JPH07281492A - Image forming device - Google Patents

Abstract

PURPOSE:To form a high-quality image by suppressing the backsurface staining of a transfer material and the density irregularities or the surface staining of the formed image. CONSTITUTION:This device is provided with a transfer power source 6a impressing a voltage on a transfer roller 6, a polarity switching means 6b for switching the polarity of a transfer voltage and a voltage control means 6c for turning off a device power source after the voltage whose polarity is opposite to toner and which is lower than that at a transfer time is impressed on the roller 6 while the roller 6 is rotated once or more and less than twice until the first transfer material arrives at a transfer part and until the following transfer material enters and the voltage whose polarity is identical to the toner is impressed on the roller 6 while the roller 6 is rotated twice or more and less than four times just after the trailing edge of the last transfer material is passed through the transfer part, turning off the device power source after the high voltage whose polarity is reverse to the toner and which is identical to that at the transfer time is impressed on the roller 6 while the roller 6 is rotated once or more and less than twice thereafter and turning off the device power source after the surface of a photoreceptor electrostatically charged to the reverse polarity to the toner by a transfer means is discharged by an electrostatic charge roller.

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 electrostatic transfer means such as an electrophotographic copying machine and a printer.

[0002]

2. Description of the Related Art In this type of image forming apparatus, a contact type transfer means such as a transfer roller is brought into contact with a moving photosensitive member, and the contact portion serves as a transfer portion, and a transfer material such as paper is attached to the transfer portion. And a toner image previously formed on the surface of the photoconductor with charged toner is superimposed on the transfer material, and a transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer means to transfer the toner image on the photoconductor side to the transfer material. Configured to transfer to.

[0003] Such a device has the advantages that the power supply for applying the transfer bias voltage is simplified and the cost of the device is reduced, and that ozone is less likely to be generated. The material is held firmly and there is an effect that transfer deviation hardly occurs. However, on the other hand, when a toner image larger than the transfer material size is formed on the photoconductor, the surface of the transfer means such as the transfer roller directly contacts the toner image, so that the toner at the contact portion is removed. There is a drawback that the transfer bias voltage attaches to the surface of the transfer means and stains the back surface of the transfer material.

As a measure for avoiding this problem, Japanese Unexamined Patent Publication No. Sho.
Japanese Patent Application Laid-Open No. 1-9840 proposes to prevent the toner from adhering to the transfer means by providing a means for applying a bias voltage having a reverse polarity to the transfer means when the transfer material is not passed. However, in the image forming apparatus using such a means, there is a disadvantage that the reverse polarity toner adheres to the transfer means and stains the back surface of the transfer material.

Further, as a means for removing toner of reverse polarity attached to transfer means such as a transfer roller, Japanese Patent Laid-Open No. 3-699 has been proposed.
There is one disclosed in Japanese Patent No. 78. FIG. 10 is a schematic configuration diagram illustrating a main part of the conventional image forming apparatus described above.
Reference numeral 01 is a photoconductor, 02a is a charging corotron which is a primary charger, 02b is a pre-electrification lamp, 03 is a laser beam, 04
Is a developing device, 04a is a developing sleeve, 04b is a developing power source,
Reference numeral 05 is a supply transport path, 06 is a transfer roller, 06a is a transfer power source, 08 is a cleaner, and 09 is a discharge transport path 010, 01.
0'is a sheet.

In the figure, the photosensitive member 01 is uniformly charged by the charging corotron 02a, and an electrostatic latent image is formed by the laser beam 03 modulated by the image signal. The electrostatic latent image is developed with the toner supplied from the developing sleeve 4a of the developing device 04 and is carried on the photoconductor 01 as a toner image. on the other hand,
A sheet 010 as a transfer material enters a transfer portion where a transfer roller 06, which is a transfer unit, is arranged via a supply conveyance path 05, and when passing between the photoconductor 01 and the transfer roller 06, a transfer power source 06a The toner image carried on the photoconductor 01 is transferred onto the sheet 010 by the applied transfer bias voltage.

The sheet 010 'onto which the toner image has been transferred is delivered to a fixing device (not shown) through the discharge transport path 09. After the residual toner is removed by the cleaner 08, the photoconductor 01 having completed the transfer is neutralized by the pre-electrification lamp 02b, and is uniformly charged again by the charging corotron 02a to prepare for the next image formation. It

In the above-mentioned image forming apparatus, when the paper is not present at the transfer portion, the bias voltage applied to the transfer roller 06 is applied at a predetermined polarity for a time longer than one rotation of the transfer roller, and then the polarity is reversed. Then, the voltage is applied for a time longer than the time required for the transfer roller to further rotate once.

[0009]

With the above arrangement, the polarity of the transfer roller is reversed to remove the same polarity toner adhering to the transfer roller. However, while the same polarity toner is being removed, Since the reverse polarity toner adheres, there is a drawback that when the application time of the bias voltage applied to the transfer roller is lengthened, toner stain of the reverse polarity to the transfer bias increases. In addition, such a configuration requires a long feeding time between transfer materials, and thus has a drawback that productivity is reduced.

FIG. 11 is a schematic configuration diagram for explaining a main part of another configuration example of a conventional image forming apparatus, in which 02 is a charging roller, 02a is a charging power source, and the same reference numerals as those in FIG. 10 correspond to the same portions. . In the figure, the image forming apparatus described with reference to FIG. 10 uses the pre-electrification lamp 02b and the charging corotron 02a as the primary charging device, but uses only the charging roller 02, so that the ozone However, since the transfer bias voltage is opposite in polarity to the charging roller in the reversal development type image forming apparatus, the charging roller 02 is charged when the transfer bias voltage is high. In some cases, a shortage easily occurs.

FIG. 12 is a timing chart for explaining the operation of FIG. 11, where (a) is the rotation of the main motor that drives the rotating mechanism such as the photosensitive member and the transfer roller, and (b) is the voltage applied to the charging roller. AC voltage, (c) DC voltage applied to the charging roller, (d) bias voltage applied to the developing sleeve, (e) developing potential (charge potential of the photosensitive member-
(Developing sleeve potential), (f) is a transfer bias voltage. The double-headed arrow in the figure indicates the period during which toner of opposite polarity is contaminated due to the development bias being turned off.

In the figure, AC voltage and DC voltage are applied to the charging roller simultaneously with the rotation of the main motor.
Since the bias voltage of the developing sleeve is off until the photosensitive member is rotationally moved to the portion where the developing device is installed, the reverse polarity toner is likely to adhere to the photosensitive member and so-called fogging occurs.

The toner of this fog directly adheres to the transfer roller before the paper enters, and the transfer roller is contaminated with toner. This phenomenon always occurs in the period when the bias voltage of the developing sleeve is turned off in (e), so that the back surface of the sheet passing through the transfer portion becomes dirty. Further, due to the adhesion of the reverse polarity toner to the photoconductor, the density unevenness of the transferred image and the stain on the background occur.

For example, in the configuration of FIG. 11, the charging roller has a peak voltage of 2000 V and a frequency of 1000 Hz of -5.
Since it is possible to operate with a bias voltage that superimposes a DC voltage of 00V, there is an advantage that cost is reduced and ozone is not generated by simplifying the power source and eliminating the static elimination lamp. Deterioration, dirt on the base, and dirt on the back of the paper.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to form a high-quality image by suppressing the back surface stain of the transfer material, the uneven density of the formed image, and the background stain. To provide.

[0016]

In order to achieve the above object, the present invention is directed to the control and transfer of a developing sleeve bias voltage in a reversal developing image forming apparatus using a charging roller as a primary charger of a photosensitive member. By controlling the polarity and potential of the bias voltage applied to the roller, stains on the back surface of the transfer material such as paper and print density unevenness, and stains on the background are prevented, and the deterioration of image quality is suppressed and the reduction in productivity is suppressed. The device is provided.

That is, according to the first aspect of the invention, a charging roller is used as a primary charging device, a charged toner image is formed by a reversal developing type developing device, and the photoconductor carrying the toner image is provided. At least a transfer roller that rotates in pressure contact with the photosensitive member is provided, and a transfer material is supplied to the transfer site by using both pressure contact parts as transfer sites, and a transfer voltage having a polarity opposite to that of the toner is applied to the transfer roller. In an image forming apparatus that transfers a toner image formed on a body, a transfer power source that applies a voltage to the transfer roller, a polarity switching unit that switches the polarity of the voltage applied to the transfer power source, and a first transfer material. Is of a polarity opposite to that of the toner and lower than that during transfer during one rotation or more and less than two rotations of the transfer roller until the transfer roller reaches the transfer portion where the transfer roller is arranged and before the subsequent transfer material enters. Immediately after the last trailing edge of the transfer material passes through the transfer portion, a voltage having the same polarity as that of the toner is applied to the transfer roller immediately after the last trailing edge of the transfer material passes through the transfer portion, and thereafter, While the transfer roller has one rotation or more and less than two rotations, the same high voltage as that at the time of transfer is applied to the transfer roller with the polarity opposite to that of the toner, and then the voltage application to the transfer roller is turned off to transfer to the polarity opposite to the toner. And a voltage control means for turning off the power source of the apparatus after the time when the surface of the photoconductor charged by the means is discharged by the charging roller.

According to a second aspect of the present invention, a charging roller is used as a primary charging device, a charged toner image is formed by a reversal developing type developing device, and a photoconductor carrying the toner image is provided.
This photoconductor is provided with a transfer roller that rotates in pressure contact, with both pressure contact parts as transfer sites, a transfer material is supplied to the transfer site, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller to perform transfer. In the image forming apparatus, a transfer power source for applying a voltage to the transfer roller, a polarity switching unit for switching the polarity of the voltage applied to the transfer power source, and a voltage application time control unit for controlling the application time of the voltage to the transfer roller. Then, the image forming and the transfer material feeding are interrupted when the specified number of prints are printed, and the voltage of the same polarity as the toner is applied immediately after the trailing end of the last transfer material of the specified number of sheets passes the transfer portion. The voltage is applied to the transfer roller for a specified time, and thereafter, during a period of one rotation or more and less than two rotations of the transfer roller, a voltage having a polarity opposite to that of the toner and lower than that during transfer is applied to the transfer roller. Characterized by resuming the printing was discontinued after cleaning the serial transfer roller.

Further, in the invention described in claim 3, a charging roller is used as a primary charging device, a charged toner image is formed by a developing device of a reversal developing system, and a photoreceptor carrying this toner image, and An image that is provided with a transfer roller that rotates in pressure contact with a photoconductor, and uses both pressure contact parts as transfer sites to supply a transfer material to the transfer site and apply a transfer bias having a polarity opposite to the toner to the transfer roller. The forming apparatus includes a polarity switching unit that switches the polarity of the voltage applied to the transfer roller, a voltage application time control unit that controls the voltage application time to the transfer roller, and a print count measurement control unit. Immediately after the trailing edge passes through the transfer portion, the time for applying a voltage having the same polarity as that of the toner to the transfer roller is changed depending on the number of print executions.

Further, the invention according to claim 4 is
Immediately before the surface of the photoconductor charged by the charging roller reaches the position of the developing sleeve, the bias of the developing sleeve is turned on, and the bias of the developing sleeve is turned off after the image forming cycle is completed. It is characterized in that it is immediately after the surface comes to the developing sleeve position. In the above-mentioned claims 1, 2, 3 and 4, the power source of the transfer roller is a constant current power source.

Simultaneously with the start of the image forming operation, a voltage is applied to the charging roller, the developing sleeve bias is turned on immediately before the surface of the photosensitive member charged by the charging roller reaches the developing sleeve position, and after the image forming cycle is completed. The charging roller bias is turned off, and the developing sleeve bias is turned off immediately after the uncharged surface of the photoconductor reaches the developing sleeve position.

[0022]

In the above structure, the toner (for example, −) and the reverse polarity (+) are low between the first transfer material and the transfer material for one rotation or more and less than two rotations until the transfer material reaches the transfer portion. Reverse polarity (+) by applying voltage to the transfer roller
The toner is removed from the transfer member and prevented from adhering, and the amount of the positive (−) toner adhering to the transfer roller is reduced.

The positive (-) toner adhering to the transfer roller at the time of transfer is prevented from adhering to the back surface of the transfer material by raising the voltage at the time of transfer. To clean the transfer roller after the transfer, a high voltage having the same polarity (-) as the toner is applied to the transfer roller during the rotation of 3 times or more and less than 4 rotations, and the positive polarity adhered and deposited during printing, that is, during the transfer of the toner image. (+) Remove toner. At this time, the reverse polarity (−) toner that has adhered is quickly removed by applying a high voltage having a polarity (+) opposite to that of the toner to the transfer roller during the subsequent one rotation or more and less than two rotations of the transfer roller means.

After that, the electric potential of the transfer roller is set to 0 V, and the surface of the photosensitive member charged by the transfer roller in the opposite polarity to the toner is discharged by the primary charger. The voltage applied to the transfer roller immediately after the start during the pre-transfer rotation has the same polarity (-) as the toner, and the positive polarity (+) fog toner adhered to the transfer roller during the post-transfer rotation and the unwanted toner such as after a jam occurs. Prevents the image from adhering to the transfer roller.

In the structure of claim 2, when the surface potential of the photosensitive member facing the developing sleeve is 500 V and the developing sleeve bias voltage is 350 V, when the uncharged photosensitive member faces the developing sleeve immediately after the start. When a bias voltage is applied to the developing sleeve, a negative polarity fog toner adheres to the photoconductor at a developing potential of + 350V, so the potential of the developing sleeve is set to 0V.

When the charged surface of the photoconductor passes through the opposite surface of the developing sleeve, a developing potential of -500 V is applied without applying a bias voltage to the developing sleeve, and a developing potential of -150 V is applied when applying a bias voltage, and the bias voltage is applied to the developing sleeve. It is more difficult to attach + polarity fog toner to the photoconductor, so
The above bias is applied. Since the charging roller is also turned on between the preceding transfer material and the following transfer material, the developing potential of −500 V is obtained when the bias voltage is not applied to the developing sleeve, and the developing potential of −150 V is applied when the bias voltage is applied to the developing sleeve, and the bias voltage is applied to the developing sleeve. In this case, the + polarity fog toner is less likely to adhere to the photoconductor, so the above bias is applied.

After the image formation is completed, the bias of the charging roller is turned off, and immediately after the surface of the uncharged photosensitive member reaches the position of the developing sleeve, the bias of the developing sleeve is turned off, thereby fogging the surface of the photosensitive member. The amount of toner is suppressed, and toner adhesion to the transfer roller is prevented.

[0028]

Embodiments of the present invention will now be described in detail with reference to the drawings. <Embodiment 1> The image forming apparatus according to Embodiment 1 of the present invention is
A4 paper is run at a process speed of 130 mm / Sec and 30 sheets per minute at a lateral feed, and the space between the transfer materials is 0.98 rotations of the transfer roller.

FIG. 1 is a schematic side view showing the structure of a first embodiment of an image forming apparatus according to the present invention, in which 1 is a photoconductor (O
(PC photoconductor), 2 charging roller, 2a charging power source, 3 laser beam, 4 developing device, 4a developing sleeve, 4b
Is a developing power source, 5 is a supply / conveyance path, 6 is a transfer roller, 6a is a transfer power source, 6b is a polarity switching means, 6c is a power source control means, 6c is a printed sheet number measuring means, 6e is a voltage application time control means, and 7 is static elimination. An apparatus, 7a is a static elimination power source, 8 is a cleaner, 9 is a discharge conveyance path, and 10 is a sheet of transfer material.

In the figure, O rotating in the direction of the arrow in the figure
The surface of the PC photoconductor 1 is -500 by the charging roller 2.
It is uniformly charged to V. By irradiating the charged surface of the photoconductor 1 with the laser beam 3 modulated by the image signal, an electrostatic latent image in which the potential of the irradiation portion is -125 V is formed. When this latent image arrives at the developing portion facing the developing device 4, negatively charged toner is supplied through the developing sleeve 4a and adheres to the latent image portion to form a toner image. The developing sleeve 4a is supplied with an alternating current having a peak-to-peak voltage of 2200 V and a frequency of 2400 Hz by the power source 4b.
A bias weighted with a DC voltage of 325V is applied.

When the transfer roller 6 reaches the transfer portion where the transfer roller 6 is in pressure contact with the photosensitive member 1, the sheet 10 is supplied to the transfer portion from the supply / conveyance path 5 at the same timing.
At the same time, a positive bias is applied to the transfer roller 6, and the toner image on the photoconductor 1 is transferred to the sheet 10. Then, the charge removing device 7 removes the charge of the sheet 10 ′ carrying the toner image, and the sheet 10 ′ is conveyed to the fixing unit (not shown) through the discharge conveyance path 9.

The toner remaining on the photoconductor without being transferred to the paper at the transfer portion is removed by the cleaner 8, and the photoconductor 1 enters the next latent image forming step. FIG. 2 is a timing chart for explaining the operation of the image forming apparatus shown in FIG. 1, in which (a) is rotation / stop of the main motor of the apparatus,
(B) is the voltage of the charging roller (DC), (c) is the voltage of the charging roller (AC), (d) is the bias voltage of the developing sleeve, (e) is the developing potential (charging potential-developing sleeve potential), ( f) is the bias voltage of the transfer roller.

First, at the same time when the start switch of the apparatus is turned on, the (a) main motor starts rotating, and the bias is applied to the (b) (c) charging roller and (f) transfer roller.
It is to be noted that the simultaneous application of the bias voltage to the charging roller 2 when the start switch is turned on means that it is necessary to charge the surface of the same photosensitive body two or more times in order to obtain uniform charging of the photosensitive body 1 by the charging roller 2. This is to shorten the pre-rotation time for improving productivity.

If a bias voltage is applied to the developing sleeve 4a when the uncharged photosensitive body 1 faces the developing sleeve 4a immediately after the start, a negative polarity fog toner adheres to the photosensitive body 1 at a developing potential of + 350V. Therefore, the potential of the developing sleeve 4a is preferably 0V. As shown in (d), when the charged surface of the photoreceptor 1 passes through the surface facing the developing sleeve 4a, a developing potential of -500V is applied unless a bias voltage is applied to the developing sleeve 4a, and a developing potential of -150V is applied. The potential becomes the potential, and the + polarity fog toner is less likely to adhere to the photoconductor when the bias is applied to the developing sleeve. Therefore, the bias voltage is applied as illustrated.

After that, the sheet 10 enters the transfer portion, and the toner image on the photoconductor 1 is transferred onto the sheet 10 by the potential difference between the bias voltage of the developing sleeve 4a and the toner image (charging potential-developing sleeve potential). FIG. 3 is a circuit configuration diagram for explaining the configuration of the power supply unit in the present embodiment, where 30 is the main power supply and 3
1 is a constant voltage power supply unit, 32 is a main control unit, 33
Is an on / off control unit, 34 is a selection control unit,
Reference numeral 35 is a high voltage power supply unit, and 36 is a load.

In the figure, a high voltage is applied from a high voltage power supply unit 35 to the charging roller 2 serving as the load 36, the transfer roller 6, the charge eliminator 7 and the developing sleeve 4a.
The high-voltage power supply unit 36 has a DC power supply, and the main power supply 30
The 24V output of the constant voltage power supply unit 31 fed from the input is used as an input to supply the AC superposition high voltage and the required DC high voltage to the corresponding load.

The high voltage power supply unit 36 includes an on / off control unit 33 controlled by the main control unit 32,
And the load 36 by the control signal from the selection control unit 34.
ON / OFF is sequence controlled. The voltage to the transfer roller 6 is − when the ON / OFF control signal from the ON / OFF control unit 33 is ON, and when the ON / OFF control signal and the + selection signal from the selection control unit 33 are ON at the same time. It becomes the H potential of the + voltage. In addition, the selection control unit 3
When all the signals from 3 are on, the L potential of the + voltage is obtained.

This type of power source is characterized by a lower cost than a +/- switching type power source.
In both cases, since the response is poor when constant current control is performed, the voltage is controlled to be constant voltage in this embodiment. Of course, a +/− switching type constant current power source is preferable, but this type of power source is used in this embodiment to reduce the cost of the device.

The optimum transfer current / cleaning current of the transfer roller 6 is determined by the structure of the image forming apparatus and the process speed, and the resistance value of the transfer roller 6 is 10 ⁶ to 10 ⁹ Ωcm.
It doesn't change until. However, the higher the resistance value, the wider the latitude to be used, but there is a drawback that a high voltage is required. In the present invention, 10 ^8.5 Ωcm is used.

FIG. 4, FIG. 5 and FIG. 6 show the environmental conditions obtained by experiments with a constant voltage power supply installed outside the image forming apparatus according to the present invention when the transfer roller having the above resistance value is used. It is explanatory drawing of the optimal transfer bias when changing. In the figure, the current value is set to +20 μA in constant current control due to environmental stability. In this explanatory diagram, the applied voltage and current value and the transferability for the front solid black original of A4 portrait (A4L) paper, the same solid black original on the back, and the front solid black original of B5 horizontal (B5S) paper and the same solid black original Looking at the side stains, in FIG. 4 where the temperature is 22 ° C. and the humidity is 50%, the applied voltage is 2500 to 3500 V, the temperature is 10 ° C., and the humidity is 1.
The applied voltage is 3000 to 5500 V in FIG. 5 at 5% and the applied voltage is 1000 in FIG. 6 at temperature 28 ° C. and humidity 80%.
It can be seen that good results are obtained at ~ 2500V.

FIG. 7 is an explanatory diagram of the optimum cleaning current value when the transfer roller having the above resistance value is used. A constant current control of −2 μA is preferable due to environmental stability. In the figure, the value is changed by the constant voltage control depending on the environment. Here, the temperature is −150, and the humidity is 55%.
The description will be given with 0V. The transfer roller 6 has a negative polarity cleaning bias voltage (-1500
V) is applied. In order to remove the + polarity toner adhering to the transfer roller at the time of applying this −voltage, the + polarity is applied to the transfer roller during the period of one rotation or more to less than two rotations until the first sheet reaches the transfer portion. Low voltage (+ 5μ
A) is applied. The transfer roller has a cleaning voltage of −150 during one rotation until the first sheet reaches the transfer portion.
When 0V was applied, the reverse polarity toner adhered to the transfer roller, and the back surface of the paper was stained. This voltage is -850V
When set to, the backside paper stain density decreased. When the voltage was further set to 0 V, the back surface stain density of the paper was further lowered, but it still occurred. When this voltage was set to +2 μA (+1500 V), the stain on the back surface of the paper was improved. This voltage is + 20μ
Even if the voltage is raised to A (+ 3500V), the back surface of the paper is not stained. The transfer roller 6 of the present invention is a urethane foam roller having a diameter of 18.7 mm.

When vertically feeding A3 size paper, one sheet of paper is rotated 7 times or more. FIG. 8 shows the relationship between the voltage applied to the transfer roller and the dirt on the transfer roller, which is obtained by examining the density level at which the transfer roller soiled at the cut portion stains the back surface of the paper after the third rotation by partially cutting the paper at the second rotation of the transfer roller. FIG. The applied voltage of the transfer roller is 1850V (+
Comparing the transfer roller stains at 5 μA) and +3500 V (+20 μA), the toner adhesion density at +20 μA is higher. Further, when the potential of the + polarity sensitive material after the transfer roller is high, the influence of the charging history of the transfer roller affects the potential after the charging roller. Therefore, the low potential + polarity bias of the transfer roller is set to +5 μA. The optimum transfer bias when the sheet passes is +20 μA.

The above-mentioned low potential + polarity voltage (+5
By applying μA), the reverse polarity (+) toner is removed from the transfer member and prevented from adhering, and the amount of the positive polarity (−) toner adhering to the transfer means is reduced. FIG. 9 shows a negative polarity bias after the trailing edge of the final sheet has passed through the transfer roller section when 200 sheets are continuously run (constant voltage control of -1500V).
FIG. 9 is an explanatory diagram of a relationship between an application time and a back surface stain of the next print.

From the figure, after the trailing edge of the final sheet passes through the transfer roller portion, a negative polarity bias (-1500 V) is applied to the transfer roller.
Constant voltage control) is applied for 3 times or more and less than 4 rotations of the transfer roll to remove the-polar toner adhered and accumulated during printing. At this time, in order to remove the adhered + polarity toner, the same high voltage as that at the time of transfer with the + polarity (+
20 μA constant current control) is applied. After that, the voltage of the transfer roller is turned off.

The bias of the charging roll is turned off after the photosensitive material surface charged by the transfer roller to the positive polarity has passed the charging roll, and the developing sleeve bias is charged after the surface of the photosensitive member charged by the charging roller has passed the developing sleeve. Laura AC
Turn off all voltage, main motor, etc. In the image forming apparatus of the present embodiment, the + polarized toner accumulated on the transfer roller between the sheets does not stain the back surface of the sheet even if the continuous 500-sheet run is repeatedly performed. <Embodiment 2> When the 1000-sheet continuous run was repeatedly carried out in the above-mentioned Example 1, slight back surface stain occurred after the third 700 sheets. This is due to the + bias applied to the transfer roller during post-rotation +
This is because the removal of the polar toner is not sufficient when the transfer roll has three or more rotations and less than four rotations.

As a countermeasure against this, it is conceivable to increase the post-rotation time, but there is a drawback that the life of the photoconductor is shortened because the photoconductor rotates for a long time even when printing one sheet. In the second embodiment, the time for applying the + polarity bias to the transfer roller is such that when the number of prints is 100 or less, the transfer roll is 1 rotation or more and less than 2 rotations, and when the number of prints is 101 to 400, the transfer roll is 2 or more. If the number of prints is 401 to 700 or less when the rotation is 3 rotations or more and less than 3 rotations, the number of prints is 7 when the transfer roll is 3 rotations or more and less than 4 rotations.
For 01 to 1000 sheets or less, the transfer roll is 4 revolutions or more and 5 sheets or more.
Applied for less than rotation.

As a result, the stain on the back surface after 1,000 sheets were run was improved. Furthermore, 97% of the total number of prints is 100
0 or less, 101 to 400 or less 2%, 1 for each others
When the transfer amount of 40,000 sheets of the total number of photosensitive materials was compared with 4 or more rotations and less than 5 rotations at a run number ratio of%, it was found that the photosensitive material wear amount was 9.5 μm.
It could be improved to μm. <Example 3> In Example 1, when 1000 sheets were continuously run under the environmental conditions of a temperature of 10 ° C and a humidity of 15%, a slight stain was generated after 900 sheets.

In the present embodiment, since the + polarity bias is applied between the sheets, the + polarity toner does not adhere to the transfer roller, but the −polarity toner adheres and is accumulated during the continuous run. Due to the stress environment where the charged potential of the toner rises,
-Polar fogging toner increased and the transfer roller became dirty. In the third embodiment, image formation and paper feeding are interrupted after printing 500 sheets, and a negative polarity bias (constant voltage control of -1500V) is applied to the transfer roller immediately after the trailing edge of the 500th sheet passes the transfer portion. It is applied for 3 times or more but less than 4 rotations of the transfer roll, and the transfer roller after that is 1
When +5 μA was applied to the transfer roller during the rotation of more than two rotations and the transfer roller was cleaned and the interrupted printing was restarted, the above-mentioned stains could be improved.

[0049]

As described above, according to the present invention,
Even when the time between the sheets of the transfer material is one rotation or less of the transfer roller which is the transfer member, it is possible to form a highly productive image without back surface stains, print density unevenness, and background stains. Further, it is possible to use a charging roll that is less likely to generate ozone for the primary charger, and it is possible to provide an excellent image forming apparatus that is less likely to generate ozone as an image forming apparatus.

[Brief description of drawings]

FIG. 1 is a schematic side view showing the configuration of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the image forming apparatus shown in FIG.

FIG. 3 is a circuit configuration diagram illustrating a configuration of a power supply unit in the embodiment of the present invention.

FIG. 4 is an explanatory diagram of an optimum transfer bias obtained by an experiment using a constant voltage power supply installed outside the image forming apparatus when a transfer roller having a resistance value is used in an example of the present invention.

FIG. 5 is an optimum transfer bias in an image forming apparatus using a transfer roller having a resistance value according to an exemplary embodiment of the present invention when an environmental condition obtained by an experiment using a constant voltage power supply installed outside the apparatus is changed. FIG.

FIG. 6 is an optimum transfer in an image forming apparatus using a transfer roller having a resistance value according to an embodiment of the present invention, obtained by an experiment using a constant voltage power supply installed outside the apparatus, and when environmental conditions are further changed. It is explanatory drawing of a bias.

FIG. 7 is an explanatory diagram of an optimum cleaning current value when a transfer roller having a resistance value is used in the example of the present invention.

FIG. 8: The relationship between the voltage applied to the transfer roller and the dirt on the transfer roller was examined at a density level at which the transfer roller soiled at the cut portion by staining a part of the paper on the second rotation of the transfer roller stains the back surface of the paper after the third rotation. It is explanatory drawing of a result.

FIG. 9 is an explanatory diagram of a relationship between a negative polarity bias (constant voltage control of −1500 V) application time after the trailing edge of the final sheet has passed through the transfer roller unit and a back surface stain of the next print when 200 sheets are continuously run.

FIG. 10 is a schematic configuration diagram illustrating a main part of a conventional image forming apparatus.

FIG. 11 is a schematic configuration diagram illustrating a main part of another configuration example of a conventional image forming apparatus.

FIG. 12 is a timing chart illustrating the operation of FIG. 11.

[Explanation of symbols]

1 ... Photoreceptor, 2 ... Charging roller, 3 ...
Laser beam, 4 ... ・ Developing device, 4a ・ ・ ・ ・ Developing sleeve, 4b ・ ・ ・ ・ Developing power source, 5 ・ ・ ・ ・ Supply / conveying path, 6 ・ ・ ・ ・ Transfer roller, 6a ・ ・ ・ ・ Transfer Power, 6
b ...- Polarity switching means, 6c ... Power supply control means, 6d ...- Printed sheet count means, 6e ...
Voltage application time control means, 7 ...
..Electrification removing power source, 8 ... Cleaner, 9 ... Ejecting and conveying path 10, 10 '...

Claims (4)

[Claims] 1. A photoconductor which uses a charging roller as a primary charging device, forms a charged toner image by a developing device of a reversal developing system, and carries the toner image, and a transfer roller which rotates in pressure contact with the photoconductor. At least, and a transfer material is supplied to the transfer portion with the pressure contact portion of both as a transfer portion, and a transfer voltage having a polarity opposite to that of the toner is applied to the transfer roller to transfer the toner image formed on the photosensitive member. In the image forming apparatus, a transfer power source that applies a voltage to the transfer roller, a polarity switching unit that switches the polarity of the voltage applied to the transfer power source, and a first transfer material in which the transfer roller is arranged are transferred. A voltage having a polarity opposite to that of the toner and lower than that at the time of transfer is applied to the transfer roller during one rotation or more and less than two rotations of the transfer roller until reaching a portion and before the subsequent transfer material enters.
Immediately after the last trailing edge of the transfer material passes through the transfer portion, a voltage having the same polarity as the toner is applied to the transfer roller while the transfer roller is at least 2 rotations and less than 4 rotations, and then at least 1 rotation 2 of the transfer roller is performed. During a period of less than rotation, after applying a voltage having a polarity opposite to that of the toner, which is the same as that at the time of transfer, to the transfer roller, the voltage application to the transfer roller is turned off, and the photoconductor charged by the transfer means has a polarity opposite to the toner. An image forming apparatus, comprising: a voltage control unit for turning off the power source of the apparatus after a time period in which the surface of the sheet is discharged by the charging roller. 2. A charging roller is used as a primary charging device, and a photosensitive member for forming a charged toner image by a developing device of a reversal developing system and carrying the toner image, and a transfer roller rotating in pressure contact with the photosensitive member. In the image forming apparatus, which comprises a pressure contact portion of both as a transfer portion, supplies a transfer material to the transfer portion, and applies a transfer bias having a polarity opposite to that of the toner to the transfer roller to perform transfer. A transfer power source that applies a voltage, a polarity switching unit that switches the polarity of the voltage applied to the transfer power source, a voltage application time control unit that controls the voltage application time to the transfer roller, a print number measurement control unit, and a regulation Image formation and transfer of the transfer material are interrupted with the printing of the number of sheets, and the voltage of the same polarity as the toner is transferred for the specified time from immediately after the trailing edge of the last transfer material of the specified number of sheets passes the transfer portion. It is applied to the roller, or one rotation subsequent transfer roller 2
An image forming apparatus characterized in that a voltage having a polarity opposite to that of the toner and lower than that at the time of transfer is applied to the transfer roller during a period of less than rotation to restart the interrupted printing after cleaning the transfer roller. 3. A charging roller is used as a primary charging device, and a photoconductor carrying a toner image formed by a developing device of a reversal developing system and carrying the toner image, and a transfer roller rotating in pressure contact with the photoconductor. In the image forming apparatus, which comprises a pressure contact portion of both as a transfer portion, supplies a transfer material to the transfer portion, and applies a transfer bias having a polarity opposite to that of the toner to the transfer roller to perform transfer, A polarity switching unit that switches the polarity of the applied voltage, a voltage application time control unit that controls the voltage application time to the transfer roller, and a print count measurement control unit are provided, and immediately after the last trailing edge of the transfer material passes through the transfer site. An image forming apparatus, wherein a time for applying a voltage having the same polarity as that of toner to the transfer roller is changed according to the number of prints to be executed. 4. The bias of the developing sleeve is turned on immediately before the surface of the photoconductor charged by the charging roller reaches the developing sleeve position, and the developing sleeve bias is turned off when the developing sleeve bias is turned off. An image forming apparatus characterized in that it is immediately after the surface of the photoconductor charged by the charging roller comes to the developing sleeve position after the completion of the creation cycle.