JP2003270965A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably obtain an excellent-quality image while realizing the reduction of cost, miniaturization and space saving. <P>SOLUTION: The image forming apparatus is equipped with an image forming carrier 1 an image forming means 2 forming an image G on the carrier 1 so that the image G is carried on the carrier 1, an intermediate transfer body 3 to which the image G on the carrier 1 is primarily transferred, and a transfer means 4 where a primary transfer area m1 for transferring the image G on the carrier 1 to the transfer body 3 and a secondary transfer area m2 for transferring the image G on the transfer body 3 to a recording medium 5 are set at opposed parts to the carrier 1 and the transfer body 3. Furthermore, a basic unit 6 for forming a monochrome image (referring to figure 2(a)) can be separated from an optional unit 7 (referring to figure 2 (b)) added to the unit 6 or added thereto after it is partially replaced. <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 such as a copying machine, a printer or a facsimile, and more particularly, to an intermediate unit for transferring an image formed on an image forming carrier onto a recording medium via an intermediate transfer member. The present invention relates to improvement of a transfer type image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an intermediate transfer type image forming apparatus of this type, for example, yellow (Y), magenta (M), cyan (C) and black (around an image forming carrier such as a photosensitive drum). K) is provided with a developing device for each color component, and a belt-shaped intermediate transfer member (intermediate transfer belt) is arranged opposite to the image forming carrier, and the image forming carrier is rotated every one rotation. After the primary transfer of the unfixed toner images of the respective color components formed on the intermediate transfer belt in sequence, the composite primary transfer image superimposed on the intermediate transfer belt is secondarily transferred to a sheet as a recording medium to obtain the desired image. It is known that a sheet is formed on a sheet (see, for example, Japanese Patent Application Laid-Open No. 2-212870).

Here, as the secondary transfer device, for example, a transfer roll arranged in contact with the intermediate transfer belt, a backup roll arranged opposite to the transfer roll with the intermediate transfer belt interposed therebetween, and these transfer rolls and backups. A roller and a power source for applying a bias for forming an electric field for transferring the toner image on the intermediate transfer belt onto the sheet are used between the roller and the roll. According to this type, since the composite primary transfer image already multi-transferred on the intermediate transfer belt is collectively transferred onto the sheet, it is possible to eliminate an unstable factor at the time of image formation, and it is possible to eliminate an unstable factor at the time of multiple transfer. This has an advantage that it is possible to effectively prevent the occurrence of image disturbance and color shift.

[0004]

However, in the above-mentioned intermediate transfer type image forming apparatus, the secondary transfer apparatus is indispensable in addition to the primary transfer apparatus. Since the functional member (transfer roll), which is relatively expensive, must be provided, the space and the number of parts dedicated to the secondary transfer device increase, which leads to an increase in size and cost of the image forming apparatus itself. That technical problem was found.

The present invention has been made to solve the above technical problems, and it is possible to stably obtain an image of good quality while achieving low cost, small size, and space saving. An image forming apparatus is provided.

[0006]

That is, according to the present invention, as shown in FIG. 1A, an image forming carrier 1 and an image forming means 2 for forming and carrying an image G on the image forming carrier 1. When,
The intermediate transfer body 3 onto which the image on the image forming carrier 1 is primarily transferred, the primary transfer area m1 for transferring the image G on the image forming carrier 1 to the intermediate transfer body 3, and the intermediate transfer body 3 on the intermediate transfer body 3. The secondary transfer area m2 for transferring the image G onto the recording medium 5 is provided with the transfer means 4 which is set at the facing portion of the image forming carrier 1 and the intermediate transfer body 3. As a typical usage of the present invention, for example, in the case of the color mode, as shown in FIGS. 1A and 1B, first, the image forming means 2 is formed on the image forming carrier 1. To sequentially form each color component image G by the image forming carrier 1
The respective color component images G above are sequentially primary-transferred onto the intermediate transfer body 3 by the transfer means 4 (used as a primary transfer cycle), and thereafter, as shown in FIG. The transfer image G may be secondarily transferred onto the recording medium 5 by the transfer means 4 (used as a secondary transfer cycle).

In such technical means, the image forming carrier 1 may be a single or plural. Further, the image forming carrier 1 and the intermediate transfer member 3 may be drum-shaped or belt-shaped, but it is preferable that either one is a belt-shaped member.
Further, the image forming means 2 may employ various image forming methods such as an electrophotographic method, an electrostatic recording method, and an inkjet method, and the formed image may include a single color or a color (two colors, full color, etc.).

Here, the intermediate transfer member 3 and the image forming carrier 1
In the mode in which any one of them is an endless belt-shaped member (in FIG. 1, the intermediate transfer member 3 is a belt-shaped member), the volume required for the image forming apparatus can be reduced. In addition, the degree of freedom of the contact width between the image forming carrier 1 and the intermediate transfer member 3 is increased, and a relatively large contact width can be secured, so that the transfer electric field can be stably applied. Like Furthermore, since the air gaps at both ends of the contact area between the image forming carrier 1 and the intermediate transfer member 3 can be reduced, the influence of the electric field in the air gap portion can be further reduced.

Further, in a mode in which either the image forming carrier 1 or the intermediate transfer member 3 is a belt-shaped member (in FIG. 1, the intermediate transfer member 3 is a belt-shaped member), the image forming carrier 1 and the intermediate transfer member 3 are transferred. It is preferable that the contact width with the body 3 is at least equal to or more than the circumferential length of the stretching roll 3a having the smallest diameter among the stretching rolls 3a stretching the belt-shaped member. According to this aspect, a minute speed cycle is generated in the intermediate transfer body 3 due to the eccentricity of the tension roll 3a of the intermediate transfer body 3 which is a belt-like member, and the intermediate transfer body 3 and the image forming carrier are utilized. A minute fluctuation cycle of the peripheral speed of the intermediate transfer member 3 (more precisely, the relative speed between the image forming carrier 1 and the intermediate transfer member 3) is caused to act in the contact area with the body 1 for at least one cycle, thereby The effect of mechanical shearing force can be obtained in the state where a defect such as a shift does not occur. Therefore, it is possible to obtain a good transfer efficiency while ensuring a high level of banding and color shift performance.

Further, in a mode in which either the image forming carrier 1 or the intermediate transfer member 3 is a belt-shaped member, it is preferable that the belt-shaped member has elasticity. In this case, it is possible to prevent image dropout due to an increase in transfer pressure.

In the transfer means 4, the primary transfer area m1 and the secondary transfer area m2 may be set at the facing portions of the image forming carrier 1 and the intermediate transfer member 3. Here, the term “opposing portion of the image forming carrier and the intermediate transfer member” is not limited to the case where the primary transfer area m1 and the secondary transfer area m2 are the same area, and the case where they are separately provided adjacent to each other. It is also intended to include such things as. The "transfer means 4" includes a wide range of means provided at the facing portion and used both for the primary transfer and the secondary transfer, and one for selectively selecting one transfer device or a plurality of transfer devices. It is possible to appropriately select a device for switching and selecting.

Further, as a preferred mode of use of the transfer means 4, there is one in which the transfer conditions are changed at least according to the image forming mode or the type of the recording medium 5. By changing the transfer conditions in this way, the transfer conditions can be optimized according to the image forming mode and the type of the recording medium 5. The term "change of transfer conditions" used here refers to changes in transfer bias, transfer current, etc., changes in which transfer device is used, changes in whether or not primary transfer is performed during the image forming cycle, etc. Including. For example, in a mode in which an image forming mode including at least a monochromatic mode and a color mode can be executed, a preferable execution condition of the monochromatic mode is that the transfer unit 4 does not perform the transfer operation to the intermediate transfer body 3 when the monochromatic mode is selected. What is directly transferred to the recording medium 5 may be used. According to this aspect, the primary transfer step is not necessary in the first place, and the sequence for omitting the step can be performed to shorten the image formation time in the single color mode.

Regarding the relationship between the primary transfer condition and the secondary transfer condition when the transfer device 4 is used, it is preferable that the transfer device 4 is used with different primary transfer conditions and secondary transfer conditions. This is because the transfer directions of the images are opposite between the primary transfer and the secondary transfer, and the targets to which the transfer electric field acts are different, so that it is necessary to make the respective transfer conditions different in principle. . However, in the case where there is a pressure condition that satisfies both the primary transfer and the secondary transfer in the pressure transfer system, both may be the same condition.

Here, as a typical mode of different transfer conditions, there is a transfer means 4 of a mode in which the primary transfer electric field and the secondary transfer electric field are set to opposite polarities. This is because the transfer directions of the images are reversed between the primary transfer and the secondary transfer, and therefore it is necessary to reverse the polarity of the transfer electric field when the electrostatic transfer method is adopted. The specific mode of polarity reversal can be appropriately selected, for example, by using one power supply unit by switching between positive and negative, or by switching and selecting a plurality of power supply units.

Further, as another typical mode under different transfer conditions, the transfer means 4 is used in which the transfer speed (corresponding to the process speed) is different between the primary transfer and the secondary transfer.
Is mentioned. According to this aspect, when thick paper or an OHP sheet is used as the recording medium 5, for example, lowering the transfer speed enables higher quality transfer.

From another point of view, the present invention can be understood as an image forming apparatus capable of upgrading from a single color (for example, black and white) machine to a color machine. In this case, the present invention is shown in FIG.
As shown in (b), the image forming carrier 1, the image forming means 2 for forming and carrying an image on the image forming carrier 1, and the image G on the image forming carrier 1 are primarily transferred. The transfer member 3 and the image G on the image forming carrier 1 are transferred to the intermediate transfer member 3
A transfer means in which a primary transfer area m1 for transferring to the recording medium 5 and a secondary transfer area m2 for transferring the image G on the intermediate transfer body 3 to the recording medium 5 are set at the facing portions of the image forming carrier 1 and the intermediate transfer body 3. 4 and a single-color image forming basic unit 6 (see FIG. 2A), and an optional unit 7 (see FIG.
(See (b)).

In this embodiment, the method of separating the basic unit 6 and the option unit 7 may be selected appropriately. As an example of the separation method, for example, the basic unit 6 includes an image forming carrier 1, an image forming unit 2 for forming and carrying an image G on the image forming carrier 1, and an image on the image forming carrier 1. Transfer means 4 for transferring G onto the recording medium 5
On the other hand, the option unit 7 is additionally provided in the image forming means 2 and is additionally provided between the image forming carrier 1 and the transfer means 4 and the option sub-unit 7a required for color image formation. The image forming carrier 1 including the optional intermediate transfer body 7b provided by the transfer means 4.
There is one in which the image G on the intermediate transfer body 3 is secondarily transferred to the recording medium 5 after the image G on the intermediate transfer body 7b (intermediate transfer body 3) is primarily transferred. In addition to this, the intermediate transfer body 3 is incorporated as the basic unit 6 and only the option subunit 7a is added, or the "option subunit 7" is added.
a + optional intermediate transfer member 7b + optional transfer unit (transfer unit is exchanged) "(assuming that the transfer unit is incorporated in the intermediate transfer unit in advance).

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. First Embodiment FIG. 3 shows the first embodiment of the image forming apparatus to which the present invention is applied.
Shows the overall configuration of. In FIG. 1, the image forming apparatus is an intermediate transfer type image forming apparatus, and includes a photosensitive drum 10 and an intermediate transfer belt 2 arranged in contact with the photosensitive drum 10.
It has 0 and. In the present embodiment, the photosensitive drum 10 is provided with a photosensitive layer whose resistance value is reduced by irradiation of light, and a charging device 11 for charging the photosensitive drum 10 is provided around the photosensitive drum 10. , An exposure device 12 for writing an electrostatic latent image of each color component (black, yellow, magenta, and cyan in this example) on the charged photoconductor drum 10, and each color component latent image formed on the photoconductor drum 10. Rotary developing device 13 that visualizes toner with each color component toner, the intermediate transfer belt 20, and the photoconductor drum 10.
A cleaning device 18 for cleaning the above residual toner is provided.

Here, as the charging device 11, for example, a charging roll is used, but a charging device such as a corotron may be used. The exposure device 12 may be any device that can write an image on the photoconductor drum 10 by light. In this example, a print head using an LED is used, but the present invention is not limited to this, and an EL device is used. Even with the conventional print head, a scanner that scans a laser beam with a polygon mirror may be appropriately selected. Furthermore,
The rotary type developing device 13 has developing devices 13a to 13d in which toners of respective color components are accommodated rotatably mounted, and, for example, attaches the toners of respective color components to a portion of the photosensitive drum 10 where the potential is lowered by exposure. Any suitable toner can be selected as long as it is used, and the toner to be used is not particularly limited in terms of shape and particle size, and any toner can be used as long as it can be accurately placed on the electrostatic latent image on the photosensitive drum 10. Although the rotary type developing device 13 is used in this example, four developing devices may be used. Furthermore, the cleaning device 18 may be appropriately selected, such as a device adopting a blade cleaning method, as long as it cleans the residual toner on the photosensitive drum 10. However, when a toner having a high transfer rate is used, the cleaning device 1
There may be a mode in which 8 is not used.

The intermediate transfer belt 20 may be made of resin, rubber or the like as appropriate, but in this embodiment, a resin material such as polyimide or polycarbonate resin is used. Here, the intermediate transfer belt 20 has a volume resistivity (for example, 10 ⁶
~10 ¹² Ω · cm) is required, also in consideration of the cleaning of the surface, it is preferable to provide a release layer on the surface.
Further, the intermediate transfer belt 20 is stretched over a plurality of (for example, four) stretching rolls 21 to 24, and in the present embodiment, one of the four stretching rolls 21 to 24 has a transfer position. The tension roll 21 located on the upstream side functions as, for example, a driving roll, and the tension rolls 22, 23, 24 located on the downstream side of the transfer position are all driven rolls.

Further, a transfer roll 31 as a transfer member is disposed in contact with the back side of the intermediate transfer belt 20, and the transfer roll 31 has a power supply unit 40 (see FIG. 4).
(See (a) and (b)) are connected, and the primary transfer bias or the secondary transfer bias is selectively applied. Here, the transfer roll 31 is a roll made of, for example, an elastic conductive member, and is made of, for example, urethane foam, acrylic foam, silicone foam, or the like. The conductivity is required to give the transfer charge, and the volume resistivity is preferably 10 ⁶ Ω · cm or less. Further, from the viewpoint of giving a stable charge and a stable pressing force at the time of transfer, the nip width that is as wide as possible is required, and in this sense, an embodiment using an elastic body is preferable. Further, the roll diameter may be, for example, 10 mm or more and 30 mm or less, and more preferably 12 mm or more and 20 mm or less. In the primary transfer, the toner on the photosensitive drum 10 is transferred to the intermediate transfer belt 20.
Since it is necessary to transfer to the side, the transfer roll 31
The reverse transfer voltage applied to the toner is used as the primary transfer bias applied to the intermediate transfer belt 2.
Since it is necessary to transfer the toner above 0 to the recording medium 50 side, the same polarity voltage as the toner is used as the secondary transfer bias applied to the transfer roll 31. The position where the transfer roll 31 is provided may be any position that allows conventional primary transfer, and is not particularly limited.

As the power supply unit 40 used in this embodiment, for example, as shown in FIG. 4 (a), one power supply 41 and two switching elements 42 for switching between positive and negative of the power supply 41, 43, and the aspect provided with 43. Here, the switching elements 42 and 43 switch positive and negative of the power source 41 in conjunction with each other, for example, in accordance with an image forming cycle, and apply a positive transfer bias during the primary transfer and a negative transfer bias during the secondary transfer. Works like. Further, as another mode of the power supply unit 40, as shown in FIG. 4B, for example, two power supplies 44 and 45 having different polarities and a switching element 46 for switching and selecting these power supplies 44 and 45 are provided. The switching element 46 applies a positive transfer bias of one power supply 44 at the time of primary transfer and a negative transfer bias of the other power supply 45 at the time of secondary transfer. Further, the primary transfer bias and the secondary transfer bias may be appropriately selected as long as they have different polarities, but in order to perform good transfer, the resistance of the paper as the recording medium 50 is lower than that of the intermediate transfer belt 20. Since the resistance is many times higher, it is preferable to set the absolute value level of the secondary transfer bias higher than that of the primary transfer bias.

A recording medium 50 such as paper is accommodated in a supply tray (not shown), and after being supplied by a feed roll 51, the photosensitive drum 10 and the intermediate transfer belt 2 are supplied.
It is guided to a portion (transfer portion) facing 0, and is conveyed to the fixing device 60. In FIG. 3, reference numeral 52 is a guide chute for guiding the recording medium 50 to the transfer portion, 53 is a guide plate for guiding the recording medium 50 on the intermediate transfer belt 20 to the fixing device 60, and 54 is the fixing device 6.
It is a shield plate for cutting off the heat of 0.

Further, in the present embodiment, the control device 70
5, the image forming mode (monochromatic mode, color mode, etc.) and the type of the recording medium 50 (plain paper, OHP)
Drive motor 71 of the photosensitive drum 10 according to the sheet).
(Figure M _D), the driving motor 72 of the intermediate transfer belt 20
(Figure M _B), sends a predetermined control signal to the power supply unit 40 or the like of the transfer roll 31, and controls the image forming condition and transfer conditions (see FIG. 6).

Next, the operation of the image forming apparatus according to this embodiment will be described. The single-color mode control device 70, when the single-color mode is selected, is set as shown in FIG.
As shown in (a), the P cycle is executed to form a monochromatic toner image (for example, a black and white image) on the photoconductor drum 10, and at the same time, the recording medium 50 (for example, plain paper) is conveyed to the transfer portion, and the monochromatic image is transferred. The toner image is transferred to the recording medium 50. At this time, in the P cycle, a predetermined process speed va is adopted, and Vt2 corresponding to the secondary transfer bias is selected as the transfer bias. As a result, in this monochromatic mode, the monochromatic toner image formed on the photoconductor drum 10 is
Instead of being primarily transferred to the intermediate transfer belt 20, it is directly transferred to plain paper as the recording medium 50, and the fixing device 6
It is fixed at 0. Incidentally, for example, the recording medium 50 to be printed
Of the recording medium 50 (for example, the print surface of the recording medium 50 is discharged face up or the print surface is discharged face down), the monochromatic image is transferred to the intermediate transfer belt. It is needless to say that the primary transfer to the recording medium 20 may be performed once and then the collective transfer to the recording medium 50.

Color Mode 1 (plain paper) When the color mode 1 (for example, a mode for selecting plain paper as the recording medium 50 in the full color mode) is selected, the control device 70 is as shown in FIG. 6 (b). After the Y cycle to the K cycle (primary transfer cycle of each color component), the P cycle is executed, and each color component (yellow (Y), magenta (M), cyan (C), A black (K) toner image is sequentially formed, and primary transfer is sequentially performed on the intermediate transfer belt 20. Then, the recording medium 50 (for example, plain paper) is conveyed to the transfer portion, and each color on the intermediate transfer belt 20 is transferred. The component toner image is transferred to the recording medium 50. At this time, a predetermined process speed va is adopted in all of the Y cycle to P cycle, and in the Y cycle to K cycle, Vt1 corresponding to the primary transfer bias is selected as the transfer bias, while Pt
In the cycle, Vt2 corresponding to the secondary transfer bias is selected as the transfer bias. As a result, in the color mode 1, the toner images of the respective color components formed on the photoconductor drum 10 are sequentially primary-transferred to the intermediate transfer belt 20, and then secondarily transferred and fixed to the plain paper as the recording medium 50. It is fixed by the device 60.

Color Mode 2 (OHP Sheet) When the control device 70 selects the color mode 2 (for example, a mode in which the OHP sheet (or thick paper) is selected as the recording medium 50 in the full color mode), the control device 70 in FIG. ), As in color mode 1, Y cycle to K
After executing the cycle (primary transfer cycle of each color component), the P cycle is executed. However, unlike the color mode 1, in Y cycle to K cycle, a predetermined process speed va is adopted and Vt1 corresponding to the primary transfer bias is selected as the transfer bias, while
In the P cycle, the process speed vb (vb <va) is adopted, and Vt2 corresponding to the secondary transfer bias is selected as the transfer bias. As a result, in the color mode 2, the toner images of the respective color components formed on the photoconductor drum 10 are sequentially primary-transferred onto the intermediate transfer belt 20 and then transferred to the OHP sheet as the recording medium 50 at a low process speed. Next transfer is performed, and thereafter, the image is fixed by the fixing device 60 at a low process speed. For this reason, transfer and fixing processing with good image quality can be realized on the OHP sheet.

Next, this embodiment will be compared with a comparative embodiment. Here, as a comparative form, for example, as shown in FIG. 7, the intermediate transfer belt 20 is arranged to face the photosensitive drum 10, and the primary transfer roll 81 is provided at the facing portion between the photosensitive drum 10 and the intermediate transfer belt 20. One of the stretching rolls 21 to 24 of the intermediate transfer belt 20 (for example, 24)
The secondary transfer roll 82 is disposed on the opposite side of the recording medium 50.
A sheet of paper is sent by a feed roll 51, is conveyed to a secondary transfer portion via a conveyance roll 55 and a resist roll 56, and is then conveyed to a fixing device 60 via a conveyance belt 57. In FIG. 7, reference numerals 58 and 59 denote guide plates for guiding the recording medium 50,
Reference numeral 61 denotes a shield plate for cutting off the heat of the fixing device 60. Further, the same components as those in the present embodiment are designated by the same reference numerals, and the detailed description thereof will be omitted here.

Referring to FIGS. 3 and 7, first, comparing the image forming times of the present embodiment and the comparative embodiment, in the present embodiment, in the case of the single color mode, the intermediate transfer belt 20.
Since it does not require a primary transfer cycle to the image forming cycle, the image forming cycle can be shortened as compared with the comparative mode. However, in the case of the color mode, the image forming time for P cycles is shorter than that in the comparative mode. , And the image forming cycle time is slightly sacrificed. However, in the present embodiment, since the transfer roll 31 realizes both primary transfer and secondary transfer, not only the secondary transfer roll 82 according to the comparative embodiment is unnecessary but also the tension roll of the intermediate transfer belt 20. 21-22
Since the space can be used as a part of the transport path of the recording medium 50, the transport space of the recording medium 50 can be reduced. In this embodiment, since the recording medium 50 passes through the surface of the intermediate transfer belt 20, paper dust or the like is likely to adhere to the intermediate transfer belt 20. The paper powder is effectively cleaned together with the residual toner.

[Second Embodiment] FIG. 8 shows a second embodiment of the image forming apparatus to which the present invention is applied. In the figure, the image forming apparatus includes a photosensitive drum 10 and an intermediate portion which contacts the photosensitive drum 10 along a shape of the photosensitive drum 10 in a certain region in order to transfer a toner image from the photosensitive drum 10. And a transfer belt 20. In the present embodiment, around the photoconductor drum 10, a charging device 11 that charges the photoconductor drum 10 and each color component (black, yellow, magenta, cyan in this example) on the charged photoconductor drum 10 are provided. Exposure device 12 for writing the electrostatic latent image, and four developing devices 14 to 17 for visualizing each color component latent image formed on the photoconductor drum 10 with each color component toner,
The intermediate transfer belt 20 and a cleaning device 18 for cleaning the residual toner on the photosensitive drum 10 are provided.

In this embodiment, the intermediate transfer belt 20 may be made of resin, rubber, or the like as appropriate. However, in order to effectively suppress image quality defects such as hollow characters, the intermediate transfer belt 20 and the photosensitive drum 10 may be selected. It is necessary to reduce the contact surface pressure, and in view of walklessness and tensionerlessness, it is preferable to use an elastic belt material based on elastic rubber or the like. In this case,
As the elastic belt material, a material having a Young's modulus of 100 MPa or less is usually used.
Volume resistance (for example, 10 ⁶ to 10 ¹² Ω · cm) is required for maintaining the transfer performance, and in consideration of the surface cleanability, a release layer is formed on the surface of the elastic base. It is preferable to provide. Here, as a preferable physical property value of the elastic substrate, one having a Young's modulus of 15 to 80 MPa is preferable in order to keep good transferability. As a good material, urethane rubber (soft type: 16.9MP
a), urethane rubber (hard type: 78.6Mp
a) and chloroprene rubber (16.2 Mpa). Conversely, as a material that is not preferable, PET (1.4
7 GPa) and PC (1.96 GPa).

Further, in the present embodiment, the intermediate transfer belt 20 is stretched over a plurality of (for example, four) tension rolls 21 to 24, and includes the developing devices 14 to 17 and the cleaning device 18. A predetermined contact area x is closely arranged along the surface of the photoconductor drum 10 located therebetween.
Here, in this embodiment, the four stretching rolls 21 to 2 are used.
4 is a driven roll, and each of the tension rolls 21 to 2
4, the tension roll 21 located upstream of the transfer position
Is set to have the largest winding angle of the intermediate transfer belt 20. In particular, in this embodiment, the photosensitive drum 1
The contact area x between 0 and the intermediate transfer belt 20 is ensured to be equal to or more than the circumferential length (πD: D is the diameter of the tension roll 21) of the tension roll 21 located on the upstream side of the transfer position. in this case,
When the diameter D of the tension roll 21 is smaller than that of the other tension rolls 22 to 24, the contact area between the two tension rolls is set to be the smallest, but not limited to this.

Further, in this embodiment, the photosensitive drum 1
As shown in FIG. 9, 0 is the drive motor 71 (reference M _D ).
The intermediate transfer belt 20 is driven and rotated by the photosensitive drum 10 as a drive source through the contact area x. Further, a transfer roll 31 is disposed in contact with the back side of the intermediate transfer belt 20 in a part of the contact area x where the intermediate transfer belt 20 is in close contact with the photosensitive drum 10. The power supply unit 40 is connected to the transfer roll 31. The primary transfer bias or the secondary transfer bias is selectively applied. Then, the control device 70, as shown in FIG. 9, in accordance with the type of image forming modes and recording medium 50, the driving motor 71 of the photosensitive drum 10 (in the figure M _D), the power supply unit 40 of the transfer roller 31 or the like A predetermined control signal is sent to control the image forming condition and the transfer condition (see FIG. 6).

A recording medium 50 such as paper is accommodated in a supply tray (not shown), and after being supplied by a feed roll 51, the photosensitive drum 10 and the intermediate transfer belt 2 are supplied.
It is guided to a portion (transfer portion) facing 0, and is conveyed to the fixing device 60. In FIG. 8, reference numeral 28 is a belt cleaning device using a cleaning roll, 62 is a guide plate for guiding the recording medium 50 to the transfer portion, and 63 is a fixing device 60 for fixing the recording medium 50 on the intermediate transfer belt 20. Guide plate to guide to 64
Is a guide plate for guiding the recording medium passing through the fixing device 60 to a discharge tray (not shown).

Next, the operation of the image forming apparatus according to this embodiment will be described. Single color mode, color mode 1 and 2
For, the image forming cycle similar to that of the first embodiment is performed. In the present embodiment as described above, a comparative mode 2 (FIG. 11) in which a secondary transfer device (secondary transfer roll 82) is provided separately from the primary transfer device (primary transfer roll 81).
Compared with (see), a space for disposing the secondary transfer device is not necessary, and the space for the transport path for the recording medium 50 can be reduced, so that the apparatus can be made smaller and smaller and the cost can be reduced. It is understood that it can be realized.
In FIG. 11, reference numeral 56 is a resist roll, 5
Reference numerals 8, 65, 65 are guide plates for guiding the recording medium 50 to a predetermined portion.

Further, in the above-described image forming process of the present embodiment, the speed of the intermediate transfer belt 20 fluctuates due to the deflection of the tension roll 21 and the eccentricity error, but in the contact area x, on the photosensitive drum 10. Of the toner image is separated from the intermediate transfer belt 20 by the mechanical shearing force, and moreover, in the contact area x, the photosensitive drum 10 and the intermediate transfer belt 2 are separated.
Almost no difference in peripheral speed from 0 occurs. Therefore, it is possible to easily obtain a beautiful color image without banding or color misregistration.

Further, in such an image forming process, in the contact area x between the photosensitive drum 10 and the intermediate transfer belt 20, the transfer electric field by the transfer roller 31 acts, but the transfer operation area of the transfer roller 31 is in the contact area. If it is set within x, the transfer electric field by the transfer roll 31 has no influence on the voids (air gaps) at both ends of the contact region x.
Therefore, the toner does not fly abnormally in the void portion, the toner image on the photosensitive drum 10 is reliably transferred to the intermediate transfer belt 20 side in the contact area x, and the toner on the intermediate transfer belt 20 is also transferred. The image is reliably transferred to the recording medium 50.

Further, although the original drive mechanism of the intermediate transfer belt 20 is omitted, the intermediate transfer belt 20 can be stably rotated in conjunction with the photosensitive drum 10,
In addition, it is possible to eliminate the original difference in peripheral speed as compared with the case where each has its own drive source. That is, when the photoconductor drum 10 and the intermediate transfer belt 20 each have a drive source, a peripheral speed difference occurs due to a rotation error of the drive source, an error of the drive transmission system, and the like, and the photoconductor drum 10 and the intermediate transfer belt 20.
There is a slip between and. Therefore, as in the present embodiment, the photosensitive drum 10 has a drive source only, and the intermediate transfer belt 20 is driven to rotate so that both speeds are the same, and accordingly, slippage between the two is suppressed. The transfer performance can be kept good. In particular, in the present embodiment, since the intermediate transfer belt 20 is an elastic belt provided with an elastic base having a predetermined Young's modulus, the driven rotation described above can be further stabilized.

Further, in the present embodiment, since the contact area x within the predetermined range is secured between the photosensitive drum 10 and the intermediate transfer belt 20, as shown in FIG. A plurality of transfer rolls 31 and 32 are disposed in a portion excluding both ends A and B of the power supply unit 40.
It may be configured to apply the primary transfer bias or the secondary transfer bias. In this case, both transfer rolls 31 and 32 may be used for both primary transfer and secondary transfer, or one transfer roll 31 may be used for primary transfer and the other transfer roll 32 may be used for secondary transfer. It can be selected appropriately. The positions where the transfer rolls 31 and 32 are disposed except for both ends A and B of the contact region x are that the transfer action area of the transfer rolls 31 and 32 is the contact region x.
Affects the air gap 90 existing at both ends of
This is to prevent toner from scattering due to abnormal discharge.

Third Embodiment FIGS. 12 and 13 show an image forming apparatus according to the third embodiment. The image forming apparatus according to the present embodiment can upgrade the single-color image forming apparatus to a color image forming apparatus in response to a user request. Here, FIG.
Reference numeral 2 denotes a monochromatic image forming apparatus according to this embodiment, which includes a monochromatic basic unit 100. The basic unit 100 includes a photosensitive drum 10, and a charging device 11, an exposure device 12, a monochromatic developing device 14 (a black developing device in this example), a transfer roll 31 are provided around the photosensitive drum 10.
And the cleaning device 18 are provided, and the recording medium 50 is conveyed to the transfer portion by the transfer roll 31, and the photosensitive drum 1
The monochromatic toner image formed on the recording medium 50 is transferred to the recording medium 50 and then guided to the fixing device 60.
In FIG. 12, reference numerals 121 to 123 denote the recording medium 5.
A guide plate for guiding 0, 124 is a part of the support frame, and reference numeral 50 'is a recording medium discharged to a discharge tray (not shown).

FIG. 13 shows a color image forming apparatus in which the single color image forming apparatus is upgraded, and the basic unit 100
In addition, the option unit 110 is added.
In the present embodiment, the option unit 110 is, for example, between the color developing devices 15 to 17 (yellow (Y), magenta (M), cyan (C)) and between the photoconductor drum 10 and the transfer roll 31. Intermediate transfer belt 20 (in this example, stretched by stretching rolls 21 to 25)
And so on. Here, the layout of the photosensitive drum 10 and the intermediate transfer belt 20 may be appropriately selected, but for example, the intermediate transfer belt 20 may be arranged in contact in a predetermined contact region along the shape of the photosensitive drum 10. Is taken. A power supply unit (not shown) is connected to the transfer roll 31 so that a primary transfer bias or a secondary transfer bias is selectively applied.
The guide plate 122 that interferes when the optional intermediate transfer belt 20 is arranged is removed.

According to this type of color image forming apparatus, for example, in the monochrome mode, a monochrome toner image can be formed on the photosensitive drum 10 and directly transferred to the recording medium 50. However, in the case of controlling the surface of the recording medium 50 to be printed, the toner image may be first transferred to the intermediate transfer belt 20 side and then secondarily transferred to the recording medium 50. On the other hand, in the case of the color mode, toner images of respective color components are sequentially formed on the photosensitive drum 10, and
The multiple primary transfer toner images on the intermediate transfer belt 20 may be sequentially transferred to the recording medium 50, and then sequentially transferred to the intermediate transfer belt 20.

In this embodiment, from the viewpoint of increasing the degree of freedom of the user, the option unit 110
May be sold as a kit so that the user can directly add the option unit 110, but from the viewpoint of maintaining high image quality, the option unit 1
The additional work of 10 may be performed by the manufacturer.
Further, the present embodiment is not limited to the case where the upgrade of the image forming apparatus is targeted, and it is also preferable from the viewpoint of cost reduction by sharing parts between the single color image forming apparatus and the color image forming apparatus. .

Further, in the present embodiment, the transfer roll 31 is used as a common component in, for example, the single-color image forming apparatus and the color image forming apparatus. However, in a mode in which the transfer roller is incorporated in the intermediate transfer belt unit, for example, Instead of the transfer roll 31 of the single-color image forming apparatus, an intermediate transfer belt unit (transfer roll assembly mode) may be exchanged and attached. Further, as shown in FIG. 14, for example, the intermediate transfer belt 20 may be incorporated in advance as the basic unit 100, and, for example, only the color developing devices 15 to 17 may be added as the option unit 110.

[0045]

EXAMPLES Example 1 This example embodies the image forming apparatus according to the first embodiment. In this embodiment, the photosensitive drum 10 is made of an organic material having a diameter of 84 mm. Also,
The intermediate transfer belt 20 is a belt whose main component is polyimide resin, and has a Young's modulus of about 3 × 10 ³ Mpa.
The volume resistance is adjusted to a high resistance of 10 ⁸ to 10 ¹² Ω · cm. Further, in this embodiment, since the toner is the negative polarity toner, the transfer roll 3 is set as the primary transfer condition.
A primary transfer bias of positive polarity is applied to 1 and 20 μA from the transfer roll 31 to the side of the intermediate transfer belt 20 by constant current control.
The current is applied to transfer the image. Furthermore, as a secondary transfer condition, a negative secondary transfer bias (-2.5 kV in this example) is applied to the transfer roll 31, and a current is applied from the transfer roll 31 to the intermediate transfer belt 20 side by constant voltage control. Was made to flow to perform transfer. In this example, a monochromatic image and a color image of good image quality were obtained in both the monochromatic mode and the color modes 1 and 2.

Example 2 This example embodies the image forming apparatus according to the second embodiment. In this embodiment, the photosensitive drum 10 is made of an organic material having a diameter of 84 mm. Also,
The intermediate transfer belt 20 is a belt whose main raw material is chloroprene rubber, and is adjusted to have a high Young's modulus of about 30 MPa and a volume resistance of about 10 ⁹ Ω · cm. The surface of the belt is coated with a urethane-based coating layer to improve the releasability of the toner. Further, the intermediate transfer belt 20 is in contact with the photosensitive drum 10 at 55 ° (40 mm in distance). Here, the intermediate transfer belt 20
Since the diameter of the tension roll 21 is 12 mm (perimeter is about 37 mm), it is set to a value larger than that. Further, in this embodiment, since the toner is the negative polarity toner, the primary transfer condition is that a primary transfer bias of the positive polarity is applied to the transfer roll 31 and the intermediate transfer belt is transferred from the transfer roll 31 by constant current control. Transfer was performed by applying a current of 10 μA to the 20 side. Furthermore, as the secondary transfer condition, the transfer roll 3
1 to the negative secondary transfer bias (-1.5 k in this example).
V) is applied, and a current is passed from the transfer roll 31 to the intermediate transfer belt 20 side by constant voltage control so that transfer is performed. In this example, a monochromatic image and a color image of good image quality were obtained in both the monochromatic mode and the color modes 1 and 2.

[0047]

As described above, according to the present invention,
In an intermediate transfer type image forming apparatus, a primary transfer area for transferring an image on an image forming carrier to an intermediate transferring body and a secondary transfer area for transferring an image on the intermediate transferring body to a recording medium are formed on the image forming carrier. Further, since the transfer means set at the facing portion of the intermediate transfer body is provided, the primary transfer and the secondary transfer can be realized by sharing one transfer means. Therefore, while adopting the image forming method using the intermediate transfer body, it is not necessary to provide a secondary transfer means separately from the primary transfer means outside the intermediate transfer body, and the cost of the image forming apparatus can be reduced accordingly. A small size and space saving can be easily realized, and an image of good quality can be stably obtained.

Further, in the present invention, since the primary transfer and the secondary transfer are realized by sharing one transfer means, the basic unit for forming a single color image and the basic unit for addition or a part of this basic unit. If it is separable from an optional unit that is added by replacement, it is possible to easily upgrade from a single color image forming apparatus to a color image forming apparatus in response to a user's request.

[Brief description of drawings]

FIG. 1A is an explanatory diagram showing an outline of an image forming apparatus according to the present invention, and FIGS. 1B and 1C are explanatory diagrams showing an image forming process of the image forming apparatus.

FIG. 2A is an explanatory diagram showing an example of a basic unit of an image forming apparatus according to the present invention, and FIG. 2B is an explanatory diagram showing an example of the configuration of a “basic unit + option unit” of the image forming apparatus according to the present invention. Is.

FIG. 3 is an explanatory diagram showing an overall configuration of the image forming apparatus according to the first embodiment.

FIG. 4A is an explanatory diagram showing a configuration example of a power supply unit used in a transfer device, and FIG. 4B is an explanatory diagram showing another configuration example of the power supply unit.

FIG. 5 is an explanatory diagram showing a control system of the image forming apparatus according to the first embodiment.

6A is an explanatory diagram showing an image forming process in a monochrome mode, FIG. 6B is an explanatory diagram showing an image forming process in a color mode 1 (plain paper), and FIG. 6C is a color mode 2 (OHP). Sheet)
It is explanatory drawing which shows the image formation process at the time.

FIG. 7 is an explanatory diagram showing an image forming apparatus according to a first comparative example.

FIG. 8 is an explanatory diagram showing an overall configuration of an image forming apparatus according to a second embodiment.

FIG. 9 is an explanatory diagram showing a control system of the image forming apparatus according to the second embodiment.

FIG. 10 is an explanatory diagram showing a modification of the transfer device used in the second embodiment.

FIG. 11 is an explanatory diagram showing an image forming apparatus according to a second comparative embodiment.

FIG. 12 is an explanatory diagram showing a basic unit configuration of an image forming apparatus according to a third embodiment.

FIG. 13 is an explanatory diagram showing a “basic unit + option unit” configuration of the image forming apparatus according to the third embodiment.

FIG. 14 is an explanatory diagram showing a modification of the image forming apparatus according to the third embodiment.

[Explanation of symbols]

1 ... Image forming carrier, 2 ... Image forming means, 3 ... Intermediate transfer member,
3a ... tension roll, 4 ... transfer means, 5 ... recording medium, 6 ...
Basic unit, 7 ... Optional unit, 7a ... Optional subunit, 7b ... Optional intermediate transfer member, m1
… Primary transfer area, m2… Secondary transfer area, G… Image

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/00 384 G03G 21/00 384 (72) Inventor Mitsuo Yamamoto 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Shuichi Nishide 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Wataru Suzuki, 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor, Masahiro Sato Kanagawa Prefecture 2274 Hongo, Ebina City Fuji Xerox Co., Ltd. (72) Inventor Atsushi Kitamura 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. F Term (reference) 2H027 DC02 DC10 EB04 ED24 EF06 EF09 FA28 2H035 CA05 CB06 2H171 FA09 FA10 FA15 FA28 GA03 GA04 JA02 JA03 JA08 JA26 JA38 QA02 QA08 QA09 QA24 QB15 QC03 QC11 QC12 UA12 WA02 WA03 WA08 WA21 2H200 FA17 GA23 GA24 GA34 GB41 JA02 JA29 JB07 JB47 JC04 JC17 JC19 LA38 MC01 PA11 212300 EA02 2300 B23 EC05 EC09 EC12 ED08 EF06 EF08 EF14 EF17 EH16 EH17 EJ01 EJ09 FF01 FF05 FF12 FF20 GG01 GG02 GG03 GG34 GG35 HH16 HH32 HH36 HH40 KK03 MM01 MM25 PP02 QQ36 QQ37

Claims (11)

[Claims] 1. An image forming carrier, an image forming means for forming and carrying an image on the image forming carrier, an intermediate transfer member on which the image on the image forming carrier is primarily transferred, and an image forming carrier. A transfer unit in which a primary transfer area for transferring the image on the intermediate transfer body and a secondary transfer area for transferring the image on the intermediate transfer body to a recording medium are set at the facing portion of the image forming carrier and the intermediate transfer body. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that either the intermediate transfer member or the image forming carrier is an endless belt member. 3. An image forming apparatus according to claim 2, wherein the contact width between the image forming carrier and the intermediate transfer member is at least the minimum tension of the tension rolls stretching the belt-shaped member. An image forming apparatus having a roll length equal to or larger than the circumference. 4. The image forming apparatus according to claim 2, wherein the belt-shaped member has elasticity. 5. The image forming apparatus according to claim 1, wherein the transfer unit changes a transfer condition according to at least an image forming mode or a type of recording medium. 6. The image forming apparatus according to claim 5, wherein in a mode in which an image forming mode including at least a monochromatic mode and a color mode can be executed, the transfer means transfers the image to the intermediate transfer member when the monochromatic mode is selected. An image forming apparatus which is directly transferred to a recording medium without performing the above. 7. The image forming apparatus according to claim 1, wherein the transfer unit is used under different primary transfer conditions and secondary transfer conditions. 8. The image forming apparatus according to claim 7, wherein the transfer unit sets the primary transfer electric field and the secondary transfer electric field to opposite polarities. 9. The image forming apparatus as claimed in claim 7, wherein the transfer means is used with different transfer speeds during primary transfer and during secondary transfer. 10. An image forming carrier, an image forming means for forming and carrying an image on the image forming carrier, an intermediate transfer member on which the image on the image forming carrier is primarily transferred, and an image forming carrier. A transfer unit in which a primary transfer area for transferring the image on the intermediate transfer body and a secondary transfer area for transferring the image on the intermediate transfer body to a recording medium are set at the facing portion of the image forming carrier and the intermediate transfer body. An image forming apparatus comprising: a basic unit for single-color image formation and an optional unit that is added to or added to the basic unit. 11. The image forming apparatus according to claim 10, wherein the basic unit includes an image forming carrier, an image forming unit for forming and carrying an image on the image forming carrier, and an image on the image forming carrier. And a transfer means for transferring the image to a recording medium, while the option unit is provided between the image forming carrier and the transfer means, and the option sub-unit additionally disposed in the image forming means and necessary for color image formation. And an optional intermediate transfer member additionally disposed in the recording medium, after the image on the image forming carrier is primarily transferred onto the optional intermediate transfer member by the transfer means, the image on the intermediate transfer member is transferred to a recording medium. An image forming apparatus characterized in that secondary transfer is performed.