DE2346221A1 - METHOD AND DEVICE FOR INCREASING THE SERVICE LIFE OF AN ELECTROGRAPHIC LAYER - Google Patents

Description

DR. MÜLLER-BORE DIPL.-PHYS. DR. MAMTZ Diru-CHEM. DR. UEUFEL DIPL.-ING. FINSTERWALD DIPL.-IN3. PATENT LAWYERS

Munich, the ^{U tD} - ^J9? 3 M / yo - T 1257

TURLABOR AG, CH-8126 Zumikon, Switzerland, Geissacherstraße

Method and device for increasing the service life of an electrographic layer

The invention relates to a method for increasing the service life of an electrographic layer and to a device for carrying out the method.

For the purposes of this document, all those processes are to be understood under electrographic processes for image generation in which the insulation properties, or the electrical conductivity, of a layer for image generation to be used.

It is preferably an electrophotographic one Layer, i.e. an electrographic layer containing photoconductive material, which also uses photoelectric properties for image formation will. For example, such a layer is first electrostatically charged and then as a function exposed by an original image, so that an image-dependent discharge of the layer occurs, whereby a latent electrostatic charge image results. Through to

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siQh known methods, for example by means of a so-called magnetic brush, can said latent charge image by means of electrostatically charged toner material to be developed. The toner image that then forms on the electrophotographic layer can be used in the so-called toner transfer process be transferred to a definitive image carrier. But it is also possible to use the latent to transfer electrostatic charge image itself to another carrier and only to this far carrier to develop. Finally, the latent electrostatic charge image can also be controlled by a Electrographic layer adjacent electrodes are generated, in which case no exposure for the generation of the latent charge image is required.

However, an image can also be generated without prior electrostatic charging, e.g. during image generation a voltage is applied to the layer. More about the various electrographic processes can be found here e.g. in Schaffert, "Electrophotography", Focal Press, 1965.

Any method can be used for the electrostatic charging of the layer mentioned, in most cases this is done uses a high-voltage corona, on which the electrographic Shift is passed.

The electrographic or electrophotographic properties of the layer in question are characterized, for example, by the saturation potential V _Q and the dark resistance f _Q or the light sensitivity. The saturation potential indicates the voltage to which a specific layer can be charged to the maximum. The dark resistance is a measure of the insulating capacity

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the unexposed electrophotographic layer.

It is known that electrographic, especially electrophotographic Layers in the imaging process in which one and the same layer is used repeatedly will show signs of aging. These signs of aging are particularly common with organic ones electrographic layers very pronounced.

References to such organic photoconductive materials can be found, for example, in:

"Organic Photoconductors in Electrophotography", L.I. Grosswdner, 1970, Most Associates Marblehead, Mass., USA.

"Organic layers" is understood in the following to mean: Electrographic layers in which the image formation depends essentially on the electrical resistance of the organic material contained therein and in which this material is also on the free surface of the layer, i.e. it can come into contact with gas discharges, e.g. layers of:

1.Organic photoconductors, especially photoconductive polymers, such as polyvinyl carbazole.

2. Pigment-organic binders, e.g. cadmium sulfide epoxy resin layers.

3. Multiple layers: e.g. with a thick organic charge transport layer on top of a photoconductive layer is applied, e.g. a PVCa layer on a selenium layer.

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The signs of aging, their causes and effects are described in detail in the article "Aging of Organic Photoconductors "by W. Lanker in" Current Problems in Electrophotography ", p. 232, Walter de Gruyter, 1972.

In repeated electrophotographic processes were So far, layers of inorganic material, above all being, have been used almost exclusively.

However, the use of organic materials for electrophotographic layers offers very decisive advantages: there is a much wider range of usable materials that are and also easier to work with result in much cheaper layers.

It is of course all the more important to have the decisive disadvantage of organic layers - their greater susceptibility to aging - to overcome.

When using electrophotographic ones that are very susceptible to aging This is because shifts in copiers have the serious disadvantage that the service intervals become much too small for the copier in question. Already after a small one for practical requirements Namely, the number of image generation cycles decreases as a result of the aging effects mentioned, the quality of the with the relevant layer generated images steadily. The aging effects show up e.g. in a decrease of the saturation potential and thus the swelling or the contrast, as well as in the occurrence of so-called point defects.

Even after a relatively short period of use, or after a relatively few image generation cycles, one must therefore

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organic layer can be replaced, which causes undesirable activities and costs. But this increases the profitability the copier equipped with such an electrographic or electrophotographic layer questioned.

It is now already known to increase the number of cycles of such layers with a protective layer to provide corona or gas discharge resistant material, since it has been found that the effects of gas discharges (e.g. the corona) a main cause for the above-mentioned, caused by decomposition of the layer surface Represent aging effects. Such corona-resistant materials such as polytetrafluoroethylene (or a few, very specific, highly crosslinked and pure polysiloxanes), however, have the serious disadvantage on that they can only deal with great difficulty and accordingly Apply effort in a sufficiently thin layer on an electrographic layer.

Such protective layers are also only limited effective} certain aging effects, such as point defects, can in fact, they are often barely eliminated or not eliminated at all.

To combat these aging effects or to render them harmless has also been suggested by periodically removing (e.g. sanding) the top Layer of such an electrophotographic layer, the aging-damaged portion thereof to be removed periodically. Although this procedure can be very effective, it is cumbersome and requires if it is to take place automatically within a copier, a great deal of effort. Because it is extreme

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difficult, only a very thin layer sufficiently even to be removed, and of course the layer will be used up over time. This grinding down the The electrophotographic layer also has the further disadvantage that it reduces the surface of this layer is roughened, which can further promote the aging effects. In the frequently used toner transfer process, in which the latent charge image is directly applied to the electrophotographic layer by means of emphasis is developed, the subsequent necessary cleaning of the electrophotographic layer is considerable difficult.

In summary, it can therefore be said that the previously known methods for combating the aging effects mentioned have various disadvantages, e.g. they are difficult to implement, only partially effective, or they require very special, relatively expensive material, or they require a relatively high outlay in terms of equipment and are therefore themselves susceptible to failure and not very suitable for copiers that are operated by laypeople and should have the largest possible service intervals in order to be economical.

The present invention is therefore based on the object of a method for increasing the service life of a To create an electrographic layer and an apparatus for carrying out said method, in which with relatively simple means in an economical way the number of cycles of the image generation and thus the Service life of one and the same electrographic layer can be increased considerably.

The invention is based on the general idea of the solution, the electrographic layer with one in short

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Replacement cycles to provide at least partially replaced insulating protective film, thereby always a to ensure a new, undecomposed surface.

The present invention relates to a method for increasing the service life of an electrographic layer, which is characterized in that to protect the surface of this layer against harmful effects on this layer as a result of the image generation process the electrographic layer is an insulating liquid Protective film is applied, which protective film is cyclically at least partially replaced by in each replacement cycle at least a part of the protective film is removed and the removed part is then fed in new protective material is replaced.

The invention also relates to a device for carrying out said method, which is characterized is that an electrographic layer on the one hand a film application device, which is intended and is designed to apply an insulating "liquid protective film to the electrographic layer, and on the other hand a film removal device which is intended and designed to remove at least a part of said To remove protective film from the electrographic layer, are assigned, in addition, leadership and drive means are provided to move between the film application device and the film removing device on the one hand and the electrographic layer on the other hand to enable a relative movement.

In the following the invention is explained by way of example with reference to the accompanying drawings. It shows

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1 shows the working principle of the present invention, shown schematically;

FIG. 1a shows a variant of FIG. 1;

FIG. 2 shows a further variant of FIG. 1 which also contains the toner cleaning process; FIG.

Fig. 3 the working principle executed with a cleaning tape, shown schematically;

4 shows a first practical embodiment with a scraper for metering the protective film thickness;

5 shows a second practical embodiment with a wick for applying the protective film;

6 shows a third practical embodiment with a cleaning belt driven by a conveyor belt;

7 shows a fourth practical embodiment with a cleaning belt driven by a conveyor roller.

The figures are not drawn to scale. Corresponding parts are given the same designations in all figures.

Prior to the description of specific exemplary embodiments, a few will be briefly referred to for a better understanding of the invention Aspects related to the effects of aging in the case of electrographic layers. In the cited publications, it is pointed out that the

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The aging effects mentioned on electrographic layers are mainly caused by the effects of gas discharge, but are only strongly expressed by the influence of moisture, for example air humidity. The aging effects are expressed both in a decrease in the saturation potential V _Q and in the dark resistance f _{0 of} the electrographic layer, as well as in local and temporal fluctuations in V and y; In addition, positive and negative recovery effects occur, ie after breaks, a strong change in the saturation potential and the dark resistance can be determined on an aged layer compared to the values measured at the beginning of the break, both in a positive and in a negative sense. It has been found that the effect of the gas discharges associated with the formation of the image results in chemical destruction of the surface of the electrographic layer, whereupon the above-mentioned aging effects result as a result of water adsorption from the air. Point-like secondary corona discharges occurring at electrical or structural inhomogeneities on the surface lead over time to so-called point defects, ie to points or spots visible on the copy.

Such gas discharges occur at the electrographic or electrophotographic image formation upon application of a corona ^E inrichtung on for the electrostatic charging of the electrographic layer, but also the so-called charge transfer (charge transfer) method and, for example in the development of a latent charge image by means of a tension standing magnetic brush. In the case of electrographic image generation, however, the direct contact between the electrographic layer and the toner material to old

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lead to phenomena of the surface of the electrographic layer.

All these signs of aging are surface effects that only affect the surface or a very thin top Layer (from nanometers to fractions of a micrometer) concern, while the inside of the electrographic Layer practically unchanged, i.e. remains fully usable for the imaging process.

These aging effects, which result in the decrease in image quality in the case of a repeatedly used electrographic The effect of the layer is practically only attributable to the destroyed surface.

Based on the consideration that a long service life can be achieved that on the surface as possible Little decomposed material is allowed, the following has been found on the basis of the present invention Solution: Instead of replacing the entire electrographic layer, only the used surface is used replaced. In principle, this corresponds to a disposable surface that is newly exposed to the outside on one side Electrographic layer applied and on the other side - and this is crucial - after use is removed from the layer again. This disposable surface on a layer protected in this way can now be particularly effective in the form of a liquid, insulating Protective film can be applied and replaced. The protective film is made so thin that the electrographic Properties of the layer are not impaired, and it can consist of very different from the layer material Material.

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With complete replacement of the protective film, or all used material of it would in principle prevent all aging effects mentioned for almost any length of time possible, which cannot be achieved with any protective layer that cannot be replaced. About that In addition, it also creates constant surface properties, which ensures a constant and optimal process of the imaging process «is very important.

It is certainly also a very rational solution to replace only what has been used, with the simplest possible, cheap material.

Compared to known methods in which to combat the electrographic layer of the aging phenomena is covered with corona-resistant material, this indicates The present method has the advantage that it does not require the use of the special coronary resistant substances mentioned there Materials such as polytetrafluoroethylene, which materials are not only expensive, but are also difficult to process. In the present invention there is a special corona resistance not mandatory. The following conditions apply to the protective film:

it must be sufficiently insulating, corresponding to the image generation process, and it must be fluid (with almost any Viscosity), i.e. plastically deformed in such a way that it can be relatively can be easily and effectively replaced and that a compact new protective film can be formed. In contrast in addition, the known solid lubricants, such as polytetrafluoroethylene or zinc stearate, are used for improvement of the toner cleaning step, especially for anor-

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ganic photoconductors, where no such decisive aging occurs, of course not to meet these conditions. There is therefore a large selection available, e.g. also much cheaper materials.

It has now been found that point defects cannot be resolved simply by filling holes or unevenness in the layer can be eliminated with a solid protective coating. Local differences in conductivity, the informational secondary corona discharges with the tent inevitably lead to point defects, are then practically always present. First a common one Replacing and renewing a liquid protective film leads to blurring and statistical compensation the places that are stressed by the secondary corona, so that localized defects no longer develop can.

Another key advantage of the present invention arises in those electrographic imaging processes in which the toner transfer principle is applied, thus a latent electrostatic The charge image is developed on the electrographic layer itself by emphasizing it, and then the toner image is transferred to the definitive image carrier. If the organic electrographic layer is unprotected, their surface due to the aforementioned harmful effects of aging, in particular gas discharges, increasingly rough and adhesive. As a result, the greater the use of the layer, the stronger the adhesion occurs of toner residues on the layer, and because of the increase in the roughness of the layer, its cleaning proves increasingly difficult. So there is an actual repercussion of the aging effects instead that reinforce each other. The present

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The invention also prevents this roughening and thus creates a synergistic effect.

By renewing the protective film with each image cycle, the required cleaning of the electrographic is seen Layer of toner residues in the toner transfer process is significantly facilitated and improved, because because of the protective film, the toner does not even come with the actual surface of the electrographic layer in contact, but it rests essentially on the protective film. This makes the pollution the real electrographic layer itself is also prevented.

The thickness of the protective film or its insulation strength is chosen so that the saturation potential Y _Q (e.g. 1000 V) is not significantly changed, e.g. less than 10%, in any case so that the process-related layer potentials in the charged or light-discharged state (e.g. 600 V) or 50 V) can be achieved.

In the most common imaging processes in which the electrophotographic layer is charged, is it is advantageous if the protective film forms a charge-carrying surface, i.e. if also at least on the protective film part of the surface charge, which is the electrostatic Charging the layer causes is present; on the underlying surface of the electrophotographic Layer then the rest of the charge, due to the small thickness of the protective film (e.g. 0.1 u to we-i nige nm) has the distribution of the charge on the film or Layer surface does not have any significant influence on the layer potential. That lies in the toner transfer test

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Layer thickness of the protective film preferably less than 0.1 u, while in charge transfer processes, in principle, higher layer thicknesses would be permissible (e.g. also 1 u).

The insulation capacity or the electrical resistance of the film must be such that that required for the relevant imaging process required values in the unexposed state, e.g. 10 - 10 iLcm, adhered to or not fallen below will.

The protective film should preferably form the image-bearing surface. Then the protective material can be chosen or modified so that for the relevant image generation process (i.e. for layer, toner, development, Transfer and cleaning step) optimal surface properties, e.g. with regard to adhesion, dielectric constant, electrical resistance and viscosity, can be adjusted. Depending on the type of film application or removal Viscosity values in a very wide range are permissible (e.g. from any thin oil to too highly viscous pastes),

In contrast to the relatively less existing ones - necessarily very pure, mostly solid - corona-resistant materials without sensitive functional groups here a very large number of often cheaper materials for Choice that can be used as a protective film in addition to saturated also unsaturated compounds (e.g. olefins), compounds with functional groups, such as higher alcohols (e.g. hexadecanol) »or even very impure ones Mixtures, such as natural products: mineral and vegetable fats or oils (e.g. Vaseline), instead of the few special ones that are fully polymerized or cross-linked siloxanes, which are corona-resistant, can

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a large number of silicones can also be used which, for example, are modified or provided with different functional groups, whereby properties, v / ie adhesion, viscosity, dielectric constant, electrical resistance, etc., can be varied. It is also possible, for example, to use esters, liquid polymers (eg stearomethacrylate), lubricants, release agents, air-permeating agents, and in principle also solutions or emulsions .

^ he present invention is specifically Aich ^£: Λτ copying machines which operate with an endless elektrcgraphisohen .Schicht where this layer, for example, is applied on an endless belt or a drum. However, it can of course also applicable to other layer forms are applied vie plate- or sheet-shaped layers JSinfachheits- convenience, the present invention is explained, for example, discuss on the following in electrophotographic layers ". Here, the electrophotographic layer is the by an assumed as known and therefore in Figures not shown drive mechanism given a movement in order to feed the electrophotographic layer past the individual stations, such as corona device, processing device , developing device, toner transfer device, cleaning device, etc., one after the other.

The operating principle of the present invention is shown schematically with reference to FIG. 1. The Flg. 1 shows a portion of a belt-shaped electrophotographic image carrier 1 having one as an electrode Serving base 2, for example an aluminized "Mylar" tape, on which an electrophotographic Layer 3, for example consisting of polyvinyl carbazole, is applied in a manner known per se.

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This electrophotographic image carrier 1 is moved by the drive mechanism in the direction of arrow 4 through a copier so that it passes through the various stations mentioned in sequence. At one point 5, a storage container 6 for a film-forming liquid protective material 7 is arranged so that its slot-shaped opening S, which preferably extends over the entire width of the image carrier 1, is at a small distance, for example fractions of millimeters, from the surface 9 of the electrophotographic layer 3 is located. Passes out of the opening 8, according to its liquid state running a small amount of the protective material 7 to the surface 9 of the elektroph ± ographischen layer 3 where it forms a protective film 10 whose thickness by a precise adjustment of the distance of the opening 8 from the surface 9, or by other means described later can be adjusted to the desired level.

In the exemplary embodiment according to FIG. 1, the substrate 2 has the thickness d (eg 100 u), the electrophotographic layer 3 has the thickness CL ₁ (eg 20 u) and the protective film 10 has an original thickness dp (eg 0.1 ii).

The electrophotographic layer provided with the protective film 10 leaves the point 5 at which the protective film has been formed and passes through an area A in which the previously mentioned devices for image formation are arranged. Since these are assumed to be known, they are not shown in FIG. 1. After passing through the work area A, the image carrier 1 now has a very small layer on the outside of the protective film 10, for example due to gas discharges, as a result of the aging effects mentioned earlier

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damaged protective material. In the further this is Layer with the thickness d, called the wear layer.

According to the definition, a replacement cycle is now carried out when the film removal point 12 and the film application parts have been run through once, i.e. the protective film has been replaced once. The present method is particularly advantageous, if a replacement cycle is also carried out for each image generation cycle (work area A), such as it is shown in the figures.

However, it is also possible to run through work area A several times per replacement cycle (and e.g. 10 to 100 Imaging cycles until the film is used up) by, for example, the film applicator and film stripper be lifted off, e.g. in the case of electrophotographic layers that are not endless.

Since, according to the prerequisites, not a particularly corona-resistant one If protective material 7 is used, the protective film can be used up relatively quickly (e.g. after 10 to 100 imaging cycles). The used part should of course be replaced as completely as possible with new material, i.e. the wear layer or the uppermost part of the protective film, preferably as completely as possible removed.

According to the invention, after each replacement cycle, and either at the end of an image generation cycle that is just running in the copier or at the beginning of the next This wearing layer 11 of the protective film 10 is removed in the subsequent imaging cycle. Through this the harmful effects of the imaging

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process, ie the aging phenomena mentioned earlier, rendered harmless. The wear layer 11 of the protective film can be removed, for example, as indicated in FIG. The edge 14 of the stripper 13 is arranged at a distance d ^ above the surface 9 of the electrophoretic layer 3, so that at least this wear layer 11 is lifted off and preferably a remaining protective film 10 'with a reduced thickness d ^ (e.g. 1/10 to 9 / 10 of d ₂ ) remains.

On its further circulation in the copier, the image carrier 1 is now just coming with its reduced protective film 10 ' then back to point 5, at which the thickness of the protective film is back to the original dimension dp is supplemented by supplying fresh protective material 7 from the container 6.

1a shows a variant of FIG. 1, the stripper 13 'here having an obtuse cutting angle to the plane of the protective film, while the stripper 13 in FIG. 1 has an acute cutting angle.

Fig. 2 shows a toner cleaning operation also containing another variant of Fig. 1, assuming here that takes place of the image carrier 1 in the work area A of the image formation after the formation of a latent electrostatic charge image development, ie toning and then the toner image in a is transferred to a definitive image carrier in a known manner in a toner transfer process.

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It is a peculiarity of this latter method of the Toner transfers that after the transfer of the "toner image on the definitive image carrier more or less residual toner adhere to the image carrier 1 "remains ..

In Fig. 2 such toner resx material can be seen with .tor designation 15, and it can be seen that the residual toner material 15 no longer comes into direct contact with the electrophotographic layer 3 thanks to the protective film 10 and therefore when the wearing layer 11 is lifted off of the protective film 10 is removed from the image carrier 1 at the same time as the wear layer. In this way, the toner cleaning step, which otherwise takes a lot of effort in electrostatic copiers, can be saved and carried out very easily.

With reference to FIG. 3, the Arbeltsprinzip will now be schematically illustrated, carried out with a cleaning tape * As the image carrier is previously designated as a whole by 1, the base 2 and the elektrophotograpnische layer 3. The image carrier 1 moves in the direction of arrow 4 . to form the protective film and for later Ent fernung its wear layer according to the exemplary embodiment of FIG. 3, a cleaning tape 16, example instance like a belt of a nonwoven fabric or, provided that layer side with the protective material 7 impregnated and on its surface is provided with protective material. This is indicated in Fig. 3 by the puncture Ren of the cleaning tape 16. The cleaning belt 16 is moved in the direction of arrow 17 by means of two, preferably driven, conveyor rollers 18 and 19, preferably against the direction of movement 4 of the image carrier 1 over the surface 9 of the electrophotographic layer 3.

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The location of the roller 18 corresponds to the point 5 in the arrangement according to FIG. 1, because by the gentle pressure which the roller 18 exerts on the cleaning tape 16 soaked with protective material 7, this cleaning tape 16 is in the narrow zone between the outer surface of the roller extending over the entire width of the image carrier 1 and a sufficient amount of the protective material 7 for the formation of the protective film 10 is continuously removed from the surface 9.

The image carrier 1 then passes through the working area of the copier one after the other to the right and finally returns back to position 12. The image carrier 1 arriving here carries a protective film with a through the image formation process used or soiled wear layer 11.

The cleaning tape 16 passes over the image carrier 1 in the opposite direction according to arrow 20 in the area B between the two conveyor rollers 18 and 19 and then revolves around roller 19 and then moves away in the direction of arrow 21, for example to be picked up by a winding device, not shown. As a result of the gentle pressure of the roller 19 in the area of the zone opposite the image carrier, the wearing layer is lifted off by the cleaning belt 16 and carried along. As a result of the more effective countercurrent principle - direction arrows 4 and 20 are directed in the opposite direction - and thanks to the film replacement process extending over the extended area B (e.g. 10 cm), an effective exchange of the protective film takes place here too, so that finally l ± h at the point 5 , sufficient new protective material 7 has been applied again to allow the fresh protective film 10 to reappear in its original thickness d ₂ .

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Although the device shown in Figs. 1 and 2 may require a more complete replacement of the protective film can result, the device shown in Fig. 3 with cleaning tape has also proven to be very effective in practice and proven to be advantageous, as the removal of the toner residues is also ensured automatically.

As a protective material 7 for the protective film 10 or the impregnation of the cleaning tape 16, for example, not only low-viscosity oils but also high-viscosity materials " When using a scraper as in Fig. 1 and 2, it is advisable to use preferably very thin-bodied materials to be used as protective material 7.

A first practical exemplary embodiment with a scraper for metering the protective film thickness is shown on the basis of FIG. The image carrier 1, which has a base 2 and an electrophotographic layer 3, runs in the direction of the arrow 26 to a preferably driven roller 27 which rotates in the direction of the arrow 28 about an axis 29 after the image-forming process has been completed. The roller 2? preferably extends over the entire width of the image carrier 1. The image carrier 1 revolves around the roller 27 over the area B ¹ , which is delimited by the scrapers 13 and 32, and leaves the roller 27 again in the direction of the arrow 30, around the previously mentioned to go through the image generation facilities of the copier.

In an area C the emerges on the outside of the Image carrier 1 arranged electrophotographic layer 3 in the liquid level 31 of the in a container 6 * protective material 7 in stock. As a result, the electrophotographic layer 3 becomes the protective material 7

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wetted, with a scraper 32 at the exit point the desired original thickness dp of the protective film 10 determines which part of the image carrier 1 running away has been provided with.

The one returning to the platen 27 after the image forming process Image carrier 1 has its protective film 10, the wear layer known from earlier exemplary embodiments 11 on.

The wear layer 11 is removed from the image carrier 1 by a scraper 13 arranged at the point at least to the extent that the remaining film has clean protective material 7. The wear layer removed is collected in a collecting container 33. The new formation of the protective film 10 with the original thickness d ₂ takes place as described above at the point 5.

The containers 6 ¹ and 33 are preferably well closed and separated from one another by a closed wall. This wall can, however, also contain a small opening 33 'at the very bottom for the purpose of keeping the protective material level constant if the used protective material remains on the container bottom or the new protective material above does not noticeably deteriorate. The volume of the protective material in the container 6 ¹ is preferably much larger (eg 10 to 10 times) than the volume of the protective film 10.

Suitable shapes for the scrapers 13 and 32 are known, for example, from windshield wiper technology. Preferably the wipers are very soft and made of resistant synthetic elastomers such as polyurethane elastomers or silicone rubbers. For the best

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The wipers, which form a compact, homogeneous film or must lift off, also transversely to the direction of movement 4 or 30, i.e. be moved back and forth along the scraper edge.

A second practical embodiment with a wick for applying the protective film is shown in a modification of the arrangement according to FIG. 4 and FIG. Here, the formation of the protective film Ί0 is caused by an im. Container 6 ¹ arranged wick 35 worried, which can for example consist of cotton, synthetic fabrics or cellulose wad paper and which sweeps the outer surface of the image carrier 1 in area C over the entire width of the image carrier. The wick 35 is under gentle pressure in the direction of the arrow 36 against the image carrier 1. This pressure can be generated, for example, by a device known from the construction of petrol lamps or by light pressure on a spring-loaded base.

The area C corresponds to the point 5 according to FIG. 1. At this point, the image carrier is provided with a protective film of the original thickness d ₂ , while it tapers towards the wick 35 with its reduced thickness d /.

Here, too, the toner residues are removed again together with the wearing layer 11 and collected in the container 33.

^{The area B 1} between positions 5 and 12, which is determined by the construction as in FIG. 4, must in any case contain the area C or C.

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Referring to Fig. 6, which shows a third practical embodiment with a cleaning belt driven by a conveyor belt, one is now presented Invention based embodiment of an electrostatic copier explained schematically. Here is the one Image carrier 1 arranged on the outer surface of a drum, and the various used for image generation Devices are arranged radially around this drum.

In Fig. 6, the image carrier 1 is arranged on a drum 37, which is in the direction of arrow 38 around their Axis 39 rotates. Drive devices for such drum-like image carriers are from the technology of electrostatic copiers known, so that further information is not necessary here. Every imaging cycle is a replacement cycle assigned here,

A device 40 ′ for applying the protective film 10 to the image carrier 1 is arranged on the right-hand side of the drum 37. The working principle of this device 40 ¹ corresponds essentially to that in FIG. 3 illustrated embodiment.

The cleaning tape 16 soaked with the protective material 7 runs in the direction of arrow 17 against the arranged on the drum 37 image carrier 1. It is by one around the rollers 40, 41 and 42 moving conveyor belt 43 entrained by adhesion, since at least one of the rollers 40-42 Drive mechanism is effective. The rollers 40-42 rotate in the direction of arrows 44, 45, 46 so that the conveyor belt 43 revolves in the direction of arrow 47. The film replacement process here extends over an area B " (e.g. 8 cm), which is limited by the positions 5 and

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12 (corresponding to the area B in Fig. 3). The cleaning tape 16 touches the image carrier 1 over the area B " with a contact pressure ρ of, for example, 20 p / cm, which is essentially exerted by the conveyor belt 43. For example, one of the rollers 40-42 and according to the size of the area B " (i.e. of the circle sector B ") the conveyor belt can be given a suitable tension so that the aforesaid Contact pressure ρ results.

The cleaning tape 16 is drawn off from a supply roll 48, which is preferably provided with a light run-off brake 52 is provided. Such a drain brake can, for example, by means of a live brake Spring 50 standing friction band 51 can be realized, which is tensioned via a hub 49 of the supply roll 48 is.

That which runs off the image carrier 1 around the roller 42 blends Cleaning tape runs "in the direction of arrow 53 to a take-up roller 54, which is in the direction of the Arrow 55 rotates and, as a result of a preferably low torque, that running in the direction of arrow 53 Picks up cleaning tape.

The tensile forces exerted by the supply roll 48 and the take-up roll 54 applied to the cleaning tape 16 are preferably small, e.g., 10 to 20 ponds per cm Bandwidth, since they only have to serve the orderly guidance of the cleaning belt 16.

The image carrier provided with the fresh protective film 10 leaves the device 40 ^f at the point 5, then passes through the working area of the copier with the

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Corona charging device 56, the exposure device 57, by means of which an exposure of the electrophotographic layer 3 corresponding to an original takes place, the Area of a development device 58, for example with a magnetic brush 59, and finally the toner image produced on it in a transfer device 60 to be given to a definitive image carrier 61.

The image carrier then runs with its worn or soiled wear layer 11 at point 12 in the area of the device 40 '.

Fig. 7 shows a fourth practical embodiment with a cleaning belt driven by a conveyor roller. This is a variant of the exemplary embodiment according to Fig. 6, wherein here the band 16 by means of a very soft, preferably made of foam made of resistant material, such as polyurethane or silicone elastomer, made conveyor roller 43 'instead of the conveyor belt 43 against the electrophotographic layer is pressed. The fat de of the soft material is, for example, 2 to 6 cm.

Since the organic electrographic layers are mostly relatively soft and mechanically sensitive, it is extremely It is important that they are removed from the film application and removal elements (cleaning tape 16; wick 35 »scraper 13, 32; Conveyor rollers 18, 19, 43 '; Conveyor belt 43) are contacted as gently as possible. Therefore, wipers and Conveyor elements (i.e. conveyor belt and conveyor rollers) are preferably designed to be soft and made of resistant elastic Material made, e.g. from synthetic elastomers such as polyurethane elastomers, silicone rubber, Neoprene or hypalon. The conveyor belt 43 consists, for example, of 1 mm thick neoprene with a hardness of 40 to 60 °

-27-

509807/1111

Shore or foams of the materials mentioned, for example polyurethane foam on a textile base. The conveyor rollers can preferably also consist of foams of the same materials. The gate elements preferably have a roughened surface in order to increase their coefficient of friction "" with respect to the cleaning tape the force required to Schutzfilmsuitrag and -abtrag or for toner cleaning is applied from the driven conveyor elements and 10 times smaller rather than from the small, such as train, the lie take-up roll 54 exerts on the tape. the pressure _p? to the conveying elements over the cleaning tape that should be applied to the sensitive electrophotographic layer should be as small as possible, e.g. 10 to 30 p / cm ^. In order to still achieve a sufficiently high force, the contact area is kept as large as possible (e.g. 3. B "at least 2 Ms 10 cm) . The pressure ρ can be the same everywhere as in Fig. 6, reach a flat maximum (Fig. 7) * or it can reach a maximum at application point 5 and at removal point 12 as in Fig. 3, where the conveyor rollers 18, 19 are preferably of the same design as the conveyor roller 43 'in FIG. 7.

A particularly advantageous cleaning tape 16 that is soft, thin, inexpensive, and effective can be made from wood-free cellulose wadding paper (tissue). In contrast to the mechanically strong papers or fleeces previously used for toner cleaning, which are comparatively thick (eg 100 ii), heavy (over 30 g / m ), expensive

-28- 509807/11 1 1

and were hard, for example, tissue paper is used here

ρ ρ

from 15 to 20 g / m, preferably below 25 g / m dry weight, used, which is advantageously light in spite of this creped surface is relatively thin (e.g. 50 u) and very soft (with correspondingly lower mechanical Strength) and also with a small amount of protection.

material (e.g. 8 g / m) can be impregnated.

With such tissue cleaning tape it was possible to use

low pressures ρ of 10 to 20 p / cm up to five times the residual amount of toner compared to the weight of the dry paper to remove the cleaning tape used for this purpose, which means that the feed of the cleaning tape is also small Consumption low and the service intervals for replacing rollers 48 and 54 and the electrographic ones Layer up.

The surface of the conveyor rollers or conveyor belt that transports the paper should preferably be rough (but not hard) surface, the unevenness of which the paper can follow, so that there is toner residue can collect. As a result, the unevenness lined with the paper, the toner residues practically dredged away. The rough surface of the conveyor elements can be produced, for example, by means of a tissue impression (possibly flaky) or sandblasting.

In addition to the exemplary embodiments described with reference to the figures, other devices are also conceivable which the principle of operation of the present invention can be carried out. For example, the protective film 10 also applied by means of rollers, as is known from printing technology, or it can also be sprayed on. FiIm-

-29- 509807/1 11 1

Ordering and removal facilities can also be different can be combined as shown herex E.g. application with wick as in Fig. 5, removal with cleaning tape (Fig. 7). In principle, the invention can also be used with advantage on those inorganic layers which Show signs of surface aging.

In summary, reference is again made to the most important advantages of the present invention, with the an enormous reduction in all surface aging effects, in particular the dangerous corona aging can be achieved. Experimentally at electrophotographic Polyvinyl carbazole layers increase the service life by more than one, even with simple means Order of magnitude can be achieved. The aging effects caused by contact with toner material are also avoided avoided, and toner cleaning is synergistically improved by continually replacing the Protective film also constant surface properties (adhesion) can be achieved. The Mahan stress in cleaning the sensitive organic layers is significantly reduced, and the large number of permissible protective materials make it possible further, by suitable choice or modification with relatively cheap Materials to create optimized conditions for the various steps of the imaging process? This is especially true in the case of high air humidity, which e.g. for the organic layers as well as for toner cleaning is a big problem. The heavy pollution generated by the toner cleaning step the copier can be almost completely avoided. From all of this, one eventually results Significant increase in service intervals and a significant reduction in number compared to the previous ones Copiers.

509807/1111 _ ₃₀ _

Claims (29)

Patent claims f 1. Λ A method for increasing the service life of an electrographic layer, characterized in that an insulating, liquid protective film is applied to the electrographic layer to protect the surface of this layer against harmful effects on this layer as a result of the image generation process, which protective film is at least partially replaced in cycles by removing at least part of the protective film in each replacement cycle and then replacing the removed part by adding new protective material. 2. The method according to claim 1, characterized in that the replacement cycle on extends a maximum of 100 imaging cycles. 3 · Method according to claim 1, characterized net that a replacement cycle is associated with each imaging cycle (Figure 6). 4. The method according to claim 1, characterized in that the protective film on an organic electrographic layer is applied. 5. The method according to claim 1, characterized in that the protective film is applied to an electrophetographic layer. 6. The method according to claim 1, characterized in that little least the wear layer of the protective film is replaced in the replacement cycle. 509807/1111 ~ ³¹ ~ 7. The method according to claim 1, characterized in that the protective film has a charge Surface formed 8. The method according to claim 1, characterized in that the protective film carries the image Surface forms. 9. The method according to claim 1, characterized in that a protective film of at most 0.1 µm thick. 10. The method according to claim 1, characterized in that the image generation according to the Toner transfer process takes place, wherein a toner image is generated on the protective film. 11. The method according to claim 1, characterized in that said replacement cycle the toner residues are also removed. 12. The method according to claim 1, characterized in that the removal of the protective film or its wearing layer and the removal of toner residues takes place together. 13. Device for performing the method according to one of the preceding claims, characterized in that an electrographic Layer (3) on the one hand a film application device (6, 7, 8), which is intended and designed to have an insulating, liquid protective film (10) to apply the electrographic layer (3), and on the other hand a film removal device (13 * 14), -32- 509807/1111 which is intended and designed to at least part (11) of said protective film (10) of to remove the electrographic layer (3), are assigned, in addition, guide and drive means (4) are provided to between the film application device (6, 7, 8) and the film removal E ± irrichtung (13, 14) on the one hand and the electrographic layer (3) on the other hand a relative movement (4) to generate. 14. Apparatus according to claim 13, characterized in that the electrographic layer is an organic electrographic layer. 15. The apparatus according to claim 13, characterized in that both the film application device (5, 18) and the film removal device (12, 19) through cleaning belt (16) on the one hand for the supply of fresh protective material (7) and on the other hand for the removal of the removed Part (11) of the protective film or the toner residues (15) is provided (FIGS. 3, 6, 7). 16. The apparatus according to claim 13, characterized in that the film application device has a container (6 ¹ ) for protective material (7), wherein the electrographic layer (3) over an area (C) in the liquid level (31) of the Protective material (7) is immersed (Figure 4). 17. The apparatus according to claim 13, characterized in that the film application device has a wick (35) which is in a protective -33- 509807/1 11 1 material (7) containing container (6 ¹ ) is arranged, and which wick (35) touches the surface of the electrographic layer (3) (Figure 5). 18. Apparatus according to claim 13, characterized in that the film application device and / or the film removal device have scrapers (13, 13 ', 32). 19. Apparatus according to claim 13 and 18, characterized in that the wipers are made of polyurethane elastomers or silicone rubbers. 20. Apparatus according to claim 13 and 15, characterized in that a drive element in the form of a conveyor belt (43) or conveyor rollers (43 ¹ , 18, 19) is used to impart a feed movement of the cleaning belt (16) over the electrographic layer (3) is provided in order to transmit the force required to carry out the method to said cleaning belt (16). 21. Apparatus according to claim 13 and 15, characterized in that the cleaning tape (16) is pressed against the electrographic layer (3) with a maximum of 30 pond / cm. 22. The apparatus according to claim 13, characterized in that the protective material (7) for the formation of the protective film an insulating, but non-coronary resistant material is used. 23. Apparatus according to claim 13 and 22, characterized in that as protective material -34-509807 / 1111 (7) Silicones, mineral oils or vegetable oils containing functional groups are used. 24. Apparatus according to claim 13 and 15, characterized in that the cleaning tape (16) the electrographic layer (3) over an area (B ") of at least 2 cm, measured in the direction of movement, with the directions of movement of the cleaning tape and the electrographic layer relative to one another are oppositely directed. 25. Apparatus according to claim 13 and 20, characterized in that the conveyor belt (43) or the conveyor rollers (43 ', 18, 19) consist of polyurethane or silicone rubber or "neoprene". 26. The device according to claim 13 and 20, characterized in that the conveyor belt (43) or the conveyor rollers (43 ', 18, 19) consist of foam from one of the materials mentioned. 27. Apparatus according to claim 13 and 20, characterized in that the cleaning tape (16) facing surface of said conveyor belt (43) or said conveyor rollers (43 ', 10, 19) is roughened. 28. Apparatus according to claim 13 and 15, characterized in that said cleaning tape (16) consists of cellulose wadding paper (tissue). -35- 509807/1111 29. Apparatus according to claim 13 and 28, characterized in that said cleaning tape (16) has a weight of at most 25 g / m "in the dry state. 509807/1 11 1 Le it . _t rs e 11 e