JP2001201954A - Image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of forming a high-quality image having no horizontal band in terms of halftone by removing the charge of an intermediate transfer belt more surely than in the case of removing the charge of the belt while brining a grounded conductive member into contact therewith. SOLUTION: This image forming device using the intermediate transfer belt 10 is provided with a secondary transfer bias roller 14 arranged to come into contact with and is separated from the belt 10 and functioning also as a charge removing member for charge removing the belt 10, a contact and separating mechanism 16 making the roller 14 contact with/separated from the belt 10, and a high voltage power source 100 applying charge removing bias for removing the electrified charge of the belt 10 electrified during image forming operation to the roller 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile and the like, and an image forming method employed in the apparatus. More specifically, the present invention relates to a method for forming a toner image on an image bearing member. The present invention relates to an image forming method and an image forming apparatus for primary-transferring a toner image on an image carrier to an intermediate transfer body and further secondary-transferring the toner image on the intermediate transfer body to a transfer material.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, a toner image formed on a photoreceptor as an image carrier is transferred to a transfer material, and then the toner image on the transfer material is heated and pressed by a fixing device. Is known. In addition, as a device for forming a full-color image, while the transfer material is held on a transfer material carrier such as a transfer drum, each color of yellow, magenta, cyan, and black developed on the photoconductor is sequentially transferred to the transfer material. Then, a transfer material peeled off from the transfer material carrier is heated and pressed by a fixing device to fix the transfer material. On the other hand, instead of transferring the toner image on the photoreceptor to the transfer material on the transfer material carrier, for example, as disclosed in JP-A-5-11562,
There is also an image forming apparatus in which four color toner images once superimposed on an intermediate transfer body are collectively transferred to a transfer material and then fixed by a fixing device. In the image forming apparatus using the intermediate transfer body, it is not necessary to hold the transfer material on the transfer material carrier, and therefore, the thin paper (40 g / m ² ), the thick paper (200 g / m ² ),
Various types of transfer materials such as postcards and envelopes can be used, and there is an advantage that the transfer material has high versatility. As the intermediate transfer member, an intermediate transfer drum or an intermediate transfer belt is generally used.

[0003]

However, an image forming apparatus using an intermediate transfer member as in the above-mentioned conventional apparatus has the following problems. At the time of image formation using the intermediate transfer body, the intermediate transfer body is repeatedly subjected to a rubbing and peeling step with a photoconductor and a transfer material, and a primary transfer step of transferring a toner image from the photoconductor to the intermediate transfer body, Further, a high voltage is applied in a secondary transfer step of transferring the toner image transferred and held on the intermediate transfer member to a transfer material. Therefore, the surface of the intermediate transfer member is charged by peeling charging, friction charging, charge injection by applying a high voltage, and the like. In particular, the charge injection at the secondary transfer portion where a high voltage is applied from the surface side of the intermediate transfer member has a very large effect on the charging of the surface of the intermediate transfer member. Further, in the reversal development in which toner development is performed on an exposed portion of the photoconductor, a toner charged to the same polarity as the surface potential of the photoconductor is used. Is applied, the surface of the intermediate transfer member is charged to a polarity opposite to the surface potential of the photoreceptor.

As described above, when the intermediate transfer member is charged during the image forming operation, when the image formation is completed and the operation of the apparatus is stopped, the photosensitive member is brought into contact with the intermediate transfer member at a portion where the intermediate transfer member is in contact. Charge injection is performed from the surface of the intermediate transfer member charged to a polarity opposite to the surface potential to the surface of the photosensitive member. For this reason, if the device is left idle for a certain period of time,
A phenomenon in which a memory effect occurs on the photoreceptor and a density is increased in a portion corresponding to a contact portion between the photoreceptor and the intermediate transfer body on the entire halftone image at the time of the next image formation (hereinafter, this phenomenon is referred to as “halftone This is called "horizontal band"). Note that the "memory effect" here means that when charge injection of a polarity opposite to the surface potential of the photoreceptor is performed on the photoreceptor, the surface potential of that portion is not sufficiently increased at the time of the next image formation and is severe. Means that the skin is covered.

Japanese Patent Application Laid-Open No. Hei 4-271379 discloses a device capable of preventing the charging of the intermediate transfer member, which includes a conductive member such as a grounded conductive brush on the front and back surfaces of the intermediate transfer member. An image forming apparatus disposed so as to be in contact with and facing is described. Also, JP-A-8-114
No. 994 discloses that a conductive neutralizing brush is brought into contact with a non-image area at an end portion of an intermediate transfer body, and is electrically grounded at the time of transfer and electrically grounded at the time of neutralization. It describes the position of the image forming layer where static elimination is performed. However, as described in the above publication, in the configuration in which the grounded conductive member is brought into contact with the surface of the intermediate transfer body to remove the charge of the intermediate transfer body, the charge on the surface of the intermediate transfer body is sufficiently released. As a result, the intermediate transfer member may not be reliably discharged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to perform more reliable static electricity removal of an intermediate transfer member as compared with a case where a grounded conductive member is contacted to remove electricity. An object of the present invention is to provide an image forming apparatus and an image forming method capable of forming a high-quality image without a horizontal band on a tone.

[0007]

According to one aspect of the present invention, there is provided an image carrier, a toner image forming means for forming a toner image on the image carrier, and an image carrier. An intermediate transfer member on which the upper toner image is transferred, and a primary transfer unit that primarily transfers the toner image on the image carrier to the intermediate transfer member;
In an image forming apparatus provided with a secondary transfer means for secondary-transferring the toner image on the intermediate transfer member to a transfer material, the intermediate transfer member disposed so as to be able to contact and separate from the intermediate transfer member is neutralized. A charging / discharging member for moving the charging / discharging member to and away from the intermediate transfer member, and a biasing / removing member for removing a charge of the intermediate transfer member charged during an image forming operation. And a bias applying means for removing static electricity. In this image forming apparatus, the charge removing bias for removing the charge of the intermediate transfer member charged during the image forming operation is provided by the charge removing bias applying unit, and the charge removing member is disposed so as to be able to contact and separate from the intermediate transfer member. Is applied. When forming an image carrying a toner image on the surface of the intermediate transfer member, the charge removing member is separated from the intermediate transfer member by the contact / separation means so as not to disturb the toner image on the intermediate transfer member. Then, when the intermediate transfer body is to be neutralized, the neutralization member to which the bias for neutralization has been applied is brought into contact with the intermediate transfer body by a contacting / separating means. Since the charge of the intermediate transfer member is positively neutralized by the contact of the charge removing member to which the charge removing bias is applied, the intermediate charge can be more reliably made as compared with a case where the charge is removed by contacting the grounded conductive member. The transfer member can be neutralized.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the area on the surface of the intermediate transfer member with which the neutralization member to which the neutralization bias is applied comes into contact when the image forming operation is completed. It is characterized by including an area where the image carrier has been in contact. In this image forming apparatus, the charge removal member to which the charge is easily applied, which has been in contact with the image carrier at the end of the image forming operation, is brought into contact with the charge removing member to which the charge removing bias is applied. be able to.

According to a third aspect of the present invention, the toner image forming means includes a charging means for uniformly charging the surface of the image bearing member, and a latent image formed by exposing the uniformly charged surface of the image bearing member. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus includes: an exposing unit that forms the toner image; and a developing unit that develops the latent image on the image carrier to form a toner image. When the absolute value of the surface potential of the intermediate transfer member is V _T2 and the absolute value of the surface potential of the image carrier uniformly charged by the charging means is V _H1 , V _T2 ≦ 0.5 × V _H1 is satisfied. In this image forming apparatus, the intermediate transfer member is neutralized so as to satisfy the above-mentioned V _T2 ≦ 0.5 × V _H1 , so that the surface potential of the uniformly charged image carrier under a plurality of conditions different from each other. Also, when the image formation is completed and the operation of the apparatus is stopped, the charge injection from the intermediate transfer member to the image carrier, which causes the phenomenon of the above-described "halftone upper horizontal band", is prevented.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, a control is provided for controlling the bias applying means for static elimination so as to change the bias for static elimination applied to the neutralizing member based on image forming conditions. A means is provided. In this image forming apparatus, by changing the bias for static elimination applied to the static elimination member based on the image forming conditions, even when the image forming conditions change, static elimination of the intermediate transfer body can be reliably performed.

According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the conditions at the time of the image forming operation include a kind of a transfer material, a temperature and a humidity in the apparatus, and a toner image on the intermediate transfer body. The number of superpositions is at least one. In this image forming apparatus, by changing the charge removing bias applied to the charge removing member based on the type of the transfer material, the intermediate transfer body is changed even when the charging potential of the intermediate transfer body changes depending on the type of the transfer material. Can be reliably performed.

In the invention of claim 5, the "type of transfer material" includes not only the type of plain paper, thick paper, OHP sheet, etc., but also the difference of whether image formation has already been experienced. The type of transfer material is also included. For example,
The first side (front side) when images are formed on both sides of the transfer material
The transfer material for forming an image on the second surface and the transfer material for forming an image on the second surface (the back surface) are different types of transfer materials.

According to a sixth aspect of the present invention, the secondary transfer means includes:
A secondary transfer member disposed so as to be able to contact and separate from the intermediate transfer body via the transfer material, and a secondary transfer bias applying unit for applying a secondary transfer bias to the secondary transfer member. 2. The image forming apparatus according to claim 1, wherein the secondary transfer member is also used as the charge removing member, and the secondary transfer bias applying unit is also used as the charge removing bias applying unit. The non-image forming step, the secondary transfer member is brought into contact with the intermediate transfer member, and the voltage applied to the secondary transfer member is switched from the secondary transfer bias to the charge eliminating bias so that the contact and disconnection are performed. Means and control means for controlling said secondary transfer bias applying means. In this image forming apparatus, the secondary transfer member also serving as the charge removing member is brought into contact with the intermediate transfer member during non-image formation after the end of the image forming operation by controlling the separation / contact means by the control means. Further, the voltage applied to the secondary transfer member is switched from the secondary transfer bias to the charge eliminating bias by controlling the secondary transfer bias applying means also serving as the charge eliminating bias applying means by the control means.

According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, the secondary transfer member has a roller-shaped member having a surface portion made of an elastic body on a cored bar to which the bias for static elimination is applied. And a resistance value between the core metal portion and the contact portion that comes into contact with the intermediate transfer member is 10 ⁵ to 10 ¹⁰ Ω. Here, the resistance value is such that the roller-shaped member is placed on a conductive metal plate, and a load of 4.9 N on one side (9.8 N on both sides) is applied to both ends of the core of the roller-shaped member. In this state, it is calculated from a current value flowing when a voltage of 1000 V is applied between the metal core and the metal plate. In this image forming apparatus, the resistance value of the roller-shaped member as the secondary transfer member is 1
Since at 0 ⁵ Omega above, even if the number of toner images superimposed and whether superposition of the toner images on the intermediate transfer body are different, the range of the secondary transfer bias for optimum secondary transfer current is large It does not slip. Therefore, even if the secondary transfer bias is set in accordance with the case where the number of superimposed toner images is large, the secondary transfer current becomes excessive when the superimposition of the toner images is not performed, and the transfer efficiency is reduced. It is less likely that the situation will occur. Furthermore, since the resistance value of the roller member is 10 ¹⁰ Ω or less, it is possible to suppress an excessive increase in the secondary transfer bias for obtaining good transferability.

According to an eighth aspect of the present invention, in the image forming apparatus of the sixth aspect, the secondary transfer member is formed of an elastic body supported by a plurality of support rollers including a conductive opposed roller facing the intermediate transfer member. comprising a belt-shaped member, the resistance value between the contact portion in contact with the contact portion and the intermediate transfer member in contact with the conductive face roller of the belt-like member, ¹⁰⁵ to
^The characteristic is ¹⁰ Ω. Here, the resistance value is determined by placing a conductive roller on a conductive metal plate via the belt-shaped member and applying a load of 4.9 N on one side (9.8 N in total on both sides) to both ends of the conductive roller. Is calculated from the value of a current flowing when a voltage of 1000 V is applied between the conductive roller and the metal plate in a state in which is applied. In this image forming apparatus, since the resistance value of the belt-shaped member as the secondary transfer member is 10 ⁵ Ω or more,
Even if the secondary transfer bias is set in accordance with the case where the number of superimposed toner images is large, the secondary transfer current becomes excessive and the transfer efficiency is reduced when there is no superimposition of toner images. Is less likely to occur. Further, since the resistance value of the belt-shaped member is 10 ¹⁰ Ω or less, it is possible to suppress an excessive increase in the secondary transfer bias for obtaining good transferability.

According to a ninth aspect of the present invention, in the image forming apparatus of the first aspect, the intermediate transfer body has a volume resistivity of 10 ⁸ to 1.
0 ¹² Ωcm and surface resistivity of 10 ⁸ to 10 ¹⁵ Ω / □
It is characterized by being. In this image forming apparatus, since the volume resistivity of the intermediate transfer member is 10 ⁸ Ωcm or more and the surface resistivity is 10 ⁸ Ω / □ or more, the intermediate transfer member can transfer the toner image from the image carrier to the intermediate transfer member. It is possible to suppress the transfer current from flowing along the surface of the transfer body. Further, the volume resistivity of the intermediate transfer member is 10 ¹² Ω.
cm or less and the surface resistivity is 10 ¹⁵ Ω / □ or less, so that the primary transfer bias necessary for transferring the toner image from the image carrier to the intermediate transfer member is kept low, and the intermediate transfer is charged during the image forming operation. The charge potential of the body can be kept low.

According to a tenth aspect of the present invention, in the image forming apparatus of the first aspect, the charge removing bias is a DC voltage having a polarity opposite to a charging potential of the intermediate transfer member charged during an image forming operation. It is assumed that. In this image forming apparatus, a DC power supply that can be configured more simply than an AC power supply applies the above-described predetermined DC voltage to the neutralizing member, thereby positively neutralizing the charged charges of the intermediate transfer body. In addition, static elimination of the intermediate transfer member can be performed more reliably than in a case where static elimination is performed by contacting a grounded conductive member.

According to an eleventh aspect of the present invention, in the image forming apparatus of the first aspect, the charge eliminating bias is an AC voltage controlled by a constant current, and the value of the frequency [Hz] of the AC voltage is:
It has a value that is at least five times the process speed [mm / sec] of the image forming apparatus. In this image forming apparatus, when a bias for static elimination composed of an AC voltage is applied to the neutralizing member to positively neutralize the charge on the intermediate transfer member and contact the grounded conductive member for static elimination, The charge removal of the intermediate transfer member can be more reliably performed. In addition, since the AC voltage is controlled at a constant current, and the value of the frequency [Hz] of the AC voltage is five times or more the process speed [mm / sec] of the image forming apparatus, the intermediate transfer member at the time of static elimination is removed. Since the pitch of the above-mentioned potential fluctuation becomes short, it is possible to suppress the charge removal unevenness of the intermediate transfer body.

According to a twelfth aspect of the present invention, in the image forming apparatus of the first aspect, the discharging bias is a DC voltage having a polarity opposite to a charging potential of the intermediate transfer member charged during an image forming operation, and a constant current control. Wherein the value of the frequency [Hz] of the AC voltage is at least five times the process speed [mm / sec] of the image forming apparatus. is there. In this image forming apparatus, by applying to the static elimination member a static elimination bias in which an AC voltage and the DC voltage having the predetermined polarity are superimposed,
The charge on the intermediate transfer member can be more positively neutralized, and the charge on the intermediate transfer member can be more reliably removed than when the grounded conductive member is contacted to remove the charge. In addition, the AC voltage is controlled at a constant current, and the value of the frequency [Hz] of the AC voltage is set to 5 times the process speed [mm / sec] of the image forming apparatus.
When the value is twice or more, the pitch of the potential change on the intermediate transfer member during the charge elimination is shortened, so that the charge elimination unevenness of the intermediate transfer member can be suppressed.

According to a thirteenth aspect of the present invention, a toner image is formed on an image carrier, the toner image on the image carrier is primarily transferred to an intermediate transfer member, and the toner image on the intermediate transfer member is further transferred to a transfer material. In the image forming method for secondary transfer, during non-image formation after the image forming operation, a charge having a polarity opposite to the charging potential of the intermediate transfer body charged during the image forming operation is applied to the intermediate transfer body to form the image. It is characterized in that the intermediate transfer member is neutralized. In this image forming method, during the non-image formation after the image forming operation, the intermediate transfer body is provided with a charge having a polarity opposite to the charging potential of the intermediate transfer body charged during the image forming operation, The neutralized charge of the intermediate transfer member can be more reliably removed as compared with the case where the charged charge is positively neutralized and the grounded conductive member is brought into contact with the charge to remove the charge.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a color image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to the present embodiment. In FIG. 1, a photoconductor cleaning unit 2, a charging device 4 as a charging unit for uniformly charging the photoconductor, a charging device 4 as a charging unit, and image information are provided around a drum-shaped photoconductor 1 as an image carrier that rotates in the direction of the arrow. Exposure unit 5 as an exposure means for irradiating light to photoreceptor 1 in accordance therewith, developing means for developing an electrostatic latent image on photoreceptor 1, intermediate transfer belt 1 as an intermediate transfer body
0, etc. are arranged. A toner image forming means for forming a toner image on the photoreceptor 1 includes the charger 4, the exposing means, the developing means, and the like.

The developing means includes a yellow developing device 6, a magenta developing device 7, a cyan developing device 8, and a black developing device 9.
It consists of developing units. When forming a full-color image, a yellow developing device 6, a magenta developing device 7, a cyan developing device 8,
A toner image (visible image) is formed in the order of the black developing device 9,
A full-color image is formed by sequentially superimposing and transferring the toner images of each color onto the intermediate transfer belt 10. The surface of the photoconductor 1 after the toner image is transferred to the intermediate transfer belt 10 is
The cleaning is performed by the blade 3 of the photoconductor cleaning unit 2.

The intermediate transfer belt 10 includes a driving roller 1
3, it is stretched by a belt transfer bias roller 11, and driven rollers 12a, 12b, and is driven by a drive motor (not shown). The intermediate transfer belt 10 is made of PVDF (vinyl fluoride), ETFE
(Ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) and the like, and a conductive material such as carbon black is dispersed.
⁸ to 10 ¹² Ωcm and a surface resistivity of 10 ⁸ to 10
It is adjusted to be in the range of ¹⁵ Ωcm. here,
The volume resistivity and the surface resistivity were measured by using a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP) with an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm).
Was connected, and a voltage of 100 V (surface resistivity: 500 V) was applied to the front and back of the intermediate transfer belt 10 and the value after 10 seconds was used. If the volume resistivity and the surface resistivity of the intermediate transfer belt 10 exceed the above upper limits, the transfer bias required for the transfer increases, which causes an increase in power supply cost. In addition, since the charging potential of the intermediate transfer belt 10 becomes high, it is necessary to repeat the charge elimination process a plurality of times, which causes a problem that the entire time of the image forming operation becomes long and the mechanical life becomes short.
On the other hand, if the volume resistivity and the surface resistivity of the intermediate transfer belt 10 are below the lower limits, the charge potential is rapidly attenuated, which is advantageous for static elimination. However, since the current at the time of transfer flows in the surface direction, toner scattering occurs. Will occur.

The surface of the intermediate transfer belt 10 may be coated with a release layer if necessary. Materials used for this coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinyldene fluoride), PEA (perfluoroalkoxy fluororesin), and FEP (four A fluororesin such as a fluoroethylene-propylene hexafluoride copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.

The belt cleaning unit 19 which can be brought into contact with and separated from the intermediate transfer belt 10 comprises a cleaning blade 18 and a contact / separation mechanism 26 for bringing the cleaning blade 18 into and out of contact with the intermediate transfer belt 10. After the first color yellow image is transferred to the belt, the second, third, and fourth colors are separated from the surface of the intermediate transfer belt 10 by the contact / separation mechanism 26 during the belt transfer. The contact / separation mechanism 26 includes an urging unit (not shown) that urges the cleaning unit 19 so that the cleaning blade 18 comes into contact with the surface of the photoconductor 1, and a state in which the cleaning blade 18 comes into contact with the swinging bottom surface of the cleaning unit 19. It is configured using an eccentric cam rotationally driven by a control unit 200 described later. Further, a belt position detection mark 23 is provided at an end in the width direction of the outer peripheral surface of the intermediate transfer belt 10, and an image forming process of each color is started at the timing when the mark 23 is detected by the mark sensor 24. Thus, accurate color superposition of each color image can be achieved.

The secondary transfer unit 15 includes a secondary transfer bias roller 14 and a contact / separation mechanism 16 for bringing the secondary transfer bias roller 14 into and out of contact with the intermediate transfer belt 10. The contact / separation mechanism 16 includes a spring member as an urging unit for urging the secondary transfer unit 15 so that the secondary transfer bias roller 14 is separated from the intermediate transfer belt 10, and a swinging bottom surface of the secondary transfer unit 15. It is configured using an eccentric cam that is rotationally driven by a control unit 200 described below in a state of contact with the unit. The secondary transfer bias roller 14 on the metal core, such as SUS, is constituted by coating an elastic body such as urethane, which is adjusted to a resistance value of 10 ⁵ ~10 ^{1 0} Ω by a conductive material. The resistance value of the secondary transfer bias roller 14 was measured by installing the secondary transfer bias roller 14 on a conductive metal plate and placing 4.9 N on one side at both ends of the metal core (a total of 9.8 N on both sides). With a load applied, 1000 V between the metal core and the metal plate
Was calculated from the value of the current flowing when the voltage was applied. Here, if the resistance value of the secondary transfer bias roller 14 exceeds the upper limit value of 10 ¹⁰ Ω, current hardly flows,
In order to obtain the necessary transferability, a higher voltage must be applied, resulting in an increase in power supply cost. In addition, since a high voltage is applied, discharge occurs in a gap before and after the secondary transfer nip, so that white spots occur due to the discharge on the halftone image. Conversely, if the resistance value of the secondary transfer bias roller 14 falls below the lower limit of 10 ⁵ Ω, transferability between a multi-color image portion (for example, a three-color superimposed image) and a single-color image portion existing on the same image can be compatible. Disappears. This is because the resistance value of the secondary transfer bias roller 14 is low, so that a sufficient current flows to transfer a single-color image portion at a relatively low voltage, but it is most suitable for a single-color image portion to transfer a multi-color image portion. This is because a voltage value higher than the required voltage is required. If the voltage is set such that the multicolor image portion can be transferred, the transfer current becomes excessive in the case of a single-color image, and the transfer efficiency is reduced.

A driving force is applied to the secondary transfer bias roller 14 by a driving gear (not shown).
The peripheral speed is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10. The secondary transfer bias roller 14 is usually separated from the surface of the intermediate transfer belt 10, but the secondary transfer bias roller 14 is formed on the surface of the intermediate transfer belt 10.
When the color superimposed images are collectively transferred onto the transfer paper 22 as the transfer material, the images are pressed by the contact / separation mechanism 16 as the contact / separation means at a time, and the secondary power is applied by the high voltage power supply 100 as the secondary transfer bias applying means. The transfer from the intermediate transfer belt 10 to the transfer paper 22 is performed by applying a secondary transfer bias to the transfer bias roller 14. Here, temperature and humidity information in the apparatus obtained from a temperature and humidity sensor (not shown), information on the type of transfer paper 22 (for example, information on plain paper or OHP sheet), information on single-color mode or multi-color mode, and information on double-sided printing From the information on whether the first side printing or the second side printing in the case, etc.,
A predetermined bias is selected.

As shown in FIG. 2, the high-voltage power supply 100 includes a bias generator 102 for generating DC biases having different polarities and a bias polarity switching unit 101 for switching the polarity. The bias polarity switching unit 101 of the high-voltage power supply 100 is connected to a C
It is connected to and controlled by a control unit 200 as a control means including a PU and an I / O interface.

In the above-structured color image forming apparatus,
The transfer paper 22 includes a paper feed roller 25 and a registration roller 21.
As a result, the leading end of the four-color superimposed image on the intermediate transfer belt 10 is fed at the timing when it reaches the secondary transfer position. The four-color superimposed image transferred to the transfer paper 22 is fixed by the fixing unit 17 and then discharged. At the time of continuous printing of a plurality of colors, the secondary transfer bias is turned off at the timing when the rear end of the transfer paper 22 sufficiently passes through the secondary transfer bias roller 14, and then the intermediate transfer belt 10 of the next page is turned off.
In order to prevent the upper toner from adhering, the toner is separated from the intermediate transfer belt 10 by the contact and separation mechanism 16. Further, at the end of the last page in single-sheet printing or continuous printing, the secondary transfer bias roller 14 is not separated from the surface of the intermediate transfer belt 10, and a cleaning bias having a polarity opposite to that of the secondary transfer bias (-1 kV in the present embodiment). ) Is applied for a predetermined time (in this embodiment, a time corresponding to four rotations of the secondary transfer bias roller). Subsequently, a bias having the same polarity as the secondary transfer bias (1 kV in the present embodiment) is applied for a predetermined time (a time corresponding to two rotations of the secondary transfer bias roller in the present embodiment), whereby the secondary transfer bias roller is applied. The toner attached to the surface of the secondary transfer roller 14 is transferred to the intermediate transfer belt 10, and the toner attached to the surface of the secondary transfer bias roller 14 is cleaned. The toner transferred from the secondary transfer bias roller 14 to the intermediate transfer belt 10 is collected from the intermediate transfer belt 10 by the belt cleaning unit 19.

FIG. 3 shows the color image forming apparatus having the above-described structure, after the image forming operation is completed, left for one hour or more in a stopped state of the apparatus, and then immediately before starting the image forming operation again before the exposure by the exposure means. The surface potential of the photoconductor 1 was measured. V _{H 1} in the figure is the surface potential of the non-contact portion between the photosensitive member 1 and the intermediate transfer belt 10, V _H2 is equivalent to the surface potential of the contact portion between the photosensitive member 1 and the intermediate transfer belt 10. As can be seen from FIG. 3, the surface potential V _H2 of the contact portion is lower than that of the non-contact portion. It is considered that this is because the charged charge of the intermediate transfer belt 10 charged during the image forming operation was injected into the photosensitive member 1.

FIG. 4 shows a state of the surface potential of the photoconductor 1 after the halftone image is exposed on the photoconductor 1 in the state of FIG. 3 described above. Compared to the surface potential V _H1 ′ corresponding to the halftone image, the contact portion between the photoconductor 1 and the intermediate transfer belt 10 is V _H2 ′, and a potential difference is generated. When image formation is performed in this state, FIG.
As shown in FIG.
A "halftone upper horizontal band" occurred at a contact portion between the belt and the intermediate transfer belt 10.

FIG. 6 shows the current value I of the secondary transfer bias (constant current control in this embodiment) applied to the secondary transfer bias roller 14 under the conditions of plain paper, multi-color mode, and first-side printing. _TR , the intermediate transfer belt 1 near the contact portion between the photoconductor 1 and the intermediate transfer belt 10 when the image forming operation is stopped.
The relationship between the charging potential _{VT1 of} 0 and the temperature / humidity environment (L /
L, N / N, H / H). here,
“L / L” is 10 ° C, 15%, “N / N” is 23 °
C, 65%, and “H / H” indicate temperature and humidity conditions of 30 ° C. and 90%. As can be understood from FIG. 6, the current value I of the secondary transfer bias applied to the secondary transfer roller 14
_The higher the _{TR, the} lower the temperature and humidity, and the lower the temperature and humidity, the higher the charging potential of the intermediate transfer belt 10.

[0033] Figure 7, in the case of changing the other image forming conditions temperature and humidity conditions is fixed to the "N / N", the current value of the secondary transfer bias applied to the secondary transfer roller 14 I _T and _R, shows the relationship between the intermediate transfer belt 10 charged potential V _T1 of the contact portion near the photosensitive member 1 and the intermediate transfer belt 10 during image forming operation is stopped. As can be understood from FIG. 7, in the multi-color mode, the number of times of the secondary transfer is larger than in the single-color mode, and the magnitude of the secondary transfer bias is increased in accordance with the superposition of the toner images. The charging potential _VT1 of the intermediate transfer belt 10 increases. Further, in the double-sided printing, the second-side printing is dried once after passing through the fixing process and has already carried the toner, and therefore, the charged potential of the intermediate transfer belt 10 is higher in the second-side printing than in the first-side printing. _VT1 will be high. Furthermore, since the OHP sheet has a higher resistivity than plain paper, the charging potential _VT1 of the intermediate transfer belt 10 is higher. Therefore, information on the above-described image forming conditions (temperature and humidity, type of transfer paper, single-color mode or multiple-color mode, first-side printing or second-side printing in double-sided printing) is recognized in advance during image formation. This makes it possible to predict the charging potential _VT1 of the intermediate transfer belt 10 without providing any special charging potential measuring means. By controlling the secondary transfer bias applied to the secondary transfer bias roller at the time of neutralization of the intermediate transfer belt 10 based on these image forming conditions,
Even if the image forming conditions change, the intermediate transfer belt 1
0 can be reliably eliminated.

FIG. 8 shows the belt of the intermediate transfer belt 10 after the charge is removed.
Electric potential V_T2And the relationship between the above "halftone upper horizontal band"
It is a graph shown. The shaded area in FIG.
This is an area where no belt is generated, and the charged potential V of the intermediate transfer belt 10 is
_T2And surface potential V of photoconductor 1 _H1Is the inequality V
_T2≦ 0.5 × V_H1Is an area that satisfies

FIG. 9 shows the charged potential V of the intermediate transfer belt 10.
And _T1, and the charge removing bias V _TR to the secondary transfer bias roller 14, the charge potential of the intermediate transfer belt 10 after neutralization V
_It shows the relationship with _T2 . Incidentally, a DC bias as the bias applied V _{T R} during neutralization in this embodiment. The predicted value of the charging potential of the intermediate transfer belt 10 obtained from the information of the conditions described above, by fitting the V _T1 in FIG. 9, charge removing bias value V _TR, and after neutralization of the secondary transfer bias roller 14 Intermediate transfer belt 10
And the charge potential _{V T2} is required.

[0036] FIG. 10 is a timing chart showing application timing of charge removing bias V _TR to the secondary transfer bias roller 14. After the last page is completed, the secondary transfer bias roller 14 is not separated from the surface of the intermediate transfer belt 10 and a cleaning bias having a polarity opposite to the secondary transfer bias and a bias having the same polarity as the secondary transfer bias are applied for a predetermined time. After the secondary transfer bias roller 14 is cleaned, the secondary transfer bias roller 1
The bias applied to the 4 switches to charge removing bias V _TR, After neutralization the range in which the intermediate transfer belt 10 is in contact with the photosensitive member 1 at least stopping the apparatus, the main motor is to stop. By controlling in this way,
A good image free of the above-mentioned "halftone upper horizontal band" was obtained even after leaving the image forming operation for a certain period of time after the completion of the image forming operation, without providing any special charge removing means.

In the above-described embodiment, the cleaning of the secondary transfer bias roller 14 is performed by applying a bias. However, as shown in FIG. 11, the cleaning blade 30 is brought into contact with the surface of the secondary transfer bias roller 14,
The surface of the secondary transfer bias roller 14 may be cleaned. FIG. 12 shows the secondary transfer bias roller 1 when the cleaning blade 30 is used.
It is a timing chart showing application timing of charge removing bias V _TR to 4. After completion of the final page, without separating the secondary transfer bias roller 14 from the surface of the intermediate transfer belt 10, switching the bias applied to the secondary transfer bias roller 14 to the charge removing bias V _TR, the intermediate transfer belt 10 at least stopping the apparatus After the charge was removed from the area in contact with the photoreceptor 1, the main motor was stopped. By controlling in this way, a good image free of the above-mentioned "halftone upper horizontal band" was obtained even after leaving the image forming operation for a certain period of time after the completion of the image forming operation without specially providing a static eliminator.

[0038] In the above embodiment uses a DC bias (DC voltage) as charge removing bias V _TR, with those obtained by superimposing the DC bias (DC voltage) and AC bias (AC voltage) Is also good. In this case, the AC bias to be superimposed is controlled by a constant current, and the frequency [Hz] is the process speed [mm / sec] of the image forming apparatus.
c] or more, and preferably 7 times or more the process speed. This is because when the frequency is lower than 5 times the process speed, pitch unevenness occurs in the static elimination effect, so that the above "halftone upper horizontal band" is slightly generated.
By performing such control, a good image in which no horizontal band occurs on the halftone even when the image forming operation is completed for a certain period of time or longer after the image forming operation is completed can be obtained without providing any static eliminator.

[0039] In addition, as the charge removing bias _{V TR,}
An AC bias (AC voltage) may be used. in this case,
The AC bias (AC voltage) is controlled by a constant current, and the frequency [Hz = cycle / sec] is set to 5 times or more, preferably 7 times or more the process speed [mm / sec] of the image forming apparatus. . This is because, when the frequency is lower than 5 times the process speed, pitch unevenness (for example, potential fluctuation unevenness of 4 cycles per 1 mm) occurs in the static elimination effect, so that image unevenness (horizontal band on the halftone) noticeable to human eyes is slightly increased. This is because it occurs. By performing such control, a good image in which no horizontal band occurs on the halftone even when the image forming operation is completed for a certain period of time or longer after the image forming operation is completed can be obtained without providing any static eliminator.

In the above-described embodiment, the roller-shaped secondary transfer bias roller 14 is used as the secondary transfer member. Instead of the roller 14, a plurality of support rollers 32 and 33 as shown in FIG. A secondary transfer belt 31 having a belt shape that has been stretched may be used. In this configuration,
The secondary transfer bias is applied from an opposing roller 34 that is in pressure contact with the driven roller 12b via the secondary transfer belt 31. According to this configuration, it is possible to obtain a good image in which the transfer property of the transfer paper 22 is good, and no horizontal band is generated even when the image forming operation is left for a certain period of time after completion of the image forming operation. Obtained.

In the above embodiment, the case where a photosensitive drum is used as an image carrier has been described. However, the present invention is not limited to this, and is applicable to all image carriers such as a photosensitive belt. It is possible. Further, in the above embodiment, the description has been made using the intermediate transfer belt as the intermediate transfer body. However, the present invention is not limited to this, and all intermediate transfer members such as an intermediate transfer drum, an intermediate transfer body such as a high-resistance film, etc. Applicable to transcripts. Further, the secondary transfer bias is controlled by the constant current, but may be controlled by the constant voltage. Further, a transfer roller and a transfer belt are used as transfer means, but an image forming apparatus using a contact transfer method such as a transfer brush, a transfer blade, and a transfer plate, as well as a rotary contact transfer method such as a rotary transfer brush. If,
The present invention is applicable.

[0042]

According to the first to thirteenth aspects of the present invention, the charge is neutralized positively on the intermediate transfer member during image formation, so that the grounded conductive member is brought into contact with the intermediate transfer member to eliminate the charge. As a result, there is an effect that the charge removal of the intermediate transfer member can be performed more reliably.

In particular, according to the second aspect of the present invention, there is an effect that static electricity can be reliably removed from an area where the image carrier is in contact with the image carrier when the image forming operation is completed.

In particular, according to the third aspect of the invention, there is an effect that the phenomenon of "horizontal band on halftone" can be prevented even under the condition that the surface potentials of uniformly charged image carriers are different from each other. .

In particular, according to the fourth and fifth aspects of the present invention, there is an effect that even when the image forming conditions are changed, it is possible to reliably perform the charge elimination of the intermediate transfer body.

In particular, according to the fifth aspect of the present invention, the charging of the intermediate transfer member is performed by at least one of the type of the transfer material, the temperature and humidity in the apparatus, and the number of superimposed toner images on the intermediate transfer member. Even when the potential changes, there is an effect that the neutralization of the intermediate transfer member can be reliably performed.

In particular, according to the invention of claim 6, since the secondary transfer member and the secondary transfer bias applying means can be used as the charge eliminating member and the bias applying means for charge eliminating, the charge eliminating member and the bias applying means for charge eliminating can be used. There is an effect that static electricity can be reliably removed from the intermediate transfer member without providing them separately.

In particular, according to the seventh and eighth aspects of the present invention, even when the secondary transfer bias is set in accordance with the case where the number of superimposed toner images on the intermediate transfer member is large, the superimposition of the toner images can be performed. The transfer efficiency can be prevented from lowering when there is no image. Moreover, the secondary transfer bias for obtaining good transferability is suppressed from becoming excessively high, the cost of the secondary transfer bias applying unit is suppressed from increasing, and the generation of discharge in the gap before and after the secondary transfer nip is suppressed. In addition, there is an effect that an image abnormality such as "white spot missing" due to electric discharge can be prevented on a halftone image.

According to the ninth aspect of the present invention, the transfer of a transfer current along the surface of the intermediate transfer member during transfer of the toner image from the image bearing member to the intermediate transfer member is suppressed. The scattering of the toner due to the transfer current along the direction can be prevented. In addition, the primary transfer bias required for transferring the toner image from the image carrier to the intermediate transfer body can be suppressed low, the cost of the primary transfer bias applying unit can be suppressed, and the intermediate transfer body charged during the image forming operation can be suppressed. Has an effect that the charge potential of the intermediate transfer member can be suppressed to be low, and the neutralization of the intermediate transfer member can be easily performed.

In particular, according to the tenth aspect of the present invention, there is an effect that the static electricity removal of the intermediate transfer member can be reliably performed with a DC power supply that can be more simply configured than an AC power supply.

In particular, according to the eleventh and twelfth aspects of the present invention, there is an effect that it is possible to suppress the charge removal unevenness of the intermediate transfer member.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a high-voltage power supply for a secondary transfer bias of the color image forming apparatus.

FIG. 3 is a graph showing a measurement result of a photoconductor surface potential before exposure immediately after the image forming operation is started again after the color image forming apparatus is left in a stopped state for one hour or more.

FIG. 4 is a graph showing a measurement result of a photoconductor surface potential after exposing a halftone image to the photoconductor in the state of FIG. 3;

FIG. 5 is an explanatory diagram of “halftone upper horizontal band” in a halftone image formed on transfer paper.

Figure 6 is a graph showing the relationship between the charge potential V _T1 of the current I _TR and the intermediate transfer belt of the secondary transfer bias.

Figure 7 is a graph showing a relationship between the charge potential V _T1 of the current I _TR and the intermediate transfer belt of the secondary transfer bias.

8 is a graph showing the relationship between neutralizing the charged potential V _T2 of the photosensitive member surface potential V _H1 and the intermediate transfer belt.

9 is a graph showing the relationship between the charge potential V _T1 and neutralizing the charged potential V _T2 of the current value I _TR and the intermediate transfer belt of the secondary transfer bias.

Figure 10 is a timing chart showing application timing of charge removing bias V _TR to the secondary transfer bias roller.

FIG. 11 is an explanatory diagram for explaining cleaning of a secondary transfer bias roller according to a modification.

Figure 12 is a timing chart showing application timing of charge removing bias V _TR to the secondary transfer bias roller in the modification.

Figure 13 is a timing chart showing application timing of charge removing bias V _TR to the secondary transfer bias roller in the modification.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 4 charging device 5 exposure unit 6 yellow developing device 7 magenta developing device 8 cyan developing device 9 black developing device 10 intermediate transfer belt 11 belt transfer bias roller 14 secondary transfer bias roller 15 secondary transfer unit 16 contact / separation mechanism 100 High voltage power supply 101 Bias polarity switching unit 101 102 Bias generation unit 200 Control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 G03G 21/00 372 F term (Reference) 2H027 DA11 DA14 DC02 DE01 DE07 DE09 EA03 EA08 EA10 EB04 EC06 EC09 ED15 ED24 ED26 JA19 JC03 JC11 2H030 AD02 AD17 BB02 BB23 BB32 BB42 BB46 BB54 2H032 AA05 AA15 BA02 BA05 BA09 BA12 BA13 BA23 BA29 CA02 CA12 CA14 CA15

Claims (13)

[Claims] An image carrier, a toner image forming means for forming a toner image on the image carrier, an intermediate transfer member to which a toner image on the image carrier is transferred, and An image forming apparatus comprising: primary transfer means for primary-transferring a toner image to the intermediate transfer member; and secondary transfer means for secondary-transferring the toner image on the intermediate transfer member to a transfer material. A static elimination member for static elimination of the intermediate transfer member disposed so as to be capable of contacting and separating from the intermediate transfer member; contacting and separating means for contacting and separating the static elimination member from and to the intermediate transfer member; and the intermediate transfer charged during an image forming operation. An image forming apparatus comprising: a charge removing bias applying unit that applies a charge removing bias for removing a charge on a body to the charge removing member. 2. An image forming apparatus according to claim 1, wherein an area on the surface of said intermediate transfer member which contacts said charge removing member to which said charge removing bias is applied contacts said image carrier at the end of image forming operation. An image forming apparatus comprising: A charging unit for uniformly charging the surface of the image carrier; and an exposing unit for exposing the uniformly charged surface of the image carrier to form a latent image. 2. An image forming apparatus according to claim 1, wherein said intermediate transfer body after being discharged by said discharging means is constituted by using developing means for developing a latent image on said image carrier to form a toner image. and the absolute value of the surface potential and V _T2, when the absolute value of the surface potential of the uniformly charged the image carrier by the charging means is a V _H1, satisfies the V _T2 ≦ 0.5 × V _H1 An image forming apparatus comprising: 4. The image forming apparatus according to claim 1, further comprising control means for controlling said biasing means for applying static electricity so as to change a bias for applying static electricity to said electricity removing member based on image forming conditions. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein the conditions at the time of the image forming operation include at least a kind of a transfer material, a temperature and a humidity in the apparatus, and a number of superimposed toner images on the intermediate transfer body. An image forming apparatus, wherein the number is one. 6. A secondary transfer member disposed so as to be capable of coming into contact with and separating from the intermediate transfer member via the transfer material, and applying a secondary transfer bias to the secondary transfer member. And a bias applying means for secondary transfer.
The image forming apparatus according to claim 1, wherein the secondary transfer member is also used as the charge removing member, and the secondary transfer bias applying unit is also used as the charge removing bias applying unit, at the time of non-image formation after the end of the image forming operation. Contacting the secondary transfer member with the intermediate transfer member, and switching the voltage applied to the secondary transfer member from the secondary transfer bias to the charge eliminating bias by using the separation / contact means and the secondary An image forming apparatus comprising a control unit for controlling a transfer bias applying unit. 7. The image forming apparatus according to claim 6, wherein said secondary transfer member is applied with said bias for static elimination.
Roller-shaped member having a surface portion made of an elastic body on a cored bar
A resistance between the cored bar and a contact portion that comes into contact with the intermediate transfer member.
The resistance value is 10⁵-10 ¹⁰Image characterized by being Ω
Image forming device. 8. The image forming apparatus according to claim 6, wherein the secondary transfer member is a belt-shaped member made of an elastic body supported by a plurality of support rollers including a conductive opposing roller facing the intermediate transfer member. A resistance value between a contact portion of the belt-shaped member that contacts the conductive opposing roller and a contact portion that contacts the intermediate transfer member is 1
An image forming apparatus, wherein the resistance is from 0 ⁵ to 10 ¹⁰ Ω. 9. An image forming apparatus according to claim 1, wherein said intermediate transfer body has a volume resistivity of 10 ⁸ to 10 ¹² Ω · c.
m and a surface resistivity of 10 ⁸ to 10 ¹⁵ Ω / □. 10. An image forming apparatus according to claim 1, wherein said bias for discharging is a DC voltage having a polarity opposite to a charging potential of said intermediate transfer member charged during an image forming operation. . 11. The image forming apparatus according to claim 1, wherein the charge eliminating bias is an AC voltage controlled by a constant current, and a value of a frequency [Hz] of the AC voltage is a process speed [mm / mm] of the image forming apparatus. [sec] of the image forming apparatus. 12. An image forming apparatus according to claim 1, wherein said bias for discharging is a DC voltage having a polarity opposite to a charging potential of said intermediate transfer member charged during an image forming operation, and an AC voltage controlled at a constant current. Wherein the value of the frequency [Hz] of the AC voltage is at least five times the process speed [mm / sec] of the image forming apparatus. 13. A toner image is formed on an image carrier, the toner image on the image carrier is primarily transferred to an intermediate transfer member, and the toner image on the intermediate transfer member is further secondary-transferred to a transfer material. In the image forming method, during non-image formation after the image forming operation, a charge having a polarity opposite to the charging potential of the intermediate transfer body charged during the image forming operation is applied to the intermediate transfer body to remove the charge of the intermediate transfer body. An image forming method.