JP2002031958A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner from adhering to an attracting member arranged to abut on a transfer material carrying body electrostatically attracting transfer material by improving releasing property to the toner without depending on the selection of material and applying bias for preventing the toner from adhering to the attracting member. SOLUTION: In this image forming device having four photoreceptor drums 1 abutting on a carrying belt 4 along the belt 4, the toner adhering to the belt 4 is transferred to the drum 1 and removed from the belt by applying cleaning bias to a transfer roller 12 on the back surface of the belt. In cleaning, the bias for preventing the toner from adhering to an attracting roller 19 is applied to prevent the toner on the belt from adhering to the roller 19 abutting on the belt on the upstream side in a transfer material carrying direction. In such a case, the roller 19 is previously coated with the powder of a compound such as hydrotalcite and the releasing property of the roller 19 is made high in order to make the prevention of adhesion by the bias effective even when the toner releasing property of the material of the roller 19 is not high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrophotographic technology.

[0002]

2. Description of the Related Art An outline of a tandem type color image forming apparatus using electrophotography will be described below.

The image forming apparatus includes four image carriers arranged at equal intervals in the center, and a charging unit, an exposure unit, a developing unit, and a cleaning unit are arranged corresponding to each image carrier. The developing means is filled with yellow, magenta, cyan, and black toners.

The image carrier has a photosensitive layer formed by applying a photoconductor on a metal substrate such as aluminum.
In order to form an image, first, the image carrier is rotated, its surface is charged to a certain potential Vd by a charging means, and then image exposure is performed by an exposure means, and the exposed portion is lowered to a potential VL. An electrostatic latent image is formed on the body surface.

Subsequently, the electrostatic latent image is developed by the developing means using toner, and is visualized as a toner image. The developing means carries a toner by the developer carrier and transports the toner to the image carrier, and a developing bias having an appropriate potential between the Vd potential and the VL potential between the developer carrier and the image carrier. Is applied, the toner on the developer carrier adheres to the latent image on the image carrier, and the latent image is developed.

[0006] The four color toner images formed on the four image carriers in this manner are transferred onto an electrostatic transport belt (abbreviated as a transport belt) which is a transfer material transporter and transported. By applying a DC bias having a polarity opposite to that of the toner to a transfer member disposed on the rear surface of the transport belt so as to face each image carrier, the images are sequentially superimposed and transferred. The transfer material is supplied to the transport belt from the paper feed cassette, and is applied on the transport belt by electrostatic attraction by applying either a positive or negative DC bias to an attraction roller disposed in contact with the transport belt.

After the transfer of the four color toner images is completed, the transfer material is separated from the transport belt and transported to fixing means, where the toner image is fixed to the transfer material by heating, pressing or the like, and a full-color fixed image and Is done.

At the time of transferring the toner image to the transfer material, the current technology cannot transfer 100% of the toner to the transfer material, and transfer residual toner is generated on the image carrier. For this reason, a cleaning means such as a blade or a brush is brought into contact with the image carrier to mechanically remove transfer residual toner on the image carrier.

In an electrophotographic color image forming apparatus, if the image density fluctuates due to various conditions such as a change in the environment in which the apparatus is used and the number of prints, an original correct color tone cannot be obtained. Therefore, a toner image (patch) for density detection is experimentally created on the transport belt with the toner of each color, and the patch density is detected by the optical image density detection means. The image density is controlled by applying feedback to a bias or the like.

[0010] By executing the image density control, the toner image is directly transferred to the transport belt, and the transport belt is contaminated with toner. In addition, toner and the like may adhere to the transport belt due to unavoidable causes such as jam of the transfer material and fogging of the image carrier, and the transport belt may be stained.

Means for removing the dirt on the transport belt has been taken. One of them is to apply a negative bias to the transfer member to transfer the dirt toner on the transport belt to the image carrier (re-use). Transfer and reverse transcription) are known. According to this method, a toner cleaning member on the belt, such as a blade or a brush, which is often used for cleaning the belt, becomes unnecessary, leading to cost reduction.

However, the dirt toner adhering to the conveyor belt passes through a nip portion between the conveyor belt and a suction roller arranged in contact with the image carrier before reaching the image bearing member. May get dirty. If the suction roller is soiled, it leads to toner stains on the transfer material and image stains, so that it is necessary to take measures to prevent such stains.

As one of the means for preventing contamination of the suction roller,
In the direct transfer mode in which patches are formed on the transport belt or in the cleaning mode by retransfer of the contaminated toner on the transport belt, the polarity of the adsorption bias is set to the same polarity as the original charge polarity of the toner, and the absolute value is set. Below the discharge start voltage to the conveyor belt (0.5 kV-
1.0 kV) and applying this to the suction roller as a bias for preventing toner adhesion,
There is a method in which an electric field is formed between the suction roller and the conveyance belt to repel the toner from adhering to the suction roller, thereby preventing the toner from adhering to the suction roller.

[0014]

However, the above-mentioned means for preventing the suction roller from being stained by the electric field is effective only for the suction roller using a material such as a fluorine-based resin having a high toner release property. If the suction roller is made of a material that is inferior in toner releasability, the toner adheres to the suction roller more strongly than the repulsive force of the toner due to the electric field. Adhesion occurs and the suction roller becomes dirty.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to release a toner from a suction member such as a suction roller disposed in contact with a transfer material conveyance member, which electrostatically suctions the transfer material onto the transfer material conveyance member such as a conveyance belt. By applying a bias to prevent toner adhesion to the adsorption member, the toner is easily prevented from adhering to the adsorption member, preventing contamination of the adsorption member and image contamination It is an object of the present invention to provide an image forming apparatus capable of performing such operations.

[0016]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which a toner image is formed, an endlessly rotating transfer material carrier for carrying the transfer material and transporting the image carrier, and carrying the transfer material on the transfer material carrier by electrostatic adsorption. A bias member, which is applied in contact with the transfer material transporting body and is capable of applying a bias, and the transfer material transporting body that transfers the toner image on the image carrier to the transfer material on the transfer material transporting body. An image forming apparatus having a transfer member in contact with the image carrier, wherein a powder that improves releasability from toner is applied to the attraction member in advance.

According to the present invention, the powder is inorganic particles. Alternatively, they are organic particles, composite particles, and lubricant powder. Alternatively, two or more of inorganic particles, organic particles, composite particles and lubricant powder are mixed. The inorganic substance is a hydroxytalcite compound.

As the toner adhesion preventing bias, a positive / negative bias having an absolute value equal to or lower than a discharge starting voltage for the transfer material conveying body is applied to the attraction member alternately at a constant cycle. In the rotation direction of the transfer material transport body,
In the region from the downstream side of the transfer member to the upstream side of the adsorption member, there is no toner removing unit for removing the toner attached to the transfer material transporting body, and the toner attached to the transfer material transporting body is The transfer member is transferred to the image carrier by applying a cleaning bias to the transfer member, and is removed from the transfer material transport body. A transfer material transporting body cleaning mode for transferring the toner adhered on the transfer material transporting body to the image carrier; and executing the cleaning mode at a predetermined timing. In the specific time region during the execution of the cleaning mode, the application of the toner adhesion prevention bias is performed.

The apparatus has a detecting means for detecting the size of the transfer material adsorbed on the transfer material transporting body, and according to the detection result,
The DC voltage value and the polarity applied to the suction member are variably controlled, and according to the detection result, it is determined that the transfer material has not passed through the contact nip between the transfer material conveyance body and the suction member. Depending on the image forming operation state in all or a part of the area, positive and negative biases having an absolute value equal to or lower than a discharge starting voltage for the transfer material transporter are applied to the suction member while being alternately switched at a constant cycle. Control. A plurality of image carriers are provided, and a plurality of color toner images are formed on the plurality of image carriers.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

As one embodiment of the image forming apparatus of the present invention,
The tandem color image formation will be described with reference to FIGS.

As shown in FIG. 1, the image forming apparatus is provided with four photosensitive drums 1 having a diameter of 30 mm, which are image carriers, arranged at equal intervals in a central portion.
Is driven to rotate at a peripheral speed of 94 mm / sec in the direction of the arrow shown in the figure. A charging roller 5 corresponding to each photosensitive drum 1,
Exposure device 7, developing device 8, and cleaning blade 1
The developing device 8 includes magenta toner,
It is filled with cyan toner, yellow toner, and black toner.

The photosensitive drum 1 has a structure in which a photosensitive layer is applied and formed on an aluminum cylinder. The photosensitive layer is usually an insulator, but there is no particular limitation on the substance as long as it is a photoconductor having the property of becoming a conductor by irradiating it with light of a specific wavelength. Mainly O
PC (organic optical semiconductor), A-Si (amorphous silicon), CdS (cadmium sulfide), Se (selenium) and the like are often used.

In this embodiment, as shown in FIG. 2, the photosensitive drum 1 has a structure in which a charge generation layer 1b and a charge transport layer 1c as a dielectric layer are provided on an aluminum cylinder 1a. Irradiation generates hole-electron pairs in the charge generation layer 1b, which serve as carriers of charge flow. The charge generation layer 1b is formed of a phthalocyanine compound to a thickness of about 0.2 μm, and the charge transport layer 1c is formed of a polycarbonate resin in which a hydrazone compound is dispersed.
It is formed to about μm.

The surface of the photosensitive drum 1 is uniformly charged by the charging roller 5. Charging roller 5 as charging member
Is, for example, an EPDM having a thickness of about 3 mm formed of a metal core,
It is covered with a conductive elastic rubber made of urethane rubber, CR, NBR or the like, and a medium resistance layer having a thickness of 200 to 600 μm and a volume resistivity of about 10 ⁶ Ωcm is provided thereon, and a protective layer of about 10 μm is further provided thereon. It is formed in the structure provided.

The charging roller 5 presses the metal cores at both ends thereof with a spring to bring the surface of the charging roller 5 into contact with the photosensitive drum 1, and is rotated by the photosensitive drum 1. When a charging bias higher than the discharge start voltage (approximately 550 V) is applied to the core of the charging roller 5, a discharge occurs near the nip where the charging roller 5 and the photosensitive drum 1 are in contact with each other. The charge is accumulated in the charge transport layer 1c. At this time, the surface potential of the photosensitive drum 1 becomes a value obtained by subtracting the discharge starting voltage from the applied bias. In the present embodiment, the applied bias is set to -1250 V, and the surface of the photosensitive drum 1 is set to Vd.
== − 700V.

The surface of the photosensitive drum 1 maintained at the Vd potential by the discharge of the charging roller 5 is subjected to scanning exposure using the exposure device 7 while controlling the light source to be ON / OFF based on a signal from the controller. An electrostatic latent image is formed on the surface of the drum 1. At the light irradiation position on the photosensitive drum 1, a hole-electron pair is formed in the charge generation layer 1b, and the holes recombine with the electrons accumulated on the surface of the photosensitive drum 1 through the charge transport layer 1c. As a result, the charge at that portion drops to the potential VL. That is, the absolute value of the surface potential of the photosensitive drum 1 decreases, and a latent image is formed.

In this embodiment, a semiconductor laser is used as a light source. The VL potential depends on the amount of charge generated during light irradiation. That is, it depends on the thickness of the charge generation layer 1b, the amount of laser exposure, and the like. In this embodiment, these values are controlled so that the VL potential becomes -150V.

After that, the electrostatic latent image on the photosensitive drum 1 is developed by the developing device 8 arranged at a position facing the photosensitive drum 1. The toner in the developing device is supplied to and supported on the developing roller 3 by a stirring member or the like. This developing roller 3
Is disposed in contact with the photosensitive drum 1 in the developing device 8,
The photosensitive drum 1 is rotated in a forward direction with respect to the rotation direction by a peripheral speed difference of about 180%. As the developing roller 3, for example, a roller in which a metal core is covered with conductive rubber and a dielectric layer is coated thereon is used.

On the upstream side of the contact portion of the developing roller 3 with the photosensitive drum 1, there is provided a regulating blade 23 contacted with a linear pressure of about 0.2 N in the counter direction. By restricting the toner carried on the developing roller 3 by passing the toner, the thin toner layer is coated and the toner is charged to a fixed negative amount. As the regulating blade 23, for example, a metal leaf spring having elasticity such as phosphor bronze or SUS is used, or urethane rubber or silicone rubber is supported by a metal leaf spring, or a rubber surface is coated with nylon. Is used.

At the time of development, a bias having an appropriate potential between Vd and VL is applied to the core of the developing roller 3 as a developing bias. By applying the developing bias, the toner corresponding to the VL portion on the photosensitive drum 1 among the toner on the developing roller 3 adheres to the photosensitive drum 1 by the developing electric field formed between the photosensitive drum 1 and the developing roller 3. Then, the latent image on the photosensitive drum 1 is developed and visualized as a toner image.

Each of the developing devices 8 is an integrally molded cartridge and is a replaceable consumable part.
In some cases, the developing device 8, the photosensitive drum 1, the charging roller 5, and the cleaning blade 11 may be formed as an integrally molded cartridge.

An electrostatic transport belt (transport belt for short) 4 as a transfer material transport body is arranged so as to contact all four photosensitive drums 1. This transport belt 4
It is wound around two rollers, a drive roller 14 and a tension roller 13, and is supported by an appropriate tension. When driven by the drive roller 14, the photosensitive drum 1 is rotated at substantially the same speed in the forward direction of the arrow. You.

The transport belt 4 has, for example, a thickness
50-300 μm, volume resistivity 10 ⁹-10¹⁶About Ωcm
Degree of PVdF (polyvinylidene fluoride), Polya
Mid, polyimide, PET (polyethylene terephthalate)
G), a resin film of polycarbonate, etc.
5 to 2 mm, volume resistivity 10⁹-10¹⁶C of about Ωcm
R (chloroprene rubber), EPDM (ethylene-pro
Pyrene-diene terpolymer), NBR (nitrile pig)
Rubber sheets such as diene rubber) and urethane rubber are used.
You. In some cases, these materials may include carbon, Z
nO, SnO_Two, TiO_TwoDisperse conductive fillers such as
And the volume resistivity is 10⁷-10¹¹Adjust to about Ωcm
Sometimes.

On the back surface of the conveyor belt 4, four transfer members are arranged corresponding to the respective photosensitive drums 1. Examples of the transfer members include an elastic roller, a corona, a blade, a brush and the like. In this embodiment, an elastic roller (transfer roller) 12 having an outer diameter of 12 mm was used. The transfer roller 12 may be, for example, a metal core having a volume resistivity of 10 ⁵ to 10 ⁸ Ω.
cm adjusted EPDM, urethane rubber, CR, NBR
And the like. The transfer roller 12 is brought into contact with the photosensitive drum 1 at a linear pressure of about 0.04 to 0.5 N, and is rotated at substantially the same speed in the forward direction with respect to the moving direction of the transport belt 4. When transferring the toner images of each color on the photosensitive drum 1 onto the transfer material on the conveyor belt 4,
An appropriate positive DC bias is independently applied to these transfer rollers 12.

The transfer material is supplied from a cassette 20 or a multi-feeder (not shown), and is conveyed to a conveyance belt 4 by a registration roller 21 in synchronization with the formation of an electrostatic latent image by laser exposure. . A suction roller 19 having a diameter of 12 mm is disposed in contact with the drive roller 14 at a position opposed to the drive belt 14 with the transfer belt 4 interposed therebetween. The transfer material conveyed to the transfer belt 4 is a nip between the suction roller 19 and the transfer belt 4. After passing through the (suction nip) portion, it is electrostatically attracted onto the conveyor belt 4. The drive roller 14 is grounded.

In this embodiment, the suction roller 19 is made of a metal core made of EPDM, urethane rubber, C
The structure is such that it is covered with a conductive elastic rubber made of R, NBR or the like, a middle layer of urethane or the like having a thickness of about 200 to 600 μm is provided thereon, and a surface layer of styrene or the like having a thickness of about 250 μm is further provided thereon.

The suction roller 19 is pressed against the drive roller 14 via the conveyor belt 4 by spring-pressing the metal cores at both ends with a linear pressure of about 0.04 to 0.5 N.
The conveyor belt 4 is driven to rotate. In this state, when the transfer material passes through the nip portion between the transport belt 4 and the suction roller 19, when a discharge start voltage (500 V to 1.0 kV depending on the situation) or more is applied to the core metal portion of the suction roller 19, Discharge occurs near the nip and the transfer material surface is charged, and at the same time, the surface of the transport belt 4
A mirror charge having a polarity opposite to that of the transfer material surface is generated, and the transfer material is electrostatically attracted to the transport belt 4 by their electrostatic interaction. By this electrostatic attraction, the transfer material is transported to the transport belt 4.
Stably carried on the photosensitive drum 1 and the transfer roller 12
Can be conveyed to the transfer nip portion facing the same. The bias applied to the suction roller 19 will be described later.

Thereafter, a transfer electric field is generated by the action of the positive DC bias applied to the transfer roller 12 on the transfer material conveyed to each transfer nip by the transfer belt 4, and the toner of each color on the photosensitive drum 1 is formed. The image is transferred. The transfer material on which the transfer of the four color toner images has been completed is the tension roller 1
3 is separated from the conveyor belt 4 by a curvature, and is conveyed to the fixing means.
0 while passing through the nip,
The four color toner images are fixed on the transfer material, and a full-color fixed image is formed.

At the time of the above-mentioned transfer, 100% of the toner on the photosensitive drum 1 cannot be transferred to the transfer material by the current technology, and the transfer residual toner is generated on the photosensitive drum 1 after the transfer of the toner image. If left as it is, the image will be transferred to the next transfer material and the image will be disturbed. For this reason, the cleaning blade 11 is installed in contact with the photosensitive drum 1 in the counter direction with respect to the rotation direction,
By 1, the transfer residual toner is mechanically removed from the photosensitive drum 1. The removed toner is collected in a waste toner collecting section.

In general, in an electrophotographic color image forming apparatus, if the image density fluctuates due to various conditions such as a change in the environment in which the apparatus is used and the number of prints, an original correct color tone cannot be obtained. Therefore, in this embodiment, the toner image (patch) for density detection is also formed on the conveyor belt 4 with the toner of each color.
Tentatively, and the patch densities of the
Is detected by an optical image density detection sensor 2 provided at the most downstream portion in the transfer material transport direction, and the image density is controlled by applying feedback to the developing bias based on the detection result.

The density detection sensor 2 is shown in FIGS.
As shown in FIG. 2, a light emitting element 2a such as an LED and a light receiving element 2b such as a photodiode are mounted on a holder 2c, and infrared light from the light emitting element 2a is
The image density of the patch P is measured by irradiating the upper patch P and measuring the reflected light from the patch P with the light receiving element 2b. The reflected light from the patch P includes a specular reflection component and an irregular reflection component, and the patch density can be measured by a method of detecting either component. The amount of light greatly fluctuates due to fluctuations in the surface state and the distance between the sensor 2 and the patch P, so that it is difficult to ensure detection accuracy.

Therefore, in this embodiment, a method for detecting irregular reflection components is adopted, and as shown in FIG. 3A, the density detection sensor 2 irradiates the patch P with respect to the normal I of the conveyor belt 4. Assuming that the incident angle of light is 45 ° and the light receiving angle of the reflected light from the patch is 0 °, the measurement is performed by allowing only the irregularly reflected light to enter the light receiving element 2b without causing the regular reflection light from the patch P to enter.

The patch P was formed in a 14 mm × 14 mm square shape, and was formed by a halftone subjected to a specific dither processing. In this embodiment, a halftone patch having an exposure amount of about 60% is adopted, assuming that the exposure amount when the entire surface is exposed is 100%. By developing and transferring the latent image of the patch while changing the developing bias at regular intervals, as shown in FIG. 4, a plurality of patches P are formed on the conveyor belt 4 with different densities, and these patches are formed. The patch density is detected by the density detection sensor 2, and a developing bias is calculated and obtained from the detected value so that the patch has a predetermined density, and this is performed for each color, and the obtained developing bias value is used at the time of image formation. Image density control was performed by developing bias control.

Instead of changing the developing bias value, the developing bias value is fixed to a constant value, and a latent image of a halftone patch subjected to a specific dither process is formed while changing the exposure amount at a constant interval, and is developed and transferred. A plurality of patches may be formed on the conveyor belt 4 with different gradations and detected by the density detection sensor 2. In some cases, halftone control for correcting the amount of exposure when performing dither processing to obtain smooth gradation based on these detection values is performed.

Prior to the execution of the density control, the patch density is determined by the light receiving value of the reflected light of the base of the transport belt 4 alone, and
It is calculated from the difference between the light reflected from the patch and the received light value.
The image density control is preferably performed when the power is turned on, when a consumable such as a cartridge is replaced, or when a predetermined number of images have been formed since the previous execution of the image density control.

In this embodiment, a registration detecting sensor (not shown) is arranged at a portion facing the conveyor belt 4.
In the tandem type color image forming apparatus as in the present embodiment, the color image is reproduced by superimposing and transferring the four color toner images on the transfer material and mixing the colors at the time of fixing. If the correct color overlay is impaired, the original correct color tone cannot be obtained. Therefore, in the present embodiment, a line image for registration detection is created on the conveyor belt 4 with each color toner on a trial basis, and their positions are detected by a registration detection sensor. Registration control is performed to feed back the start timing of the formation of a latent image by scanning exposure.

As the resist detection sensor, an optical image density sensor similar to the density detection sensor 2 can be used. The registration control detects the transfer position from the intensity change of the amount of light received by the sensor when the line on the conveyor belt passes the location of the registration detection sensor, and based on that, corrects the latent image formation start timing temporally Is added. In image density control, the purpose of the sensor is to detect the density difference between patches, so the diffuse reflection light detection method that can expect stable detection of the amount of reflected light is preferably used. Since the purpose of the sensor is to detect a change in the absolute value of the reflected light amount at the point, it is necessary that the absolute value of the reflected light amount be large, and the specular reflected light amount detection method shown in FIG. Can be

However, both the density detection and the resist detection can be practically performed by any of the reflected light detection methods. Therefore, in some cases, in order to reduce costs, only one optical density detection sensor 2 using either the regular reflection light detection method or the irregular reflection light detection method is arranged, and density detection and registration detection are performed using the optical density detection sensor 2. Sometimes they do both.

The timing for performing the resist control is as follows.
It is preferable to perform this operation when the power is turned on, when a consumable such as the cartridge or the transport belt 4 is replaced, or when a predetermined number of images have been formed since the previous registration control. In this embodiment, the image density control and the registration control are always performed at the same timing.

Next, the cleaning of the toner adhered on the conveyor belt 4 will be described. After the toner image is intentionally transferred onto the transport belt 4 such as after the above-described image density control and registration control are performed, a transport belt cleaning mode by the following electrostatic collection method is executed.

First, among the first, second, third, and fourth transfer portions formed by the contact between the photosensitive drum 1 and the transfer belt 4 along the transfer material transfer direction of the transfer belt 4, 1
The transfer bias and the surface potential of the photosensitive drum 1 are adjusted so that an electric field (transfer reverse electric field) having a polarity opposite to the electric field at the time of transfer is generated at a transfer portion relating to the magenta toner image of the color, that is, a first transfer portion. .

For example, when the surface of the photosensitive drum 1 is set to the potential Vd, a negative bias having an absolute value larger than Vd is applied to the transfer roller 12 as a transfer bias. Hereinafter, this negative transfer bias is referred to as a transfer reverse bias. Alternatively, when the surface potential of the photosensitive drum 1 is set to the VL potential, a bias having an absolute value larger than VL is applied as a transfer reverse bias. In the latter case, there is an advantage that the absolute value of the transfer reverse bias can be reduced. However, in order to prevent the toner from being developed on the photosensitive drum 1, a positive developing bias is applied to the developing roller 3 at the same time. And other measures are required.

A method of positively charging the surface of the photosensitive drum 1 is also conceivable. However, it is difficult to uniformly charge the photosensitive drum 1 or the photosensitive layer may be destroyed. Not very realistic.

The toner transferred onto the conveyor belt 4 during image density control and registration control is toner charged to the negative polarity by the regulating blade 23 in the developing device 8.
Since the transfer reverse electric field is formed at the first transfer portion, most of the toner is transferred to the photosensitive drum 1 (re-transfer, reverse transfer), and is collected by the cleaning blade 11 to the waste toner collecting section.

Simply, if the strength of the transfer reverse electric field is strong,
That is, the toner is easily transferred to the photosensitive drum 1. On the contrary, if the strength of the transfer reverse electric field is too strong, a discharge phenomenon occurs between the photosensitive drum 1 and the transport belt 4 as shown in FIG. I do. When the discharge phenomenon occurs, the transport belt 4
In the above toner, a positive charge is applied, so that the charge amount decreases and the polarity is reversed. In this state,
Even when the transfer reverse electric field is formed, the toner affected by the discharge is not transferred onto the photosensitive drum 1.

Therefore, it is necessary to select the intensity of the transfer reverse electric field to an optimum value. Although the temperature slightly fluctuates due to the temperature and humidity of the atmosphere inside the image forming apparatus, in the configuration of this embodiment, the transfer reverse bias is about -1.5 kV when the surface of the photosensitive drum is set at the Vd potential (-700 V). It has been found that the state to which is applied has the highest retransfer performance.

Next, the transfer bias and the photosensitive drum 1 are set so that a positive electric field having the same polarity as the electric field at the time of transfer is generated at the transfer portion relating to the transfer of the second color cyan toner image, that is, the second transfer portion. Adjust the surface potential. Less than,
This positive electric field is called a transfer positive electric field. In order to execute this, a method is generally used in which the surface of the photosensitive drum 1 is set to the Vd potential, and a positive bias having an absolute value larger than Vd is applied as a transfer bias. However, there is no need to stick to this method as long as a transfer positive electric field can be formed.

At the first transfer portion, the discharge between the photosensitive drum 1 and the conveyor belt 4 is suppressed as much as possible by adjusting the transfer reverse bias applied to the transfer roller 12. However, it is difficult to completely avoid such a situation, and a certain amount of toner causes a decrease in charge amount and a reversal of polarity.

At the second transcription site, as shown in FIG.
By forming a transfer positive electric field, the toner (positive charge toner) of which polarity is inverted is transferred to the photosensitive drum 1, and a discharge is caused between the photosensitive drum 1 and the transport belt 4, so that the toner has a negative polarity. Recharging is going on. That is, unlike the first transfer site, the second transfer site has a configuration in which discharge is positively generated. Therefore, compared with the absolute value of the transfer reverse electric field at the first transfer site, There is a feature that the transfer positive electric field at the transfer site 2 becomes large. For example, in this embodiment, the surface of the photosensitive drum is set to the Vd potential (−700 V), and +1.0 kV is applied as the second transfer bias.

Further, at the transfer portion related to the transfer of the third color yellow toner image, that is, at the third transfer portion, a transfer reverse electric field similar to that at the first transfer portion was formed. Its purpose and effects are the same as those at the first transcription site.

Further, at the transfer site relating to the transfer of the fourth color black toner image, that is, at the fourth transfer site, the second
A transfer positive electric field similar to that of the transfer site was formed. At the fourth transfer portion, the removal of all the toner on the conveyor belt 4 is completed by completely transferring the positively charged toner to the photosensitive drum 1.

In the above-described transport belt cleaning mode, the transfer reverse electric field is applied to the first transfer portion to the fourth transfer portion.
Although the electric field is formed in the order of the transfer positive electric field → the transfer reverse electric field → the transfer positive electric field, the electric field is not particularly limited to this. It is important that the transfer reverse electric field and the transfer positive electric field are mixed so that the toner is collected and charged at each transfer portion.

For example, even if an electric field is formed in the order of the transfer positive electric field, the transfer reverse electric field, the transfer positive electric field, and the transfer reverse electric field, the toner can be removed from the transport belt 4. In this case,
After the entire toner is uniformly negatively charged at the first transfer site, the toner is mainly collected at the second transfer site.

The transfer reverse electric field → the transfer positive electric field → the transfer positive electric field → the transfer reverse electric field may be in this order. In this case, the toner that could not be collected at the first transfer site is uniformly charged to the negative polarity at the second and third transfer sites and collected at the fourth transfer site.

When the cleaning mode of the transport belt is executed, in order to further increase the toner removing ability, in addition to the above-described electrostatic recovery method using the transfer reverse electric field and the transfer positive electric field,
A mechanical recovery scheme can also be used.

The mechanical recovery method differs from the image forming method in that the toner is supplied to the photosensitive drum 1 by providing a large positive or negative peripheral speed difference between the rotation speed of the conveying belt 4 and the rotation speed of the photosensitive drum 1. Is to be collected mechanically. In the present embodiment, when performing the mechanical recovery method, the rotation speed of the conveyor belt 4 is set to 50% of the rotation speed of the photosensitive drum 1.
Fast speed.

The transport belt cleaning mode is used not only after the toner is intentionally transferred onto the transport belt 4 such as after image density control and registration control are performed, but also when a transfer material feeding jam occurs during image formation. For example, it is also effective to execute it during the returning operation of the apparatus main body after the toner is unavoidably transferred onto the transport belt 4.

The control of the suction bias applied to the suction roller 19 will be described. As described above, when the transfer material passes through the suction nip portion of the conveyance belt 4 and the suction roller 19, a suction bias equal to or higher than the discharge start voltage is applied to the core of the suction roller 19, and the vicinity of the suction nip portion is applied. By causing discharge, the surface of the transfer material is charged, and the transfer material is electrostatically attracted to the surface of the transport belt 4 by electrostatic interaction with the mirror charge induced on the surface of the transport belt 4.

If the electrostatic attraction force is weak, even if the transfer material is transported by the transport belt 4, the photosensitive drum 1
The transfer material may be displaced on the transport belt 4 due to an external impact such as a shock when entering the nip between the transfer belt and the transfer roller 12. This leads to inaccurate color superposition, which hinders accurate image reproducibility, and the effect is not exhibited even if the registration control is performed.

The bias value necessary to secure a sufficient electrostatic attraction force varies depending on the material, thickness, size, etc. of the transfer material. When the resistance of the transfer material or the conveyance belt 4 is low, the electric charge given by the suction roller 19 is easily attenuated by recombination, so that a large amount of electric charge needs to be given to the transfer material. Conversely, when the resistance of the transfer material or the conveyor belt 4 is high, the charge applied to the transfer material is less attenuated, so that it is not necessary to apply much charge to the transfer material. However, since the current (discharge amount) flowing from the attraction roller 19 to the transfer material itself becomes small, a large voltage is required as the attraction bias. The resistance of the transfer material and the conveyor belt 4 is determined by the temperature and humidity of the atmosphere.

FIG. 7 shows the relationship between the absolute value of the attracting current and the absolute moisture content of the atmosphere necessary for securing a sufficient electrostatic attracting force when using thick paper having a basis weight of 199 g / m ² as the transfer material.
Thick paper tends to be easily displaced on the conveyor belt 4 due to an external impact such as a rush impact on the nip portion between the photosensitive drum 1 and the transfer roller 12, and it is considered that a large electrostatic attraction force is required.

FIG. 7 shows that the absolute water content was 2 g / m ³ ,
For ^{g / m 3, 25g / m} 3, the suction current value 1.7μ
A, 4 μA, and 19 μA, the attraction bias necessary to obtain the attraction current value is shown in Table 1.

[0074]

[Table 1]

The resistance of the transfer material and the conveyance belt 4 are affected by environmental fluctuations. Therefore, contrary to the current value, the smaller the absolute moisture content of the atmosphere, the higher the suction bias is required. Since the absolute value of the suction current flowing from the suction roller 19 only needs to be in the state shown in FIG. 7, either a positive or negative bias can be used as the suction bias depending on the situation.

When the resistance of the conveyor belt 4 is low, electrical interference may occur between the transfer roller 12 and the suction roller 19 of the first color. In this case, if a negative-polarity attracting bias is used, the transfer current may escape from the transfer roller 12 to which the positive-polarity bias is applied to the attracting roller 19, and transferability may be impaired. Therefore, in such a case, it is preferable to use a positive-polarity adsorption bias.

On the other hand, when the resistance of the conveyor belt 4 is high,
The transfer material is easily charged up by the influence of the suction bias. In this case, if a positive adsorption bias is used,
The transfer material is charged up to a positive polarity, and a large potential difference is generated between the transfer material and the photosensitive drum 1 charged to a negative polarity. When the transfer is performed in such a situation, abnormal discharge may occur between the photosensitive drum 1 and the transfer material, and a phenomenon that an image is disturbed may occur. Therefore, the adsorption bias has a good negative polarity.

In this embodiment, since a belt having relatively low resistance is used as the transport belt 4, a positive-polarity attracting bias is employed. Since the electrostatic attraction force increases as the attraction bias increases, a method of fixing the attraction bias to +2 kV, for example, which requires the most attraction force, can be adopted. However, in this case, if the absolute moisture content of the atmosphere is high, an unnecessarily large current flows, and for example, a phenomenon such as a high-pressure leak may lead to damage to the device main body. This is not a preferable method because it is necessary to construct a new means for preventing such a problem.

For example, if a temperature / humidity detector is arranged in the apparatus, it is possible to control the required attraction bias based on the output value. In fact, the image forming apparatus which performs such control is used. The device actually exists. However, in the apparatus of the present embodiment, a temperature / humidity detector is not arranged in the machine for cost reduction.

In this embodiment, utilizing the fact that the resistance of the transport belt 4 changes uniformly in accordance with the absolute moisture content of the internal atmosphere, the idle speed, that is, the suction roller 19 and the transport belt 4 are used.
With no transfer material in the suction nip portion, the suction roller 1
A predetermined bias, for example, +1 kV, is applied to 9, the value of the current flowing at that time is detected, and the absolute moisture content of the in-machine atmosphere is indirectly measured from the value.

However, in practice, it is difficult to improve the accuracy of the transport belt 4 due to factors such as resistance variation between products, and therefore, when the absolute value of the detected current value is smaller than a certain value, As a result, it is recognized that the absolute moisture content of the atmosphere inside the device is low, and as shown in FIG.
When 2 kV is applied, and when the absolute value of the current value is larger than a certain value, it is recognized that the absolute moisture content of the atmosphere in the apparatus is high, and +1 kV is applied as the adsorption bias.

In this embodiment, the suction current during idle rotation is used as a means for indirectly detecting the absolute moisture content of the atmosphere in the apparatus. However, the present invention is not limited to this.
For example, the photosensitive drum 1 (for example, Vd
Potential) and the transfer roller 12 (eg, transfer bias + 1k)
A method of detecting the value of the current flowing between V) may be used.

In this embodiment, the description has been made on the assumption that the adsorption bias is controlled at a constant voltage. However, the above-mentioned means for indirectly detecting the absolute moisture content of the atmosphere in the apparatus is used to change the constant current value. Control may be performed. However, in this case, when using small size paper as the transfer material,
The current may escape to the non-sheet passing area, and a necessary current value for the transfer material may not be secured. For this reason, it is necessary to add a control for changing the constant current value according to the size of the transfer material, which makes the control complicated and requires an automatic transfer material size detector light, leading to an increase in cost. Therefore, in the present embodiment, the adsorption bias constant voltage control in which the constant voltage value is variable in two stages is employed.

The control of the attraction bias during the execution of the transport belt cleaning mode will be described with reference to FIG. In the present embodiment, in order to reduce the size of the device body and cost,
No separation mechanism between the suction roller 19 and the transport belt 4 is provided. When the direct transfer mode such as image density control, registration control, etc., the jam recovery and the conveyance belt cleaning mode are executed, toner is adhered to the conveyance belt 4, and the toner flows between the suction roller 19 and the conveyance belt 4. Will pass.

Therefore, in order to prevent the toner from adhering to the suction roller 19, at the same time as starting the transport belt cleaning mode, the suction roller 19
A bias having a negative polarity (having the same polarity as the original charge polarity of the toner) whose absolute value is equal to or lower than the discharge start voltage is applied. Suction roller 1
The toner that has passed between the transfer belt 9 and the transport belt 4 is transferred to the photosensitive drum 1 by executing the transport belt cleaning mode.
Is removed from the conveyor belt 4.

After the transfer of the toner directly transferred onto the transport belt 4 by the jam or the like to the photosensitive drum 1 is completed (cleaning is performed for one or more rounds of the transport belt 4), toner adsorption is prevented. As a bias,
A positive polarity bias whose absolute value is equal to or lower than the discharge starting voltage is applied to the attraction roller 19. After the positive bias is applied for at least one rotation of the suction roller 19, the suction bias is switched to a negative bias whose absolute value is equal to or less than the discharge starting voltage. After repeating these operations several times, the application of the bias for preventing toner adhesion is stopped, the transport belt 4 is stopped, and the transport belt cleaning mode is ended.

During execution of the transport belt cleaning mode, it is assumed that the potential of the photosensitive drum 1, the transfer bias, and the peripheral speed difference between the photosensitive drum 1 and the transport belt 4 hold the above-mentioned values.

The reason why a positive toner adhesion preventing bias whose absolute value is equal to or lower than the discharge starting voltage is applied to the suction roller 19 is that a small amount of the positive toner adheres to the transport belt 4. Because there is. The toner is charged to a positive polarity by, for example, rubbing between the toners in the developing device 8, and adheres to the Vd portion by the electric field between the developing roller 19 and the Vd portion of the photosensitive drum 1. It has been transferred.

Simultaneously with the execution of the cleaning mode of the transport belt 4, a bias for preventing the adhesion of the negative toner whose absolute value is equal to or less than the discharge starting voltage is applied to the attraction roller 19. An electric suction force is generated between the suction rollers 19 and adheres to the suction roller 19. Here, by inverting the polarity of the bias for preventing toner adhesion, control is performed to apply a positive polarity toner adhered to the suction roller 19 and a positive polarity adhesion prevention bias equal to or lower than the discharge start voltage to the suction roller 19. , An electric repulsive force is generated between the suction rollers 19, so that the toner is transferred from the suction roller 19 to the transport belt 4, and the dirt on the suction roller 19 can be removed.

Even in this situation, the toner is collected on the photosensitive drum 1 because the above-described transport belt cleaning mode is continued. Since the switching of the polarity of the suction roller 19 is performed after the cleaning of the transport belt 4 is completed, the suction roller 19 is not contaminated by normal negative polarity toner directly transferred to the transport belt 4.
However, since the suction roller 19 may be contaminated by toner or the like remaining slightly on the conveyance belt 4 without being collected, the polarity applied to the suction roller 19 is switched again, and the conveyance roller 4 is moved from the suction roller 19 to the conveyance belt 4. Is to be discharged to the toner. By repeating these steps, it is possible to further reduce the dirt on the suction roller 19.

FIG. 10 shows the relationship between the suction bias in an environment where the absolute water content is 13 g / m ³ and the suction current flowing to the transport belt at that time. When the bias is −500 V or less, the absolute value of the current value sharply increases, and it can be seen that the discharge starting voltage is about 500 V. Therefore, in this embodiment, at the time of cleaning the transport belt, the bias for preventing toner adhesion is −300 V and +300 V.
Was used.

Even if the bias control for preventing toner adhesion is performed in the above-described belt cleaning mode, the toner contamination of the suction roller 19 can be prevented because a part of the material of the fluorine resin having high toner releasing property is used. It was limited only to the case where it was used on the suction roller surface. With other materials (such as styrene), the toner on the conveyor belt 4 adheres to the suction roller 19 when passing through the suction roller 19.

This is presumed to be due to poor releasability from the toner due to the presence of tack on the surface of the suction roller. Since the toner easily adheres to the suction roller and is difficult to separate, the adhesion force to the suction roller is stronger than the electric repulsion force. It remained on the suction roller. Therefore, when the transfer material passes through the suction roller during a subsequent printing operation,
An image defect occurred due to the toner adhering to the transfer material.

Therefore, in the present invention, the powder is applied to the surface of the suction roller 19 to improve the releasability from the toner. Examples of the powder that can be used to enhance the releasability include inorganic or organic particles having a particle size of several nm to several tens of μm, composite particles, and lubricant powder. In this embodiment, as an example, DHT-4A (a hydrotalcite compound; manufactured by Kyowa Chemical Industry Co., Ltd .; Mg _4.3 Al ₂ OH _12.6 CO ₃
MH ₂ O).

In this embodiment, in order to investigate the effect of applying powder to the suction roller 19, DHT-
An adsorption roller to which 4H was applied and an adsorption roller to which no powder was applied were prepared, and these were used for image formation, and an experiment was conducted to check toner adhesion to the adsorption roller. The experimental method is
After a solid image is formed on the conveyor belt 4 and the cleaning mode is executed, the toner adhered to the suction roller is sampled with a colorless and transparent Mylar tape, and the toner density on the tape is measured with a density meter RD918 manufactured by Macbeth. did. Table 2 shows the results.

[0096]

[Table 2]

As shown in Table 2, although a large amount of toner adhered to the suction roller to which the powder was not applied, only a toner that could not be visually confirmed adhered to the suction roller to which the powder was applied. I didn't. Table 2 shows the results when the cyan toner was used. Similar results were obtained for the black, yellow, and magenta toners.

The method of applying the powder is not particularly limited. For example, the powder may be sprinkled or sprayed on the surface of the suction roller. You may rub using a brush, a blade, etc. It is preferable to apply the coating uniformly over the entire surface of the suction roller.

In the above description, the powder applied to the surface of the suction roller gradually peels off due to the use of the suction roller, so that the effect of preventing the toner adhesion is lost. Fine particle components such as
Since the toner particles tend to adhere more easily than the toner, as the suction roller is used, the fine particle component gradually adheres to the surface of the suction roller and replaces the powder for preventing toner adhesion. Therefore, if powder is applied in the early stage of use of the suction roller 19, toner adhesion to the suction roller can be prevented over a long period of use.

Examples of the inorganic particles that can be used as the powder for improving the releasability of the suction roller include powders of silica, alumina and the like in addition to the hydrotalcite compounds. These may optionally be silane coupling agents,
The surface may be treated with a titanium coupling agent, silicone oil, or the like.

Further, inorganic particles such as magnesium, zinc, aluminum, cerium, cobalt, iron, zirconium, chromium, manganese, strontium, tin,
Metal oxides such as antimony, composite metal oxides such as calcium titanate, magnesium titanate, and strontium titanate; metal salts such as barium sulfate, calcium carbonate, magnesium carbonate, and aluminum carbonate; viscous minerals such as kaolin; and apatite Phosphoric acid compound, silicon carbide,
Examples include powders of silicon compounds such as silicon nitride, and carbons such as carbon black and graphite.

The organic particles that can be used as the powder for improving the releasability of the suction roller include particles of polyamide resin, silicone resin, silicone rubber, urethane resin, melamine-formaldehyde resin, acrylic resin, and the like. The composite particles that can be used as a powder for improving the releasability of the suction roller include rubber, wax, an aliphatic compound, a resin, and the like, and a composite of a metal oxide, a salt, and an inorganic substance such as carbon black. Particles.

Examples of the lubricant powder that can be used as the powder for improving the releasability of the suction roller include fluororesins such as Teflon (registered trademark) and polyvinylidene fluoride, fluorine compounds such as carbon fluoride, and zinc stearate. And fatty acid derivatives such as fatty acid metal salts, fatty acids and fatty acid esters, molybdenum sulfide, amine acid and amine acid derivatives.

The above particles are used as a powder for improving releasability.
They may be used alone or in combination.

[0105]

As described above, in the image forming apparatus of the present invention, the transfer material is electrostatically attracted to a transfer material transporting body such as a transport belt, and the suction roller or the like is disposed in contact with the transfer material transporting body. Since the powder is applied to the surface of the member to improve the releasability of the toner, application of a bias for preventing the toner from adhering to the adsorbing member easily prevents the toner from adhering to the adsorbing member, so that the adhering member can be easily removed. It is possible to prevent stains and image stains, and the releasability of the suction member is improved irrespective of the selection of the material.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view illustrating a layer configuration of a photosensitive drum in the image forming apparatus of FIG.

FIG. 3 is a cross-sectional view illustrating an example of a density detection sensor usable in the image forming apparatus of FIG.

FIG. 4 is an explanatory diagram illustrating a patch density detection method in the image forming apparatus of FIG. 1;

FIG. 5 is an explanatory diagram showing that a discharge may occur at a first transfer portion at the time of conveying belt cleaning performed by the image forming apparatus of FIG. 1;

FIG. 6 is an explanatory diagram showing that the toner is recharged by the discharge at the second transfer portion.

7 is a graph showing the relationship between the amount of moisture in the internal atmosphere of the image forming apparatus in FIG. 1 and the amount of suction current required to secure a sufficient suction force on thick paper.

FIG. 8 is a graph showing a setting of an adsorption bias with respect to a moisture amount in an in-machine atmosphere performed by the image forming apparatus of FIG. 1;

FIG. 9 is an explanatory diagram illustrating a method of controlling an attraction bias when the conveyance belt cleaning mode is executed in the one image forming apparatus of FIG.

FIG. 10 is a graph showing a relationship between an adsorption bias and an adsorption current in an environment where the absolute moisture content of the atmosphere is 13 g / m ³ .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Density detection sensor 4 Conveying belt 8 Developing device 11 Cleaning blade 12 Transfer roller 19 Suction roller

Claims (13)

[Claims] 1. An image carrier on which a toner image is formed, an endlessly rotating transfer material carrier for carrying a transfer material and transporting the image carrier, and a transfer material electrostatically attracted to the transfer material carrier. A transfer member for transferring a toner image on the image carrier to a transfer material on the transfer material transporter, wherein the transfer member transports the toner image on the image carrier to the transfer material on the transfer material transporter. An image forming apparatus, comprising: a transfer member that comes into contact with the image carrier via a conveying body; wherein a powder that improves releasability from toner is applied to the suction member in advance. 2. The powder according to claim 1, wherein the powder is inorganic particles.
Image forming apparatus. 3. The powder according to claim 1, wherein the powder is organic particles.
Image forming apparatus. 4. The method according to claim 1, wherein the powder is a composite particle.
Image forming apparatus. 5. The image forming apparatus according to claim 1, wherein the powder is a lubricant powder. 6. The powder according to claim 1, wherein the powder is any one of inorganic particles, organic particles, composite particles, and lubricant powder.
2. The image forming apparatus according to claim 1, wherein a mixture of at least one kind is provided. 7. The image forming apparatus according to claim 2, wherein the inorganic substance is a hydroxytalcite compound. 8. The method according to claim 1, wherein a positive / negative bias having an absolute value equal to or lower than a discharge starting voltage for the transfer material transporting body is alternately switched at a constant cycle as the toner adhesion preventing bias. An image forming apparatus according to any one of the above items. 9. A toner removing means for removing toner attached to the transfer material transporting body in a region from a downstream side of the transfer member to an upstream side of the suction member in a rotation direction of the transfer material transporting body. 9. The method according to claim 1, wherein the toner adhered to the transfer material transporting body is transferred to the image carrier by applying a cleaning bias to the transfer member, and is removed from the transfer material transporting body. An image forming apparatus according to any of the above items. 10. A transfer material transporter cleaning mode for transferring toner adhered on the transfer material transporter to the image carrier, wherein the cleaning mode is executed at a predetermined timing. Image forming device. 11. The image forming apparatus according to claim 10, wherein the toner adhesion prevention bias is applied in a specific time period during the execution of the cleaning mode. And a detecting means for detecting a size of the transfer material adsorbed on the transfer material transporter, variably controlling a DC voltage value and a polarity applied to the adsorbing member in accordance with the detection result, and According to the detection result, in all or a part of the area where it is determined that the transfer material has not passed through the contact nip portion between the transfer material transporter and the suction member, depending on the image forming operation state, The method according to any one of claims 1 to 11, wherein control is performed such that positive and negative biases having an absolute value equal to or lower than a discharge start voltage for the transfer material transporting body are alternately switched at a constant cycle. Image forming device. 13. The image carrier according to claim 1, wherein a plurality of image carriers are provided, and a plurality of color toner images are formed on said plurality of image carriers.
13. The image forming apparatus according to any one of the above items 12.