Image forming device

Abstract

To provide a configuration capable of preventing toner from adhering to portions other than a recording material after fixation in a rimless image forming mode, while suppressing complication and size increase of a device.SOLUTION: When rimmed printing is performed, a control circuit unit controls a fixing heater in a first period where a recording material is passing through a fixing nip part so that a temperature detected by a belt back thermistor becomes a first control temperature (target basic temperature Tb). When rimless printing is performed, the control circuit unit controls the fixing heater in the first period so that the temperature detected by the belt back thermistor becomes a second control temperature (corrected fixing target temperature) that is higher than the first control temperature.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or a multifunction machine having multiple functions of these. [Background technology]

[0002] As an image forming apparatus, a configuration is known that performs a bordered image forming mode in which an image is formed with a margin at the edge of the recording material, as well as a borderless image forming mode in which an image is formed up to the edge of the recording material (Patent Document 1).

[0003] In the borderless image formation mode, an image is formed at a size larger than the recording material and transferred to the recording material, which causes toner to adhere to the edges of the recording material. Toner that adheres to the edges of the recording material is difficult to fix to the recording material and easily peels off when touched, causing the toner to adhere to areas other than the recording material and causing contamination inside the image forming device. For this reason, Patent Document 1 proposes a technology that provides a cleaning device to remove toner that has adhered to the edges of the recording material and cleans the sides of the recording material after the fixing process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-53198 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if a means for cleaning the recording material after fixing is provided as in Patent Document 1, the apparatus becomes complicated and large in size.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can prevent toner from adhering to areas other than the recording material after fixing in a borderless image forming mode, while suppressing an increase in the complexity and size of the apparatus. [Means for solving the problem]

[0007] One aspect of the present invention is an image forming apparatus capable of executing a borderless image forming mode in which a toner image is formed on the edge of a recording material, and a bordered image forming mode in which a toner image is not formed on the edge of the recording material, the image forming apparatus comprising: an image forming unit that forms a toner image on the recording material; a fixing member; a heating unit that heats the fixing member; a nip forming member that forms a fixing nip between the fixing member and the fixing member and that fixes the toner image to the recording material as the recording material carrying the toner image passes through the fixing nip; and a temperature detection unit that detects the temperature of the fixing member or the heating unit; and a control unit that controls the heating unit based on the detection result of the temperature detection unit, wherein the period during which the recording material passes through the fixing nip is defined as a first period, and when the borderless image forming mode is executed for a specified recording material, the control unit controls the heating unit to have a first control temperature during the first period, and when the borderless image forming mode is executed for the specified recording material, the control unit controls the heating unit to have a second control temperature during the first period that is higher than the first control temperature.

[0008] One aspect of the present invention is an image forming apparatus capable of executing a borderless image forming mode in which a toner image is formed on the edge of a recording material, and a bordered image forming mode in which a toner image is not formed on the edge of a recording material, the image forming apparatus including: an image forming unit that forms a toner image on the recording material; a fixing member; a heating unit that heats the fixing member; a nip forming member that forms a fixing nip portion that sandwiches and conveys the recording material between the fixing member and the fixing member, and fixes the toner image to the recording material when the recording material carrying the toner image passes through the fixing nip portion; and a temperature detecting unit that detects the temperature of the fixing member or the heating unit; and a control unit that controls the heating unit based on the detection result of the temperature detecting unit. and a fixing unit, wherein a second period is defined as the time from when the upstream end of a first recording material in the conveying direction passes through the fixing nip unit until the downstream end of a second recording material following the first recording material in the conveying direction reaches the fixing nip unit, and the control unit controls the heating unit to have a first control temperature during the second period when the bordered image forming mode is executed for a specified recording material, and controls the heating unit to have a second control temperature higher than the first control temperature during the second period when the borderless image forming mode is executed for forming an image on the edge of the specified recording material in the conveying direction. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the toner from adhering to areas other than the recording material after fixing in a borderless image forming mode, while suppressing an increase in the complexity and size of the apparatus. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a control block diagram of the image forming apparatus according to the first embodiment. [Figure 3] 1A is a schematic cross-sectional view of the fixing device according to the first embodiment, and FIG. 1B is a schematic view showing the arrangement of the thermistor in the longitudinal direction and the heat generation amount of the fixing heater in the longitudinal direction. [Figure 4]3A and 3B are schematic diagrams showing a first example and a second example of a fixing heater according to the first embodiment. [Figure 5] 6 is a graph showing the temperature control temperature and the temperature transition of the fixing belt in (a) a bordered image forming mode and (b) a borderless image forming mode according to the first embodiment. [Figure 6] 4 is a flowchart of an image forming operation according to the first embodiment. [Figure 7] 10A and 10B are schematic diagrams showing temperature distribution in the longitudinal direction in a bordered image forming mode and a borderless image forming mode according to a second embodiment. [Figure 8] 10 is a flowchart of an image forming operation according to a second embodiment. [Figure 9] 11 is a graph showing the temperature control temperature and the temperature transition of the fixing belt in a borderless image forming mode according to the third embodiment. [Figure 10] 10 is a flowchart of an image forming operation according to a third embodiment. [Figure 11] 5A and 5B are schematic diagrams of images in a bordered image forming mode and a borderless image forming mode. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment The first embodiment will be described with reference to Figures 1 to 6 and 11. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0012] [Image forming device] The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Py, Pm, Pc, and Pk corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Py, Pm, Pc, and Pk are arranged in tandem along the rotation direction of an intermediate transfer belt 105 (described later). The image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) (not shown) or a host device such as a personal computer connected to the image forming apparatus 1 so as to be able to communicate with the image forming apparatus 1. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0013] Each of the image forming units Py, Pm, Pc, and Pk includes a photosensitive drum 101 as an image carrier, a charging roller 102 as a charging device, a developing device 104, a primary transfer roller 111 as a primary transfer device, and a drum cleaner 107 as a cleaning device. The photosensitive drum 101 is driven to rotate at a predetermined process speed (peripheral speed) in the counterclockwise direction indicated by the arrow in FIG. 1. During the rotation, the photosensitive drum 101 is charged to a predetermined polarity by the charging roller 102.

[0014] The charged surface of the photosensitive drum 101 is exposed to light based on input image information by a laser beam 103 output from an exposure device 110. The exposure device 110 outputs the laser beam 103 modulated (on / off) in response to time-series electric digital pixel signals of image information from an image signal generating device such as an image reading unit (not shown), and scans and exposes the surface of the photosensitive drum 101. This scanning and exposure forms an electrostatic latent image corresponding to the image information on the surface of the photosensitive drum 101. The laser beam 103 output from the exposure device 110 is deflected by a mirror 109 to an exposure position on the photosensitive drum 101.

[0015] The developing device 104 develops the electrostatic latent image formed on the photosensitive drum 101 with a developer. The developing device 104 of each image forming station Py, Pm, Pc, and Pk contains toner of a color corresponding to the image forming station, and a toner image of that color is formed on the photosensitive drum 101 of each image forming station. The toner image on the photosensitive drum 101 is primarily transferred to the surface of the intermediate transfer belt 105 at a primary transfer station T1, which is the contact point between the photosensitive drum 101 and the intermediate transfer belt 105 serving as an intermediate transfer body. Specifically, a primary transfer roller 111, which is arranged opposite to the photosensitive drum 101 across the intermediate transfer belt 105, discharges electricity from the back surface of the intermediate transfer belt 105 and applies a primary transfer bias of opposite polarity to the toner. This transfers the toner image on the photosensitive drum 101 to the surface of the intermediate transfer belt 105. Any toner remaining on the surface of the photosensitive drum 101 after the primary transfer is cleaned by a drum cleaner 107.

[0016] The above-mentioned cycle of charging, exposure, development, primary transfer, and drum cleaning is repeated in each image forming unit, thereby forming a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image on the photosensitive drum 101 of each image forming unit. Then, at each primary transfer unit T1, the toner images of each color are transferred onto the intermediate transfer belt 105 in order so as to be superimposed on top of each other, forming a full-color toner image on the intermediate transfer belt 105.

[0017] The toner images on the intermediate transfer belt 105 are secondarily transferred onto the recording material all at once at the secondary transfer portion T2. The secondary transfer portion T2 is a contact portion between the outer peripheral surface of the intermediate transfer belt 105, which is stretched around an inner secondary transfer roller 106a, and an outer secondary transfer roller 106b. A secondary transfer bias is applied to the secondary transfer portion T2, thereby secondarily transferring the toner images from the intermediate transfer belt 105 onto the recording material passing through the secondary transfer portion T2. The recording material is stored in a cassette 113, and the recording material fed from the cassette 113 is conveyed to a pair of registration rollers 114, where it waits. The timing of the pair of registration rollers 114 is then controlled to align the toner image on the intermediate transfer belt 105 with the recording material, and the recording material is conveyed to the secondary transfer portion T2. Note that any toner remaining on the intermediate transfer belt 105 after the secondary transfer is cleaned by a belt cleaner 108.

[0018] The recording material onto which the toner image has been transferred in the secondary transfer section is conveyed to fixing device 100, where it is heated and pressurized to fix the toner image carried on the recording material to the recording material. After passing through fixing device 100, the recording material is discharged outside the machine, completing a series of image forming operations. When forming images on both sides of the recording material (double-sided printing), once the toner image has been transferred and fixed to the first side (front side) of the recording material, the recording material is reversed through reversal conveyance section 115, and a toner image is transferred and fixed to the second side (rear side) of the recording material before being discharged outside the machine.

[0019] The image forming apparatus 1 of this embodiment is capable of bordered printing and borderless printing, as shown in Fig. 11. That is, it is possible to execute a borderless image formation mode (borderless printing) in which a toner image is formed on the edge of the recording material, and a bordered image formation mode (bordered printing) in which a toner image is not formed on the edge of the recording material. When printing with borders, an electrostatic latent image is formed on the surface of the photosensitive drum 101 in an area narrower than the recording material, thereby providing a margin of about 2 to 5 mm on the edge of the recording material in the finished product, as shown in the image diagram of "bordered printing" in Fig. 11.

[0020] On the other hand, during borderless printing, an electrostatic latent image is formed on the surface of the photosensitive drum 101 over an area larger than the recording material, resulting in no margins on the edges of the recording material in the finished product, as shown in the "bordered printing" image in FIG. 11. The "bordered printing" image in FIG. 11 is an example of borderless printing, in which images are formed without margins on at least one of the four edges of the recording material, including both edges in the conveyance direction and both edges in the width direction intersecting the conveyance direction. For example, in the first image (1) from the left of the "borderless printing" image in FIG. 11, images are formed on the entire surface of the recording material, i.e., all four edges. In the second image (2), margins are formed on both edges in the conveyance direction of the recording material in the finished product, but no margins are formed on both edges in the width direction. In the third image (3), margins are formed on both edges in the width direction of the recording material in the finished product, but no margins are formed on both edges in the conveyance direction. In the fourth image (4), margins are provided on one edge of the recording material in the conveying direction and one edge of the recording material in the width direction in the finished product, but no margins are provided on the other edge of the recording material in the conveying direction and the other edge of the width direction. The type of "borderless printing" is not limited to the image in Figure 11, and can be any type in which a toner image is formed on the edge of the recording material.

[0021] [Control Unit] 1, the image forming apparatus 1 is provided with a control circuit unit 21 represented by a CPU etc., and an operation panel 112 which serves as an interface for communicating with a user or external devices and for accessing the apparatus. The operation panel 112 as an operation unit is composed of a liquid crystal touch panel, buttons etc., and various settings of the image forming apparatus 1 can be made by operating these.

[0022] 2 shows a control block diagram of the image forming apparatus 1. A control circuit section 21 serving as a control unit is connected to an operation panel 112, image forming sections Py, Pm, Pc, and Pk, a recording material conveying section 116, and the fixing device 100, and controls the operation of the entire image forming apparatus by managing the command system between each section while monitoring the status of each section within the apparatus. The recording material conveying section 116 has a motor for driving a roller for conveying the recording material within the image forming apparatus 1, and a sensor for detecting the recording material.

[0023] The control circuit section 21 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each section by reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs.

[0024] The control circuit section 21 also has a fixing drive control section 14, a heater drive control section 28, and a cooling control section 31. The fixing drive control section 14 controls the fixing drive section 15, the heater drive control section 28 controls the fixing heater 16 based on the detection results of the thermistors 18 and 19, and the cooling control section 31 controls the cooling fan 29 and the shutter 30. These configurations will be described later.

[0025] In this embodiment, the user can select between a borderless image formation mode and a bordered image formation mode from the operation panel 112 or the host device. In the borderless image formation mode, it is also possible to select whether any edge of the recording material is to be borderless, as explained in Figure 11. Furthermore, if the image read by the image reading unit connected to the image forming apparatus 1 or the image data sent from the host device is a borderless image, the control circuit unit 21 executes the borderless image formation mode in accordance with the image data.

[0026] [Fixing device] Next, the fixing device 100 will be described with reference to Figures 3(a) to 4(b). Figure 3(a) is a cross-sectional view of the fixing device 100 in a direction perpendicular to the longitudinal direction, and Figure 3(b) is a diagram schematically showing the arrangement of thermistors 18 and 19 in the longitudinal direction of the fixing device 100, the arrangement of the cooling fan 29, and the heat generation amount in the longitudinal direction of the fixing heater 16. Figures 4(a) and 4(b) are schematic diagrams showing two examples of the configuration of the heating elements 16a and 16b or 16c and 16d of the fixing heater 16.

[0027] The fixing device 100 includes a fixing belt 20 as a fixing member, a fixing heater 16 as a heating unit, a pressure roller 22 as a nip portion forming member, and thermistors 18 and 19 as temperature detecting units. The fixing belt 20 is a cylindrical endless belt equipped with an elastic layer. The fixing heater 16 is supported by a heat-resistant heater holder 17 having a generally trough-shaped cross section, and heats the fixing belt 20. The pressure roller 22 forms a fixing nip portion 27 between the fixing belt 20 and the pressure roller 22, which sandwiches and conveys a recording material. When the recording material carrying a toner image passes through the fixing nip portion 27, the toner image is fixed to the recording material.

[0028] In this embodiment, the fixing heater 16 is adhesively fixed to the lower surface of the heater holder 17 along the longitudinal direction, and is configured to be slidable relative to the fixing belt 20. The fixing belt 20 is fitted around the heater holder 17. The longitudinal direction is the lengthwise direction of the fixing belt 20, and is also the direction (width direction) that intersects with the conveying direction of the recording material.

[0029] The fixing heater 16 is capable of changing the temperature in the longitudinal direction between the end and center of the area where the recording material passes through the fixing nip 27. Specifically, as shown in Figures 4(a) and (b), the fixing heater 16 has, in the longitudinal direction, a heating element 16a or 16c as a first heating element that generates more heat in the center than at the end of the area where the recording material passes through the fixing nip 27, and a heating element 16b or 16d as a second heating element that generates more heat at the end than at the center of the area where the recording material passes through the fixing nip 27. Hereinafter, the generation of heat by energizing a heating element is referred to as "lighting," and the ratio of the energizing time between heating elements is referred to as "lighting ratio."

[0030] The heating elements 16a and 16b shown in Figure 4(a) have the same length in the longitudinal direction. However, the heating element 16a is configured so that when energized, the amount of heat generated is greater at the center than at the ends in the longitudinal direction. Similarly, the heating element 16b is configured so that when energized, the amount of heat generated is greater at the ends than at the center in the longitudinal direction. The areas of the heating elements 16a and 16b that generate more heat correspond to the width of the recording material passing through the fixing nip portion 27, and as will be described later, the lighting ratio is controlled according to the size of the recording material.

[0031] The heating elements 16c and 16d shown in FIG. 4(b) have different lengths in the longitudinal direction, with the heating element 16c located in the longitudinal center and the heating element 16d located at both longitudinal ends. That is, the heating elements 16c and 16d have different longitudinal heat-generating regions. Therefore, when the lighting ratio of the heating element 16c to the heating element 16d is high, the overall heat generation amount of the fixing heater 16 is greater in the longitudinal center than at the longitudinal ends. On the other hand, when the lighting ratio of the heating element 16c to the heating element 16d is low, the overall heat generation amount of the fixing heater 16 is greater in the longitudinal ends than at the longitudinal center. The longitudinal lengths and positions of the heating elements 16c and 16d correspond to the width of the recording material passing through the fixing nip portion 27, and as described below, the lighting ratio is controlled according to the size of the recording material. The fixing heater 16 may be provided with three or more heating elements with different heat generation amounts in the longitudinal direction, and the lighting ratio of each heating element may be finely controlled according to the size, basis weight, and type of recording material (e.g., coated paper, plain paper, etc.).

[0032] A specific example of controlling the lighting ratio of the heating elements according to the size of the recording material will be described. The lighting ratio of heating elements 16a or 16c to heating elements 16b or 16d is controlled by control circuit 21 via heater drive control unit 28. For example, in the case of a maximum-sized recording material, the lighting ratio is set to 50 (heating element 16a or 16c):50 (heating element 16b or 16d). In addition, in the case of a small-sized recording material, the lighting ratio is controlled to 70 (heating element 16a or 16c):30 (heating element 16b or 16d), making it possible to lower the temperature of the longitudinal end portions through which the recording material does not pass.

[0033] The fixing belt 20 is an endless belt, and is constructed by forming a silicone rubber layer (elastic layer) about 300 μm thick on a cylindrical stainless steel substrate about 30 μm thick, and covering the surface with a PFA (perfluoroalkoxyalkane) resin tube (outermost layer) about 30 μm thick. The pressure roller 22 is constructed by laminating a silicone rubber layer about 2.5 mm thick and a PFA resin tube about 50 μm thick on the surface of an iron core. Both ends of the core of the pressure roller 22 are rotatably held between the side plates of the fixing device 100.

[0034] A fixing unit 200 including a fixing heater 16, a heater holder 17, and a fixing belt 20 is installed above the pressure roller 22. The fixing unit 200 is installed parallel to the pressure roller 22 so that the fixing heater 16 contacts the pressure roller 22. The heater holder 17 is made of a highly heat-resistant liquid crystal polymer resin and serves to hold the fixing heater 16 and guide the orbit of the fixing belt 20. Both ends of the heater holder 17 are biased in the axial direction of the pressure roller 22 by a pressure mechanism (not shown) with a force of 157 N on each side, for example, a total pressure of 314 N. As a result, the surface of the fixing heater 16 is pressed against the elastic layer of the pressure roller 22 via the fixing belt 20 with a predetermined pressure, forming a fixing nip 27 of a predetermined width required for fixing.

[0035] Fixing heater 16 is a ceramic heater. That is, fixing heater 16 has a resistance heating element (heating element 16a or 16c, 16b or 16d) in which a conductive paste containing a silver-palladium alloy is applied to a ceramic substrate made of alumina or aluminum nitride in the form of a uniform film of about 10 μm thickness by screen printing. Furthermore, a glass coating is applied to the heating element to ensure pressure resistance.

[0036] Thermistors 18 and 19 functioning as temperature detectors detect the temperature of the fixing belt 20 or the fixing heater 16. Specifically, as shown in Fig. 3(a), thermistor 19 (also called heater backside thermistor) is installed on the surface (called backside) opposite the sliding surface of the fixing heater 16, and serves the function of detecting the backside temperature of the fixing heater 16. A plurality of thermistors (also called belt backside thermistors) 18 are installed above the heater holder 17 so as to be in elastic contact with the inner circumferential surface of the fixing belt 20, and serve the function of detecting the temperature of the inner surface of the fixing belt 20 and determining the temperature of the edge of the recording material.

[0037] The belt-back thermistor 18 is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17. The arm 25 resiliently swings, so that the belt-back thermistor 18 remains in stable contact with the inner surface of the fixing belt 20 even when the movement of the inner surface of the fixing belt 20 becomes unstable. As shown in FIG. 3(b), the belt-back thermistor 18 is made up of multiple thermistors 18a to 18f. That is, multiple belt-back thermistors 18 are arranged and detect the temperature of the fixing belt 20 at positions corresponding to the respective ends of recording materials of different sizes in the longitudinal direction of the fixing belt 20. In FIG. 3(a) and this specification, any of these thermistors 18a to 18f may be simply referred to as thermistor 18.

[0038] Thermistors 18a and 18b are arranged at both widthwise ends of an area (also referred to as a maximum paper passing area) through which a maximum-size recording material (A4 in this embodiment) passes through the fixing nip portion 27. Thermistors 18c and 18d are arranged at both widthwise ends of an area through which a recording material (A4R in this embodiment) having a widthwise length smaller than the maximum size passes. Thermistors 18c and 18d are arranged at both widthwise ends of an area through which an even smaller-size recording material (e.g., a minimum-size recording material) passes through. Note that an A4-size recording material passing through the fixing nip portion 27 means that the A4-size recording material passes through the fixing nip portion 27 with its short side aligned with the conveyance direction of the recording material, and an A4R-size recording material passing through the fixing nip portion 27 means that the A4-size recording material passes through the fixing nip portion 27 with its long side aligned with the conveyance direction of the recording material.

[0039] The heater back thermistor 19 and the belt back thermistor 18 are connected to the control circuit 21 via A / D converters 64 and 65, respectively. The control circuit 21 samples the outputs from the respective thermistors at predetermined intervals and reflects the temperature information thus obtained in temperature control.

[0040] That is, the control circuit unit 21 determines the temperature control content of the fixing heater 16 based on the outputs of the belt-back thermistor 18 and the heater-back thermistor 19, and controls the power supply to the fixing heater 16 using the heater drive control unit 28, which is a power supply unit. The temperature control method of this fixing device primarily determines the power supply value to the heater so that the temperature detected by the belt-back thermistor 18 can be stably maintained at the desired temperature. Specifically, the power is changed by calculating the target temperature of the belt-back thermistor 18, the detected temperature, the temperature change per unit time, the heater input power value, and PI control parameters, so that the temperature quickly reaches the target temperature (hereinafter also referred to as the controlled temperature) and is maintained stably. Since the direct heat source is the fixing heater 16, the detected temperature and temperature change rate of the heater-back thermistor 19 are also used as auxiliary PI control to prevent the temperature of the fixing belt 20 from fluctuating too suddenly, thereby stabilizing the inner temperature of the fixing belt 20 more quickly.

[0041] When the image forming operation starts, the control circuit unit 21 drives the fixing drive unit 15 via the fixing drive control unit 14, which rotates the pressure roller 22 at a predetermined peripheral speed in the direction indicated by the arrow. The fixing drive unit 15 is, for example, a motor that rotates the pressure roller 22. The fixing belt 20, which is in pressure contact with the pressure roller 22, rotates at a predetermined speed driven by the pressure roller 22. At this time, the inner circumferential surface of the fixing belt 20 is in a driven rotation state in the direction indicated by the arrow while sliding in close contact with the sliding surface of the fixing heater 16 around the outer periphery of the heater holder 17. Heat-resistant grease is applied to the inner surface of the fixing belt 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing belt 20.

[0042] When the pressure roller 22 is driven to rotate and the cylindrical fixing belt 20 is driven to rotate, power is supplied to the fixing heater 16. When the fixing belt 20 reaches a desired temperature, the recording material P carrying the unfixed toner image t is guided along the entrance guide 23 and introduced into the fixing nip portion 27.

[0043] In the fixing nip portion 27, the toner image bearing surface of the recording material P is in close contact with the outer peripheral surface of the fixing belt 20, and the recording material P moves together with the fixing belt 20. As the recording material P is nipped and conveyed through the fixing nip portion 27, heat from the fixing belt 20 is imparted to the recording material P, and the unfixed toner image t is melted and fixed onto the recording material P. Having passed through the fixing nip portion 27, the recording material P is separated from the fixing belt 20 by its curvature and is discharged by the fixing discharge roller 26.

[0044] The fixing device 100 is formed so as to be elongated in the width direction (axial direction), which is the longitudinal direction of the fixing belt 20. As shown in Fig. 3(b), in the longitudinal direction of the fixing belt 20 (the left-right direction in Fig. 3(b)), the area Q of the recording material passing through the fixing nip portion 27 (hereinafter referred to as the fixing paper passing area) varies depending on the width of the recording material, and for example, when the maximum size is A4, almost the entire area in the longitudinal direction of the fixing belt 20 becomes the fixing paper passing area Q1, and the temperature of the edge of the recording material is detected by the back-of-belt thermistors 18a and 18b, which detect the temperature inside the maximum paper passing area.

[0045] On the other hand, when small-sized recording materials (e.g., A4R) are passed through, the area is divided into a fixing paper-passing area Q2 through which the recording material P always passes and small-size non-passing areas R on either side of the fixing belt 20, through which the small-size recording material P does not pass. A pair of cooling fans 29 and a shutter 30 are arranged above the fixing belt 20 at positions corresponding to the small-size non-passing areas R. That is, the cooling fan 29 blows air toward the longitudinal ends of the fixing belt 20. The shutter 30 is arranged between the cooling fan 29 and the fixing belt 20, and has an opening whose width is changeable so that air blown from the cooling fan 29 toward the fixing belt 20 can pass through.

[0046] The cooling fan 29 and the shutter 30 constitute a fixing cooling unit that cools the non-sheet passing area R of the fixing belt 20 to prevent the temperature from rising in the non-sheet passing area R. The cooling fan 29 and the shutter 30 provided for the non-sheet passing area R perform the following cooling control operation based on an operation command from the control circuit unit 21 via the cooling control unit 31.

[0047] First, when small-sized recording materials P, which are narrower than the maximum size, are used for image formation and fixing is performed continuously on these small-sized recording materials P, the recording materials P do not pass through the non-sheet-passing region R as described above, and the heat absorption effect of the small-sized non-sheet-passing region R of the fixing belt 20 disappears, causing the temperature to rise. The temperature of the small-sized non-sheet-passing region R of the fixing belt 20 is detected by the back-of-belt thermistors 18a and 18b for the maximum size. When the temperature detected by the back-of-belt thermistors 18a and 18b reaches a predetermined temperature, the opening width of the shutter 30 is set to a width corresponding to the small-sized sheet-passing width (e.g., the width of A4R or the width of the smallest size recording material), and the cooling operation of the cooling fan 29 begins. This suppresses the temperature rise in the small-sized non-sheet-passing region R of the fixing belt 20.

[0048] The belt back thermistors 18c and 18d are arranged inside the width of the A4R recording material passing through the fixing nip portion 27 (since the width of A4R is 210 mm, the belt back thermistors 18e and 18f are arranged inside the width of the minimum size recording material passing through the fixing nip portion 27 (the minimum width that can be passed) (for example, if the minimum width is 100 mm, the belt back thermistors 18e and 18f are arranged 48 mm from the longitudinal center of the fixing belt 20). In this way, the belt back thermistors 18c, 18d, 18e, and 18f detect the temperature inside the paper passage area for recording materials smaller than the maximum size, and detect or estimate the temperature of the edge of a small-size recording material (in this embodiment, A4R, the minimum size recording material).

[0049] The graph at the bottom of FIG. 3(b) shows the heat generation characteristics of the heating element 16a (or 16c) and the heating element 16b (or 16d) in the longitudinal direction. In this embodiment, the heating element 16a (or 16c) generates more heat in the fixing paper passage region Q2 than in the non-paper passage region R, and the heating element 16b (or 16d) generates more heat in the non-paper passage region R than in the fixing paper passage region Q2. Also, as shown in the upper graph of FIG. 3(b), the pair of cooling fans 29 and shutter 30 are each positioned outward in the longitudinal direction from a position corresponding to the width of the minimum-size recording material. When a recording material smaller than the maximum size is being passed through, the opening width of the shutter 30 can be appropriately adjusted so that the cooling fan 29 can blow air onto the region of the fixing belt 20 through which the recording material does not pass.

[0050] [Control in borderless image formation mode] Next, control in the borderless image formation mode will be described. As described above, when performing borderless printing, a toner image larger than the recording material is formed and transferred to the recording material. However, when a toner image larger than the recording material is transferred to the recording material, toner adheres to the edges of the recording material. Toner that adheres to the edges of the recording material is difficult to fix to the recording material and easily peels off when touched, causing toner to adhere to areas other than the recording material and resulting in smearing.

[0051] However, the inventors' investigations have shown that it is possible to fix the toner on the edges of the recording material by increasing the temperature near the edges of the recording material, as shown in Table 1. According to the paper, it has been found that when the temperature of the fixing belt 20 near the edges of the recording material is set to 200°C, it is possible to prevent the toner from peeling off from the edges. [Table 1]

[0052] Therefore, in this embodiment, when a bordered image formation mode is executed for a predetermined recording material, the control circuit 21 controls the fixing heater 16 so that the temperature detected by the belt back thermistor 18 becomes a first control temperature (controlled temperature) during a first period (during paper passing) when the recording material is passing through the fixing nip 27. On the other hand, when a borderless image formation mode is executed for a predetermined recording material, the control circuit 21 controls the fixing heater 16 so that the temperature detected by the belt back thermistor 18 becomes a second control temperature (controlled temperature) that is higher than the first control temperature during at least one of the first period (during paper passing) when the first recording material is passing through the fixing nip 27 and a second period (between sheets) from when the upstream end of the first recording material in the transport direction passes through the fixing nip 27 to when the downstream end of a second recording material following the first recording material reaches the fixing nip 27. In this case, the belt back thermistor 18 is a sensor that detects the temperature near the end of the fixing paper passing area Q according to the size of the recording material passing through the fixing nip portion 27, among the above-mentioned thermistors 18a to 18f.

[0053] Note that a heater back thermistor 19 may be used instead of the belt back thermistor 18. For example, the belt back thermistor 18 may be omitted, and in addition to the thermistor at the center in the longitudinal direction, the heater back thermistor 19 may also be provided at positions in the longitudinal direction corresponding to the above-described thermistors 18a to 18f. This makes it possible to perform control similar to that using the above-described thermistors 18a to 18f.

[0054] FIG. 5(a) shows the regulated temperature and the temperature transition of the fixing belt 20 during bordered printing, i.e., bordered image formation mode. At the regulated temperature in bordered image formation mode, it can be seen that the temperature of the fixing belt 20 near the edge of the recording material (edge belt temperature) while the recording material is passing through the fixing nip 27 (during paper feeding) is below the edge fixing temperature. For this reason, in this embodiment, the regulated temperature of the fixing heater 16 is controlled as shown in FIG. 5(b). FIG. 5(b) shows the regulated temperature and the temperature transition of the fixing belt 20 during borderless printing, i.e., borderless image formation mode.

[0055] As is clear from Figures 5(a) and (b), during bordered printing, the surface temperature of the fixing belt 20 is controlled to a temperature above the fixing temperature of the print surface (the surface carrying the toner image). During borderless printing, the surface temperature of the fixing belt 20 is controlled to a temperature above the edge fixing temperature, which is higher than the fixing temperature of the print surface, in order to fix the toner at the edges to the recording material. In Figures 5(a) and 5(b), the horizontal axis represents time and the vertical axis represents the temperature of the fixing belt 20. The "edge fixing temperature" is, for example, 200°C as described in Table 1, and varies depending on the size, basis weight, and type of recording material. The "print surface fixing temperature" is, for example, the temperature at which a toner image can be fixed to the surface of the recording material during bordered printing, and varies depending on the size, basis weight, and type of recording material. The "center belt temperature" is the temperature at the longitudinal center of the fixing belt 20, and the "edge belt temperature" is the temperature near the edge of the fixing paper passing area Q, which varies depending on the size of the recording material.

[0056] Furthermore, the "start-up temperature control" is the temperature control temperature during the start-up period from when heating of the fixing heater 16 begins (i.e., when power is turned on) until the downstream end of the first recording material in the conveying direction reaches the fixing nip portion 27. The "inter-paper temperature control" is the temperature control temperature during the period when the recording material is passing through the fixing nip portion 27 (first period, during paper passing). The "inter-paper temperature control" is the temperature control temperature during the period when the upstream end of the first recording material in the conveying direction passes through the fixing nip portion 27 until the downstream end of the second recording material following the first recording material in the conveying direction reaches the fixing nip portion 27 (second period, between sheets). In this embodiment, in both the bordered image formation mode and the borderless image formation mode, the start-up temperature control and the inter-paper temperature control are set lower than the inter-paper temperature control.

[0057] In this embodiment, when the borderless image formation mode is executed, the control circuit 21 controls the fixing heater 16 at the second control temperature during the first period (during paper passage). That is, the start-up temperature control and the sheet-to-sheet temperature control are the same for the bordered image formation mode and the borderless image formation mode, and the temperature control during paper passage is set to a higher temperature for the borderless image formation mode than for the bordered image formation mode. Note that the start-up temperature control and the sheet-to-sheet temperature control may also be set to a higher temperature for the borderless image formation mode than for the bordered image formation mode.

[0058] Furthermore, the relationship between the controlled temperature in the bordered image formation mode (first controlled temperature) and the controlled temperature in the borderless image formation mode (second controlled temperature) is the relationship when the same recording material (same basis weight and paper type) is used in both the bordered image formation mode and the borderless image formation mode. Therefore, when the bordered image formation mode is performed on a predetermined recording material, the fixing heater 16 is controlled at the first controlled temperature, and when the borderless image formation mode is performed on the same recording material, the fixing heater 16 is controlled at the second controlled temperature, which is higher than the first controlled temperature.

[0059] Next, the image formation process in this embodiment will be described with reference to the flowchart in FIG. 6. When the control circuit 21 receives an image formation signal for an image formation job (S1), it sets the image formation mode (print mode) based on the received information (S2). Here, the control circuit 21 determines the target base temperature Tb and print speed S for controlling the temperature of the fixing belt 20 using the belt back thermistor 18 from an internal table based on information about the recording material used in image formation (type, basis weight, size), image information (monochrome mode / color mode, bordered / borderless), and ambient temperature information. For example, in the case of 64g plain paper, color mode, and a 25°C environment, Tb = 190°C and S = 100%. Next, the control circuit 21 determines from the received information whether the image formation process to be performed is borderless printing (borderless image formation mode) or bordered printing (bordered image formation mode) (S3).

[0060] First, the flow for bordered printing will be described. If the control circuit unit 21 determines in S3 that bordered printing is being performed (No in S3), it determines the target basic temperature Tb set in S2 above as the target fixing temperature (S4). Then, the control circuit unit 21 performs image formation while controlling the fixing heater 16 at this target fixing temperature (first control temperature) (S5). Furthermore, the control circuit unit 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S6). If it is not the final recording material (No in S6), the image forming operation in S5 is repeated until it becomes the final recording material. If it becomes the final recording material (Yes in S6), the final recording material is ejected from the apparatus, and the image forming job is terminated.

[0061] Next, the flow for borderless printing will be described. If the control circuit unit 21 determines in S3 that borderless printing is being performed (Yes in S3), it calculates a correction amount (e.g., 15°C) for the target basic temperature Tb set in S2 (S7). Next, it determines the temperature obtained by adding the calculated correction amount to the target basic temperature Tb as the fixing target temperature (e.g., 205°C) (S8). Then, the control circuit unit 21 performs image formation while controlling the fixing heater 16 at this fixing target temperature (second control temperature) (S5). Furthermore, the control circuit unit 21 determines whether the recording material on which the image has been formed is the final recording material in the image formation job (S6). If it is not the final recording material (No in S6), the image formation operation in S5 is repeated until the final recording material is reached. If it is the final recording material (Yes in S6), the final recording material is ejected from the apparatus and the image formation job is terminated.

[0062] As described above, in this embodiment, during borderless printing, the fixing heater 16 is controlled to a higher fixing target temperature than during bordered printing, and the fixing device 100 fixes the toner image to the recording material. Therefore, by raising the fixing temperature at the edge of the recording material, the toner can be more reliably fixed to the edge of the recording material. This makes it difficult for toner adhering to the edge of the recording material to peel off, thereby preventing toner from adhering to areas other than the recording material. Furthermore, since this embodiment only controls the temperature of the fixing heater 16, there is no need to add a component for cleaning the edge of the recording material, for example. As a result, it is possible to prevent toner from adhering to areas other than the recording material after fixing in the borderless image formation mode, while minimizing the device's complexity and size.

[0063] <Second embodiment> The second embodiment will be described with reference to FIGS. 7 and 8. In the first embodiment described above, the target fixing temperature was controlled so that the temperature of the entire recording material during borderless printing was higher than during bordered printing. In contrast, in this embodiment, when borderless printing is performed on the edge of the recording material parallel to the conveyance direction of the recording material (for example, the image diagrams (2) and (4) in FIG. 11), the temperature near the edge of the recording material parallel to the conveyance direction of the recording material is controlled to be equal to or higher than the edge fixable temperature. The other configurations and operations are the same as those of the first embodiment described above. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0064] Figure 7 shows the temperature distribution in the longitudinal direction during borderless printing and bordered printing. Normally, when the fixing belt 20 is heated by the fixing heater 16, the surface temperature of the fixing belt 20 tends to be lower at the ends in the longitudinal direction than at the center because heat is dissipated from both ends in the longitudinal direction. In the borderless image formation mode, an image can be formed on the edge of the recording material in the longitudinal direction of the fixing belt 20, which intersects with the conveyance direction of the recording material. Furthermore, during borderless printing, which forms an image on the longitudinal edge of the recording material (the edge of the recording material parallel to the conveyance direction), it is necessary to fix the toner on the edge to the recording material by raising the temperature of the fixing belt 20 near both edges in the width direction of the recording material.

[0065] As a method for increasing the temperature of the fixing belt 20 near both edges in the width direction of the recording material, for example, as shown in Fig. 4(a), there is a method of using a fixing heater 16 having a heating element 16a that generates more heat in the center than in the longitudinal ends and a heating element 16b that generates more heat in the longitudinal ends than in the longitudinal center, and increasing the lighting ratio of the heating element 16b relative to the heating element 16a.Also, as shown in Fig. 4(b), a similar effect can be obtained by using a fixing heater 16 having multiple heating elements 16c and 16d that have different heating regions in the longitudinal direction, and increasing the lighting ratio of the heating element 16c that corresponds to both edges of the recording material.

[0066] Furthermore, as described above, by using a cooling fan 29 that cools the non-paper passing area and a shutter 30 whose opening width can be changed, for example, when the recording material is small in size, it is possible to increase the temperature of the fixing belt 20 near the edges on both sides of the recording material by controlling the heat generation amount of the fixing heater 16, the air volume of the cooling fan 29, and the opening width of the shutter 30 in combination.

[0067] In this embodiment, as described above, one of the thermistors 18a to 18f serving as the belt-back thermistor 18 detects the temperature near the edge of the fixing paper passing area Q corresponding to the size of the recording material passing through the fixing nip 27. That is, one of the thermistors 18a to 18f serving as a temperature detection unit detects the temperature of the fixing belt 20 at a position corresponding to the longitudinal edge of the recording material passing through the fixing nip 27. In this embodiment, when a borderless image formation mode (borderless printing) in which an image is formed on the longitudinal edge of a specific recording material is executed, the control circuit 21 changes the heat generation amount of the fixing heater 16 in the longitudinal direction during a first period (during paper passing) so that the temperature (the edge of the fixing heater 16) detected by the thermistor (hereinafter, the belt-back thermistor 18) at the position corresponding to the longitudinal edge of the recording material becomes the second control temperature. Specifically, the control circuit unit 21 increases the lighting ratio of the heating element 16b (or 16d: second heating element) to the heating element 16a (or 16c: first heating element) during the first period when the borderless image formation mode is executed compared to when the bordered image formation mode is executed for a specified recording material.

[0068] Furthermore, as described above, this embodiment includes the cooling fan 29 that blows air toward the longitudinal ends of the fixing belt 20, and the shutter 30 that is disposed between the cooling fan 29 and the fixing belt 20 and that can change the opening width of the opening 30a through which the air blown from the cooling fan 29 toward the fixing belt 20 can pass. When the borderless image formation mode is executed, the control circuit unit 21 controls the air volume of the cooling fan 29 and changes the opening width of the shutter 30 so that the temperature detected by the belt back thermistor 18 becomes the second control temperature during the first period.

[0069] For example, when performing "bordered printing" and forming an image on a large-size (A4) recording material, as shown in the upper left column of FIG. 7, the control circuit 21 stops the cooling fan 29 and closes the opening 30a of the shutter 30. Then, during the first period, the control circuit 21 controls the fixing heater 16 so that the temperature detected by the belt back thermistor 18 (thermistors 18a and 18b) becomes the first control temperature for A4-size recording material. Note that the power control of the fixing heater 16, including the control using the detected temperature of the heater back thermistor 19, is as described in the first embodiment, and is basically the same for bordered printing and borderless printing, except that the fixing target temperatures (first control temperature, second control temperature) based on the detection result of the belt back thermistor 18 are different.

[0070] Next, when performing "borderless printing" and forming an image on a large-size (A4) recording material, as shown in the lower left column of FIG. 7, the control circuit 21 stops the cooling fan 29 and closes the opening 30a of the shutter 30. Then, during a first period, the control circuit 21 changes the heat generation amount in the longitudinal direction of the fixing heater 16 so that the temperature detected by the belt back thermistor 18 (thermistors 18a, 18b) becomes a second control temperature that is higher than the first control temperature for A4-size recording material (as shown in the upper left column of FIG. 7). Specifically, when the borderless image formation mode is executed, the lighting ratio of the heating element 16b (or 16d) relative to the heating element 16a (or 16c) during the first period is set higher than when the bordered image formation mode shown in the upper left column of FIG. 7 is executed.

[0071] Next, when performing "bordered printing" and forming an image on a small-sized (A4R) recording material, as shown in the upper right column of Fig. 7, the control circuit 21 drives the cooling fan 29 and changes the opening width of the opening 30a of the shutter 30 to an opening width corresponding to the small-sized recording material. Then, during the first period, the control circuit 21 changes the heat generation amount in the longitudinal direction of the fixing heater 16 so that the temperature detected by the belt back thermistor 18 (thermistors 18c, 18d) becomes the first control temperature for the A4R-sized recording material.

[0072] Furthermore, when performing "borderless printing" and forming an image on a small-size (A4R) recording material, as shown in the lower right column of FIG. 7, the control circuit unit 21 drives the cooling fan 29 and changes the opening width of the opening 30a of the shutter 30 as follows. That is, the opening width of the opening 30a of the shutter 30 is made smaller than the opening width when performing "bordered printing" and forming an image on a small-size (A4R) recording material (see the upper right column of FIG. 7). Specifically, the position and opening width of the opening of the shutter 30 are changed so that the air from the cooling fan 29 does not hit the widthwise edges of the small-size recording material and so that the air from the cooling fan 29 hits the ends of the fixing belt 20 to prevent the temperature of the widthwise ends of the fixing belt 20 from rising. In this case, the air volume of the cooling fan 29 is reduced compared to when performing bordered printing. Then, during the first period, the control circuit unit 21 changes the heat generation amount in the longitudinal direction of the fixing heater 16 so that the temperature detected by the belt back thermistor 18 (thermistors 18c, 18d) becomes a second control temperature that is higher than the first control temperature for A4R size recording material (in the case of the upper right column of Figure 7).

[0073] When performing borderless printing and forming an image on a small-sized (A4R) recording material, one or two of the heat generation amount of the fixing heater 16 in the longitudinal direction, the airflow rate of the cooling fan 29, and the opening width of the shutter 30 may be changed compared to when performing bordered printing and forming an image on a small-sized (A4R) recording material. For example, only the heat generation amount of the fixing heater 16 in the longitudinal direction may be changed when performing bordered printing and forming an image on a small-sized (A4R) recording material, or in addition to changing the heat generation amount of the fixing heater 16 in the longitudinal direction, either the airflow rate of the cooling fan 29 or the opening width of the shutter 30 may be changed. Alternatively, without changing the heat generation amount of the fixing heater 16 in the longitudinal direction, either the airflow rate of the cooling fan 29 or the opening width of the shutter 30 may be changed when performing bordered printing and forming an image on a small-sized (A4R) recording material.

[0074] Here, if the heat generation amount of the fixing heater 16 in the longitudinal direction is not changed, it is preferable to change both the air volume of the cooling fan 29 and the opening width of the shutter 30 when performing "bordered printing" and forming an image on a small-size (A4R) recording material. In other words, if the heat generation amount of the fixing heater 16 in the longitudinal direction is not changed, the temperature rise at the end of the fixing belt 20 will be large, and the air volume of the cooling fan 29 will be increased accordingly. However, if the air volume of the cooling fan 29 is increased, the edge of the recording material will become too cold, so the opening width of the shutter 30 is narrowed to prevent the air from the cooling fan 29 from hitting the edge of the recording material.

[0075] Next, the image formation process in this embodiment will be described with reference to the flowchart in FIG. 8. When the control circuit unit 21 receives an image formation signal for an image formation job (S101), it sets the image formation mode (print mode) based on the received information (S102). Here, the control circuit unit 21 determines the target base temperature Tb and print speed S for controlling the temperature of the fixing belt 20 using the belt back thermistor 18 from an internal table based on information about the recording material used in image formation (type, basis weight, size), image information (monochrome mode / color mode, bordered / borderless), and ambient temperature information. For example, in the case of 64g plain paper, color mode, and a 25°C environment, Tb = 190°C and S = 100%. Next, the control circuit unit 21 determines from the received information whether the image formation process to be performed is borderless printing (borderless image formation mode) or bordered printing (bordered image formation mode) (S103).

[0076] First, the flow for bordered printing will be described. If the control circuit unit 21 determines in S103 that bordered printing is being performed (No in S103), it determines the target basic temperature Tb set in S102 as the target fixing temperature (S104). Then, the control circuit unit 21 performs image formation while controlling the fixing heater 16 at this target fixing temperature (first control temperature) (S105). Furthermore, the control circuit unit 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S106). If it is not the final recording material (No in S106), the image forming operation of S105 is repeated until it becomes the final recording material. If it becomes the final recording material (Yes in S106), the final recording material is ejected from the apparatus, and the image forming job is terminated.

[0077] Next, the flow for borderless printing will be described. If control circuit 21 determines in S103 that borderless printing is being performed (Yes in S103), it checks the size of the recording material set in S102 (S107). For example, if the maximum size is A4 and an image is to be formed on an A4 recording material (Yes in S107), it changes the heat generation amount (heater duty) of fixing heater 16 so as to increase the lighting ratio of heating element 16b (or 16d), which generates more heat at the end portions in the longitudinal direction than at the center, compared to heating element 16a (or 16c), which generates more heat at the center than at the end portions in the longitudinal direction, thereby raising the temperature at the edge portions of the A4 recording material (S108).

[0078] The control circuit 21 then detects the temperature of the edge of the A4 recording material using the belt back thermistor 18 (thermistors 18a and 18b in the case of A4 size) and determines whether the detected temperature is equal to or higher than the edge fixable temperature (S109). If the temperature detected by the belt back thermistor 18 has not reached the edge fixable temperature (No in S109), the process returns to S108 and changes the heat generation amount of the fixing heater 16 to raise the temperature of the edge of the recording material. For example, a correction amount is calculated for the target basic temperature Tb set in S102, and the temperature obtained by adding the calculated correction amount to the target basic temperature Tb is determined as the fixing target temperature. The control circuit 21 then changes the heat generation amount of the fixing heater 16 in the longitudinal direction so that the temperature detected by the belt back thermistor 18 becomes the fixing target temperature (second control temperature, edge fixable temperature).

[0079] In S109, if the detected temperature of the belt back thermistor 18 reaches the edge fixable temperature (Yes in S109), an image forming operation is performed (S105). Furthermore, the control circuit section 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S106), and if it is not the final recording material (No in S106), the operation from S103 is repeated until it becomes the final recording material, and if it becomes the final recording material (Yes in S106), the final recording material is discharged outside the apparatus, and the image forming job is terminated.

[0080] On the other hand, in S107, if the size of the recording material is a small size (e.g., A4R) that is not the maximum size (No in S107), the heat generation amount of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30 are changed according to the size (S110). For example, the settings of the heat generation amount (heater duty) of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30 are changed by, for example, reducing the lighting ratio of the heating element 16b (or 16d), which generates more heat at the end portion in the longitudinal direction than at the center, compared to the heating element 16a (or 16c), which generates more heat at the center than at the end portion in the longitudinal direction, reducing the airflow rate of the cooling fan 29, and closing the opening width of the shutter 30 by a predetermined amount. This increases the temperature at the edge of the small-size recording material.

[0081] Then, the control circuit unit 21 detects the temperature of the edge of the small-size recording material using the belt back thermistor 18 (thermistors 18c and 18d in the case of A4R size) and determines whether the detected temperature is equal to or higher than the edge fixable temperature (S111). If the temperature detected by the belt back thermistor 18 has not reached the edge fixable temperature in S111 (No in S111), the process returns to S110 and changes the settings of the heat output of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30 to raise the temperature of the edge of the small-size recording material.

[0082] In S111, if the detected temperature of the belt back thermistor 18 reaches the edge fixable temperature (Yes in S111), an image forming operation is performed (S105). Furthermore, the control circuit section 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S106), and if it is not the final recording material (No in S106), the operation from S103 is repeated until it becomes the final recording material, and if it becomes the final recording material (Yes in S106), the final recording material is discharged outside the apparatus, and the image forming job is terminated.

[0083] 8 describes a method of controlling the temperature of the edge of the recording material by changing all of the heat output of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30. However, as described above, the temperature of the edge of the recording material may be controlled by using any one or more of these methods. Also, in the above example, borderless printing on both edges of the recording material parallel to the conveyance direction of the recording material (i.e., both edges in the width direction) was described. However, when borderless printing on one edge of the recording material parallel to the conveyance direction of the recording material, the heat output of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30 on the side corresponding to the edge that will become borderless may be controlled.

[0084] As described above, in this embodiment, when performing borderless printing on the edges of the recording material parallel to the recording material transport direction, the temperature near the edges of the recording material parallel to the recording material transport direction is controlled to be equal to or higher than the edge-fixing temperature. This increases the fixing temperature of the edges of the recording material, allowing toner to be more reliably fixed to the edges of the recording material. This prevents toner adhering to the edges of the recording material from peeling off, thereby preventing toner from adhering to areas other than the recording material. Furthermore, this embodiment only controls the components already present in the image forming apparatus, such as the heat output of the fixing heater 16, the airflow rate of the cooling fan 29, and the opening width of the shutter 30. Therefore, there is no need to add a component for cleaning the edges of the recording material. As a result, the device can be prevented from becoming too complex and large, while preventing toner from adhering to areas other than the recording material after fixing in the borderless image formation mode.

[0085] <Third embodiment> The third embodiment will be described with reference to Figures 9 and 10. In the first embodiment described above, the target fixing temperature was controlled so that the temperature of the entire recording material during borderless printing was higher than during bordered printing. In contrast, in this embodiment, when borderless printing is performed on one of the leading or trailing edges of the recording material (for example, the image diagram of (3) in Figure 11), the temperature near one of the leading or trailing edges is controlled to be equal to or higher than the edge fixable temperature. The other configurations and operations are the same as those of the first embodiment described above. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0086] FIG. 9 shows the temperature transition of the fixing belt 20 when multiple recording materials are continuously passed through the fixing nip 27. The solid line in FIG. 9 shows the temperature at the longitudinal center of the fixing belt 20 when the control of this embodiment is performed (center belt temperature with control), and the dashed line shows the temperature at the longitudinal center of the fixing belt 20 when the control of this embodiment is not performed (control in which the temperature control temperature is not increased during the start-up period between sheets). Normally, when sheets are continuously passed through, the surface temperature of the fixing belt 20 tends to gradually decrease at the trailing end (upstream end in the conveying direction) of the first recording material compared to the leading end (downstream end in the conveying direction), as shown by the dashed line. When printing without a border, it is necessary to fix the toner at the edges to the recording material by raising the temperature of the fixing belt 20 near the leading and trailing edges of the recording material.

[0087] As a method for raising the temperature of the fixing belt 20 near the leading and trailing edges of the recording material, for example, the controlled temperature during the gap between sheets (second period) is set higher than the controlled temperature during the passage of the recording material (first period). Then, for the leading edge of the recording material, when the recording material is passed through the fixing nip 27, the controlled temperature is switched to the controlled temperature during the passage so as to ensure that the temperature of the leading edge of the recording material is equal to or higher than the edge fixable temperature. On the other hand, for the trailing edge of the recording material, there is a method for switching to the controlled temperature during the gap between sheets so as to ensure that the temperature of the trailing edge of the recording material is equal to or higher than the edge fixable temperature when the recording material leaves the fixing nip 27.

[0088] A more detailed explanation follows. First, in this embodiment, when the borderless image forming mode is executed, the control circuit 21 controls the fixing heater 16 at the second control temperature during the second period (between sheets). This second control temperature is higher than the first control temperature during the period (first period) when the recording material passes through the fixing nip 27 during the bordered image forming mode for the same recording material. In particular, in this embodiment, the second control temperature is higher than the third control temperature during the period (first period) when the recording material passes through the fixing nip 27 during the borderless image forming mode. That is, as shown in FIG. 9 , when the borderless image forming mode is executed for a specific recording material, the control circuit 21 controls the fixing heater 16 during the first period so that the temperature detected by the belt back thermistor 18 becomes the third control temperature (the paper-passing controlled temperature, the print controlled temperature), and also controls the fixing heater 16 during the second period so that the temperature detected by the belt back thermistor 18 becomes the second control temperature (the paper-interval controlled temperature), which is higher than the temperature during the first period.

[0089] Furthermore, in this embodiment, when the borderless image formation mode is executed, the control circuit 21 controls the fixing heater 16 so that the temperature detected by the belt back thermistor 18 becomes the second control temperature (start-up controlled temperature) during the start-up period from when the fixing heater 16 starts heating until the downstream end (leading edge) of the first recording material in the conveyance direction reaches the fixing nip 27. This start-up controlled temperature is also higher than the first control temperature and the third control temperature. This allows the leading edge of the first recording material in the image formation job to be heated to or above the edge fixing temperature.

[0090] In this embodiment, in the case of bordered printing, the controlled temperature at start-up is controlled to be slightly lower than the controlled temperature during paper feed (controlled print temperature). Also, the controlled temperature between sheets is the same as the controlled print temperature when the paper gap is shorter than a predetermined time, and is lower than the controlled print temperature when the paper gap is longer than the predetermined time.

[0091] Furthermore, in borderless printing, the timing of switching from the startup controlled temperature to the paper-passage controlled temperature and from the sheet-gap controlled temperature to the paper-passage controlled temperature varies depending on the temperature difference between the startup controlled temperature and the paper-gap controlled temperature, and the temperature difference between the sheet-gap controlled temperature and the paper-passage controlled temperature. If the temperature difference between the startup controlled temperature (or the paper-gap controlled temperature) and the paper-passage controlled temperature is large, the switching may occur before the leading edge of the recording material enters the fixing nip 27. This is because the temperature near the leading edge of the recording material can be raised to a temperature at which edge fixation is possible or higher when the recording material passes through the fixing nip 27. On the other hand, if the temperature difference between the startup controlled temperature (or the paper-gap controlled temperature) and the paper-passage controlled temperature is small, switching the controlled temperature may immediately cause the temperature to drop to the paper-gap controlled temperature, which may prevent the temperature near the leading edge of the recording material from being raised to a temperature at which edge fixation is possible or higher. For this reason, if the temperature difference is small, it is preferable to switch after the leading edge of the recording material enters the fixing nip 27. In short, when the leading edge of the recording material passes through the fixing nip portion 27, the temperature near the edge of the leading edge becomes higher than the edge fixing temperature, and the temperature control is switched from the start-up temperature control (or the paper-interval temperature control) to the paper-passing temperature control.

[0092] Furthermore, in borderless printing, the timing for switching from the controlled temperature during paper passage to the controlled temperature between sheets is set to be before the trailing edge of the recording material exits the fixing nip 27. This timing also varies depending on the temperature difference between the controlled temperature during paper passage and the controlled temperature between sheets. That is, the controlled temperature during paper passage should be switched to the controlled temperature between sheets when the temperature near the edge of the trailing edge of the recording material passes through the fixing nip 27 reaches or exceeds the edge fixable temperature. If the temperature difference is large, the power input to the fixing heater 16 increases when the controlled temperature is switched, resulting in a rapid temperature rise. On the other hand, if the temperature difference is small, the change in power input to the fixing heater 16 when the controlled temperature is switched is small, resulting in a gradual temperature rise. For this reason, the controlled temperature during paper passage to the controlled temperature between sheets is switched at a timing that corresponds to the temperature rise rate.

[0093] 9, the timing for switching from the start-up controlled temperature to the mid-sheet-passage controlled temperature is the timing when the leading edge of the first recording material enters the fixing nip 27. The timing for switching from the mid-sheet-passage controlled temperature to the inter-sheet controlled temperature is before the trailing edge of the recording material exits the fixing nip 27. The timing for switching from the inter-sheet controlled temperature to the mid-sheet-passage controlled temperature is after the leading edge of the recording material enters the fixing nip 27. As described above, each of these timings is determined by the temperature difference between the controlled temperatures, and is not limited to the example shown in FIG. 9.

[0094] Next, the image formation process in this embodiment will be described with reference to the flowchart in FIG. 10. When the control circuit unit 21 receives an image formation signal for an image formation job (S201), it sets the image formation mode (print mode) based on the received information (S202). Here, the control circuit unit 21 determines the target base temperature Tb and print speed S for controlling the temperature of the fixing belt 20 using the belt back thermistor 18 from an internal table based on information about the recording material used in image formation (type, basis weight, size), image information (monochrome mode / color mode, bordered / borderless), and ambient temperature information. For example, in the case of 64g plain paper, color mode, and a 25°C environment, Tb = 190°C and S = 100%. Next, the control circuit unit 21 determines from the received information whether the image formation process to be performed is borderless printing (borderless image formation mode) or bordered printing (bordered image formation mode) (S203).

[0095] First, the flow for bordered printing will be described. If the control circuit unit 21 determines in S203 that bordered printing is being performed (No in S203), it determines the target basic temperature Tb set in S202 as the target fixing temperature (S204). Then, the control circuit unit 21 performs image formation while controlling the fixing heater 16 at this target fixing temperature (first control temperature) (S205). Furthermore, the control circuit unit 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S206). If it is not the final recording material (No in S206), the image forming operation of S205 is repeated until it becomes the final recording material. If it becomes the final recording material (Yes in S206), the final recording material is ejected from the apparatus, and the image forming job is terminated.

[0096] Next, the flow for borderless printing will be described. If the control circuit 21 determines in S203 that borderless printing is being performed (Yes in S203), it sets the start-up controlled temperature and the sheet-interval controlled temperature 15° C. higher than the sheet-passage controlled temperature (print controlled temperature) (S207). Then, the control circuit 21 starts the image formation operation (S208) and controls the fixing heater 16 at the corrected start-up controlled temperature to raise the temperature of the fixing belt 20 (S209). Next, when the leading edge of the recording material passes through the fixing nip 27, the control circuit 21 switches from the start-up controlled temperature to the print controlled temperature at a timing when the temperature near the leading edge of the recording material can maintain the required temperature, i.e., when the temperature reaches or exceeds the edge-fixable temperature (S210). Then, it controls the fixing heater 16 at the print controlled temperature to pass the recording material through the fixing nip 27 (S211).

[0097] Next, before the trailing edge of the recording material passes through the fixing nip portion 27, the print controlled temperature is switched to the corrected sheet interval controlled temperature (S212). The fixing heater 16 is controlled with the corrected sheet interval controlled temperature (S213). Furthermore, the control circuit portion 21 determines whether the recording material on which the image has been formed is the final recording material in the image forming job (S214). If it is not the final recording material (No in S214), the operation from S208 is repeated until it becomes the final recording material. If it becomes the final recording material (Yes in S214), the final recording material is discharged outside the apparatus, and the image forming job is terminated.

[0098] The above example describes borderless printing on the leading and trailing edges of the recording material. However, when borderless printing is performed on either the leading or trailing edge of the recording material, the temperature of only the borderless edge may be adjusted. For example, if the leading edge of the recording material is borderless and the trailing edge is bordered, the start-up controlled temperature and the sheet-gap controlled temperature are set higher than the sheet-passage controlled temperature, and the timing of switching from the start-up controlled temperature to the sheet-gap controlled temperature and from the sheet-gap controlled temperature to the sheet-gap controlled temperature are set as described above. Meanwhile, the timing of switching from the sheet-gap controlled temperature to the sheet-gap controlled temperature is set the same as when printing with a border. Furthermore, if the trailing edge of the recording material is borderless and the leading edge is bordered, the sheet-gap controlled temperature is set higher than the sheet-gap controlled temperature, and the timing of switching from the sheet-gap controlled temperature to the sheet-gap controlled temperature is set as described above. Meanwhile, the timing of switching from the start-up controlled temperature and the sheet-gap controlled temperature to the sheet-gap controlled temperature is set the same as when printing with a border.

[0099] As described above, in this embodiment, when performing borderless printing on one of the leading or trailing edges of a recording material, the temperature near either the leading or trailing edge is controlled to be equal to or higher than the edge fixable temperature. Therefore, the fixing temperature of the edge of the recording material is increased, allowing the toner to be more reliably fixed to the edge of the recording material. This prevents toner adhering to the edge of the recording material from peeling off, thereby preventing toner from adhering to areas other than the recording material. Furthermore, as with the first and second embodiments, this prevents the device from becoming too complicated and large, and prevents toner from adhering to areas other than the recording material after fixing in the borderless image forming mode.

[0100] <Other embodiments> The second and third embodiments may be combined. That is, when borderless printing is performed on either one of the leading or trailing edges of the recording material, or on either one of the edges of both sides of the recording material parallel to the conveyance direction of the recording material, or when borderless printing is performed on the entire surface of the recording material, the first embodiment may be implemented, or the second and third embodiments may be combined. In this case, when the borderless image formation mode is executed, the control circuit 21 changes the heat generation amount of the fixing heater 16 in the longitudinal direction so that the temperature detected by the belt back thermistor 18 becomes the second control temperature during startup, the first period (during paper feed), and the second period (between sheets), and also controls the airflow rate of the cooling fan 29 and changes the opening width of the shutter 30 so that the temperature detected by the belt back thermistor 18 becomes the second control temperature during the first period (during paper feed).

[0101] For example, for one of the leading or trailing edges of the recording material, the temperature control temperature is varied so as to be higher than the print control temperature during start-up and between sheets. For one of the widthwise edges of the recording material, the lighting ratio of the heating element 16b (or 16d), which generates more heat at the longitudinal end than at the center, is increased compared to the heating element 16a (or 16c), which generates more heat at the center than at the longitudinal end, thereby raising the temperature of the fixing belt 20 near the edge of the recording material. Since the temperature of the edge of the recording material cannot be fully controlled by the ratio of the heat output of the fixing heaters 16 alone, the opening width of the shutter 30 is controlled according to the width of the recording material being passed while the cooling fan 29 is driven. Note that the control of the fixing heater 16 for one of the widthwise edges of the recording material is maintained constant until the image formation job is completed, regardless of whether or not the recording material is in the fixing nip 27. That is, control is performed to increase the lighting ratio of the heating element 16b (or 16d) compared to the heating element 16a (or 16c) both during paper passage and between papers. [Explanation of symbols]

[0102] 1. Image forming device 16 Fixing heater (heating unit) 16a, 16c Heating element (first heating element) 16b, 16d Heating element (second heating element) 18. Belt back thermistor (temperature detection part) 19. Thermistor behind the heater (temperature detection part) 20 Fixing belt (fixing member) 21 Control circuit section (control section) 22 Pressure roller (nip forming member) 27 Fixing nip 29. Cooling fan (fan) 30..Shutter 30a...Opening 100 Fixing device Py, Pm, Pc, Pk...Image forming section

Claims

1. An image forming apparatus capable of executing a borderless image forming mode in which a toner image is formed on the edge of a recording material, and a bordered image forming mode in which a toner image is not formed on the edge of a recording material, an image forming unit that forms a toner image on a recording material; a fixing device including a fixing member, a heating section for heating the fixing member, a nip section forming member for nipping and conveying a recording material between the fixing member and the nip section forming member, and fixing the toner image onto the recording material when the recording material carrying the toner image passes through the fixing nip section, and a temperature detecting section for detecting the temperature of the fixing member or the heating section; a control unit that controls the heating unit based on a detection result of the temperature detection unit, a period during which the recording material passes through the fixing nip portion is defined as a first period, The control unit When the bordered image forming mode is executed for a predetermined recording material, the heating unit is controlled so that the temperature becomes a first control temperature during the first period; When the borderless image forming mode is executed for the predetermined recording material, the heating unit is controlled so that the temperature becomes a second control temperature higher than the first control temperature during the first period. An image forming apparatus characterized by:

2. In the borderless image forming mode, an image can be formed on the edge of the recording material in the longitudinal direction of the fixing member, which intersects with the conveying direction of the recording material.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. the heating unit is capable of changing temperature control between an end portion and a center portion of an area where the recording material passes through the fixing nip portion in the longitudinal direction; the temperature detection unit detects the temperature of the fixing member or the heating unit at a position corresponding to an end portion in the longitudinal direction of the recording material passing through the fixing nip portion; The control unit When the bordered image forming mode is executed for a predetermined recording material, the edge of the heating unit is controlled to have the first control temperature during the first period, When the borderless image forming mode for forming an image on the edge in the longitudinal direction of the predetermined recording material is executed, the end of the heating unit is controlled to have the second control temperature during the first period.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. the heating section includes a first heating element that generates more heat in a central portion than in an end portion of an area where the recording material passes through the fixing nip portion in the longitudinal direction, and a second heating element that generates more heat in the end portion than in the central portion of an area where the recording material passes through the fixing nip portion, The control unit increases the lighting ratio of the second heating element to the first heating element during the first period when the borderless image forming mode for forming an image on the edge in the longitudinal direction is executed compared to when the bordered image forming mode is executed.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

5. a fan that blows air onto the end portion of the fixing member in the longitudinal direction; When the borderless image forming mode for forming an image on the edge in the longitudinal direction is executed, the control unit controls the air volume of the fan so that the temperature detected by the temperature detection unit becomes the second control temperature during the first period.

5. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

6. a shutter that is disposed between the fan and the fixing member and that is capable of changing an opening width of an opening through which air blown from the fan toward the fixing member can pass, When the borderless image forming mode for forming an image on the edge in the longitudinal direction is executed, the control unit controls the air volume of the fan and changes the opening width of the shutter so that the temperature detected by the temperature detection unit becomes the second control temperature during the first period.

6. The image forming apparatus according to claim 5,

7. a fan that blows air against an end portion of the fixing member in a longitudinal direction that intersects with a conveyance direction of the recording material; a shutter that is disposed between the fan and the fixing member and that is capable of changing an opening width of an opening through which air blown from the fan toward the fixing member can pass, the temperature detection unit detects the temperature of the fixing member or the heating unit at a position corresponding to an end portion in the longitudinal direction of the recording material passing through the fixing nip portion; When the borderless image forming mode for forming an image on the edge in the longitudinal direction is executed, the control unit controls the air volume of the fan and changes the opening width of the shutter so that the temperature detected by the temperature detection unit becomes the second control temperature during the first period.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

8. a second period is defined as a period from when an upstream edge of a first recording material in the conveying direction passes through the fixing nip portion until when a downstream edge of a second recording material following the first recording material in the conveying direction reaches the fixing nip portion; The control unit controlling the temperature of the heating unit so that the temperature of the heating unit during the second period when the bordered image forming mode is executed on the predetermined recording material is the same as the temperature of the heating unit during the second period when the borderless image forming mode is executed on the predetermined recording material; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. An image forming apparatus capable of executing a borderless image forming mode in which a toner image is formed on the edge of a recording material, and a bordered image forming mode in which a toner image is not formed on the edge of a recording material, an image forming unit that forms a toner image on a recording material; a fixing device including a fixing member, a heating section for heating the fixing member, a nip section forming member for nipping and conveying a recording material between the fixing member and the nip section forming member, and fixing the toner image onto the recording material when the recording material carrying the toner image passes through the fixing nip section, and a temperature detecting section for detecting the temperature of the fixing member or the heating section; a control unit that controls the heating unit based on a detection result of the temperature detection unit, a second period is defined as a period from when an upstream edge of a first recording material in the conveying direction passes through the fixing nip portion until when a downstream edge of a second recording material following the first recording material in the conveying direction reaches the fixing nip portion; The control unit When the bordered image forming mode is executed for a predetermined recording material, the heating unit is controlled so that the temperature becomes a first control temperature during the second period. When the borderless image forming mode is executed, in which an image is formed on the edge of the predetermined recording material in the conveyance direction, the heating unit is controlled to have a second control temperature higher than the first control temperature during the second period. An image forming apparatus characterized by:

10. When the borderless image forming mode is executed, the control unit controls the heating unit so that the temperature detected by the temperature detection unit becomes the second control temperature during a start-up period from when the heating unit starts heating until the downstream end of the first recording material in the conveying direction reaches the fixing nip unit.

10. The image forming apparatus according to claim 9,

11. a period during which the recording material passes through the fixing nip portion is defined as a first period, When the borderless image forming mode is executed, in which an image is formed on the edge of the predetermined recording material in the conveying direction, The control unit controls the temperature of the heating unit in the second period to be higher than the temperature of the heating unit in the first period.

10. The image forming apparatus according to claim 9,

12. a fan that blows air against an end portion of the fixing member in a longitudinal direction that intersects with a conveyance direction of the recording material; a shutter that is disposed between the fan and the fixing member and that is capable of changing an opening width of an opening through which air blown from the fan toward the fixing member can pass, the heating unit is capable of changing temperature control of an end portion and a center portion of an area where the recording material passes through the fixing nip portion in a longitudinal direction of the fixing member that intersects with a conveying direction of the recording material, the temperature detection unit detects the temperature of the fixing member or the heating unit at a position corresponding to an end portion in the longitudinal direction of the recording material passing through the fixing nip portion; a second period is defined as a period from when an upstream edge of a first recording material in the conveying direction passes through the fixing nip portion until when a downstream edge of a second recording material following the first recording material in the conveying direction reaches the fixing nip portion; When the borderless image forming mode is executed, the control unit During the first period and the second period, the temperature control of the heating unit in the longitudinal direction is changed so that the temperature detected by the temperature detection unit becomes the second control temperature, and During the first period, the air volume of the fan is controlled and the opening width of the shutter is changed so that the temperature detected by the temperature detection unit becomes the second control temperature.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

13. The fixing member is an endless fixing belt.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

14. The heating unit is a ceramic heater.

14. The image forming apparatus according to claim 13.

15. The heating section heats the inner circumferential surface of the fixing belt by contacting the inner circumferential surface of the fixing belt.

14. The image forming apparatus according to claim 13.

16. The heating section forms the fixing nip section together with the nip section forming member via the fixing belt.

15. The image forming apparatus according to claim 14.

17. The temperature detection unit is arranged in plurality, and detects the temperature of the fixing member at positions corresponding to the respective ends of recording materials of different sizes in a longitudinal direction of the fixing member that intersects with a conveying direction of the recording material passing through the fixing nip portion.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images