Image heating device and image forming apparatus

Abstract

To provide a technique that can prevent an image defect caused by hot offset while maintaining high image productivity even when a pressure roller has a difference in temperature in a longitudinal direction.SOLUTION: In an image heating device, a nip includes a first paper feed area through which both a first recording material and a second recording material having a smaller size than the first recording material pass, and a second paper feed area through which the first recording material passes but the second recording material does not pass. The image heating device acquires a first temperature that is the temperature of an area of a roller corresponding to the first paper feed area, and a second temperature that is the temperature of an area of the roller corresponding to the second paper feed area, and when performing heat treatment on the first recording material, if the second temperature is higher than the first temperature, decreases a second control target temperature used for power supply to a second heat generator for heating the second paper feed area compared to a first control target temperature used for power supply to a first heat generator for heating the first paper feed area.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an image heating device mounted on an image forming apparatus using an electrophotographic method, such as a printer (e.g., laser printer, LED printer) or a digital copier. [Background technology]

[0002] A film-based image heating device is known to be installed in image forming machines such as photocopiers and laser printers. This image heating device comprises a cylindrical film, a plate-shaped heater that contacts the inner surface of the film, and a pressurizing member (pressure roller) that forms a nip section together with the heater via the film. The toner image is fixed onto the recording material by passing it through the nip section. In an image forming machine equipped with this image heating device, if paper narrower than the maximum size that can be fed (hereinafter referred to as small-size paper) is continuously printed as the recording material, a phenomenon called non-feed area temperature rise occurs, in which the temperature of the area in the nip section that the paper does not pass through gradually rises. If paper wider than the small-size paper (hereinafter referred to as large-size paper) is fed while non-feed area temperature rise has occurred, image defects due to hot offset may occur in the area where non-feed area temperature rise occurred. For this reason, as described in Patent Document 1, control is sometimes implemented to feed the paper until the temperature of the non-feed area drops. Furthermore, Patent Document 2 proposes a method for suppressing the temperature rise of the non-paper-passing area by using a heater in which the heating range of the heater is divided into multiple heating regions in a direction perpendicular to the transport direction of the recording material (hereinafter referred to as the longitudinal direction). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-282039 [Patent Document 2] Japanese Patent Publication No. 2014-059508 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] As described in Patent Document 2, when the target temperature of the heater in the non-paper-feeding section is lowered, the film and pressure roller in the non-paper-feeding section also do not heat up easily. However, there is a limit to how low the target temperature of the heater in the non-paper-feeding section can be lowered. This is because if the heater temperature is too low, the torque required to drive the image heating device increases, causing slippage. For this reason, for example, it is conceivable to set the target temperature of the heater in the paper-feeding section to 220°C and the target temperature of the heater in the non-paper-feeding section to 180°C. In that case, the pressure roller in the paper-feeding section loses heat to the recording material, and its temperature drops to around 70-80°C. On the other hand, since there is no recording material to absorb heat in the non-paper-feeding section, the heat from the heater is constantly supplied to the pressure roller, and the pressure roller temperature rises to a value close to the heater temperature (for example, around 120°C). Therefore, even when the target temperature of the heater in the non-paper-feeding section is lowered, if small-sized paper is fed continuously, the pressure roller temperature in the non-paper-feeding section gradually rises and becomes higher than that of the pressure roller in the paper-feeding section. At that time, the following challenges arose.

[0005] Generally, pressure rollers with an elastic layer such as rubber expand in outer diameter due to thermal expansion. Pressure rollers with a temperature difference between the paper-feeding and non-paper-feeding sections due to the heating of the non-paper-feeding section result in a difference in outer diameter. This difference in outer diameter causes a difference in paper transport speed, resulting in a force acting along the longitudinal direction of the film. It has been found that when large-sized paper is fed under these conditions, hot offset is more likely to occur. In other words, when feeding large-sized paper after continuously feeding small-sized paper by lowering the target temperature of the heater in the non-paper-feeding section, hot offset may occur due to the temperature difference between the paper-feeding and non-paper-feeding sections of the pressure roller, even though the heater and film have not heated up in the non-paper-feeding section. To prevent fuzzing, it was necessary to wait until the temperature of the pressure roller in the non-feeding section dropped, which could potentially reduce image productivity.

[0006] The objective of the present invention is to provide a technology that can suppress image defects caused by hot offset while maintaining high image productivity, even when there is a temperature difference in the longitudinal direction of the pressure roller. [Means for solving the problem]

[0007] To achieve the above objective, the image heating apparatus of the present invention is A cylindrical film and A heater having multiple heating elements arranged in the internal space of the film and aligned in the width direction of the recording material perpendicular to the transport direction of the recording material, A roller that contacts the outer surface of the film and forms a nip between itself and the film together with the heater, A temperature detection means for detecting the temperature of each of the multiple heating elements, A control unit controls the power supplied to the plurality of heating elements so that the temperature detected by the temperature detection means reaches a predetermined control target temperature. Equipped with, An image heating device that heats an image formed on a recording material that is held and conveyed by the nip by the heat of the heater, The aforementioned nip, A first paper passage area through which both a first recording material and a second recording material smaller in size than the first recording material pass, A second paper passage area through which the first recording material passes but the second recording material does not, Includes, The plurality of heating elements, A first heating element for heating the aforementioned first paper feeding area, A second heating element for heating the second paper-feeding area, In an image heating apparatus including, The system includes a roller temperature acquisition means that acquires a first temperature, which is the temperature of the roller region corresponding to the first paper feeding region, and a second temperature, which is the temperature of the roller region corresponding to the second paper feeding region. The control unit is characterized in that, when performing the heat treatment on the first recording material, if the second temperature is higher than the first temperature, it lowers the second control target temperature used for supplying power to the second heating element to a first control target temperature used for supplying power to the first heating element. To achieve the above objective, the image heating apparatus of the present invention is A cylindrical film and A heater having multiple heating elements arranged in the internal space of the film and aligned in the width direction of the recording material perpendicular to the transport direction of the recording material, A roller that contacts the outer surface of the film and forms a nip between itself and the film together with the heater, A temperature detection means for detecting the temperature of each of the multiple heating elements, A control unit controls the power supplied to the plurality of heating elements so that the temperature detected by the temperature detection means reaches a predetermined control target temperature. Equipped with, An image heating device that heats an image formed on a recording material that is held and conveyed by the nip by the heat of the heater, The aforementioned nip, Either a first recording material or a second recording material that is smaller in size than the first recording material. The first paper passage area through which the paper passes, A second paper passage area through which the first recording material passes but the second recording material does not, Includes, The plurality of heating elements, A first heating element for heating the aforementioned first paper feeding area, A second heating element for heating the second paper-feeding area, In an image heating apparatus including, The control unit is characterized in that, when it continuously performs the heat treatment on the first recording material after the heat treatment on the second recording material, it sets the second control target temperature used for supplying power to the second heating element to a lower temperature than the first control target temperature used for supplying power to the first heating element. To achieve the above objective, the image forming apparatus of the present invention is An image forming unit that forms an image on the recording material, A fixing unit that fixes the image formed on the recording material to the recording material, In an image forming apparatus having, The fixing unit is characterized by being the image heating device of the present invention. [Effects of the Invention]

[0008] According to the present invention, even when there is a temperature difference in the longitudinal direction of the pressure roller, it is possible to suppress image defects due to hot offset while maintaining high image productivity. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic cross-sectional view of an image forming apparatus [Figure 2] Schematic cross-sectional view of the image heating device [Figure 3] Heater configuration diagram [Figure 4] Heater control circuit diagram [Figure 5] Figure showing the target temperature distribution for heater control when feeding large-size paper. [Figure 6] Figure showing the target temperature distribution for heater control when feeding small-sized paper. [Figure 7] Temperature distribution and temperature changes of the pressure roller. [Figure 8] A diagram showing the temperature dependence of the outer diameter of the pressure roller. [Figure 9] Schematic diagram explaining the hot offset generation mechanism. [Figure 10] Flowchart for determining the heater control target temperature in Example 1 [Figure 11] Figure showing the temperature change of the pressure roller in Example 2 [Figure 12] Flowchart for determining heater control target temperature and waiting time in Example 2 [Modes for carrying out the invention]

[0010] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. Note that the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments should be appropriately modified depending on the configuration and various conditions of the device to which the invention is applied. In other words, the scope of this invention is not intended to be limited to the following embodiments.

[0011] (Example 1) 1. Configuration of the image forming apparatus Figure 1 is a schematic cross-sectional view showing the general configuration of an image forming apparatus 100 using electrophotographic recording technology in Embodiment 1 of the present invention. The image forming apparatus 1 shown in Figure 1 is a laser printer that forms an image on a recording material P using an electrophotographic method.

[0012] When a print signal is generated, the scanner unit 21 emits a laser beam modulated according to the image information, and the photosensitive drum (electrophotographic) is charged to a predetermined polarity by the charging roller 16. The surface of the photosensitive drum 19 is scanned. The scanner unit 21 includes a light source 22, a polygon mirror 23, and a reflective mirror 24. Laser light emitted from the light source 22 is irradiated onto the photosensitive drum 19 via the polygon mirror 23 and the reflective mirror 24, forming an electrostatic latent image on the photosensitive drum 19, which acts as an image carrier. Toner charged to a predetermined polarity is supplied from the developing roller 17 to this electrostatic latent image, and the electrostatic latent image on the photosensitive drum 19 is developed as a toner image (developer image). Meanwhile, the recording material (recording paper) P loaded in the paper feed cassette 11 is fed one sheet at a time by the pickup roller 12 and transported toward the resist roller pair 14 by the transport roller pair 13. Furthermore, the recording material P is transported from the resist roller pair 14 to the transfer position in time with the timing when the toner image on the photosensitive drum 19 reaches the transfer position formed by the photosensitive drum 19 and the transfer roller 20, which acts as a transfer member. As the recording material P passes through the transfer position, the toner image on the photosensitive drum 19 is transferred to the recording material P. The apparatus configuration responsible for the process of forming the above-described unfixed toner image on the recording material P corresponds to the image forming unit of the present invention.

[0013] Subsequently, the recording material P is heated using the heat from a heater in the fixing device (image heating device) 200, which serves as the fixing unit (image heating unit), and the toner image is heated and fixed to the recording material P. The recording material P, which carries the fixed toner image, is discharged to the output tray 31 at the top of the image forming apparatus 100 by the transport roller pairs 26 and 27.

[0014] The photoreceptor 19 is cleaned by the cleaner 18 to remove any remaining toner from its surface. The motor 30 drives the fuser unit 200, etc. Power is supplied to the fuser unit 200 from the control circuit 400, which acts as a power supply control unit connected to the commercial AC power supply 401.

[0015] In this embodiment, a developing unit including a photosensitive drum 19, a charging roller 16, and a developing roller 17, and a cleaning unit including a drum cleaner 18 are configured to be detachably attached to the main body of the image forming apparatus 100 as a process cartridge 15.

[0016] The image forming apparatus described above uses a monochrome laser printer with a single-color monochrome toner as a representative example, but it is not limited to this. For example, it can also be applied to color laser printers such as tandem printers that transfer two or more color toners onto a recording material via an intermediate transfer belt to form an image.

[0017] The image forming apparatus 100 of Example 1 has a maximum paper feed width of 216 mm for recording material P that can be fed (and processed for image formation and fixing), and a transport speed of 300 mm / sec for the recording material P.

[0018] 2. Configuration of the image heating device Figure 2(A) is a schematic cross-sectional view showing the general configuration of the fixing device 200 of Example 1. The fixing device 200 includes a fixing film 202, a heater 300 disposed inside the fixing film 202 (the internal space of the fixing film 202, which is the region facing the inner circumferential surface of the fixing film 202), a pressure roller 208 as a pressing member that contacts the outer surface of the fixing film 202 and clamps the fixing film 202 between itself and the heater 300, and a metal stay 204. A fixing nip portion N is formed between the fixing film 202 and the pressure roller 208 by the heater 300 contacting the inner surface of the fixing film 202 and the pressure roller 208 contacting the outer surface of the fixing film 202.

[0019] The fixing film (hereinafter referred to as "film") 202 is a tubular, multi-layered heat-resistant film, with a heat-resistant resin such as polyimide or a metal such as stainless steel as the base layer. Furthermore, the surface of the film 202 is treated with a release agent such as tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) to prevent toner adhesion and ensure separation from the recording material P. A release layer is formed by coating with a heat-resistant resin. Furthermore, to improve image quality, a heat-resistant rubber such as silicone rubber may be formed as an elastic layer between the base layer and the release layer. The pressure roller 208 has a core metal 209 made of a material such as iron or aluminum, and an elastic layer 210 made of a material such as silicone rubber. The heater 300 is held by a heater holding member 201 made of heat-resistant resin, and heats the film 202 by heating the inside of the fixing nip N. The heater holding member 201 also has a guide function that guides the rotation of the film 202. The heater 300 is provided with an electrode E on the opposite side of the fixing nip N, and power is supplied to the electrode E from an electrical contact C. The metal stay 204 receives an applied pressure (not shown) and presses the heater holding member 201 toward the pressure roller 208. Furthermore, safety elements 212, such as a thermoswitch or thermal fuse, which activate in the event of abnormal overheating of the heater 300 and cut off the power supplied to the heater 300, are arranged on the heater 300 via a heater holding member 201.

[0020] The pressure roller 208 receives driving force from the motor 30 and rotates in the direction of arrow R1. As the pressure roller 208 rotates, the film 202 is driven to rotate in the direction of arrow R2. At the fixing nip section N, the recording material P is held and conveyed while heat is applied to the film 202, thereby fixing the unfixed toner image on the recording material P. To ensure the sliding properties of the film 202 and obtain a stable driven rotation state, a highly heat-resistant grease (not shown) is interposed between the heater 300 and the film 202.

[0021] Furthermore, the pressure roller 208 has an inverted crown shape in which the outer diameter increases from the center to the end in the longitudinal direction. This difference in outer diameter creates a difference in transport speed between the center and the end, and a force acts to pull the recording material P toward the outward (end) side of the film 202 in the longitudinal direction. This force pulling the recording material P toward the outward side in the longitudinal direction has the effect of preventing paper wrinkles. In this embodiment, the pressure roller 208 has a maximum difference in outer diameter of 160 μm between the center and the end.

[0022] Here, the longitudinal direction of the film 202 is the direction along the central axis of the cylindrical shape of the film 202, and coincides with the longitudinal direction (rotation axis direction) of the pressure roller 208, the longitudinal direction of the heater 300 (substrate 305), and the width direction of the recording material that is perpendicular to the direction of transport of the recording material P.

[0023] Figure 2(B) is a view of the fixing device 200 from the downstream side in the transport direction of the recording material P. Multiple pressure roller thermistors 220, specifically seven in this embodiment, are arranged as temperature sensing elements for detecting the temperature of the pressure roller (pressure roller thermistors 220-1 to 220-7). The pressure roller thermistors 220-1 to 220-7 are arranged along the longitudinal direction of the pressure roller 208 so as to correspond to the positions of the heating blocks HB1 to HB7 of the heater 300, which will be described later. In Embodiment 1, the temperature of the pressure roller 208 detected by the pressure roller thermistors 220 is used for temperature control of the heater 300.

[0024] 3. Heater Configuration The configuration of the heater 300 according to Example 1 will be explained using Figure 3. Figure 3(A) is a cross-sectional view of the heater 300, Figure 3(B) is a schematic plan view of each layer of the heater 300, and Figure 3(C) is a schematic plan view of the heater holding member 201 illustrating the method of connecting the electrical contacts C to the heater 300.

[0025] Figure 3(B) shows the transport reference position X of the recording material P in the image forming apparatus 100 of Example 1. In Example 1, the transport reference is the center reference, and the recording material P is transported so that its center line in the width direction of the recording material, perpendicular to the transport direction, lies along the transport reference position X, however, the setting position is not limited to a specific position. Figure 3(A) is a schematic cross-sectional view of the heater 300 at the transport reference position X.

[0026] The heater 300 is provided on one surface of the ceramic substrate 305. It is composed of a back surface layer 1, a back surface layer 2 covering the back surface layer 1, a sliding surface layer 1 provided on the other side of the substrate 305 opposite to one side, and a sliding surface layer 2 covering the sliding surface layer 1.

[0027] The back layer 1 has conductive members 301 (301a, 301b) provided along the longitudinal direction of the heater 300. Conductive members 301 are separated into conductive members 301a and conductive members 301b, with conductive member 301b being positioned downstream of conductive member 301a in the transport direction of the recording material P. The back layer 1 also has conductive members 303 (303-1 to 303-7) provided parallel to conductive members 301a and 301b. Conductive members 303 are provided along the longitudinal direction of the heater 300 (substrate 305) between conductive members 301a and 301b in the short direction (transport direction of the recording material P) perpendicular to the longitudinal direction of the heater 300 (substrate 305). Furthermore, the back layer 1 has heating elements (heating resistors) 302a (302a-1 to 302a-7) and heating elements 302b (302b-1 to 302b-7). Heating element 302a is provided between conductor 301a and conductor 303 in the short direction of the heater 300, and generates heat when power is supplied via conductor 301a and conductor 303. Heating element 302b is provided between conductor 301b and conductor 303 in the short direction of the heater 300, and generates heat when power is supplied via conductor 301b and conductor 303.

[0028] The heating section, composed of conductor 301, conductor 303, heating element 302a, and heating element 302b, is divided into seven heating blocks HB (HB1 to HB7) along the longitudinal direction of the heater 300. Specifically, the heating element 302a on the upstream side in the transport direction of the recording material P is divided into seven heating elements 302a-1 to 302a-7 arranged along the longitudinal direction of the heater 300, with seven heating regions from each heating element aligned along the longitudinal direction. Similarly, the heating element 302b on the downstream side in the transport direction of the recording material P is also divided into seven heating elements 302b-1 to 302b-7 arranged along the longitudinal direction of the heater 300, with seven heating regions from each heating element aligned along the longitudinal direction. Furthermore, the conductor 303 is divided into seven conductors 303-1 to 303-7 in the longitudinal direction of the heater 300, corresponding to the division positions of the heating elements 302a and 302b.

[0029] The division width of the heating block HB is as shown in Figure 3(B), and is designed to accommodate A5, B5, A4, and Letter paper sizes. Specifically, the heater 300 is divided into heating blocks HB1 to HB7 symmetrically from the center of the heater 300 in the longitudinal direction (width direction perpendicular to the recording material transport direction) (symmetrically with respect to the transport reference position X). The division positions of the heating blocks HB correspond to "A5 size," "B5 size," "A4 size," and "Letter size," respectively. Specifically, the width of heating block HB4 is 150 mm, which is approximately the same as the short side length of A5 size. The widths of heating blocks HB3 to HB5 are 185 mm, which is approximately the same as the short side length of B5 size. The widths of heating blocks HB2 to HB6 are 210 mm, which is approximately the same as the short side length of A4 size. The widths of heating blocks HB1 to HB7 are 220 mm, which is approximately the same as the short side length of Letter size. However, the number of divisions and the width of the divisions are not limited to these.

[0030] The planar shapes of the heating elements 302a and 302b are both formed as point-symmetrical parallelograms. Furthermore, the heating element 302a on the upstream side in the transport direction of the recording material P and the heating element 302b on the downstream side are arranged symmetrically with respect to the center in the short-side direction (the transport direction of the recording material P) of the heater 300 so that the heat distribution in the short-side direction (the transport direction of the recording material P) is symmetrical. In addition, the heating elements 302a and 302b are arranged at an angle with respect to the longitudinal and short-side directions of the heater 300, respectively, which reduces the influence of the gaps between the divided heating elements and improves the uniformity of the heat distribution in the longitudinal direction of the heater 300.

[0031] The back layer 1 has electrodes E (E1 to E7, E8-1, E8-2). Electrodes E1 to E7 are each located within the regions of conductors 303-1 to 303-7, and conductor 303-1 These electrodes supply power to the heating blocks HB1 to HB7 via 303-7. Electrodes E8-1 and E8-2 are provided to connect to the conductor 301 at the longitudinal end of the heater 300, and are electrodes that supply power to the heating blocks HB1 to HB7 via the conductor 301. In Embodiment 1, electrodes E8-1 and E8-2 are provided at both longitudinal ends of the heater 300, but for example, a configuration with only one electrode E8-1 is also acceptable. Furthermore, power is supplied to the conductors 301a and 301b using a common electrode, but separate electrodes may be provided for each of the conductors 301a and 301b, and power may be supplied to each of them.

[0032] The back layer 2 is composed of an insulating surface protective layer 307 (glass in Example 1) and covers the conductor 301, conductor 303, and heating elements 302a and 302b. The surface protective layer 307 is formed except for the area of ​​electrode E, and the configuration allows electrical contact C to be connected to electrode E from the back layer 2 side of the heater.

[0033] The sliding surface layer 1, located on the substrate 305 on the side opposite to the back surface layer 1, has thermistors T (T1-1 to T1-4, T2-5 to T2-7), which are temperature sensing elements for detecting the temperature of each heat-generating block HB1 to HB7. The thermistors T are PTC (Positive It is made of a material having temperature coefficient (OTC) or negative temperature coefficient (NTC) characteristics. By detecting the resistance value of each thermistor T, the temperatures of all heat-generating blocks HB1 to HB7 can be detected individually.

[0034] Furthermore, the sliding surface layer 1 has conductors ET (ET1-1 to ET1-4, ET2-5 to ET2-7) and conductors EG (EG1, EG2) to energize the thermistor T and detect its resistance. Conductors ET1-1 to ET1-4 are each connected to thermistors T1-1 to T1-4. Conductors ET2-5 to ET2-7 are each connected to thermistors T2-5 to T2-7. Conductor EG1 is connected to the four thermistors T1-1 to T1-4, forming a common conductive path. Conductor EG2 is connected to the three thermistors T2-5 to T2-7, forming a common conductive path. Conductors ET and EG are each formed along the longitudinal side of the heater 300 to its longitudinal end, and are connected to the control circuit 400 at the longitudinal end of the heater via electrical contacts (not shown).

[0035] The sliding surface layer 2 is composed of a surface protective layer 308 (glass in Example 1) which has sliding and insulating properties, covering the thermistor T, conductor ET, and conductor EG, and ensuring sliding properties with the inner surface of the film 202. Furthermore, the surface protective layer 308 is formed except for both longitudinal ends of the heater 300 in order to provide electrical contacts with the conductor ET and conductor EG.

[0036] Next, the method of connecting the electrical contacts C to each electrode E will be explained. Figure 3(C) is a plan view from the heater holding member 201 side showing how the electrical contacts C are connected to each electrode E. The heater holding member 201 is provided with through holes at positions corresponding to the electrodes E (E1~E7, E8-1, E8-2). At each through hole position, the electrical contacts C (C1~C7, C8-1, C8-2) are electrically connected to the electrodes E (E1~E7, E8-1, E8-2) by methods such as spring biasing or welding. The electrical contacts C are connected to the control circuit 400 of the heater 300, which will be described later, via a conductive material (not shown) provided between the metal stay 204 and the heater holding member 201.

[0037] 4. Heater control circuit configuration Figure 4 shows the circuit diagram of the control circuit 400 of the heater 300 in Embodiment 1. The control circuit 400 is supplied to the heater 300 from a commercial AC power supply 401 connected to the image forming apparatus 100. This is a circuit that controls power. Power control of heater 300 is performed by energizing / cutting off triacs 411 to 417. Triacs 411 to 417 operate according to FUSER1 to FUSER7 signals from CPU 420, respectively. The drive circuits for triacs 411 to 417 are omitted from the diagram. The control circuit 400 of heater 300 has a circuit configuration that allows for independent control of seven heat-generating blocks HB1 to HB7 by seven triacs 411 to 417.

[0038] The zero-cross detection unit 421 is a circuit that detects the zero-crossing of the AC power supply 401 and outputs a ZEROX signal to the CPU 420. The ZEROX signal is used for detecting the timing of phase control and wavenumber control of triacs 411 to 417, etc.

[0039] Next, the method for detecting the temperature of heater 300 will be explained. The temperature of heater 300 is detected by thermistors T (T1-1 to T1-4, T2-5 to T2-7). The voltage division between thermistors T1-1 to T1-4 and resistors 451 to 454 is detected by CPU 420 as Th1-1 to Th1-4 signals, and CPU 420 converts Th1-1 to Th1-4 signals into temperature. Similarly, the voltage division between thermistors T2-5 to T2-7 and resistors 465 to 467 is detected by CPU 420 as Th2-5 to Th2-7 signals, and CPU 420 converts Th2-5 to Th2-7 signals into temperature.

[0040] In the internal processing of CPU420, the power to be supplied is calculated based on the temperature detected by the thermistor, for example, using PI control (proportional-integral control). Furthermore, the supplied power is converted into control levels for the phase angle (phase control) and wavenumber (wavenumber control) corresponding to the power, and triacs 411-417 are controlled according to these control conditions.

[0041] Relays 430 and 440 are used as means of cutting off power to heater 300 when the power is turned off, in sleep mode, or when heater 300 overheats due to a malfunction or other reason.

[0042] The circuit operation of relays 430 and 440 is explained below. When the RLON signal is high, transistor 433 turns ON, current flows from the power supply voltage Vcc to the secondary coil of relay 430, and the primary contact of relay 430 turns ON. When the RLON signal is low, transistor 433 turns OFF, the current flowing from the power supply voltage Vcc to the secondary coil of relay 430 is interrupted, and the primary contact of relay 430 turns OFF. Similarly, when the RLON signal is high, transistor 443 turns ON, current flows from the power supply voltage Vcc to the secondary coil of relay 440, and the primary contact of relay 440 turns ON. When the RLON signal is low, transistor 443 turns OFF, the current flowing from the power supply voltage Vcc to the secondary coil of relay 440 is interrupted, and the primary contact of relay 440 turns OFF. Note that resistors 434 and 444 are current limiting resistors.

[0043] Next, the operation of the safety circuit using relays 430 and 440 will be explained. If any one of the temperatures detected by thermistors T1-1 to T1-4 exceeds a predetermined value, the comparison unit 431 activates the latch unit 432, and the latch unit 432 latches the RLOFF1 signal in a Low state. When the RLOFF1 signal is Low, even if the CPU 420 sets the RLON signal to High, the transistor 433 remains in the OFF state, so the relay 430 can remain in the OFF state (safe state). Note that in the non-latched state, the latch unit 432 outputs the RLOFF1 signal in an open state. Similarly, if any one of the temperatures detected by thermistors T2-5 to T2-7 exceeds a predetermined value, the comparison unit 441 activates the latch unit 442, and the latch unit 442 latches the RLOFF2 signal in a Low state. When the RLOFF2 signal is low, even if the CPU420 sets the RLON signal to high, transistor 443 remains in the OFF state. Therefore, relay 440 can be kept in the OFF state (safe state). Similarly, latch unit 442 outputs the RLOFF2 signal as an open state when not latched.

[0044] 5. Basic Temperature Control Methods Figure 5 shows the target temperature distribution of the heater 300 and the positional relationship of the heater 300 when feeding LETTER paper (width 216 mm), which is the maximum paper width of the image forming apparatus 100 in Example 1. The configuration of the heater 300 is the same as the configuration shown in Figure 3(B). When feeding LETTER paper, the target temperature of the heater 300 is kept constant (220°C in Example 1) in order to fix the toner image over the entire length direction. The heating area is long at 220 mm relative to the paper width of 216 mm, which is to ensure that the toner image is fixed even to the edges of the paper. The relationship between the paper width and the length of the heating area is the same for paper other than LETTER paper.

[0045] Figure 6 shows the target temperature distribution of the heater 300 and the positional relationship of the heater 300 when feeding A5 paper (width 148 mm). Heating block HB4, which corresponds to the width of A5 paper, is set to a temperature (220°C) at which the toner image can be fixed, while heating blocks HB1-3 and HB5-7, which correspond to the non-feeding areas of the A5 paper, are set to lower temperatures to suppress the temperature rise of the non-feeding areas.

[0046] However, lowering the heater temperature increases the torque required to drive the fixing device 200, which can cause the image heating device to stop rotating, a phenomenon known as slippage. In Example 1, slippage sometimes occurred when the heater temperature fell below 150°C, so a higher temperature of 180°C was set as the target control temperature for the heater 300 in the non-paper-feed section.

[0047] In the following explanation, LETTER paper will be referred to as large-size paper (wide paper), and A5 paper as small-size paper (narrow paper). However, in this invention, large-size paper (first recording material) and small-size paper (second recording material) refer to two types of recording materials of different sizes. For example, in a combination of A4 size paper and B5 size paper, the former is the large-size paper and the latter is the small-size paper. Similarly, for example, in a combination of LETTER paper and A4 size paper, the former is the large-size paper and the latter is the small-size paper.

[0048] Furthermore, in the following description, heating block HB4 is defined as the first heating region, and heating blocks HB1-HB3 and HB5-HB7 are defined as the second heating region. That is, in this embodiment, heating block HB4 is a heating block that includes a heating element (first heating element) for heating the paper passage section (first paper passage region) through which both large and small sized paper passes in the fixing nip section N. Furthermore, in this embodiment, heating blocks HB1-HB3 and HB5-HB7 are heating blocks that include heating elements (second heating elements) for heating the paper passage section (second paper passage region) through which large sized paper passes but small sized paper does not. Furthermore, in the following description, the control target temperature of the first heating region (first control target temperature) is defined as T HT1 The second target temperature for the heating region (second target temperature) is set to T HT2 Let's assume that.

[0049] 6. Heating of the non-paper-feeding section of the pressure roller. As shown in Figure 6, the heating of the heater 300 and film 202 in the non-paper-feeding section can be suppressed by controlling the heater to lower the target temperature of the non-paper-feeding section. However, if small-sized paper such as A5 paper is fed continuously, heating of the non-paper-feeding section may occur in the pressure roller 208.

[0050] Figure 7(A) shows the longitudinal temperature distribution of the pressure roller 208 when A5 paper is passed through it. Below, the temperature of the region of the pressure roller 208 corresponding to the first heating region (heating block HB4) is referred to as T. PR1、Set the temperature of the area of the pressure roller 208 corresponding to the second heating area (heating blocks HB1 to HB3, HB5 to HB7) to T PR2 Let the temperature difference between the non-paper-passing part and the paper-passing part of the small-sized paper be ΔT PR = T PR2 - T PR1 When passing three sheets of A5 paper, T PR1 = 88 °C, T PR2 = 91 °C, ΔT PR = 3 °C. When passing ten sheets of A5 paper, T PR1 = 80 °C, T PR2 = 100 °C, ΔT PR = 20 °C.

[0051] If the small-sized paper is continuously passed as described above, the temperature rise of the non-paper-passing part of the pressure roller 208 progresses, and the reason why T PR2 and ΔT PR increase will be explained using Fig. 7(B). Fig. 7(B) shows the time change (change in the number of printed sheets) of the temperature T PR1 and T PR2 of the pressure roller 208 when passing small-sized paper. T PR1 becomes the highest just before the recording material P reaches the fixing device 200. As the paper passes, the heat of the pressure roller 208 is taken away by the recording material P, and the temperature drops.

[0052] On the other hand, the temperature T PR2 of the non-paper-passing part of the pressure roller 208 is lower than the temperature T PR1 of the paper-passing part of the pressure roller 208 before the recording material P arrives because the temperature of the heater 300 in the non-paper-passing part is low. However, since the recording material P does not pass, the heat of the heater 300 is constantly supplied to the pressure roller 208, and the temperature gradually rises. As a result, the values of T PR1 , T PR2 , and ΔT PR when passing three sheets of A5 paper and when passing ten sheets of A5 paper increase as the paper passes, as shown in Fig. 7(B).

[0053] ​​In this example, the heater temperature 300 is controlled to achieve the temperature distribution shown in Figure 6 by the time the first recording material P reaches the fixing device 200, but the temperature control is not limited to this. For example, the longitudinal temperature may be controlled uniformly as shown in Figure 5 until the recording material P arrives, and then controlled to achieve the temperature distribution shown in Figure 6 after the recording material P arrives. Even in this case, as the small-sized paper feed progresses, ΔT PR It will get bigger.

[0054] 7. Reasons for deterioration of hot offset when the non-paper-feeding section of the pressure roller heats up. When feeding small-sized paper, the temperature difference Δ between the paper-feeding and non-feeding sections of the pressure rollers increases. Feeding large-sized paper under these conditions worsens the hot offset. The reason for this is explained below.

[0055] The outer diameter of the pressure roller 208 increases as the temperature rises due to thermal expansion of the rubber layer, etc. Figure 8 shows the temperature dependence of the outer diameter of the pressure roller 208 having the elastic layer 210 used in Example 1. The outer diameter of the pressure roller 208 at a pressure roller temperature of 23°C is 25.0 mm. At a pressure roller temperature of 80°C, the outer diameter of the pressure roller 208 becomes 25.3 mm, and at a pressure roller temperature of 100°C, the outer diameter of the pressure roller 208 becomes 25.4 mm, resulting in a difference of 0.1 mm in the outer diameter of the pressure roller 208.

[0056] As mentioned above, the inverted crown shape of the pressure roller 208 exerts a pulling force on the recording material P toward the longitudinal outward direction of the film 202. Pressure roller temperature difference ΔT PR When the difference in outer diameter increases, the force pulling on the recording material P becomes greater. The inventors of this invention have discovered that when the force pulling on the recording material P toward the longitudinal outward direction increases, hot offset is more likely to occur. The mechanism can be explained as follows.

[0057] Hot offset is an image defect that becomes apparent when excessive heat is applied to the toner image, causing the toner to stretch during the separation of the film 202 and the recording material P. Some of the toner adheres to the film 202, and the attached toner is ejected after one pass around the fixing film.

[0058] Figure 9(A) is a schematic diagram illustrating the forces related to the occurrence of hot offset downstream of the nip section N in the fixing device 200. It shows how the film 202 and the recording material P separate and the toner stretches as the recording material P exits the nip section N.

[0059] In Figure 9(A), the upward force represents the adhesion force F1 of the toner to the film 202. In Figure 9(A), the downward force represents the viscous stress F2 that resists the elongation of the toner.

[0060] Hot offset occurs when the adhesive force F1 becomes greater than the viscous stress F2. Figure 9(B) shows the case where the force pulling the recording material P outward in the longitudinal direction is greater than in Figure 9(A). In this case, the separation direction of the recording material P becomes oblique due to the longitudinal force. The adhesive force F1 is determined by the release properties of the film 202, the toner material, and the contact area between the film 202 and the toner, and therefore does not depend on the force pulling the recording material P outward in the longitudinal direction. The viscous stress F2 is determined by the toner material and the separation speed when the film 202 and the toner separate, and its absolute value hardly changes even if the force pulling the recording material P outward in the longitudinal direction changes. However, since the viscous stress F2 acts in the direction in which the toner stretches, it acts obliquely as shown in Figure 9(B). In Figure 9(B), the viscous stress opposite to the adhesive force F1 is only the component F2x decomposed downward in the figure. Since F2 > F2x, when the force pulling the recording material P outward in the longitudinal direction is greater than when it is small, the viscous stress opposite to the adhesive force F1 becomes smaller. As a result, hot offset is more likely to occur.

[0061] Furthermore, when the longitudinal temperature of the pressure roller 208 is uniform, the inverse crown amount is set so that the viscous stress is greater than the adhesive force, and therefore hot offset does not occur. Hot offset occurs when the outer diameter of the end of the pressure roller 208 increases further due to the heating of the non-paper-feeding section.

[0062] For the reasons stated above, the pressure roller temperature difference ΔT is caused by feeding small-sized paper. PR When large-size paper is fed through the machine while the pressure roller is enlarged, hot offset is likely to occur if image formation is performed in the area with a high pressure roller temperature.

[0063] 8. Characteristics and effects of temperature control in Example 1 In this embodiment, the pressure roller temperature difference ΔT PR Considering that the temperature becomes larger and hot offset is more likely to occur, the control target temperature of the heater in the non-paper-feeding section, i.e., the control target temperature of the heating block corresponding to the non-paper-feeding section, is set to ΔT PR A key feature is that it changes according to ΔT. PR A key feature is that the larger the value, the lower the target temperature of the heat-generating block corresponding to the non-paper-feeding section.

[0064] Figure 10 shows the control target temperature T of the heater 300 in Example 1. HT1 , T HT2 This is a flowchart for determining the paper feed section. First, as explained in Figures 5 and 6, the T will be the paper feed section for both small and large size paper. HT1 Set the temperature to 220°C (S502). Determine whether the heating blocks HB1~HB3 and HB5~HB7 are paper feed sections (S503), and if they are not paper feed sections, as shown in Figure 6, T HT2 Set the temperature to 180°C (S504). The information on the width of the recording material P may be obtained from an external device such as a host computer, or the image forming apparatus 100 may be equipped with a paper width sensor (not shown) that detects the width of the recording material P, and that information may be used.

[0065] If the heat-generating blocks HB1-HB3 and HB5-HB7 are in the paper feeding section, the pressure roller temperature T PR1and T PR2 Measure (S505), ΔT PR Determine whether it is a positive value (S506). As a means of determining the temperature, T PR1 This was measured with a pressure roller thermistor 220-4, and T PR2 This is measured with a pressure roller thermistor 220-3. Here, T PR2 Since it was known that the temperature was the same regardless of whether pressure roller thermistors 220-1~3 or 220-5~7 were used, the measurement was performed using pressure roller thermistor 220-3, but other pressure roller thermistors may also be used. In other words, the values ​​measured with pressure roller thermistors 220-1, 2, or 220-5~7 may be used.

[0066] ΔT PR If the value is not positive, the temperature at the end of the pressure roller is low, and there is no need to lower the temperature, so T HT2 =T HT1 (S507)

[0067] ΔT PR When the value is positive, T follows the following equation (1) HT2 Decide (S508). T HT2 =T HT1 -K1·ΔT PR (1)

[0068] Here, K1 is ΔT PR T by HT2 This is a coefficient that determines the amount of change, and is a value that can be freely set according to the properties of the fuser 200 and the toner used. In Example 1, K1 = 0.2. Also, as a result of the calculation of equation (1), T HT2 If a decimal value occurs, the decimal part is rounded to the nearest whole number. HT2 The above process from S503 to S508 is repeated until the print job is completed (S509).

[0069] As explained in the S508 process, T HT2 ΔT PRHot offset can be prevented by lowering it according to its magnitude. This is because as the temperature decreases and the viscosity of the toner increases, the adhesion force F1 decreases, while the viscous stresses F2 and F2x increase, resulting in F1 <F2xとなるからである。なお、T HT2 The range in which the temperature is lowered should preferably be limited to a temperature that ensures adhesion. Normally, to ensure stable adhesion at all times, the control target temperature of heater 300 is set slightly higher than the minimum temperature at which adhesion can be ensured, and also, since a high pressure roller temperature is a favorable condition for adhesion, T HT2 Even if the temperature is lowered, adhesion can still be ensured. Considering the above points, the lower limit temperature at which adhesion can be ensured in this embodiment was 215°C, so the control target temperature of the heater 300 is limited so that it does not fall below 215°C.

[0070] To demonstrate the effectiveness of this embodiment, a comparison was made between the occurrence of hot offset when feeding small-sized paper followed by large-sized paper. As the small-sized paper, A5-sized "Canon PB-PAPER" was fed through, and then as the large-sized paper, "Xerox Vitality" letter paper was fed through. Three or ten sheets of small-sized paper were fed through, and one sheet of large-sized paper was fed through. The toner image was printed across the entire area of ​​the recording material P.

[0071] As Comparative Example 1, the fixing device configuration was the same as in Example 1, but the target temperature for controlling the heater was different. Specifically, the target temperature distribution for controlling the heater when feeding small-sized paper was the same as in Example 1, but the target temperature for controlling large-sized paper was the same as the pressure roller temperature difference ΔT PR Regardless of the above, this is an example where the target temperature for controlling the heater in the paper feeding section is uniform.

[0072] Table 1 shows the temperature and whether or not hot offset occurred when feeding large-size paper after feeding three small-size sheets. Table 2 shows the temperature and whether or not hot offset occurred when feeding large-size paper after feeding ten small-size sheets. The pressure roller temperatures shown in Tables 1 and 2 are the temperatures after the small-size paper feeding is complete.

[0073] In Table 1, in Example 1, ΔT PR Since =3℃, from equation (1) T HT2 =219℃. In the comparative example, ΔT PR Regardless of, T HT2 =T HT1 The temperature was set to 220°C. Under these conditions, no hot offset occurred in either Example 1 or Comparative Example 1.

[0074] Table 2 shows ΔT PR Since =20℃, in Example 1, T HT2 =216℃. PR As the size increased, the control target temperature T of heater 300 HT2 This is made lower. As a result, no hot offset occurred in Example 1. On the other hand, in Comparative Example 1, ΔT PR Regardless of size T HT2 =T HT1 As a result of setting the temperature to 220°C, a hot offset occurred.

[0075] TIFF2023156013000002.tif32170

[0076] TIFF2023156013000003.tif32170

[0077] As explained above, according to this embodiment, the pressure roller temperature difference ΔT PR By changing the target temperature of the heater 300 at the edge (the non-feeding area when small-sized paper is fed), the occurrence of image defects due to hot offset can be suppressed. More specifically, the pressure roller temperature difference ΔT PR The above effect can be obtained by lowering the control target temperature of the heater 300 when the value is small or large. In particular, when the number of small-sized paper sheets passed through increases, the pressure roller temperature difference ΔT PR The effects of this embodiment are more easily obtained when the value increases.

[0078] In Example 1, the pressure roller temperature difference ΔT PRAs an example of the conditions under which the pressure roller temperature difference ΔT becomes large, the example given was that of feeding small-sized paper, but this is not limited to the case of feeding small-sized paper. For example, even when feeding large-sized paper, the toner may form an image only in the longitudinal center. The center is more susceptible to heat loss by the toner, while the edges (areas without toner) lose less heat than the center. Even in such cases, although not as much as in the case of feeding small-sized paper, the pressure roller temperature difference ΔT becomes larger. PR Since this can occur, the present invention can be utilized. Also, although the paper feeding history is unknown, the pressure roller temperature difference ΔT PR If this occurs, the present invention can be used to suppress image defects caused by hot offset.

[0079] In Example 1, the target temperature for controlling the basic heater 300 was set to 220°C, and ΔT PR The target temperature of heater 300 was changed from 220°C depending on its size. However, the target temperature of heater 300 is also changed depending on the type of recording material P, the ambient temperature and humidity in which the image forming apparatus 100 is used, and the warm-up state. In that case, the temperature is changed from the basic target temperature of heater 300 of 220°C, and then ΔT PR The final target temperature for controlling the heater 300 may be determined according to its size.

[0080] Furthermore, while the first heating region is designated as heating block HB4 and the second heating region as heating blocks HB1-HB3 and HB5-HB7, the system is not limited to this configuration. For example, when feeding B5 paper as small-size paper and then feeding LETTER paper, the first heating region may be heating blocks HB3-HB5, and the second heating region may be heating blocks HB1, HB2, HB6, and HB7. Additionally, when the pressure roller temperature becomes high only in certain areas, such as when toner is unevenly distributed on the recording material, only those areas may be designated as the second heating region. For example, if only heating block HB3 is at a high temperature, the first heating region may be heating block HB4 and the second heating region may be heating block HB3.

[0081] In Example 1, the pressure roller temperature T PR1 , TPR2 Measured with a pressure roller thermistor 220 However, the method for obtaining the temperature of the pressure roller 208 (roller temperature acquisition means) is not limited to this. For example, the control unit may, in advance, have a detailed understanding of the temperature rise during printing and the temperature drop during standby, and combine this with the operating status of the image forming apparatus 100 to obtain the pressure roller temperature T PR1 , T PR2 The temperature can be predicted (temperature prediction means). When using the temperature prediction means, the pressure roller thermistor 220 is not required, which has the advantage of reducing the size of the image forming apparatus 100. Pressure roller temperature T PR1 , T PR2 Whether to measure or predict the temperature should be chosen based on the required accuracy for determining the target temperature of the heater 300.

[0082] Furthermore, while the effects of the present invention were explained using a heater divided into multiple heating regions in the longitudinal direction as Comparative Example 1, the present invention is also advantageous for other types of heaters. For example, when using the heater described in Figure 4 of Patent Document 1 (a heater not divided into multiple heating regions in the longitudinal direction), when feeding small-sized paper, the heater and fixing film also heat up in the non-paper-feeding areas, causing the edge temperature of the pressure roller to rise. As a result, hot offset becomes even more unfavorable than with a heater divided into multiple heating regions in the longitudinal direction, and to prevent hot offset, it is necessary to wait for the edge heater, fixing film, and pressure roller to cool down, which reduces image productivity. In other words, the present invention is advantageous over image heating devices using heaters not divided into multiple heating regions in the longitudinal direction in that it can suppress image defects due to hot offset while maintaining high image productivity.

[0083] (Example 2) Next, Embodiment 2 of the present invention will be described. The basic configuration and operation of the image forming apparatus and fixing apparatus in Embodiment 2 are the same as those in Embodiment 1. Therefore, elements having the same or equivalent functions and configurations as in Embodiment 1 are denoted by the same reference numerals, and detailed descriptions are omitted. Matters in Embodiment 2 that are not specifically described here are the same as in Embodiment 1.

[0084] In Example 1, when the temperature difference ΔT of the pressure roller PR is large, the control target temperature at the end of the heater is lowered to suppress the hot offset. However, when the number of sheets of small-sized paper passing through increases and ΔT PR becomes even larger, there is a possibility that a hot offset may occur. Therefore, in Example 2, when ΔT PR becomes larger than that in Example 1 and it is difficult to achieve both fixing performance and hot offset suppression only by lowering the control target temperature at the end of the heater, an example of control to be performed will be described.

[0085] FIG. 11 shows the time change (printing sheet number change) of the pressure roller temperatures T PR1 and T PR2 when A5 paper is passed through under the same conditions as in Example 1. Up to the 10th sheet of A5 paper, it is as described in Example 1. When passing A5 paper continuously thereafter, ΔT PR becomes even larger. At the 30th sheet of A5 paper, ΔT PR = 30°C. When performing the same control as in Example 1, T HT2 = 214°C, but in the heater configuration of this example, it is known that when the control target temperature of the heater is lower than 215°C, fixing failure due to insufficient melting of the toner may occur regardless of the pressure roller temperature. The hot offset is disadvantageous as ΔT PR becomes larger, but the lower limit temperature at which fixing can be achieved is not a value that changes in conjunction with ΔT PR . As a result, there may be cases where it is impossible to achieve both ensuring fixing performance and suppressing the hot offset.

[0086] Therefore, in Example 2, a threshold value (denoted as ΔTth) is set in advance for ΔT PR , and when ΔT [[ID=3,2]] PR exceeds ΔTth, a waiting time is provided before passing the large-sized paper until ΔT PR ≦ΔTth. That is, the start of the heat treatment for the large-sized paper is delayed until the temperature difference in the longitudinal direction of the pressure roller becomes below a predetermined threshold value. In Example 2, ΔTth = 25°C is set so that the control target temperature of the heater does not fall below 215°C.

[0087] FIG. 12 is a flowchart for determining the control target temperature and standby time of the heater. The processing contents from S601 to S607 are the same as the processing from S501 to S507 in FIG. 10. is the same. ΔT PR When > 0, before determining T HT2 , it is determined whether ΔT PR ≦ ΔTth (S608). When ΔT PR > ΔTth, the process of S608 is repeated and standby is performed until ΔT PR ≦ ΔTth. After satisfying the condition of ΔT PR ≦ ΔTth, T HT2 is determined based on Equation (1) (S609). The above processes from S603 to S609 are repeated until the end of the printing job (S610).

[0088] Table 3 shows the results of an experiment demonstrating the effects of Example 2. Except that the number of sheets of small-sized paper passed is 30, the experimental conditions are the same as those of Example 1. Since ΔT PR after passing small-sized paper is 30°C, the value is larger than ΔTth = 25°C. Therefore, in Example 2, by delaying the paper feeding from cassette 11 before passing large-sized paper, standby was performed until ΔT PR ≦ ΔTth. The standby time at that time was 2 seconds, and no hot offset occurred on the large-sized paper.

[0089] Comparative Example 2, similar to Comparative Example 1, uses an example where the configuration of the fixing device is the same as that of Example 1 but the control target temperature of the heater is different. Specifically, it is an example of determining the control target temperature of the heater regardless of the pressure roller temperature difference ΔT PR . In that case, even when a standby time of 2 seconds, the same as in Example 2, was provided, a hot offset occurred on the large-sized paper.

[0090] Comparative Example 3 has the same configuration as Comparative Example 2 but is an example of standby until no hot offset occurs. To prevent the occurrence of hot offset, as in Table 1 in Example 1, ΔT PRIt is necessary to wait until the temperature reaches 3°C. As a result, hot offset no longer occurs, but a waiting time of 50 seconds is required. In other words, the image productivity is inferior to that of Example 2.

[0091] TIFF2023156013000004.tif29170

[0092] As explained above, in this embodiment, the pressure roller temperature difference ΔT PR If the value exceeds a pre-set threshold ΔTth, the system will wait for paper to be fed, and will wait until the value falls below ΔTth before proceeding. PR The target temperature of the heater end is changed accordingly. By doing so, it is possible to suppress the occurrence of image defects due to hot offset without reducing image productivity as much as possible. Also, as in Example 1, the pressure roller temperature T PR1 and T PR2 This can be measured using a pressure roller thermistor 220, or predicted using a temperature prediction means.

[0093] (Example 3) Next, Embodiment 3 of the present invention will be described. The basic configuration and operation of the image forming apparatus and fixing apparatus in Embodiment 3 are the same as those of Embodiment 1 or Embodiment 2. Therefore, elements having the same or equivalent functions and configurations as those in Embodiment 1 or Embodiment 2 are denoted by the same reference numerals, and detailed descriptions are omitted.

[0094] Example 3 is an example in which there is neither a temperature sensing element nor a temperature prediction means for detecting the temperature of the pressure roller 208. Unlike Examples 1 and 2, the pressure roller temperature ΔT PR Although the exact method is unclear, the occurrence of hot offset is suppressed using a simple history of the number of small-sized paper sheets fed, in the same principle as in Example 1.

[0095] In Example 3, the number of small-sized paper sheets to be fed is P. mini In this case, the target temperature T of the heater is HT2 This is determined by equation (2). T HT2 =THT1 -K2·P mini (2)

[0096] Here, K2 is P mini T by HT2 This is a coefficient that determines the amount of change, and it is a value that can be freely set according to the properties of the fuser 200 and the toner used. In Example 3, K2 = 0.4. Also, as a result of the calculation of equation (2), T HT2 If a decimal value occurs, the decimal part is rounded to the nearest whole number. HT2 Let's assume that.

[0097] Furthermore, although the pressure roller temperature is unknown in Example 3, if there is a period of time when paper is not fed after feeding small-sized paper and before feeding large-sized paper, then ΔT PR It is thought that this value is becoming smaller. Therefore, if there is a certain waiting time (let's say 50 seconds here) after feeding small-sized paper, the value determined by equation (2) is reset, and T HT2 =T HT1 The timing for resetting can be determined by a fixed time, such as after 50 seconds have elapsed, or P mini Linked to the value of P mini The larger the value, the later the decision can be made.

[0098] Tables 4 and 5 show the experimental results demonstrating the effect of Example 3. The configuration and method for determining the heater control target temperature in Comparative Example 4 are the same as in Comparative Example 1. As shown in Table 4, no problems due to hot offset occurred in either Example 3 or Comparative Example 4. On the other hand, as shown in Table 5, when the number of small-size paper sheets passed was 10, no hot offset occurred in Example 3, but it did occur in Comparative Example 4. In Example 3, the heater control target temperature T was lower when the number of small-size paper sheets passed was higher (10 sheets) than when it was lower (3 sheets). HT2 Because the value is reduced, the occurrence of hot offset is suppressed. The reason why hot offset occurs in Comparative Example 4 is as explained in Example 1.

[0099] TIFF2023156013000005.tif32170

[0100] TIFF2023156013000006.tif32170

[0101] As described above, when the number of small-sized paper sheets being fed is greater than when the number of small-sized paper sheets is greater, lowering the target temperature of the heater edge when feeding large-sized paper can suppress the occurrence of hot offset.

[0102] Alternatively, as in Example 2, a threshold may be set, and if the threshold is exceeded, a waiting time may be provided between feeding small-sized paper and feeding large-sized paper. In the fixing device of Example 3, when the threshold for the number of small-sized paper sheets fed was set to 13, and a predetermined waiting period of (number of sheets exceeding 13) × (0.15 seconds) was set, no hot offset occurred. For example, when the number of small-sized paper sheets fed was 30, the waiting time was 2.55 seconds.

[0103] Although Example 3 does not use pressure roller temperature and therefore has lower accuracy compared to Examples 1 and 2, it can suppress the occurrence of hot offset with a simple configuration while minimizing the reduction in image productivity.

[0104] Furthermore, the control described in each of the above embodiments is suitable for situations such as when a printing job occurs in which small-sized paper is fed first, followed by large-sized paper without any other paper being fed in between, resulting in a continuous feeding of small-sized and large-sized paper. For example, if the period between feeding small-sized and large-sized paper becomes longer than planned due to reasons such as jamming, depending on the length of that period, the longitudinal temperature difference of the pressure roller may be eliminated by the time the large-sized paper is fed. Therefore, in such cases, the control described in each embodiment may be configured not to be executed.

[0105] The disclosure of embodiments of the present invention includes the following configurations. (Composition 1) A cylindrical film and A heater having multiple heating elements arranged in the internal space of the film and aligned in the width direction of the recording material perpendicular to the transport direction of the recording material, A roller that contacts the outer surface of the film and forms a nip between itself and the film together with the heater, A temperature detection means for detecting the temperature of each of the multiple heating elements, A control unit controls the power supplied to the plurality of heating elements so that the temperature detected by the temperature detection means reaches a predetermined control target temperature. Equipped with, An image heating device that heats an image formed on a recording material that is held and conveyed by the nip by the heat of the heater, The aforementioned nip, A first paper passage area through which both a first recording material and a second recording material smaller in size than the first recording material pass, A second paper passage area through which the first recording material passes but the second recording material does not, Includes, The plurality of heating elements, A first heating element for heating the aforementioned first paper feeding area, A second heating element for heating the second paper-feeding area, In an image heating apparatus including, The system includes a roller temperature acquisition means that acquires a first temperature, which is the temperature of the roller region corresponding to the first paper feeding region, and a second temperature, which is the temperature of the roller region corresponding to the second paper feeding region. The image heating apparatus is characterized in that, when the control unit performs the heat treatment on the first recording material, if the second temperature is higher than the first temperature, it lowers the second control target temperature used for supplying power to the second heating element to a first control target temperature used for supplying power to the first heating element. (Configuration 2) The image heating apparatus according to configuration 1, characterized in that the control unit lowers the second target temperature to the first target temperature so that the greater the difference between the second temperature and the first temperature, the greater the difference between the second target temperature and the first target temperature. (Composition 3) The image heating apparatus according to configuration 1 or 2, characterized in that, if the difference between the second temperature and the first temperature exceeds a predetermined threshold, the start of the heating treatment on the first recording material is delayed until the difference between the second temperature and the first temperature falls below the threshold. (Composition 4) The image heating apparatus according to any one of configurations 1 to 3, characterized in that when the control unit performs the heat treatment on the first recording material, if the second temperature is not higher than the first temperature, the second control target temperature is set to the same temperature as the first control target temperature. (Composition 5) The image heating device according to any one of configurations 1 to 4, characterized in that the roller temperature acquisition means includes a temperature sensing element for detecting the temperature of the roller. (Composition 6) The image heating device according to any one of configurations 1 to 4, characterized in that the roller temperature acquisition means includes a temperature prediction means that predicts the temperature of the roller based on information including the operating status of the image heating device. (Composition 7) A cylindrical film and A heater having multiple heating elements arranged in the internal space of the film and aligned in the width direction of the recording material perpendicular to the transport direction of the recording material, A roller that contacts the outer surface of the film and forms a nip between itself and the film together with the heater, A temperature detection means for detecting the temperature of each of the multiple heating elements, A control unit controls the power supplied to the plurality of heating elements so that the temperature detected by the temperature detection means reaches a predetermined control target temperature. Equipped with, An image heating device that heats an image formed on a recording material that is held and conveyed by the nip by the heat of the heater, The aforementioned nip, A first paper passage area through which both a first recording material and a second recording material smaller in size than the first recording material pass, A second paper passage area through which the first recording material passes but the second recording material does not, Includes, The plurality of heating elements, A first heating element for heating the aforementioned first paper feeding area, A second heating element for heating the second paper-feeding area, In an image heating apparatus including, The image heating apparatus is characterized in that, when the control unit performs the heat treatment on the first recording material continuously after the heat treatment on the second recording material, it sets the second control target temperature used for supplying power to the second heating element to a lower temperature than the first control target temperature used for supplying power to the first heating element. (Composition 8) The image heating apparatus according to configuration 7, characterized in that, when the control unit performs the heat treatment on the first recording material continuously after the heat treatment on the second recording material, the control unit lowers the second control target temperature to the first control target temperature so that the difference between the second control target temperature and the first control target temperature increases as the number of second recording materials that have been subjected to the heat treatment increases. (Composition 9) The image heating apparatus according to configuration 7 or 8, characterized in that, when the first recording material is subjected to the heat treatment after the second recording material has been subjected to the heat treatment, the start of the heat treatment on the first recording material is delayed if the number of second recording materials subjected to the heat treatment exceeds a predetermined threshold. (Composition 10) The control unit determines that the heating treatment of the first recording material is performed on the second recording material. If the process is not performed continuously after the initial processing, the image heating device according to any one of the configurations 7 to 9, characterized in that the second control target temperature is set to the same temperature as the first control target temperature in the heating process of the first recording material. (Composition 11) An image forming unit that forms an image on the recording material, A fixing unit that fixes the image formed on the recording material to the recording material, In an image forming apparatus having, An image forming apparatus characterized in that the fixing unit is an image heating device according to any one of the configurations 1 to 10. [Explanation of Symbols]

[0106] 200...Image heating device, 202...Fixing film, 208...Pressure roller, 220...Pressure roller thermistor, 300...Heater

Claims

1. A cylindrical film; a heater disposed in an internal space of the film and having a plurality of heating elements arranged in a width direction of the recording material perpendicular to a conveying direction of the recording material; a roller in contact with an outer peripheral surface of the film and forming a nip between the film and the roller and the heater via the film; A plurality of temperature detection means for detecting the temperatures of the plurality of heating elements, respectively; a control unit that controls power supplied to the plurality of heating elements so that temperatures detected by the respective temperature detection means become predetermined control target temperatures; Equipped with an image heating device that heats an image formed on a recording material that is nipped and conveyed by the nip by using heat from the heater, an image heating device in which, when heat-treating a second recording material having a smaller size in the width direction than a first recording material, a control target temperature of a second heating element corresponding to a second region, which is a region through which the recording material does not pass, is set lower than a control target temperature of a first heating element corresponding to a first region, which is a region through which the recording material passes; a roller temperature acquisition means for acquiring a first temperature, which is a temperature of a region of the roller corresponding to the first region, and a second temperature, which is a temperature of a region of the roller corresponding to the second region; an image heating device characterized in that, when the first recording material is heated, when the second temperature is higher than the first temperature, the control unit sets a second control target temperature that is the control target temperature of the second heat element to be lower than a first control target temperature that is the control target temperature of the first heat element.

2. 2. The image heating apparatus according to claim 1, wherein the control unit sets the second control target temperature lower than the first control target temperature such that the difference between the second temperature and the first temperature becomes larger as the difference between the second temperature and the first temperature becomes larger.

3. 3. The image heating apparatus according to claim 2, wherein, when a difference between the second temperature and the first temperature exceeds a predetermined threshold, the start of the heating process on the first recording material is delayed until the difference between the second temperature and the first temperature becomes equal to or less than the threshold.

4. 4. The image heating apparatus according to claim 1, wherein, when the first recording material is heated, if the second temperature is not higher than the first temperature, the control unit sets the second control target temperature to the same temperature as the first control target temperature.

5. 5. The image heating apparatus according to claim 4, wherein the roller temperature acquisition means includes a temperature detection element for detecting the temperature of the roller.

6. 5. The image heating apparatus according to claim 4, wherein the roller temperature acquisition means includes a temperature prediction means for predicting the temperature of the roller based on information including an operating status of the image heating apparatus.

7. A cylindrical film; a heater disposed in an internal space of the film and having a plurality of heating elements arranged in a width direction of the recording material perpendicular to a conveying direction of the recording material; a roller in contact with an outer peripheral surface of the film and forming a nip between the film and the roller and the heater via the film; A plurality of temperature detection means for detecting the temperatures of the plurality of heating elements, respectively; a control unit that controls power supplied to the plurality of heating elements so that temperatures detected by the respective temperature detection means become predetermined control target temperatures; Equipped with an image heating device that heats an image formed on a recording material that is nipped and conveyed by the nip by using heat from the heater, an image heating device in which, when heat-treating a second recording material having a smaller size in the width direction than a first recording material, a control target temperature of a second heating element corresponding to a second region, which is a region through which the recording material does not pass, is set lower than a control target temperature of a first heating element corresponding to a first region, which is a region through which the recording material passes; an image heating device characterized in that, when the control unit performs heating processing on the first recording material continuously after heating processing on the second recording material, the control unit sets a second control target temperature that is the control target temperature of the second heat element to be lower than a first control target temperature that is the control target temperature of the first heat element.

8. 8. The image heating apparatus according to claim 7, wherein, when the control unit performs heat treatment on the first recording material continuously after the heat treatment on the second recording material, the control unit sets the second control target temperature lower than the first control target temperature so that the difference between the second control target temperature and the first control target temperature becomes larger as the number of the second recording materials that have been subjected to the heat treatment increases.

9. 9. The image heating apparatus according to claim 8, wherein, when the heat treatment of the first recording material is performed consecutively after the heat treatment of the second recording material, if the number of the second recording materials that have been subjected to the heat treatment exceeds a predetermined threshold value, the start of the heat treatment of the first recording material is delayed.

10. The image heating apparatus according to any one of claims 7 to 9, characterized in that, when the heating process of the first recording material is not performed consecutively after the heating process of the second recording material, the control unit sets the second control target temperature to the same temperature as the first control target temperature in the heating process of the first recording material.

11. an image forming section for forming an image on a recording material; a fixing section for fixing the image formed on the recording material to the recording material; In an image forming apparatus having 2. An image forming apparatus comprising: a fixing unit that is an image heating device according to claim 1;

Images