JP2007298839A - Image forming apparatus and cleaning method for transfer member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method for a transfer member where biases applied to a transfer roller upon transferring are used for the cleaning of the transfer roller, and an image of high quality is realized at a low cost without generating the back soiling of paper. <P>SOLUTION: In the image forming apparatus comprising: an image carrier of carrying a toner image; a transferring means of transferring the toner image to a recording material by applying biases to a transferring member; and a cleaning means of removing the toner stuck to the surface of the transferring member, the image forming apparatus is provided with: a first power source of feeding a bias required for the transfer of the toner image by the transferring means; and a second power source of feeding a bias required for the removal of the toner stuck to the surface of the transferring member by the cleaning means. The cleaning means applies the biases of both positive and negative polarities fed from the first power source and the second power source to the transferring member. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, a digital multifunction machine, and the like, and a cleaning method for a transfer member to which toner used in the image forming apparatus is attached.

  Currently, the most widely used color image forming apparatus uses an intermediate transfer member, develops an image on a photosensitive member one by one, sequentially transfers it onto the intermediate transfer member, and overlays four colors on the intermediate transfer member. This is a method of batch transfer to paper. In such an apparatus, in order to perform batch transfer onto paper, a secondary transfer member that contacts the back side of the paper is often used. When this secondary transfer member causes a paper jam or the like, it may come into direct contact with the intermediate transfer member holding the toner image. If such a direct contact is made, the secondary transfer member becomes soiled with toner, and the next printing is performed. In addition, the back of the paper was soiled, or the image surface was soiled during double-sided printing.

As a method for removing this stain, a method of mechanically scraping the secondary transfer member with a blade or the like, and a method of applying an electric field to the secondary transfer member to collect toner on the intermediate transfer member side have been proposed. . Specifically, for example, Patent Document 1 discloses an invention in which the polarity of the voltage applied to the secondary transfer roller can be switched, and a voltage having the same polarity as that of the toner is applied during cleaning. An invention in which a voltage having the opposite polarity to the toner is applied to the transfer roller with a constant current and a voltage having the same polarity as the toner is applied to the transfer roller at a constant voltage during cleaning is disclosed in Patent Document 3 in which a constant current control is performed on the secondary transfer roller. However, Patent Document 4 discloses a first application unit that applies a negative voltage to a secondary transfer member, a second application unit that applies a positive voltage to the secondary transfer member, and the secondary transfer member. A switching unit that alternately switches between the first application unit and the second application unit to be applied to the first transfer unit, and a time that is alternately switched by the switching unit and applied to the intermediate transfer member, and the transfer rotator. Is limited to less than one continuous rotation And a control unit which, at a constant voltage control, the invention for cleaning by applying a secondary transfer member for positive and negative polarities alternately is disclosed, respectively.
Japanese Patent Laid-Open No. 10-123792 JP-A-8-220900 JP 2004-012482 A JP 2004-272206 A

  By the way, in the inventions described in Patent Documents 1 and 2, transfer and cleaning are performed using two power supplies. However, cleaning is impossible because a voltage having the same polarity as that of toner is applied. In the invention described in Patent Document 3, the secondary transfer roller is controlled with constant current, but cleaning is not particularly described. Further, in the invention described in Patent Document 4, cleaning is performed by applying positive and negative polarities alternately to the secondary transfer member by constant voltage control. Further, constant voltage control is performed for secondary transfer of toner. That is, it can be understood that the control during the secondary transfer and the control during the cleaning can be performed by the same control.

  However, when the secondary transfer control is performed with constant voltage control, the voltage is controlled to be constant even when the resistance or thickness of the paper changes, so a large number of voltage control tables are provided for an unspecified number of paper types. It is almost impossible to cover all paper types. However, if the secondary transfer control of constant current control is performed, the voltage fluctuates in order to output the set current with respect to the resistance value fluctuation when the paper thickness or paper type changes, so that the optimum transfer voltage can be obtained. Is set. For this reason, it is necessary to have a secondary transfer voltage table for each transfer material in order to perform secondary transfer control with a constant voltage and guarantee a stable image quality. Thus, if each transfer material has a secondary transfer voltage table, a large amount of memory is required, and cost increases and development takes time. To avoid this, if the secondary transfer control is controlled by constant current control and the secondary transfer member is cleaned by positive / negative constant voltage control, good transferability and cleanability can be obtained reliably, but bipolar output is possible. A high voltage power source for constant voltage and a high voltage power source for constant current capable of positive output are required, resulting in an increase in cost.

  In view of the above, the problem to be solved by the present invention is to use a bias applied to the transfer roller at the time of transfer for cleaning the transfer roller, and to realize a high-quality image at low cost without the backside of the paper. It is in.

  In order to solve the above problems, the first means includes an image carrier for carrying a toner image, a transfer means for applying a bias to the transfer member to transfer the toner image to a recording material, and a surface of the transfer member. In an image forming apparatus having a cleaning unit that removes adhering toner, a first power source that supplies a bias necessary for the transfer unit to transfer a toner image, and the cleaning unit adhered to the surface of the transfer member. A second power source for supplying a bias necessary for removing toner, and the cleaning unit transfers biases of both positive and negative polarities supplied from the first power source and the second power source. It applies to a member, It is characterized by the above-mentioned.

  The second means is characterized in that in the first means, there is switching means for switching between the first power source and the second power source.

  A third means is characterized in that, in the first means, the first power supply supplies a bias having the same polarity as that of the toner, and the second power supply supplies a bias having a polarity opposite to that of the toner.

  The fourth means is characterized in that, in the first means, the first power supply supplies a bias having a polarity opposite to that of the toner, and the second power supply supplies a bias having the same polarity as that of the toner.

  According to a fifth means, in any one of the first to fourth means, the bias supplied from the first power source is constant current controlled so that the bias is a constant current, and the bias supplied from the second power source is A constant voltage control is performed so that a constant voltage is obtained.

  The sixth means is that the fifth means is that the cleaning bias having the polarity for performing the constant voltage control is not passing through the constant current control set to obtain the cleaning bias having the other polarity. It is characterized by being set to the absolute value of the voltage.

  The seventh means is characterized in that, in the fifth or sixth means, the set current at the time of the constant current control is changed depending on the environment.

  The eighth means is characterized in that, in any of the fifth to seventh means, the current value after correction is used as the cleaning bias when the environmental correction is included in the set current during the constant current control. To do.

  A ninth means is characterized in that, in any one of the first to seventh means, the secondary transfer roller is provided with a foam made of foamed urethane containing a mixture of single foam and continuous foam.

  A tenth means is a transfer material cleaning method in which toner attached to a transfer member for transferring a toner image to a recording material is cleaned by applying a bias, and supplied from a first power source necessary for transferring the toner image. And a bias supplied from a second power source necessary for removing the toner adhering to the surface of the transfer member are set to both positive and negative polarities, and the positive and negative biases are applied to thereby apply the positive and negative biases. It is characterized in that the toner adhering to the surface of the transfer member is cleaned.

  An eleventh means is characterized in that, in the tenth means, the first power supply supplies a bias having the same polarity as that of the toner, and the second power supply supplies a bias having a polarity opposite to that of the toner.

  A twelfth means is characterized in that, in the tenth means, the first power supply supplies a bias having a polarity opposite to that of the toner, and the second power supply supplies a bias having the same polarity as that of the toner.

  According to a thirteenth means, in any one of the tenth to twelfth means, the bias supplied from the first power source is constant current controlled so that the bias is a constant current, and the bias supplied from the second power source is A constant voltage control is performed so that a constant voltage is obtained.

  In a fourteenth means according to the thirteenth means, the cleaning bias having the polarity for performing the constant voltage control is a non-sheet-passing time for the constant current control set to obtain the cleaning bias having the other polarity. It is characterized by being set to the absolute value of the voltage.

  The fifteenth means is characterized in that, in the thirteenth or fourteenth means, the set current during the constant current control is changed depending on the environment.

  The sixteenth means is characterized in that, in any of the thirteenth to fifteenth means, the current value after correction is used as the cleaning bias when environmental correction is included in the set current during the constant current control. To do.

  In the embodiments described later, the image carrier is the intermediate transfer belt 10, the transfer member is the secondary transfer roller 14, the transfer means is the secondary transfer bias applying power source 26, and the cleaning means is the secondary transfer rollers 14 and 2. The secondary transfer bias power supply 26 corresponds to the secondary transfer bias power supply 26 and the switching circuit, respectively.

  According to the present invention, both positive and negative polarity biases supplied from the first power source and the second power source are applied to the transfer member, so that the toner attached to the transfer member can be transferred to the transfer medium side. Therefore, it is possible to realize a high-quality image at a low cost without the backside of the recording material.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an example of an electrophotographic image forming apparatus according to the present embodiment, in which an image carrier is a drum-shaped photosensitive member, and an intermediate transfer member (intermediate image carrier) is an intermediate transfer belt. 2 is a schematic configuration diagram around a photoconductor and an intermediate transfer belt in the color image forming apparatus. In FIG. 1, reference numeral 1 denotes a cylindrical photosensitive member that rotates in the direction of an arrow. Around the photosensitive member 1, a photosensitive member cleaning unit 2, a charger 4, an exposure unit 5, a black developing unit 6, and a cyan developing unit. A device 7, a magenta developing device 8, a yellow developing device 9, an endless intermediate transfer belt 10, and the like are arranged. Reference numeral 3 denotes a rubber blade of the photoconductor cleaning unit 2.

  The intermediate transfer belt 10 is stretched by a group of rollers such as a drive roller 13, a belt transfer bias roller 11 and a driven roller 12, and is driven in a direction indicated by an arrow in the drawing by a drive motor (not shown). Reference numeral 19 denotes a belt cleaning unit, which includes a rubber blade 18 and a contact / separation mechanism 20 that contacts and separates the rubber blade 18 from the intermediate transfer belt 10. During the belt transfer of the cyan, magenta, and yellow images of the second, third, and fourth colors after the belt transfer to the intermediate transfer belt 10, the rubber blade 18 of the belt cleaning unit 19 is intermediately transferred by the contact / separation mechanism 20. The belt is separated from the surface of the belt 10. Further, a belt position detection mark 23 is provided at the end of the intermediate transfer belt 10, and the accurate color of each color image is started by starting the image forming process of each color at the timing when the mark is detected by the mark sensor 24. Overlay is possible.

  Reference numeral 15 in FIG. 1 denotes a secondary transfer unit, a secondary transfer (bias) roller 14 as a secondary transfer unit, and a contact / separation mechanism 16 that contacts and separates the secondary transfer roller 14 from the intermediate transfer belt 10. , And a secondary transfer bias application power source 26 that applies a predetermined transfer bias or cleaning bias to the secondary transfer roller 14. The secondary transfer bias application power source 26 can be switched between positive and negative polarities by a switching circuit or the like. The secondary transfer roller 14 is usually separated from the belt surface of the intermediate transfer belt 10, but the timing when the four color superimposed images formed on the belt surface of the intermediate transfer belt 10 are collectively transferred to the transfer paper 22. Then, it is pressed by the contact / separation mechanism 16 and applied to the transfer paper 22 by applying a predetermined bias voltage (in this example, +1.5 kV is applied) from the secondary transfer bias application power source 26. The transfer paper 22 is fed by the paper feed roller 25 and the registration roller 21 at the timing when the leading end of the four-color superimposed image on the belt surface of the intermediate transfer belt 10 reaches the secondary transfer position. The four-color superimposed image transferred to the transfer paper 22 is fixed by the fixing unit 17 and then discharged.

  At the time of continuous printing of a plurality of colors, the bias voltage (the bias voltage necessary for transferring the toner image) is turned off at the timing when the trailing edge of the transfer paper 22 sufficiently passes through the secondary transfer bias roller 14, and then the next page In order to prevent the toner on the intermediate transfer belt 10 from adhering, the secondary transfer bias roller 14 is separated from the intermediate transfer belt 10 by the contact / separation mechanism 16. Further, at the end of the final page during single-sheet printing or continuous printing, the secondary transfer bias roller 14 is not separated from the belt surface of the intermediate transfer belt 10, and the secondary transfer bias application power source 26 has a polarity opposite to that of the transfer bias. A cleaning bias is applied for a certain period of time to transfer the toner adhering to the surface of the secondary transfer bias roller 14 to the intermediate transfer belt 10, cleaning the surface of the secondary transfer bias roller 14, and then separating from the intermediate transfer belt 10. Let The toner transferred to the intermediate transfer belt 10 is collected from the belt surface by the belt cleaning unit 19. After the series of printing operations as described above is completed, the rotation of the motor is stopped and a print standby state is entered.

  FIG. 2 shows an image forming unit in which the relationship between the photosensitive drum 1 of FIG. 1 and the four color developing units is made independent for each color, and this image forming unit is arranged in parallel to the intermediate transfer belt. This is an example of a color image forming apparatus. It should be noted that the same reference numerals are assigned to the same components as those in the image forming apparatus shown in FIG. 1, and duplicate descriptions are omitted as appropriate.

  In this type of image forming apparatus, each image forming unit is provided with a photoconductor, and each color image is sequentially superimposed on an intermediate transfer medium to form a full-color toner image, and the full-color toner image is formed by a secondary transfer unit. I try to transfer it to the paper. That is, as shown in FIG. 2, an image forming unit having four image carriers (photosensitive members) 101a, 101b, 101c, and 101d carries an image along the rotation direction of the intermediate transfer belt 10 (arrow direction in FIG. 2). The rotation axis of the body is arranged in parallel so as to be orthogonal to the conveyance direction of the intermediate transfer belt 10. The intermediate transfer belt 10 is stretched between the driving roller 13 and the tension roller 12 with a predetermined tension. The drive roller 13 is also provided with functions of a secondary transfer counter roller and a cleaning blade 114 counter roller. A predetermined voltage is applied to the primary transfer rollers 102a, 102b, 102c, and 102d from the upstream side in the running direction of the intermediate transfer belt 10. Is applied to superimpose the colors on the intermediate transfer belt 10 to form a full-color image.

  As described above, the intermediate transfer belt 10 rotates in the direction of the arrow, and the formed color image is fed by the paper (transfer material) P fed from the registration roller 21 to the secondary transfer section through the pre-transfer guide 115. Then, by applying a predetermined voltage to the secondary transfer roller 14, it is transferred to the paper P, fixed (not shown) and output. Toner that cannot be transferred by the secondary transfer roller 14 and remains on the intermediate transfer belt 10 is collected by a cleaner blade 114 in a cleaner unit (not shown).

  Examples of the material of the intermediate transfer belt 10 include polymer materials such as TPE (thermoplastic elastomer alloy), PC (polycarbonate), PI (polyimide), PAA (polyamide alloy), PVDF (polyvinylidene fluoride), and the like. As the material of the secondary transfer roller 110, an elastic roller is suitable, and an ion conductive roller (urethane + carbon dispersion, NBR, hydrin), an electronic conductive type roller (EPDM), or the like is prominent. .

  FIG. 1 shows an example of a system in which a developing device for four colors is provided for one photosensitive drum 1 and an image is formed for each color and superimposed on the intermediate transfer belt 10 to form a color image. FIG. 2 shows an example of an indirect transfer type tandem image forming apparatus. The configuration of the intermediate transfer unit is a biaxial stretch, and the secondary transfer counter roller has various functions. However, the present invention is not limited to this configuration. A transfer system having secondary transfer can have the features of this patent as described below.

  In the example of FIG. 2, the transfer and cleaning control circuits are the same as those in the example of FIG.

  On the other hand, in order to ensure a high-quality image, it is necessary to eliminate or reduce secondary transfer properties and paper stains. The secondary transfer roller 14 is easily assumed to be contaminated when a toner pattern is printed on the intermediate transfer during jamming or process control. In order to reduce the contamination of the secondary transfer roller 14, a method of applying a plus / minus electric field to the secondary transfer roller 14 and returning the toner charged in various polarities to the intermediate transfer belt 10 is generally used. . Otherwise, the secondary transfer roller 14 is physically scraped off with a cleaning brush or blade. However, if a cleaning brush or blade is attached to the secondary transfer roller 14, the cost is increased and the installation volume is increased. Therefore, in this embodiment, the toner cleaning performance is further improved by improving the control and the toner liberty of the material of the secondary transfer roller 14 itself.

  FIG. 3 is a detailed diagram of VI characteristics (current-voltage characteristics) of constant current control of a secondary transfer portion for a certain transfer material, with the secondary transfer current as a parameter on the horizontal axis and the output voltage on the vertical axis as parameters. . Generally, the resistance of members such as the functional material, secondary transfer roller, and transfer belt fluctuates with respect to the environment (high temperature and high humidity HH, normal environment NN, and low temperature and low humidity environment LL). change. However, since the current-voltage characteristic (VI characteristic) at the time of paper passing varies depending on the type of paper (arrow A), the voltage varies with respect to the set current, and an appropriate voltage is set. The fluctuation of the VI characteristics depending on the type of paper means that the voltage increases when high resistance paper is passed, and the voltage decreases when low resistance paper is passed.

  On the other hand, the VI characteristic at the time of non-passage shows a constant VI characteristic with respect to the environment, that is, a stable V1 characteristic with respect to a constant current value, because the sheet is not passed. The stable V1 characteristic here means that even if the voltage V at the time of paper passage varies, the voltage V1 at the time of non-paper passage does not change because the current is constant. It is considered that the current I at the time of paper passing is set to a current I that provides an optimum V characteristic for the toner to move to the transfer material. V1 for returning the toner adhering to the roller to the intermediate transfer belt 10 needs to be lower than the toner transfer to the transfer material. However, the current I set as the transfer current is slightly lower than the voltage V when the transfer material is present because there is no transfer material when the paper is not passed (arrow B). Therefore, the optimum voltage V1 is applied to the toner moving electric field for returning the toner adhering to the secondary transfer roller 14 to the intermediate transfer belt 10 when paper is not passed. That is, it can be seen that it is sufficient to set I at the time of the secondary transfer current as one voltage V1 applied alternately for roller cleaning. Further, it is understood that the voltage V2 necessary for obtaining the other electric field of the clean polarity is controlled by constant voltage control, and the voltage V2 may be set to the reverse polarity of the absolute value of the voltage V1 monitored in advance in the development study stage. .

  In addition, when the environmental correction is entered, the transfer current I of the transfer material changes, and accordingly, by changing the voltages V1 and V2 for obtaining the alternate polarity cleaning potential, the roller cleaning can be performed more reliably. I understand that. Therefore, it can be seen that one of the alternating cleaning polarities for obtaining the cleaning performance is set to the secondary transfer current I and the absolute value of the V characteristic obtained when I is set as the other cleaning polarity.

  This is because the current I set as the secondary transfer current can be used as it is as one current of the cleaning bias, and the absolute value of the voltage of the other polarity is determined when the set current I is not passed. The absolute value of the voltage V1 can be used, so that it is possible to obtain highly accurate cleaning performance with an easy configuration and without increasing the cost.

  In FIG. 3, specific values of V1 and V2 and values for each environment of I are not described, but this indicates electrostatic characteristics (resistance, dielectric constant, and the like of the secondary transfer roller and the intermediate transfer belt to be used. (Thickness) and the primary transfer method change the optimum value, and it is needless to say that an optimal secondary transfer current suitable for each system is set.

  FIG. 4 is a cross-sectional view of the secondary transfer roller 14. In the present embodiment, the secondary transfer roller 14 includes a cored bar 14a and an elastic foam 14b provided on the outer periphery of the cored bar 14a, and the foamed body 14b includes bubbles 14c and 14d and a rubber layer 14e. Has been. Bubbles are also exposed on the surface, and the shape is composed of a mixture of single bubbles 14c and open bubbles 14d in which single bubbles are connected to each other. The ratio of the single bubbles 14c and the continuous bubbles 14d has an influence on the liberation of the toner. When the single bubble 14c is 80% or more, the toner almost stays on the roller surface 14, so that a considerable amount of toner remains on the surface of the roller 14 even when the cleaning bias is applied for three rotations of the transfer roller, and the paper is passed through In the case of contamination, the backside dirt is confirmed. On the other hand, in the case of the transfer roller 14 having a single bubble 14c of less than 80%, the balance between the toner staying on the surface of the transfer roller 14 and the toner penetrating into the foam 14b is good, and the staying portion is on the transfer belt 14 side. However, it was confirmed that the amount remaining on the transfer roller 14 penetrated into the roller 14 and no back-stain occurred.

  On the other hand, as a result of confirming the life and deterioration with time as the performance of the transfer roller 14, when the closed cell ratio is less than 20%, the toner penetrates into the roller 14, the hardness of the roller 14 is increased, and the resistance is also increased. Confirmed to do. As a result, the voltage at the time of transfer rises, and a discharge image is generated, and feedback transfer control is performed over time, causing problems in both image quality and control. When the closed cell ratio is 20% or more, the toner does not penetrate into the roller 14 extremely, the roller hardness does not change, or the resistance value does not change, and a good transfer property can be obtained.

  From the above results, it can be seen that it is optimal to mix closed bubbles (single bubbles) 14c and open bubbles 14d having a closed cell ratio of 20% to 80% in the transfer roller.

  As a voltage application method at the secondary transfer portion, there are a case where the voltage is applied to the secondary transfer roller 14 (attraction transfer), a case where the voltage is applied to the counter roller 13 (repulsive force transfer). Neither type is superior or inferior to the effect of the electric field on the toner, but the electrostatic effect on the periphery is different. In the case of repulsive transfer, a voltage is applied to the inner side of the transfer belt 10, and there is a concern about potential interference with the primary transfer roller 102a.

  On the other hand, in the case of attractive transfer, current may leak due to a transfer material from the pre-transfer guide 115 and the registration roller 116 around the secondary transfer roller 14, and a necessary transfer electric field may not be obtained. However, if the potential characteristics around the secondary transfer are hoisted by the optimum resistance, or if the material characteristics (resistance) of the secondary transfer peripheral member are set to the optimum, there is no leakage current due to the moisture state of the transfer material. Stable transferability can be obtained. For this reason, in the present embodiment, the transfer bias is applied to the secondary transfer portion by attractive transfer in which a bias is applied to the secondary transfer roller 14 side.

As described above, according to the present embodiment, the following effects can be obtained.
For cleaning the secondary transfer roller, biases of both polarities are applied alternately, and a cleaning bias control method for one polarity uses a control method for moving toner to the transfer material during the secondary transfer, and the other polarity In this cleaning control method, constant voltage control is performed. As a result, the same value as the secondary transfer current can be used as one cleaning bias, and the absolute value of the non-sheet-passing voltage output at that time becomes the cleaning bias value of the other polarity. As a result, there is no need to use a high-voltage power supply for performing another control as a cleaning bias, and it is possible to configure with only two power supply specifications of a control power supply for secondary transfer and a power supply having a polarity opposite to that of the secondary transfer. Can be planned. In addition, the development efficiency is greatly improved without the need for optimal examination of cleaning bias. In this way, low cost, development efficiency is improved, and there is no stain on the back of the paper, and a good image is reproduced.

  At this time, the power source for bias used at the time of transfer and the power source for bias used at the time of cleaning (two because of positive / negative switching) are required. According to the present invention, the number of power sources required can be reduced to one.

  By performing secondary transfer with constant current control, a stable transfer voltage can be obtained even if the sheet resistance or the sheet thickness changes, and a large transfer voltage table corresponding to the sheet type becomes unnecessary.

  The secondary transfer current is changed according to the environmental change, and the cleaning bias is also changed accordingly. As a result, even when the environment fluctuates, the cleaning performance of the secondary transfer roller does not deteriorate, and an optimum transfer property can be obtained.

  By setting the ratio of single bubbles in the foamed state of the secondary transfer roller to 20% to 80%, the amount of toner adhered to the surface of the secondary transfer roller stays on the surface and returns to the belt by applying a cleaning bias; The toner that penetrates into the transfer roller is efficiently distributed, and the toner that stains the back and edges of the paper does not remain on the surface of the transfer roller that is soiled with toner. By using such a transfer roller, it is possible to reduce the stain on the back side of the sheet, and the edge of the sheet is not stained, so that a high-quality image can be realized.

  By performing the secondary transfer by attractive transfer, it is possible to realize a high-quality secondary transfer image that is stable in both environment and life without potential interference with the primary transfer.

  Since the secondary transfer current is changed according to the environmental change, and the cleaning bias is also changed accordingly, the cleaning performance of the secondary transfer roller does not deteriorate even when the environmental change occurs, and the optimum transfer performance is achieved. Can also be obtained.

  By setting the ratio of single bubbles in the foamed state of the secondary transfer roller to 20% to 80%, the amount of toner adhered to the surface of the secondary transfer roller stays on the surface and returns to the belt by applying a cleaning bias; The toner that penetrates into the transfer roller is efficiently distributed, and the toner that stains the back and edges of the paper does not remain on the surface of the transfer roller that is soiled with toner. Therefore, by using such a transfer roller as a transfer member, it is possible to reduce the backside contamination of the paper, and the paper edge is not stained, so that a high-quality image can be realized.

FIG. 2 is a schematic configuration diagram showing the periphery of a photoreceptor and an intermediate transfer belt in a color image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating an arrangement example of a photoconductor, an intermediate transfer belt, and a transfer member in a tandem type image forming apparatus according to another embodiment of the present invention. It is a figure which shows the detail of VI characteristic (current voltage characteristic) of the constant current control of the secondary transfer part with respect to a certain transfer material. It is a cross-sectional view of a secondary transfer roller according to an embodiment of the present invention.

Explanation of symbols

10 Intermediate transfer belt 14 Secondary transfer roller 26 Secondary transfer bias power source

Claims (16)

Image formation comprising: an image carrier that carries a toner image; a transfer unit that applies a bias to a transfer member to transfer the toner image to a recording material; and a cleaning unit that removes toner adhering to the surface of the transfer member In the device
A first power source for supplying a bias necessary for transferring the toner image to the transfer unit; and a second power source for supplying a bias necessary for removing the toner attached to the surface of the transfer member by the cleaning unit. With power supply,
The image forming apparatus according to claim 1, wherein the cleaning unit applies a bias having both positive and negative polarities supplied from the first power source and the second power source to the transfer member.   The image forming apparatus according to claim 1, further comprising a switching unit that switches between the first power source and the second power source.   The image forming apparatus according to claim 1, wherein the first power supply supplies a bias having the same polarity as the toner, and the second power supply supplies a bias having a polarity opposite to that of the toner.   The image forming apparatus according to claim 1, wherein the first power supply supplies a bias having a polarity opposite to that of the toner, and the second power supply supplies a bias having the same polarity as that of the toner.   The bias supplied from the first power source is controlled at a constant current so as to be a constant current, and the bias supplied from the second power source is controlled at a constant voltage so as to be a constant voltage. Item 5. The image forming apparatus according to any one of Items 1 to 4.   The cleaning bias having the polarity for performing the constant voltage control is set to the absolute value of the non-sheet-passing voltage for the constant current control set to obtain the cleaning bias having the other polarity. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 5, wherein the set current during the constant current control is changed according to an environment.   8. The image forming apparatus according to claim 5, wherein a current value after correction is used as a cleaning bias when environmental correction is included in the set current during the constant current control. 9.   The image forming apparatus according to claim 1, wherein the secondary transfer roller includes a foam made of urethane foam including a mixture of single bubbles and continuous bubbles. In a transfer member cleaning method for cleaning toner attached to a transfer member for transferring a toner image to a recording material by applying a bias,
A bias supplied from a first power source required to transfer the toner image and a bias supplied from a second power source required to remove toner adhering to the surface of the transfer member are both positive and negative. And cleaning the toner adhering to the surface of the transfer member by applying the positive and negative biases.   11. The transfer member cleaning method according to claim 10, wherein the first power supply supplies a bias having the same polarity as that of the toner, and the second power supply supplies a bias having a polarity opposite to that of the toner.   11. The transfer member cleaning method according to claim 10, wherein the first power supply supplies a bias having a polarity opposite to that of the toner, and the second power supply supplies a bias having the same polarity as that of the toner.   The bias supplied from the first power source is controlled at a constant current so as to be a constant current, and the bias supplied from the second power source is controlled at a constant voltage so as to be a constant voltage. Item 13. The transfer member cleaning method according to any one of Items 10 to 12.   The cleaning bias having the polarity for performing the constant voltage control is set to the absolute value of the non-sheet-passing voltage for the constant current control set to obtain the cleaning bias having the other polarity. The transfer member cleaning method according to claim 13.   The transfer member cleaning method according to claim 13 or 14, wherein the set current during the constant current control is changed according to an environment.   The transfer member cleaning method according to claim 13, wherein a current value after correction is used as a cleaning bias when environmental correction is included in the set current during the constant current control. .

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