JP2015138212A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that controls paper powder attached to a transfer member so as to minimize downtime, and remove a residual toner attached to the transfer member so as to prevent abnormality in quality.SOLUTION: An image forming apparatus includes an image carrier that carries toner images, a transfer member that forms a transfer nip with the image carrier, a power source that can output a transfer bias for transferring a toner image on the image carrier onto a recording material at the transfer nip and a cleaning bias for cleaning the transfer member before or after a print job, and a control unit that controls the power source. The control unit changes the cleaning bias according to the type of the recording material.

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile.

  In the process of image formation, the transfer member (for example, the secondary transfer roller) is soiled. As the cause of the contamination, for example, residual toner before and after transfer, ground contamination toner that adheres between papers or outside the paper width, scattering toner, or image forming toner at the time of jamming may be mentioned. In addition, foreign matter (especially paper dust) generated from the recording material may be attached.

  As a technique for removing such stains on the transfer member, a reverse polarity to the transfer bias is applied to the transfer member at a timing other than the time of transfer to the recording material, or the same polarity / reverse polarity as the transfer bias is switched and applied. There is bias cleaning.

  For example, in Patent Document 1, it is determined whether or not an image is protruding from the relationship between the size of the recording material and the size of the image for the purpose of removing contamination on the transfer member at the time of protruding the image. A configuration to perform is disclosed. However, control for paper dust is not particularly considered for the purpose of removing the protruding toner.

  With regard to such a bias cleaning technique, it is known that there is a difference in the removal of dirt on the transfer member depending on, for example, the order of polarity to be applied, the time to be applied, the magnitude of the bias, or the number of times to be applied.

  For example, Patent Document 2 discloses a configuration in which the cleaning time is determined according to the number of printed sheets for the purpose of extending the life of the image carrier. In such a configuration, when a large amount of recycled paper in which a large amount of paper dust accumulates is passed, cleaning is performed for a long time after the paper passing, and in a direct transfer type etc. in which paper dust is held on a transfer member, a large amount of paper dust is accumulated. Paper dust is carried to the image carrier cleaning unit.

  Patent Document 3 discloses a configuration that eliminates the back stain of a large size paper after using the small size paper during continuous printing while ensuring the maximum productivity. That is, the necessary bias cleaning time is obtained according to the width of the small size paper and the width of the large size paper, and the paper interval that can secure the time is set at the time of switching the paper size, and cleaning is performed. However, such a configuration has no effect except during continuous printing.

  An object of the present invention is to provide an image forming apparatus capable of preventing quality abnormality by controlling paper dust attached to a transfer member, minimizing downtime and removing residual toner attached to the transfer member.

  An object of the present invention is to transfer an image carrier that carries a toner image, a transfer member that forms a transfer nip between the image carrier and a toner image on the image carrier to a recording material at the transfer nip. A power source capable of outputting a cleaning bias for cleaning the transfer member before or after the print job and a print job, and a control unit for controlling the power source, the control unit depending on the type of the recording material This can be solved by changing the cleaning bias.

  According to the present invention, the toner can be removed while minimizing the downtime by changing the cleaning bias control according to the paper type to control the paper dust.

1 is a schematic configuration diagram of an entire image forming apparatus according to an embodiment of the present invention. FIG. 4 is an enlarged schematic diagram of a tandem intermediate transfer type transfer unit. 6 is a timing chart showing a typical sequence of secondary transfer bias control. FIGS. 4A and 4B are timing charts showing the latter half of the transfer of the secondary transfer bias control, FIG. 4A shows the basic mode, and FIG. 4B shows the case where the paper type is recycled paper. 6 is a timing chart showing the second half and after of the secondary transfer bias control when the paper type is coated paper. It is a figure which shows the specific structure of a cleaning unit. FIG. 6 is a schematic diagram illustrating an image forming unit of an image forming apparatus according to a second embodiment. 6 is a timing chart showing a typical sequence of transfer bias control in the case of a direct transfer method. FIGS. 9A and 9B are timing charts showing the latter half of the transfer of the transfer bias control in the direct transfer method, FIG. 9A shows the basic mode, and FIG. 9B shows a mode in which post-job cleaning is extended. Indicates a case where the paper type is recycled paper and cleaning is not performed after the job. FIGS. 10A and 10C are timing charts showing a state between sheets when the transfer unit is passed through single-sided / double-sided printing. FIG. 10A shows a case of single-sided printing, and FIG. 10C shows a case of double-sided printing. FIG. 11A is a basic mode, FIG. 11B shows a mode in which the bias is increased, and FIG. 11C shows a mode in which the bias is reduced. Show. FIG. 12A is a timing chart showing a pattern for monotonously changing the output bias of post-job cleaning stepwise, FIG. 12A is a pattern for monotonically increasing, and FIG. 12B is a pattern for monotonically decreasing. 10 is a timing chart showing a waveform variation pattern in which only positive polarity in post-job bias cleaning is increased for negatively charged toner. FIG. 14A is a timing chart showing a waveform variation pattern in which only the absolute value of the negative polarity in post-job bias cleaning is increased with respect to negatively charged toner. FIG. b) shows a case where it is larger than the transfer bias. FIG. 15A is a timing chart showing a pattern for changing the magnitudes of a plurality of biases in post-job bias cleaning. FIG. 15A is a pattern for changing the magnitude of the absolute value in the positive polarity and the negative polarity, and FIG. It is a pattern that changes the absolute value within the polarity.

  Hereinafter, before describing the embodiment, a preliminary matter for facilitating understanding of the embodiment will be described.

  The above-described bias cleaning is mainly intended to remove toner stains on a transfer member such as a secondary transfer roller. For example, when removing ground stain toner outside the paper width, cleaning may be performed for a long time. It was broken. The “toner” may include a carrier in the two-component development using the carrier.

  In recent years, recycled paper that is environmentally friendly has come to be used as recording paper. Generally, recycled paper uses recycled pulp, so it has weak fibers and contains a large amount of calcium carbonate as a filler. Therefore, it is easy to generate paper dust when being conveyed. Here, “paper dust” refers to fibrous foreign matter mainly generated from the recording material, but also includes foreign matter that is mixed in the recording material manufacturing process. The recording material is also referred to as a transfer medium, recording paper, and the like, and there are various types. However, the recording material is roughly classified into plain paper (PPC paper), recycled paper, and coated paper.

  When paper dust adheres to the transfer roller, a transfer current flows into the roller portion or becomes a base point of discharge, resulting in white spots on the image. Further, when the paper dust accumulated on the transfer roller is carried in a state where the next paper is unstable and dropped into the fixing unit, the paper dust may be fixed to the pressure roller in the fixing unit. In order to cope with these problems, it is desirable to remove not only toner but also paper dust from the transfer roller.

  In addition, in a direct transfer type image forming apparatus, if the cleaning unit does not have a paper dust removal brush or the like, the paper dust adheres to the photosensitive drum and becomes a starting point for poor cleaning, or the charging member is soiled. I'll be relaxed. In such an apparatus, it is desirable to hold the paper dust on the transfer roller as much as possible and collect it with the next paper, or drop the paper powder down from the transfer roller and collect it with the collection box. In this way, removing paper dust or holding it on a transfer roller is expressed as “controlling paper dust” below.

  However, if the cleaning method is changed in order to control paper dust, the following trade-off occurs. If the number of cleanings is always increased in order to remove the paper dust from the roller portion, the downtime of the apparatus increases. On the other hand, if the number of times of cleaning is always reduced in order to hold the paper dust at the roller portion, the original toner removal function is degraded. For this reason, there is a risk of causing quality abnormalities such as the backside of the paper and the dirt on the edge surface due to the toner falling on the conveyance path. The edge surface contamination is contamination generated on an end surface of about 500 or more printed sheets bundled.

  In the following embodiments, an object of the present invention is to provide an image forming apparatus that controls paper dust attached to a transfer member, minimizes downtime, and removes residual toner attached to the transfer member, thereby preventing quality abnormalities. To do.

(First embodiment)
FIG. 1 is a schematic diagram illustrating an internal configuration of the image forming apparatus according to the first embodiment. The present embodiment is an example applied to a tandem intermediate transfer type full-color printer 100.

  As shown in FIG. 1, the printer 100 includes an image forming unit 120, a paper feeding unit 130, and a paper discharging unit 140 that are arranged in the apparatus main body 110 and have a configuration for forming an image. The paper feeding unit 130 is disposed below the apparatus main body 110 and has a configuration for feeding the paper S to the paper feeding cassette 20 that stores the paper S that is a sheet-like recording material and the image forming unit 120. The paper discharge unit 140 is disposed on the upper surface of the apparatus main body 110 and includes a paper discharge roller 24 for discharging the paper S on which an image is formed, a paper discharge tray 25 for stacking the discharged paper S, and the like.

  In the image forming unit 120, an intermediate transfer belt 10 constituted by an endless belt as an intermediate transfer member is disposed. Below the intermediate transfer belt 10, four image forming units 2Y, 2M, 2C, and 2K are arranged in order from the upstream side in the transport direction of the intermediate transfer belt 10. These are image forming units corresponding to yellow, magenta, cyan, and black, and the configuration thereof is the same except that colors used in the image forming process are different. Therefore, in the following description and FIG. 2 and subsequent figures, only the reference numerals common to the respective image forming units are described, and the alphabetic suffixes indicating the color of the toner and the like are omitted unless obscured.

  The image forming unit 2 includes a photoconductor 1 and a charging unit, a developing unit, a primary transfer roller 4, a cleaning unit, and the like disposed around the photoconductor 1. The configuration of each of these members is basically the same as the conventional one, and a well-known process (charging process, exposure process, development process) is executed on the photoreceptor 1 to form a desired toner image on the photoreceptor 1. . In other words, in the developing unit, the latent image formed on the photoreceptor 1 through the charging process and the exposure process is subjected to a visible image process with a two-component developer containing toner (yellow toner if 2Y) and carrier. .

  The toner image formed on the photoreceptor 1 is transferred onto the intermediate transfer belt 10 in the primary transfer portion (primary transfer nip) where the primary transfer roller 4 is disposed (primary transfer step). After the transfer, the surface of the photoconductor 1 is recovered by the cleaning unit such as untransferred toner remaining on the photoconductor 1 (cleaning step). After cleaning, the potential of the surface of the photoreceptor 1 is initialized by a neutralizing roller (not shown). By going through such steps, a series of image forming processes performed on the photoreceptor 1 is completed.

  The above-described image forming process is executed at the time of forming a single image of only a monochrome image and at the time of forming a full color image. At the time of forming a full color image, each process is performed in each of the four image forming units 2Y to 2K shown in FIG. Executed. The toner images of the respective colors formed on the respective photoreceptors 1 through the development process are transferred onto an intermediate transfer belt 10 as an image carrier, and a color image is formed on the intermediate transfer belt 10. The toner image primarily transferred onto the intermediate transfer belt 10 reaches a secondary transfer portion (secondary transfer nip) where a secondary transfer roller 16 as a secondary transfer unit is disposed, and the sheet S sent to the secondary transfer portion. It is batch-transferred on the top.

  On the other hand, in the paper feed unit 130 that transports the paper S to the position of the secondary transfer nip, a plurality of paper S are stacked and stored in the paper feed cassette 20, and one by one by the cooperative action of the paper feed roller 21 and the separating means. Separated and fed. The fed paper S is temporarily stopped by the registration rollers 22 and corrected for oblique deviation and the like, and then conveyed toward the secondary transfer nip by the registration rollers 22 at a predetermined timing.

  The sheet S on which the toner image is transferred at the position of the secondary transfer nip is conveyed to the fixing device 23. Here, the toner is dissolved by the heat and clamping pressure of the fixing roller and the pressure roller, and the toner image transferred to the surface of the paper S is fixed. In the case of single-sided printing, the fixed sheet S is discharged as an output image to the discharge tray 25 formed on the upper surface of the apparatus main body 110 by the discharge roller 24 and stacked. In the case of duplex printing, the sheet S is sent again to the upstream side of the registration roller 22 through the sheet conveyance path (not shown) for duplex printing, and image formation is performed on the back surface.

  FIG. 2 is an enlarged schematic view showing a tandem intermediate transfer type transfer unit. The intermediate transfer belt 10 includes a tension roller 11 (located at the leftmost in FIG. 2) that receives a tensile force by a spring (not shown), a driving roller 13, and an inlet roller 12 installed upstream of the belt rotation. It is wound around the shaft. Further, a secondary transfer roller 16 is disposed so as to face the driving roller 13 through a belt. Further, a belt cleaning unit 15 is installed on the tension roller 11. The printer 100 also includes a power supply 17 that can output a secondary transfer bias and a cleaning bias, and a control unit (CPU) 18 that controls the output of the power supply 17. The power source 17 is connected to the driving roller 13, and the secondary transfer bias and the cleaning bias output from the power source 17 are applied to the driving roller 13.

  The inner surface resistance of the polyimide intermediate transfer belt 10 is 9th to 12th power Ω / sq, and the volume resistance is 8.5th to 13.5th power Ω · cm. The intermediate transfer belt 10 carries a toner image charged to a predetermined polarity and rotates in the direction of the arrow.

  In order to prevent interference between the primary transfer bias and the secondary transfer bias, the entrance roller 12 is grounded directly or via a resistor, and is electrically floated when it is not necessary. In this embodiment, it is directly grounded.

  A drive roller 13 that rotationally drives the intermediate transfer belt 10 by a drive motor (not shown) also serves as a repulsive roller to which a repulsive bias (secondary transfer bias) is applied. A cleaning bias is applied to the repulsive roller during non-transfer. This cleaning bias generates an electrostatic force between the secondary transfer roller 16 and the intermediate transfer belt 10. The toner adhering to the secondary transfer roller 16 is transferred from the secondary transfer roller 16 side to the intermediate transfer belt 10 side by electrostatic force and removed from the secondary transfer roller 16 (hereinafter, this removal operation is referred to as bias cleaning). Call). In place of the configuration shown in FIG. 2, bias cleaning may be performed by grounding the repulsive roller (drive roller 13) and connecting the power source to the secondary transfer roller 16.

  The secondary transfer roller 16 as a transfer member is made of a sponge material having a resistance of 7 to 8 Ω and may have a mechanism that can contact and separate from the intermediate transfer belt 10. When the repulsive roller applies a repulsive bias (secondary transfer bias) to the secondary transfer roller 16, the toner image primarily transferred onto the intermediate transfer belt 10 is transferred onto the sheet (secondary transfer). Further, even if the secondary transfer bias is applied to the secondary transfer roller 16 as an attractive bias, the same effect can be obtained, and in this case, the secondary transfer bias polarity is reversed. Instead of the secondary transfer roller 16, secondary transfer may be performed using a secondary transfer belt that is also a transfer member.

  In the present embodiment, the secondary transfer roller 16 does not have a mechanical cleaning mechanism (for example, a cleaning brush, a cleaning blade, and a cleaning web). However, even when a cleaning mechanism is provided, bias cleaning is effective.

  Toner and paper dust removed from the secondary transfer roller 16 by bias cleaning are carried by the intermediate transfer belt 10 and collected by the belt cleaning unit 15. Hereinafter, bias cleaning for the secondary transfer roller 16 will be described, and then the belt cleaning unit 15 will be described.

  FIG. 3 is a timing chart showing a typical sequence of secondary transfer bias control. The control unit (CPU) 18 controls the output of the power source 17, that is, the output of the secondary transfer bias and the cleaning bias. The control unit (CPU) 18 controls the polarity of the cleaning bias output from the power supply 17, the output time, the output magnitude, and the like. The horizontal axis represents time (msec) and the vertical axis represents bias (V), and the timing, output, and time for applying the bias are represented. Hereinafter, steps (1) to (6) in FIG. 3 will be described in order.

  First, steps (1) to (3) are bias cleaning before image transfer. Toner and paper dust are removed from the transfer roller by alternately switching the bias between the positive electrode and the negative electrode. A sequence such as (1) to (3) is called a cleaning sequence.

  In this embodiment, the positive polarity is set at the stages (1) and (3), and the negative polarity is set at the stage (2). For example, the number of times of applying the bias is increased, the polarity order is reversed, The absolute values at the stages 1) and (3) may be different. Further, in the stages (1) and (3), high voltage output control is performed by constant current control or constant voltage control, respectively. For example, in the stage (1), the first half is set to 15 μA and the second half is set to 10 μA. For example, the output may be changed. Further, in the example of FIG. 3, there is no waiting time for switching between positive and negative polarities, but a switching waiting time may be entered if necessary due to the specifications of the power supply.

  Generally, the cleaning sequence (1) to (3) is more effective as the number of repetitions is increased. However, since the number is increased before the image transfer, the first copy time is increased. For this reason, it is often carried out as much as possible within the minimum value of the first copy time determined by the layout and process line speed.

  Accordingly, the cleaning sequence (1) to (3) may not sufficiently remove the transfer roller. For this reason, conventionally, the cleaning time is increased when there is a lot of toner contamination (Patent Document 1), or the maximum cleaning is performed on the premise that the life of the photoreceptor can be secured (Patent Document 2). ing.

  Next, stage (4) represents transfer in the image area. In this embodiment, since negatively charged toner is used to transfer by repulsive force, (4) is negative. When the charging polarity, repulsive force, or attractive method of the toner changes, the polarity changes accordingly.

  As shown in FIG. 3, in the stage (4), the bias is raised at once after the application of the cleaning bias. However, for example, the output is divided into two stages and the first 100 msec is set to 50%, and after 100 msec has passed. Adjustments such as 100% output may be made. Further, the output may be changed only at the tip of the image portion.

  Next, stage (5) represents the bias state at the rear end of the image portion current. FIG. 3 shows the case where the absolute value of the transfer bias in the image portion is made smaller. The bias at the trailing edge is made small for the purpose of stabilizing the conveying behavior at the trailing edge of the paper, but conversely, it may be increased in order to eliminate “conveying dust” in which toner is scattered during conveyance. Further, the bias of the rear end and the image portion may be the same magnitude, and may also serve as the cleaning bias after the image transfer in the step (5).

  Finally, stage (6) represents the cleaning bias state after image transfer. At this stage, the bias is applied for the same time as before the print job at a positive polarity and smaller than before the image transfer, but this is not restrictive. What is necessary is just to select the most suitable one depending on the target to be cleaned and the system, and it may take a longer time than before the print job or the output may be high. A print job is a unit of work that applies a transfer bias during transfer in the transfer process.

  In general, in an image forming apparatus to which bias cleaning is applied, as described above, cleaning bias before a print job of (1) to (3), image portion bias of (4) to (5), and printing of (6) Consists of post-job cleaning bias. Furthermore, there is a bias between sheets (not shown) during continuous printing. As described above, the bias can be broadly classified into four types.

  By the way, it is difficult to remove the paper dust from the transfer roller with certainty in a normal cleaning sequence. Since bias cleaning does not change the primary purpose of toner removal, the output voltage is usually optimally matched to toner removal. Since the toner is originally charged and has a property of being charged, the toner can be controlled and removed by applying a bias.

  On the other hand, since paper dust does not have such properties, it is forcibly charged and eliminated. In order to do so, it is necessary to perform cleaning for a longer time than toner cleaning. That is, in order to remove paper dust, the cleaning sequence must be lengthened.

  However, as described above, the cleaning sequence before the print job is related to the first print time, and is usually determined from the layout and the process linear velocity. If the cleaning sequence is extended at the expense of this, the use of high quality paper with less paper dust undesirably reduces productivity. Conversely, the original purpose of removing paper dust and preventing problems caused by paper dust cannot be achieved only by the conventional cleaning sequence.

  Therefore, in this embodiment, the amount of paper dust emitted from the recording material is estimated, and when the paper dust is large, cleaning is performed after the print job or the cleaning time is extended. “Estimation of the amount of paper dust” refers to paper type setting, and the paper is classified into one of recycled paper, coated paper, and plain paper (non-coated paper that is not recycled paper).

  In general, recycled paper uses recycled pulp and thus has weak fibers, and often contains a large amount of calcium carbonate as a filler. Therefore, it is easy to drop paper dust when conveyed in an image forming apparatus. As an example of paper dust, the above-mentioned calcium carbonate is a typical example. Therefore, in the case of recycled paper, the amount of paper dust is basically large. On the other hand, in the case of coated paper, since the surface layer is coated, the filler of the paper rarely falls during conveyance, and the paper dust is very small. Plain paper is the middle of them.

  Therefore, in this embodiment, the cleaning sequence is changed by estimating the amount of paper dust based on whether the paper is classified into recycled paper, coated paper, or plain paper. As shown in FIG. 1, the printer 100 includes an operation panel 115. The operation panel 115 includes a selection unit for selecting the type of paper (recycled paper, coated paper, plain paper, etc.) used by the user. The user can select the type of paper stored in the paper feed cassette 20 (the type of paper to be used) by operating the operation panel 115. The control unit 18 of the printer 100 changes the cleaning bias based on the paper type selected by the user. Instead of selecting the paper type on the operation panel 115, the paper type may be selected on a computer connected to the printer 100 via a network. Also, detection means such as an optical sensor for detecting the type of paper is provided on the paper feed cassette 20 of the printer 100 and the paper conveyance path, and the control unit 18 controls the cleaning bias based on the type of paper detected by the detection means. It is good also as a structure which changes.

  The cleaning sequence when the paper type setting is changed will be specifically described below. As a basic control, when the paper type is plain paper, a sequence as shown in FIG. 3 is used. This is called a basic mode. On the other hand, in the case of recycled paper, a sequence as shown in FIG. In the case of coated paper, a sequence as shown in FIG.

  For comparison, FIG. 4A shows the (4) and subsequent steps in the basic mode. In the basic mode, a predetermined bias is applied in steps (5) and (6) as a process after the image portion is transferred. However, when recycled paper containing a large amount of paper dust is used (mode 1), FIG. As shown in (), a bias is applied in stages (5), (6), and (7). Thus, in mode 1, the number of cleanings after image transfer is increased in order to reliably remove paper dust from the transfer roller.

  On the other hand, when a coated paper with a small amount of paper dust is used (mode 2), as shown in FIG. 5, (6) stage bias is not applied. The reason why the application in the step (6) is not executed is to reduce the substantial downtime of the apparatus. For example, when a print job comes intermittently and the next job is executed after the image forming unit is lowered once (printing is completed), the time corresponding to step (6) can be shortened.

  As described above, according to the present embodiment, by changing the cleaning bias sequence after the transfer to the paper according to the paper type setting, the paper dust adhered to the transfer roller is controlled, and the downtime is minimized and the remaining toner is controlled. Can be removed. In addition, as the recording material, high quality paper, an OHP sheet, Kent paper, and the like are also used. If the paper type classification selectable by the user is set more finely based on brands and characteristic values, paper dust can be controlled more effectively.

  In this embodiment, the cleaning sequence after the print job has been described. However, the same effect can be obtained even if operations similar to these are changed before the print job. However, cleaning before the print job generally affects the first copy time, and even if it is too short, the time until the toner image reaches the transfer portion does not change anyway, so cleaning was performed after the print job. Is more convenient in terms of timing.

  FIG. 6 is a diagram specifically illustrating the configuration of the cleaning unit 15. In the cleaning unit 15, a paper dust removing brush 30 and a cleaning blade 31 are arranged from the upstream side in the running direction of the intermediate transfer belt 10, and a lubricant application brush 32 is further arranged downstream thereof. A coating bar 33 for the lubricant is in contact with the lubricant application brush 32.

  In the present embodiment, paper dust is collected on the intermediate transfer belt 10 together with toner, and scraped off with toner using the paper dust removing brush 30 of the belt cleaning unit 15. When paper dust is accumulated on the transfer roller, it leads to a discharge image, pressure fixation in the fixing unit, and the like, and therefore all is collected at the transfer unit.

  In the belt cleaning unit 15, the paper dust and most of the toner are first scraped off by the paper dust removing brush 30, and the toner remaining on the intermediate transfer belt 10 is scraped off by the cleaning blade 31. Basically, paper dust does not come to the cleaning blade 31, but even if it is removed without being scraped off by the paper dust removing brush 30, there is basically no problem because it is small. The main purpose of the lubricant application brush 32 is to apply the lubricant, but even if the paper powder passes through here, the lubricant application brush 32 also serves as a final recovery.

  As described above, in the present embodiment, the belt cleaning unit 15 has a member for removing paper dust and is configured to be safe. For this reason, all the paper dust can be collected by the belt cleaning unit 15.

(Second Embodiment)
FIG. 7 is a schematic diagram illustrating an image forming unit of the image forming apparatus according to the second embodiment. The present embodiment relates to a direct transfer method, and transfers a toner image on a photoreceptor directly to a sheet.

  The image forming unit in the direct transfer method is basically the same as the configuration of the image forming unit 2 for each color in the intermediate transfer method shown in FIG. 1, and executes an image forming process around the drum-shaped photoconductor 1. Necessary members are arranged. The photosensitive member 1 as an image carrier is negatively charged by a contact-type charging roller 41 which is a charging unit. Next, after the latent image is written by the exposure unit 42, a desired toner image is formed by the developing device 43. A positive bias is applied to the transfer roller 44 serving as a transfer member (attractive transfer method) to directly transfer the toner image on the photoconductor 1 onto a sheet, and then the photoconductor 1 is cleaned by a cleaning blade 31. In the first embodiment, the belt cleaning unit 15 has the paper dust removing brush 30 and the like, but in this embodiment, only the cleaning blade 31 is cleaned.

  Because of such a configuration, the present embodiment has a concept that paper dust is not transferred as much as possible to the side of the photoreceptor 1 that is an image carrier. When the paper dust is transferred to the photoconductor 1 side, a small amount can be removed. However, when the amount increases or a large particle size or an extremely small particle size moves to the photoconductor 1 side, paper dust is caught between the cleaning blade 31 and the photoconductor 1. Cause poor cleaning. As a result, the residual toner stains the charging roller 41 and streaks of poor charging occur on the image. Further, residual toner also appears on the image.

  Therefore, in the present embodiment, the paper dust is held on the transfer roller 44 and is dropped by gravity on the paper dust collection box 46 disposed below during rotation or attached to the next paper (not shown). They are collected by the fixing unit.

  FIG. 8 is a basic mode cleaning sequence in the present embodiment. Since it is an attractive transfer system, positive and negative polarities are opposite to those of the first embodiment, but the purpose of applying the biases (1) to (6) is the same. In addition, the basic mode is used when plain paper is selected as the paper type, as in the first embodiment.

On the other hand, the case where recycled paper or coated paper is selected as the paper type is greatly different from that of the first embodiment.
When recycled paper is selected as the paper type, as described above, paper dust adheres to the transfer roller 44 more than other paper types. In this embodiment, since it is not desired to transfer the paper dust to the photoreceptor 1, bias cleaning cannot be performed. Therefore, the “mode 2” shown in FIG. 9C is selected.

  On the other hand, when coated paper that does not easily generate paper dust is used, the presence or absence of cleaning is free from the viewpoint of paper dust, so the basic mode is left as it is, or “mode 1” shown in FIG. Can be used. Whether the coated paper is set to the basic mode or the mode 1 is a difference in how much toner contamination of the transfer roller 44 is removed. Naturally, the longer the cleaning is performed, the more the substantial downtime increases. Therefore, the basic mode may be applied as long as the system does not stain the toner.

  In this embodiment, in the case of coated paper, Mode 1 is used in consideration of the fact that even a slight back stain is visible. In addition, because of such circumstances, even when coated paper is used, the mode is switched according to the temperature / humidity environment, the total number of printed sheets of the apparatus, the travel distance of the transfer roller 44, the travel distance of the developing device 43, and the like. Depending on the mode, the mode is switched. As a result, it is possible to further reduce the abnormality due to the back dirt and the downtime of the apparatus.

As described above, the present embodiment is common in that the cleaning sequence is switched depending on the paper type, as in the first embodiment, but the mode selection method is different. Table 1 shows these basic concepts.

  However, since Table 1 represents a general theory, it is not always necessary to take such measures, and it is important to switch to a cleaning sequence that is considered to be optimal according to the type of paper.

(Third embodiment)
This embodiment is based on the first embodiment and further adds functions. That is, in addition to switching by paper type, the cleaning sequence is switched by determining whether to perform single-sided printing or double-sided printing with that paper type.

  Normally, when the same size paper is continuously passed by single-sided printing, the distance between the nth paper and the (n + 1) th paper is always printed at a constant interval. For example, when A4 paper is passed through LEF (Long Edge Feed), if the paper passage length is 210 mm and the paper gap is 50 mm, as shown in FIG. Proceed between the paper.

  On the other hand, in the case of double-sided printing, the paper interval changes depending on the time until it is reversed and returned, so it is not always possible to print at regular intervals as in single-sided printing. In many cases, as shown in FIG. 11 (b), the gap between the sheets becomes larger in the case of duplex printing. For this reason, the roller contamination due to the ground toner between the sheets increases in the case of double-sided printing.

基本モード、モード１、モード２は、図４、図５に示した各モードである。 In consideration of the above, there is also a method of making the gap between papers constant regardless of one side or both sides by creating a conveyance distance and a process linear velocity. In this case, there is no difference between the single-sided printing and the double-sided printing on the roller dirt caused by the ground dirt toner. However, the amount of paper dust generated differs depending on whether single-sided printing or double-sided printing. The cause of the generation of paper dust is that the paper filler can be removed during the conveyance, but it often occurs especially when the paper surface is rubbed by a roller or the like used for conveyance. In double-sided printing, the heated paper after toner fixing passes through the reversing unit and again passes through the paper feeding resist unit, so that the amount of paper dust is larger than that in single-sided printing. Therefore, in the case of the intermediate transfer system, it is preferable to lengthen the cleaning sequence for recycled paper and to lengthen the cleaning sequence even for plain paper in the case of duplex printing. Therefore, in the present embodiment, according to the selection table in Table 2, the cleaning mode is controlled not only depending on the paper type but also on the simplex printing or the duplex printing.

The basic mode, mode 1 and mode 2 are the modes shown in FIGS.

  In the present embodiment, single-sided printing and double-sided printing may be compatible with various paper sizes (for example, A3SEF / A4LEF / A4SEF / DLTSEF / LTSEF / LLTLEF / LegalSEF / LegalLEF), and the space between papers is not necessarily It does not match. For this reason, the basic mode is changed to double-sided printing on coated paper, including the handling of background stains. For this reason, the malfunction by the paper dust generation | occurrence | production at the time of double-sided printing can be reduced. In this example as well, the concept of the background toner is the same as that in the first embodiment, and it is preferable to design the image taking into account downtime according to necessity.

(Fourth embodiment)
The amount of paper dust that enters the transfer member increases as the length of the paper increases. When a large number of sheets are printed in a single print job, the amount of paper dust that enters the transfer member naturally increases. Also, when passing a lot of narrow paper, paper dust concentrates only on a specific area of the transfer member, so even if bias cleaning is performed, paper dust is evenly adhered to the entire area. There is a problem that it becomes difficult to remove. This is presumed to be because the ease of current flow and the ease of discharge change when a bias is applied between a portion with and without paper dust.

基本モード、モード１、モード２は図４、図５に示した各モードである。「モード１×２回」は、モード１のクリーニングシーケンスを実行した後に、再度モード１のシーケンスを実行することを意味する。 In this embodiment, paper dust is controlled by changing the cleaning sequence according to the paper size (paper length and width) and the job size (number of printed sheets) based on the first embodiment. The paper length is a dimension in the paper transport direction, and the paper width is a dimension in a direction orthogonal to the paper transport direction. Table 3 shows the cleaning mode for each condition.

Basic mode, mode 1 and mode 2 are the modes shown in FIGS. “Mode 1 × 2 times” means that after the mode 1 cleaning sequence is executed, the mode 1 sequence is executed again.

  As can be seen from Table 3, when the amount of paper dust is large or difficult to remove, a long sequence is selected or the cleaning sequence is repeated.

  In consideration of the fact that it is difficult to remove paper dust when the paper width is smaller, in this embodiment, paper dust is controlled by extending bias cleaning for narrow paper. It may change depending on the resistance. Since the amount of paper dust and ease of removal vary depending on the paper size and job size, it is desirable to control the paper dust by switching the cleaning sequence to an appropriate one for each system due to these factors, and more effectively The powder can be controlled.

(Fifth embodiment)
In the present embodiment, the effect is enhanced by changing the sequence of each mode based on the first to fourth embodiments. In this embodiment, not only the bias application time per change, but also the sequence and paper dust that can effectively remove paper dust by changing the cleaning ability by changing the size and number of output biases. A sequence is generated in which only toner can be removed without removal. As a result, the paper dust is reliably controlled and the toner is removed to the maximum. The application time per bias is the time from when the bias is applied until the polarity is switched or the bias is turned off.

  11 to 15 are time charts showing specific basic modifications. In FIG. 11, the mode 3 in FIG. 11B increases the output bias and the mode 4 in FIG. 11C decreases the output bias with respect to the basic mode (FIG. 11A). is there. Mode 5 in FIG. 12A is a pattern in which the cleaning bias after the job is monotonically increased in a stepwise manner, and mode 6 in FIG. 12B is a pattern in which the cleaning bias after the job is monotonously decreased in a stepwise manner. is there.

  These are modifications of mode 3 or 4, and which is effective depends on the image forming system (particularly toner characteristics), and is selected according to each system. An example will be described.

  For example, when it is desired to remove the toner adhering to the transfer member, if a large bias is applied to the weakly charged toner, discharge may start and the toner cannot be removed. Therefore, in mode 5, the toner is removed in a wide range of charge amount by applying a bias with a small stepwise increase. This is often not so high as paper dust removal capability.

  On the other hand, in mode 6, after a large bias is discharged first to discharge the toner, the toner is removed by gradually applying a small bias. This assumes a case where the non-electrostatic adhesive force is larger and the weakly charged toner is discharged first when the bias is raised to move by the electrostatic force.

  According to the inventor's experiment, mode 6 is more effective for paper dust that is not charged originally, so these are selected based on the tendency of each system to remove toner and the idea of control of paper dust. do it.

  In mode 7 in FIG. 13, only the absolute value of positive polarity in bias cleaning after a job is increased for negatively charged toner. Such a mode is effective when it is assumed that there is a relatively large amount of reversely charged toner that causes roller contamination, and the distribution of the charge amount is widened. For the control of paper dust, the effect can be enhanced by adjusting the absolute value.

  FIG. 14 shows a mode in which only the absolute value of the negative polarity in post-job bias cleaning is increased for negatively charged toner. In mode 8 of FIG. 14A, only the absolute value of the negative polarity bias is increased, but is smaller than the transfer bias for the image portion. This is effective when it is assumed that there is a relatively large amount of reversely charged toner that causes roller contamination, and the distribution of the charge amount is widened. The control of paper dust also increases slightly by increasing the bias and discharging.

  In mode 9 in FIG. 14B, only the absolute value of the negative polarity bias is increased to be equal to or greater than the transfer bias for the image portion. It is effective only for paper dust that cannot be removed with a normal bias, and is usually not used much. For example, in a system in which paper dust is to be removed, it is effective to use periodic maintenance once every several thousand sheets or change to this special sequence when activated after a long stop.

  In mode 10 in FIG. 15A, absolute values of a plurality of buy ices are set at random in post-job bias cleaning. As in the case of mode 9, the effect can be obtained when executed on paper dust that is difficult to remove with a normal bias. In the mode 11 of FIG. 15B, the absolute value of the plurality of biases in the post-job bias cleaning is changed within the same polarity. This mode can be said to be a simplified version of modes 3 to 6, and is a mode that aims at both a reduction in cleaning time and a high effect of controlling paper dust by reducing the number of times of polarity switching.

  Although specific examples of sequences have been described above, it is effective to perform specific output value adjustments and mode selections according to the system of the image forming apparatus, and the modes described so far are combined. The thing is the same. Moreover, also about paper dust, it is good to adjust a removal mode or a holding | maintenance mode according to the paper dust with the assumed commercial paper. For example, common paper fillers include calcium carbonate, talc, kaolin, and titanium oxide, which often fall into paper dust when they fall off the paper, but these are mainly controlled by removing them. It is good to change.

(Effect confirmation)
In order to correspond to the first to third embodiments, 20,000 double-sided sheets are passed for each paper type to the intermediate transfer type apparatus and the direct transfer type apparatus capable of double-sided printing, and problems caused by paper dust at that time The toner stain was evaluated. In addition, as a conventional example to be compared, evaluation was performed for a total of six types of combinations of two types of transfer system configurations and three types of cleaning bias conditions. Specifically, for the intermediate transfer type and the direct transfer type, three types of sequences were prepared: a case where the cleaning count was always small, a case where the cleaning count was always high, and a case where the standard count was always set.

  Note that when the number of cleanings is small and the number of cleanings is large, the number of times of cleaning is matched with the three bias application conditions in the first and second embodiments, respectively. Originally, the first and second embodiments are intended to control more and less than usual because of the control for each paper type, so the confirmation of the effect of this time is the degree of the effect that can be ensured to the minimum Yes, the original ability is even higher. Only when performing double-sided printing, the cleaning may be performed further than the conventional example where there is much cleaning.

Tables 4 and 5 are tables showing the evaluation results.

  “Abnormal paper dust” indicates that paper dust adheres to the fixing unit in the intermediate transfer type. Further, in the direct transfer type, black stripes appearing on the surface of the paper due to chipping of the drum cleaning blade due to paper dust wrapping around the photoreceptor or contamination of the charging member are shown. The “edge surface contamination” is a phenomenon in which the secondary transfer roller becomes soiled with a background toner or the like, and the contamination is noticeable particularly when the paper is bundled by picking up the paper from the edge of the paper. “CL” is an abbreviation for cleaning.

  In the item of abnormal paper dust in Table 4, “◯” indicates that there is no sticking matter on the pressure roller, and “△” indicates that sticking matter is observed on the pressure roller, but there is a problem with image and conveyance. Indicates that it does not occur. In addition, “x” indicates that the degree of fixation to the pressure roller is poor, and an image defect such as a white spot occurs on the image due to the fixed substance, or a conveyance defect such as a paper jam or a corner fold occurs. It shows that In addition, in the item of edge contamination, “○” indicates that there is no contamination, “△” indicates that it is not of concern, and “×” indicates that there is contamination, both of which are visually confirmed results. .

  In the item of abnormal paper dust in Table 5, “◯” indicates that paper dust is not confirmed at the edge of the cleaning blade after passing paper, and no image abnormality occurs, and “△” indicates the edge of the cleaning blade. Paper dust is observed in the area, but no image abnormality has occurred. “X” indicates that a screen abnormality such as a black streak occurs in the image. In addition, in the item of edge contamination, “○” indicates that there is no contamination, “△” indicates that it is not of concern, and “×” indicates that there is contamination, both of which are visually confirmed results. .

  In the intermediate transfer type, the first embodiment has the same ability as the case where the cleaning of the conventional example is always large, and some abnormality occurs when the number of times of cleaning is standard or small. This is because in an intermediate transfer type in which paper dust is to be removed, it is desirable to remove both toner and paper dust, and more cleaning is better for removal.

  However, when the number of times of cleaning is always large in the conventional machine, the downtime increases naturally without depending on the paper type, whereas in the first embodiment, the number of times of cleaning is smaller in the plain paper / coated paper than in the conventional example. Productivity is high. Therefore, in the first embodiment, it was confirmed that paper dust could be controlled while maintaining high productivity.

  The double-sided printing of the third embodiment has a higher capability than these because of the bias extension during double-sided printing. On the other hand, in the direct transfer type, since the optimum bias for each paper type changes with each paper type, only the second embodiment can maintain all the qualities at a high level.

  From the above experimental results, the usefulness of the disclosed technology could be confirmed.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Image forming unit 4 Primary transfer roller 10 Intermediate transfer belt 11 Tension roller 12 Input roller 13 Drive roller 15 Belt cleaning unit 16 Secondary transfer roller 17 Power supply 18 Control part (CPU)
DESCRIPTION OF SYMBOLS 20 Paper feed cassette 21 Paper feed roller 22 Registration roller 23 Fixing device 24 Paper discharge roller 25 Paper discharge tray 30 Paper dust removal brush 31 Cleaning blade 32 Lubricant application brush 33 Coating bar 41 Charging roller 42 Exposure part 43 Developer 44 Transfer roller 46 Paper dust collection box 100 Full color printer 110 Main body 115 Operation panel 120 Image forming unit 130 Paper feed unit 140 Paper discharge unit
S paper

JP 2006-058349 A Japanese Patent No. 3279523 JP 2012-42641 A

Claims (9)

An image carrier for carrying a toner image;
A transfer member that forms a transfer nip with the image carrier;
A power supply capable of outputting a transfer bias for transferring a toner image on the image carrier to a recording material at the transfer nip and a cleaning bias for cleaning the transfer member before or after a print job;
A control unit for controlling the power source,
The image forming apparatus, wherein the control unit changes the cleaning bias according to a type of a recording material.   The image forming apparatus according to claim 1, wherein the control unit changes the cleaning bias according to a length or a width of a recording material.   The image forming apparatus according to claim 1, wherein the control unit changes the cleaning bias according to the number of printed sheets of the print job.   The image forming apparatus according to claim 1, wherein the control unit changes the cleaning bias depending on whether the print job is single-sided printing or double-sided printing. The cleaning bias consists of alternately switching a bias having the same polarity as the transfer bias and a bias having a reverse polarity,
5. The control unit according to claim 1, wherein the control unit changes an output time per one time of at least one of the bias having the same polarity and the bias having the opposite polarity according to a type of the recording material. The image forming apparatus according to one item. The cleaning bias consists of alternately switching a bias having the same polarity as the transfer bias and a bias having a reverse polarity,
5. The image forming apparatus according to claim 1, wherein the control unit changes the number of outputs of the bias of the same polarity and the bias of the reverse polarity according to a type of the recording material. . The cleaning bias consists of alternately switching a bias having the same polarity as the transfer bias and a bias having a reverse polarity,
5. The control unit according to claim 1, wherein the control unit changes an absolute value of at least one of the bias having the same polarity and the bias having the opposite polarity according to a type of the recording material. Image forming apparatus. The cleaning bias consists of alternately switching a bias having the same polarity as the transfer bias and a bias having a reverse polarity,
The image forming apparatus according to claim 1, wherein at least one of the same-polarity bias and the reverse-polarity bias includes a plurality of biases having different absolute values.   The image forming apparatus according to claim 8, wherein the control unit controls the power supply so that the plurality of biases are continuously applied without switching the polarity of the bias.

Images