JPH01287589A - Transfer material separating device for image forming device - Google Patents

Abstract

PURPOSE:To adapt a transfer material separating device to an image forming device by distorting a bias applied to an electrostatic separating discharger so that crest values nearby the positive and negative peak values are decreased, and specifying the frequency of a rectangular alternating current. CONSTITUTION:When a transfer material reaches a separation position where the electrostatic separating discharger 3 is provided, the separating discharger 3 applied a voltage generated by superposing voltages from a rectangular wave AC power source 4 and a variable DC power source 5 for controlling the difference current between the positive and negative components of a discharging current to discharge the transfer material electrostatically, which is separated from an image carrier. At this time, the rectangular wave is used as the applied alternating current for the image forming device which uses an amorphous silicon photosensitive body and performs electrostatic separation and its frequency is set to 250 to 1,000Hz, preferably, 400 to 600Hz. Abnormal discharge is therefore evaded and the deterioration and damage of the photosensitive body due to the abnormal discharge and further an image defect are prevented to perform the separation excellently. Consequently, the image forming device of this kind is speeded up and reduced in size.

Description

Detailed Description of the Invention (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine or a printer, and particularly to a transfer material separation device thereof. It is something.

(Prior Art and Issues to be Solved) In a well-known image forming apparatus that includes a process of electrostatically transferring a transferable toner image formed on the surface of an image carrier to a sheet-like transfer material such as paper, a transfer process is performed at the time of transfer. It is well known that, due to the electric charge imparted to the material, transfer materials have been widely used in the past in a structure in which an image carrier is used to neutralize and eliminate the electric charge imparted to the transfer material. It is.

* In this type of separation charger, static electricity is usually removed by AC corona discharge, which is a combination of sine wave AC and DC.
It has been found that the static elimination function tends to be greater as the peak-to-peak voltage value of the applied AC voltage is higher.

By the way, since the discharge current in this case naturally flows in the direction of the image carrier, the photosensitive layer on the surface of the image carrier by the discharge current, in particular, has high surface hardness and high mechanical strength. Amorphous materials are highly durable, with no potential fluctuations or crystallization caused by repeated charging and exposure, so they have recently come to be used in high-speed printers and for continuous printouts over long periods of time. The case of a silicon photoreceptor will be briefly described.

While the amorphous silicon photoreceptor has the above-mentioned advantages, looking at the withstand voltage characteristics, the OPC (organic semiconductor) photoreceptor has a layer thickness of approximately 20 JLII with a voltage of 5 kV or more (2
50V/xm), 5e-Te, 5e-As, etc. are 3kV (60V/4m) or more in a layer thickness of 501Lm, whereas amorphous silicon has a voltage of 2kV (60V/4m) in a layer thickness of 25Lm.
kV, and by exposing it to a high-pressure corona for a long time,
If you use the device with long maintenance intervals and the charged wire is dirty, abnormal discharge is likely to occur.

In addition, the amorphous silicon photoreceptor has a relative dielectric constant of O
It is about 10, which is larger than about 3.6 for PC and Se-based photoreceptors, and a large amount of corona discharge is required to obtain the same photoreceptor potential, so a high discharge bias is also required. Abnormal discharge is likely to occur.

The above-mentioned problems can be solved to some extent by increasing the layer thickness, but in the case of amorphous silicon, it is not practical due to the high cost in terms of film formation technology.

Furthermore, when amorphous silicon is used as a photoreceptor, it is common to first laminate a surface protective layer, a photosensitive layer, and a charge injection barrier layer on the surface of the substrate.
In this way, when an excessive charge is applied to something,
In particular, breakdown of the charge injection blocking layer occurs first,
It has been found that this causes pinholes to occur throughout the photosensitive layer.

As described above, even if an attempt is made to increase the static elimination efficiency after transfer by increasing the applied voltage as described above, problems such as abnormal discharge such as spark discharge and creeping discharge occur and damage to the photoreceptor due to this occur. Therefore, it is difficult to extremely increase the applied bias.

Furthermore, the scope of use of this type of image forming apparatus has expanded in recent years, and there is a tendency for people to use it without any knowledge of the internal structure of the apparatus or the principles of image formation. From this point of view, it goes without saying that a lower separation bias is preferable, although it is not limited to this.

For this reason, in recent years, rectangular waves, pulse waves, etc., which are substantially more advantageous than sine waves, have come to be used as high-voltage AC waveforms applied to separation and electrical appliances. By keeping the peak-to-peak voltage value relatively low, an excellent static elimination function can be expected.

By the way, in general, in this type of image forming apparatus, the member to be statically neutralized or charged is often a moving object.For this reason, in the case of static neutralization using alternating current, as the speed of the device increases, the frequency However, in the case of high-pressure corona discharge, increasing the frequency causes distortion of the waveform and reduces the static elimination function, increases the risk of leakage and abnormal discharge, and makes it difficult to design the device itself. The problem arises.

The present invention was completed under the above-mentioned current situation, and by applying square wave alternating current to maintain high static elimination efficiency and appropriately setting the frequency, an amorphous silicon photoreceptor can be produced. It is an object of the present invention to provide a transfer material separation device suitable for application to an image forming apparatus that uses, but is not limited to, -.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above-mentioned objects, the present invention provides a transfer material that is brought into contact with a toner image formed on the surface of an image carrier, and a transfer charger is used. In an image forming apparatus configured to electrostatically separate the transfer material from the image carrier by applying a separation bias to a separation static eliminator after transfer, the bias applied to the separation static eliminator is set to a peak of positive and negative values. It is distorted to lower the peak value near the value, and the frequency is 250 to LOOOOHz, preferably 400 to 600.
It is characterized by being a rectangular wave alternating current selected in the R range of Hz.

With this configuration, the separation latitude can be increased while avoiding the risk of abnormal discharge, and stable and good separation can be performed at all times.

(Explanation of Embodiments) FIG. 1 shows a schematic side of the main parts of an image forming apparatus, which has an amorphous silicon photoreceptor formed on its surface and is equipped with a cylindrical image carrier that rotates in the direction of arrow A. It is.

When the toner image formed by the negatively charged toner adhering to the positively charged area on the surface of the image carrier 1 reaches the transfer area where the transfer charger 2 is located, the transfer material P is applied to the area at the same timing. reaches, at this time, a positive transfer bias is applied and the toner image is transferred to the transfer material P, and at the same time, the transfer material tends to be electrostatically attracted to the image carrier due to the electric charge applied at this time. .

Applying a superimposed voltage from a current power source 4 and a variable DC power source 5 that controls the difference current between the positive and negative components of the discharge current to remove static from the transfer material and separate the transfer material from the image carrier; Thereafter, the transfer material is conveyed to a fixing site (not shown), and the toner image is fixed and fixed on the transfer material.

It goes without saying that around the image carrier 1, there are provided a charger, an image information writing means, a developing device, a cleaning device, and other members necessary for forming a fine-toothed image.
Since they are not directly related to the present invention, they are all omitted.

First, the static elimination function depends on the sum of the absolute values of the positive and negative components of the discharge current (called the total current), and the probability of abnormal discharge occurrence increases as the peak-to-peak voltage value of the applied voltage increases. .

FIG. 2 is a graph showing the change in the relationship between the peak-to-peak voltage of the applied voltage and the total current in a sine wave and a rectangular wave. In the case of , the square wave can lower the peak-to-peak voltage of the applied voltage.In the case shown in the figure, the square wave has a lower voltage of 14 kV compared to the 14 kV of the sine wave.
It is shown that the voltage could be lowered to 2kV.

Figure 3 shows the relationship between frequency and discharge current. Overall, there is a tendency for the discharge current to increase as the frequency becomes higher. As can be seen from the rate of increase, the rate of increase in current decreases as the frequency increases.

This means that if the rise time is constant, as the frequency increases,
This is because the shoulder portion of the waveform becomes rounded and becomes close to a sine waveform, reducing the static elimination efficiency. To compensate for this, it becomes necessary to increase the peak-to-peak voltage value.

Furthermore, as the frequency increases, high pressure leaks tend to occur, and this condition is illustrated in the graph of FIG.

In the case of high voltage AC (frequency f = ω/2π), the leakage current is:
If there is a capacitance C in the power supply case, cables, etc., it increases in proportion to 1/ωC, so at 1000Hz, it is twice as dangerous as at 500Hz, and it is dangerous. The noise also became harsher as it approached 1000 Hz.

By the way, in the case of electrostatic separation, it is already known that if the static electricity is removed insufficiently, the transfer material will not be separated sufficiently, causing jams, etc., and if the static electricity is removed excessively, a retransfer phenomenon will occur, resulting in deterioration of image quality. Therefore, in order to always perform good separation regardless of differences or changes in the characteristics of the transfer material itself, the minimum current required for 1 separation (DCI), the current ID at which retransfer starts, and 2. It is desirable that the width between them (separation latitude; I x c2-I, .1) be as large as possible.

FIG. 5 shows the relationship between frequency and separation latitude, with the horizontal axis representing the difference current, which is the difference between the positive and negative components of the discharge current, with the total current being constant.

As can be seen from this, as the frequency increases, the retransfer initiation current increases, and the separation latitude increases.At the same time, due to waveform distortion, the latitude does not widen beyond a certain level, and below 250Hz, the latitude narrows. It's too much to be practical.

Furthermore, in the case of a high frequency, it becomes difficult to design with high voltage leakage in mind, and in the case of a low frequency, problems such as an increase in the size of the transformer occur.

From the above results, in an image forming apparatus that uses an amorphous silicon photoreceptor and performs electrostatic separation, a rectangular wave is used for the applied alternating current, and its frequency is set to 250 to 1000.
It is suitable to set the frequency to Hz, preferably 400 to 600 Hz.

FIG. 6 shows another embodiment of the present invention, in which a resistive element 7 (a nonlinear element, A grid 6 is provided to which a bias power source (the same effect can be applied) is connected.

Such a configuration not only stabilizes the single-separation discharge, but also makes it possible to vary the balance between the single-separation property and retransferability by adjusting the discharge distribution.
FIG. 7 shows the relationship between the frequency of the wave alternating current and the separation latitude in which the grid potential follows the transfer material potential due to the self-bias effect of the element 7.

Thus, by using a grid, the separation latitude can be further expanded.

However, when using a grid, a portion of the discharge current flows through the grid, so the total current must be increased to compensate for this.

For this reason, leakage due to creeping discharge also increases, so the output may become unstable at around 1000 Hz in a high temperature environment, but this situation did not occur below 100 Hz.

FIG. 8 shows still another embodiment, in which the device is disposed between the developing device and the transfer charger to reduce the adsorption force of the toner to the image bearing member and to connect the weak force to the image carrier. ,
A dedicated power source 9 is connected as a DC power source.

FIG. 9 shows the relationship between frequency and separation latitude in this case.

As will be seen, the use of a post charger can also suppress the occurrence of retransfer and expand the separation latitude.

Note that if we consider that the function of the post charger also depends on the total current flowing toward the image carrier, then the square wave AC8. 5k
It was found that V corresponds to 9.2 kV of a sine wave alternating current, and that it is possible to reduce the peak-to-peak voltage and suppress the occurrence of abnormal discharge. Furthermore, by sharing the power source of the 1-minute Ml electric device with the post charger, it also contributes to cost reduction.

Through the above, when the charging wire of the charger becomes dirty due to long-term use, re-transfer is likely to occur, and this tendency is
This was noticeable when a power source near z was used.

This is thought to be because, as mentioned above, the separation latitude is narrow at low frequencies, and since there is a large amount of insulating material attached to the charged wire, it becomes even more difficult for discharge to occur.

Therefore, in consideration of durability and separation latitude, it is preferable that the frequency is 400 Hz or more.

A summary of the results so far is roughly as shown in the table below.

Judging from the table above, it is generally usable in the range of 250 to 1000 H2, but it seems that the best results can be obtained by eliminating static electricity by rectangular wave alternating current preferably in the range of 400 to 600 Hz.

Although the case where amorphous silicon is used as the photoreceptor has been described above, it is easy to understand that the present invention is not limited to this and is also effective for photoreceptors using other materials. .

(3) As described in detail, according to the present invention, in an image forming apparatus in which a roller is separated from an image bearing member, occurrence of abnormal discharge can be avoided and damage to the photoreceptor due to this can be avoided. deterioration,
It is possible to prevent damage and even image defects and to enable good separation, which greatly contributes to speeding up and downsizing this type of image forming apparatus.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of an image forming apparatus showing an embodiment of the present invention. FIG. 2 is a graph showing differences in separation bias depending on the waveform in the above device. FIG. 3 shows differences in separation bias depending on frequency. Figure 4 is a graph showing the relationship between separation bias and leakage current according to frequency. FIG. 5 is a graph showing the separation latitude in the same device as above, FIG. 6 is a schematic side view of another example device, FIG. 7 is a graph showing separation latitude in the same device as above, and FIG. 8 is a graph showing still another example device. The schematic side view and Figure 9 are graphs showing the separation latitude in the same as above. DESCRIPTION OF SYMBOLS 1... Image carrier, 2... Transfer charger, 3. Hayashi... Mingi charger, 411... Square wave AC bias power supply, 5.9... DC power supply, 7... Resistance element , 8/・φ
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Claims (1)

[Claims] After a transfer material is brought into contact with the toner image formed on the surface of the image carrier and transferred by a transfer charger, a separation bias is applied to a separation static eliminator to remove the electrostatic charge from the transfer material from the image carrier. In an image forming apparatus configured to separate static electricity, the bias applied to the separation static eliminator distorts the wave height near the peak value on the positive and negative sides, and the frequency is set to 250.
A transfer material separation device for an image forming apparatus that uses a rectangular wave alternating current selected in the range of ~1000 Hz, preferably 400 ~ 600 Hz.