DE1597889A1 - Device for removing a copy from a xerographic image carrier - Google Patents

Description

HAlJK XEROX LIMITED

Rank Xerox House

338, Euston Road

London, Ii.W. 1

England

Device for removing a copy from a xerographic

ce image carrier

The invention relates to xerography, in particular to a device for detaching a copy with the powder image transferred onto it from a xerographic image carrier.

In the xerographic process, as described, for example, in US Pat. No. 2,297,691, for generation electrostatic latent images uses a xerographic image carrier comprising a layer of photoconductive insulating material on a conductive surface. In the normal implementation of this procedure, this is xerographic Plate uniformly electrostatic on its surface

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charged and then with a light pattern of the reproduced Image exposed, whereby the charge in the exposed parts of the surface is diverted. The unexposed In this way, surface parts of the layer form an electrostatic charge image, the configuration of which corresponds to the original image is equivalent to.

The electrostatic latent image can then be formed by contact with a finely divided electrostatically attractable material can be developed in the form of a powder. The powder is in the image area parts through the existing on the layer electrostatic charge held. Most of the developer material is deposited at the points with the greatest charge. To the There is little or no developer in places with the slightest charge. In this way a powder image is created, whose distribution corresponds to the light image of the image to be reproduced. The powder is then placed on a sheet of paper or transferred to another image carrier and fixed in a suitable manner on this, so that there is a permanent print.

The electrostatically attractable developer, which is generally used in xerography, consists of a pigmented one Synthetic resin powder, hereinafter referred to as toner, and a coarse-grained substance, which is referred to as a carrier will. The carrier is coated with a material which is at a distance from the toner within the triboelectric series so that between the powder and the granular carrier material, when there is mutual interaction, there is a triboelectric

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Charge is generated. This causes the powder to adhere to the carrier particles. Besides the charge-generating effect allows the carrier also a mechanical control of the toner movement, so that this with the exposed xerographic surface can be easily brought into contact for developing the latent image. The powder particles are attracted by the granular carrier to the electrostatic image and create a visible powder image on the xerographic image surface.

If the xerographic imaging carried out on a cylindrical endless xerographic image area as a xerographic drum in U.S. Pa ^- ent C magazine 3,062,536 and French Patent 1,459,931 is described, the copy paper during a portion of the Tronmelbewegung with their Surface moved and brought into contact synchronously. During this time, a potential with a polarity opposite to the charge of the toner is applied to the side of the paper facing away from the drum, see above

ι that the toner image is electrostatically transferred from the drum to the paper. Then an air stream is used to separate of the copy paper from the drum is used. The toner image is then used in making the final xerographic copy the paper melted or fixed on this.

During the transfer of the toner image from the drum to the paper, the polarity of the transfer corotron when the toner is negatively charged, a uniform positive laic acid,; - applied to the copy paper. This is

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an insulator and induces a negative charge in the non-image areas on the xerographic drum surface, so that an electrostatic binding force is created between the paper and the drum.

In order to separate the paper from the drum, the electrostatic bonding force between the two must be overcome. Will If an air flow is used to separate the paper, a relatively high air pressure must be used to achieve the attraction of the paper to overcome the drum. However, if the air pressure is high, there is a chance that it will not The configuration of the toner image fixed on the paper is disturbed and thus impaired. This will preserve the copy a smeared appearance. The blowing apart of the toner powder also leads to soiling of individual machine parts. In addition, when the copy paper is separated from the xerographic drum with high air pressure, that with the Paper containing toner hit the paper conveyor so hard that the toner can be shaken together, when its electrostatic bond to the paper is poor.

The invention is based on the object of avoiding the disadvantages described above which occur when a copy sheet is detached from a xerographic image carrier. For a xerographic copying machine for generating toner images which are electrostatically transferred from the xerographic image carrier to a copy sheet brought into contact with it, which is detached from the image carrier after the image transfer , this object is achieved in that device

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to reduce electrostatic image transfer are provided between copy sheet and image carrier generated binding force.

In the following an embodiment of the invention is described with reference to the figure, which shows the schematic representation an automatic xerographic copying machine shows, which is formed according to the invention.

In the figure, an embodiment of the invention is shown within an automatically operating copying machine, which works with a xerographic image carrier 10 in the form of a drum, which is the conductive base for a photoconductive layer forms. The drum is on an axis in the frame of the machine in the direction of the illustrated Rotatable arrow. In this way the drum surface is successively passed through a number of xerographic process stations moves past.

For a better understanding of the invention are in the following the various xerographic process stations described in terms of their function;

At the charging station A there is a uniform electrostatic Charge on the phoboleit, capable layer of xerographic Drum applied.

At the BeIi; Processing station B becomes a light or radiation pattern an image to be reproduced on the drum upper

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projected surface, whereby the charge in the exposed parts of the surface and an electrostatic latent image is generated.

At the development stage G, a developer, the toner particles containing an electrostatic charge opposite to that of the electrostatic latent image cascades the drum surface, causing the toner particles to adhere to and to the electrostatic latent image xerographic powder image corresponding to the reproducing image produce.

At the image transfer station D, the xerographic powder image electrostatically transferred from the drum surface to an image sheet, which is then removed from the drum by compressed air is separated.

At the drum cleaning and unloading station E, the Drum surface to remove residual toner particles brushed off the image transfer and illuminated with a relatively bright light source to achieve a practically complete discharge of any residual electrostatic charge.

The foregoing brief description, dec * procedure should be seen to understand the operation of the illustrated xerography Copier are sufficient. more details with regard to the construction and operation of such a machine can be found in the patents already mentioned.

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While the surface of the 'drum at the image transfer station D is moved past, an image sheet 12, such as paper, becomes with the surface of the xerographic drum 10 brought into contact, for which purpose the sheet conveying mechanism 14 is used. The sheet and drum move with it Speed past a transfer corotron 16 which causes an electrostatic separation of the toner image from causes the drum and its binding on the paper. At the same time, the effect emitted by the transfer corotron electrostatic charge an electrostatic sticking of the paper to the drum. The drum is then put together with the paper moved past the detachment device 18, through which the paper is blown with compressed air and from the drum is replaced. Then the paper is moved to a fixing station with the second sheet conveying mechanism 20, with the the final copy is made. The above described Functions correspond to the processes described in the patents mentioned.

In addition to the transfer corotron 16 and the peeling device 18, a corotron 22 and an optical pre-transfer corotron 24 are provided. That to reduce the adhesive effect Serving corotron 22 is arranged in the direction of rotation of the drum just behind the transfer corotron 16 and sprays an alternating discharge on the back of the copy sheet immediately after the electrostatic image transfer. Of the The purpose of this process is to reduce the electrostatic Attraction between the paper and the drum caused by the transfer corotron 16. That

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Pre-transfer corotron 24 is also for spraying an alternating discharge on the drum surface, however, this is preferably after the image development, however before the drum contacts the copy sheet. This transfer corotron serves to reduce the difference in tension between the image surface parts and the surface parts of the latent that do not belong to the image electrostatic image, so these voltage differences across the drum have a minimal effect on the amount of corona emission of the corotron 22 exercise to reduce the adhesive effect.

Assume now that the charge initially applied to the photoconductive surface is positive and that for image development negatively charged toner particles are used. In this case, the toner particles become positive by means of the Image transfer corotrons 16 from the xerographic drum is attracted to the copy sheet, resulting in the image transfer. The positive ones generated with the transmission corotron 16 Emissions also produce a uniform positive charge per unit area on the non-conductive copy paper. In the the charges picked up on the parts of the copy sheet lying above the surface parts that do not belong to the image induce a negative charge in the base of the photoconductive layer under the surface parts not belonging to the image. This charge distribution There is an electrostatic attraction between the drum and the paper.

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The emissions of the transmission corotron cause sticking of the paper with a constant charge per unit area. The entire charge between various copy sheets and xerographic The image area changes according to the total amount of surface parts not belonging to the image that have a charge be able to record. For example, if a copy has relatively small parts of the image area, there is a large rear surface area, whereby the total electrostatic attractive forces between the paper and the drum are large. However, they become great, consistently tinted areas are developed and transferred, so there is a minimal amount of background area so that the overall display effect between paper and drum accordingly gerinp; is. As can be readily understood, a peeling device must be provided to separate the copy sheet from a drum to be able to overcome the highest possible force of attraction corresponding to the total charge in order to function properly. However, if a correspondingly high air pressure is used, your image will be smeared more intensely, in particular with a low electrostatic total binding force of the toner on paper.

The elimination or neutralization of the electrostatic The bond between the paper and the drum can be rendered ineffective the forces producing this bond can be achieved. The bond is created by positive transmission emissions remaining in the paper so these can be of equal size and opposite polish emissions are removed.

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The bond between paper and drum consists of charges, those present with a constant charge density per unit area are. It has been found that the charge causing the bond on the copy sheet is removed by applying an alternation Stress corotrons can be neutralized, which has greater emissions with opposite to the charge of the paper Creates polarity. Such an alternating emission can be achieved through correct selection of the corotron wire and its pretension can be achieved. Contains a suitable corotron device an approx. 0.1 mm thick platinum-iridium wire and an alternating voltage source of 4-500 volts rms value at 400 Hz, the biased with a positive DC voltage of 1000 volts isb. The wire diameter and the pre-tensioning allow this Generation of the required excess of negative emissions. Although positive and negative ions are emitted; are effected the excess of negative ions has the necessary negative polarization effect.

Pure DC emissions that are equal in size and opposite the loading of the paper can also deactivate the binding of the paper to the drum. A flow of ions from a DC voltage source that is great for reducing the bond enough, but a little less than the one rejection of the toner The potential acting on the drum has also been used unsuccessfully. The intended source of emissions Contained an approx. 0.1 mm thick Plabin-Iridium-Korotrondrahfc and a negative DC bias, so that a current of

ρ
0.31 microamps per cm "in one according to the above

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ORIGINAL

Patent specification built copying machine was generated. The critical values for such a DC voltage crotron must be complied with, but make the use of an alternating voltage corotron appear more favorable. These values are uniformity of the Koi? Otron wire diameter, uniformity of the wire material, uniformity of speed between corotron and image as well as uniformity of the feed flow for the corotron. Strict compliance such values are not required for an alternating voltage corotron.

The above-described, anti-stick corotrons, for which examples have been given, achieve the desired reduction in adhesive effect by itself, unless other variable sizes are present. Effect in practice however, the charge distribution on the image area parts of the photoconductive layer a change in the neutralizing negative emissions of the corotron. The ones that do not belong to the picture Surface parts of the xerographic image area have a smaller size Potential than the image area parts, so that their effect on the change in negative emissions is negligible is.

Since the alternating-voltage corona discharge source alternates between positive and negative values, it exceeds the Schv / c IJ.voltage _t given for the generation of ion emissions in both directions, which has a corresponding positive and negative value hot ,. The iichwell tension unites; ο corotron is that tension of a corotron wire, b-si -lcven exceed in de

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Ambient air of the wire breakdowns occur, the ion emissions produce. However, there are extensive image surface parts with the corresponding charges on the xerographic surface present in the vicinity of the corotron reducing the adhesive effect, the positive emissions of this corotron become suppressed by the high potential of the charges on the xerographic surface. With the reduction of positive emissions there is a proportional increase in negative emissions. On the other hand, are on the xerographic image surface in the In the vicinity of the corotron, if there are line drawing images with minimal surface charges, only slight suppression occurs of positive emissions. Accordingly, there is a proportional reduction in negative emissions. Therefore change due to the effect of the changing charge distributions of the xerographic surface on the alternating emissions the negative or neutralizing emissions in their quantity. The changing degree of neutralization by negative Corona emissions are generally unsuitable for reducing the adhesion of the charge-containing paper to the drum, namely through the effects of the changing size of surface parts that do not belong to the image.

To reduce these problems, a pre-transfer corotron can be provided which separates the charge differences between the two Image area parts and the non-image area parts of the xerographic image area reduced. This suppressed it the entire area of the xerographic drum the anti-sticking emissions in a uniform manner, so that the amount of these emissions remains stable.

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For example, an initial charge potential is applied to a xerographic imaging plate and is provided by a Exposure the voltage in the unexposed image area parts to 1000 volts and in the exposed, not to the image If the corresponding surface parts are brought to 300 volts, there is a voltage difference of 700 volts on the xerographic image surface. If the image surface is moved past the corotron, which reduces the adhesive effect, with this difference in tension, thus the amount of corona emissions is detrimentally changed. Theoretically, it can be completely switched off the adhesive effect with alternating discharges is only achieved when the voltage is applied over the entire xerographic image area is even. In practice, however, it turned out that when the voltage difference on the An operational device is given to a certain value of the xerographic image area, which the output evenly allows high emissions, as required to reduce the adhesive effect according to the present invention are.

The appropriate reduction in the voltage differences between image surface parts and surface parts not belonging to the image is achieved according to the invention by the action of alternating voltage emissions on the image surface, which overall have a negative effect and act on the drum surface before the drum and copy sheet come into contact. These emissions are generated with the pre-transfer corotron 24 ·. For example, on the image area, if there is an electrostatic latent image with 1000 volts in the area parts and 300 volts in

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the parts of the surface that do not belong to the image are present by means of suitable corona emissions prior to the image transfer these voltages on the xerographic image area to 500 volts in the image area parts and 250 volts in the not Area parts belonging to the image are reduced. The voltage difference is therefore reduced from 700 volts to 250 volts. Will the xerographic image surface treated in this way is moved past the corotron 22, which reduces the adhesive effect, and is located If the electrostatically bound copy sheet is attached to it, the reduced voltage difference has only a slight change Effect on the amount of neutralizing emissions of the corotron 22.

The reduction of the stresses in the image areas and the parts of the surface that do not belong to the picture are different in each case This is possible because a corona source acts to bring the treated areas into a state of equilibrium with their own tension. The! Corotron changes those Surface parts whose tensions are most different from its tension, depending on the time .. That will developed xerographic image on the pre-transfer corotron Moved past, the parts of the picture surface carrying a higher tension are reduced more rapidly with regard to their tension than the surface parts that do not belong to the picture. Since then Corotron reduces the tension in the two types of surface ropes practically at the same time, causing the tension to be reduced more quickly in the parts of the image, within the time of the corotron's action, a reduction in tension

There is a difference between parts of the image and flat axes that do not belong to the image 009836 / 1B97

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A suitable pre-transfer corotron 24 to produce a stress reduction in the xerographic image surface operates in an exemplary embodiment with an AC voltage source of 5000 volts effective value at 60 PIz and a positive one Bias voltage of 270 volts. It was using a corona wire DC bias used to allow an excess of negative emissions. The changing amount of negative Emissions occurs as a function of the load on the drum in the same way as with the corotron, which reduces the stickiness.

If, during operation of the machine, the developed xerographic image on the surface of the drum 10 is guided past the developing station C, it also passes under the pre-transfer corotron 24. This reduces the tension in the image surface parts and the surface parts of the drum that do not belong to the image between the two prevailing tension differences. Then the image is guided to a point in front of the transfer corotron 16, at which a sheet of paper is brought up to the drum and moved on together with it. The movement of both parts past the transfer corotron 16 causes an electrostatic adhesive effect of the paper on the drum as well as an electrostatic transfer of the toner image from the drum to the paper. The further movement of the paper together with the drum past a third corotron 22, which reduces the adhesive effect, causes a reduction in the molecular attraction between paper and drum, so that the l'i_n; üi, roman [· ;, dio through the ab- ¹ ; 1β generated; confused], the paper effective from dor

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Drum can separate. The second sheet conveying device 20 moves the sheet from the drum to the fixing device, which the final copy completes.

When using the pre-transmission corotron 24 and the Adhesive reducing corotrqns 22 in the manner described can be required to separate the Paxler from the drum Air pressure can be reduced from 0.9 at to 0.35 at. The reduced air pressure brings the possibility of toner smear due to too strong air flow to a minimum value and also reduces the possibility of in the Toner clouds blown into the machine.

In certain cases the air pressure release device is used not necessary, as the natural resilient property of the paper is a return to a plane, tangential to the drum. The paper will then detach itself from the drum.

The invention has been described using an exemplary embodiment, however, it is not limited to this. All possible embodiments within the scope of the following claims are encompassed by the spirit of the invention.

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Claims (1)

1. Xerography see copier for the generation of toner images, which are electrostatically transferred from the xerographic image carrier to a copy sheet brought into contact with it, which is detached from the image carrier after the image transfer, characterized in that devices (22, 24) for reducing the binding force generated by the electrostatic image transfer between the copy sheet (12) and the image carrier (10) are provided. 2. Zerographic copying machine according to claim 1, characterized in that that the means (22,24) for reducing the binding force comprise a corona discharge source (22), the emissions with an opposite polarity to the charge applied to the copy sheet (12) during the image transfer Polarity generated. 5. Xe ro graphic copier according to claim 2, characterized in that that the corona discharge source (22) is a DC voltage discharge source is. 4. Xerographic copying machine according to one of claims 1 to 3, characterized in that a transport device (14) for bringing the copy sheet (12) to the developed Image-bearing image carrier (10) and a device for receiving the copy sheet (12) provided with the toner image Separation from the image carrier (10) and provided after the action of the devices (22, 24) to reduce the binding force are. 0 0 9 8 3 6/1597 ^BAD c - 18 - 5. Xerographic copying machine according to one of claims 1 to 3, characterized in that a transport device (14) for bringing the copy sheet (12) up to the image carrier (10) carrying the developed image and a device (18) for Detachment of the copy sheet (12) carrying the toner image from the image carrier (10) after it has passed the devices (22, 24) are intended to reduce the binding force. 6. Xerographic copying machine according to claim 5 »characterized in that that the detachment device (18) blows an air jet between the copy sheet (18) and the image carrier (10). 7. Xerographic copying machine according to one of the preceding claims, characterized in that the devices (22, 24) also has a device to reduce the binding force (24), which reduce the charge difference between exposed and unexposed areas of the developed image area of the image carrier (10) and in Direction of movement of the image surface is provided in front of the image transmission point (D). 8. Xerographic copying machine according to claim 7, characterized in that that the device (24) for reducing the charge difference is an AC voltage corona discharge source, the emissions generated, the predominant part of which has a polarity opposite to the polarity of the latent electrostatic Image has. 009836/1597 bad original