JP2000250336A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to clean a transfer roller by the application of low cleaning bias potential, by switching development bias potential to development reverse bias potential which is opposite in polarity and hinders the movement of toner to a photoreceptor, and switching transfer bias potential to cleaning bias potential which is opposite in polarity and enables the movement of toner to the photoreceptor. SOLUTION: During the cleaning of a transfer roller, the surface potential of a photoreceptor 1 is maintained at zero substantially, and development bias potential to a developing roller is switched to development reverse-bias potential RDP which is opposite in polarity and, furthermore, hinders the movement of toner to the photoreceptor. Also, transfer bias potential to a transfer roller 5 is switched to cleaning bias potential CTP which is opposite in polarity to a transfer bias, is lower in absolute value than the transfer bias potential, and, further, enables the movement of the toner to the photoreceptor. This makes it possible to clean the transfer roller 5 efficiently and to form an image having no soil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to an electrophotographic process (image forming method) used for a facsimile or the like. More specifically, in an image forming method using a transfer roller, the transfer roller can be cleaned by applying a relatively low cleaning bias potential (CTP). Further, the present invention relates to an image forming method which eliminates contamination due to toner adhesion around a transfer roller.

[0002]

2. Description of the Related Art A method of transferring toner on a photosensitive drum to a transfer sheet using a transfer roller is widely used in an image forming method because discharge products such as ozone due to corona discharge are less generated. At the time of the transfer by the transfer roller, it is necessary to apply a negative transfer bias to, for example, the positively charged toner, so that the toner adheres to the transfer roller itself and needs to be cleaned.

Conventionally, it has been known to apply a reverse bias voltage to the axis of the transfer roller in order to clean the toner adhered to the surface of the transfer roller.
In a digital multifunction machine using reversal development, the photoconductor surface potential is +850 V, the toner used is + charged toner,
At the time of transfer, a transfer bias potential of -1.5 kV is applied to the transfer roller.
A voltage of 2 kV was applied to return the toner adhered to the surface of the transfer roller to the photoreceptor.

[0004]

However, as in the above-mentioned known example, in the prior art, even when a cleaning voltage is applied to the transfer roller, the surface potential of the photoconductor is maintained at the same surface potential due to main charging. Was normal. Due to the influence, the voltage for cleaning to be applied to the transfer roller also becomes high in absolute value, and there is a disadvantage that the cost of the power supply increases. In addition, there is a problem that peripheral members such as a pre-transfer guide and a post-transfer guide are charged by the influence of a high cleaning voltage applied to the transfer roller, and toner adheres to the surface thereof to cause contamination. The above tendency is particularly remarkable in non-contact transfer in which the transfer roller and the photoconductor are not in contact, because the absolute value of the voltage in non-contact transfer is larger than that in contact transfer.

Accordingly, an object of the present invention is to provide a method of forming an image using a transfer roller, in which the transfer roller can be cleaned by applying a relatively low cleaning bias potential (CTP), thereby reducing the cost of parts required for the transfer roller cleaning. Another object of the present invention is to provide an image forming method in which contamination due to toner adhesion to the periphery of a transfer roller is eliminated. Another object of the present invention is to provide an image forming method capable of cleaning a transfer roller at the same time as developing bias control for preventing toner from adhering to a photoconductor at the start of output. Still another object of the present invention is to substantially turn off the main charging of the photoreceptor when cleaning the transfer roller, thereby saving power consumption and reducing the amount of discharge products such as ozone. It is an object of the present invention to provide an image forming method which enables the following.

[0006]

According to the present invention, a photoreceptor is charged to a fixed polarity by a main charger to form a latent image.
Using a developing roller which has the same polarity as the latent image and to which a developing bias potential (DP) enabling reverse development is applied, the latent image is reversely developed with charged toner having the same polarity as the latent image, and the reverse image is developed. In an image forming method in which toner on a photoconductor is transferred to a transfer material by a transfer roller having a polarity and to which a transfer bias potential (TP) enabling transfer of toner from the photoconductor surface is applied, the potential of the photoconductor surface is substantially reduced. Maintained at zero, the developing bias potential is switched to a developing reverse bias potential (RDP) which has the opposite polarity and can prevent the toner from moving to the photoconductor, and the transfer bias potential has the opposite polarity to the transfer bias potential. The value of the transfer roller potential is lower than the absolute value of the transfer bias potential, and by switching to a cleaning bias potential (CTP) that allows the toner to move to the photoconductor, the transfer roller is closed. Image forming method and performing Ningu is provided. In the image forming method of the present invention, the toner is a positively charged toner, and the initial surface potential (SP) of the photoconductor at the time of image formation is from +400 to +9.
00V, developing bias potential (DP) is +300 to +7
00V and the transfer bias potential (TP) are -3000 to -1000 V, and the developing reverse bias potential (RDP) during transfer roller cleaning is -400 to-
100V and cleaning bias potential (CTP) is 0
To + 900V. According to the invention, the latent image is formed by charging the photosensitive member to a fixed polarity by the main charger, and a developing bias potential (DP) having the same polarity as the latent image and enabling reverse development is applied. The developing roller is used to perform reversal development of the latent image with charged toner having the same polarity as the latent image, and a transfer bias potential (TP) is applied which has a polarity opposite to that of the latent image and enables the transfer of the toner from the photoconductor surface. (1) At the start of the operation, (1) a development reverse bias potential which is negative and which can prevent the toner from moving to the photoreceptor; (RDP) applied to the developing roller, 2 simultaneously starts the rotation of the uncharged photoconductor, and 3 applies a cleaning bias potential (CTP) to the transfer roller which is positive and enables the toner to move to the photoconductor. I 4 main charger as on, performs charging of the photosensitive member, timed to the passage of 5 charged photoreceptor,
Applying a developing bias potential (DP) to the developing roller, which has a positive polarity and enables the development of the toner on the photoreceptor surface, to the developing roller. (2) At the time of transfer, 6 7. Apply a transfer bias potential (TP) to the transfer roller, which is negative and enables the transfer of toner from the photoreceptor surface. Applying a cleaning bias potential (CTP) to the transfer roller to enable movement to the body,
And (3) at the end of the operation, 8 the main charger is turned off, 9 the developing reverse bias potential (RDP) which is negative in polarity and can prevent the toner from moving to the photoconductor in time with the passage of the uncharged photoconductor. ) Is applied to the developing roller, and the cleaning bias potential (CT
P) is turned off, 11 the developing reverse bias potential (RDP) to the developing roller is turned off, and the machine is stopped, thereby providing an image forming method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an image forming method of the present invention, a photoreceptor is charged to a fixed polarity by a main charger to form a latent image.
Using a developing roller having the same polarity as the latent image and to which a developing bias potential (DP) enabling reverse development is applied, the latent image is subjected to reverse development with charged toner having the same polarity as the latent image.
Next, the toner on the photoreceptor is transferred to a transfer material by a transfer roller having a polarity opposite to that of the latent image and to which a transfer bias potential (TP) enabling transfer of toner from the photoreceptor surface is applied. The image forming means by controlling such a potential is the same as the conventional reversal developing method.

The image forming method of the present invention has a feature in controlling the potential of each of the above-described portions when the transfer roller is cleaned. Specifically, (1) the surface potential of the photosensitive member is made substantially zero. (2) The developing bias potential is switched to a developing reverse bias potential (RDP) having the opposite polarity and capable of preventing the toner from moving to the photoconductor, and (3) the transfer bias potential is set to the opposite polarity to the transfer bias potential. , The absolute value of which is lower than the absolute value of the transfer bias potential, and switching to a cleaning bias potential (CTP) that allows the toner to move to the photosensitive member.

In the present invention, to make the surface potential of the photoreceptor substantially zero means that the surface potential of the photoreceptor is originally zero or that the main charger for the photosensitive layer is turned off. In the latter case, the power supply to the corona wire is cut off in the case of the corotron type charger, and the voltage application to the control grid is turned off in the case of the scotron type charger. The type of the container is not limited to the above, but in short, any device may be used as long as the surface potential (SP) of the photoconductor is maintained at substantially zero. According to the present invention, the surface potential of the photosensitive member (S
By setting P) to substantially zero, the toner adhering to the surface of the transfer roller is cleaned with a cleaning bias potential having a polarity opposite to the transfer bias potential and an absolute value lower than the initial charging potential (SP) of the photoconductor. With (CTP), the transfer to the surface of the photoconductor can be performed to clean the transfer roller.

When the transfer roller is cleaned, the surface potential (SP) of the photosensitive member is set to substantially zero,
If the bias potential of the developing roller is maintained as it is, toner moves from the developing roller to the photoconductor. In the present invention, at the time of cleaning the transfer roller, the surface potential (SP) of the photosensitive member is set to substantially zero, and the developing bias potential is of the opposite polarity, and the developing reverse bias potential is capable of preventing the toner from moving to the photosensitive member. By switching to (RDP), the transfer roller can be cleaned by limiting the movement of the toner to the transfer from the transfer roller to the photoconductor. Of course, in this case, there is no problem if the toner moves from the surface of the photoconductor to the developing roller and the toner is cleaned on the surface of the photoconductor.

According to the image forming method of the present invention, the cleaning bias potential (CTP) applied to the transfer roller is
For example, a low voltage such as +600 V is sufficient, and a high voltage of approximately +1.5 to 2.0 kV is required in the conventional method for maintaining the photoconductor surface potential of +850 V even during transfer roller cleaning. Further, the cost of the power supply for cleaning the transfer roller can be significantly reduced, and the inconvenience of unnecessarily charging the members around the transfer roller during cleaning can be eliminated. This advantage is particularly effective in a non-contact transfer method using a transfer roller.

In the present invention, the cleaning of the transfer roller surface is not necessarily performed after the transfer by the transfer roller is completed. That is, the cleaning of the transfer roller
It can be performed at any stage such as at the start of output, after output, and at the time of other mechanical aging. For example, in the actual machine, since the surface potential of the photoconductor passes 0 V for about 0.2 seconds after the start of output, the development roller is biased to the development roller so that the toner does not transfer to the surface of the photoconductor during this time. It is necessary to apply a potential (RDP). In the present invention, by utilizing this, the cleaning bias potential (C
By applying (TP), the transfer roller surface can be cleaned.

In the present invention, the main charging of the photoconductor is substantially turned off when the transfer roller is cleaned, thereby saving power consumption and reducing the amount of generation of discharge products such as ozone. There is also an advantage that it becomes possible.

In FIG. 1 showing an image forming apparatus used in the present invention, a main charging corona charger 2, an image exposure optical system 3 having a laser light source, and a developing unit 4 are provided around a rotary photosensitive drum 1. , A transfer roller 5 and a residual toner cleaning device 6 are disposed.

The photosensitive drum 1 comprises a conductive drum base and an electrophotographic photosensitive layer provided on the surface of the base.
As the electrophotographic photoreceptor, any known per se is used, for example, selenium, selenium-tellurium, a photoreceptor on which a photoconductive substance such as amorphous silicon is deposited,
An organic photoreceptor containing a charge generating agent and a charge transporting agent in a photosensitive layer is used. As the organic photoreceptor, a laminated photoreceptor having a charge generation layer (CGL) and a charge transport layer (CTL) provided on a conductive substrate in this order or the reverse order, or a single charge generation agent and a single charge transport agent are used. As the dispersed photosensitive layer, a photosensitive member provided on a conductive substrate can be used.

As the main charger 2, a corotron charger composed of a combination of a shield 21 and a corona wire 22 or a scorotron charger composed of a shield and a corona wire combined with a control grid 23 is used. The latter scorotron charger is advantageous because the photoconductor surface potential (SP) can be controlled by controlling the voltage applied to the control grid. This main charger 2 is provided at the highest position (upper part) with respect to the photoreceptor 1, and the upper part of the shield 21 is open to allow ventilation so that discharge of ozone or the like is possible. Preferred to prevent product accumulation. The corona wire 21 of the main charger 2 is connected to a power supply for corona generation so as to be able to be turned on / off, or when a control grid 23 is present, the control grid 23 is a power supply capable of controlling an applied voltage. It is connected to the.

During image formation, the corona charger 2 charges the photosensitive layer of the photosensitive drum 1, for example, positively and uniformly. By this main charging, the surface potential of the photosensitive layer is generally set in the range of 400 to 900 V in absolute value.

Next, image exposure is performed from the optical system 3 using laser light, and a portion corresponding to the light beam image of the photosensitive layer (ie, a portion corresponding to the light image)
The potential of the laser beam irradiated portion) becomes 0 V to 300 V,
The potential of the portion not irradiated with the laser beam (background) is maintained at the dark decay potential from the main charging potential, and an electrostatic latent image is formed.

The electrostatic latent image is developed by the developing device 4, and a toner image is formed on the surface of the photosensitive layer. Developing device 4
Can be performed using a magnetic or non-magnetic one-component toner or a two-component developer, but the development using a non-magnetic one-component toner charged to the same polarity as the main charging polarity of the photosensitive layer is performed. It is preferred to carry out by a method.

An elastic developing roller 41 for applying a non-magnetic one-component toner to a photoreceptor, a sub-roller 42 for supplying toner to the elastic developing roller, and a stirring and mixing toner are provided inside the developing device 4. Agitator (not shown)
Is housed. An opening 43 is provided on the side of the developing device 4 close to the photoreceptor. An elastic developing roller 41 is located in the opening 43, and a sub-roller 42 is provided close to the developing roller 41. Elastic developing roller 41
A blade 44 for controlling the toner layer to a constant thickness and additionally charging the toner is provided on the toner layer sending side. A bias potential (DP) having the same polarity as that of the dark portion charge of the photoconductor is applied to the elastic body development roller 41, and is pressed against the photoconductor at the nip position with the photoconductor 1, and is inverted according to a principle known per se. Development takes place.
A bias voltage slightly higher than the bias voltage applied to the elastic developing roller 41 may be applied to the sub roller 42 so that the toner is smoothly transferred from the sub roller 42 to the elastic developing roller 41. preferable.

In the present invention, an arbitrary toner known per se is used, but a non-magnetic one-component toner is preferably used.

Next, the toner image on the photosensitive member 1 is transferred onto a transfer sheet by a transfer roller 5. That is, a transfer bias potential (TP) which has a polarity opposite to that of the latent image and the toner and enables the transfer of the toner from the photoreceptor surface is applied to the transfer roller 5.
The toner on the photoconductor is transferred to a transfer material. The transfer roller 5 is provided with a pre-transfer guide 51 and a post-transfer guide 52, and the toner image is transferred to the transfer sheet supplied between the transfer roller 5 and the photosensitive drum 1 through the pre-transfer guide 51, The sheet on which the toner image has been transferred is conveyed by a post-transfer guide 52 to a fixing zone or the like. The transfer roller 5 and the photosensitive drum 1 may be of a contact type or a non-contact type. In the latter case, both are maintained at a predetermined gap by an interval regulating roller. The transfer bias potential should be opposite in polarity to the charge potential of the toner and the surface potential of the photoreceptor.

The transfer roller 5 can be formed of any conductive rubber composition so that a transfer bias voltage (TP) can be applied. Suitable conductive rubber compositions include, but are not limited to, conductive polyurethane rubber compositions. A conductive polyurethane rubber composition having a rubber hardness of more than 50 ° (JIS A), preferably a rubber hardness of 70 ° is suitable. The surface resistance of this conductive rubber is generally in the range of 10 ^{4 to} 10 ¹⁰ Ω · cm, particularly 10 ^{5 to} 1
It is preferably in the range of 0 ¹⁰ Ω · cm.

When the transfer of the toner is completed and the transfer roller is cleaned, the surface potential of the photosensitive member 1 is maintained at substantially zero, and the developing bias potential to the developing roller 41 is of the opposite polarity and the toner is transferred to the photosensitive member. The transfer bias potential to the transfer roller 5 is switched to a development reverse bias potential (RDP) that can prevent the transfer of the toner, and the absolute value of the transfer bias potential is lower than the absolute value of the transfer bias potential. By switching to a cleaning bias potential (CTP) that enables the transfer of the transfer roller 5 to the photoconductor, the transfer roller 5 is effectively cleaned, and a clean image can be formed.

In the image forming method of the present invention, when the photosensitive member is a positively charged photosensitive member and the toner is a positively charged toner, generally, the initial surface potential (SP) of the photosensitive member at the time of image formation is from +400 to +400. +900 V, the developing bias potential (DP) is +300 to +700 V, and the transfer bias potential (TP) is -3000 to -1000 V;
Further, it is preferable that the developing reverse bias potential (RDP) at the time of transfer roller cleaning is -400 to -100 V, and the cleaning bias potential (CTP) is 0 to +900 V. Of course, when the photoconductor is a negatively charged photoconductor and the toner is a negatively charged toner, the potentials can be reversed and the absolute values can be used in the same range.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the present invention is used for all control of image formation using the image forming apparatus of FIG. 1 will be described below with reference to a timing chart of FIG. (1) At the start of operation (print key ON): 1 A developing reverse bias potential (RDP = −200 V) that is negative and that can prevent toner from moving to the photoconductor is applied to the developing roller 4. As a result, toner movement from the developing roller 4 to the photosensitive drum 1 is prevented. -Timing A-2 At the same time, the rotation of the uncharged photoconductor 1 (SP = 0V) is started. −Timing A− 3 Positive polarity, the absolute value of which is the transfer bias potential (TP =
A cleaning bias potential (CTP = + 600 V) lower than the absolute value of (-1500 V) and enabling the toner to move to the photoconductor 1 is applied to the transfer roller 5. Thus, the cleaning of the transfer roller 5 is started.
-Timing B- 4 The main charger 2 is turned on to charge the photosensitive member 1 (SP =
+850 V). This charging is performed so as to increase the voltage stepwise for stabilizing the operation. -Timing C-5 A developing bias potential (DP = + 650 V) is applied to the developing roller 4 in synchronization with the passage of the charged photoconductor 1 (SP = + 850 V). This voltage is applied so as to increase the voltage stepwise for stabilizing the operation. As a result, reversal development is performed with the toner on the surface of the photoconductor. -Timing D-(2) At the time of transfer, 6 a transfer bias potential (TP = -1500 V) which is negative and enables transfer of toner from the photoreceptor surface, in synchronization with the passage of the leading end of the transfer material. 5
Is applied. Thereby, the transfer of the toner on the photosensitive member surface to the transfer sheet proceeds. -Timing F-7 A cleaning bias potential (CTP = + 600 V) that is positive and allows the toner to move to the photoconductor is applied to the transfer roller 5 in synchronization with the passage of the rear end of the transfer material. As a result, when the surface potential of the photoreceptor decreases, preparation is made so that cleaning of the transfer roller 5 is started. -Timing G- and (3) At the end of the operation, 8 the main charger 2 is turned off (SP = 0V). -Timing H-9 A developing reverse bias potential (RDP = −200 V) that is negative and that can prevent the toner from moving to the photoconductor is applied to the developing roller 4 in synchronization with the passage of the uncharged photoconductor. -Timing I- 10 Cleaning bias potential (CT
P = + 600V) is turned off. -Timing K- 11 The developing reverse bias potential (RDP =-
200V), and stop the machine. -Timing L
As described above, according to the present invention, cleaning of the transfer roller can be easily performed at a low voltage.

[0027]

According to the present invention, a latent image is formed by charging a photoreceptor to a fixed polarity by a main charger, and a developing bias potential (DP) having the same polarity as the latent image and enabling reversal development.
Is applied to the developing roller to perform reversal development of the latent image with charged toner having the same polarity as that of the latent image, and a transfer bias potential (of opposite polarity to the latent image and enabling transfer of toner from the photoconductor surface). In the image forming method of transferring the toner on the photoreceptor to the transfer material by the transfer roller to which (TP) is applied, the photoreceptor surface potential is maintained at substantially zero, the developing bias potential is of the opposite polarity, and the toner is transferred to the photoreceptor. Is switched to a development reverse bias potential (RDP) that can prevent the transfer of the toner, and the transfer bias potential has a polarity opposite to that of the transfer bias potential, and its absolute value is lower than the absolute value of the transfer bias potential. By switching to a cleaning bias potential (CTP) that enables movement, (1) cleaning of the transfer roller is performed at a relatively low cleaning bias potential (CTP). , The cost of parts required for transfer roller cleaning can be reduced, and contamination due to toner adhesion around the transfer roller can be eliminated. (2) The transfer roller can be cleaned simultaneously with the development bias control for preventing the toner from adhering to the photoconductor at the start of output. (3) Further, the main charging of the photoconductor is substantially turned off at the time of cleaning the transfer roller, so that it is possible to save power consumption and reduce the amount of discharge products such as ozone. .

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional side view of an example of an image forming apparatus used in the present invention.

FIG. 2 is a timing chart of the embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naoki Michiwaki 1-2-28 Tamatsukuri, Chuo-ku, Osaka-shi Inside Mita Kogyo Co., Ltd. F term in Industrial Co., Ltd. (reference) 2H027 DA23 DC04 EA01 EA03 EA05 EA09 ED09 ED24 2H032 AA05 BA02 BA19 BA26 BA30 CA01 CA13 2H073 AA09 BA09 BA13 BA21

Claims (4)

[Claims] A latent image is formed by charging a photosensitive member to a fixed polarity by a main charger, and a developing roller to which a developing bias potential (DP) having the same polarity as the latent image and enabling reversal development is applied. And a reverse bias of the latent image using charged toner having the same polarity as the latent image, and a transfer bias potential (T
In the image forming method of transferring the toner on the photoreceptor to the transfer material by the transfer roller to which P) is applied, the photoreceptor surface potential is maintained at substantially zero, the developing bias potential is reversed, and the toner is transferred to the photoreceptor. Is switched to a development reverse bias potential (RDP) that can prevent the transfer of the toner, and the transfer bias potential has a polarity opposite to that of the transfer bias potential, and its absolute value is lower than the absolute value of the transfer bias potential. Cleaning bias potential (CT
An image forming method, wherein the transfer roller is cleaned by switching to P). 2. The toner is a positively charged toner, and has an initial surface potential (SP) of +400 to +900 V, a developing bias potential (DP) of +300 to +700 V, and a transfer bias potential (TP) of −400 during image formation. 300
0 to −1000 V, and the developing reverse bias potential (RDP) during transfer roller cleaning is −400.
To -100 V and the cleaning bias potential (CT
2. The image forming method according to claim 1, wherein P) is 0 to +900 V. 3. A developing roller to form a latent image by charging the photoreceptor to a predetermined polarity by a main charger, and to which a developing bias potential (DP) having the same polarity as the latent image and enabling reversal development is applied. Is used to perform reversal development of the latent image with charged toner having the same polarity as the latent image, and a transfer bias potential (T
An image forming method comprising transferring a toner on a photoreceptor to a transfer material by a transfer roller to which P) is applied,
(1) At the start of the operation, 1 a developing reverse bias potential (RDP), which is negative and can prevent the toner from moving to the photosensitive member, is applied to the developing roller; 2 simultaneously, the rotation of the uncharged photosensitive member is started; 3 Applying a cleaning bias potential (CTP) to the transfer roller, which is positive polarity and allows the toner to move to the photoconductor, 4 Turns on the main charger to charge the photoconductor, 5 Charges the photoconductor At the same time as passing
Applying a developing bias potential (DP) to the developing roller which has a positive polarity and enables the development of the toner on the surface of the photoreceptor to the developing roller. (2) At the time of transfer, 6 And a transfer bias potential (TP) that enables the transfer of toner from the photoreceptor surface to the transfer roller. To the transfer roller, applying a cleaning bias potential (CTP) that enables the transfer to
And (3) at the end of the operation, 8 the main charger is turned off, 9 the developing reverse bias potential (RDP) which is negative in polarity and can prevent the toner from moving to the photoconductor in time with the passage of the uncharged photoconductor. ) Is applied to the developing roller, and the cleaning bias potential (CT
P) is turned off, 11 the developing reverse bias potential (RDP) to the developing roller is turned off, and the machine is stopped. 4. The image forming method according to claim 1, wherein a roller facing the photosensitive member in non-contact is used for transfer.