JP4684902B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a transfer material.

As an image forming apparatus that forms an image on a transfer material using an electrophotographic method, an image forming apparatus having a borderless print function that forms a toner image with a size that protrudes from the edge of the transfer material has been proposed (Patent Document 1). ).

In such an image forming apparatus, the transfer material is conveyed through the apparatus in a state in which toner is carried without forming a blank over the entire area of the transfer material, and is introduced into an image heating fixing device (fixing device). The transfer material is nipped and conveyed at the heating nip portion to heat and fix the toner on the transfer material. When the transfer material is nipped and conveyed at the nip portion, there is a problem that toner adheres to the fixing member and the pressure member that form the nip portion, and the toner stains the transfer material.

In particular, when toner at the leading edge of the transfer material adheres to the fixing member, the attached toner may be offset on the image and appear as an image defect on the transfer material. In order to prevent this image defect, it is necessary to reduce adhesion of toner to the fixing member and to clean the toner attached to the fixing member.

Therefore, an image forming apparatus having a borderless printing function as described above generally has a configuration in which a cleaning member is disposed on a fixing member.
JP 2004-45457 A

In the conventional image forming apparatus, the cleaning member is brought into direct contact with the fixing member. Therefore, the material selection and the contact configuration of the cleaning member are very difficult for the heat resistance of the cleaning member and the prevention of scratches on the fixing member by the cleaning member.

In particular, when the cleaning member is brought into contact with the fixing member, it is necessary to maintain good cleaning properties over the durable life of the apparatus and to suppress the occurrence of scratches and scraping on the fixing member. However, the occurrence of scratches due to the contact of the cleaning member with the fixing member is a very serious problem because it appears directly as an image defect.

An object of the present invention is to transfer toner when the toner adhering to the edge portion at the leading edge of the transfer material is offset to the first rotating body during borderless printing and returns to the fixing nip portion by the rotation of the first rotating body. In addition to suppressing the phenomenon of adhering to the image forming surface of the material, it suppresses image disturbance that may occur due to vibration when the leading edge of the transfer material comes into contact with the second rotating body during printing with a border An object of the present invention is to provide an image forming apparatus that can suppress image disturbance by giving priority to the above.

The configuration of the image forming apparatus according to the present invention includes an image forming unit that forms an unfixed toner image on a transfer material, a first rotating body that is in contact with a surface of the transfer material on which the unfixed toner image is formed , and the first of an unfixed toner image while conveying the transfer material a second rotating body forming the fixing nip portion together with the rotating body Bei example the fixing nip portion has a fixing portion for fixing the transfer material, a transfer material and bordered printing to form a toner image, leaving a margin in the peripheral portion, in an image forming apparatus that can perform a marginless printing for forming a toner image without leaving a blank space in the periphery of the transfer material, the fixing part The leading edge of the transferred transfer material is set so as to contact the second rotating body, and when executing the borderless printing, the transfer material is transported to the fixing unit rather than the moving speed of the transfer material. The peripheral speed of the second rotating body is set slow, When performing printing with a border, the peripheral speed of the second rotating body is slower than the moving speed of the transfer material conveyed to the fixing unit, and the speed difference between the two is smaller than in the case of borderless printing. it shall be the said to set the rotational speed of the second rotating body or, as the speed difference is eliminated so.

According to the present invention, the toner adhering to the edge portion at the tip of the transfer material during borderless printing is offset to the first rotating body, and is transferred when the toner returns to the fixing nip portion by the rotation of the first rotating body. In addition to suppressing the phenomenon of adhering to the image forming surface of the material, it suppresses image disturbance that may occur due to vibration when the leading edge of the transfer material comes into contact with the second rotating body during printing with a border Therefore, it is possible to provide an image forming apparatus capable of suppressing image disturbance by giving priority to the operation.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[Reference Example 1]

[ First Reference Example ]
(1) Overall Configuration of Image Forming Apparatus FIG. 1 is an overall configuration diagram of an example of an image forming apparatus according to this reference . This image forming apparatus is a color image forming apparatus (full color laser beam printer) that forms an image on a transfer material such as recording paper or an OHP sheet using an electrophotographic image forming system.

The image forming apparatus of this reference example has a control unit (control means) 102 including a CPU and a memory such as a ROM and a RAM in the apparatus main body 101. The control unit 102 receives a print signal with a border from a personal computer (not shown). S1 or borderless print signal S2 is input.

Further, in the image forming apparatus main body 101, first to first toner images of respective colors of yellow Y, magenta M, cyan C, and black K are formed as image forming means (image forming unit) for forming an image on a transfer material. It has a fourth four image forming stations SY, SM, SC, and SK. Each station S (Y to K) has a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. Around each photosensitive drum 1, there are a charging roller 2 as a charging means, a laser scanner unit 3 as an exposure means, a developing device 4 as a developing means, a transfer roller 5 as a transferring means, and a cleaning means. A cleaning device 6 is provided. An electrostatic conveyance belt 7 as a recording medium conveyance unit is disposed so as to face the photosensitive drum 1 of each station S (Y to K). The conveyor belt 7 is stretched around three axes of a driving roller 8a and driven rollers 8b and 8c. A transfer roller T is formed between the photosensitive drum 1 and the conveyor belt 7 by disposing the transfer roller 5 so as to face each photosensitive drum 1 with the conveyor belt 7 interposed therebetween.

An image forming operation of the image forming apparatus of this reference example will be described.

When the control unit 102 inputs a print signal S1 with a border, the image forming apparatus drives a predetermined member of the station S (Y to K) according to a print sequence control with a border, and creates a margin on the peripheral edge of one side of the transfer material. The image forming operation of the print with margin to be formed is performed. In addition, when the control unit 102 inputs a borderless print signal S2, a predetermined member of the station S (Y to K) is driven according to a predetermined borderless print sequence control, and a margin that does not form a margin on one edge of the transfer material. The image forming operation of the no print is performed. In this reference example, a case of borderless printing will be described as an image forming operation.

  Each station S (Y to K) is sequentially driven, and each photosensitive drum 1 is rotated in the direction of the arrow at a predetermined peripheral speed (process speed). Further, the transport belt 7 is rotated in the direction of the arrow by the driving roller 8a at a peripheral speed corresponding to the rotational peripheral speed of each photosensitive drum 1.

  First, in the first color yellow Y station SY, the outer peripheral surface (surface) of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. Next, the scanner unit 3 scans and exposes the surface of the photosensitive drum 1 with a laser beam corresponding to the image information. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the uniformly charged photosensitive drum 1. The latent image is developed with yellow toner (developer) by the developing device 4 to form a yellow toner image (developed image) on the surface of the photosensitive drum 1. A similar image forming process is performed in each of the magenta M, cyan C, and black K stations S (M to K). A toner image (development image) of each color is formed on the surface of the photosensitive drum 1 of each station S (Y to K).

On the other hand, the transfer material P stacked and stored in the feeding cassette 9 is sent to the registration roller pair 11 by the pickup roller 10. Next, the transfer material P is transported between the transport belt 7 and the electrostatic transfer roller 12 by the roller pair 11 in the vicinity of the driven roller 8b. The electrostatic transfer roller 12 electrostatically attracts the transfer material P to the outer peripheral surface (front surface) of the transport belt 7. The transfer material P is conveyed from the transfer portion T on the upstream side in the rotation direction to the transfer portion T on the downstream side in the rotation direction by the rotation of the conveyance belt 7. In the transfer process, the toner images on the respective photosensitive drums 1 are transferred onto the transfer material P in order by the transfer roller T by the transfer roller 5 on the transfer material P surface. The transfer material P is separated from the conveying belt 7 in the vicinity of the driving roller 8a and is conveyed to an image heating and fixing device 13 as an image heating unit. Then, when the transfer material P passes through the fixing device (fixing unit) 13, the toner image is fixed on the transfer material P surface.

  The transfer material P exiting the fixing device 13 is discharged onto a discharge tray 15 at the top of the apparatus main body 100 by discharge rollers 14a and 14b.

  In each station S (Y to K), the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is removed by the cleaning device 6. Thus, the photosensitive drum 1 is repeatedly used for the next image formation.

(2) Fixing device 13
FIG. 2 is a diagram illustrating a schematic configuration of a main part of the fixing device 13 and a relationship between the fixing device 13 and the conveyance belt 7.

Reference numeral 21 denotes a flexible endless fixing belt (first rotating body), which is a cylindrical member in which an elastic layer is provided on a polyimide base layer. Reference numeral 22 denotes an elastic pressure roller (second rotating body). Reference numeral 23 denotes a vertical heat-resistant heater holder (heating body holding member) having a substantially semicircular cross section. Reference numeral 24 denotes a heater (heating body) as a heat source, which is held by a holder 23. The fixing belt 21 is loosely fitted on the holder 23. As the heater 24, a ceramic heater is used in this reference example.

The holder 23 is a molded product of liquid crystal polymer resin having high heat resistance. The holder 23 of this reference example serves not only to hold the heater 24 but also to guide the rotation locus of the fixing belt 21.

  The pressure roller 22 is formed by forming a silicone rubber layer 22b as an elastic layer on the outer periphery of a stainless steel core 22a and coating a PFA resin tube thereon as a release layer 22c. The pressure roller 22 is provided with both ends of the cored bar 22a rotatably supported between the rear and front side plates of the apparatus frame (not shown). On the upper side of the pressure roller 22, the heating assembly including the heater 24, the holder 23, the fixing belt 21 and the like is arranged in parallel to the pressure roller 22 with the heater 24 facing downward, and both end portions of the holder 23 are not attached. It is urged toward the pressure roller 22 by the illustrated pressure mechanism. Thus, a nip portion (heating nip portion) N having a predetermined width necessary for heat fixing is formed between the fixing belt 21 held by the holder 23 and the pressure roller 22.

  FIG. 3 is a schematic configuration diagram of the heater 24.

  The heater 24 has an elongated substrate (insulating substrate) a in a direction orthogonal to the transfer direction of the transfer material P. The substrate a is formed of highly insulating ceramics such as alumina, aluminum nitride, and silicon carbide.

On the surface of the substrate a (surface on the nip portion N side), an energization heating element (heating resistor) b along the longitudinal direction
Is formed. The energization heating element b is formed by applying a material paste along the width direction of the substrate a in the form of a line or a narrow band by screen printing or the like and firing it. The energization heating element b is made of, for example, Ag / Pd (silver palladium: silver alloy), RuO ₂ , Ta ₂ N, or the like.

  At both ends of the energization heating element b, there is an electrode part c formed of Ag / Pt (silver / platinum) or the like provided in an electrically conductive state.

  In addition, it has an insulating protective layer d such as a thin glass coat or a fluororesin coat that can electrically insulate the surface of the energization heating element b and can withstand sliding with the fixing belt 21.

  In the heater 24, the side on which the insulating protective layer d is provided is the front side, and the inner surface of the fixing belt 21 slides on the surface of the insulating protective layer d. The heater 24 is held in the width direction of the transfer material P by the holder 23.

  Reference numeral 31 denotes a power feeding connector, which is fitted to the electrode portion c of the heater 24 fixedly supported by the holder 23, and the electrical contacts on the connector 31 side are in contact with the electrode portion c. 32 is a commercial power supply (AC), 33 is a triac, and 34 is a DC controller which is a temperature control circuit (temperature control means). The heater 24 is rapidly and rapidly heated by the heat generated by the energization heating element b by being fed from the commercial power source 32 to the electrode portion c via the triac 33.

  TH is a thermistor as temperature detecting means, and is provided on the back surface (surface opposite to the nip portion N) of the substrate a of the heater 24 (FIG. 3). The thermistor TH detects the temperature of the heater 24 and outputs a temperature detection signal (temperature information) to the DC controller 34.

  The DC controller 34 takes in a detection signal from the thermistor TH and controls the triac 33 so that the detection signal is maintained at a predetermined temperature (target temperature). That is, energization from the commercial power supply 32 to the energization heating element b is controlled (power supply control).

(3) Positional relationship between the fixing device 13 and the conveying belt 7 The fixing device 13 is configured to introduce the leading end of the transfer material P, which is conveyed by being separated from the conveying belt 7 in the vicinity of the driving roller 8a, into the nip portion N. The transfer material P is disposed at a position where the front end of the transfer material P is in contact with the surface of the pressure roller 22 on the downstream side of the nip portion N in the rotation direction of the pressure roller 22. In this reference example, the fixing device 13 is arranged at a position facing the surface of the pressure roller 22 on the extension line A in the conveyance direction of the transfer material P conveyed from the conveyance belt 7. As a result, the surface of the transfer material P that is conveyed with the curvature being separated from the conveyor belt 7 during printing on one side (one side) of the transfer material P can be brought into contact with the surface of the pressure roller 22. .

(4) Measures for optimizing the transfer speed of the transfer material P at the transfer portion T and the nip portion N, and the switching configuration of the rotation speed of the pressure roller 22 FIG. It is explanatory drawing of a system.

The image forming apparatus according to this reference example performs two processing operations of a transfer material P, that is, a toner image transfer at the transfer unit T of the station S and a heat fixing of the toner image at the nip N of the fixing device 13 in parallel. It is made compact so that it can be done. Therefore, the transfer speed of the transfer material P in the nip portion N is controlled so that the transfer speed (movement speed) of the transfer material P in the nip portion N has an appropriate relationship with the transfer speed of the transfer material P in the transfer portion T. ing.

In this reference example, a loop sensor 41 as a loop detection unit is provided between the conveyance belt 7 and the pressure roller 22 in the conveyance direction of the transfer material P, and the loop sensor 41 is used between the conveyance belt 7 and the pressure roller 22. The loop R (sag) of the transfer material P is detected. The loop sensor 41 includes a flag 41a that can rotate around a shaft portion, and an optical sensor 41b such as a photo interrupter that detects the flag 41a. Then, whether or not the loop amount of the transfer material P becomes a certain amount or more is detected by whether or not the flag 41a blocks light by the optical sensor 41b.

  The pressure roller 22 is rotated at a predetermined rotational speed (circumferential speed) in the direction of an arrow by driving a driving gear (not shown) provided at one end of the cored bar 22a by a motor M1 as a driving unit. The rotation speed (driving speed) of the pressure roller 22 is switched stepwise by at least two steps by the speed switching means 42. The speed switching means 42 includes a CPU and a memory such as a ROM and a RAM, and electrically controls the motor M according to the detection result of the loop sensor 41 to change the rotation speed of the motor M from high speed to low speed or from low speed to high speed. It is supposed to switch to. That is, the loop amount of the transfer material P is made constant by switching the driving speed of the pressure roller 22 by decreasing or increasing the rotational speed of the motor M by the speed switching means 42 according to the detection result of the loop sensor 41. I am doing so.

In this reference example, the driving speed of the pressure roller 22 is switched in two stages. As shown in FIG. 4, when the transferred transfer material P has no loop R (in the case of a broken line), the optical sensor 41b is shielded from light by the flag 41a (off). When the loop R becomes larger than a predetermined amount in the transferred transfer material P (in the case of a solid line), the loop R comes into contact with the flag 41a. The flag 41a comes into contact with the loop R and rotates to the position where the optical sensor 41b detects open (on), that is, the position where light is not shielded.

  The speed switching means 42 slows the transfer speed of the transfer material P at the nip N when the optical sensor 41b is off, and increases the transfer speed of the transfer material P at the nip N when the optical sensor 41b is on. To switch the rotation speed of the motor M. That is, when the optical sensor 41b is on, the rotational speed of the motor M is slowed down so that the driving speed of the pressure roller 22 is slower than the transport speed of the transfer material P conveyed from the belt 8 to the pressure roller 22. ing. When the optical sensor 41b is off, the rotation speed of the motor M is increased so that the driving speed of the pressure roller 22 is higher than the conveying speed of the transfer material P conveyed from the belt 8 to the pressure roller 22. .

  When the rotation speed of the motor M is slowed, the transfer material P drawing amount of the nip portion N is reduced relative to the transfer speed of the transfer material P in the transfer portion T. On the other hand, when the rotational speed of the motor M is increased, the transfer material P drawing amount of the nip portion N increases relative to the transfer speed of the transfer material P in the transfer portion T. As described above, by increasing or decreasing the transfer material P drawing amount of the nip portion N, the loop amount of the transfer material P between the transfer portion T and the nip portion N can be made constant.

In this reference example, the control of switching the driving speed of the pressure roller 22 is performed by using the above-described loop control method, but the driving of the pressure roller 22 is performed using a loop control method other than the above-described loop control method. Control for switching the speed may be performed. Further, by appropriately setting the distance between the transfer portion T and the nip portion N and the transport speed of the transfer material P by the transport belt 7, control for switching the driving speed of the pressure roller 22 may be performed.

  Further, as the speed switching means 42, a mechanism / device that can mechanically switch the driving speed of the pressure roller 22 may be employed.

(5) Heat Fixing Operation of Fixing Device 13 The heat fixing operation of the fixing device 13 will be described with reference to FIGS. 2, 5, 6A, 6B, and 6C.

  In FIG. 2, the pressure roller 22 is rotated at a predetermined peripheral speed in the direction of the arrow by the motor M1. Along with the rotation of the pressure roller 22, a rotational force acts on the fixing belt 21 by the frictional force at the nip portion N between the surface of the pressure roller 22 and the surface of the fixing belt 21. As a result, the fixing belt 21 rotates around the outside of the holder 23 in the nip portion N while the inner surface of the fixing belt 21 is in close contact with the downward surface of the heater 24 and slides. Sliding grease (not shown) is applied between the inner surface of the fixing belt 21 and the holder 23. Thereby, the slidability of the fixing belt 21 with respect to the holder 23 is maintained.

  As described above, the fixing belt 21 is rotated by the rotational driving of the pressure roller 22. Further, when the heater 24 is energized, the heater 24 is heated and adjusted to a predetermined target temperature. In this state, the transfer material P carrying the unfixed toner image t is introduced onto the surface of the pressure roller 22 by the transport belt 7 at a predetermined transport speed.

  In the following description, the surface of the transfer material P on which the toner image t is formed and supported is referred to as the surface. A surface on which no toner image is formed and supported is referred to as a back surface.

In the image forming apparatus of this reference example, the conveyance speed of the transfer material P conveyed to the fixing device 13 and the driving speed of the pressure roller 22 are set as follows. That is, in the conveyance direction of the transfer material P, the transfer material P conveyance speed V1 when the leading edge of the transfer material P is introduced into the nip portion N, the driving speed of the pressure roller 22 (fixing conveyance speed (in this case, pressure) The peripheral speed of the roller)) V2 is such that V2 <V1. Specifically, the process speed of the image forming apparatus used in the present reference example is the conveyance speed V1 of the transfer material P = 180 mm / sec, and the fixing conveyance speed V2 is equal to the conveyance speed V1 of 180 mm / sec. The peripheral speed ratio was 3% slower and V2 = 174.6 mm / sec. In this reference example, the peripheral speed ratio is defined as (V1−V2) / V1.

  FIG. 5 shows a state in which the leading edge of the transfer material P conveyed from the conveyance belt 7 contacts the surface of the pressure roller 22 of the fixing device 13.

  When the transfer material P is conveyed from the conveyance belt 7, the leading end of the transfer material P comes into contact with the surface of the pressure roller 22 of the fixing device 13. Here, the distance on the circumference of the pressure roller 22 from the position where the tip of the transfer material P abuts on the surface of the pressure roller 22 to the nip portion N was set to L = about 3 mm. By setting L = about 3 mm, the back surface of the transfer material P comes into contact with the surface of the pressure roller 22 before the toner t on the front end surface, and thereafter, the transfer material P along the circumferential direction of the surface of the pressure roller 22. Is conveyed to the nip portion N. Accordingly, only the toner portion on the front surface of the transfer material P does not directly contact the surface of the fixing belt 21 or the pressure roller 22 before the back surface of the transfer material P. For this reason, there is little offset toner on the surface of the fixing belt 21 and the pressure roller 22.

  Further, even when the toner t is carried on the edge portion at the front end of the transfer material P and introduced into the nip portion N, toner contamination on the surface of the fixing belt 21 and the pressure roller 22 can be suppressed. That is, by setting the fixing conveyance speed V2 slower than the transfer material conveyance speed V1, when the leading edge of the transfer material P enters the nip N, the toner is transferred to the front edge of the transfer material P by the surface of the fixing belt 21. It will be in the state pushed into the edge part. Therefore, the toner is more easily fixed to the edge portion at the front end of the transfer material P, and the toner is fixed to the front end of the transfer material P and discharged from the nip portion N. It is possible to suppress toner contamination on the surface of the pressure roller 22.

  Next, a state in which the transfer material P in contact with the surface of the pressure roller 22 is further conveyed and reaches the nip portion N will be described.

  6A, FIG. 6B, FIG. 6C, and FIGS. 7A, 7B, and 7C, the toner t at the front end of the transfer material P is offset to the pressure roller 22 surface. The positional relationship between the offset toner t1 and the leading edge of the transfer material P is shown. 6A, 6B, and 6C are diagrams illustrating the positional relationship between the offset toner t1 and the leading edge of the transfer material P when the fixing conveyance speed V2 is slower than the transfer material conveyance speed V1. . FIGS. 7A, 7B, and 7C are comparative examples of FIGS. 6A, 6B, and 6C, respectively, where the transfer material conveyance speed V1 and the fixing conveyance speed V2 are equal. FIG. 6 is a diagram illustrating a positional relationship between the offset toner t1 and the leading edge of the transfer material P.

  When the transfer material transport speed V1 and the fixing transport speed V2 are equal, that is, when there is no speed difference between the transfer material transport speed V1 and the fixing transport speed V2, the offset toner on the surface of the pressure roller 22 as shown in FIG. The positional relationship between t1, the transfer material P tip position, and the pressure roller 22 does not change. Therefore, the offset toner t1 is introduced into the nip portion N without the transfer material P. That is, the offset toner t1 is introduced into the nip portion N before the front end of the transfer material P, and is offset to the surface of the fixing belt 21 or the pressure roller 22 (FIG. 7B).

  As described above, the offset toner t1 once offset on the surface of the pressure roller 22 is offset on the surface of the fixing belt 21 or the surface of the pressure roller 22, and therefore, the image of the transfer material P after one rotation of the fixing belt 21 and the pressure roller 22. It will appear as an offset image on the surface. Therefore, for example, when there are cleaning members 30 and 31 arranged in contact with the surface of the pressure roller 22 and the surface of the fixing belt 21 as shown in FIG. 7C, the offset toner t1 is set by these cleaning members 30 and 31. By collecting the image, image defects are prevented.

On the other hand, when the fixing conveyance speed V2 is slower than the transfer material conveyance speed V1 as in this reference example, the offset toner t1 on the surface of the pressure roller 22 is conveyed slower than the conveyance of the transfer material P. . Therefore, as shown in FIG. 6A, the offset toner t1 enters the rear end side of the rear surface of the transfer material P. Accordingly, the toner that exists without passing through the transfer material P, that is, the offset toner t1 introduced before the front end of the transfer material P hardly enters the nip portion N. Therefore, toner adhesion to the surface of the fixing belt 21 can be prevented, and adhesion of the offset toner t1 to the pressure roller 22 surface can be suppressed.

  When the transfer material P is further conveyed and the transfer material P is discharged from the nip portion N, the offset toner t1 adheres to the back surface at the front end of the transfer material P and is discharged as shown in FIG. It will be. That is, every time image formation is performed, the offset toner t1 can be attached to the back surface of the front end of the transfer material P and discharged by the transfer material P in a very small amount, so that it is possible to form an image without image defects.

  The offset toner t1 on the surface of the pressure roller 22 is introduced into the nip portion N along the surface of the pressure roller 22 due to the speed difference between the transfer material conveyance speed V1 and the fixing conveyance speed V2. In addition, the transfer material P is scraped by the edge portion on the back surface of the front end. The offset toner t1 is introduced into the nip portion N together with the transfer material P, so that the offset toner t1 is fixed to the edge portion on the back surface of the transfer material P. The offset toner t1 can be discharged from the nip portion N together with the transfer material P.

  Further, when the offset toner t1 cannot be completely fixed on the edge portion on the back surface of the front end of the transfer material P, or the offset toner t1 remains on the surface of the pressure roller 22 without being completely discharged on the back surface of the transfer material P. Also, the offset toner t1 can be collected. That is, as shown in FIG. 6C, the cleaning member 30 is disposed in contact with the surface of the pressure roller 22, and the offset toner t1 on the surface of the pressure roller 22 is collected by the cleaning member 30.

  Here, the relationship between the distance L and the speed difference between the transfer material conveyance speed V1 and the fixing conveyance speed V2 will be described in more detail.

  As described above, the distance on the circumference of the pressure roller 22 from the position where the front end of the transfer material P contacts the surface of the pressure roller 22 to the nip portion N is set to L = about 3 mm, and the transfer material The fixing conveyance speed V2 is set to be 3% slower than the conveyance speed V1 in terms of the peripheral speed ratio.

  In this case, when the offset toner t1 is generated on the surface of the pressure roller 22, a very small amount cannot be confirmed with the naked eye at a position of about 0.09 mm from the front end to the rear end of the transfer material P on the back surface of the transfer material P. It was confirmed that the offset toner t1 can be attached to the toner and discharged. At this time, no adhesion of the offset toner t1 to the surface of the pressure roller 22 and the surface of the fixing belt 21 was observed.

  As another comparative setting, when the above peripheral speed ratio was confirmed to be 2 to 10% in the same manner, the transfer material P was in the range of 0.06 to 0.3 mm from the front end to the rear end side, and could not be confirmed with the naked eye. It was confirmed that the offset toner t1 can be attached and discharged in a minute amount. Also at this time, the adhesion of the offset toner t1 to the surface of the pressure roller 22 and the surface of the fixing belt 21 was not observed.

  Further, when L = 5 mm, the above peripheral speed ratio was confirmed to be 2 to 10%. As a result, a slight offset within the range of 0.10 to 0.5 mm from the front end of the transfer material P was also made that could not be confirmed with the naked eye. It was confirmed that the toner t1 can be adhered and discharged. Also at this time, adhesion of the offset toner t1 to the surface of 22 and the surface of the fixing belt 21 was not observed.

  In addition, when L = 10 mm or more, the effects of avoiding toner contamination on the fixing belt 21, improving the cleaning performance of the fixing belt 21, and increasing the margin are also seen. However, there may be other problems such as scattering and blurring of the leading edge image when the leading edge of the transfer material P enters, and image blurring caused by a large peripheral speed ratio. Therefore, it is preferable to set the distance L in the range of L <10 mm.

  However, for example, in the case where the pressure roller 22 is configured by an endless pressure belt and the leading end of the transfer material P is introduced into the nip portion N along the pressure belt, L is in the above range. There are no harmful effects even outside. Therefore, when the pressure roller 22 is formed of a pressure belt, it is possible to obtain effects such as toner contamination avoidance, cleaning performance improvement, and margin increase.

As described above, according to the color image forming apparatus of this reference example, toner adhesion to the fixing belt 21 can be prevented, and toner adhesion to a pressure member such as the pressure roller 22 or the pressure belt can be suppressed. Further, even when the toner adheres to the surface of the pressure member, the toner adhesion amount can be reduced as compared with the conventional case. Therefore, the pressure member is removed by the cleaning member 30 disposed in contact with the surface of the pressure member. The toner adhering to the surface can be easily collected.
[Reference Example 2]

[Second Reference Example ]
FIG. 8 is an overall configuration diagram of another example of the image forming apparatus according to this reference example . This image forming apparatus is also a color image forming apparatus (full color laser beam printer) that forms an image on a transfer material such as recording paper or an OHP sheet using an electrophotographic image forming system.

The image forming apparatus of the present reference example is an apparatus that includes an endless belt-shaped intermediate transfer member 16 as a second image carrier. In this reference example, members / parts having the same functions as those of the image forming apparatus of Reference Example 1 are denoted by the same reference numerals, and description thereof is omitted.

Also in the image forming apparatus of this reference example, an image forming operation for forming an image on one side of the transfer material P is performed according to a predetermined image forming sequence. That is, each station S (Y to K) is sequentially driven, and each photosensitive drum 1 is rotated in the direction of the arrow at a predetermined peripheral speed (process speed). Further, the intermediate transfer member 16 stretched around the three axes of the driving roller 17a and the driven rollers 17b and 17c is rotated by the driving roller 19a in the direction of the arrow at a peripheral speed corresponding to the rotational peripheral speed of each photosensitive drum 1. .

  In each station S (Y to K), the toner image (development image) of each color is formed on the surface of the photosensitive drum 1 of each station S (M to K) by performing the image forming process described above. The toner images of the respective colors formed on the surface of the photosensitive drum 1 are transferred onto the outer peripheral surface (front surface) of the intermediate transfer member 16 by the transfer roller 5 in order in the rotation direction of the intermediate transfer member 16 (primary transfer).

  On the other hand, the transfer material P stacked and stored in the feeding cassette 9 is sent to the registration roller pair 11 by the pickup roller 10, and the intermediate transfer body 16 and the secondary transfer roller 18 in the vicinity of the driven roller 17 c by the roller pair 11. Is conveyed to the secondary transfer portion T2. Then, the toner image on the surface of the intermediate transfer body 16 is collectively transferred onto the transfer material P surface by the transfer roller 18 (secondary transfer).

  The transfer material P onto which the toner image has been transferred is separated in curvature from the intermediate transfer body 16 in the vicinity of the driven roller 16c, and is nipped and conveyed by the intermediate transfer body 16 and the secondary transfer roller 18 and introduced into the fixing device 13. The transfer material P passes through the fixing device 13 to fix the toner image on the surface of the transfer material P.

  In each station S (Y to K), the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is removed by the cleaning device 6. Thus, the photosensitive drum 1 is repeatedly used for the next image formation.

  The post-transfer toner remaining on the surface of the intermediate transfer body 16 after the secondary transfer is removed by a cleaning device as the cleaning means 19. Thus, the intermediate transfer member 16 is repeatedly used for the next image formation.

FIG. 9 is a diagram illustrating a schematic configuration of a main part of the fixing device 13 in this reference example and a relationship between the fixing device 13 and the intermediate transfer member 16.

When the leading end of the transfer material P, which is conveyed by being separated from the intermediate transfer body 16 in the vicinity of the driven roller 17c, is introduced into the nip portion N, the fixing device 13 has the leading end of the transfer material P more than the nip portion N. The pressure roller 22 is disposed at a position in contact with the surface of the pressure roller 22 on the downstream side in the rotation direction. In this reference example, the fixing device 13 is disposed at a position facing the surface of the pressure roller 22 on the extension line A in the conveyance direction of the transfer material P conveyed from the intermediate transfer body 16. Thereby, the back surface of the transfer material P which is conveyed with the curvature being separated from the intermediate transfer body 16 when printing on one side (one side) of the transfer material P can be brought into contact with the surface of the pressure roller 22.

  Further, in the conveyance direction of the transfer material P, the relationship between the conveyance speed V1 of the transfer material P when the leading end of the transfer material P is introduced into the nip portion N and the driving speed of the pressure roller 22 (fixing conveyance speed V2). Also, V2 <V1.

  Specifically, the conveyance speed V1 of the transfer material P is 180 mm / sec, and the fixing conveyance speed V2 is 3% slower than the conveyance speed V1 of 180 mm / sec in terms of the peripheral speed ratio, V2 = 174.6 mm. / Sec.

By setting in this way, the same effect as in Reference Example 1 can be obtained also in the image forming apparatus of this Reference Example using the intermediate transfer member 16.
[Example 1]

[First Embodiment]
In this embodiment will be described an image forming equipment according to the present invention.

  The image forming apparatus according to the present exemplary embodiment is configured to perform transfer material conveyance speed V <b> 1 during normal printing with margins that form margins on the peripheral edge of the transfer material P and during borderless printing that does not form margins on the peripheral edge of the transfer material P. And the fixing conveyance speed V2.

Specifically, the difference between the transfer material conveyance speed V1 and the fixing conveyance speed V2 is eliminated during printing with a border, and the fixing conveyance velocity V2 is higher than the transfer material conveyance speed V1 during printing without a border as described in Reference Example 1. To slow down.

  At the time of printing with a border, since there is no toner at the edge portion of the front surface of the transfer material P, it is not always necessary to make the fixing conveyance speed V2 slower than the transfer material conveyance speed V1. If the transfer material conveyance speed V1 and the fixing conveyance speed V2 are too different from each other, for example, transfer material image blurring or rubbing may occur. For this reason, there is a possibility that other problems such as scattering and blurring of the front end toner image when the leading end of the transfer material P enters the surface of the pressure roller 22 and image blurring caused by a large peripheral speed difference may occur. Therefore, the peripheral speed difference between the transfer material conveyance speed V1 and the fixing conveyance speed V2 is eliminated at the time of printing with a border.

On the other hand, at the time of borderless printing, the fixing conveyance speed V2 is set slower than the transfer material conveyance speed V1 in the same manner for the reasons described in Reference Examples 1 and 2.

The Ru control system switches the rotation speed of the pressure roller 22 shown in FIGS. 10 and 11. FIG. 10 shows a case where the control system of this embodiment is applied to the image forming apparatus of Reference Example 1. FIG. 11 shows a case where the control system of this embodiment is applied to the image forming apparatus of Reference Example 2.

  As shown in FIGS. 10 and 11, the speed switching means 42 inputs a borderless print signal S2, and the motor M1 is set so that the fixing conveyance speed V2 is slower than the transfer material conveyance speed V1 in accordance with the input signal S2. To control. Further, the speed switching means 42 receives the bordered print signal S1, and controls the motor M1 so as to eliminate the peripheral speed difference between the transfer material conveyance speed V1 and the fixing conveyance speed V2 according to the input signal S1.

  According to the image forming apparatus of the present embodiment, a good image without image defects can be obtained at the time of printing with a border, and at the time of printing without a border, the pressure roller 22 is soiled by the toner on the front end surface of the transfer material P, offset toner, etc. Therefore, it is possible to form a good image without any harmful effects.

  In this embodiment, regarding the transfer material conveyance speed V1 and the fixing conveyance speed V2, the speed difference is eliminated at the time of printing with a border and the speed difference is given at the time of printing without a border. The same effect can be obtained even if the peripheral speed ratio β is set at the time of non-printing.

Overall configuration diagram of an example of an image forming apparatus according to Reference Example 1 1 is a diagram illustrating a schematic configuration of a main part of the fixing device in FIG. 1 and a relationship between the fixing device and a conveyance belt. Schematic configuration diagram of the heater Illustration of an example control system for switching the rotation speed of the pressure roller The figure which shows the state which the front-end | tip of a transfer material contact | abuts to the pressure roller surface FIG. (1) showing the positional relationship between the offset toner and the leading edge of the transfer material when the fixing conveyance speed is slower than the transfer material conveyance speed. FIG. 2 is a diagram showing the positional relationship between the offset toner and the front end of the transfer material when the fixing conveyance speed is slower than the transfer material conveyance speed. FIG. 3 shows the positional relationship between the offset toner and the leading edge of the transfer material when the fixing conveyance speed is slower than the transfer material conveyance speed. FIG. (1) showing the positional relationship between the offset toner and the leading edge of the transfer material when the transfer material conveyance speed and the fixing conveyance speed are equal. FIG. 2 is a diagram showing the positional relationship between the offset toner and the leading edge of the transfer material when the transfer material conveyance speed is equal to the fixing conveyance speed (2). FIG. 3 shows the positional relationship between the offset toner and the leading edge of the transfer material when the transfer material conveyance speed and the fixing conveyance speed are equal. Overall configuration diagram of another example of an image forming apparatus according to Reference Example 2 FIG. 8 is a diagram illustrating a schematic configuration of a main part of the fixing device in FIG. 8 and a relationship between the fixing device and the intermediate transfer member. Explanatory drawing (1) of the control system of the other example which switches the rotational speed of the pressure roller in the fixing device of the image forming apparatus according to Embodiment 1 . Explanatory drawing (2) of the control system of the other example which switches the rotational speed of the pressure roller in the fixing device of the image forming apparatus which concerns on Example 1. FIG.

13: fixing device, 21: fixing belt, 22: pressure roller, N: heating nip,
V1: transfer speed of transfer material P, V2: rotation speed of pressure roller, 30: cleaning member

Claims (1)

An image forming portion for forming an unfixed toner image on the transfer material, a first rotating body that contacts the surface of the transfer material on which the unfixed toner image is formed, and a fixing nip portion that forms a fixing nip portion together with the first rotating body . anda fixing unit for fixing the transfer material an unfixed toner image while conveying the transfer material and second rotating body Bei example the fixing nip, a toner image, leaving a margin in the peripheral portion of the transfer material In an image forming apparatus capable of executing a print with a border and a print without a border to form a toner image without leaving a margin in the peripheral portion of the transfer material ,
The transfer material conveyed to the fixing unit is set so that the leading end of the transfer material is in contact with the second rotating body. When performing the borderless printing, the transfer material conveyed to the fixing unit is moved. The peripheral speed of the second rotating body is set to be slower than the speed, and when executing the print with the edge, the second rotating body has a speed higher than the moving speed of the transfer material conveyed to the fixing unit. An image forming apparatus characterized in that the rotational speed of the second rotating body is set so that the peripheral speed is low and the speed difference between the two is smaller than in the case of the borderless printing or the speed difference is eliminated. .