JPH06195001A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent defective cleaning on an image forming part by making the cleaning means of at least one image forming part possess a cleaning blade and a cleaning auxiliary means, and making another image forming part possess only the cleaning blade among plural image forming parts. CONSTITUTION:Among the cleaning devices 13a-13d, for example, the cleaning devices 13a-13c on the image forming part forming an image having a color other than black are provided in proximity to the periphery of photosensitive drums 9a-9c rotating in a direction shown by an arrow A as shown in figure (a), and the cleaning blades 18a-18c are provided on a downstream side in a drum rotating direction in a state where they are brought into press-contact with a drum surface from a direction opposite to the drum rotating direction. On the other hand, as to the cleaning device 13d of the image forming device forming the black image; in addition to the cleaning blade 18d similar to the cleaning blades 18a-18c, a fur brush 21 being the cleaning auxiliary means is provided in the device in a state where it is made to abut on the surface of the photosensitive drum 9d. Thus, for example, toner melting peculiar to a black image forming part can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having an image bearing member and a plurality of image forming portions which act on the image bearing member to form an image on a recording material.

[0002]

2. Description of the Related Art Conventionally, as an example of an image forming apparatus having an image bearing member and a plurality of image forming portions which act on the image bearing member to form an image on a recording material, a 4-drum type color image forming apparatus is provided. Is shown in FIG. The four-drum type color image forming apparatus is provided with four image forming units each having an image carrier and process means arranged around the image carrier in order to increase the speed of the apparatus.
The image on the image carrier formed by each image forming unit is sequentially transferred onto the recording material carried and carried by the carrying means moving adjacent to the image carrier.

Referring to FIG. 7, the image forming apparatus includes image forming units P _a , P _b , which are necessary for forming a full-color image.
Photosensitive drums 51a and 51 that are image bearing _members for P _c and P _d
b, 51c and 51d, and chargers 52a, 52b, 52c and 52d, which are charging means, scanning optical devices (not shown), which are optical scanning means, and developing devices 53a, which are developing means.
Process means such as 53b, 53c, 53d and cleaning devices 54a, 54b, 54c, 54d as cleaning means are arranged. The transfer means includes an endless belt-shaped transfer belt 55 common to each image forming unit, and transfer chargers 56a, 56.
b, 56c, 56d, and the photosensitive drum 51 at each image forming portion on the transfer material 57 carried and conveyed on the transfer belt 55.
Each color image formed on a, 51b, 51c and 51d is transferred. The transfer material 57 is supplied from the feeding cassette 58, and after the transfer process, separated from the transfer belt 55 and the transfer image is fixed by the fixing device 59, and the transfer tray 57 is discharged.
Discharge over 60.

The cleaning devices 54a, 54b, 54c,
54d (hereinafter referred to as "cleaning device 54"),
As shown in FIG. 8, cleaning blades 61 are provided respectively, and the cleaning blades 61 rotate on photosensitive drums 51a, 51b, 51c, 51d (hereinafter abbreviated as "photosensitive drum 51") that rotate in the arrow A direction. It is pressed against the drum surface from the opposite direction. The toner remaining on the photosensitive drum 51 without contributing to the transfer in the image transfer step is conveyed to the cleaning device 54, scraped off on the squeeze sheet 62 by the cleaning blade 61, and transferred into the cleaning container 64 by the conveying screw 63. Be transported.

Since the blade cleaning system has a very simple structure and is inexpensive, in the 4-drum system color image forming apparatus, there are four cleaning devices.
The blade cleaning method is a very effective cleaning method in order to realize cost reduction and downsizing of the apparatus as compared with other cleaning methods because each blade is required.

By the way, particularly in an office or the like which requires a large amount of document processing, the amount of black monochromatic originals is still overwhelmingly larger than that of color originals due to running costs and document preparation reasons. Movements are frequent. For example, the 4-drum type image forming apparatus shown in FIG. 7 is capable of performing high-speed continuous image forming operations similar to those of a high-speed black-and-white copying machine, and it is considered that the use opportunities in the black monochromatic mode will increase. Therefore, it is effective to reduce the running cost by using an inexpensive developer in the black image forming portion.

Conventionally, a two-component developer composed of a magnetic carrier and a non-magnetic toner has been adopted as a developer used in a color copying machine, but a black developer has a magnetic property.
By using the component developer, the running cost can be significantly reduced. Further, unlike the two-component developer, it is not necessary to always keep the toner concentration constant, so that the apparatus structure can be simplified. As described above, the use of the one-component developer having the magnetic material only for the black developer has many advantages such as reduction of running cost and simplification of maintenance, especially when many black monochromatic images are used.

[0008]

However, the one-component developer having the above-mentioned magnetic material is liable to cause so-called "toner fusion" in which the developer is fixed to the drum surface, and the developer remains on the photosensitive drum. In some cases, the blade cleaning method may not be able to perform sufficient cleaning. Therefore, when toner fusion occurs on the photosensitive drum, an image defect such as a white spot occurs in the image transferred to the transfer material.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an image forming apparatus capable of preventing defective cleaning in an image forming portion.

[0010]

A typical means for solving the above-mentioned problems of the prior art and applied to the embodiments described below is an image carrier and an image carrier acting on the image carrier. In an image forming apparatus having a plurality of image forming units for forming an image, each of the image forming units has a cleaning unit for removing the developer remaining on the image carrier, and at least one of the image forming units has a cleaning unit. It is characterized in that it has a cleaning blade and a cleaning assisting means, and the cleaning means of the other image forming portion has only the cleaning blade.

[0011]

According to the above means, among the plurality of image forming units,
At least one image forming unit (for example, a black image forming unit)
Cleaning means has a cleaning assisting means in addition to the cleaning blade, and the cleaning means of the other image forming section (for example, an image forming section of a color other than black) has only the cleaning blade so that the black By improving the cleaning blade performance in the image forming section, it is possible to prevent a specific cleaning failure (for example, “toner fusion”) in the black image forming section.

[0012]

【Example】

[First Embodiment] Next, an image forming apparatus according to an embodiment of the present invention to which the above means is applied will be described. In this example,
A color electrophotographic copying machine having a plurality of image carriers and equipped with a plurality of image forming units will be described. FIG. 1 is an explanatory diagram showing the configuration of a cleaning device, and FIG. 2 is a sectional explanatory diagram showing the overall configuration of a copying device.

First, the schematic structure of the color copying apparatus will be described with reference to FIG. 2. In the four-drum type color copying apparatus shown in this embodiment, a process means is provided around the image carrier and its periphery in order to speed up the apparatus. Four image forming sections are arranged, and the image on the image carrier formed by each of the image forming sections is carried by the transporting means that moves adjacent to the image carrier.
It is configured to be sequentially transferred onto the conveyed recording material.

Specifically, inside the apparatus main body 1, image forming portions P _a , P _b , P _c and P _d containing process means are laterally arranged, and each image forming portion P _a , P _b , P
_{Below the c} and P _d , an endless transfer belt 3 is stretched around belt drive rollers 2 a and 2 b. The transfer belt 3 is rotated in the arrow C direction by rotating the belt drive rollers 2a and 2b in the arrow B direction by a drive motor (not shown). Reference numeral 4 denotes a cassette, which stores a transfer material 5 which is a recording material, and the transfer material 5 stored in the cassette 4 is fed by a pickup roller 6 from the uppermost side. And with skew is corrected by the registration roller pair 7, the image forming section P _a, P _b,
The sheet is conveyed onto the transfer belt 3 in synchronization with P _c and P _d . Reference numeral 8 denotes a conveyance guide for guiding the transfer material 5 from the registration roller pair 7 to the transfer belt 3.

Next, the image forming portions P _a , P _b , P _c , P
Explaining the structure of _d , the photosensitive drum 9 which is an image carrier.
a primary chargers 10a, 10b, 10c and 10d having a, 9b, 9c and 9d and constituting process means around them, and a developing device
11a, 11b, 11c, 11d, transfer chargers 12a, 12b, 12
c, 12d and cleaning devices 13a, 13b, 13c, 13d, respectively. The photosensitive drums 9a, 9b,
A laser beam scanner (not shown), which is an exposure unit, is provided above 9c and 9d.

The above primary chargers 10a, 10b, 10c, 10d
Is for uniformly charging the drum surface prior to exposing the photosensitive drums 9a, 9b, 9c, 9d, and the developing devices 11a, 11b, 11c, 11d are exposed to static charge formed on the drum surface. Black, magenta, yellow on the latent image
The toner of each color of cyan is adhered to form a visible image. The transfer chargers 12a, 12b, 12c and 12d transfer the toner images formed on the photosensitive drums 9a, 9b, 9c and 9d onto the transfer material 5, and the cleaning device 13
Reference numerals a, 13b, 13c and 13d are for removing the residual toner adhering to the drum surface after the image transfer. Further, the laser beam scanner has a semiconductor laser, a polygon mirror, an fθ lens, etc., and receives an electric digital image signal input and modulates the laser beam corresponding to the signal to the photosensitive drums 9a, 9b, 9c, 9d. Exposure is performed by irradiating in the direction of the generatrix.

Reference numeral 14 is a separation charging device for separating the transfer material 5 conveyed on the transfer belt 3, and 15 is a fixing device for fixing the transfer image transferred onto the transfer material 5. , A fixing roller 15 having a heating means such as a heater inside
It has a pressure roller 15b and a pressure roller 15b. Reference numeral 16 is a discharge tray for stacking the transfer material 5 discharged outside the apparatus. A fur brush 17 as a belt cleaning means is in contact with a part of the transfer belt 3, and the transfer belt 3 is rotated by rotating the fur brush 17 at a high speed.
The toner accumulated on the belt is removed from the belt.

Next, the image forming operation will be described. When an image forming operation start signal is input to the apparatus main body 1, the photosensitive drum 9a starts rotating in the direction of arrow A, and the primary charger 10a.
Are uniformly charged by a laser beam scanner (not shown), and a laser beam modulated by an image signal corresponding to the black component of the original image is applied to the drum surface to form an electrostatic latent image (exposure). . Next developing device
The yellow toner is supplied by 11a to form a toner image by visualizing the latent image.

On the other hand, the transfer material 5 stored in the cassette 4
Is fed by the pick-up roller 6 and the skew is corrected by the registration roller pair 7 which is temporarily stopped. Then, the transfer belt 3 is timed with the toner image formed on the photosensitive drum 9a. Transported on. Transfer material 5 fed into the transfer belt 3, the transfer charging by the transfer charger 12a at the transfer portion of the image forming portion P _a is performed, the toner image is transferred onto the transfer material 5. The above steps are similarly performed in the image forming portions P _b , P _c and P _d , and the magenta toner image, the cyan toner image and the black toner image are sequentially transferred to the transfer material 5.

The transfer material 5 on which the image transfer has been completed is separated from the transfer belt 3 while being subjected to AC static elimination by the separation charging device 14 at the left end portion of the transfer belt 3, and is conveyed to the fixing device 15.
Then, the transfer material 5 on which the image is fixed by the fixing device 15 is discharged to the discharge tray 16 outside the apparatus.

After the image transfer process is completed, the photosensitive drum 9
The toner remaining on the a, 9b, 9c, and 9d reaches the cleaning devices 13a, 13b, 13c, and 13d. Be scraped off. In this blade cleaning method, the toner particles must be removed from the drum surface by overcoming the electrostatic attraction of the toner particles to the surface of the photosensitive drums 9a, 9b, 9c, 9d. You must press against the surface.

Next, the cleaning devices 13a, 13b, 13
The configuration of c and 13d (hereinafter abbreviated as "cleaning device 13") will be described in detail with reference to FIG. Above cleaning device
The cleaning devices 13a, 13b, and 13c in the image forming portions P _a , P _b , and P _c other than black among 13 are shown in FIG.
, The photosensitive drum 9a, which rotates in the direction of arrow A,
9b and 9c are provided in the vicinity of the periphery of the cleaning blades 18a,
18b and 18c are provided so as to come into pressure contact with the drum surface from the direction opposite to the drum rotation direction. Further, squeeze sheets 19a, 19b, 19c are provided upstream of the cleaning devices 13a, 13b, 13c in the drum rotation direction, respectively, and the residual toner scraped off the drum surface by the cleaning blades 18a, 18b, 18c is collected. To do. Also, the cleaning devices 13a, 13b, 13c
Conveying screws 20a, 20b, 20c are provided inside, and the collected residual toners are sequentially conveyed into the container.

On the other hand, as shown in FIG. 1B, the cleaning device 13d for the black image forming portion P _d has the same schematic structure as the cleaning devices 13a, 13b and 13c,
The difference is that a fur brush 21 which is a cleaning assisting means is provided in the apparatus so as to abut the surface of the photosensitive drum 9d. After the transfer process is completed, the toner remaining on the photosensitive drum 9d is conveyed to the cleaning device 13d,
The fur brush 21 scrapes some of the residual toner onto the squeegee sheet 19d, and the cleaning blade 18
The remaining toner is completely scraped off by d. The residual toner collected in the cleaning device 13d is carried into the container by the carrying screw 20d.

The toner used in the image forming portions P _a , P _b and P _c is composed of a magnetic carrier and a non-magnetic toner.
Component developer is used, but black image forming part P _d
The toner used in the above is a one-component developer having magnetism. As a result, the cost of the black toner is suppressed, so that the running cost is reduced especially when a large amount of copying is performed in the black monochromatic mode. Conventionally, in a one-component developer having a magnetic material, a phenomenon of so-called "toner fusion", in which toner adheres to the drum surface, easily occurs. This is a phenomenon in which toner adheres to the drum and cannot be sufficiently cleaned by the blade cleaning method.

It has been found that the fur brush + blade cleaning method is very effective for this toner fusion. That is, in the case of only the blade cleaning system, there is a possibility that the durability life of the cleaning blade 18d and the photosensitive drum 9d may be shortened by increasing the contact pressure of the cleaning blade 18d with respect to the photosensitive drum 9d. Toner fusion can be effectively prevented without increasing the contact pressure of the blade. Therefore,
It is possible to effectively prevent the toner fusion peculiar to the black image forming portion and maintain the cleaning performance while realizing the downsizing and cost reduction of the entire apparatus.

[Second Embodiment] Next, another example of the image forming apparatus shown in the first embodiment will be described with reference to FIG.
Since the schematic configuration of the entire apparatus is the same as that of the first embodiment, the same members are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, as shown in FIG. _3A , only the blade cleaning method is used in the image forming portions P _a , P _b and P _c other than black, and FIG.
As shown in, the fur brush + blade cleaning method is used in the black image forming portion P _d . Cleaning device 13d in the black image forming portion P _d
The coating layer 18e for reducing the frictional force between the cleaning blade 18d and the photosensitive drum 9d is provided on all or part of the surface of the cleaning blade 18d.

From the viewpoint of chemical resistance, wear resistance, moldability, mechanical strength, etc., urethane rubber has been mainly used as the material of the cleaning blade. This urethane rubber cleaning blade is an OPC whose surface layer is made of a polymer resin such as polycarbonate.
Since the friction coefficient with the photosensitive drum is very high, a large frictional force is generated between the photosensitive drum and the cleaning blade, and the cleaning blade reverses along the rotation direction of the photosensitive drum (blade flipping), The photosensitive drum may not be driven, or cleaning may not be performed properly.

In the case of only the blade cleaning method, toner or an external additive in the toner is present between the blade and the drum, and serves as a lubricant to prevent the blade from curling up. On the other hand, as in the first embodiment, the fur brush +
Black image forming part P using a blade cleaning method
_{At d} , the toner remaining on the photosensitive drum 9d without contributing to the transfer after the transfer process is first removed to some extent by the fur brush 21, and then the cleaning blade.
Although the residual toner which cannot be completely removed by the fur brush 21 is removed by 18d, the cleaning blade 18
In the vicinity of d, the amount of toner to be used as a lubricant or the amount of lubricant in the toner is small, and defects such as blade turnover are likely to occur.

Therefore, in this embodiment, as shown in FIG. 3B, the cleaning blade 18d is provided on the surface of the cleaning blade 18d.
By applying a coating agent for reducing the frictional force between the photosensitive drum 9d and the photosensitive drum 9d, the blade is prevented from being turned over and cleaning is effectively performed.

According to the experiments conducted by the present inventors, OP in which the surface layer is composed of a polymer resin such as polycarbonate is used.
When the cleaning blade made of polyurethane rubber is brought into contact with the C photosensitive drum to perform cleaning,
The coating layer at the contact portion of the cleaning blade with the photosensitive drum is a resin layer in which fluorinated graphite powder is dispersed in a polymer resin solvent such as nylon, applied to the cleaning blade by dipping, and then dried, heated and cured. It was found that the blade curling can be very effectively prevented by applying a coating agent consisting of.

Here, usable as the above fluorinated graphite are, for example, (C2F) n type Cefbon DM (manufactured by Central Glass Co., Ltd.) and (CF) n type Cefbon CM.
A, Cefbon CMF (Central Glass Co., Ltd.), Hooker Carbon # 2065, # 1030, # 1000 (Asahi Glass Co., Ltd.), CF-100 (Nippon Carbon), and (CF) n
Fluorocarbons # 2028, # 20 with different fluorination rates by mold
10 (manufactured by Asahi Glass Co., Ltd.), and further, those obtained by treating the above fluorinated graphite with a base such as amine to remove fluorine on the surface, but are not limited thereto. Further, the average particle size of the fluorinated graphite is preferably 20 μm or less, and particularly preferably in the range of 1 μm to 8 μm so as not to impair the cleaning performance of the toner.

[Third Embodiment] Next, another example of the image forming apparatus shown in the first embodiment will be described with reference to FIG.
Since the schematic configuration of the entire apparatus is the same as that of the first embodiment, the same members are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, as shown in FIG. _4A , only the blade cleaning method is used in the image forming portions P _a , P _b and P _c other than black, as shown in FIG.
As shown in, the black image forming portion P _d employs the auxiliary charging + blade cleaning method. The cleaning device 13d in the image forming portion P _d of the black is equipped only cleaning blade 18d is, is provided with a cleaning auxiliary charger 22 in the drum rotation direction upstream side of the cleaning device 13d.

In the color copying apparatus, the toner adhered on the photosensitive drum is usually positively or negatively charged so that the photosensitive drum and the toner are strongly attracted to each other by the electrostatic attraction force. Therefore, as shown in FIG. 4B, by disposing the auxiliary cleaning charger 22 on the upstream side of the cleaning blade 18d in the drum rotation direction,
By reducing the charge amount of the residual toner before the residual toner reaches the cleaning blade 18d, the electrostatic attraction force can be reduced and the cleaning process by the cleaning blade 18d can be assisted. Therefore, it is possible to effectively prevent the fusion of the toner peculiar to the black image forming portion by the cleaning auxiliary charging and maintain the cleaning performance.

[Fourth Embodiment] Next, another example of the image forming apparatus shown in the first embodiment will be described with reference to FIGS. Since the schematic configuration of the entire apparatus is the same as that of the first embodiment, the same members are designated by the same reference numerals and the description thereof will be omitted. In the first to third embodiments, the cleaning means including the cleaning blade and the auxiliary means is adopted only for the black image forming portion P _d where the toner fusion is likely to occur.
It is not limited to the black image forming portion that the cleaning method different from the other image forming portions is used. For example,
If toner fusion is likely to occur in the black and cyan image forming portions, only the blade cleaning method is used in the yellow and magenta image forming portions, and the cleaning blade + auxiliary means is used in the black and cyan image forming portions. It is also possible to adopt a cleaning method by.

In the first to third embodiments, a 4-drum type color copying machine has been described as an apparatus having a plurality of image forming sections, but the number of image forming sections need not be four. For example, as shown in FIG. 5, it is also possible to adopt two different cleaning methods in a copying machine or a printer having two image forming sections for black and red. In FIG. 5, in the red image forming portion P _a ′, a blade cleaning type cleaning device 13 a ′ is used,
In the black image forming portion _Pb ', a cleaning device 13b' using a blade and auxiliary means is used.

Further, in the first to third embodiments,
The black image forming portion P _d is located at the
Although it was disposed in the fourth image forming portion corresponding to the second, when the magnetic one-component toner is used as the black toner,
The image quality peculiar to the magnetic toner becomes less noticeable when the first one is used. Therefore, as shown in FIG. 6, it is also possible to dispose the black image forming portion P _d in the first image forming portion. In this case, the cleaning device including the blade and the auxiliary unit may be any of the first to fourth image forming units.

[0039]

As described above, according to the present invention, the cleaning means for at least one image forming portion (for example, a black image forming portion) among the plurality of image forming portions has the cleaning assisting means in addition to the cleaning blade. However, since the cleaning means of the other image forming portion (for example, the image forming portion of a color other than black) has only the cleaning blade, the cleaning failure peculiar to the black image forming portion (for example, toner fusion) ) Can be prevented. Therefore, the cleaning performance can be maintained while realizing downsizing and cost reduction of the entire apparatus.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a cleaning device.

FIG. 2 is a cross-sectional explanatory diagram showing an overall configuration of a copying apparatus.

FIG. 3 is an explanatory diagram showing a configuration of a cleaning device according to another example.

FIG. 4 is an explanatory diagram showing a configuration of a cleaning device according to another example.

FIG. 5 is an explanatory diagram showing a configuration of a copying apparatus according to another example.

FIG. 6 is an explanatory diagram showing a configuration of a copying apparatus according to another example.

FIG. 7 is an explanatory diagram of a conventional copying apparatus.

FIG. 8 is an explanatory diagram showing a configuration of a conventional cleaning device.

[Explanation of symbols]

P _a , P _b , P _c , P _d , P _a ′, P _b ′ ... Image forming unit 1 ... Device body 2 a, 2 b, 2 a ′, 2 b ′ ... Belt driving roller 3, 3 ′ ... Transfer belt 4, 4 ′ ... Cassette 5,5 ′ ... Transfer material 6,6 ′ ... Pickup roller 7,7 ′ ... Registration roller pair 8,8 ′ ... Conveyance guide 9a, 9b, 9c, 9d, 9a ′, 9b ′ ... Photosensitive drum 10a, 10b, 10c, 10d, 10a ', 10b' ... Primary charging device 11a, 11b, 11c, 11d, 11a ', 11b' ... Developing device 12a, 12b, 12c, 12d, 12a ', 12b' ... Transfer charging device 13a, 13b, 13c, 13d, 13a ', 13b' ... Cleaning device 14, 14 '... Separation charging device 15, 15' ... Fixing device 15a, 15a '... Fixing roller 15b, 15b' ... Pressure roller 16, 16 '... Ejection Tray 17, 21 ... Fur brushes 18a, 18b, 18c, 18d ... Cleaning blade 18e ... Coating layer 19a, 19b, 19c, 19d ... Squi sheet 20a, 20b, 20c, 20d ... Conveying screw 22 ... Cleaning auxiliary charger

Claims (6)

[Claims] 1. An image forming apparatus having an image carrier and a plurality of image forming units that act on the image carrier to form an image on a recording material, wherein each of the image forming units remains on the image carrier. Characterized in that the cleaning means for removing the developer to be used has at least one cleaning means for the image forming portion has a cleaning blade and a cleaning assisting means, and the other image forming portion has only the cleaning blade. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the image forming unit having the cleaning blade and the cleaning assisting unit is a black image forming unit. 3. The image forming apparatus according to claim 1, wherein the cleaning assisting means is a fur brush. 4. The image forming apparatus according to claim 1, wherein the cleaning auxiliary unit is a cleaning auxiliary charger. 5. An image forming unit having the cleaning blade and a cleaning assisting means, wherein the cleaning blade has a coating layer applied on a surface of a urethane rubber blade to reduce a frictional force with the image carrier. The image forming apparatus according to claim 1. 6. The image forming apparatus according to claim 5, wherein the coating layer is composed of a resin layer in which fluorinated graphite particles are dispersed.