JPH06289757A - Color image forming device - Google Patents

Abstract

PURPOSE:To prevent faulty image quality caused by the peeling discharge of a transfer material and image blurring by a discharge product produced by corona discharge. CONSTITUTION:A degree that a stripe is formed in the aixal direction of a photosensitive body 1 is different according to environment (humidity) near the photosensitive body 1 and the moisture content of the transfer material 16. Therefore, a negative DC component (voltage and current) impressed on a destaticizing means 5 for the photosensitive body 1 is controlled by a humidity detecting means provided near the photosensitive body 1 and a moisture content detecting means measuring the moisture content of the transfer material 16 according to the current flowing in a transfer material pressing means. Relation among the humidity, the moisture content and the negative DC component to be pressed is previously stored in a memory, and the appropriate negative DC component is outputted based on the detected result on the humidity and the moisture content. The image blurring is prevented by setting the discharge timing of a destaticizer 7 before and after a spot where the trailing edge of the transfer material 16 comes in contact with the photosensitive body 1 passes a corona destaticizer and starting and stopping discharge.

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, and more particularly, it suppresses discharge products generated by corona discharge, and image defects due to peeling discharge of a transfer material generated in a copying machine using a transfer belt or transfer drum. The present invention relates to a corona discharge static eliminator for removing electricity.

[0002]

2. Description of the Related Art In recent years, color copying machines have been developed, and color copying machines using a transfer belt or a transfer drum have become widespread. In these color copying machines, the transfer material is not directly transferred as in conventional black and white or flat color copying machines, but is transferred by electrostatically adsorbing the transfer material onto a transfer belt or a transfer drum. For this reason, when the trailing edge of the transfer material is peeled off, peeling discharge occurs between the photosensitive drums on the negatively charged photosensitive drum, and at that time, the positive charge generated in the air moves and remains as a history of charges. There is a problem that the charge history is printed as a streak in the axial direction of the drum in the next cycle or thereafter. Various proposals have been made to solve this problem.

In Japanese Patent Laid-Open No. 2-73278,
The rear end portion of the supporting area of the transfer material supported by the transfer drum is made conductive and grounded to prevent positive charging of the photoconductor even if peeling discharge occurs at the time of peeling the rear end of the transfer material.
In Japanese Patent Laid-Open No. 4-52680, the surface potential of the photosensitive drum corresponding to the history generation position is set higher than the original VH outside the image area in advance, and VH is set so that the surface potential after exposure does not fall below the developing bias. The contrast of the developing bias is maintained so that the history portion is not printed.

In Japanese Patent Laid-Open No. 4-62581,
A corona charging unit having the same negative polarity as that for charging the photoconductor is provided between the developing unit and the transfer unit to charge the contact portion of the front end and the rear end of the transfer material with a sufficient negative charge in advance. Even if a positive charge is applied to the surface of the photoconductor, peeling discharge occurs at the front end and the rear end, but the surface potential is lowered, but it is not reached to the opposite polarity. As a result, the charge eliminating lamp and the primary charging are activated to uniformly charge the photoconductor, thus preventing the printing of the history portion.

In Japanese Patent Laid-Open No. 3-87884,
The AC (voltage, current) is placed between the transfer means and the means for cleaning the residual toner on the surface of the photoconductor after the transfer.
The corona charging means on which C (voltage, current) is superimposed removes the charge on the surface of the photoconductor corresponding to the portion of the history of positive charging generated by the peeling discharge at the time of peeling the rear end of the transfer material. At this time, the discharge of the AC component is always on throughout the sequence. Furthermore,
The environmental condition (temperature and humidity) in the vicinity of the photoconductor is detected, and the negative DC current value is controlled based on the detection result to prevent printing of the history portion.

The inventor of the present application has the same problem, and as a result of repeated experiments, various experimental results have been obtained. As one example, it is well known that the axial muscle has a high occurrence frequency particularly when the environment is high humidity, but the worst occurrence is low humidity,
It was found that the condition is a high water content transfer material at low temperature. It was also found that when the high water content transfer material was conveyed at high humidity and high temperature, the degree of axial streaking was lower than when the high water content transfer material was conveyed at low humidity and low temperature. Also,
It was also found that the degree of streaking depends on whether the water content of the transfer material is uniform or not.

In view of these matters, the environment inside the image forming apparatus is detected as in the above-mentioned Japanese Patent Laid-Open No. 3-87884, and the residual toner on the transfer means and the photoreceptor after transfer is detected based on the detection result. Only by controlling the negative DC current value of the corona charging means in which DC (voltage, current) is superimposed on AC (voltage, current) arranged between the cleaning means, the transfer material becomes uneven from the leading edge to the trailing edge. If it contains water, the optimum negative DC current value may not always be obtained. Originally, the water content information of the transfer material necessary for preventing the axial streaks of the photoconductor drum is the water content of a certain width from the rear end of the transfer material, and therefore, a suitable minus D
Output of C value is desirable. Furthermore, environmental changes and changes in the water content of transfer materials change separately in the market.

[0008] For example, the humidity becomes high at night in the summer and is air-conditioned during the day, so the temperature and humidity inside the room are low, but the moisture content of the transfer material does not immediately follow the changes in the environment and remains high. . Therefore, a condition close to the condition of the high water content transfer material at low humidity and low temperature may occur. At this time, the water content of the transfer material is determined based only on the humidity information detected by the means for detecting the environment arranged near the photoconductor, and the transfer means and means for cleaning the residual toner on the photoconductor after the transfer are used. Axial streaks may occur only by controlling the negative DC current value of the corona charging means in which DC (voltage, current) is superimposed on AC (voltage, current) arranged between the two.

On the other hand, the conventional corona discharger for uniformly removing the surface potential of the photosensitive member after transfer was always in a discharged state during copying. In the case of such specifications, the saturated ozone concentration is as high as 6 to 7 ppm during continuous copying, and there is a problem that the charging property is deteriorated when exposed to the surface of the photoconductor. Further, in corona discharge, a discharge product called nitrogen oxide is generated in proportion to ozone concentration in addition to ozone. When this nitrogen oxide adheres to the photoconductor drum, it deteriorates the charge transport layer of the photoconductor, disturbs the electrostatic latent image potential, and causes a blurred image, that is, a so-called parking defect. The inventor of the present application has attempted to reduce the amount of these discharge products by improving the air flow. However, in the tandem type machine configuration, the image forming units are close to each other, which makes it difficult to form the air flow and increases the suction force. Although the duct shape was changed, the improvement effect was hardly seen at the ozone concentration of 5 to 6 ppm.

[0010]

SUMMARY OF THE INVENTION The present invention is based on the generation of parking interruption due to the suppression of discharge products generated by corona discharge and the peeling discharge of transfer material generated in an image forming apparatus using a transfer belt or a transfer drum. An object of the present invention is to provide a corona discharge static eliminator that prevents the occurrence of image quality defects.

[0011]

DISCLOSURE OF THE INVENTION The present invention is directed to a corona charge-eliminating means corresponding to the amount of inflow current which varies depending on the water content of the transfer material by means of a detection means for detecting a current flowing from a ground (earth) into the transfer material pressing means. The negative DC current value table and the humidity information detected by the environment detecting means arranged near the photoconductor are arranged between the transfer means and the means for cleaning the residual toner on the photoconductor after the transfer. It outputs a negative DC current value of the corona charge eliminating means in which DC (voltage, current) is superimposed on AC (voltage, current). The timing of measuring the inflow current is when a transfer material having a certain length passes the transfer material pressing and attracting roll with reference to the rear end of the transfer material. The current flowing into the transfer material pressing means is detected for a predetermined time after the leading edge of the material.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial schematic view of a color image forming apparatus of the present invention. The image forming units in the color image forming apparatus are arranged in parallel in the order of black (BLACK) # 1, yellow (YELLOW) # 2, magenta (MAGENTA) (not shown), and cyan (CYAN) (not shown). ing. The transfer material 16 that has passed through the transfer material passage detection device 17 from the right side of the drawing and is sent by the transfer material transport roll 14 is the transfer belt 1 that rotates.
5 and the transfer material pressing and adsorbing roll 9 on the upstream side. The transfer material 16 is electrostatically adsorbed to the transfer belt 15 by the positive discharge of the transfer material adsorbing corotron 13 while being pressed by the roll on the downstream side of the transfer material pressing and adsorbing roll, and then adsorbed to the rear end of the transfer material. . The transfer material pressing / adsorbing roll 9 is composed of two rolls, the upstream roll is directly grounded, and the downstream roll is grounded via an ammeter 10. The ammeter 10 is the transfer material adsorption corotron 1
The current flowing from the ground to the downstream roll by the positive discharge electric field of 3 is measured. The timing of measurement is determined when the transfer material 16 passes through the transfer material passage detection device 17 according to the transfer material size detection information determined by the user selecting the transfer material size or the automatic selection on the operation panel. After detecting the leading edge or the trailing edge of the transfer material, the area from about 50 mm before the trailing edge of the transfer material to the trailing edge is measured at a preset measurement timing for each transfer material size.

FIG. 2 shows a partially enlarged view of the transfer material attracting portion.
When a positive discharge is made by the transfer material suction corotron 13 via the transfer material belt 15, negative charges are generated on the surface of the transfer material 16, and a positive current flows into the transfer material pressing / sucking roll 9. It is generally known that the amount of charges induced in the transfer material 16 changes depending on the water content of the transfer material 16. As shown in FIG. 3, the current flowing through the transfer pressure adsorption roll 9 along with the electric charge induced in the transfer material 16 is substantially proportional to the water content of the transfer material 16, and the inflow current increases as the water content increases. have. Therefore, the amount of this charge is expressed as a current value from the ground to the transfer material pressing / adsorbing roll 9, and the change in the current can be regarded as a change in the water content of the transfer material.

FIG. 4 shows the relationship between the water content of the transfer material and the DC current of the static elimination corotron required to prevent the generation of streaks in the axial direction. According to this, if the water content of the transfer material is high, the degree of generation of the axial streaks is poor, and the DC current of the static elimination corotron must be increased. But,
The current is not proportional to the water content of the transfer material. If the water content is below a certain water content, a very small amount of DC current may be used, and if the water content is above a certain water content, the DC current may be saturated.

FIG. 5 is a view showing the axial line of the photoconductor with respect to the moisture content of the transfer material and the humidity change detected by the environment detection means (not shown) provided near the photoconductor in the image forming apparatus. It shows how the degree of occurrence affects.
According to this, when the DC component of the corona charge eliminator is constant and a transfer paper with a water content of 10% is used, the degree of axial streak generation is poor in a low humidity environment, and the axial streak generation is high in a high humidity environment. It can be seen that the degree of occurrence is good.

Based on the above consideration results, the humidity H detected by the environment detecting means, the current I flowing into the transfer material pressing and adsorbing roll, and the DC of the charge eliminating corotron.
Table 1 shows the relationship between the component output levels. In Table 1, the humidity H detected by the environment detecting means is H5>H4>H3>H2> H1, and the current I flowing into the transfer material pressing and attracting roll is I5>I4>I3>I2> I.
1 and indicates that the DC component output level of the static elimination corotron is A>B> C.

As can be seen from FIG. 5 and Table 1, the degree of generation of streaks in the axial direction of the photoconductor (the DC of the static eliminating corotron is
It is necessary to change the component output level) depends on the water content of the transfer material when the humidity is low, and does not depend on the water content of the transfer material when the humidity is high. A method of controlling the DC current value of the static elimination corotron according to the present invention will be described. As shown in Table 1,
DC of the static elimination corotron according to the humidity H detected by the environment detection means and the inflow current amount I of the transfer material pressing suction roll.
Areas (levels A, B, and C) where the current is changed are stored in advance, and the DC of the static elimination corotron is stored based on the humidity detected by the environment detecting means and the measurement result of the inflow current of the transfer material pressing suction roll. It suffices to output an electric current, which controls the degree of generation of axial streaks of the photoconductor to be always good.

Next, FIG. 6 shows the discharge timing of the conventional static eliminator corotron. During the cycle, almost all of the discharge depends on the corona charger. In the corona discharge, a discharge product called nitrogen oxide is generated in addition to ozone, but since this is proportional to the amount of ozone generated, at the discharge timing of the conventional static elimination corotron, the parking delay (image blur) is generated. Had occurred.

The present invention shortens the discharge time of the static elimination corotron as shown in FIG. 7 in order to prevent the occurrence of the parking interruption. In FIG. 8 (A), discharge of the static elimination corotron is started several seconds after the driving of the transfer material detection sensor is stopped, and in FIG. 8 (B), discharge of the static elimination corotron is started several seconds after the start of driving the transfer material detection sensor. The timing is shown. That is, the discharge is started and stopped before and after the portion where the rear end of the transfer material contacts the photoconductor passes through the corona charge eliminator. The discharge time during this period is about 440 msec, and the distance is about 70 cm.
As a result, the conventional ozone concentration becomes 1 as shown in FIG.
It was reduced to / 3 to 1/2 and it was possible to prevent the occurrence of parking interruption.

[0020]

As described above, according to the present invention, the occurrence of parking depletion (image blur) is prevented by suppressing the discharge products generated by corona discharge, and an image forming apparatus using a transfer belt or a transfer drum is provided. It is possible to achieve both prevention of image quality defects due to peeling discharge of the transfer material.

[Brief description of drawings]

FIG. 1 is a schematic view of a color image forming apparatus of the present invention.

[Fig. 2] Detailed view of transfer material adsorption unit

FIG. 3 is a diagram showing the relationship between the water content of the transfer material and the inflow current of the transfer pressure adsorption roll.

FIG. 4 is a diagram showing the relationship between the water content of the transfer material and the DC current of the static eliminator corotron required to prevent the generation of streaks in the axial direction of the photoconductor.

FIG. 5 is a diagram showing the extent to which streaks are generated in the axial direction of the photoconductor depending on the water content of the transfer material in each environment.

FIG. 6 is a diagram showing a discharge timing of a conventional static elimination corotron.

FIG. 7 is a diagram showing the discharge timing of the static eliminator corotron of the present invention.

FIG. 8 is a diagram showing ozone concentration.

[Explanation of symbols]

 1 Photoconductor 2 Developing Device 3 Transfer Aid Scorotron 4 Transfer Corotron 5 Electrification Corotron 6 Cleaner 7 Electrification Lamp 8 Scorotron 9 Transfer Material Pressing Adsorption Roll 10 Ammeter 11 Belt Electrification Corotron 12 Belt Electrification Corotron 13 Transfer Material Adsorption Corotron 14 Transfer Material Conveying Roll 15 transfer belt 16 transfer material 17 transfer material passage detection device

Claims (5)

[Claims] 1. A means for charging a photoconductor, a means for superimposing a minus DC component of a voltage or a current on an AC component of a voltage or a current to remove the charge of the photoconductor after the transfer, and a residue after the transfer on the photoconductor. Means for cleaning the toner, means for detecting the environment in the vicinity of the photoconductor, means for detecting the water content of the transfer material, and controlling the amount of current of the minus DC component of the charge eliminating means based on the detection results of both of the detecting means A color image forming apparatus comprising: 2. The means for detecting the water content of the transfer material detects the current flowing into the transfer material pressing means when the transfer material is pressed,
The color image forming apparatus according to claim 1, wherein the water content of the transfer material is determined based on the amount of current. 3. The apparatus according to claim 1, wherein the water content in a certain range is detected with reference to the trailing edge of the transfer material. 4. The apparatus according to claim 1, further comprising means for measuring a transit time of the transfer material. 5. The apparatus according to claim 1, wherein the means for detecting the environment in the vicinity of the photoconductor detects the environment when the image forming apparatus is powered on or each time copying is started.