JP2923155B2 - Image forming device - Google Patents

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 a plurality of image forming units for forming an image on a recording medium by acting on an image carrier.

[0002]

2. Description of the Related Art As an example of an image forming apparatus having a plurality of image forming units for forming an image on a recording medium by acting on an image carrier, a four-drum type color image forming apparatus is conventionally shown in FIG.
Shown in In order to increase the speed of the apparatus, the four-drum type color image forming apparatus is provided with four image forming units each having an image carrier and process means disposed around the image carrier, and the image carrier formed by each image forming unit is provided. The image on the body is configured to be sequentially transferred onto a recording medium carried and conveyed by a conveyance unit that moves adjacent to the image carrier.

More specifically, as shown in FIG. 6, the image forming apparatus includes, as image carriers, image forming units Pa, Pb, Pc, and Pd of each color necessary for forming a full-color image. Photosensitive drums 51a, 51b, 51c, 51
and a charger 52a, 52b, 52c, 52d as a charging unit, a scanning optical device (not shown) as an optical scanning unit, and a developing unit 53 as a developing unit.
a, 53b, 53c, 53d, and process means such as cleaners 54a, 54b, 54c, 54d as cleaning means are arranged. The transfer means includes an endless belt-like transfer belt 55 common to the image forming units, and transfer chargers 56a and 56.
b, 56c, and 56d, and images of respective colors formed on the photosensitive drums 51a, 51b, 51c, and 51d of the image forming units on a recording medium 57 carried and conveyed on the transfer belt 55. Is to be transcribed. The recording medium 57 is supplied from a feeding cassette 58, and after a transfer step, a transfer belt 55.
The transfer image is separated from above, fixed by the fixing device 59, and discharged onto the discharge tray 60.

[0004] The four cleaners 54a, 54b, 54c, 54
7D, the cleaning blades 54a1, 54b1, 54c1, and 54d1 rotate in the direction of arrow A and contact the surfaces of the photosensitive drums 51a, 51b, 51c, and 51d with a contact angle θ1. Touched. Therefore, the toner as the developer remaining on the surfaces of the photosensitive drums 51a, 51b, 51c, and 51d without contributing to the transfer at the transfer position is transferred to the photosensitive drums by the cleaning blades 54a1, 54b1, 54c1, and 54d1.
From the surfaces of 51a, 51b, 51c and 51d, squeeze sheets 54a2,
It is scraped off on 54b2, 54c2, 54d2.

Such a blade cleaning system is more advantageous in reducing the price and size of the cleaner than other cleaning systems. In particular, in a four-drum type color image forming apparatus as shown in FIG. Since there are a plurality of cleaning devices, this is a very effective cleaning method for realizing downsizing and cost reduction of the entire apparatus.

The cleaning blades 54a1, 54b1,
The contact angles θ1 of 54c1 and 54d1 with respect to the respective photosensitive drums 51a, 51b, 51c and 51d are set to the same value in the four image forming units. If the contact angle θ1 is too small, the waste toner on the photosensitive drums 51a, 51b, 51c, and 51d cannot be sufficiently cleaned, and if too large, the contact angle between the photosensitive drums 51a, 51b, 51c, and 51d can be reduced. Of the photosensitive drums 51a, 51b, 51c, and 51d are not driven to rotate or cleaning is not performed properly. In particular, in the case of toners of magenta, cyan, yellow and the like in a color image forming apparatus, since the mixture of external additives and the like cannot be mixed into the toner due to color development, the contact angle θ1 is set quite accurately. There must be.

[0007]

In offices and the like that require 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. In such places,
Copying operation in black is often performed. The above-described conventional four-drum type image forming apparatus (see FIG. 6) can perform a high-speed continuous operation comparable to a high-speed monochrome copying machine.
It is thought that the use opportunity in the black monochromatic mode will also increase.

Therefore, using an inexpensive developer for the black image forming portion is a very effective means for reducing running costs. For example, as a developer of a conventional color image forming apparatus, a two-component developer of a magnetic carrier and a non-magnetic toner is employed. The use of an agent makes it possible to greatly reduce running costs. Further, since it is not necessary to always keep the toner concentration constant unlike the two-component phenomena agent, the apparatus configuration is simplified. As described above, the use of the one-component phenomenon agent having only black magnetism has many advantages such as a reduction in running cost and a simplified maintenance, particularly when a large number of black single-color images are used.

However, the one-component developer having magnetism tends to cause a phenomenon called "toner fusion" in which toner adheres to the photosensitive drum, and if this phenomenon occurs, cleaning cannot be performed sufficiently. There was a problem that would. Further, when the toner fusion occurs, there is a problem that an image defect such as a white point is generated on an image.

Accordingly, an object of the present invention is to prevent a cleaning failure due to fusion of a developer to an image carrier.

[0011]

To achieve the above object, a typical image forming apparatus according to the present invention comprises an image forming apparatus having a plurality of image forming units for forming an image on a recording medium by acting on an image carrier. In the apparatus, each of the image forming units has a cleaning blade that comes into contact with the image carrier and scrapes off a developer attached to a surface of the image carrier. Is different from the contact angle of the cleaning blade of another image forming section with the image carrier.

[0012]

In the image forming apparatus having the above structure, the contact angle of at least one image forming section with the cleaning blade of the image forming unit and the contact angle of the cleaning blade of another image forming unit with the image carrier. Since the contact angle is different from the contact angle of the cleaning blade in the black image forming section with the image carrier, for example, if the contact angle of the cleaning blade in the other image forming section with the image carrier is different. More specifically, by making the contact angle of the former larger than the contact angle of the latter, the fusion of the developer to the image carrier hardly occurs, and the cleaning can be performed effectively. Becomes

[0013]

【Example】

First Embodiment A first embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. In this embodiment, a description will be given using a color image forming apparatus provided with a plurality of image forming units for forming an image on a recording medium by acting on an image carrier as the image forming apparatus. FIG. 1 is a cross-sectional explanatory view showing the overall configuration of the color image forming apparatus, and FIG. 2 is an enlarged explanatory view schematically showing a cleaning device.

First, a schematic configuration of a color image forming apparatus will be described with reference to FIG. 1. The color image forming apparatus in this embodiment is a four-drum type color image forming apparatus, and the speed of the apparatus is increased. Therefore, there are provided four image forming sections each having an image carrier and process means disposed around the image carrier, and the image formed on each image forming section on the image carrier is moved adjacent to the image carrier. It is configured to be sequentially transferred onto a recording medium carried and conveyed by means.

More specifically, the image forming units Pa, Pb, and P containing process means are built in the apparatus main body 1.
c, Pd are arranged in the horizontal direction, and each image forming unit P
a, Pb, Pc, Pd, a belt driving roller 2
An endless transfer belt 3 is hung around a and 2b. The transfer belt 3 is rotated in the direction of arrow C by rotating the belt driving rollers 2a and 2b in the direction of arrow B by a drive motor (not shown).

Reference numeral 4 denotes a cassette in which recording sheets 5 as recording media are stacked and stored. The recording sheets 5 stored in the cassette 4 are separated and fed one by one from a top by a pickup roller 6. Sent. Then, the skew is corrected by the pair of registration rollers 7, and the sheet is conveyed onto the transfer belt 3 in synchronization with the image forming units Pa, Pb, Pc, and Pd. 8 is the recording sheet 5
Is a conveyance guide for guiding the toner image to the transfer belt 3 from the registration roller pair 7.

Next, the image forming units Pa, Pb, Pc, P
To explain the configuration of d, a primary charger 10 having photosensitive drums 9a, 9b, 9c and 9d as image carriers and surrounding the photosensitive drum as process means acting on the photosensitive drum is provided.
a, 10b, 10c, 10b, developing units 11a, 11b, 11c, 11
d, transfer chargers 12a, 12b, 12c, and 12d, and cleaning devices 13a, 13b, 13c, and 13d, respectively. Above the photosensitive drums 9a, 9b, 9c, 9d,
A laser beam scanner (not shown) as an exposure unit is provided.

The primary chargers 10a, 10b, 10c, 10d
Is for uniformly charging the drum surface before exposing the photosensitive drums 9a, 9b, 9c, 9d. The developing units 11a, 11b, 11c, and 11d apply black, magenta, yellow, and cyan developers (hereinafter, referred to as toners) to the exposed electrostatic latent images formed on the drum surface. This is to make a visible image. The transfer chargers 12a, 12b, 12c, and 12d are connected to the photosensitive drum 9
a, 9b, 9c, and 9d are transferred to the recording sheet 5. The cleaning devices 13a, 13b, 13c and 13d remove residual toner adhering to the drum surface after image transfer. The laser beam scanner has a semiconductor laser, a polygon mirror, an fθ lens, etc., receives an electric digital image signal, and modulates a laser beam corresponding to the input signal to the photosensitive drums 9a, 9b, 9c, 9d. In the direction of the generatrix.

In FIG. 1, reference numeral 14 denotes a separation charger for separating the recording sheet 5 conveyed on the transfer belt 3. Further, reference numeral 15 denotes a fixing device for fixing the transferred image transferred to the recording sheet 5, and has a fixing roller 15a having a heating means such as a heater and a pressure roller 15b pressed against the fixing roller 15a. . Reference numeral 16 denotes a discharge tray for stacking the recording sheets 5 discharged outside the apparatus.

Next, an 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 is started.
The drum is irradiated with laser light modulated by an image signal corresponding to a black component of a document image by a laser beam scanner (not shown) to form an electrostatic latent image (exposure). Next, a yellow toner is supplied by the developing device 11a to form a toner image in which the latent image is visualized.

On the other hand, the recording sheet 5 accommodated in the cassette 4 is fed by a pickup roller 6, and the skew thereof is corrected by a registration roller pair 7 which is temporarily stopped, and then formed on the photosensitive drum 9a. The toner image is conveyed onto the transfer belt 3 at the timing with the toner image.
The recording sheet 5 sent to the transfer belt 3 is transferred and charged by the transfer charger 12a at the transfer position of the image forming unit Pa, and the toner image is transferred to the recording sheet 5. The above steps are similarly performed in the image forming units Pb, Pc, and Pd, and a magenta toner image, a cyan toner image,
The black toner images are sequentially transferred to the recording sheet 5.

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

A part of the transfer belt 3 is in contact with a fur brush 17 as a belt cleaning means. By rotating the fur brush 17 at a high speed, the toner accumulated on the transfer belt 3 is transferred onto the belt. Is configured to be removed from.

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. The cleaning device 13 removes toner remaining on the photosensitive drums 9a, 9b, 9c and 9d (hereinafter abbreviated as photosensitive drum 9) without contributing to the transfer after the image transfer process. Cleaning blade 18 which comes into contact with the drum surface from the direction opposite to the rotation direction (direction of arrow A). The cleaning blade 18 includes a cleaning container 19
Is fixed to a blade support member (not shown) provided on the downstream side in the drum rotation direction by screwing or the like. A squeeze sheet 21 for storing the toner scraped off by the cleaning blade 18 in the container is provided downstream of the cleaning container 19 in the drum rotation direction. Further, a transport screw 22 for collecting and transporting waste toner is provided in the cleaning container 19.

In this embodiment, the three (yellow, magenta, cyan) image forming units Pa, Pb, Pc
Is a two-component developing agent of a magnetic carrier and a non-magnetic toner.
As the developer d, a one-component developer having magnetism is used. As a result, the price of the toner in the black image forming portion Pd can be suppressed, and low running cost is realized, particularly when a large number of copies are made in the black single-color mode.

This one-component developer having magnetism has a problem that the toner sticks to the photosensitive drum, that is, a phenomenon called "toner fusion" tends to occur. In order to prevent the cleaning failure, the contact angle θ2 of the cleaning blade 18d with respect to the photosensitive drum 9d in the black image forming unit Pd is changed to the photosensitive drum 9a of the cleaning blades 18a, 18b, 18c in the other image forming units Pa, Pb, Pc. , 9b, 9c
Is larger than the contact angle θ1 (θ1 <θ
2). In this case, problems such as blade turn-up tend to occur, but black toner is used for other colors (yellow, magenta,
Compared with the cyan toner, the color does not change much when the external additive is mixed. Therefore, the external additive can be mixed relatively freely than the other color toners, and the contact angle of the cleaning blade with the photosensitive drum can be reduced. Even if it is set to a large value, it is possible to prevent the blade from being turned up by mixing a submicron-order external additive such as silica for reducing the friction between the cleaning blade and the photosensitive drum into the toner. is there.

The contact angle of the cleaning blade 18 with the photosensitive drum 9 is set as shown in FIG.
That is, each of the yellow, magenta, and cyan image forming portions P
a, Cleaning blades 18a, 18 at Pb, Pc
The contact angle θ1 of the b, 18c with respect to the photosensitive drums 9a, 9b, 9c is defined as the lower limit of the value at which toner does not slip and the upper limit of the value at which blade turning does not occur. On the other hand, the contact angle θ2 of the cleaning blade 18d with respect to the photosensitive drum 9d in the black image forming portion Pd is set to a value at which toner fusion does not occur, and a value at which blade turning does not occur is set to an upper limit. Is set to the average of the lower limit and the upper limit. Therefore, the relationship between the contact angles is θ1 <θ2.
As shown in FIG. 2, the setting of the contact angle of the blade in the black image forming unit is different from that of the other image forming units. This makes it possible to prevent a cleaning failure due to fusion of toner in the frequently used black image forming unit.

[Second Embodiment] Next, a description will be given of a second embodiment of the image forming apparatus according to the present invention. Since the overall configuration of the apparatus is substantially the same as that described in the first embodiment, a detailed description is omitted here.

In this embodiment, a coating layer for reducing the frictional force between the blade and the photosensitive drum is provided on part or all of the surface of the cleaning blade in the black image forming portion.

Conventionally, urethane rubber is mainly used as a material of the cleaning blade from the viewpoints of chemical resistance, abrasion resistance, moldability, and mechanical strength. For example,
Since the coefficient of friction between the OPC photosensitive drum whose surface layer is made of a polymer resin such as polycarbonate is very high, in such a combination, a large frictional force is generated between the photosensitive drum and the cleaning blade. In addition, the cleaning blade is reversed in the rotation direction of the photosensitive drum, that is, the blade is turned up, so that the photosensitive drum is not driven to rotate or the cleaning is not properly performed.

Therefore, in the present embodiment, a coating material for reducing the frictional force between the blade and the photosensitive drum is applied to the surface of the cleaning blade in the black image forming portion, so that the blade is turned up. The configuration is such that generation can be prevented and cleaning can be performed effectively.

In the above-described first embodiment, the occurrence of the blade turning or the like is prevented by the external additive mixed in the developer of the black image forming portion.
Further, the occurrence of blade turnover can be prevented, and the blade contact angle can be set to an optimum value. Further, since only the coating layer for reducing the frictional force can be effectively provided on the surface of the cleaning blade to prevent the blade from being turned up and the like, toner fusion is likely to occur especially at portions other than the black image forming portion. It can also be applied to an image forming unit.

According to the experiment of the present inventor, in particular, when cleaning is performed by bringing a polyurethane rubber cleaning blade into contact with an OPC photosensitive drum whose surface layer is made of a polymer resin such as polycarbonate, the cleaning is performed. As a coating layer to be provided on the contact portion of the blade with the photosensitive drum, fluorinated graphite powder is dispersed in a polymer resin solvent such as nylon, dipped and applied to a cleaning blade, and then dried, heated and cured. It has been found that the blades can be very effectively prevented from being turned up.

Further, as the fluorinated graphite, for example,
(C2F) n-type Cefbon DM (manufactured by Central Glass), (CF) n-type Cefbon CMA, Cefbon C
MF (manufactured by Central Glass), Fluorocarbon $ 2065, $ 10
30, ♯1000 (manufactured by Asahi Glass Co.), CF-100 (Nippon Carbon), and (CF) n-type fluorocarbon with changed fluorination rate 化 2028, ♯2010 (manufactured by Asahi Glass Co., Ltd.) Examples thereof include graphite obtained by treating graphite with a base such as an amine to remove fluorine on the surface, but are not limited thereto.
The average particle size of the fluorinated graphite is preferably 20 μm or less, more preferably 1 μm to 8 μm, so as not to impair the cleaning of the toner.
The range of μm is good.

[Third Embodiment] Next, a third embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 4 is an enlarged explanatory view schematically showing the cleaning device. Since the overall configuration of the apparatus is substantially the same as that described in the first embodiment, a detailed description is omitted here. Members having the same function are denoted by the same reference numerals.

Also in this embodiment, the three (yellow, magenta, cyan) image forming units Pa, Pb, Pc
Is a two-component developer composed of a magnetic carrier and a non-magnetic toner.
As the developer, a one-component developer having magnetism is used to realize low running cost. For this reason, although toner fusion is likely to occur in the black image forming portion Pd,
It has been found that the fur brush + blade cleaning method is very effective for this toner fusion. For the above reasons, the image forming units Pa, Pb, Pc, Pd
The cleaning devices 13a, 13b, 13c, and 13d in are configured as described below.

First, the cleaning device 13 in the yellow, magenta, and cyan image forming units Pa, Pb, and Pc.
As shown in FIG. 3B, a, 13b, and 13c employ a blade cleaning method that can be configured in a space-saving manner and at low cost. On the other hand, the cleaning device 13d in the black image forming portion Pd is provided to prevent toner fusion.
As shown in FIG. 3A, a fur brush + blade cleaning system is employed.

Here, the cleaning blades 18a, 18b, 18c of the image forming sections Pa, Pb, Pc employing the blade cleaning system are provided with the photosensitive drums 9a, 9b, 9c as shown in FIG. The blade is configured to come into contact with the surfaces of the photosensitive drums 9a, 9b, and 9c in a direction opposite to the rotation direction (the direction of the arrow A) with a contact angle θ1 at which sufficient cleaning performance can be exhibited by the blade alone. However, as shown in FIG. 3A, the cleaning blade 18d of the black image forming portion Pd adopting the fur brush + blade cleaning method has a contact angle θ3 (θ3 <θ1) as shown in FIG. It is configured to contact the surface of 9d.

In the case of the blade cleaning system alone, toner and an external additive in the toner intervene between the blade and the drum and serve as a lubricant to prevent the blade from being turned up. When the blade cleaning method is used, toner remaining on the surface of the photosensitive drum 9d without contributing to the transfer at the transfer position and external additives in the toner are provided on the upstream side in the rotation direction of the photosensitive drum 9d with respect to the cleaning blade 18d. Fur brush 23
Is removed from the surface of the photosensitive drum 9d to some extent.
There is a problem that the amount of the toner to be used as the lubricant and the amount of the external additive in the toner is very small, so that a defect such as blade turning easily occurs. Therefore, the contact angle θ3 of the cleaning blade 18d with respect to the photosensitive drum 9d in the black image forming portion Pd is set to be different from the contact angle θ3 of the cleaning blades 18a, 18b, and 18c with respect to the photosensitive drums 9a, 9b, and 9c in the other image forming portions Pa, Pb, and Pc. It is set smaller than the contact angle θ1 (θ3 <θ1). This prevents the blade from being turned up.

In fact, in a cleaning apparatus using the fur brush + blade cleaning system, since the waste toner is considerably removed by the fur brush before reaching the cleaning blade, the blade cleaning for removing the toner by itself is performed. Sufficient cleaning can be performed even if the contact angle is small as compared with the system.

As described above, only the cleaning device in the black image forming section employs the fur brush + blade cleaning system, and the cleaning devices in the other image forming portions employ the blade cleaning system. In the image forming apparatus, the cleaning angle is effectively set by setting the contact angle of the cleaning blade to the photosensitive drum in the black image forming section to be smaller than the contact angle of the cleaning blade in the other image forming sections to the photosensitive drum. Will be able to do it.

[Fourth Embodiment] Next, a fourth embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 5 is an enlarged explanatory view schematically showing the cleaning device. Since the overall configuration of the apparatus is substantially the same as that described in the first embodiment, a detailed description is omitted here. Members having the same function are denoted by the same reference numerals.

In this embodiment, similarly to the third embodiment, the cleaning devices 13a and 13c in the yellow, magenta and cyan image forming units Pa, Pb and Pc are used.
b and 13c are space-saving as shown in FIG.
The blade cleaning method, which can be configured at a low cost, is adopted. On the other hand, the cleaning device 13d in the black image forming portion Pd is used to prevent the toner from fusing.
As shown in (a), a fur brush + blade cleaning system is employed.

Here, the cleaning blades 13a, 13b, 13c in the image forming sections Pa, Pb, Pc employing the blade cleaning system are provided with photosensitive drums 9a, 9b.
The photosensitive drums 9a, 9a, and 9b have a contact angle θ1 from the direction (counter direction) opposite to the rotation direction of the b and 9c (the direction of the arrow A) so that sufficient cleaning performance can be exhibited by the blade alone.
The cleaning blade in the black image forming portion Pd which is configured to contact with the surfaces of 9b and 9c, but employs a fur brush + blade cleaning system
Reference numeral 18d is configured to contact the surface of the photosensitive drum 9d with a contact angle θ4 from the same direction (the direction of the arrow A) as the rotation direction (direction of arrow A) of the photosensitive drum 9d. The contact angle θ1 is set to 90 ° or less, and the contact angle θ4 is set to 90 ° or more.

As described above, when the cleaning blade is brought into contact with the photosensitive drum from the wise direction, the cleaning performance is significantly reduced as compared with the case where the cleaning blade is brought into contact with the photosensitive drum from the counter direction. However, when the cleaning is performed by the fur brush and the blade, the toner removal ability by the fur brush is extremely high, so that the cleaning can be sufficiently performed even when the blade is brought into contact with the fur direction, thereby preventing the blade from being turned.

As described above, in the four-drum type color image forming apparatus employing the fur brush + blade cleaning system only for the black image forming unit and the blade cleaning system for the other image forming units, the black image forming unit is used. The cleaning blade of the forming section is brought into contact with the photosensitive drum from the wise direction, and the cleaning blade of the other image forming section is brought into contact with the photosensitive drum from the counter direction, that is, the contact angle of the former and the contact angle of the latter. By setting the angle to a different value, cleaning can be performed effectively.

The image forming section using a cleaning blade having a contact angle different from that of the other image forming sections is not limited to black, and may be used in an image forming section in which cleaning failure due to toner fusion is particularly likely to occur.

[0048]

As described above, according to the present invention, in an image forming apparatus having a plurality of image forming units for forming an image on a recording medium by acting on an image carrier, an image of a cleaning blade in a black image forming unit is provided. Since the contact angle with respect to the carrier is set to a value different from the contact angle of the cleaning blade with respect to the image carrier in the other image forming units, while the entire apparatus is made compact, the black Insufficient cleaning due to fusion of toner specific to the image forming unit can be prevented, and cleaning can be performed effectively. Also, the black developer is more
Even if the external additive is mixed, the color does not change much, so the external additive can be mixed relatively freely than the developer of other colors, and the contact angle of the cleaning blade to the image carrier is set to be large. Also, by mixing a submicron-order external additive such as silica for reducing the friction between the blade and the image carrier into the developer, the blade can be prevented from being turned.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view illustrating an entire configuration of a color image forming apparatus.

FIG. 2 is an enlarged explanatory view schematically showing the cleaning device according to the first embodiment.

FIG. 3 is an explanatory diagram of a contact angle of a blade with respect to a photosensitive drum.

FIG. 4 is an enlarged explanatory view schematically showing a cleaning device according to a third embodiment.

FIG. 5 is an enlarged explanatory view schematically showing a cleaning device according to a fourth embodiment.

FIG. 6 is an explanatory diagram of a conventional technique.

FIG. 7 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 Pa, Pb, Pc, Pd: image forming unit 1: apparatus main body 2a, 2b: belt driving roller 3: transfer belt 4: cassette 5: recording sheet 6, pickup roller 7, registration roller pair 8, transport guide 9a, 9b, 9c, 9d: photosensitive drums 10a, 10b, 10c, 10b: primary chargers 11a, 11b, 11c, 11d: developing devices 12a, 12b, 12c, 12d: transfer chargers 13a, 13b, 13c, 13d: cleaning device 14 ... Separation charger 15 Fixing device 15a Fixing roller 15b Pressure roller 16 Discharge tray 17 Fur brushes 18a, 18b, 18c, 18d Cleaning blades 19a, 19b, 19c, 19d Cleaning containers 21a, 21b, 21c, 21d: Squeeze sheet 22a, 22b, 22c, 22d: Conveying screw 23: Fur brush

Claims (4)

(57) [Claims] 1. An image forming apparatus having a plurality of image forming units that form an image on a recording medium by acting on an image carrier, wherein each of the image forming units is in contact with the image carrier and adheres to the surface thereof. A cleaning blade that scrapes off and removes the developer, wherein at least one image forming unit has a contact angle between the cleaning blade and the image carrier, and another image forming unit has a contact between the cleaning blade and the image carrier. An image forming apparatus characterized by having a different angle from a corner. 2. The image forming unit according to claim 1, wherein the contact angle of the cleaning blade with the image carrier is different from that of the other image forming units, and the image forming unit has a black developer. The image forming apparatus as described in the above. 3. A one-component developer having magnetism as a developer used in an image forming portion having the black developer, wherein the developer is used to reduce a frictional force between a cleaning blade and an image carrier. 3. The image forming apparatus according to claim 2, wherein an external additive is mixed. 4. A one-component developer having magnetism is used as a developer to be used in the image forming section having the black developer, and a part or all of the surface of the cleaning blade of the image forming section is cleaned. 3. The image forming apparatus according to claim 2, further comprising a coat layer for reducing a frictional force between the blade and the image carrier.