JP3604876B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus for transferring a toner image formed on an image carrier to a transfer material via an intermediate transfer member, for example, a copying machine and a laser beam printer.
[0002]
[Prior art]
FIG. 7 shows a schematic configuration of a four-color full-color image forming apparatus.
[0003]
In the image forming apparatus shown in the figure, the surface of the photosensitive drum 1 rotating in the direction of arrow R1 is charged by the charging member 2 and is exposed (L) by the exposure device 11 to form an electrostatic latent image. The developing device rotates a rotary 3 on which developing devices 4a, 4b, 4c, and 4d of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are mounted. In the figure, a Y developing device 4a) is disposed at a developing position facing the photosensitive drum 1, and toner is adhered to the electrostatic latent image on the photosensitive drum 1 and developed as a toner image. This toner image is firstly transferred by a primary transfer roller 6 onto an intermediate transfer belt 5d constituting an intermediate transfer device 5 by being stretched over rollers 5a, 5b and 5c. The toner remaining on the surface of the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is cleaned by the photosensitive drum cleaning device 10.
[0004]
The above-described series of image forming processes of charging, exposure, development, primary transfer, and cleaning are repeated for the remaining three color toners other than the Y toner, that is, the toners of the respective colors M, C, and K. The four color toner images are superimposed on the transfer belt 5d.
[0005]
The toner images of the four colors are collectively secondary-transferred onto a transfer material P such as paper by the secondary transfer roller 7 and then fixed on the surface of the transfer material P by heating and pressing by the fixing device 9.
[0006]
After the secondary transfer, the toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 5d is removed by the cleaning roller 8 of the intermediate transfer belt cleaning device.
[0007]
[Problems to be solved by the invention]
In the above-described image forming apparatus, the transfer width (the dimension in the axial direction) Wt of the secondary transfer roller 7 is set to be equal to or larger than the maximum transfer material width (the width of the largest one of the transfer materials P) Wp. If this is done, it is possible to cope with the feeding of transfer materials P of various widths. That is, generally, Wt> Wp (1) is set.
[0008]
In addition, if the charging width Wc of the charging device as the intermediate transfer belt cleaning device is set to be equal to or larger than the maximum image width Wi, it is possible to charge the secondary transfer residual toner of any image. Become. That is, Wc> Wi ... (2) is set.
[0009]
Further, the relationship between the maximum transfer material width Wp and the maximum image width Wi is Wp ≧ Wi... (3).
[0010]
The above three expressions (1), (2), and (3), that is,
Wt> Wp ... ▲ 1 ▼
Wc> Wi ... ▲ 2 ▼
Wp ≧ Wi… ▲ 3 ▼
From, the magnitude relationship between Wt and Wc cannot be specified.
[0011]
That is, from the equation, it should not be necessary to satisfy Wc ≧ Wt at all. However, actually, when Wc <Wt is set, the surface of the portion of the surface of the intermediate transfer belt 5a that is not charged (discharged) by the charging device 8, that is, the portion of the surface to which only the secondary transfer bias is applied. There is a problem in that the surface layer causes dielectric breakdown in a short period of time, and minute holes are formed, and the holes gradually expand to become cracks. When the cracks reach the image area, there is a problem that an image defect is caused.
[0012]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus which prevents cracks on the surface of an intermediate transfer belt and prevents image defects caused by cracks.
[0013]
[Means for Solving the Problems]
According to an aspect of the present invention, there is provided an image carrier that carries a toner image, and a first transfer portion that receives a primary transfer of the toner image formed on the image carrier. An intermediate transfer belt, transfer means for secondary-transferring the toner image on the intermediate transfer belt onto a transfer material at a second transfer portion to form a toner image on the transfer material, and Charging means for applying electric charge to the secondary transfer residual toner remaining on the transfer belt, wherein the intermediate transfer belt has a thickness of 2 to 100 μm and a volume resistivity of 10 ⁸ to 10 ¹⁸ Ω · cm. The transfer unit has a function of charging the intermediate transfer belt within a range of a transfer width Wt, and transfers the secondary transfer residual toner charged by the charging unit to the first transfer portion. Reverse transfer onto the image carrier in parallel with the primary transfer In that the color image forming apparatus, the AC bias is applied to the charging means, the AC bias is the center value of the amplitude of the voltage is 0V, and applying a charge required for the reverse transcription to the secondary transfer residual toner The intermediate transfer belt has a function of discharging the surface of the intermediate transfer belt to approximately 0 V, and a transfer width Wt of the transfer unit in a direction orthogonal to a moving direction of the intermediate transfer belt is equal to a moving direction of the intermediate transfer belt of the charging unit. It is characterized by being in a range corresponding to the inside of the charging width Wc in the direction perpendicular to the direction.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
<Embodiment 1>
FIG. 1 shows an example of a color image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a four-color full-color laser beam printer.
[0018]
The four-color full-color laser beam printer (hereinafter, referred to as “image forming apparatus”) shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 1 as a first image carrier.
[0019]
A primary charger 2 and an exposure device 11 are provided above the photosensitive drum 1, a developing device 3 is provided on the left side, an intermediate transfer device 5 is provided below, and a photosensitive drum cleaning device is provided above. An apparatus 10 is provided.
[0020]
The above-described photosensitive drum 1 is formed by applying a photoconductor such as OPC (organic optical semiconductor), a-Si (amorphous silicon), CdS (cadmium sulfide), or Se (selenium) on the outer peripheral surface of an aluminum cylinder. It is. The photosensitive drum 1 is rotatably supported by an apparatus main body (not shown), and is driven to rotate in a direction of an arrow R1 by driving means (not shown).
[0021]
The primary charger 2 is a charging roller arranged in contact with the surface of the photosensitive drum 1 and is applied with a charging bias by a power source (not shown), thereby uniformly charging the surface of the photosensitive drum 1 to a predetermined polarity and a predetermined potential. Is what you do.
[0022]
The exposure unit 11 includes a laser oscillator, a reflection mirror 11b, and the like, and performs exposure (L) according to image information to form an electrostatic latent image.
[0023]
The developing device 3 includes four developing devices 4a, 4b, 4c, and 4d mounted on a rotatable rotary 4A. Each of the developing devices 4a, 4b, 4c, and 4d stores a toner of each color of yellow (Y), magenta (M), cyan (C), and black (K), respectively, as the rotary 4A rotates. Is driven such that the developing opening surface of the developing device always faces outward. The developing device 3 has a developing device (yellow developing device 4a in the figure) used for developing the electrostatic latent image on the photosensitive drum 1 by rotation of the rotary 4A, which is disposed at a developing position facing the surface of the photosensitive drum 1. The electrostatic latent image is developed by attaching toner to the electrostatic latent image.
[0024]
The intermediate transfer device 5 includes three rollers as a support, namely, a driven roller 5a, a secondary transfer opposing roller 5b, and a drive roller 5c. An intermediate transfer belt 5d as a second image carrier is wound around these three rollers 5a, 5b, 5c. The intermediate transfer belt 5d is a rubber belt formed in an endless shape (endless shape), and is driven in a direction of an arrow R5 by a driving unit (not shown). A primary transfer roller (first transfer unit) 6 is disposed inside the intermediate transfer belt 5d at a position substantially opposed to the photosensitive drum 1. The primary transfer roller 6 is pressed against the intermediate transfer belt 5d surface of the photosensitive drum 1 to form a primary transfer portion t _1. A secondary transfer roller (second transfer unit) 7 is disposed outside the intermediate transfer belt 5d at a position corresponding to the secondary transfer opposing roller 5b. The secondary transfer roller 7, an intermediate transfer are separable freely disposed against the belt 5d, to the time of contact, forms a secondary transfer portion t _2. Further, between the secondary transfer portion t ₂ along the moving direction of the intermediate transfer belt 5d and the primary transfer portion t _1, the intermediate transfer belt cleaning device (charging unit) 8 is provided.
[0025]
A fixing device 9 for fixing the toner image secondary-transferred onto the surface of the transfer material P is provided downstream of the secondary transfer roller 7 in the moving direction of the transfer material P.
[0026]
Next, the operation of the image forming apparatus having the above configuration will be described.
[0027]
The photosensitive drum 1 is driven to rotate in the direction of arrow R <b> 1 by driving means, and the surface thereof is charged by the primary charger 2. A superimposed voltage in which an AC voltage is superimposed on a DC voltage is applied to the primary charger 2, whereby the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential. Subsequently, when a signal according to yellow image information is input to a laser driver (not shown) of the exposure device 11, laser light is emitted from the laser oscillator 11a. The laser light is applied to the surface of the photosensitive drum 1 via a polygon mirror (not shown), a reflection mirror 11b, and the like, and removes the charge on the irradiated portion to form an electrostatic latent image.
[0028]
The electrostatic latent image on the photosensitive drum 1 is developed as a yellow toner image by a yellow developing device 4a disposed at a developing position by the rotation of the rotary 4A.
[0029]
The yellow toner image on the photosensitive drum 1 is primarily transferred onto the surface of the intermediate transfer belt 5d by a primary transfer bias applied to the primary transfer roller 6 from a power supply (not shown). At this time, toner (primary transfer toner) remaining on the surface of the photosensitive drum 1 without being primarily transferred to the intermediate transfer belt 5d is removed by the photosensitive drum cleaning device 10, and the photosensitive drum 1 is used for forming a toner image of the next color. Be provided.
[0030]
The above-described series of image forming processes of charging, exposure, development, primary transfer, and cleaning (of the photosensitive drum 1) are sequentially performed for three colors other than the above-described yellow, that is, magenta, cyan, and black toners. To superimpose toner images of four colors on the intermediate transfer belt 5d.
[0031]
The four color toner images on the intermediate transfer belt 5d are collectively and secondarily transferred onto the transfer material P by a secondary transfer bias applied to the secondary transfer roller 7 by a power supply (not shown). The transfer material P, which has been stored in a paper feed cassette (not shown), is rotated by a transport device (all not shown) having a paper feed roller, a transport roller, a registration roller and the like to rotate the intermediate transfer belt 5d. Are supplied in synchronization with.
[0032]
The transfer material P after the secondary transfer is conveyed to the fixing device 9, where the transfer material P is heated and pressurized to fix the four color toner images on the surface, and then discharged outside the apparatus main body.
[0033]
The toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 5d without being secondary-transferred onto the transfer material P during the above-described secondary transfer is charged by the intermediate transfer belt cleaning device 8, and the above-described toner image is formed. During the primary transfer, the image is reversely transferred from the surface of the intermediate transfer belt 5 d to the surface of the photosensitive drum 1, and then removed by the photosensitive drum cleaning device 10.
[0034]
Here, the above-mentioned intermediate transfer belt 5d will be described in detail. The intermediate transfer belt 5d has a thickness of 0.3 to 2 mm and a volume resistivity of 10 ⁴ to 10 ⁸ Ω · cm, acrylonitrile butadiene rubber (NBR), Styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylic rubber, fluororubber, urethane rubber, etc., on a rubber base layer formed endlessly, with a thickness of 2 to 100 μm, volume It has a configuration in which rubber or a resin such as PVdF, PET, polycarbonate, polyethylene, or silicone, which is adjusted to a resistivity of 10 ⁸ to 10 ¹⁸ Ω · cm, is provided as a surface layer.
[0035]
Further, an intermediate transfer belt cleaning device 8 for applying electric charges to the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 5d is formed of a plurality of layers as a charging member and has an elastic cleaning roller (roller-shaped charger). ) 8a, an AC power supply 8b for applying an AC voltage thereto, and a DC power supply 8c for applying a DC voltage. The intermediate transfer belt cleaning roller 8a is disposed so as to be able to contact and separate from the intermediate transfer belt 5d.
[0036]
Next, features of the present invention will be described.
[0037]
FIG. 2 shows the respective widths (lengths in the axial direction or lengths in the left-right direction in the transport direction of the transfer material P) of the intermediate transfer belt 5d, the secondary transfer roller 7, and the intermediate transfer belt cleaning roller 8a in FIG. This is schematically shown in FIG. First, as shown in the figure, the width of the intermediate transfer belt 5d is the largest among these members.
[0038]
Next, assuming that the transfer width of the secondary transfer roller 7 is Wt and the charging width of the intermediate transfer belt cleaning roller 8a is Wc, when Wc ≧ Wt and Wc <Wt, the occurrence of cracks in the intermediate transfer belt 5d is reduced. The difference was examined.
[0039]
As a common condition, the secondary transfer bias applied to the secondary transfer roller 7 was set to a constant current control of +10 μA. As shown in FIG. 3, the bias waveform applied to the intermediate transfer belt cleaning roller 8a has a peak-to-peak voltage of 2.5 kV _PP , a frequency of 2 kHz, a duty ratio of 80% on the plus side, 20% on the minus side, and The DC voltage was set to 0 V, and the surface of the intermediate transfer belt 5 d was set to be almost 0 V while giving a positive charge to the secondary transfer residual toner.
[0040]
FIG. 6 shows the state of occurrence of cracks in the intermediate transfer belt 5d. ○ indicates no occurrence, △ indicates a case where a minute hole is formed on the surface of the intermediate transfer belt 5d, X indicates a case where a crack has occurred, and XX indicates a case where the crack extends to the image area.
[0041]
As is clear from the figure, in the case of Wc <Wt, a minute hole was generated at the end when the durability was about 5k (5000), and a crack was generated at the end when the durability was 10k (10000). . Then, in the case of 50k sheets (50,000 sheets), cracks were achieved up to the image area.
[0042]
On the other hand, when Wc ≧ Wt, a small hole was formed in the entire intermediate transfer belt for 50k sheets, but no crack was caused which caused an image defect.
[0043]
When Wc <Wt, the secondary transfer bias is always applied to the end of the intermediate transfer belt 5d without being neutralized by the intermediate transfer belt cleaning roller 8a, and the surface of the intermediate transfer belt 5d is charged. Will be up. For this reason, it is considered that the electric field was concentrated on the high-resistance layer on the surface of the belt, resulting in dielectric breakdown.
[0044]
On the other hand, when Wc ≧ Wr, the surface of the intermediate transfer belt 5d is always discharged by the intermediate transfer belt cleaning roller 8a, so that the surface of the intermediate transfer belt 5d does not charge up and dielectric breakdown occurs. It seems that it has become difficult.
[0045]
<Embodiment 2>
FIG. 4 is a longitudinal sectional view of the color image forming apparatus according to the second embodiment. The same reference numerals are given to members having the same configuration and operation as those shown in FIG. 1, and the description thereof will not be repeated.
[0046]
In the first embodiment, the intermediate transfer belt cleaning device 8 that applies electric charge to the secondary transfer residual toner on the surface of the intermediate transfer belt 5d has an intermediate transfer belt cleaning roller 8a that can contact the surface of the intermediate transfer belt 5d as a charging member. However, according to this method, since a high frequency region is used, a small amount of charging noise is generated. Further, the intermediate transfer belt cleaning roller 8a has a disadvantage that the change in performance is small with respect to environmental fluctuations, but the cost is slightly increased.
[0047]
Therefore, in the second embodiment, as a charging member of the intermediate transfer belt cleaning device 8 for applying a charge to the secondary transfer residual toner on the intermediate transfer belt 5d, a non-charging member as shown in FIGS. A contact-type charging electrode 8A was used. The charging electrode 8A is formed in a long plate shape having a length of 10 mm along the conveyance direction of the intermediate transfer belt 5d, a charging width of Wc, and a width of 70 μm between the charging electrode 8A and the surface of the intermediate transfer belt 5d. Was established. When the charging width Wc is wider than the transfer width Wt of the secondary transfer roller 7, that is, when Wc ≧ Wt, and conversely, when Wc <Wt, the conditions are exactly the same as those in the first embodiment. As a result, the same result as in the first embodiment shown in FIG. 6 was obtained. That is, if Wc ≧ Wt, cracking of the intermediate transfer belt 5d could be prevented, and in addition, charging noise and cost could be reduced.
[0048]
In the above-described first and second embodiments, an example in which the intermediate transfer belt 5d is used as the second image carrier has been described. Needless to say, the same effect can be obtained even when the intermediate transfer drum is used.
[0049]
【The invention's effect】
As described above, according to the present invention, the toner images sequentially formed on the first image carrier are collectively and secondarily transferred to the transfer material via the second image carrier, Color image formation in which the secondary transfer residual toner is reverse-transferred onto the first image carrier in parallel with the primary transfer by applying a charge to the secondary transfer residual toner on the image carrier by a charging unit. In the apparatus, when the transfer width of the second transfer means is Wt and the charging width of the charging means is Wc, by satisfying Wc ≧ Wt, cracks generated on the second image carrier are prevented and cracks are prevented. Thus, a stable image free of image defects due to the above can be formed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.
FIG. 2 is a diagram illustrating a relationship between widths of an intermediate transfer belt, a secondary transfer roller, and an intermediate transfer belt cleaning roller.
FIG. 3 is a diagram showing a waveform of a cleaning bias in the first embodiment.
FIG. 4 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment.
FIG. 5A is a perspective view of a charging electrode according to a second embodiment.
FIG. 4B is a side view illustrating a gap between the charging electrode and the intermediate transfer belt according to the second embodiment.
FIG. 6 is a diagram showing a difference in cracks on the surface layer of the intermediate transfer belt due to a difference in magnitude relationship between a charging width Wc of the intermediate transfer belt cleaning roller and a transfer width Wt of the secondary transfer roller.
FIG. 7 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus.
[Explanation of symbols]
1. First image carrier (photosensitive drum)
5d Second image carrier (intermediate transfer belt)
6 First transfer means (primary transfer roller)
7. Second transfer means (secondary transfer roller)
8 Charging means (intermediate transfer belt cleaning device)
8A Charging member (charging electrode)
8a Charging member (roller-shaped charger)
P Transfer material t ₁ First transfer site t ₂ Second transfer site Wc Charging width Wt of charging unit Transfer width of second transferring unit

Claims (1)

An image carrier that carries the toner image; an intermediate transfer belt that receives primary transfer of the toner image formed on the image carrier at a first transfer portion; A transfer unit that forms a toner image on the transfer material by performing a secondary transfer on the transfer material at a transfer portion; and a charging unit that applies a charge to the secondary transfer residual toner remaining on the intermediate transfer belt after the secondary transfer. And the intermediate transfer belt has a layer having a thickness of 2 to 100 μm and a volume resistivity of 10 ⁸ to 10 ¹⁸ Ω · cm, and the transfer unit performs the intermediate transfer in a transfer width Wt range. A color that has a function of charging a transfer belt and reversely transfers the secondary transfer residual toner, which is charged by the charging unit, onto the image carrier in parallel with the primary transfer at the first transfer portion; In the image forming apparatus,
An AC bias is applied to the charging unit, and the AC bias has a center value of a voltage amplitude of 0 V, and applies a charge required for the reverse transfer to the secondary transfer residual toner while causing the intermediate transfer belt surface to be charged. It has the function of neutralizing the substantially 0V, the transfer width Wt in the direction perpendicular to the moving direction of the intermediate transfer belt of the transfer unit, the intermediate transfer belt direction of the charging width Wc orthogonal to the moving direction of said charging means Within the range corresponding to the inside,
An image forming apparatus comprising:

Images