DE3645310C2 - Photocopier for multi-coloured images - Google Patents

Abstract

A charge image is produced on the image receiver and a second process is then instituted for the production of a toner image, which is arranged with a cleaning unit positioned in the vicinity of the surface of the receiver (1) and can be brought into contact with it. The cleaning unit has a fixed (81) and a rotatable element as a second cleaning element (82) which contacts the upper or mantle surface of the image receiver in the movement direction. A cleaning process is undertaken at the image receiver surface by the rotating element (82) according to a point of time, related to the cleaning effect displayed by the first cleaning element (81) at the image receiver.

Description

The invention relates to a color image forming device in which the steps of generating a La or latent image by embossing an image on an image sensor and the development of the latent be repeated several times.

For the electrophotographic production of a multi-color are usually several steps by Aufla development, exposure or image recording, development and Transfer for each individual color component again brings to each other superimposed toner images in each colors on a recording or copy paper to be transferred as a record carrier. For example are electrostatic in each step separate latent images or latent charge images generated by different colors by color extract filters, such as blue, green and red filters and in yellow, magenta and cyan or if necessary with black toner to create monochromatic Toner images are developed. Those toner images who in the order of their creation on the record transfer media to produce multi-color images. This multi-color imaging process occurs each time but the following difficulties:  

• 1. At the end of development for each color is one Transfer to the record carrier required; this requires large dimensions of the device and a Extension of imaging time; and
• 2. It may be because of the repeated operations lack of congruence easily.

For this reason, multi-color imaging is already in progress process has been developed with which the aforementioned Difficulties should be eliminated that the colors of the optical information of a template using a CCD solid-state image sensor via color filters separated and several toner images in against side overlay on a common light sensitive element or image sensor are developed, the transfer steps to a single step to reduce. With this method, however, it follows also the difficulty of being in a previous one Toner image developed in a subsequent step Development step is disturbed or impaired or that in a development unit for one previous step contained toner in a Ent winding unit for a subsequent step drags and thus the color balance of the multicolor picture is disturbed.

To avoid this difficulty, a ver drive developed for generating a multicolor image been in which a preload with a superimposed AC component to a development unit for a second or later development process is applied to a toner on an imager to skip the generated charge image. With this method, the developer layer does not rub  against the one (s) generated in the previous step Toner image (s) so that no image interference or leg pregnancy occurs.

The principle of this multi-color image formation method is explained below using a flowchart or flow chart according to FIG. 15. Fig. 15 illustrates the changes in the surface potential of the photosensitive member assuming a case of positive charge polarity. Here, PH denotes an exposed part of the photosensitive element (hereinafter referred to as image sensor), DA denotes an unexposed part of the image sensor and DUP denotes an increase in potential which occurs because positively charged toner T adheres to the exposed during the first development Part PH attaches.

The image sensor is charged uniformly with a constant positive surface potential E by a Scorotron charging unit (cf. (a) in FIG. 15). An image exposure is then carried out by means of an exposure light source, e.g. B. a laser, a cathode ray tube or a light-emitting diode unit, so that the potential of the exposed part PH drops in accordance with the amount of light (see FIG. 15 (b)). A latent charge image generated in this way is developed by means of a development unit which is subjected to a positive bias practically equal to the surface potential E of the unexposed part. As a result, positively charged toner accumulates in the exposure area of a lower potential to generate the first toner image T (see FIG. 15 (c)). The area on which this toner image has been formed is subject to the potential increase DUP as a result of the attachment of the positively charged toner, but it does not receive the same potential as the unexposed part DA. Next, the image pickup surface carrying the first toner image is subjected to a second charge by a charger so that it assumes a uniform surface potential regardless of whether the toner image T is present or not (see Fig. 15 (d)). The surface of the imager is then subjected to a second image exposure to form a charge image ( Fig. 15 (e)), and a positively charged toner image T 'in a color different from the toner image T becomes the second toner image in a similar manner to that in Fig. 15 (c) shown, developed (see Fig. 15 (f)). The above process is repeated to form a multi-color toner image on the image sensor. This toner image is transferred onto a recording paper or a recording medium and then heated and treated for fixing to obtain a multi-color recording image. Then the image pickup is freed of residual toner and residual charge on its surface and then used for the generation of a next multi-color image. However, another method is also known in which a toner image is recorded on an image sensor or a recording medium in another way.

In the method described with reference to FIG. 15, it is desirable that at least development step (f) is carried out in such a way that the developer layer is not in contact with the surface of the image receptor (as the image receiving material).

In the multi-color imaging process described, by the way, the second and later recharge steps can also be omitted. If for any pictures  generation a charge can be repeated before a charging removal step in each charging step be switched on. The exposure light can also be used source the same or one each time for image exposure be different light source.

For example, in DE 34 25 006 A1 or DE 34 25 575 A1 electrophotographic color image generation ver drive known to the multiple image exposure units deploy. With these procedures, the different Latent images for the respective colors in total only one revolution of the imaging unit.

In electrophotography is used as an image exposure unit a gas or semiconductor laser beam, a light emitting diode, a Cathode ray tube or a liquid crystal used.

As a latent image forming method for producing the multicolor In addition to the electrophotographic Method also a method in which to generate a latent charge image charges using a multi-needle electrode implanted directly in the image sensor be, or a method in which a magnetic latent image is generated by means of a magnetic head, applied become.

In the described non-contact or non-contact Development is preferred to alternating bias Development unit created to supply enough toner to the Add latent image. In addition, the AC bias only to the development unit created the toner one of each to be developed Contains color. If this bias to the not Development-contributing development unit is created, the toner contained in this development unit adheres the latent image surface with clouding of the color, or the Image sensor deposited toner of a different color is in  introduced this development unit, which the Color rendering is significantly affected.  

For the reasons mentioned, it is necessary to change Preload in every development process for everyone Switch development unit on and off. You can however, switching noises or interference signals occur, which disturb the latent image generation unit and missing Pixels or to a collapse of the image data being able to lead.

It is with such a multi-color image forming apparatus also desirable to provide drives to the Ent winding sleeves or cylinders or the inner Magnetic rollers for the individual development units separately rotated. This is the following in case of using a common drive explains:

• 1. Each development unit must have a driving force Transmission device, e.g. B. a strap or one Chain, be provided, and
• 2. They are means of separate connection and separation of the drive (e.g. a clutch) is required.

If these requirements are met, the device complicated, and the drive must have a large torque can endure. If, on the other hand, separate drives are used can be seen, the transmission facilities can be omitted, and any drive can be used for the loading only one development unit at a time be designed small enough. In this case it is also appropriate that each development unit only during a period in which they are developing contributes or carries it out, is driven. If driven a non-developing development unit toner builds up, clouding the color  the latent image, or that already on the image sensor accumulated toner mixes with the toner Development unit (or is introduced into the latter).

For this reason, the drive for each drive or Development unit for each development process and be turned off. Here, however, there is Ge drive for the generation of switching noises, which the above-mentioned latent image generation disorders introduce. The causes of the switching noise are not fully understood yet, but they seem to be from electromagnetic waves, changes in the earth or ground potential or the stray capacitance, that arise when the drives are switched on and off.

There are also sources of interference for the latent images generation unit in the case of electrophotography in Ab cuts or components for applying high voltage, such as charging or transfer electrodes.

The interference of the latent image generation unit by the mentioned switching noises can in particular result in the so-called "digital type imaging" at which the picture or the illustration by reading and Save a template image in an image memory and playback based on the image storage content is produced.

The invention is now in view of the above described conditions have been developed. Task of The invention is thus the creation of a color image generation device with which a picture of consistently high quality is always available can be generated, without the risk that the A latent image generation unit adversely affects the latent image actual disturbance due to the generation of switching noises, e.g. B. due to sudden changes in the state of the device, is subjected to no recording image can produce high quality.

This object is achieved by the in claims 1 and 2 marked features solved.

Preferred developments of the invention result from the Subclaims.

The color image forming device according to the invention has one Image sensor, a charging device for loading the image an exposure device for exposing the Image sensor to point to it during several revolutions of the Imager a separate first and second latent image generate a first development unit for developing the first latent image to a first toner image with a first To produce color toner, being the first developing unit a first development sleeve and one in the first Development sleeve provided first magnetic roller has one first control unit for controlling the first development sleeve or the first magnetic roller to the first toner image generate a second development unit for developing the second latent image to form a second toner image with a to produce second color toner, the second developing unit a second development sleeve and one in the second Development sleeve provided second magnetic roller, one second control unit for controlling the second developer tion sleeve or the second magnetic roller to the second To generate a toner image, a biasing device  to apply a development bias to the first and second development sleeve, with the image sensor for over storage of the second toner image over the first toner image is rotated several turns, and each developing units by the corresponding control unit for each Rotation of the image sensor is controlled so that each the first and second toner images during one revolution of the image sensor is formed on the image sensor, a Transfer device for transferring the multicolor images on a recording medium and a control device, which controls the first and second control units such that between the end of exposure to form the first Latent image and the start of exposure to form the second latent image the control of the first development interrupted sleeve or the first magnetic roller and the Control of the second development sleeve or the second Magnetic roller has started.  

According to a further aspect of the invention there is Color imaging device from an image sensor, one Charging device for loading the image sensor, an exposure device for exposing the image sensor to it a first during several revolutions of the image sensor and to generate a second latent image separately, a first one Development unit for developing the first latent image, to form a first toner image with a first color toner generate, wherein the first development unit a first Development sleeve and one in the first development sleeve provided first magnetic roller, a second Ent development unit for developing the second latent image, um a second toner image with a second color toner generate, wherein the second development unit a second Developing sleeve and one in the second developing sleeve provided second magnetic roller, a bias Application device for applying a development bias to the first and second developing sleeves, the Image sensor for overlaying the second toner image the first toner image is rotated several revolutions, and the bias application device the development tension on each development sleeve for each revolution of the Imager creates so that each of the first and second Toner images during one revolution of the imager the image sensor is formed, a transmission direction to transfer the multicolor images to Recording medium and a controller that the Bias application device controls such that between the termination of the exposure to form the first Latent image and the start of exposure to form the second latent image, the application of the development bias interrupted to the first development sleeve and the application the development bias on the second development sleeve started.  

The following are preferred embodiments of the invention compared to the prior art with reference to the drawing explained. Show it:

Fig. 1 (a) is a block diagram of an image forming operation in an image forming apparatus according to the invention He,

Fig. 1 (b) is a block diagram of the operation of the feed (preparing) of an image memory according to Fig. 1 (a),

Fig. 2 is a schematic representation of a wesentli chen part of the image forming apparatus,

Fig. 3 is a schematic representation of a portion of a laser beam scanner Wesent union,

Fig. 4 is a sectional view of a developing unit,

FIGS. 5 and 6 are graphical representations of the density characteristic as a function of the changing intensity and frequency of an electric field,

FIGS. 7 and 14 are timing charts for illustrating the operation of the individual portions or components of the image forming apparatus,

Fig. 8, 9 and 10 are timing charts of the sequential hindrance one to be applied to the developing unit bias

Fig. 11 to 13 are circuit diagrams of an essential part of a bias-supply circuit for the developing unit, and

Fig. 15 is a flow or flow chart of a general my image forming operation,

Fig. 1 (a) is a basic block diagram of an image forming apparatus. Image data is supplied from an image memory to an image data processor, in which this data is converted into a type suitable for recording before it is supplied to an electrophotographic type recording device. A light-sensitive element (image sensor) is provided with a marking so that an oscillator is reset when the marking is read out by a position detector in the form of an optical measuring sensor or sensor. A control unit controls the recording device in accordance with a clock pulse supplied by the oscillator.

Fig. 1 (b) is a basic block diagram showing the. Device for reading out and storing a template image using a suitable reader in accordance with the template image. The original image is generally obtained from an original, but can also be a still image supplied by a television camera or an image transmitted by another device via telephone lines or the like. The image memory used can be, for example, a floppy disk or a magnetic tape.

Fig. 2 illustrates the structure of the multicolor imaging device according to Fig. 1 (a), with which a multicolor image can be generated in the manner described below. A light-sensitive element (as an image sensor or image receiving material) 1 is evenly charged on its upper or outer surface by a scorotron charging electrode 2 . Subsequently, image exposure light L is emitted by an optical laser system 10 in order to irradiate the photosensitive element 1 and to record or impress the image on it. In this way, an electrostatic latent image or latent charge image is generated, which is then developed by a developing unit A containing yellow toner. The photosensitive member 1 carrying the toner image thus generated is again uniformly charged by means of a scorotron charging electrode 2 and exposed to the light L (see FIG. 15 (b)). The electrostatic latent image thus generated is developed by a developing unit B containing magenta toner. Then, a two-tone yellow and magenta toner image is formed on the photosensitive member 1 . In a similar manner, the latent image is successively developed with cyan and black toner in mutual superimposition, so that a four-color toner image is finally produced on the photosensitive element 1 . This four-color toner image is charged by means of a transfer electrode 9 and is transferred through a transfer electrode 4 to a recording paper or a recording medium P, which is then separated by a separating electrode 5 from the photosensitive element 1 and is fixed in a fixing unit 6 . In the meantime, the photosensitive element 1 is removed by a charge removal electrode 7 and a cleaning unit 8 from residual charge or residual toner.

In Fig. 2, the image data processor, the image memory and the recording device are denoted by 37 , 38 and 39 , respectively.

The cleaning unit 8 comprises a cleaning blade 81 and a fur brush 82. These components are kept out of contact with the light-sensitive element 1 during the image formation and then brought into contact with this element for stripping off the toner remaining on the light-sensitive element 1 after the image transfer, if the multicolor image has been produced on the photosensitive element 1 . Then the cleaning blade 81 separates from the photosensitive element 1 , followed by the fur brush 82 with a short delay. The fur brush 82 is used to remove the toner left on this after the cleaning blade 81 has been moved away from the photosensitive element 1 .

In this multi-color image forming apparatus, the unloading is done in development of each color at each revolution of the photosensitive member 1, and the exposure for each picture must be used at each same place on the photosensitive member. 1 On the other hand, the photosensitive member 1 is not affected by any of the development units not involved in the image development, the individual electrodes, with the exception of the charging electrode 2 , by the paper feed device, the paper transport device and the cleaning unit 8 in this process.

The optical laser system 10 shown in FIG. 3 comprises a semiconductor laser oscillator 12 , a rotating polygonal mirror 35 and an f-θ lens 36.

The development devices to be used in the device according to FIG. 2 comprise four separate units, each of which may be of the same or similar design, as illustrated in FIG. 4 for the first development unit A. When rotating a magnetic roller or roller 41 with six N and S poles in the direction of arrow F while rotating a developer-conveying sleeve 42 in the direction of arrow G, a developer De is transported in the direction of arrow G. The thickness of the developer De transported is adjusted to form a developer layer by a layer rule blade 43 . In a developer reservoir 44 there is a circulating screw 45 for appropriately circulating and loosening the developer De. The toner T is supplied from a toner hopper 47 upon rotation of a toner supply roller 46 when the developer De contained in the reservoir 47 is depleted.

A clearance or gap is maintained between the sleeve 42 and the photosensitive member 1 so that the developer layer on the sleeve 42 does not come into contact with the photosensitive member 1 . Between the sleeve 42 and the element 1 , a DC power source 48 and an AC power source 49 for applying a development bias for performing reverse development are connected in series. The sleeve 42 , the screw 45 and the magnetic roller 41 are driven by a drive motor 50 .

With the developer to be used with this device either a two-component developer a toner and a carrier or a one-component developers deal with only one toner. Of the Two-component developers require an exact one position of the amount of toner relative to the carrier, but offers he the advantage that the friction charge control of Toner particles is easy to carry out. Especially the of a magnetic carrier and a non-magnetic existing toner needs two-component developers not a big part of a black magnetic  To contain material in the toner particles so that advantageously a color toner from a magneti material that does not cloud the color causes for the generation of a clear and crisp Color images can be used.

The two-component device to be used winder is preferably made of a magnetic Carrier and a non-magnetic toner which follow the specified type:

toner

• 1. Thermoplastic resin: binder 80-90% by weight
  Examples: polystyrene, styrene-acrylic copolymer, polyester, polyvinylbuyral, epoxy resin, polyamide resin, polyethylene, ethylene-vinyl acetate copolymer or mixtures thereof;
• 2. Pigment or dye: colorant 0-15% by weight
  Examples:
  Black: soot;
  Cyan: copper phthalocyanine or sulfonamide derivative dye;
  Yellow: benzidine derivative;
  Magenta: Rhodamine Black (Rhodamine B Lake) or Carmine 6B;
• 3. Charge control agent: 0-5% by weight
  Positive toner: Mainly an electron donor dye such as nigrosine, alkoxylated amine, alkyl amide, chelate, pigmet or a quaternary ammonium salt;
  Negative toner: organic electron-receiving complex, chlorinated paraffin, chlorinated polyester, polyester with excess acid residues or chlorinated copper phthalocyanine;
• 4. Superplasticizer:
  Examples: colloidal or phosphoric or hydrophobic silicon dioxide, silicone varnish, metal soap or anionic surface-active agent;
• 5. Cleaning agent: (to prevent filming of the toner on the photosensitive member)
  Examples: metal salts of fatty acids, oxidized silica or a fluorine-based surfactant;
• 6. Filler: (To improve the surface gloss of the image and to reduce the raw material costs)
  Examples: calcium carbonate, clay, talc or pigment.

In addition to the specified substances, the developer can also a magnetic material to prevent a Fogging and a toner dispersion or ver scatter included.

Powder of ferriferrooxide are suitable as magnetic powder, γ-iron oxide, chromium dioxide, nickel ferrite or an iron alloy, each with a particle size of 0.1-1 µm.  

At present, ferriferrooxide is most commonly used in an amount of 5-70% by weight for the toner. Although the resistance of the toner varies considerably depending on the kind and the amount of the magnetic powder, the magnetic material is preferably used in an amount of not more than 55% by weight to have a sufficiently high resistance corresponding to at least 10 ⁸ Ω. cm and preferably 10 ¹² Ω. cm to ensure. On the other hand, to ensure the color clarity, the color toner should contain 30% by weight or less of a magnetic material.

An adhesive resin such as wax, polyolefins, ethylene-vinyl acetate copolymer, polyurethane or rubber or rubber is selected as the resin suitable for a pressure-fixable toner so that this resin adheres with a force or a pressure of approximately 20 kg / cm ² can be plastically deformed on paper. Encapsulated toner can also be used.

The toner can be made from the substances listed above a known process or be prepared.

To create a perfect image with the Device should be in terms of toner the desired resolution is usually a weight averaged particle diameter of about 50 µm or own less. In the present case it is the toner particle diameter basically no restrictions subject, but it should with respect to toner dispersion and conveyability in the range of 1-30 µm lie. In the described embodiment the toners of the four different colors have a weight average particle diameter of 10 µm.  

Is the weight average particle diameter it is a size that uses a conventional Measuring or counting device is determined.

carrier

The carrier basically corresponds to the above, the toner-forming substances. For playback finer Dots or lines or to improve gradation the carrier particles can preferably be made of magnetic Particles and a resin or synthetic resin exist for example, a system dispersed in resin magnetic powder and resin or synthetic resin or else magnetic particles coated with a resin and preferably rounded particles of a weight average Particle diameter of 50 microns and preferably of 5-30 µm. In the illustrated embodiment for all four colors carrier particles of a weight average particle diameter of 50 microns used.

In order to prevent the charges embossed by the prestress from penetrating into the carrier particles and hindering the proper image formation by the carrier particles being able to adhere to the lateral surface of the image sensor and thus the prestress not being sufficiently impressed, the carrier can have an insulating resistance of 10 ⁸ Ω . cm or more, preferably 10 ¹³ Ω. cm or more and particularly preferably from 10 ¹⁴ Ω. cm or more in the above particle diameter.

The carrier having the specified grain size is produced from the magnetic material described in connection with the toner and a thermoplastic resin in such a way that either the magnetic material is surface-coated with the resin or particles are produced from a resin in which fine particles of the magnetic material are dispersed, and the diameter of the particles thus produced is selected by means of a known means for classifying according to the mean diameter. In order to improve the circulation of the toner and the carrier and the conveyability of the developer and to improve the charge controllability of the toner so as to make it resistant to agglomeration of either the toner particles or the toner and carrier particles, the carrier particles are preferably rounded off. These rounded magnetic carrier particles are obtained in such a way that the roundest possible magnetic particles are selected and coated with the resin, for which purpose the finest possible magnetic particles are used and the dispersed resin particles are rounded off with hot air or hot water, or rounded dispersed resin particles immediately after the spray drying process be generated. The inherent resistances of the toner and the carrier are measured in the following manner. In particular, the resistances are determined by compressing the particles in a container with a cross-sectional area of 0.50 cm ² by tapping, then loading the compressed particles with 1 kg / cm ³ (or kg / cm ² ) and between the load and a voltage is applied to the bottom electrode which generates an electric field of 10 ² -10 ⁵ V / cm, whereupon the magnitude of a current flow is read and a predetermined calculation is performed. The carrier particle layer has a thickness of approximately 1 mm.

The development process is detailed below described. The development can be done with immediate  Friction contact made with a magnetic brush be led, but is preferred from at least the second development a non-contact or contact free development process in which the Developer layer on a developer carrier other than rubbing contact with the outer surface of the photosensitive Elements is held so that damage or Impairment of an already created toner image is prevented. With this non-contact development an alternating electrical field is moved in one Development area generated so that development without friction between the photosensitive Element and the developer layer are carried out can. This procedure is he closer in the following purifies.

In the repeated development processes using said alternating electric field, development can be repeatedly carried out on the photosensitive member on which the toner image has already been formed; the toner image generated on the photosensitive element in a previous process step is disturbed in the subsequent development, unless suitable development conditions are selected. On the other hand, in this case, the toner attached to the photosensitive element can also be returned to the next developer carrier and thus brought into the development unit used in the next step with a developer of a different color, which results in the problem of color mixing. To solve this problem, the development process is carried out in principle in such a way that the developer layer on the developer carrier does not come into contact with the photosensitive element. For this purpose, the space or gap between the image sensor and the developer carrier is set to a size which exceeds the thickness of the developer layer in the development region on the developer carrier (provided there is no potential difference between them). Experiments have shown that in this case there are perfect development conditions for the complete elimination of the problem mentioned and the individual images are produced with a satisfactory image density. It has been shown that under these conditions it is difficult to produce a perfect image even if the gap d (in mm) between the image sensor in the development area and the developer carrier and the magnitudes of the amplitude V _AC and the frequency f (in Hz) the AC component of the development bias for generating the alternating electric field as such (by themselves) and that these parameters are closely related.

With the multi-color image forming apparatus shown in Fig. 2, tests were carried out to examine the influences of the parameters such as voltage and frequency of the AC voltage component of the development bias on the developing unit B in the event that a two-color toner image was formed by the developing units A and B. .

The development units were used for development A and B used in the order given.

In the Ent contained in the development unit B. winder De it was a magnetic One component developer who by mixing and Powdering 70% by weight of a thermoplastic  Resin, 10% by weight of dye (i.e., carbon black), 20% by weight of one magnetic material and a charge control agent with adjustment to an average particle diameter water of 15 microns and by adding a flow agent, such as Silicon dioxide was produced. The amount of charge was adjusted by means of the charge control substance.

The tests were carried out with changes in the specified conditions; the results can be evaluated according to FIG. 5 in relation to the amplitude E _AC and the frequency of the intensity of the electrical alternating voltage field.

In Fig. 5, A is an area in which an uneven development may occur, B an area in which the influence of the AC component does not appear, and C an area in which a toner image which has already been formed can be destroyed, and denoted by D and E areas in which the influence of the AC voltage component appears with a satisfactory development density and without destroying or impairing the toner image already formed; area E is the most preferred area.

These results show that amplitude and frequency of the electrical alternating voltage field within a expedient range must be in order after following development step a later one Develop toner image with appropriate density without previously in a previous development step toner image formed on the photosensitive member to affect.

From the experimental results described, it can be concluded that a subsequent development with a wall-free density and without disturbing or impairing the toner image already formed on the photosensitive element can be carried out if the development is carried out in such a way that it satisfies the following condition:

0.2 ≦ V _AC / (d. F) ≦ 1.6

This applies in the event that the amplitude and frequency of the AC component of the development bias are denoted by V _AC (in V) or f (in Hz) and the gap or space between the photosensitive element 1 and the sleeve 42 by d (in mm) . In order to achieve a sufficient image density and to prevent impairment of the toner image generated in the previous step, the following condition should preferably be observed:

0.4 ≦ V _AC / (d. F) ≦ 1.2

Of these areas, the following range should preferably be adhered to, in which a slightly weaker electric field than that which saturates the image density is maintained:

0.6 ≦ V _AC / (d. F) ≦ 1.0

When the frequency f of the AC component is on 200 Hz or higher is set to be unequal moderate development due to the AC component to prevent and if a rotating magnetic roller as Device for supplying the developer to the photosensitive element is used, the Frequency of the AC voltage component preferably  500 Hz or higher set to the influences of the Turn off bumps or blows caused by the AC component and the rotations of the magnet roller are caused.

Subsequently, similar tests were carried out using a two-component developer on the device according to FIG. 2. The developer De contained in the developing unit B is a two-component developer composed of a magnetic carrier and a non-magnetic toner; the carrier was produced by dispersing fine iron oxide particles in a resin for setting such physical properties that there was an average particle diameter of 20 μm, a magnetization of 30 EME / g and a specific resistance of 10 ¹⁴ Ω. cm result. For the production of the toner, a small amount of a charge control agent was added to 90% by weight of a thermoplastic resin and 10% by weight of a pigment or dye (for example carbon black) while setting an average particle diameter of 10 μm. To obtain the developer De, the toner was mixed with the carrier in a ratio of 20% by weight to 80% by weight. The toner was charged by friction with the carrier negative.

The development unit B contained a two component developer for yellow development. The Development units A and B were given in the Sequence used for development.

The tests were carried out under variation of the specified conditions; the results can be evaluated according to FIG. 6 with regard to the relationship to the amplitude E _AC and frequency f of the intensity of the electrical AC voltage field.

In Fig. 6, A is an area in which an uneven development is most likely to occur, B is an area in which the influence of the AC component does not appear, and C is an area in which the toner image already formed is destroyed or can be impaired, and denoted by D and E areas in which the influence of the AC voltage component occurs with satisfactory development density and without impairing the already generated toner image; area E is the most preferred area.

These results show that amplitude and frequency of the electrical alternating voltage field within a expedient range must be a subsequent or subsequently generated toner image with flawless To develop density without doing that in the previous step toner image formed on the photosensitive member to affect.

As previously described, it can be concluded from the test results given that the following development can be carried out with perfect density and without impairing the toner image already formed on the photosensitive element, if the development takes place under the following conditions:

0.2 ≦ V _AC / (d. F)
[(V _AC / d) - 1500] / f ≦ 1.0

Here again, the amplitude and frequency of the AC component of the development bias are denoted by V _AC (V) or f (Hz) and the gap or space between the photosensitive element 1 and the sleeve 42 is denoted by d (mm). In order to achieve a satisfactory image density and to prevent the toner image generated in the previous step from being adversely affected, the following condition is preferably met:

0.5 ≦ V _AC / (d. F)
[(V _AC / d) - 1500] / f ≦ 1.0

If the following conditions are met under these relationships or conditions, an even clearer multi-color image can be obtained after several operations without any cloudiness and without the introduction of a toner of a different color into a developing unit used below:

0.5 ≦ V _AC / (d. F)
[(V _AC / d) - 1500] / f ≦ 0.8

In the event that the frequency f of the AC component, as in the case of the one-component developer, is set to 200 Hz or higher to prevent uneven development due to the AC component, and the rotating magnetic roller for transferring the developer to the photosensitive member 1 is used, it has been shown that the frequency of the AC component should be set to 500 Hz or higher in order to eliminate the influences of the bumps or blows caused by the AC component and the rotations of the magnetic roller.

Although an image forming method is exemplified above, the methods given below can each be used alone or in any combination with one another for the successive developments for developing toner images with a constant density that are successively produced on the photosensitive element 1 without affecting what is already on the element 1 use the generated toner image even more advantageously:

• 1. A process in which successive toner larger amounts of charge are used;
• 2. a method in which the amplitude is continuously the intensity of the electric field AC component of the development bias is reduced; and
• 3. a procedure in which the frequency of the change stress component of the development bias is progressively increased.

More specifically: the larger charge-carrying toner particles are more influenced by the electric field. Therefore, if toner particles with large amounts of charges were attached to the photosensitive member 1 in the first development, these toner particles can jump back to the developer carrier sleeve. This is prevented in the method mentioned under 1. that for the first or initial development toner particles of smaller amounts of charge are used ver. With the method mentioned under 2. the same phenomenon can be prevented by weakening the electric field more strongly in each subsequent development process. For the weakening of the electrical field, a progressive decrease in the voltage of the AC component and an increase in the gap d between the photosensitive element 1 and the sleeve 42 are available . In the method mentioned under 3, the toner particles are prevented from jumping back by the light-sensitive element as the frequency of the AC voltage component increases with each repetition of the development processes. The methods given under 1, 2 and 3 above are each effective per se, but they are even more effective if, for example, they are combined with one another in such a way that the charge sizes of the toner increase sequentially and the AC bias during the repetitions of the development processes can be reduced sequentially. When using the three methods mentioned, a perfect image density or a perfect color balance can be achieved by setting the DC bias voltages accordingly.

The multi-color image forming apparatus of Fig. 2 operates in accordance with the timing chart of Fig. 7. During the image exposure or stamping, the control is carried out such that the development bias, the motor for driving the development sleeve, the magnetic roller and the circulating screw, or the individual discharge electrodes, such as the charging electrodes, are neither switched on nor off. This control takes place by means of conventional sequence control according to a program on a time series basis in a predetermined sequence for actuating the specified individual sections or components in accordance with this program.

The yellow, magenta, cyan and Black components sequentially turned on from image storage give. The imaging conditions are as follows set:  

Image sensor:

Photosensitive layer: a-Se
Drum diameter: 120 mm
Linear speed: 220 mm / s

Surface potential:

Charge potential: +700 V
Potential in the exposed section: 0 V

Imaging conditions:

Light source: semiconductor laser
Wavelength: 700 nm
Recording density: 12 dots / mm

Developing device:

Sleeve: Made of non-magnetic, stainless steel; Linear speed 220 mm / s
Magnet: 12 poles; Speed 1000 / min
Magnetic flux density: max. 700 gauss on the sleeve surface

Developer:

Carrier: Specific resistance 10 ¹⁴

Ω. cm or more; Magnetic powder in one Resin system dispersed; middle Particle diameter 20 µm; Magnetization 30 E.M.E./g

Toner:

Yellow: resistivity 10 ¹⁴

Ω. cm or more; average particle diameter 10 µm; average amount of charge 10 µC / g (or toner concentration = 20% by weight)
Magenta: Specific resistance 10 ¹⁴

Ω. cm or more; average particle diameter 10 µm; average amount of charge 11 µC / g or toner concentration = 20% by weight
Cyan: Specific resistance 10 ¹⁴

Ω. cm or more; average particle diameter 10 µm; average amount of charge 11 µC / g or toner concentration = 20% by weight
Black: resistivity 10 ¹⁴

Ω. cm or more; average particle size knife 10 µm; average amount of charge 12 µC / g or toner concentration 20% by weight

Development conditions:

Development biases:
A (Y) + 500 VDC; 1.5 kV (RMS value) AC voltage of 2 kHz;
B (M) + 550 VDC; 1.2 kV (RMS value) AC voltage of 2 kHz;
C (C) + 600 VDC; 1.0 kV (rms value) AC voltage of 2 kHz;
D (K) + 600 V DC; 0.8 kV (rms value) AC voltage of 2 kHz;

Development order: Y → M → C → K

Other operations:

Transmission: corona transmission (with pre-transmission)
Fixation: Using a heating roller
Cleaning: using a blade and fur brush.

When performing multi-color image generation among the above conditions can always be stable or consistently good recording image achieve without any image data interference.

As indicated, in the multi-color image forming apparatus shown in Fig. 2, the image data is input from the image memory; however, this data can also be provided by converting the original image into electrical signals using a solid-state image pickup element or by transmitting electrical signals from another device.

A second embodiment is described below ben.

In FIGS. 8 to 10, the symbol To denotes a time range or a time band in which the area of the image recorder not charged by the charging unit 2 according to FIG. 2 passes through a development area K (cf. FIG. 4); the symbol Tv represents a time range in which the image-free charged area of the image sensor 1 has been charged by the charging unit 2 but has not yet been exposed to the image and passes through the development area K; the symbol Ti represents a time range in which the image-bearing area of the image sensor 1 carrying an image passes through the development area K; the symbol Tv 'represents a time range in which an image-free area following the image area passes through the development area K; and the symbol To 'represents a time range in which the non-charged area charged by the charging unit 2 runs through the development area K. FIG. 8 also illustrates an example in which a DC voltage is applied first in the time range or time band Tv; then an alternating voltage of a constant period with gradually decreasing amplitude is superimposed; the imaging region of the image sensor 1 passes through the state in which the amplitude of the alternating voltage reaches a predetermined size; the bias voltage consisting of superimposed DC and AC voltages is maintained during the time period Ti; the amplitude of the alternating voltage is damped or weakened in order to return to the application of only the direct voltage when the time range Tv 'is reached; and the application of the DC voltage is interrupted or ended before the uncharged area passes through the development area K. If the unidirectional electric field is generated in this way before the arrival of the imaging area in the development area and the vibrating electric field is gradually strengthened to ensure the predetermined development conditions, no interference occurs, so that the latent image is always in the normal manner is generated to maintain the predetermined vibrating electric field as the imaging region passes through the development region. In this way, a clear or sharp toner image can be developed without any obfuscation and with a reduction in power consumption.

FIG. 9 illustrates an example in which a half-way rectified AC voltage is superimposed on the DC voltage instead of gradually increasing and decreasing the amplitude of the AC voltage in the example of FIG. 8. With the example shown in FIG. 9, results similar to those in the example shown in FIG. 8 can be achieved.

Fig. 10 illustrates an example in which the unidirectional electric field is generated by application of a pulsating voltage generated by half-way rectification of the superposed voltage for development instead of the unidirectional electric field by applying only an identical or the same polarity by applying only the DC voltage beforehand, as in the examples of FIGS. 8 and 9; hereby the same effects are achieved as with the gradual increase and decrease of the alternating voltage amplitude according to FIG. 8 and the superimposition of the half-way rectified alternating voltage according to FIG. 9. In the manner shown in FIG. 10, the same effect can thus be achieved as with the Examples according to FIGS. 8 and 9.

The embodiment of FIG. 8 can be implemented as a bias supply or source 11 by means of the circuit according to FIG. 11. If a switch 13 is flipped over to a contact in which an oscillator is not put into operation, a DC voltage is applied to the developer carrier or the sleeve 42 . When the oscillator is put into operation after a movable short-circuit contact 14 on a secondary winding is shifted up to the position in which the contact 14 is connected to the fully short-circuited point, the DC voltage becomes an AC voltage with gradually increasing Amplitude superimposed. When the movable short-circuit contact 14 is returned from the position in which the amplitude of the AC voltage reaches a predetermined size, the amplitude of the AC voltage decreases to 0. When the switch 13 is flipped to the contact b, the application of the bias voltage to the developer carrier 42 is ended. Instead of using the movable contact 14 on the secondary winding, the amplitude of the AC voltage can also be gradually increased or decreased on the oscillator side.

The embodiment of FIG. 9 can be realized with the circuit shown in FIG. 12 as a bias voltage supply 11 . If the switch 13 is placed on the contact a without actuating the oscillator, the developer carrier 42 is impressed with the DC voltage. If the oscillator is put into operation with a closed switch 15 of the rectifier, a half-way rectified AC voltage is superimposed on the DC voltage. When the switch 15 is opened, the beat voltage from the DC voltage and the AC voltage is applied. Then, when the switch 15 is closed again, the state is restored in which the voltage at which the DC voltage is superimposed on the half-way rectified AC voltage can be applied. Takes place before voltage application of FIG. 9 the operation of the oscillator and then by folding Be termination of the switch 13 b to the contact.

For the exemplary embodiment according to FIG. 10, the circuit according to FIG. 13 can be used as a bias voltage supply 11 . If the oscillator works while the switch 15 of the rectifier is switched to contact b and the switch 13 is connected to contact a, a pulsating bias of a unidirectional polarity is applied to the developer carrier (ie the sleeve) 42 , which is caused by rectification the superimposed voltage is generated from the direct voltage and the alternating voltage. When the switch 15 is then opened, the bias voltage consists of the superimposed voltage of the direct voltage and the alternating voltage. When the switch 15 is closed again, there is a return to the pulsating voltage, the application of which is interrupted or ended by switching the switch 13 to the contact b.

The operations described above are illustrated in the timing diagram of FIG. 14.

In this example, the developer carrier or sleeve 42 ( FIG. 4) is rotated by the DC motor 50 ( FIG. 4), the speed of which can be changed. Referring to FIGS. 9 to 11 the tension in the time band or time Tv is continuously or stepwise increased, hold upright a constant voltage to ensure a constant speed in the time domain Ti and the voltage fed back continuously or stepwise from 0 of 0 when the transition in the time range Tv 'takes place. In the time chart of FIG. 14, the change of the impressed voltage to the motor on time-series basis are the changes in the bias same.

The different from the above conditions Conditions are the same as the previous one wrote first embodiment.  

In the manner described, stable or consistently an excellent one Recording image can be obtained.

In both embodiments, the electrical Changes in the imaging device to voltage changes stanchions. For changes from other electrical Sizes as the voltage can be based on a control of the Charging electrodes with the current changes instead of the Switching the charging electrodes on and off or by Regulation of the speed of the developer Sleeve or the frequency by means of an AC motor be resorted to.

Claims (7)

1. Color image forming device with:

• 1. an image sensor ( 1 ),
• 2. a charging device ( 2 ) for loading the image recorder,
• 3. an exposure device ( 10 ) for exposing the image sensor ( 1 ) in order to separately generate a first and second latent image thereon during several revolutions of the image sensor,
• 4. a first developing unit (A) for developing the first latent image to form a first toner image with a first color toner, the first developing unit (A) having a first developing sleeve ( 42 ) and one in the first developing sleeve ( 42 ) has the first magnetic roller ( 41 ),
• 5. a first drive unit ( 11 ) for driving the first development sleeve ( 42 ) or the first magnetic roller ( 41 ) to generate the first toner image,
• 6. a second developing unit (B) for developing the second latent image to form a second toner image with a second color toner, the second developing unit (B) having a second developing sleeve ( 42 ) and one provided in the second developing sleeve ( 42 ) second magnetic roller,
• 7. a second drive unit for driving the second development sleeve ( 42 ) or the second magnetic roller ( 41 ) in order to generate the second toner image,
• 8. a bias application device ( 48 , 49 ) for applying a development bias to the first and second development sleeves,
• 9. wherein the image sensor ( 1 ) is rotated to overlay the second toner image over the first toner image by several revolutions, and each of the development units is controlled by the corresponding control unit ( 11 ) for each revolution of the image sensor so that each of the first and second toner images are formed on the image sensor during one revolution of the image sensor,
• 10. a transfer device ( 4 ) for transferring the multicolor images to a recording medium (P) and
• 11. A control device which controls the first and second control units such that between the end of the exposure to form the first latent image and the start of exposure to form the second latent image, the control of the first development sleeve or the first magnetic roller is interrupted and the control the second developing sleeve or the second magnetic roller is started.

2. Color image forming device with:

• 1. an image sensor ( 1 ),
• 2. a charging device ( 2 ) for loading the image recorder,
• 3. an exposure device ( 10 ) for exposing the image sensor ( 1 ) in order to generate a first and second latent image separately during several rotations of the image sensor,
• 4. a first developing unit (A) for developing the first latent image to form a first toner image with a first color toner, the first developing unit (A) having a first developing sleeve ( 42 ) and one in the first developing sleeve ( 42 ) has the first magnetic roller ( 41 ),
• 5. a second developing unit (B) for developing the second latent image to form a second toner image with a second color toner, the second developing unit (B) having a second developing sleeve ( 42 ) and one provided in the second developing sleeve ( 42 ) second magnetic roller,
• 6. a bias application device ( 48 , 49 ) for applying a development bias to the first and second development sleeves,
• 7. wherein the imager ( 1 ) is rotated several turns to overlay the second toner image over the first toner image, and the bias applying means applies the developing bias to each developing sleeve for each revolution of the imager so that each of the first and second toner images during one revolution of the image sensor is formed on the image sensor,
• 8. a transfer device ( 4 ) for transferring the multicolor images to a recording medium (P) and
• 9. A control device which controls the biasing means ( 48 , 49 ) such that between the termination of exposure to form the first latent image and the start of exposure to form the second latent image, the application of the development bias to the first development sleeve interrupted and the application of the development bias to the second development sleeve is started.

3. Color image forming apparatus according to one of claims 1 or 2, in which the exposure device ( 10 ) generates the latent image on the basis of image data. 4. A color image forming apparatus according to claim 3, wherein the exposure device ( 10 ) emits image exposure light for illumination. A color image forming apparatus according to claim 1 or 2, wherein the second developing unit (B) develops the second latent image on the image pickup ( 1 ) on which the first toner image is recorded so as to form the multicolor image, and the transfer device ( 4 ) transfers the multicolor image from the image sensor ( 1 ) to the recording medium. 6. Color image forming apparatus according to one of claims 1 or 2, in which at least the second development unit (B) the second latent image after a non-contact Development method developed. 7. Color image forming apparatus according to one of claims 1 or 2, wherein the development bias of the bias application means ( 48 , 49 ) has a superimposed DC and AC voltage.