JP2003057965A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of restraining the occurrence of an abnormal image by optimizing a way to give charge to transfer paper. SOLUTION: This image forming device is provided with a plurality of photoreceptor drums 1M to 1BK, a transfer unit for successively performing transfer while carrying paper in a state where the paper is attracted to a transfer belt 3, and a paper attracting part 6 capable of applying both positive and negative polarities so as to attract the transfer paper to the belt 3, and a paper attraction current value is switched in accordance with absolute humidity. The bias applied to the paper attracting part 6 in a high-humidity state is made to have a reverse polarity to that in a low-humidity state. Alternatively, the bias in the high-humidity state is applied so that the surface of the transfer paper coming into contact with the photoreceptor drum has the same polarity as the polarity of toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-drum tandem color image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
The four-tandem tandem structure conveys the transfer paper on the transfer belt, and the bias applying member is arranged at a position opposed to the drum via the transfer belt, and the bias is applied to the bias applying member to apply the bias to the photosensitive drum. A color image forming apparatus is known in which the above toner image is sequentially transferred onto a transfer paper.

In such an image forming apparatus, a transfer paper is charged by a paper suction unit and sucked by a transfer belt to be conveyed. It is known that the paper is attracted to the transfer belt regardless of whether the applied bias polarity at this time is positive or negative. For example, the image forming apparatus of Japanese Patent No. 3007479 discloses a method in which the bias applied to the paper suction portion is set to the same polarity as the toner polarity. Further, Japanese Patent Application Laid-Open No. 7-44027 discloses a method in which the polarity of toner is opposite to that of toner, as in an image forming apparatus.

However, when a negative polarity is applied to the surface of the transfer paper in an image forming apparatus having a four-tandem tandem structure using a negative polarity toner, the electric charge given by the transfer current of each color is accumulated on the transfer paper, There is a problem that a higher applied voltage is required toward the downstream side in the transfer paper transport direction, and a power source with a large power source capacity and a high cost needs to be used in the downstream station.

On the other hand, when the positive polarity is applied to the surface of the transfer paper in the image forming apparatus using the negative polarity toner, the above problem is solved, but as in the case of the four-tandem structure. In a system in which transfer bias is sequentially applied, there is a region where the charge on the surface of the transfer paper switches from positive to negative (the point where the charge amount on the paper becomes 0), and this becomes a force that hinders stable transfer of the transfer paper. There is a problem. This phenomenon becomes remarkable when the resistance of the paper is lowered due to the humidity adjustment of the paper at a high temperature and a high humidity, and there is a problem that an abnormal image such as a color shift is likely to occur.

If a power supply capable of applying both positive and negative polarities is mounted on the paper suction portion (whichever is known, whether positive or negative polarity is used as the bias applied to the paper suction portion, it is known). Although the problem can be solved, the mounting of such a power source increases the manufacturing cost.
Therefore, the known color image forming apparatus is currently equipped with only a positive or negative application power source.

Further, in this type of image forming apparatus, as a cleaning method of the transfer belt, there are a method of directly contacting the blade with the transfer belt and a method of using a bias cleaning roller. In the blade method, the blade edge is damaged by paper dust and the like over time, so the unit life tends to be shortened, but when the roller method is adopted, such a problem does not occur, so the unit life becomes longer compared to the blade method. There is an advantage. Further, there is also an advantage that the transport speed of the transfer belt can be stabilized. That is, the bias cleaning roller is rotating, and the force that hinders the transfer belt transport speed can be made relatively constant.

However, when the bias cleaning roller is used, the blade system completely cleans the toner on the transfer belt in one time, whereas the toner having a very small background stain level slips through the cleaning portion and the paper suction portion There was a problem that the bias applying member was contaminated. In other words, this problem can be solved by mounting a power supply capable of applying both polarities so that paper suction cleaning can be performed by applying positive and negative alternating electric fields to the paper suction unit. However, the mounting of the above causes a problem of increasing the cost.

The present invention has been made in view of the above-mentioned problems of the prior art, and switches between positive and negative polarity voltage application to the paper adsorbing portion by the absolute humidity which greatly influences the electrostatic adsorbing force of the paper to transfer the paper. To optimize how to give
An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of abnormal images.

[0010]

In order to achieve the above object, the image forming apparatus of the present invention according to claim 1 conveys a plurality of photosensitive drums and paper by adsorbing paper onto a transfer belt. An image forming apparatus that has a transfer unit that sequentially transfers while performing a transfer, and a paper suction unit that sucks a transfer paper that can apply both positive and negative polarities to the transfer belt, and that can switch the paper suction current value according to absolute humidity. In the above, the bias applied to the paper suction unit at high humidity is opposite in polarity to the bias applied to the paper suction unit at low humidity.

In order to achieve the above-mentioned object, a second aspect of the present invention comprises a plurality of photoconductor drums, a transfer unit for adhering paper to a transfer belt and sequentially transferring while conveying, and positive and negative polarities. In an image forming apparatus that has a paper attracting portion that attracts paper that can be applied to the transfer belt, and that can switch the paper attracting current value according to absolute humidity, the applied bias of the paper attracting portion at high humidity can be set. The transfer paper is applied so that the surface of the transfer paper in contact with the photosensitive drum has the same polarity as the toner polarity.

According to a third aspect of the present invention, in order to achieve the above object, in the image forming apparatus according to the first or second aspect, the bias applied to the paper suction unit is set to a polarity opposite to the toner polarity when the humidity is low, and a high polarity. It is characterized by having the same polarity as the toner polarity when wet.

According to a fourth aspect of the present invention, in order to achieve the above object, in the image forming apparatus according to any one of the first to third aspects, the surface of the transfer paper opposite to the surface in contact with the photosensitive drum at high humidity is used. The bias applied to the paper attracting portion when printing on the paper is set to the opposite polarity of the paper attracting bias used when the front surface is printed.

According to a fifth aspect of the present invention, in order to achieve the above object, the transfer belt used in the image forming apparatus according to any one of the first to fourth aspects has a volume resistivity of 1E +.
It is characterized by being 09-1E + 12 Ω · cm.

According to a sixth aspect of the present invention, in order to achieve the above object, in the image forming apparatus according to any one of the first to fifth aspects, the cleaning method of the transfer belt is a bias cleaning method. To do.

In order to achieve the above object, the image forming apparatus according to any one of claims 1 to 6 determines that an absolute humidity of 15 g / m ³ or more is a high humidity condition. Characterize.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the following, M is magenta and C
Indicates a toner color of cyan, Y indicates a yellow toner color, and Bk indicates a black toner color. These symbols attached to the respective symbols indicate that the constituent elements correspond to the colors.

FIG. 1 is a conceptual diagram showing an embodiment at normal time (low humidity or normal temperature / normal humidity), and FIG. 2 is a conceptual view showing an embodiment at high humidity. In these figures, 1M to 1Bk are photosensitive drums, 2M
2Bk is a drum driving motor, 3 is a transfer belt, 4 is a transfer bias applying section (only one for the photosensitive drum 1Bk is shown in the figure), 5 is a transfer belt cleaning section, and 6 is a paper suction section. The transfer bias applying section 4 includes a power supply 7 and a bias applying member 8. The transfer belt cleaning unit 4 includes a power supply 9, a bias cleaning roller 10 that is a metal roller, a sponge roller 11 that faces the bias cleaning roller 10, and a cleaning blade 12 that is in sliding contact with the bias cleaning roller 10. The paper suction unit 6 includes a power supply 13 that can be applied in both positive and negative polarities, a paper suction roller 14 made of foam sponge, and a metal roller 15 facing the paper suction roller 14.

The criteria for determining low humidity, normal humidity and high humidity may be determined by a condition recognition table based on the relationship between relative humidity and temperature shown in FIG.
The numerical value of the absolute humidity may be used as a reference, such as in the case where the high humidity condition is g / m ³ or more. Of course, you may judge by conditions other than these.

The normal time (low humidity or normal temperature / normal humidity) shown in FIG. 1 will be described. In the paper suction unit 6, the paper suction roller 1
An electric charge is applied to the transfer paper (not shown) by 4 and the paper is attracted to the transfer belt 3. Normally, a bias having a polarity opposite to that of the toner is applied to the front side of the transfer paper. For example, if a toner having a Q / M of −20 to −30 μc / g is used, +2 kV is applied as a positive bias voltage to the front side of the transfer paper. This bias control may be constant current control or constant voltage control. Further, it is desirable to perform control to change the control value according to the paper width and the paper thickness of the transfer paper, so that a more suitable paper suction force can be obtained.

The transfer sheet is conveyed while being attracted to the transfer belt 3, and is transferred from the photosensitive drum 1M on the upstream side in the conveying direction (the direction from the photosensitive drum 1M to the photosensitive drum 1Bk as indicated by the arrow in the figure). Colors are sequentially stacked and finally pass through the photoconductor drum 1BK. For example, a current of +10 μA for each color is passed from the bias applying member 8 to the photosensitive drum side.

At this time, the transfer paper whose surface is positively charged by the paper adsorbing section 6 is sequentially applied with a transfer current, so that the paper surface potential is switched from positive to negative, and the downstream station (hereinafter, referred to as a photosensitive member). In the transfer area composed of the body drum and the bias applying member), negative charges are accumulated.
Unless the transfer paper has a low resistance, such as when the humidity is controlled under high temperature and high humidity, the influence of the decrease in the paper adsorption force due to the switching of the paper surface potential from positive to negative is a problem such as color misregistration. It is experimentally known that the level does not occur. Although the mechanism has not been determined at present, even if the suction force of a part of the entire paper is reduced, if the other part is firmly sucked onto the transfer belt 3, stable paper conveyance can be performed. I think. Further, at this time, the applied bias required to flow the transfer current of 10 μA in the most downstream BK station is +1 kV when the surface of the transfer paper is positively charged by the paper suction unit 6, while the paper suction is performed. It was +2 kV when the surface of the transfer paper was negatively charged in the part 6. The lower the applied bias is, the more the occurrence of abnormal images is suppressed. Therefore, under normal temperature and low humidity conditions, a positive (reverse polarity to toner) bias is applied to the front side of the transfer paper in the paper suction unit 6. In the transfer belt cleaning unit 5, the applied current from the power source 9 is 10 to 15 A, and the toner attached to the bias cleaning roller 10 is scraped off by the cleaning blade 12. Note that FIG. 4 shows the relationship between the position of the photosensitive drum and the attraction force when a positive bias is applied.

Next, the case of high humidity will be described as a case where a temperature / humidity sensor (not shown) determines that it is under high humidity conditions. Transfer paper (not shown) by the paper suction roller 14 in the paper suction unit 6.
Is charged to the transfer belt 3 to attract the paper. When the humidity is high, a bias having the same polarity as the toner is applied to the front side of the transfer paper. For example, if a toner having a Q / M of −20 to −30 μc / g is used, −2 kV is applied as a positive bias voltage to the front side of the transfer paper. If this bias control may be constant current control or constant voltage control, and if control is performed to change the control value according to the paper width and paper thickness of the transfer paper, then a more suitable paper suction force can be obtained. This is the same as usual.

The transfer sheet is conveyed while being attracted to the transfer belt 3, and is transferred from the photosensitive drum 1M on the upstream side in the conveying direction (the direction from the photosensitive drum 1M to the photosensitive drum 1Bk as indicated by the arrow in the figure). Colors are sequentially stacked and finally pass through the photoconductor drum 1BK. For example, a current of +10 μA for each color is passed from the bias applying member 8 to the photosensitive drum side.

At this time, a transfer current is sequentially applied to the transfer paper whose surface is negatively charged by the paper attracting portion 6, and a larger negative charge is accumulated on the surface of the transfer paper toward the downstream station.
Even when the transfer paper is conditioned under high temperature and high humidity and has a low resistance, the paper surface potential can be switched from positive to negative by this paper suction application method (negative surface is applied by the paper suction unit 6). Since it does not exist, it is possible to reduce the influence of the decrease in the paper suction force, and it is possible to reduce problems such as color misregistration.

At this time, the applied bias required to flow 10 μA in the most downstream BK station is +1 k.
It was V. This is because the resistance of the transfer belt 3 decreases in a high temperature and high humidity environment, and the resistance of the transfer paper decreases due to humidity adjustment, so that a negative bias is applied to the front side of the transfer paper in the paper suction unit 6 under normal temperature and low humidity conditions. The required applied bias in the most downstream Bk station can be reduced more than in the case of Therefore, in high humidity, even if the surface of the transfer paper is made negative in the paper suction unit 6, the image disturbance due to abnormal discharge can be reduced. Note that FIG. 5 shows the relationship between the position of the photosensitive drum and the attraction force when a negative bias is applied.

The advantage of using the bias cleaning roller for cleaning the transfer belt 3 will be described. The transfer belt 3 has, for example, a volume resistivity of 1E + 09 to 1E +.
Use 12 Ω · cm. This transfer belt is capable of self-removing electricity and does not need to be provided with a destaticizing mechanism, which leads to cost reduction. Since the paper suction and conveyance force is lower than when using a high resistance belt, it is very effective to apply a bias sequentially at multiple transfer positions to accumulate the charge on the transfer paper when the humidity is high. Is.

Further, when the bias cleaning roller 10 is used as a cleaning method for the transfer belt 3, a mechanical method that hinders the traveling of the transfer belt 3 is more mechanical than a cleaning method in which a blade or the like is directly applied to the transfer belt 3. The force can be managed relatively constant, and the transfer belt 3 can be conveyed at a constant speed, as described above, because the bias cleaning roller 10 rotates. On the other hand, in the method of directly contacting the blade with the transfer belt 3, the change in frictional force between the blade and the transfer belt 3 (this change in frictional force depends on the amount of toner input to the blade).
Along with this, a force that makes the traveling of the transfer belt 3 unstable is generated. Therefore, when the bias cleaning roller 10 is used, the conveyance speed of the transfer belt 3 can be made relatively constant, and a high-quality image without color misregistration or density unevenness in the sub-scanning direction can be obtained.

However, as a harmful effect of using the bias cleaning method for cleaning the transfer belt 3, as described above, since a large amount of toner passes through the cleaning section as compared with the blade method, it is a constituent member of the paper suction section 6. It causes dirt. Therefore, in the device of this embodiment,
The paper attracting section 6 is cleaned by alternately applying positive and negative biases from the power supply 13.

Regarding the second side printing of the transfer paper, since the paper once passes through the heating and fixing section, the moisture content is lowered and the resistance is increased even if the paper is conditioned, so this point is taken into consideration. , The surface of the paper is charged to the opposite polarity at the time of printing on the second surface by the paper suction portion when printing on the second surface. As a result, both the color misregistration reduction effect at the time of printing on the first side and the abnormal discharge prevention at the time of printing on the second side can be achieved. Further, with respect to the second surface of the transfer paper, the moisture content decreases by passing through the heat fixing unit even during humidity control, so that the paper adsorption force that does not affect the color misregistration can be secured.

[0031]

As described above, in the image forming apparatus according to the first aspect of the present invention, the bias applied to the paper attracting portion at high humidity is opposite to the bias applied to the paper attracting portion at low humidity. Therefore, when forming a color image in low humidity, it is possible to charge the surface of the paper at the paper adsorption part to the opposite polarity to the toner, and when sequentially applying bias to multiple transfer positions on multiple photoconductor drums. In addition, it is possible to adopt a configuration in which a relatively high bias application is not required at the transfer position on the downstream side, and it is possible to prevent abnormal discharge and prevent the generation of abnormal images. When the humidity is high, the transfer paper surface can be charged with the same polarity as the toner at the paper suction unit, so even if the paper suction transport force decreases when using humidity control paper, multiple transfer positions Since the electric charges on the transfer paper are accumulated in the sequential bias application in step 1, there is an effect that it is possible to prevent a further decrease in the paper suction force. That is, it is possible to obtain an effect that it is possible to suppress a decrease in the paper suction force when the humidity is high, while preventing an abnormal image when the humidity is low.

In the image forming apparatus according to the second aspect, as described above, since the bias applied to the paper attracting portion at high humidity is applied so that the surface of the transfer paper has the same polarity as the toner polarity, There is an effect that it is possible to very effectively suppress a decrease in the paper suction force at high humidity.

As described above, in the image forming apparatus according to the third aspect of the present invention, the bias applied to the paper attracting portion has the polarity opposite to the toner polarity when the humidity is low and the same polarity as the toner polarity when the humidity is high. In addition to the effects common to those of the image forming apparatus according to claims 1 and 2, while effectively preventing abnormal images at low humidity,
There is an effect that it is possible to suppress a decrease in the paper suction force at high humidity.

As described above, in the image forming apparatus according to the fourth aspect, the bias applied to the paper attracting portion when printing on the surface of the transfer paper opposite to the surface in contact with the photosensitive drum at high humidity. Has the reverse polarity of the paper suction bias at the time of the above-mentioned surface printing, and in addition to the effect common to the image forming apparatus of the above-mentioned claims 1 to 3, the effect that an abnormal image at the time of the second surface printing can be prevented. There is. Further, there is an effect that both the color misregistration reduction effect at the time of the first side printing and the abnormal discharge at the time of the second side printing can be prevented.

In the image forming apparatus according to the fifth aspect, as described above, the transfer belt has a volume resistivity of 1E + 0.
Since 9 to 1E + 12 Ω · cm is used, the transfer belt can be self-erased, and in addition to the effects common to those of the image forming apparatus according to any one of claims 1 to 4, a low-cost configuration without a neutralization mechanism is used. There is an effect that can be.

As described above, the image forming apparatus according to the sixth aspect uses the bias cleaning method as the cleaning method for the transfer belt. Therefore, in addition to the effects common to the image forming apparatuses according to the first to fifth aspects, There is an effect that the durability of the transfer unit is increased, the transfer speed of the transfer belt can be made more constant, and uneven density in the sub-scanning direction can be reduced.

As described above, the image forming apparatus according to claim 7 determines that the absolute humidity of 15 g / m ³ or more is the high humidity condition. In addition to the common effects, there is an effect that environmental conditions can be effectively recognized and effective control can be performed.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a state in a normal time (low humidity or normal temperature / normal humidity) in an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a conceptual diagram showing a state at the same high humidity.

FIG. 3 is a diagram showing a condition recognition table based on the relationship between relative humidity and temperature.

FIG. 4 is a diagram showing the relationship between the position of the photosensitive drum and the attraction force when a positive bias is applied at the paper attraction unit.

FIG. 5 is a diagram showing the relationship between the position of the photosensitive drum and the attraction force when a negative bias is applied to the paper attraction unit.

[Explanation of symbols]

1M-1Bk photoconductor drum 2M-2Bk drum drive motor 3 Transfer belt 4 Transfer bias application section 5 Transfer belt cleaning section 6 Paper suction part 7 power supply 8 Bias applying member 9 power supplies 10 Bias cleaning roller 11 Sponge roller 12 cleaning blade 13 power supply 14 Paper suction roller 15 Metal roller

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H030 AB02 AD05 BB23 BB44 BB46                       BB54 BB63                 2H200 FA04 FA18 GA12 GA23 HA03                       HA29 HB11 HB46 JA02 JA28                       JB06 JB26 JB42 JB48 JB49                       JB50 NA02 NA08 NA16 PA03                       PA18 PA23 PA29 PB28                 3F101 LA02 LA07 LB03

Claims (7)

[Claims] 1. A plurality of photosensitive drums, a transfer unit for sequentially transferring while adsorbing paper onto a transfer belt and conveying the paper, and a paper for adsorbing transfer paper capable of applying positive and negative polarities on the transfer belt. In an image forming apparatus that has a suction unit and is capable of switching the paper suction current value according to absolute humidity, the bias applied to the paper suction unit at high humidity is reverse to the bias applied to the paper suction unit at low humidity. An image forming apparatus having a polarity. 2. A plurality of photoconductor drums, a transfer unit for sequentially transferring the paper while adsorbing the paper to the transfer belt and conveying the paper, and a paper adsorbing device for adhering the paper to which the positive and negative polarities can be applied to the transfer belt. In an image forming apparatus that has a unit and can switch the paper adsorption current value according to absolute humidity, the bias applied to the paper adsorption unit at high humidity is set so that the surface of the transfer paper in contact with the photosensitive drum has a toner polarity. An image forming apparatus, wherein the voltage is applied so as to have the same polarity as. 3. The image forming apparatus according to claim 1 or 2, wherein the bias applied to the paper attracting portion has a polarity opposite to the toner polarity when the humidity is low, and the same polarity as the toner polarity when the humidity is high. Image forming apparatus. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the bias applied to the paper suction portion when printing on the surface of the transfer paper opposite to the surface in contact with the photosensitive drum at high humidity is An image forming apparatus having a polarity opposite to that of a paper suction bias during surface printing. 5. The image forming apparatus according to claim 1, wherein the transfer belt used has a volume resistivity of 1E.
An image forming apparatus having a characteristic of +09 to 1E + 12 Ω · cm. 6. The image forming apparatus according to claim 1, wherein the cleaning method of the transfer belt is a bias cleaning method. 7. The image forming apparatus according to claim 1, wherein an absolute humidity of 15 g / m ³ or more is determined as a high humidity condition.