DE2112538A1 - Liquid electrostatic latent image developing device - Google Patents

Description

PATENT LAWYERS

DR. E. WIEGAND DIPL-ING. W. NOBODY? 1 1

DR. M. KÖHLER DIPL-ING. C. GERNHARDT ''

MÖNCHEN HAMBURG

TELEPHONE: 5554 76 8000 MONKS 15,

TELEGRAMS: KARPATENT NUSSBAUMSTRASSE 10

March 16, 1971

W. 40 413/71 Loe

Fuji Photo Film Co., Ltd.
Ashigara-Kamigun, Kanagawa (Japan)

Liquid electrostatic latent image developing device

The present invention relates to a developing device for electrophotography, and more particularly to a liquid developing device capable of preventing fogging due to uniform background stain resulting from a residual electrostatic charge? to prevent the formation of white, light-developed parts (so-called "halos" or halos) in areas of low density that adjoin areas of high density near the border? to prevent the formation of comet-like streaks on the developed image along the downward flow of the liquid developer; a wide area

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with a uniform charge density into a uniform image density and thereby the so-called edge effect to prevent; and ensure high-speed development.

Generally show the photoconductive insulating layers used in electrophotography a certain amount of a residual or remanence potential. If such a photoconductive insulating Layer is subjected to imagewise exposure after uniform electrostatic charge, the Charge in the areas that are irradiated with light, while the charge on the areas that are not irradiated with light remains unchanged on the layer remain. The amount of discharged charge becomes greater when the intensity of the light leads to the formation of an electrostatic latent image corresponding to the light image becomes larger. In fact, however, the derivation is progressing the electrostatic charge does not proceed in accordance with the increase in light intensity and the rate of dissipation falls when the intensity of the light exceeds a certain limit and remains there an electrical charge, which is observed as a so-called remanence potential, on the areas on which the electrostatic charge should be completely dissipated if exposure is stopped before the electrostatic charge is completely dissipated. On the other hand, if the exposure is large enough to fully derive the remanence potential, the electrostatic charge in the areas where the charge cannot be dissipated beyond a certain limit should, overly derived, making it impossible to obtain a latent image that is faithful to the original pattern is equivalent to. In the ongoing proceedings is therefore

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the imagewise exposure carried out so that a certain remanence potential is formed and the resulting Veils are removed by appropriate procedures. When such a hemanence charge is faithfully developed becomes an unsatisfactory image with a uniform haze on the background generated.

In order to prevent the formation of fog caused by the remanence potential, it has already been proposed that a direct voltage from the outside on the development electrode to be used, which forms a potential comparable to the remanence potential. However, this procedure is accompanied by the following disadvantage when used in an automatic developing apparatus in which electrophotographic Material is fed continuously, is applied. This disadvantage is caused by the fact that the electrophotographic material on which the latent image is formed by the liquid Developer is shifted from the opposite position to the development electrode, with a progressive Decay of the electrostatic charge is caused due to the dissipation in the liquid developer. More accurate said, is the remanent charge that occurs while on a certain area of the surface that carries the latent image the time from the moment when this area of the development electrode faces smaller until the moment when the area leaves the developing electrode. Polically, it is impossible to apply the remanence potential, which changes continuously, as stated above a constant external voltage to be applied to the developing electrode, and it is therefore impossible to obtain a faithful Reproduction of the original pattern. With these

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BATH ORIGINAL

known methods it is also necessary to adjust the external tension according to the type of used to regulate electrophotographic material as these materials have different remanence potentials. Consequently, in the known methods, the disadvantage it must be accepted that the remanence potential must be measured in a suitable manner.

It is also known that another unpleasant phenomenon called "halo" phenomenon for electrophotography is specific. This phenomenon occurs when a low density area and a high charge density adjoin each other and at the same time the charge density at the boundary between the areas shows a quick change. This halo phenomenon appears as a white undeveloped part with no toner deposition observed, the original pattern not being reproduced in the area of low charge density near the boundary will. Furthermore, this halo phenomenon is more pronounced when the distance between the developing electrode and the area that bears the latent image is smaller ^ This can, as explained below, theoretically supported, although it seems to contradict the theory.

One more specific for electrophotography The disadvantage is the formation of streaks on the developed image, which act as a toner deposition in the form of a comet's tail Shape can be observed along the flow of the liquid developer down when the liquid developer is allowed to flow along the surface bearing the latent image. This phenomenon also makes it impossible

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to get a good quality picture. This phenomenon is directly due to the presence of a relative Speed component between the area bearing the latent image and the liquid developer parallel to the surface. In practice, however, it is difficult to get this speed component up 0, and it is not beneficial to reduce this speed component to decrease to a very small value due to the supply of the liquid developer, Indeed, the presence of the velocity component of a certain magnitude must therefore be accepted. Though the streak phenomenon is associated with various factors, and the mechanism of it is not yet is clarified, it has already been made possible to effectively reduce this phenomenon with the help of various methods to reduce. The stripe phenomenon is empirically more pronounced, when the electrostatic charge on the toner particles is smaller, and particularly pronounced at the limit where the latent image charge is rapidly changing from high density to low density shows. It is of course believed that the streak phenomenon is easily observed when the relative velocity component is large, but it is known empirically that this phenomenon becomes more pronounced even at an equal relative speed if the ability of the developing electrode to control the flow of the to increase and absorb electrical force generated by the surface bearing the latent image, is available,

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The invention relates to a developing device in which an electrostatic latent image formed on an insulating layer provided on an electroconductive substrate and a developing electrode are held facing each other at a narrow distance in a liquid developer, the liquid developer from fine charged particles dispersed in an electro-insulating liquid, and wherein the developing electrode is provided with a larger ratio of open areas at the beginning of the development in order to reduce the effect of the developing electrode on the lines of electric force generated from the latent image increased, and absorbed so that they are insufficient to toner particles to attract and so _w that no stripes are formed on the developed image, and wherein the ratio of the open areas will be reduced to the developer electrode after the Remanenzpotential wesentl I decayed during the developing process, so that no areas where the charge density of the latent image shows a rapid change remain, thereby intensifying the effect of the developing electrode and terminating the development in this state. The development electrode effect is understood to mean the action thereof to increase the number of lines of force and to absorb the flow of electric force resulting from the electrostatic charge present on the surface bearing the electrostatic latent image. With the device according to the invention the above-mentioned drawbacks are avoided and this device is suitable for high-speed development. The distance between the development electrode and the area bearing the latent image can be constant along the path of the electrophotographic material

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The invention is based on the following principles. In the event that the ratio of open areas on the developing electrode is kept very small from the beginning and the distance (hereinafter referred to as "g ⁿ ) between the developing electrode and the area bearing a latent BiH is small, a residual charge becomes small also faithfully developed, which leads to fogging and gaps caused by a lack of halftone in fields of low density in the parts where the charge density is suddenly changed. Also a so-called edge effect (this does not lead to disturbances) if g is very small since it cannot be visually observed) is generated when the edge part of the high density area is developed at a higher density as compared with the inner part (central part), and streaks may also appear on the image.

These disadvantages are alleviated by the use of a developing electrode with a large ratio of open areas at the start of development and through use an electrode with a small ratio of open areas at the later stage of development. At the 'beginning' there would be the electric field between the electrode and the area bearing the latent image is deposited with the toner particles by the remanent charge on the area of the surface and in the meantime the remanence charge would be dissipated by the Liquid developer is drained off while developing the peripheral portion of the high density area emphasizes, which leads to a more moderate change in charge density. Then the later development using a. Development electrode with one small ratio of open areas carried out, pull the surfaces that have a remanent charge,

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the toner particles hardly come on, since this remanence charge decays due to the discharge and therefore does not cause any fogging. Except in the parts where the charge density shows an abrupt change, the developing electrode with a small ratio of open areas facing the area bearing the latent image does not generate reverse electric fields and therefore does not show a halo phenomenon because this abrupt change has already been changed to a more moderate one. Further, ^a: faithful reproduction of the OriginalMldes be obtained even in the inner parts of high density regions with the aid of the combination of a first development with accentuated edge effect and the second development without edge effect. Further, although streaks are easy to form, if the action of the developing electrode is large (if the ratio of open areas is small) and if the charge density shows abrupt changes, such streaks will be formed in a method employing a developing device according to the invention is prevented in the first development because the effect of the developing electrode in the space between the electrode and the area bearing the latent image is kept small and also in the second development under the increased effect of the developing electrode, because the abrupt change in the Charge density has already disappeared is prevented.

According to the invention, the action of the development electrode is regulated by placing on the surface the developer electrode, which faces the area that bears the latent image, open areas are provided. The ratio of the open areas

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is a ratio of the area of the openings on the developer electrode. For example, if there is no opening on the electrode, this ratio is zero. The ratio of open areas can be changed on a development electrode. However, several electrodes with different ratios of the open areas can also be used. The ratio of the open areas is hereinafter referred to as ^M S ".

The invention is explained below with reference to the drawing.

Fig. 1 is a cross-sectional view of an electrophotographic material in which the right half the surface is uniformly charged.

Fig. 2 shows the distribution of electrostatic charge on the surface of an electrophotographic Material that is electrostatically charged as shown in FIG.

Figs. 3 and 4 show the distribution in the absence and presence of a development electrode, respectively, the electric field is perpendicular to and in the vicinity of the surface of an electrophotographic material, which has an electrostatic charge distribution as shown in FIG.

Fig. 5 shows the distribution of electrostatic charge obtained when an electrostatic Charge similar to that shown in Fig. 1 is applied to the surface of an electrophotographic material.

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is turned, which has a uniform remanence charge.

FIG. 6 shows the distribution of the electric field in the vicinity of the area corresponding to that shown in FIG has the charge distribution shown when the effect of the developing electrode is large.

Fig. 7 shows the electric field distribution when this effect is small.

Fig. 8 shows an electrostatic charge distribution with an area of uniform low density and an area of uniform high density is contiguous.

Fig. 9 shows the electric field distribution in the vicinity of the surface of an electrophotographic Material having the charge distribution shown in FIG.

Fig. 10 shows the distribution of electrostatic charge exhibiting a gradual change from lower charge density shows too high a charge density.

FIG. 11 shows the distribution of the electric field generated by the charge distribution shown in FIG will.

Fig. 12 is a plan view showing the developing state observed when liquid developer is used see over the area of an electrophotograph Material is allowed to flow, which is provided with a gradual distribution of the electrostatic charge.

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Figures 13 to 17 show longitudinal sectional views of developing electrodes for use in an apparatus according to the invention.

Figures 18 and 19 are plan views of developing electrodes for use in a device according to the invention.

Fig. 1 shows a cross section of an electrophotographic material 10, its right half the surface carries a uniform, uniform electrostatic charge. The photoconductive isolJa? End Layer 11 consists of known materials, such as amorphous selenium or photoconductive, powdery Materials, e.g. photoconductive zinc oxide powder mixed with insulating, resinous binder. the electroconductive substrate layer 12 may e.g. from a metal plate or a plastic film or consist of paper that was previously an electroconductive Had been subjected to treatment. Layer 12 is usually grounded during development. Fig. 1 shows an example of an electrostatic latent image composed of a positive charge that is uniform is arranged on the right half of the surface of the layer 11 and from a negative charge of the same size that is induced on the corresponding half below the limit j exists.

FIG. 2 graphically shows the distribution of the positive charge shown in FIG. 1, with the abscissa the lateral dimension of the area and where the original point is at the border of the Electrostatic charge range shown in FIG. In this case it is assumed that the electrostatic charge with a charge density

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of 6 = 6 is present on the right side of the surface.

The Pig. 3 and 4 are curves showing the component (of the electric field), perpendicular to 'the' surface, 'the the latent image is shown in the vicinity of the surface that originates from the charge density shown in FIG. In Fig. 3, there is shown the case where there is no developing electrode is present or the distance between the electrode and the latent image is very large and the Distribution of the electric field has a completely different form from that of the electrostatic Field shows. This phenomenon is known as the edge effect. In this case it can be seen that even a negative Field occurs on the left half of the surface as shown in Fig. 3 where 6 = 0 as shown in Fig. 3 Fig. 2 is shown (the electric field is said to be positive if the direction thereof is from the surface, bearing the latent image faces upward, as shown in Fig. 1). Such a negative field becomes hereinafter referred to as the reverse electric field. It is observed that such reverse electrical Fields near the border areas are particularly large are.

Fig. 4 is a graph showing the VertelLung the observed electric field when the surface bearing the latent image is kept facing an earthed developing electrode at a fixed interval ^1. The curves B and A in Fig. 4 correspond to the cases in which the distance between the fourth developing electrode and the area bearing the latent image is made very small (eg several tens of microns) or made large (5 to 10 mm). The distribution of the electric field

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and the electrostatic charge shows a pretty good match when (g) is very small, though a weak reversed electric field still remains, which especially in the vicinity of the edge parts (represented by the origin of the graphic Representation) in comparison with the ones removed from it Areas is poured. So the reversed field remains large, even if (g) is kept small. When (g) is large, the reverse field becomes small. Curve A changes to curve B when S is large is made even if (g) is kept small.

Fig. 5 shows the distribution of the electrostatic Charge if there is a remanent charge (9/0 in the area (left of the origin) where 2> = Should be zero. The charge distribution shown in Fig. 2 is an ideal charge distribution, while an actual imagewise Exposure causes a distribution as shown in Fig. 5.

Fig. 6 is a graph showing the component of the ctric field perpendicular to and in the vicinity of the area bearing the latent image, the charge distribution shown in Fig. 5 shows in. Arrangement facing the surface with relatively small g-S values. As shown in Fig. 6, this is electric field in the areas where the remanent charge of FIG. 5 is present, positive except at the frenzy parts

the electrostatic charge distribution. In such boundary portions, the electric field shows im.Gegenteil a negative minimum point due to the residual edge effects. If a liquid developer (the one in this

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Fall from tiny negatively charged particles or so-called. Toners, which are suspended in an insulating liquid) on the surface that the latent image carries, when applied to such an electric field distribution, toner particles are also deposited, which are attracted by the positive electric field, on the left half of the surface, where a "Such a deposit is initially undesirable because it causes haze due to the remanent charge.

Fig. 7 is a graph showing the electric field distribution corresponding to the charge distribution shown in Fig. 5 when the value of (g) is kept relatively small and S is kept relatively large and uniform on the electrode. Because of the enlarged S, in this case (which corresponds to curve B in FIG. 4) the reverse electric field, which _{originates from the areas with a charge density 6 o} (right half), and the positive electric field, which comes from the areas with a charge density Ό * (left half) arise against each other, so that no positive electric field remains even in the areas with a static charge. In this case, no toner deposit appears on the left half of the surface.

The following explanations relate to

the HaIo phenomenon, which occurs in known development processes is observed.

Fig. 8 shows the distribution of electrostatic charge with abrupt changes at the boundary between the area of low density with the charge density

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and the high-density region with the charge density _Q. The solid line in FIG. 9 shows the distribution of the electric field when the values of (g) and S are kept very small in the case of the charge distribution shown in FIG . The toner deposition appears as if development is carried out by supplying liquid developer to the area bearing the latent image, while keeping the values of (g) and S small, as shown in the solid line. If the development is interrupted in this course, the distribution of the remanent charge after neutralization with toner shows the form indicated by the broken line in Fig. 8. Since the values of (g) and S are very small in this case, the neutralization of the charge proceeds approximately in proportion to the charge distribution thereof except at the boundary parts. Accordingly, when the values of (g) and S are very small, the distribution of the electric field caused by the remaining charge distribution takes the form shown by the broken line in Fig. 9, which is substantially similar to that shown in FIG is shown by the solid line, and in this way is also provided with a negative electric field in the boundary parts. Consequently, due to the developing electrode having very small (g) and S values from the beginning of the development, the reverse electric field becomes during the development in the vicinity of the boundary parts where the charge density becomes abrupt. Change shows, sustained, which reduces the build-up in these parts, which leads to so-called halos or halos.

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Fig. 10 shows the distribution of the remaining electrostatic charge when development is carried out on the charge distribution represented by the solid line in Fig. 8 with a relatively large S value and a relatively small (g) value ( e.g. about several 100 Ai) and is terminated in the course of the same. The initial electric field distribution takes the form of Fig. 7 because of the large S value, and therefore the deposition of the toner particles begins preferentially from the areas of strong electric field near the boundaries.

Such a deposit neutralizes the electrostatic charge only in the parts where the electric field is strong while the electrostatic Charge in the parts remote from the boundaries remains fairly unchanged. To be precise, it shows

the charge a slight decay due to the dissipation by the liquid developer during development, which leads to a more moderate charge distribution as shown in FIG. 10. The distribution of the electric field changes to the shape shown in Fig. 11, which does not have a reverse electric field shows more due to the absence of abrupt changes in the electrostatic charge distribution.

FIG. 11 shows the distribution of the electric field which corresponds to the charge distribution of FIG. 10, if the values g and S are kept very small. In this case the values of g and / or S can be made as small as possible in the practical range, since the electric field, as shown in Fig. 9,

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in this case, due to the absence of the abrupt change in charge density, is no longer formed, even if the value of g is kept very small. Hence "accompanies a moderate distribution of the electric field as shown in Fig. 11 hardly any halos or stripes.

Although veils and stripes are advantageous through . While maintaining large S values during development, such an operation should be avoided because the development speed is excessively slowed down and it is impossible to obtain a satisfactory image which is a faithful representation of the latent image and which has no edge effects . As a result, it is necessary to decrease the S value after a suitable time. This time is generally in the range of several tens of seconds. up to several 100 see. and sometimes exceeds this range, although this time depends strongly on various factors such as the properties of the electrophotographic material, the resistance of the liquid developer, the electrostatic charge on the toner particles, the concentration of the toner particles in the liquid developer, the migration speed of the Toner and the like

Fig. 12 shows the influence of the values of g and S on the phenomenon of streaks and shows the result of development when the liquid developer is in Direction of the arrow on the electrostatic charge is allowed to flow, which is distributed in a stepped form is under extremely small g- and S-

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Values. The developed image experimentally shows long streaks and dark short streaks in the direction of the Liquid developer flow. If the development with relatively small g-value and relatively If the S-value is large, the short stripes disappear while the long ones Streaks persist. These long strips can also be removed if the flow rate is slow of the liquid developer is made smaller. The long streaks also disappear when the flow rate increases of the liquid developer is made smaller, regardless of the g- and S-value, however, the short stripes persist until the value of g or S is made larger. It has also confirmed that these short streaks no longer occur even if the value of g or S is during the development is made bigger.

For example, it is experimentally confirmed that the dark short stripes do not appear when the Development 0.3 to 5 see. with a g-value of several hundred microns and with a large S-value will.

The scope of the present invention is summarized below:

1. Veil

Since it is practically impossible to avoid the formation of a core potential in electrophotography, the formation of a fog is inevitable due to the electric field generated by the remanence potential,

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when developing with a small ratio of open areas and small distance between the the latent image bearing surface and the developing electrode are performed from the start of development will. However, it is possible to remove this haze by increasing the ratio of the open areas at the beginning of the development is kept large in order to keep the remanence potential below the small distance between development electrode and electrostatic to weaken latent image.

2. Halo and edge effects in the image areas;

In electrophotography, so-called halo or toner deficiency areas occur in parts of the density near the limits where the charge density becomes abrupt; Shows change and the areas of high charge density on the graphs show a higher image density compared with that in the inner parts of the areas, which leads to the so-called edge effect. These phenomena are theoretically inevitable unless the distance between the development electrode and the electrostatic latent image is reduced to zero. On the other hand, according to the invention, it is possible to reduce this edge effect to a practically acceptable level by developing under large M ratios

the open areas of the development electrode at the beginning and then under small proportions open areas.

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5. Stripes:

The developed image shows streaks when the parts showing an abrupt change in charge with a liquid developer, which has a relative speed component with respect to the lataie image having. This phenomenon is more easily formed at a certain relative speed when that Ratio of open areas or the distance between the electrode and the area containing the latent Image is smaller or when the change in charge density is greater. It is possible to education prevent such streaks by developing at the beginning with an enlarged ratio of open Areas is carried out and even with a small distance between the development electrode and the latent Image with emphasizing the edge parts and making the change in charge density weaker, and then the ratio of open areas is reduced will.

The invention is explained in more detail below with the aid of some embodiments.

13 shows a schematic cross-sectional view of a device according to the invention of one grounded flat metal developing electrode 1 is provided. This developing electrode 1 comprises several thin ones narrow-strip-shaped electrodes 2 to 9, which at right angles to the path of the electrophotographic material, with gaps (openings) 14 to 19 between these. An endless belt 20, which is made of metal plates, a metal mesh, plastic ma-

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material, rubber, cloth or the like. is made, is guided around the two rollers 21 and 22. ' Electrophotographic sheet material 10, hereinafter referred to as Sheet labeled with electrostatic latentaa Images is provided thereon, wM carried by the belt 20 and guided from right to left. The electroconductive one Layer of sheet 10 is separated or grounded by tape 20.

The sheet-carrying surface of the belt 20 is slightly inclined with respect to the horizontal surface, so that the liquid developer from right to left %

flows. The liquid developer is stored in a container 23, fed to the line 25 through the outlet 24 of the container 23 with the aid of a pump (not shown) and fed onto the sheet 10 through the openings or gaps provided in the line 25. All electrodes 2 to 9 have the same size and are arranged at the same distance from the surface of the sheet 10. The gaps 13-19 between the electrodes are gradually narrowed along the path of the sheet. That is, the gap 13 is the largest and gap 19 is the smallest. Each electrode surface is parallel to and almost at right angles to A along the path of the sheet. As mentioned above, multiple electrodes or a metal plate provided with openings corresponding to columns 13 to 19 can be used for the development electrode. In the case that multiple electrodes are used, it is preferred to electrically connect these electrodes. These electrodes can be electrically biased to various potentials. E.g.

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it is necessary when the residual charge of the latent The image is large and the charge is not dissipated enough due to the dissipation of the liquid developer to apply a bias voltage to the electrodes. In this case it is advantageous to adjust the preload gradually to decrease, since the remanent charge decreases in the course of development.

In the device, as shown in Fig. 13, the length of the electrode strips is along the length of the The path of the sheet is practically between about 1/10 mm W and several tens of centimeters, and preferably several millimeters to several centimeters. The longitudinal cross-sectional shape of these electrode strips, which in FIG. 13 is rectangular is shown, can be round, oval, square, triangular or the like. be.

Fig. 14 shows another embodiment of the development electrode used in the device according to the invention. The reference numerals 22 to 29 denote strip-shaped electrodes, the length of which is greater along the sheet path in the order of the reference numerals. The reference numerals 33 to 39 denote the distance between these electrodes and are kept approximately constant. In other words, the ratio of the open areas S is greater on the right-hand side and smaller on the left-hand side of this figure.

Fig. 15 shows another embodiment of the developing electrode. The electrode strips 42 to have the same size uncf / stripe 51 is larger in Direction of the leaf path. The column 52 to 60 between. these strips gradually narrow. The relationship

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S is zero for the strip 51.

Fig. 16 shows an example of an apparatus using a semi-cylindrical developing electrode in which a flexible electrophotographic web material 10 is continuously fed at a constant speed around the drum 70 with the latent image outside. The electrode strips 61 to 69 are arranged in a cylindrical shape at a constant distance from the surface of the material with gaps 72 to 79. The gaps 72 to JS gradually decrease in that order. Reference numeral 71 denotes the level of the liquid developer.

Fig. 17 shows an embodiment of the developing electrode using thin metal wires. The reference numerals 80 to 89 denote screw electrodes which are stretched in parallel. The reference numerals 91 to 99 denote the distances between adjacent electrodes. These distances become smaller with the order of the reference symbols.

Although the examples given so far are in the case where the number of electrode strips or wires between 8 and 16, according to the invention, more or fewer electrodes can be used will..

The distance g between the latent image bearing area and the developing electrode is not necessarily constant. The ratio S may partly become large during the developing process.

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According to the invention, S is at the start of development large and then the exchange or agitation of the liquid developer between the surface is and the developing electrode, and this leads to a high developing speed.

Figs. 18 and 19 show another embodiment of the developing electrode. The one shown in FIG The development electrode is a flat metal plate 100 provided with rectangular holes. Fig. Fig. 4 shows a development electrode provided with circular holes. With both development electrodes S becomes smaller from right to left.

It is not necessary that the developing electrode used according to the invention Grounded electrodes have a tendency to fog due to the remanence potential. It is also possible to use this electrode at the beginning of the. development not to be earthed and only to be earthed as development progresses.

As explained above, according to the invention, it is possible to develop with reduced Effect of the development electrode to carry out the lines of electric force that are generated by the latent Image caused by being absorbed by a developing electrode with a large ratio of the open areas is used at the beginning of development and then under the reinforcing effect of the Development electrode is worked by using a development electrode with a small S ratio is used.

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If the remanence potential is not reduced enough while making the abrupt change in charge density at the beginning more moderate it is preferred to apply a bias voltage to drive the toner particles away from the latent image in order to to prevent fogging.

With the device according to the invention, an electrophotographic image without fog, halo and edge effect while enabling high-speed development.

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Claims (8)

Claims Π }> Liquid electrostatic latent image developing device characterized by a developing electrode having open areas and in which the ratio of open areas decreases along the path of the electrophotographic material. 2) liquid development device according to claim 1, characterized in that the development electrode conductive narrow strips perpendicular to the advancement of the electrophotographic material are arranged, with columns that become narrower along the way, includes. 3) Device according to claim 2, characterized in that that the strips along the way are the same width and the gaps become narrower. 4) Device according to claim 2, characterized in that that the width of the strips increases along the way and the gaps are equal. 5) Device according to claim 1, characterized in that that the development electrode is a conductive plate with openings, the area ratio of which on the Electrode along the path of the electrophobgraph Material decreases, includes. 6) Device according to claim 5 »characterized in that the shape of the openings is rectangular and all spaces between the openings, which are arranged at right angles to the progression, do not lie on a line parallel to the path. 109840/1579 7) Device according to claim 5, characterized in that the shape of the openings is circular. 8) Device according to claim 1, characterized in that that the development electrode is a wire mesh electrode, which is stretched in parallel, and where the Distances zv / i see the wires decrease along the path of the electrophotographic material. 109840/15 79