JP2005091397A - Image forming device and transfer material destaticizing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device and a transfer material destaticizing method thereof, which allow images of high quality to be formed by preventing separation defects of transfer materials and toner scattering regardless of moisturized states of transfer papers and operation environments. <P>SOLUTION: The image forming device has: an image carrier 10 carrying a toner image; a transfer means 28 for transferring the toner image on the image carrier 10 to a transfer material; a transfer bias applying means 34 for applying a transfer bias to the transfer means 28; a destaticizing means 33 which is provided in the vicinity of the transfer means 28 below the transfer means 28 and destaticizes the transfer material 22; a destaticizing bias applying means 36 for applying a destaticizing bias to the destaticizing means 33; and a destaticizing bias control means 37 for controlling the bias applied to the destaticizing means 33, by a constant current. A constant current circuit of the destaticizing bias control means 37 is provided with a limiter for controlling the upper limit of the voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a facsimile machine, and a transfer material discharging method thereof.

Rather than transferring the toner image to a transfer material on a transfer material carrier, each color of yellow, magenta, cyan, and black developed on the photosensitive member is sequentially superimposed on the intermediate transfer member (hereinafter referred to as primary transfer). In addition, image forming apparatuses that perform four-color toner images formed on an intermediate transfer member on a transfer material in a batch (hereinafter referred to as secondary transfer) and then fix them with a fixing device are also on the market (for example, Patent Document 1).
In a conventional image forming apparatus, a toner image formed on a first image carrier (hereinafter referred to as a photoconductor) is transferred to a second image carrier (hereinafter referred to as a transfer material) such as paper, and then on the transfer material. There is known a technique in which a toner image is fixed by thermocompression using a fixing device.
In addition, as a conventional image forming apparatus for forming a full-color image, each color of yellow, magenta, cyan, and black developed on the photoconductor is transferred while the transfer material is held on a transfer material carrier such as a transfer drum. It is known that a transfer material is sequentially transferred onto a transfer material on a material carrier, and then the transfer material peeled off from the transfer material carrier is fixed by thermocompression using a fixing device to obtain a full color image.
The feature of the color image forming apparatus described above is that there is no need to hold the transfer material on the transfer material carrier as in the conventional image forming apparatus, so thin paper (40 g / m ² ), thick paper (200 g / m ² ), and postcards. It can be transferred to various types of transfer materials such as envelopes, and has the advantage of high versatility in transfer materials.
In any of the image forming apparatuses described above, the transfer material is once electrostatically adsorbed to the image carrier or the transfer material carrier, and then receives a high voltage during transfer. The
If the transfer material is transported while being charged in this way, paper jams due to sticking of the transfer material to the transport path, abnormal images of lightning patterns that occur when the charge on the transfer material moves creeping, and transport This causes a circular abnormal image due to protrusions in the vicinity of the path and leakage of charges to the metal.
Further, the larger the radius of curvature at the transfer portion of the image carrier, the more difficult it is to separate the electrostatically attracted transfer material. Therefore, in order to prevent paper jams and abnormal images as described above, as well as poor separation from the image carrier, a charge removal member (hereinafter referred to as a charge removal needle) is provided in the vicinity of the downstream side of the transfer unit, thereby overcharging the transfer material. Prevention and separation from the image carrier are poor.
JP-A-5-11562

However, the image forming apparatus using the static elimination needle has the advantages as described above, but still has the following problems to be solved. First, in a low-humidity environment, the sheet itself is strongly charged by a discharge generated when the sheet is separated from the image carrier.
For this reason, it is necessary to set the bias applied to the static elimination needle high. However, in a low humidity environment, the transfer material itself does not decrease in resistance due to moisture absorption, so there is almost no current flowing from the transfer means to the static elimination means through the transfer material. The effect of the static elimination bias on the transfer property is small.
On the other hand, since the resistance of the paper itself is reduced by moisture absorption in a high humidity environment, the transfer current that should flow to the image carrier side flows from the transfer means to the static elimination means through the transfer material with low resistance, and the effective value of the transfer current is insufficient. This will cause image defects.
Even in a high humidity environment as described above, some transfer materials with special surface coatings have inherently low resistance. In such transfer materials, transfer means and static elimination needles are used. Inferior transfer occurred because an inflow current to the static elimination needle was generated due to the potential difference between the transfer current and the charge removal needle.
Further, since the neutralization bias polarity is generally the same polarity as the toner polarity, if the neutralization bias is too high, excessive neutralization will occur, and toner scattering may occur due to the loss of electrostatic toner holding power of the transfer material. there were.
Accordingly, an object of the present invention is to solve the above-mentioned problems by preventing transfer material separation failure and toner scattering regardless of the moisture absorption state and operating environment of the transfer paper, and forming a high-quality image. An object of the present invention is to provide an image forming apparatus and a transfer material neutralizing method thereof.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, and a transfer bias that is applied to the transfer unit. A transfer bias applying means for applying a charge, a charge removing means provided near the transfer means on the downstream side of the transfer means for removing charge, a charge removing bias applying means for applying a charge removing bias to the charge removing means, and the charge removing means An image forming apparatus having a static elimination bias control unit that controls a bias to be applied with a constant current and provided with a limiter that regulates an upper limit of a voltage in a constant current circuit of the static elimination bias control unit is the main feature.
According to a second aspect of the present invention, the image forming apparatus according to the first aspect is characterized in that the transfer is a contact transfer in which the transfer is performed in contact with the back surface of the transfer material.
According to a third aspect of the present invention, the static elimination means is a static elimination needle provided so that a metal flat plate is processed so that the tip has an acute angle shape and is not in contact with the transfer material. An image forming apparatus is a main feature.
According to a fourth aspect of the present invention, the image forming apparatus according to the first or second aspect is characterized in that the charge eliminating means is a charge eliminating brush in which a conductive thread is formed into a brush shape.
According to a fifth aspect of the invention, the image forming apparatus according to any one of the first to fourth aspects is characterized in that the image carrier is an intermediate transfer belt carrying a toner image of a plurality of colors.
According to a sixth aspect of the present invention, in a transfer material static elimination method for neutralizing a transfer material of an image forming apparatus, a toner image is carried on an image carrier, and the toner image on the image carrier is transferred to a transfer material by a transfer means. A transfer bias is applied to the transfer unit by a transfer bias applying unit, the transfer material is neutralized by a neutralizing unit provided in the vicinity of the transfer unit on the downstream side of the transfer unit, and the neutralizing unit is neutralized by the neutralizing bias applying unit. An image is characterized in that a bias is applied, a bias applied to the static eliminator is controlled with a constant current by a static eliminator bias controller, and an upper limit of a voltage is regulated by a limiter provided in a constant current circuit of the static eliminator bias controller. The most important feature is the transfer material static elimination method of the forming apparatus.

According to the first aspect, by providing the constant current circuit of the static elimination bias control means with a limiter for regulating the upper limit of the voltage, the inflow current from the transfer means to the static elimination needle can be reduced even if a moisture-absorbing transfer material is used. Thus, it is possible to prevent the occurrence of image defects due to the charge elimination needle bias.
On the other hand, when a transfer material with high resistance is used, by controlling the voltage value of the neutralization bias with the upper limit of the limiter, abnormal situations such as toner scattering and secondary transfer bias roller burnout can be avoided, and always good transferability and Separability can be obtained.
According to the second aspect of the present invention, stable transferability and paper transportability can be obtained because the transfer means is contact transfer that performs transfer by contacting the back surface of the transfer material.
According to the third aspect of the present invention, since the static elimination means is a static elimination needle that is processed so that the tip of the metal plate has an acute angle shape and is not in contact with the transfer material, a stable discharge is generated from the acute angle shape tip. As a result, even when a high-resistance transfer material is used, it is possible to always obtain good separation properties.
According to claim 4, the static elimination means is a static elimination brush having a conductive thread in the shape of a brush, whereby a stable discharge is obtained from the brush tip, and even when a high-resistance transfer material is used, It becomes possible to always obtain a good separability.
According to the fifth aspect, since the image carrier is an intermediate transfer belt carrying toner images of a plurality of colors, it is possible to obtain a good full color image without color misregistration.
According to the sixth aspect of the present invention, there is provided a transfer material charge eliminating method for an image forming apparatus in which a constant current circuit of the charge eliminating bias control means is provided with a limiter for regulating the upper limit of the voltage. By reducing the inflow current, it is possible to prevent the occurrence of image defects due to the neutralization needle bias.
On the other hand, when a high-resistance transfer material is used, it is possible to avoid abnormal situations such as toner scattering and secondary transfer bias roller burnout by regulating the voltage value of the static elimination bias with the upper limit of the limiter. It becomes possible to obtain sex.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a color image forming apparatus according to an embodiment of the present invention in which an image carrier is an intermediate transfer member (hereinafter referred to as an intermediate transfer belt).
In FIG. 1, the photosensitive belt 1 rotating in the direction of the arrow is stretched by a primary transfer counter roller 16, a driving roller 17, and a driven roller 18. Around the photoreceptor belt 1, a photoreceptor cleaning unit 2 having a blade 3, a charging unit 4, an exposure unit 5, an intermediate transfer belt 10, and the like are arranged.
The developing device includes four developing units including a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9. When a full color image is formed, a visible image is formed in the order of the yellow developing unit 6, the magenta developing unit 7, the cyan developing unit 8, and the black developing unit 9, and the visible images of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 10. As a result, a full-color image is formed.
The intermediate transfer belt 10 is stretched by a drive roller 11a, a primary transfer bias roller 11b, a secondary transfer counter roller 11c, a tension roller 11d, and a cleaning counter roller 11e, and is driven by a drive motor (not shown).
The primary transfer bias roller 11b is pressed in the direction of the photosensitive belt 1 by a pressure spring 27. Each roller is supported from both sides of the intermediate transfer belt by an intermediate transfer belt unit side plate (not shown).
The intermediate transfer belt 10 is composed of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) or the like in a single layer or a plurality of layers, such as carbon black. The conductive material is dispersed, and the volume resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹² Ωcm, and the surface resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹⁵ Ωcm.
If necessary, a release layer may be coated on the surface of the intermediate transfer belt 10. Materials used for the coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluorocarbon resin), FEP (four-fluorocarbon). Fluorine resin such as ethylene fluoride-propylene hexafluoride copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.
The intermediate transfer belt 10 can be produced by a casting method, a centrifugal molding method, or the like, and the surface thereof can be polished if necessary.

If the volume resistivity and surface resistivity of the intermediate transfer belt 10 exceed the ranges described above, the bias required for transfer increases, which increases the power supply cost, which is not preferable. Further, since the charging potential of the intermediate transfer belt 10 becomes high and the self-discharge becomes difficult in the transfer process, the transfer material peeling process, and the like, it is necessary to provide a static eliminating unit.
On the other hand, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but toner splatter occurs because the current during transfer flows in the surface direction. End up. Therefore, it is desirable that the volume resistivity and the surface resistivity of the intermediate transfer belt 10 in the present invention are within the above ranges.
The volume resistivity and the surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP), and the intermediate transfer belt 10. A value of 10 seconds after applying a voltage of 100 V (surface resistivity of 500 V) on the front and back was used.
The belt cleaning unit 19 can be brought into and out of contact with the intermediate transfer belt 10, and includes a contacting / separating mechanism 26 (an eccentric cam rotating mechanism) for making contact with and separating from the intermediate transfer belt 10. Therefore, the belt cleaning unit 19 is separated from the surface of the intermediate transfer belt 10 by the contact / separation mechanism 26 during the belt transfer of the second, third, and fourth colors after the yellow image of the first color is transferred.
When the secondary transfer is performed, pressure contact is performed at a predetermined timing, and the secondary transfer residual toner is cleaned. A belt position detection mark 23 is provided at the end of the intermediate transfer belt 10, and an image forming process for each color is started at the timing when the mark is detected by the mark sensor 24, so that each color image is accurately overlaid. It becomes possible.

The secondary transfer unit 11 includes a secondary transfer bias roller 13 and a contact / separation mechanism 14 that contacts and separates the secondary transfer bias roller 13 from the intermediate transfer belt 10.
The secondary transfer bias roller 13 is configured by covering a metal core such as SUS with an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material.
Here, if the resistance value of the secondary transfer bias roller 13 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, which increases the power supply cost. Invite.
In addition, since a high voltage is applied, a discharge occurs in the gap before and after the transfer portion nip, so that white spots are lost due to the discharge on the halftone image. Conversely, if the resistance value of the secondary transfer bias roller 13 is below the above range, the transferability between the multicolor image portion (for example, three-color superimposed image) and the single color image portion existing on the same image cannot be achieved.
This is because the resistance value of the secondary transfer bias roller 13 is low, and a current sufficient to transfer the monochrome image portion at a relatively low voltage flows. However, since a voltage value higher than the optimum voltage for the single color image portion is required to transfer the multiple color image portion, if the voltage is set to a voltage at which the multiple color image portion can be transferred, the transfer current is excessive in the single color image and the transfer efficiency is increased. Incurs reduction.
The resistance value of the secondary transfer bias roller 13 is measured by installing the secondary transfer bias roller 13 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. In the state which applied, it computed from the electric current value which flows when a voltage of 1000V is applied between a metal core and the said metal plate.
The secondary transfer bias roller 13 is given a driving force by a drive gear (not shown), and the peripheral speed thereof is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10.
The secondary transfer bias roller 13 is usually separated from the surface of the intermediate transfer belt 10, but contact is made at a timing when the four color superimposed images formed on the surface of the intermediate transfer belt 10 are collectively transferred to the transfer material 22. The image is transferred to the transfer material 22 by being pressed by the separation mechanism 14 and applying a predetermined bias voltage.
The static elimination needle 33 neutralizes the charged transfer material 22 by applying a predetermined bias at the timing when the tip of the transfer material reaches the static elimination needle position. The polarity of the bias applied to the static elimination needle 33 is opposite to the polarity applied to the secondary transfer bias roller 13, and a negative polarity is applied in this embodiment.

FIG. 2 is a schematic view showing the structure of the static elimination needle. The bias applied to the static elimination needle 33 in the present invention will be described later. In the present embodiment, the static elimination needle 33 is formed by processing SUS301 having a thickness of 0.2 mm into a saw-tooth shape as shown in FIG. 2 and having an adjacent tooth tip pitch of 3 mm.
The transfer material 22 is fed by the paper feed roller 25, the transport roller 29, and the registration roller 21 at the timing when the leading end portion of the four-color superimposed image on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. The four-color superimposed image transferred to the transfer material 22 is fixed by the fixing unit 17 and then discharged by a discharge roller 32.

Here, full color image formation will be described in detail. First, the photoreceptor belt 1 is uniformly charged to a surface potential of −500 V by the charger 4, and then is exposed by the exposure means 5 to form an electrostatic latent image. The electrostatic latent image on 1 is visualized with a one-component developer made of yellow toner by the yellow developing device 6 to become a yellow image (yellow toner image).
At this time, the developing bias applied to the yellow developing device 6 is −300V. The primary transfer bias roller 11 b is applied with a transfer bias from a high-voltage power supply (not shown), contacts the back surface of the intermediate transfer belt 10, and applies a charge to transfer the yellow image on the photosensitive belt 1 to the intermediate transfer belt 10. The primary transfer bias at this time was set to 700V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the yellow image is transferred.
Next, the photoreceptor belt 1 is uniformly charged to a surface potential of -500 V by the charger 4, and then exposed by the exposure means 5 to form an electrostatic latent image, whereby an image is written. The electrostatic latent image on the belt 1 is visualized with a one-component developer made of magenta toner by a magenta developing device 7 to form a magenta image (magenta toner image).
The developing bias applied to the magenta developing device 7 is −300V. The primary transfer bias roller 11 is applied with a transfer bias from a high-voltage power source and contacts the back surface of the intermediate transfer belt 10 to apply a charge, thereby transferring the magenta image on the photosensitive belt 1 to the intermediate transfer belt 10.
The primary transfer bias at this time was set to 800V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the magenta image is transferred.

Next, the photosensitive belt 1 is uniformly charged to a surface potential of -500 V by the charger 4, and then exposed by the exposure means 5 to form an electrostatic latent image, whereby an image is written. The electrostatic latent image on the body belt 1 is visualized with a one-component developer made of cyan toner by a cyan developing device 8 to become a cyan image (cyan toner image).
At this time, the developing bias applied to the cyan developing device 8 is −300V. The primary transfer bias roller 11b is applied with a transfer bias from a high-voltage power supply and is brought into contact with the back surface of the intermediate transfer belt 10 to apply a charge, whereby a cyan image on the photosensitive belt 1 is applied to the intermediate transfer belt 10 as a yellow image and a magenta image. And superimpose and transfer.
The primary transfer bias at this time was set to 900V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the cyan image is transferred.
Further, the photosensitive belt 1 is uniformly charged to a surface potential of −500 V by the charger 4 and then exposed by the exposure means 5 to form an electrostatic latent image, whereby an image is written. The electrostatic latent image on the belt 1 is visualized with a one-component developer made of black toner by the black developing device 9 to become a black image (black toner image).
At this time, the developing bias applied to the black developing device 9 is −300V. The primary transfer bias roller 11b is applied with a transfer bias from a high-voltage power supply and is brought into contact with the back surface of the intermediate transfer belt 10 to apply a charge, thereby transferring a black image on the photoreceptor belt 1 to the intermediate transfer belt 10 as a yellow image and a magenta image. The image is transferred with being superimposed on the cyan image.
The primary transfer bias at this time was set to 900V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the transfer of the black image.

The full-color image (4-color superimposed image) on the intermediate transfer belt 10 is transferred by the secondary transfer bias roller 13 to the transfer material 22 fed from the paper feeding device by the paper feed roller 25 and the registration roller 21, and the transfer material 22. Is transferred after the image transferred from the intermediate transfer belt 10 is fixed by the transfer means 17.
In the present embodiment, a single color mode for forming an image of any one color of yellow, magenta, cyan, or black, a two-color mode for forming an image of any two colors of yellow, magenta, cyan, or black, There are three-color mode that forms images of three colors of yellow, magenta, cyan, and black, and full-color mode that forms four-color images as described above. These modes can be specified on the operation unit. It is.
When any one of the single color mode, the two color mode, and the three color mode is designated, in the full color mode as described above, images of yellow, magenta, cyan, and black are formed on the photosensitive belt 1 and intermediate. Transfer to the transfer belt 10.
However, when one of the single color mode, the two color mode, and the three color mode is designated, instead of the above operation, an image is formed on the photosensitive belt 1 in a single color corresponding to the single color mode, and the intermediate transfer belt 10 is formed. An image transfer operation, a two-color image corresponding to the two-color mode is formed on the photosensitive belt 1 and transferred to the intermediate transfer belt 10, or a three-color image corresponding to the three-color mode is transferred to the photosensitive belt. 1 is formed and transferred to the intermediate transfer belt 10.
The single-color image, the two-color superimposed image, or the three-color superimposed image on the intermediate transfer belt 10 is transferred to the transfer material 22 by the secondary transfer bias roller 13 and fixed by the fixing unit 17, and then discharged by the paper discharge roller 32. .

FIG. 3 is a schematic diagram of a secondary transfer unit showing a secondary transfer bias roller and a high voltage power source. Here, when an image forming operation for forming a superimposed image of a plurality of colors on the transfer material 22 is continuously performed by the number set by the operation unit, the rear end of the transfer material 22 sufficiently passes through the secondary transfer bias roller 13. At this timing, the secondary transfer bias voltage from the high voltage power supply 34 to the secondary transfer bias roller 13 is turned off.
Thereafter, the secondary transfer bias roller 13 is separated from the intermediate transfer belt 10 by the contact / separation mechanism 16 so that the toner image of the next page on the intermediate transfer belt 10 does not adhere to the secondary transfer bias roller 13.
By the way, the toner particle size of the toner used in the image forming apparatus is desirably in the range of 4 to 10 μm in terms of volume average particle size. When the particle size is smaller than this, it becomes a cause of background stains during development, fluidity is deteriorated, and the particles are more likely to be aggregated.
On the other hand, when the particle diameter is larger than this, high-definition images cannot be obtained due to toner scattering and resolution deterioration. In this embodiment, a toner having a volume average particle diameter of 7.5 μm is used.
The schematic diagram of the secondary transfer portion in FIG. 3 will be described in detail. When the transfer material 22 is aligned with the toner image formed on the intermediate transfer belt 10 and is conveyed to the secondary transfer portion constituted by the intermediate transfer belt 10 and the secondary transfer bias roller 13, the high-voltage power supply 34 and the transfer bias are transferred. A predetermined bias voltage is applied by the value control means 35.

FIG. 4 is a schematic diagram showing a static elimination needle portion. The static elimination needle 33 is connected to a high voltage power source 36 for controlling the static elimination bias with a constant current and a static elimination bias control means 37. The static elimination bias control means 37 controls the static elimination needle 33 with a constant current, while controlling the voltage value of the static elimination bias with a predetermined limiter upper limit value.
By controlling in this way, for example, when the transfer material 22 that absorbs moisture and has a low resistance is used, a transfer current tries to flow into the static elimination needle 33 through the transfer material 22. At this time, the static elimination bias control means 37 Therefore, since the static elimination bias is controlled to a constant current, the voltage value is lowered to a predetermined current value.
For this reason, since the potential difference with the secondary transfer bias roller 13 is reduced, the flow of transfer current is also reduced, and the occurrence of transfer failure can be prevented.
In addition, when the transfer material 22 has a high resistance as in the case of using the transfer material 22 that has not been absorbed, for example, immediately after opening, it is difficult for the static elimination current to flow. Therefore, the voltage is very high when controlled at a constant current. There is a case.
Thus, if the voltage becomes too high, toner splattering occurs at the pitch of the static elimination needle 33 tip, or electric discharge occurs between the secondary transfer bias roller 13 due to the potential difference, and in the worst case, the secondary transfer. The bias roller 13 may be burned out. For this reason, it is important to control so that the voltage value of the static elimination bias is regulated by a predetermined limiter upper limit value.

FIG. 5 is a diagram showing the experimental results of the separability and the occurrence of transfer omission. FIG. 5 shows a result of an experiment conducted on the separation property of the transfer material 22 from the intermediate transfer belt 10 and the occurrence of transfer omission in the control as described above. In the experiment, NBS45Kg paper (manufactured by Nippon Business Supply Co., Ltd.) was used as the transfer material 22.
In addition, the meaning which the symbol in the table | surface of FIG. 5 represents is as follows.
<Separability>
◎ During 10,000 sheets passing, there is no separation failure and the sheet passing posture is good ○: During 10,000 sheets passing, there is no separation failure, but the sheet passing posture is slightly poor △: 10,000 sheets passing failure, separation failure Less than 10 sheets (incidence less than 0.1%)
×: 10 or more sheets with poor separation during 10,000 sheets (occurrence rate 0.1% or more)
<Transfer missing>
◎: No transfer omission ○: Transfer occlusion is very small but not a concern △: Transfer omission is a concern level x: Transfer occlusion is extremely occurring From the result of FIG. In this embodiment, by setting the current value to 2 μA and the voltage limiter upper limit value to −2.2 KV, a good image and stable separation can be obtained regardless of the moisture absorption state of the transfer material.
As for the set values of the current value and the voltage limiter upper limit value, the optimum conditions are determined depending on the relative positional relationship between the intermediate transfer belt, the secondary transfer bias roller and the charge eliminating needle, the difference in process speed, and the like. It is not limited to the set value.
As described above, by controlling the static elimination bias with a constant current, even if a moisture-absorbing transfer material is used, the inflow current from the transfer means to the static elimination needle is reduced, thereby causing an image defect due to the static elimination needle bias. It becomes possible to prevent.
On the other hand, when the high-resistance transfer material 22 is used, by controlling the voltage value of the static elimination bias with the limiter upper limit value, it is possible to avoid abnormal situations such as toner scattering and burnout of the secondary transfer bias roller 13, and always good transfer. And separability can be obtained.

FIG. 6 is a perspective view showing a static elimination brush. Instead of the static elimination needle 33, a static elimination brush 38 as shown in FIG. 6 can be used. When using this static elimination brush 38, it can be set as the structure similar to embodiment mentioned above except this.
As a result of conducting an evaluation experiment similar to the above in the configuration using the static elimination brush 38, in this configuration, the constant current value of the static elimination bias is set to 1.5 μA and the upper limit value of the voltage limiter is set to −2.5 KV. Regardless of the moisture absorption state of the transfer material 22, a good image and stable separation were obtained.
Even in this configuration, the optimum values for the current value and the set value of the voltage limiter upper limit are determined by the relative positions of the intermediate transfer member, the secondary transfer bias roller and the static elimination brush, the difference in process speed, and the like. And are not limited to the above set values.

FIG. 7 is a schematic view showing another embodiment of the color image forming apparatus according to the present invention. The difference between the configuration of FIG. 7 and the configuration described above is that a plurality of photoconductors (four in this configuration) are provided as shown in FIG. 4 is a four-drum type image forming apparatus.
Four photosensitive drums 39 are arranged in series on the intermediate transfer belt 10. A charging unit 4 and an exposure unit 5 for uniformly charging the surface of the photosensitive drum are disposed around each photosensitive drum 39.
In the developing device, four developing units, a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9, and the photosensitive member cleaning unit 2 are arranged on the photosensitive drum 39. Since other configurations are the same as those described above, description thereof will be omitted.
As a result of performing the same neutralization bias setting as described above in such a configuration, a good image and stable separation were obtained regardless of the moisture absorption state of the transfer material 22. Also in this configuration, the optimum values for the set values of the current value and the voltage limiter upper limit value are determined depending on the relative positional relationship between the intermediate transfer belt, the secondary transfer bias roller and the static elimination brush, the process speed, and the like. And are not limited to the above set values.

The configuration described above is described for facilitating understanding of the present invention, and does not limit the present invention. For example, in the above-described embodiment, the intermediate transfer belt is used as the image carrier. However, the present invention is not limited to this, and a medium resistance rubber or the like is provided on the surface of the metal cylinder. The present invention is applicable to all image carriers such as an intermediate transfer drum, a photosensitive drum as a latent image carrier, and a photosensitive belt.
Furthermore, the transfer roller was used as the primary transfer means and the secondary transfer means, but not only the rotary contact transfer system such as the rotary transfer brush but also the contact transfer system such as the transfer belt, transfer brush, transfer blade, transfer plate, etc. The present invention can also be applied to an image forming apparatus using the image forming apparatus.

1 is a color image forming apparatus showing an embodiment of the present invention in which an image carrier is an intermediate transfer member. It is the schematic which shows the structure of a static elimination needle. It is a schematic diagram of a secondary transfer unit showing a secondary transfer bias roller and a high voltage power supply. It is a schematic diagram which shows a static elimination needle part. It is a figure which shows the experimental result of separability and the transcription | transfer omission generation | occurrence | production situation. It is a perspective view which shows a static elimination brush. It is the schematic which shows other embodiment of the color image forming apparatus by this invention.

Explanation of symbols

10 Image carrier (intermediate transfer belt)
22 Transfer material 28 Transfer means (secondary transfer bias roller)
33 Static elimination means (static elimination needle)
36 Static elimination bias application means (high voltage power supply)
37 Static elimination bias control means (limiter)
38 Static elimination means (static brush)

Claims (6)

  An image carrier that carries a toner image; a transfer unit that transfers the toner image on the image carrier to a transfer material; a transfer bias application unit that applies a transfer bias to the transfer unit; and the downstream side of the transfer unit. A neutralization unit provided near the transfer unit for neutralizing the transfer material; a neutralization bias application unit for applying a neutralization bias to the neutralization unit; and a neutralization bias control unit for controlling the bias applied to the neutralization unit with a constant current. An image forming apparatus comprising a constant current circuit of the static elimination bias control means provided with a limiter for regulating an upper limit of the voltage.   The image forming apparatus according to claim 1, wherein the transfer is contact transfer in which transfer is performed by contacting a back surface of the transfer material.   3. The image forming apparatus according to claim 1, wherein the charge eliminating unit is a charge eliminating needle which is formed so that a tip of a metal flat plate has an acute angle shape and is not in contact with the transfer material. .   3. The image forming apparatus according to claim 1, wherein the charge eliminating unit is a charge eliminating brush having a conductive thread in a brush shape.   5. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt that carries toner images of a plurality of colors. In a transfer material static elimination method for neutralizing a transfer material of an image forming apparatus,
A toner image is carried on the image carrier, the toner image on the image carrier is transferred to a transfer material by a transfer unit, a transfer bias is applied to the transfer unit by a transfer bias application unit, The transfer material is neutralized by a neutralizing unit provided in the vicinity of the transfer unit, the neutralizing bias is applied by the neutralizing bias applying unit to the neutralizing unit, and the bias applied to the neutralizing unit is controlled at a constant current by the neutralizing bias control unit. A transfer material static elimination method for an image forming apparatus, wherein the upper limit of the voltage is regulated by a limiter provided in a constant current circuit of the static elimination bias control means.

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