US3713422A - Apparatus for developing an electrostatic latent image by liquid development - Google Patents

Apparatus for developing an electrostatic latent image by liquid development Download PDF

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Publication number
US3713422A
US3713422A US00122692A US3713422DA US3713422A US 3713422 A US3713422 A US 3713422A US 00122692 A US00122692 A US 00122692A US 3713422D A US3713422D A US 3713422DA US 3713422 A US3713422 A US 3713422A
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United States
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electrode
development
latent image
charge
rollers
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Expired - Lifetime
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US00122692A
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English (en)
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M Sato
O Fukushima
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Fujifilm Holdings Corp
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Fuji Photo Film Co Ltd
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
    • G03G15/108—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer with which the recording material is brought in contact, e.g. immersion or surface immersion development

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  • ABSTRACT A development device of an electrostatic latent image wherein rotatable and cylindrical development electrodes comprising the conductive center portion which has a small radius and will face to an electrostatic latent image on a flexible electrophotographic material, and two flange portions which have a large radius respectively and will support the both ends of said material are placed such that differences between I said radius of the center portion and said radius of flange portions become smaller with the proceeding of the development, thereby a print can be made with extremely small halos, streaks, fogs and edge effects.
  • v L ⁇ y is FIG. 2 v 2;
  • FIG. I2 is a diagrammatic representation of FIG. I2
  • This invention relates to a development apparatus for electrophotography and more specifically to one which can rapidly provide a high quality image preventing the formation of i. background toner deposition due to the residual potential,
  • a photoconductive insulating coating employed in electrophotography always exhibits a more or less residual potential after exposure to light, that is, when the coating is uniformly charged at darkness, subjected to image exposure, the surface charge is neutralized at the illuminated area, but retained at the non-illuminated area; the extent of neutralization depends on the amount of exposure thus forming an electrostatic latent image.
  • the efficiency of charge neutralization gradually lowers, and thus a small level of residual potential is generally observed at the high light region of an light image.
  • halo occurs where two areas having markedly different charge densities are contiguously present and the charge density gradient is large at the border between them.
  • the name halo is given to the phenomenon in which the low charge density area is not developed proportionally to its charge density but left as toner deficient area at the border adjacent to the higher density area. Halo becomes more noticeable as the spacing between the development electrode and the surface to be developed is reduced, which might seem to conflict with the theory which, however, will be shown afterwards to support the experimental results.
  • a still further defect intrinsic to electrophotography is streak in the developed image. Streaks take plate along the direction of the flow of the developer liquid blurring at the downstream side of a toner-deposited area. Such streaks look like a trail of a comet. Streaks which are easily distinguishable tremendously deteriorate the quality of a developed image.
  • the most direct factor to cause streak is a relative velocity component of developer flow parallel to the surface to be developed. Perfect exile of this parallel component is practically impossible and also disadvantageous as for the ample supply of the developer liquid. Therefore one has to regard and solve this problem on the assumption of the existence of the parallel component. Though the mechanism by which streak generates is not clarified as yet, many methods of reducing streak have been found.
  • the streak becomes more noticeable (i) with a toner having a smaller electrostatic charge, (ii) with a steeper change of charge density in an electrostatic latent image, (iii) as the relative velocity between the surface to be developed and the developer liquid increases, and (iv) as the development electrode comes closer to the surface to be developed so as to absorb more effectively the electric lines of force emanating from the latent image (at a constant relative velocity).
  • the development apparatus in accordance with the present invention is for use in developing an electrostatic latent image formed on an insulating coating provided on a flexible conductive backing, and comprises development electrodes which are faced with close spacings to the coating surface in the presence of a developer liquid comprising a finely-divided charged toner dispersed in an insulating liquid.
  • the apparatus can achieve development of an electrophotographic recording material with an electrode placed far from said material at the initial stage and subsequently with another electrode placed close to said material.
  • a most representative construction of the development electrode is a drum having different diameters at the middle and edge portions thereof.
  • the essential feature of the present invention is to provide an apparatus which performs development comprising an initial development with little aid of a development electrode, followed by a successive development with the full use of an electrode: And details of the change of the spacing through the overall development little affect the result; the most important thing is that the electrode spacing should gradually decrease (in other words, the effect of the electrode should monotonously increase) from the commencement to the end of the development and a minor change of the effect during the development is not so significant. For example, as a minor modification, the electrode spacing may be made practically infinite in the course of development,
  • the electrode may or may not have a ground potential
  • an electrode potential different from earth potential is sometimes preferable. Also, the situation is similar for the conductive backing of the recording material.
  • Electrodes spacing which is small from the start of development will result in a faithful visualization of the slight residual potential to form a considerable background, and will give a toner image accompanied by halos at the regions where steep charge density changes occur, and by streaks.
  • a high density solid area adjacent to a low density area is subjected, to an edge development, at the commencement of the development, allowing the originally steep charge density gradient at the edge to become gentle.
  • the background with a negligible residual potential will hardly attract toner, while the areas with abrupt charge density changes, by virtue of the already deposited toner, exhibit milder charge density gradient which is accompanied with a weaker repulsive electric field. Accordingly, the development brings about little halo at the low-density area adjacent to the high density area.
  • a toner image of greatly improved quality can be obtained with a first development an emphasized edge development combined with a second development which does not cause any edge effect.
  • Streak which is prone to occur with a close electrode spacing at the area where the gradient of charge density change is large, is also effectively prevented with the use of a large electrode spacing at the first development and by a reduced charge density gradient by virtue of the edge development owing to the first development at the second development.
  • FIG. I is a cross-sectional view of an electrophotographic material of which half of the surface thereof is uniformly charged electrostatically.
  • FIG. 2 shows the distribution of electrostatic charge on the surface of an electrophotographic material electrostatically charged as shown in FIG. 1.
  • FIGS. 3 and 4 show the distribution in the absence and presence of developing electrode respectively of electric field perpendicular to and in the proximity of the surface of an electrophotographic material provided with the electrostatic charge distribution as shown in FIG. 2.
  • FIG. 5 shows the distribution of electrostatic charge obtained when electrostatic charging similar to that in FIG. 1 is applied to the surface of an electrophotographic material provided with uniform retentive charge.
  • FIG. 6 shows the distribution of electric field in the proximity of the surface provided with the charge distribution shown in FIG. 5 when the developing electrode is placed close thereto.
  • FIG. 7 shows the distribution of electrode field when said distance is large.
  • FIG. 8 shows a distribution of electrostatic charge in which a uniform low density area and a uniform high density area are adjacent.
  • FIG. 9 shows the distribution of electric field in the proximity of the surface of an electrophotographic material provided with the charge distribution shown in I 1 FIGS.
  • FIG. 10 shows the distribution of electrostatic charge showing gradual change from low charge density to high charge density.
  • FIG. 11 shows the distribution of electric field generated by the charge distribution shown in FIG. 10.
  • FIG. 12 is a plan view showing the state of developing observed when liquid developer is made to flow on the surface of an electrophotographic material provided with stepwise distribution of electrostatic charge in a direction perpendicular to said stepwise distributron.
  • FIG. 13 is a perspective view of developing electrode used in the apparatus of this invention.
  • FIGS. 14 and 15 show longitudinal cross-sections of this invention.
  • FIG. 1 illustrates an electrophotographic material 10 on one half surface of which is uniformly charged.
  • the material comprises a photoconductive insulating layer 11 and a conductive substrate 12.
  • the former may comprise amorphous selenium, a homogeneous mixture of photoconductive zinc oxide and an insulating resin, while suitable materials for the latter include metal plate, plastic films treated with conductive agents, and paper imparted with a suitable conductivity by special treatments.
  • the substrate 12 is usually kept at ground potential.
  • the electrostatic latent image in this figure is composed of positive charge distributed on the right hand half of the surface 11 with a uniform density 0,. An equivalent amount of charge of the opposite polarity is induced at the interface between 11 and 12. The positive charge distribution is shown graphically in FIG.
  • FIG. 3 and FIG. 4 illustrate the electric field configuration arising from the above charge distribution, observed near the charged surface.
  • curves correspond to the fields vertical to the charged plane.
  • FIG. 3 shows the field configuration without or with a development electrode placed quite apart from the plane.
  • the field configuration is quite different from that of charge which is the origin of the field. This fact is, as is well known, closely related with the so-called edge-effect.
  • a region of filed with reversal direction exists in the left hand half of the plane adjacent to the border. (Taking the field upward positive, this inverted field is negative.)
  • the electric field opposite to that existing above the charged region will be referred to as inverted field.
  • the inverted field has its maximum near the very edge from which the plane is charged.
  • FIG. 4 illustrates the field configuration associated with the charge pattern shown in FIGS. 1 or 2 with a development electrode placed parallel to the plane with different spacings.
  • the three curves, A, B and C correspond to an extremely small (several microns), medium (1mm), and a relatively large (about 10mm) spacing respectively.
  • the spacing or gap will be designated g.
  • the field configuration With a small g., the field configuration becomes quite similar to that of charge. However, still the inverted field remains which has a maximum near the edge, rapidly decreasing to the far left. With the increase of g., the inverted field becomes remarkable, while the positive field strength decreases.
  • FIG. 5 illustrates a charge distribution with a uniform residual charge with a density 0,, on the left half of the plane.
  • the charge distribution in FIG. 2 is an ideal one with 0' 0 at the left half, while the charge distribution which really results form a uniform charging and light exposure may be schematically such as is shown in FIG. 5.
  • FIG. 6 shows the electric field component perpendicular to the plane associated with the charge distribution shown in FIG. 5 in the presence of an electrode placed thereabove with a relatively small g. As is seen from this figure, the field on the left half is positive except the small region adjacent to the highly charged region. A small minimum of negative or inverted field still remains owing to the edge effect.
  • a developer liquid here, comprising a negatively charged finely divided toner dispersed in an insulating liquid
  • the toner will deposit where a positive field exists, thus forming a background on the left half though this region is not desired to attract any toner.
  • FIG. 7 shows the field configuration above the latent image shown in FIG. 5 with an electrode fairly separated from the plane.
  • the positive field due to the residual charge 0 is cancelled with the negative field caused by the uniformly charged area (right half) not leaving a net positive field on the left half of the plane. Accordingly, any toner will not deposit thereon.
  • FIG. 8 illustrates another example of charge distribution comprising two regions each having a uniform high and low density 0-,, and respectively. An abrupt change of density occurs at the border of the two regions.
  • the solid line in FIG. 9 shows the field configuration associated with the distribution shown in FIG. 8 in the presence of an electrode with a small g. value.
  • toner When a developer liquid is applied on the plane under the electrode separated by the small g., toner will deposit in accordance with the field configuration shown by the solid line in FIG. 9.
  • the remaining charge on the plane left unneutralized will be expressed schematically by the broken line in FIG. 8. This means that due to the small g., charge neutralization proceeds substantially uniformly except around the border of the two regions.
  • the field will then become such as shown by the broken line in FIG. 9, which retains all the essential features of the original configuration with reduced absolute value. From the figure one may see that the inverted field still remains outside the high charge density area showing that the use of an electrode closely placed above the plane from the commencement of and throughout the development leaves the inverted field even after toner deposition has proceeded to a considerable extent, causing halo which designates the toner deficient region corresponding to the inverted field area.
  • the lower limit for 3 may be several 10 microns, which will increase to about 100 microns for an automatic developing apparatus. For 3 around such value an inverted field will be formed to give rise to halo.
  • an extremely high quality image free of halo, background, and streak could be obtained by a three-step development, comprising a first step without electrode (g for 24 seconds, a second one with an electrode 20 mm apart from the paper surface for 14 seconds and the final one with g 0.] mm for 14 seconds.
  • Developer liquids for suitable use in an apparatus of the present invention may be those comprising a finelydivided pigment as toner with a particle diameter ranging from about 0.01 to 1 micron dispersed in an insulating carrier liquid selected from various non-polar hydrocarbons or mineral oils.
  • the developers may include a variety of charge controlling agents which are effective to improve the dispersion stability of the pigment particles and to control the electrostatic charge thereon. Control of charge may be accomplished by dissolving or dispersing resinous materials in the insulating liquid.
  • FIG. 12 illustrates a developer optical wedge showing the effect of g. on streak.
  • the electrode may be placed apart from the image plane at the commencement of development (as an extreme case the spacing is made infinite) allowing the residual potential to leak away. After the residual potential has sufficiently reduced, the electrode is permitted to come closer to the plane.
  • a toner deficient area which is referred to as halo, is formed at the border in the low-charge density region, while an edge development takes place near the border in the high density region.
  • the perfect resolution of these disadvantageous performances is theoretically impossible as long as a finite electrode spacing is employed.
  • the edge effect is made as little as possible by the second-step development following the first development.
  • FIG. 13 is a bird eye view of an electrode roller suitable for the apparatus of the present invention
  • FIGS. 14 and 15 are the cross-sectional view of developing devices of the invention.
  • the electrode roller shown in FIG. 13 comprises a middle portion 20 and flanges at both ends of the roller with a larger diameter than that of the middle cylinder which is made of an electrically conductive material.
  • the middle portion works as development electrode, and the flanges 21 are for holding the edges of a flexible electrophotographic material to be processed. The difference of the diameters of the two portions determines the spacing between the cylinder and the developed surface.
  • a plurality of such electrode rollers are provided in a processing tank along the path of the electrophotographic material in such a manner that the spacing or diameter difference decreases from roller to roller as the material advances.
  • the middle portion diameters of the three electrode rollers 22, 23 and 24 are expressed by dotted lines.
  • the electrophotographic material changes its advancing direction by winding itself around the supplementary rollers 25 and 26. As the material is driven in the direction shown by arrows with its lightssensitive side up, the electrode spacing becomes smaller and due to the mechanism explained above an image free of edge effect, halo and streak results.
  • the dimension of the path is designed so that one image frame comes to a standstill just facing to any one of the electrode and that the boundaries between the frames rest at the supplementary rollers. Such arrangement is not necessary for a constantly advancing material.
  • the electrode rollers may be rotated to drive the electrophotographic material or the material may be transported by other suitable means.
  • FIG. illustrates another embodiment in which electrode rollers provided in a processing tank (not shown in the Figure) as shown in FlG. 13 are again employed.
  • the middle portion of each roller has the same diameter as others but the flange diameter is different decreasing from the first roller 28 to the last one 31.
  • Rollers 32, 33, 34 and 35 rotate the electrode rollers by conductive endless belts suspended between the corresponding electrode and the driving roller.
  • Rollers 36, 37 and 38 turn the direction of the web to be developed; the developer liquid is filled up to the level shown by 39.
  • an electrophotographic material carrying an electrostatic latent image is applied a developer liquid without employing any electrode or with one placed apart from the material, the electrode being characterized by a roller comprising a middle conductive portion and flanges having a noticeably larger diameter than the middle portion, and then after sufficient time of such development with electrodes which are placed gradually nearer to the material by the use of electrode rollers which have smaller diameter differences in their arranged order.
  • the resulting developed image is a faithful reproduction of the original free of edge development, halo and streak.
  • a liquid development apparatus for developing an electrostatic latent image formed on a flexible electrophotographic material comprising a plurality of rotating electrode rollers with a middle conductive portion which the latent image bearing surface faces and flange portions at the both ends of the rollers having a larger diameter than the middle portion, said flange portions supporting the image bearing surface by direct contact,-said electrode rollers arranged in the path of said carried material and the difference in the diameters of said flange and middle conductive portions of said electrode rollers progressively decreasing along said path.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Wet Developing In Electrophotography (AREA)
  • Developing For Electrophotography (AREA)
US00122692A 1970-03-10 1971-03-10 Apparatus for developing an electrostatic latent image by liquid development Expired - Lifetime US3713422A (en)

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JP45020362A JPS5117913B1 (enrdf_load_stackoverflow) 1970-03-10 1970-03-10

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US (1) US3713422A (enrdf_load_stackoverflow)
JP (1) JPS5117913B1 (enrdf_load_stackoverflow)
BE (1) BE763992A (enrdf_load_stackoverflow)
CA (1) CA932953A (enrdf_load_stackoverflow)
DE (1) DE2111494C3 (enrdf_load_stackoverflow)
FR (1) FR2084408A5 (enrdf_load_stackoverflow)
GB (1) GB1341626A (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816114A (en) * 1972-03-03 1974-06-11 Xerox Corp Electro-photographic method
US3870514A (en) * 1973-06-18 1975-03-11 Xerox Corp Liquid development for the electronic photography
US3893417A (en) * 1974-01-17 1975-07-08 Eastman Kodak Co Apparatus for liquid development of electrostatic images
US3913524A (en) * 1972-03-13 1975-10-21 Rank Xerox Ltd Liquid developing apparatus for electrophotography
US4410260A (en) * 1981-12-09 1983-10-18 Coulter Systems Corporation Toning apparatus and method
US12239149B1 (en) 2023-09-26 2025-03-04 David Walsh Compositions and methods of producing cooked egg products

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5131241U (enrdf_load_stackoverflow) * 1974-08-28 1976-03-06
JPS52119642U (enrdf_load_stackoverflow) * 1976-03-08 1977-09-10
JPS52130828U (enrdf_load_stackoverflow) * 1976-03-31 1977-10-05

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816114A (en) * 1972-03-03 1974-06-11 Xerox Corp Electro-photographic method
US3913524A (en) * 1972-03-13 1975-10-21 Rank Xerox Ltd Liquid developing apparatus for electrophotography
US3870514A (en) * 1973-06-18 1975-03-11 Xerox Corp Liquid development for the electronic photography
US3893417A (en) * 1974-01-17 1975-07-08 Eastman Kodak Co Apparatus for liquid development of electrostatic images
US4410260A (en) * 1981-12-09 1983-10-18 Coulter Systems Corporation Toning apparatus and method
US12239149B1 (en) 2023-09-26 2025-03-04 David Walsh Compositions and methods of producing cooked egg products

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DE2111494B2 (de) 1975-04-30
FR2084408A5 (enrdf_load_stackoverflow) 1971-12-17
DE2111494A1 (de) 1971-09-23
BE763992A (fr) 1971-08-02
DE2111494C3 (de) 1976-01-08
GB1341626A (en) 1973-12-25
CA932953A (en) 1973-09-04
JPS5117913B1 (enrdf_load_stackoverflow) 1976-06-05

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