatic image, said apparatus comprising:

(a) liquid developer supplying means,

(b) a pair of pressure rollers adapted to contact opposite surfaces of said web, one of said rollers being adapted to have said web contact a substantial portion of the periphery thereof, the other of said rollers being positioned in'a plane above said one roller so as to make substantially line contact with said web and providing means for bringing liquid developer composition into contact with said web,

(0) means providing a continuous column of said liquid developer extending transversely substantially across said other roller for applying said liquid developer composition to said other roller to develop said latent image on said Web and to substantially obliterate offset imagesformed on said other roller as a resultof previous development of electrostatic 7 images on said web with said other roller,

(:1) said liquid applying means comprising an element having one edge surface and adjacent end surfaces contacting said other roller and shaped to conform to the curvature thereof, and having another undercut edge surface betweensaid end surfaces closely spaced from said other roller along a substantial portion of its length, and a longitudinal slotted portion between each of said surfaces, said slotted portion communicating with the developer supplying means, g

a (e) spring actuated means for biasing said surfaces to contact said other roller, and

(f) means for rotating said rollers and moving said web therebetween.

3. Apparatus for applying liquid developer composition to a continuous web bearing a latent electrostatic image, said apparatus comprising:

(a) liquid developer supplying means,

(b) a pair of pressure rollersadapted to contact 0p posite surfaces of said web, one of said rollers being adapted to have said web contact a substantial portion of the periphery thereof, the other of said rollers being positioned in a plane above said one roller so as to make substantially line contact with said web and providing means for bringing liquid developer composition into contact with said web,

(0) means providing a continuous column of said liquid developer extending transversely substantially across said other roller for applying said liquid developer composition to said other roller to develop said latent image on said web and to substantially obliterate ofi'set images formed on said other roller 7 as a result of previous development of electrostatic images on said web with said other roller,

(d) said liquid applying means comprising an element having one edge surface and adjacent end surfaces contacting said other roller and shaped to conform to the curvature thereof, and having another undercut edge surface between said end surfaces closely spaced from said other roller along a substantial portion of its length, and a longitudinal slotted portion between each of said surfaces, said slotted portion communicating with the developer supplying means,

(e) wherein said element includes other end surfaces for contacting said web on the periphery of said one roller and shaped to conform to the curvature of said one roller, and having a second undercut edge surface between said other end surfaces closely spaced from said web, and

(f) means for rotating said rollers and moving said web therebetween.

8 (b) drive means for rotating said rollers to move said web therebetween, (c) applicator means for applying liquid developer composition to said other roller in a continuous column extending transversely substantially across said web to develop said latent image and with sufficient force to substantially obliterate offset images formed on said other roller as a result of previous development of electrostatic images on said web with said other roller,

(a') container means for a supply of said liquid de- Neloper composition,

(e) pump means for drawing liquid developer composition from said container means and supply it to said applicator means under pressure, and

(f) sump means positioned below said rollers for collecting excess developer composition and returning it to said container means.

6. Apparatus for applying liquid developer composi- 4. Apparatus for applying liquid developer composition to a continuous web bearing a latent electrostatic image, said apparatus comprising:

(a) liquid developer supplying means,

(b) a pair of pressure rollers adapted to contact option to a continuous web of electrophotographic material bearing a latent electrostatic image, said apparatus comprising:

(a) a pair of pressure rollers adapted to contact opposite surfaces of said web, one of said rollers being P0site surfaces of one Of Said P011659 being adapted to have said web contact a substantial porp t0 Y 531d Web Contact a substaqtlal P tion of the periphery thereof, the other of said rollers tion of the periphery thereof, the other of said rollers being positioned in a Plane above said one Toner so bemg Posmoned m above said rqller so as to make substantially line contact with said web, as to malfe substantially 11116 contact Wtth Sa W65 (b) drive means for rotating said rollers to move said and providing means for bringing liquid developer web therebetween composmon m? Contact ,Wlth sald (c) applicator means for applying liquid developer (C) means Y a cfmtmuous column of sa1d composition to said other roller in a continuous coluld dewfoper transvelsely ,subta1}t1auy umn extending transversely substantially across said across Sald applymg Sald hquld web to develop said latent image and with sufficient veloper composition to said other roller to develop force to substantially obliterate offset images formed latent on Sald web and 9 Substantlany on said other roller as a result of previous developobliterate offset images formed on said other roller ment of electrostatic images on said web with said as a result of previous development of electrostatic other Toner, Images 9 .Sald wlth Sald (d) container means for a supply of said liquid de- (d) said liquid applymg means comprising an element 40 veloper composition having one edge surface and ad acent end surfaces (8) pump means ,foladrawing liquid developer composi contacting said other roller and shaped to conform vtion from Said container means and supplying it to to the curvature thereof, and hav1ng another undersaid applicator means under pressure and out edge Surfalm between Sald end SurfaCes .Closely (f) sump means positioned below said rollers for col- SPaced F sald other roller along a substantlal lecting excess developer composition and returning tion of its length, and a longitudinal slotted portion it to Said Container means and between of .Sald Surfaces Said Pomon (g) additional container means for a supply of concomniumcatmg Wlth developer Supplymg. centrated liquid developer composition, and (e) Spnng actuated lmper meians for contactmg Sald (h) means for supplying metered amounts of said con- Web on the underilde Sald one roller i centrated composition to said first mentioned con- (f) means for rotating said rollers and moving said miner means web therebetween. 5 Apparatus f applying fliq id developer i- References Cited in the file of this patent tion to a continuous web of electrophotographic material UNITED STATES PATENTS beain a ltntlt tt" i p g g a 6 e ec ms a 10 Image Sald apparatus com 2 624 14 Rhodes Jam 13 953 (a) a pair of pressure rollers adapted to Contact opg f a? posite surfaces of said web, one of said rollers being {9 J i 1961 adapted to have said web contact a substantial p01'- 21 O nson u y tion of the e h th 3,008,404 Metcalfe et al Oct. 10, 1961 perip ery ereof, the other of said rollers 01 S h th N 28 1961 being positioned in a plane above said one roller so 5 c elmer as to make substantially line contact with said web FOREIGN PATENTS d p i ng m ans for bringing liquid developer 812 013 Great Britain Apr. 15, 1959 composition into contact with said web,

Claims

1. APPARATUS FOR APPLYING LIQUID DEVELOPER COMPOSITION TO A CONTINUOUS WEB BEARING A LATENT ELECTROSTATIC IMAGE, SAID APPARTUS COMPRISING: (A) LIQUID DEVELOPER SUPPLYING MEANS, (B) A PAIR OF PRESSURE ROLLERS ADAPTED TO CONTACT OPPOSITE SURFACES OF SAID WEB, ONE OF SAID ROLLERS BEING ADAPTED TO HAVE SAID WEB CONTACT A SUBSTANTIAL PORTION OF THE PERIPHERY THEREOF, THE OTHER OF SAID ROLLERS BEING POSITIONED IN A PLANE AB OVE SAID ONE ROLLER SO AS TO MAKE SUBSTANTIALLY LINE CONTACT WITH SAID WEB AND PROVIDING MEANS FOR BRINGING LIQUID DEVELOPER COMPOSITION INTO CONTACT WITH SAID WEB, (C) MEANS PROVIDING A CONTINUOUS COLUMN OF SAID LIQUID DEVELOPER EXTENDING TRANSVERSELY SUBSTANTIALLY ACROSS SAID OTHER ROLLER FOR APPLYING SAID LIQUID DEVELOPER COMPOSITION TO SAID OTHER ROLLER TO DEVELOP SAID LATENT IMAGE ON SAID WEB AND TO SUBSTANTIALLY OBLITERATE OFFSET IMAGES FORMED ON SAID OTHER ROLLER AS A RESULT OF PREVIOUS DEVELOPMENT OF ELECTROSTATIC IMAGES ON SAID WEB WITH SAID OTHER ROLLER, (D) SAID LIQUID APPLYING MEANS COMPRISING AN ELEMENT HAVING ONE EDGE SURFACE AND ADJACENT END SURFACES CONTACTING SAID OTHER ROLLER AND SHAPED TO CONFORM TO THE CURVATURE THEREOF, AND HAVING ANOTHER UNDERCUT EDGE SURFACE BETWEEN SAID END SURFACES CLOSELY SPACED FROM SAID OTHER ROLLER ALONG A SUBSTANTIAL PORTION OF ITS LENGTH, AND A LONGTITUDINAL SLOTTED PORTION BETWEEN EACH OF SAID SURFACES, SAID SLOTTED PORTION COMMUNICATING WITH THE DEVELOPER SUPPLY MEANS, AND (E) MEANS FOR ROTATING SAID ROLLERS AND MOVING SAID WEB THEREBETWEEN.