JPH04308877A - image transfer device - Google Patents

Abstract

PURPOSE:To provide a transfer device provided with a means to make a belt influx current to a dielectric belt to be constant. CONSTITUTION:The relevant high voltage electric power source 2 is controlled by a belt influx current measuring device 4, electrifying a carrying means such as the dielectric belt 3 and measuring the value of the belt influx current flowing toward the dielectric belt 3 from a corona electrifying device 1, and an electric power source control device 5, making its value always constant based on the measured result of the device 4. The dielectric belt and the constitution of the device are set so that the value of the most appropriate belt influx current value is made always constant. This is carried out by making the greatness of surface resistance from a center of electric charge imparted range to the grounded member of the carrying means such as the dielectric belt, etc., to be more than 10<10>OMEGA per 1cm width which is at a right angle to the carrying direction of the before mentioned dielectric belt.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention applies to electrophotographic image forming apparatuses such as laser beam printers and copying machines.
The present invention relates to an image transfer device.

0002

2. Description of the Related Art As an image transfer device for electrophotography, a toner image formed on a photoreceptor drum 6 is transferred to a recording paper 8 between the photoreceptor drum and the surface of a dielectric belt 3, as shown in FIG. A device is known in which a toner image is transferred onto recording paper 8 by applying a charge from the back side of the dielectric belt with a high-voltage power supply 9 and a corona charger 1 when the dielectric belt is held. Compared to the conventionally widely used corona transfer method in which the back surface of the recording paper is directly irradiated with corona, such a device charges the dielectric belt 3 instead of the recording paper, so the recording paper 8 is electrostatically charged to the dielectric belt. A suction effect is produced, and the recording paper 8 can be easily peeled off from the photoreceptor drum 6 after transfer, and the recording paper 8 can be stably transported thereafter to the next process. .

Generally speaking, in order to perform good transfer, it is desirable that the electric field around the toner particles, that is, the transfer electric field E, be always constant. The electric field in the transfer process using the dielectric belt described above is mainly determined by the charge Q applied to the dielectric belt, and is expressed as E=Q/ε, where ε is the dielectric constant of air. In principle, charging by a corona charger occurs so that the surface potential of the charged object becomes uniform, so in the transfer device described above, the charge is generated so that the potential on the back surface of the dielectric belt is almost constant. Granted. At this time, the potential V on the back surface of the dielectric belt, the electrical capacitance C of the area between the grounded metal substrate of the photoreceptor and the back surface of the dielectric belt, and the amount of charge Q applied to the back surface of the dielectric belt. The relationship Q=C·V holds true. Therefore, if C changes due to temperature/humidity, recording paper thickness, aging of the dielectric belt, etc., even if the back side of the belt is charged to a constant potential V, the amount of charge Q will vary. Therefore, the transfer electric field E also fluctuates as Q changes.

[0004] To prevent this, for example, a first prior art technique uses a constant current source as the high voltage power source 9 of the corona charger, as disclosed in Japanese Patent Laid-Open No. 57-27286. In addition, as a second prior art,
No. 4-111830, there is known a device that measures the resistance of paper and controls the output voltage of the power source of the corona charger according to the measured value.

[0005]

[Problems to be Solved by the Invention] However, the above-mentioned prior art has the following problems.

That is, in the first prior art, even if the current supplied to the corona charger 1, that is, the corona wire current IC, is constant, it flows toward the dielectric belt 3 and contributes to charging it. The belt flowing current IB is not necessarily constant. That is, the corona wire current IC is the belt inflow current I flowing into the belt.
B and the shield current IS flowing into the shield, but even if the corona wire current IC is constant, due to temperature, humidity, changes in the dielectric belt 3 over time, etc., the current closest to the back side of the dielectric belt 3 No consideration was given to the fact that when the electrical resistance and the electrical capacitance C to the grounding point in the belt change, the ratio between the belt flowing current IB and the shield current IS changes.

[0007] The second prior art also has the following problems. In other words, the dielectric belt, like paper, changes its electrical properties such as surface resistance and volume resistance depending on humidity, and also changes over time due to the adhesion of floating toner inside the device and the influence of corona irradiation, making it impossible to achieve optimal transfer. Conditions will change accordingly. In the second prior art, this influence was not taken into consideration. Furthermore, even if sensors were installed to detect all of these changes, complex control would be required based on a large amount of data.

[0008]

[Means for Solving the Problems] In order to solve the above problems, the image transfer device of the present invention, as shown in FIG. A high voltage power source 2, a conveyance means such as a dielectric belt 3 supported by rollers 29 and 30, and a conveyance means from the corona charger 1 to charge the dielectric belt 3 in order to transfer a toner image onto the recording paper 8. It has a belt inflow current measurement device 4 that measures the value of the corona current flowing toward the belt, and a power supply control device 5 that controls the high voltage power source 2 based on the measurement result of the belt inflow current measurement device 4.

Furthermore, in the image transfer apparatus of the present invention, in order to make the above-mentioned means more effective, the surface of the conveying means such as a dielectric belt from the center of the charge applying area to the grounding member 7 at the ground potential is The resistance is 1010 per cm of width perpendicular to the conveying direction of the dielectric belt.
The dielectric belt and device configuration are set so that the resistance is Ω or more.

0010

[Operation] The power source control device controls the output voltage or output current of the high voltage power source based on the measurement result of the belt current measuring device so that the value is always constant. As a result, even if there are changes in environmental conditions such as temperature and humidity, the type of recording paper, or the electrical characteristics of the dielectric belt, the dielectric belt can always be charged to a constant amount of charge. Optimal transfer conditions can always be maintained without being affected by environmental conditions or changes over time. In addition, the inventors have discovered that it is effective to satisfy certain conditions regarding the dielectric belt and the device configuration in order to always maintain optimal transfer conditions using the above control method.

FIG. 3 shows an example of experimental results regarding the relationship between belt current IB and transfer efficiency. Here, the transfer efficiency is
(Reflection density of the transferred image on the recording paper)/(Reflection density of the image before transfer on the photosensitive drum) was determined. This experiment was conducted at a relative humidity of 50% RH, using a process speed of 10 inches/second, a negatively charged organic photoreceptor drum as the photoreceptor drum, and a reversal development type laser beam printer as the development method. The dielectric belt used has a surface resistivity of 5 x 1012Ω and a volume resistivity of 2 x 1011Ω.
cm, thickness 0.6 mm. Since there is a grounded metal roller 2 cm from the wire of the positive polarity corona charger for transfer, the surface resistance R of the belt from the center of the charge application area on the back side of the belt to this grounded roller is per 1 cm width. It is 1013Ω. Under the present experimental conditions, the belt flowing current IB showing the maximum transfer efficiency was 25 μA. Similar experiments were conducted on a number of dielectric belts with different electrical properties, and the relationship between the surface resistance and the optimum belt inflow current IB, which shows the maximum transfer efficiency, was determined by the resistance in the belt thickness direction and the storage of the recording paper used in the experiment. When shown in a graph using environmental humidity as a parameter, it becomes as shown in FIG. From this graph, it can be seen that only when the surface resistance of the belt is 10 11 Ω or more, the belt inflow current IB showing the maximum transfer efficiency is always a constant value, that is, 25 μA in this experiment. The value of I itself is not universal because it varies depending on the process speed, development conditions, etc., but it is a universal characteristic that it always shows the maximum transfer efficiency for a constant belt flowing current I. The reason why the optimal belt current IB increases as the surface resistance of the belt decreases below 1011Ω is because the proportion of current flowing toward the belt flowing toward the grounded metal roller without remaining on the belt surface increases. By increasing. Therefore,
The dielectric belt and device are arranged so that the surface resistance from the center of the charge imparting area of the dielectric belt or other conveying means to the grounded member is 1011Ω or more per 1 cm of width perpendicular to the conveying direction of the dielectric belt. By configuring
Optimum transfer characteristics can always be obtained with a constant belt current.

0012

EXAMPLES The present invention will be explained in more detail by way of examples and with reference to the drawings.

FIG. 5 shows a transfer device using the present invention. This embodiment is a transfer device for an electrophotographic printer of a reversal development type using a negatively charged organic photoreceptor drum 22 with a process speed of 10 inches/second. The transfer device includes a dielectric belt 15 that rotates while being supported by grounded rollers 10, 11, 12, 13, and 14, a positive corona charger 16, a high voltage power source 17, a corona wire current monitor 18, and a shield current monitor 19. , high voltage power supply control device 2
Consists of 0. The recording paper 21 reaches the dielectric belt 15 from a paper feeding system not shown in FIG. 5, and positive corona is irradiated from the back side of the dielectric belt in the nip area where the organic photoreceptor drum 22 and the dielectric belt 15 are in contact. As a result, the toner image on the photosensitive drum is transferred, electrostatically attracted to the dielectric belt, and transported to a fixing device not shown in FIG.

The high voltage power supply 17 is capable of changing its output voltage according to the voltage level of the control signal 31. However, any current source that controls the output current may be used as long as the magnitude of the output current can be similarly controlled from the outside. Control of the output voltage will be explained using FIG. 6. The corona wire current monitor 18 is a 10 kΩ resistor 23 connected in series between the output of the high voltage power supply 17 and the corona wire of the positive corona charger, and the shield current monitor 19 is also connected between the shield of the positive corona charger and the ground. This is a resistance element 24 of 10 kΩ connected in series. The high-voltage power supply control device 20 determines a value corresponding to the belt current flowing into the dielectric belt by determining the difference in voltage between both ends of the resistive elements 23 and 24, and the belt current flowing into the dielectric belt is always 25 μA.
The output of the high voltage power supply is controlled so that it remains constant. As shown in FIG. 6, the configuration of the high-voltage power supply control device is such that the monitor voltage from the resistance elements 23 and 24 is transferred to the buffer amplifier 25.
The signal is then input to a differential amplifier 27 via an isolation amplifier 26. The differential amplifier outputs a voltage corresponding to the difference in the monitor voltages, and the comparator 32 compares this value with the predetermined value V when the belt inflow current is 25 μA, and calculates a voltage corresponding to the difference between the two. A voltage signal is generated, and the output of the high voltage power supply 17 is adjusted via the output amplifier 28 based on the signal so that the current flowing into the belt is controlled to be 25 μA.

The dielectric belt is a urethane rubber belt with a fluorine-based thin film formed on its surface, and the surface resistivity at the initial stage of use and the normal service life of the dielectric belt in this example after printing 1.5 million pages of A4 size paper are as follows: The humidity dependence of the surface resistivity is shown in FIG. The reason why the resistance is higher than the initial state at low humidity is due to dirt from insulating materials such as toner adhering to the surface.At high humidity, this is the main cause of the sudden decrease in surface resistivity after 1.5 million pages have been printed. The cause is that nitrogen oxides generated due to corona irradiation adhere to the belt surface and become ionized under high humidity conditions, producing an ionic current. From this figure, the lowest value of the surface resistivity of the dielectric belt during use of the transfer device in this example is 1011Ω. Therefore, in order to set the resistance from the back surface of the belt to the grounded roller to be 1011 Ω or more per 1 cm of width perpendicular to the conveying direction of the dielectric belt, from the transfer device directly above the corona wire, which is approximately the center of the area where the charge is applied to the dielectric belt, The distance to the nearest ground roller 10 is 2 cm, and the distance to the roller 11 is 15 cm. Here, when the ground roller is close to the shield opening of the corona charger, a corona current component is generated that flows into the ground roller. Therefore, in such a case, in order to detect the corona current component flowing into the ground roller by the shield current monitor, the ground roller is also grounded via the shield current monitor, that is, the shield and the ground roller are electrically connected. After connecting, the total current can be detected using a current monitor.

Note that the volume resistivity of the dielectric belt in this example is 6×10 10 Ω·cm or more during the printing period of 1.5 million pages even at a humidity of 80%RH, and the thickness of the dielectric belt is 600 μm. The resistance in the thickness direction was 3 x 109 Ω per 1 cm2 of area, but the dielectric belt had a resistance in the thickness direction of less than 108 Ω per 1 cm2 of area, and the recording paper was left at a humidity of 80% RH for a long time. When using this method, the transfer efficiency decreased to 50% or less. This phenomenon is caused by the positive charge applied to the back side of the dielectric belt while the recording paper is sandwiched between the dielectric material and the belt reaching the front side of the dielectric belt, that is, the paper contact surface. Paper that has been left in a humid environment has significantly reduced both surface resistivity and volume resistivity, so the positive charge does not remain on the paper surface but leaks through the paper surface, preventing the transfer electric field from increasing. This is because the amount of toner that is electrostatically attracted by the transfer electric field is reduced by penetrating the toner and reaching the side facing the photoreceptor drum and neutralizing the charge of the toner. Therefore, in order to maintain better transfer characteristics, the resistance in the thickness direction of the dielectric belt is also important, and is preferably 108Ω or more, preferably 109Ω.
It is preferable that it is above.

In the image transfer device according to the present invention, the current flowing into the belt is always controlled to be constant, but within the output voltage limit and output current limit of the high voltage power source of the corona charger, the above-mentioned If the control is not achieved, the maintainability of the apparatus is improved by performing a second control such as stopping the image transfer apparatus by outputting an error signal from the high-voltage power supply control apparatus 20, for example. . For example, a situation where the current flowing into the belt cannot be set to the desired value is due to belt deterioration.
This is a case where the surface resistance is extremely low and the IB/IC ratio becomes large, such that IB is 25μ as in this example.
This is the case when the IC value for setting A is small and the corona discharge becomes unstable or the output falls below the lower limit of the high voltage power supply. In addition to this, for example, wire cutting can also be detected as an error.

[0018]

According to the image transfer device according to the present invention, optimum transfer characteristics can always be realized with a simple configuration even under changes in temperature, humidity, type of transfer material, and change in conveying means over time.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an image transfer device of the present invention.

FIG. 2 is a diagram for explaining a prior art.

FIG. 3 is a diagram showing the relationship between belt current flowing into the belt and transfer efficiency in order to explain the effect of the present invention.

FIG. 4 is a diagram showing the relationship between belt surface resistance and optimum belt flowing current to explain the operation of the present invention.

FIG. 5 is a diagram showing an embodiment of the present invention.

FIG. 6 is a configuration diagram of a high voltage power supply control device in an embodiment of the present invention.

FIG. 7 is a diagram showing the humidity dependence of the surface resistivity of a dielectric belt in an example of the present invention.

[Explanation of symbols]

1...Corona charger, 2...High voltage power supply, 3...Dielectric belt,
4... Belt inflow current measuring device, 5... Power supply control device,
6... Photosensitive drum, 7... Grounding member, 8... Recording paper, 9... High voltage power supply, 10, 11, 12, 13, 14... Grounding roller,
15...Dielectric belt, 16...Positive corona charger, 17
...High voltage power supply, 18...Corona wire current monitor, 19...
Shield current monitor, 20... High voltage power supply control device, 21
... Recording paper, 22 ... Organic photoreceptor drum, 23, 24 ... Resistance element, 25 ... Insulation amplifier, 26 ... Buffer amplifier, 27
... Differential amplifier, 28 ... Output amplifier, 29, 30 ... Roller, 31 ... Control signal, 32 ... Comparator.

Claims (7)

[Claims] 1. An image in which an image formed on an image carrier by an image forming medium is transferred to the transfer material by applying an electric charge to the transfer material conveyed by the conveyance means via the conveyance means. An image transfer device, wherein a constant electric charge is always applied to the conveying means. 2. An image in which an image formed on an image carrier by an image forming medium is transferred to the transfer material by applying an electric charge to the transfer material conveyed by the conveyance means via the conveyance means. In the transfer device, the means for applying electric charge is a corona charger, and means for detecting a current flowing from the corona charger toward the conveying means;
An image transfer device comprising means for controlling the amount of corona current of the corona charger. 3. The image transfer device according to claim 2, further comprising:
The means for detecting the current flowing from the corona charger toward the conveying means includes means for measuring the wire current of the corona charger and means for measuring the shield current of the corona charger, and controls the amount of corona current. An image transfer apparatus characterized in that the means for controlling the power supply of the corona charger is a means for controlling the power supply of the corona charger so that the current flowing toward the conveying means is constant based on the values of the shield current and the wire current. 4. The image transfer apparatus according to claim 2, wherein the means for detecting the current flowing from the corona charger toward the conveying means includes first measuring means for measuring the wire current of the corona charger; A second method for measuring a corona current flowing directly from the corona charger to a member other than the conveyance means.
and a means for controlling the amount of corona current so that the current flowing toward the conveying means is constant based on the results obtained from the first measuring means and the second measuring means. An image transfer device characterized in that it is a means for controlling a power source of a corona charger. 5. The image transfer device according to claim 3 or 4, wherein a means for detecting that the current flowing toward the conveying means does not reach a desired constant value even if the power source of the corona charger is controlled. and a control means for stopping the image transfer device based on the detection result of the detection means. [Claim 6] Claim 1, Claim 2, Claim 3, Claim 4
In the image transfer device described above, the conveying means is a dielectric belt, and at least a part of the charge-applying surface of the dielectric belt is in contact with a grounded member, and an area of the dielectric belt to which the charge is applied is provided. An image transfer device characterized in that a surface resistance from the center of the dielectric belt to the nearest grounded member is 10 11 Ω or more per 1 cm of width perpendicular to the conveyance direction of the dielectric belt. [Claim 7] Claim 1, Claim 2, Claim 3, Claim 4
The image transfer device as described above, wherein the conveying means is a dielectric belt, and the dielectric belt has a resistance in the thickness direction of 10 8 Ω or more per 1 cm 2 of area.