JP2002169389A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely removes a large amount of residual toner on an intermediate transfer body without using a complex and expensive cleaner. SOLUTION: The image forming device is provided with the intermediate transfer body 2 disposed opposite to an image carrier 1 on which a toner image T is formed and held, a primary transfer means 3 which receives a primary transfer bias applied thereto and transfers the toner image T on the image carrier 1 onto the intermediate transfer body 2, and a secondary transfer means 4 which receives a secondary transfer bias applied thereto and transfers the toner image on the intermediate transfer body 2 onto a recording medium K, an image carrier blade 5 which is disposed in pressure contact with the image carrier 1 and removes residual toner on the image carrier 1, and an intermediate transfer blade 6 which is disposed so as to freely come into contact with the intermediate transfer body 2 and move apart therefrom and which removes residual toner on the intermediate transfer body 2. In the image forming device, an opposite bias application means 7 is provided for applying an opposite bias, the polarity of which is opposite to that of the primary transfer bias and the absolute value of which is smaller than the primary transfer bias, to the primary transfer means 3.

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 copying machine or a laser printer.
A toner image formed on an image carrier such as a photosensitive drum is
The present invention relates to an improvement in an image forming apparatus of a type that transfers an image to a recording medium such as a sheet via an intermediate transfer member.

[0002]

2. Description of the Related Art As a conventional intermediate transfer type image forming apparatus, for example, an image carrier (for example, a photosensitive drum) on which a toner image corresponding to an electrostatic latent image is formed and carried, and a photoconductor drum is disposed opposite to the image carrier. Intermediate transfer body (eg, intermediate transfer belt)
A primary transfer device for transferring the toner image on the photosensitive drum onto the intermediate transfer belt, and a secondary transfer device for transferring the toner image on the intermediate transfer belt onto a recording medium (for example, paper). Are known.

[0003] In such an image forming apparatus, the toner (residual toner) remaining after the primary transfer cannot be transferred onto the photosensitive drum after the primary transfer adheres. Therefore, the residual toner is cleaned and removed by a drum cleaner. Thereafter, the next toner image is formed. On the other hand, since the residual toner remaining after the secondary transfer is not adhered to the intermediate transfer belt after the secondary transfer, the residual toner is cleaned with a belt cleaner.
After the removal, the next toner image is transferred. Conventionally, this type of drum cleaner or belt cleaner uses a blade made of rubber or other material having appropriate hardness, and a cleaning blade system in which the edge of this blade is pressed against a photosensitive drum or an intermediate transfer belt to scrape off toner. Or a magnetic brush (Japanese Unexamined Patent Publication No.
No. 2) or a conductive brush (JP-A-7-6444).
A fur brush method for removing toner by using a cleaning brush method is known. In particular, a cleaning blade method is widely used because it is simpler in cost, has lower cost, and has higher reliability than the fur brush method. Have been.

[0004] In this type of image forming apparatus, the belt cleaner not only has a residual toner after the secondary transfer but also a residual toner that cannot be secondary-transferred due to a trouble such as paper jam (hereinafter, untransferred residual toner). Cleaning is also performed. Particularly, when forming a full-color image, it is necessary to remove up to about three times the amount of toner as compared with when forming a monochrome image. Therefore, the load applied to the belt cleaner becomes extremely large with the blade or the fur brush alone, and there is a possibility that a large amount of the untransferred residual toner generated cannot be removed. Therefore, in consideration of the cleaning performance at the time of such a trouble, it is necessary to use a high-performance belt cleaner such as a combination of a blade and a brush, which causes an increase in the complexity of the apparatus and an increase in the cost of the belt cleaner. There was a technical problem of getting lost.

[0005] In order to solve such a technical problem, for example, when a large amount of untransferred residual toner is generated due to the occurrence of paper jam or the like, the belt cleaner is separated from the intermediate transfer belt to remove the primary transfer. The untransferred residual toner is reverse-transferred onto the photoconductor drum by applying a DC bias having a polarity opposite to that of the primary transfer to the transfer device, and then the untransferred residual toner reverse-transferred onto the photoconductor drum is cleaned with a drum cleaner. (See JP-A-5-297739).

[0006]

However, in the above-mentioned prior art, it may be possible to reduce the load on the belt cleaner, but this time, the load on the drum cleaner is significantly increased. become.
That is, in this case, it is necessary to use a high-performance drum cleaner, which causes a technical problem that the cleaner becomes complicated and that the cost of the drum cleaner increases.

Further, by applying a DC bias having a polarity opposite to that of the primary transfer to the residual toner on the intermediate transfer belt, the residual toner is charged to a polarity opposite to a normal charging polarity,
After the residual toner on the intermediate transfer belt is reverse-transferred onto the photosensitive drum at the same time as the primary transfer, the residual toner reverse-transferred onto the photosensitive drum is cleaned with a drum cleaner, thereby eliminating the need for a belt cleaner. A technique has also been proposed (see JP-A-9-44007). However, even in this prior art, when a large amount of untransferred residual toner is reverse-transferred, the load on the drum cleaner is significantly increased. Therefore, it is necessary to use a high-performance drum cleaner. This causes a technical problem that the cleaner becomes complicated and that the cost of the drum cleaner increases. Further, in this type, a primary transfer process for transferring the toner image on the photosensitive drum onto the intermediate transfer belt,
Since the reverse transfer process of reversely transferring the residual toner on the intermediate transfer belt onto the photosensitive drum is performed at the same time, if the amount of toner to be reverse-transferred is large, such as untransferred residual toner, the primary transfer is performed. The transfer of the remaining toner image may be hindered by the untransferred residual toner, leading to a transfer failure.

In this type of image forming apparatus, an image quality adjusting toner is provided in an area (inter-image area) between images on the intermediate transfer belt for the purpose of, for example, image density and image alignment. An image is formed, but this toner image for image quality adjustment remains on the intermediate transfer belt without being secondary-transferred to paper, and the amount of toner is larger than the normal residual toner after the secondary transfer. Thus, the same problem as the above-mentioned untransferred residual toner occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and is intended to solve the above problems without using a complicated and expensive cleaner as an image carrier cleaner or an intermediate transfer body cleaner. An object of the present invention is to provide an image forming apparatus capable of surely removing a large amount of generated residual toner.

[0010]

That is, according to the present invention, as shown in FIG. 1, an image carrier 1 on which a toner image T is formed and carried, and an intermediate transfer member 2 arranged to face the image carrier 1
A primary transfer bias is applied and the intermediate transfer body 2
A primary transfer unit 3 for transferring the toner image T on the image carrier 1 onto the recording medium K;
A secondary transfer means 4 for transferring a toner image on the intermediate transfer member 2 thereon; and an image carrier blade 5 disposed in pressure contact with the image carrier 1 and removing residual toner on the image carrier 1
And an intermediate transfer member blade 6 that is disposed so as to be able to contact and separate from the intermediate transfer member 2 and removes residual toner on the intermediate transfer member 2. And a reverse bias applying means 7 for applying a reverse bias having a polarity opposite to that of the primary transfer bias and having an absolute value smaller than the primary transfer bias.

In such technical means, the present invention is applicable not only to the embodiment having one image carrier 1 as shown in FIG. 1, but also to the embodiment having a plurality of image carriers 1. The object is also applicable to the object (so-called tandem type) and the aspect in which these are combined.

As long as the image carrier 1 can form and carry the toner image T, a photoconductor, a dielectric, or the like may be appropriately selected, and its shape may be appropriately selected, such as a drum shape or a belt shape. You can do it. Further, as long as the intermediate transfer member 2 can carry and convey the toner image T, its shape may be appropriately selected such as a drum shape or a belt shape, but the present invention reduces the pressing force of the intermediate transfer member blade 6. It is effective to apply it to a type having a belt-shaped intermediate transfer member which is difficult to increase. Furthermore, the primary transfer unit 3 may be any unit that electrostatically transfers the toner image T on the image carrier 1 to the intermediate transfer member 2 by applying a primary transfer bias. The recording medium K is applied by applying the next transfer bias.
Any material may be used as long as the toner image T on the intermediate transfer body 2 is electrostatically transferred thereon.

Further, the toner constituting the toner image T may be appropriately selected from various toners. However, the present invention is directed to a type in which the residual toner is difficult to clean by a blade, particularly, a shape factor of 130 or less. Application to a type using a spherical toner is effective.

Further, the image carrier blade 5 is provided with the image carrier 1.
The shape, material, and the like may be appropriately selected as long as the toner remaining on the image carrier 1 is removed by pressing the toner. On the other hand, as long as the image carrier blade 5 removes the residual toner on the intermediate transfer member 2 by pressing against the intermediate transfer member 2, its shape, material, etc. may be appropriately selected. However, among these, the intermediate transfer member blade 6 needs to be disposed so as to be able to contact and separate from the intermediate transfer member 2.

The reverse transfer bias has a polarity opposite to that of the primary transfer bias and is smaller in absolute value than the primary transfer bias. That is, the toner image T is transferred from the image carrier 1 to the intermediate transfer member 2. It is necessary to make the reverse transfer force for reversely transferring the residual toner from the intermediate transfer member 2 to the image carrier 1 smaller than the primary transfer force for the primary transfer. The magnitude of the reverse transfer bias may be set according to the residual toner removing ability of the image carrier blade 5, and the amount of residual toner returned from the intermediate transfer body 2 to the image carrier 1 by application of the reverse transfer bias is reduced. It is preferable to set the size so as to be not more than the removal ability of the image carrier blade 5, for example, not more than 1.5 g / m ² .

In the above-described image forming apparatus, the intermediate transfer member blade 6 is separated from the intermediate transfer member 2 under the condition that the residual toner is generated on the intermediate transfer member 2 in an amount equal to or larger than a predetermined allowable amount. Then, it is preferable to execute an excessive toner cleaning process in which the intermediate transfer body 2 is idled and the reverse bias is applied by the reverse bias applying unit 7. Here, in the present invention, since the magnitude of the reverse bias is smaller than the primary transfer bias in absolute value, a large amount of residual toner is transferred to the image carrier 1 at a time when performing the excessive toner cleaning process. Can be avoided.

In the above-described image forming apparatus, the applied current value of the primary transfer bias is set to It (μ).
A), the applied current value of the reverse bias is Ic (μA), the toner amount of the 100% single color toner image T transferred onto the intermediate transfer member 2 is Tr (g / m ² ), and the reverse bias is applied. The amount of toner returned from the intermediate transfer member 2 onto the image carrier 1 is Tc (g / m ² ), and the image carrier 1 is brought into contact with the residual toner on the intermediate transfer member 2 when the reverse bias is applied. | Ic | ≦ (Tc / Tr), where X is the number of times of application, and Z is the number of colors primary-transferred to the intermediate transfer body 2 (excluding black in the case of a plurality of colors) before the application of the reverse bias. It is preferable to satisfy the relational expression of || It | X ≧ (Tr / Tc) × Z.

Further, in the above image forming apparatus, after the excess toner cleaning process is executed,
The intermediate transfer body blade is pressed against the intermediate transfer body,
In addition, if the post-cleaning process for rotating the intermediate transfer member at least one round idle is performed,
The residual toner on the intermediate transfer body 2 can be completely removed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. In the figure, reference numeral 11 denotes a photosensitive drum as an image carrier, which is rotated in the direction of arrow A, and has a charging device 12 and an exposure device 13 on its surface (an exposure beam is denoted by a reference numeral Bm in the figure). An electrostatic latent image corresponding to image information is formed by a well-known electrophotographic process. Further, around the photosensitive drum 11, developing units 14Y and 14 corresponding to respective colors of yellow (Y), magenta (M), cyan (C) and black (K) are provided.
Rotary developing device 14 equipped with M, 14C, 14K
The toner image T is formed by developing the electrostatic latent image formed on the photosensitive drum 11 by any of the developing units 14Y, 14M, 14C, and 14K. Reference numeral 16 denotes a drum cleaner provided with a blade 17 for removing residual toner on the photosensitive drum 11, and reference numeral 18 denotes a charge removing lamp for removing residual charges on the photosensitive drum 11. In the present embodiment, the blade 17
Is made of, for example, urethane rubber, and the photosensitive drum 11
Is set to 25 °, the free length is 8 mm, and the amount of penetration formed with the photosensitive drum 11 is 1.1 mm.

In the present embodiment, the photosensitive drum 11
Is constituted by providing a negatively charged organic optical semiconductor layer on the surface of a base tube made of aluminum. Further, since the development is performed by a reversal development method, all the toners used are charged to a negative polarity. In the present embodiment, the styrene acrylic resin fine particles and the yellow, magenta, cyan, and black pigment fine particles are agglomerated and united as the respective color component toners to have a volume average particle diameter of about 3%.
A toner prepared by an emulsion aggregation coalescence method (EA method) having a thickness of about 7 μm was used. The particle size distribution index (GSD) was 1.23. The average particle size is a value of a volume average particle size measured by a Coulter counter (manufactured by Coulter, Inc.). Then, adjust the heating time and heating temperature during polymerization,
Four types (four colors) of toners having substantially the same average particle size and particle size distribution were prepared. The shape of the toner is represented by a shape factor ML ² / A, and an enlarged photograph of the toner obtained with an optical microscope (Microphoto FXA; manufactured by Nikon Corporation) is taken by an image analyzer Lu.
This is a value calculated by the following equation 1 by performing image analysis using zex3 (manufactured by NIRECO).

[0021]

(Equation 1)

The shape factor ML ² / A is represented by the ratio of the projected area of the toner to the area of a circle circumscribing the toner, and is 100 for a true sphere, and increases as the shape is broken. The shape factor is calculated for a plurality of toner particles, and the average value is used as a representative value. In the present embodiment, the shape factor 13
A substantially spherical toner of 0 or less was used. In order to enhance the releasability, an appropriate amount of inorganic fine particles such as silica and titanium oxide (titania) having an average particle diameter of 10 to 150 nm is externally added to the toner as an external additive. And the resulting mixture was used as a developer. In addition, as the toner, besides the toner created by the present manufacturing method,
Spherical toners formed by suspension polymerization, dissolution suspension, emulsion polymerization, kneading and pulverization may be used, or a two-component developer in which a toner and a carrier are mixed as described above. Needless to say, a one-component developer containing only toner may be used.

Reference numeral 20 denotes an intermediate transfer belt as an intermediate transfer member disposed so as to be in contact with the surface of the photoreceptor drum 11, and stretched on a plurality of (four in this embodiment) rolls 21 to 24. It is constructed so as to be pivoted in the direction of arrow B. Here, reference numeral 21 denotes a driving roll of the intermediate transfer belt 20, reference numeral 22 denotes a driven roll, reference numeral 23 denotes a tension roll for controlling the tension of the intermediate transfer belt 20 to a constant value, and reference numeral 24 denotes an opposing roll for secondary transfer (backup roll). ). The intermediate transfer belt 20 is made of a resin such as polyimide or polyamide containing an appropriate amount of an antistatic agent such as carbon black, and is formed such that its volume resistivity is 10 ⁶ to 10 ¹⁴ Ω · cm. The thickness is set to, for example, 0.1 mm.

Further, at a portion (primary transfer position) of the intermediate transfer belt 20 facing the photosensitive drum 11, a primary transfer device (primary transfer roll in the present embodiment) 15 is disposed on the back side of the intermediate transfer belt 20. A primary transfer bias power supply 67 (described later) is connected to the primary transfer roll 15.
By applying a primary transfer bias (positive in this embodiment) having a polarity opposite to the charge polarity of the toner (see FIG. 3), the toner image T on the photosensitive drum 11 is statically transferred onto the intermediate transfer belt 20. It is designed to be electrically attracted. The primary transfer roll 15 is made of foamed urethane rubber, and its resistance value is adjusted to 10 ⁶ Ω to 10 ⁸ Ω. In the present embodiment, a reverse transfer bias power supply 68 (see FIG. 3) described later. A reverse transfer bias of the same polarity (negative in this embodiment) as the charge polarity of the toner can be applied to the primary transfer roll 15.

A secondary transfer device 30 is disposed at a secondary transfer position of the intermediate transfer belt 20 facing the transport path of the paper P. In the present embodiment, the secondary transfer device 30 is provided.
Secondary transfer roll 25 which is pressed against the toner carrying surface of the
And a counter roll (back-up roll) 24 disposed on the back side of the intermediate transfer belt 20 and serving as a counter electrode of the secondary transfer roll 25. A transfer bias is stably applied to the backup roll 24. A metal power supply roll 26 to be contacted is disposed. This feeding roll 2
6 is applied to the intermediate transfer belt 20 by applying a secondary transfer bias having the same polarity (negative in this embodiment) as the charge polarity of the toner by a secondary transfer bias power supply 63 (see FIG. 3) described later. Is electrostatically attracted onto the paper P. Reference numeral 27 denotes a polyurethane cleaning blade 27a disposed in contact with the surface of the secondary transfer roll 25.
It is a roll cleaner provided with.

Here, the backup roll 24 is formed by covering an insulating roll with a semiconductive thin film. This thin film has a thickness of 10 to 200 μm and is adjusted so that its surface resistivity is 10 ⁷ to 10 ¹¹ Ω / □ (□: unit area).

The secondary transfer roll 25 is a grounded conductive roll, and its volume resistivity is as low as 10 ⁷ Ωcm or less in order to keep its surface potential always equal to the ground potential. Is preferred.

Further, a belt cleaner 40 having a blade 41 is disposed downstream of the secondary transfer device 30 and at a position facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween. In the present embodiment, the blade 41 is the blade 17 of the drum cleaner 16.
The contact angle (BSA) with the intermediate transfer belt 20 is set to 17 °, the free length is 10 mm, and the digging amount formed with the intermediate transfer belt 20 is 1 mm. It is.

Further, in the image forming apparatus according to the present embodiment, the secondary transfer roll 25 and the belt cleaner 40 are disposed so as to be able to contact and separate from the intermediate transfer belt 20, so that a multi-color image, that is, a superimposed image is formed. When the toner images are formed, they are separated from the intermediate transfer belt 20 until the toner image T of the final color (BK in the present embodiment) is primarily transferred to the intermediate transfer belt 20.

Further, the paper transport system sends out the paper P from the paper tray 50 by the feed roll 51 and
The paper P is sent to a secondary transfer position at a predetermined timing after the positioning is stopped once by a registration roll (registration roll) 53 through the second transfer roller 2. The sheet is conveyed to a fixing device 54 via a sheet conveyance guide, and then discharged by a conveyance roller 52.

FIG. 3 shows details of the image forming apparatus according to the present embodiment. In the figure, reference numeral 61 denotes a registration sensor provided downstream of the registration roll 53;
Is a switch for applying a secondary transfer bias to the power supply roll 26; 63 is a secondary transfer bias power supply for the power supply roll 26;
Reference numeral 4 denotes a contact / separation device for retracting the secondary transfer roll 25 from the intermediate transfer belt 20 (secondary transfer roll contact / separation device). Reference numeral 65 denotes a contact / separation device for retracting the belt cleaner 40 from the intermediate transfer belt 20 (belt cleaner contact / separation device). ), 66 are polarity switching switches for bias supplied to the primary transfer roll 15;
Reference numeral 7 denotes a primary transfer bias power supply for supplying a primary transfer bias to the primary transfer roll 15, and reference numeral 68 denotes a reverse transfer bias power supply for supplying a reverse transfer bias having a polarity opposite to that of the primary transfer bias to the primary transfer roll 15. Reference numeral 81 denotes a drum drive motor for driving the photosensitive drum 11, and reference numeral 82 denotes a belt drive motor for driving the drive roll 21 of the intermediate transfer belt 20. Reference numeral 28 denotes a belt position detection sensor that detects a reference position detection reflection mark 20a provided at an end portion of the intermediate transfer belt 20 and a non-image portion.

FIG. 4 is a block diagram of the control device 70. In the figure, an image forming signal from an image forming instructing section 60, a sheet passage detection signal from a registration sensor 61, and a belt position detection signal from a belt position detection sensor 28 are input to a CPU 72 via an input interface 71, and then the CPU 72 Executes the control program stored in advance in the ROM 73 and performs appropriate data processing with the RAM 74, and then executes the output interface 7
5, a drum drive motor 81 and a belt drive motor 8
2, switch 62, secondary transfer bias power supply 63, secondary transfer roll contact / separation device 64, belt cleaner contact / separation device 65,
Control signals are sent to the polarity switch 66, the primary transfer bias power supply 67, and the reverse transfer bias power supply 68, respectively.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. First, after the surface of the photosensitive drum 11 is charged by the charging device 12, a latent image is written by the exposure beam Bm from the exposure device 13. At this time,
If the electrostatic latent image written on the photosensitive drum 11 corresponds to yellow image information, the electrostatic latent image is developed by a yellow developing device 14Y containing yellow toner. A yellow toner image T is formed thereon. The toner image T formed on the photosensitive drum 11 is transferred to the photosensitive drum 11 and the intermediate transfer belt 20.
Is transferred to the intermediate transfer belt by the primary transfer bias applied to the primary transfer roll 15 at the primary transfer position where the contact is made. On the other hand, the residual toner remaining on the photosensitive drum 11 after the primary transfer is removed by the blade 17 of the drum cleaner 16, and the residual charge on the photosensitive drum 11 is removed by the charge removing lamp 18.

At this time, when forming a monochrome image,
The toner image T primarily transferred to the intermediate transfer belt 20 is secondarily transferred to the sheet P immediately. When a color image in which a plurality of color toner images T are superposed is formed, the toner image T is formed on the photosensitive drum 11. Of the toner image T and the primary transfer process of the toner image T are repeated for the number of colors. For example, when a full-color image is formed by superimposing four color toner images T, the toner image T is formed on the photosensitive drum 11 in the order of yellow, magenta, cyan, and black for each rotation thereof, These toner images T are sequentially primary-transferred onto the intermediate transfer belt 20. On the other hand, the intermediate transfer belt 2
0 rotates at the same cycle as the photosensitive drum 11 while holding the yellow toner image T that has been primarily transferred first, and the magenta and cyan toners are placed on the intermediate transfer belt 20 at predetermined positions every one rotation thereof. And the black toner image T are superimposed.

The toner image T primarily transferred to the intermediate transfer belt 20 in this manner is conveyed to a secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the paper P is taken out of the paper tray 50 by the feed roll 51, sent out by the transport roll 52, and carried out to the position of the registration roll 53. Thereafter, the paper P is supplied to the secondary transfer position at a predetermined timing, and the secondary transfer roll 25 nips the paper P with respect to the backup roll 24. Then, at the secondary transfer position, the toner image T carried on the intermediate transfer belt 20 is collectively transferred onto the paper P by the action of a transfer electric field formed between the secondary transfer roll 25 and the backup roll 24 (secondary transfer). The paper P on which the toner image T has been secondarily transferred is transferred to the fixing device 54, and the toner image T on the paper P is fixed. Further, the residual toner remaining on the intermediate transfer belt 20 after the secondary transfer is removed by the blade 41 of the belt cleaner 40.
FIG. 5 shows a timing chart of the above-described image forming process (at the time of forming a full-color image).

Next, the blade 41 of the belt cleaner 40
Will be described. FIG.
The relationship between the residual toner amount on the intermediate transfer belt 20 and the cleaning result by the blade 41 is shown. This evaluation was performed in a low-temperature and low-humidity environment, which is a stress for cleaning, and the size of the toner image was set to be JIS3 size.
In the same figure, も の indicates that the cleaning was completed, and △ indicates
Indicates a part in which a streak-like cleaning defective portion has occurred, and indicates a part in which cleaning was hardly performed.
From this result, it is understood that if the residual toner amount on the intermediate transfer belt 20 is 1.2 g / m ² or less, good cleaning performance can be obtained.

FIGS. 7 and 8 show a secondary transfer device 30.
Shows the relationship between the secondary transfer voltage applied to the intermediate transfer belt 20 and the remaining amount of secondary transfer (the amount of residual toner) on the intermediate transfer belt 20 after the secondary transfer. Here, FIG. 7 shows the results in a high-temperature and high-humidity environment, and FIG. 8 shows the results in a low-temperature and low-humidity environment. Symbol R indicates red (overlapping two colors of Y + M), and symbol PK indicates black (process black: Y + M + C). Three colors are superimposed). From these results, by selecting the secondary transfer voltage from an appropriate setting range according to the environment, the secondary transfer remaining amount is 0.8 g /
It can be seen that it can be suppressed to m ² or less.

Therefore, in the above-described ordinary image forming process, the amount of the residual toner on the intermediate transfer belt 20 after the secondary transfer does not exceed the scraping ability of the blade 41 of the belt cleaner 40. Can be easily removed.

However, when toner that cannot be transferred (untransferred residual toner) occurs due to troubles such as paper jam, the residual toner amount is, for example, 4 g / m ^{2 for} 100% monochromatic toner and 300% for the PK. (Y,
Since each of M and C reaches 12 g / m ² at 100%), the removal ability of the blade 41 of the belt cleaner 40 is exceeded, and the untransferred residual toner can be completely removed by passing the blade 41 once. Will be gone.

On the other hand, the blade 17 of the drum cleaner 16
Are as follows. FIG.
The relationship between the residual toner amount on the photosensitive drum 11 and the cleaning result by the blade 17 is shown. In addition, this evaluation,
As in the case of the above-described belt cleaner 40, cleaning was performed in a low-temperature and low-humidity environment that causes stress, and the size of the toner image was JIS3 size. In the same figure, は indicates that cleaning was completed completely, △ indicates that a streak-like cleaning defective portion occurred, and X indicates that cleaning was almost impossible. From this result, it is understood that if the residual toner amount on the intermediate transfer belt 20 is 1.6 g / m ² or less, good cleaning performance can be obtained. However, since the scraping ability is much smaller than the residual toner amount of the untransferred residual toner, the untransferred residual toner generated on the intermediate transfer belt 20 is moved to the photosensitive drum 11 at one time. Then, the scraping ability of the blade 17 of the drum cleaner 16 is exceeded, and the untransferred residual toner cannot be completely removed only by passing the blade 17 once.

Therefore, in this embodiment, when untransferred residual toner is generated due to a paper jam or the like during image formation, an excessive toner cleaning process for removing the untransferred residual toner by a fixed amount at a time. Is to be executed. Hereinafter, the excessive toner cleaning process will be described with reference to a flowchart shown in FIG. 10 and a timing chart shown in FIG.

In the flowchart shown in FIG. 10, if there is no trouble during image formation, as shown in the timing chart of FIG.
The cleaning is performed by pressing the blade 41 of the belt cleaner 40 against 0. On the other hand, when a trouble occurs during image formation, first, the apparatus is forcibly stopped, whereby the rotation of the photosensitive drum 11 and the intermediate transfer belt 20 is stopped as shown in FIG. Also, the secondary transfer roll 25
When the blade 41 of the belt cleaner 40 is already in pressure contact with the intermediate transfer belt 20, these are separated from the intermediate transfer belt 20. Here, a case where an abnormality occurs in the detection result of the registration sensor 61 (when a paper jam occurs) while the full color image of YMCK is transferred onto the intermediate transfer belt 20 will be described as an example.

When it is confirmed that the cause of the trouble (here, the jammed sheet) has been removed, the number of times the intermediate transfer belt 20 is rotated idle is set. This is defined by the following equation. X ≧ (Tr / Tc) × Z where X: Number of times the photosensitive drum 11 contacts the residual toner on the intermediate transfer belt 20 when a reverse bias is applied. Z: On the intermediate transfer belt 20 before the start of the reverse bias application. Number of primary-transferred colors (excluding black for multiple colors) Tr: 100% of a single color transferred on intermediate transfer belt 20
The toner amount of the toner image ^{T (g / m 2) Tc} : the amount of toner returned from the intermediate transfer belt 20 onto the photosensitive drum 11 when a reverse bias is applied (g / m ²⁾ In the present embodiment, Since the intermediate transfer belt 20 makes only one contact with the photosensitive drum 11 during one rotation, X directly becomes the idle speed of the intermediate transfer belt 20.

In this description, at this point, YMCK
Are formed on the intermediate transfer belt 20 (see FIG. 11), so that Z = 3 (K is excluded). Tr is 4 (g / g) as described above.
m ² ). Further, Tc is set to, for example, 1.5 (g / m ² ) which is equal to or less than the maximum scraping ability (1.6 (g / m ² )) of the blade 16 of the drum cleaner 17. As a result, X
(= The number of idle rotations of the intermediate transfer belt 20) is X ≧ 8, and the idle rotation number is determined to be 8. If a trouble occurs when the transfer of the two-color toner image of YM is completed, X ≧ 5.67, the idle speed is determined to be 6, and Y is determined.
(Or, if a trouble occurs when the transfer of the single-color toner image of K (at the time of monochrome image creation) is completed, X
≧ 2.67, and the idle speed is determined to be 3.

Further, a reverse bias value to be applied to the primary transfer roll 15 when the intermediate transfer belt 20 is idling is also set. This is defined by the following equation. | Ic | ≦ (Tc / Tr) × | It | where, It: applied current value of primary transfer bias (μA) Ic: applied current value of reverse bias (μA)

When these settings are completed, FIG.
As shown in FIG. 1, the photosensitive drum 11 and the intermediate transfer belt 2
The idle rotation of 0 and the application of the reverse bias to the primary transfer roll 15 are started. Then, at the primary transfer portion, the untransferred residual toner on the intermediate transfer belt 20 is reduced to approximately 1.5 (g / m 2) by the reverse bias applied to the primary transfer roll.
² ) The untransferred residual toner transferred to the photosensitive drum 11 side by side is transferred to the photosensitive drum 11 side by the blade 17 of the drum cleaner 16. At this time, since the amount of toner to be scraped is smaller than the scraping ability of the blade 17, no cleaning failure occurs.
Further, since the application of the reverse bias is performed while the intermediate transfer belt 20 makes eight rotations, substantially all of the untransferred residual toner on the intermediate transfer belt 20 is transferred to the photosensitive drum 11 and the blade 17 of the drum cleaner 16 is moved. Will be removed.

Thereafter, when the photosensitive drum 11 and the intermediate transfer belt 20 are idle for the set number of rotations, the application of the reverse bias to the primary transfer roll 15 is stopped. However, the photosensitive drum 11 and the intermediate transfer belt 20
Continues idle rotation, while the blade 41 of the belt cleaner 40 is pressed against the intermediate transfer belt 20 to rotate the intermediate transfer belt 20 once in this state. Then, the untransferred residual toner slightly remaining on the intermediate transfer belt 20 (such as toner charged to the opposite polarity) is completely removed.
Then, after one rotation, the belt cleaner 40 is separated from the intermediate transfer belt 20, the driving of the photosensitive drum 11 and the intermediate transfer belt 20 is stopped, and the excessive toner cleaning process ends.

As described above, in this embodiment, when a large amount of residual toner is generated on the intermediate transfer belt 20, that is, when the amount of residual toner that exceeds the scraping ability of the blade 41 of the belt cleaner 40 is generated. Since the residual toner is transferred to the photosensitive drum 11 by an amount corresponding to the scraping ability of the blade of the drum cleaner 16 to perform the cleaning, even when a simple blade is used as the cleaner, Such a large amount of residual toner can be effectively removed. Further, in removing a large amount of residual toner on the intermediate transfer belt 20,
Residual toner is removed multiple times by blade 17 or blade
Therefore, it is possible to avoid a situation in which such residual toner is fixed to the photosensitive drum 11 or the intermediate transfer belt 20 due to friction.

In this type of image forming apparatus, a toner patch may be created for image quality adjustment, but this toner patch is not transferred to the paper P but remains on the intermediate transfer belt 20. And many of them have high concentrations. Therefore, when a toner patch is created, it is preferable to execute the above-described excess toner removal process after the end of the job or at the timing immediately after the end of the job and immediately before the next job.

Second Embodiment FIG. 12 shows a schematic configuration of an image forming apparatus according to a second embodiment of the present invention. In FIG. 1, an image forming apparatus according to the present embodiment includes a plurality of image forming units 100 on which respective color component toner images T are formed by, for example, an electrophotographic method.
(Specifically, 100Y, 100M, 100C, 100
K), an intermediate transfer belt 110 as an intermediate transfer body for sequentially transferring (primary transfer) each color component toner image T formed by each image forming unit 100, and a superimposed image transferred on the intermediate transfer belt 110. Paper P as recording material
Batch transfer device 120 for batch transfer (secondary transfer) to
And a fixing device 150 for fixing the toner image T transferred at a time on the sheet P.

In this embodiment, the image forming unit 100 for each color component (specifically, 100Y, 100M,
00C, 100K) are photosensitive drums 101 (specifically, 101Y, 101Y, 1K) as image carriers rotating in the direction of arrow A.
01M, 101C, and 101K), a uniform charging device 102 (specifically, 1
02Y, 102M, 102C, 102K), a laser exposure apparatus 1 for writing an electrostatic latent image on the photosensitive drum 101
03 (specifically, 103Y, 103M, 103C, 10
3K, a laser beam is represented by a symbol Bm in the figure), and a developing device 104 (specifically, 104) in which toner of each color component is stored and an electrostatic latent image on the photosensitive drum 101 is visualized.
Y, 104M, 104C, 104K), a drum cleaner 1 for cleaning the photosensitive drum 10 after passing through the transfer area
06 (specifically, 106Y, 106M, 106C, 10
6K) are sequentially arranged. Then, each photosensitive drum 101 and the intermediate transfer belt 1
At the primary transfer position facing the transfer belt 10, a primary transfer roll 105 as a primary transfer device is provided on the back side of the intermediate transfer belt 110.

The intermediate transfer belt 110 is wound around a plurality of (four in the present embodiment) support rolls 111 to 114. In this embodiment, the support roll 111 is As drive roll 110,
When the support roll 112 is a driven roll, the support roll 11
As a steering roll 3 is arranged to be tiltable,
Further, the support roll 114 is used as a backup roll of the batch transfer device 120 as described later. Here, the same intermediate transfer belt 110 as that described in the first embodiment is used.

Further, a collective transfer device 120 is disposed at a collective transfer position (secondary transfer position) of the intermediate transfer belt 110 facing the transport path of the paper P. In this embodiment,
A secondary transfer roll 115 that is pressed against the toner image bearing surface of the intermediate transfer belt 110 and a counter roll (backup roll) 114 that is disposed on the back side of the intermediate transfer belt 110 and forms a counter electrode of the secondary transfer roll 115. And A roll cleaner 121 is provided on the peripheral surface of the secondary transfer roll 115, and an electrode roll (not shown) is in contact with the backup roll 114 to supply power. Further, a belt cleaner 141 for removing residual toner on the intermediate transfer belt 110 is provided downstream of the collective transfer device 120. As the secondary transfer roll 115, the backup roll 114, and the like, those similar to those described in the first embodiment are used.

Further, in this embodiment, the paper transport system feeds the paper P from the paper tray 116 to the feed roll 1.
The sheet P is sent out to the secondary transfer position at a predetermined timing, and the sheet P after the secondary transfer is
To be transported to Reference numeral 118 denotes a transport roll provided in the paper transport path, and reference numeral 119 denotes a registration roll (registration roll).

In the so-called tandem type image forming apparatus according to the present embodiment, similarly to the first embodiment, it is possible to execute the excessive toner removing process. However, in the case of the tandem-type image forming apparatus, the intermediate transfer belt 110 comes into contact with the photosensitive drum 101 four times during one rotation (specifically, 101Y, 101M, 101C, and 101K). The number may be X / 4 (a quarter of the first embodiment).

[0056]

As described above, according to the present invention,
A large amount of residual toner on the intermediate transfer member is gradually moved toward the image carrier by applying a reverse transfer bias smaller than the primary transfer bias, and then removed by the image carrier cleaner. A large amount of residual toner generated on the intermediate transfer member can be reliably removed without using a complicated and expensive cleaner as a cleaner or an intermediate transfer member cleaner.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of the present invention.

FIG. 2 is a schematic configuration diagram of Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 3 is an explanatory diagram illustrating a drive system and the like of the image forming apparatus according to the first embodiment;

FIG. 4 is a block diagram of a control device of the image forming apparatus according to the first embodiment.

FIG. 5 is a timing chart of a normal image forming process.

FIG. 6 is an evaluation result of a cleaning performance of a blade of a belt cleaner.

FIG. 7 is a graph showing a relationship between a secondary transfer voltage and a secondary transfer remaining amount under a high temperature and high humidity environment.

FIG. 8 is a graph showing a relationship between a secondary transfer voltage and a secondary transfer remaining amount under a low-temperature and low-humidity environment.

FIG. 9 is an evaluation result of cleaning performance of a blade of a drum cleaner.

FIG. 10 is a flowchart of an excessive toner cleaning process.

FIG. 11 is a timing chart of an excessive toner cleaning process.

FIG. 12 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Intermediate transfer body, 3 ... Primary transfer means, 4
... Secondary transfer means, 5 ... Image carrier blade, 6 ... Intermediate transfer blade, K ... Recording medium

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/01 114 G03G 9/08 361 F-term (Reference) 2H005 AA15 AA21 2H027 DA39 DA44 DA45 DE04 DE07 DE09 EA03 EB04 EC06 ED24 ED28 EE02 EE07 EF09 2H030 AA04 AB02 AD17 BB02 BB24 BB42 BB46 BB54 BB63 2H032 AA05 AA15 BA09 BA23 BA30 CA04 CA13

Claims (6)

[Claims] 1. An image carrier on which a toner image is formed and carried; an intermediate transfer body disposed to face the image carrier; a primary transfer bias being applied, and A primary transfer unit for transferring a toner image; a secondary transfer unit to which a secondary transfer bias is applied and for transferring the toner image on the intermediate transfer member onto a recording medium; Image forming apparatus comprising: an image carrier blade for removing residual toner on a carrier; and an intermediate transfer member blade disposed so as to be able to contact and separate from the intermediate transfer member and removing residual toner on the intermediate transfer member. The apparatus is characterized in that the primary transfer means is provided with a reverse bias applying means for applying a reverse bias having a polarity opposite to the primary transfer bias and an absolute value smaller than the primary transfer bias. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer body blade is removed from the intermediate transfer body under a condition that a residual toner of a predetermined amount or more is generated on the intermediate transfer body. An image forming apparatus, wherein an excessive toner cleaning process of separating the intermediate transfer member, causing the intermediate transfer member to idle, and applying a reverse bias by the reverse bias applying unit is executed. 3. The image forming apparatus according to claim 2, wherein after the excess toner cleaning process is performed, the intermediate transfer body blade is pressed against the intermediate transfer body, and the intermediate transfer body is rotated at least once. An image forming apparatus, wherein a post-cleaning process for idling is performed. 4. The image forming apparatus according to claim 1, wherein the reverse bias value is set so that an amount of residual toner transferred from the intermediate transfer member to the image carrier is 1.5 g / m ² or less. An image forming apparatus comprising: 5. The image forming apparatus according to claim 1, wherein the toner image is formed of a spherical toner having a shape factor of 130 or less. 6. The image forming apparatus according to claim 1, wherein the applied current value of the primary transfer bias is It (μA), the applied current value of the reverse bias is Ic (μA), and the image is transferred onto the intermediate transfer body. The toner amount of the 100% single-color toner image is Tr (g / m ² ), and the toner amount returned from the intermediate transfer member to the image carrier when the reverse bias is applied is Tc.
(G / m ² ), the number of times the image carrier is brought into contact with the residual toner on the intermediate transfer member when the reverse bias is applied is X, and the color primarily transferred to the intermediate transfer member by the time the reverse bias application is started. When the number (however, black is excluded in the case of a plurality of colors) is Z, the relational expression of | Ic | ≦ (Tc / Tr) × | It | X ≧ (Tr / Tc) × Z is satisfied. Image forming device.