DE2105278A1 - Electrostatic latent image development process - Google Patents

Description

Patent attorneys Dipl.-Ing. F. Weickmann, 2105278

Dipl.-Ing. H.Weickmann, Dipl.-Phys. Dr.K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber

RANK XEROX LIMITED
Rank Xerox House

338 Euston Road
London NW1
England

8 MUNICH 86, POST BOX 860 820

MÖHLSTRASSE 22, NUMBER 4 »39 21/22

<983921/22>

Electrostatic latent image development process

The invention relates to an electrostatic development method latent images in which a liquid developer is placed between a recording medium and a development electrode with in an electrically non-conductive carrier liquid suspended, electrically charged particles is arranged.

The photoconductive insulating material layers used as recording media in electrophotography generally show a certain residual voltage when they are used. Will a photoconductive insulation layer after more uniform exposed to electrostatic charges in an image exposure, their charge is dissipated in the exposed parts of the surface, while they get in the non-irradiated areas remain. The discharge of charge occurs proportionally to the respective light intensity, which creates a latent electro- Static image is created that corresponds to an original image used for exposure. In practical implementation However, the charge dissipation is not proportional to the light intensity and is also lower if the Light intensity is increased beyond a certain point. Will the exposure before full discharge finished, those parts of the layer that could be completely discharged still contain a certain residual charge,

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which forms the residual stress. On the other hand, if the exposure is increased to completely remove the residual stress, so the charges on other parts of the surface are diverted too much beyond the desired value, making it impossible to generate a latent image that exactly corresponds to the original image. At present, most procedures use exposure carried out in such a way that a certain residual stress is retained, which results in fogging on the image can. These veils can be avoided by various measures.

If the residual stress is developed without countermeasures, a uniform one appears in the background of the developed image Fogging, which results in a practically unacceptable image quality.

In order to avoid the formation of fog due to residual stresses, it has already been proposed to apply a DC voltage to the development electrode in order to generate a potential which is comparable to the residual stress during development. However, when used in automatic reproduction machines with continuously moving recording media suffer from the following disadvantages. In such machines the recording medium is close to the development electrode placed inside the developing liquid, and the electrostatic charges are gradually reduced, However, not continuously drained, since the developing liquid allows leakage currents. In other words, the Residual charge on some files with a latent electrostatic Image provided recording area reduced during the time in which the relevant part of the recording area facing the development electrode. Therefore, one connected to the developing electrode causes constant tension does not completely neutralize the in this way changing residual potential, so that no faithful reproductions result. Further should the potential switched on from the outside in the known processes to the respective electrophotographic recording

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material, as such substances differ in terms of their residual potential. So it is necessary to measure the residual potential in a suitable manner.

The so-called "HaIo" phenomenon also occurs in electrophotography on. It is generated at the boundaries between areas of low charge density and areas of high charge density, when the change in charge density is very large. It manifests itself in white areas without toner deposits, like this that in the areas of low charge density near the boundary crossings no sufficient reproduction is produced. the KaIo appearance is even more pronounced when the distance between the developing electrode and the display area is less. Although this initially contradicts the theory, the halo phenomenon can theoretically be explained as yet is described.

There is also another disadvantage associated with electrophotography consists in the formation of "streaks" in the developed image. The developing liquid flows over the recording surface moved, so toner remains in the foremost parts of the image to be developed in the flow direction, so that kometenschv / e if-like stripes are generated. This phenomenon prevents of course the production of a high quality of reproduction. It is primarily due to the presence of one Relative speed component parallel to the recording surface between the surface and the developing liquid. In practice, however, it is technically difficult to completely eliminate such a speed component, and it is also disadvantageous to greatly reduced when the problem of supplying developing liquid is taken into account. Hence this should Speed component allowed to some extent bec Although the stripe formation; influencing Factors are very complicated and have not yet been fully clarified, certain methods of suppression already exist. It has been empirically shown that the formation of stripes

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becomes more pronounced as the charge of the toner weakens. This occurs especially at the transition zones when the The charge density of the latent image undergoes a large change. Furthermore, the banding becomes more pronounced when the relative velocity component described is larger, however, when a developing electrode is used, it becomes empirical confirms that, for one and the same relative velocity component, the banding becomes stronger when the effect of the development electrode to increase the number of electric field lines and to increase their absorption.

The object of the invention is to provide a development process for creating electrostatic latent images that avoid the halo appearances and banding and no external voltage source is required to neutralize the residual potential. Generated by residual potential Fog formation should be avoided, so that especially when used in automatic reproduction machines reproductions true to the original are produced »

A development method of the type mentioned is designed according to the invention to achieve this object in such a way that the effect of the development electrode initially until strong changes in the charge density of the latent image disappear is suppressed and then made to rise.

In the method according to the invention, the action of the development electrode is controlled in such a way that it is lower at the beginning of development, whereby the electric field generated by the residual charges is weakened, so that it is too weak to attract toner and the formation of stripes is avoided. The effect of the development electrode is increased after the residual charges are practically attenuated and the areas containing strong changes in charge density no longer exist. In this state, the development can be completed ₉ The effect of the development electrode is that it the number of the scene of the charges

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-5 outgoing electric lines of force increases and absorbs them.

The effect of the development electrode can be on the most varied Wise controlled, the easiest way to control is by changing the distance between the recording medium the grounded development electrode. This procedure can be implemented in a number of ways, depending on whether the electrophotographic recording medium is moved continuously or in steps. The action of the development electrode can also be controlled by regulating the earth resistance associated with it, a dielectric Material is arranged on its surface facing the latent image and its thickness is changed or by several Electrodes are assigned to a continuously moving electrophotographic recording medium and the distance between them Electrodes is regulated. According to the invention, development is achieved by reducing the effect of the development electrode in the first development period and by increasing the effect of the development electrode in the second development period, the purpose attainable with the invention however, it can also be realized as long as the effect of the electrode is from the first development period to the second development period is increased, the method according to the invention is made possible by small changes in the action of the development elec- trode is not impaired in any development period. For example, the distance between the recording medium and the Electrode can be increased during a development period. Furthermore, the earth resistance can be decreased in the first development period and increased in the second development period will.

The method according to the invention consists essentially in a change in the action of the development electrode, this The effect is weakened in the first development period and intensified in the second development period. A simple exit

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Management example of the method according to the invention is that the distance between the grounded development electrode and of the latent image recording area is changed will. The change in the action of the developing electrode can of course also be carried out in other ways. Will the The distance between the development electrode and the recording surface at the start of development can be kept very small tiny residual charges also develop, and veils appear. At the same time, HaIo appearances appear in the Areas of large charge density change in the low charge density parts, and the developed image shows streaking. Therefore, the development is first carried out with a sufficiently "large distance between the recording medium and the development electrode, to suppress the electric field of the residual charges so that they do not attract toner, and at the same time the Attenuate residual charges by being discharged through the leakage currents of the developing liquid. There will be a development generated with a strong edge effect in the areas of high charge density near the areas of strong charge density changes, whereby the peripheral lines of the image surface parts are strengthened and the changes in the charge density are alleviated. The second The development period then becomes with a smaller distance between the development electrode and the recording surface carried out. In this state, the residual charge is already dampened by the leakage currents to such an extent that it hardly contains any toner attracts and thus does not create any haze. Furthermore, the smaller distance between the development electrode and the recording surface no electric field reversal in the areas of strong charge density changes as a result of their mitigation generate, which is why there are also no halo phenomena. In the inner areas of high charge density result in an image development true to the original, since the first development with reinforced edge effect and the second development without edge effect can be combined. The stripe formations are also extremely low or nonexistent, even in those border areas in which the charge density changes significantly learns. As a result of the initially large distance to the development

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electrode hardly any streaking occurs in the following At a small distance from the development electrode, no streaking occurs either, because of the large changes in the charge density have already been eliminated.

Embodiments of the invention are based on the following of the figures. Show it:

1 shows the cross section of an electrophotographic recording medium with half uniformly charged surface,

FIG. 2 shows the charge distribution on the surface of the in FIG. 1 the recording medium shown,

3 and 4 show the distribution of the electric field in the presence of a charge distribution shown in FIG and lack of a developing electrode,

5 shows the charge distribution when charging an electrophotographic Recording medium which contains a uniform residual charge, according to FIG. 1,

6 shows the distribution of the electric field for a charge distribution of the type shown in FIG Distance of the recording medium to the development electrode,

7 shows a similar charge distribution at a large distance from the development electrode;

8 shows the charge distribution on a recording medium for an area of low charge density and one thereon adjacent area of high charge density,

FIG. 9 shows the distribution of the electric field for a charge distribution according to FIG. 8,

10 shows a charge distribution with a smaller change Charge density too high charge density,

11 shows the distribution of the electric field for a charge distribution according to FIG. 10,

'Fig.12 is a plan view of a recording medium with step-by-step Change in charge density after exposure to a developing liquid parallel and perpendicular to the distribution shown and

13 to 23 embodiments of devices for carrying out the method according to the invention.

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In Pig. 1, an electrophotographic recording medium 10 is shown in section, the half surface of which is uniform is electrostatically charged. Its photoconductive insulating layer 11 consists of known material, for example amorphous »selenium or a photoconductive powder such as e.g. photoconductive powdered zinc oxide mixed with a non-conductive synthetic resin. The electrically conductive Base 12 consists for example of a metal plate, an electrically conductive coated plastic film or made of paper. Layer 12 is normally used during the development process grounded. Fig. 1 shows an example of a latent image resulting from the uniform electrostatic positive charge exists on one half of the surface of the layer 11, on the lower boundary layer are correspondingly accumulates negative charges.

FIG. 2 shows the graphical representation of the distribution of the positive charges on the recording medium shown in FIG. 1, the distance in the lateral direction is plotted on the abscissa, the zero point is at the transition point of the electrical charges in FIG. 1. It is assumed that that the right half of the recording medium has a charge density of the value <f * 01.

3 and 4 are graphs of a component of the electric field of the latent image for those shown in FIG shown charge distribution shown. Fig. 3 shows the distribution in the absence of a developing electrode or very little large distance between the recording medium and the development electrode, the charge and the electric field being a completely have different distribution. This phenomenon is known as the edge effect. It should also be noted that a negative field is generated in the manner shown in FIG. 3 on the left side of the recording medium, where according to FIG

& «■ Ό is. (The electric field is defined as positive when its direction is upward from the image surface shown in Fig. 1). This electric field is hereinafter

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referred to as reverse electric field, it is "special pronounced in the area of transition zones.

Fig. 4 shows a representation of the distribution of the electric field in the presence of a grounded development electrode at a constant distance from the recording surface. Curves C, B and A show those cases in which the distance (hereinafter referred to as g) between the development electrode and the recording surface is very small (for example a few tens of microns), somewhat larger (for example a few millimeters) and relatively large (for example in of the order of ten millimeters). As can be seen from this representation ' M , the distributions of the electrostatic charge and the electric field correspond to one another when g is very small. Even in this state, however, there is a weak reversed electric field, which is stronger in the area of the transition (i.e. the zero point). A larger value for g results in a stronger inverse field and a weaker positive field.

Fig. 5 shows the charge distribution for the case of the residual charge density 6 _"0. A charge density 6" ₀ φ 0 is in the part present (left from the zero point) where actually (ST ₀ should "be 0. The charge distribution of FIG. 2 shows only an ideal case, the actual distribution, which results from charging and image- wise exposing m, corresponds more to the state shown in Fig. 5.

6 shows a graphic representation of the distribution of the field component running perpendicular to the recording surface for a grounded development electrode associated with the recording surface. As can be seen from FIG. 6, the electric field remains positive in the region of the residual charge density <Sj from FIG. 5, with the exception of the region of the charge density transition, where a negative minimum point remains as a result of the edge effect. A developing liquid (which in this case consists of negatively charged particles) is suspended

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in a non-conductive carrier liquid) is guided in this state onto the recording surface provided with the latent image, the toner which can be attracted by the positive electric field also adheres to the left half of the recording surface, where this adhesion is not desired, so that fogging is formed info2 _v c-; the residual charges occur.

7 shows a graphical representation of the distribution of the electric field on the recording surface with a charge distribution of the type shown in FIG. 5. In this case, larger values for g (corresponding to curve A in FIG. 4) lead to the cancellation of the reverse electric field which is generated by the part of the charge density (right half) and the positive electric field which is generated by the part of the charge density 6 _O (left half), thereby eliminating the positive electric field in the area provided with residual charges will. Therefore, no toner adhesion occurs in the left half of the recording medium.

The following explains the halo phenomenon which occurs in the known development processes. 8 shows the distribution of the electrostatic charge with a strong change in charge density between an area of low charge density (6 "/ i) and an area of high charge density (6" _o ). The solid line in FIG. 9 shows the corresponding distribution of the electric field when the distance g is very small. If the developing liquid is supplied to the recording surface at this very small distance g, the toner adheres in accordance with the distribution of the electric field shown in solid line in FIG. If the development is interrupted after half the development time, the charge distribution changes to the state shown in FIG. 8 after partial neutralization by the toner. In other words, the charge is almost neutralized in accordance with the charge distribution, since the value g is very small. However, this does not apply to the transition area of the charge distribution. The field distribution resulting from the remaining charge

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then has the course shown in dashed lines in Fig. 9, if the distance is ο very small. This distribution is close to proportional to the field variation shown in solid line in FIG. division, 'it still contains a negative field part in the transition area. Is the development electrode at the beginning of the Development arranged at a very small distance g, so there is a reversed electric field in the transition area obtained in-which the charge density undergoes a strong change. This creates a build-up of toner during development prevents and creates the HaIo appearance.

In the previous technology, it was assumed that the distance g must be as small as possible. However, it has now been confirmed that W this concept does not necessarily apply if the condition g = 0 is not completely fulfilled. In practice, the minimum limit for g is a few tens of microns and in automatic reproduction machines is of the order of 100 microns. However, the value of g in this order of magnitude creates a reversed electric field in the transition area and thus halo phenomena.

Fig. 10, the distribution shows the remaining charge after neutralization by toner as a charge distribution of the pulled type shown in FIG. 8 g at a relatively large distance is being developed (for example 5-10 mm) and * a developing after half the development time interrupted . The initial electric field distribution has the form shown in FIG. 7, since a larger value g is present, and accordingly the toner begins to be deposited in the parts of the stronger electric field in the transition region. As a result, the charge in this area is selectively neutralized, while the charge is practically retained in other areas that are at a distance from the transition area. The electrostatic charge is thus attenuated somewhat during development due to the leakage currents in the developing liquid, so that it has a less steep distribution, as shown in FIG. If the strong change in charge density is

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is weak as described above the electric field distribution suddenly takes the form shown in Fig. 11 and loses the negative part.

FIG. 11 shows the distribution of the electric field for a charge distribution of the type shown in FIG. 10 when the distance g is very low. The distance g can have the smallest technically possible value here, since a very low value of g no reverse electric field of the kind shown in FIG. 9 is generated because there is no longer a large change in charge density available. In addition, a gradual distribution of the electric field as shown in Fig. 11 is hardly effective for the creation of HaIo appearances and the formation of stripes.

If a large value for g is maintained during development, it favors the formation of fog and stripes, but such a value should be because of the extremely slow development speed and the poor development quality can be avoided, because a development true to the original is free from edge effects difficult to get to. It is therefore necessary to decrease the value of g after a suitable time. This time is variable and depends on various factors, for example on the properties of the electrophotographic recording medium ^ the resistance of the developing liquid, the amount of charge of the toner particles, the concentration of the toner in the developing liquid, the migration speed of the toner, etc. The time is usually on the order of magnitude of a few tens of seconds and can be shorter or longer depending on the type of development.

For example, it becomes an electrophotographic recording medium is used with a photosensitive layer composed of a zinc oxide and a synthetic resin, it gives a satisfactory one Image free of halos, fogging, and banding when developing for 24 seconds at an infinite distance to the development electrode, namely without a development electrode. At a distance g = 2.0 mm, the

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Development time 14 seconds, also at a distance g = 0.1 mm.

The developing liquid to be used in the method of the present invention can be selected from, for example, various non-polar ones Hydrocarbons, mineral oil, etc. as a non-conductive liquid and from pigment particles of about 0.01 to 1 micron Diameter exist as a toner. The pigment particles are suspended in the non-conductive liquid. It can also It may be beneficial to use various additives in order to improve the suspension of the pigment particles and to regulate their charge. For this purpose, for example, a small proportion of a synthetic resin can be provided in the non-conductive Liquid is soluble or dispersible.

Fig. 12 shows the influence of the distance g on the banding. More specifically, FIG. 12 shows the development result of a step-changed electrostatic charge, when the developing liquid is in the direction of the arrow at a very small distance g from the developing electrode has been moved over the recording medium. The developed image shows a thin and long banding and also a thick and short streaking in the direction of flow of the developing liquid. The short banding disappears, the long banding remains when developing at a greater distance g is carried out * The long banding also disappears when the flow rate of the developing liquid is decreased. Furthermore appears long banding does not occur if the flow rate of the developing liquid is slower regardless of the value of g while the short banding remains if g is not increased. It is also confirmed that the short Banding does not go away even if g is decreased after the first half of the development time.

It has been confirmed experimentally that the thick and short banding can be prevented when developing

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Is carried out for 0.3 to 5 seconds without a developing electrode.

The edge effect created at the beginning of development for large fourth g seems to be still present in the final image too, so it is difficult to find a flattened tint however, this problem can be solved in the following manner. For example, a latent image has a Charge density distribution of the type shown in Fig. 5, a development with a small value g produces a from the beginning the distribution of the electric field according to FIG. 6 corresponding image with a certain edge effect caused by the difference of the electric fields in parts A and B in FIG. 6 is generated. This effect appears as a density difference in the area high density and is therefore negligible compared to the halo phenomenon that occurs in the low density area. On the other hand, if the development is started with a large value g and thus facilitates the selective deposition of toner in the edge areas in the field distribution shown in FIG. 7, and if the development is then continued with a small value g, a field distribution according to FIG. The developed image is superimposed, resulting in an overall image with no edge effect. This also makes the reproduction one flat tint area possible.

The properties of the method according to the invention can be summarized as follows:

1. Fogging

Since the formation of residual potentials is practically unavoidable in electrophotography, development also leads to it At the beginning already a small distance to the development electrode inevitably to form a fog, as this is caused by the residual potential generated electric field becomes strong. The fog can be prevented by increasing the distance between the developing electrode and making the recording medium large (including infinite), thereby attenuating the residual potential will.

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2. Halo phenomena and edge effects in parts of the picture surface

In areas of rapid change in charge density, the adjacent low density area shows no toner deposits, creating the so-called halo phenomenon while the adjacent high-density area towards the transition area receives a greater density than at a greater distance, as a result of which the so-called edge effect arises. These phenomena cannot be completely eliminated if not the distance between the developing electrode and the electrostatic latent image is theoretically reduced to zero. According to the invention, however, the edge effect can be weakened to a negligibly small value by the Develop first with a large distance (including infinite) from the development electrode and then with a small one Distance is carried out.

3. Banding

A latent image is developed with developing liquid, with a relative speed between the two components occurs, banding appears in that part of the image in which the charge density shows large changes. The banding becomes even more pronounced when the distance between the development electrode and the recording medium with a constant speed difference between developing liquid and recording medium is lower and the Change in charge density is stronger.

The banding can be essentially eliminated, if the development initially takes place at a large distance from the development electrode in the sense of an intensification of the edge effect, thereby weakening the charge density changes. then the development is carried out with a small electrode spacing, d

- "-. ■": ·. "·: .. ^ ix. ';., ■■. ■: ,, ■■■ - ..: The invention is described below with the aid of some devices

their implementation further explained. ... *., - _,., *,

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13 shows a device for carrying out the method according to the invention, which contains a plate-shaped, grounded development electrode 80 made of metal and an endless belt 83 made, for example, of metal, metal mesh, plastic, rubber, etc. and on two rollers 81 and 82 is due. Furthermore, an electrophotographic recording medium 10 is provided, which has the shape of a sheet, for example; it is transported with its electrostatic latent image from right to left on the belt 83. The electrically conductive layer of the sheet 10 is grounded directly or via the belt 83. The surface of the belt 83 is inclined slightly so that the developing liquid can flow from right to left. The developing liquid stored in the container 85 is fed into a tube 84 with a pump (not shown) and then fed onto the recording medium through holes or slits in the tube. The distance g between the development electrode and the recording surface is g ^ when the sheet enters the development zone with the side facing the development electrode. At the end of the development zone, let the distance g ₂ . In the embodiment shown in FIG. 13, the following operating values are provided: g ^ = 10 mm, g ₂ = 0.2 mm, length of the development electrode (in the direction of movement) = 80 cm, speed of the recording medium = 2 cm / sec., More specifically

11 Resistance of the developing liquid approx. 10 ohm cm.

Although the value of g undergoes a linear change between g 1 and g ₂ in the device shown in FIG. 13, a non-linear change is also possible in accordance with the event properties of the residual charge. After the end of development, the developing liquid is removed from the recording medium, for example with two pressure rollers 86 and 87, and the recording medium is then subjected to a fixing or drying process.

In Fig. 14 an apparatus is shown, in which the distance g uneven undergoes changes _e The apparatus shown in Fig.i3 is provided for such operation, wherein

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which the development electrode and the recording surface are displaced with a constant relative speed against each other and are opposite to each other. However, it may also be necessary to provide discontinuous changes at certain points in order to achieve a uniform processing of each image field when the images are present on a belt that is driven in steps. 14 shows a recording medium 90 in the form of a continuous belt (hereinafter also referred to as a belt), it is electrostatically charged with a charging device (not shown) and then subjected to an imagewise exposure with an exposure device 95, whereby an electrostatic latent · W image is generated. The entire belt is stopped during the image exposure and then moved forward by one image field in order to bring the latent image into the developable area. The device shown in FIG. 14 is an example of the step-by-step transport of the tape-shaped recording medium by one image field at a time. The tape 90 is guided on rollers 96 and 97 into the developing liquid 99, which is located in a container 98. At the same time, it faces a first development electrode 91. If the latent image produced has just reached this position opposite the development electrode, the belt is stopped and the image exposure for the subsequent image takes place at the same time. The belt is then advanced again M when the image exposure is complete so that the new latent image is positioned opposite the first development electrode and the first latent image is positioned opposite the second development electrode 92. In this way, each latent image is developed by placing it in front of the developing electrodes 91, 92, 93 and 94 one after the other. The development electrodes are arranged in such a way that the recording surface provided with a latent image is a constant distance from each development electrode, but different distances from the different development electrodes' !! has, whereby the distance to the end of the development period becomes smaller. The number of i ', nt winding electrodes corresponds to the respective Eatv / wicklungs-

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requirements. After the end of development, the tape will run out the developing liquid led out with the roller 100, by two pinch rollers 101 and 102 for removing the developing liquid passed through and then dried and fed onto a take-up roll.

In the device shown in FIG. 14, for example, the following operating values can be provided: distance between belt and development electrode 91 g * = 10 mm, distance to development electrode 92 g ₂ = 2 mm, distance to development electrode 93 sz - 0.5 mm, distance to Development electrode 94 g ^ = 0.1 mm, image exposure approx. 15 seconds (mean value), speed of movement of the sheet 5 cm / sec, specific resistance of the development

Winding liquid approx. 5 x 10 0hm cm. With such a developing device the result is an image that is free from fogging, edge effects and halo appearances.

15 shows the cross section of a further device for carrying out the method according to the invention. This device is constructed similarly to the device shown in Fig. 13, but a different development electrode 100 is provided. The developing electrode 100 consists of a part 101 for which the value g becomes linearly smaller and a part 102, in which the value g is kept small and constant. The apparatus shown in Fig. 15 is preferably for such Type of process suitable in which the residual charges can be sufficiently discharged, while the recording surface is Part 101 of the development electrode 100 is opposite «,

16 shows a further embodiment of an apparatus for carrying out the method according to the invention, in which slits 111, 112, 113, 114 etc. are formed in a development electrode of the type shown in Fig. 13 are provided. In the device roped in FIG. 13, the flow velocity increases the developing fluid gradually increases, wölirsnd it flows into the recording medium, since the distance g will decrease * This can? .ur formation of stripes in

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Direction of flow of the developing liquid starting from Areas of high density, which seriously degrades the image quality. The slots shown in Fig. 16 are used for Avoiding this disadvantage. The flow rate of the developing liquid is not increased so much when the Distance g becomes smaller as the developing liquid emerges from the developing zone through the slits and can flow off via the development electrode.

FIG. 17 shows a device which fulfills the same purpose as the device shown in FIG. Developing electrodes 121, 122 and 123 are arranged parallel to the recording medium and form a gradually decreasing one Distance g, which is greatest for electrode 121 and smallest for electrode 15. Such a device achieves the same effect as the jFig. 16 as the developing electrodes Form spaces from one another through which the developing liquid from the developing zone can flow off via the respective electrode.

Although flat developing electrodes have been described above, they can be of any other shape and include also work satisfactorily in the process according to the invention.

In Fig. 18, a device is shown with a cylindrical development electrode works and in which a continuous belt 130 with latent images with constant Speed is guided around a drum 132. The developing electrode 131 is formed into a semi-cylindrical shape and eccentric to the axis of the drum 132, whereby the distance g during the development before gear is smaller. When the latent image to be developed is located on the inner surface of the recording belt, the drum 132 can pass through an eccentric and fixed drum 133 can be replaced, and the recording medium is guided on rollers which provided on both sides of the fixed drum

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and produce the same profile as the drum 132.

FIG. 19 shows a modification of the device shown in FIG with a curved development electrode. The continuous recording tape 90, on the outer surface thereof the electrostatic latent images are arranged, is guided around drums 140, 141 and 142, on which semi-cylindrical Developing electrodes 143, 144 and 145 are arranged. A constant distance g is provided for each electrode, the however, as development proceeds, per electrode becomes smaller. The belt 90 can be either continuous or incremental be moved.

The above has been a mutual movement of the developing electrode and the recording medium provided parallel to one another, but it is also possible to have such to interrupt mutual displacement during development and to produce a time-dependent change in the distance g.

In Fig. 20 to 23 cross sections of devices are shown, in which the distance between the development electrode and the recording medium is increased during development or at where the developing electrode is absent.

Fig. 20 shows a developing device provided with a developing electrode works with a cylindrical surface. A continuous belt 90 is wrapped around drums 201, 202, 203 and 204 with its direction changed by rollers 205, 206, 207 and 208, respectively. The development electrodes 210, 211, 212, 213 are arranged so that the distance between the respective development electrode and the latent image is greatest (e.g. 10 mm) for the developing electrode 210 and the smallest (e.g. 0.1 mm) for the developing electrode 213 is. Between the rollers 207 and 208 there is a gap 209 where there is no electrode. The diameter of the drums 210, 211, 212 and 213 as well as the width of the space 209 can with continuous? Movement of the belt 90

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can be chosen arbitrarily, but they should be set so that each picture touches the drums or in the space is arranged when the tape is stepped. The gap 209 without a developing electrode is used, for example for arranging a pump between the drums 202 and or for other processing or maintenance of the device.

Fig. 21 shows an apparatus in which developing electrodes 214 to 221 are used in roll form, the distance from the recording medium 10 gradually decreases. The distance between the respective development electrode and the recording medium 10 is ί in the area of the distances between the rollers

larger, so it is a device in which W increases the distance to the development electrode between the individual electrodes. It should be noted, however, that the main object of the invention is already achieved in that area where the distance between the roller and the recording medium is large and before this distance becomes sufficiently small.

Fig. 22 shows a developing device with inclined electrodes 222, 223 and 224, the rear end 225 of the first electrode 222 being a greater distance from the recording surface than from the front end 226 of the second electrode 223. Such a device also works according to the Principle of the invention when the first electrode already fulfills the purpose of the method according to the invention.

23 shows a device with four development electrodes 231 to 234, which are arranged parallel to the recording medium 10 and the spacing thereof except that of the developing electrode 233 becomes smaller and smaller. One reason that the The distance of the electrode 233 is greater, is that developing liquid is supplied past this electrode can.

The first development period of the method according to the invention runs up to the point in time at which a reverse electrical

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Field no longer present in the distribution of the electric field is the second development period, even when the development electrode is used with practically the maximum development effect follows the first and continues until the point in time at which the electrostatic charge is largely eliminated is derived. It should be noted, however, that this definition cannot be uniformly applied because the development periods correspond to the kind of the photosensitive layer and the developing liquid or the respective developing method.

During the development, the residual charges become with the action of the development electrode suppressed to absorb electric Lines of force of the latent image and mitigation of the strong changes in charge density not sufficiently damped, so it is favorable to prevent fogging by applying a bias voltage to the developing electrode and the electrical to avoid conductive support of the recording medium, thereby repelling toner from the recording surface. This method is particularly advantageous when the residual charge density is very big.

As already stated, it has heretofore been assumed that the distance between the development electrode and the recording surface should be as low as possible in order to obtain a high quality reproduction that guarantees a reproduction that is true to the original. In the practical case, however, this distance cannot be reduced to the value zero, and it also occurs further problems such as halos at a short distance. It was explained above that a faithful Satisfactory quality image can only be achieved by developing at a large distance from the developing electrode and then developing it Reducing this distance can be achieved. However, the invention is not to the effect of changing the The distance between the development electrode and the recording surface is limited, but it relates in particular to the influence on the electrode effect of developing electrodes

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or the absorption capacity for lines of electric force emanating from an electrostatic latent image. These According to the invention, the effect is reduced or increased in the first and second development period, but this is the case no special value is given, but such changes can be made during the entire development process will.

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Claims (3)

Claims / ί Electrostatic latent image development process, in which between a recording medium and a development electrode a liquid developer with in electrically charged particles suspended in an electrically non-conductive carrier liquid are placed, characterized in that the action of the development electrode (80) is initially stronger until it disappears The change in the charge density of the latent image is suppressed and then made to increase. 2. The method according to claim 1, characterized in that the distance of the development electrode (80) to the to be developed latent image reduced during the development process will. 3. The method according to claim 1, characterized in that the value of a ground resistance of the development electrode (80) is reduced during the development process. 109834/1521 Blank page