JP2003241482A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent toner scattering and faulty transfer at the time of transfer associated with the waviness of transfer material in a transfer material vertical carrying path. <P>SOLUTION: The image forming apparatus is provided with a carrying belt 1 carrying the transfer material P nearly in a vertical direction, a plurality of transfer rollers 4 (M, C, Y and K) arranged to be opposed to a plurality of photoreceptor drums 6 arranged along the belt 1 through the belt 1 on a downstream side in a transfer material carrying direction, and pre-transfer rollers 30 (M, C, Y and K) arranged on the upstream side of all of or a part of the drums 6 in the transfer material carrying direction and pushing the belt 1 toward the drum 6. Assuming that the intrusion amount in the case of pushing the belt 1 toward the drum 6 by the roller 30 is (x), and a distance between the contact of the roller 30 with the belt 1 and a perpendicular A drawn to the belt 1 from the center of the corresponding drum 6 is (y), the roller 30 is arranged to satisfy 0.03≤x/y≤0.2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electrophotographic apparatuses have been advanced in speed, function and color, and various types of printers have been put on the market. From the viewpoint of speeding up printers, research and development of an in-line system that arranges multiple electrophotographic units that form images of different colors in series and drives them simultaneously to form an image is progressing. Since it can form color images at high speed, it has wide potential for business use.

In particular, since the number of process components is small, it is easy to reduce the size and cost. Therefore, a plurality of electrophotographic units that integrate electrophotographic processes such as charging, exposure, development, and cleaning are arranged and also serve as a transfer belt. Many transfer belt type in-line printers have been developed in which a transfer material (recording paper) is adsorbed to a transfer belt and a toner image is transferred from a plurality of electrophotographic units onto the transfer material in an overlapping manner.

FIG. 5 shows an example of a conventional in-line system device configuration. The conventional apparatus has a transfer material transport belt (ETB) 1 stretched by a driving roller 2 and a tension roller 3.
Magenta (M), cyan (C), yellow (Y), and black (K) process stations 20 on the peripheral surface of
M, 20C, 20Y, and 20K are arranged so as to be aligned in a horizontal row.

Each process station 20 (20M-2
The surface of the photosensitive drum 6 in (0K) is uniformly charged by the charging device 7, a latent image is formed on the surface by the exposure optical system 8, and the latent image is developed by the developing device 9 to be visualized as a toner image. Then, the toner images of the respective colors on the photosensitive drums 6 are transferred onto the transfer material on the conveyor belt 1 by the transfer roller 4 at the transfer portion facing the photosensitive drums 6, and the toner images of the four colors are transferred onto the transfer material. A color image in which is superimposed is formed. The transfer residual toner remaining on the photosensitive drum 6 due to the transfer of the toner image is scraped off by the cleaner 10,
The surface of the photoconductor drum 6 is cleaned.

The transfer material is fed from the feeding cassette 14,
The transfer material is guided to the conveyor belt 1 by the pickup roller 15, and a bias is applied when the transfer material passes through the nip portion formed by the suction roller 5 and the tension roller 3 to electrostatically transfer the transfer material to the conveyor belt 1. Be adsorbed. The transfer material attracted to the conveyor belt 1 is conveyed by the conveyor belt 1 in the lateral direction indicated by the arrow.

The transfer material to which the four color toner images have been transferred is separated by the curvature at the downstream rear end of the conveyor belt 1 and conveyed to the fixing device 11 to be fixed. The fixing device 11 is
A heating roller 121 having a halogen heater 121a,
Fixing unit 1 having pressure heater 122 abutting on this
2 and a discharge unit 13 including a pair of discharge rollers 131 and 132 provided at the exit of the fixing unit 12.

The transfer material is heated and pressed while being nipped and conveyed in the fixing nip portion between the heating roller 121 and the pressure roller 122 to fix the toner images of four colors, and the fixing portion 12
The transfer material having the toner image fixed thereon is guided to the outside of the fixing device 11 by the discharging portion 13 and finally stacked on the discharging tray 16.

Furthermore, in recent years, for the purpose of reducing the installation area, an in-line printer of a vertical conveyance type has been developed in which electrophotographic units constituting a process station are vertically arranged. This is a form in which the horizontal transfer type inline printer shown in FIG. 5 is rotated by 90 °, and while transferring the transfer material adsorbed on the transfer belt upward against gravity, from each process station. The toner images of the respective colors are transferred to form a full-color image on the transfer material, and the fixing device installed on the upper part of the device heats and fixes the image.

FIG. 6 shows an example of the apparatus configuration of a vertical conveyance type inline printer. Since the operation of each unit in FIG. 7 is the same as that in FIG. 5, members having the same function are denoted by the same reference numerals and description thereof will be omitted.

[0011]

By the way, in the vertical conveyance type inline printer as described above, as shown in FIG.
As shown in FIG. 7A, when the transfer material P becomes slightly floating from the conveyor belt 1 due to the action of gravity or the like at the time of transfer, FIG.
As described above, when the transfer is performed by the transfer roller 4, the floating may occur partially (adhesion failure to the conveyor belt 1). In this case, the toner may be partially scattered at the time of transfer in the case of the light floating, and the transfer failure may be partially caused in the case of the heavy floating. The floating of the transfer material P is particularly likely to occur when the transfer material P has waviness or the like. The waving of the transfer material P may occur depending on the environmental conditions under which the transfer material is left (for example, waving is likely to occur at high temperature and high humidity), but it is also likely to occur during double-sided printing described below.

That is, in the case of a horizontal conveyance type inline printer in which electrophotographic units are arranged side by side as in the conventional case,
The fixing device 11 is arranged beside the transport belt 1, and the positional relationship between the heating roller 121 and the pressure roller 122 in the fixing device 11 is such that the heating roller 121 is above the pressure roller 122. Therefore, as shown in FIG. 8, the transfer material P has its discharge direction downward due to its own weight, that is, on the pressure roller 122 side, and forms a downwardly bent path as shown by the solid line Ts, while the discharge roller pair 131 is formed. , 132 to the outside of the apparatus.

On the other hand, in the case of a vertical transport type in-line printer in which electrophotographic units are vertically arranged, it becomes as shown in FIG. In this system, the fixing device 11 is located on the conveyor belt 1 and the positional relationship inside the fixing device 11 is such that the discharging portion 13 is located substantially directly above the fixing portion 12 and the transfer is performed at the fixing nip portion. The material P is substantially vertical. Therefore, unlike the case of the lateral conveyance method, the effect that the discharge direction is directed toward the pressure roller 122 side due to the weight of the transfer material P cannot be obtained, and the transfer material P is not shown in FIG.
In addition to the inner path T0, a path T1 that is bent toward the heating roller 121 side is formed, or a path T that is bent toward the pressure roller 122 side is formed.
2, the route is not stable.

Therefore, at the time of fixing, in the vertical conveyance method, irregular corrugations are more likely to occur on the transfer material P than in the horizontal conveyance method, and in double-sided printing, irregularities are caused at the time of fixing the first side. The transfer material P that has been wavy is 2
Scattering and transfer failure are likely to occur when the surface is transferred.

On the other hand, for example, a method of increasing the contact pressure of the suction roller 5 with respect to the conveyor belt 1 to correct the waviness of the transfer material P can be considered, but good transfer performance is obtained for all transfer stations. Things are very difficult.

As another method, it is conceivable to increase the contact pressure of the transfer roller 4 at each station with respect to the conveyor belt 1 to correct the waviness of the transfer material P at each transfer station. When the contact pressure of the transfer roller 4 is increased, a phenomenon that the toner falls out during transfer (a part of the toner agglomerates due to the pressure and adheres to the photosensitive drum 6,
This causes a problem in image quality, such as a phenomenon that a partial dropout occurs.

Therefore, an object of the present invention is to prevent toner scattering and transfer failure at the time of transfer due to waviness of the transfer material,
It is to significantly improve the transfer performance in the vertical transport path.

[0018]

A typical constitution of the present invention for achieving the above object is a transfer material conveying means for conveying a transfer material in a substantially vertical direction, and a transfer material conveying means arranged along the transfer material conveying means. A plurality of image carriers that carry images and a plurality of image carriers that are arranged on the downstream side in the transfer material transport direction with respect to each of the image carriers via the transfer material transporting means, and the image on the image carrier is transferred onto the transfer material. A plurality of transfer members to be transferred, and a pressing member arranged on the upstream side of all or a part of the plurality of image carriers in the transfer material transport direction, for pressing the transfer material transport means toward the image carrier. The pressing amount of the pushing member in the direction of the image carrier is x, and the contact point of the pressing member with the transfer material conveying means and the center of the corresponding image carrier are subtracted from the transfer material conveying means. When the distance from the vertical line is y, the pressing member is 0.03 ≦ x / y ≦ 0.2 is satisfied, by arranging at a position upstream of the holding member by a distance y in the transfer material conveying direction and at a position where the transfer member is moved in by an intrusion amount x in the image carrier direction. It is characterized by doing so.

According to the above construction, it is possible to prevent a defective image due to defective transfer or scattering at the time of transfer.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However,
The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the following embodiments should be appropriately changed depending on the configuration and various conditions of the device to which the present invention is applied, and are particularly specific. Unless otherwise stated, the scope of the present invention is not intended to be limited thereto.

[First Embodiment] FIG. 1 is a schematic sectional view showing an embodiment of an image forming apparatus to which the present invention is applied.
The image forming apparatus has a transfer material transport belt (ETB) 1 stretched by a driving roller 2 and a tension roller 3 arranged above and below as a transfer material transport means.
On the peripheral surface of the process station 20 of magenta (M), cyan (C), yellow (Y), and black (K).
M, 20C, 20Y, and 20K are arranged vertically in a line, and in each process station, a photoconductor drum (drum-shaped photoconductor) 6 as an image carrier serves as a transfer member via the conveyor belt 1. Each transfer roller 4M,
It is in contact with 4C, 4Y and 4K.

At the lower end of the conveyor belt 1, an adsorption roller 5 is arranged at a position upstream of the process station 20M, and the adsorption roller 5 contacts the tension roller 3 which also serves as an adsorption counter roller via the conveyor belt 1. Touching.
A fixing device 11 is arranged above the conveyor belt 1.

The transfer material P is fed from the feeding cassette 14, the transfer material P is guided to the conveyor belt 1 by the pickup roller 15, and passes through the nip portion formed by the suction roller 5 and the tension roller 3. At that time, a bias is applied and the transfer material P is electrostatically adsorbed to the conveyor belt 1. The transfer material P adsorbed on the conveyor belt 1 is conveyed vertically upward by the conveyor belt 1.

To form an image, first, the surface of the photosensitive drum 6 in each process station 20 (20M to 20K) is uniformly charged by the charger 7, and a latent image is formed on the surface by the exposure optical system 8. It is formed. This photoconductor drum 6
The upper latent image is developed by the developing device 9 and visualized as a toner image, and then the transfer rollers 4M, 4C, 4Y, 4K.
Is transferred to the transfer material P on the conveyor belt 1. The transfer residual toner remaining on the photosensitive drum 6 due to the transfer of the toner image is scraped off by the cleaner 10, and the surface of the photosensitive drum 6 is cleaned.

In the generally used reversal development method, a negative polarity OPC photosensitive member is used for the photosensitive drum, and the exposed portion is developed with negative polarity toner. Therefore, the transfer roller 4 is positively charged by a bias power source (not shown). Transfer bias is applied. A low resistance roller is used as the transfer roller 4.

In the actual image forming process, in consideration of the moving speed of the conveyor belt 1 and the distance between the transfer positions of the process stations, the toner images of the respective colors transferred onto the transfer material P are aligned at the same timing. The transfer material P is conveyed, the image is formed and transferred at each process station, and four colors are transferred onto the transfer material P while the transfer material P passes through the magenta, cyan, yellow, and black process stations 20M to 20K once. Toner images are superposed and transferred to form a color image.

The transfer material P on which the color image is formed is separated by the curvature at the upper end of the conveyor belt 1, that is, the downstream end, and is conveyed to the fixing device 11 to be fixed.

The fixing device 11 is provided with a fixing unit 12 arranged on the conveyance path of the transfer material P by the conveyance belt 1 and a discharging unit 13 arranged above the fixing unit 12.

The fixing section 12 is composed of a heating roller 121 having a halogen heater 121a in the center thereof and a pressure heater 122 abutting against the heating roller 121. In this embodiment, the heating roller 121 and the pressure roller 122 are provided. Has a fixing nip portion in the vertical direction. The fixing device 11 heats and pressurizes the transfer material onto which the toner image has been transferred while being sandwiched between the heating roller 121 and the pressure roller 122 to convey the toner image, thereby melting and fixing the toner image on the transfer material P.

In order to satisfactorily melt and fix the toner on the transfer material P, it is necessary to secure a contact nip between the heating roller 121 and the pressure roller 122. Therefore, each roller 12
1, 122 has a structure in which an elastic layer of silicon rubber is provided around a core metal such as aluminum. In addition, the rollers 121, 1
To prevent toner and paper powder from sticking to the surface of 22,
The outermost layer of the roller is coated with a resin having a good releasability such as PFA or PTFE.

The discharging section 13 is a pair of discharging rollers 13.
5, 136, and is provided above the exit of the fixing unit 12. The transfer material on which the toner image is fixed after passing through the fixing unit 12 is guided to the outside of the fixing device 11 by the second pair of discharge rollers 137 and 138, and finally stacked on the discharge tray 16.

In the present embodiment, when the transfer material P is wavy as described in the conventional example, the scattering and the transfer failure that occur when the transfer material P is transferred while being transferred along the vertical transfer path are prevented. The method will be described below.

FIG. 2 shows a diagram for explaining the present embodiment using a cyan (C) station as an example.

In FIG. 2, the conveyor belt 1 has a circumferential length of approximately 8
PV having a volume resistivity of about 10 ¹¹ [Ωcm] by dispersing carbon or the like having a thickness of 00 [mm] (see FIG. 1) and a thickness of 100 [μm]
DF resin film is used. In addition to this, a resin film such as ETFE or PI whose resistance is appropriately adjusted may be used. In addition, the transfer roller 4C has an elastic rubber layer in which resistance is adjusted by mixing NBR rubber and epichlorohydrin rubber on a cored bar, length 220 [mm], diameter φ14 [mm].
Roller, the Asker-C500 [g] weight hardness measurement is about 35 °. Other than this, urethane rubber, EPDM, or the like is appropriately used as the material of the transfer roller 4C. The transfer roller 4C has a resistance value of 5 × 10 ⁶ [Ω] when a metal foil having a width of 1 [cm] is wound around the outer circumference of the roller and a voltage of 500 [V] is applied between the transfer roller and the core metal. there were. In addition, the transfer roller 4C is formed by a spring (not shown) on the conveyor belt 1.
Through the pressure roller and is brought into contact with the photosensitive drum 6 at a total pressure of 400 [g].

Here, with reference to the perpendicular A drawn from the center of the photosensitive drum 6 to the conveyor belt 1, the center of the transfer roller 4C is z downstream of the perpendicular A (upward) in the conveying direction.
It is arranged with a shift of [mm].

Next, the pre-transfer roller 30C, which is a pressing member for the conveyor belt 1 and is provided upstream of the photosensitive drum 6 in the conveying direction, will be described. The pre-transfer roller 30C has an insulating tube (thickness: 30 [μm]) on the surface of the core bar in a state where it is not electrically connected to anything (for example, the core bar is supported by a bearing of an insulating member). (Not shown) and has an outer diameter of φ5 [mm]. As the insulating tube, a Teflon (registered trademark) -based material such as PVDF, PFA, or PTFE is preferable because it is unlikely to be contaminated, but nylon-based, ABS-based, or other resin may be used as appropriate.

Here, the contact point between the pre-transfer roller 30C and the conveyor belt 1 is a distance y [mm] from the perpendicular line A.
Is placed so that it is located upstream (downward) in the transport direction,
Further, the conveyance belt 1 is arranged so as to enter the photosensitive drum 6 side (rightward in FIG. 2) by the penetration amount x [mm] when the pre-transfer roller 30C does not exist.

In this way, the transfer material P is transferred to the photosensitive drum 6 prior to transfer as the amount of penetration x increases.
Therefore, even if the transfer material P is wavy, the transfer material P is transferred to the pre-transfer roller 30C at the entrance of the transfer station (transfer portion where the photosensitive drum 6 and the transfer roller 4 face each other). It is rubbed and smoothed so that no transfer failure occurs. Further, since the transfer material P first comes into contact with the photosensitive drum 6 and then receives the transfer bias at the transfer roller 4C, the toner is generated by the transfer bias electric field at the entrance of the transfer nip (the sandwiched portion between the photosensitive drum 6 and the transfer roller 4). Will not be scattered.

On the other hand, however, when the above-mentioned intrusion amount x becomes too large, the transfer material P loses its adhesion to the conveyor belt 1 in the vicinity of the pre-transfer roller 30C, and the conveyor belt is a vertical conveyor path. The gravitational action in one direction cannot be obtained, and the transfer material P is separated from the conveyor belt 1 in front of the transfer station. In this case, even if the transfer material P is once guided to the transfer nip, while moving the four transfer stations,
The transfer material P is gradually separated from the conveyor belt 1 or the transfer material P is displaced on the conveyor belt 1, causing problems such as color misregistration.

On the other hand, with respect to the distance (shift amount) z from the perpendicular A of the transfer roller 4C to the downstream side in the transport direction, there is the following tendency. That is, when the shift amount z becomes large, it becomes possible to reincrease the electrostatic adhesion between the transfer belt 1 and the transfer belt 1 which has been weakened at the time of passing through the transfer station. However, if the shift amount z becomes too large, the transfer roller 4C cannot contact the photosensitive drum 6 via the conveyor belt 1 and the transfer current value decreases, so that the transferability and the electrostatic adhesion are both imparted. Getting worse.

Regarding the above-mentioned intrusion amount x [mm], the distance y [mm] from the perpendicular A of the pre-transfer roller 30C to the upstream side in the transport direction.
In combination with, the incident angle of the conveyor belt 1 with respect to the photosensitive drum 6 (offset angle θ in FIG. 2) is determined by the following mathematical expression (1). Therefore, when an appropriate range for this x / y is obtained, It became like 1. At this time, the shift amount z of the transfer roller 4C was fixed at z = 1.0 [mm].

[0042]

[Equation 1]

[0043]

[Table 1]

As a result of the above Table 1, when (x / y) ≦ 0.02, the effect of preventing the corrugation of the transfer material P is insufficient,
The lower limit of x / y was 0.03, which was the practical limit. On the other hand, x
When /y≧0.25, the transfer material P is peeled off from the conveyor belt 1, which causes a problem. Therefore, the upper limit of x / y is 0.2.
Was the practical limit. That is, it is preferable to use the following formula (2).

[0045]

[Equation 2]

Even if the value of θ determined by x / y = tan θ is maintained at a predetermined value, if the value of the intrusion amount x is too large, the transfer material P will peel off from the conveyor belt 1 by itself, while
If the value of the intrusion amount x is too small, the distance y is consequently reduced to bring the pre-transfer roller 30C too close to the photosensitive drum 6, which is not practical. Therefore, the intrusion amount x
Is preferably used within the range of the following mathematical expression (3).

[0047]

[Equation 3]

Similarly, the distance y is preferably set so that the pre-transfer roller 30C does not come into contact with the photosensitive drum 6 via the conveyor belt 1, and is preferably used within the range of the following mathematical expression (4).

[0049]

[Equation 4]

Next, x = 1.0 [mm], y = 10.0 [mm]
Then, when the proper position (shift amount) z of the transfer roller 4C was examined while fixing x / y = 0.1, the results shown in Table 2 below were obtained.

[0051]

[Table 2]

As a result of the above Table 2, when z ≦ 0.3 [mm], the transfer material P once squeezed by the pre-transfer roller 30C is electrostatically attracted to the conveyor belt 1 again by the bias voltage of the transfer roller 4C. The force for doing so was too weak, and the lower limit of z was about 0.5 [mm], which was the practical limit. (If z is too small, the effect of winding the transfer material P around the photoconductor drum 6 at the transfer nip portion decreases, and the electrostatic attraction between the transfer material P and the conveyor belt 1 at the transfer portion decreases. It will be.)

Particularly, in the vertical conveying system, when the electrostatic attraction between the transfer material P and the conveyor belt 1 is weakened, the transfer material passes through the transfer station in the order of 4M → 4C → 4Y → 4K. Since the transfer material P is gradually separated from the conveyor belt 1, it is important to surely obtain the electrostatic attraction force with each transfer station as the transfer charge is transferred during transfer.

In Table 2 above, when z ≧ 3.5, the transfer roller 4C was too far from the photosensitive drum 6, and the transfer roller 4C and the photosensitive drum 6 did not come into contact with each other via the conveyor belt 1. Almost no transfer current flows through the transfer material P, and a transfer failure and a suction failure of the transfer material P on the transport belt 1 occur.

Therefore, the shift amount z is preferably set so that the transfer roller 4C comes into contact with the photosensitive drum 6 via the conveyor belt 1, and is preferably used in the range of the following mathematical expression (5).

[0056]

[Equation 5]

In order to keep the transfer roller 4C sufficiently in contact with the photosensitive drum 6 via the conveyor belt 1, it is preferable that the transfer roller is an elastic roller capable of elastic deformation. It is important to soften the hardness of the transfer roller 4C to some extent. In this embodiment, as described above, the roller of about 35 ° is used in the Asker-C, but the transfer rollers 4M, 4C, 4Y, 4K, etc.
It is preferable to use one having a hardness in the range of about 50 ° to 50 °.

In the present embodiment, as an example, M (magenta), C (cyan), Y (yellow), K (black).
In each station of, for each photosensitive drum 6,
X = 1.0 [mm], y = 10.0 [m] so that the relative positional relationship between the transfer rollers 4M, 4C, 4Y, 4K and the pre-transfer rollers 30M, 30C, 30Y, 30K is the same.
When m] and z = 1.2 [mm], high temperature and high humidity (30
Even if 1000 sheets of automatic double-sided printing are performed using an A4 size transfer material having a basis weight of 64 [g / m ² ] at 80 ° C. and 80% RH), transfer failure due to waviness of the transfer material or toner scattering at the time of transfer , And the transfer rollers 4M, 4C, 4Y,
Since the contact pressure of 4K can be kept low, a good image was always obtained without causing image defects such as hollow spots.

Second Embodiment In the above first embodiment, an example in which the transfer roller and the pre-transfer roller have the same relative positional relationship in each transfer station has been described.

However, in each transfer station, the transfer rollers 4M, 4C, 4
Y, 4K and pre-transfer rollers 30M, 30C, 30Y, 30
The values of the above-mentioned parameters x, y, and z for determining the position of K may be different values.

As an example, the size of the corrugation of the transfer material P changes as the transfer material P passes through each station, but in the most common case, the transfer is performed at the final black (K) station. It is conceivable that the waviness of the material P becomes maximum (due to the accumulation of strain). In such a case, the transfer roller 4K and the pre-transfer roller 3 of the fourth station, which is the final station.
It is sufficient to change 0K to a direction in which the ripple correction force is larger than that of other stations.

For this purpose, for example, the distance y is reduced or the intrusion amount x is increased, and the above-mentioned equation (1) is used.
A possible method is to increase the value of. Specifically, in such a case, for the transfer rollers 4M, 4C, 4Y and the pre-transfer rollers 30M, 30C, 30Y, x =
1.0 [mm] and y = 10 [mm], and x = 1.0 [mm] and y = 9 [m] for the transfer roller 4K and the pre-transfer roller 30K.
m], good results were obtained.

As shown in FIG. 1, in the present embodiment, the case where the photosensitive drums of the colors M, C, Y, and K are arranged vertically on a substantially straight line has been described.
In some cases, the center C, Y may be offset from M, K on the transfer roller side (left side in FIG. 1) by about 0.1 [mm] to 3 [mm]. Even in such a case, the arrangement of the transfer rollers 4M, 4C, 4Y, 4K and the pre-transfer rollers 30M, 30C, 30Y, 30K at each station is determined by the formulas (1) to (5) in the first embodiment. It goes without saying that the values of x, y, and z may be adjusted to different values for each color within the range. Further, the pre-transfer roller 30 may not be applied to all the transfer stations, but may be provided, for example, only in the black (K) station which is the final station.

[Third Embodiment] In the above-described first embodiment, pre-transfer rollers 30M, 30C, 30Y, 30K.
The core bar is in a state where it is not electrically connected to anything (for example, the core bar is supported by a bearing of an insulating member), but this has an insulating coating on the surface, so the pre-transfer roller This is because the transfer of electric charge is not positively performed between 30 and the conveyor belt 1. Actually, if the surface layers of the pre-transfer rollers 30M, 30C, 30Y and 30K are made of a conductive material and the core metal is grounded, for example, the transfer rollers 4M,
Transfer currents from 4C, 4Y and 4K are transferred to the pre-transfer roller 30.
It flows into M, 30C, 30Y, and 30K, and causes inconveniences such as defective transfer and toner scattering at the transfer nip entrance.

However, the pre-transfer rollers 30M, 30C, 3
Even if the surface layers of 0Y and 30K are made of an insulating layer, if electric charges are gradually accumulated in the metal core and the creepage distance from the surroundings is insufficient, inconvenience such as discharge may occur. In such a case, as shown in FIG. 3, the core metal 33M of the pre-transfer rollers 30M, 30C, 30Y and 30K,
33C, 33Y and 33K are respectively associated with transfer rollers 4
M, 4C, 4Y, 4K transfer bias 31M, 31C,
It is better to keep the same potential as 31Y and 31K. Note that FIG.
Describes the configuration according to the present embodiment by exemplifying a cyan (C) station, and other stations are similarly configured.

In this manner, the pre-transfer roller is a roller having a core metal surface layer made of an insulating member, and the same bias voltage as the transfer bias applied to the corresponding transfer roller is applied to the core metal. It is possible to prevent excessive charge from being accumulated in the pre-transfer roller, and prevent abnormal discharge due to overcharge of the pre-transfer roller. Moreover, since the cores of the transfer roller and the pre-transfer roller have the same potential, it is possible to prevent electric discharge from occurring between the cores.

Incidentally, in FIG. 3, the static elimination needles 32M, 32
C, 32Y, and 32K are charge eliminating members for eliminating charge on the rear surface of the transport belt 1 after the transfer is completed, and are grounded to the casing of the printer body in the present embodiment. This static elimination needle is
For example, when the transfer material P passes through the transfer nip, discharge is generated between the transfer roller 4 and the conveying belt 1 downstream of the contact nip, which is effective in the case where a dot-shaped image defect occurs. Needless to say, even if the static elimination needle 32C or the like is provided downstream of an arbitrary transfer station, the action itself of the pre-transfer roller 30C or the like is not impaired.

[Fourth Embodiment] In the above-described first to third embodiments, the pre-transfer roller 30 (30M, 30C, 3) is used.
(0Y, 30K) has a straight cylindrical shape in the width direction orthogonal to the transport direction, but when the corrugation of the transfer material P is large, an inverted crown shape as shown in FIG. It is also possible to adopt a shape without a center as shown in b). In FIGS. 4A and 4B, 33 is a core metal of the pre-transfer roller.

As the inverted crown shape (tapered shape whose outer diameter decreases from both sides in the width direction orthogonal to the transfer material conveying direction toward the central portion) as shown in FIG. In contrast to (diameter 5 [mm]), when the central part is squeezed into a substantially V shape and the diameter of the central part is 4.4 [mm] (that is, the amount of reverse crown is 300 [μm]), the transfer is performed. Good ripple correction effect was exhibited for the material P, and transfer failure could be prevented. In addition, it is considered that the amount of reverse crown is preferably about 50 [μm] to 500 [μm] depending on the waving condition.

As for the hollowed-out shape as shown in FIG. 4B, both ends in the width direction are left by about 50 [mm] to 100 [mm], and the central portion is removed (that is, the pre-transfer roller is left and right). The shape was good. Note that the number of divisions of the rollers is an example, and the number of divisions is not limited to this, and may be appropriately set as necessary.

[0071]

As described above, according to the present invention,
It is possible to prevent toner scattering and transfer failure at the time of transfer due to waviness of the transfer material, and it is possible to significantly improve the transfer performance in the vertical transport path.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an image forming apparatus embodying the present invention.

FIG. 2 is an explanatory diagram of a transfer station according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a transfer station according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a shape of a pre-transfer roller according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional device.

FIG. 6 is an explanatory view of a conventional device.

FIG. 7 is an explanatory diagram of a conventional device.

FIG. 8 is an explanatory diagram of a conventional device.

FIG. 9 is an explanatory view of a conventional device.

[Explanation of symbols]

P ... Transfer material 1 ... Conveying belt 2 ... Driving roller 3 ... Tension rollers 4M, 4C, 4Y, 4K ... Transfer roller 5 ... Adsorption roller 6 ... Photosensitive drum 7 ... Charging device 8 ... Exposure optical system 9 ... Developing device 11 ... Fixing device 13 ... Ejection unit 15 ... Pickup roller 16 ... Ejection trays 20M, 20C, 20Y, 20K ... Process stations 30M, 30C, 30Y, 30K ... Pre-transfer rollers 31M, 31C, 31Y, 31K ... Transfer bias 32M, 32C, 32Y , 32K ... Static elimination needles 33M, 33C, 33Y, 33K ... Mandrel 121 ... Heating roller 121a ... Halogen heater 122 ... Pressure heater 135, 136 ... Ejection roller pair 137, 138 ... Ejection roller pair

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H030 AA06 AB02 AD05 BB02 BB23                       BB44 BB46                 2H200 FA01 FA08 GA23 GA34 GA44                       GA47 GB12 GB25 GB41 HA03                       HB12 JA02 JA25 JA26 JA27                       JB07 JB13 JB20 JB26 JB32                       JB37 JB40 JB41 JB45 JB46                       JB47 JB48 LA14 LA17 LA18                       LA36 MA03 MA04 MA20 MB04                       MB06 MC01 MC02 NA02

Claims (9)

[Claims] 1. A transfer material conveying means for conveying a transfer material in a substantially vertical direction, a plurality of image carriers arranged along the transfer material conveying means and carrying an image, and the image carrier for each of the image carriers. A plurality of transfer members that are arranged to face each other on the downstream side in the transfer material transport direction via the transfer material transport means and transfer the image on the image carrier onto the transfer material; A pressing member arranged on the upstream side in the transfer material conveying direction for pressing the transfer material conveying means toward the image carrier, and an intrusion amount of the pressing member in the direction toward the image carrier is x, When the distance between the contact point of the pressing member with the transfer material conveying means and the perpendicular line drawn from the center of the corresponding image carrier to the transfer material conveying means is y, the pressing member is the image carrier. A distance y more than the upstream side in the transfer material transport direction, Intrusion amount x in the holding direction
Placed in a position in which only 0.03 ≦ x / y ≦ 0.
2. An image forming apparatus characterized by satisfying 2. 2. The amount x of penetration of the pressing member toward the image carrier is in the range of 0.2 [mm] ≦ x ≦ 2.0 [mm]. The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the distance y is set so that the pressing member does not come into contact with the image carrier via the transfer material conveying unit. 4. The transfer member is in the shape of a roller, and when the distance between the center of rotation of the transfer member and the perpendicular line drawn from the center of the corresponding image carrier to the transfer material conveying means is z, The image forming apparatus according to claim 1, wherein the distance z is within a range of 0.5 [mm] ≦ z ≦ 3.0 [mm]. 5. The transfer member is composed of an elastic roller that is elastically deformable so as to come into contact with the image carrier via the transfer material transporting means.
The image forming apparatus according to claim 1. 6. The transfer member transfers an image on an image carrier onto a transfer material by applying a bias voltage, and the pressing member uses an insulating member on a surface layer of a metal cored bar. It is a roller configured, for each core metal of the pressing member,
The image forming apparatus according to claim 1, wherein a bias voltage applied to each transfer member corresponding thereto is applied. 7. The pressing member has a roller shape having a taper shape whose outer diameter decreases from both sides in the width direction orthogonal to the transfer material conveying direction toward the central portion. The image forming apparatus according to any one of items. 8. The pressing member has a roller shape divided in the width direction having a non-contact portion at the center with respect to the transfer material conveying means in the width direction orthogonal to the transfer material conveying direction. The image forming apparatus according to any one of claims 1 to 6. 9. A charge removing member for removing charge from the rear surface (that is, the side where the transfer member is present) of the transfer material conveying means is provided on the downstream side of the transfer member.
The image forming apparatus according to any one of 6 above.