JP5717818B2 - Image forming apparatus and fixing unit cleaning method - Google Patents

Description

The present invention relates to an image forming apparatus that forms a color image on a recording material , and a fixing unit cleaning method .

  2. Description of the Related Art Image forming apparatuses such as electrophotographic copying machines and printers transfer a toner image carried by a photosensitive drum or an intermediate transfer member as an image carrier onto a recording material by a transfer unit. The recording material is heated and pressed by a fixing device (fixing device) to heat and fix an unfixed toner image on the recording material.

  In the above fixing device, the toner of the unfixed toner image and paper dust of the recording paper as the recording material adhere to the outer peripheral surface (surface) of the constituent roller with the use of the image forming apparatus, and the surface of the constituent roller becomes Dirty. This is due to electrostatic offset caused by charging of the recording material and constituent rollers, thermal offset due to excessive or insufficient fixing, adhesion of unfixed toner to the constituent roller surface during recording material jam processing, and recording materials with low surface strength. It is caused by these causes such as falling off of paper dust. When the contamination on the surface of the constituent roller exceeds the accumulation limit on the surface of the constituent roller, it is discharged onto the recording material at the nip portion, and the image on the recording material is damaged. In addition, the recording roller surface is likely to cause the recording material to be easily wound around the surface of the component roller, which may cause a jam in the fixing device or damage to the component roller.

  In order to solve such a problem, the present applicant has proposed an image forming apparatus that can clean the surface of the constituent rollers (Patent Documents 1 to 4). In this image forming apparatus, a recording material on which a cleaning toner pattern is formed is prepared as a cleaning sheet. Then, the dirt on the surface of the constituent roller is cleaned by refeeding the toner pattern of the cleaning sheet so as to contact the constituent roller side to be cleaned.

  By the way, when a large number of recording materials containing a large amount of filler such as calcium carbonate and talc are passed (introduced) through the nip, these fillers adhere to the surface of the constituent roller and reduce the releasability of the constituent roller surface. Let For this reason, the contamination due to the toner or paper dust on the surface of the constituting roller is rapidly deteriorated and becomes a bad level of contamination. Under such conditions, even if the above-described cleaning is performed, it may be difficult to completely remove the dirt on the surface of the constituent roller by a single cleaning operation.

  In order to solve such problems, there are a method of passing a cleaning sheet of a plurality of pages and a method of frequently performing a cleaning operation. However, normal image formation (printing) is hindered for a long time, and many recording materials are used for cleaning.

Japanese Patent No. 2651232 JP-A-10-111619 JP 2004-240447 A Japanese Patent No. 3292568

The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce the amount of heat applied to the recording material by lowering the temperature of the fixing unit at the time of creating the cleaning sheet than at the time of normal image formation. An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of defective fixing and hot offset by adjusting a heat amount suitable for the toner amount of a toner image for cleaning , and a method for cleaning a fixing unit.

Construction of an image forming apparatus according to the present invention for achieving the above object,
An image forming unit capable of forming a toner image in which toner images of a plurality of colors are superimposed on a recording material, and fixing the toner image on the recording material by heating the recording material on which the toner image is formed while being conveyed in the nip portion A fixing unit that
A cleaning toner image in which a plurality of colors of toner are superimposed is formed on the recording material in the image forming unit, and the cleaning toner image formed on the recording material is fixed on the recording material in the fixing unit and cleaned. In the image forming apparatus capable of executing a cleaning mode in which the cleaning sheet is transported at the nip portion and the fixing portion is cleaned after the sheet for cleaning is prepared.
The amount of toner per unit area of the toner image for cleaning is larger than the maximum amount of toner per unit area that can be superimposed on a recording material with a plurality of color toners superimposed during normal image formation,
Conveying speed of the recording material in said nip when creating a sheet for the cleaning, rather slow than the transport speed of the recording material in the nip portion when the normal image formation using the recording medium, wherein The temperature of the fixing unit when creating a cleaning sheet is lower than the temperature of the fixing unit when performing normal image formation using the recording material .
Another configuration of an image forming apparatus according to the present invention for achieving the above object,
An image forming unit capable of forming a toner image on a recording material, and a fixing unit for fixing the toner image to the recording material by heating the recording material on which the toner image is formed while being conveyed at the nip portion,
After forming a cleaning toner image on the recording material in the image forming unit and fixing the cleaning toner image formed on the recording material on the recording material in the fixing unit to create a cleaning sheet, In the image forming apparatus capable of executing a cleaning mode in which the cleaning sheet is conveyed at the nip portion to clean the fixing portion.
The amount of toner per unit area of the toner image for cleaning is larger than the maximum amount of toner per unit area that can be placed on a recording material during normal image formation,
Conveying speed of the recording material in said nip when creating a sheet for the cleaning, rather slow than the transport speed of the recording material in the nip portion when the normal image formation using the recording medium, wherein The temperature of the fixing unit when creating a cleaning sheet is lower than the temperature of the fixing unit when performing normal image formation using the recording material .

Configuration of cleaning method of a fixing unit according to the present invention for achieving the above object,
An image forming apparatus comprising: an image forming unit capable of forming a toner image on a recording material; and a fixing unit configured to heat the recording material on which the toner image is formed while being conveyed at the nip portion and fix the toner image on the recording material. A method of cleaning the fixing unit in
In the image forming unit, the amount of toner per unit area of the recording material is larger than the maximum amount of toner per unit area that can be superimposed on the recording material when a plurality of colors of toner are superimposed when performing normal image formation. As described above, a toner image for cleaning is formed on a recording material by superimposing a plurality of color toner images,
In the fixing unit, the recording material on which the cleaning toner image is formed is transported at a transport speed slower than the transport speed of the recording material when the recording material is used for normal image formation, and the recording material is used. At a temperature lower than the temperature of the fixing unit at the time of normal image formation, the sheet is heated while being conveyed at the nip unit, and the cleaning toner image is fixed on a recording material to create a cleaning sheet,
In the fixing unit, the cleaning sheet is conveyed by the nip portion to clean the fixing unit.

  Further objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

According to the present invention, the temperature of the fixing unit at the time of preparation of the cleaning sheet is made lower than that at the time of normal image formation, so that the amount of heat applied to the recording material is reduced and adjusted to a heat amount suitable for the toner amount of the cleaning toner image Thus, it is possible to provide an image forming apparatus and a fixing unit cleaning method that can prevent the occurrence of fixing failure and hot offset .

FIG. 3 is a cross-sectional view of a fixing unit mounted on the image forming apparatus of the present invention. 1 is a cross-sectional view of an image forming apparatus of the present invention. The figure which showed the cleaning sheet in which the image pattern for cleaning was formed. When a cleaning image pattern having the same toner amount per unit area is heated and fixed on a recording material having a small surface roughness, and the pressure roller is cleaned using this cleaning sheet, FIG. 3 is a schematic diagram showing a relationship with a cleaning image pattern carried on a recording material. When a cleaning image pattern having the same toner amount per unit area is heated and fixed on a recording material having a large surface roughness, and the pressure roller is cleaned using this cleaning sheet, FIG. 3 is a schematic diagram showing a relationship with a cleaning image pattern carried on a recording material. When a cleaning image pattern having a large amount of toner per unit area is heat-fixed on a recording material having a large surface roughness, and the pressure roller is cleaned using this cleaning sheet, the dirty toner on the pressure roller and the recording material The schematic diagram which shows the relationship with the image pattern for cleaning carry | supported on the top. Sectional drawing of the fixing device using an endless belt.

  The present invention will be described with reference to the drawings.

[Example 1]
(1) Example of color image forming apparatus
FIG. 2 is a structural model diagram of an example of a color image forming apparatus according to the present embodiment . This color image forming apparatus is a full color laser printer that obtains a full color image by superimposing four color toner images of yellow, cyan, magenta, and black using an electrophotographic system.

  The color image forming apparatus shown in the present embodiment includes conveying means 12 and 24 for the recording material P, and four image forming stations 41Y, 41C, 41M, and 41K that are arranged substantially linearly in the vertical direction. In this embodiment, the four image forming stations are collectively referred to as an image forming unit. The color image forming apparatus includes a heat fixing device (fixing unit) 20, a control unit 100 as a control unit, and a video controller 101 that forms an image signal for image formation.

  The control unit 100 includes a memory such as a ROM or a RAM and a CPU. The memory stores an image formation control sequence for forming an image on the recording material P, a cleaning control sequence for cleaning the heat fixing device 20, and the like.

  Of the four image forming stations 41Y, 41C, 41M, and 41K, 41Y is a yellow image forming station that forms a yellow (hereinafter abbreviated as Y) color image. Reference numeral 41C denotes a cyan image forming station for forming a cyan (hereinafter abbreviated as C) color image. Reference numeral 41M denotes a magenta image forming station for forming a magenta (hereinafter abbreviated as M) color image. A black image forming station 41K forms a black (hereinafter abbreviated as K) image.

  Each of the image forming stations 41Y, 41C, 41M, and 41K includes an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1Y, 1C, 1M, and 1K as a drum-type image carrier, and a charging roller 3Y as a charging unit. , 3C, 3M, 3K. Each of the image forming stations 41Y, 41C, 41M, and 41K includes developing devices 2Y, 2C, 2M, and 2K as developing means, and cleaning devices 4Y, 4C, 4M, and 4K as cleaning means.

  The photosensitive drum 1Y, the charging roller 3Y, the developing device 2Y, and the cleaning device 4Y are housed in one frame (frame body) and configured as a yellow cartridge Y. Further, the photosensitive drum 1C, the charging roller 3C, the developing device 2C, and the cleaning device 4C are also housed in one frame (frame body) and configured as a cyan cartridge C. Further, the photosensitive drum 1M, the charging roller 3M, the developing device 2M, and the cleaning device 4M are also housed in one frame (frame body) and configured as a magenta cartridge M. Further, the photosensitive drum 1K, the charging roller 3K, the developing device 2K, and the cleaning device 4K are also housed in one frame (frame body) and configured as a black cartridge K. The developing device 2Y of the yellow cartridge Y stores yellow toner, and the developing device 2C of the cyan cartridge C stores cyan toner. The developing device 2M of the magenta cartridge M stores magenta toner, and the developing device 2K of the black cartridge K stores black toner.

  Reference numeral 5 denotes a laser scanning exposure apparatus (hereinafter referred to as an exposure apparatus) as an exposure means. The exposure device 5 is provided corresponding to each cartridge Y, C, M, K, and exposes the photosensitive drums 1Y, 1C, 1M, 1K of the corresponding cartridges Y, C, M, K. An electrostatic latent image is formed on each photosensitive drum.

  An intermediate transfer belt (intermediate transfer member) 6 is an endless belt-shaped image carrier. The intermediate transfer belt 6 is provided along the arrangement direction of the image forming stations 41Y, 41C, 41M, and 41K. The intermediate transfer belt 6 is stretched around three rollers: a driving roller 7, a tension roller 8, and a secondary transfer counter roller 14. The intermediate transfer belt 6 is moved in the direction of the arrow along the photosensitive drums 1Y, 1C, 1M, and 1K of the image forming stations 41Y, 41C, 41M, and 41K by driving of the driving roller 7.

  Primary transfer rollers 9Y, 9C, 9M, and 9K are used as primary transfer means for transferring the toner images on the surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K to the outer peripheral surface (front surface) of the intermediate transfer belt 6. . The primary transfer rollers 9Y, 9C, 9M, and 9K are disposed so as to face the photosensitive drums 1Y, 1C, 1M, and 1K with the intermediate transfer belt 6 interposed therebetween.

  Reference numeral 15 denotes a collection roller 15 as a cleaning unit for the intermediate transfer belt 6. The collection roller 15 is provided so as to face the intermediate transfer belt 6 between the secondary transfer roller 14 and the yellow image forming station 41Y.

  The conveying means includes a feeding roller 11, a registration roller 12, a discharge roller 24, a reverse roller 25, a duplex printing conveyance path 26, and the like. The duplex printing conveyance path 26 also has a function of a conveyance path for conveying (refeeding) the cleaning sheet to the fixing unit 20.

  When the video controller 101 receives image data from an external device (not shown) such as a host computer, the video controller 101 transmits a print signal to the control means 100 and converts the received image data into bitmap data. The control means that has received the print signal executes an image formation control sequence. When the image formation control sequence is executed, first, the photosensitive drums 1Y, 1C, 1M, and 1K are rotated in the arrow direction. The outer peripheral surfaces (surfaces) of the photosensitive drums 1Y, 1C, 1M, and 1K are uniformly charged to predetermined polarities and potentials by the charging rollers 3Y, 3C, 3M, and 3K. In this embodiment, the surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K are negatively charged. The charged surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K are scanned and exposed by the exposure device 5 with laser light corresponding to an image signal depending on the bitmap data. As a result, electrostatic latent images corresponding to the image data are formed on the charged surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K. The developing devices 2Y, 2C, 2M, and 2K respectively apply a developing bias applied to the developing rollers 21Y, 21C, 21M, and 21K from a developing bias power source (not shown) between a charging potential and a latent image (exposure portion) potential. Set to an appropriate value. As a result, the negatively charged toner adheres to the exposed portion, and a toner image is formed on the photosensitive drum.

  Monochromatic toner images developed on the surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K by the developing devices 2Y, 2C, 2M, and 2K are substantially equal in synchronization with the rotation of the photosensitive drums 1Y, 1C, 1M, and 1K. The toner image is transferred to the outer peripheral surface (front surface) of the intermediate transfer belt 6 that rotates at high speed. That is, toner is transferred from the first transfer bias power sources V1Y, V1C, V1M, and V1K (not shown) to the primary transfer rollers 9Y, 9C, 9M, and 9K corresponding to the photosensitive drums 1Y, 1C, 1M, and 1K. A positive polarity transfer bias having the opposite polarity is applied. As a result, the toner images of the respective colors are primarily transferred from the surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K so as to overlap the surface of the intermediate transfer belt 6. As a result, a color toner image is carried on the surface of the intermediate transfer belt 6.

  Transfer residual toner remaining on the surfaces of the photosensitive drums 1Y, 1C, 1M, and 1K after the primary transfer of the toner image is caused by cleaning members 41Y, 41C, 41M, and 41K provided in the cleaning devices 4Y, 4C, 4M, and 4K. Removed. The transfer residual toner removed by the cleaning members 41Y, 41C, 41M, and 41K is collected in waste toner containers (not shown) of the cleaning devices 4Y, 4C, 4M, and 4K. In this embodiment, a cleaning blade made of a urethane blade is used as the cleaning member.

  As described above, the charging process by the charging roller, the exposure process by the exposure device, the developing process by the developing device, and the primary transfer process by the primary transfer roller 9 are synchronized with the rotation of the intermediate transfer belt 6, and yellow, magenta, Perform for each color of cyan and black. As a result, the toner images of the respective colors are sequentially stacked on the surface of the intermediate transfer belt 6. That is, the intermediate transfer belt 6 carries an unfixed toner image of a color image to be formed on the recording material P.

  On the other hand, the recording material P set in the recording material cassette 10 serving as the recording material supply unit is fed by the feeding roller 11. The leading edge of the recording material P is detected by a top sensor S 1 provided immediately after the registration roller 12. The registration roller 12 matches the image position and timing of the surface of the intermediate transfer belt 6 according to the detection of the leading edge of the recording material by the top sensor S1, and the recording material P is transferred to the intermediate transfer belt 6 and the secondary transfer roller 13 as a secondary transfer means. It is conveyed to the transfer nip portion between. The transfer nip portion is disposed between the intermediate transfer belt 6 and the secondary transfer roller 13 by placing the secondary transfer roller 13 in contact with the surface of the intermediate transfer belt 6 at a position facing the secondary transfer counter roller 14. Is formed. The conveyance speed of the recording material P in the image forming apparatus of this embodiment is 180 mm / second.

  The color toner image carried on the surface of the intermediate transfer belt 6 is recorded on the recording material P by applying a bias having a polarity opposite to that of the toner to the secondary transfer roller 13 from a second transfer bias power source V2 (not shown). Batch transfer (secondary transfer) is performed on the top.

  The color toner image T transferred onto the recording material P is introduced into a nip portion (fixing nip portion) N of a heat fixing device (fixing device) 20 as a fixing means, and receives heat and pressure, thereby being applied onto the recording material P. Heat fixing. The recording material P that has exited the nip N of the heat fixing device (hereinafter referred to as a fixing device) 20 is discharged onto a discharge tray by a pair of discharge rollers 24.

  The transfer residual toner remaining on the surface of the intermediate transfer belt 6 after the transfer of the color toner image T is applied to the outer peripheral surface (front surface) of the collection roller 15 to which a positive bias is applied from a third transfer bias power source V3 (not shown). Static electricity is collected and accumulated. Further, after the secondary transfer operation for a predetermined page is completed, the image forming operation is interrupted, and a negative bias is applied to the collection roller 15 from the third transfer bias power source V3. As a result, the transfer residual toner accumulated on the surface of the collection roller 15 is electrostatically discharged from the surface of the collection roller 15 to the surface of the intermediate transfer belt 6. At the same time, transfer residual toner on the surface of the intermediate transfer belt 6 is transferred from the surface of the intermediate transfer belt 6 to the surface of the photosensitive drum 1Y in the primary transfer portion between the photosensitive drum 1Y and the intermediate transfer belt 6 of the yellow image forming station 41Y. An electric field that is reversely transferred is formed. For example, the surface of the photosensitive drum 1Y is set to −100 V, a transfer bias of −300 V is applied to the transfer roller 9Y from the first transfer bias power source V1Y, and the transfer residual toner on the surface of the intermediate transfer belt 6 is reversed to the surface of the photosensitive drum 1Y. Make a copy. The transfer residual toner reversely transferred to the surface of the photoreceptor drum 1Y is finally removed from the surface of the photoreceptor drum 1Y by the cleaning member 42Y and collected in a waste toner container.

(2) Fixing Device FIG. 2 is a cross-sectional side view of an example of the fixing device 20. The fixing device 20 is a heat roller type fixing device.

  In the following description, regarding the fixing device and members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the short direction.

  The fixing device (fixing unit) 20 includes a halogen lamp 21 as a heating unit, and a fixing roller 22 and a pressure roller 23 as fixing members. The halogen lamp 21, the fixing roller 22, and the pressure roller 23 are all elongated members in the longitudinal direction.

  The fixing roller 22 has a cylindrical hollow core bar 22a made of aluminum or stainless steel. On the outer peripheral surface of the hollow cored bar 22a, an elastic layer 22b formed of a thin silicone rubber or the like is formed. Further, a release layer 22c made of polytetrafluoroethylene (PTFE) and perfluoroalkoxytetrafluoroethylene copolymer (PFA), which has excellent release properties, is formed on the outer peripheral surface of the elastic layer 22b. Yes. In the fixing roller 22, both ends in the longitudinal direction of the hollow cored bar 22a are rotatably held by an apparatus frame (not shown).

  A halogen lamp 21 is disposed inside the hollow cored bar 22 a of the fixing roller 22. In the halogen lamp 21, both end portions in the longitudinal direction of the halogen lamp 21 are held by the apparatus frame. The halogen lamp 21 is energized from a power source (not shown) to cause the halogen lamp 21 to generate heat, and the radiant heat of the halogen lamp 21 causes the hollow core metal 22a to pass through the hollow core metal 22a, the elastic layer 22b, and the release layer 22c. Then, the outer peripheral surface (surface) of the fixing roller 22 is heated.

  The pressure roller 23 has a round shaft-shaped cored bar 23a made of aluminum or stainless steel. On the outer peripheral surface of the metal core 23a, an elastic layer 23b formed with a thick silicone rubber or foamed silicone rubber is formed. Further, a release layer 23c made of PTFE or PFA is formed as an outermost layer on the outer peripheral surface of the elastic layer 23b. The pressure roller 23 is disposed substantially in parallel with the fixing roller 22 and holds both ends in the longitudinal direction of the cored bar 23a rotatably on the apparatus frame. The pressure roller 23 urges both ends in the longitudinal direction of the metal core 23a of the pressure roller 23 in the axial direction of the fixing roller 22 by a pressure means (not shown) such as a pressure spring. The outer peripheral surface (surface) is brought into contact with the surface of the fixing roller 22 in a pressurized state. In the pressure roller 23, the elastic layer 23 b is elastically deformed along the longitudinal direction of the surface of the fixing roller 22 by the pressure applied by the pressure unit, and a nip portion having a predetermined width is formed between the surface of the pressure roller 23 and the surface of the fixing roller 22. (Fixing nip portion) N is formed.

(3) Heat Fixing Operation of Fixing Device The control unit 100 uses a driving gear (not shown) provided at one end of the cored bar 23a of the pressure roller 23 as a driving source in response to a print signal input. The pressure roller 23 is rotated in the direction of the arrow by being rotationally driven by the motor M (FIG. 2). The rotation of the pressure roller 23 causes a rotational force to act on the fixing roller 22 by the frictional force between the surface of the pressure roller 23 and the surface of the fixing roller 22 at the nip portion N. Due to the rotational force, the fixing roller 22 is driven to rotate in the direction of the arrow at substantially the same peripheral speed as the pressure roller 23.

  The control unit 100 turns on a triac (not shown) as an energization control unit. As a result, the halogen lamp 21 is energized from a power source (not shown). When the halogen lamp 21 is energized, it emits radiant heat and heats the hollow core metal 22 a of the fixing roller 22. The surface of the fixing roller 22 is heated by the heat of the hollow metal core 22a being transmitted to the release layer 22c through the elastic layer 22b. The temperature of the surface of the fixing roller 22 is detected by temperature detecting means S such as a thermistor arranged so as to be in contact with or not in contact with the surface of the fixing roller 22. The control unit 100 takes in the output signal (temperature detection signal) of the temperature detection means S, and controls the power supplied to the halogen lamp 21 by the triac based on the output signal, thereby setting the surface temperature of the fixing roller 22 to a predetermined fixing temperature. Maintain at (target temperature). In this embodiment, the fixing temperature is maintained at 190 ° C.

  In a state where the surface temperature of the fixing roller 22 is maintained at the fixing temperature and the rotation peripheral speed of the fixing roller 22 is stabilized by the rotation of the pressure roller 23, the recording material P carrying the unfixed color toner image T is nipped. Part N is introduced. The recording material P is nipped and conveyed by the surface of the fixing roller 22 and the surface of the pressure roller 23 at the nip portion N, and receives the heat of the surface of the fixing roller 22 and the pressure of the nip portion N. It is fixed by heating.

(4) Description of Cleaning Mode When receiving a cleaning mode instruction from an external device or an operation panel (not shown) of the image forming apparatus, the control unit 100 executes a cleaning control sequence. When the cleaning control sequence is executed, the cleaning image pattern stored in the ROM is first developed. A cleaning toner image pattern is formed on the recording material P by the same operation as the above-described image forming operation (normal image forming operation), and a cleaning sheet is created. That is, the following processes are performed in synchronization with the rotation of the intermediate transfer belt 6 by using two or more predetermined image forming stations among the four image forming stations provided in the image forming unit. That is, the charging process by the charging roller, the exposure process by the exposure device, the developing process by the developing device, and the primary transfer process by the primary transfer roller 9 are performed in synchronization with the rotation of the intermediate transfer belt 6. As a result, the toner images of the respective colors of two or more predetermined image forming stations are sequentially superimposed on the surface of the intermediate transfer belt 6. As a result, an unfixed toner image pattern used for cleaning is carried on the surface of the intermediate transfer belt 6 using toner of two or more colors. On the other hand, the recording material P is fed from the recording material cassette 10 by the feeding roller 11. The recording material P is conveyed by the registration roller 12 to the transfer nip portion in accordance with the image position on the surface of the intermediate transfer belt 6 in accordance with the detection of the leading edge of the recording material by the top sensor S1. The secondary transfer roller 13 is applied with a transfer bias from the second transfer bias power source V2, whereby an unfixed toner image pattern (predetermined toner image) C (see FIG. 3) on the surface of the intermediate transfer belt 6 is recorded. Transferred and supported on P. FIG. 3 is an explanatory view showing an unfixed toner image pattern C carried on the recording material P.

  Further, the control unit 100 turns on the triac and energizes the halogen lamp 21 to heat the surface of the fixing roller 22 to the fixing temperature, and also drives the fixing motor M to rotate the pressure roller 23 to follow the fixing roller 22. Rotate. Then, the recording material P carrying the unfixed toner image pattern C is introduced into the nip portion N of the fixing device 20 and is nipped and conveyed by the fixing roller 22 and the pressure roller 23 at the nip portion N. As a result, the toner image pattern C is heated and fixed on the recording material P, and the toner image pattern C is formed on the recording material P. Then, the recording material P that has exited the nip portion N is discharged onto the discharge tray 25 by the discharge roller pair 24. When the fixing device 20 is cleaned using the recording material P, that is, the cleaning sheet on which the predetermined toner image C is formed, the following operation is performed. That is, the surface of the recording material P on the toner image pattern C side is directed toward the fixing roller 22 to be cleaned, and the recording material P is conveyed by the conveying means (the feeding roller 11 and the registration roller 12). Refeed the nip portion N. Alternatively, the recording material P is fed again to the nip portion N of the fixing device 20 by the conveying means with the surface of the recording material P on the toner image pattern C side facing the pressure roller 23 to be cleaned. Hereinafter, the sign of the cleaning sheet is CP to distinguish it from the recording material P that does not carry the predetermined toner image C.

  In the image forming apparatus of the present embodiment, the cleaning sheet CP once formed with the toner image pattern C and discharged to the outside of the image forming apparatus is reset in the recording material cassette 10 by the user of the image forming apparatus and re-supplied. Do paper. Here, when the fixing roller 22 is to be cleaned, the cleaning sheet CP is set in the recording material cassette 10 with the toner image pattern C facing downward. When the pressure roller 23 is to be cleaned, the cleaning sheet CP is set in the recording material cassette 10 with the toner image pattern C facing upward. Since the method for setting the cleaning sheet CP differs depending on the configuration of the conveying means, it is necessary for the user to be able to determine which direction the toner image pattern C should be directed to reset the cleaning sheet CP. For this purpose, it is desirable to print and show information in the set direction on the cleaning sheet CP together with the toner image pattern C. When the pressure roller 23 is to be cleaned, the cleaning sheet CP is introduced into the double-sided printing conveyance path 26 using the reversing roller 25 provided in the vicinity of the discharge tray 25, and the cleaning sheet CP is turned upside down. The paper may be reversed and fed again to the nip portion N. Note that when the cleaning sheet CP is conveyed, image formation on the cleaning sheet CP by the above-described image forming unit is not performed.

  In the heat roller type fixing device, the surface temperature of the pressure roller 23 is generally lower than that of the fixing roller 22 provided with a halogen heater 21 for heating therein. In addition, toner and paper dust are easily stained. Accordingly, by refeeding the cleaning sheet CP with the toner image pattern C facing the pressure roller 23, the surface of the pressure roller 23 can be cleaned using the adhesiveness of the toner image C that has been fixed. it can.

  The reason why the surface of the fixing roller 22 or the surface of the pressure roller 23 can be cleaned by refeeding the cleaning sheet CP on which the toner image pattern C is formed is that the toner image of the fixed toner image pattern C is in the nip portion N. Reheats and melts. Accordingly, it is considered that paper powder or the like is adsorbed by the viscosity of the melted toner image pattern C and that the melted toner image pattern C has a good affinity with the dirt toner, and thus is easily adsorbed with the dirt toner. The surface of the fixing roller 22 or the pressure roller 23 can be cleaned by refeeding the cleaning sheet CP on which the toner image pattern C is formed in this way toward the fixing roller 22 or the pressure roller 23 to be cleaned. That is, the fixing member can be cleaned by conveying the recording material with the toner image pattern surface on the recording material facing the fixing member to be cleaned.

  FIG. 3 is a diagram illustrating a toner image pattern C carried by the cleaning sheet CP.

The toner image pattern C is a solid image as shown in FIG. The length L of the solid-coated image in the recording material conveyance direction is set to be equal to or longer than one rotation of the rotating body, that is, the fixing roller 22 or the pressure roller 23 to be cleaned. In this embodiment, the length L of the solid-coated image in the recording material conveyance direction is set to a length equal to or longer than one rotation of the pressure roller 23. This is because a non-cleaning area that cannot be cleaned by a solid image is not left on the surface of the pressure roller 23 to be cleaned. Further, the length W in the width direction orthogonal to the recording material conveyance direction of the solid-coated image is narrower than the width orthogonal to the recording material conveyance direction of the recording material P to be fed. Set the maximum printable range. This is because cleaning is performed in the widest possible range with respect to the longitudinal direction of the pressure roller 23 to be cleaned.
Incidentally, a normal color image forming apparatus has, as a normal image forming mode, a monochrome image forming mode for forming an image using only black toner and a full color image forming mode for forming an image using four color toners. . In the cleaning mode, the toner image pattern C is formed using only black toner on the recording material.

  Here, in the conventional color image forming apparatus, the toner amount on the recording material when forming the cleaning image pattern is less than the maximum toner amount that can be formed on the recording material per unit area with one color toner during normal image formation. It was set to. That is, the maximum amount of toner per unit area that can be placed on the recording material when the monochrome image forming mode using only black toner is executed is set to 100%. In this case, the toner amount per unit area of the toner image pattern C formed on the recording material when the cleaning mode is executed (using only black toner) is set to 100% or less.

  In the image forming apparatus of this embodiment, the toner image pattern C is formed on the recording material P using toners of two or more colors. The toner amount per unit area of the unfixed toner image pattern C at that time is as follows. That is, when a normal image formation (monochrome image formation mode) in which a monochrome image is formed on the recording material P by executing an image formation control sequence, the amount of toner exceeds a maximum amount of toner that can be formed per unit area on the recording material P. It is set. More preferably, the toner amount per unit area of the toner image pattern C is a unit area during normal image formation (full color image formation mode) in which an image is formed on the recording material P using two or more colors of toner. Set to a range that exceeds the maximum amount of toner that can be formed per hit.

In particular, in the case of a color image forming apparatus such as a full-color laser printer, an image is formed by superposing a plurality of color toners on the recording material P, so that the amount of toner per unit area on the recording material P increases. When the amount of toner per unit area on the recording material P increases, transfer problems such as scattering of the upper layer toner of the color toner image formed on the recording material P and transfer failure may occur. In addition, the color toner image formed on the recording material P may cause a fixing problem such as burning due to insufficient heating of the lower toner. In order not to cause such problems, during normal image formation (monochrome image formation mode and full-color image formation mode), the toner development conditions are set so that a predetermined toner amount per unit area is not exceeded. It is common to adjust and control. For example, in the image forming apparatus of this embodiment, toner having a true specific gravity of 1.1 is used, and the toner amount per unit area of the recording material P of one color toner is set to 0.45 mg / cm ² as 100%. That is, in the black image forming mode, the upper limit of the toner amount per unit area that can be placed on the recording material is 0.45 mg / cm ² . In the black image formation mode, a black toner image is formed on the photosensitive drum 1K so that the toner amount per unit area on the recording material does not exceed 0.45 mg / cm ² . When two or more color toners are superimposed to form an image (full color image formation mode), the maximum toner amount per unit area on the recording material P is set to 180%. That is, in the full color image forming mode, the upper limit of the toner amount per unit area that can be placed on the recording material is 0.81 mg / cm ² . In the full-color image forming mode, four photosensitive drums (1Y, 1C) are used so that the toner amount per unit area on the recording material in a state where the four color toners are superimposed on the recording material does not exceed 0.81 mg / cm ^2. 1M, 1K) toner images are formed. Also in the full-color image forming mode, the upper limit of the toner amount per unit area that can be placed on the recording material by each image forming station is 100% (0.45 mg / cm ² ). Note that in the normal image formation mode (monochrome image formation mode and full-color image formation mode), the video controller 101 sets the upper limit of the toner amount per unit area to 100% or 180%. That is, when the received image data is converted into bitmap data, the maximum toner amount is adjusted to 100% or 180%. The charging bias applied to the charging roller and the developing bias applied to the developing roller are not changed. The transfer bias at the time of transferring the toner image from the intermediate transfer belt to the recording paper may be changed between the monochrome image formation mode and the full color image formation mode.

  The image forming apparatus is controlled so that the maximum toner amount per unit area becomes 100% when an image is formed on the recording material P with only one color toner (black toner). Therefore, when a solid image is formed during normal image formation (monochrome image formation mode), the toner amount per unit area on the recording material is 100% or less. With this setting, the conventional image forming apparatus has the toner amount per unit area of the cleaning image pattern set to 100% or less.

  Incidentally, the toner image pattern C on the recording material P used in the cleaning mode is not used as an image sample, and the image quality may be neglected. On the other hand, according to the examination by the present applicant, it has been found that the cleaning effect is higher as the toner amount of the toner image pattern C is larger. As the amount of toner increases, the toner on the recording material easily follows the various sizes of dirt on the surface of the fixing member to be cleaned, and the toner on the recording material has a high effect of enveloping the dirt. This is probably because the cleaning effect is enhanced.

  Further, due to the increase in the toner amount, the surface of the toner image pattern C can be smoothed regardless of the unevenness of the surface of the recording material P that becomes the cleaning sheet CP. Therefore, the toner image pattern C can be easily adhered to the surface of the fixing member, and a high cleaning effect can be obtained regardless of the type of the recording material P that becomes the cleaning sheet CP.

  4, 5, and 6 are schematic views showing the relationship between the surface irregularities of the recording material P and the cleaning property. In these figures, 23 is a pressure roller, D is a dirt toner adhering to the surface of the pressure roller 23, P is a recording material to be a cleaning sheet, and CT is a toner of a toner image pattern used for cleaning. FIG. 4 shows the case of the recording material P with small surface irregularities, while FIG. 5 shows the case of the recording material P with large surface irregularities. When the unevenness of the recording material P is small, the toner CT carried on the recording material adheres to the dirty toner D on the pressure roller 23 and can be cleaned. However, when the unevenness of the recording material P is large, the toner CT carried on the recording material cannot be brought into close contact with the dirty toner D on the pressure roller 23 (G portion), and a cleaning residue is generated. However, as shown in FIG. 6, when the toner amount of the toner CT of the image pattern C is increased, the unevenness of the recording material P is concealed by the toner CT and becomes a smooth surface regardless of the unevenness of the surface of the recording material P. Therefore, the toner CT can be cleaned by being in close contact with the dirty toner D on the pressure roller 23.

  Therefore, in the image forming apparatus of the present embodiment, when the cleaning mode is executed, the toner image for forming the toner image pattern C on the recording material P uses two or more colors of toner, and the toner amount per unit area on the recording material. Is formed in an amount exceeding 100%. In other words, the amount of toner per unit area of a predetermined toner image on the recording material is the unit amount per unit area that can be placed on the recording material when normal image formation is performed using only black toner (monochrome image formation mode). More than the maximum toner amount (100%). More preferably, the toner image for forming the toner image pattern C on the recording material P is formed using toner of two or more colors so that the toner amount per unit area on the recording material exceeds 180%. In other words, the toner amount per unit area of a predetermined toner image on the recording material is the unit area that can be placed on the recording material when normal image formation is performed using a plurality of colors of toner (full color image formation mode). More than the maximum amount of toner (180%) per unit. As the toner amount of the toner image pattern C increases, the cleaning effect increases, but the toner consumption also increases. Therefore, the toner image pattern C may be appropriately set according to the characteristics of the image forming apparatus.

  As means for setting the toner amount as described above, when the image data is converted into bitmap data by the video controller 101, conversion dedicated to the cleaning mode different from the normal image formation is performed. Then, the toner amount exceeding 100% or the toner amount exceeding 180% may be adjusted by the conversion.

[Evaluation 1]
As shown in (i) and (ii) below, a toner image for cleaning is formed on the recording material, and the cleaning sheet on which the toner image for cleaning has been fixed is heated while being nipped and conveyed by the fixing nip portion. The pressure roller was cleaned. (Example)
(I) Toner image pattern = 150% toner amount per unit area on the recording material in a combination of magenta and black toner,
Cleaning frequency = every 5000 sheets,
Number of recording materials P used for one cleaning = 1 sheet passing.

(Ii) a toner amount of 400% per unit area on the recording material by a combination of yellow, cyan, magenta, and black toner;
Cleaning frequency = every 5000 sheets,
Number of recording materials P used for one cleaning = 1 sheet passing.

Further, as shown in (iii), (iv) and (v) below, a cleaning toner image is formed on the recording material, and the cleaning sheet on which the cleaning toner image has been fixed is heated while being nipped and conveyed at the fixing nip portion. The cleaning of the fixing unit (pressure roller) was performed. (Comparative example)
(Iii) 100% toner amount per unit area on the recording material using only black toner as in the conventional image forming apparatus,
Cleaning frequency = every 5000 sheets,
Number of recording materials P used for one cleaning = 1 sheet passing.

(Iv) 100% toner amount per unit area on the recording material using only black toner as in the conventional image forming apparatus,
Cleaning frequency = every 5000 sheets,
Number of recording materials P used for one cleaning = 5 sheets.

(V) 100% toner amount per unit area on the recording material using only black toner as in the conventional image forming apparatus,
Cleaning frequency = every 500 sheets,
Number of recording materials P used for one cleaning = 1 sheet passing.

  Table 1 below shows the results of endurance for passing paper while performing each of the above five cleaning modes. The recording material P used for the paper passing is OnHig HuiDong paper (manufactured by OnHig).

  As shown in Table 1, when cleaning (i) according to this example was performed, the recording material was stained from 70,000 sheets, but no winding jam was generated up to 100,000 sheets. Further, when the cleaning of (ii) according to this example was performed, the recording material was not soiled or jammed up to 100,000 sheets. On the other hand, when the conventional (iii) cleaning is performed, the recording material is contaminated from 30,000 sheets, and a winding jam is generated from 60,000 sheets. Also, in the conventional cleaning method, the cleaning effect can be improved by increasing the recording material used for one cleaning as in (iv), but the effect is in proportion to the increase in the recording material consumption. Is small. Further, in the conventional cleaning method, if the cleaning is performed frequently as shown in (v), the effect similar to the cleaning of (i) according to the present embodiment can be obtained, but the cleaning needs to be performed 10 times more frequently. .

[Evaluation 2]
Next, in the same manner as in Evaluation 1, a cleaning sheet was prepared and the cleaning performance was verified with the image forming apparatus of this example. Table 2 shows the results when the recording material P used for cleaning was Fox River Bond paper (manufactured by Fox River Paper; basis weight 75 g / m ² ). The conditions of the cleaning mode are the same as (i) and (ii) in Evaluation 1.

  As shown in Table 2, it can be seen that the cleaning ability is lower in the cleaning condition (i) than in the case of evaluation 1. This is thought to be because the surface of the Fox River Bond paper is rougher than the OnHig HuiDong paper, and it becomes difficult to adhere to the surface of the pressure roller to be cleaned, and the cleaning ability is lowered. On the other hand, under the cleaning condition (ii), since the amount of toner on the recording material is larger, the surface characteristics of the recording material are concealed, whereby the entire toner image can be closely adhered to the pressure roller surface to be cleaned, and the cleaning capability Is maintained regardless of the type of recording material.

  As described above, according to the color image forming apparatus of this embodiment, a higher cleaning effect can be obtained than in the conventional cleaning mode. Further, according to the image forming apparatus of the present embodiment, it is not necessary to perform a cleaning operation frequently without using a plurality of recording materials as a cleaning sheet.

  Accordingly, even when a large amount of recording material containing a large amount of calcium carbonate, talc, or the like is passed (introduced) through the nip portion N, even under conditions where the surface of the fixing roller 22 or the pressure roller 23 becomes particularly dirty. The dirt can be removed by a single cleaning operation. Therefore, it is not necessary to perform a cleaning operation frequently without using a plurality of recording materials P as the cleaning sheet CS. As a result, the number of cleanings of the fixing roller 22 or the pressure roller 23 to be cleaned can be reduced.

[Example 2]
Another example of the color image forming apparatus will be described.

  The color image forming apparatus shown in the present embodiment is capable of transporting a recording material at a plurality of transport speeds, and at the time of executing the cleaning mode, except that the recording material is transported at a transport speed other than the fastest transport speed, The configuration is the same as that of the image forming apparatus of the first embodiment.

  In this embodiment, the same members / portions as those in the image forming apparatus of Embodiment 1 are denoted by the same reference numerals, and description thereof is omitted. The same applies to Example 3.

  When the toner image pattern C is formed on the recording material P, the image quality of the toner image pattern can be ignored. However, the unfixed toner image pattern C per unit area on the recording material P is smaller than that at the time of normal image formation. The amount of toner increases. Therefore, the recording material conveyance speed when the toner image pattern C is formed on the recording material P is set to the fastest recording material conveyance speed as in the normal image formation. Then, particularly when the toner image pattern C is formed in a low temperature environment, a problem of fixing failure such as burning is likely to occur. As long as the recording material P is not rubbed strongly, it will not cause a big problem if it is at a level that does not cause toner separation, but if it is at a level that easily causes toner separation, a member that conveys the fixing device 20 or the recording material P. This is undesirable because it causes toner contamination. Setting a high fixing temperature can solve these problems, but for a cleaning mode that rarely operates, it is not preferable to design a fixing device to realize a higher fixing temperature, which causes unnecessary cost increase. .

  Further, the conveyance speed when conveying the recording material P (= cleaning sheet CP) carrying the fixed toner image while being sandwiched by the fixing nip portion N is set to a recording material conveyance speed slower than that during normal image formation. . Then, even when the surface temperature of the fixing roller 22 is the same, the amount of heat received by the cleaning sheet CP increases as the time for passing through the nip portion N increases. As a result, the toner image of the toner image pattern C on the cleaning sheet CP and the fouling toner on the surface of the fixing roller 22 or the pressure roller 23 are melted, and a higher cleaning effect can be obtained.

  Therefore, in the image forming apparatus of the present embodiment, the recording material conveyance speed when the toner image pattern C is formed on the recording material P (when creating the cleaning sheet CP) is slower than that during normal image formation. The transfer speed is assumed. Alternatively, the transport speed when transporting the recording material with the toner image pattern surface on the recording material P facing the surface of the fixing roller 22 to be cleaned is set to a transport speed slower than that during normal image formation. Here, when the recording material is conveyed while the toner image pattern surface on the recording material P faces the surface of the fixing roller 22 to be cleaned, the fixing cleaning sheet CP is heated while being sandwiched by the fixing nip portion N. It is time to carry. Alternatively, both when the toner image pattern C is formed on the recording material P and when the recording material is transported while the toner image pattern surface on the recording material P faces the surface of the fixing roller 22 to be cleaned, The conveyance speed is slower than that during normal image formation. Here, when the toner image pattern C is formed on the recording material P, the cleaning sheet CP is formed. When the recording material is transported with the toner image pattern surface on the recording material P facing the surface of the fixing roller 22 to be cleaned, it is transported while being heated while being sandwiched by the fixing nip N. It is. That is, it is the fastest at the time of at least one of the operations of forming the toner image pattern on the recording material and transporting the recording material with the toner image pattern surface on the recording material facing the fixing member to be cleaned. The recording material is transported at a transport speed other than the transport speed. Specifically, it is preferable that the recording material conveyance speed when forming the toner image pattern C on the recording material P is ½ or less compared to the recording material conveyance speed during normal image formation. Further, compared with the recording material conveyance speed at the time of normal image formation, the recording material conveyance speed when conveying the recording material with the toner image pattern surface on the recording material P facing the surface of the fixing roller 22 to be cleaned is 1. / 2 or less is preferable. In this embodiment, the control unit 100 controls the driving of the fixing motor M so that the recording material P is conveyed at a conveyance speed slower than the recording material conveyance speed during normal image formation when the cleaning mode is executed. Here, the time when the cleaning mode is executed means both when the cleaning sheet CP is created and when the fixed cleaning sheet CP is conveyed while being heated while being sandwiched between the fixing nips N.

  When a toner image pattern is formed on a recording material with a toner amount of 400% in a 10 ° C. and 50% RH environment (when a cleaning sheet is formed), the surface of the toner image pattern is used under the conditions of the image forming apparatus of Example 1. The toner was peeled off simply by hand. Here, the conditions of the image forming apparatus of Example 1 are that the recording material conveyance speed when creating the cleaning sheet CP is 180 mm / second (= the same speed as during normal image formation), and the surface temperature of the fixing roller 22 is 190 ° C. is there.

  On the other hand, under the conditions of the image forming apparatus when the cleaning sheet CP of the present embodiment is produced (the toner amount per unit area is 400%), the toner image pattern can be rubbed with a plastic piece even if the surface of the toner image pattern is rubbed. Did not wake up. Here, the conditions of the image forming apparatus when creating the cleaning sheet CP of the present embodiment are that the recording material conveyance speed is 60 mm / second (= 1/3 speed during normal image formation) and the cleaning sheet CP is created. The surface temperature of the fixing roller 22 at that time is 180 ° C.

  Also, when the fixed cleaning sheet CP is nipped and conveyed at the nip portion N, up to 100,000 sheets can be recorded under the conditions of the image forming apparatus of the present embodiment, compared with the cleaning conditions of the first embodiment, evaluation 1, and (i). Dirt of the material P and wrapping jam did not occur. That is, the cleaning effect was improved as compared with the case of Example 1. Here, the cleaning conditions of Example 1, Evaluation 1, and (i) are the toner amount of the unfixed toner image pattern being 150%. Then, the recording material conveyance speed when the fixed cleaning sheet CP is nipped and conveyed at the nip portion N is 180 mm / second (= the same speed as in normal image formation), and the fixed cleaning sheet CP is nipped and conveyed at the nip portion N. The surface temperature of the fixing roller at the time is 190 ° C. The condition of the image forming apparatus of the present embodiment is that the toner amount of the unfixed toner image pattern is 150%. Then, the recording material conveyance speed when the fixed cleaning sheet CP is nipped and conveyed at the nip portion N is 60 mm / second (= 1/3 speed during normal image formation), and the fixed cleaning sheet CP is transferred to the nip portion N. The surface temperature of the fixing roller is 180 ° C. when nipping and conveying.

  As described above, when the cleaning sheet is formed or when the cleaning sheet is conveyed while being heated by the fixing unit, the sheet conveying speed of at least one fixing unit is the sheet conveyance of the fixing unit during normal image formation. Slower than speed. In particular, at the time of forming the cleaning sheet or transporting the cleaning sheet while being heated by the fixing unit, at least one of the recording material transport speeds is set lower than the fastest recording material transport speed of the image forming apparatus. By making the sheet conveyance speed of the fixing unit when forming the cleaning sheet slower than the sheet conveyance speed of the fixing unit during normal image formation, there is an effect of preventing the image forming apparatus from being soiled by toner image pattern creation. A high cleaning effect is obtained by lowering the sheet conveyance speed of the fixing unit when the cleaning sheet is conveyed while being heated by the fixing unit (during fixing unit cleaning) than the sheet conveyance speed of the fixing unit during normal image formation. be able to.

[Example 3]
Another example of the color image forming apparatus will be described.

  In the color image forming apparatus shown in the present embodiment, when the cleaning mode is executed, the transfer condition of the transfer unit that transfers the unfixed toner image from the image carrier onto the recording material is changed from the normal image forming condition. Yes. Further, when the cleaning mode is executed, the cleaning condition of the cleaning unit for cleaning the transfer residual toner on the image carrier after the unfixed toner image is transferred is changed from the normal image forming condition. Except for this point, the image forming apparatus of the present embodiment has the same configuration as the image forming apparatus of the first embodiment.

  The toner image pattern C formed on the recording material P is an image obtained by neglecting the image quality, but the toner amount of the unfixed toner image pattern C per unit area on the recording material P is smaller than that at the time of normal image formation. Become more. For this reason, for example, in the case of adopting the intermediate transfer belt 6 as an image carrier as in the image forming apparatus of the present embodiment, the following problems are likely to occur. In the case of the configuration employing the intermediate transfer belt 6, in the toner transfer process to the recording material P by the secondary transfer roller 13, when the unfixed toner image pattern C is transferred under the same transfer conditions as in normal image formation, In particular, transfer defects are likely to occur in a high humidity environment. For this reason, the toner image pattern C having the assumed toner amount cannot be formed on the recording material P, and the cleaning effect when the cleaning mode is executed is reduced. On the other hand, the transfer failure of the unfixed toner image pattern C means an increase in the residual toner on the surface of the intermediate transfer belt 6. For this reason, for example, in the image forming apparatus of this embodiment, a large amount of untransferred toner is directed to the collection roller 15 that is a cleaning unit for the intermediate transfer belt 6, which easily causes a cleaning failure.

  Therefore, in this embodiment, the toner transfer condition from the intermediate transfer belt 6 onto the recording material P when the cleaning mode is executed and the cleaning condition for the transfer residual toner on the surface of the intermediate transfer belt 6 are changed from those during normal image formation. .

  An example will be specifically described according to the configuration of the image forming apparatus of the present embodiment. When the cleaning mode is executed (when the cleaning sheet CP is created), a transfer bias larger than the transfer bias applied during normal image formation is applied to the secondary transfer roller 13 from the second transfer bias power source V2. During normal image formation, if the transfer bias is too large, the charge polarity of some toners is reversed from negative to positive, and some toner returns from the recording material P to the intermediate transfer belt 6. End up. For this reason, an image defect that a part of the image on the recording material P is lost occurs. On the other hand, when the toner image pattern C for cleaning is created, the image quality can be overlooked. Therefore, the transfer bias applied to the secondary transfer roller 13 may be set to a transfer bias that can transfer the largest amount of toner onto the recording material P regardless of the occurrence of image defects. That is, the image forming unit includes a transfer unit that transfers the toner image to the recording material, and the setting of the transfer unit when forming the cleaning sheet is different from that during normal image formation.

On the other hand, during normal image formation, the collection roller 15 collects toner for a period during which printing for a predetermined page is performed, and then collects the collected transfer residual toner and electrostatically discharges it onto the surface of the intermediate transfer belt 6. However, in the image forming apparatus of this embodiment, every time the cleaning mode is executed (each time one page of the cleaning sheet is created), the transfer residual toner is collected and electrostatically discharged. That is, every time the cleaning mode is executed, the transfer residual toner on the surface of the intermediate transfer belt 6 is recovered by the recovery roller 15, and the recovered transfer residual toner is electrostatically discharged onto the surface of the intermediate transfer belt 6 each time. In normal image formation, the transfer residual toner discharged onto the intermediate transfer belt 6 is reversely transferred only to the photosensitive drum 1Y by applying a bias from the first transfer bias power source V1Y. In the image forming apparatus according to the present embodiment, every time the cleaning mode is executed, a predetermined transfer bias is applied to the primary transfer rollers 9C, 9M, and 9K so that the downstream photosensitive drums 1C, 1M, and 1K are also reversely transferred. Apply. That is, a predetermined transfer bias is applied to the primary transfer rollers 9C, 9M, and 9K from the first transfer bias power sources V1C, V1M, and V1K of each image forming station.
That is, the control unit 100 controls the transfer bias power sources V1C, V1M, and V1K so that a predetermined transfer bias is applied after each cleaning sheet CP is created. That is, the control unit 100 controls the transfer bias power supplies V1C, V1M, and V1K so as to apply a predetermined transfer bias to the primary transfer rollers 9Y, 9C, 9M, and 9K from the transfer bias power supplies V1Y, V1C, V1M, and V1K. doing.
That is, the image forming unit includes a toner image carrier that carries a toner image transferred to a recording material, and a cleaning unit that cleans the toner image carrier. Here, the toner image carrier is the intermediate transfer belt 6 in this embodiment. In the case of this embodiment, the cleaning unit corresponds to the collection roller 15 and four image forming stations. The setting of the cleaning unit when forming the cleaning sheet (the toner discharge timing of the collecting roller 15 and the setting of the four image forming stations when collecting the toner) is different from that during normal image formation.

  By changing the conditions, it is possible to prevent image defects due to poor cleaning of the intermediate transfer belt 6 after execution of the cleaning mode without reducing the toner amount of the unfixed toner image pattern C on the recording material P.

  The change of the toner transfer condition during execution of the cleaning mode of this embodiment can also be applied to a color image forming apparatus having an endless belt-like electrostatic attraction conveyance transfer belt. In this color image forming apparatus, during normal image formation, a recording material is electrostatically adsorbed onto the outer peripheral surface (surface) of the electrostatic adsorption conveyance transfer belt, and the electrostatic adsorption conveyance transfer belt is used as a plurality of photosensitive elements as image carriers. It moves around the body drum. Each of the plurality of photosensitive drums carries a toner image to be formed on a recording material. Then, by applying a transfer bias to a primary transfer roller (transfer means) as a transfer means, a single color toner image is successively transferred from the photosensitive drum onto the recording material on the surface of the electrostatic attraction conveyance transfer belt. If the change of the toner transfer condition during the execution of the cleaning mode of the present embodiment is applied to this color image forming apparatus, the same effect as that of the image forming apparatus of the present embodiment can be obtained.

  In the color image forming apparatus of this embodiment, the method of cleaning the transfer residual toner on the surface of the intermediate transfer belt 6 is a method using the collection roller 15. The cleaning method is not limited to the method using the collection roller 15, but the blade-type cleaning method can also apply the change in conditions during execution in the cleaning mode as in this embodiment.

  Further, the application condition for applying the transfer bias to the secondary transfer roller 13 and the cleaning condition for the intermediate transfer belt 6 by the recovery roller 15 when the cleaning mode is set are both set for the normal image forming mode setting. There is no need to change. Only one of them may be changed.

  In the above-described embodiments, the configuration of the fixing device has been described using a heat roller system having a fixing roller 22 incorporating a halogen lamp 21 and a pressure roller 23. However, the present invention can also be applied to an image forming apparatus having a fixing device as shown in FIG. The fixing device shown in FIG. 7 includes an endless belt 50, a heater (ceramic heater) 52 that contacts the inner surface of the endless belt 50, and a backup member (for example, an additional member) that forms a fixing nip N together with the heater 52 via the endless belt 50. Pressure roller) 51. In FIG. 7, reference numeral 53 is a temperature detecting element for detecting the temperature of the heater 52, reference numeral 54 is a guide member for guiding the rotation of the endless belt 50, and reference numeral 55 is a heating resistor formed on the ceramic substrate of the heater 52. is there. This fixing device controls the power supplied to the heating resistor 55 according to the temperature detected by the temperature detecting element 53. In the normal image forming mode and when the cleaning sheet is created in the cleaning mode, the recording material P carrying the unfixed toner image is heated and fixed to the recording material P while being nipped and conveyed by the fixing nip portion N. Further, when the cleaning sheet CP is conveyed in the cleaning mode (when the fixing unit is cleaned), the cleaning sheet CP carrying the fixed toner image (predetermined toner image) is fixed to the fixing nip so that the image surface is in contact with the pressure roller 51. It is heated while being nipped and conveyed by the section.

  In particular, the fixing device using the endless belt 50 can raise the temperature in a short time from a standby state waiting for a print instruction to a fixable state, so there is no need to preheat the fixing device during the standby state. Even in the case of preheating, it may be warmed to keep a very low temperature. Therefore, the temperature of the backup member (pressure roller) 51 during the standby state is lower than that of the fixing device of the heat roller method, and the temperature of the backup member is lower than that of the heat roller method even when printing is started. is there. The toner easily accumulates on a member having a low temperature, and in the case of a fixing device using an endless belt, the toner easily accumulates on the pressure roller. Therefore, the present invention described below is very effective when applied to an image forming apparatus equipped with a fixing device using an endless belt. In the present invention, the toner amount per unit area of a predetermined toner image (cleaning image) on a recording material can be placed on the recording material when normal image formation is performed using only black toner. The present invention refers to an embodiment in which the toner amount is larger than the maximum toner amount per unit area. In particular, the amount of toner per unit area of a predetermined toner image on the recording material is larger than the maximum amount of toner per unit area that can be placed on the recording material when performing normal image formation using multiple color toners. This is even more effective.

1Y, 1C, 1M, 1K: photoconductor drum, 20: fixing device, 41Y, 41C, 41M, 41K: image forming station, C: toner image, P: recording material

Claims (20)

An image forming unit capable of forming a toner image in which toner images of a plurality of colors are superimposed on a recording material, and fixing the toner image on the recording material by heating the recording material on which the toner image is formed while being conveyed in the nip portion A fixing unit that
A cleaning toner image in which a plurality of colors of toner are superimposed is formed on the recording material in the image forming unit, and the cleaning toner image formed on the recording material is fixed on the recording material in the fixing unit and cleaned. In the image forming apparatus capable of executing a cleaning mode in which the cleaning sheet is transported at the nip portion and the fixing portion is cleaned after the sheet for cleaning is prepared.
The amount of toner per unit area of the toner image for cleaning is larger than the maximum amount of toner per unit area that can be superimposed on a recording material with a plurality of color toners superimposed during normal image formation,
Conveying speed of the recording material in said nip when creating a sheet for the cleaning, rather slow than the transport speed of the recording material in the nip portion when the normal image formation using the recording medium, wherein An image forming apparatus , wherein a temperature of the fixing unit when forming a cleaning sheet is lower than a temperature of the fixing unit when forming a normal image using the recording material . Each color toner image constituting the cleaning toner image is formed with a toner amount equal to or less than the maximum toner amount per unit area that can be placed on a recording material during normal image formation using only a single color toner. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The conveyance speed of the recording material in the nip portion when the cleaning sheet is prepared is ½ or less of the conveyance speed of the recording material in the nip portion when normal image formation is performed using the recording material. The image forming apparatus according to claim 1 , wherein the image forming apparatus is provided. The maximum amount of toner per unit area that can be placed on a recording material when a normal image is formed by superimposing a plurality of color toners is placed on the recording material when a normal image is formed using only a single color toner. The image forming apparatus has a maximum toner amount per unit area that is larger than a maximum toner amount per unit area that can be placed on a recording material when a normal image is formed using only a single color toner. 4. The image forming apparatus according to claim 1, wherein the amount of toner is less than the amount of toner multiplied by the number of colors of toner that can be used. The image forming apparatus includes an image processing unit that converts image data into bitmap data, and an exposure unit that forms an electrostatic latent image corresponding to the bitmap data.
In the image processing unit, the toner amount per unit area of the cleaning toner image is the maximum toner amount per unit area that can be superimposed on a recording material by superposing a plurality of color toners during normal image formation. more composed manner, the image forming apparatus according to any one of claims 1 to 4, characterized in that converting the image data of the toner images for the cleaning to bitmap data. When the cleaning sheet is conveyed at the nip portion and the fixing portion is cleaned, the conveyance speed of the cleaning sheet at the nip portion is usually determined by using a recording material used as the cleaning sheet. the image forming apparatus according to any one of claims 1 to 5, characterized in that slower than the conveying speed in the nip portion when the image formation. The image forming unit includes an image carrier that carries a toner image, and a transfer member that transfers the toner image carried on the image carrier to a recording material.
The transfer bias applied between the image carrier and the transfer member when the cleaning toner image carried on the image carrier in the cleaning mode is transferred to a recording material is used for normal image formation. the image forming apparatus according to any one of claims 1 to 6, wherein greater than the maximum transfer bias can be set. The fixing unit, an image forming apparatus according to any one of claims 1 to 7, characterized in that it has a tubular film. The image forming apparatus according to claim 8 , wherein the fixing unit includes a heater that contacts an inner surface of the film, and a pressure member that forms the nip portion together with the heater through the film. . An image forming apparatus comprising: an image forming unit capable of forming a toner image on a recording material; and a fixing unit configured to heat the recording material on which the toner image is formed while being conveyed at the nip portion and fix the toner image on the recording material. A method of cleaning the fixing unit in
In the image forming unit, the amount of toner per unit area of the recording material is larger than the maximum amount of toner per unit area that can be superimposed on the recording material when a plurality of colors of toner are superimposed when performing normal image formation. As described above, a toner image for cleaning is formed on a recording material by superimposing a plurality of color toner images,
In the fixing unit, the recording material on which the cleaning toner image is formed is transported at a transport speed slower than the transport speed of the recording material when the recording material is used for normal image formation, and the recording material is used. At a temperature lower than the temperature of the fixing unit at the time of normal image formation, the sheet is heated while being conveyed at the nip unit, and the cleaning toner image is fixed on a recording material to create a cleaning sheet,
In the fixing unit, the cleaning sheet is transported through the nip portion to clean the fixing unit. Each color toner image constituting the cleaning toner image is formed with a toner amount equal to or less than the maximum toner amount per unit area that can be placed on a recording material during normal image formation using only a single color toner. The fixing unit cleaning method according to claim 10, wherein the fixing unit cleaning method is performed. The conveyance speed of the recording material in the nip portion when the cleaning sheet is prepared is ½ or less of the conveyance speed of the recording material in the nip portion when normal image formation is performed using the recording material. The method for cleaning a fixing unit according to claim 11 , wherein the cleaning method is provided. The maximum amount of toner per unit area that can be placed on a recording material when a normal image is formed by superimposing a plurality of color toners is placed on the recording material when a normal image is formed using only a single color toner. The image forming apparatus has a maximum toner amount per unit area that is larger than a maximum toner amount per unit area that can be placed on a recording material when a normal image is formed using only a single color toner. 13. The fixing unit cleaning method according to claim 10, wherein the toner amount is less than the amount of toner multiplied by the number of colors of toner that can be used. An image forming unit capable of forming a toner image on a recording material, and a fixing unit for fixing the toner image to the recording material by heating the recording material on which the toner image is formed while being conveyed at the nip portion, After forming a cleaning toner image on the recording material in the image forming unit and fixing the cleaning toner image formed on the recording material on the recording material in the fixing unit to create a cleaning sheet, In the image forming apparatus capable of executing a cleaning mode in which the cleaning sheet is conveyed at the nip portion to clean the fixing portion.
The amount of toner per unit area of the toner image for cleaning is larger than the maximum amount of toner per unit area that can be placed on a recording material during normal image formation,
Conveying speed of the recording material in said nip when creating a sheet for the cleaning, rather slow than the transport speed of the recording material in the nip portion when the normal image formation using the recording medium, wherein An image forming apparatus , wherein a temperature of the fixing unit when forming a cleaning sheet is lower than a temperature of the fixing unit when forming a normal image using the recording material . The conveyance speed of the recording material in the nip portion when the cleaning sheet is prepared is ½ or less of the conveyance speed of the recording material in the nip portion when normal image formation is performed using the recording material. The image forming apparatus according to claim 14 , wherein the image forming apparatus is provided. The image forming apparatus includes an image processing unit that converts image data into bitmap data, and an exposure unit that forms an electrostatic latent image corresponding to the bitmap data.
In the image processing unit, the cleaning toner image has a toner amount per unit area that is larger than a maximum toner amount per unit area that can be placed on a recording material when a normal image is formed. 16. The image forming apparatus according to claim 14 , wherein image data of a toner image for use is converted into bitmap data. When the cleaning sheet is conveyed at the nip portion and the fixing portion is cleaned, the conveyance speed of the cleaning sheet at the nip portion is usually determined by using a recording material used as the cleaning sheet. the image forming apparatus according to any one of claims 14 to 16, wherein the slower than the conveying speed in the nip portion when the image formation. The image forming unit includes an image carrier that carries a toner image, and a transfer member that transfers the toner image carried on the image carrier to a recording material.
The transfer bias applied between the image carrier and the transfer member when the cleaning toner image carried on the image carrier in the cleaning mode is transferred to a recording material is used for normal image formation. the image forming apparatus according to any one of claims 14 to 17 and greater than the maximum transfer bias can be set. The fixing unit, an image forming apparatus according to any one of claims 14 to 18, characterized in that it has a tubular film. The image forming apparatus according to claim 19 , wherein the fixing unit includes a heater that contacts an inner surface of the film, and a pressure member that forms the nip portion together with the heater through the film. .