JP2002365874A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can prolong the life of an image carrier by suppressing the occurrence of a defective image due to the printing amount by reducing the damage of an image carrier surface caused by the rubbing of the image carrier with an intermediate transfer body while maintaining the image quality when monochromatic and full-color images are formed. SOLUTION: In the image forming apparatus in which an image forming system to collectively perform the secondary transfer of an image formed on a first image carrier 1 on a transfer material 24 after the primary transfer of the image on the intermediate transfer body 5 is carried out and which possesses a means to change a difference in the circumferential speed of the image carrier 1 and that of the intermediate transfer body 5, the difference in the circumferential speed of the image carrier 1 and that of the intermediate transfer body 5 is changed at a color image forming time to form the color image of two or more colors by repeatedly superposing images on the intermediate transfer body 5 and at a monochromatic image forming time to form a monochromatic image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a transferable image (a visible image) on a first image carrier by an image forming process, and transferring the transferable image once to an intermediate transfer member. The present invention relates to an image forming apparatus, such as a copying machine, a printer, and a facsimile, which collectively transfers images onto a material and outputs an image-formed product.

[0002]

2. Description of the Related Art FIG. 6 shows an example of an image forming apparatus using an intermediate transfer member.

FIG. 6 is a cross-sectional view of a main part of a color image forming apparatus (copier or laser beam printer) utilizing an electrophotographic process. In FIG. 6, reference numeral 1 denotes a repeated use as a first image carrier. Is a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as an image carrier), which is driven to rotate at a predetermined peripheral speed (process speed) in a direction indicated by an arrow (counterclockwise).

The image carrier 1 is uniformly charged to a predetermined polarity and potential by a primary charger 2 during the rotation process, and then is subjected to image exposure means (not shown) (color separation / imaging exposure of a color original image). A first color component image of a target color image by receiving an image exposure 3 by an optical system, a scanning exposure system using a laser scanner that outputs a laser beam modulated corresponding to a time-series electric digital pixel signal of image information, etc. (For example, a magenta component image) is formed.

Next, the electrostatic latent image is developed by a first developing device (magenta developing device) 41 with a magenta toner (colored charged particles) M as a first color and visualized as a magenta toner image. At this time, the second to fourth developing units (each developing unit for cyan, yellow and black) 42, 43, 4
Reference numeral 4 denotes an operation OFF, which does not act on the image carrier 1,
The first color magenta toner image is not affected by the second to fourth developing units 42 to 44.

Reference numeral 5 denotes a rotary drum type intermediate transfer member which is held in pressure contact with the image carrier 1 with a predetermined pressing force. A transfer nip portion N1 as a transfer portion is formed therebetween.

The intermediate transfer member 5 is driven to rotate at a peripheral speed slightly different from that of the image carrier 1 in a direction indicated by an arrow (clockwise) in the figure. A transfer bias having a polarity (plus) opposite to the toner charge polarity (minus in this example) of the toner image is applied.

The first color magenta toner image formed and carried on the surface of the image carrier 1 is formed by the transfer bias applied to the transfer nip area in the process of passing through the transfer nip N1. The magenta toner image is sequentially transferred to the outer surface of the intermediate transfer member 5 by the electric field. The surface of the image carrier 1 after the transfer of the first color magenta toner image onto the intermediate transfer member 5 is cleaned by the cleaning device 14.

Similarly, charging of the image carrier 1 → image exposure corresponding to the second color component image (cyan component image) → development with cyan toner C of the second developing device (cyan developing device) 42 → formation The second
Transfer of a cyan toner image, which is a color, to the intermediate transfer member 5 → Cleaning of the surface of the image carrier 1 by the cleaning device 14 Charging of the image carrier 1 → Image exposure 3 corresponding to the third color component image (yellow component image) → Development of the third developing device (yellow developing device) 43 with the yellow toner Y → Transfer of the formed yellow toner image of the third color to the intermediate transfer member 5 → Cleaning of the image carrier 1 surface by the cleaning device 14 Charging on the carrier 1 → image exposure 3 corresponding to the fourth color component image (black (black) component image) → development with black toner B of the fourth developing device (black developing device) 44 → formed fourth color Transfer of the black toner image to the intermediate transfer member 5 → cleaning of the surface of the image carrier 1 by the cleaning device 14 The above-described image forming / transfer cycle is sequentially executed to rotate the intermediate transfer Above with respect to the outer surface of the body 5 4
The two toner images (magenta, cyan, yellow, and black toner images) are sequentially superimposed and transferred to form a composite color toner image (mirror image) corresponding to the target color image.

Next, the paper feed roller 1 is moved from the paper feed cassette 9 to the paper feed roller 1.
0 indicates a transfer material (sheet) 2 as a second image carrier
4 are separated and conveyed one by one, and are fed to the transfer nip N2 at a predetermined timing via the registration roller pair 11 and the pre-transfer guide 12.

Then, a bias having a polarity (+) opposite to that of the toner of the transfer composite color toner image on the intermediate transfer member 5 is applied to the intermediate transfer member 5 from a bias power supply (not shown). The transfer composite color toner image on the intermediate transfer body 5 is sequentially transferred to the surface of the transfer material 24 fed by the transfer.

The transfer material 24 having received the transfer of the toner image on the intermediate transfer member 5 through the transfer nip portion N2 is introduced into a fixing device 15 and is pressed against a fixing roller 16 which has been heated and regulated at a predetermined temperature. The toner image is heated and pressed by the roller 17 to undergo a fixing process of the toner image, and is output as a color image formed product.

The transfer residual toner on the intermediate transfer member 5 after the completion of the secondary transfer is transferred to an intermediate transfer member cleaning device (contact type cleaning roller (contact charging member) of contact charging means) 1
8, a charge having a polarity opposite to that of the toner in the developing device is applied and is reversely transferred onto the image carrier 1;
4 removed.

[0014]

However, the color image forming apparatus using the intermediate transfer member 5 has the following problems.

That is, the intermediate transfer member 5 is superposed by the superposition of the color component images.
When a color image is formed thereon, the image carrier 1 and the intermediate transfer member 5 are in contact with a predetermined pressing force in order to prevent the image from being lost. When a contact nip occurs during rotation, a rotation speed difference (peripheral speed difference) is generated between the image carrier 1 and the intermediate transfer member 5, and each color component image is shifted and transferred onto the intermediate transfer member 5 at the time of forming a color image. An image defect due to a so-called color shift occurs.

In view of the above, a method has been proposed in which a predetermined peripheral speed difference is intentionally provided between the image carrier 1 and the intermediate transfer member 5 to drive the image carrier 1 to prevent a defective image due to color misregistration and obtain a good image. .

However, when a peripheral speed difference is provided between the image carrier 1 and the intermediate transfer member 5 as in the above-described method, solids such as toner are deposited in the contact nip portion N1 between the image carrier 1 and the intermediate transfer member 5. If interposed, the surface of the image carrier 1 may be scratched due to excessive displacement. The rubbing scratches on the surface of the image carrier 1 gradually grow deeper as the printing durability increases, causing local uneven charging on the image carrier 1, resulting in white spots, Appears on the image as defects such as black stripes.
The life of the image carrier 1 is determined mainly by the remaining film thickness of the surface layer of the image carrier 1 and the scratches formed on the surface. The image carrier 1 reaches the end of its life even if it has a large remaining film thickness.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an image formed by rubbing an image carrier and an intermediate transfer member while maintaining the image quality at the time of forming a mono-color or full-color image. It is an object of the present invention to provide an image forming apparatus capable of reducing the damage on the surface of a carrier, suppressing the occurrence of image defects due to the printing durability, and extending the life of the image carrier.

[0019]

According to the first aspect of the present invention,
When forming a full-color image, a predetermined peripheral speed difference is provided between the image carrier and the intermediate transfer body due to problems such as color misregistration. By making the speed difference close to zero, the chance of occurrence of scratches causing image defects is reduced.

According to a second aspect of the present invention, a clutch is provided in a drive mechanism of the intermediate transfer member as a means for changing a peripheral speed difference between when a monocolor image is formed and when a full-color image is formed.

According to a third aspect of the present invention, as a means for changing the peripheral speed difference between the formation of a monocolor image and the formation of a full-color image, the image carrier side and the intermediate transfer body side are driven at a predetermined speed by separate motors. It is characterized by.

According to a fourth aspect of the present invention, a sensor for detecting a peripheral speed difference between the image bearing member and the intermediate transfer member is provided to detect a deviation of the peripheral speed difference due to environmental fluctuation and abrasion of a member, thereby providing an optimum peripheral speed difference. The present invention is characterized in that feedback control is performed in which the peripheral speed is repeatedly changed so as to obtain a peripheral speed difference.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a schematic sectional view of a color image forming apparatus (copier or laser printer) utilizing an electrophotographic process. This color image forming apparatus has a medium resistance as an intermediate transfer member. And a transfer belt as a secondary transfer means.

(At the time of full-color image formation) In FIG.
Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as an image bearing member) which is repeatedly used as an image bearing member, and is rotated at a predetermined speed in a direction indicated by an arrow (counterclockwise).

The image carrier 1 is uniformly charged to a predetermined polarity and potential by the primary charging roller 2 in the course of rotation, and then image exposure means (not shown) (color separation image of a color original image) Receives a first color component image (eg, a magenta component image) of a target color image by receiving image exposure 3
Is formed.

Next, the electrostatic latent image is developed with a negatively charged first color magenta toner M on a developing sleeve of a first developing device (magenta developing device) 41 to form a magenta toner image. Imaged.

The magenta developing device 41, the cyan developing device 42 and the yellow developing device 43 are incorporated in a rotary rotary, and these are rotated in the direction shown by arrows in the developing process so as to be opposed to the image carrier 1. Each is arranged. In addition, the black developing device 44 is independently arranged to face the image carrier 1.

Here, the structure of the drive mechanism of the image carrier 1 and the intermediate transfer member 5 is schematically shown in FIG. The image carrier 1 and the intermediate transfer member 5 are driven by a single drive motor 7 via separate gears in the direction of the arrow in FIG. 1, and the intermediate transfer member 5 is rotationally driven with a predetermined peripheral speed difference from the image carrier 1. You. At this time, the clutch 8 provided between the drive motor 7 and the gear of the intermediate transfer member 5 is in a state where power is being transmitted (hereinafter, referred to as an OFF state).

The first color magenta toner image formed and carried on the image carrier 1 is applied to the intermediate transfer member 5 while passing through the nip portion N1 between the image carrier 1 and the intermediate transfer member 5. The intermediate transfer is performed on the outer peripheral surface of the intermediate transfer body 5 by the electric field and pressure formed by the next transfer bias. Hereinafter, this step is referred to as “primary transfer”.

Thereafter, similarly, the second color cyan toner image, the third color yellow toner image and the fourth color black toner image are sequentially transferred while being superimposed on the intermediate transfer member 5, and correspond to the target color image. Thus, a full-color toner image is formed.

In FIG. 1, reference numeral 6 denotes a transfer belt,
This is supported in parallel with the intermediate transfer member 5 and is arranged in contact with the lower surface of the intermediate transfer member 5. The image carrier 1
The primary transfer bias for the sequential superimposition transfer of the first to fourth color toner images from the printer to the intermediate transfer member 5 is a reverse polarity (+) to the intermediate transfer member 5 from a bias power supply (not shown). ).

The first transfer from the image carrier 1 to the intermediate transfer member 5
A cleaning roller 18 for cleaning the transfer belt 6 and the intermediate transfer member 5 is provided so as to be able to contact and separate from the intermediate transfer member 5 in the sequential transfer process of the toner images of the fourth to fourth colors.

The transfer of the toner image formed by the toner superimposedly transferred onto the intermediate transfer member 5 onto the transfer material 24 is performed while the transfer belt 6 is brought into contact with the intermediate transfer member 5 and supplied from the paper feed cassette 9. Registration roller 1 by paper roller 10
1 and a pre-transfer guide 12, a transfer material 24 is fed at a predetermined timing to a transfer nip N2 between the intermediate transfer body 5 and the transfer belt 6, and at the same time, a secondary transfer bias is applied from a bias power supply (not shown). It is done when done. That is,
The transfer material 2 is transferred from the intermediate transfer member 5 by the secondary transfer bias.
4 is transferred to the toner image. Hereinafter, this step is referred to as “secondary transfer”.

On the other hand, the transfer material 2 on which the toner image is secondarily transferred
The toner 4 is sent to the fixing device 15, and the toner is melted and fixed on the transfer material 24 by the fixing roller 16 and the pressure roller 17.

After the image transfer to the transfer material 24 is completed, the transfer residual toner on the intermediate transfer member 5 is brought into contact with the charging position of the intermediate transfer member 5 by a cam driven by a motor and a clutch (not shown). When a positive bias is applied during contact with a high-voltage power supply (not shown), the transfer residual toner is positively charged. This toner is reversely transferred to the image carrier 1 at the same time as the primary transfer of the magenta toner image to be formed on the second transfer material 24, and the primary transfer residual toner is removed by the cleaning device 14 on the image carrier 1. Collected with.

(At the time of monocolor image formation) As an example at the time of monocolor image formation, image formation with a single color of black toner will be described.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as an image bearing member) repeatedly used as an image bearing member, which rotates at a predetermined peripheral speed in a direction indicated by an arrow (counterclockwise). Is done.

The image carrier 1 is rotated by a primary charger 2 during the rotation process.
Is charged uniformly to a predetermined polarity and potential, and then subjected to image exposure 3 by image exposure means (not shown) to form an electrostatic latent image corresponding to a target image.

Next, the electrostatic latent image is developed with a negatively charged toner on the developing sleeve of the black developing device 44 to be visualized as a toner image.

Here, the image carrier 1 and the intermediate transfer member 5 are driven to rotate at a predetermined peripheral speed in a direction indicated by an arrow in FIG. At this time,
Since the clutch 8 provided between the drive motor 7 and the gear of the intermediate transfer member 5 is in a state where power is not transmitted (hereinafter, referred to as an ON state), the power from the drive motor 7 transfers the image carrier 1 to the image carrier 1. (Hereinafter, referred to as driven drive), there is no peripheral speed difference between the image carrier 1 and the intermediate transfer member 5.

The toner image formed and carried on the image carrier 1 is a nip N1 between the image carrier 1 and the intermediate transfer member 5.
, The primary transfer is performed on the outer peripheral surface of the intermediate transfer member 5 by the electric field and the pressure generated by the primary transfer bias applied to the intermediate transfer member 5.

Here, since the image transferred from the image carrier 1 onto the intermediate transfer member 5 is a monochromatic black monochromatic image, it is not necessary to take measures against the shift of the color components unlike the case of forming a full-color image. . Since the intermediate transfer member 5 is driven and driven by the image carrier 1, there is no peripheral speed difference between the image carrier 1 and the intermediate transfer member 5, and at the same time, no abrasion due to the peripheral speed difference occurs.

The transfer of the toner image formed by the toner transferred onto the intermediate transfer member 5 onto the transfer material 24 is performed while the transfer belt 6 is in contact with the intermediate transfer member 5 and the transfer material 2 is transferred.
4 is transported from a paper feed cassette 9 by a paper feed roller 10 and passes through a registration roller 11 and a pre-transfer guide 12 to a transfer nip portion N2 between the intermediate transfer body 5 and the transfer belt 6 at a predetermined timing. Is applied from a bias power supply (not shown). That is, the toner image is secondarily transferred from the intermediate transfer member 5 to the transfer material 24 by the secondary transfer bias.

Thereafter, the transfer material 24 on which the toner image has been secondarily transferred is sent to the fixing device 15, where the toner is melted and fixed on the transfer material 24. The transfer residual toner remaining on the intermediate transfer member 5 after the transfer of the toner image onto the transfer material 24 is charged by the cleaning roller 8 in contact with the intermediate transfer member 5 and returned to the image carrier 1. It is removed by the cleaning device 14 on the image carrier 1.

The case of forming a full-color image and the case of forming a mono-color image have been described above. FIG. 3 is a flowchart showing the procedure from reading of a document to completion of printing.

Image Carrier 1 During Monocolor Image Formation
The difference between the ten-point average roughness (Rz) and the maximum height (Rmax) (JIS-B-0601-1982) for the difference in the scratches on the surface of the image carrier 1 depending on the presence or absence of the peripheral speed difference between the intermediate transfer member 5 and the intermediate transfer member 5 is compared. It is shown in the table below.

[0048] The examination was performed using a magnetic one-component black toner in a jumping development method, pressing the image carrier 1 and the intermediate transfer member 5 at the same pressure, and printing A4 size paper with a print rate of 5% intermittently.
I passed the sheet. After the endurance of the image carrier 1 was removed from the surface of the image carrier 1 with an air gun, the surface roughness at five points in the longitudinal direction was measured.

As a result of the examination, it was confirmed that the rubbing of the surface of the image carrier 1 was reduced by about 50% in Rz and about 38% in Rmax by the follow-up operation, and the life of the image carrier 1 was greatly extended. .
It should be noted that no deterioration in image quality due to driven driving during mono-color image formation was observed in both mono-color and full-color image formation.

Second Embodiment Next, a second embodiment of the present invention will be described.

In this embodiment, the peripheral speed difference between the image carrier 1 and the intermediate transfer member 5 is more reliably controlled by the driven drive of the image carrier 1 and the intermediate transfer member 5. In this embodiment, since the configuration of the image forming process of the image forming apparatus using the intermediate transfer member is the same as that of the first embodiment, the members having the same functions as those of the first embodiment will be described below. Will be described using the same reference numerals.

If the image carrier 1 and the intermediate transfer member 5 do not have a sufficient friction coefficient μ for some reason due to environmental fluctuations such as dew condensation on the intermediate transfer member 5, or if the friction coefficient μ increases, the clutch In the driven drive, the image carrier 1 and the intermediate transfer member 5 may slip and cause an image defect.

FIG. 4 schematically shows the structure of the drive system for the image carrier 1 and the intermediate transfer member 5 in the present embodiment.

As shown in FIG. 4, the image carrier 1 and the intermediate transfer member 5 are connected to independent variable speed drive motors 7 and 19, respectively. In addition, a speed sensor (not shown) for detecting a rotation speed is attached to the intermediate transfer member 5.

FIG. 5 shows a flowchart of the feedback control performed immediately after the main power supply is turned on or every several hundred prints.

The drive motor 7 makes several revolutions of idle rotation at a constant speed with the clutch 8 turned on. Here, when the peripheral speed of the drive motor 7 of the image carrier 1 is not the same as the peripheral speed of the intermediate transfer body 5 detected by the speed sensor connected to the intermediate transfer body 5, the CPU 21 controls the image carrier 1 and the intermediate transfer body. 5
Is determined to be slipping. When such a determination is made, the intermediate transfer body 5 is in the state where the clutch 8 is
An instruction is sent from the CPU 21 to drive the image carrier 1 at the same speed by the connected motor 19. In the full-color image forming mode, the intermediate transfer body 5 is driven by the motor 19 with a peripheral speed difference at which no color shift occurs. This operation is repeated until the image carrier 1 and the intermediate transfer member 5 reach a predetermined speed range. By such feedback control, the peripheral speed difference control between the image carrier 1 and the intermediate transfer member 5 can be more reliably performed.

In the embodiment described above, the elastic roller is used as the intermediate transfer member. However, even when a resin belt is used, according to the driven driving of the image carrier and the intermediate transfer member, the elastic roller is used. Although not as good as a roller-made intermediate transfer member, the effect of reducing the scratches on the surface of the image carrier was confirmed.

[0058]

As apparent from the above description, according to the present invention, after the image formed on the first image carrier is primarily transferred onto the intermediate transfer member, it is collectively transferred onto the transfer material. In an image forming apparatus adopting an image forming method for secondary transfer and having a means capable of changing a peripheral speed difference between an image carrier and an intermediate transfer member, an image is repeatedly superimposed on the intermediate transfer member to form two or more colors. At the time of forming a color image to form a color image and at the time of forming a single-color image to form a single-color image, the peripheral speed difference between the image carrier and the intermediate transfer body is changed. This has the effect of reducing scratches on the surface of the image carrier due to rubbing with the intermediate transfer member and consequently reducing the occurrence of image defects due to the printing capacity and extending the life of the image carrier. This effect is more remarkable as the monocolor image formation ratio within the printing life is higher.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a color image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a drive system of an image carrier and an intermediate transfer member in the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure from image reading to printing end in the image forming apparatus according to Embodiment 1 of the present invention.

FIG. 4 is a schematic diagram illustrating a configuration of a drive system of an image carrier and an intermediate transfer member in an image forming apparatus according to Embodiment 2 of the present invention.

FIG. 5 is a flowchart of feedback control in the image forming apparatus according to Embodiment 2 of the present invention.

FIG. 6 is a schematic sectional view of a conventional color image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Primary charging device 3 Laser exposure 5 Intermediate transfer member 6 Secondary transfer belt 7 Drive motor 8 Clutch 19 Drive motor 21 CPU 24 Transfer material 41 Magenta developing device 42 Cyan developing device 43 Yellow developing device 44 Black developing device N1 Primary transfer nip N2 Secondary transfer nip

Continued on front page F-term (reference) 2H027 ED02 ED24 EE02 EE03 EE04 FA28 FA35 FA37 2H030 AA01 AD08 AD17 BB24 BB36 BB42 BB46 BB52 BB55 BB56 BB63 2H200 FA04 GA23 GA44 GA47 GB12 HA03 HB13 JA02 JB06 JB13 PA20 JB06 JB13

Claims (4)

[Claims] 1. An image forming method comprising: firstly transferring an image formed on a first image bearing member onto an intermediate transfer member; And an image forming apparatus having means for changing the peripheral speed difference between the intermediate transfer member and the intermediate transfer member, wherein a color image of two or more colors is formed by repeatedly superimposing an image on the intermediate transfer member, and a monochrome image is formed. An image forming apparatus characterized in that a difference in peripheral speed between an image carrier and an intermediate transfer member is changed between the time of forming a single color image. 2. The image forming apparatus according to claim 1, wherein a clutch is provided in a drive transmission section of the intermediate transfer body as a means for changing a peripheral speed difference between the image carrier and the intermediate transfer body. 3. The image bearing member directly connected to a variable speed drive motor and the intermediate member directly connected to a separate variable speed drive motor as means for changing a rotational speed difference between the image carrier and the intermediate transfer member. 2. The image forming apparatus according to claim 1, wherein a method is used in which the transfer member is driven with a predetermined difference in peripheral speed between when a color image is formed and when a single color image is formed. 4. A sensor for detecting the peripheral speed of the intermediate transfer body, wherein the image carrier and the intermediate transfer body are connected to a drive motor that can independently change the speed, and the peripheral speed of the image carrier is provided. When the peripheral speed of the intermediate transfer body detected by the sensor that detects the peripheral speed of the intermediate transfer body is different from a predetermined numerical value, the intermediate transfer body is driven by a variable speed drive motor connected to the intermediate transfer body, 4. The image forming apparatus according to claim 1, further comprising a feedback control mechanism that repeatedly adjusts a speed of the intermediate transfer member so as to rotate the intermediate transfer member with a predetermined peripheral speed difference.