JP2001100600A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which properly removes oil on a drum to obtain a satisfactory image. SOLUTION: In an image forming device provided with a transfer device 105 which transfer a toner image developed on a photoreceptor drum 101 to a transfer material in a transfer part and fixing devices 171 and 172 which fix toner on the transfer material, toner ion the photoreceptor drum 101 is transferred to the transfer material, and toner is fixed to form an image by passage of the transfer material in fixing device; and if toner on the drum 101 is transferred to the transfer material to form an image again or plural times thereafter, the drum 101 is idly rotated for a time longer than the time for only one image formation.

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 using an electrophotographic method used for a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art Conventionally, copying using a method of transferring a toner onto a transfer material and fixing the image by a fixing device, and then transferring or fixing the toner onto the same transfer material again or a plurality of times to form a final image. There are image forming apparatuses such as machines.

[0003] Such a method is roughly divided into two types, "double-sided" and "multiplexed".

[0004] Double-sided is a method of forming an image on both sides of paper by transferring toner on the side opposite to the side on which the toner has been transferred once. On the other hand, multiplexing is a method of forming an image by transferring toner of a different color from the first color on the same surface as the surface on which the toner has been transferred.

FIG. 2 shows an example of a conventional copying machine employing such a method. In FIG. 2, reference numeral 101 denotes a photosensitive drum, which is an electrostatic latent image carrier, which rotates in the direction of arrow a, and the surface of the photosensitive drum is uniformly charged by a primary charger 102, and then a scanner 103 is placed on a platen. When reading the placed document, a latent image is written through the mirror groups 131, 132, and 133. Reference numeral 141 denotes a developing device, which develops the electrostatic latent image created as described above using toner by a predetermined method. The developed image is transferred to the transfer charger 105.
Is transferred onto paper as a transfer material. The transferred paper is further conveyed to a fixing unit and fixed by fixing rollers 171 and 172, and then conveyed to a transfer unit again for multiple or double-sided image formation via roller groups 191 and 192. For example, this time, the developed image visualized by the developing device 142 is transferred onto paper and again fixed to the fixing rollers 171, 17
After the image is fixed by the image forming unit 2, the sheet is discharged to the discharge unit 111. The remaining toner that has not been transferred is cleaned by the cleaning blade 106 and stored as waste toner.

In the conventional example described above, the photosensitive drum 10
The cleaning failure for No. 1 is even more severe during "multiple" image formation where the fixed toner image surface again contacts the photosensitive drum surface. In other words, when forming a "double-sided" image, the surface that comes into contact with the photosensitive drum again is the transfer material itself without toner, and the transfer material generally absorbs oil, and almost no oil is present on the surface. On the other hand, at the time of “multiple” image formation, there is the toner that has been melted and smoothed by the fixing device on the surface that comes into contact with the surface of the photosensitive drum again, and the smoothed toner removes the oil in the fixing device. This is because it is easy to hold on the surface and, if it is strong, the amount of transfer to the photosensitive drum increases.

[0007]

By the way, oil is applied to the surface of a fixing roller used in an image forming apparatus such as the above-mentioned conventional example.
This is an essential technique that is used to extend the life of the fixing roller itself and to prevent offset of toner to be fixed to the roller. Therefore, a small amount of oil is naturally applied to the fixed paper. Therefore, if "double-sided" or "multiple" image formation is performed particularly continuously on a plurality of sheets, oil adheres to the surface of the photosensitive drum.
Therefore, when an image is to be formed normally thereafter, the toner adheres to the originally white area by the adhesive force of the oil and appears as fog, while the original originally solid area also shows the toner by the adhesive force of the oil. This time, there is a problem that the toner is not sufficiently transferred from the drum onto the paper, resulting in a light image.

An object of the present invention is to provide an image forming apparatus which can solve the above-mentioned problems, appropriately removes oil on a drum, and can obtain a good image.

[0009]

According to a first aspect of the present invention, there is provided an electrostatic latent image carrier, and a toner image developed on the electrostatic latent image carrier is provided at a portion closest to the electrostatic latent image carrier. And a fixing device for fixing the toner on the transfer material in the transfer unit, wherein the transfer unit transfers the toner onto the transfer material. Is transferred, and the transfer material passes through a fixing device to fix the toner and form an image. Then, the toner on the electrostatic latent image carrier is transferred onto the transfer material again or multiple times. When an image is formed, the electrostatic latent image carrier is idly rotated for a longer time than at least once image formation.

According to a second aspect of the present invention, there is provided an electrostatic latent image carrier, and a toner image developed on the electrostatic latent image carrier is transferred to a transfer portion which is the closest part to the electrostatic latent image carrier. In an image forming apparatus having a transfer device for transferring onto a transfer material and a fixing device for fixing the toner on the transfer material, the toner on the electrostatic latent image carrier is transferred onto the transfer material, When the toner is fixed and the image is formed by passing the transfer material through the fixing device, and then the toner on the electrostatic latent image carrier is transferred onto the transfer material again or plural times to form an image. In addition, the amount of toner to be developed in the non-image area is larger than that in at least one-time single-sided image formation.

[0011]

1 and 3 show a first embodiment of the present invention. <Embodiment 1> FIG. 1 is an enlarged schematic view around a photosensitive drum in an image forming apparatus for explaining the effect of the present invention.

In FIG. 1, not all of the toner visualized on the photosensitive drum is transferred onto the transfer paper by the transfer charger 105, but rather adheres to the photosensitive drum 101 as indicated by 181. The cleaning blade 106 is transported to the cleaning unit 110 where the cleaning blade 106 and the photosensitive drum 101 are in contact with each other.
It is scraped off by 6. The scraped toner is received by the rake sheet 162 so as not to be spilled, and is collected inside the cleaner 161.

At this time, the oil adhering to the photosensitive drum adheres to the toner particles 108 accumulated in the cleaning unit 110 when passing through the cleaning unit 110, and is cleaned from the photosensitive drum 101 together with the adhered toner particles 108. Is done. The following experiment was performed to confirm this. <Confirmation Experiment> The oil adhering to the photosensitive drum was tried to be scraped off with only the cleaning blade 106 without placing any toner on the photosensitive drum, but could not be sufficiently removed.

On the other hand, in the present embodiment, when the toner is accumulated in the cleaning unit 110 and the cleaning is performed by the cleaning blade 106, the oil adhering to the photosensitive drum is completely removed.

According to this experiment, the oil adhering to the photosensitive drum permeates (adheres) to the toner particles accumulated in the cleaning section, and is removed together with the toner by removing the toner particles with a cleaning blade. The mechanism of oil removal is easily imagined.

Accordingly, increasing the idling speed of the photosensitive drum makes it easier for the oil adhering to the photosensitive drum to adhere to the toner particles, thereby improving the oil cleaning performance.

Based on the above idea, "multiple"
During post-rotation when forming a "double-sided" image, the number of idle rotations of the photosensitive drum is increased by one rotation, preferably three or more rotations compared to the normal one-sided image formation, so that the oil adhering to the photosensitive drum is completely removed. Could be removed. <Embodiment 2> As described above, oil is most likely to adhere to the photosensitive drum during "multiplex" image formation. Therefore, it is necessary to further increase the number of idle rotations of the photosensitive drum by one rotation, preferably two rotations at the time of "multi-sided" image formation as compared with the case of "double-sided" image formation. Is fully demonstrated. <Embodiment 3> In the present embodiment, the toner is placed on the photosensitive drum during the idle rotation as described in the first embodiment, thereby further improving the oil cleaning property. Can be improved.

That is, as described in the first embodiment of the oil cleaning mechanism, the oil adheres to the toner and is cleaned together with the toner. Therefore, as the amount of the toner participating in the cleaning increases, the oil cleaning ability increases. Will be improved. Actually, it is sufficient to develop a solid image by a desired width during idle rotation. By doing so, the idle rotation time can be shortened. <Embodiment 4> The embodiment described above can be applied to a full-color image forming apparatus having a so-called transfer drum, and a similar effect can be obtained.

FIG. 3 shows an example of such a general full-color image forming apparatus.

In FIG. 3, the full-color image forming apparatus has a photosensitive drum 101 which is rotatably supported and rotates in the direction of an arrow, and an image forming means is arranged on the outer periphery thereof. The image forming means may be any means, but in the present embodiment, a primary charger 102 for uniformly charging the photosensitive drum 101, and irradiating a color-separated light image or a light image corresponding thereto to the photosensitive drum 101, An exposure unit 130 such as a laser beam exposure unit for forming an electrostatic latent image on the photosensitive drum 101 and a rotary developing device 140 for visualizing the electrostatic latent image on the photosensitive drum 101 are provided.

The rotary developing device 140 includes four developing devices 104 for separately storing four color developers of a yellow developer, a magenta developer, a cyan developer, and a black developer.
Y, 104M, 104C, and 104K, and a substantially cylindrical support that holds these four developing units and is rotatably supported on the shaft. The rotary developing device 140 transports a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 101 by rotating the support, and develops an electrostatic latent image on the photosensitive drum 101 to perform full-color development for four colors. Is configured to be possible.

The visible image on the photosensitive drum 101, that is, the toner image, is transferred onto a transfer material P carried and conveyed by a transfer drum 150 as a transfer material carrier. In this embodiment, the transfer drum 150 is rotatably supported on a shaft, and a transfer material carrying member 151 is stretched in the opening area on the outer peripheral surface. As the transfer material carrying member 151, for example, a film-shaped dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin film is used. Further, the transfer drum 150 has a transfer material gripper 157 for gripping the transfer material P fed from the sheet feeding device.
Further, inside and outside the transfer drum 150, a transfer discharger 152, an inner discharger 153 and outer dischargers 154 and 155 constituting a discharging unit are disposed.

The process of forming a full-color image by the full-color electrophotographic copying apparatus having the above-described configuration will be briefly described.

The photosensitive drum 101 is uniformly charged by the primary charger 2 and is irradiated with a light image E corresponding to image information by the exposure means 130 to form an electrostatic latent image on the photosensitive drum 101. The electrostatic latent image is visualized as a toner image on the photosensitive drum 101 with a toner having an average particle diameter of 8 to 10 μm on the photosensitive drum 101 by the rotary developing device 140. On the other hand, the transfer material P is guided to the transfer portion, which is the area where the photosensitive drum 101 and the transfer drum 150 are closest, through the paper feed guide 118 in synchronization with the image by the registration roller 114. At this time, a corona discharge having a polarity opposite to that of the toner is performed from the back surface of the dielectric sheet 151 by the transfer discharger 152, so that the first color toner image on the photosensitive drum 101 is transferred onto the transfer material P. After the transfer material P has been further subjected to the necessary number of transfer steps, the discharger 153, 1
The transfer belt 116 is separated from the transfer drum 150 by the action of the separation claw 115 while being subjected to the charge removal by 54 and 155.
After being fixed by the heat roll in the fixing device 117, the sheet is discharged out of the apparatus.

At this time, when images are formed on both surfaces of the transfer material P, the transfer material transport guide 119 is driven immediately after the fixing device 117 is discharged, and the transfer material is guided to the transport guide 120. The image is temporarily stored in the transfer material stocker 121, and an image is formed on the other surface again by the above-described image forming process.

On the other hand, the photosensitive drum 101 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 160.

The cleaning device 1 also includes a fur brush and the like on the surface of the dielectric sheet of the transfer drum 150.
After being cleaned by the action of 80 and the cleaning assisting means 181, it is again subjected to the image forming process.

At this time, when the toner is transferred to the back surface after the image on the front surface is formed, the fixing oil, which has been once passed through the fixing roller, adheres to the transfer material P, particularly on the front surface (on the toner). The oil is first transferred onto the dielectric sheet of the transfer drum, and the oil is transferred onto the surface of the photosensitive drum when the photosensitive drum and the transfer drum sheet come into contact with each other at the transfer section.

Therefore, in the full-color image forming apparatus having the transfer drum as described above, the number of rotations of the photosensitive drum is at least one rotation at the time of double-sided formation compared to the normal one-sided image formation. By increasing the number of rotations by three or more, oil adhering to the photosensitive drum can be removed. <Embodiment 5> FIGS. 4 and 5 show Embodiment 5 of the present invention.
Is shown.

In this embodiment, the amount of toner on the photosensitive drum is increased to facilitate removal of oil adhering to the photosensitive drum.

FIG. 4 is an enlarged schematic view around the photosensitive drum in the image forming apparatus.

In FIG. 4, not all of the toner visualized on the photosensitive drum is transferred onto the transfer paper by the transfer charger 205, but rather adheres to the photosensitive drum 201 as indicated at 281. The cleaning blade 20 is transported to the cleaning section 210, which is a contact portion between the cleaning blade 206 and the photosensitive drum 201.
It is scraped off by 6. The scraped toner is received by the rake sheet 262 so as not to be spilled, and is collected inside the cleaner 261.

However, the oil adhering to the photosensitive drum was not scraped off with only the cleaning blade 6 without any toner on the photosensitive drum, but could not be sufficiently removed. On the other hand, when the toner was sprayed on the photosensitive drum and the cleaning was performed by the cleaning blade 206, the oil adhering to the photosensitive drum was completely removed.

According to this experiment, the oil adhering to the photosensitive drum permeates (adheres) to the toner particles spread on the photosensitive drum, and is removed together with the toner by removing the toner particles with a cleaning blade. It is easy to imagine the mechanism of oil removal.

Therefore, increasing the amount of toner on the photosensitive drum makes it easier for the oil adhered on the photosensitive drum to adhere to the toner particles, thereby improving the oil cleaning performance.

On the other hand, in order to prevent the cleaning blade from being turned up, a method of developing the toner on the photosensitive drum during pre-rotation, post-rotation or both is used (hereinafter, abbreviated as "batch-in"). The toner image pattern to be developed is to reduce the toner consumption as much as possible only in front of and behind the photosensitive drum,
It does not actively remove oil adhering to the photosensitive drum.

Based on the above idea, "multiple"
During the post-rotation when forming a “double-sided” image, the amount of toner consumed for developing on the photosensitive drum from the developing device is conventionally about 5 m.
g / A4, but 50 mg / A4, preferably 1
The oil attached to the photosensitive drum could be removed by increasing the width of the photosensitive drum and the consumption thereof by increasing the thickness of the photosensitive drum to at least 00 mg / A4. <Embodiment 6> As described above in connection with the conventional problem, oil is most easily applied to the photosensitive drum during "multiplex" image formation.

For this reason, in the present embodiment, the amount of toner consumed in the "multiple" image formation is 50 mg / A4, preferably F20, more than in the "double-sided" image formation.
The toner is developed on the photosensitive drum so as to be 0 mg / A4 or more. Thereby, the effect of the present invention is sufficiently exhibited. <Embodiment 7> In this embodiment, "multiple" and "double-sided"
When a large number of images are continuously formed, the developing operation is appropriately performed as in the fifth embodiment. Thereby, the effects of the present invention can be more effectively exhibited.

Here, the term “appropriate amount” depends on the number of sheets, paper size, and density of the image formed at that time. For example, since the larger the number of sheets, the larger the amount of oil adhering thereto, the developing operation may be performed each time an appropriate number of images are formed on the non-image portion during image formation.

When the paper size is a small size such as B5 size, the oil adhering to the photosensitive drum is only the paper size, so there is no need to wastefully consume the toner. In the case of an analog optical system, a shutter or the like may be operated, and in the case of a digital optical system, a laser may be operated to perform the above-described developing operation only on necessary portions. <Embodiment 8> The configuration of the embodiment described above is also effective in a full-color image forming apparatus having a so-called transfer drum, and the same effects can be obtained.

FIG. 5 shows an example of a full-color image forming apparatus having a transfer drum.

In FIG. 5, the full-color image forming apparatus has a photosensitive drum 201 which is rotatably supported and rotates in the direction of the arrow, and an image forming means is arranged on the outer periphery thereof. The image forming means may be any means, but in this embodiment, a primary charger 202 for uniformly charging the photosensitive drum 201, and irradiating a color-separated light image or a light image corresponding thereto to the photosensitive drum 201 An exposure unit 230 such as a laser beam exposure unit that forms an electrostatic latent image on the photosensitive drum 201 and a rotary developing device 240 that visualizes the electrostatic latent image on the photosensitive drum 201 are provided.

The rotary developing device 240 includes four developing devices 204 for separately storing four color developers of a yellow developer, a magenta developer, a cyan developer, and a black developer.
Y, 204M, 204C, and 204K, and a substantially cylindrical support that holds these four developing units and is rotatably supported. The rotary developing device 240 transports a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 201 by rotating the support, and develops an electrostatic latent image on the photosensitive drum 201 to perform full-color development for four colors. Is configured to be possible.

The visible image on the photosensitive drum 201, that is, the toner image, is transferred to a transfer material P carried and transported by a transfer drum 250 as a transfer material carrier. In this embodiment, the transfer drum 250 is rotatably supported on a shaft, and a transfer material carrying member 251 is stretched in an outer peripheral surface opening area. As the transfer material carrying member 251, a film-like dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin film is used, for example. Further, the transfer drum 250 has a transfer material gripper 257 that grips the transfer material P fed from the sheet feeding device.
Further, inside and outside the transfer drum 250, a transfer discharger 252, and an inner discharger 253 and outer dischargers 254 and 255 constituting a discharger are disposed.

The process of forming a full-color image by the full-color electrophotographic copying apparatus having the above-described configuration will be briefly described.

The photosensitive drum 201 is uniformly charged by the primary charger 202, and the exposure means 230 irradiates a light image E corresponding to image information to form an electrostatic latent image on the photosensitive drum 201. The electrostatic latent image has an average particle diameter of 8 to 1 based on a resin as a base material on the photosensitive drum 201 by the rotary developing device 240.
It is visualized as a toner image with 0 micron toner. On the other hand, the transfer material P passes through the paper feed guide 218 in synchronization with the image by the registration roller 214 and passes through the photosensitive drum 201.
And the transfer drum 250 is guided to a transfer portion which is a region where the transfer drum 250 comes closest. Then, at this time, the corona discharge of the polarity opposite to that of the toner is performed from the back surface of the dielectric sheet 251 by the transfer discharger 252, so that the toner image on the photosensitive drum 201 of the first color is transferred onto the transfer material P. After the transfer material P has been further subjected to the necessary number of transfer steps, the discharger 25
The separation claw 215 while being neutralized by 3,254,255
The sheet is separated from the transfer drum 250 by the action of, and after being fixed by a heat roll in the fixing device 217 by the transport belt 216, is discharged out of the apparatus.

At this time, when images are formed on both sides of the transfer material P, the transfer material transport guide 219 is driven immediately after the fixing device 217 is discharged, and the transfer material is guided to the transport guide 220, and then the transfer material is transferred. Is temporarily stored in the material stocker 221,
An image is formed on the other surface again by the above-described image forming process.

On the other hand, the photosensitive drum 201 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 260.

The surface of the dielectric sheet of the transfer drum 250 is also a cleaning device 2 made of a fur brush or the like.
After being cleaned by the action of 80 and the cleaning assisting means 281, it is again subjected to the image forming process.

At this time, when the toner is transferred to the rear surface after forming the image on the front surface, the fixing oil, which has been once passed through the fixing roller, adheres to the transfer material P particularly on the surface (on the toner). The oil is first transferred onto the dielectric sheet of the transfer drum, and the oil is transferred onto the surface of the photosensitive drum when the photosensitive drum and the transfer drum sheet contact each other at the transfer section.

Therefore, even in the full-color image forming apparatus having the transfer drum as described above, the amount of toner consumed for developing on the photosensitive drum from the developing device during post-rotation when forming an image is conventionally considered. Unlike the banding, the oil adhering to the photosensitive drum could be removed by increasing the width of the photosensitive drum and the consumption thereof to 100 mg / A4, preferably 500 mg / A4 or more.

[0052]

As described above, the effects of the present invention are as follows.

According to the first invention, "double-sided" / "multiple"
When forming an image, the number of idle rotations of the photosensitive drum is increased at least compared with the case of forming an image only once on one side, so that the oil adhering to the photosensitive drum can be removed, and “double-sided” / “multiplex” image formation can be performed. Even if it is performed, toner adheres to the originally white area and appears as fog due to the adhesive force of oil seen in the conventional example, or the originally solid area does not transfer toner sufficiently from the drum to the paper The problem that the image becomes faint was solved.

According to the second invention, "double-sided" / "multiple"
At the time of image formation, the oil adhering to the photosensitive drum can be removed by increasing the consumption of the toner to be developed in the non-image area than at least once on one side of the image formation,
Even if multiple "double-sided" and "multiple" image formations are continuously performed, toner adheres to the originally white area and appears as fog due to the adhesive force of the oil seen in the conventional example. This solves the problem that the solid area is not sufficiently transferred from the drum to the toner on the paper, resulting in a light image.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged view around a photosensitive drum for describing Embodiment 1 of an image forming apparatus of the present invention;

FIG. 2 is a diagram illustrating a conventional image forming apparatus.

FIG. 3 is a diagram showing Embodiment 4 of the image forming apparatus of the present invention.

FIG. 4 is a schematic enlarged view around a photosensitive drum for describing Embodiment 5 of the image forming apparatus of the present invention.

FIG. 5 is a diagram showing an eighth embodiment of the present invention.

[Explanation of symbols]

101 photosensitive drum 102 primary charger 103 optical scanner 141 142 developing device 105 transfer charger 106 cleaning blade 171, 172
Fixing roller 108 toner 110 cleaning section 150 transfer drum 151 transfer sheet 180 fur brush cleaner 121 stocker 201 photosensitive drum 205 transfer charger 206 cleaning blade 208 toner 210 cleaning section 250 transfer drum 251 ... Transfer sheet 280 ... Fur brush cleaner 221 ... Stocker

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuo Nami 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Ryuichiro Maeyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Masakazu Eto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Ken Kenjo 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (7)

[Claims] An electrostatic latent image carrier and a toner image developed on the electrostatic latent image carrier are transferred onto a transfer material at a transfer portion closest to the electrostatic latent image carrier. Transfer device,
An image forming apparatus having a fixing device for fixing toner on the transfer material, wherein the toner on the electrostatic latent image carrier is transferred onto the transfer material, and the transfer material passes through the fixing device. Then, when the toner is fixed and an image is formed, and then the toner on the electrostatic latent image carrier is transferred onto the transfer material again or plural times to form an image, the image is formed at least once. An image forming apparatus wherein the electrostatic latent image carrier is idly rotated for a long time. 2. The image forming apparatus according to claim 1, wherein the idle rotation is performed during a subsequent rotation after a series of image formation at that time is completed. 3. The image forming apparatus according to claim 1, wherein the idle rotation is performed for the longest time when forming an image on the transfer material at the time of forming a multiple image. 4. An electrostatic latent image carrier, and a toner image developed on the electrostatic latent image carrier is transferred onto a transfer material at a transfer portion closest to the electrostatic latent image carrier. Transfer device,
An image forming apparatus having a fixing device for fixing toner on the transfer material, wherein the toner on the electrostatic latent image carrier is transferred onto the transfer material, and the transfer material passes through the fixing device. When the toner on the electrostatic latent image carrier is transferred onto the transfer material again or plural times after the toner is fixed and an image is formed, thereby forming an image, at least one time of forming a single-sided image. An image forming apparatus characterized in that the amount of toner used for developing a non-image portion is larger than that of a non-image portion. 5. The image forming apparatus according to claim 4, wherein the developing operation on the non-image portion is performed during post-rotation after a series of image forming at that time is completed. 6. The image forming apparatus according to claim 4, wherein the developing operation on the non-image portion is performed for the longest time when the image forming method on the transfer material is formed on a multiplex image. 7. The image forming apparatus according to claim 4, wherein the developing operation for the non-image portion is performed in an appropriate amount in accordance with the number of images to be formed, the paper size, and the image density.