JP2006119508A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intermediate transfer belt type image forming apparatus of high image quality, wherein a force of carrying a toner image on the intermediate transfer belt is maintained, and then, the deterioration of an image such as toner image scattering is prevented. <P>SOLUTION: Regarding the intermediate transfer system image forming apparatus for primarily transferring the toner image on the image carrier onto the intermediate transfer body, and secondarily transferring the toner image to a transfer material in batch, the intermediate transfer body is stretched to be laid between a plurality of stretching members so as to be rotationally driven, and the apparatus is provided with a discharging member, a detecting means for detecting the charge amount flowing into the discharging member and a high voltage power source for applying a prescribed current on the stretching members on the side of the non-toner carrying surface of the belt, between the primary transfer part and the stretching member on the nearest downstream side of the primary transfer part in the driving direction of the intermediate transfer body, The current value to be applied by the high voltage power source on the stretching member arranged on the nearest downstream side in the driving direction of the intermediate transfer body is controlled based on the detection result of the charge amount flowing into the discharging member detected by the detecting means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an intermediate transfer belt type image forming apparatus that maintains a force for supporting a toner image on an intermediate transfer belt and prevents image deterioration such as scattering of the toner image.

  As one of the image systems for forming a color image, after performing primary transfer in which toner images of each color formed on an image carrier are transferred in an endless manner so as to overlap each other on an intermediate transfer belt that circulates and rotates. An intermediate transfer image forming apparatus is known in which images on an intermediate transfer belt are collectively transferred onto a recording medium.

  In this intermediate transfer type image forming apparatus, the toner images formed on the image carrier are collectively transferred to the transfer medium, so that the toner for each color is sequentially transferred onto the recording medium. In addition to having the advantage of high adaptability, the structure in which the intermediate transfer belt is stretched by a plurality of rollers allows the belt routing to be freely determined, and the size of the apparatus can be reduced.

  FIG. 2 shows a conventional color image forming apparatus of an intermediate transfer belt type.

  As shown in FIG. 2, the color image forming apparatus includes a photosensitive drum 1 that rotates in the A direction, a charging roller 3 that uniformly charges the photosensitive drum 1, light applied to the photosensitive drum, and a latent image on the drum surface. An exposure device 4 for drawing, a developing device 5 for developing a latent image on a drum in which toners of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) are drawn by the exposure device, and a primary transfer unit The intermediate transfer belt 2 that carries the toner image transferred in step 2 to the secondary transfer portion, the transfer roll 5 that primarily transfers the toner image on the drum to the intermediate transfer belt 2 in the primary transfer portion N1, and the conveyance and tension of the intermediate transfer belt 2 The metal rollers 8 and 10 in charge of the rack, the secondary transfer roller 13 for secondary transfer of the toner image on the intermediate transfer belt onto the recording medium in the secondary transfer portion N2, and the toner remaining on the intermediate transfer belt The intermediate transfer belt cleaner 11 for removing has a photoreceptor cleaner 12 for removing the toner remaining on the photosensitive drum 1.

  In this color image forming apparatus, the exposure device 4 gives the photosensitive drum 1 uniformly charged by the charging roller 3 to the surface of the photosensitive drum 1 by utilizing the feature of the photosensitive drum whose surface potential is changed by exposure to light. An electrostatic latent image is formed by applying light so as to draw the image information. The electrostatic latent image is developed by the rotary developing unit 5, and yellow (Y), magenta (M), cyan (C), and black (Bk) toner images are formed on the photoreceptor.

  The toner images of the respective colors are transferred from the photosensitive drum to the intermediate transfer belt by applying a bias to the primary transfer roller 6 in the primary transfer portion N1 where the photosensitive drum and the intermediate transfer belt are nipped. A multicolor toner image is formed, which is sequentially transferred in a superimposed manner. The multi-color toner image is collectively transferred onto the recording medium in the secondary transfer portion N2 in accordance with the timing at which the toner image formed on the intermediate transfer belt is conveyed by the rollers 8 and 10 in charge of stretching and conveyance. Thereafter, the toner image is fixed by heat and pressure to form a color image.

JP 2002-82532 A

  However, it is known that the following problems occur when an image is formed by this intermediate transfer method. That is, when the multi-color toner image on the intermediate transfer belt moves from the primary transfer unit N1 toward the secondary transfer unit N2, the charge amount of the intermediate transfer belt 2 is not sufficiently attenuated in the vicinity of the conveying belt 8. In the gap between the intermediate transfer belt and the conveyance roller 8, discharge occurs when the toner image approaches the roller 8 and when the toner image moves away from the roller 8. The electric discharge generated in the gap between the conveying roller and the belt is likely to occur when the roller 8 is made of metal.

  Due to the influence of this discharge, the image of the toner image on the intermediate transfer belt is deteriorated. This phenomenon causes the toner to scatter due to the disturbance of the charge distribution on the belt caused by the discharge in the toner having a low adhesion force such as a spherical toner, and greatly affects the toner image on the intermediate transfer belt. In particular, in the case of a halftone image, the toner scattering occurs remarkably, leading to image degradation.

  The cause is considered as follows. That is, in electrophotography, the density is changed by changing the density of toner, so that the density of toner is lower in halftone than in solid. In this state, when the charge of the belt attracting the toner is lost, in the case where the toner is densely packed, the movement in the direction parallel to the surface of the belt is restricted, but the area where the toner can move freely This makes it easier for splattering to occur.

Several methods are known as a method for improving the image deterioration due to the discharge at the roller portion. (See Patent Document 1)
First, in order to prevent the occurrence of discharge between the belt and the belt that stretches and conveys the intermediate transfer belt, the roll material is made of an insulating resin, or the roller surface is insulated. And a method of forming a rubber layer and a resin layer.

  However, the resin roller wears due to repeated friction with the back of the belt during long-term use, or the dimensions change due to environmental fluctuations, etc. Causes color misregistration during formation. In addition to the cost of the process itself, the surface treatment of the metal roll and the insulating layer formation process involve an additional process such as polishing. It is not desirable from the aspect of.

  As a second method, there is a method of sufficiently increasing the distance between the primary transfer portion and the roll in order to sufficiently attenuate the charge amount of the intermediate transfer belt. However, this method impairs the advantage of the intermediate transfer belt system that the belt can be routed relatively freely and has a problem that the layout of the image forming apparatus is restricted.

Third, there is a method of providing a mechanism for neutralizing a charged belt downstream of the primary transfer portion. For example, there is a case where the problem is solved by using a static elimination mechanism such as a static elimination fur brush or a static elimination needle after the primary transfer and before the intermediate transfer belt reaches the stretching roll.
However, this method inherently reduces the charge required to carry the toner image on the intermediate transfer belt. As the charge decreases, the force that electrostatically restrains the toner image carried on the belt is lost, which may cause toner scattering and deteriorate the toner image.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus of an intermediate transfer belt type with high image quality.

  In order to achieve the above object, in the present invention, in an intermediate transfer type image forming apparatus that primarily transfers a toner image on an image carrier onto an intermediate transfer body and performs secondary transfer collectively on a transfer material, The intermediate transfer member is stretched by a plurality of stretching members and is rotationally driven, and the stretching member disposed immediately downstream of the primary transfer unit with respect to the driving direction of the intermediate transfer member Between the belt and the toner non-carrying surface, a neutralizing member, a detecting means for detecting the amount of electric charge flowing into the neutralizing member, and a downstream of the intermediate transfer member in the driving direction. A high-voltage power source that applies a predetermined current to the stretching member, and is applied from the high-voltage power source to a stretching member that is disposed immediately downstream with respect to the driving direction of the intermediate transfer member. The current value is the amount of charge that flows into the static elimination member. It is embodied by an image forming apparatus characterized by being controlled based on the results.

  According to the present invention, there is a mechanism for detecting the amount of attenuation of the charge amount in the intermediate transfer belt generated during the conveyance of the toner image from the primary transfer portion to the nearest conveyance roller, and the amount of the detected attenuation amount is conveyed. The roller can be supplemented by passing an electric current. For this reason, since the force for supporting the toner image on the intermediate transfer belt can be recovered, scattering of the toner image can be avoided.

<Embodiment 1>
Embodiments of the present invention will be described below.

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

  In this color image forming apparatus, a toner image is formed on the surface, and the toner image is formed on the photosensitive drum 1 that rotates in the A direction while carrying the toner image, and the photosensitive drum such as the charging device 3, the exposure device 4, and the developing device 5. An intermediate transfer belt 2 rotating in the B direction for carrying the toner image transferred by the primary transfer portion N1 to the secondary transfer portion N2, and a toner image on the drum at the primary transfer portion N1. The toner image on the intermediate transfer belt 2 is secondarily transferred onto the recording medium at the transfer roller 6 for primary transfer to the transfer belt 2, the conveying rollers 8 and 10 for stretching and conveying the intermediate transfer belt, and the secondary transfer portion N <b> 2. And a secondary transfer roller 13 for fixing the toner image formed on the recording medium to form an image.

  In the primary transfer N1 in which the photosensitive drum and the intermediate transfer belt are in contact with each other to form a nip, the primary transfer roll 6 is pressed toward the photosensitive drum from the back side with respect to the surface carrying the toner image of the intermediate transfer belt 2. The primary transfer roller 6 is connected to a positive primary transfer high-voltage power supply.

  In the secondary transfer portion N2, a nip for secondary transfer is formed by the opposing roller 9 disposed so as to face the secondary transfer roller 13, and the secondary transfer roller 13 has a positive secondary transfer high pressure. The power supply is connected.

  Further, metal transport rollers 8 and 10 that are in charge of transporting the intermediate transfer belt, an intermediate transfer belt cleaner 11 that removes toner remaining on the intermediate transfer belt, and a photoreceptor cleaner that removes toner remaining on the photoreceptor drum. 12. The charge elimination needle 7 disposed between the primary transfer portion N1 and the transport roller 8 in front of the secondary transfer portion N2 and the amount of charge lost while the belt moves from the primary transfer portion to the transport roller 8 are recovered. Therefore, the power supply 14 for applying a bias to the conveying roller, the resistor 15 installed between the static elimination needle 7 and the ground, the electrometer 16 for measuring the potential applied to the resistor 15, the electrometer 16 and the power supply 14 are connected. And a circuit 17 capable of controlling the power source 14.

  Here, the transport rollers 8 and 10 are made of metal in terms of durability and cost.

  The neutralizing needle 7 is attached to avoid the deterioration of the toner image due to the discharge phenomenon in the vicinity of the conveying roller 8 when the conveying roller 8 is made of metal, regardless of the increase in the size of the main body.

  Then, the circuit 17 calculates a relaxation constant for the static elimination needle and the intermediate transfer belt 2, obtains the amount of charge lost from the belt while being transported from the relaxation constant to the transport roller, and further supplies the power connected to the transport roller. 14 is controlled at a constant current, and has a role of recovering the amount of charge.

  A mechanism for obtaining the amount of charge lost in the circuit 17 will be briefly described.

  Here, the static elimination current and the voltage applied between the static elimination needle and the belt have specific IV characteristics depending on the system as shown in FIG. This is calculated at the design stage in the system as shown in FIG.

  The system of FIG. 3 shows a cross-sectional view of the intermediate transfer belt 2 on a plane perpendicular to the moving direction of the transport roller. A high-voltage power source 19 and a metal plate 20 for the belt allow a uniform charge distribution in the belt to be generated in a plane. The distances between the intermediate transfer belt 2, the static elimination needle 7 and the static elimination needle-belt used are the same as those in FIG. 1. Then, the static elimination current Ie flowing through the static elimination needle 7 is detected, and the IV characteristic between the static elimination needle 7 and the intermediate transfer belt 2 is known.

Note that the voltage Ve applied to the resistance can be measured in the system shown in FIG. 3. However, if the internal resistance of the electrometer 16 is R ₀ and the value of the resistance 15 is Re, the static elimination current can be calculated from Equation (1). Ie can be measured.

Ie = (Re + Ro) Ve / R · Ro (1)
Thus, if the IV characteristic between the static elimination needle and the belt is calculated in the design stage, the voltage V applied between the static elimination needle and the belt with respect to the static elimination needle injection current Ie can be known. And the electric potential after static elimination falls to static elimination discharge start voltage V '.

Furthermore, if the current is integrated over time, the amount of charge is obtained. Therefore, if the static elimination current is integrated over time in the circuit, the amount of charge Qe flowing by the static elimination needle can be obtained.
Since the potential generated by the charge in the belt is proportional to the amount of charge, if the amount of charge in the belt before static elimination is Qb and the amount of charge after static elimination is Qa, the ratio x between Qa and Qb is expressed by the following equation: It can be calculated by

Qb / Qa = V / V ′ = x (2)
Then, the following relationship is established between Qa, Qb, and Qe.

Qb = Qa + Qe (3)
Therefore, Qa and Qb are expressed using equations (2) and (3), respectively.
Qb = xQe / (x-1)
Qa = Qe / (x-1)
It can be asked.

  Furthermore, Q is the amount of charge applied to the belt by the high-voltage power source at the primary transfer portion, v is the speed at which the belt moves, L1 is the distance from the primary transfer portion to the static elimination needle, and τ is the relaxation constant of the electric field strength. The relationship of the formula (4) is established between the charge amount Qb when reaching the static elimination needle.

Qb = Qexp (−L1 / v · τ) (4)
Since Q is a value that can be obtained by time-integrating the current flowing from the power supply attached to the primary transfer roller, the relaxation constant τ can be obtained from Equations (3) and (4).

If the distance from the static elimination needle 7 to the conveyance roller 8 is L2, the amount of charge in the belt when it reaches the conveyance roller 8 is relaxed while the amount of charge Qa after passing the static elimination needle moves through L2. To go
Qaexp (-L2 / v · τ))
From the above, all the charge amount lost while the belt moves from the primary transfer portion N1 to the conveyance 8 is
Q-Qaexp (-L2 / v · τ)
It becomes.

  Here, assuming that the length of the toner image in the belt conveyance direction is Lt, the time τt required for the toner image to pass through the contact point between the conveyance roller 8 and the intermediate transfer belt 2 can be calculated by Expression (5).

Δt = L1 / v (5)
Therefore, in order to recover the lost charge amount on the belt, the power source 14 may be controlled at a constant current so that the current Ir obtained by the following equation (6) flows.

Ir = (Q−Qaexp (−L2 / vτ)) / Δt (5)
The above configuration is almost the same as the conventional color image forming apparatus described with reference to FIG. 2, but the color image forming apparatus of the present embodiment is different from the conventional color image forming apparatus in the following points. Is different.

  That is, in the present embodiment, the mechanisms 15 and 16 that perform constant current control of the power source by calculating the current value Ir necessary for recovering all charges lost while the belt moves from the primary transfer unit to the transport roller. , 17 and a power source 14 for applying the calculated current value Ir to the conveying roller. As a result, in this embodiment, while the discharge generated in the vicinity of the conveying roller 8 by the static elimination needle 7 is prevented, the reduction in the toner image bearing force of the intermediate transfer belt 2 by the static elimination needle 7 is recovered, and further, Even the reduction of the toner image holding force on the intermediate transfer belt 2 due to the temporal decay of the charge is recovered. For this reason, it is possible to improve the image quality of the toner image on the intermediate transfer belt more than ever, while avoiding discharge near the transport roller without impairing durability and size freedom. .

1 is a schematic diagram illustrating an example of a configuration of a printing apparatus according to an embodiment of the present invention. It is a schematic diagram showing an example of the composition of the conventional general printing apparatus. It is the schematic of the measuring system which measures the IV characteristic between a static elimination needle and an intermediate transfer belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Intermediate transfer belt 3 Charging roller 4 Exposure apparatus 5 Rotary developing device 6 Primary transfer roller 7 Static elimination needle 8 Conveyance roller 9 Opposed roller 10 Conveyance roller 11 Intermediate transfer belt cleaner 12 Photoconductor cleaner 13 Secondary transfer roller 14 High pressure Power source 15 Resistance 16 Electrometer 17 Circuit 18 Fixing device 19 High voltage power source 20 Measurement electrode N1 Primary transfer portion N2 Secondary transfer portion A Driving direction of the photosensitive drum B Driving direction of the intermediate transfer belt

Claims (4)

In an intermediate transfer type image forming apparatus that primarily transfers a toner image on an image carrier onto an intermediate transfer member and performs secondary transfer collectively on a transfer material.
The intermediate transfer member is stretched by a plurality of stretching members and is rotationally driven,
Between the primary transfer portion and a stretching member disposed immediately downstream with respect to the driving direction of the intermediate transfer member, a neutralizing member on the side of the belt and the toner non-carrying surface,
Detecting means for detecting the amount of electric charge flowing into the static elimination member;
A high-voltage power source that applies a predetermined current to a stretching member disposed immediately downstream with respect to the driving direction of the intermediate transfer member,
The value of the current applied from the high-voltage power source to the stretching member disposed immediately downstream with respect to the driving direction of the intermediate transfer member is based on the result of the detection means for the amount of charge flowing into the static elimination member. And an image forming apparatus controlled by the control.   2. The image forming apparatus according to claim 1, wherein the neutralizing unit includes a resistance element for current detection and a voltmeter for measuring a voltage across the resistance element.   The image forming apparatus according to claim 1, wherein the static elimination member is configured by a static elimination needle.   The image forming apparatus according to claim 1, wherein the neutralizing member is configured by a neutralizing brush.

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