JP5949464B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, the present invention relates to an image forming apparatus in which a by-product generated in a fixing device that fixes a toner image on a sheet by applying pressure while heating is reduced.

  Conventionally, in an image forming apparatus such as a copier, printer, facsimile, or a multi-function machine having a combination of these functions, an image is formed on a sheet by fixing the toner image transferred on the sheet with a fixing device. doing. The fixing device performs a fixing process by passing a sheet through a fixing nip formed by press-contacting a pair of fixing members and applying pressure while heating the passing sheet.

  The fixing member includes a cylindrical roller, an endless belt member, and the like. These rollers and belt members generally have an elastic layer that covers the surface of the substrate and a surface layer that covers the surface of the elastic layer.

  In recent years, it is known that such a fixing device generates ultra fine particles (UFP) during the fixing process. Specifically, it is considered that UFP is generated from a silicone material constituting the elastic layer of the fixing member or a toner that melts by heating during the fixing process. On the other hand, for example, Patent Document 1 discloses a technique for collecting UFP generated from the vicinity of the fixing device. In Patent Document 1, a filter provided in a duct for exhausting the fixing device is impregnated with silicone oil. According to Patent Document 1, UFP generated from the fixing device can be efficiently recovered by the filter impregnated with the silicone oil.

JP 2012-32663 A

  By the way, like the above-mentioned prior art, in order to collect the UFP, a configuration such as a fan or a filter for that purpose is required. That is, there is a problem that the image forming apparatus becomes expensive because of the configuration for collecting UFP. In addition, it is difficult to completely recover all the generated UFP. For this reason, it is preferable to reduce the generation amount of UFP itself.

  Here, the amount of UFP generated can be reduced by lowering the fixing processing temperature of the fixing device. This is because the amount of UFP generated generally increases as the temperature of the fixing device increases. Further, when the fixing temperature is lowered, the passing speed of the sheet at the fixing nip is slowed down. If the fixing temperature is lowered without slowing the passing speed of the sheet at the fixing nip, the toner transferred onto the sheet cannot be heated sufficiently, resulting in poor fixing of the toner image to the sheet. It is.

  The amount of UFP generated per unit time is also reduced by slowing the sheet passing speed at the fixing nip. This is because the amount of toner melted by heating per unit time is reduced. Therefore, the amount of UFP generated can be reduced by lowering the fixing temperature and slowing the sheet passing speed at the fixing nip. However, when such control for suppressing UFP is performed, productivity of image formation is lowered by slowing the sheet passing speed at the fixing nip. For this reason, it is preferable that the control for suppressing UFP is not performed as much as possible from the viewpoint of productivity of image formation.

  The present invention has been made for the purpose of solving the problems of the prior art described above. That is, an object of the present invention is to provide an image forming apparatus capable of suppressing the generation amount of UFP while maintaining high image forming productivity.

  The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, fixes a toner image on a sheet by a fixing process in which the sheet carrying unfixed toner is passed and the sheet is pressurized and heated. The device, the normal mode in which images are formed without taking measures to suppress the amount of ultrafine particles generated in the machine, and the measures to suppress the amount of ultrafine particles generated in the machine to a predetermined upper limit value or less. An image forming apparatus having an apparatus control unit that switches to an ultrafine particle suppression mode for forming an image, and controls a fixing temperature control unit that controls a temperature of the fixing device and a sheet passing speed in the fixing device A passing speed control unit, a generation amount state value output unit that outputs a generation amount state value that affects the generation amount of ultrafine particles due to image formation in the image forming apparatus, and an amount of continuous image formation. A mode that outputs a continuous printing status value output unit that outputs a continuous printing status value and a mode switching value that is a threshold for the continuous printing status value for mode switching in the device control unit according to the generated amount status value The generation amount state value output unit outputs a higher generation amount state value when the amount of generated ultrafine particles is larger. The apparatus control unit outputs the generation amount state during image formation. The generation amount status value is acquired from the value output unit, the mode switching value is acquired and determined from the mode switching value output unit based on the acquired generation amount state value, and the continuous printing state value acquired from the continuous printing state value output unit is determined. If it is less than or equal to the mode switching value, the image is formed in the normal mode, and if the continuous printing state value acquired from the continuous printing state value output unit exceeds the set mode switching value, the ultrafine particle suppression mode Form an image with When forming an image in the ultrafine particle suppression mode, the fixing temperature control unit sets the temperature of the fixing device to a temperature lower than that in the normal mode, and the passing speed control unit sets the sheet passing speed in the fixing device to normal. An image forming apparatus characterized in that the passing speed is slower than that of the mode.

  The image forming apparatus of the present invention can perform image formation by switching between the normal mode and the ultrafine particle suppression mode by the apparatus control unit. In the image forming apparatus of the present invention, at the start of image formation, the mode switching value is obtained from the mode switching value output unit based on the generated amount state value and determined. Then, image formation is performed in the normal mode until the continuous printing state value reaches the set mode switching value.

  In the ultrafine particle suppression mode, the sheet passing speed in the fixing device is set slower than in the normal mode. For this reason, in the ultrafine particle suppression mode, the productivity of image formation is lower than in the normal mode. Here, the mode switching value output unit outputs the mode switching value according to the generated amount state value. The generation amount state value output unit outputs a higher generation amount state value as the amount of generated ultrafine particles increases. That is, the generation amount state value output unit outputs a generation amount state value corresponding to the generation amount of ultrafine particles. For this reason, for example, if the amount of ultrafine particles generated is small, the mode switching value can be set to a high value. Therefore, an image can be formed in the normal mode until the continuous printing state value becomes as high as possible. Thereby, the productivity of image formation can be kept high.

  Further, in continuous printing in which images are continuously formed on a plurality of sheets, image formation after the continuous printing state value exceeds the set mode switching value is performed in the ultrafine particle suppression mode. The ultrafine particle suppression mode is a control mode in which measures are taken to suppress the generation amount of ultrafine particles below a predetermined upper limit value. Therefore, the generation amount of ultrafine particles can be suppressed to the upper limit value or less.

  Further, in the image forming apparatus described above, the generation amount state value output unit indicates the amount of standby time elapsed from the completion of the previous image formation until the start of image formation by the apparatus control unit. It is preferable to output it as a state value. The inventors of the present invention have found that the amount of ultrafine particles generated in the subsequent image formation varies depending on the waiting time. That is, it has been found that the longer the waiting time, the larger the amount of ultrafine particles generated in the image formation started thereafter. For this reason, the mode switching value output unit outputs a lower mode switching value as the standby time is longer, that is, as the generation amount state value is higher. Therefore, an optimum mode switching value can be determined for the amount of ultrafine particles generated depending on the standby time, and the amount of ultrafine particles generated can be suppressed below the upper limit value while maintaining high image forming productivity.

  Further, in the image forming apparatus described above, the continuous printing state value output unit calculates the cumulative number of sheets on which image formation has been performed continuously from the start of image formation by the apparatus control unit. It may be output as a value. This is because the cumulative number of sheets related to continuous printing can be used as a value indicating a state value related to continuous printing.

  Further, the continuous printing state value output unit may output an elapsed time during which image formation is continuously performed from when the image forming is started by the apparatus control unit as a continuous printing state value. The longer an image is formed on many sheets, the longer it takes. That is, the continuous printing time becomes longer as the cumulative number of sheets related to the continuous printing increases. For this reason, the continuous printing time can also be used as a value indicating a state value related to continuous printing.

  In the image forming apparatus described above, it is preferable that the apparatus control unit determines the upper limit value by an input from a user. The higher the upper limit of the amount of ultrafine particles generated, the higher the productivity of image formation. However, the image forming apparatus may be installed in an environment where ventilation cannot be performed, for example. In such a case, some users may want to reduce the generation amount of ultrafine particles even if the productivity of image formation is reduced. Therefore, it is preferable that the upper limit of the amount of ultrafine particles generated can be set by the user.

  In the image forming apparatus described above, it is preferable that the apparatus control unit sets the mode switching value to be lower as the environmental temperature is lower. The lower the ambient temperature, the more the fixing device must be heated. This is because the temperature of the fixing device is set to an appropriate temperature for fixing the toner image to the sheet. This is because the amount of ultrafine particles tends to increase as the fixing device is heated.

  Further, in the image forming apparatus described above, the apparatus control unit may set the mode switching value to be lower as the type of the sheet having a smaller amount of heat taken from the fixing apparatus when the sheet passes through the fixing apparatus. preferable. For example, when the sheet is thin, the sheet takes less heat than the fixing device when passing through the fixing device. For this reason, when continuous printing is performed using a thin sheet, the temperature of the fixing device tends to rise more than when a thick sheet is used. This is because the amount of ultrafine particles tends to increase as the temperature rises.

  In the image forming apparatus described above, it is preferable that the apparatus control unit sets the mode switching value to be lower as the length in the direction perpendicular to the sheet passing direction to the fixing apparatus is shorter. The length of the sheet passing area provided in the direction orthogonal to the sheet passing direction of the fixing device is set to the maximum size of the sheet corresponding to the image forming apparatus. For this reason, for example, when an image is formed on an A4 size sheet by an image forming apparatus corresponding to the A2 size, the sheet passing area of the fixing device has a portion not in contact with the sheet. In the portion that does not come into contact with the sheet, the amount of heat taken away by the passing sheet is small, so the temperature tends to rise. This is because the amount of generated ultrafine particles tends to increase in the portion where the temperature has risen, compared to the other paper passing regions.

  In the image forming apparatus described above, it is preferable that the apparatus control unit sets the mode switching value to be lower as the coverage, which is the ratio of the area of the toner image to the area of the sheet related to image formation, is higher. . The higher the coverage for image formation, the greater the amount of toner melted by heating per unit time. Therefore, the higher the coverage for image formation, the greater the amount of ultrafine particles generated.

  Further, the image forming apparatus described above has a plurality of image forming units that form toner images, and the apparatus control unit uses one image forming unit when image forming is performed by a plurality of image forming units. It is preferable that the mode switching value is set lower than when image formation is performed. For example, when a color image is formed by fixing a multi-layered toner image on a sheet by a plurality of image forming units that form toner images of respective colors, a single-layer toner image is fixed on the sheet by one image forming unit. Thus, the fixing temperature may be set higher than when a monochrome image is formed. This is to fix a multilayer toner image in which the toner images of the respective colors overlap. This is because the amount of ultrafine particles tends to increase due to the high temperature of the fixing device.

  In the image forming apparatus described above, the apparatus control unit sets the mode switching value lower when forming a glossy image than when forming an image that is not a glossy image, and the normal speed is controlled by the passage speed control unit. The passing speed of the sheet in either the mode or the ultrafine particle suppression mode in the fixing device is preferably set to be a slower passing speed than that in the case of forming a non-glossy image. When forming a glossy image, the sheet passing speed in the fixing device is set slower than when forming a non-glossy image. This is for uniformly melting the toner. By reducing the sheet passing speed in the fixing device, the amount of heat per unit time taken by the sheet from the fixing device is reduced. This is because the temperature of the fixing device is likely to rise, and the amount of ultrafine particles generated tends to increase.

  According to the present invention, there is provided an image forming apparatus capable of reducing the amount of UFP generated while maintaining high image forming productivity.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. 2 is a schematic diagram of a control configuration of the image forming apparatus according to the present embodiment. FIG. 1 is a schematic configuration diagram of a fixing device of an image forming apparatus according to the present embodiment. It is the graph which showed transition of the incidence rate of UFP when continuous printing is performed in the normal mode. It is the graph which showed transition of the incidence rate of UFP when performing continuous printing in normal mode for every waiting time. It is a threshold value table by the relationship between waiting time and the number of mode switching. 4 is a flowchart illustrating an image forming procedure in the image forming apparatus according to the present embodiment. It is a threshold value table by the relationship between waiting time and mode switching time. It is a correction table which shows the correction coefficient by environmental temperature.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is embodied in an electrophotographic printer.

  FIG. 1 shows a schematic configuration of an image forming apparatus 1 of the present embodiment. The image forming apparatus 1 is a so-called tandem color printer having an intermediate transfer belt 30. The intermediate transfer belt 30 is an endless belt member having conductivity, and both ends in FIG. 1 are supported by rollers 31 and 32. At the time of image formation, the roller 31 on the right side in FIG. 1 is driven to rotate counterclockwise. As a result, the intermediate transfer belt 30 and the roller 32 on the left side in FIG. 1 are each driven to rotate in the direction indicated by the arrow in the drawing.

  A secondary transfer roller 40 is provided on the outer peripheral surface of the portion of the intermediate transfer belt 30 supported by the right roller 31 in FIG. The secondary transfer roller 40 is pressed against the intermediate transfer belt 30 in a direction perpendicular to the axis (leftward in FIG. 1). A transfer nip N1 for transferring the toner image on the intermediate transfer belt 30 onto the paper P is formed at a portion where the intermediate transfer belt 30 and the secondary transfer roller 40 are in contact with each other. At the time of image formation, the secondary transfer roller 40 is driven to rotate by a frictional force generated by pressure contact with the rotating intermediate transfer belt 30.

  Also, a belt cleaner 41 is provided on the outer peripheral surface of the portion of the intermediate transfer belt 30 supported by the left roller 32 in FIG. The belt cleaner 41 is in pressure contact with the outer peripheral surface of the intermediate transfer belt 30. Further, a recovery area 42 for recovering transfer residual toner and the like that has not been transferred to the paper P in the transfer nip N1 is formed by a portion that is in contact with the pressure contact.

  In the lower part of the intermediate transfer belt 30 in FIG. 1, the image forming units 10Y, 10M, 10C for yellow (Y), magenta (M), cyan (C), and black (K) are sequentially arranged from left to right. 10K is arranged. Each of the image forming units 10Y, 10M, 10C, and 10K is for forming a toner image of the corresponding color and transferring it onto the intermediate transfer belt 30. The image forming units 10Y, 10M, 10C, and 10K all have the same configuration. For this reason, in FIG. 1, the image forming unit 10 </ b> Y is represented by a reference numeral.

  Each of the image forming units 10Y, 10M, 10C, and 10K includes a photosensitive member 11 that is a cylindrical electrostatic latent image carrier, and a charger 12, a developing device 14, and a photosensitive member cleaner 16 disposed around the photosensitive member. doing. A primary transfer roller 15 is disposed at a position facing the photoconductor 11 with the intermediate transfer belt 30 therebetween. Further, an exposure device 13 is disposed below the image forming units 10Y, 10M, 10C, and 10K for each color in FIG. The charger 12 is for uniformly charging the surface of the photoconductor 11. The exposure device 13 is for irradiating the surface of each photoconductor 11 with laser light based on image data to form an electrostatic latent image. The developing device 14 is for applying the contained toner to the surface of the photoreceptor 11.

  The primary transfer roller 15 is pressed against the intermediate transfer belt 30 in a direction perpendicular to the axis (downward in FIG. 1). As a result of this pressure contact, a primary transfer nip for transferring the toner image on the photoreceptor 11 of each color onto the intermediate transfer belt 30 is formed at the portion where the intermediate transfer belt 30 and each photoreceptor 11 are in contact with each other. Yes. The photoconductor cleaner 16 is for collecting toner that has not been transferred from the photoconductor 11 to the intermediate transfer belt 30.

  Although FIG. 1 shows a roller charging type charging device 12 having a roller shape, the present invention is not limited to this. A corona discharge charging charger, a blade charging member, a brush charging member, or the like may be used. Further, although the photosensitive member cleaner 16 is a plate and has one end portion in contact with the outer peripheral surface of the photosensitive member 11, the present invention is not limited to this. Other cleaning members, for example, a fixed brush, a rotating brush, a roller, or a combination of a plurality of them can be used. Alternatively, if a cleaner-less system in which the untransferred toner on the photoconductor 11 is collected by the developing device 14, the photoconductor cleaner 16 is not necessary.

  Further, hoppers 17Y, 17M, 17C, and 17K that store toners of the respective colors are disposed above the intermediate transfer belt 30 in FIG. The toner of each color accommodated in these is appropriately replenished to the developing device 14 of the corresponding color.

  A density sensor for detecting the image density of the toner image transferred onto the intermediate transfer belt 30 is located downstream of the image forming unit 10K in the rotation direction of the intermediate transfer belt 30 and upstream of the transfer nip N1. 20 is provided. The density sensor 20 uses the outer peripheral surface of the intermediate transfer belt 30 as a detection position. The density sensor 20 includes, for example, a light projecting unit that irradiates light toward a detection position and a light receiving unit that receives the reflected light, which are used for adjusting the image density.

  A detachable paper feed cassette 51 is mounted at the bottom of the image forming apparatus 1. A conveyance path 50 is provided above the right side in FIG. Then, the sheets P stored in the sheet feeding cassette 51 by stacking are sent out one by one from the uppermost one to the conveying path 50 by the sheet feeding roller 52. A pair of registration rollers 53, a transfer nip N 1, a fixing device 100, and a paper discharge roller 54 are arranged in this order on the conveyance path 50 of the paper P sent out by the paper feed roller 52. A paper discharge unit 55 is provided on the upper surface of the image forming apparatus 1 further downstream of the transport path 50. The registration roller 53 is for adjusting the timing of feeding the paper P to the transfer nip N1. The fixing device 100 is for fixing the toner image transferred to the paper P by heating and pressurizing the paper P in the fixing nip N2.

Next, an example of a normal image forming operation by the image forming apparatus 1 of this embodiment will be briefly described. The following description is an example of an image forming operation when a color image is formed on the paper P stored in the paper feed cassette 51 using four colors of toner. The procedure of the image forming operation is the same in both the normal mode and the UFP suppression mode described later.

  When a normal color image is formed, first, the intermediate transfer belt 30 and each color photoconductor 11 are rotated at a predetermined peripheral speed in a direction indicated by an arrow in FIG. The outer peripheral surface of the photoconductor 11 is charged almost uniformly by the charger 12. Light corresponding to the image data is projected onto the outer peripheral surface of the charged photoconductor 11 by the exposure device 13 to form an electrostatic latent image. Subsequently, the electrostatic latent image is developed by the developing device 14 and a toner image is formed on the photoreceptor 11.

  The toner image formed on each photoconductor 11 is transferred (primary transfer) onto the intermediate transfer belt 30 by the primary transfer roller 15. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30 in this order. Then, the superimposed four color toner images are conveyed to the transfer nip N <b> 1 by the rotation of the intermediate transfer belt 30. Further, the transfer residual toner that is not transferred to the intermediate transfer belt 30 and remains on the photoconductor 11 after passing the primary transfer roller 15 is scraped off by the photoconductor cleaner 16 and removed from the photoconductor 11. Is done.

On the other hand, the paper P stored in the paper feed cassette 51 is pulled out one by one from the uppermost one to the transport path 50. The drawn paper P is transported along the transport path 50 to the transfer nip N1. The entry timing of the paper P into the transfer nip N1 is adjusted by the registration roller 53 so as to coincide with the entry timing of the toner image on the intermediate transfer belt 30 into the transfer nip N1. As a result, the superimposed four color toner images are transferred (secondary transfer) onto the paper P in the transfer nip N1.

  The paper P on which the toner image has been transferred is further conveyed downstream of the conveyance path 50. That is, the paper P is discharged to the paper discharge unit 55 by the paper discharge roller 54 after the toner image is fixed by the fixing device 100. Note that the transfer residual toner remaining on the intermediate transfer belt 30 even after passing through the transfer nip N1 is collected by the belt cleaner 41 in the collection area 42. As a result, the intermediate transfer belt 30 is removed.

  FIG. 2 shows an outline of the control configuration of the image forming apparatus 1. The image forming apparatus 1 includes an apparatus control unit 60, a system speed control unit 70, a fixing temperature control unit 80, and a controller unit 90. The apparatus control unit 60 includes a CPU 61 that performs control processing for the entire apparatus, a storage unit 62, a standby time count unit 63, and a continuous print count unit 64.

  The storage unit 62 of the present embodiment stores a threshold table 65 that will be described in detail later. The CPU 61 performs calculations related to the image forming operation of the image forming apparatus 1 based on the print job input by the user, the state of each part of the apparatus, and the like. In addition, the CPU 61 instructs switching between the normal mode and the UFP suppression mode based on the threshold table 65 of the storage unit 62 and the like.

  The normal mode is a mode for performing a normal image forming operation. The UFP suppression mode is a mode in which the temperature of the fixing device 100 is set lower than that in the normal mode. Further, in the UFP suppression mode, the image forming speed is set slower than in the normal mode. In this embodiment, the control mode of the image forming apparatus 1 is set to the normal mode at the start of image formation when a print job is input.

  The standby time counting unit 63 is for counting the standby time when the image forming operation is not performed in the image forming apparatus 1 and transmitting the standby time to the CPU 61. That is, the standby time counting unit 63 starts counting the standby time when the image forming apparatus 1 completes the image forming operation related to the input print job and enters the standby state. Then, the CPU 101 transmits to the CPU 61 the waiting time that is counted until the image forming operation related to the input print job is started after the waiting time is counted.

  The continuous printing count unit 64 is for counting the state values in which the image forming apparatus 1 is continuously forming images on a plurality of sheets P and transmitting the state values to the CPU 61. The continuous print count unit 64 of this embodiment counts the number of continuous prints as a state value in which images are continuously formed. That is, the continuous printing count unit 64 of this embodiment sets the continuous printing number, which is the cumulative number of sheets P on which image formation has been continuously performed since the start of image formation, every time image formation is performed on the sheet P. It transmits to CPU61. Note that the continuous print counting unit 64 of this embodiment counts the cumulative number of sheets P continuously performed in image formation related to one print job as the number of continuous prints.

  The system speed control unit 70 is a system such as the moving speed of the surface of the photoconductor 11 due to the rotation of the photoconductor 11, the moving speed of the surface of the intermediate transfer belt 30 due to the rotation of the roller 31, and the transport speed of the paper P transported through the transport path 50. Control the speed so that both speeds are the same. The passing speed of the paper P at the fixing nip N2 of the fixing device 100 is controlled by the system speed controlled by the system speed controller 70. Further, the system speed control unit 70 controls all of the system speeds so that image formation is performed at a speed instructed by the apparatus control unit 60. For example, when the apparatus control unit 60 is switched from the normal mode to the UFP suppression mode, the system speed control unit 70 performs control to reduce all the system speeds. As a result, when the normal mode is switched to the UFP suppression mode, the passing speed of the paper P at the fixing nip N2 of the fixing device 100 is also lowered.

  The fixing temperature control unit 80 is for automatically controlling the temperature of the fixing device 100 described later to a predetermined temperature for performing the fixing process. That is, the fixing temperature control unit 80 automatically controls the temperature of the fixing device 100 so that the fixing temperature instructed by the device control unit 60 is maintained. Further, when the apparatus control unit 60 is switched from the normal mode to the UFP suppression mode, the fixing temperature control unit 80 performs control to decrease the temperature of the fixing device 100.

  The controller unit 90 is connected to an external personal computer or the like and receives an instruction input. For example, a print job is generated in the image forming apparatus 1 by receiving an image formation command from a personal computer. Further, various information such as a dot counter value is exchanged between the device control unit 60 and the controller unit 90.

  Next, the fixing device 100 of this embodiment will be described. FIG. 3 is a schematic configuration diagram of the fixing device 100. The fixing device 100 is an electromagnetic induction heating type fixing device having a fixing roller 110, a pressure roller 120, and an induction heating device 130. The fixing roller 110 and the pressure roller 120 are arranged in parallel, and both are rotatably supported. Further, the fixing roller 110 and the induction heating device 130 are disposed on the side of the surface carrying the toner image of the paper P that passes through the fixing nip N2. The fixing roller 110 and the induction heating device 130 are configured on the heating side for heating the paper P passing through the fixing nip N2.

  On the other hand, the pressure roller 120 on the pressure side facing the configuration on the heating side across the conveyance path 50 is pressed against the fixing roller 110 in a direction perpendicular to the axis. As a result, a fixing nip N <b> 2 that performs a fixing process on the paper P is formed between the fixing roller 110 and the pressure roller 120.

  The outermost periphery of the fixing roller 110 is constituted by a surface layer 111 having high releasability so that the paper P that has passed through the fixing nip N2 does not remain stuck. On the inner peripheral side of the surface layer 111, an elastic layer 112 for improving the adhesion between the outer peripheral surface of the fixing roller 110 and the paper P is provided. Further, the innermost side of the fixing roller 110 is constituted by a core metal 113 which is a base material having sufficient strength and heat resistance.

  Also in the pressure roller 120, the outermost periphery is comprised by the surface layer 121 with high mold release property. An elastic layer 122 is provided on the inner peripheral side of the surface layer 121. Further, the innermost side of the pressure roller 120 is constituted by a core metal 123.

  In this embodiment, PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) tubes are used for the surface layers 111 and 121 of the fixing roller 110 and the pressure roller 120. In addition, as the surface layers 111 and 121, a fluorine resin material such as PTFE (polytetrafluoroethylene) or ETFE (tetrafluoroethylene / ethylene copolymer) is used as a fluorine tube or a fluorine coating. You can also.

  In this embodiment, silicone rubber is used for the elastic layers 112 and 122 of the fixing roller 110 and the pressure roller 120. Other silicone materials such as silicone rubber sponge, which is a foam of silicone rubber, can also be used.

  The induction heating device 130 is disposed along the axial direction of the fixing roller 110 and faces the outer periphery of the fixing roller 110 as shown in FIG. Induction heating device 130 is connected to high-frequency inverter 131. The induction heating device 130 generates a magnetic field by the high frequency power supplied from the high frequency inverter 131 and heats the fixing roller 110 by the magnetic field.

  Below the fixing roller 110 in FIG. 3, a temperature sensor 140 is disposed close to the fixing roller 110. The temperature sensor 140 is for measuring the surface temperature of the fixing roller 110 such as a non-contact infrared sensor. The high frequency inverter 131 and the temperature sensor 140 are connected to the fixing temperature control unit 80.

  During the fixing process, the fixing temperature control unit 80 performs control so that the surface temperature of the fixing roller 110 becomes a predetermined fixing temperature instructed by the device control unit 60. Specifically, the fixing temperature control unit 80 controls the electric power supplied from the high frequency inverter 131 to the induction heating device 130 based on the surface temperature of the fixing roller 110 detected by the temperature sensor 140. As a result, the surface temperature of the fixing roller 110 is automatically controlled to a predetermined fixing temperature for performing the fixing process.

  In the fixing device 100 as described above, ultrafine particles (UFP) are generated when the fixing process is performed on the paper P carrying the toner image. UFP generally has a particle size of 100 nm or less. Specifically, UFP is generated from the elastic layers 112 and 122 of the fixing roller 110 and the pressure roller 120 during the fixing process. That is, when the fixing roller 110 and the pressure roller 120 are heated during the fixing process, siloxane which is a volatile component is generated from the silicone rubber forming the elastic layers 112 and 122. It is understood that UFP is generated by the aggregation of the produced siloxane. It should be noted that UFP occurs not only when silicone rubber is used, but also when other silicone materials such as silicone sponge are used.

  UFP is also generated from toner. The toner carried on the paper P is melted by being pressurized while being heated during the fixing process, and is fixed on the paper P. For example, UFP is generated from the toner at the time of melting.

  A solid line in FIG. 4 indicates the amount of UFP generated when continuous printing is performed in the normal mode in the image forming apparatus 1. The continuous printing number indicated on the horizontal axis in FIG. 4 is the cumulative number of sheets P when image formation is continuously performed. The UFP occurrence rate shown on the vertical axis is a value obtained by measuring the number of UFP occurrences during continuous printing. Note that the UFP generation rate on the vertical axis indicates the number of UFP generation detected at the time of measurement by the measuring device, and does not represent an integrated value of the number of UFP generation detected until the measurement. . As shown by the solid line in FIG. 4, it can be seen that when continuous printing is performed in the normal mode, the amount of UFP generated per unit time increases as the number of continuously printed sheets increases.

  Therefore, for example, an upper limit value of the occurrence rate of UFP is set as indicated by L in FIG. From this, it can be seen that the UFP occurrence rate in the image forming apparatus 1 in the normal mode reaches the upper limit L when the number of continuously printed sheets is n2. Then, the image forming apparatus 1 performs control so that the UFP occurrence rate is equal to or lower than the upper limit value L.

  Specifically, the control mode is switched from the normal mode to the UFP suppression mode before the continuous print number reaches n2. The continuous printing number when switching the control mode is referred to as mode switching number. The mode switching sheet number is a threshold value of the continuous printing number set so that continuous printing can be performed in the normal mode on as many sheets P as possible while the UFP occurrence rate is suppressed to the upper limit value L or less. For example, in FIG. 4, the mode switching number is indicated by n1. As shown in FIG. 4, the mode switching sheet number n1 is a value of the continuous printing sheet number smaller than n2. When the continuous printing number is the mode switching number n1, the control mode is switched to the UFP suppression mode, the fixing temperature of the fixing device 100 is lowered, and the system speed of the image forming apparatus 1 is decreased.

  The amount of UFP generated is reduced by lowering the fixing temperature of the fixing device 100. In addition, when only the fixing temperature is lowered as compared with the normal mode while the system speed is set to the normal mode speed, there is a possibility that poor fixing of the toner image onto the paper P may occur due to insufficient heating of the toner. is there. Therefore, in the UFP suppression mode, the system speed is set slower than the normal mode so that the toner can be sufficiently heated even at a low fixing temperature.

  Further, by reducing the system speed, the passing speed of the toner image carried on the paper P at the fixing nip N2 is reduced. As a result, the amount of toner melted in the fixing nip N2 per unit time is reduced. In other words, the amount of UFP generated per unit time is reduced by reducing the system speed. Therefore, the amount of UFP generated can be reduced by switching from the normal mode to the UFP suppression mode.

The transition of the UFP occurrence rate after switching from the normal mode to the UFP suppression mode when the continuous printing number is the mode switching number n1 is shown by a broken line in FIG. Then, as indicated by a broken line in FIG. 4, the UFP occurrence rate after switching to the UFP suppression mode is suppressed to an upper limit value L or less. Further, the upper limit L of the UFP occurrence rate can be set to 30000 / cm ³ · sec, for example.

  Here, the present inventors have found that the amount of UFP generated when continuous printing is performed in the normal mode differs depending on the waiting time before the start of image formation. FIG. 5 shows the results of measuring the amount of UFP generated when continuous printing is performed in the normal mode for the image forming apparatus 1 in the case of waiting for 3 hours and in the case of waiting for 1 hour. . A thin solid line in FIG. 5 shows the transition of the UFP occurrence rate when the image forming apparatus 1 is kept in standby for 3 hours and then continuously printed in the normal mode. A bold solid line in FIG. 5 shows the transition of the occurrence rate of UFP when the image forming apparatus 1 is kept on standby for one hour and then continuously printed in the normal mode.

  As shown in FIG. 5, it can be seen that the UFP occurrence rate when performing continuous printing in the normal mode tends to increase after waiting for 3 hours than after waiting for only 1 hour. That is, the present inventors have found that the longer the waiting time, the larger the amount of UFP generated during subsequent continuous printing. It has been found that the transition of the UFP occurrence rate has almost the same tendency when the standby time is 3 hours or more as in the case of 3 hours shown by a thin solid line in FIG.

  As described above, in the UFP suppression mode, the system speed is set slower than in the normal mode. For this reason, it is preferable that the mode switching number of sheets to be switched from the normal mode to the UFP suppression mode is set to a large number of continuous printing sheets from the viewpoint of productivity. This is because as the number of mode switching sheets increases, more image formation can be performed in the normal mode, so that the productivity of image formation can be kept high.

  As shown in FIG. 5, in the image forming apparatus 1 after waiting for 3 hours, the upper limit L is reached when the number of continuously printed sheets is n4. In order to suppress the occurrence rate of UFP to the upper limit value L or less, when the standby time is 3 hours, the mode switching sheet number must be set to a continuous sheet number that is smaller than n4. In FIG. 5, the number of mode switching sheets when the standby time is 3 hours is indicated by n3. Further, in the image forming apparatus 1 after waiting for 3 hours, the transition of the UFP occurrence rate after switching from the normal mode to the UFP suppression mode when the continuous printing number is the mode switching number n3 is shown in FIG. It is indicated by a broken line.

  On the other hand, in the image forming apparatus 1 after waiting for one hour, the upper limit L is reached when the number of continuously printed sheets is n6, which is larger than n4. For this reason, when the standby time is 1 hour, it is sufficient to set the mode switching sheet number to a continuous printing sheet number smaller than n6. The number of mode switching sheets when the standby time is 1 hour is indicated by n5 in FIG. Further, in the image forming apparatus 1 after waiting for 1 hour, the transition of the UFP occurrence rate after switching from the normal mode to the UFP suppression mode when the continuous printing number is the mode switching number n5 is shown in FIG. It is indicated by a broken line.

  As shown by a broken line in FIG. 5, the occurrence rate of UFP after switching to the UFP suppression mode is suppressed to the upper limit value L or lower in both cases where the standby time is 1 hour and 3 hours. As shown in FIG. 5, the mode switching number n5 when the standby time is 1 hour is a value of the continuous printing number that is larger than the mode switching number n3 when the standby time is 3 hours. That is, when the standby time is 1 hour, the mode switching number can be set to a larger value for continuous printing than when the standby time is 3 hours. That is, in the case where image formation is continuously performed, it has been found that the shorter the standby time, the greater the number of mode switching sheets that can be switched from the normal mode to the UFP suppression mode.

  Therefore, the inventors performed continuous printing in the normal mode for each of the image forming apparatuses 1 that have been on standby for different times, and determined the relationship between the UFP occurrence rate and the number of continuous prints for each standby time. From these relationships, the number of mode switches was determined for each standby time. FIG. 6 shows the relationship between the obtained waiting time and the mode switching number. As shown in FIG. 6, the shorter the waiting time, the greater the number of mode switching sheets corresponding to the waiting time. In the storage unit 62 of the image forming apparatus 1 according to the present embodiment, the relationship between the standby time and the mode switching number shown in FIG.

  Next, the procedure of the image forming operation in the image forming apparatus 1 of this embodiment will be described with reference to the flowchart of FIG. As shown in FIG. 7, when there is an image formation instruction relating to a print job, the CPU 61 of the image forming apparatus 1 first obtains a standby time from the standby time counting unit 63 (S101). Also, the value of the continuous print count unit 64 is initialized (S102). Next, referring to the threshold value table 65 (FIG. 6) stored in the storage unit 62 based on the acquired standby time, the mode switching number is determined (S103). For example, if the waiting time is 50 minutes, the mode switching number is determined to be 160 as shown in FIG.

  Subsequently, the CPU 61 acquires the number of continuous prints from the continuous print count unit 64 (S104). Further, the image forming operation is performed while comparing the acquired continuous printing number and the determined mode switching number. That is, first, when the continuous printing number is equal to or less than the mode switching number (S105: YES), image formation is performed in the normal mode set at the start of image formation (S106). The continuous printing count unit 64 counts each time an image is formed on the paper P, and increases the value of the continuous printing number by one (S107). If the number of image formations related to the input print job has not been completed (S108: NO), the process returns to step 104 to perform image formation using the next sheet P.

  On the other hand, when the number of continuous prints is larger than the mode switching number by performing image formation continuously in the normal mode (S105: NO), the control mode is switched from the normal mode to the UFP suppression mode (S109). . Accordingly, the fixing temperature control unit 80 sets the fixing temperature of the fixing device 100 to be lower than the fixing temperature in the normal mode. Furthermore, the system speed control unit 70 makes the system speed slower than the system speed in the normal mode. Then, the remaining number of image forming operations related to the print job are performed in the UFP suppression mode (S110).

  When image formation for the number of print jobs is completed in the normal mode (S108: YES), or when image formation for the number of print jobs is completed in the UFP suppression mode switched from the normal mode (S111: YES), end processing of each unit such as the fixing device 100 of the image forming apparatus 1 is performed (S112). In addition, the completion processing of each unit such as the fixing device 100 is completed, and the standby time of the standby time counting unit 63 is initialized (S113). The standby time counting unit 63 starts counting the standby time (S114). ), The image forming apparatus 1 enters a standby state.

  As described above, in the image forming apparatus 1 of the present embodiment, first, continuous printing is performed while performing the fixing process in the normal mode until the continuous printing number reaches the determined mode switching number. Further, in the image formation after the continuous printing number exceeds the determined mode switching number, the fixing process is performed in the UFP suppression mode. The mode switching number is determined by the threshold table 65 based on the standby time when image formation is started. For this reason, it is possible to form as many sheets of images as possible in the normal mode with high productivity while suppressing the amount of UFP generated depending on the standby time to the upper limit L or less.

  Further, the continuous printing time during which continuous printing has been continued since the start of continuous printing becomes longer as the number of continuously printed sheets increases. This is because the longer the image is formed on the larger number of sheets P, the longer the time required for the image. Therefore, as the threshold value table 65 stored in the storage unit 62, the relationship between the standby time and the mode switching time as shown in FIG. 8 is used instead of the relationship between the standby time and the mode switching number shown in FIG. You can also. The mode switching time can be continuously printed in the normal mode for as long as possible while suppressing the UFP generation amount to the upper limit L or less when the normal mode is switched to the UFP suppression mode while performing the continuous printing in the normal mode. This is the threshold for continuous printing time.

  When the relationship between the standby time and the mode switching time in FIG. 8 is used as the threshold value table 65, the continuous printing count unit 64 uses the continuous printing time that has elapsed since the start of continuous printing as the state value for continuous printing. Count. In the procedure shown in FIG. 7, image formation may be performed while comparing the continuous printing time and the mode switching time while counting the continuous printing time instead of the continuous printing number.

  Furthermore, the storage unit 62 may have a plurality of threshold tables. For example, when the image forming apparatus 1 is used in a place where ventilation cannot be sufficiently performed, the user may want to reduce the amount of UFP generated even if the productivity of image formation is reduced. On the contrary, when the image forming apparatus 1 is used in an environment where UFP can be appropriately processed, there is no problem even if the amount of UFP generated is large, and it may be desired to increase the productivity of image formation. Therefore, the storage unit 62 stores a plurality of threshold tables created with different upper limit values of UFP generation amounts. At the time of image formation, the user selects the upper limit value of the UFP generation amount. The image forming apparatus 1 may perform image formation using a threshold table in which the amount of UFP generated does not exceed the upper limit value selected by the user.

  Further, the relationship between the standby time and the mode switching number may differ depending on the use environment of the image forming apparatus 1 and image forming conditions. For example, the amount of UFP generated tends to increase as the environmental temperature of the image forming apparatus 1 decreases. This is because the lower the environmental temperature, the greater the amount of heat required for the fixing device 100 to reach an appropriate fixing temperature. That is, the lower the environmental temperature is, the more the fixing device 100 is heated, and the amount of UFP generated increases due to the heating.

  Also, depending on the paper P to be used, the relationship between the standby time and the mode switching number may differ. For example, when thin paper is used as the paper P used for image formation, the amount of heat taken by the fixing device 100 from the paper P passing through the fixing nip N2 is less than when thick paper is used. For this reason, when thin paper is used, the fixing device 100 tends to be hot due to continuous printing. The amount of UFP generated increases as the temperature of the fixing device 100 increases. Therefore, the amount of UFP generated tends to increase as the type of paper P used is less likely to lose heat.

  Further, even when a small paper size (for example, A4 paper) is used, the amount of heat taken by the fixing device 100 from the paper P passing through the fixing nip N2 is smaller than when a large paper (for example, A2 paper) is used. Few. The length of the sheet passing area through which the sheet P in the axial direction (depth direction in FIG. 3) of the fixing roller 110 and the pressure roller 120 of the fixing device 100 passes is set to the maximum sheet size that the image forming apparatus 1 can handle. Is set. For this reason, when the paper size of the paper P is smaller than the maximum paper size, there may be a portion that does not contact the paper P at the axial ends of the fixing roller 110 and the pressure roller 120. The portion that does not contact the paper P tends to have a higher temperature than the portion that contacts the paper P because the amount of heat taken away by the passage of the paper P is small. Thus, the smaller the paper size, the greater the amount of UFP generated.

  In the image forming apparatus 1, for example, when the user replenishes the paper P in the paper feed cassette 51, the type of the paper P can be selected by the operation panel. Thereby, the image forming apparatus 1 can grasp the type of the paper P used at the time of image formation. As for the paper size, for example, by installing a sensor that can detect the paper size when the paper P is replenished in the paper feed cassette 51, the image forming apparatus 1 determines the paper size of the paper P. I can grasp it. Alternatively, in the case of an image forming apparatus having a plurality of paper feed cassettes for each paper size, the paper size can be grasped by a paper feed cassette that feeds paper during image formation.

  Also, the higher the coverage, which is the ratio of the area of the image to the area of the paper P, tends to increase the amount of UFP generated. The higher the coverage, the greater the amount of toner fixed on the paper P. Therefore, the amount of toner melted by heating the fixing device 100 per unit time increases.

  Also, for example, when a color image is formed by the image forming units 10Y, 10M, 10C, and 10K for each color, the amount of UFP generated may be larger than when a monochrome image is formed by the image forming unit 10K alone. is there. The toner image in the case of forming a color image is a multi-layered toner image in which the toner images formed by the image forming units are overlapped. In order to fix the multilayer toner image, when forming a color image, the fixing temperature may be set higher than when forming a monochrome image with a single-layer toner image. In this case, the temperature of the fixing device 100 is likely to be higher when a color image is formed than when a monochrome image is formed.

  Further, the image forming apparatus 1 may be provided with a function for forming a glossy image having a beautifully finished photograph or the like. When the glossy image is formed by the image forming apparatus 1 having this function, the system speed is set slower than that in the case of forming a non-glossy image in both the normal mode and the UFP suppression mode. This is because the toner image is melted uniformly by slowing the passing speed of the paper P in the fixing device 100, thereby giving gloss to the toner image to be fixed. The fixing temperature of the fixing device 100 is the same when a glossy image is formed and when a non-glossy image is formed. For this reason, when forming a glossy image, the fixing device 100 tends to be at a high temperature. Therefore, even when a glossy image is formed, the amount of UFP generated tends to increase.

  As described above, when image formation is performed in an environment or condition in which the amount of UFP generated is large, it is preferable to perform correction to reduce the number of mode switching sheets. This is because the amount of UFP generated is suppressed below the upper limit value. Conversely, when image formation is performed in an environment or condition in which the amount of UFP generation is reduced, it is preferable to perform correction to increase the number of mode switching sheets in the threshold table 65. This is because as the number of mode switching sheets increases, more image formation can be performed in the normal mode, so that the productivity of image formation can be kept high.

  Specifically, for example, when the correction is performed based on the environmental temperature, a correction table as illustrated in FIG. 9 is stored in the storage unit 62. When the environmental temperature of the image forming apparatus 1 is 24 ° C., correction is performed by multiplying the number of mode switching determined in step S103 in FIG. 7 by the correction coefficient 1.1. For example, when forming a glossy image, correction is performed by multiplying the number of mode switching sheets by a correction coefficient of 0.9. Further, as a mode of correction different from the correction multiplied by the correction coefficient, for example, when forming a glossy image, every time the number of sheets counted by the continuous print count unit 64 in step S107 in FIG. Correction may be performed so as to reduce one by one.

  In addition, when there are a plurality of correction conditions related to the mode switching number, a plurality of corrections may be performed in an overlapping manner. For example, when a glossy image is formed at an ambient temperature of 24 ° C., correction may be performed by multiplying the number of mode switching by both the correction factors 1.1 and 0.9.

  Further, in the above description, the continuous print count unit 64 of the present embodiment has been described as counting the cumulative number of sheets P on which image formation has been performed continuously in one print job as the number of continuous prints. However, the continuous print count unit 64 may count the cumulative number of sheets P on which images have been continuously formed by a plurality of print jobs as the number of continuous prints. That is, when a plurality of print jobs are simultaneously input and image formation related to the plurality of print jobs is continuously performed, the continuous print count by the continuous print count unit 64 is initialized for each print job. It may be done without doing.

  Even if there are a plurality of print jobs, if the interval from the completion of the previous print job to the input of the next print job is short, for example, less than 5 minutes, those print jobs Is a group of print jobs. In image formation related to a group of print jobs, the continuous print count by the continuous print count unit 64 can be performed through the group of print jobs without being initialized for each print job. Also in this case, when the last print job is completed when it is determined that a group of print jobs have been completed (for example, 5 minutes or more after the last print job is completed and no next print job is input) The standby time counting unit 63 may start counting the standby time retroactively.

  As described above in detail, the image forming apparatus 1 according to the present embodiment performs image formation by switching between the normal mode and the UFP suppression mode. In the UFP suppression mode, the passing speed of the paper P through the fixing device 100 is slower than the normal mode, and the fixing temperature of the fixing device 100 is set lower. In continuous printing in which images are continuously formed on a plurality of sheets P, the image forming apparatus 1 first determines the number of mode switching sheets by referring to the threshold table 65 from the standby time. If the continuous printing number is equal to or less than the determined mode switching number, image formation is performed while fixing processing by the fixing device 100 is performed in the normal mode. As a result, as many images as possible can be formed in the normal mode with high productivity. In the image formation after the continuous printing state value exceeds the mode switching number determined by continuous printing, the fixing process by the fixing device 100 is performed in the UFP suppression mode. Thereby, the generation amount of UFP can be suppressed below the upper limit value. Therefore, an image forming apparatus capable of suppressing the generation amount of UFP while maintaining high image forming productivity has been realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a color printer, and can be applied to an image forming apparatus that transmits and receives a print job via a public line, for example. Further, for example, the heating configuration of the fixing device is not limited to the electromagnetic induction heating type, but may be a configuration in which a heater is provided inside the core metal of the fixing roller.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 60 Apparatus control part 62 Memory | storage part 63 Standby time count part 64 Continuous printing count part 65 Threshold table 70 System speed control part 80 Fixing temperature control part 100 Fixing apparatus

Claims (11)

A fixing device for fixing a toner image on the sheet by a fixing process of pressing and heating the sheet while passing the sheet carrying unfixed toner;
Form normal images in which images are formed without taking measures to reduce the amount of ultrafine particles generated in the machine, and images while taking measures to reduce the amount of ultrafine particles generated in the machine below a predetermined upper limit. An image forming apparatus having an apparatus control unit for switching to an ultrafine particle suppression mode.
A fixing temperature controller for controlling the temperature of the fixing device;
A passage speed control unit for controlling the passage speed of the sheet in the fixing device;
A generation amount state value output unit that outputs a generation amount state value that affects the generation amount of ultrafine particles due to image formation in the image forming apparatus;
A continuous printing state value output unit for outputting a continuous printing state value indicating the amount of image formation continuously performed;
A mode switching value output unit that outputs a mode switching value that is a threshold value for the continuous printing state value for mode switching in the device control unit according to the generated amount state value;
The generation amount state value output unit outputs a higher generation amount state value as the amount of generated ultrafine particles increases.
The apparatus control unit is configured to
Obtain the generation amount state value from the generation amount state value output unit,
A mode switching value is acquired from the mode switching value output unit according to the acquired generation state value and determined.
If the continuous printing state value acquired from the continuous printing state value output unit is less than or equal to the determined mode switching value, an image is formed in the normal mode,
When the continuous printing state value acquired from the continuous printing state value output unit exceeds a determined mode switching value, an image is formed in the ultrafine particle suppression mode,
When forming an image in the ultrafine particle suppression mode,
The fixing temperature control unit sets the temperature of the fixing device to a temperature lower than that in the normal mode,
An image forming apparatus, wherein the passage speed control unit sets a passage speed of the sheet in the fixing device to be slower than the normal mode. The image forming apparatus according to claim 1,
The generation amount state value output unit is:
A standby time elapsed from the completion of the previous image formation to the start of image formation by the device control unit is output as the generated amount state value;
The mode switching value output unit
An image forming apparatus that outputs a lower mode switching value as a generation amount state value is higher. The image forming apparatus according to claim 1, wherein:
The continuous printing state value output unit
An image forming apparatus characterized in that an integrated number of sheets on which image formation has been performed continuously from the start of image formation by the apparatus control unit is output as the continuous printing state value. The image forming apparatus according to claim 1, wherein:
The continuous printing state value output unit
An image forming apparatus, characterized in that an elapsed time during which image formation is continuously performed since image formation is started by the apparatus control unit is output as the continuous printing state value. The image forming apparatus according to claim 1, wherein:
The device controller is
An image forming apparatus, wherein the upper limit value is determined by an input from a user. The image forming apparatus according to any one of claims 1 to 5,
The device controller is
An image forming apparatus characterized in that the mode switching value is set lower as the environmental temperature is lower. The image forming apparatus according to any one of claims 1 to 6,
The device controller is
An image forming apparatus characterized in that a mode switching value is set to be lower as the type of sheet that takes less heat from the fixing device when passing through the fixing device. The image forming apparatus according to claim 1, wherein:
The device controller is
An image forming apparatus characterized in that a mode switching value is set lower as a length of a sheet passing direction to the fixing device and a direction perpendicular to the fixing device are shorter. The image forming apparatus according to claim 1, wherein:
The device controller is
An image forming apparatus characterized in that a mode switching value is set to be lower as a coverage, which is a ratio of a toner image area to an area of a sheet for image formation, is higher. The image forming apparatus according to any one of claims 1 to 9,
A plurality of image forming portions for forming a toner image;
The device controller is
An image forming apparatus characterized in that a mode switching value is set lower when image formation is performed by the plurality of image forming units than when image formation is performed by one image forming unit. The image forming apparatus according to any one of claims 1 to 10,
When the device control unit forms a glossy image,
The mode switching value is set lower than when forming a non-glossy image,
The passage speed control unit sets the passage speed of the sheet in either the normal mode or the ultrafine particle suppression mode in the fixing device to a slower passage speed than when a non-glossy image is formed. An image forming apparatus.

Images