JP2001249576A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the frequency of replacement work by making a replacing timing in plural photoreceptive drums coincident. SOLUTION: In the plural photoreceptive drums 11 whose contact frictional force applied to a photoreceptive layer is mutually different, it is formed so as to obtain the excellent friction resistance durability of the photoreceptive layer of the photoreceptive drum 11 whose contact frictional force is larger. Thus, the replacing timings of the plural photoreceptive drums are made coincident.

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 color copying machine or a color printer based on an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art FIG. 5 is a schematic structural view of a conventional image forming apparatus capable of forming a color image. This image forming apparatus includes:
In order to speed up color image output, a plurality of photoconductors are mounted, and each photoconductor sequentially transfers a toner image to a transferred transfer material (ie, multiple transfer).

As shown in FIG. 5, this image forming apparatus comprises:
Image forming units M, C, Y, and B of four colors of magenta, cyan, yellow, and black are used as image forming units.
and a transfer belt 30 and a fixing device 40 as transfer means. The image forming unit of each image forming unit includes a photosensitive drum 11 serving as an image carrier.
M, 11C, 11Y, and 11Bk, around which charging rollers 12M, 12C, 12Y, and 12Bk, laser exposure devices 13M, 13C, 13Y, and 13Bk, and a developing device 14
M, 14C, 14Y, and 14Bk are provided, respectively. The transfer belt 30 includes the photosensitive drums 11M, 11C, 1
1Y, 11Bk, and are arranged in contact with the driving rollers 31,
It is stretched and driven by a separation roller 82.

The photosensitive drums 11 are uniformly negatively charged on the surface by respective charging rollers 12, and then are exposed by respective laser exposure devices 13. As a result, an electrostatic latent image corresponding to the document is formed on each photosensitive drum 11. Further, each developing unit 14 performs development using negative toner, and a toner image is formed on the surface of each photosensitive drum 11. Each image forming unit performs the image forming operation at a predetermined timing, and forms a toner image on each photosensitive drum.

The transfer material P fed by the feed roller 20
Is carried on the transfer belt 30 and sequentially conveyed to the transfer sections of the image forming units M, C, Y, and Bk, where each color is transferred onto the transfer material P by the transfer rollers 15M, 15C, 15Y, and 15Bk. Is transferred.

The transfer material P that has completed the transfer process is separated from the transfer belt 30 by a separation roller 32,
The toner image thus transferred is fixed by being pressed and heated by the fixing device 40.

[0007]

However, most of the photosensitive drums (photoreceptors) used in the image forming apparatus of the electrophotographic type or the like as described above have a photoreceptor layer thickness that increases with the durable paper passing. It gradually decreases. This is because the photosensitive drum comes into contact with the charging roller, the developing device, the transfer material, and the like, and is mechanically polished by rubbing with these members.

By the way, in order for the image forming apparatus to maintain a good image, the minimum required thickness of the photosensitive layer is determined, and the photosensitive drum having lost a predetermined thickness must be replaced. In an image forming apparatus equipped with a plurality of photosensitive drums as in the above-described conventional example, the use conditions often differ among the individual photosensitive drums, and therefore, the replacement time of each photosensitive drum often differs. If the replacement time is different for each photosensitive drum, the frequency of replacement work increases and usability deteriorates.

For example, when a user uses an image forming apparatus, in many cases not only color printing but also monochrome (black) printing is frequently used, and the ratio tends to increase in recent years. In order to reduce the running cost of monochrome printing to the same level as a conventional monochrome image forming apparatus, the developing method may be different for color toner and black toner. As an example, the color toner adopts a non-magnetic one-component toner developing method that has excellent gradation reproducibility and good maintainability, and the black toner has low cost, excellent durability stability and text reproduction. There is a case where a magnetic toner developing method having a property is used. In general,
Magnetic toner has a stronger polishing force on the photosensitive drum than non-magnetic toner, and as a result, the photosensitive drum used for black image formation is shorter than other photosensitive drums (the photosensitive drum used for color toner). It is consumed in the cycle.
In other words, the timing for replacing the photosensitive drum for the color toner and the photosensitive drum for the black toner are different, and the frequency of replacing these photosensitive drums increases, resulting in reduced usability.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus which can replace a plurality of photosensitive drums at the same time, reduce the frequency of replacement work, and improve usability.

[0011]

According to the present invention, there is provided a photoreceptor having a photoreceptor layer on which a toner image can be formed, and a method for transferring the toner image formed on the photoreceptor layer to a transfer member. A plurality of image forming / transferring units each including a transfer unit that performs a contact operation that acts on the photoconductor layer when a toner image is formed and transferred to a transfer member. An image forming apparatus including an image forming / transferring unit having different frictional forces, wherein the photoconductor layer of the image forming / transferring unit having the larger contact frictional force forms the image forming unit having the smaller contact frictional force. -The image forming apparatus is characterized in that the transfer unit has a higher durability against friction than the photosensitive layer.

The friction durability of the photoconductor layer can be increased by increasing the thickness of the photoconductor layer, and the photoconductor layer is formed of a material having high wear resistance. It is also possible to make it higher.

Further, among the plurality of image forming / transferring units, an image forming / transferring unit for black toner and an image forming / transferring unit for other color toners are included. The photoreceptor layer of the image forming / transfer unit is formed to have higher friction durability performance than the photoreceptor layer of the image forming / transfer unit for the other color toners.
An image forming apparatus characterized by the above is also possible.

With the above arrangement, the photoreceptor layer has a uniform life between a plurality of image forming / transferring units.

[0015]

(Embodiment 1) FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. The image forming apparatus shown in FIG. 1 is a four-drum type full-color printer. Note that the same reference numerals are given to members and the like having the same configuration and the same function as those of the image forming apparatus illustrated in FIG. 5 described in “Prior Art”.

As shown in FIG. 1, this image forming apparatus comprises:
A transfer belt 30, which has a plurality of image forming units M, C, Y, and Bk (image forming / transferring units), and extends through each image forming unit, is provided.
Each of the image forming units M, C, Y, and Bk has a cylindrical photosensitive drum (photosensitive member) 1 as an electrostatic latent image carrier.
1M, 11C, 11Y, and 11Bk are rotatably supported in the direction of arrow a. 12M, 12C, 12Y, 12
Bk is a charging roller as a primary charger, and is arranged at a predetermined interval from the photosensitive drums 11M, 11C, 11Y, and 11Bk. Reference numerals 13M, 13C, 13Y, and 13Bk denote laser exposure devices, which are charging rollers 12M,
2C, 12Y, and 12Bk, photosensitive drums 11M, 1
The photosensitive drum is exposed on the downstream side in the rotation direction of 1C, 11Y, and 11Bk. 14M, 14C,
Reference numerals 14Y and 14Bk denote developing units containing magenta, cyan, yellow, and black toners, respectively, which are arranged further downstream of the respective exposure devices of the photosensitive drums 11M, 11C, 11Y, and 11Bk so as to be adjacent to the photosensitive drums. Have been.

Reference numeral 30 denotes a transfer belt which carries and conveys the transfer material P (transfer member) supplied from the paper supply unit 20, is stretched by a drive roller 31 and a separation roller 32, and
1M, 11C, 11Y and 11Bk are brought into contact with each other and driven to rotate in the direction of arrow b.

Transfer rollers 15M and 15 as transfer chargers
C, 15Y, and 15Bk (transfer means) are the transfer belt 30
Are arranged corresponding to the respective photosensitive drums in order from the upstream side in the moving direction of, and the transfer belt is sandwiched between the corresponding photosensitive drums.

Reference numerals 16M, 16C, 16Y and 16Bk denote cleaners for the respective photosensitive drums, and reference numeral 33 denotes a belt cleaner for cleaning the transfer belt 30.

The operation of the image forming apparatus configured as described above will be described using the image forming unit M as an example.

The photosensitive drum 11M has a photoconductive layer on the surface of a conductive substrate such as aluminum, and rotates in the direction of arrow a in the figure. Then, after the surface is uniformly negatively charged by the charging roller 12M, exposure is performed by the laser exposure device 13M to form an electrostatic latent image corresponding to the document. The developing device 14M performs development using the negatively charged toner, and forms a toner image corresponding to the electrostatic latent image on the surface of the photosensitive drum 11M. The transfer material P is conveyed by the transfer belt 30 from the paper supply unit 20 in synchronization with the rotation of the photosensitive drum 11M, and the toner image formed on the surface of the photosensitive drum 11M is transferred onto the transfer material P by the transfer roller 15M. Transcribed.

On the other hand, the residual toner adhering to the surface of the photosensitive drum 11M after the transfer is removed by the cleaner 16M, and is used for the next image formation.

By performing the above operations in each image forming unit at a predetermined timing, the toner images formed on each photosensitive drum are sequentially transferred to the transfer material P held on the transfer belt 30. In the case of the full-color mode, the transfer is performed on the transfer material P in the order of M, C, Y, and Bk. Is multiplex-transferred onto the transfer material P.

The transfer material P to which the toner image has been transferred is supplied to the fixing device 40 by the transfer belt 30 and is heated and pressed to fix the toner image, thereby completing the formation of a full-color image.

The surface of the transfer belt 30 which has finished supplying the transfer material P to the fixing device 40 is cleaned by a belt cleaner 33. In the color image formation in the present embodiment, a non-magnetic one-component toner is used as a color toner, and a magnetic toner is used as a black toner.

Next, the photosensitive drum 11 will be described in detail with reference to FIG. The photosensitive drum 11 is formed by applying a photosensitive layer 11b made of an organic photoconductor layer (OPC) to an outer peripheral surface of a grounded drum base 11a made of a conductive material such as aluminum. Further, the photoreceptor layer 11b includes an undercoat layer (CPL) 11p, an injection blocking layer (UCL) 11q, a charge generation layer (CGL) 11r, and a charge transport layer (CTL) 11
s consists of four layers. In the first embodiment, the thickness d of the charge transport layer 11 s, which is the outermost layer of each photosensitive drum 11, is set to, for example, a black image forming unit B as described below.
Values are set differently for k and the image forming units M, C, and Y for other colors.

D (11M) = 20 μm, d (11C)
= 20 μm, d (11Y) = 20 μm, d (11B
k) = 24 μm By the way, the thickness of the charge transport layer, which is the outermost layer of the photosensitive drum, gradually decreases as the paper passing durability decreases, and the value becomes 1
If the thickness is 0 μm or less, sufficient charging characteristics and photosensitive characteristics cannot be obtained, and if the degree is poor, image defects such as image streaks and fogging will occur. That is, when the thickness of the charge transport layer reaches 10 μm, the life of the photosensitive drum is reached, and the photosensitive drum needs to be replaced. In the image forming apparatus according to the first embodiment, the amount of scraping of the charge transport layer 11s is about 1.0 μm per 1000 prints when the non-magnetic toner is used, and about 1.4 μm when the magnetic toner is used. . That is, the magnetic toner has 1.4 times the photoreceptor polishing power of the non-magnetic toner.

From the above, in the first embodiment,
The life of the photosensitive drum 11 of each color is the same between the image forming units of each color. That is, for the image forming units M, C, and Y using non-magnetic toner, (20 μm [CT
L initial film thickness] −10 μm [CTL lifetime film thickness]) ÷ 1.0
× 1000 = 10000 sheets, and for the black image forming unit Bk using the magnetic toner, (24 μm)
m [CTL initial film thickness] -10 μm [CTL lifetime film thickness])
Since × 1.4 × 1000 = 10000 sheets, the life time of the photosensitive drum 11 of each color can be made the same,
The replacement times of the plurality of photosensitive drums can be made coincident, the frequency of replacement work can be suppressed, and usability can be improved.

As described above, in the first embodiment, the thickness of the photosensitive layer of the photosensitive drum used in the black image forming unit Bk is made thicker than that of the image forming units M, C, and Y of the other colors. Although the life of the photosensitive drum was adjusted at the same time, in the present embodiment, a case where the photosensitive drum of the Bk image forming unit is greatly scraped was described. Even if it is different from the photosensitive drum of the color of
It is needless to say that the service lives of all the photosensitive drums can be adjusted at the same time by appropriately adjusting the thickness of the photosensitive member layer as in the first embodiment.

(Embodiment 2) In Embodiment 2, an example will be described in which the mechanical strength of the outermost layer of the photosensitive layer of the photosensitive drum is adjusted so that the service lives of the photosensitive drums of the respective colors are adjusted at the same time. The main configuration of the image forming apparatus used in the second embodiment is the same as that of the image forming apparatus described in the first embodiment, and a detailed description thereof will be omitted. In the second embodiment, a magnetic toner is used for the black toner, and a non-magnetic toner is used for the color toner.

The photosensitive drum 11Bk for black toner used in the second embodiment will be described in detail with reference to FIG. The photosensitive drum 11Bk is formed by applying and coating a photosensitive layer 11b made of an organic photoconductor layer (OPC) on an outer peripheral surface of a drum base 11a made of a conductive material such as aluminum and grounded, and has excellent abrasion resistance thereon. The protective layer (OCL) 11c is formed by coating. The photoreceptor layer 11b includes an undercoat layer (CPL) 11p and an injection blocking layer (UC
L) 11q, a charge generation layer (CGL) 11r, and a charge transport layer (CTL) 11s. The above protective layer 1
1c is a material in which a conductive material is dispersed in a resin having extremely high mechanical strength as compared with the charge transport layer 11s, and sufficient durability can be obtained by coating a thin film. When the black toner (magnetic toner) is used, the shaving amount of the protective layer 11c is about 0.2 μm per 1,000 prints.

In the second embodiment, for example, the initial thickness of the protective layer 11c is 2 μm, and the thickness of the charge transport layer 11s thereunder is 10 μm. Further, the photosensitive drum reaches its life when the protective layer 11c is completely removed and the charge transport layer 11s is exposed. That is, the photosensitive drum 1 for black toner
The life of 1 Bk is 2 μm [OCL initial film thickness] ÷ 0.2
× 1000 = 10000 sheets. Note that the photosensitive drums 11M, 11C, and 11Y for the color toner are the same as those in the first embodiment.
Similarly to the above, the protective layer 11c was not provided, and the film thickness of the outermost charge protective layer 11s was 20 μm. As a result, the life of the photosensitive drums 11M, 11C, and 11Y can be increased by 10,000 prints.
It is a sheet.

As described above, also in the second embodiment, the service life of the photosensitive drums 11 of the respective colors can be made the same, the replacement time of a plurality of photosensitive drums can be matched, and the frequency of replacement work can be suppressed to improve usability. Can be improved.

In the second embodiment, in order to adjust the mechanical strength of the outermost layer of the photosensitive layer of the photosensitive drum,
Although the protective layer (OCL) 11c is used, the strength may be adjusted by another method. For example, as the binder resin of the charge transport layer (CTL) 11s, which is the outermost layer of the four-layer photosensitive drum, materials having different strengths between the respective photosensitive drums may be used.

(Embodiment 3) FIG. 4 is a schematic configuration diagram of an image forming apparatus of Embodiment 3. In the third embodiment, an intermediate transfer belt 50 (transfer member) is used instead of the transfer belt 30 in the first embodiment. The intermediate transfer belt 50 includes a driving roller 51, a tension roller 5
It is stretched and driven by three rollers, that is, two and two transfer opposing rollers 53.

Obtained in the same manner as in Embodiment 1,
The images revealed on each photosensitive drum 11 are sequentially transferred onto the intermediate transfer belt 50 by the primary transfer rollers 54M, 54C, 54Y, and 54Bk, and are thus once inverted on the intermediate transfer belt 50. A full color image is formed. Thereafter, the image on the intermediate transfer belt 50 is collectively transferred by the secondary transfer roller 55 to the transfer material P supplied at a predetermined timing by the paper feed roller 20.

In the system of the third embodiment, in which an intermediate transfer belt is used and a full-color image is formed on the intermediate transfer belt, the image is directly transferred from a photosensitive drum onto a transfer material to form a full-color image. As compared with the forming method, the influence of the transfer material (size, thickness, standing state, etc.) can be reduced, which is advantageous for ensuring the stability of belt conveyance.

In the third embodiment, non-magnetic toner is used for all of the image forming units M, C, Y, and Bk, and all the photosensitive drums 11 use the four-layer photosensitive drum described with reference to FIG. ing. Furthermore, each photosensitive drum 11
The thicknesses of the charge transport layers 11s of M, 11C, 11Y, and 11Bk are respectively set to 20 μm, 21 μm, 22 μm, and 23 μm.
m, the thickness of the charge transport layer 11s of the photosensitive drum 11 on the downstream side is set to be large.

In general, in a color image forming apparatus that performs sequential transfer as in the third embodiment, the toner on the transfer material increases in order of 1, 2, 3, and 4 colors toward the downstream side. Re-transfer of toner (a defect that the toner transferred to the transfer material is reverse-transferred to the downstream photoconductor)
Is more likely to occur. Further, the amount of toner on the transfer material also increases as it goes downstream. That is, it is necessary to improve the transferability as it goes downstream. Therefore, in the third embodiment, the peripheral speed difference between the photosensitive drum 11 and the intermediate transfer belt 50 is increased by increasing the rotation speed of the photosensitive drum 11 as it goes downstream, and the transfer bias is also sequentially increased. This ensures the transferability on the downstream side.

As described above, the more the photosensitive drum 11 is on the downstream side, the greater the polishing force of the photosensitive layer is due to the difference in peripheral speed of transfer and the increase in transfer bias. However, as described above, the film thickness of the charge transport layer 11s is set to be larger toward the photosensitive drum 11 on the downstream side, so that the durability is improved on the photosensitive drum 11 on the downstream side. Thereby, the lifespans of all the photosensitive drums 11 on the upstream and downstream sides were adjusted to be the same period. Therefore, the life time of the photosensitive drum 11 of each color can be made the same, the replacement time of a plurality of photosensitive drums can be matched, the frequency of replacement work can be suppressed, and usability can be improved.

Incidentally, in the overall configuration of the third embodiment using the intermediate transfer belt 50, the durability of each photosensitive drum 11 is adjusted by the method of adjusting the mechanical strength described in the second embodiment, and all the photosensitive drums 11 are adjusted for all the upstream and downstream portions. It is also possible to adjust the life of the photosensitive drum 11 so as to be at the same time.

As described above, in the first, second, and third embodiments, when the shaving amounts of the photosensitive drums of the respective colors are different, the photosensitive layer structure such as the film thickness and the mechanical strength of the photosensitive drums is adjusted so that the photosensitive drums can be formed. The method for improving usability with the same period of service life has been described. Needless to say, the longer the photosensitive layer thickness or the stronger the strength of the photosensitive layer, the longer the life of the photosensitive drum. Can be made longer, but on the other hand, they cause problems such as deterioration of image quality and fusion of toner to the photosensitive drum. Therefore, the gist of the present invention is to fine-tune the layer configuration of the photoreceptor layer within a range that does not impair the image quality level, to make the life of each photosensitive drum uniform, and to optimize the balance between the frequency of exchange of the photosensitive drum and the image quality. It is to plan.

The present invention is also applicable to a case in which usability is to be improved by extending the life of a photosensitive drum of a specific color. For example, in a color image forming apparatus in which monochrome printing is frequently performed, when it is considered that usability is improved by making the life of the photosensitive drum for black toner longer than that of the photosensitive drum for other colors, the black toner The durability of the photosensitive drum may be further increased as compared with the above-described embodiments to extend the life. In this case, the image quality of the black toner image is slightly lowered, but in the case of monochrome printing, high image quality is often not required.In other words, usability is improved by optimizing the balance between the frequency of exchanging the photosensitive drum and the image quality. Therefore, it is not against the gist of the present invention.

[0044]

As described above, according to the present invention, the lifespan of the photoreceptor layer becomes uniform among a plurality of image forming / transferring units, so that the exchange times of a plurality of photoreceptors can be made as coincident as possible. . Thereby, usability can be improved by suppressing the frequency of replacement work.

Further, the photosensitive layer of the image forming / transfer unit for the black toner is formed to have higher friction durability than the photosensitive layer of the image forming / transfer unit for the other color toners. The method 4) is advantageous because, in a situation where monochrome printing is frequently used, the frequency of replacement of the photoconductor for black toner can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating a photoconductor layer used in the first embodiment.

FIG. 3 is a diagram illustrating a photoconductor layer used in a second embodiment.

FIG. 4 is a diagram illustrating an image forming apparatus according to a third embodiment.

FIG. 5 is a diagram illustrating a conventional image forming apparatus.

[Explanation of symbols]

 M, C, Y, Bk Image forming unit 11M, 11C, 11Y, 11Bk Photosensitive drum 11a Drum base 11b Photoconductor layer 11c Protective layer 11p Undercoat layer 11q Injection blocking layer 11r Charge generation layer 11s Charge transport layer

Claims (4)

[Claims] 1. An image forming / transfer unit comprising: a photoreceptor having a photoreceptor layer capable of forming a toner image; and transfer means for transferring a toner image formed on the photoreceptor layer to a transfer member. A plurality of image forming / transferring units, wherein the plurality of image forming / transferring units include image forming / transferring units having different contact frictional forces acting on the photoconductor layer when a toner image is formed and transferred to a transfer member. In the image forming apparatus, the photoconductor layer of the image forming / transfer unit having the higher contact friction force has a higher friction durability than the photoconductor layer of the image forming / transfer unit having the lower contact friction force. An image forming apparatus having high performance. 2. The friction resistance durability of the photoconductor layer is as follows:
The image forming apparatus according to claim 1, wherein the thickness of the photoconductor layer is increased by increasing the thickness. 3. The friction resistance durability of the photoconductor layer is as follows:
The image forming apparatus according to claim 1, wherein the photoconductor layer is formed of a material having a high abrasion resistance to increase the photoconductor layer. 4. An image forming / transferring unit for black toner and an image forming / transferring unit for other color toners are included in the plurality of image forming / transferring units. The photosensitive member layer of the image forming / transfer unit is formed to have higher friction durability than the photosensitive member layer of the image forming / transfer unit for the other color toner. 3. The image forming apparatus according to 3.