Electrographic apparatus

The present invention relates to an electrophotographic copying machine according to the preamble of US Pat. No. 5,476,811 An electrophotographic copying method is known in which an electrostatic charge image is formed on a photosensitive recording material having a conductive layer and a photoconductive layer and then transferred to another recording material such as an electrostatic recording paper becomes, followed by development of the other recording material, as in the case of the TESI method. In a copying machine for carrying out this method, the surface of the former photosensitive material is not subjected to development, which is different from the copying machines which use the xerographic copying method in which charging, exposure and development are performed on the photosensitive recording material and then developed Image is transferred to an image receiving material. On the other hand, as in the case of using the ion current modulation method, there is another system using a photosensitive ion current-adjusting grid having a conductive layer and a photoconductive layer provided with a number of fine pores. wherein an electrostatic charge image is formed on the photosensitive grating and this charge image is then transferred to another recording material located separately from the ion current accommodating grid. Subsequently, the other recording material carrying the electrostatic charge image formed by the ion current modulation method is subjected to development.

In these methods, since there is no need to work with cleaning materials, for example, to remove excess toner from the surface of the photosensitive recording material or the photosensitive grid on which the electrostatic latent image is formed, and not touch the recording material particularly in the case of the ion beam modulation method must be, there is no possibility That the photosensitive surface is subjected to a mechanical stress, so that it is expected that the photosensitive surface over a long period of use has a stable nature.

When such a photosensitive recording material is subjected to corona discharge for an extended period of time to form an electrostatic charge image, differences in the surface condition result. It often happens that it becomes impossible to form an electrostatic charge image. The reason for this is that fine dust-like particles of 0.1 to 50 μ, consisting mainly of oxidized silicon and floating in the air, take charge as a result of the corona ions and adhere to the surface of the photosensitive recording material and the grid, respectively justify a decrease in surface resistance. When the surface resistance of the recording material falls too much, it is no longer possible to sufficiently charge the surface of the recording material, so that the contrast of the reproduced image is deteriorated. Finally, it becomes impossible to obtain a usable reproduced image. In particular, in the case of the aforementioned photosensitive grating, it is difficult to provide a cleaning device for

To remove dust from its surface. On the other hand, the accumulation of dust on the photosensitive recording material in the xerographic process is not a problem since it is anyway developed and purified.

In the DT-OS 17 72 487 a corona discharge device is described in which measures are taken that the deposition of dust or toner particles is avoided on the electrode wire, so that no weakening of the corona current occurs. It is believed that the so-called corona winds exert a cleaning action on the electrode. To increase this cleaning effect, an air flow is introduced into the corona discharge device by means of a blower and lines via a filter.

Furthermore, in the DT-OS 22 39 236 a device for supplying a corona discharge device with dust-free air is described, in which the corona discharge device is traversed by a continuous flow of air, which previously flows through a porous filter zo and this downstream electrical dust. In the electric dust collector, the dust particles are charged by means of a corona discharge and electrostatically drawn to lying on a reference potential screens.

The invention has for its object to provide a copying machine of the type specified in the preamble of claim 1, wherein the quality of the copies is not reduced even with prolonged use of the device.

This object is achieved according to the invention mn given in the characterizing part of claim I means.

The action of the corona discharge device surrounding the corona discharge device with dust-free air achievable with the aid of the air duct provided according to the invention ensures that the recording material is kept dust-free over a large area and, moreover, that the discharge electrode arrangement of the corona discharge device remains clean. This effect is the well known Koronaeniladungsvorrichtunger. not available. .It leads to the fact that the copy quality remains good even after an extremely long use of the copier.

Further advantageous embodiments of the copying machine according to claim 1 are the subject of the dependent claims.

The invention will be explained in more detail below with reference to the description of exemplary embodiments with reference to the drawing. It shows

1 is a schematic partial sectional dimming of an embodiment of the invention, in which a corona discharger and an electric dust collector are connected by an air duct,

Fig. 2 is a schematic partial sectional view of another embodiment in which a circulation of purified air is provided, and

Fig. 3 is a schematic sectional view of a copying machine according to the invention, which operates according to the TESI method.

When a corona discharge is applied to a photosensitive material, for example, a nonperforated photosensitive material or a photosensitive grating, dust or the like is liable to adhere foreign matters to the photosensitive material. Uni to this

To avoid this, an electric dust collector is used which makes dust-free air between and in the vicinity of the photosensitive material and the corona delacler. In the case that the corona discharger and the photosensitive recording material move relative to each other as shown in FIG. 1 is shown, an inflow of air takes place in the space between the corona discharge electrode and the photosensitive material only from one side, considering the air flow. Considering this phenomenon, the arrangement is such that cleaned air is supplied to one side of the corona discharger. According to FIG. 1 For example, there are provided a photosensitive recording material 10, a corona discharger 1 of a conventional type having a corona discharge wire 25, and a tube 20 arranged to discharge purified air in the vicinity of the discharge medium. The tube 20 is connected by means of a connecting member 19, for example a flexible tube, with a corona discharge ausnützenden electrical dust collector 2. By a Geblästreinnchtung 21. For example, a fan, air is first fed into the interior of the Staubsamm lers 2. The dust contained in the air thus fed is charged by a corona discharge of needle electrode !! 22 is suspended. The charged dust adheres thinly to a conductive grid 23 and the walls of the dust collector 2. The conductive good 23 charges the dust collector 2 passing air flow, so that the Staubabscheidevermögen is increased. The dust-free air passes through the connecting member 19 and reaches the tube 20. In the tube ribs or guide surfaces 24 are arranged at various locations. These ribs or baffles serve to provide some resistance to the flow of air so that the possibility of formation of a high flow local area avoids the purified air from escaping uniformly from the outlet. It is possible to use glass or the like at a portion of the shield of the corona discharger 1 opposite to the opening side to make it optically open. In such a corona discharger, the discharge can be performed simultaneously with the image exposure, whereby the photosensitive material is concurrently protected from the dust adhering thereto. In F i g. 1, a glass plate 33 is shown on the corona discharger 1. As indicated by dashed lines, a suction line 126 may be provided on the other side of the corona discharger 1, so that the air sucked in by it can advantageously be returned to the electric dust collector 2.

Fig. 2 shows another embodiment for the discharge of purified air in the vicinity of the corona discharger. In this structure, purified air exits on both sides of the corona discharger 1. For this purpose, a channel member 26 is provided, which surrounds the corona discharger 1. The channel member 26 is divided into two channel portions 27 and 28 on both sides of the corona discharger 1 in the vicinity of the photosensitive recording material 10. In the channel sections ribs or fins 29 and 30 are housed to achieve the same effects as in the embodiment of FIG. 1. In addition, the cleaned air in the presence of an opening in the Abschirmplatle the Koronaentladcrs 1 also through this opening in the direction of the photo-sensitive recording / measuring

terial 10 are led. In the case where the photosensitive material has a number of pores or openings, as in the case of a photosensitive grid, it is advantageous in view of the dust collecting effect to arrange a suction pipe 3t under the photosensitive material 10, as shown in Figs. 2, so that the purified air sucked in this way can be returned to the blower 21 via a connecting member 32. In this case, however, care must be taken that no ambient air is sucked through the photosensitive grid by the suction line 31, which is not cleaned.

In the previously described embodiments according to the F i g. 1 and 2, a corona discharge is utilized in the electric dust collector 2, with needle electrodes serving as the source of this corona discharge. However, it should be noted that any replacement can be made. This means that the needle electrodes can be replaced, for example, by charging wires. Needless to say, any other type of corona discharge device can be used instead. In addition, it does not present a problem for those skilled in the art to place the conductive walls and conductive grids forming the housing of the electric dust collector 2 at an appropriate potential including ground potential. With regard to the voltage to be applied to the corona discharge electrodes of the dust collector 2, it is further understood that this may not only be an AC voltage or a DC voltage, but in the broadest sense also an AC voltage superimposed on a DC voltage. and even an AC voltage that may have an asymmetrical negative and positive waveform.

In the following, reference will be made to an embodiment in which the electric dust collector shown in Fig. 2 is incorporated in an electrophlographic copying machine. FIG. 3 Fig. 10 shows an electrophotographic copying machine adopting the TESI method using a photosensitive recording material 47 having three layers, namely, a conductive substrate, a photoconductive layer, and an insulating overcoat as disclosed in U.S. Patent No. 3,666,363 is. The electrophotographic process for forming an electrostatic latent image comprises a precharge step on the photosensitive material 47, a discharging step to be carried out simultaneously with the image exposure, and a further step of uniform exposure of the photosensitive material 47, so that an electrostatic charge image corresponding to the original image is formed on the photosensitive recording material 47. The formation of the charge image on a drum-type photosensitive recording material 47 which is rotatable in the arrow direction shown. is performed in the above-described copying machine 46 by using a pre-clearing lamp 48, a pre-charging corona discharger 49, an AC corona discharger 50 simultaneously performing image exposure, and a uniform illumination lamp 51. In the image exposure, an original (not shown) placed on a document support 52 movable in the direction indicated by the arrow is illuminated by means of an illumination lamp 53, and an image is focused on the photosensitive recording material 47 through mirrors 54 and 55 and an objective 56 becomes. Into the spaces between the corona discharger 49 for the precharge, the AC corona discharger 50 and the photosensitive recording material 47, air is supplied after passing through the electric dust collector 57 described in detail in connection with FIG. For this reason, the environment of each of the corona dischargers 49 and 50 and the photosensitive material 47 is filled with purified air during a period during which the discharged photosensitive material 47 is discharged. It is therefore avoided that any dust adheres to the photosensitive recording material 47 due to the corona discharge. The electrostatic charge image thus formed on the photosensitive material 47 is transferred to an electrostatic recording paper 58. The electrostatic recording paper 58 is picked up by a peeling roller 59 and then transported on the recording material 47 in synchronization with the movement of the charge image by means of a synchronizing roller 60. The recording paper 48 is then subjected to corona discharge by means of the discharger 61 to thereby discharge the surface, and is then transported into contact with the photosensitive material 47 by means of a suction device 62 and a belt 63 to which a voltage is applied. During this period, the charge image on the photosensitive material 47 is transferred to the recording paper. The recording paper is then developed by the developing device 64, fixed by a fixing device 65 operating with a heat roller, and then discharged from the copying machine.

When the electric dust collector 57 of the copying machine 46 is kept inoperative, noticeable deterioration of the reproduced image occurs after reproducing approximately 5000 images. On the contrary, in the operation of the electric dust collector 57, no perceptible deterioration of the reproduced image could be detected even after 30 ° C image reproduction.

For this 1 sheet drawings