JPH0619262A - Image forming device - Google Patents

Abstract

PURPOSE:To efficiently remove the memory effect of a photosensitive drum for a transfer material with different quality. CONSTITUTION:A transfer electrifier 5b is arranged inside a transfer drum 5 which is opposite the photosensitive drum 1. An auxiliary electrifier 8 is arranged downstream from this. When positive charges are injected from the transfer electrifier 5b to transfer negative toner on the photosensitive drum 1 to a transfer material P, the positive memory effect is produced on the photosensitive drum 1, especially in the part corresponding to the end of the transfer material P. This memory effect is removed by the auxiliary electrifier 8; however, since this varies with the thickness of the transfer material P, quality such as a type, and a transfer-electrification current, it is removed after a voltage is adjusted by a control means 8a based on them. Thus, the memory is efficiently removed without impairing cleaning performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic system or an electrostatic recording system, and more specifically, to an image carrier depending on the properties of a transfer material to be image-formed and the transfer conditions of a transfer means. The present invention relates to an image forming apparatus that changes a decharging condition.

[0002]

2. Description of the Related Art Conventionally, various multicolor electrophotographic copying apparatuses have been proposed. FIG. 3 shows an example of a multicolor electrophotographic copying machine (hereinafter simply referred to as "copying machine") equipped with a typical developing machine called a so-called rotary developing machine.

To briefly describe with reference to FIG. 3, a copying machine of this type has an image carrier, that is, a photosensitive drum 1, which is rotatably supported by a shaft and rotates in the direction of an arrow, and an image is formed on its outer peripheral portion. Means are arranged. This image forming means may be any means, but in the present example, the photosensitive drum 1 is irradiated with a primary charger 2 for uniformly charging the photosensitive drum 1 and a color-separated optical image or an optical image corresponding thereto. It is provided with an exposing means 3 for forming an electrostatic latent image thereon, for example, a laser beam exposing device, and a rotary developing device 4 for making the electrostatic latent image on the photosensitive drum 1 a visible image.

The rotary developing device 4 includes, for example, four developing devices 4Y4M4C4BK for accommodating four color developers of yellow color developer, magenta color developer, cyan color developer and black color developer, respectively. These four developing devices 4Y4M
4C4BK and a cylindrical body 4a having a substantially cylindrical shape and rotatably rotatably supported. The rotary developing device 4 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 1 by the rotation of the cylindrical body 4a, develops the electrostatic latent image on the photosensitive drum 1, and the cylindrical body 4a moves. By performing one rotation, so-called full-color development for four colors can be performed.

A visible image on the photosensitive drum 1, that is, a toner image is transferred at a transfer position onto a transfer material P carried and conveyed by a transfer device 5. In this example, the transfer device 5 is a transfer drum that is rotatably supported, and the transfer drum 5 includes a cylinder 5a and transfer means provided in the cylinder 5a, as can be seen from FIGS. 3 and 4. It has a transfer charger 5b and a transfer material gripper 5c for gripping the transfer material P fed from a sheet feeding device (not shown). Further, an inner charge eliminating charger 5d and an outer charge eliminating charger 5e, which constitute charge eliminating means, are arranged inside and outside the transfer drum 5. A transfer material carrying sheet 501 is stretched over the outer peripheral surface opening area of the cylinder 5a, and as the transfer material carrying sheet 501, polyethylene terephthalate, polyvinylidene fluoride resin film or the like is usually used.

Next, a process of forming a full-color image by the copying apparatus having the above structure will be briefly described. First, the photosensitive drum 1 is driven by driving the primary charger 2 and the exposure unit 3.
A blue color-separated electrostatic latent image is formed on the outer peripheral surface of, and the electrostatic latent image is developed with a yellow developer housed in the developing device 4Y. On the other hand, the transfer material P fed to the transfer drum 5 is gripped by the gripper 5c and is brought into contact with the toner image formed on the outer peripheral surface of the photosensitive drum 1 as the transfer drum 5 rotates. The toner image is transferred onto the transfer material P by the operation of the transfer charger 5b, and at the same time, the transfer material P is attracted to the transfer material carrying sheet 501.

The above-mentioned image forming operation and transfer operation are repeated for each color of magenta, cyan and black, and the operation of the transfer charger 5b is also repeated until the transfer operation for the fourth color is completed. Transfer material P for four color visible images
When the superimposing transfer to the sheet is completed, the transfer material P is discharged by the inner charging device 5d and the outer charging device 5e, then separated from the transfer drum 5, fixed by the heat roller fixing device 6 and discharged to the outside of the device. It On the other hand, the residual toner remaining on the surface of the photosensitive drum 1 is removed by the cleaner 7, and the surface of the photosensitive drum 1 is destaticized by the destaticizing lamp 9 to prepare for the next image forming process starting from the charging of the primary charger 2.

[0008]

Although the copying apparatus having the above-described structure operates extremely favorably, according to the research and experiment conducted by the present inventors, in the transfer step, especially as the transfer material carrying sheet 501 of the transfer drum 5. It has been found that when a polyvinylidene fluoride resin film or the like is used and a transfer paper is used as the transfer material P, a problem occurs especially when the humidity is high.

In FIG. 5, a toner image of one color is transferred onto the transfer material P on the transfer drum 5, and the toner image is held on the transfer material P. The transfer material P is not yet separated. The charge state of the transfer material P at the time of being wound around the transfer drum 5 and being rotated together with the transfer drum 5 to transfer the toner image corresponding to the image of the next color is shown.
Here, the polarity of the transfer voltage supplied to the transfer charger 5b is, for example, a latent image is formed with a negative charge, and the toner of each developer is negatively charged in order to reverse develop the latent image. In case it is set to plus.

According to a research experiment by the present inventors, when a polyvinylidene fluoride resin film is used as the transfer material carrying sheet 501 of the transfer drum 5 and a transfer paper is used as the transfer material P, the polyvinylidene fluoride resin film is used. Has a volume resistivity of 10 ¹³ Ω · cm, while the transfer paper has a volume resistivity of 10 ⁹ (at high humidity) to 10 ¹² (at low humidity) Ω.
Since it is cm, it has been found that positive charges from the transfer charger 5b are injected into the transfer material P via the transfer material carrying sheet 501, and the positive charges are accumulated in the surface area of the transfer material P. It was

Further, the inventors of the present invention have found that the positive charges accumulated in the surface area of the transfer material form a high electric field with the surface of the photosensitive drum, and as shown in FIG. At this time, peeling discharge is generated, and the negative charge in the air is attracted by the positive charge of the transfer material P and moves onto the transfer material P. However, the positive charge in the air is on the photosensitive drum 1 having the negative charge. And found that the photosensitive drum 1 is damaged, that is, causes a memory effect. This memory effect reduces the primary charge amount on the photosensitive drum 1 by the primary charger 2 along the axial width direction of the photosensitive drum 1, making it impossible to uniformly charge the photosensitive drum 1 and causing image unevenness. Caused

The memory effect as described above occurs mainly in response to the operation of the transfer charger 5b, but as shown in FIG. 5, the positive charge is likely to be accumulated especially at the transfer material end portion Pa. As a result, the memory effect also occurred more strongly, causing strong streak-like image unevenness along the axial direction of the photosensitive drum 1.

For the purpose of reducing the memory effect, a separate charging device is provided in the subsequent stage of the transfer means, and the photosensitive drum after the transfer process is discharged by this charging device. Alternatively, precharging to the same polarity as the primary charging has been performed so that the memory effect area can be sufficiently reduced by performing the static elimination exposure and the primary charging on the photosensitive drum 1.

However, it has been clarified by the experiments conducted by the inventors of the present invention that the memory effect as described above has different strength depending on the properties such as the type of the transfer material P. That is, the strength of the memory effect depends on properties such as the material, thickness, and smoothness of the transfer material P. For example, when a transfer resin P such as a projection resin film or coated paper is used, plain paper is used. The memory effect tends to be relatively stronger than that in the case where it is present, and the memory effect tends to be relatively stronger as the thickness of the transfer material P is increased. Therefore, in the case of reducing the memory effect by using the charger provided in the latter stage of the transfer unit as described above, it is difficult to sufficiently reduce the memory effect when the transfer charging condition is different under a certain static elimination condition. Becomes

Further, irrespective of the transfer charging condition, the effect of reducing the memory effect was recognized when charged to the same polarity as the primary charging in order to sufficiently reduce the memory effect, but on the photosensitive drum 1. Since the toner remaining in the toner is also charged, there is a problem that cleaning failure occurs. That is, there is a problem in that the charging conditions corresponding to the reduction of the memory effect and the prevention of cleaning failure due to the charging of toner are in a trade-off state.

Further, since the optimum conditions for the transfer charging change depending on the environmental condition, the property of the transfer material P, the condition of the electrostatic latent image, the condition of the developer, the condition of the photosensitive drum 1, etc., a high quality image is obtained. To achieve this, it is necessary to change and optimize the transfer charging conditions according to various image forming conditions, and especially in the full-color image forming apparatus as described above, the optimum transfer charging conditions are different for each color, and more detailed control is possible. is necessary.

However, as described above, the memory effect occurs in response to the operation of the transfer charger 5b, and when the memory effect is reduced by using the charger provided in the latter stage of the transfer means as described above, It is difficult to sufficiently reduce the memory effect under a certain static elimination condition and when the transfer charging condition is different.

Further, in the case of transferring a plurality of times, even if the transfer charging conditions are made the same every time, the memory effect is different for each number of times, so that the memory effect is sufficient under a certain static elimination condition. Becomes difficult to reduce.

Further, providing a separate charger in addition to the general image forming means has a problem that it is difficult to downsize the apparatus and the cost is increased.

In addition to this, there is a deterioration phenomenon due to exposure of the photoconductor, and some kind of deterioration reduction measure is desired.

Therefore, according to the present invention, by changing the decharging condition based on the property of the transfer material P and the transfer condition, it is possible to prevent the occurrence of image unevenness or cleaning failure due to the memory effect generated on the image carrier. It is an object of the present invention to provide an image forming apparatus configured as described above.

That is, the object of the present invention is to generate an image on the image carrier while forming an image with high image quality by setting the optimum transfer condition, and also realizing good cleaning property under all conditions. An image forming apparatus that prevents problems such as image unevenness due to the memory effect without adverse effects such as cleaning, further reduces cost space performance, and reduces deterioration of the photoconductor. Is to provide.

[0023]

The present invention has been made in view of the above circumstances, and is a transfer means for transferring a visible image formed on an image carrier to a transfer material at a transfer position, and the transfer means. In an image forming apparatus having a decharging means for decharging the image carrier that has passed through a position, a control means for changing the decharging condition of the decharging means based on the property of the transfer material is provided. It is characterized by

An image forming apparatus similar to the one described above is characterized by further comprising control means for changing the decharging condition of the decharging means based on the transfer condition of the transferring means.

[0025]

Based on the above configuration, for example, when the transfer conditions are constant, the memory effect described above is
It is greatly affected by properties such as smoothness. Therefore, the decharging for eliminating the memory effect is also largely influenced by the properties of the transfer material, and conversely, if it is performed under decharging conditions that match the properties of the transfer material, the memory effect can be effectively removed. is there.

Even when the decharging condition is changed according to the transfer condition of the transfer means instead of changing the decharging condition according to the property of the transfer material, almost the same operation is performed with respect to the removal of the memory effect. To do.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a cross-sectional view of a main part showing an embodiment 1 of an image forming apparatus according to the present invention, in which a conventional multicolor image forming apparatus having a rotary developing device shown in FIGS. It shows a case where the invention is applied to an electrophotographic copying machine. The structure and operation of this multicolor electrophotographic copying apparatus will be described below with reference to FIG.
A description of the same components as those in FIG. 4 will be omitted, and the description will focus on the parts different from these. In this embodiment, the diameter of the photosensitive drum 1 is set to 80 mm, and the diameter of the transfer drum 5 is set to 160 mm (twice the diameter of the photosensitive drum).
Further, the photosensitive drum 1 is rotated in the direction of the arrow at 160 mm / sec, and the surface of the surface of the photosensitive drum 1 is set to -300 to about 300 by the primary charger 2.
It is charged to -900V. The surface potential of the photosensitive drum 1 is monitored by the drum surface potential sensor 10, and an appropriate photosensitive drum surface potential is calculated. A laser beam exposure device was used as the exposure means 3. Each of the developing devices 4Y, 4M, 4C, and 4BK of the rotary developing device 4 has a toner of each color having a negative charge, and is used as a developing sleeve that carries the toner and conveys it to the developing area in the vicinity of the photosensitive drum 1. Toner is attached to the electrostatic latent image formed on the photosensitive drum 1 by a reversal phenomenon by a voltage applied (hereinafter referred to as “developing bias”) and a developing electric field formed by the potential of the photosensitive drum 1 to visualize the toner. .

As can be seen from FIG. 1, the transfer means is the transfer drum 5 having the same structure as that shown in FIGS. 3 to 5, but in this embodiment, the transfer material carrying sheet 501 has a thickness of 100 μm.
A polyvinylidene fluoride resin film having m to 175 μm and a volume resistivity of 10 ¹³ Ω · cm was used. Further, a corona charger is used as the transfer charger 5b, a voltage of +6 kV to +9 kV is applied in this embodiment, and the transfer current is +10.
It was set to 0 μA to +600 μA. The visible image on the photosensitive drum 1, that is, the toner image, is transferred to the transfer material P carried on the transfer drum 5 and conveyed.

Further, in the present embodiment, a projection resin film detection sensor and a transfer material thickness detection sensor are provided in the paper feed section (not shown) in order to determine the property (type) of the transfer material P.

Further, in this embodiment, a scorotron type charger as shown in FIG. 2 is used as the primary charger 2, and a charging wire 2-1 which is discharged by a high voltage applied from a high voltage power source 2-2. The discharge amount of the photosensitive drum 1 is controlled by applying a predetermined control voltage from the grid bias power source (control means) 2-4 to the grid line 2-3.
Is charged to a desired potential.

FIG. 7 shows a case in which the electrostatic latent image forming area of the photosensitive drum 1 having a memory effect area when the resin film for projection having a very strong memory effect is used as the transfer material P is subjected to the primary charging as in the prior art. The transition of the surface potential when performing is shown. As is clear from FIG. 7, the potential of the memory effect region (+
100 V to +700 V) remains even after the charge on the photosensitive drum 1 is removed, and the surface potential of the photosensitive drum 1 is reduced to − by performing primary charging.
When charged to 700 V, the potential of the memory effect area is about −
It becomes 300V-650V. Therefore, the potential of the memory effect region is -300V to -650V and the developing bias voltage is -5.
Since a developing electric field corresponding to a potential difference (shown by a dotted line in the drawing) which is a difference from 50 V is formed, an electrostatic latent image due to a memory effect area is formed in an area where the electrostatic latent image is not originally formed in the conventional apparatus. Is formed, and this is developed to form a toner image. As a result, this toner image is transferred to the transfer material P, and image unevenness occurs.

Alternatively, in the memory effect region, the potential becomes lower than the potential of the electrostatic latent image when normal image formation is performed, so that image unevenness occurs. That is, since the memory effect region is charged with a potential having a polarity opposite to that of the electrostatic latent image to be formed, that is, positive polarity in this example, the charge is removed by the charge removal exposure by the operation of the charge removal lamp 9. Then, the next primary charging process is performed. Therefore, in order to charge the memory area to a desired potential, it is necessary to charge more than a normal area that has been subjected to static elimination, and as a result, the memory area is charged after primary charging. Will be charged to a lower potential than the normally charged area. In particular, in the memory area corresponding to the edge of the transfer material, since the memory effect is extremely strong, the surface potential difference from the normal area after primary charging also remains remarkably, and as a result, it appears as a large image density difference. .

Further, FIG. 12 shows a transfer material P of 80 g / m 2.
^{In the case of using 2} plain paper, 105 g / m ² plain paper, coated paper, projection resin film (hereinafter referred to as “OHP film”), the memory effect area of the photosensitive drum 1 after the transfer process is performed. 3 shows the surface potential of the. It is understood from FIG. 12 that the strength of the memory effect is different depending on the material (thickness), the smoothness, and other properties (type) of the transfer material P.

In this embodiment, the following constitution is adopted in order to solve the above-mentioned problems.

FIG. 8 is a sectional view of the main part of the image forming apparatus in this embodiment. As shown in FIG. 8, in the present embodiment, when the present invention is applied, a corona discharger (hereinafter, referred to as “decharger” as a decharging unit is provided at a subsequent stage of the transfer area (downstream of the transfer position), facing the photosensitive drum 1. "Auxiliary charger") 8
Is provided. In the present embodiment, the set value of the auxiliary charger 8 is changed (controlled) by applying a voltage obtained by superimposing the _AC voltage (VAC) on the DC bias voltage ( _VDC ) by the control means 8a. The applied voltage conditions (de-charging conditions) in this example were set to the values shown below.

V _DC : -1 kV to +2 kV variable V _AC : Peak voltage V _PP 10 kV Frequency V _f 500 Hz In this embodiment, the DC bias voltage is controlled according to the property of the transfer material P. By adopting the configuration shown in this embodiment and controlling the DC bias voltage applied to the auxiliary charger 8 according to the property of the transfer material P, the memory effect as described above is sufficiently reduced and the occurrence of image defects is prevented. can do.

Hereinafter, description will be made with reference to the drawings. FIG. 9 shows the transition of the surface potential of the photosensitive drum 1 when an OHP film is used as the transfer material P. In this case, the auxiliary charger 8
The DC bias voltage V _{DC of} is set to -300V.

Under the above conditions, the photosensitive drum 1 receives a charging memory of about + 100V to + 700V by the operation of the transfer charger 5b, but the surface potential of the memory area is converged to near 0V by the operation of the auxiliary charger 8. It Therefore,
The next normal cleaning process is performed without the residual toner on the photosensitive drum 1 being charged, and the memory region can be uniformly charged to a desired potential by further performing the primary charging.

FIG. 13 shows a case where the transfer material P is 8 in comparison with the above example.
When using 0 g / m ² of plain paper, the value of the DC bias voltage V _DC of the auxiliary charger 8 is set to −300 V as in the above example, and is also changed to +200 V and set. The transition of the surface potential of the photosensitive drum 1 is shown. When the _VDC value of the auxiliary charger 8 is not changed and is set to -300V, the surface potential of the memory area is converged to about -300V. Therefore, the static elimination exposure and the primary charging are performed. Although the memory area can be uniformly charged, the residual toner on the photosensitive drum 1 is charged by the operation of the auxiliary charging device 8, so that cleaning failure occurs. On the other hand, when the _VDC value of the auxiliary charger 8 is set to + 200V according to the transfer current value, the surface potential of the memory area is converged to around 0V as in the above-described example, so that the photosensitive drum 1 has the same surface potential. By performing the normal cleaning process of the residual toner and further performing the primary charging, the memory area can be uniformly charged to a desired potential.

In this embodiment, as described above, the paper feed unit is provided with the OHP film detection sensor and the transfer material thickness detection sensor, and the property of the transfer material P is discriminated based on the output values of these sensors. The DC bias voltage value of the auxiliary charger 8 is controlled.

FIG. 14 shows the control values of the thickness of the transfer material P and the DC bias voltage of the auxiliary charger 8 with respect to the OHP film in this embodiment. 17 shows the transition of the surface potential of the memory effect region according to the property (type and thickness) of the transfer material P, and the DC bias voltage of the auxiliary charger 8 as shown in FIG. The following shows the case of controlling with respect to the above, and the case of setting the conditions for an OHP film having a very strong memory effect for all the transfer material P properties.

As will be understood with reference to FIG. 17, by controlling the DC bias voltage of the auxiliary charger 8 according to the property of the transfer material P, as described above, the photosensitive material after the transfer process is performed. The surface potential of the drum 1 is always controlled to be near 0 V in both the memory area and the normal area regardless of the transfer current value. Therefore, it is possible to uniformly charge the memory area to a desired potential as in the normal area by performing the primary charging without causing the bad effect of cleaning failure.

Next, the operation will be described. The photosensitive drum 1
Is charged to a surface potential of −700V by the primary charger 2. The developing bias voltage for forming the developing electric field is set to -550V. The difference between the charging potential of the photosensitive drum 1 of −700 V and the developing bias voltage of −550 V is 150 V, which is a fog removing voltage. The electric field formed by this potential difference causes the toner to be constantly attracted to the developing sleeve and adhere to the photosensitive drum 1. It is possible to obtain a good image without fogging in the white part of the image. On the other hand, since the portion of the photosensitive drum 1 corresponding to the image pattern is irradiated with the laser beam with the intensity corresponding to the image density, the potential of the portion exposed by this laser beam drops to a potential lower than the developing bias voltage, and The toner adheres to the photosensitive drum 1 by the electric field formed by the bias voltage and the surface potential of the exposed photosensitive drum, and a toner image is formed. Due to the above image exposure, the surface potential of the photosensitive drum is -35.
The portion where the voltage has dropped to 0 V is shown by dotted lines in FIGS. 9 and 13.

That is, in the present embodiment to which the present invention is applied, the surface of the photosensitive drum 1 is primarily charged by the operation of the auxiliary charger 8 and the discharging lamp 9 shown in FIG. The charge is removed to a substantially uniform potential before. Therefore, after that, the primary charging and the developing process are normally performed, and the toner image is not formed in the memory effect area and transferred to the transfer material P as in the conventional case, and thus the image is not disturbed. Moreover, problems such as poor cleaning did not occur. <Embodiment 2> FIG. 10 is a schematic configuration diagram showing Embodiment 2 of the image forming apparatus of the present invention. The image forming apparatus of this embodiment is applied to a multicolor electrophotographic copying machine having four image forming units I to IV.

In this image forming apparatus, each of the image forming units I to IV has photosensitive drums 11a to 11d, around which primary chargers 12a to 12d and exposing means 13a to 13a.
13d, developing devices 14a to 14d, transfer charging devices 15a to 1
5d, cleaners 16a to 16d, static elimination lamps 19a to 1
9d is arranged, and an endless transfer material carrying belt 17 is arranged below the photosensitive drums 11a to 11d as a conveying means in a manner of penetrating the image forming units I to IV.
The transfer material P fed by the paper feed roller 80 is placed in the image forming unit I at a position where the transfer chargers 15a to 15d are arranged.
To IV of the photosensitive drums 11a to 11d are configured to be conveyed so as to come into contact with the photosensitive drums 11a to 11d.

Furthermore, in the present embodiment, as shown in FIG. 10, in applying the present invention, the memory area of the photosensitive drums 11a to 11d is set to 0 after the transfer process is performed.
Auxiliary chargers 18a to 18 for removing electric charges to a potential near V
d is provided for each of the image forming units I to IV at the same position on the surface of the photosensitive drums 11a to 11d.

The image forming process by the multi-color electrophotographic copying apparatus having the above-mentioned structure is basically the same as that of the above-mentioned embodiment, so that it will not be described in detail, but in this embodiment, the photosensitive drums 11a to 11d are respectively transferred. After the transfer process is performed by the operation of the chargers 15a to 15d, the auxiliary charger 18a
.About.18d, the surface potentials of both the area that has received a memory having the opposite polarity to the electrostatic latent image and the normal area that has not received the memory due to the operation of the transfer chargers 15a to 15d have a surface potential of 0.
The charge is removed so that it is near V.

In this embodiment as well, the property of the transfer material is discriminated based on the outputs of the OHP film detection sensor and the transfer material thickness detection sensor (not shown), and the DC of the auxiliary chargers 18a to 18d is determined accordingly. Bias voltage value is controlled.

After the charge removing process by the auxiliary chargers 18a to 18d is performed, the charge removing lamps 19a to 19d, the primary chargers 12a to 12d, and the laser beam exposing devices 13a to 13d as image exposing means are operated. Drum 1
A color-separated electrostatic latent image corresponding to an image pattern is formed on 1a to 11d, and the electrostatic latent images are respectively formed of yellow, magenta, cyan, and black toners by the operation of the developing devices 14a to 14d. After being developed into a visible image, the visible image is sequentially transferred to the transfer material P carried on the transfer material carrying belt 17 by the operation of the transfer chargers 15a to 15d, and a full color image is formed on the transfer material P. To be done. In the figure, 60 is a paper feed cassette, 90, 10
Reference numeral 0 is a separation charger, 70 is a fixing device, 110 is a belt cleaner, and 13 is a polygon mirror.

Also in this embodiment, as in the previous embodiment, the surface of the photosensitive drum 1 is provided with a primary charger by the operations of the auxiliary chargers 18a to 18d and the discharge lamps 19a to 19d shown in FIG. Before being discharged, the charge is discharged to a substantially uniform potential. Therefore, after that, the primary charging and the developing process are normally performed, and the toner image is formed in the memory effect area and transferred to the transfer material P regardless of the properties of the transfer material P, so that the image is disturbed. I didn't. Moreover, problems such as poor cleaning did not occur. <Third Embodiment> FIG. 11 is a schematic configuration diagram showing a third embodiment of the image forming apparatus of the present invention. The image forming apparatus of this embodiment is an image forming apparatus having no transfer device, for example, a black and white electrophotographic digital laser beam printer.

This image forming apparatus has a photosensitive drum 31, around which a primary charging device 32, a laser beam scanner 33 as an exposing means, a developing device 34, a transfer charging device 35, a cleaner 37, and a discharging lamp 39 are arranged. It

Further, in the present embodiment, as shown in the figure, in applying the present invention, after the transfer process is performed, the auxiliary charger is provided to eliminate the charge in the memory area of the photosensitive drum 31 to a potential near 0V. 38 are provided.

In this embodiment as well, the DC bias voltage value of the auxiliary charger 38 is controlled in accordance with the properties of the transfer material as in the above embodiments. After the charge removing step is performed on the auxiliary charger 38, an electrostatic latent image corresponding to an image pattern is formed on the photosensitive drum 31 by the operation of the primary charger 32 and the laser beam scanner 33 which is an image exposing means. , Developing unit 34
The electrostatic latent image is visualized by the operation of.

Also in this embodiment, as in the previous embodiment, FIG.
Auxiliary charger 38 and static elimination lamp 3 shown in FIG.
By the operation of 9, the surface of the photosensitive drum 31 is discharged to a substantially uniform potential before the primary charging. After that, the primary charging and the developing process are normally performed, and the image is not disturbed due to the toner image being formed on the memory effect area and being transferred to the transfer material P regardless of the kind of the transfer material as in the above-described embodiment. It was Moreover, problems such as poor cleaning did not occur. Reference numeral 36 is a conveyance roller that conveys the transfer material P toward the photosensitive drum 31. <Embodiment 4> In Embodiments 1 to 3, the case where the corona charger is used as the transfer means has been described, but the present invention is not limited to this, and the brush shown in FIG. 15 is used. Also in an image forming apparatus using a contact charging means to which a bias voltage is applied, such as a transfer means or a transfer means using a roller as shown in FIG. 16, the DC bias voltage value of the auxiliary charger depends on the transfer bias voltage. It is possible to obtain the same effect as that of the above-described embodiment by controlling the above. <Embodiment 5> In the embodiment described above, the charge is removed by the operation of the auxiliary charger so that the surface potential of the photosensitive drum after the transfer process is near 0V. In order to more effectively erase the memory effect received by the photosensitive drum 1 within a range in which a defect such as a cleaning failure due to the residual toner being strongly charged does not occur, a potential offset to the same polarity side as the primary charging (for example, − (50 V, -100 V, etc.), or slightly opposite to the primary charge in order to obtain sufficient cleaning property of the residual toner within a range in which the memory effect can be reduced to a practical range. The characteristics of the image forming apparatus to which the present invention is applied, such as charging so as to converge in the vicinity of a potential offset to the polarity side (for example, + 20V + 50V, etc.), are supported. Control can be carried out was. <Embodiment 6> In the embodiment described above, the DC bias voltage value of the auxiliary charger is controlled. However, the AC bias amplitude, the AC bias frequency, the AC bias duty ratio,
The same effect can be obtained by controlling any one of the charging current values or by combining with a plurality of conditions. <Embodiment 7> Furthermore, the surface potential of the photosensitive drum after primary charging, the surface potential after exposure to a laser beam, the developing bias voltage, etc. in each of the above embodiments are not limited to the above values, and may be changed by changes in the ambient environment. It can take various values depending on the type. Of course, the exposure is not limited to the laser beam exposure. Further, the present invention is equally applicable to various copying machines such as electrophotographic systems and electrostatic recording systems other than multicolor electrophotographic copying machines, and image forming apparatuses such as printers. <Embodiment 8> In this embodiment, the transfer current value in FIG. 10 is set to a different value for each color transfer process based on the environmental condition, the property of the transfer material P, and the like. As an example,
When using standard paper in a normal temperature and normal humidity environment, the transfer current value for each color is 1st color + 200μA, 2nd color + 225μA, 3rd color + 250μA, 4th color + 300μ
Set to A.

FIG. 19 shows an example of the correlation between the transfer current and the strength of the memory effect. As understood with reference to FIG. 19, the strength of the memory effect depends on the transfer current, and tends to increase as the transfer current increases.

Further, FIG. 20 shows the correlation between the transfer current and the memory effect strength for each number of transfers, that is, for each color. As can be seen with reference to FIG.
The intensity of the memory effect depends on the transfer current, and the degree of the dependency is different for each color, and the degree of the memory effect tends to weaken as the number of transfers increases for the same transfer current. .

Further, in the present embodiment, as shown in FIG. 18, the auxiliary charger 8 is provided with a charge removing function of the photosensitive drum 1 without using the charge removing lamp 9 in the conventional example.

In the present embodiment, the DC bias voltage of the auxiliary charger is controlled on the basis of the transfer current value, and at the same time, the control function form showing the correlation between the DC bias voltage and the transfer current value is set for each color. Different from.

Hereinafter, description will be given with reference to the drawings.

FIG. 9 shows the transition of the surface potential of the photosensitive drum 1 when the transfer current value is set to +450 μA. In this case, the DC bias voltage _VDC of the auxiliary charger 8 is -300.
It is set to V.

Under the above conditions, the photosensitive drum 1 receives a charging memory of about + 100V to + 700V by the operation of the transfer charger 5b, but the surface potential of the memory area is converged to near 0V by the operation of the auxiliary charger 8. It Photosensitive drum 1
The next normal cleaning step is performed without the residual toner above being charged, and the memory area can be uniformly charged to a desired potential by performing the primary charging even without performing the static elimination exposure. It will be possible.

FIG. 21 shows that the optimum transfer current value for image formation is lower than that in the above example, and is set to +200 μA.
The transition of the surface potential of the photosensitive drum 1 when the value of the DC bias voltage V _DC of the auxiliary charger 8 is set to -300V as in the above example and when changed to + 400V is shown. When the _VDC value of the auxiliary charger 8 is not changed and is set to −300V, the surface potential of the memory area is converged to about −300V, so that the primary charge is applied to the memory area. On the other hand, although uniform charging is possible, the charging potential becomes higher than a desired potential, and the residual toner on the photosensitive drum 1 is charged by the operation of the auxiliary charging device 8, so that cleaning failure occurs. Will occur.

On the other hand, when the _VDC value of the auxiliary charger 8 is set to + 200V in accordance with the transfer current value, the surface potential of the memory area is converged to around 0V as in the above-described example, so the photosensitive drum By performing the normal cleaning process of the residual toner No. 1 and performing the primary charging without further performing the static elimination exposure, the memory region can be uniformly charged to a desired potential.

FIG. 22 shows the transfer charger 5b in this embodiment.
3 shows the control value of the DC bias voltage value V _DC of the auxiliary charger 8 for each transfer current value for each color. Also,
FIG. 23 shows the transition of the surface potential of the memory effect region for each color, and the DC bias voltage value V _DC of the auxiliary charger 8 is shown in FIG.
The case where each color is controlled as shown in FIG. 2 and the case where the condition of the first color is used for all the colors will be described.

As will be understood with reference to FIG. 23, by controlling the DC bias voltage of the auxiliary charger based on the transfer current value and changing the control function for each color at the same time,
By controlling V _DC , the surface potential of the photosensitive drum 1 after the transfer process is performed as described above is
Regardless of the transfer current value, the normal region is always controlled to be near 0V. Therefore, it is possible to uniformly charge the memory area to a desired potential, as in the normal area, by performing the primary charging without performing the charge-removing exposure without causing a bad effect such as a cleaning failure. <Embodiment 9> In this embodiment, the DC bias voltage values of the auxiliary chargers 18a to 18d are controlled according to the transfer current values of the transfer chargers 15a to 15d shown in FIG. Further, also in this embodiment, the control value of the DC bias voltage with respect to the transfer current value is made different for each image forming unit. That is, in the image forming unit in the latter stage, since the residual charges due to the transfer process in the image forming unit in the former stage are present on the transfer material carrying belt 17, the same amount of transfer current is applied to the photosensitive drums 11a to 11d. It corresponds to the difference in the strength of the memory received.

After the charge removal process by the auxiliary chargers 18a to 18d is performed, the primary chargers 12a to 12d and the laser beam exposure devices 13a to 13d as the image exposure means are operated so that the photosensitive drums 11a to 11d are exposed. A color-separated electrostatic latent image corresponding to the image pattern is formed, and the electrostatic latent image is developed by yellow, magenta, cyan, and black toners by the operation of the developing devices 14a to 14d, respectively, to form a visible image. After being visualized, the visible image is transferred to the transfer material carrying belt 1 by the operation of the transfer chargers 15a to 15d.
7 is sequentially transferred to the transfer material P carried on the transfer material P.
A full color image is formed on top.

Also in this embodiment, the surface of the photosensitive drum 1 is discharged to a substantially uniform potential by the operation of the auxiliary chargers 18a to 18d shown in FIG. 10 before the primary charging. After that, the primary charging and the developing process were normally performed, and the toner image was formed in the memory effect area and transferred to the transfer material P as in the above-described embodiment, so that the image was not disturbed. Moreover, problems such as poor cleaning did not occur.

[0068]

As described above, according to the present invention,
After the transfer process is performed on the image carrier, the memory effect generated on the image carrier by the peeling discharge caused by the charge accumulation on the surface of the transfer medium, especially the charge accumulation at the edge of the transfer medium is performed. By performing destaticization controlled on the basis of the transfer material properties and transfer conditions, the memory effect area is developed to form a visible image as in the prior art, and this is not transferred to the transfer material. There is a remarkable effect that image disturbance and image unevenness due to the memory effect area can be surely prevented regardless of the type of the transfer material without causing a bad effect such as cleaning failure.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an outline of an image forming apparatus according to the present invention.

FIG. 2 is a vertical cross-sectional view showing the configuration of a scorotron-type primary charger.

FIG. 3 is a vertical sectional view showing an outline of a conventional image forming apparatus.

FIG. 4 is a perspective view showing a configuration of a transfer drum.

FIG. 5 is an operation explanatory diagram showing charge transfer.

FIG. 6 is an operation explanatory diagram showing charge transfer.

FIG. 7 is a diagram showing a memory effect area on the surface of a conventional photosensitive drum.

FIG. 8 is an operation explanatory diagram showing charge transfer.

FIG. 9 is a diagram showing a memory effect area on the surface of the photosensitive drum of the present invention.

FIG. 10 is a vertical sectional view showing the outline of a multicolor electrophotographic apparatus.

FIG. 11 is a vertical sectional view showing the outline of a laser beam printer.

FIG. 12 is a diagram showing a relationship between a property of a transfer material and a memory effect area.

FIG. 13 is a diagram showing a memory effect area on the surface of the photosensitive drum of the present invention.

FIG. 14 is a diagram showing a relationship between a property (type) of a transfer material and an auxiliary charging DC bias value.

FIG. 15 is a vertical cross-sectional view showing a transfer unit using a brush.

FIG. 16 is a vertical sectional view showing a transfer unit using a roller.

FIG. 17 is a diagram showing the relationship between the properties of the transfer material and the memory effect area.

FIG. 18 is a vertical cross-sectional view showing the outline of another image forming apparatus.

FIG. 19 is a diagram showing a relationship between a transfer current value and a memory effect area.

FIG. 20 is a diagram showing a relationship between a transfer current value for each color and a memory effect area.

FIG. 21 is a diagram showing a memory effect area on the photosensitive drum surface of the present invention.

FIG. 22 is a diagram showing a relationship between a transfer current value and an auxiliary charging DC bias value.

FIG. 23 is a diagram showing a transition of a memory effect area for each color.

[Explanation of symbols]

1, 11a to 11d, 31 Image carrier (photosensitive drum) 2, 12a to 12d, 32 Electrostatic latent image forming means (primary charger) 3, 13a to 13d, 33 Electrostatic latent image forming means (exposure means) 5b , 15a to 15d, 35 Transfer means (transfer charger) 7, 16a to 16d, 37 Cleaning means (cleaner) 8, 18a to 18d, 38 Decharging means (auxiliary charger) P Transfer material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G03G 21/00 116

Claims (11)

[Claims] 1. A transfer unit for transferring a visible image formed on an image carrier to a transfer material at a transfer position, and a decharging unit for decharging the image carrier that has passed through the transfer position. An image forming apparatus having the image forming apparatus, further comprising a control unit that changes a decharging condition of the decharging unit based on a property of the transfer material. 2. A transfer means for transferring a visible image formed on an image carrier to a transfer material at a transfer position, and a decharging means for decharging the image carrier passing through the transfer position. An image forming apparatus having the image forming apparatus, further comprising a control unit that changes a decharging condition of the decharging unit based on a transfer condition of the transfer unit. 3. An electrostatic latent image forming means for forming an electrostatic latent image on the image carrier, the electrostatic latent image forming means uniformly charging the image carrier to a desired potential. The image forming apparatus according to claim 1 or 2, further comprising: a charging unit and an exposing unit that exposes the image bearing member according to an image pattern. 4. The image forming apparatus according to claim 1, wherein the decharging unit is a corona decharging device. 5. The image forming apparatus according to claim 1, wherein at least one of a DC bias and an AC bias is applied to the decharging unit. 6. The condition of at least one of a DC bias amplitude, an AC bias amplitude, an AC bias frequency, an AC bias duty ratio, and a decharging current of the decharging means is controlled. Image forming device. 7. The image forming apparatus according to claim 1, wherein the transfer unit is a corona charger. 8. The image forming apparatus according to claim 1, wherein the transfer unit is a contact charger. 9. The image forming apparatus according to claim 1, wherein the decharging unit is controlled based on a voltage or a charging current applied to the transfer unit. 10. A cleaning unit for removing residual toner on the image carrier, the decharging unit being disposed between the transfer position and the cleaning unit. The image forming apparatus according to claim 9. 11. The image forming apparatus according to claim 1, wherein a next electrostatic latent image is formed immediately after the image carrier is decharged by the decharging unit.