JPH07261565A - Belt charge removing device and image forming device - Google Patents

Abstract

PURPOSE:To provide a belt charge removing device having no environmental problem and not occupying a large space. CONSTITUTION:A color printer has multiple photoreceptors 1a-1d, the images formed on them are transferred on a paper sheet in sequence while the paper sheet is conveyed by a transfer belt 7. The transfer belt 7 is made of a high- resistance polyimide belt having the resistance of 10<15>OMEGAcm. A charge removing brush roller 18 is arranged in contact with the surface of the transfer belt 7 to face a driving roller 10. An AC power source 14 is connected to the brush roller 18. The cleaning and charge removal on the surface of the transfer belt 7 are conducted by the brush roller 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt static eliminator and an image forming apparatus, and more particularly to an improvement of a static eliminator mechanism of an apparatus such as a color printer.

[0002]

2. Description of the Related Art Insulating and high-resistance belts are used as paper conveying belts and transfer belts of electrophotographic apparatuses. These insulative and high-resistance belts are charged by the device and frictionally charged by rubbing against various things.
It is easy to hold extra charges on the front and back screens. If such an electric charge is provided, the original function cannot be fulfilled. Therefore, in an apparatus using this type of belt, it is general to use a corona discharger to eliminate the charge on both sides of the belt.

[0003]

Corona dischargers generate ozone, which causes environmental problems. In particular, when the both sides of the belt are discharged, two corona dischargers are required, which not only generates a large amount of ozone but also requires a large space. The present invention has been made based on this point of view, and an object thereof is to provide a belt static eliminator that has no environmental problems and does not occupy a large space.

[0004]

The first aspect of the present invention is as follows.
A static eliminator for sandwiching a traveling belt between a pair of static elimination members to which a voltage is applied to eliminate static electricity, wherein both static elimination members are gradually separated from the belt in a traveling direction of the belt from a position in contact with the belt. Each has a curved surface, and the ratio of the curvatures of both curved surfaces is in the range of 1/2 to 2,
In addition, the radius of curvature of each is 4 mm or more.

A second aspect of the present invention is a static eliminator for eliminating static electricity by sandwiching a traveling belt with a pair of static eliminator members to which a voltage is applied, and a position where one of the static eliminator members contacts the belt. To a curved surface that gradually separates from the belt in the traveling direction of the belt, and the other of the static eliminating members has a large number of contact points facing the curved surface and to the belt.

A third aspect of the present invention is a static eliminator for eliminating static electricity by sandwiching a traveling belt with a pair of static eliminator members to which a voltage is applied, wherein one of the static eliminator members supports the belt. It is a roller, and the other of the charge removing members is in contact with the belt while facing the curved surface in the traveling direction of the belt from the position of the supporting roller in contact with the belt.

An image forming apparatus according to the present invention is an apparatus which has a plurality of image carriers and which sequentially transfers the images formed on the image carriers to the paper while conveying the paper by a transfer belt. , As a charge eliminating device for the transfer belt,
The static eliminator according to the first to third aspects is incorporated.

[0008]

The belt static eliminator according to the present invention does not generate harmful substances such as ozone and eliminates static electricity by sandwiching the belt between a pair of static eliminator members. A voltage, preferably an AC voltage, is applied between the charge eliminating members. When sandwiching the belt with a pair of curved conductive members, such as rollers,
By setting the curvatures of the outer curved surfaces of both rollers to 1/2 to 2 and setting the radius of curvature to 4 mm or more, good static elimination can be performed even if a mounting error of a member occurs. When a member having a large number of contact points, such as a brush, is used as the charge removing member, the charge removing and cleaning of the belt can be performed simultaneously. Space is reduced by using the belt support roller as one of the static eliminating members.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a color printer which is an image forming apparatus having a belt static eliminator according to an embodiment of the present invention.
The image forming apparatus, that is, the color printer includes the first to fourth
Images of yellow, magenta, cyan, and black are formed on the photosensitive drums, which are the image bearing members of the stations Sa to Sd, respectively, and are sequentially transferred to a sheet conveyed by a transfer belt 7 composed of a high resistance belt or an insulating belt. To obtain an image. The printing speed is 8 sheets / minute and the process speed is 66 mm / sec. As the belt, a high-resistance polyimide belt (carbon dispersion) having a thickness of 80 μm and a resistance of 10 ¹⁵ Ω · cm is used.

[0010] Since the general charge accumulation in the following materials 10 ⁸ Ω · cm is not a problem, the present invention is 10 ⁸ Ω · c
Applies to belts using materials above m. The material of the belt to which the present invention is applied is not limited to polyimide, and materials such as PET and urethane rubber are also included.

In each of the stations Sa to Sd, the photoconductors 1a to 1d, which are image bearing members, are charged by the charging rollers 2a to 2d. Next, the exposure means 3a-
An electrostatic latent image is formed by 3d and visualized by the developing devices 4a to 4d to obtain a toner image. After transfer to paper,
The remaining residual toner is removed from the surfaces of the photoconductors 1a to 1d by the toner cleaners 5a to 5d. 6a to 6 in the figure
d is a corona charger.

The sheet is fed by a sheet feeding means (not shown) and is conveyed between the suction roller 8 and the transfer belt 7. The transfer belt 7 is supported by the tension roller 9 and the driving roller 10 while being wound around the rollers 9. The paper is bias voltage (-180) together with the transfer belt 7.
(0 V) is applied between the attraction roller 8 and the tension roller 9 connected to the ground, and is charged by the electric field between the rollers and attracted to the transfer belt 7. As a tension roller, from the viewpoint of preventing the belt from meandering,
A metal roller is used because deformation is not desirable. On the other hand, the suction roller 8 needs to form a stable nip with the tension roller 9 from the viewpoint of stably applying the suction charge to the paper. Therefore, a conductive elastic roller made of urethane rubber in which carbon is dispersed is used as the attraction roller 8.

In order to obtain a stable nip, the suction roller needs to be soft to some extent, but if it is too soft, roller deformation due to permanent distortion tends to occur. The suitable range of the rubber hardness is 25 degrees to 65 degrees (JIS-A). Within this range, the electric charge can be stably applied to the paper and the roller is not deformed.

Further, the resistance of the roller material is also important in order to stably apply the electric charge to the paper by electric discharge. 10
^{If it is 8} Ω · cm or more, stable charge application cannot be obtained. The bias voltage applied to the suction roller 8 has a polarity opposite to the charging polarity of the toner. The polarity of the bias voltage may be any polarity as long as the attraction is performed. However, if the polarity of the bias voltage is opposite to the polarity of the toner, the toner is pre-transferred before the transfer area where the transfer belt 7 and the photoconductor 1a are in contact with each other. As a result, double images, image blurring, etc. occur. In the present embodiment, as the photoconductors 1a to 1d, the negative polarity OPC is subjected to the reversal development with the negative toner. Therefore, the suitable range of the adsorption bias voltage is −100.
It is 0-3000V.

The sheet is conveyed while being attracted to the transfer belt 7, and is sandwiched between the photoconductor 1a of the first station Sa and the transfer area formed by the transfer belt. By applying an electric charge to the back of the transfer belt with a corona discharger,
The toner image on the photoconductor 1a is transferred to the paper. Similarly,
At the second station Sb, the third station Sc, and the fourth station Sd, transfer is performed on the sheet, and a full-color image is formed on the sheet. The transfer voltage is
The first station Sa is 5.2 kV, the second station Sb is 6.0 kV, and the third station Sc is 6.9 kV.
The fourth station Sd has a voltage of 7.8 kV, and a higher voltage is required in the subsequent stages.

The sheet on which the toner image is received is fixed by heat and pressure in the fixing device 11 and discharged to the outside of the apparatus. When the surface of the transfer belt 7 becomes dirty, backside dirt of the paper and poor suction of the paper occur. Therefore, the brush roller as a roller-like rotating member cleans the belt to remove electricity. The transfer belt 7 enters a new cycle after being discharged and cleaned.

When continuous printing is performed without removing the charge on the belt, the transfer charge accumulated on the belt changes the transfer electric field in the next cycle.
The transfer gradually deteriorates from the third sheet. Furthermore, belt 7
On the other hand, scattered toner, toner on the drum, and the like are deposited and accumulated, which lowers the transfer performance and stains the back of the paper. In particular, when a paper jam occurs, the paper may be contaminated, and when the next printing is performed, the back surface of the paper may be significantly contaminated. Therefore, a mechanism for cleaning the belt is required.

Conventionally, a pair of belt neutralization devices by corona discharge and a belt cleaning device using a cleaning blade have been used. However, if all of them are arranged, a large amount of ozone is generated and the structure of the device becomes complicated, leading to an increase in cost. On the other hand, in the present invention, as shown in FIG. 1, the brush-type static elimination roller 18 which is used for both static elimination and cleaning of the belt is arranged, whereby the apparatus is downsized and ozone is not generated. A bias voltage is applied to the discharging roller 18 from the high frequency power supply 14.

The static elimination roller 18 has a brush bristle having a fiber diameter of 3
-15D (denier), brush bristle density 20,000 to 300,000 / in ² , specific resistance of brush bristle material is 10 ³ to 10 ⁹ Ω
・ It is desirable to be in the range of cm. Drive roller 10
Is a metal roller having a diameter of 20 mm and is grounded. The bias voltage applied to the charge eliminating roller 18 is 18
The range of 00 to 3200 Vp-p (AC peak-to-peak voltage) is good, and the frequency is suitably about 300 to kHz.

As shown in FIG. 2, the brush of the charge eliminating roller 18 is preliminarily subjected to beveling treatment so as to flutter in the direction of rotation of the roller 18. As shown in FIG. 3, the static eliminator roller 18 is manufactured such that a tape-shaped brush is wound around a shaft so that a roll is formed. By performing this slanting treatment, uniform charge removal and cleaning can be performed.

The charge eliminating roller 18 rotates in the against direction at a speed twice the peripheral speed of the belt. The rod-shaped conductive member 20 to which 1 + 50V is applied from the DC power supply 19 is in contact with the brush of the roller 18. The member 20 removes toner, paper dust, and the like attached to the brush from the brush, and the toner, paper dust, and the like are removed by the cleaner unit 2.
It is stored in 1.

Next, the difference in function between the solid roller and the brush roller will be described. Compared to brush rollers, solid rollers have a slightly larger deterioration in function when they become dirty.
In connection with this point, continuous printing tests were conducted under four different conditions to examine the occurrence of transfer defects. The first is a case where the charge eliminating and cleaning means is not used. The second is a case where a solid roller is used as a cleaning member for removing static electricity and a cleaning blade is brought into contact with the roller. The third is a case where a brush roller is used as a charge removing / cleaning member and a member for cleaning the brush roller is not provided. The fourth case is a case where a brush roller is used as a charge removal / cleaning member and a rod-shaped member 20 for cleaning the brush roller is brought into contact with the brush roller.

In the first case, the transfer failure occurred from the third sheet, and the backside stain of the sheet also occurred from about 100 sheets. In the second case, the charge removal of the belt was insufficient after about 30,000 sheets, and the transfer failure occurred. Also, the back side of the paper was smeared from around 20,000 sheets. In the third case, the transfer was good up to 50,000 sheets, and the back side of the paper did not stain up to 30,000 sheets. On the other hand, in the case of the above-mentioned fourth case, there was no problem even when printing was performed up to 100,000 sheets in terms of both transfer failure and stain on the back of the paper. Furthermore, even if a jam occurs, the back side of the paper does not stain.

As described above, by using the roller as a charge removing / cleaning member for the belt, it is possible to provide an apparatus which is small in size, does not generate ozone, can perform good transfer, and does not stain the back of the paper. Particularly, by using the brush roller, the life of the belt transfer device can be remarkably extended.

FIG. 4 shows a color printer having a belt static eliminator according to another embodiment of the present invention. With reference to this embodiment, an apparatus for holding a belt between a pair of members having a curved surface and removing electricity will be described. The steps of forming the toner image on the drum, the steps of sucking and conveying the paper, and the steps of sequentially transferring the image to the paper are the same as those in the embodiment shown in FIG.

The sheet that has received the toner image is fixed by heat and pressure by the fixing device 11 and is discharged to the outside of the apparatus.
If the surface of the transfer belt 7 becomes dirty, backside dirt of the paper or improper suction of the paper occurs, so cleaning is performed by the belt cleaner 15. Further, the transfer belt 7 is subjected to a new cycle after the charge is removed from both sides by the belt back surface neutralization roller 12 and the belt front surface neutralization roller 13.

The state of charge removal of the belt was examined by using an experimental apparatus in FIG. Here, the drum E1 was charged by a charging roller, and paper was passed without printing. y1, y2, y
3, y4 are surface potential sensors, x1, x2, x3,
x4 is a grounded counter electrode for measurement. y1 is the surface charge of the paper after passing through the transfer area, y2 is the charge on the back surface of the belt after passing through the transfer area, y3 is the charge on the front surface of the belt after the paper is peeled off, and y4 is the belt after the paper is peeled off Indicates the charge on the back surface.

As shown in FIG. 6, when the surface of the paper after passing through the transfer area is separated from the photosensitive body 1 in the transfer area, discharge from the photosensitive body imparts (-) charge having a polarity opposite to that of the transfer charge. To be done. A (+) charge is applied to the back surface of the belt 7 by the transfer corona. As a result of the experiment, as shown in Table 1 (1), y1 is -600V and y2 is + 1000V.
The surface potential of was detected. After the paper is peeled off, the front surface of the belt is y3 at -480V and the back surface is y4 at +
A charge of 600 V remained.

[0029]

[Table 1]

Table 2 (1) shows the results of a print test performed by a color printer without performing the belt charge removal. In Table 2, “◯” indicates no transfer failure, and “x” indicates the occurrence of transfer failure.

[0031]

[Table 2]

When continuous printing was performed without removing the belt charge, transfer failure occurred after the fifth sheet. It is considered that this phenomenon occurred because (−) charges were accumulated on the surface of the belt and the (−) charges on this surface weakened the transfer electric field in the transfer region.

Then, as shown in FIG. 7, the surface of the belt was discharged by the roller. Table 1 (2) shows the surface potential of each part at this time. Although y3 was almost 0 V, a potential of +550 V remained on y4. In general, a corona discharger to which an AC bias voltage is applied is used to remove the charge on such a belt, but it is not desirable because a large amount of ozone and NOx are generated.

Table 2 (2) shows the evaluation results of the transferred image when the charge removal structure shown in FIG. 7 was used to remove the charge on only the surface of the belt and a print test was performed with a color printer. A good image was obtained on about 10 sheets of continuous printing, but when printing was performed more than that, transfer blurring of characters and the like occurred. It is considered that this is because residual (+) charges are accumulated on the back surface of the belt, and the toner (-polarity) on the photoconductor is pre-transferred before the transfer area.

Therefore, as shown in FIG. 8, a belt surface destaticizing roller and back destaticizing rollers 13 and 12 are provided, and the surface potential of the belt is measured. The same material (conductive urethane rubber) roller was used as the two static elimination rollers. As a result, Table 1
As shown in (3), it was confirmed that both sides of the belt were discharged. When a color printer was used to perform a print test using the static elimination structure shown in FIG. 8, no transfer failure or transfer blur occurred even when continuous printing was performed, as shown in Table 2 (3).

The entire transfer device to which the charge eliminating structure shown in FIG. 8 is applied is as shown in FIG. In this way, by sandwiching the belt with a pair of conductive rollers and applying an AC bias voltage, it is possible to eliminate charges on both sides of the belt, and it is possible to obtain a good image even when continuous printing is performed.

Under the experimental conditions shown in FIGS. 5 to 8, the charging start voltage is about 900 V when the belt 7 is charged by applying a DC bias voltage.
The C voltage is 1800 Vp-p or more, which is twice the charging start voltage or more. Also, regarding the frequency, the process speed 66
At mm / sec, if the frequency is 300 Hz or less, static elimination unevenness occurs and transfer failure occurs.

The static elimination characteristics are also affected by the diameters of both rollers. Diameter r1 (mm) of the belt back neutralization roller 12 in FIG.
Is fixed at 15 mm, and the belt surface static elimination roller 13 has a diameter r
Table 3 shows the electric potentials on the front and back of the belt after the charge removal when the value of 2 (mm) was changed. In Table 3, “y3” and “y4” correspond to the positions in the experimental device shown in FIG. Applied bias voltage is 2
It was set to 200 Vp-p and 1 kHz. It can be seen from Table 3 that when there is a difference in the roller diameters, the belt surface on the roller side having a large diameter is not sufficiently discharged.

[0039]

[Table 3]

FIG. 9 shows the relationship between the distance from the surface of the roller 13 to the surface of the belt 7 and the X-axis direction distance when the belt traveling direction is the X axis. According to Paschen's discharge curve, when the gap is 10 μm, the discharge is most likely to occur, and when the gap is large, the discharge start voltage becomes high and the discharge is difficult to occur. Therefore, when the roller diameter is small, the gap quickly becomes large, so that the belt is sufficiently discharged, but when the roller diameter is large, the gap is not 10 μm or more, and the charge is not discharged. 10μ
When the gap becomes m, the surface of the small roller to be the counter electrode is far away and the charge cannot be removed. Therefore, it is desirable that the diameters of both rollers are the same as much as possible. As is clear from Table 3, the ratio of the two roller diameters is
The range of 1/2 to 2 is preferable.

Further, even if the diameters are the same, if the diameters are small and there is a deviation between the axes of the rollers in the belt traveling direction as shown in FIG. In mass production, there is a possibility that a deviation of about 200 μm may occur depending on the accuracy of parts and the accuracy of mounting.

For example, the gap on the roller A side is 10 μm under the condition that the diameter of both rollers is 5 mm and the shafts of both rollers are displaced by 200 μm as shown in FIG.
(P1 in FIG. 9), the gap on the roller B side is still 1 μm (Q1 in FIG. 9), and static elimination of the belt does not start. When the gap on the roller B side is 10 μm (Q2 in FIG. 9), the gap on the A side is 25 μm.
As described above (P2 in FIG. 9), the belt cannot be neutralized unless a considerably large AC voltage is applied. However, if the rollers A and B have a diameter of 20 mm, the gap on the b side is 1 when the gap on the A side becomes 10 μm.
The thickness is 8 μm, and both sides of the belt are discharged even if a large AC voltage is not applied.

The rollers A and B have the same diameter, and the diameter is 5
Both sides of the belt are neutralized under the condition that the distance between the rollers is changed to about 40 mm and the rollers are displaced by about 200 μm as shown in FIG. 10 (approximately 10 V or less) AC
The voltage (Vp-p) is shown in FIG. Here, DC to the roller
The belt is charged by applying a bias voltage,
The voltage at which charging is started is 900V. The frequency of the AC bias voltage is 1 kHz.

With a diameter of 40 mm, 1800 Vp-p, diameter 3
At 0 mm, both sides are sufficiently discharged even at 2000 Vp-p. However, when the diameter is 20 mm, it is 2300 Vp-p and the diameter is 1
2800Vp-p at 0mm, 3000V at 8mm diameter
Static electricity cannot be removed unless applied at pp or more. 3 for a diameter of 5 mm
Even if a high voltage of 200 Vp-p is applied, the charge cannot be removed. If an AC voltage higher than this is applied, problems such as dielectric breakdown of the belt, electric noise, and AC vibration noise will occur, which are not practical.

That is, when the belt is sandwiched between two members each having a curved surface, the ratio of the radii of curvature of both curved surfaces is in the range of 1/2 to 2, and the radius of curvature is 4 m.
m (corresponding to a diameter of 8 mm) or more, and the AC applied voltage has a peak value that is more than twice the charging start voltage when the belt is charged with a DC bias voltage and has a peak value of 3200 Vp-p.
If it is set as follows, both sides of the belt can be effectively discharged.

Further, as described above in the explanation regarding the suction roller, the hardness of the roller is preferably low in order to obtain a stable nip. However, if the hardness is too low, apart from the problem of permanent set, the point of separation from the belt changes significantly, and the belt cannot be stably discharged. In Table 4, the belt back neutralization roller 12 is a metal roller, and the belt front neutralization roller 13 is a rubber roller (resistor 10 ⁶
Ω · cm) and shows the range of potentials on both surfaces of the belt when the hardness of the rubber roller is changed from 15 to 80 degrees. Table 4
Medium "y3" and "y4" correspond to the positions in the experimental device shown in FIG.

[0047]

[Table 4]

As is clear from Table 4, the rubber hardness is 25.
Good charge removal is performed in the range of up to 65 degrees. Even if both the rollers 12 and 13 are rubber rollers, 2
Good results are obtained at 5 to 65 degrees.

In the above description, the conductive rollers 12 and 13 are taken as an example of the member for holding the belt. However, it is also possible to use curved conductive blades instead of rollers. FIG. 12 shows an embodiment of a color printer in which a belt is sandwiched between the roller 12 and an elastic and conductive blade 23. In this case, the same result can be obtained if the relationship between the surface of the roller 12 and the radius of curvature of the curved surface of the conductive blade 23 in the traveling direction of the belt satisfies the above relationship.

Next, a case will be described in which a member having a large number of contact points is brought into contact with the belt as a charge removing member to perform charge removal. FIG. 13 shows an embodiment of a color printer in which a belt is sandwiched between the back static elimination roller 12 and the static elimination brush 33.
The brush 33 is preferably the same as the charging brush, and has a brush bristle fiber diameter of 3 to 15 D (denier), a brush bristle density of 20,000 to 300,000 / in ² , and a specific resistance of the brush bristle material. The range of 10 ³ to 10 ⁹ Ω · cm is preferable. Roller 12
Is a metal roller having a diameter of 20 mm and is grounded.
The roller 12 does not have to be made of metal, and may be a roller having a resistance of 10 ⁸ Ω · cm or less. The bias voltage applied to the brush 33 is preferably in the range of 1800 to 3200 Vp-p, and the frequency is preferably about 300 to 2 kHz, as in the case of performing static elimination with two rollers.

The static elimination structure of the static elimination roller 12 and the static elimination brush 33 shown in FIG. 13 was attached to the experimental apparatus shown in FIG. As shown in FIG.
(B) and (c) Table 5 shows the results obtained by changing the applied bias voltage from 1800 to 3200 V and changing the belt as shown in FIG. In Table 5, “y3” and “y4” correspond to the positions in the experimental device shown in FIG. The electric potential of the belt before static elimination was −480 V on the front surface and +600 V on the rear surface.

[0052]

[Table 5]

With respect to the surface of the belt, the brush 33 has a large number of contact points and is a series of approaching and separating.
Therefore, if the contact points are separated from each other within a range where the roller 12 can act as an electrode, the belt surface is discharged. However, as to the back surface, as described above, a member that can be a pair of electrodes of the roller 12 needs to be present on the front side of the belt in a region where the roller 12 is separated from the belt. Therefore, the roller 1 which is a member having a curved surface at the contact portion
A brush 33, which is an abutting member having a large number of contact points, is brought into contact with an area in which 2 is gradually separated from the area where the belt 7 is in contact with the belt 7. As a result, it was confirmed that the transfer failure due to the charge removal failure did not occur and good printing could be performed for a long time.

FIG. 15 shows an embodiment of a color printer in which a brush 33 is used as a back charge eliminating member for the front charge eliminating roller 13. FIG. 16 shows an embodiment of a color printer in which a bias voltage is applied to the belt back surface neutralization roller 12. Also in these embodiments, the same effect as the embodiment shown in FIG. 13 can be obtained.

Next, a static elimination structure using one of the two rollers (driving roller and tension roller) supporting the belt as the static elimination member will be described. FIG. 17 shows an embodiment of a color printer incorporating such a structure.

As shown in FIG. 17, the belt surface charge eliminating roller 1
3 is arranged such that the position where it is separated from the belt 7 is substantially the same as the position where the inner belt drive roller 30 and the belt 7 are separated from each other. The drive roller 30 is made of metal and is grounded. A conductive urethane rubber roller (10 ⁶ Ω · cm) having a rubber hardness of 60 degrees (JIS-A) is used as the belt surface charge-eliminating roller 13.

As described above, in general, charging / discharging using discharge is performed at a portion where the charging / discharging member and the object to be charged / discharging approach or separate. In particular, in the case of applying an AC bias voltage to remove electricity, the areas that are separated are important. Therefore, the position where the belt is separated from the driving roller 10 and the belt surface static elimination roller 13 are
If the positions separated from do not match, the charge removal on one side will be insufficient. Under the condition that the shaft of the belt surface charge-eliminating roller 13 is displaced by 200 μm in the traveling direction of the belt with respect to the shaft of the driving roller 10, the potentials on the front and back sides of the belt after charge-eliminating are set in the same manner as the experimental apparatus shown in FIG. The measurement result,
Table 1 shows the results of continuous printing with a color printer.
(4) is shown in Table 2 (4). From these tables, it can be seen that the front and back of the belt have been sufficiently neutralized.

The static elimination characteristics are also affected by the diameters of both rollers. Also in this case, the ratio of the diameters of the two rollers is 1/2 to
In the range of 2, the size is suitably 8 mm or more in diameter. In Table 6, the diameter r1 (mm) of the driving roller 10 is fixed to 15 mm, the diameter r2 (mm) of the charge eliminating roller 13 is changed, and the charge eliminating bias voltage is 2000 Vp-p, 600H.
The electric potentials of the front and back of the belt after static elimination when the voltage of z is applied are shown. In Table 6, "y3" and "y4" correspond to the positions in the experimental device shown in FIG. From the table, it can be seen that when the ratio of the diameters of the two rollers is in the range of 1/2 to 2, both sides of the belt are sufficiently formed.

[0059]

[Table 6]

When the axis of the belt surface charge-eliminating roller 13 is displaced from the axis of the driving roller 10 by 200 μm in the traveling direction of the belt, and the two roller diameters are changed by the same value, both sides of the belt are discharged. 18 shows the AC voltage.
Here, the belt is charged by applying a DC bias voltage to the roller, and the voltage at which charging is started is 900V.
Is. The frequency of the AC bias voltage is 1 kHz.

With a diameter of 40 mm, 1800 Vp-p, diameter 3
At 0 mm, both sides are sufficiently discharged even at 2000 Vp-p. However, when the diameter is 20 mm, it is 2300 Vp-p and the diameter is 1
2800Vp-p at 0mm, 3000V at 8mm diameter
Static electricity cannot be removed unless applied at pp or more. 3 for a diameter of 5 mm
Even if a high voltage of 200 Vp-p is applied, the charge cannot be removed. If an AC voltage higher than this is applied, problems such as dielectric breakdown of the belt, electric noise, and AC vibration noise will occur, which are not practical. That is, the drive roller 10 and the belt surface charge-eliminating roller 13 need to have a diameter of 8 mm or more.

As shown in FIG. 19, a conductive blade 23 may be used as the belt surface charge removing member. In this case, the same effect can be obtained if the relationship between the radius of the drive roller 10 and the radius of curvature of the curvature of the elastic and conductive blade 23 at the contact portion satisfies the above relationship.

Further, as shown in FIG. 20, a member having a large number of contact points, for example, a brush 33, can be used as the belt surface charge eliminating member. The brush 33 is preferably the same as the charging brush, and has a brush bristle fiber diameter of 3 to 15 D (denier), a brush bristle density of 20,000 to 300,000 / in ² , and a specific resistance of the brush bristle material. The range of 10 ³ to 10 ⁹ Ω · cm is preferable. The roller is a metal roller having a diameter of 20 mm and is grounded. The bias voltage applied to the brush 33 is 18 as in the case of performing the static elimination by the two rollers.
The range of 00-3200Vp-p is good, and the frequency is 300-
2 kHz is suitable. Tables 1 (5) and 2 (5) show the measurement results of the potentials on the front and back sides of the belt of this example and the results of continuous printing with a color printer. From these tables, it can be seen that the front and back of the belt have been sufficiently neutralized.

If the brush 33 comes into contact with the belt 7 in a region where the drive roller 10 is separated from the belt 7, that is, facing the outer surface of the roller 10 in the traveling direction of the belt, it is as good as the embodiment of FIG. Static elimination can be performed. Therefore,
Even if continuous printing is performed, transfer defects due to the accumulation of charges on the belt do not occur.

Further, as shown in FIG. 21, the brush roller 18 as described with reference to FIGS. 1 and 2 may be used as the belt surface charge removing member. Also in this case, if the brush roller 18 is in contact with the belt 7 in a region where the drive roller 10 is separated from the belt 7, that is, in opposition to the outer surface of the roller 10 in the traveling direction of the belt, good charge removal is performed. Similarly, good printing can be performed without transfer failure.

That is, the area where the drive roller 10 is separated from the belt, that is, the roller 10 in the traveling direction of the belt.
By sandwiching the belt between the belt driving roller 10 and the belt surface charge-eliminating member so that the belt surface charge-eliminating member faces the outer surface of the belt, charge removal on the front and back of the belt can be favorably performed. Further, by using such a static eliminator as a static eliminator for a transfer belt of a color printer, a clear image can be obtained and the life of the transfer belt can be extended.

[0067]

According to the present invention, the use of the contact type static eliminator enables the static elimination of the belt without generating harmful substances such as ozone. When sandwiching the belt between the conductive members having a pair of curved surfaces, by setting the curvatures of both curved surfaces to a specific relationship, good static elimination can be performed even if a mounting error of the members occurs. it can.

When a brush-shaped conductive member having a large number of contact points is used as the charge eliminating member, the charge eliminating and cleaning of the belt can be performed at the same time, which is effective for downsizing the apparatus.

When the supporting roller of the belt is used as one of the static eliminating members, only one static eliminating member needs to be added, so that the space is reduced. An image forming apparatus for a color image, which sequentially transfers images on a plurality of drum units to paper, requires accumulation of charges on a transfer belt or an intermediate transfer belt even though precise transfer is required. Occurs. The belt static eliminator according to the present invention is very effective for such an image forming apparatus.

[Brief description of drawings]

FIG. 1 is a schematic side view showing a color printer having a belt static eliminator according to an embodiment of the present invention.

FIG. 2 is an enlarged side view showing a brush roller used as a belt surface static eliminator roller of the static eliminator shown in FIG.

FIG. 3 is a plan view showing the brush roller shown in FIG.

FIG. 4 is a schematic side view showing a color printer having a belt static eliminator according to another embodiment of the present invention.

FIG. 5 is a schematic side view showing an experimental apparatus for examining the charge removal state of the belt.

FIG. 6 is a diagram showing a charged state of a belt after transfer.

FIG. 7 is a schematic side view showing an experimental mode in which only the front surface of the belt is neutralized.

FIG. 8 is a schematic side view showing an experimental mode in which both the front and back sides of the belt are destaticized.

FIG. 9 is a graph showing the relationship between the distance from the surface of the roller to the surface of the belt and the distance in the X-axis direction when the belt traveling direction is the X axis.

FIG. 10 is a schematic side view showing a mode in which a deviation occurs between the shafts of the charge eliminating rollers in the belt traveling direction.

FIG. 11 is a graph showing an AC voltage (Vp-p) for discharging both sides of the belt when the axes of the discharging rollers are displaced by about 200 μm in the belt traveling direction.

FIG. 12 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 13 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 14 is a schematic side view showing a mode in which the position of the static elimination brush is changed in the static eliminator shown in FIG.

FIG. 15 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 16 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 17 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 18 is an AC voltage (Vp-p) that eliminates static electricity on both sides of the belt when the axis of the belt surface static eliminator is displaced from the axis of the drive roller by about 200 μm in the belt traveling direction.
The graph showing.

FIG. 19 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 20 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

FIG. 21 is a schematic side view showing a color printer having a belt static eliminator according to still another embodiment of the present invention.

[Explanation of symbols]

1a-1d ... Photoreceptor, 2a-2d ... Charging roller, 3a-
3d ... Exposure means, 4a-4d ... Developing device, 5a-5d ... Toner cleaner, 6a-6d ... Corona charger, 7 ... Transfer belt, 8 ... Adsorption roller, 9 ... Tension roller, 10 ...
Drive roller, 11 ... Fixing device, 12 ... Belt back neutralizing roller, 13 ... Belt front neutralizing roller, 14 ... AC power source, 15
... belt cleaner, 18 ... static elimination brush roller, 19 ... DC power supply, 20 ... rod-shaped conductive member, 21 ... cleaner unit, 23 ... static elimination blade, 30 ... drive roller, 33 ... static elimination brush.

Claims (6)

[Claims] 1. A static eliminator for performing static elimination by sandwiching a traveling belt with a pair of static elimination members to which a voltage is applied, wherein both static elimination members are in a traveling direction of the belt from a position where they are in contact with the belt. A static eliminator having curved surfaces that are gradually separated from the belt, a curvature ratio of the curved surfaces being in the range of 1/2 to 2, and a radius of curvature of each being 4 mm or more. 2. A static eliminator for performing static elimination by sandwiching a traveling belt with a pair of static elimination members to which a voltage is applied, in a traveling direction of the belt from a position where one of the static elimination members comes into contact with the belt. A static eliminator having a curved surface that gradually separates from the belt, and the other one of the static elimination members has a large number of contact points facing the curved surface and contacting the belt. 3. A static eliminator for sandwiching a traveling belt between a pair of static eliminator members to which a voltage is applied to eliminate static electricity, wherein one of the static eliminator members is a support roller for supporting the belt, A static eliminator which is in contact with the belt while facing the curved surface in the traveling direction of the belt from the position where the other of the supporting rollers comes into contact with the belt. 4. A sheet having a plurality of image bearing members, and an image formed on the image bearing members is conveyed by a transfer belt,
In an image forming apparatus for sequentially transferring to the sheet, a static eliminator for sandwiching the belt with a pair of static eliminator members to which a voltage is applied to eliminate static electricity, wherein both static eliminators are in contact with the belt. The static eliminator includes curved surfaces that are gradually separated from the belt in the traveling direction of the belt, the curvature ratio of the curved surfaces is in the range of 1/2 to 2, and the radius of curvature is 4 mm or more. An image forming apparatus comprising: 5. A plurality of image carriers, wherein an image formed on the image carriers is conveyed by a transfer belt,
In an image forming apparatus for sequentially transferring to the sheet, a static eliminator for sandwiching the belt with a pair of static eliminator members to which a voltage is applied to eliminate static electricity, and one of the static eliminator members comes in contact with the belt. An image removal device having a curved surface that gradually separates from the belt in the traveling direction of the belt, and the other static elimination member includes a plurality of contact points facing the curved surface and having a large number of contact points with the belt. Forming equipment. 6. A sheet having a plurality of image bearing members, and an image formed on the image bearing members is conveyed by a transfer belt,
An image forming apparatus for sequentially transferring onto a sheet of paper, which is a static eliminating device for eliminating static electricity by sandwiching the belt with a pair of static eliminating members to which a voltage is applied, wherein one of the static eliminating members supports the belt. An image forming apparatus further comprising: a static eliminator that faces the curved surface in the traveling direction of the belt from a position where the other static eliminator is in contact with the belt, and contacts the belt. apparatus.