JP2852776B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method in which a transfer material of an image forming apparatus such as an electrophotographic copying machine is electrostatically supported and transported to transfer a toner image on an image carrier to a physical means. The present invention relates to an image forming apparatus having a transfer belt device for transferring the toner image onto the transfer material and then transferring the toner image to a fixing unit.

[Conventional technology]

FIG. 7 is a sectional view showing an embodiment of a conventional electrophotographic copying machine. In the figure, 10 is a photosensitive drum which is a drum-shaped image carrier, 20 is a charger for charging the peripheral surface of the photosensitive drum 10, 30 is an exposure device, 13 is an image exposure unit, 40 is a developing device, and 50 is a transfer material. Supply device, P is a recording paper as a transfer material, 16 is a transfer device as a transfer charger, 17 is a separator as a separation static eliminator,
Reference numeral 80 denotes a fixing device, 90 denotes a cleaning device, and 56 denotes a transport belt as transport means for the recording paper P.

The operation of the copying machine will be described. After the peripheral surface of the photoreceptor drum 10 is uniformly charged by the charger 20, the peripheral surface of the photoreceptor drum 10 is exposed by the image Form a latent image. Thereafter, the developing device 40 develops and visualizes the latent image to form a toner image. This toner image is transferred onto the recording paper P fed from the transfer material supply device 50 in a timely manner. This transfer is performed by applying a charge having a polarity opposite to that of the toner by the transfer device 16 from behind the recording paper P. After the transfer, a high voltage of AC is applied by a separator 17 to eliminate the charge, and the recording paper P is removed from the photosensitive drum 10.
More separated. The separated recording paper P is transported to the fixing device 80 by the transport belt 56, and the toner image is fixed and discharged outside the apparatus.

On the other hand, the photosensitive drum 10 to which the toner image has been transferred is cleaned by the cleaning device 90 to remove the toner remaining on the peripheral surface.

However, in the above configuration, the transfer unit 16 and the separator 17 are required to ensure the transferability and separation of the toner image.
The discharge efficiency must be adjusted to find the point that works best, and this discharge efficiency is greatly affected by the environment and the tolerance for reliability is narrow. The transferability is influenced by the charge of the recording paper P and the mechanical properties (stiffness, surface smoothness, curl, etc.) of the recording paper P, and these are the storage state of the recording paper P and the environment at the time of transfer ( (Temperature, humidity), etc., and it is difficult to always maintain a good state.

Further, when the drum diameter of the photosensitive drum 10 is large, the force for returning the recording paper P to the original flat state when the recording paper P is wound around the photosensitive drum 10 is smaller than that when the drum diameter is small, so that the toner image The recording paper P after the transfer of the recording paper P directly adheres to the photoreceptor drum 10 and is liable to cause a paper jam.

A belt-shaped transfer / transport apparatus shown in FIG. 8 is disclosed in U.S. Pat.

8, reference numeral 10 denotes a photosensitive drum which is a drum-shaped image carrier; 71, a transfer belt composed of a single-layer dielectric belt; 72, 73 rollers for supporting, extending, and rotating the transfer belt 71; 79 is a roller for guiding the recording paper P, 60 is a paper charger for performing corona discharge to attract the recording paper P to the transfer belt 71 by electrostatic force, and 16 is a toner image transferred from the photosensitive drum 10 to the recording paper P. A transfer unit 160, which is a charging unit for performing the transfer, is a transfer unit. With this configuration, the recording paper P can be firmly adhered to the transfer belt 71 and transported reliably, and excellent transfer efficiency and separation efficiency can be obtained.

The belt-shaped transfer / transport device is preferably a photosensitive drum.
This is a preferable apparatus in a color image forming apparatus in which a toner image is formed on the recording paper P and transferred onto the recording paper P at one time. In the color image forming apparatus, the diameter of the drum is increased because the toner image is superimposed on the photosensitive drum 10, and a sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. What is necessary is that if toner images are superimposed, the amount of adhered toner increases,
This is because a belt-type transfer / transport device is excellent in two points that a large transfer charge amount is required and a large transfer charge holding capacity is required.

[Problems to be solved by the invention]

However, in the transfer / transport device (transfer belt device) shown in FIG. 8, when the transfer belt 71 is released from contact with the photosensitive drum 10 and a certain amount of charge is present on the transfer belt (approximately 5 ×). 10 ^-5 c / m ² or more) When the contact is released, the potential of the transfer belt 71 rises sharply.
There is a problem that a spark discharge occurs between the photoconductor drum 10 and the peripheral surface of the photoconductor drum 10 and damages the photoconductor layer of the photoconductor drum 10.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an image forming apparatus that does not damage the photoconductor layer.

[Means for solving the problem]

The object is to form a multicolor toner image on the peripheral surface of the image carrier while providing a plurality of developing units of different color toners on the peripheral edge of the rotating image carrier. An image forming apparatus in which the transferred toner image is transferred onto recording paper conveyed by a transfer belt device, wherein the transfer belt device makes contact with a rotating transfer belt to contact and release contact with the image carrier. A release unit, and a transfer unit for transferring the toner image on the image carrier onto the recording paper by corona discharge, wherein the transfer belt keeps the image until the final developing unit of the developing unit develops the image. After the transfer belt is separated from the carrier and brought into contact with the transfer belt by the contact / release means, a corona discharge is performed by the transfer device to transfer a toner image onto a recording sheet adhered to and conveyed to the transfer belt. Is line After the transfer of the toner image onto the recording paper is performed, the transfer device stops corona discharge or controls the discharge current to be equal to or less than a set discharge current. This is achieved by an image forming apparatus characterized in that control is performed to release contact with the carrier.

〔Example〕

FIG. 1 is a sectional view showing the configuration of an embodiment of the image forming apparatus of the present invention.

In the figure, reference numeral 10 denotes a drum-shaped image carrier, that is, a photoconductor drum, which is obtained by applying an OPC photoconductor on a drum, is grounded, and is driven to rotate clockwise. Reference numeral 20 denotes a scorotron charger for applying a charge to the photoconductor on the peripheral surface of the photoconductor drum 10, and 13 denotes a photoconductor drum 10 by an exposure optical system (not shown).
This is an image exposure section on which image exposure light or a laser beam is projected so as to be focused on the peripheral surface.

For example, a laser writing system unit is used for the exposure optical system. When a color signal output from an image reading device separate from the image forming apparatus is input to the laser writing system unit, the laser writing system unit generates a laser beam (wavelength 78
(0 nm) is rotationally scanned by a polygon mirror, the optical path is bent by a reflection mirror via an fθ lens, and projected on the peripheral surface of the photosensitive drum 10 which is uniformly charged in advance by the charger 20.

On the other hand, when scanning is started, the laser beam is detected by the index sensor, modulation of the laser beam by the first color signal is started, and the modulated laser beam scans the peripheral surface of the photosensitive drum 10. Accordingly, a latent image for the first color is formed on the image portion on the photosensitive drum 10 by the main scanning by the laser beam and the sub-scanning by the rotation of the photosensitive drum 10. This latent image is subjected to reversal development by a developing unit that contains, for example, yellow (Y) toner as the first color, and a yellow toner image is formed on the peripheral surface of the photosensitive drum 10. The obtained toner of the image portion passes under the transfer unit and the cleaning unit separated from the peripheral surface of the photosensitive drum 10 while being held on the peripheral surface of the photosensitive drum 10, and enters the next copy cycle.

That is, the photosensitive drum 10 is charged again by the charger 20, and then the second color signal output from the signal processing unit is input to the writing unit, and the same as in the case of the first color signal described above. Then, writing is performed on the peripheral surface of the photosensitive drum 10 by the second color signal, and a latent image is formed.
This latent image is subjected to reversal development by a developing means containing, for example, magenta (M) toner as a second color, and a magenta toner image is formed. The magenta toner image is formed so as to overlap the already formed yellow toner image.

The toner image of the image area obtained in this way passes under the transfer means and the cleaning means which are separated from the peripheral surface of the photoconductor drum 10 while being held on the peripheral surface of the photoconductor drum 10, and the next copy cycle to go into.

Similarly, writing is performed on the photosensitive drum 10 by the third color signal to form a latent image. This latent image is subjected to reversal development by a developing unit containing, for example, cyan (C) toner as a third color. By forming this cyan toner image on top of the above-mentioned yellow and magenta toner images, a color image is obtained. In some cases, the image forming apparatus further includes a developing unit containing a black toner, and obtains a high-quality color image by further overlapping the black toner image as described above.

Reference numerals 41 to 43 denote developing units as developing means for accommodating yellow, magenta, and cyan toners for performing the above-described development, respectively.

FIG. 2 shows the structure of the developing device 41, in which a developing sleeve 411, a magnet roller 412, stirring screws 413 and 414, a scraping plate 415 and the like are provided. The gap between the developing sleeve 411 and the photoconductor drum 10 is always set by a roller (not shown) that is provided coaxially with the developing sleeve 411 and abuts on the outer peripheral surface of the photoconductor drum 10 outside the image area.
It is kept at a constant gap of about 0.5 mm.

The toner supplied from a toner storage device (not shown) is sufficiently stirred and mixed with the magnetic carrier by a stirring screw 414 and a stirring screw 413 rotated in opposite directions. The two-component developer D composed of the magnetic carrier and the toner is supplied to the developing sleeve 411 after being stirred and mixed. A magnet roller 412 having a fixed magnetic pole is disposed inside the developing sleeve 411, and the developing sleeve 411 and the magnet roller 412 form a thin layer of the developer D described above.

The thickness of the thin layer of the developer D on the surface of the developing sleeve 411 is made smaller than the gap between the developing sleeve 411 and the photosensitive drum 10, for example, a column made of a magnetic material provided opposite to the magnetic pole of the magnet roller 412. Means 416 for forming thin layer of stick
Is pressed against the developing sleeve 411 to form the developer D into a uniform thin layer of about 300 μm. A developing bias is applied to the developing sleeve 411, and the photosensitive drum 10
The upper image portion latent image is developed. After the development, the thin layer of the developer D on the developing sleeve 411 is once scraped off by the scraping plate 415, and a thin layer of the developer D is newly formed by the above-described method.

The charging by the charger 20 provided on the photosensitive drum 10 and its peripheral portion, the exposure by the laser writing system unit for each color, and the developing processing by the developing units 41 to 43 are performed three times for each color. A color toner image is formed on the image portion on the peripheral surface of the body drum 10 by superposition.

Reference numerals 51 and 52 denote passages of recording paper, which are transfer materials of different sizes fed one by one from the transfer material supply device, and 53 denotes a transfer unit 16 in synchronization with the movement of the color toner image on the photosensitive drum 10.
It is a registration roller for conveying the recording paper to zero.

70 is a transfer belt device, 71 is a transfer belt which is a belt portion, 72 and 73 are rollers made of a conductive metal material, and the upstream roller 72 is a ground or a ground which is set at a predetermined potential close to the ground. Roller with possible axis, downstream roller 73
Is a roller for driving the transfer belt 71 having a fixed shaft.
Reference numeral 74 denotes a belt support member, one end of which has a fixed shaft around the axis of the roller 73 and the other end connected to the movable shaft of the roller 72, and biases the roller 72 downward by an elastic member (not shown). Have been. Therefore, the transfer belt 71 is always retracted from the peripheral surface of the photoconductor drum 10, and the eccentric cam 77 which is operated under the control of the apparatus control unit at the time of transfer moves the belt support member 74 upward in the drawing via the leaf spring 78. Pressing, rotating counterclockwise around the roller 73 as a swing center, the rollers 76 provided on both ends of the belt support member 74 abut against the side end of the peripheral surface of the photosensitive drum 10 outside the image portion, The transfer belt 71 is in contact with the transfer unit 160 of the photosensitive drum 10.

Reference numeral 79 denotes a cleaning blade for scraping off the toner adhered on the transfer belt 71 for cleaning, and reference numeral 95 denotes a toner transport pipe having a flexible transport screw therein to transfer the toner scraped off by the cleaning blade 79 to a toner collection box (not shown). Transport.

Reference numeral 16 denotes a transfer unit which is a transfer charger provided at a position facing the transfer unit 160, and 60 denotes a transfer belt 71 and a photosensitive drum.
This is a paper charger in which the opening is opposed to the transfer belt 71 at a position opposed to the roller 72 in a wedge-shaped cross-sectional space between the transfer belt 71 and the paper charger.

After the development by the developing device 43 containing the third color toner on the photosensitive drum 10 is started as described above, the operation of the registration roller 53, the pressing operation of the transfer belt device 70, and the discharge wire of the paper charger 60 are performed. The high voltage is applied almost simultaneously.

Accordingly, the paper charger 60 performs corona discharge toward the recording paper fed one by one from the transfer material supply device, and charges the recording paper to the same polarity as the toner on the photosensitive drum 10. The paper charger 60 performs charging efficiently and reliably using the roller 72 which is close to the grounded state as a counter electrode, and is provided very close to the transfer unit 160, so that the charge during transportation is reduced little and the recording paper is reduced. The transfer belt 160 can be firmly sucked and held on the transfer belt 71 and conveyed to the transfer unit 160.

When the front end of the recording paper reaches the transfer section 160, the transfer belt 71
As a result, the recording paper is pressed against the photosensitive drum 10. Then, the transfer unit 16 performs charging of a polarity opposite to that of the toner on the photosensitive drum 10, and transfers the toner image onto recording paper. The recording paper onto which the toner image has been transferred is further conveyed by the transfer belt 21, reaches a fixing unit (not shown), is fixed by heat welding, and then is discharged to an external discharge tray. Reference numeral 55 denotes a separation claw for preventing the recording paper from erroneously invading upward.

FIG. 3 is a sectional view showing the vicinity of the paper charger 60 of FIG. In the figure, 61 is a stainless steel plate of the paper charger 60,
A back plate made of a surface-treated steel plate or an aluminum plate or the like for forming a shielding action and a stable electric field has an opening 64 provided to face the transfer belt 71. 62 is a discharge wire made of a tungsten wire having a diameter of 60 to 100 μm. Back plate 61 is a paper charger
It has the effect of forming a stable electric field during the charging operation of 60 to stabilize corona discharge and prevent unnecessary parts from being charged. 5-6K on discharge wire 62 during charging operation
A voltage of V is applied. At this time, if the distance between the discharge wire 62 and the bare back plate 61 is not more than 6 to 7 mm, spark discharge occurs and charging is not performed, which is dangerous. Therefore, in the present embodiment, a tape made of, for example, a polyester resin is attached to the inner wall of the back plate 61 on the photosensitive drum 10 side to form an insulating layer 63. It does not occur.

The back plate 61 has a key-shaped cross section as shown in FIG. 3 so as to be suitable for the installation space of the wedge-shaped cross section. It is possible to provide.

The paper charger 60 is provided at a position facing the roller 72, performs corona discharge toward the recording paper P fed by the registration roller 53, and efficiently and reliably uses the roller 72 close to the ground state as a counter electrode. And the distance to the transfer section 160 can be significantly shortened, so that the transfer belt 71 can firmly hold and transport the recording paper P, and transfer the recording paper P after transfer. Also, good separability from the photosensitive drum 10 was always maintained.

Further, a high voltage having the same polarity as that of the toner of the developer is applied to the discharge wire 62 of the paper charger 60 so that the toner of the recording paper P is charged to the same polarity. Therefore, the toner on the photosensitive drum 10 is not attracted to the recording paper P until the recording paper P reaches the transfer unit 160, so that a clear copy image quality can be obtained without blurring or blurring of the image. it can.

The high voltage applied, moving line speed of the photosensitive drum 10 peripheral surface is 140 mm / sec image width 300～350Mm, if the paper thickness 65 g / m ² 20 to 5
The discharge current is controlled to be 0 μA. At this time, the current component flowing in the recording paper P direction is 10 to 20 μA in the case of high humidity.
In the case of low humidity, it becomes 5 to 10 μA.

As shown in FIGS. 6 (a) and 6 (b), before and after the recording paper P is conveyed and its front end passes through the transfer section, a transfer voltage having a polarity opposite to that of the toner charging is applied to the transfer unit 16 as shown in FIGS. The toner image is transferred by starting corona discharge under the constant current control. This constant current control is, for example, 300 in case of high humidity.
The switching control is performed so as to be 250 μA in the case of μA and low humidity, and charging is performed. As described above, the charging current is changed in accordance with the change in humidity, which is most susceptible to the influence, so that good adsorption force and transfer efficiency can always be maintained.

In the transfer voltage application shown in FIG. 6B, a non-image portion is formed at the front end of the recording paper P by slightly delaying the start time of the scanner reading of image reading or the start time of the printer writing to form a non-image portion. A transfer voltage is applied while the non-image portion passes through the transfer portion 160, so that the image portion has sufficient transferability when it reaches the transfer portion 160, so that the image front end portion is clearly copied. FIG.

As shown in FIG. 6, before the transfer belt 71 is released from the peripheral surface of the photosensitive drum 10, the transfer voltage application of the transfer device 16 is stopped and the corona discharge is stopped. Since there is no charge, spark discharge with the photoconductor drum 10 that is likely to occur when the contact is released is prevented, and the photoconductor is not damaged or damaged. The stop of the transfer voltage application before the contact release of the transfer belt 71 is set to be equal to or less than the set discharge current, which is not more than completely stopped, and is set to be equal to or smaller than the discharge current that gives only the minimum electric charge at which spark discharge occurs. The discharge current may be controlled so that the discharge current is maintained.

Instead of stopping the transfer voltage application of the transfer unit 16, an openable / closable shutter may be provided at the opening of the transfer unit 16, and the shutter may be opened and closed to discharge / stop the transfer belt 71.

The configuration of the transfer belt 71 used as the transfer means is, for example, composed of two layers, and the main body has an endless volume resistance of about 10 ¹⁰ Ω · cm such as silicon rubber, polyurethane rubber, butyl rubber, etc. having a thickness of about 0.5 to 1 mm. In the resistance sheet, for example, a fluororesin is spray-coated on the upper layer of the sheet to reduce the frictional resistance.

On the other hand, the photosensitive drum 10 after the transfer is cleaned by a cleaning device 90 as a cleaning means.
91. Toner collection roller that collects residual toner electrostatically
The cleaning blade 91 is in a retracted state while a toner image is being formed on the peripheral surface of the photoconductor drum 10, and performs cleaning by pressing against the photoconductor drum 10 after transfer is completed. A discharge lamp 93 is located upstream of the cleaning device 90, and a discharge lamp 94 is located downstream of the cleaning device 90. The discharge lamp 93 discharges electricity so that residual toner on the peripheral surface of the photosensitive drum 10 is easily removed. The lamp 94 uniformly removes electricity from the cleaned peripheral surface of the photosensitive drum 10 so that uniform charging is performed. Further, a toner conveying pipe 95 having a toner conveying screw made of a flexible material is provided at the bottom of the cleaning device 90, and conveys waste toner collected by cleaning to a toner collecting box (not shown). After the cleaning, the photosensitive drum 10 enters the next image forming process.

In the color image forming apparatus shown in FIG. 1 described above, the image forming means is located at the peripheral portion of the photoreceptor drum 10 in the arrangement shown in FIG. Then, as shown in the time chart of FIG. 5, sequence control is performed by the control unit provided in the apparatus main body, and a color image is formed.

〔The invention's effect〕

According to the present invention, since the configuration, control, and operation as described above are employed, it is possible to prevent a spark discharge that easily occurs when the transfer belt is released from contact with the photosensitive drum, and to provide a long-life image carrier. An image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a color image forming apparatus according to the present invention, FIG. 2 is a sectional view showing a developing unit shown in FIG. 1, and FIG. Cross-sectional configuration diagram shown,
FIG. 4 is an explanatory diagram showing an arrangement relationship of each device in the image forming apparatus, FIG. 5 is a time chart of image formation performed based on the arrangement relationship, and FIG. 6 is a contact between a transfer belt and voltage application to a transfer device. FIG. 7 is a sectional view showing an embodiment of a conventional electrophotographic copying machine, and FIG. 8 is a schematic view showing an embodiment of a conventional transfer belt apparatus. 10 photoreceptor drum, 16 transfer device 17 separator, 60 paper charger 61 backplate, 62 discharge wire 63 insulating layer, 64 opening 70 transfer Belt device, 71 Transfer belt 72, 73 Roller, 74 Roller support member 160 Transfer unit, P Recording paper

Continuation of the front page (56) References JP-A-1-167868 (JP, A) JP-A-52-139431 (JP, A) JP-A-1-116670 (JP, A) JP-A-63-85674 (JP, A) , A) JP-A-49-62135 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/16 G03G 15/01 114

Claims (1)

(57) [Claims] 1. A multi-color toner image is formed on a peripheral surface of an image bearing member while a plurality of developing means of different color toners are provided at a peripheral portion of the rotating image bearing member. The transferred toner image is transferred onto a recording sheet conveyed by a transfer belt device, wherein the transfer belt device contacts and releases the rotating transfer belt to and from the image carrier. A transfer unit for transferring the toner image on the image carrier onto recording paper by corona discharge, wherein the transfer belt is maintained until the final developing unit of the developing unit develops the transfer belt. After being separated from the image carrier, the transfer belt is brought into a contact state by the contact / release means, a corona discharge is performed by the transfer device, and a toner image is formed on the recording paper adhered to and conveyed to the transfer belt. Transcription After the transfer of the toner image onto the recording paper, the transfer device stops the corona discharge or controls the discharge current to be equal to or less than the set discharge current. An image forming apparatus wherein control is performed to release contact with a carrier.