JP2768678B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an image forming apparatus used as a copying machine or a printer.

(Prior Art) As a device for copying a document, an electronic copying machine or a plate making / printing device is known. In general, an electronic copying machine is easy to set up for a copying operation and easy to handle. On the other hand, plate-making / printing machines can create originals from originals and repeat the transfer to recording paper using these originals. There is an advantage that the printing cost becomes lower as the number of sheets increases.

(Problems to be Solved by the Invention) The conventional plate making / printing apparatus has a high printing cost as compared with an electronic copier because the ratio of the cost of the original plate is large when the number of copies from the same original is about four or less, Since the process of making the master is required, it takes time and effort to set up the work. On the other hand, an electronic copying machine repeats processes such as charging, exposure, development, and static elimination each time one original is copied, so that even if the number of copies from the same original increases, the copying cost per sheet does not decrease. However, the copying speed is considerably slower than that of a printing press.

In order to cope with such a problem, an electronic copying machine has been put into practical use that can perform copying at a thinner speed for printing and that does not require a skillful operation or setup such as a printing machine. However, in order to further increase the copying speed, the electric power required for exposing the original, fixing the developer, or charging becomes extremely large, so that a normal commercial power supply cannot be used, or if the copying speed is increased, the developing speed and the like are increased. However, there is a problem that image quality is sacrificed due to excessive force.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus capable of copying a large number of clear sheets from the same document as in a printing machine by a simple operation similar to that of a conventional electronic copying machine.

[Structure of the Invention] (Means for Solving the Problems) According to the present invention, there is provided a latent image forming means (17) for forming an electrostatic latent image on an image carrier, and a first conductive member provided on the image carrier. A first developer image forming means (21) for supplying the magnetic developer, and a fixing means for fixing the developer image formed by the first developer image forming means (21) on the image carrier. (Four
0); magnetizing means (42) for permanent magnetizing the developer image fixed by the fixing means to form a master image; and supplying an insulating second magnetic developer to the image carrier. A second developer image forming unit (22), a charging unit (29) for charging the developer image formed by the second developer image forming unit (22), and a charging unit (29). Transfer means (31) for electrostatically transferring the charged developer image to a transfer-receiving material; moving the image carrier at a first speed or a second speed higher than the first speed; Supplying the second magnetic developer from the second developer image forming unit (22) to the electrostatic latent image formed by the latent image forming unit (17). A first image forming mode (copying mode) for forming an image by using the first magnetic developer Wherein this master image After forming the master image second
A second image forming mode (printing mode) for forming an image by supplying the second magnetic developer from the developer image forming means (22); When the formation mode is selected,
While moving the image carrier at a first speed, an electrostatic latent image is formed on the image carrier by the latent image forming means (17). After the developer is electrostatically attached, and a master image is formed by the first magnetic developer when the second image forming mode is selected,
While moving the image carrier at a second speed, the second magnetic developer is magnetically attached to the master image, and on the image carrier in the first and second image forming modes. The developer image to be formed is electrostatically transferred onto the material to be transferred by the charging means (29) and the transfer means (31), so that the second image forming mode is higher than the first image forming mode. Is also characterized in that an image is formed on the transfer material at a high speed. It should be noted that the reference numerals in this text are merely added to facilitate understanding of the invention, and do not limit the scope of rights.

(Operation) The apparatus of the present invention having the above configuration can be implemented in a print mode described below when a large number of copies are to be made from the same document. First, in the electrostatic latent image forming means, a latent image corresponding to a document image is formed on an image carrier. By visualizing this electrostatic latent image using a conductive first magnetic developer, a first developer image is formed. This developer image is fixed on the image carrier by, for example, fusion or the like,
Further, it is permanently magnetized by the magnetizing means to become a master image. Next, by performing development by magnetically attaching an insulating second magnetic developer using the magnetic force of the master image, a second developer image is formed.
The developer image is charged by a charging unit, and the charged developer image is electrostatically transferred to a transfer-receiving material such as recording paper. In the present invention, since the first magnetic developer having conductivity is used in the first developer image forming means, an edge effect at the time of development is suppressed, and a master image with extremely excellent image quality can be obtained.

Even after the second developer image is transferred to the recording paper, the master image remains on the image carrier as it is. When the same copy of the second and subsequent sheets is performed, the magnetic force of the master image is used again. The insulating magnetic developer is attached, and the developer image is transferred to a transfer member. By repeating the above steps, the same document can be copied any number of times. That is, in this print mode, once the master image is formed, the above-described step of forming the electrostatic latent image, the step of forming the first developer image, and the step of fixing the developer image on the image carrier No step is performed. Therefore, when a large number of copies are made using this print mode, power can be saved, and the copy speed in the print mode can be much faster than in the first mode (copy mode).

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

The image forming apparatus 1 shown in FIG. 1 has an original mounting table 3 on the upper surface of a housing 2 and an openable / closable original presser 4.
The document A placed on the document table 3 is photoelectrically read by a document reading means 5 using a known scanner or the like.

A drum 7 is rotatably provided inside the housing 2. The drum 7, by a not shown drive mechanism functions as moving means, can be rotated in the drawing clockwise least speed v ₁ and the velocity v _2. Velocity v ₂ is several times to several tens of times faster than the speed v _1.

A photoreceptor belt 8 as an image carrier is provided on an outer peripheral portion of the drum 7. The photoreceptor belt 8 has a photosensitive layer 9 made of zinc oxide, which is a dielectric capable of forming an electrostatic latent image, as shown in FIGS. It makes one round around it. The photoreceptor belt 8 is moved every time a printing mode described below is performed.
The roll is fed out from the supply roll 10 onto the drum 7 by a predetermined size, and the used portion is taken up by the take-up roll 11.
It is designed to be wound up.

A scorotron-type corona charger 13 disposed opposite to the outer peripheral portion of the drum 7 charges the photosensitive belt 8 uniformly at -300 to -500 volts.

The exposure device 15 equipped with the laser scanner 14 transmits the image information read by the reading means 5 and converted into an electric signal to the photosensitive layer 9 via an optical member 16 such as a mirror or a lens.
By exposing upward, an electrostatic latent image corresponding to image information is formed on the photosensitive layer 9. The charger 13 and the exposure device 15
Constitutes the electrostatic latent image forming means 17.

Further, a first developing device 21 as a first developer image forming device and a second developing device 22 as a second developer image forming device are arranged along the circumferential direction of rotation of the drum 7.

The first developing device 21 employs a so-called conductive magnetic one-component developing method, and a first magnetic developer 23 which is a carrierless toner.
Is housed. The magnetic developer 23 is made of fine powder such as barium ferrite or γ-Fe ₂ O _{3 having} excellent magnetization characteristics. In short, any magnetic developer that can easily be permanently magnetized in a magnetic field by the following magnetizing device 42 is used. For this reason, a magnetic powder having high magnetization characteristics other than the above may be used. The magnetic developer 23 is conveyed to the photoreceptor belt 8 side with the rotation of the magnet sleeve 24 and can be given a positive charge by frictional charging with the rotation of the sleeve 24.

The second developing device 22 contains a second magnetic developer 26. As the magnetic developer 26, a magnetic one-component toner having a triboelectric charging property and made of a magnetic fine powder such as Fe ₂ O ₄ having a large electric resistance and a small permanent magnetization is suitable. This developer 26
Is transported toward the photoreceptor belt 8 with the rotation of the magnet sleeve 27, and can be given a positive charge by frictional charging with the rotation of the sleeve 27.

Further, a pre-transfer corona charger 29 functioning as a charging unit in the present invention, a paper supply unit 30, and an endless transfer belt 31 as a transfer unit are arranged along the rotational direction of the drum 7. The charger 29 preferably has a negative polarity so that the charge remaining on the photosensitive layer 9 can be erased by light (static light). The paper supply unit 30 synchronously sends out a recording paper 33 as an example of a material to be transferred laminated on the recording paper storage unit 32 between the transfer belt 31 and the photosensitive belt 8 via a guide 34. It is.

The transfer belt 31 is formed by laminating a dielectric film such as polyester having a thickness of about 20 to 40 μm on the surface of a belt body made of a conductive material, and has a polarity opposite to that of the corona before transfer by the charger 29. A bias voltage of 1000 volts is applied. A well-known heat roller type fixing device 36 and a paper discharge table 37 are arranged on the transfer end side of the transfer belt 31. Instead of applying the bias voltage to the transfer belt 31, the recording paper 33 may be charged by corona discharge.

Further, a fixing flash 40 using a xenon lamp or the like as an example of a fixing unit is provided along the rotation circumferential direction of the drum 7.
And a static elimination lamp 41 for removing residual charges on the photosensitive layer 9 and a magnetizing device 42 functioning as a magnetizing means in the present invention.

Next, the operation of the image forming apparatus 1 having the above configuration will be described. This apparatus 1 can copy the document A in any one of a print mode suitable for copying many sheets from the same document and a copy mode suitable for copying a few sheets.
First, the print mode will be described.

Along with initiating the reading of the document A by the document reading unit 5, the photosensitive belt 8 and the drum 7 while rotating in the illustrated clockwise direction at a speed v ₁ in unison, charging as shown in Figure 3 The photosensitive layer 9 of the photosensitive belt 8 is uniformly negatively charged by the unit 13. Reading means 5
The image information read photoelectrically by means of is converted into a signal by a known means, and the photosensitive layer 9 is irradiated with light as an image signal by a laser scanner 14, whereby an electrostatic latent image is formed one after another. (FIG. 4).

The electrostatic latent image thus obtained is developed by passing through the first developing device 21. That is, in the first developer image forming step, as shown in FIG. 5, the first magnetic developer 23 having a positive charge is electrostatically attached to the negative charge of the photosensitive layer 9. As a result, a developer image corresponding to the image is obtained.

Further drum 7 and the photoconductor belt 8, as well is rotated at a speed v ₁ as far as the fixing flash 40, fused instantaneously photosensitive layer 9 by heat ray is irradiated by the fixing flash 40 (FIG. 6 ). That is, through this fixing step, a master image 45 using the first magnetic developer 23 is obtained.

The master image 45 thus fixed is moved to the magnetizing device 42 together with the photosensitive layer 9 as shown in FIG. The magnetic head 46 is provided over the entire effective width of the photoreceptor belt 8. As schematically shown in FIG. 11,
The fixed master image 45 is sequentially magnetized in the moving direction of the photoconductor belt 8. Since the photosensitive layer 9 itself is a non-magnetic material, it is not magnetized, and only the master image 45 is magnetized. Therefore, since the magnetic head 46 only needs to apply a magnetic field of the same polarity in the width direction of the photosensitive belt 8,
A long but simple structure can be used.

As described above, during the first rotation of the drum 7, a magnetized pattern is formed as a magnetized master image, that is, a magnetic latent image. Subsequently Although the drum 7 is rotated by the second rotation onwards is rotated at high speed at the speed v _2, transfer is made to the development and the recording sheet 33 by the second developing device 22.

That is, when the master image 45 magnetized by the above-described process moves to the position of the second developing device 22, the second magnetic developer 26 reduces the magnetic force of the master image 45 as shown in FIG. The developer 26 is attracted and adheres to the surface of the master image 45. Thus, a second developer image is formed. Since the developer 26 is attracted to the master image 45 by magnetic force,
It is not necessary to provide a charge. After the second development, a negative charge is given by receiving a pre-transfer corona discharge by the charger 29 (FIG. 9).

Recording paper 33 sent one by one from the paper supply unit 30
Is transferred between the photosensitive belt 8 and the transfer belt 31 while being transferred by the transfer belt 31 in synchronization with the rotation direction of the drum 7. Since a bias voltage having a polarity opposite to that of the pre-transfer corona is applied to the transfer belt 31, the second developer 26 is electrostatically transferred to the recording paper 33 one after another. Recording paper after transfer 33
Is transported to the heat roller type fixing device 36 as the transfer belt 31 travels, and is heated and pressurized to fix the image.

If the second developer 26 can be charged sufficiently during development by using a toner having frictional charging property, the corona discharge before transfer by the charger 29 can be omitted. However, in order to reliably perform electrostatic transfer in a short time, such as when high-speed transfer is required,
It is preferable that sufficient charge be given to the developer 26 by performing a pre-transfer corona discharge.

In order to continue copying the second and subsequent sheets from the same original in this print mode, the second developer image forming step (eighth
Figure), corona discharge before transfer (Fig. 9) and transfer process (Fig. 9).
By repeating 10 view) at the speed v _2, it is capable of replicating the same content as the any number of images. That is, once the master image 45 is formed and magnetized, the charging process (third step) is performed.
Figure), exposure step (FIG. 4), first developer image forming step (FIG. 5), fixing step (FIG. 6), and magnetizing step (FIG. 7).
Need not be performed at all. The electric power required for charging, image exposure, and the like can be applied to the fixing device 36. Thus not only attained power saving, by after forming a master image can perform print mode at a high rotational speed v _2, can significantly speed up the copying speed. Also, as the number of copies from the same document increases, the cost per sheet decreases. This rotation speed v ₂ corresponds to the second speed in the present invention.

In order to prevent the photosensitive layer 9 from being charged by the residual charge after the second rotation of the drum 7 in the above print mode, it is better to turn on the charge removing lamp 41. When a plurality of copies of one original in the print mode are completed, the photoreceptor belt 8 is taken up by the take-up roll 11 by a size corresponding to the size of the fixed master image 45, and an unused new length is taken up. It is paid out on the drum 7.

Next, a copy mode suitable for copying a small number of sheets will be described.

The copy mode differs from the print mode in that a master image is not formed. In this copying mode, the drum 7 is rotated at a speed v ₃ than the speed v _1. However, the speed v ₃ is slower than the speed v ₂ at the time of the printing mode. This rotational speed v _3, which corresponds to a first rate referred to in the present invention.

As in the case of printing mode, the reading of the document A by the reading means 5 due to be started, the photoreceptor belt 8 and the drum 7 is rotated in the illustrated clockwise direction at a speed v ₃ in unison, third As shown in the figure, the photosensitive layer 9 is uniformly charged by the charger 13. As in the predetermined potential can be obtained even when the rotational speed v ₃ of the drum 7 is faster than v _1,
The voltage of the charger 13 and the like are adjusted according to the rotation speed of the drum 7.

The image information read by the reading unit 5 is converted into a signal, and the photosensitive layer 9 is irradiated with light as an image signal by the laser scanner 14 to form an electrostatic latent image one after another (FIG. 4). The electrostatic latent image thus obtained is visualized by passing through the second developing device 22. In this copy mode, development using magnetic force cannot be performed. Therefore, as shown in FIG. 12, the second magnetic developer 26 which is positively charged by frictional charging or the like is applied to the photosensitive layer 9.
A developer image corresponding to an image is obtained by electrostatically adhering to a negative charge.

Subsequently, the drum 7 is rotated and subjected to corona discharge before transfer by the charger 29 as shown in FIG. 13 to be given an electric charge. Then, as shown in FIG.
Transferred to 33. The recording paper 33 after the transfer is fixed by the heat roller type fixing device 36 in the same manner as in the print mode, and then is discharged onto the paper discharge tray 37.

As shown in FIG. 15, if a voltage is applied to the transfer belt 31 or a corona discharge is performed with a polarity such that the recording paper 33 is negatively charged, the corona discharge before transfer (the thirteenth
The developer 26 can be transferred to the recording paper 33 without performing the process shown in FIG.

The developer 26 remaining on the photosensitive layer 9 after the transfer is removed by a discharging lamp.
After the charge is removed by 41, the drum 7 is further removed by the magnetic brush effect in the second developer 22 and is collected by the second developer 22 during the next one rotation. In other words, the copy mode of the apparatus 1 is a two-rotation, one-copy method using magnetic brush cleaning, in which a process such as formation, development, and transfer of an electrostatic latent image is performed at the first rotation of the drum 7, and at the second rotation. The photosensitive layer 9 is cleaned. In this copying mode, the photosensitive belt 8 has the same photosensitive surface, for example.
It is used repeatedly about 1000 times, and when it reaches the specified number of times, it is wound up by the winding roll 11 by a predetermined length,
A new unused size is fed out onto the drum 7 and is ready for use.

As described above, in the device 1 of the present embodiment, the first developer 23 having conductivity and the second developer 26 having insulating properties are used. The reason for using the conductive toner for the first developer 23 is that the edge effect is suppressed by using the conductive toner when forming a master image in the print mode,
This is because a very high-quality master image can be obtained. The first developer 23 may be conductive since it is attached on the insulating photosensitive layer 9. This developer 23
Is used to obtain the master image and has nothing to do with the actual copy color, so the color can be anything. Therefore, it is easy to select a material having easy magnetization.

On the other hand, the reason why the insulating toner is used as the second developer 26 is to transfer the developer 26 to the recording paper 33 by electrostatic transfer, and this developer 26 uses a high-resistance toner having excellent chargeability. Must be used.

In the above-described embodiment, zinc oxide is used for the photoreceptor belt 8. However, the present invention is not limited to this, and other dielectric materials such as other photoreceptor materials and a dielectric belt for electrostatic recording can be used.
In addition, the apparatus of the present invention exposes the photosensitive layer of the image carrier to light reflected or transmitted from a document obtained by irradiating the document with illumination light, via an optical member, instead of exposing the document by the laser scanner 14. Such a format may be used. The apparatus of the present invention can of course be used as a copying machine, but is also very effective when, for example, a large number of copies are made in a laser printer or the like.

[Effects of the Invention] As described above, according to the present invention, by setting the print mode when the number of copies is large, copying from the same original can be performed at high speed and at low cost. The first magnetic developer image fixed above is permanently magnetized to form a master image, and the magnetic force of the master image is used to magnetically attach a second magnetic developer to repeat copying. Therefore, there is no need to repeat the step of charging the master image every time copying is performed, and power saving and improvement in copying speed can be achieved. Since a clear master image can be obtained by using the conductive first magnetic developer as the master image forming material, an image having excellent image quality can be reproduced based on the master image.

In the present invention, there are a first mode (copying mode) in which a developer is directly adhered to a latent image for copying, and a second mode (printing mode) in which copying is performed based on a master image. In the first mode, the developer image is electrostatically transferred while the image carrier rotates at a higher speed than in the first mode. In addition, the developing conditions of the insulative developer (second developer) are changed in accordance with each of the above modes. It is used properly with a neutral developer. That is, since no master image is formed in the first mode, an image is formed by electrostatically attaching a charged insulating developer, and in the second mode, a magnetic master image is formed. High-speed transfer is performed by magnetically depositing an insulating developer, charging the insulating developer, and then transferring electrostatically. In the second mode, a conductive developer (first developer) is used when forming a magnetic master image. For this reason, a good master image can be formed,
High image quality and high-speed transfer can be compatible.

[Brief description of the drawings]

1 to 14 show an embodiment of the present invention. FIG. 1 is a sectional view schematically showing the internal structure of an image forming apparatus.
The figure is an enlarged view of the vicinity of the drum in FIG. 1, and FIGS.
Figures are side views each showing an image forming process in a printing mode in the order of steps, FIG. 11 is a plan view showing a part of a magnetizing device and a master image, and FIGS. 12 to 14 are image forming processes in a copying mode, respectively. FIG. 15 is a side view showing a part of the transfer order, and FIG. 15 is a side view when the polarity of the transfer belt is changed. 1 image forming apparatus, 5 document reading means, 7 drum, 8 photosensitive belt (image carrier), 9 photosensitive layer,
13 ... Charging device, 15 ... Exposure device, 17 ... Electrostatic latent image forming means, 21 ... First developing device (first developer image forming means), 22
... Second developing device (second developer image forming means), 23 first magnetic developer, 26 second magnetic developer, 29 corona charger before transfer, 31 transfer Belt (transfer means), 33 ...
... recording paper (transfer material), 40 ... fixing flash (fixing means), 42 ... magnetizing device, 45 ... master image.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/00 104 G03G 13/26-13/32 G03G 15/08 G03G 19/00

Claims (1)

(57) [Claims] A latent image forming means for forming an electrostatic latent image on an image carrier; a first developer image forming means for supplying a first magnetic developer having conductivity to the image carrier; Fixing means for fixing the developer image formed by the first developer image forming means on the image carrier; and forming a master image by permanently magnetizing the developer image fixed by the fixing means. Magnetizing means, second developer image forming means for supplying a second magnetic developer having insulating properties to the image carrier, and a developer image formed by the second developer image forming means A transfer unit that electrostatically transfers the developer image charged by the charging unit to a transfer target material; and a first speed or a speed lower than the first speed. Moving means for moving at a large second speed; A first image forming mode for forming an image by supplying the second magnetic developer from the second developer image forming means to the electrostatic latent image formed by the image forming means; And a second image forming mode in which an image is formed by supplying the second magnetic developer from the second developer image forming means to the master image after forming a master image with the magnetic developer. When the first image forming mode is selected, the latent image forming unit moves the image carrier at a first speed while the electrostatic latent image is formed on the image carrier by the latent image forming unit. Is formed, a frictionally charged second magnetic developer is electrostatically adhered to the electrostatic latent image, and when the second image forming mode is selected,
After forming a master image with the first magnetic developer,
While moving the image carrier at a second speed, the second magnetic developer is magnetically attached to the master image, and on the image carrier in the first and second image forming modes. The developer image to be formed is electrostatically transferred onto the transfer material by the charging unit and the transfer unit, so that the second image forming mode has a higher speed than the first image forming mode. An image forming apparatus for forming an image on the transfer material.