JP5907594B2 - Image heating device - Google Patents

Description

  The present invention is used in an image forming apparatus such as a printer, a copying machine, a facsimile, or a multi-function machine having a plurality of these functions, which employs an electrophotographic system or an electrostatic recording system, and heats an image on a recording material. The present invention relates to an image heating apparatus.

  Examples of the image heating device include a fixing device that fixes an unfixed image on the recording material, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material. it can.

  In the image forming apparatus as described above, an unfixed toner image is formed on a sheet-like recording material (hereinafter also referred to as paper) by an image forming unit, and then the toner image is fixed as a fixed image by a fixing unit. . A structure having a thin film sleeve, a ceramic heater that contacts the inner surface of the sleeve, and a pressure roller that forms a nip portion with the ceramic heater sandwiched between the sleeves, as a heat fixing device mounted on a copying machine or printer Have been put to practical use. This heat fixing device heats and fixes a toner image onto a recording material while conveying the recording material carrying the toner image at the nip portion.

  This heat-fixing device (referred to as a film heating method) has a very low heat capacity, so the warm-up to the fixable temperature is quick, the print waiting time is short, and the power consumption in the standby state waiting for a print command is low. There are advantages such as. The sleeve material is polyimide or stainless steel. The ceramic heater is a plate-shaped ceramic substrate with excellent heat resistance, thermal conductivity, and electrical insulation, such as alumina and aluminum nitride, on which a heating resistor mainly composed of silver and palladium is printed. . Based on the temperature detected by the thermistor in contact with the ceramic heater, energization to the heating resistor is controlled to manage the temperature of the heater.

  On the other hand, there are usually a plurality of recording material (recording paper) sizes that can be used with a single copying machine or printer. In particular, when a toner image formed on a small size recording material is heat-fixed, the heat of the ceramic heater is taken away by the recording material in an area where the recording material passes, but the heat of the ceramic heater is recorded in an area where the recording material does not pass. It may overheat because it is not robbed by the material. Excessive temperature rise causes a decrease in durability of the heat fixing device, and when fixing a large size paper following a fixing process of a small size paper, an image defect such as a hot offset of a toner image is caused. It is not preferable because it also causes.

  Therefore, Patent Document 1 discloses a heat fixing device that can change the heat generation distribution in the longitudinal direction of the ceramic heater in accordance with the size of the recording material. The ceramic heater mounted in the heat fixing device includes a first heating resistor having a resistance value at the center in the longitudinal direction larger than both ends on the ceramic substrate, and a second heating resistor having a resistance value at both ends greater than the center. ,have. The energization of the two heating resistors can be individually controlled. In this case, the center in the longitudinal direction is a conveyance reference for the recording material through which recording materials of all sizes pass. By setting various energization ratios to the first heating resistor and the second heating resistor, it is possible to set various heat generation distributions as a whole ceramic heater.

  For example, in the case of small-size paper, the heating ratio of the first heating resistor whose resistance value at the center in the longitudinal direction is larger than both ends is set large, and the heating ratio of the second heating resistor whose resistance value at both ends is larger than the center is set small. To do. Thereby, as a whole ceramic heater, it becomes possible to set the heat generation rate near the center in the longitudinal direction to be large and the heat generation rate near both ends in the longitudinal direction to be small.

  However, as above. Even if the overheating of the non-sheet passing area of the ceramic heater can be suppressed by setting various energization ratios to the first heating resistor and the second heating resistor, the non-sheet passing area of the recording material can be suppressed. The calorific value cannot be made zero. When the printing speed is high or when a thick paper is passed, the amount of heat absorbed in the paper passing area is large, so that the amount of heat generated by the entire heater increases. For this reason, the amount of heat generated in the non-sheet-passing area also increases, and an excessive temperature rise in the non-sheet-passing area is unavoidable.

  In that case, in order to prevent the temperature rise of the non-sheet passing portion, a configuration in which a blower fan is provided in the fixing device and air cooling is performed on the heating rotating body and the pressure rotating body of the non-sheet passing portion to suppress the temperature rise. It is described in Patent Document 2 and Patent Document 3. In the fixing device of Patent Document 2, cooling air is blown from the cooling fan to the non-sheet passing area side of the rotary heating body.

  In addition, an element for detecting the temperature of the fixing area is provided when a small-size sheet is passed, and ON / OFF control of the blower fan is performed based on the signal value. In the fixing device of Patent Document 3, when the cooling air is blown from the cooling fan to the non-sheet passing area side, the length in the width direction of the blower opening is adjusted by the shutter according to the width of the recording material to be used. Therefore, the temperature rise of the non-sheet passing portion is prevented even for recording materials having different width sizes.

  As another conventional example shown in FIG. 12, a fixing sleeve cooling fan, a duct, a cooling device for preventing temperature rise in the non-sheet passing portion, and a pressure roller provided with a shutter for adjusting the length in the width direction of the air blowing port. Shows a fixing device provided with a fan and a duct for blowing air. In FIG. 12, reference numerals 40a and 40b denote blower fans for cooling the fixing sleeve 22 of the non-sheet passing portion, and 45a. Reference numeral 45b denotes a fixing sleeve cooling duct for guiding the cooling air of the blower fans 40a and 40b to the fixing sleeve.

  50a and 50b are provided with cooling fans 40a. A shutter disposed between the duct 40a and the fixing sleeve 22 at the outlet of the ducts 45a and 45b. The shutters 50 a and 50 b can be displaced according to the size of the paper to be passed, and uniformly cool the non-paper passing area outside the heated paper passing area of the fixing sleeve 22.

Japanese Patent Laid-Open No. 10-177319 Japanese Patent Application Laid-Open No. 60-136779 JP 2008-32903 A

  As described above, in recent years, image heating devices (for example, 50 sheets per minute or more with A4 paper) that have an energy-saving fixing method with a low heat capacity and high print productivity have been put to practical use. The structure of the apparatus tends to be complicated by the heater configuration for the above and the air cooling mechanism of the excessive temperature raising portion. Here, as described above, air-cooling a portion that has been overheated deteriorates energy savings, and thus prevents excessive temperature rise in the non-sheet-passing area as much as possible and minimizes air cooling in the non-sheet-passing area as much as possible. Is required.

  In particular, in the case of small-size paper, the degree of excessive temperature rise is large near the boundary between the paper passing area and the non-paper passing area, and the temperature near the end in the longitudinal direction away from the boundary between the paper passing area and the non-paper passing area is excessive. The degree is small. For this reason, if the non-sheet passing region is air-cooled uniformly, the vicinity of the end portion is supercooled, and the temperature unevenness in the longitudinal direction becomes large. The temperature unevenness in the longitudinal direction causes a difference in the thermal expansion amount of the pressure roller and causes the fixing sleeve to be twisted. Therefore, it is necessary to perform cooling so that the temperature is uniform in the longitudinal direction in the non-sheet passing region. It becomes.

  The present invention has been made in view of such a technical problem, and in a non-sheet-passing region, an image that enables cooling so as to have a uniform temperature in the longitudinal direction (the rotation axis direction of the heating rotator). An object is to provide a heating device.

To achieve the above object, an image heating apparatus according to the present invention includes a rotating member, a heater for heating the rotary member, and a control unit for controlling the heater, disposed opposite previously Kikai rolling body , before a pressure member to form a two-up portion between the Kikai rotating body, and the rotating body, wherein a pressure member, the air blowing means for blowing air in at least one of the non-paper passing area, the anda blowing regulating member for regulating the air blowing region of the to the non-paper passing area in the rotation axis direction of the rotation of the blowing means, the image while conveying the recording material on which the image is formed by the nip In the image heating apparatus for heating the heater, the heater is configured to be able to change a heat generation distribution in the rotation axis direction, and the control unit is configured to transfer a small size recording material at the nip portion when the non-sheet passing region of the heater is used. The heat generation distribution in FIG. The heater is controlled so that the amount of generated heat becomes smaller, and the air flow restricting member is configured such that the amount of air blown to the non-sheet passing area by the blowing unit is the sheet passing area in the non-sheet passing area with respect to the rotation axis direction. The area near the boundary with the area is the largest, and the area is restricted so as to decrease as the distance from the paper passing area increases .

  According to the present invention, it is possible to provide an image heating apparatus capable of cooling so as to have a uniform temperature in the longitudinal direction (rotational axis direction of the heating rotator) in the non-sheet passing region.

FIG. 3A is a perspective view of a fixing device as an image heating apparatus according to the first embodiment as viewed in a recording material conveyance direction, and FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with a fixing device according to a first embodiment. (A), (b), (c) is a top view which shows operation | movement of the shutter as a ventilation control means in the case of passing the recording paper from which paper width differs, respectively. FIG. 2 is a partial cross-sectional schematic diagram of a fixing device according to a first embodiment. 1 is a partially exploded perspective view of a fixing device according to a first embodiment. It is a schematic diagram which shows resistance value distribution of the main heater relevant to a heating rotary body, and a sub heater. It is a block diagram of a power supply control system of a main heater and a sub heater related to a heating rotator. FIG. 5 is a schematic diagram showing a heat generation distribution of a heater and a position of a shutter when a recording material having a maximum width is passed. FIG. 6 is a schematic diagram showing a heat generation distribution of a heater and a position of a shutter when a recording material having an intermediate width is passed. FIG. 6 is a schematic diagram showing a heat generation distribution of a heater and a position of a shutter when a recording material having a minimum width is passed. (A), (b), (c) is a top view which shows a different shutter shape, respectively. It is a perspective view of the fixing device provided with the air blower in a prior art example.

<< First Embodiment >>
(Image forming device)
FIG. 2 is a schematic configuration diagram of an image forming apparatus equipped with the image heating apparatus according to the present embodiment. The image forming apparatus includes a photosensitive drum 10 as an image carrier, and the photosensitive drum 10 is rotationally driven in a direction of an arrow at a predetermined process speed by a main body driving motor (not shown) as a driving unit. Here, the process speed of the image forming apparatus is 250 mm / sec. Around the photosensitive drum 10, a charging roller 11 as a charging device, an exposure device 8, a developing device 14, a transfer roller 12 as a transfer device, and the like are arranged in order along the rotation direction. These devices and the photosensitive drum constitute image forming means for forming an image on a recording material.

  In addition, a feeding cassette 1 that stores a recording material (paper, printing paper, paper sheet, OHT sheet, glossy paper, glossy film, etc.) P is disposed at the lower part of the apparatus main body. In addition, a feeding roller 7, a conveyance roller 5, a photosensitive drum 10 and a transfer roller 12, conveyance guides 4, 6 and 13, a fixing device F, a discharge roller 35, and a discharge tray 34 are sequentially arranged along the conveyance path of the recording material P. Has been placed.

  Next, the operation of the image forming apparatus having the above-described configuration will be described. The photosensitive drum 10 rotated in the direction of the arrow by a main body drive motor (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 11. The exposure device 8 is a laser scanner that outputs a laser beam corresponding to a target image information signal input from a host device such as a computer or an image reading device (not shown), and that laser beam passes through a folding mirror 9. The surface of the photosensitive drum 10 is scanned and exposed. Then, the charge on the exposed portion of the photosensitive drum 10 is removed, and an electrostatic latent image is formed. The electrostatic latent image is developed by the developing device 14.

  The developing device 14 has a developing roller, and a developing bias is applied to the developing roller so that toner is attached to the electrostatic latent image on the photosensitive drum 10 and developed (visualized) as a toner image. The toner image on the photosensitive drum 10 is transferred to the recording material P by the transfer roller 12.

  On the other hand, the recording material P is fed one by one from the feeding cassette 1 by the feeding roller 7 and is conveyed by the conveying roller 5 toward the transfer nip portion between the photosensitive drum 10 and the transfer roller 12. At this time, the leading edge of the recording material P is detected by a top sensor (not shown) and synchronized with the toner image on the photosensitive drum 10. A transfer bias is applied to the transfer roller 12, whereby the toner image on the photosensitive drum 10 is transferred to a predetermined position on the recording material P. The recording material P carrying the unfixed toner image on the surface by the transfer is conveyed along the conveyance guide 13 to the fixing inlet guide 16 and guided to a fixing device F as an image heating device.

  The unfixed toner image is heated and pressurized here and fixed on the recording material P. The recording material P on which the toner image is fixed is conveyed along the discharge separation guide 29 to the separation guide roller 33 and is discharged from the discharge roller 35 onto the discharge tray 34 on the upper surface of the apparatus main body. By repeating the above operation, image formation can be performed one after another.

(Image heating device)
With respect to the fixing device as an image heating device described below or a member constituting the fixing device, the “longitudinal direction” is a direction orthogonal to the recording material conveyance direction in the recording material conveyance path surface, and will be described later. This is the direction of the rotation axis of the fixing belt and the pressure roller as belt members. Regarding the fixing device, “front” means a surface on the recording material introduction side, and “left and right” means left or right when the device is viewed from the front. The “width” of the recording material is a recording material dimension in a direction orthogonal to the recording material conveyance direction on the recording material surface. 1A and 1B are external perspective views of the fixing device F, and FIG. 4 is a cross-sectional view of the fixing device F. FIG. As shown in FIG. 4, the fixing device F is roughly composed of a belt heating type fixing unit (fixing device) Fa and a blower unit Fb.

1) Fixing unit Fa
First, the configuration of the fixing unit Fa is described with reference to FIGS. 4 and 5. FIG. 5 is an exploded perspective view of the fixing unit F-a. The fixing unit F-a is an on-demand fixing device of a belt (film) heating method and a pressure rotating body driving method (tensionless type).
Reference numeral 22 denotes a fixing sleeve, and 23 denotes an elastic pressure roller as a pressure rotator. A fixing nip portion N is formed by the pressure contact between the fixing sleeve 22 and the pressure roller 23.

  Reference numeral 21 denotes a fixing stay (heater holding member / fixing sleeve guide member) having a heat resistance and rigidity having a substantially semicircular arc shape in cross section. Reference numeral 20 denotes a ceramic heater (hereinafter abbreviated as a heater) as a heating source (heating body), which heats the belt by rubbing against the inner peripheral surface of the belt and forms a pressure roller and a nip portion. It also functions as a backup member for pressurizing. The heater 20 is disposed on the outer surface of the fixing stay 21 by being fitted into a recessed groove portion 21a provided along the length of the fixing stay. The fixing sleeve 22 is loosely fitted to the fixing stay 21 to which the heater 20 is attached.

  Reference numerals 24a and 24b denote flanges fitted to the outward projecting arm portions at the left and right ends of the fixing stay 21, respectively. The fixing sleeve 22 is a composite layer structure in which a heat-resistant resin belt or a metal belt is used as a base layer, and an elastic layer, a release layer, or the like is added to the outer peripheral surface thereof. It is a member with high thermal conductivity and low heat capacity.

  The pressure roller 23 is obtained by reducing the hardness by providing an elastic layer 23b such as silicone rubber on the core metal 23a. In order to improve surface properties, a fluororesin layer such as PTFE, PFA, FEP or the like may be further provided on the outer periphery. The pressure roller 23 is disposed such that both left and right end portions of the metal core 23 a are rotatably supported by bearings between the left and right side plates 38 </ b> L and 38 </ b> R of the apparatus frame 38 via a bearing member 39.

  Here, the fixing sleeve 22 is arranged in parallel with the pressure roller 23 so as to face the heater 20 side. The left and right flanges 24 are urged in the axial direction of the pressure roller 23 with a predetermined force F by left and right pressure mechanisms constituted by pressure springs 61a and 61b. The surface of the heater 20 is pressed against the pressure roller 23 through the fixing sleeve 22 against the elasticity of the elastic layer 32b. As a result, a fixing nip portion N having a predetermined width in the recording material conveyance direction necessary for heat fixing is formed. The entrance guide 16 and the exit guide 29 are assembled to the device frame 38.

  Reference numeral 25 denotes a pressure roller gear fixed to the left end portion of the core metal 32 a of the pressure roller 23. When the rotational force of the fixing motor M1 is transmitted to the pressure roller gear 25 via a power transmission mechanism (not shown), the pressure roller 23 is rotationally driven in the counterclockwise direction indicated by an arrow in FIG. Due to the rotational drive of the pressure roller 23, a rotational force acts on the fixing sleeve 22 by a frictional force at the fixing nip N between the pressure roller 23 and the outer surface of the fixing sleeve 22. As a result, the fixing sleeve 22 rotates around the fixing stay 21 in the clockwise direction indicated by the arrow while the inner surface of the fixing sleeve 22 slides in contact with the heater 20 in the fixing nip portion N.

  The fixing sleeve 22 rotates at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 23. The left and right flanges 24 serve to receive the belt end portion on the near side and restrict the movement when the rotating fixing sleeve 22 moves to the left or right side along the length of the fixing stay 21. Grease (lubricant) is applied to the inner surface of the fixing sleeve 22 to ensure the slidability of the fixing sleeve 22 with respect to the heater 20 and the fixing stay 21.

  In FIG. 4, the recording material P guided by the entrance guide 16 and introduced into the fixing nip portion N is nipped and conveyed by the rotating pressure roller 23 and the fixing sleeve 22. In the present embodiment, the conveyance of the recording material P is performed on the basis of the so-called center sheet passing center of the recording material. In other words, the recording material in the width direction central portion passes through the fixing sleeve 22 in the longitudinal direction central portion of the recording material having any width that can be used in the apparatus.

  In FIG. 5, TH is a thermistor as temperature detection means (temperature detection element). The thermistor TH is disposed in contact with the back surface of the heater at a substantially central position in the longitudinal direction of the heater 20 so as to detect the temperature of the heater portion where the recording material of any width is large and small. . As will be described in detail later, the heater 20 is energized from the heater drive circuit as the power supply unit to the energized heat generating layer provided on the heater substrate surface, so that the heater 20 rapidly increases over the entire effective heat generating width in the longitudinal direction. Raise the temperature. The heater temperature is detected by the main thermistor TH, and the control circuit unit determines the temperature control content of the fixing heater 20 based on the output of the main thermistor TH, and controls the energization of the fixing heater 20 from the heater driving circuit. To do.

(Description of printing operation)
The control circuit unit drives the fixing motor M1 by controlling the fixing motor driving circuit based on a print signal from the external host device or another control signal. As a result, the pressure roller 23 is driven to rotate, and the fixing sleeve 22 also rotates. Further, the heater drive circuit is controlled to start the temperature increase of the heater 20. The recording material P carrying the unfixed toner image Ta from the image forming portion side to the fixing nip portion N along the entrance guide 16 in a state where the rotation speed of the fixing sleeve 22 becomes steady and the temperature of the heater 20 rises to a predetermined level. Guided and introduced. The toner image carrying surface side of the recording material P faces the fixing sleeve 22.

  The recording material P is brought into close contact with the heater 20 via the fixing sleeve 22 in the fixing nip portion N, and moves and passes through the fixing nip portion N together with the fixing sleeve 22. In the moving and passing process, heat is applied to the recording material P by the fixing sleeve 22 heated by the heater 20, and the toner image Tc is fixed to the recording material P surface by heat and pressure by the fixing nip pressure. The recording material P that has passed through the fixing nip N is separated from the surface of the fixing sleeve 22 and discharged and conveyed.

(heater)
Below, the heater 20 as a heating member is demonstrated in detail. The heater 20 has a plurality of heating resistors so that the heat generation ratio in the longitudinal direction (the rotation axis direction of the heating rotator) can be controlled. FIG. 6 is a plan view of the heater surface side, a heat generation distribution of the main heater and the sub heater, and a heat generation distribution of the combination of both. The energization of the main heater and the sub heater can be individually controlled. FIG. 7 is a block diagram of a power supply circuit (AC circuit) and a control circuit (DC circuit) for the heater 23. Reference numeral 20a denotes a heater substrate. The heater substrate 20a is a heat-resistant / good heat-conductive / electrically insulating ceramic material such as alumina or aluminum nitride, and is a horizontally long thin plate member whose longitudinal direction is a direction intersecting (orthogonal) with the recording material conveyance direction D. .

  Reference numerals 20b and 20c denote first and second heating resistors (hereinafter referred to as a main heater and a sub-heater) that are formed on the surface side of the heater substrate 20a as a heating element that generates heat by energization by thick film printing. It is. The main heater 20a and the sub heater 20b are formed along the longitudinal direction of the heater substrate and arranged in the recording material conveyance direction. The main heater 20b and the sub-heater 20c have different heat distributions in the longitudinal direction.

  Specifically, the resistance value per unit length of the main heater 20b (first heating resistor) decreases as it goes toward both ends in the longitudinal direction of the substrate. Further, the resistance value per unit length increases in the majority of the region of the sub-heater 20c (second heating resistor) toward the both ends in the longitudinal direction of the substrate. The combined heating value (synthetic resistance value) of the heating value (resistance value) of the main heater 20b and the heating value (resistance value) of the sub heater 20c is substantially uniform along the longitudinal direction of the heating resistor. Reference numeral 20d denotes a power feeding electrode portion (hereinafter referred to as a main contact) formed at one end portion in the longitudinal direction of the main heater 20b.

  Reference numeral 20e denotes a power feeding electrode portion (hereinafter referred to as a sub-contact) formed at one end portion in the longitudinal direction of the sub-heater 20c, and reference numeral 20f denotes a portion common to both the main heater 20b and the other end portion in the longitudinal direction of the sub-heater 20c. This is a power supply electrode section (hereinafter referred to as a common contact). The main contact 20d, the sub-contact 20e, and the common contact 20f are all formed as conductor patterns by thick film printing on the surfaces on both ends of the heater substrate. Reference numeral 20g denotes a surface protective layer, which is formed on the surface of the heater substrate 20a so as to cover the main heater 20b, the sub heater 20c, a part of the main contact 20d, a part of the sub contact 20e, and a part of the common contact 20f. .

  This surface protective layer 20g is formed as a glass coat pattern by thick film printing. The inner surface of the fixing film 22 is in close contact with and slides on the surface of the surface protective layer 20g. TH is a temperature detection means (temperature detection element) such as a thermistor. In this example, it is a thermistor, and is disposed in contact with a position corresponding to the sheet passing area width of the minimum size recording material on the back surface side of the heater substrate 20a. Further, TS is a thermo switch or the like, and like the thermistor TH, TS is disposed on the back surface side of the heater substrate 20a in contact with a position corresponding to the sheet passing area width of the minimum size recording material.

  In FIG. 8, A is the maximum sheet passing area width. The lengths of the main heater 20b and the sub heater 20c in the longitudinal direction substantially correspond to the maximum sheet passing area width A. B is the sheet passing area width of the minimum size recording material. C and C are non-sheet passing area widths ((A−B) / 2) when a minimum size recording material is passed.

  FIG. 7 is a block diagram of a power supply circuit (AC circuit) and a control circuit (DC circuit) for the heater 20. Reference numeral 100 denotes a control unit (engine controller, CPU). Reference numeral 101 denotes an AC power source. 102 and 103 are first and second triacs. Then, the following two power supply paths (AC lines) of a) and b) are configured. The control unit 100 controls the first and second triacs 102 and 103 to control power supply to the main heater 20b and the sub heater 20c.

a) AC power supply 101 → thermo switch TS → first triac 102 → main contact 20d → main heater 20b → common contact 20f → AC power supply 101
b) AC power supply 101 → thermo switch TS → second triac 103 → sub contact 20e → sub heater 20c → common contact 20f → AC power supply 101
Further, the temperature information of the heater 20 detected by the thermistor TH is fed back to the control unit 100 as a digital signal through the thermistor contacts 38 and 39 (DC line). The control unit 100 controls the first and second triacs 102 and 103 based on the heater temperature detection information fed back from the thermistor TH. Then, power supply to the main heater 20b and the sub heater 20c is controlled so that the heater temperature is maintained at a predetermined target temperature. Further, according to the size information of the recording material P to be passed, the first and second triacs 102 and 103 are controlled to control the power supply ratio to the main heater 20b and the sub heater 20c.

2) Blower unit Fb
Next, the blower unit F-b will be described. The blower unit F-b has a non-sheet passing portion temperature rise that occurs when a recording material having a narrower width than the maximum width recording material that can be used for paper feeding (hereinafter referred to as a narrow width recording material) is continuously fed. Is suppressed by blowing the non-sheet passing area of the fixing unit Fa. For this purpose, a blower mechanism including a duct for blowing air to the fixing sleeve 22 is provided. Fig.1 (a) is an external appearance perspective view of the ventilation cooling unit Fb. Moreover, FIG.1 (b) is the external appearance perspective view which looked at the ventilation cooling unit Fb from another direction. F-a is the above-described fixing device F.

  In FIGS. 1A and 1B, reference numerals 40a and 40b denote blower fans of non-sheet passing portions, and 45a. A blower duct 45 b guides the cooling air blown from the blower fans 40 a and 40 b to the fixing sleeve 22. In the present embodiment, axial fans are used as the blower fans 40a and 40b, but a centrifugal fan such as a sirocco fan can also be used.

(Shutter member as blower regulating means)
Reference numerals 41a and 41b denote shutters that are disposed between the blower fans 40a and 40b and the fixing sleeve 22 and serve as blower regulating means disposed at the outlets of the blower ducts 45a and 45b. The shutters 41a and 41b serving as the air flow restricting means restrict the air blowing area in the paper width direction (rotational axis direction of the heating rotator) to the non-paper passing area, and further away from the paper passing area of the recording material in the non-paper passing area. The amount of airflow that reaches is made smaller than the amount of airflow that reaches the side closer to the paper passing area.

1) Shuttable shutters The shutters 41a and 41b can be displaced in the width direction of the paper to be passed in order to cool the outside of the heating sleeve through the fixing sleeve 22 in accordance with the width direction size of the paper to be passed. Composed.

  That is, the shutters 41a and 41b are held by the frame member 47 so as to be slidable in the left-right direction. The left and right shutters 41a and 41b include left and right rack portions 43a and 43b and a pinion gear 44a for moving the left and right shutters 41a and 41b in the left-right direction in conjunction with each other. The left and right shutters and the rack are integrally formed, and the pinion gear 44a meshes with the left and right rack portions 43a and 43b. The pinion gear 44 a is driven forward or reversely by a shutter motor (pulse motor) 44.

  When the pinion gear 44a is driven to rotate forward or reversely by the shutter motor 44, the left and right shutters 41a and 42b are interlocked and reciprocate with the same amount of movement in a direction toward or away from each other. The shutters 41a and 41b have a flag portion 43c for position detection, and the home position of the shutter is detected by a detection member 48 such as a photosensor. The shutters 41a and 41b are controlled to be driven, stopped, etc. to a position suitable for the paper width through which the paper passes, according to the home position detection mechanism and the number of pulses of the signal sent to the pulse motor.

2) Shutter opening shape The shutters 41a and 41b, which are displaceable in the width direction of the paper to be passed, are provided with trapezoidal openings 49a and 49b, and the rectangular openings to which the air ducts 45a and 45b are fixed. Air is supplied from the overlapped opening, and the non-sheet passing portion of the fixing sleeve 22 is cooled. For example, trapezoidal openings 49a and 49b whose opening width changes in the paper width direction, the amount of air that reaches the side farther from the sheet passing area of the recording material in the non-sheet passing area is sent to the side closer to the sheet passing area. Can be smaller than the air volume.

FIG. 3 is a view as seen from the side facing the duct portion fixing sleeve of the blower unit F-b. In FIG. 3 (a), for the rectangular openings to which the air ducts 45a and 45b are fixed,
A state where the overlapping portions of the openings 49a and 49b of the shutters 41a and 41b are not present (air blower closed) is shown. FIG. 3B shows a state in which the openings 49a and 49b of the shutters 41a and 41b are overlapped by half with respect to the rectangular openings to which the air ducts 45a and 45b are fixed (blower opening half-open). Indicates. Further, in FIG. 3C, the openings 49a and 49b of the shutters 41a and 41b are sufficiently overlapped with the rectangular openings to which the air ducts 45a and 45b are fixed (the air outlets are fully opened). Indicates.

  The shape of the opening portions of the shutters 41a and 41b is not limited to a trapezoidal shape, and may be any shape as long as the width near the center in the longitudinal direction of the fixing device is wide and narrows toward the end. In other words, in the non-sheet passing area, it is only necessary to increase the amount of air supplied and reached from the blowing port on the side closer to the sheet passing area and to decrease on the side far from the sheet passing area. For example, the same effect can be obtained when the shape shown in FIGS. 11A to 11C (one side constituting the trapezoid is convex, concave, or stepped). Note that the shape of the opening of the shutter can be made variable according to the width of the recording paper.

(Heat generation distribution and air flow distribution in non-sheet passing area)
In the case of small size paper compared to the case of the maximum size paper, the heat generation amount distribution in the non-sheet passing area is changed by adjusting the heater, and the air flow distribution in the non-sheet passing area corresponding to the small size paper is changed by the shutter. change.

  When controlling the heat generation of the heater according to each paper size, in the non-sheet passing area of the fixing device Fa, the accumulated heat amount is closer to the non-sheet passing area near the sheet passing area. Adjustment is made so that the side far from the paper passing area becomes smaller. Accordingly, the portion with a large amount of heat storage has a larger amount of cooling air blown, and the portion with a smaller amount of heat storage has a smaller amount of cooling air blown so that the fixing sleeve 22 and the pressure roller of the fixing device Fa are reduced. The temperature unevenness in the longitudinal direction of 23 is further reduced. As an example, heater control and shutter for printing A3 size paper (297 mm wide), Executive size paper (266.7 mm width), A4 size paper (vertical feed, 210 mm width) in FIGS. The control will be described.

  In each figure, the uppermost part is a schematic diagram showing the opening amounts of the shutters 41 a and 41 b, the central part is a schematic diagram of the heater heating element, and the lowermost part is a heat generation amount distribution in the longitudinal direction of the heater 20. In this graph, the main heat transfer destination is shown where the heat generated from the heater 20 is transferred. What is shown is the amount of heat removed by the paper, the amount of heat stored in the non-sheet passing region of the fixing device components such as the fixing sleeve 23 and the pressure roller 22, and then the amount of heat radiated to the outside of the fixing device.

  FIG. 8 shows a case where the A4 size is laterally fed (maximum width size recording material 297 mm). When the A4 size is laterally fed, it is a sheet of the maximum width A that can be printed by the heater device, and the energization ratio of the main heater 20b and the sub heater 20c is made equal (100 to 100). At this time, since the width of the heating element of the heater 20 is substantially equal to the width of the paper, the temperature of the non-sheet passing portion hardly increases. Most of the heat generated from the heater is used for removing the heat from the paper and dissipating it outside the fixing machine. Therefore, the air blowing port is closed and there is no need to cool the fixing device Fa.

  FIG. 9 shows a case where an Executive-size paper (width 266.7 mm) is passed. In this case, since the paper width is smaller than the maximum width size recording material, the energization ratio of the main heater 20b and the sub-heater 20c is set to 100: 50 so that the heat generation amount in the non-paper passing area is smaller than the paper passing area. . With this configuration, the heat generation amount decreases from the center side toward the end side in both the paper passing area and the non-paper passing area. The reason why the heat generation amount is not uniform in the paper passing area for small size paper is that the heat generation amount needs to be reduced in the non-paper passing area including the boundary position between the paper passing area and the non-paper passing area. The smaller the size of the paper, the smaller the amount of heat generated in the non-sheet passing area with respect to the sheet passing area.

  In FIG. 9, the blower opening is half open, and the non-sheet passing portion of the fixing device Fa and the non-sheet passing portion of the pressure roller are blown to the non-sheet passing portion outside the width of 266.7 mm of the Executive size paper. Cooling. At that time, the shape of the opening portions 49a and 49b of the shutters 41a and 41b is large in the central portion in the longitudinal direction and the opening near the end portion is small, so that it is possible to perform cooling according to the heat generation distribution of the heater. Become. Therefore, it is possible to make the temperature in the longitudinal direction of the fixing sleeve and the pressure roller of the fixing device Fa substantially uniform while suppressing both the heat generation amount of the heater and the blowing amount of the cooling air.

  FIG. 10 shows a case where A4 size paper (vertical feed, width 210 mm) is passed. Paper of this size is a recording material of the minimum width size that can be printed by this apparatus. The energization ratio of the main heater 20b and the sub heater 20c is 100 to 0, only the main heater 20b is heated, and the amount of heat generated on the side close to the end of the non-sheet passing area is further reduced as shown in the graph.

  Further, the blower port is fully opened, and air is blown to the outer non-sheet passing portion from the width of A4 size paper (vertical feed, width 210 mm), so that the fixing sleeve of the fixing device Fa and the non-sheet feeding of the pressure roller are not performed. The part is cooling. At this time, the shape of the openings 49a and 49b of the shutters 41a and 41b is such that the central part in the longitudinal direction is large and the opening near the end is small, so that it is possible to perform cooling according to the heat generation distribution of the heater. Become. Accordingly, in this case as well, it is possible to make the temperature in the longitudinal direction of the fixing sleeve 22 and the pressure roller 23 of the fixing device Fa substantially uniform while suppressing both the heat generation amount of the heater and the blowing amount of cooling air.

  As described above, according to the present embodiment, the excessive temperature rise of the non-sheet passing portion is suppressed with the minimum necessary air flow amount, the fixing sleeve temperature is made uniform to prevent sleeve twisting, etc. Power consumption during paper feeding can also be reduced. In addition, by minimizing the necessary air flow of the cooling fan, it is possible to reduce the size and cost of the apparatus.

  As in this embodiment, by making the temperature distribution in the longitudinal direction of the fixing sleeve 22 and the pressure roller 23 uniform, changes in the longitudinal shape of the roller due to thermal expansion of the pressure roller are suppressed, and paper wrinkles and gloss unevenness are prevented. I can do it. In addition, it is possible to suppress a decrease in durability of the heat fixing device, and it is also possible to suppress hot offset of the toner image when fixing a large size paper next time.

  Various combinations of the above-described technical matters are possible within the scope of the present invention, and various modifications described below are also within the scope of the present invention.

(Modification 1)
Regarding air blowing to the non-sheet passing area, air blowing to the heating rotator (belt) side has been described. However, the present invention is not limited to this, and air blowing to the pressure roller side or heating rotator (belt) side, It may be one that blows air to both sides of the pressure roller. A fixed pressure pad may be used instead of the pressure roller that can rotate as the pressure member. Further, regarding the air blowing to the non-sheet passing area, the recording material may be passed on the one-side paper passing basis instead of the central paper passing basis.

(Modification 2)
In the above-described embodiment, the shape of the opening of the shutter is a trapezoidal shape, but the shape of the opening of the shutter is a rectangular shape, and it is also possible to obtain a similar distribution of the air flow amount reaching the non-sheet passing region. . For example, the number of fine openings for blowing in the recording material conveyance direction in the non-sheet passing area may be formed to be smaller on the side farther from the sheet passing area of the recording material and larger on the side closer to the sheet passing area.

(Modification 3)
In the above-described embodiment, in the case of small size paper, a non-uniform heat generation amount distribution is formed in the paper passing region, and a non-uniform air flow amount distribution is given in the non-paper passing region. However, the present invention is not limited to this, and also includes a case where a uniform heat generation amount distribution is formed in the sheet passing area even in the case of small size paper and a non-uniform air flow amount distribution is given in the non-sheet passing area. .

(Modification 4)
The fixing device 30 as the image heating device is not limited to the belt heating method and the pressure rotating body driving method of the above-described embodiment, but can be a thing of other methods such as a heat roller method and an electromagnetic induction heating method.

20 ... Heating body, 22 ... Fixing sleeve, 23 ... Pressure roller, 40a, 40b ... Blower fan, 41a, 41b ... Shutter, 43a, 43b ... Shutter rack, 45a, 45b ... Air blower Duct, 49a, 49b ... Air blower, N ... Nip part, P ... Recording material

Claims (6)

And a rotating body,
A heater for heating the rotating body;
A control unit for controlling the heater;
A pressure member to form a two-up portion between the front provided opposite to Kikai rolling body, pre Machinery rotating body,
And the rotating body, wherein a pressure member, the air blowing means for blowing air in at least one of the non-paper passing area, the blowing area of the the non-paper passing area in the rotation axis direction of the rotation of the blowing means An air flow regulating member to regulate,
In an image heating apparatus that heats the image while conveying a recording material on which an image is formed at the nip portion,
The heater is configured to be able to change the heat generation distribution in the rotation axis direction,
The controller controls the heater so that when the small-size recording material is conveyed at the nip portion, the heat generation amount in the non-sheet passing area of the heater decreases with increasing distance from the sheet passing area in the rotation axis direction. Control
The air flow restricting member has the largest air volume blown to the non-sheet passing area by the blowing means in the vicinity of the boundary between the non-sheet passing area and the sheet passing area in the rotation axis direction, and is separated from the sheet passing area. An image heating apparatus characterized by being restricted so as to become smaller . The heater substrate and, formed on the substrate, the first heating resistor resistance value may turn reduced per the One is in unit length toward the end portion from the center of the rotation axis of the rotary body When, and a second heating resistor ing resistance increases per the one is in unit length toward the end portion from the center of the rotation axis of the rotating body, the first heating resistor The image heating apparatus according to claim 1 , wherein energization of the body and the second heating resistor can be independently controlled. The blowing regulating member, an image heating apparatus according to claim 1 or 2, characterized in that a shutter member movable to the rotating shaft direction. The shutter member, an image heating apparatus according to claim 3, characterized in that the area of the opening per unit length relates to the aforementioned rotation axis direction is have a smaller becomes the opening toward the outside in the rotation axis direction. The image heating apparatus according to claim 1, wherein the rotating body is a belt member having flexibility. The heater is in contact with the inner peripheral surface of the belt member;
The image heating apparatus according to claim 5 , wherein the pressing member forms the nip portion together with the heater via the belt member.