JPH08137183A - Color image forming device - Google Patents

Abstract

PURPOSE: To realize a color output device low in running cost and high in image quality. CONSTITUTION: By constituting the surface roughness of an image carrier 12, an intermediate transfer belt 19 and an image receiving paper 37 so as to be successively higher, the occasion being in contact with toner is increased, and mechanical power acting among toners is weakened to obtain an excellent color image without partial omission. In the case a toner image is retransferred from the belt 19 to the image receiving paper 37, the partial omission is avoided, high efficiency transfer is realized and an excellent color image is obtained by constituting so that the center of a nip constituted by the belt 19 and a transfer roller 28 may not exist on a plane including the center shaft of the transfer roller 28 and the center shaft of a roller for backing up the roller 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a printer, and more particularly to a color image device.

[0002]

2. Description of the Related Art In recent years, documents have been created and edited using color displays in offices by enhancing the equipment centering on personal computers. However, an output device that prints a created sentence on paper is mainly a monochrome machine. The reason for this is that the existing color output device has major problems in terms of performance and price. The electrophotographic color output device can also print on plain paper.
It has excellent advantages such as excellent halftone reproduction and high printing speed, but since the device is complicated, maintenance is expensive,
The cost is 10 to 50 times higher than that of a black-and-white output device, so that it is not popular enough.

An electrophotographic color output device optically or electrically color-separates an original image, forms a latent image corresponding to each color of yellow, magenta, and cyan, and then charges powder particles (corresponding to each color). The process of visualizing with toner is the same as in a black and white machine. What is most different from the black-and-white machine is the step of superposing each of these colors on the transfer material.

FIG. 3 shows a schematic configuration of a conventional color output device disclosed in JP-A-6-19331 and JP-A-6-19332. In FIG. 3, reference numeral 50 is a photosensitive drum, 51 is an exposing means, 52 is a developing device provided with a group of rotatable developing devices of yellow (Y), magenta (M), cyan (C), and black (BK), 54 is a corona discharger, 56
Is a transfer drum and is made of a dielectric or resistor film. 58 is a cleaning means, 60 is a conveyor belt, and 62
Is a fixing device, and 64 is a paper feed roller. Next, the operation will be described. A color original is read by an image scanner (not shown) to obtain yellow, magenta, cyan, and black information.
These pieces of information are temporarily stored in the memory. To form a color image, color signals are sequentially sent to the illustrated apparatus. First, the exposure unit 51 forms a yellow latent image on the photosensitive drum 50. The latent image formation is similar to that of a normal monochrome output device. The developing device 52 rotates to press the yellow (Y) developing device against the photosensitive drum 50 to visualize the latent image with yellow toner. The image receiving paper is supplied onto the transfer drum 56 by the paper feed roller 64 in synchronization with the image formation and is attracted by the electrostatic force. The yellow image on the photosensitive drum 50 is transferred onto the image receiving paper by the transfer charger 57. The photosensitive drum 50 after the transfer is cleaned by the cleaning device 58.
The transfer residual toner is removed by, and the toner is charged by the corona discharger 54, and the next latent image is formed. When all the images of the yellow signal are transferred onto the image receiving paper, the magenta (M) image formation is performed similarly to the case of yellow. Following the magenta image formation, cyan and black image formation are sequentially performed. The image receiving paper on the transfer drum 56 is yellow,
The magenta, cyan, and black images are sequentially superimposed, and at the same time when the black image formation is completed, the image receiving paper is peeled off from the transfer drum 56, passes through the transfer belt 60, and reaches the fixing device 62.
It is fixed to obtain an image.

Different from the above-mentioned color image forming method, in consideration of the paper passing property of the image receiving paper, for example, Japanese Patent Laid-Open No. 2-18327.
No. 6 discloses a toner image formed on an image carrier,
A method is disclosed in which four colors are held on an intermediate transfer belt and then collectively transferred to an image receiving paper. This system uses a belt-shaped image bearing member with a long circumference, a developing device is arranged around this image bearing member, and a developing device is pressed against the image bearing member for each color to form a toner image, and then an intermediate transfer is performed. Transfer to the belt. Two
After the color, toner images are superposed on the intermediate transfer belt.
Toner images of a plurality of colors are formed on the intermediate transfer belt and then collectively transferred to the image receiving paper.

[0006]

In the color image forming method described above, the image receiving paper is wound around the transfer drum to form three color images and a black image. For this reason, since the image receiving paper is adsorbed to the transfer drum and is separated from the transfer drum, the image receiving paper path becomes complicated and causes paper jam. In particular, adsorption and peeling using electrostatic force depend on the usage environment and the physical properties of the image receiving paper, and thus lack stability and impair reliability. The above method has an advantage that the deterioration of the image can be minimized because the image is directly transferred from the photosensitive drum to the image receiving paper, but the holding of the image receiving paper is complicated and the maintenance cycle is increased and the cost is increased. , Color output devices are not popular. It is believed that the image will be dramatically popularized by simplifying the path of the image receiving paper and maintaining high image quality.

In the system in which the toner image is temporarily transferred from the image carrier to the intermediate transfer medium and then retransferred to the image receiving paper, the toner images of four colors are superposed on the intermediate transfer medium, so that the toner layer becomes thick and There is no layer, or a pressure difference with a thin area is likely to occur. Therefore, due to the toner aggregating effect, the "blankhole" phenomenon in which a part of the image is not transferred and becomes a hole is likely to occur. Furthermore, if a material having a high toner releasing effect is used for the intermediate transfer medium in order to reliably perform cleaning when the image receiving paper is jammed, hollow defects will appear remarkably and the image quality will be significantly deteriorated.

[0008]

In order to solve the above problems, the present invention is a color image forming apparatus having the following constitution.

A plurality of moving image forming units arranged in an annular shape, each of which includes at least an image carrier that rotates, a charging unit that charges the image carrier, and a developing unit that has a developer of a different color. Possible image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the image formation each time the toner image is transferred to the intermediate transfer belt. By moving the unit group around the rotation center, a moving unit that changes the image carrier in contact with the intermediate transfer belt,
And a conductive transfer roller for retransferring the toner image held in a state of being superposed on the intermediate transfer belt to the image receiving paper by pressing the image receiving paper against the intermediate transfer belt. 10-point average roughness of body (Rz1)
And 10-point average roughness (Rz2) of the intermediate transfer belt
And the 10-point average roughness (Rz3) of the image receiving paper has the following relationship.

Rz1 <Rz2 <Rz3, or an image forming unit having an image carrier that rotates at least, a charging unit that charges the image carrier, and a developing unit that has a developer of a different color. A plurality of movable image forming unit groups arranged in an annular shape, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image transferred to the intermediate transfer belt. By moving the image forming unit group around the rotation center each time, the moving means for changing the image carrier in contact with the intermediate transfer belt and pressing the image receiving paper against the intermediate transfer belt, The pressing force of the conductive transfer roller that retransfers the toner image held in a state of being superposed on the intermediate transfer belt to the image receiving sheet and the pressing force of the transfer roller is set to the intermediate transfer belt. A backup roller for supporting from the back surface of the transfer roller, and the center of the nip formed by the intermediate transfer belt and the transfer roller is not within a plane including the central axis of the transfer roller and the central axis of the backup roller. Is a color image forming apparatus.

[0011]

In order to simplify the image receiving sheet passage of the color image forming apparatus, the image corresponding to each color is temporarily held on the intermediate transfer belt and then retransferred to the image receiving sheet at once. With this method, it is possible to realize an image receiving paper conveyance path equivalent to that of a conventional black and white image forming apparatus, and reduce the frequency of occurrence of image receiving paper jams.

In the system using the intermediate transfer belt, transfer of the toner image from the image carrier to the intermediate transfer belt, retransfer from the intermediate transfer belt to the image receiving paper, and double transfer are performed. These transfers are performed by bringing the transfer member into contact with the transfer target and using electrostatic force and pressure, so that part of the characters are not transferred due to electrical discharge and uneven pressure, resulting in image deterioration called "middle void". Cheap. Particularly, the toner image is attached to the image carrier or the like by a large mechanical force in addition to the electrostatic force. Therefore, in order to perform good transfer, it is necessary to control the surface properties of the transferred material and the transfer material.

In the first aspect of the present invention, the surface roughness of the intermediate transfer belt was changed to examine the degree of occurrence of a hollow image in the image which occurs when the image is transferred from the image carrier to the intermediate transfer belt. Result is,
When the surface roughness of the transfer belt on which the toner image is transferred is larger than the surface roughness of the image carrier on which the toner image is transferred, the frequency of stopping the void is significantly reduced. This is because the slight unevenness on the surface of the intermediate transfer belt on which the toner image is transferred increases the chance of contact with the toner and the horizontal force.
Alternatively, it is considered to weaken the mechanical force between the toners. This is considered to be the same between the intermediate transfer belt and the image receiving paper. That is, by making the surface roughness of the image receiving paper larger than the surface roughness of the intermediate transfer belt, the mechanical force acting on the toner is weakened and good retransfer is performed.

The second aspect of the present invention is a method different from that of the first aspect of the present invention to prevent hollow defects when retransferring the toner image from the intermediate transfer belt to the image receiving paper. As described above, the voids can be prevented by reducing the mechanical force acting on the toner. According to the present invention, the center of the nip formed by the intermediate transfer belt and the transfer roller is not in the plane including the central axis of the transfer roller and the central axis of the backup roller, so that the intermediate transfer belt and the image receiving paper have a width. Since a slight unevenness on the surface of the image receiving paper increases the contacting machine with the toner, the cohesive force acting between the toners can be cut off and the hollow defects can be prevented.

[0015]

【Example】

(Embodiment 1) FIG. 1 is a schematic view of the configuration of a color image forming apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes an image forming unit, which has four colors of yellow, magenta, cyan, and black, and each has an image carrier 12 (diameter 30 mm), a charging roller 14, a developing device 16, and a cleaning blade 17.
It has. The image forming unit 10 is composed of two blocks: a developing section in which an image carrier 12 and a developing device 16 are combined, and a toner collecting section in which a charging roller 14 and a cleaning blade 17 are combined. The unit group of four colors can be rotated around the center of movement rotation of the unit group by the unit moving device 18. The image forming unit group is
When it is moved counterclockwise, the developing section is located at the bottom and the toner collecting section is located at the top at the image forming position. Reference numeral 20 denotes an exposure unit, which allows one unit in the image forming unit 10 to be exposed through a substantially parallel slit between the developing unit and the toner collecting unit of the image forming unit 10 and a reflecting mirror 21 near the center of rotation. Are arranged as follows. Reflection mirror 2
1 is fixed without rotating with the rotation of the image forming unit 10. Reference numeral 19 is an intermediate transfer belt having a circumference of 377 mm so that at least one A4 size image can be held.
Is. The intermediate transfer belt 19 is used by kneading a conductive filler in an insulating resin and forming a film with an extruder. In this embodiment, a polycarbonate resin (for example, Iupilon Z300 manufactured by Mitsubishi Gas Chemical Co., Inc.) 9 is used as the insulating resin.
5 parts of conductive carbon (for example, Ketjen black) was added to form a film. The thickness of the film was about 350 μm. An antioxidant, a dispersion aid, a release member and the like may be mixed in the resin. The resistance of this film was about 10 ⁷ to 10 ⁸ Ω · cm.

The surface roughness of the intermediate transfer belt 19 was about 3 to 5 μm as a 10-point average roughness after molding and the like. This surface roughness can be freely controlled by an abrasive such as sandpaper or polisher. Electric resistance is 10 ⁵ to 10 ¹¹ Ω
The cm range is effective. When it is less than 10 ⁵ Ω · cm, electric discharge occurs to the image carrier and a conductive roller that transfers an image to an image receiving paper described later. On the other hand, when it exceeds 10 ¹¹ Ω · cm, there arises inconveniences such as an increase in the resin ratio of the conductive portion forming the intermediate transfer belt 19, an increase in applied voltage, and a large environmental change. The intermediate transfer belt 19 is not limited to the configuration described above, and may be, for example, an insulating base material coated with a conductive layer. In this case, polyethylene terephthalate (PET), polyimide, polyamide, polyurethane or the like is used as the insulating substrate. As described above, the conductive layer is provided by dispersing a conductive filler in an insulating resin and spraying or dipping. The intermediate transfer belt 19 is stretched around a pressing roller 24, a stretching roller 26, and a driving roller 27. The pressure roller 24 has a diameter of 1
A foam sponge is provided on a 0 mm metal shaft, and the hardness is 30 ° or less on the JIS A scale. The conductive foam sponge layer is made by dispersing a conductive filler such as carbon in a rubber material such as polyurethane or EPDM or containing an ionic conductive material. The metal shaft of the pressing roller 24 is grounded. The diameter of the pressing roller 24 most affects the image quality when the toner image is transferred from the image carrier 12 onto the intermediate transfer belt 19. In this embodiment, the image carrier 12
Was 30 mm, and the diameter of the pressing roller 24 was adjusted so that the diameter ratio (the diameter of the transfer roller 24 divided by the diameter of the image carrier) was 0.6 or less. This is because when the diameter ratio of the pressing roller 24 exceeds 0.6, the intermediate transfer belt 19
This is because toner scatters around the upper transferred characters and the image quality is degraded.

The intermediate transfer belt is pressed by the separation / contact device while the image forming unit 10 is moving for color exchange.
4 is moved so as to be brought into contact with or separated from the image carrier 12 of the image forming unit 10, or the image forming unit 10 is located at a position where there is no toner image on the intermediate transfer belt 19.
Prevents damage to the toner image due to replacement of the toner.

28 is a transfer roller, which is an intermediate transfer belt 19
When the upper toner image is retransferred to the image receiving paper 37, the image receiving paper 37
Is a backup roller for pressing the intermediate transfer belt 19 to transfer the toner image. Transfer roller 28 is φ1
Elastic rubber made by adding conductive fillers such as lithium salt and carbon to polyurethane rubber on a 0 mm metal shaft,
Alternatively, it is made of a metal material integrally with the shaft. Outer diameter is φ
It is 19 mm. A roller made of a rubber material on a metal shaft has a resistance of about 10 ⁷ to 10 ⁹ Ω · cm.
The transfer roller 28 is transferring the toner image onto the intermediate transfer belt 19 while the toner image is being transferred from the image carrier.
Are separated from each other by a separating / contacting device (not shown), and when transferring to the image receiving paper 37, they contact the intermediate transfer belt 19 and a voltage having a polarity opposite to that of the toner is applied from the transfer power supply 30.

Reference numeral 26 denotes a tension roller, which has a diameter of 10 mm and is made of a metal roller. Reference numeral 27 denotes a drive roller for rotating the intermediate transfer belt 19, which is made of a metal roller and has a diameter of 16 mm and is grounded. 31 is the intermediate transfer belt 1
9 is an electrode for applying a voltage, and has a diameter of 10 in this embodiment.
A stainless steel rod of mm is used, and is driven to rotate as the intermediate transfer belt 19 rotates. The power supply position to the intermediate transfer belt 19 is from the contact position between the image carrier 12 and the intermediate transfer belt 19 to the downstream side where the intermediate transfer belt 19 rotates, that is,
Place it past the transfer nip. Intermediate transfer belt 19
Since it is composed of a resistor as described above, if a voltage is applied from the downstream side, the voltage on the upstream side of the transfer nip becomes lower and the toner jumps forward (toner flies before the transfer site and disturbs the image).
The phenomenon can be avoided. An intermediate transfer power source 32 is applied to the intermediate transfer belt 19. Same and opposite polarity of toner,
Flexible application is possible.

Reference numeral 34 denotes an image receiving paper 37 from the intermediate transfer belt 19.
This is a cleaning device for removing the unnecessary toner remaining on the surface after the transfer to the. Cleaning device 3
4 is a cleaning roller 3 similar to the transfer roller 28.
5 is brought into contact with the intermediate transfer belt 19 and a voltage having a polarity opposite to the charging polarity of the toner is applied to remove the toner on the intermediate transfer belt 19. The cleaning roller 35 may be made of a metal material, or a conductive rubber material may be provided on the metal shaft. The toner attached to the surface of the cleaning roller 35 is scraped off by a scraper and collected in a toner reservoir in the cleaning device 34. However, in the sequence, a reverse polarity voltage is applied after the transfer of the toner image on the intermediate transfer belt 19 to the image receiving paper 7 is completed, and in other cases, that is, color superimposition is performed on the intermediate transfer belt 19. During that time, a voltage having the same polarity as the toner is applied to the cleaning roller 35 so that the toner is not collected. Alternatively, a device may be provided that separates and contacts the entire cleaning device 34 from the intermediate transfer belt 19 and may be separated and contacted when cleaning is unnecessary.

Reference numeral 38 denotes a paper feed roller which feeds the image receiving paper 37 one by one from the cassette tray. The manual paper feed roller 40 is a roller for feeding paper that is not set in the cassette. A timing roller 42 is a roller that is in contact with the metal roller 43 and sends out the fed image receiving paper 37 to the transfer portion according to the image signal. A scraper for removing paper dust is attached to the metal roller 40. A fixing device 46 fixes the toner image on the image receiving paper 37 that has been transferred. After the fixing process, the image receiving paper 37 is ejected outside the machine. Image carrier 1 of each unit
2 rotates at a speed of 33 mm / s. The appropriate speed difference between the image carrier 12 and the intermediate transfer belt 19 is about 1 to 5%. The transfer roller 28 and the intermediate transfer belt 19 also rotate at almost the same speed difference.

The intermediate transfer belt 19, the pressing roller 24, the stretching roller 26, the driving roller 27, the electrode 31, and the cleaning device 34 are integrated into a unit. As shown in FIG. 1, the pressing roller 24 side is set to a length that makes it easier for the entire unit to be taken in and out than the length between the stretching roller 26 and the driving roller 27, and the manual feed roller shown in the dotted line on the right side in FIG. By mounting the 40, the timing roller 42, the metal roller 43, the transfer roller 28, and the fixing device 46 on the opening / closing lid of the color image forming apparatus, the unit can be easily pulled out to the transfer roller 28 side. When this unit is pulled out to the side of the opening / closing lid (front side of the apparatus) and when it is pulled out in the axial direction of the image carrier 12, it is easy to design a positioning mechanism and an avoidance mechanism for preventing damage to devices such as the image carrier 12, and at the same time. Maintainability is greatly improved.

The operation will be described with reference to FIG. The process of printing a color image will be described. When printing a color image, images are formed in the order of yellow (Y), magenta (M), cyan (C), and black (BK). First, when a yellow image signal is sent, the image forming unit 10 rotates and rotates until the yellow image forming unit 10 contacts the intermediate transfer belt 19 at a horizontal position. The intermediate transfer belt 19 contacts the image carrier 12 in synchronization with the movement of the yellow image forming unit 10 to the image forming position. The exposure device 20 emits a laser beam corresponding to a yellow image signal, and charges the same as a normal black-and-white printer.
The latent image is formed and developed, and then visualized. In this embodiment, the image carrier 12 is negatively charged, and the toner is also negatively charged. The yellow toner image is transferred onto the intermediate transfer belt 19 to which a voltage is applied via the electrode 31 by the intermediate transfer power supply 32. The applied voltage at this time was + 200V. The transfer roller 28 keeps a state in which no voltage is applied so as not to disturb the toner image on the intermediate transfer belt 19 and separates from the intermediate transfer belt 19.

When the image formation for one screen is completed, the intermediate transfer belt 19 is temporarily stopped at the position where the portion not holding the toner image comes into contact with the image carrier 12. The stop position on the intermediate transfer belt 19 is about 80 mm between the leading edge and the rear end when the A4 size image is fed vertically, and the distance from the charging position of the image forming unit 10 to the transfer position is considered. To set. During the series of operations for transferring the toner image to the intermediate transfer belt 19, the cleaning roller 35 of the cleaning device 34 is applied with the same polarity and voltage as the transfer roller 28, and the toner on the intermediate transfer belt 19 is applied to the cleaning device 34. The image is never recovered. When the intermediate transfer belt 19 stops, the group of image forming units 10 rotates and moves to a position where the next magenta image forming unit 10 can contact the intermediate transfer belt 19. When the rotational movement of the unit is completed, a magenta toner image is formed on the image carrier 12 through the same process as the yellow image formation, and the intermediate transfer belt 19 is aligned with the front end of the yellow image and the intermediate transfer is performed. The belt 19 starts to rotate again,
A voltage of about +300 V is applied from the power source 30 for the intermediate transfer belt, and the magenta toner image is transferred onto the yellow toner image on the intermediate transfer belt 19 in an overlapping manner. The transfer roller 28 is the intermediate transfer belt 19 as in the case of yellow transfer.
Remains separate from. Since a voltage higher than that at the time of yellow transfer is applied to the intermediate transfer belt 19, the yellow toner previously transferred to the image carrier 12 of the magenta image forming unit 10 does not reversely transfer. Similarly, a cyan image of +350 V is applied to the intermediate transfer belt 19,
A cyan image is superimposed on the yellow and magenta toner images and transferred. The transfer roller 28 remains separated as in the case of yellow and magenta. When the black toner image of the fourth color is transferred by applying a voltage of +400 V to the intermediate transfer belt 19, the transfer roller 28 shifts the timing to a portion of the intermediate transfer belt 19 where there is no toner image (slightly before the leading edge of the image portion). Together, they contact the intermediate transfer belt 19. Almost at the same time + 1000V which is opposite to the charging polarity of toner
Is applied. During the transfer of the black image of the fourth color from the image carrier 12 onto the intermediate transfer belt 19, retransfer to the image receiving paper 37 is also being performed at the same time. After the image receiving paper 37 is fed by the paper feed roller 38 or the manual paper feed roller 40, the timing roller 42 aligns the timing with the leading edge of the image on the intermediate transfer belt 19. When all the toner images on the intermediate transfer belt 19 are retransferred to the image receiving paper 37, the transfer roller 2
8 is again brought into contact with and separated from the intermediate transfer belt 19. At this time, +400 applied to the intermediate transfer belt 19 at the time of transferring the black image.
V remains applied. The image receiving paper 37 on which the toner images of four colors are placed is fixed by the fixing device 46 and the toner is ejected to the outside of the machine.

While the toner images of the respective colors are superposed and transferred onto the intermediate transfer belt 19, the cleaning device 34 remains in contact with the intermediate transfer belt 19, but a voltage of about -300 V is applied to the cleaning roller 35. By doing so, the toner image on the intermediate transfer belt 19 can be held without being disturbed. However, since the toner remaining on the intermediate transfer belt 19 without being retransferred to the image receiving paper 37 and the toner adhering to the outside of the width of the image receiving paper 37 remain, the cleaning device 3
A voltage of about + 1000V is applied to the cleaning roller 35 of No. 4 because it has a positive polarity which is the opposite polarity to the charging polarity of the toner
The toner remaining on the intermediate transfer belt 19 is cleaned at least while the intermediate transfer belt 19 makes one round. After this cleaning operation, the unit was changed from the black image forming unit 10 to the yellow image forming unit 10,
At the same time, the voltage applied to the transfer belt 19 is switched from the transfer voltage of the black toner image + 400V to the transfer voltage of the yellow image + 200V, the image carrier 12 of the yellow image forming unit 10 contacts the intermediate transfer belt 19, and the same operation is performed. A new image is formed by.

The transfer voltage applied to the transfer roller 28 is
The state of the image receiving paper 37, for example, low in a high temperature and high humidity environment,
Further, it may be set higher in a low temperature and low humidity environment so that optimum retransfer can be obtained. This is because the resistance fluctuation of the resistance layer of the transfer roller 28 is absorbed. Similarly, from the image carrier 12 of the image forming unit 10 to the intermediate transfer belt 19
The voltage applied to the intermediate transfer power supply 32 at the time of transferring the toner image may be adjusted according to the environment. For these adjustments, a humidity sensor and a temperature sensor may be arranged in the machine, and after the reading, the adjustment may be performed according to a predetermined program.

A color image can be obtained by the above operation, but an image such as a character or a vertical line where pressure is likely to concentrate is formed on the image carrier 1.
2. Depending on the surface roughness of the intermediate transfer belt 19 and the image receiving paper 37, a hollow portion occurred. The hollow image occurs when the image is transferred from the image carrier 12 to the intermediate transfer belt 19 or when the image is retransferred from the intermediate transfer belt 19 to the image receiving paper 37. Table 1 summarizes the surface roughness (10-point average roughness) of each of the image carrier 12, the intermediate transfer belt 19, the image-receiving paper 37, and the occurrence of a void.

[0028]

[Table 1]

The surface roughness of the image carrier 12 and the image receiving paper 37 is not intentionally changed. The image receiving paper 37 is generally called plain paper and has a basis weight of 50 to 90 g / m ² . A vertical line with a line width of about 100 μm was used for the evaluation of voids.
Indicates a good image with no voids, Δ indicates a little, and x indicates a large number. From this result, it was found that an image with good voids cannot be obtained unless the surface roughness of the side receiving the transfer of the toner image is larger than the surface roughness of the side transferring the image.

FIG. 2 is an enlarged sectional view showing the retransfer portion from the intermediate transfer belt 19 to the image receiving paper 37 in the second embodiment. 2A shows the case where the center of the nip formed by the intermediate transfer belt 19 and the transfer roller 27 is in a plane including the central axis of the drive roller 27 and the central axis of the transfer roller 28 (nip center (A)). , (B) show the case where the nip is not in the plane including the central axis of the driving roller 27 and the central axis of the transfer roller 28 (nip center (a)). As the state of FIG. 2B approaches, the time for the image receiving paper 37 and the intermediate transfer belt 19 to contact each other becomes longer, so the slight unevenness of the surface of the image receiving paper increases the contact machine with the toner, and the toner It is expected to break the cohesive force that acts in between. Table 2 summarizes the situation of occurrence of voids comparing the cases of (a) and (b). The symbols have the same meanings as in Table 1. The surface roughness of the intermediate transfer picture belt 19 used is about 5-1 in terms of 10-point average roughness.
2 μm. Further, the position of (a) is set to about 20 mm below the position of (a).

[0031]

[Table 2]

As is clear from Table 2, it is better to shift the horizontal plane. Further, the transfer efficiency in FIG. 2 (b) was much better, and a good image was obtained.

[0033]

INDUSTRIAL APPLICABILITY As described above, the present invention forms an image with an image carrier that rotates at least, a charging unit that charges the image carrier, and a developing unit that has developers of different colors. A plurality of movable image forming unit groups in which the units are arranged in an annular shape, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by these image forming unit groups, and a toner image on the intermediate transfer belt. Moving means for rotating and moving the image forming unit group around the center of rotation for each transfer, and toner for holding the image receiving paper against the intermediate transfer belt in a state of being superposed on the intermediate transfer belt. A color image forming apparatus having a conductive transfer roller for retransferring an image onto an image receiving paper, wherein the 10-point average roughness (Rz1) of the image carrier of the image forming unit and the 10-point average of the intermediate transfer belt are used. Rough (Rz2) and the 10-point average roughness (Rz3) of the image receiving paper have a relationship of Rz1 <Rz2 <Rz3, or in a similar color image forming apparatus, an intermediate transfer belt and a transfer roller are used. It is an object of the present invention to provide a color image forming apparatus in which the center of the formed nip is not in a plane including the central axis of the transfer roller and the central axis of the backup roller.

As described above, the surface roughness of the image carrier, the intermediate transfer belt, and the image receiving paper is gradually increased, so that the chances of contact with the toner are increased and the mechanical force acting between the toners is increased. To obtain a good color image with no voids. When the toner image is retransferred from the intermediate transfer belt to the image receiving paper, the center of the nip formed by the intermediate transfer belt and the transfer roller is within a plane including the central axis of the transfer roller and the central axis of the roller that backs up the central axis of the transfer roller. By adopting the constitution which does not exist in the above, it is possible to realize a high-efficiency transfer without a hollow portion and to obtain a good color image as in the above.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view of a retransfer portion of a toner image from the intermediate transfer belt of the color image forming apparatus to the image receiving paper in the second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional color output device.

[Explanation of symbols]

 10 image forming unit 12 image carrier 14 charging roller 16 developing device 17 cleaning blade 19 intermediate transfer belt 20 exposure means 24 pressing roller 28 transfer roller 30 transfer power supply 32 intermediate transfer power supply 34 cleaning device 35 cleaning roller 37 image receiving paper 38 paper feed roller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hajime Yamamoto Hajime Yamamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A plurality of annularly arranged image forming units each including at least a rotatable image bearing member, a charging unit for charging the image bearing member, and a developing unit having a developer of a different color. A movable image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image is transferred to the intermediate transfer belt every time the toner image is transferred to the intermediate transfer belt. By moving the image forming unit group around the rotation center to change the image carrier in contact with the intermediate transfer belt, and by pressing the image receiving paper against the intermediate transfer belt, A conductive transfer roller for retransferring the toner images held in a superimposed state onto the image receiving paper, and a 10-point average roughness (Rz1) of the image carrier and the intermediate transfer. 10-point average roughness belt and (Rz2), the color image forming apparatus 10 point average roughness of the image receiving paper (Rz3) is the following relationship. Rz1 <Rz2 <Rz3 2. A plurality of annularly arranged image forming units each including at least a rotatable image bearing member, a charging unit for charging the image bearing member, and a developing unit having a developer of a different color. A movable image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image is transferred to the intermediate transfer belt every time the toner image is transferred to the intermediate transfer belt. By moving the image forming unit group around the rotation center to change the image carrier in contact with the intermediate transfer belt, and by pressing the image receiving paper against the intermediate transfer belt, A conductive transfer roller for retransferring the toner images held in an overlapping state to the image receiving paper and a bar for supporting the pressing force of the transfer roller from the back surface of the intermediate transfer belt. A color image forming apparatus including a backup roller and a center of a nip formed by the intermediate transfer belt and the transfer roller is not within a plane including a central axis of the transfer roller and a central axis of the backup roller. .