JPH10254253A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the occurrence of a color smear and excellent in peeling property of a sheet of paper. SOLUTION: The image forming device is provided with four groups of image forming units 11-14, an intermediate transfer belt 2, a primary transfer roller 3, a primary transfer power source 4, a backup roller 5, a secondary transfer roller 8 and a paper chute 7. In such a case, the image forming device is provided with the primary transfer roller 3 for supporting the intermediate transfer belt 2 from a primary transferring position P1 on the most upstream side in the circulating direction of the intermediate transfer belt 2 to a primary transferring position P4 on the most downstream side, from the rear surface, so that the occurrence of the color smear can be prevented.

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 used in an electrophotographic color copying machine, a color printer, and the like.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a color copying machine or a color printer, primary transfer is performed such that toner images of a plurality of colors formed by image forming units for a plurality of colors are sequentially superimposed on an intermediate transfer member. An image forming apparatus is known which forms a multicolor toner image on an intermediate transfer member and then secondary-transfers the multicolor toner image onto paper to obtain a color image. Examples of such an intermediate transfer type image forming apparatus are disclosed in JP-A-5-241457 and JP-A-6-16.
No. 1290 is cited.

FIGS. 10 and 11 are schematic views of an image forming apparatus of the intermediate transfer system in the above-mentioned conventional example. FIG.
0, for example, the image forming units 11 to 14 that form toner images of each color of black (K), yellow (Y), magenta (M), and cyan (C), and circulate in the direction of arrow A;
An intermediate transfer belt 2 on which primary transfer is performed so that toner images of respective colors formed by the image forming units 11 to 14 are sequentially superimposed, and a multicolor toner image formed by primary transfer is transferred from the intermediate transfer belt 2 to a sheet 6. 1 shows an image forming apparatus provided with a secondary transfer device 15 for secondary transfer and a fixing device 10 for fixing a multicolor toner image secondary-transferred onto the paper 6.

FIG. 11 shows an image forming apparatus using an intermediate transfer drum 2 'rotating in the direction of arrow A as an intermediate transfer member, instead of the intermediate transfer belt 2 of the image forming apparatus shown in FIG. ing.

[0005]

In an image forming apparatus of the type using a belt as an intermediate transfer member as shown in FIG.
The toner images of the respective colors formed by the image forming units 11 to 14 are transferred so as to be superimposed on the intermediate transfer belt 2 successively. At this time, the roll for driving the belt is eccentric or the intermediate transfer is performed. When the belt 2 expands or contracts, the position where the toner image of each color is superimposed on the intermediate transfer belt 2 is shifted in the belt traveling direction, and a color shift is generated in the multicolor toner image formed by the primary transfer. is there. As a method of preventing the color misregistration, a method of synchronizing the circumferential length of the belt driving roll with the distance between the image forming units 11 to 14 and a method of using a material with little expansion and contraction for the intermediate transfer belt 2 are used. Although there are methods to use such a method, there are problems that the apparatus becomes large and that the cost tends to increase.

In an image forming apparatus of the type using a drum for an intermediate transfer member as shown in FIG. 11, color misregistration is relatively small, but in this type of image forming apparatus, the diameter of the intermediate transfer drum 2 'is small. It has to be big,
Therefore, the releasability of the sheet 6 is poor in a portion where the sheet 6 is separated from the intermediate transfer drum 2 ′ after the secondary transfer. In particular, when a thin sheet is used, the sheet 6 is wound around the intermediate transfer drum 2 ′ and jams. There is a problem that is easily caused.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus in which color misregistration is prevented and in which the sheet is easily peeled.

[0008]

According to the image forming apparatus of the present invention which achieves the above object, a toner image of any one of a plurality of color toner images is formed on a surface thereof. A plurality of image carriers that convey the toner image to the respective primary transfer positions, and the toner formed on each image carrier that circulates while approaching or contacting each image carrier at each primary transfer position The multi-color toner image is formed on the surface by receiving the primary transfer of each of these toner images so that the images are sequentially superimposed, and an intermediate transfer belt that conveys the multi-color toner image to a predetermined secondary transfer position; A primary transfer unit that primarily transfers each toner image formed on each image carrier onto the intermediate transfer belt; and a portion of the intermediate transfer belt where the multicolor toner image is formed on the surface is an intermediate transfer belt. From the back side of the image carrier, before the timing of receiving the primary transfer from the image carrier located at the most upstream side in the circulating direction of the intermediate transfer belt among the plurality of image carriers, the image located at the most downstream side in the circulating direction. A support member that continues to support after the timing of receiving the primary transfer from the carrier; a sheet transporting unit that transports a sheet that receives the transfer of the multicolor toner image to the secondary transfer position; and a transporting unit that transports the sheet to receive the secondary transfer position. And a secondary transfer means for secondary-transferring the multicolor toner image on the intermediate transfer belt onto a sheet conveyed to the secondary transfer position.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the image forming apparatus of the present invention. First, the configuration of the image forming apparatus 1 shown in FIG. 1 will be described. As shown in FIG. 1, the image forming apparatus 1 has black (K), yellow
(Y), image forming units 11 to 14 for forming toner images of respective colors of magenta (M) and cyan (C); an intermediate transfer belt 2 receiving primary transfer of the toner images from the image forming units 11 to 14; A primary transfer roller 3 for supporting the transfer belt 2, a primary transfer power source 4 for applying a primary transfer voltage to the primary transfer roller 3, a paper chute 7 for supplying a sheet 6 to a secondary transfer position S, and an intermediate transfer belt A backup roller 5, a secondary transfer roller 8, a secondary transfer power supply 9, and a fixing device 10 for secondary transfer of a multicolor toner image formed on the sheet 2 to a sheet 6 are provided.

The image forming units 11 to 14 include, for example, an image carrier drum, a primary charging device, an exposure device including an LED (light emitting diode), a laser scanner, and the like, which are used in a normal electrophotographic image forming device. And a developing device. FIG. 1 shows the image carrier drum 11 among these components.
Only a to 14a are shown, and other components are not shown. The image forming units 11 to 14 are arranged in an arc shape along the primary transfer roller 3, and the image carrier drums 11 a to 14 a of each unit are located at four primary transfer positions P 1, P 2, P 3 on the primary transfer roller 3. , P4, is in proximity to or in contact with the primary transfer roller 3 via the intermediate transfer belt 2.

Here, "arranged in an arc shape" does not only mean that each image forming unit is arranged on the circumference of a concentric circle. For example, some of the plurality of image forming units are arranged. It also includes a configuration in which the material and the diameter of the image carrier drum of the image forming unit are different from the material and the diameter of the primary transfer roller of the image carrier drum of another image forming unit.

Incidentally, the image carrier drums 11a to 14a in this embodiment correspond to the image carrier according to the present invention. Silicon rubber, EPD is used for the primary transfer roller 3.
A material obtained by adding a conductive filler such as carbon black to a synthetic rubber such as M (ethylene propylene diene monomer) or urethane rubber to make the rubber conductive is used. The diameter of the primary transfer roller 3 is about 40 to 200 mm. A primary transfer power supply 4 for applying a voltage of about +0.5 to 1.5 kV for transferring the toner images formed by the image forming units 11 to 14 to the primary transfer roller 3 by electrostatic force is applied to the primary transfer roller 3. Is connected. The primary transfer roller 3 is connected to a stepping motor by a timing belt or the like, is driven at an accurate angular velocity, and rotates in the direction of arrow A. The front surface of the primary transfer roller 3 is in contact with the back surface of the intermediate transfer belt 2. When the primary transfer roller 3 rotates in the direction of arrow A, the intermediate transfer belt 2 follows and circulates in the direction of arrow B.

Although the primary transfer roller 3 in this embodiment corresponds to the support member according to the present invention, the support member according to the present invention is not limited to a rotating body, The portion where the multicolor toner image is formed on the front surface is subjected to primary transfer from the rear surface side of the intermediate transfer belt from the image carrier, which is the most upstream in the circulation movement direction of the intermediate transfer belt among the plurality of image carriers. Any function may be used as long as it has a function of continuing to support before the timing and after the timing of receiving the primary transfer from the image carrier located at the most downstream side in the circulating movement direction. For example, an intermediate transfer in which a multicolor toner image is formed on the surface A horizontally movable support member or the like that moves from the primary transfer position of the first color to the primary transfer position of the final color while supporting the belt portion may be used.

In the present embodiment, the intermediate transfer belt 2 is moved from a position before the primary transfer position 11a on the most upstream side in the circulating movement direction B of the intermediate transfer belt 2 to a primary transfer position 14a on the most downstream side.
It is supported from the back side by the primary transfer roller 3 continuously thereafter. The intermediate transfer belt 2 is made by adding a conductive filler such as carbon black to a polymer film such as polyimide, polycarbonate, or PVdF (polyvinylidene fluoride) or a synthetic rubber such as silicon rubber or fluorine rubber. Are used.

Incidentally, the primary transfer roller 3 and the power supply 4 in this embodiment correspond to the primary transfer means in the present invention. The backup roller 5 is made of a material similar to that of the primary transfer roller 3. The diameter of the backup roller 5 is smaller than that of the primary transfer roller 3, for example, about 1 mm in diameter.
A roller of 0 to 30 mm is used. The backup roller 5 rotates following the intermediate transfer belt 2.

The secondary transfer roller 8 is made of the same material as that of the backup roller 5. The diameter of the secondary transfer roller 8 is substantially the same as the diameter of the backup roller 5, for example, a roller having a diameter of about 10 to 30 mm is used. The secondary transfer roller 8 is supplied to the intermediate transfer belt 2 by a secondary transfer power source 9.
A voltage of about +0.5 to 3 kV for transferring a multicolor toner image from the printer to the paper 6 by electrostatic force is applied.

The backup roller 5, the secondary transfer roller 8, and the secondary transfer power source 9 in the present embodiment correspond to the secondary transfer means according to the present invention, and the backup roller 5 corresponds to the secondary transfer means according to the present invention. It also corresponds to the second roller.
The paper chute 7 guides the sheet 6 so that an angle (sheet entry angle) θ between a portion of the intermediate transfer belt 2 toward the secondary transfer position S and the sheet 6 toward the secondary transfer position S is as small as possible. . Note that the paper chute 7 corresponds to a part of the paper conveying means according to the present invention, and in the present embodiment, the paper chute 7 is separated from the secondary transfer position S of the intermediate transfer belt 2 by: At the secondary transfer position S, the paper 6 is transferred to the secondary transfer position S at a paper entry angle θ smaller than the angle (paper separation angle) φ between the multicolor toner image transferred from the secondary transfer position S and the paper 6 separated from the secondary transfer position S. Transport to

Next, the operation of the image forming apparatus 1 shown in FIG. 1 will be described. Each of the image forming units 11 to 14 forms an image by a normal electrophotographic process. That is, after the image carrier drum is uniformly charged by the primary charging device, an electrostatic latent image corresponding to the image of each color is formed on the image carrier drum by the exposure device, and the electrostatic latent image is formed. The toner is developed by the developing device with each color toner to form a toner image.

Next, these toner images of each color are primarily transferred at respective primary transfer positions P1 to P4 so as to be superimposed on the intermediate transfer belt 2 sequentially. FIG. 2 is a diagram illustrating a process in which a toner image is primarily transferred from each image forming unit to an intermediate transfer belt. As shown in FIG. 2, the intermediate transfer belt 2 has a primary transfer roller 3 rotating in the direction of arrow A.
And is circulated in the direction of arrow B following the primary transfer roller 3. A voltage having a polarity opposite to the charging polarity of the toner image (for example, a voltage of about +1 kV for negative polarity toner) is applied to the primary transfer roller 3 by a primary transfer power supply 4. In the first color image forming unit 11, the first color toner image formed on the image carrier drum 11a through a series of electrophotographic processes of primary charging, exposure, and development is intermediate with the image carrier drum 11a. At the primary transfer position P <b> 1 where the transfer belt 2 comes into contact, primary transfer is electrostatically performed on the intermediate transfer belt 2. When the first color toner image transferred onto the intermediate transfer belt 2 reaches the primary transfer position P2 of the second color due to the movement of the intermediate transfer belt 2, the toner image on the image carrier drum 12a of the image forming unit 12 of the second color. The toner image of the second color formed on
The primary transfer is performed so as to be superimposed on the first color toner image. Similarly, primary transfer is performed so that toner images of the third and fourth colors are sequentially superimposed on the toner images of the first and second colors, and finally, the toner images of four colors are superimposed. A multicolor toner image is formed on the intermediate transfer belt 2.

In the course of the primary transfer, the rotational angular velocity of the primary transfer roller 3 is accurately controlled by a stepping motor or the like. Further, since a rubber material having a relatively high friction coefficient is used as the primary transfer roller 3, the intermediate transfer belt 2 rotates in a state of being in close contact with the primary transfer roller 3. Accordingly, color shift due to speed fluctuation, walk (meandering), or expansion and contraction of the intermediate transfer belt 2 hardly occurs. The relationship between the color shift and the speed fluctuation of the intermediate transfer belt 2 will be described later.

The multicolor toner images formed by the primary transfer from the image forming units 11 to 14 onto the intermediate transfer belt 2 sequentially and superimposed thereon are conveyed to the secondary transfer position S as the intermediate transfer belt 2 moves. Is secondary-electrostatically transferred to the sheet 6 at the secondary transfer position S. After the toner image is transferred between the intermediate transfer belt 2 and the sheet 6 sandwiched between the backup roller 5 and the secondary transfer roller 8 at the secondary transfer position S, the intermediate image is formed by the backup roller 5 having a relatively small diameter. Due to a sharp change in the curvature of the transfer belt 2, the sheet 6 cannot be followed by the curvature and is separated from the intermediate transfer belt 2. The peeled sheet 6 is conveyed to a fixing device 10 (see FIG. 1), and is fixed by the fixing device 10 to complete image formation.

Next, the relationship between the color shift and the speed fluctuation of the intermediate transfer belt 2 will be described. FIG. 3 is a diagram illustrating an apparatus for measuring a speed fluctuation of the intermediate transfer belt. The intermediate transfer belt 2 used in the measuring apparatus shown in FIG. 3 is obtained by dispersing carbon black in silicon rubber, and has a thickness of 2 mm. The primary transfer roller 3 is formed by forming a 5 mm thick urethane foam layer in which carbon black is dispersed on the surface of a metal core, and has a diameter of 100 mm. The backup roller 5 is formed by forming a 5 mm thick urethane foam layer in which carbon black is dispersed on the surface of a metal shaft, and has a diameter of 20 mm. The secondary transfer roller 8 is a roller of the same shape made of the same material as the backup roller 5. The primary transfer roller 3 is configured to be driven at a constant angular velocity by a stepping motor 16, a pulley 16a, and a timing belt 16b.

This measuring device is designed to circulate the intermediate transfer belt 2 by driving the backup transfer roller 5 in addition to driving the primary transfer roller 3 to circulate the intermediate transfer belt 2. The backup roller 5 can be driven at a constant angular velocity by the stepping motor 17, the pulley 17a, and the timing belt 17b.

The surface speed of the intermediate transfer belt 2 is measured at four measurement points A to D using a Canon laser Doppler velocimeter. These measurement points A to D are shown in FIG.
Image carrier drums 11a to 14a of each image forming unit
Respectively correspond to the primary transfer positions P1 to P4. First, the surface speed of the intermediate transfer belt 2 when the primary transfer roller 3 was driven to move the intermediate transfer belt 2 was measured.

FIG. 4 is a graph showing the measurement results of the surface speed of the intermediate transfer belt when the primary transfer roller is driven.
4A to 4D show the surface speed (linear speed) of the intermediate transfer belt 2 on the vertical axis and the time at the measurement points A to D in FIG. 3 when the horizontal axis shows time. 5 is a measurement result of the surface speed of the intermediate transfer belt 2. As shown in FIGS. 4 (a) to 4 (d), a swell-like speed fluctuation with a period of about 3.14 seconds was measured at each of the measurement points A to D. Each waveform shown in FIGS. 4A to 4D shows the same waveform having a certain time difference. That is, the waveform of FIG.
(A) is a waveform shifted to the right by a time difference d,
The waveform in FIG. 4C is a waveform in which the waveform in FIG. 4B is further shifted to the right by a time difference d, and the waveform in FIG.
4C is a waveform further shifted to the right by a time difference d.

These periodic speed fluctuations are nothing but the speed fluctuations due to the eccentricity of the primary transfer roller 3. That is, although the primary transfer roller 3 rotates at a constant angular velocity,
If the primary transfer roller 3 is eccentric, the apparent radius fluctuates, and accordingly, the peripheral speed (tangential speed) of the primary transfer roller 3 at each measurement point also fluctuates. However, paying attention to the speed fluctuation at a certain point on the intermediate transfer belt 2, the intermediate transfer belt 2 is supported in a state of being in close contact with the primary transfer roller 3, and the intermediate transfer belt 2
Under the condition that no slip occurs between the primary transfer roller 3 and the primary transfer roller 3, for example, when the part eccentric in the direction in which the diameter of the primary transfer roller 3 is expanded reaches the point A,
If the transfer of the first color toner image is performed at that point, the toner image is transferred in a distorted form slightly extended in the moving direction of the intermediate transfer belt 2. However, FIGS.
As shown in (d), the waveform at each measurement point is the same waveform with a fixed time difference, so when the first color toner image formed at point A reaches point B, the transfer of the second color toner image is started. The image is superimposed and transferred onto the first color toner image in a distorted manner as in the case of the point A. The same applies to the third color and the fourth color. Accordingly, a multicolor toner image formed by being superimposed on the intermediate transfer belt 2 does not lead to color misregistration, although a shape distortion in the moving direction of the intermediate transfer belt 2 occurs.

As described above, in the present embodiment, the intermediate transfer belt 2 is driven by the primary transfer roller 3, but the intermediate transfer belt 2 is driven by the backup roller 5 instead. The following test was performed to confirm the effect on the surface speed of the belt 2. FIG. 5 is a graph showing a measurement result of the surface speed of the intermediate transfer belt when the backup roller is driven.

As shown in FIG. 5, a swelling speed fluctuation having a period of about 0.6 seconds was measured at each of the measurement points A to D.
This periodic speed fluctuation is considered to be due to the eccentricity of the backup roller 5 in view of the ratio of the diameter of the primary transfer roller 3 to the diameter of the backup roller 5. In this case, the surface speed of a certain point on the intermediate transfer belt 2 is measured at each of the measurement points A, B,
C and D show different values. Therefore, when a multicolor toner image is formed by sequentially superimposing toner images at these measurement points A, B, C, and D, a color shift occurs.

In order to prevent the occurrence of such color misregistration,
The circumferential length of the backup roller 5 and each primary transfer position P
The image forming apparatus may be designed so that the rotation unevenness of the backup roller 5 is canceled by synchronizing the interval between 1 to P4. However, since the addition of one such design constraint greatly affects the design conditions of other parts of the image forming apparatus,
A method in which the intermediate transfer belt 2 is driven by the primary transfer roller 3 is more preferable.

Next, the behavior of the toner image when the toner image is secondarily transferred from the intermediate transfer belt 2 to the sheet 6 will be described. FIG. 6 is an enlarged view near the secondary transfer position in the present embodiment. At the time of the secondary transfer, the paper chute 7 is used to convey the paper so that the paper entering angle θ formed by the paper 6 toward the secondary transfer position S and the portion of the intermediate transfer belt 2 toward the secondary transfer position S is as small as possible. It is necessary to regulate the route. The practical value of the paper entering angle θ is practically a minimum of about 15 degrees due to restrictions on the shape of the end of the paper chute 7 and the strength of the paper 6.
By restricting the paper entering angle θ in this way, the paper 6 enters the secondary transfer position S after coming into contact with the intermediate transfer belt 2, and at the secondary transfer position S in a high electric field, the toner image Discharge is prevented from occurring prior to transfer, so that an image with good image quality can be obtained without image deterioration due to toner scattering.

Next, the influence of the sheet entering angle in the secondary transfer process will be described. FIG. 7 is a schematic diagram of an apparatus for testing the effect of the paper entry angle on the secondary transfer position. The test apparatus shown in FIG. 7 includes an image forming apparatus according to the present embodiment,
Three types of paper chute 7 for paper entrance angle test
a, 7b and 7c are added. The paper entering angle θ1 of the paper chute 7a arranged at the set position A is 15
The paper entry angle θ2 of the paper chute 7b disposed at the set position B is 40 degrees, and the paper entrance angle θ3 of the paper chute 7c disposed at the set position C is 60 degrees.

In the test apparatus shown in FIG. 7, the multicolor toner images which are sequentially primary-transferred from the image forming units 11 to 14 and are superimposed on the intermediate transfer belt 2 are formed.
The sheet is conveyed to the secondary transfer position S with the movement of the intermediate transfer belt 2, and at the secondary transfer position S, the paper chute 7
a, 7b, and 7c, the sheet is secondarily transferred onto the sheet 6 supplied from the paper chute. At this time, the scattering degree of the toner near the secondary transfer position S was measured.

FIG. 8 is a graph showing the relationship between the paper entry angle θ and the evaluation value of toner scattering. As shown in FIG. 8, it can be seen that the smaller the sheet entrance angle θ, the better the toner scattering evaluation value. This toner scattering phenomenon will be described with reference to FIG.

FIG. 9 is a schematic diagram showing the behavior of the toner near the secondary transfer position S. As shown in FIG. 9, when the sheet 6 enters the secondary transfer position S at a large sheet entry angle θ3 by the paper chute set at the setting position C, the sheet 6 directly enters the secondary transfer position S. Alternatively, the sheet enters the secondary transfer position S after coming into contact with the secondary transfer roller 8. Accordingly, due to the action of the high electric field formed between the backup roller 5 and the secondary transfer roller 8, a discharge may occur between the intermediate transfer belt 2 and the paper 6 prior to the transfer of the toner. When a discharge occurs between the toner and the secondary transfer roller 8 or a discharge occurs between the intermediate transfer belt 2 and the secondary transfer roller 8 in the vicinity of the toner, the toner on the intermediate transfer belt 2 becomes an electric field. In some cases, the toner may jump into the space due to the action, causing toner disturbance and causing image deterioration. Further, since the charge amount of the toner may be attenuated or the polarity of the toner may be inverted, the toner having the attenuated charge amount or the inverted polarity may have a small electrostatic force with the paper 6 and a weak adhesion to the paper 6. As a result, after the paper 6 has passed through the secondary transfer position S, the toner on the upper layer side of the toner layer on the paper 6 having a small adhesive force to the paper 6 scatters from the paper 6 or the upper toner having the opposite polarity May be repelled by the toner in the lower layer and scattered to cause image deterioration.

On the other hand, the paper chute provided at the installation position A causes the paper 6 to enter a small paper entry angle θ1.
When the sheet 6 enters the secondary transfer position S, the sheet 6 once contacts the intermediate transfer belt 2 and then enters the secondary transfer position S. Therefore, the backup roller 5 in which a high electric field is formed
Also, between the intermediate transfer belt 8 and the secondary transfer roller 8, no discharge occurs between the intermediate transfer belt 2 and the paper 6 prior to the toner transfer. Accordingly, it is possible to form an image of good image quality without toner scattering. Such an effect cannot be obtained by the conventional image forming apparatus using only the intermediate transfer drum 2 'as shown in FIG.

Next, using the test apparatus shown in FIG.
A peel test of the paper 6 from the secondary transfer means was performed. The sheet 6 for testing, the second original drawing for translucent paper having a basis weight of 58 g / m ^2, color for plain paper having a basis weight of 82 g / m ^2, and were prepared three kinds of cardboard having a basis weight of 220 g / m ² . Also,
To change the curvature of the intermediate transfer belt 2 at the paper peeling section,
10 mm diameter, 30 m as backup roller 5
Three types of rollers of m and 50 mm were prepared.

Table 1 is a table showing the relationship between the sheet releasability and the backup roller diameter.

[0038]

[Table 1]

As shown in Table 1, the larger the paper basis weight, that is, the more rigid the paper, the more the backup roller 5
It can be seen that the smaller the diameter of FIG. 7 is, the better the paper releasability from the intermediate transfer belt is. In particular, the effect is remarkable when a sheet having a small basis weight is used or in a high-temperature and high-humidity environment (H / H environment) where the sheet absorbs moisture and the stiffness of the sheet becomes weak. Specifically, the diameter of the backup roller is preferably 30 mm or less, but this upper limit value must be appropriately adjusted according to the material of the intermediate transfer belt and toner, the type of paper, the use environment of the image forming apparatus, and the like. .

In the image forming apparatus of this embodiment, the diameter of the backup roller 5 is
If the diameter is larger than the diameter of the conventional image forming apparatus using an intermediate transfer drum (see FIG. 11), the releasability is equal to or less than that of the conventional image forming apparatus, and is meaningless. At this time, if the diameter of the backup roller 5 is simply reduced, the paper entering angle θ is increased, so that the toner is easily scattered. Therefore, it is preferable to make the paper entering angle θ sufficiently small (preferably about 10 degrees) and make the diameter of the backup roller 5 smaller than the diameter of the primary transfer roller. In the present embodiment, as shown in FIG. 9, a sheet conveyance unit such as a paper chute is configured to enter a sheet formed by a portion of the intermediate transfer belt 2 toward the secondary transfer position S and a sheet 6 toward the secondary transfer position S. An angle θ is a sheet separation angle φ between a portion of the intermediate transfer belt 2 away from the secondary transfer position S and a sheet 6 that receives the transfer of the multicolor toner image at the secondary transfer position S and leaves the secondary transfer position S. By designing the transport path of the paper 6 so as to be smaller than that, it is possible to achieve both image quality and paper releasability as described below.

Table 2 is a table showing the relationship between the image quality, the paper peeling property, the paper peeling angle φ, and the paper entering angle θ.

[0042]

[Table 2]

As shown in Table 2, by setting the paper peeling angle φ to be larger than the paper entering angle θ, an image forming apparatus with less toner scattering and good paper peeling properties can be realized.

[0044]

As described above, according to the image forming apparatus of the present invention, the intermediate transfer belt continuously moves from before the primary transfer position on the most upstream side in the circulating movement direction of the intermediate transfer belt to after the primary transfer position on the most downstream side. Since the primary transfer is performed on the support member that supports the intermediate transfer belt, it is possible to prevent a color shift from occurring in the multicolor toner image formed by sequentially superimposing the toner images of each color.

Further, by using the primary transfer roller as the support member and driving the intermediate transfer belt by the primary transfer roller, the design constraints of the image forming apparatus are reduced, and the degree of freedom in miniaturizing the image forming apparatus is reduced. Can be increased. Further, when the sheet conveying means is configured so that the sheet entrance angle is smaller than the sheet peeling angle, it is possible to realize an image forming apparatus that prevents scattering of toner and improves sheet peelability. .

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a process in which a toner image is primarily transferred from each image forming unit to an intermediate transfer belt.

FIG. 3 is a diagram showing an apparatus for measuring a speed fluctuation of an intermediate transfer belt.

FIG. 4 is a graph showing a measurement result of a surface speed of an intermediate transfer belt when a primary transfer roller is driven.

FIG. 5 is a graph showing a measurement result of a surface speed of an intermediate transfer belt when a backup roller is driven.

FIG. 6 is an enlarged view near a secondary transfer position in the embodiment.

FIG. 7 is a schematic diagram of an apparatus for testing the effect of a sheet entering angle on a secondary transfer position.

FIG. 8 is a graph showing a relationship between a sheet entering angle θ and a toner scattering evaluation value.

FIG. 9 is a schematic diagram illustrating the behavior of toner near the secondary transfer position S.

FIG. 10 is a schematic view of an intermediate transfer type image forming apparatus in a conventional example.

FIG. 11 is a schematic view of an intermediate transfer type image forming apparatus in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Intermediate transfer belt 2 'Intermediate transfer drum 3 Primary transfer roller 4 Primary transfer power supply 5 Backup roller 6 Paper 7, 7a, 7b, 7c Paper chute 8 Secondary transfer roller 9 Secondary transfer power supply 10 Fixing device 11, 12, 13, 14 Image forming unit 11a, 12a, 13a, 14a Image carrier drum 15 Secondary transfer device 16, 17 Stepping motor 16a, 17a Pulley 16b, 17b Timing belt

Claims (5)

[Claims] 1. A plurality of image carriers for forming a toner image of any one of a plurality of color toner images formed on a surface thereof and conveying the formed toner images to respective primary transfer positions. Receiving the primary transfer of each toner image such that the toner image formed on each image carrier is sequentially superimposed while circulating at or near each image carrier at each primary transfer position. A multicolor toner image is formed on the surface of the intermediate transfer belt, and the multicolor toner image is conveyed to a predetermined secondary transfer position. Each toner image formed on each image carrier is placed on the intermediate transfer belt. A primary transfer unit for performing primary transfer; and a portion of the intermediate transfer belt, on the surface of which the multicolor toner image is formed, from the back side of the intermediate transfer belt, the intermediate transfer belt of the plurality of image carriers. A support member that continues to support from before the timing of receiving primary transfer from the image carrier located on the most upstream side in the circulation movement direction to after the timing of receiving primary transfer from the image carrier located on the most downstream side in the circulation movement direction, A sheet conveying unit that conveys a sheet to which a multicolor toner image is transferred to the secondary transfer position; and a multicolor toner image on an intermediate transfer belt that is conveyed to the secondary transfer position. An image forming apparatus comprising: a secondary transfer unit that performs secondary transfer on a sheet conveyed to a position. 2. The image forming apparatus according to claim 1, wherein the supporting member is a roller that rotates in contact with the back surface of the intermediate transfer belt, and the plurality of image carriers are arranged in an arc along the roller. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer belt is driven by rotation of the roller. 4. The image forming apparatus according to claim 1, wherein an angle formed between a portion of the intermediate transfer belt toward the secondary transfer position and a sheet toward the secondary transfer position is equal to or smaller than the secondary transfer position of the intermediate transfer belt. The sheet is to be conveyed so as to form an angle smaller than the angle formed between the portion separated from the transfer position and the sheet separated from the secondary transfer position after receiving the transfer of the multicolor toner image at the secondary transfer position. The image forming apparatus according to claim 1, wherein: 5. The image forming apparatus according to claim 1, further comprising a second roller having a diameter smaller than that of the roller for supporting the intermediate transfer belt from a back surface at the secondary transfer position.