JPH11344878A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image defects from occurring, even when environment is changed by rotating an image carrier and an intermediate transfer body, after printing is finished. SOLUTION: A printer is constituted of a photoreceptor drum 4 which is the image carrier, an electrifying roller 41, a cleaning device 44, an intermediate transfer drum 1 being the intermediate transfer body, a developing equipment 43 and a transfer device 5. It is provided with a temperature sensor and a humidity sensor functioning as a means of detecting environmental fluctuations. When the temperature of the environment, where the printer is used is 20 deg.C or lower or when the temperature changes by 2 deg.C for ten minutes or when humidity changes by 5% for ten minutes or at a standby time, that is at the time of finishing the printing, a mode is shifted to a fine rotation mode. When the required time elapses after finishing the printing, the drums 4 and 1 are rotated for the required time. Thus, the image defects are prevented from occurring when it is low-temperature and low-humidity environment, or when the environment is changed from high temperature and high humidity to low temperature and low humidity.

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 using an electrophotographic method such as a printer or a copying machine, and more particularly to a color image forming apparatus having an intermediate transfer member.

[0002]

2. Description of the Related Art With the flow of computerization, needs for outputting documents and images in color are expanding, and image forming apparatuses of various types are commercially available. As a color image forming method, a sublimation type, a thermal transfer type, an ink jet method and the like are used, and an electrophotographic method is said to be the most excellent for forming an image at high speed.

In recent years, among the electrophotographic systems, an image forming apparatus of an intermediate transfer system, which is capable of forming an image regardless of the type of a transfer material and is excellent in color registration, is becoming mainstream.

In such an electrophotographic image forming apparatus of the intermediate transfer system, a single-color image of yellow, magenta, cyan, or, in some cases, black formed on a photosensitive drum as an image carrier is solid-state drum or belt-shaped, respectively. (Hereinafter referred to as "primary transfer"),
Finally, a full-color image is collectively transferred onto a transfer material (hereinafter referred to as “secondary transfer”).

[0005] This method does not require the transfer material to be wound around the transfer drum, and therefore can be used for envelopes and thick paper.
There are advantages of high versatility and high image quality because the color registration does not change depending on the thickness of the transfer material.

[0006]

However, in general, since the photosensitive drum and the intermediate transfer member are kept in contact with each other under a certain pressure, the following problems exist. I do.

That is, there is a problem that a nip portion where the photosensitive drum and the intermediate transfer member are in contact with each other causes an image defect that appears in a band shape on the image. In particular, when the environment in which the image forming apparatus is used fluctuates rapidly from low temperature and low humidity, or from high temperature and high humidity to low temperature and low humidity, the level of image defects deteriorates.

The following are conceivable causes of this.

That is, during printing, heat and pressure are applied by a fixing device in order to fix the toner transferred to the transfer material. At this time, the photosensitive drum and the intermediate transfer member are warmed by radiant heat from the fixing device and ambient temperature. Can be After the printing is completed, the temperatures of the surface of the photosensitive drum and the surface of the intermediate transfer member gradually decrease.

In general, a photosensitive drum has a structure in which an undercoat layer, a charge injection layer, a charge transport layer and the like are coated on an aluminum drum in a thickness of several tens of μm. On the other hand, the intermediate transfer body is made of resin or rubber, and has a thickness of several hundred μm to several mm for reasons such as durability and tensile strength. Therefore, the temperature of the photosensitive drum is lower than that of the intermediate transfer body. It's easy to do.

As a result, at the end of printing, the temperature decreases in the order of the photosensitive drum, the nip between the photosensitive drum and the intermediate transfer member, and the intermediate transfer member.

At this time, if the environment in which the printer is used is low temperature and low humidity, the temperature difference between them becomes large. When printing is started with this temperature difference increased, the photosensitivity characteristics of the photosensitive drum are different between the nip and other parts, and a band-shaped image defect appears in the rotation cycle of the photosensitive drum. become.

Further, in the intermediate transfer member, the nip portion has a higher electric resistance than the other portions, so that the transfer current in the nip portion during the primary transfer and the secondary transfer decreases, and the portion has poor transfer. And, as a result, an image defect occurs.

When the environment in which the image forming apparatus is used changes from high temperature and high humidity to low temperature and low humidity, image defects become remarkable. This is due to the fact that, in addition to the above-mentioned temperature difference, the moisture absorbed by the intermediate transfer body at high temperature and high humidity cannot be released at the nip between the photosensitive drum and the intermediate transfer body at low temperature and low humidity, and the surface properties of the nip and It is believed that the difference in electrical resistance increases and the level of image defects worsens.

Accordingly, an object of the present invention is to provide an intermediate transfer type image forming apparatus which can prevent the occurrence of image defects even in a low-temperature and low-humidity environment or when the environment changes from high-temperature and high-humidity to low-temperature and low-humidity. It is.

[0016]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier, an intermediate transfer member that temporarily holds the toner image formed on the image carrier, and a secondary transfer unit that collectively transfers the toner image held on the intermediate transfer member to a transfer material. Wherein the image carrier and the intermediate transfer member are rotated after printing is completed.

According to another aspect of the present invention, there is provided an image carrier, an intermediate transfer member for temporarily holding a toner image formed on the image carrier, and a toner image held on the intermediate transfer member. An image forming apparatus having a secondary transfer unit for batch-transferring to a transfer material, comprising: a unit for separating the image carrier and the intermediate transfer body; after printing, the image carrier and the image carrier; There is provided an image forming apparatus characterized by separating an intermediate transfer member.

In the above invention, it is preferable that after the printing is completed, the image carrier and the intermediate transfer member are rotated for a predetermined time. According to another aspect, it is preferable that after the printing is completed, the image carrier and the intermediate transfer body are rotated a fixed number of times. Further, it is preferable that a means for detecting an environmental change is provided, and only when the environmental change is detected, the image carrier and the intermediate transfer member are rotated after printing is completed. The environmental change is preferably a specific change.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 schematically shows the configuration of an electrophotographic full-color printer which is an image forming apparatus of the present embodiment. The printer of this embodiment has a maximum sheet passing width size A3 and a process speed of 100 mm / sec.

As shown in FIG. 1, the printer of this embodiment includes an OPC photosensitive drum 4 serving as an image carrier and a charging roller 4.
1, a cleaning device 44, an intermediate transfer drum 1, which is an intermediate transfer member, a developing device 43, a transfer device 5, and the like.

The photosensitive drum 4 has a diameter of 62 mm and is provided with an undercoat layer, a charge injection preventing layer, a charge generation layer, and a charge transport layer on an aluminum drum. The photosensitive drum 4 is uniformly charged to -500 V by the charging roller 41 to form an image. The bias applied to the charging roller 41 is a DC voltage of -500 V at 1 kHz and 2000 Vp.
This is a bias on which a sine wave AC voltage of p is superimposed. The charging roller 41 performs charging by moving charges by discharging with respect to the photosensitive drum 4 which is an insulator.

The surface of the charged photosensitive drum 4 is image-exposed by a laser beam 42 whose intensity is modulated in synchronization with an image signal, and an electrostatic latent image is formed. The laser beam intensity is set so that the surface potential of the photoreceptor in the exposed portion becomes -200V.

The thus formed electrostatic latent image is developed by the developing device 43 with toner. The developing device 43 of this embodiment is of a rotary type, and a yellow (Y) developing device 43Y, a magenta (M) developing device 43M,
A cyan (C) developing device 43C and a black (BK) developing device 43BK are detachably supported. The black image is a black developing device 43BK using a magnetic one-component developer (toner), and the color image is a color developing device using a non-magnetic one-component developer (toner), that is, a yellow developing device 43BK.
The image is developed by Y, magenta developing device 43M and cyan developing device 43C.

The black toner is obtained by subjecting a pulverized toner having a particle diameter of 6 μm to a spheroidizing treatment, and is obtained by internally adding 100 parts of magnetite, a charge control agent, a lubricant and the like to a polyester binder. The color toner is a capsule type spherical non-mag toner which is manufactured by a polymerization method and contains wax.

When printing is performed, the developing device moves to a predetermined position facing the photosensitive drum 4 according to a required color to develop the electrostatic latent image. -3 for each developer
Reverse voltage is applied by applying a bias in which a rectangular wave AC voltage of 2000 Hz and 2000 Vpp is superimposed on a DC voltage of 50 V, and an alternating electric field is formed between the developing sleeve of each developing device and the photosensitive drum 4 to fly toner. I do.

Next, the intermediate transfer member 1 will be described. The intermediate transfer member 1 of the present embodiment is a solid drum having a diameter of 186 mm, and has a peripheral length such that an image corresponding to a transfer sheet having a maximum sheet passing size (A3 size in this embodiment) can be written.

The intermediate transfer member 1 is provided with a medium-resistance rubber having a thickness of 5 mm as an elastic layer on a metal cylinder, and further has a coating of 5 μm to ensure releasability. The rubber is composed of NBR and ethylene oxide, and has a volume resistivity of 1 × 10 ⁷ Ωcm reduced by ethylene oxide. The coating is made of a fluorine-based resin and has a volume resistivity of 1 ×.
It is 10 ¹⁴ Ωcm.

The actual resistance value of the intermediate transfer body 1 is such that a metal drum having a diameter of 62 mm and a nip width of 7 m
m, and a current of 1 × 10 ⁷ Ω was obtained by converting a current measured by applying a voltage of 1000 V between the two.

To transfer the toner on the photosensitive drum 4 to the intermediate transfer member 1 in the primary transfer, a primary transfer power supply 11 applies a primary transfer bias to the intermediate transfer member cylinder.

When a full-color image is formed, the intermediate transfer member 1 rotates four times, and Y, M, C, and B are sequentially rotated at each rotation.
The K toner image is transferred from the photosensitive drum 4.

When the toner is overlaid, the primary transfer voltage is sequentially increased because the potential of the previously transferred toner layer acts in a direction to hinder the transfer. In this embodiment, 100V, 30
The primary transfer voltage was set at 0V, 400V, and 100V.

In this way, a laminated full-color toner image of each color is finally formed on the intermediate transfer member 1.

The primary transfer residual toner on the photosensitive drum 4 is scraped off by the cleaning device 44 in contact with the photosensitive drum 4 to prepare for the next image formation.

Next, the toner image on the intermediate transfer body 1 is secondarily transferred onto the fed transfer material P at an appropriate timing by the registration roller 7.

The intermediate transfer member 1 of this embodiment has a diameter of 18
The secondary transfer from the intermediate transfer body 1 to the transfer material P is performed by the transfer belt 5 because the curvature cannot be greatly separated to 6 mm.

[0038] Since the transfer belt 5 which performs the adsorption of the transfer material P, onto the urethane belt conductive perform coating of 30μm of PVDF is obtained by increasing the capacitance, 10 cm ² area of the belt surface and the belt The resistance value measured by applying a voltage of 1000 V between the substrates is 1 × 10
¹⁰ Ω.

The transfer roller 51 and the drive roller 52 that hang the transfer belt 5 are low-resistance rubber rollers, and the impedance of the transfer belt 5 substantially depends only on the surface resistance of the transfer belt 5. A transfer current of +20 μA is applied to the transfer belt 5 to secondary-transfer the toner image onto the transfer material P.

The secondary transfer residual toner on the intermediate transfer member 1 is scraped off by the cleaning device 2. The cleaning device 2 is configured to be capable of coming in contact with and separating from the intermediate transfer body 1, and comes into contact only when cleaning the secondary transfer residual toner.

Next, the features of the present invention will be described with reference to FIGS.

The printer of this embodiment is provided with a temperature sensor 91 and a humidity sensor 92 as means for detecting environmental fluctuations. And the environment where the printer is used is 20 ° C
In the following cases, when the temperature changes by 2 ° C. in 10 minutes, or when the humidity changes by 5% in 10 minutes, the mode is shifted to the minute rotation mode at the time of standby, that is, at the end of printing.

In the minute rotation mode, both the photosensitive drum 4 and the intermediate transfer body 2 are moved (rotated) by 2 cm every two minutes.
It is decided to end the process 30 minutes after shifting to this mode.

The process of shifting to the minute rotation mode will be described below.

The output of the temperature sensor 91 and the output of the humidity sensor 92 are A / D-converted every 10 minutes, and then input to the CPU 93 to determine whether to shift to the minute rotation mode. FIG. 3 is a flowchart showing the flow of the judgment at this time.

Step 1: It is determined whether the current temperature T1 is higher than 20 ° C.

Step 2: It is determined whether the difference from the temperature T2 10 minutes ago is smaller than 2 ° C.

Step 3: It is determined whether the difference from the humidity H2 10 minutes ago is smaller than 5%.

In the case of No in each of the above steps, the mode shifts to the minute rotation mode. Next, step 4: the current temperature T1 is T2, and the current humidity is H1.
To H2. And the values of T2 and H2 are CPU
93 and save in RAM 94, step 2 or 3
Is read from the RAM 94 to the CPU 93 and used for the above determination.

In order to confirm the effect of the present embodiment, an image quality evaluation comparison was made under the following environmental conditions. 1. Micro rotation is performed in an environment of a temperature of 15 ° C. and a humidity of 10%. Under the same conditions as in 2.1, micro-rotation is not performed. 3. The environment is shifted from an environment of a temperature of 30 ° C. and a humidity of 80% to an environment of a temperature of 15 ° C. and a humidity of 10% over a period of 60 minutes, and minute rotation is performed. Under the same conditions as in 4.3, micro-rotation is not performed.

Immediately after turning on the printer, the images were compared by halftone of a black image 60 minutes after continuous printing of 20 sheets. The results are shown in Table 1 below.

[0052]

[Table 1]

The image quality was evaluated as ○ when there was no band unevenness, Δ when the band unevenness was slightly conspicuous, and x when the band unevenness was conspicuous.

From the above results, a temperature sensor and a humidity sensor are provided as environment detecting means, and when the environment where the printer is used is 20 ° C. or less, or when the temperature changes by 2 ° C. in 10 minutes, or When the humidity changed by 5%, the mode was shifted to the minute rotation mode, thereby preventing the occurrence of band unevenness.

Embodiment 2 In the first embodiment, an environment change detecting means is provided, and when the environment is low temperature and low humidity, or when the environment change is detected, the photosensitive drum and the intermediate transfer body are kept in a standby state, that is, after the end of printing. By shifting to the rotation mode, occurrence of image defects such as band unevenness could be prevented. However, in the second embodiment, instead of the minute rotation mode, separation control is performed by a device for separating the intermediate transfer member and the photosensitive drum. By doing so, the same effect as in the first embodiment is obtained.

Next, an apparatus for separating the photosensitive drum 4 from the intermediate transfer member 1 in this embodiment will be described with reference to FIG.

The intermediate transfer member 1 is freely movable along a guide (not shown), and normally contacts the photosensitive drum 4 by a spring 9 as shown in FIG. Fixed to.

When the intermediate transfer member 1 and the photosensitive drum 4 are separated from each other, the cam 8 rotates by 180 °, and the intermediate transfer member 1 is pushed out as shown in FIG.
Are separated from the photosensitive drum 4.

In the present embodiment, the determination of the separation between the intermediate transfer member and the photosensitive drum has the same flow as the determination up to the shift to the minute rotation mode in the first embodiment.

In order to confirm the effect of the present embodiment, an image quality evaluation comparison was made under the following environmental conditions. 1. Separate the environment at a temperature of 15 ° C and a humidity of 10%. No separation is performed under the same conditions as in 2.1. 3. The environment is shifted to an environment of a temperature of 15 ° C. and a humidity of 10% over a period of 60 minutes from the environment of a temperature of 30 ° C. and a humidity of 80%, and separated. No separation is performed under the same conditions as in 4.3.

The image conditions were the same as those in the comparison in the first embodiment. The results are shown in Table 2 below.

[0062]

[Table 2]

From the above results, in this embodiment, when the environment in which the printer is used is 20 ° C. or less, or when the temperature changes by 2 ° C. in 10 minutes or when the humidity changes by 5%, By separating the intermediate transfer member and the photosensitive drum, it was possible to prevent the occurrence of band unevenness.

In the above embodiment, the case where the present invention is applied to an image forming apparatus having an intermediate transfer drum as an intermediate transfer body has been described. However, the present invention is applied to an image forming apparatus having an intermediate transfer belt as an intermediate transfer body. It can also be applied.

[0065]

As is apparent from the above description, according to the present invention, after printing is completed, means for rotating the image carrier and the intermediate transfer body or detecting means for detecting environmental fluctuation is provided. Only when environmental change is detected,
By rotating the image carrier and the intermediate transfer member after printing, it is possible to prevent image defects from occurring even in a low-temperature and low-humidity environment or when the environment changes from high-temperature and high-humidity to low-temperature and low-humidity.

Further, by providing means for separating the image carrier and the intermediate transfer member, and separating the image carrier and the intermediate transfer member after printing is completed, it is possible to prevent the occurrence of image defects.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus of an intermediate transfer system according to a first embodiment.

FIG. 2 is a block diagram illustrating an environment sensor according to a first embodiment.

FIG. 3 is a flowchart of a determination relating to execution of a minute rotation mode.

FIG. 4 is an explanatory diagram illustrating a separation device for an intermediate transfer member according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 1 intermediate transfer member 4 photosensitive drum (image carrier) 5 transfer belt (secondary transfer unit) 8 cam 9 spring 91 temperature sensor (environment detection unit) 92 humidity sensor (environment detection unit)

Claims (9)

[Claims] An image bearing member, an intermediate transfer member for temporarily holding a toner image formed on the image bearing member, and an image transfer member for transferring the toner image held on the intermediate transfer member onto a transfer material at once 2
An image forming apparatus having a next transfer unit, comprising: a unit for rotating the image carrier and the intermediate transfer body; and a unit for measuring an elapsed time from the end of printing, and a specific time after the end of printing. The image forming apparatus rotates the image carrier and the intermediate transfer member for a specific time when the time has elapsed. 2. A means for measuring an elapsed time from the end of rotation of the image carrier and the intermediate transfer body, and a specific time after the end of rotation of the image carrier and the intermediate transfer body. 2. The image according to claim 1, wherein the image carrier and the intermediate transfer member are rotated for a specific time after a lapse of a predetermined time after the rotation of the image carrier and the intermediate transfer member. Forming equipment. 3. An image according to claim 1, further comprising means for detecting an environmental change, wherein only when the environmental change is detected, the image carrier and the intermediate transfer member are rotated after printing is completed. Forming equipment. 4. The image forming apparatus according to claim 3, wherein said environmental change detecting means includes a temperature sensor and a humidity sensor. 5. The image forming apparatus according to claim 3, wherein the environmental change is a specific change. 6. An image bearing member, an intermediate transfer member for temporarily holding a toner image formed on the image bearing member, and an image transfer member for collectively transferring the toner image held on the intermediate transfer member to a transfer material. 2
An image forming apparatus having a next transfer unit, comprising: a unit for separating the image bearing member and the intermediate transfer member, wherein the image bearing member and the intermediate transfer member are separated after printing is completed. Image forming apparatus. 7. An image forming apparatus according to claim 6, further comprising means for detecting an environmental change, and separating the image carrier and the intermediate transfer member after printing is completed only when the environmental change is detected. . 8. The image forming apparatus according to claim 7, wherein said environmental change detecting means includes a temperature sensor and a humidity sensor. 9. The image forming apparatus according to claim 7, wherein the environmental change is a specific change.