JPH05173410A - Method and device for image formation - Google Patents

Abstract

PURPOSE:To greatly reduce sticking of toner to the transfer roll at the time of standby before an image forming action, to stably obtain an image of high quality, to prevent soiling of the back of paper, and furthermore, to prevent the needless consumption of developer in the method and device for image formation utilizing a transfer roll. CONSTITUTION:In the device where a toner image T1 is formed by visualizing an electrostatic latent image by feeding toner T to the electrostatic latent image along with the rotation of a developing and cleaning roll 33 faced to a photosensitive drum 3 and carrying out electrostatic transfer of this toner image T1 to paper through a transfer roll 9, the developing and cleaning roll 33 is controlled so that the developing and cleaning roll 33 is stopped at the time of standby before the image forming action, and thus, the unnecessary flow of toner T from the developing and cleaning roll 33 can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method in which an electrostatic latent image is formed on an image bearing member such as a photosensitive drum, and the electrostatic latent image is developed and transferred to a transfer material such as paper. Regarding the device.

[0002]

2. Description of the Related Art As this type of image forming apparatus, an electrophotographic apparatus, an electrostatic printer, etc. are known.

In these image forming apparatuses, after an electrostatic latent image is formed on a photosensitive drum, a developer (toner) is electrostatically attached to the electrostatic latent image to form a developer image. The image is recorded by transferring the developer image onto paper.

As a transfer method, a paper is superposed on a developer image, and a corona transfer method in which a charge having a polarity opposite to the developer charge (toner charge) is applied from the back side by a corona charger, or a voltage is directly applied to the paper through a roller. There is known a roller transfer method or the like in which the toner layer is transferred by applying an electric field to the toner layer.

Of these, the roller transfer method does not generate ozone, and since the transfer roller directly transfers the paper while pressing it against the photoconductor drum, it is easy to obtain close contact between the paper and the photoconductor drum surface. Compared with corona transfer, it has the feature that it is easy to obtain a transferred image of high quality, and in recent years, it has received particular attention.

[0006]

However, in the case where this roller transfer method is adopted, since the surface of the photoconductor drum and the transfer roller are in contact with each other, the photoconductor drum is in a state where no paper is interposed. The upper developer (toner) adheres to the transfer roller, and the back side of the paper is smeared when the paper is passed. In addition, if the amount of adhesion to the transfer roller is large, there is a problem that a good transfer state cannot be maintained and a high quality image cannot be stably obtained.

Particularly, in the case where the reversal development in which the potential on the photoconductor drum is low is developed by the high developing bias, the photoconductor drum is not charged during initialization (standby before the image forming operation). In the state of 0 V, there is a problem that the developer on the developing roller moves to the photosensitive drum side regardless of the presence or absence of the developing bias, and a large amount of this is transferred to the transfer roller.

Therefore, the present invention has been made based on the above circumstances, in which toner adhesion to the transfer roller can be remarkably reduced, a high-quality image can be stably obtained, and stains on the back of the paper can be prevented. An object of the present invention is to provide an image forming method and apparatus capable of preventing wasteful consumption of developer.

[0009]

The present invention provides, as a first means for solving the above problems, an electrostatic latent image forming step of forming an electrostatic latent image on an image carrier, and a step of facing the image carrier. A developing step of visualizing the electrostatic latent image by supplying a developer to the electrostatic latent image with the rotation of the developing roller, and forming the image on the image bearing member via a transfer roller in contact with the image bearing member. An image forming method comprising the step of electrostatically transferring the formed developer image to a transfer material that passes between an image carrier and a transfer roller. At the time, the developing roller is stopped.

Further, as a second means, an electrostatic latent image forming means for forming an electrostatic latent image on the image carrier, and an electrostatic latent image is developed by the rotation of the developing roller facing the image carrier. A developing unit that visualizes the electrostatic latent image by supplying a developer, and a developer image formed on the image carrier through a transfer roller that contacts the image carrier are transferred between the image carrier and the transfer roller. A transfer means for electrostatically transferring to a transfer material passing through the space; and a control means for controlling the developing roller so that the developing roller is stopped in a standby state before an image forming operation. It is configured.

[0011]

In the image forming method and apparatus of the present invention,
Since the developing roller is stopped during the standby before the image forming operation, only the developer at the contact portion adheres to the image carrier, and the other developer is not supplied. This makes it possible to significantly reduce the toner adhesion to the transfer roller as compared with the conventional case.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows the configuration of the image forming apparatus 1 of the cleanerless process type.

In FIG. 2, an image carrier having a diameter (30 mm in the embodiment) whose peripheral surface length is smaller than the length of an image to be recorded is provided at a substantially central portion of the image forming apparatus main body 2. The photoconductor drum 3 is rotatably provided in the direction of arrow A. The photoconductor drum 3 is made of an organic photoconductor (OPC) photoconductive material.

Further, around the photosensitive drum 3, along with its rotation direction, an erasing lamp 4 as a discharging means for performing a function to be described later and a depatterning device 5 as a depatterning means for the untransferred toner. A scorotron charger 6 as a charging means, a laser device 7 as an electrostatic latent image forming means,
A developing / cleaning device 8 as a means for developing and cleaning and a transfer roller 9 as a transferring means are provided. And
A toner image TI as a developer image is formed on the peripheral surface of the photosensitive drum 3.
The image forming means 10 for forming In addition, in the apparatus main body 2, a paper P as a transfer target material taken out from a paper feed cassette 11 mounted on one side of the apparatus main body 2 is
A sheet conveying path 14 is formed which leads to a sheet discharge tray 13 arranged on the other side of the apparatus main body 2 via an image transfer section 12 between the photosensitive drum 3 of the image forming unit 10 and the transfer roller 9. There is.

Further, the image transfer section 1 of the sheet conveying path 14
On the upstream side of 2, there is arranged an aligning roller pair 16 for aligning the leading edge of the paper P taken out from the paper feeding cassette 11 via the paper feeding roller 15 and then feeding it to the image transfer portion 12 at a timing. ing. In addition, the image transfer unit 1
A fixing device 17 for fixing the toner image TI transferred onto the paper P and a paper discharge roller pair 18 for discharging the fixed paper P to the paper discharge tray 13 are provided on the downstream side of 2.
Further, a gate 20 is provided between the fixing device 17 and the pair of paper discharge rollers 18 to guide the paper P fixed by the fixing device 17 to the reverse conveyance path 19 as necessary.

The sheet P guided to the reversal conveyance path 19 is placed with a sheet discharge roller pair 21 and a sheet discharge section 22 formed of a recess formed on the upper surface side of the apparatus main body 2 with its image forming surface facing down. It is designed to be ejected. Next, the configuration of the developing and cleaning device 8 will be described with reference to FIGS. 1, 3, and 4. FIG. 1 is a sectional view of the developing and cleaning device 8. The developing / cleaning device 8 has a toner storage portion 30 inside which serves as a developer storage portion.
It has a developing device main body 32 integrally formed with a toner hopper 31.

The developing device main body 32 is in a state in which a portion facing the photoconductor drum 3 is opened, and a nip width is elastically and deformed with respect to the photoconductor drum 3 in the vicinity of the opening. There is provided a developing roller (hereinafter referred to as a developing and cleaning roller) 33 which also functions as a cleaning roller and rotates in a state of being in contact with the photosensitive drum 3 in the direction of the width (arrow direction) with respect to the rotating direction of the photosensitive drum 3.

A toner transfer roller 34 as a developer transfer means for transferring the toner T to and from the developing cleaning roller 33 is provided at a portion of the rear side of the developing cleaning roller 33 which abuts on the bottom of the toner containing portion 30. There is.

Located inside the developing device main body 32 above the developing cleaning roller 33, the amount of toner conveyed by the developing cleaning roller 33 is regulated, and a thin layer of the toner T is formed on the surface of the developing cleaning roller 33. A blade 35 is provided as a developer layer forming means. The recovery blade 37 is provided in contact with the lower surface side of the developing and cleaning roller 33. A mixer 38 as a stirring means is provided in the toner storage portion 30 to stir the toner T.

As shown in FIGS. 1 and 3, the developing / cleaning roller 33 has elastic layers 33B and 10 ^{2 made of} urethane foam, silicone rubber, EPDM or the like around the metal shaft 33A. ~ 10 ⁸ A surface conductive layer 33C having an electric resistance of Ωcm is sequentially formed to form a roller having elasticity as a whole.

Further, a bias power source V is connected to the developing roller 33 and is electrically connected to the surface conductive layer 33C. As a result, a predetermined developing bias is applied during development and cleaning.

The toner transfer roller 34 has a structure in which a conductive soft polyurethane foam layer 34B is provided on the outer periphery of the metal shaft 34A, and rotates in the against direction with respect to the rotating direction of the developing and cleaning roller 33. It is like this. Further, it plays a role of conveying and supplying the toner T and preventing aggregation of the toner T on the inner bottom of the hopper 3.

Further, a bias voltage having the same potential as that of the developing and cleaning roller 33 is applied by the bias power source V so that good toner T mobility can be obtained.

The blade 35 includes a first blade holder 40, a spacer 41 and a second blade holder 42.
Is held by. The first blade holder 40 is rotatably supported via a shaft 43, and is constantly biased by a plurality of compression springs 44 for pressurization so as to rotate in a predetermined direction. 35
Is pressed against the developing and cleaning roller 33 by the urging force of the compression spring 44.

A foam material 45 made of maltoprene or the like is adhered to the back surface of the blade 35, and the foam material 45 contacts the baffle plate 46 attached to the first blade holder 40. Is becoming As a result, the vibration of the blade 35 can be suppressed and a good toner T layer can be formed.

As shown in FIG. 4, the blade 35 has a thin spring material 35A made of phosphor bronze or the like, and a tip 35B made of a rubber elastic material such as silicon rubber or urethane or a resin over substantially the entire length of the tip portion of the thin spring material 35A. It is bonded in the longitudinal direction. The tip of the chip 35B has a semicircular cross section, and the arcuate portion of the tip 35B is pressed against the developing and cleaning roller 33 with a predetermined weight.
The toner T passing therethrough is negatively triboelectrically charged with the same polarity as that of the photosensitive drum 3, and forms a layer of the toner T of about 1 to 3 layers. Further, the sealing material 3 is provided on both ends of the blade 35.
5C and 35C are attached.

The surface of the developing and cleaning roller 33 is
It is necessary to select in consideration of triboelectrification with the toner T and appropriate elasticity and friction. The surface conductive layer 33C
As the material of, for example, urethane resin mixed with 10 to 30 weight percent of conductive carbon is applied. Further, a bias power source V is connected to the developing and cleaning roller 33, and is electrically connected to the surface conductive layer 33C. As a result, a predetermined developing bias is applied during development and cleaning.

The transfer roller 9 has elastic layers 9B and 10 ⁵ around the metal shaft (rotating shaft) 9A, like the developing roller 33 described above. A surface conductive layer 9C having an electric resistance of -10 ¹⁰ Ωcm is sequentially formed. Here, a voltage of 600 to 2000 V is applied to the metal shaft 9A of the transfer roller 9 by the DC power source 36 (see FIG. 2), and 30 to 40 weight of conductive carbon is added to the silicon resin provided on both ends of the transfer roller 9. A voltage is applied to the surface conductive layer 9C via the conductive portion formed by the percentage. The bias applied to the transfer roller 9 is the paper P.
Is controlled to be "on" only when is between the photoconductor drum 3 and the transfer roller 9.

When the transfer bias is turned "on" in the portion where there is no paper P (paper interval), the photosensitive drum 3 in this portion is positively charged, and the toner T of the negative polarity accumulated in the depatterning device 5 is generated. A large amount of the toner is suddenly ejected, and the developing and cleaning device 8 cannot completely clean the image, so that an image is smeared on the next page. Therefore, the transfer bias is controlled so as to be “off” between the sheets, but if the transfer is turned off too early, the non-image area at the rear end of the sheet P becomes large, which is inconvenient. Become. Therefore, the transfer bias is turned off about 5 mm before the trailing edge of the paper.

Further, as shown in FIG. 5, the photosensitive drum 3
To supply electric power to the photoconductor drum drive motor 50 for driving the developer cleaning roller drive motor 51 for driving the development cleaning roller 33, the transfer roller drive motor 52 for driving the transfer roller 9, and the scorotron charger 6. The charging charger transformer 53 and the input unit 54 for inputting image forming information such as the number of copies and size are connected to a control device 55 as a control unit. Next, the image forming operation of the image forming apparatus 1 configured as described above will be described.

Rotate the photosensitive drum 3 in the direction of arrow A,
By using the scorotron charger 6 on the peripheral surface of the photosensitive drum 3,
It is negatively charged substantially uniformly at about -450 to -800 volts.
Then, a laser beam R is irradiated to the charged area from the laser device 7 in accordance with image information to be recorded and exposed to form an electrostatic latent image on the surface of the photosensitive drum 3. Then, this electrostatic latent image faces the developing and cleaning device 8 as the photosensitive drum 3 rotates.

At this point, the developing and cleaning roller 33 on which a layer of toner T as a so-called one-component developer having a triboelectric charging property is started to rotate, and the toner T is applied to the electrostatic latent image on the photosensitive drum 3. The toner image TI is formed by adhering. In this case, the toner T adheres to the light irradiation area and undergoes so-called reversal development. The toner T having an average particle size of about 8 to 15 μm is used, and is charged to about −5 to 30 μc / g by friction with the blade 35 and the developing and cleaning roller 33. -1150-400
A voltage of about volt is applied. Toner image TI after development
Are then conveyed to the transfer area facing the transfer roller 9.

On the other hand, in the transfer area, the paper P is taken out from the paper feed cassette 11 by the rotation of the paper feed roller 15 and is sent through the aligning roller pair 16 in synchronization with the rotation of the photosensitive drum 3. ..

The rear surface of the paper P conveyed here is charged to a positive polarity by the transfer roller 9. Therefore, the toner image TI on the surface of the photosensitive drum 5 is electrostatically attracted to the paper P and transferred.

Since such contact type transfer means exhibits stable transfer characteristics even under high humidity, it has the effect of reducing the amount of residual developer remaining on the transfer sheet and reducing the cleaning load. The paper dust is also removed to prevent the toner T from being mixed. Further, the sheet P after transfer is sent to the fixing device 17, where the toner T is melted and fixed on the sheet P by heat and pressure, and then discharged.

By the way, on the surface of the photosensitive drum 3 after the transfer, a small amount of the toner T left without being completely transferred or the positive and negative electrostatic latent images left after the transfer of the toner T remains. There is. These toner T or electrostatic latent image is first erased by the erasing lamp 4 to a negative latent image, and then conveyed to the non-patterning device 5 to be disturbed and unpatterned.

The non-patterning device 5 is 10 ³ -10 ⁹ Ωcm
The brush 5A made of a fiber having electric resistance (trade name: trading card, Kynol, etc.) is contacted. Conductive brush 5
A is rubbed with the rotation of the photosensitive drum 3, is connected to a bias power source (not shown), and a voltage of 200 to 1500 V is applied to temporarily adsorb the transfer residual toner T on the photosensitive drum 3. ..

Since most of the transfer residual toner T has a negative polarity, it is adsorbed to the brush 5A, but some of the transfer residual toner of the fog toner is positively charged, and these toner T is not adsorbed. Although it passes through, it is not a problem because the amount is very small.

The transfer-residual toner T temporarily trapped in the brush 5A is the time depending on the conditions such as the applied bias, the resistance of the brush 5A, the toner particle size, and the resistance.
Positive charges are injected and returned to the photoconductor drum 3 by the electric field formed by the brush 5A and the photoconductor drum 3. The toner T returned to the photoconductor drum 3 has a positive polarity, which is opposite to the normal polarity, but when the photoconductor drum 3 is charged by the scorotron transfer device 6, the toner T is also exposed to a negative corona. It has a negative polarity and is cleaned by the developing and cleaning device 8. The disturbed area is then conveyed to a charging position facing the scorotron charger 6,
It is piled up from above and charged with corona. After charging, it is exposed by the laser device 7 to form an electrostatic latent image, and again reaches the developing and cleaning position facing the developing and cleaning device 8 (second time).

In this case, in the electrostatic latent image formed the second time, even in the exposed portion (image portion to which toner should adhere) and the non-exposed portion (non-image portion), the roller transfer greatly reduces. In addition, since the residual toner is substantially evenly and sufficiently thinly scattered in advance, exposure unevenness does not occur.
Therefore, even in the second development, the residual potential after exposure becomes uniform, so that a uniform toner image can be obtained.

Here, the cleaning and developing roller 33 is in contact with the photosensitive drum 3 with a contact width (nip) so as to enhance the cleaning ability, and moreover, the residual potential of the exposed portion and the potential of the non-exposed portion are set. A developing bias having a value in between is applied. As a result, new toner T is attached from the developing / cleaning roller 33 to the exposed portion, and at the same time, in the non-exposed portion, the toner T that is attached because the attraction force by the developing bias exceeds that of the photosensitive drum 3 is successively applied. And is attracted to and collected by the developing and cleaning device 8.

In this way, the photosensitive drum 3 is rotated in an overlapping manner and used in duplicate, so that one recorded image is obtained. Then, after development and cleaning, the toner image TI is transferred to the paper P at a position facing the transfer roller 9. Hereinafter, similar steps are repeated.

According to the present invention, as shown in FIG.
5, when the photosensitive drum drive motor 50, the charging charger transformer 53, and the transfer roller drive motor 52 are simultaneously turned “on” during standby (initialization) before the image forming operation of the image forming apparatus 1, as shown in FIG. The development cleaning roller 33 is controlled so as to be delayed by the phase difference time t ₁ between the scorotron charger (charger) 6 and the development cleaning roller 33 shown in FIG. Then, as shown in the lower position of FIG. 6, the toner T is prevented from adhering to the photosensitive drum 3 for t ₁ hours. FIG. 8 shows a conventional operation timing, that is,
The case where all of them are turned “on” at the same time is shown, and it can be seen that toner is remarkably attached to the drum for t ₁ hours.

In the reversal development, a portion having a low potential on the photosensitive drum 3 is developed with a high developing bias.
As shown in FIG. 9, the non-magnetic one-component contact development described in the present invention prints a solid black image with a very high developing effect even when the difference between the surface potential of the photoconductor and the developing bias is zero, that is, even when the potential is the same. Since it has a level of developing ability, the above control is required.

Using the apparatus of the embodiment, a print test was carried out under the conditions of the surface potential of the photosensitive drum 3 of 550 v, the developing bias of the developing cleaning roller 33 of 200 v, and the applied voltage of 1000 v of the transfer roller 9, and the back stain was a problem. Markedly reduced to a level without. In addition, unnecessary toner consumption can be prevented.

[0046]

As described above, according to the present invention, in the image forming method and apparatus using the transfer roller, toner adhesion to the transfer roller during standby before the image forming operation can be remarkably reduced, and high image quality can be achieved. It is possible to obtain an image in a stable manner, prevent back stains on the paper, and prevent wasteful consumption of the developer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a main part of an image forming apparatus of the present invention.

FIG. 2 is a front view schematically showing the internal configuration of the image forming apparatus of the present invention.

FIG. 3 is a perspective view showing a cross section of a part of the developing and cleaning roller shown in FIG.

FIG. 4 is a perspective view of the blade shown in FIG.

FIG. 5 is a block diagram showing a control system.

FIG. 6 is an explanatory diagram showing the amount of toner adhered on the drum according to the operation timing of the present invention.

FIG. 7 is an explanatory diagram showing a phase difference time between a charging charger and a developing cleaning roller.

FIG. 8 is an explanatory diagram showing a comparative example with respect to FIG.

FIG. 9 is an explanatory diagram showing the relationship between the difference between the photosensitive member surface potential and the developing bias and the developing ability.

[Explanation of symbols]

1 ... Image forming apparatus, 3 ... Photosensitive drum (image bearing member), 4
... Erase lamp (static elimination means), 5 ... Non-patterning device (non-patterning means), 6 ... Scorotron charger (charging means),
Reference numeral 7 ... Laser device (electrostatic latent image forming means), 8 ... Development cleaning device (developing and cleaning means), 9 ... Transfer roller (transfer means), 33 ... Development cleaning roller, 55 ... Control device (control means), T Toner (developer), TI ... Toner image (developer image), P ... Paper (transfer material).

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigenobu Osawa 70 Yanagicho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi factory

Claims (2)

[Claims] 1. An electrostatic latent image forming step of forming an electrostatic latent image on an image bearing member, and supplying a developer to the electrostatic latent image with the rotation of a developing roller facing the image bearing member. And a developing step of visualizing the electrostatic latent image by means of a transfer roller which is in contact with the image carrier and passes the developer image formed on the image carrier between the image carrier and the transfer roller. A transfer step of electrostatically transferring to a transfer material,
In the image forming method, the image forming method is characterized in that the developing roller is stopped when the developing roller is on standby before an image forming operation. 2. An electrostatic latent image forming unit that forms an electrostatic latent image on an image carrier, and a developer is supplied to the electrostatic latent image as the developing roller facing the image carrier rotates. A developing unit that visualizes the electrostatic latent image and a transfer roller that is in contact with the image carrier, and a developer image formed on the image carrier, and a transferred image that passes between the image carrier and the transfer roller. Transfer means for electrostatically transferring to the material, control means for controlling the developing roller so that the developing roller is stopped during standby before image forming operation,
An image forming apparatus comprising: