JP2010072086A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reliably prevent backside staining from occurring on a recording medium. <P>SOLUTION: The image forming apparatus includes: an intermediate transfer belt 100 to which a toner image on a photoreceptor 15 is transferred while coming into contact with the photoreceptor 15 and which holds the toner image; a primary transfer roller 16 which rotates while coming into contact with the intermediate transfer belt 100; and a secondary transfer roller 102 and a secondary transfer counter roller 103 which are installed on a downstream side of the primary transfer part formed by the photoreceptor 15 and the primary transfer roller 16. The apparatus is provided with a polarity reversing means 19 which reverses a polarity of a toner patch formed in a non-image area between the recording medium and the next recording medium on the intermediate transfer belt 100 before reaching a secondary transfer part formed by the secondary transfer roller 102 and the secondary transfer counter roller 103. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and in particular, primarily transfers a toner image formed on a photosensitive member to an intermediate transfer member, and further transfers the toner image transferred to the intermediate transfer member to paper. The present invention relates to an image forming apparatus of a system for secondary transfer to a recording medium such as.

  In an image forming apparatus, fluctuations in image density or color misregistration may occur due to environmental changes or changes over time. For the purpose of making the image density constant and correcting the color misregistration, a toner patch is formed in a non-image forming area between the recording medium on the intermediate transfer body at a certain printing number cycle, and the primary transfer section And a sensor installed between the secondary transfer section and detecting the toner density and position of the toner patch, and applying feedback control, a method of always obtaining a stable high image has been proposed.

  When this method is employed, the toner patch detected by the sensor is transferred to the secondary transfer roller at the secondary transfer portion. Since the toner patch transferred to the secondary transfer roller is transferred to the back surface of the recording medium as it is and becomes dirty, the secondary transfer roller is provided with a cleaning mechanism, and the toner of the toner patch is collected by this cleaning mechanism. In addition, the back side of the recording medium is prevented.

  However, in order to stably guarantee high-quality image formation, it is necessary to frequently form toner patches in the non-image forming area. For this reason, the load on the cleaning mechanism for the secondary transfer roller increases, and cleaning failure may occur in the secondary transfer roller. As a result, the toner remaining on the secondary transfer roller adheres to the back surface of the next recording medium, resulting in backside contamination.

  As a countermeasure, when the toner formed in the non-image forming area arrives at the secondary transfer portion, the bias applied to the secondary transfer portion is switched to a polarity opposite to the bias when the image portion passes, A method has been proposed in which the toner formed in the non-image forming area is left on the intermediate transfer member without being transferred to the secondary transfer roller (Japanese Patent Laid-Open No. 2004-361859).

  Further, in order to enhance the effect of this method, the toner formed in the non-image forming area is increased in the toner charge amount with a charger or the like before entering the secondary transfer section, so that the non-image forming area in the secondary transfer section. There has also been proposed a method for enhancing the effect of the reverse bias applied to.

  As another countermeasure, when the toner formed in the non-image forming area reaches the secondary transfer portion, the toner formed in the non-image forming area is removed by separating the secondary transfer roller from the intermediate transfer member. It has been proposed to reduce the cleaning load at the secondary transfer portion without transferring to the secondary transfer roller.

  JP-A-8-63011, JP-A-8-272235, JP-A-8-328401, JP-A-9-6146, and the like pass a recording medium between an intermediate transfer member and a transfer unit. In this case, the toner image formed on the surface of the intermediate transfer member is transferred to the recording medium by applying a transfer bias to the transfer means, and at the time of cleaning when the recording medium does not exist at the transfer position, the toner has the same polarity as the charging polarity of the toner. A configuration has been proposed in which the voltage on the transfer unit is applied to prevent the toner on the intermediate transfer member from being transferred to the transfer unit when there is no recording medium at the transfer position.

  Further, the techniques disclosed in Japanese Patent Laid-Open Nos. Hei 8-272235 and Hei 8-328401 apply a voltage having the same polarity as the charging polarity of the toner to the transfer means during cleaning when the recording medium is not present at the transfer position. At the same time, by applying a voltage of the opposite polarity to the charging polarity of the toner, the toner adhering to the transfer means is completely reverse-transferred onto the intermediate transfer member to prevent the recording medium from being stained. It is.

Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 9-6146 is left on the intermediate transfer member and the secondary transfer member after paper jam release by controlling the contact and separation of the cleaner blade and the secondary transfer member. The toner can be efficiently cleaned, and it is possible to form a clean image without causing stains such as fog and streaks due to residual toner in the image forming operation performed after the paper jam is cleared. It is disclosed.
JP 2004-361859 A JP-A-8-63011 JP-A-8-272235 JP-A-8-328401 Japanese Patent Laid-Open No. 9-6146

  In recent years, in image forming apparatuses such as color copying machines, in order to guarantee the image quality of color images as the quality of images increases, toner patches for process control and resist control can be used before image forming operations are started or recorded. The image is transferred onto the intermediate transfer member at the timing between the passage of the medium, and this process or the toner patch for resist control is detected to control the image forming operation.

  In the method of switching the bias of the secondary transfer portion when the toner patch formed in the non-image region reaches the secondary transfer portion as described above, the bias applied to the toner in the non-image region is the bias in the image portion. It is necessary to switch to the opposite characteristics, and as the printing speed increases, the time is not reached in time, and it becomes difficult to prevent the recording medium from being stained. Even in the configuration in which the secondary transfer roller is separated and contacted every time the non-image area passes, there is a possibility that the printing speed may become too fast in time. Further, when the secondary transfer roller is separated from and brought into contact, an impact is applied to the intermediate transfer member, which may cause problems such as color misregistration.

  Further, as in the techniques disclosed in Japanese Patent Laid-Open No. 8-63011, Japanese Patent Laid-Open No. 8-272235, Japanese Patent Laid-Open No. 8-328401, Japanese Patent Laid-Open No. 9-6146, etc. When the toner image is not transferred to the recording medium as described above, the reverse bias voltage having the same polarity as the toner charging polarity is transferred for a certain period of time when the transfer bias is turned off or when the recording medium is not present at the transfer position. It has been confirmed that the method of cleaning the secondary transfer roller by applying to the means is insufficient as a countermeasure against toner contamination of the secondary transfer roller.

  As disclosed in Japanese Patent Laid-Open No. 8-328401, when the bias voltage applied to the transfer member is turned off between sheets of the recording medium, the recording medium on the intermediate transfer member The toner patch for process or registration control transferred between the sheets is transferred onto the transfer member by the pressure contact force between the intermediate transfer member and the transfer member, and this toner patch is transferred to the back surface of the next recording medium, There is a problem of causing backside contamination.

  Further, as disclosed in Japanese Patent Laid-Open No. 8-63011, when a recording medium is present at the transfer position, a voltage having a polarity opposite to the charged polarity of the toner is mechanically applied to the transfer means. In this case, if the position of the image area on the intermediate transfer body and the recording medium is shifted due to a conveyance failure of the recording medium or an error in the size of the recording medium, a toner patch that is not transferred to the recording medium is formed on the transfer body. It is transferred and causes the back side of the recording medium to become dirty. Further, there is a new problem that a process or a toner patch for resist control formed in a non-image area corresponding to the interval between sheets of the intermediate transfer member is transferred onto a recording medium.

  Further, as disclosed in Japanese Patent Laid-Open No. 8-272235 and Japanese Patent Laid-Open No. 8-328401, when a recording medium is not present at the transfer position, a current having the same polarity as that of the toner is applied. In the case where cleaning is performed by applying a reverse polarity current having a polarity opposite to that of the toner and having a current value equal to or greater than the absolute value of the same polarity current, the intermediate transfer is started before the image forming operation is started. When a toner patch for process or resist control is transferred onto the body, it is necessary to apply a current having the same polarity as that of the toner and then to carry out a cleaning cycle in which a current having a polarity opposite to that of the toner is applied. Therefore, there is a new problem that the time until the actual image forming operation is started is increased, and the productivity is greatly reduced.

  Further, as disclosed in Japanese Patent Laid-Open No. 9-6146, when the secondary transfer member can be selectively switched to the press contact state or the separated state with respect to the intermediate transfer member, the cleaning cycle becomes long. Therefore, after forming a toner patch for process and resist control by that amount, the image forming operation cannot be executed for one rotation or more of the secondary transfer member, and the productivity is also greatly reduced. Has new problems.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to transfer a process or resist control toner patch onto an intermediate transfer member in order to improve image quality. An image forming apparatus configured as described above can reliably prevent the occurrence of backside contamination on a recording medium, and provide an image forming apparatus capable of preventing a significant reduction in productivity. is there.

  In order to achieve the above object, the present invention provides a photoconductor for forming a toner image, a belt-shaped intermediate transfer member that contacts and contacts the photoconductor and holds the toner image on the photoconductor, At a position downstream of the primary transfer roller rotating in contact with the intermediate transfer body and rotating along the intermediate transfer body, and the intermediate body of the primary transfer portion formed by the photosensitive body and the primary transfer roller, The present invention is intended for an image forming apparatus including a secondary transfer roller that rotates along an intermediate transfer body with an intermediate transfer body interposed therebetween, and a secondary transfer counter roller.

  The first means of the present invention is configured such that the polarity of the toner patch formed in the non-image area between the recording medium on the intermediate transfer member and the next recording medium is determined based on the secondary transfer roller and the secondary transfer counter roller. A polarity reversing means for reversing before reaching the secondary transfer portion formed in step (1) is provided.

  According to a second means of the present invention, in the first means, a sensor for detecting the toner patch is installed between the primary transfer portion and the secondary transfer portion in the rotation direction of the intermediate transfer member, and the polarity inversion is performed. Means is provided between the sensor and the secondary transfer portion.

  According to a third means of the present invention, in the first means, a plurality of primary transfer portions are provided along the rotation direction of the intermediate transfer member, and an applied bias for reversing the charging polarity of the toner patch is provided. Is changed according to the charge amount of the toner patch formed in each primary transfer portion.

  A fourth means of the present invention is characterized in that, in the third means, the bias applied when the charging polarity of the toner patch is reversed is changed according to the color of the toner patch formed in the non-image area. It is.

  The present invention is configured as described above, and even in an image forming apparatus configured to transfer a process or resist control toner patch onto an intermediate transfer body for high image quality, It is possible to provide an image forming apparatus that can reliably prevent the occurrence of backside contamination and can prevent the productivity from being significantly lowered.

  Next, each embodiment of the present invention will be described with reference to the drawings.

First, the overall configuration of the image forming apparatus will be described with reference to FIGS.
The drum-shaped photoconductors 15a to 15d rotate counterclockwise as shown in the drawing. On the other hand, the intermediate transfer belt 100 is stretched by rollers 30 and 31, and rotates in the clockwise direction in contact with the photoreceptors 15a to 15d.

  Each of the image forming units includes photoreceptors 15a to 15d, static eliminators 13a to 13d, cleaners 14a to 14d arranged around the photosensitive member 15 from a position in contact with the intermediate transfer belt 100, and charging. And 10a to 10d, exposure units 11a to 11d, and developing units 12a to 12d.

  The primary transfer rollers 16a to 16d are arranged to be pressed from the back side of the area where the photoconductors 15a to 15d and the intermediate transfer belt 100 are in contact with each other, and primary transfer is performed from the photoconductors 15a to 15d and the primary transfer rollers 16a to 16d. The part is composed.

  Next, an image forming method and a primary transfer method will be described. The surface of the photoreceptor 15 is uniformly charged by the charger 11. Thereafter, an electrostatic latent image is formed on the charged photoreceptor 15 by irradiating a laser beam from the exposure device 11 based on image data from the scanner and the PC. Next, the toner charged by the developing device 12 is attached to the photoreceptor 15 to visualize the electrostatic latent image, thereby forming a toner image. The toner image formed on the photoconductor 15 is transferred onto the intermediate transfer belt 100 by applying a controlled transfer electric field to the primary transfer roller 16. After the transfer, the remaining charge on the photoconductor 15 is removed by the static eliminator 13, the residual toner on the photoconductor 15 is removed by the cleaner 14, and the process of returning to the charger 10 is repeated.

  In this embodiment, there are four color image forming portions of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 100, and the photoconductor 15a. After the yellow toner image formed in Step 1 is subjected to primary transfer onto the intermediate transfer belt 100, the intermediate transfer belt 100 moves to the photoconductor 15b, and on the toner image transferred from the photoconductor 15a, The magenta toner image formed on the photoconductor 15b is transferred. Thereafter, cyan and black toner images formed on the photoconductor 15c and the photoconductor 15d are sequentially superimposed and transferred.

  The toner image transferred onto the intermediate transfer belt 100 is conveyed by registration rollers 22 and 23 in a secondary transfer portion formed by a secondary transfer roller 102 and a secondary transfer counter roller 103 that sandwich the intermediate transfer belt 100. The images are collectively transferred to the recording medium 1 made of cut paper.

  In the secondary transfer portion, a current is applied to the secondary transfer roller 102, and the transfer current flows into the secondary transfer counter roller 103, whereby the toner image on the intermediate transfer belt 100 can be transferred to the recording medium 1. it can. The toner image thus transferred is heated and pressure-fixed on the recording medium 1 by the fixing rollers 20 and 21, and then taken out of the apparatus.

  The toner characteristics may change due to continuous printing or environmental fluctuations, and the toner density may fluctuate accordingly, and color misregistration may occur in full-color printing as in this embodiment.

  In order to eliminate these inconveniences, a toner patch is periodically created in a non-image area between the recording medium 1 on the intermediate transfer belt 100 and the next recording medium 1, and the toner density and position of the toner patch are set to the primary. Detection is performed by a toner density detection sensor 18 installed between the transfer portion and the secondary transfer portion. Based on the detection result, the toner supply control is corrected. When the toner density is low, a large amount of toner is replenished to the developing device 12, and when the toner concentration is high, the toner is replenished to the developing device 12 to reduce the toner concentration on the intermediate transfer belt 100 at all times. High-quality printing without color misregistration can be maintained.

  Further, when a printing pattern with a small amount of toner consumption continues, the toner is not consumed much, and the characteristics of the toner may be deteriorated by stirring for a long time in the developing devices 12a to 12d. Since the deterioration of the characteristics of the toner causes poor image quality, the toner may be periodically transferred to the non-image area of the intermediate transfer belt 100 for the purpose of refreshing the toner in the developing units 12a to 12d. The toner in the non-image area of the intermediate transfer belt 100 is transferred to the secondary transfer roller 102 when passing through the secondary transfer portion, and is removed by a cleaning mechanism (not shown) of the secondary transfer roller 102.

  However, there is a limit to the cleaning capability of the secondary transfer roller 102, and when the limit is exceeded, the toner remains on the secondary transfer roller 102 and adheres to the recording medium 1 that has arrived next and becomes dirty from the back. Will occur.

  Therefore, in this embodiment, a corona charger 19 is installed as means for reversing the charging polarity of the toner between the primary transfer portion and the secondary transfer portion. As for the installation position, a bias is applied from the corona charger 19 when reversing the charging polarity of the toner patch. As a result, the toner patch may be disturbed and accurate detection by the sensor 18 may not be possible. The corona charger 19 is installed downstream of the sensor 18 in the intermediate transfer belt rotation direction, that is, between the sensor 18 and the secondary transfer unit.

  As shown in FIG. 1, a grounding roller 17 is installed on the opposite side of the corona charger 19 through the intermediate transfer belt 100, so that the toner on the intermediate transfer belt 100 can be stably biased with a reverse polarity. Perform charging. First, by grounding the grounding roller 17, an electrically stable state can be created as compared with a case where the grounding roller 17 is not grounded. As a result, the corona discharge electricity from the corona charger 19 can be stably applied to the toner on the intermediate transfer belt 100.

  Further, by arranging the grounding roller 17 on the back surface of the intermediate transfer belt 100, fluttering of the intermediate transfer belt 100 due to rotational movement of the intermediate transfer belt 100 can be suppressed. As a result, the distance between the corona charger 19 and the intermediate transfer belt 100 can always be kept constant, so that electricity can be stably applied to the toner on the intermediate transfer belt 100.

  Since the charging polarity of the toner patch formed in the non-image area is reversed, the toner in the non-image area is transferred to the secondary transfer roller 102 without switching the secondary transfer bias to the reverse bias of the image area in the secondary transfer unit. It will not be done. Therefore, it is possible to reduce the cleaning load on the secondary transfer roller 102 and prevent the recording medium 1 from being stained on the back side.

  Since the overall configuration and operation of the image forming apparatus are the same as those in the first embodiment, description thereof is omitted.

  When the charge amount of the toner is high, the charge polarity before the toner reaches the secondary transfer portion is reversed, and the toner charge polarity cannot be sufficiently reversed. Therefore, the toner is transferred to the secondary transfer roller 102 at the secondary transfer portion. Is transferred and the recording medium 1 is stained on the back. Further, when the charge amount of the toner is low, the polarity of the toner is excessively reversed, and the toner may be scattered at the secondary transfer portion. Since the charge amount of the toner varies depending on the color, it is easily affected by the charge amount.

  In the developing units 12a to 12d, even if the charge amounts of the toners of the respective colors are the same, the charge amount varies depending on the color (that is, the position of the image forming unit) when reaching the secondary transfer unit. As shown in FIG. 2, the toner of the most upstream color (yellow in this embodiment) in the rotation direction of the intermediate transfer belt 100 must pass through the three primary transfer stations before reaching the secondary transfer portion. In addition, since the charge is injected into the toner every time it passes, the charge amount of the toner tends to gradually decrease. On the contrary, the toner of the most downstream color (black in this embodiment) reaches the secondary transfer portion with almost no decrease in the charge amount.

  For this reason, in this embodiment, the applied bias of the corona charger 19 before the secondary transfer for reversing the charge amount of the toner from the most upstream image forming unit to the most downstream image forming unit is sequentially increased, so that It is possible to keep the charge amount of the toner in the image area constant and prevent the toner in the non-image area from being transferred to the secondary transfer roller 102 stably.

FIG. 3 is an enlarged schematic configuration diagram from the final primary transfer unit to the secondary transfer unit of the image forming apparatus according to the embodiment of the present invention. 1 is a schematic configuration diagram of the entire image forming apparatus.

Explanation of symbols

1: recording medium,
10a-10d: Y, M, C, K chargers for each color,
11a to 11d: Y, M, C, and K color exposure units,
12a to 12d: Y, M, C, and K color developing devices,
13a to 13d: neutralizers for Y, M, C, and K colors,
14a-14d: Y, M, C, K color cleaners,
15a to 15d: Y, M, C, and K photoconductors,
16a to 16d: Y, M, C, K primary transfer rollers for each color,
17: grounding roller,
18: Toner density detection sensor
19: Corona charger (polarity reversing means)
20, 21: fixing roller,
22, 23: Registration roller,
30, 31: Intermediate transfer belt stretching roller,
100: Intermediate transfer belt,
102: secondary transfer roller,
103: Secondary transfer counter roller.

Claims (4)

A photoreceptor for forming a toner image;
A belt-like intermediate transfer member that contacts the photosensitive member and transfers and holds the toner image on the photosensitive member;
A primary transfer roller that contacts the intermediate transfer member and rotates along the intermediate transfer member;
A secondary transfer roller that rotates along the intermediate transfer body while sandwiching the intermediate transfer body at a position downstream in the rotation direction of the intermediate body of the primary transfer portion formed by the photoconductor and the primary transfer roller; In the image forming apparatus provided with the next transfer counter roller,
The polarity of the toner patch formed in the non-image area between the recording medium on the intermediate transfer body and the next recording medium reaches the secondary transfer portion formed by the secondary transfer roller and the secondary transfer counter roller. An image forming apparatus comprising a polarity reversing means for reversing before performing. The image forming apparatus according to claim 1.
A sensor for detecting the toner patch is installed between the primary transfer portion and the secondary transfer portion in the rotation direction of the intermediate transfer member;
The image forming apparatus, wherein the polarity reversing unit is provided between the sensor and the secondary transfer unit. The image forming apparatus according to claim 1.
A plurality of primary transfer portions are provided along the rotation direction of the intermediate transfer member,
An image forming apparatus, wherein an applied bias for reversing the charging polarity of the toner patch is changed depending on a charge amount of the toner patch formed in each primary transfer portion. The image forming apparatus according to claim 3.
An image forming apparatus, wherein an applied bias for reversing a charging polarity of the toner patch is changed depending on a color of the toner patch formed in the non-image area.

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