JP2002174964A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is further miniaturized and whose degree of freedom of layout is high while performing appropriate cleaning. SOLUTION: The image forming device provided with an image carrier to carry a toner image and an intermediate transfer body to which the toner image is transferred from the image carrier possesses a toner holding means to hold residual toner after transfer by abutting on the intermediate transfer body and a bias controlling means to control so that holding bias by which the residual toner is held at a normal time and discharge bias by which the residual toner held at the normal time is discharged at a cleaning time are applied between the intermediate transfer body and the toner holding means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, and a multifunction machine thereof, and more particularly to a technique for removing residual toner on an intermediate transfer member. Related.

[0002]

2. Description of the Related Art Electrophotographic and electrostatic recording type image forming apparatuses such as copying machines and printers have been widely known. One of the problems that hinders miniaturization of such an image forming apparatus is the presence of a photoconductor cleaning box. In particular, an image forming apparatus of a type that includes a plurality of photoconductors and obtains a full-color image has an advantage that a relatively high-speed full-color image can be formed, while each photoconductor includes a cleaning box.
The disadvantage of increasing the size of the device tends to become apparent.

In view of such a problem, there has been proposed an image forming apparatus of a type in which a photosensitive member is not provided with a cleaning box. For example, JP-A-11-24945
In Japanese Patent Laid-Open Publication No. 2000-205, each photoconductor is provided with a relatively small toner holding unit instead of a cleaning box, and the toner temporarily held in the toner holding unit is released at a predetermined timing. A configuration in which collection is performed by a single cleaning box provided is disclosed.

[0004]

Problems to be Solved by the Invention
According to the technique described in Japanese Patent No. 249452, it is not necessary to provide a cleaning box for each photoconductor, which contributes to downsizing of the apparatus. However, it is sometimes difficult to provide a cleaning box on the intermediate transfer member from the viewpoints of further downsizing of the image forming apparatus or layout problems of the image forming apparatus.

The present invention has been made in view of such technical problems, and an object of the present invention is to provide a smaller image forming apparatus having a high degree of freedom in layout while performing appropriate cleaning. .

[0006]

That is, the present invention relates to an image forming apparatus including an image carrier on which a toner image is carried, and an intermediate transfer body on which the toner image is transferred from the image carrier. A toner holding means capable of holding the residual toner after contact and transfer, a holding bias for normally holding the residual toner, and a release bias for releasing the normally held residual toner during cleaning are provided by the intermediate transfer member. And a control means for controlling so as to be between the toner holding means and the toner holding means. Further, the control means may be a means for controlling so as to apply a holding bias for normally holding the residual toner to the toner holding means during cleaning, and to apply a release bias for releasing the residual toner held at the normal time to the toner holding means. Such a control mode includes a mode in which a bias is positively applied to the toner holding unit.

By configuring the image forming apparatus in this manner, at the time of cleaning performed at a predetermined timing,
Since the residual toner held in the normal state is released from the toner holding means, a small toner holding means is sufficient.
The timing at which the cleaning is performed is generally other than during the image forming operation.
After image formation, after turning on the power to the image forming apparatus, after forming a predetermined number of images, between the image formation of one page and the image formation of the next page (so-called page interval), and the like.

In addition, as such an image forming apparatus, a configuration in which one or a plurality of image carriers are provided for one intermediate transfer member can be adopted. Further, the intermediate transfer member includes a primary intermediate transfer member on which a toner image is transferred (directly) from an image carrier, and a secondary intermediate transfer member on which a toner image is transferred from the primary intermediate transfer member. But
Further, a plurality of primary or secondary intermediate transfer members may be provided. Note that the secondary intermediate transfer member also transfers (indirectly) a toner image from the image carrier.

Further, as such an image forming apparatus, a configuration in which one or a plurality of toner holding means is provided for one intermediate transfer member can be adopted. When there are a plurality of intermediate transfer members, a configuration in which each intermediate transfer member includes a toner holding unit, a configuration in which some of the plurality of intermediate transfer members include a toner holding unit, and the like are employed. can do. Further, when the intermediate transfer member is divided into the above-described primary intermediate transfer member and the secondary intermediate transfer member, a structure in which both the primary and secondary intermediate transfer members are provided with a toner holding unit, or a primary or secondary intermediate transfer member Can be adopted in which only one of them has the toner holding means.

In the case where such a toner holding means is provided on the intermediate transfer member (not on the image carrier), it is necessary to consider the transmission current between the toner holding means and the intermediate transfer member provided with the toner holding means. More likely. That is, since the electrical resistance of the intermediate transfer member is generally smaller than that of the image carrier,
When the holding bias (magnitude) is increased, the value of the transmission current flowing between the toner holding means and the intermediate transfer member increases, so that the transmission current causes charge injection and the residual toner held in the toner holding means is removed. In some cases, the charging polarity is reversed and the toner is unintentionally discharged from the toner holding unit.
Such a problem is likely to occur when the electric resistance value between the toner holding means and the intermediate transfer member is 10 ¹⁰ Ω or less.
⁸ Ω or less.

On the other hand, if the holding bias (magnitude) is small, the toner holding means cannot hold the residual toner (of the original charging polarity).

As described above, it is preferable to set the holding bias in consideration of the reversal of the charging polarity of the residual toner due to the transmission current. Specifically, the magnitude of the holding bias is:
Preferably, the lower limit is set to a value at which the residual toner can be electrostatically held by the toner holding unit, and the upper limit is set to a value at which the charging polarity of the residual toner can be reversed. Is within a range in which the lower limit is a value capable of electrostatically holding the residual toner in the toner holding unit, and the upper limit is a value capable of reversing the charging polarity of the residual toner. It is more preferable that the transmission current between the toner holding unit and the intermediate transfer member is set to a value at which the transmission current is substantially minimum, or a value near the minimum. Further, the upper limit and the lower limit of the holding bias are not universally determined, but can be appropriately set according to assumed characteristics of the image forming apparatus, required image quality, and the like. In order to check the upper limit and the lower limit, it is possible to check the weight increase of the toner holding unit after forming a predetermined number of images, the amount of toner passing through the toner holding unit, and the like.

The factors which affect the transmission current between the toner holding means and the intermediate transfer member are the above-mentioned holding bias, the electric resistance of the toner holding means, the electric resistance of the intermediate transfer member, the toner holding A contact state (such as a contact area) between the means and the intermediate transfer member is exemplified. For example, when the toner holding unit is a rotating brush in which a brush member is attached to a metal pipe, by appropriately setting the electric resistance value of the brush member, and by appropriately setting the brush flock density of the brush member. The transmission current can be set to an appropriate value. Further, for example, when the intermediate transfer member is configured with a multilayer structure, the outermost layer is formed of a material having a higher resistance value than the other layers, and the layer thickness of the outermost layer is appropriately set, so that the transmission is improved. The current can be set to an appropriate value.

By the way, in this image forming apparatus, at the time of cleaning, the residual toner held at normal time is released. The released residual toner can be transferred to a recording medium (for cleaning). The following configuration can also be adopted. That is, the image forming apparatus includes a transfer unit that contacts the intermediate transfer body to transfer a toner image from the intermediate transfer body to a recording medium, and a collection unit that contacts the transfer unit and collects residual toner after discharge. It is also possible to adopt a configuration in which the residual toner released from the holding unit reaches the transfer unit.

[0015]

FIG. 1 shows a tandem-type full-color printer (image forming apparatus) according to an embodiment of the present invention. In addition, the arrow in FIG. 1 has shown the rotation direction of each rotating member.

As shown in FIG. 1, this full-color printer has photosensitive drums (image carriers) 10 (Y) to yellow (Y), magenta (M), cyan (C), and black (K). Image forming unit 1 having (K)
(Y) to (K) and these photosensitive drums 10 (Y) to (K)
, Charging rollers 11 (Y) to (K) for charging, laser optical units (not shown) for irradiating laser beams L (Y) to (K) of each color, and photoconductor drums 10 (Y) to (Y). K) developing devices 13 (Y) to (K) for visualizing (visualizing) a latent image formed on the surface with each color toner, and two of the four photosensitive drums 10 (Y) to (K). Photoconductor drums 10
(K) The first primary intermediate transfer drum (intermediate transfer member) 21a and the other two photosensitive drums 10 (M) that come into contact with (C)
(Y), a second primary intermediate transfer drum (intermediate transfer body) 21b, and the first and second primary intermediate transfer drums 2
1a and 21b, a secondary intermediate transfer drum (intermediate transfer member) 22, a final transfer roll (transfer means) 30 contacting the secondary intermediate transfer drum 22, and a toner collection box (collection means) 6 Unit is configured.

The photosensitive drums 10 (Y) to 10 (K) are arranged at regular intervals so as to have a common tangent plane (indicated by a dashed line in the drawing) M. Also, a first primary intermediate transfer drum 21a and a second primary intermediate transfer drum 21b
Are arranged such that each rotation axis is parallel to the axes of the photoconductor drums 10 (Y) to (K) and has a plane target relation with a predetermined target plane as a boundary. Further, the secondary intermediate transfer drum 22 is arranged so that the rotation axis is parallel to the photosensitive drums 10 (Y) to 10 (K).

A signal corresponding to the image information for each color is rasterized by an image processing unit (not shown) and input to a laser optical unit (not shown). In this laser optical unit, yellow (Y), magenta (M),
Laser light L of each color of cyan (C) and black (K)
(Y) to (K) are modulated, and the photosensitive drum 1 of the corresponding color is modulated.
Irradiation is performed from 0 (Y) to (K).

Around the photosensitive drums 10 (Y) to 10 (K), an image forming process for each color is performed by a known electrophotographic method. First, the photosensitive drum 10
As (Y) to (K), for example, OPC having a diameter of 20 mm
A photoconductor is used, and these photoconductor drums 10 (Y) to (K) are driven to rotate at a rotation speed of, for example, 95 mm / sec. The photosensitive drum 10 (Y)-
The surface of (K) is, as shown in FIG.
By applying a DC voltage of, for example, about -840 V to (Y) to (K), the battery is charged to, for example, about -300 V. The contact-type charging device includes a roll-type charging device, a film-type charging device, and a brush-type charging device, but any type may be used.
In this embodiment, a charging roll generally used in an electrophotographic apparatus in recent years is employed. Further, in this embodiment, in order to charge the surfaces of the photosensitive drums 10 (Y) to (K), a charging method of applying only DC is used, but a charging method of applying AC + DC may be used.

Thereafter, the surfaces of the photosensitive drums 10 (Y) to (K) are irradiated with laser beams L (Y) to (K) corresponding to respective colors by a laser optical unit as an exposure device.
An electrostatic latent image corresponding to the input image information for each color is formed.
When an electrostatic latent image is written on the photosensitive drums 10 (Y) to 10 (K) by the laser optical unit, the surface potential of the image exposed portion is removed to about -60V or less.

The photosensitive drums 10 (Y) to 10 (K)
Yellow (Y), magenta (M) formed on the surface of
The electrostatic latent images corresponding to the respective colors of cyan (C) and black (K) are developed by developing devices 13 (Y) to (K) of the corresponding colors, and on the photosensitive drums 10 (Y) to (K). Is visualized as a toner image of each color. In this embodiment, as the developing devices 13 (Y) to (K), a magnetic brush contact type two-component developing system is adopted. However, the application range of the present invention is not limited to this developing system. Of course, the present invention can be sufficiently applied to other developing systems such as a non-contact developing system.

Each of the developing devices 13 (Y) to (K) has a developer composed of a toner of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier of different colors. Is filled. These developing devices 13
In (Y) to (K), when toner is supplied from a toner supply device (not shown), the supplied toner is sufficiently stirred with the carrier by an auger (not shown) and is triboelectrically charged. Inside the developing rolls 130 (Y) to (K) 130 (Y) to (K), a magnet roll (not shown) having a plurality of magnetic poles arranged at a predetermined angle is arranged in a fixed state. The developing rolls 130 (Y) to (K) 130 (Y) to (K) are driven by paddles (not shown) that transport the developer to the developing rolls 130 (Y) to (K) 130 (Y) to (K). The amount of the developer transported to the vicinity of the surface is regulated by a developer amount regulating member (not shown) to the amount transported to the developing section. In this embodiment, the amount of the developer is 30 to 50 g / m ² ,
At this time, the charge amount of the toner existing on the developing rolls 130 (Y) to (K) is about -20 to 35 μC / g.

The toner supplied onto the developing rolls 130 (Y) to (K) is changed by the magnetic force of the magnet roll.
It is in the form of a magnetic brush composed of a carrier and toner, and this magnetic brush is in contact with the photosensitive drums 10 (Y) to 10 (K). AC is applied to the developing rolls 130 (Y) to (K).
+ DC with a developing bias voltage of
The toner on (Y) to (K) is transferred to the photosensitive drum 10 (Y) to
(K) By developing the electrostatic latent image formed on
A toner image is formed. In this embodiment, the developing bias voltage is 4 kHz for AC, 1.5 kVpp, and -2 for DC.
It is about 30V.

In this embodiment, the developing device 13 (Y)
In (K), so-called “spherical toners” which are substantially spherical toners and have an average particle diameter of about 3 to 10 μm are used.

Here, as the “spherical toner”, for example, a scanning electron microscope FE-SEM (S
= 800), 100 toner images magnified at a magnification of 500 times are randomly sampled, and the image information is introduced into an image analyzer, for example, manufactured by Nicole, via an interface, and analyzed. The shape coefficient value MLS2 defined as a value obtained by calculation from the equation is 100 to 1
It is called a substantially spherical toner having a value of 40. MLS2 =
{(Absolute maximum length of toner particles) × 2} / {(projected area of toner particles) × π × １ ／ × 100} The shape of the toner produced by the ordinary kneading and pulverizing method is irregular, and MLS
2 is about 140 to 160.

Next, the photosensitive drums 10 (Y) to 10 (Y)
(K) The toner images of each color formed on the first primary intermediate transfer drum 21a and the second primary intermediate transfer drum 21
b is electrostatically secondary-transferred onto the substrate b. Photoconductor drum 10
The black (K) and cyan (C) toner images formed on (K) and (C), respectively, are both on the first primary intermediate transfer drum 21a and on the photosensitive drums 10 (M) and (Y). The magenta (M) and yellow (Y) toner images formed on the second primary intermediate transfer drum 21b are respectively (primarily) transferred.

The first and second primary intermediate transfer drums 2
The surface potential required for electrostatically transferring a toner image from the photosensitive drums 10 (Y) to 10 (K) onto 1a and 21b is as follows:
+250 to 500V. This surface potential is set to an optimum value depending on the charged state of the toner, the ambient temperature, and the humidity. The ambient temperature and the humidity can be easily known by detecting the resistance value of a member having a characteristic in which the resistance value changes depending on the ambient temperature and the humidity. As described above, when the charge amount of the toner is in the range of −20 to 35 μC / g and under the normal temperature and normal humidity environment, the first and second charge
The surface potential of the primary intermediate transfer drums 21a and 21b is +38
About 0V is desirable.

The first and second primary intermediate transfer drums 21a and 21b used in this embodiment have an outer diameter of, for example, 42 mm and a resistance value of about 10 ⁸ Ω. First,
The second primary intermediate transfer drums 21a and 21b are single-layer or multiple-layer cylindrical rotating bodies having flexible or elastic surfaces, and are generally made of metal such as Fe or Al. On a metal pipe as a core, a low-resistance elastic rubber layer (R = 10
² to 10 ³ Ω) with a thickness of about 0.1 to 10 mm. Further, the first and second intermediate transfer drums 21a, 21b
The outermost surface is typically made of a high release layer (R = 10 ⁵ to
10 ⁹ Ω) and bonded with a silane coupling agent-based adhesive (primer). The important thing here is that
It is the resistance value and the surface release property, and the resistance value of the high release layer is R =
The material is not particularly limited as long as it is about 10 ⁵ to 10 ⁹ Ω and has high releasability.

The toner images thus formed on the first and second primary intermediate transfer drums 21a and 21b are electrostatically (secondarily) transferred onto the secondary intermediate transfer drum 22. Therefore, on the secondary intermediate transfer drum 22, a final toner image from a single color image to a quadruple color image of yellow (Y), magenta (M), cyan (C), and black (K) is formed. Will be.

The surface potential required for electrostatically transferring the toner images from the first and second primary intermediate transfer drums 21a and 21b onto the secondary intermediate transfer drum 22 is +600 to 12
It is about 00V. The surface potential of the photosensitive drum 10
As in the case of transferring from (Y) to (K) to the first primary intermediate transfer drum 21a and the second primary intermediate transfer drum 21b, the optimal values are set according to the charged state of the toner, the ambient temperature, and the humidity. become. What is needed for transcription is
Since it is a potential difference between the first and second primary intermediate transfer drums 21a and 21b and the secondary intermediate transfer drum 22,
It is necessary to set a value corresponding to the surface potential of the second primary intermediate transfer drums 21a and 21b. As described above, the charge amount of the toner is in the range of -20 to 35 .mu.C / g, and the surface potential of the first and second primary intermediate transfer drums 21a and 21b is +380 V under normal temperature and normal humidity environment. In this case, the surface potential of the secondary intermediate transfer drum 22 is +880
V, that is, the first and second primary intermediate transfer drums 21
It is desirable that the potential difference between the a, 21b and the secondary intermediate transfer drum 22 be set to about + 500V.

The secondary intermediate transfer drum 2 used in this embodiment
2 has an outer diameter of, for example, 42 mm, which is the same as the first and second primary intermediate transfer drums 21a and 21b, and a resistance value of 1
It is set to about 0 ¹¹ Ω. Further, the secondary intermediate transfer drum 22 also includes first and second primary intermediate transfer drums 21a and 21a.
As in b, the surface of a single layer or a plurality of layers is a cylindrical rotating body having flexibility or elasticity, and is generally placed on a metal pipe as a metal core made of Fe, Al, or the like. , A low-resistance elastic rubber layer (R = 10 ² to 10 ³ Ω) represented by conductive silicone rubber, etc., having a thickness of 0.1 to 10 mm
Provided to the extent. Further, the secondary intermediate transfer drum 22
The outermost surface is typically formed as a high release layer having a thickness of 3 to 100 μm of fluororubber in which fluororesin fine particles are dispersed, and is bonded with a silane coupling agent-based adhesive (primer). . Here, the resistance value of the secondary intermediate transfer drum 22 is determined by the first and second primary intermediate transfer drums 21a and 21a.
It must be set higher than b. Otherwise, the secondary intermediate transfer drum 22 charges the first and second primary intermediate transfer drums 21a and 21b, and it is difficult to control the surface potential of the first and second primary intermediate transfer drums 21a and 21b. Become. The material is not particularly limited as long as it satisfies such conditions.

Next, the final toner image from the single-color image to the quadruple-color image formed on the secondary intermediate transfer drum 22 is transferred onto the paper passing through the paper transport path P by the final transfer roll 30 (3). Next) is transcribed. This sheet passes through a sheet transport roll pair 4 through a sheet feeding step (not shown), and is sent to a nip portion between the secondary intermediate transfer drum 22 and the final transfer roll 30. After the final transfer step, the final toner image formed on the sheet is fixed by the fixing device 5 including the heating roll 50 and the pressure roll 51, and a series of image forming processes is completed.

On the other hand, an untransferred patch toner image used in so-called process control and the like and residual toner (described later) released during cleaning adhere to the final transfer roll 30 and are scraped off by the scraper 61.
It is collected in the collection box housing 60.

The final transfer roll 30 is a metal roll such as SUS provided with a polyimide resin layer. Here, in order to reliably prevent leakage to the metal roll,
After forming an oxide film on the surface of the metal roll by anodizing treatment, it is preferable to provide a polyimide resin layer on the oxide film. This polyimide resin layer preferably has a volume resistance of 6 to 12 log Ωcm, more preferably 9 to 11 log Ωcm under the condition of 100 V applied. In order to give such a volume resistance condition to the polyimide resin layer, for example, a polyimide resin constituting the polyimide resin layer is made of an electronic conductive type material, and an appropriate amount of a volume resistance adjuster such as carbon (for example, 2 to 25%) is contained. Can be. Further, in order to improve the electric resistance maintaining property and uniformity of the polyimide resin, it is preferable to use a conductive polymer material as the conductive material of the polyimide resin. Further, the surface roughness of the final transfer roll 30 may be any value as long as the external additives of the toner are not easily adhered. For example, the ten-point average roughness Rz is 0.3.
It may be about 1.0 μm.

The voltage applied to the final transfer roll 30 is
The optimum value varies depending on the ambient temperature, humidity, type of paper (resistance value, etc.), and is generally about +1200 to 5000V. In this embodiment, a constant current method is employed, and a current of about +6 μA is applied in a normal temperature and normal humidity environment to obtain a substantially appropriate transfer voltage (+1600 to 2000 V).

The scraper 61 is made of, for example, SUS as its material. In order to ensure a scraping function, it is preferable that an edge surface of the scraper 61 that comes into contact with the final transfer roll 30 is subjected to edging. Further, in order to reduce friction with the final transfer roll 30, a scraper 61 is used.
It is preferable to cover a portion of the first transfer roller 30 which comes into contact with the final transfer roll 30 with a low friction coat layer (for example, a fluorine coat layer).
The thickness, free length, pressing pressure, and the like of the scraper 61 can be set as appropriate. In addition, as the mounting state,
In consideration of the scraping performance, a layout in which the tip of the scraper 61 is arranged in the direction facing the rotation direction of the final transfer roll 30, that is, in the doctor direction, is preferable.
The set angle with respect to the tangent is preferably, for example, about 15 to 45 degrees.

In the secondary transfer and tertiary transfer steps of the tandem type full-color printer (image forming apparatus) shown in FIG. 1, the toner image is not completely transferred, and only a part of the toner image is transferred to the intermediate transfer rolls 21a and 21b. , 22. Therefore, in the full-color printer according to the present embodiment, the intermediate transfer body rolls 21a, 21b, 22
The above residual toner is temporarily held by toner removing brushes (toner holding means) 71a, b and 72, and the toner removing brush 71 is used for cleaning performed at a predetermined timing.
The residual toner is discharged from a, b, and 72, moved to the final transfer roll 30, and finally discarded in the toner collection box 6. In this embodiment, the target is a normal negative (−) polarity charged toner (normal polarity toner).
The cleaning of the toner charged to the polarity (the opposite polarity toner) will be described as a modified example described later.

As shown in FIG. 1, the first primary intermediate transfer roller 21a is located downstream of the secondary transfer portion in the rotational direction and upstream of the primary transfer portion of the photosensitive drum 10 (K). A first primary toner removing brush 71a is provided in contact with the intermediate transfer roll 21a. Also, the second primary intermediate transfer roll 21b is brought into contact with the intermediate transfer roll 21b downstream of the secondary transfer portion in the rotation direction and upstream of the primary transfer portion with the photosensitive drum 10 (M). A second primary toner removing brush 71b is provided. Further, the secondary intermediate transfer roll 22 contacts the secondary intermediate transfer roll 22 downstream of the tertiary transfer portion in the rotation direction of the secondary intermediate transfer roll 22 and upstream of the secondary transfer portion with the second primary intermediate transfer roll 21b. And a secondary toner removing brush 72 is provided. These toner removing brushes 71a, b,
Reference numeral 72 denotes a rotating brush in which a brush member having a predetermined electric resistance is implanted in a metal pipe such as SUS.

Further, these toner removing brushes 71a,
The b and 72 are driven to rotate at a peripheral speed difference of 20% or more with respect to the moving speed of the surface of each of the intermediate transfer rolls 21a, b and 22.

FIG. 2 is a block diagram showing a control system for cleaning the residual toner (positive toner) held by the toner removing brush according to this embodiment.
On the other hand, FIG. 3 is a potential gradient diagram for explaining the operation of the control system shown in FIG. 2, in which FIG. 3A shows a potential gradient in a normal state, and FIG. Each potential gradient is shown.

As shown in FIG. 2, this control system mainly includes a potential control unit (bias control means) 8, and the potential control unit 8 detects the potential of the printer transmitted from the main controller 100 of the printer. This is a signal indicating the state, and the control target of the potential control unit 8 is a bias voltage applied to the developing rolls 130 (Y) to (K), the toner removing brushes 71 a, b, 72, and the like. Although not shown in FIG. 2, the control target of the potential control unit 8 may be other than the photosensitive drum 10 (Y).
To (K) and the bias voltage applied to the intermediate transfer drums 21a, 21b, and 22.

When a signal indicating that a printing operation is being performed is received from the main control device 100, the potential control unit 8 returns to the state shown in FIG.
A bias voltage having a potential gradient shown in FIG. That is, the developing roll 130 during the printing operation
Is V (130), and the potential of the photosensitive drum 10 is V
(10) The potential of the primary intermediate transfer roll 21 is set to V (2
1), the potential of the primary toner removing brush 71 is set to V (71),
Assuming that the potential of the secondary intermediate transfer roll 22 is V (22), the potential of the secondary toner removing brush 72 is V (72), and the potential of the final transfer roll 30 is V (30), V (30) is between these potentials. (130) <V (10) <V (21) <V (71)
The relationship of <V (22) <V (72) <V (30) holds.

Therefore, during the printing operation, the toner image undergoes primary to tertiary transfer, and most of the toner image is finally transferred onto the paper, and a very small part is held by the primary toner removing brushes 71a and 71b and the secondary toner removing brush 72. You. In this embodiment, V (130) = − 230 [V] and V (10) = − 6.
0 (image part) [V], V (21) = + 380 [V], V
(71) = + 600 [V], V (22) = + 880
[V], V (72) = + 1100 [V], V (30) =
+1800 [V].

In this embodiment, the potential difference between each of the primary intermediate transfer rolls 21 and the primary toner removing brush 71 (see ΔV1 in FIG. 3A) and the electric resistance between them are appropriately set. As a result, it is possible to regulate the transmission current between the two, thereby retaining the residual toner, and also prevent the retained residual toner from being inverted and unintentionally discharged. Similarly, the potential difference between the secondary intermediate transfer roll 22 and the primary toner removing brush 72 (FIG. 3)
(See ΔV2 in (a)), the transmission current between the two is defined by appropriately setting the electrical resistance value between the two, and as a result, the polarity of the remaining toner is maintained while maintaining the remaining toner. It can be prevented from being inverted and unintentionally released. The relationship among these potential differences, electric resistance values, transmission currents, and toner retention will be described in experimental examples described later.

On the other hand, when signals indicating their states are received from the main control device 100 at a predetermined timing, such as before the printing operation, after the printing operation, at a predetermined number of sheets for continuous printing, and the like, the potential control unit 8 returns to FIG. A bias voltage having a potential gradient shown in b) is applied to each control target.

That is, the potential of the developing roll 130 during the cleaning operation (of the normal polarity toner) is set to V ′ (13
0), the potential of the photosensitive drum 10 is V ′ (10), the potential of the primary intermediate transfer roll 21 is V ′ (21), the potential of the primary toner removing brush 71 is V ′ (71), and the secondary intermediate transfer roll 22 is Potential V ′ (22), the secondary toner removal brush 7
2 is V ′ (72), and the potential of the final transfer roll 30 is V ′ (30).
0) <V '(72) = V' (71) = V '(130) <
The relationship V '(21) <V' (22) <V '(30) holds.

Therefore, the residual toner held by each of the toner removing brushes 71a, 71b, 72 during the cleaning operation (of the normal polarity toner) is transferred to the final transfer roll 30 through the secondary to tertiary transfer, and The toner is scraped off by 61 and finally collected in the toner collection box 6. In this embodiment, V ′ (130) = V ′
(10) = V ′ (71) = V ′ (72) = 0 [V],
V '(21) = + 380 [V], V' (22) = + 88
0 [V] and V '(30) = + 1800 [V].

The potential gradients shown in FIGS. 3A and 3B in this embodiment are obtained by supplying voltage to the metal parts (shafts and pipes) of each member. If a desired surface potential can be obtained by electrically floating the primary intermediate transfer drums 21a and 21b or the secondary intermediate transfer drum 22 and the resistance value of these members, such a method may be adopted.

Experimental Example In this example, each toner removing brush 71 was used for printing.
The toner removal brushes 71a, b, 72 and the intermediate transfer rolls 21a, b, and 72a are used to electrostatically hold the residual toner on the a, b, and 72 and not to reverse the charged polarity of the retained toner. 22, the electric resistance value,
The transmission current value is specified. Hereinafter, an experiment for appropriately setting these parameters will be described.

FIG. 4 illustrates a method of measuring a potential difference, an electric resistance value, and a transmission current value described in the present embodiment and the present experimental example. As shown in the figure, the toner removing brush 7 (71a, 71b, 72) and the intermediate transfer roll 2
(21a, 21b, 22) are brought into contact with each other, and a high-voltage power supply is connected to the metal part at the center of the cross section of both, and the voltage value and current value at that time are measured. The outer diameter of the toner removing brush 7 is 14 mm, and the outer diameter of the intermediate transfer roll 2 is 4 mm.
2 mm, the distance between the rotation axes was 27.5 mm,
There is a 5 mm overlap. The toner removal brush 7 has 100,000 brushes implanted per square inch.

[0051]

[Table 1] Table 1 summarizes the experimental results showing the relationship between the potential difference between the toner removing brush 7 and the intermediate transfer roll 2, the transmission current value, and the residual toner retention. The inventor sets the potential difference ΔV (corresponding to ΔV1 or ΔV2 in FIG. 3) between the toner removing brush 7 and the intermediate transfer roll 2 to 0, 100, 20.
0, 300, 400, and 500 [V], and continuously print 20 images of the standard evaluation pattern at each potential difference, and increase the weight of the toner removing brush 7 [m
g], tape transfer image reflection density [G], transfer residual image grade [Grade], applied voltage [V], transmission current [μA] near the downstream side of the contact portion of the surface of the intermediate transfer roll 2 with the toner removing brush 7. Is observed and measured. The weight increase indicates the amount of the residual toner retained by the toner removing brush 7, and the larger the more, the more preferable the transfer image density is the amount of the toner not retained by the toner removing brush 7 (the amount of toner passing through the toner removing brush 7 The transfer residual image grade indicates the amount of untransferred toner appearing on the recording medium, and the smaller, the better.

FIG. 5 is a graph showing the experimental results shown in Table 1. The horizontal axis represents the potential difference ΔV between the toner removing brush 7 and the intermediate transfer roll 2, the vertical axis represents the weight increase of the toner removing brush 7, the tape transfer image reflection density,
It shows the transfer afterimage grade. As shown in this graph, first, as the potential difference ΔV increases from 0, the weight of the toner removing brush 7 gradually increases, the tape transfer image reflection density gradually decreases, and the transfer residual image grade gradually decreases. And the potential difference ΔV
Is between 180 [V] and 280 [V], the weight of the toner removal brush 7 takes the maximum value, the reflection density of the tape transfer image takes the minimum value, and the transfer residual image grade is a level that does not substantially affect the image quality. Calm down to G1. Further, the potential difference Δ
As V increases from 280 [V], the weight of the toner removing brush 7 gradually decreases, the tape transfer image reflection density gradually increases, and the transfer residual image grade maintains a level G0 at which there is no problem.

In order to increase the weight of the toner removing brush 7, the reflection density of the transferred image of the tape, and the transfer residual image grade by the potential difference ΔV, the potential difference ΔV is set to 1
It is considered that it is difficult for the toner removing brush 7 to hold the residual toner electrostatically in the range of less than 80 [V], and once the potential difference ΔV is larger than 280 [V], the toner removing brush 7 temporarily holds the residual toner. Charge is injected into the residual toner,
It is considered that this is because the charging polarity is reversed and the toner is removed from the toner removing brush 7.

Therefore, from this experiment, the potential control unit 8
The lower limit of the magnitude of the holding bias applied to the toner removing brush 7 at the time of printing is such that the potential difference ΔV between the toner removing brush 7 and the intermediate transfer roll 2 becomes 180 [V]. It is preferable that the upper limit is a potential at which the potential difference ΔV between the removing brush 7 and the intermediate transfer roll 2 becomes 280 [V]. In this case, the value of the transmission current between the toner removing brush 7 and the intermediate transfer roll 2 is about 1.1 to 2.1 μm.

Further, when the potential difference ΔV between the toner removing brush 7 and the intermediate transfer roll 2 is within the range of 180 [V] to 280 [V], the magnitude of the holding bias applied to the toner removing brush 7 is increased. Saha removal brush 7
It is preferable that the potential is such that the value of the transmission current flowing between the transfer roller 2 and the intermediate transfer roll 2 is minimized. Here, as the potential difference ΔV decreases, the transmission current tends to decrease. Therefore, the magnitude of the holding bias is such that the potential difference ΔV is 180 °.
It is preferable to set the value to be [V].

[0056]

[Table 2] Table 2 summarizes the experimental results showing the relationship between the potential difference between the toner removing brush 7 and the intermediate transfer roll 2, the electric resistance value, the transmission current value, and the form of the toner removing brush 7. The inventor sets the potential difference ΔV between the toner removing brush 7 and the intermediate transfer roll 2 to 0, 100, 200, 30.
0, 400, 500 [V], and the toner removing brush 7 (5) in which 50,000 brushes are implanted per square inch as the toner removing brush 7 and 100,000 brushes per square inch The applied voltage [V] and the transmitted current [μA] are measured using the flocked toner removing brush 7 (10), and the toner removing brush 7 and the intermediate transfer roll obtained from the applied voltage and the transmitted current are measured. It is a summary of the electrical resistance between the two.

FIG. 6 is a graph showing the experimental results shown in Table 2. The horizontal axis shows the voltage [V] applied to the toner removing brush 7, and the vertical axis shows the transmitted current [μA]. As shown in this graph, in each of the toner removing brushes 7 (5) and (10), a substantially directly proportional relationship is recognized between the applied voltage and the transmission current, and the inclination is smaller than that of the brush 7 (5). Is smaller than the brush 7 (10).

Therefore, from this experiment, the potential control unit 8
It can be seen that the preferred range and value of the holding bias applied to the toner removing brush 7 during printing vary depending on the flocking density of the toner removing brush 7.

In a series of transfer steps (primary transfer to tertiary transfer) of the tandem type full-color printer (image forming apparatus) shown in FIG. 1, when a toner image passes through a transfer portion of each transfer step. , By Paschen discharge or charge injection,
(-) A part of the positive polarity toner in the charged image may become a (+) charged toner having the opposite polarity. This (+) charged toner is not transferred to the next step but flows backward to the upstream side, so that the charging device 11 having the highest negative potential is used.
Attach and deposit on (Y)-(K). These charging devices 11
In the portions where the toners (Y) to (K) adhere, the discharge becomes active and the surface potential of the photosensitive drums 10 (Y) to (K) tends to increase. The surface potentials of the photosensitive drums 10 (Y) to 10 (K) become uneven at portions where the toner is not adhered and where toner is not attached. If the surface potentials of the photoconductor drums 10 (Y) to (K) become uneven, an image is uniformly exposed on the surfaces of the photoconductor drums 10 (Y) to (K) to form an electrostatic latent image. Even so, unevenness occurs in the latent image potential, resulting in a difference in the development amount. Therefore, particularly when a halftone image is to be developed, density unevenness becomes conspicuous.

Therefore, the charging devices 11 (Y) to
In order to prevent the occurrence of density unevenness due to the toner adhered to (K), in this modified example, at a predetermined timing, such as before a printing operation, after a printing operation, every predetermined number of sheets with continuous printing, and between pages, the following is performed. Another cleaning operation is performed.

The charging devices 11 (Y) to (K), the photosensitive drums 10 (Y) to (K), the first and second primary intermediate transfer drums 21a and 21b, the secondary intermediate transfer drum 22, and the final transfer roll By applying a voltage with a potential gradient in order so that the final transfer roll 30 has the highest negative potential in the order of 30, the charging device 11 during the printing operation.
The (+) charged toner of the opposite polarity deposited and deposited on (Y) to (K) is sequentially transferred and moved to the final transfer roll 30, and is moved by the metal scraper 61 provided in pressure contact with the final transfer roll 30. to recover.

In this embodiment, the charging devices 11 (Y) to (Y)
(K) has a surface potential of 0 V, and the photosensitive drum 10 (Y) to
The surface potential of (K) is -300V, the surface potential of the first and second primary intermediate transfer drums 21a and 21b is -800V,
The surface potential of the secondary intermediate transfer drum 22 is set to -1300V, and the surface potential of the final transfer roll 30 is set to -2000V. In such a minus application cleaning mode, that is, the (+) charged toner recovery mode of the opposite polarity, it is possible to prevent the occurrence of density unevenness due to the toner attached to the charging devices 11 (Y) to (K).

[0063]

As described above in detail, according to the present invention, it is possible to provide a smaller-sized image forming apparatus having a high degree of freedom in layout while performing appropriate cleaning.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a full-color printer according to an embodiment.

FIG. 2 is a control block diagram illustrating a potential control system.

FIG. 3 illustrates a potential gradient during printing and during cleaning.

FIG. 4 illustrates a method for measuring electric resistance.

FIG. 5 is a graph illustrating various characteristics of the toner removing brush.

FIG. 6 is a graph illustrating a difference in electric resistance value depending on the flock density of the toner removing brush.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Photoreceptor drum (image carrier), 21 ... Primary intermediate transfer roll (intermediate transfer body), 22 ... Secondary intermediate transfer roll (intermediate transfer body), 30 ... Final transfer roll (transfer means), 6 ...
Toner collection box (collection means), 71: primary toner removal brush, 72: secondary toner removal brush, 8: potential control section (bias control means),

Claims (5)

[Claims] An image forming apparatus including an image carrier on which a toner image is carried, and an intermediate transfer body on which the toner image is transferred from the image carrier, retains residual toner after transfer by abutting on the intermediate transfer body. And a holding bias that normally holds the residual toner, and a release bias that releases the normally held toner during cleaning is applied between the intermediate transfer body and the toner holding unit during cleaning. An image forming apparatus comprising: 2. Between the toner holding means and an intermediate transfer member.
Has an electric resistance of 10 ^TenThe image according to claim 1, which is equal to or less than Ω.
Image forming device. 3. The lower limit of the magnitude of the holding bias is set to a value capable of electrostatically holding the residual toner in the toner holding unit, and the upper limit is set to a value capable of reversing the charging polarity of the residual toner. The image forming apparatus according to claim 1, wherein the image forming apparatus is set within a range. 4. The lower limit of the magnitude of the holding bias is set to a value capable of electrostatically holding the residual toner in the toner holding unit, and the upper limit is set to a value capable of reversing the charging polarity of the residual toner. The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus is set within a range, and is set near a value at which a transmitted current between the toner holding unit and the intermediate transfer member is minimized within the range. 5. A cleaning device comprising: a transfer unit that abuts on the intermediate transfer body to transfer a toner image from the intermediate transfer body to a recording medium; and a collection unit that abuts on the transfer unit and collects residual toner after discharge. The image forming apparatus according to claim 1, wherein the residual toner released from the toner holding unit sometimes reaches the transfer unit.