JP2012018312A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly heat the whole circumference in standby and intensively heat near a nip part when passing a sheet (in printing) in an image heating device using a resistance heat generating body as a heat source.SOLUTION: This image heating device includes, as power supply part pairs of a heating rotor: a first power supply part pair, while passing a sheet, whose circumferential positions in one end side and the other end side in the rotational shaft direction are accorded with each other; and a second power supply part pair, while on standby, whose circumferential positions in one end side and the other end side in the rotational shaft direction are different from each other.

Description

  The present invention relates to an image heating apparatus used in an image forming apparatus such as a copying machine or a printer. Examples of the image heating device include a fixing device that heats and fixes an unfixed image formed on a recording material as a fixed image, and a glossiness increasing device that increases the glossiness of an image by heating the image fixed on the recording material. Can be mentioned.

  In an electrophotographic image forming apparatus, various methods have been proposed as a heating method of a fixing device for heating and fixing an unfixed toner image. One of them is an intermediate layer heating type fixing device for a fixing member.

  In the fixing device proposed in Patent Document 1, the fixing roller has a configuration in which a resistance heating layer is provided on a base material, and an elastic layer and a release layer are stacked thereon. Since the portion close to the surface of the fixing roller can be heated, the thermal response and thermal efficiency are excellent as compared with the halogen heater system that heats from the innermost surface of the fixing roller.

  For the purpose of further improving the thermal efficiency of such a fixing device, Patent Document 2 proposes a fixing device that generates heat only in the vicinity of the nip portion. In this fixing device, a plurality of resistance heating elements in the fixing roller are divided in the circumferential direction, and power supply to the heating elements is performed only on several heating elements on the contact surface with the pressure roller. ing. Since only the vicinity of the nip portion generates heat, there is an advantage that there is little heat radiation to the atmosphere and heat transfer efficiency from the fixing roller to the recording material is high.

JP 04-328594 A Japanese Patent Laid-Open No. 07-028349

  In order to obtain a uniform gloss of the fixed image, the fixing member preferably has a uniform temperature distribution in the circumferential direction. In the type of fixing device that uniformly heats the entire circumference of the fixing member, there is no need to rotate at the time of start-up, so there is a merit that heat is not radiated by air convection and heat is not taken away by the pressure roller, Quick startup is possible. On the other hand, in a fixing device that locally heats the nip portion, rotation of the fixing member is essential in order to uniformly heat the entire circumference of the fixing member at the time of startup. In this case, not only does the heat release to the air increase, but in the case of a fixing device that rotates by being driven by the pressure roller, heat is taken away by the pressure roller and the start-up time is significantly delayed.

  Further, at the time of paper feeding, it is more efficient to heat the vicinity of the nip portion intensively than to heat the entire circumference uniformly. This is because the amount of heat released into the air at the non-nip portion is reduced, and when the amount of heat generated at the nip portion is large, the amount of heat received by the toner when passing through the fixing nip portion is large even at the same fixing member surface temperature. This is because there is a merit that the fixing property is improved.

  Considering these, it is preferable that the efficient heat generation distribution of the fixing device is to uniformly heat the entire circumference during standby and to intensively heat the vicinity of the nip portion during the paper feeding operation (printing).

  However, the above-described prior art has a problem that an efficient heat distribution cannot be obtained both during standby and during paper feeding operation.

  An object of the present invention is to provide an image heating apparatus capable of obtaining an efficient heat distribution both during standby and during paper feeding operation.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a heating rotator having a resistance heating layer that generates heat when energized, and a nip portion formed with the heating rotator. An image heating device that heats an image by sandwiching and conveying a recording material carrying an image at the nip portion, and having one end side and the other end side of the heating rotator. Are formed in a ring shape along the peripheral surface, and are electrically connected to one end side and the other end side of the resistance heating layer, respectively, and the electrode layer on the one end side, A pair of power supply members that are in contact with the electrode layer on the other end side and are applied with a voltage from a power supply device to cause the resistance heating layer to generate heat, and the resistance heating layer corresponds to the nip portion. Of the first power supply member for locally generating heat in the portion And a second pair of power feeding members different from the first pair of power feeding members for causing the resistance heat generating layer to generate heat overall, and during the paper feeding operation of the image heating apparatus, A voltage is applied to one pair of power supply members, and a voltage is applied to the second pair of power supply members during standby.

  According to the present invention, the heat generation distribution in the circumferential direction of the heating body can be set so that the vicinity of the nip portion is in a high heat generation state during a sheet passing operation, and the entire circumference can be in a substantially uniform heat generation state during standby. .

It is the schematic of the electric power feeding position switching mechanism in 1st Embodiment. It is a block diagram of an example of the image forming apparatus carrying the image heating apparatus of this invention. FIG. 2 is a structural model diagram of a fixing device according to the first embodiment. FIG. 3 is a structural model diagram of a side portion of the fixing device according to the first embodiment. FIG. 2 is a layer structure diagram of a fixing belt in the first embodiment. FIG. 3 is a schematic diagram of a fixing belt heat generation distribution in the first embodiment. 5 is a flowchart of print control in the first embodiment. Regarding the second embodiment, (A) is a schematic diagram of the heat generation distribution in the first mode during standby, and (B) is a schematic diagram of the heat generation distribution in the second mode during standby. (A) is sectional drawing of a longitudinal direction regarding 3rd Embodiment, (B) is the arrangement | positioning figure of the electric power feeding member seen from the longitudinal direction. It is a figure which shows all the processes including the standby process concerning an image forming apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are denoted by the same reference numerals.

<< First Embodiment >>
(Image forming device)
In the apparatus shown in FIG. 2, first, second, third, and fourth image forming portions Pa, Pb, Pc, and Pd are provided, and toner images of different colors (yellow, magenta, cyan, and black) are provided. Is formed through a process of latent image, development and transfer. Each of the image forming portions Pa, Pb, Pc, and Pd includes a dedicated image carrier, and in this embodiment, electrophotographic photosensitive drums 3a, 3b, 3c, and 3d, and each color is provided on the drums 3a, 3b, 3c, and 3d. The toner image is formed. An intermediate transfer member 130 stretched by rollers 13, 14, 15 is installed adjacent to each drum 3a, 3b, 3c, 3d. The toner images of the respective colors formed on the drums 3a, 3b, 3c, and 3d are superimposed and primarily transferred onto the intermediate transfer member 130, and are collectively transferred onto the recording material P at the secondary transfer portion. Further, the recording material P onto which the toner images have been collectively transferred is fixed to the toner image by heating and pressurization in the fixing device 9 and then discharged out of the apparatus as a recorded image.

  Drum chargers 2a, 2b, 2c, and 2d, developing devices 1a, 1b, 1c, and 1d, primary transfer chargers 24a, 24b, 24c, and 24d, and a cleaner 4a are disposed on the outer circumferences of the drums 3a, 3b, 3c, and 3d, respectively. 4b, 4c, 4d are provided. A light source device and a polygon mirror (not shown) are installed above the device. The laser light from the light source device is scanned by rotating the polygon mirror, the light beam of the scanning light is deflected by the reflection mirror, and is condensed on the buses of the drums 3a, 3b, 3c and 3d by the fθ lens and exposed. In this way, latent images corresponding to the image signals are formed on the drums 3a, 3b, 3c, and 3d.

  The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners, respectively, as developers. The developing devices 1a, 1b, 1c, and 1d develop the latent images on the drums 3a, 3b, 3c, and 3d, respectively, and visualize them as yellow toner images, magenta toner images, cyan toner images, and black toner images.

  The intermediate transfer member 130 is rotationally driven at the same peripheral speed as the drum 3 in the direction of the arrow. The yellow toner image of the first color formed and supported on the drum 3 a passes through the nip portion between the drum 3 and the intermediate transfer member 130, and the electric field and pressure due to the primary transfer bias applied to the intermediate transfer member 130. As a result, intermediate transfer is performed on the outer peripheral surface of the intermediate transfer body 130. Similarly, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are sequentially superimposed and transferred onto the intermediate transfer body 130, and a composite color toner image corresponding to the target color image is obtained. Is formed.

  Reference numeral 11 denotes a secondary transfer roller, which corresponds to the intermediate transfer member 130 and is provided in parallel and in contact with the lower surface portion. A desired secondary transfer bias is applied to the secondary transfer roller 11 by a secondary transfer bias source. The composite color toner image superimposed and transferred onto the intermediate transfer body 130 is transferred to the recording material P as follows. That is, the recording material P is fed at a predetermined timing to the contact nip between the intermediate transfer body 130 and the secondary transfer roller 11 through the registration roller 12 and the pre-transfer guide from the paper feeding cassette 10, and simultaneously the secondary transfer. A bias is applied from a bias power source. The composite color toner image is transferred from the intermediate transfer body 130 to the recording material P by the secondary transfer bias. The composite color toner image is formed from the four side edges of the recording material P leaving a certain margin. In the present embodiment, the tip margin is about 2 to 3 mm.

  The drums 3a, 3b, 3c, and 3d that have undergone the primary transfer are cleaned and removed of the transfer residual toner by the respective cleaners 4a, 4b, 4c, and 4d, and are subsequently prepared for forming the next latent image. The toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing a cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130.

  The recording material P that has received the transfer of the toner image is sequentially introduced into the fixing device 9 and fixed by applying heat and pressure to the transfer material.

  In the case of duplex printing, the recording material P fed from the paper feed cassette 10 passes through the registration roller 12, the pre-transfer guide, and the contact nip between the intermediate transfer member 130 and the secondary transfer roller 11, and is fixed on the one side by the fixing device 9. After the fixing, the flapper 110 guides the reversal path 111. Thereafter, the recording material P is reversed by the reversing roller 112 and guided to the double-sided path 113. Then, the recording material P again passes through the contact roller nip between the registration roller 12, the pre-transfer guide, the intermediate transfer body 130 and the secondary transfer roller 11, and the second surface is transferred and both surfaces are fixed by the fixing device 9. Then, the flapper 110 is switched while the recording material is forming a double-sided image, and the recording material P fixed on both sides is discharged out of the apparatus as a recorded image.

(Fixing device)
In the following description, the longitudinal direction of the fixing device 9 or a member constituting the fixing device 9 is a direction parallel to the direction orthogonal to the recording material conveyance direction in the recording material conveyance path surface. The short direction is a direction parallel to the recording material conveyance direction. Further, regarding the fixing device 9, the front means the surface when the apparatus is viewed from the recording material entrance side, the back is the opposite surface (recording material exit side), and the left and right are the left or right when the device is viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction. FIG. 3 is a structural model diagram of the fixing device 9, and FIG. 4 is a lateral structural model diagram of the fixing device 9.

  In FIG. 3, reference numeral 120 denotes a cylindrical fixing belt (endless belt) as a heating rotator provided with a resistance heating element. Reference numeral 122 denotes a pressure roller as a pressure rotator that forms a fixing nip with the fixing belt. In FIG. 4, reference numeral 140 denotes left and right fixing flanges as regulating members that regulate the longitudinal movement and the circumferential shape of the fixing belt 120. Reference numeral 117 denotes a support stay disposed inside the fixing belt 120 and supports the belt pressure member 116. The fixing belt 120 is loosely placed on the outside of the belt pressure member 116, and the support stay 117 is inserted inside the belt pressure member 116. The left and right fixing flanges 140 are fitted to the left and right outward extending arm portions 117a of the support stay 117, respectively.

  The fixing belt 120 is pressed with a predetermined pressing force against the upper surface of the pressure roller 122 through the right and left fixing flanges 140, the support stay 117, and the belt pressing member 116 by a pressing unit (not shown). A fixing nip N having a width is formed. The applied pressure in this embodiment is 156.8N at one end and the total applied pressure is 313.6N (32 kgf).

  The support stay 117 is preferably made of a material that is difficult to bend even when a high pressure is applied. In this embodiment, SUS304 is used. The belt pressing member 116 is preferably made of a material with low heat conduction to the support stay 117 from the viewpoint of energy saving. For example, heat resistant glass or heat resistant resin such as polycarbonate is used.

  The pressure roller 122 has a multilayer structure in which a silicon rubber layer having a thickness of about 3 mm and a PFA resin tube having a thickness of about 40 μm are sequentially laminated on a stainless steel core. Both end portions of the metal core of the pressure roller 122 are rotatably supported by bearings between a rear side plate (not shown) and a front side plate of the apparatus frame 121.

  Reference numeral 118 denotes a thermistor as temperature detecting means. The thermistor 118 is installed above the support stay 117 so as to elastically contact the inner surface of the fixing belt 120, and has a function of detecting the temperature of the inner surface of the fixing belt 120. The abutting position is immediately before the entrance of the nip. Specifically, the thermistor 118 is attached to the tip of a stainless steel arm fixedly supported on the support stay 117. The thermistor is kept in contact with the inner surface of the fixing belt 120 even when the movement of the inner surface of the fixing belt 120 becomes unstable due to the elastic swing of the arm.

  The thermistor 118 is connected to a CPU 125 as control means via an A / D converter 124. The control circuit unit of the CPU 125 samples the output from the thermistor 118 at a predetermined cycle, and reflects the obtained temperature information in the energization control to the heating element. That is, the control circuit unit determines the energization control content to the heating element based on the output of the thermistor 118, and the fixing belt through the fixed power supply member 136 and the rotating electrode 135 shown in FIG. The energization supplied to 120 resistance heating layers 132 is controlled. Note that the above control in the fixing device of the present embodiment is controlled so that the temperature detected by the thermistor 118 is constant at 180 ° C. in consideration of the temperature for fixing the toner image on the recording material.

  In FIG. 3, the pressure roller 122 is rotationally driven in the direction of the arrow at a predetermined peripheral speed. The fixing belt 120 that is in pressure contact with the belt is driven by the pressure roller 122 and rotates at a predetermined speed.

  Grease is applied to the inner surface of the fixing belt 120, and the frictional force between the inner surface of the fixing belt 120 and the belt pressing member 116 is reduced, thereby reducing wear on the inner surface of the fixing belt 120.

  The pressure roller 122 is driven to rotate, and the energization is performed on the resistance heating layer 132 of the fixing belt 120 after the cylindrical fixing belt 120 is driven to rotate. When the temperature of the fixing belt 120 rises to the set temperature and is adjusted, the recording material P carrying the unfixed toner image is guided to the fixing nip portion N along the entrance guide 123 and introduced.

  In the fixing nip portion N, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing belt 120, and the recording material moves together with the fixing belt 120. In the process of nipping and conveying the recording material at the fixing nip portion N, heat from the heating element is applied to the recording material P, and the unfixed toner image T is melted and fixed on the recording material P. The recording material P that has passed through the fixing nip N is separated from the fixing belt 120 by the curvature, and is discharged by the fixing discharge roller 127.

(Fixing belt layer structure)
Next, the configuration of the fixing belt 120 will be described in detail. As shown in the schematic diagram of the layer configuration in FIG. 5, the fixing belt 120 according to the present exemplary embodiment includes a ring-shaped base layer 131, a resistance heating layer 132, an elastic layer 133, and a surface release layer 134 in order from the inner surface side to the outer surface side. This is a flexible film having a four-layer composite structure. Further, electrode layers 135 that are electrically conductive are provided on the base layer 131 at both ends, and are electrically connected to the resistance heating layer 132. The elastic layer and the release layer are not provided on the electrode layer 135, and the electrode layer is exposed.

  For the base layer 131, a heat-resistant material having a thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more can be used in order to reduce the heat capacity and improve the quick start property. Examples of the heat-resistant material include resin belts such as polyimide, polyimide amide, PEEK, PTFE, PFA, and FEP, and metal belts such as SUS and nickel. In the present embodiment, a polyimide belt having a thickness of 30 μm and a diameter of 25 mm was used. Note that in the case where a conductive material is used for the base layer 131, it is necessary to provide an insulating layer such as polyimide between the base layer 131 and the heat generating layer 132.

  As the elastic layer 133, silicone rubber having a rubber hardness of 10 degrees (JIS-A), a thermal conductivity of 1.3 W / m · K, and a thickness of 300 μm was used.

  As the surface release layer 134, a PFA tube having a thickness of 20 μm was used. A PFA coat may be used as the surface release layer, and the PFA tube and the PFA coat can be used properly according to the required thickness, mechanical and electrical strength. The surface release layer 134 is bonded to the elastic layer 133 with an adhesive made of silicone resin.

  The resistance heating layer 132 is a resistance heating element in which a conductor containing a silver / palladium alloy is uniformly coated on the base layer 131. The total resistance value of the heating element, which is a heating element, is 10.0Ω. Therefore, the electric power generated when the 100V power supply is energized is 1000W. The resistance value may be determined as appropriate depending on the amount of heat generated as a fixing device.

  The electrode layer 135 for energizing the resistance heating layer 132 is a resistor in which a conductive material is uniformly applied on the base layer 31 with a thickness of about 30 μm, and the total resistance value is about 0.5Ω. It is about 5% of the heat generating layer 132. That is, the amount of heat generated in the electrode layer 135 with respect to the resistance heating layer 132 is about 5%, and an excessive temperature rise does not occur in a region where the recording material of the fixing belt does not pass through, and the fixing belt 120 is not damaged. The power supply member 136 contacts the electrode layer 135. Details of the contact position between the power supply member 136 and the electrode layer 135 will be described later.

  In the longitudinal direction, the length of the base layer 131 is 327 mm, and the lengths of the resistance heating layer 132, the elastic layer 133, and the surface release layer 134 are 315 mm, which is 18 mm longer than the maximum longitudinal width of the recording material 297 mm. At both ends of the base layer 131, there are electrode layers 135 at portions where there is no heat generation layer, elastic layer, and release layer, and the length is 6 mm at both ends. Further, the elastic body portion of the pressure roller 122 is 312 mm, which is shorter than the heat generation area of the fixing belt 120. Therefore, in a state where the fixing belt 120 and the pressure roller 122 are in pressure contact, the electrodes 135 at both ends are not in contact with the pressure roller 122.

  As described above, since the fixing belt 120 contacts the receiving surface 140a of the fixing flange 140 on the inner surface side, the trajectory of the fixing belt 120 during driving is always constant. In particular, in the present embodiment, the sum of the lengths of the receiving surface 140a that contacts the fixing belt and the portion of the belt pressing member 116 that contacts the fixing belt is about 2% smaller than the inner diameter of the fixing belt 120. Further, the peripheral length of the receiving surface 140a of the fixing flange is set. Therefore, the fixing belt 120 is not slackened or wavy when the fixing device is driven, and is conveyed along the receiving surface 140a of the fixing flange, so that the trajectory is constant.

(Electrode layer and power supply member)
Since the conductive leaf spring (not shown) presses the power supply member 136 (conductive and made of carbon), the power supply member 136 fixed in a spot shape and the electrode layer rotating in a ring shape even during driving of the fixing device. The electrical connection 135 is maintained. The power supply member 136 is electrically connected to the power supply device 126, and the power supplied from the power supply device 126 can be supplied between the power supply members in contact with the electrode layers at both ends. Further, the power supply device 126 can arbitrarily switch the voltage of 0 or 100 V between the power supply members 136 in contact with the electrode layers 135 at both ends under the control of the CPU 125.

  The power supply member 136 is not in contact with the electrode layers 135 at both ends, but is in contact with a part thereof. Therefore, the potential of the electrode layer 135 is not uniform with respect to the circumferential direction, and the potential is highest at the portion where the power supply member is in contact, the potential is lowered when it is away from the contact portion, and is lowest at the back, and the heat generation distribution Is not uniform in the circumferential direction.

  FIG. 6 shows a heat generation distribution, and includes a case where the power supply members 136 at both ends are brought into contact with an intermediate position (0 degree-0 degree) in the circumferential direction of the fixing nip. Further, the case where the power supply member at one end is brought into contact with the intermediate position of the fixing nip and the power supply member at the other end is brought into contact with the back of the intermediate position of the fixing nip (0 to 180 degrees) is included. Each is a heat generation distribution when a voltage of 100 V is applied between the power supply members. In FIG. 6, for a certain circumferential position X degree on the horizontal axis, the value of the vertical axis is the average of the calorific value at each position in the longitudinal direction.

  When both ends are brought into contact with the intermediate position of the fixing nip (0 degree to 0 degree), the heat generation amount is the largest at the nip portion, and the heat generation amount is the smallest at the back. On the other hand, when the position of the power supply member 136 is one end at the middle of the nip portion and the other end at the opposite position displaced by 180 degrees in the circumferential direction (0 degrees to 180 degrees), the circumferential temperature distribution is almost uniform. It has become.

  Thereafter, a case where heat is generated at 0 ° to 0 ° as a pair of first power supply members for locally generating heat is a nip portion high heat generation mode, and a case of second power supply members for generating heat as a whole is 0. A case where heat is generated at a degree of -180 degrees is referred to as a uniform heating mode for the entire circumference.

(Energization switching mechanism)
Hereinafter, switching of the power feeding member, which is a feature of the present invention, will be described. FIG. 1 is a schematic diagram of a power supply switching mechanism. In this embodiment, a total of three power supply members 136 are in contact with the electrode layers 135 at both ends of the fixing belt 120, and the front side is in the middle in the circumferential direction of the nip portion formed by the opposing pressure roller 122. One (A) is provided. The back side is in contact with one (B) at the middle of the nip portion and one (C) at the opposite position displaced 180 degrees in the circumferential direction. (A) and (B) are selected as a pair of first power supply members for generating heat locally, and (A) and (C) are selected as a pair of second power supply members for generating heat entirely. However, power is supplied only to the pair of power supply members selected by the CPU under the pre-wired condition.

  The temperature data input from the thermistor 118 is input to the CPU 125 as a digital signal by the A / D converter, and an ON / OFF command for applying a voltage of 100 V between the power supply members is issued to the power supply device 126 according to the temperature.

(Flow chart including separation / contact between fixing belt and pressure roller)
FIG. 7 is a flowchart when the present invention is executed. The result of performing the printing operation according to this flowchart is shown. The process speed of the fixing device 9 was 210 mm / sec, the temperature adjustment temperature was 180 ° C., and 50 sheets of 105 g / m 2 paper were passed at 50 ppm.

  First, when a print start command is received, a voltage of 100 V is applied from the power supply device 126 between the power supply member A and the power supply member C shown in FIG. 1 as a pair of power supply members for generating heat as a whole. The fixing belt 120 is heated to a temperature adjustment temperature of 180 ° C. in the uniform heating mode for all circumferences while still rotating without rotating. At this time, that is, during standby, the fixing belt 120 that is a heating rotator is not in contact with the pressure roller 122 that is a pressure rotator. This is because when the fixing belt 120 and the pressure roller 122 are not in contact with each other, the heat of the fixing belt 120 is not taken away by the pressure roller 122 and rises faster. After reaching 180 ° C., the nip high heating mode is switched, and the fixing belt 120 abuts on the pressure roller 122 and rotates. The temperature control remains unchanged at 180 ° C. At this time, a voltage of 100 V is applied between the power supply member A and the power supply member B as a pair of power supply members for locally generating heat. Thereafter, the sheet passing operation is started, and after the last recording material passes through the nip, the temperature control is turned off, the pressure is released, and the sheet is stopped.

(Fusing belt surface temperature and toner temperature)
The “fixing belt surface temperature” during the paper feeding operation was measured using a non-contact thermometer. The measured location is the center of the longitudinal direction of the fixing belt 120 and the position immediately after the exit of the nip portion in the circumferential direction. In this experiment, the lowest point of the fixing belt temperature was 170 ° C.

  Note that the lowest point of the fixing belt temperature did not change at 170 ° C. even when only the all-around heating mode was performed without executing the present invention. However, although the temperature is the same 170 ° C., the toner fixing property is different between the uniform heating mode for the entire circumference and the high heating mode for the nip portion. This is because the amount of heat generated at the nip portion is different between the two heat generation modes, and the amount of heat supplied to the toner from the resistance heating layer 132 while the recording material passes through the nip is different between the uniform heating mode around the entire circumference and the nip portion high heating mode. It is. Actually, the recording material loaded with unfixed toner under the same fixing belt condition of 170 ° C. is passed through the fixing device, and the “toner temperature” immediately after the nip outlet is measured. It was 117 ° C. in the nip high heating mode.

(Fixability evaluation)
In consideration of the above, in both the uniform heating mode for the entire circumference and the high heating mode for the nip, the exit temperature of the fixing belt surface was changed from 150 ° C. to 180 ° C. in increments of 5 ° C., and the fixing property at each temperature was measured. Note that a tape peeling method was used for the evaluation of the fixability. When the reflection density after peeling was 80% or less with respect to the reflection density before peeling of the tape, fixability was possible (◯ mark), and other than that, fixing ability was impossible (x mark). The following table lists the fixing results.

  In the all-around uniform heating mode, the fixing temperature was 170 ° C., and in the high nip heating mode, the same fixing property was obtained at 160 ° C. Therefore, in the high nip heating mode, the temperature of the fixing belt can be lowered by 10 ° C. in order to obtain the same fixing property, and the power during the sheet passing operation can be reduced. That is, the average power during sheet passing required for obtaining the same fixing performance at the lowest fixing belt temperature was 1000 W in the case of uniform heating all around the circumference and 900 W in the case of high heating of the nip.

  The rise time also differs between the two heating modes. When starting up in the all-around uniform heating mode, there is no need to rotate the fixing belt, so there is no need to press the fixing belt and the pressure roller, and the fixing belt and the pressure roller should be started up in a non-contact state. Can do. At this time, the time required for the thermistor temperature of the fixing belt to reach the temperature control temperature of 180 ° C. was 5 seconds. On the other hand, when starting up in the high heating mode of the nip portion, temperature unevenness occurs in the circumferential direction when heated while still, so it is necessary to start up while rotating. Since the fixing belt is driven and rotated by the pressure roller, the fixing belt and the pressure roller need to be pressurized. Therefore, due to the effect of heat transfer from the fixing belt to the pressure roller, the rise time becomes longer in the case of rotation with high heating of the nip portion than in the case of stationary heating with uniform heating on the entire circumference. When actually measured, the time required for the thermistor to reach the temperature control temperature of 180 ° C. was 10 seconds.

  From the above consideration, the following demerits occur when only one of the uniform heating mode and the nip high heating mode can be selected without implementing the present invention. That is, in the case of only the all-around uniform heating mode, there is a demerit that the power during the sheet passing operation becomes larger than that in the high nip heating mode. Further, in the case of only the nip portion high heating mode, there arises a demerit that the start-up time takes twice as long as the entire circumference uniform heating mode. Therefore, by implementing the present invention and switching the distribution of heat generation in the circumferential direction between standby and paper feeding, the effect of shortening the rise time and reducing the power during paper feeding can be obtained. These relationships are summarized in the following table.

  Here, it has been described that the voltage is applied between the power supply member A and the power supply member C as the all-around uniform heating mode while the fixing belt 120 is not in contact with the pressure roller 122 during standby. However, the entire circumference may be heated uniformly in contact with the pressure roller 122. That is, in general, the drive system is stopped and the pressure roller 122 is also stopped during standby, but by applying a voltage between the power supply member A and the power supply member C, it is expected that the rise time will be shortened by uniform heating throughout. it can.

(Positioning of standby processes in all processes)
As shown in FIG. 10, the entire process including the standby process related to the image forming apparatus is as follows.

A. Pre-multi-rotation process A printer start-up operation period (start-up operation period, warming period). When the main power switch SW-on of the printer is turned on, a main motor (not shown) of the printer is driven to rotate the photosensitive drum 11 (FIG. 2), and a preparatory operation for a predetermined process device is executed. The drum 11 starts rotating at the same time as the main motor is turned on, and stops rotating at the same time as the main motor is turned off. The main motor drives drive systems such as the drum 11, the paper feed mechanism unit, the recording material transport mechanism unit, the developing device 15, and the fixing device 40.

B. Pre-rotation process This is a period in which a pre-printing operation is executed when the print start signal S is input, and image forming preparation operations of various process devices are performed. Mainly, the drum 11 is precharged, the laser scanning unit 13 is started, the transfer bias is determined, the temperature of the fixing device 40 is adjusted, and the like.

  This pre-rotation process is executed subsequent to the pre-multi-rotation process when the print start signal S is input during the pre-multi-rotation process. When the print start signal is not input, the main motor is temporarily stopped after the pre-multi-rotation process is finished, the drum 11 is stopped rotating, and the printer is in a standby (standby) state until the print start signal S is input. to go into. When the print start signal S is input, the pre-rotation process is executed.

C. Image Forming Process When the predetermined pre-rotation process is completed, an image forming process (print job) is subsequently started. In the image forming process, the recording material P is fed at a predetermined timing, the drum surface is uniformly charged by the charger 12, image exposure for forming an electrostatic latent image on the drum 11, toner development, and the like are performed. That is, an image forming process is performed on the drum 11, the toner image formed on the surface of the drum 11 is transferred to a recording material, and the toner image is fixed by the fixing unit, and the image formed product is printed out.

  In the case of the continuous print mode, the above-described print operation is repeatedly executed for a predetermined set number of prints.

D. Inter-paper process In the continuous print mode, the transfer nip part from when the trailing edge of the recording material of the preceding print passes the transfer nip until the leading edge of the recording material of the next print reaches the transfer nip. This is a non-sheet passing state period of the recording material.

E. Post-rotation process This is a period in which the main motor continues to be driven for a while after the last print is completed to rotate the drum 11 and execute a predetermined post-operation. In the post-rotation process, processes such as cleaning of the transfer roller are performed.

F. Standby Step When the predetermined post-rotation step is completed, the drive of the main motor is stopped, the rotation of the drum 11 is stopped, and the printer enters a standby state until the next print start signal S is input.

  In the case of printing only one sheet, after the end of the printing, the printer enters a standby state through a post-rotation process. Thereafter, when the print start signal S is input, the printer proceeds to the pre-rotation process.

<< Second Embodiment >>
FIG. 8 is a schematic diagram showing the positional relationship between the fixing belt and the power supply member in the present embodiment. The figure shows a view in which the fixing belt is cut open, the central portion shows a heat generating layer 132, and both ends thereof show an electrode layer 135. Two feeding members 136 are in contact with the electrodes at both ends, and the circumferential positions are provided at 0 ° and 180 ° at both ends.

In the first embodiment, the electrode member pair to which a voltage is applied is changed during standby and during paper feeding. However, in this embodiment, the electrode member pair to which a voltage is applied periodically changes during standby. This is intended to make the heat generation distribution in the longitudinal direction as uniform as possible. As a first mode, when a voltage is applied to a pair of power supply members whose one end is 0 degree and the other end is 180 degrees, as shown in FIG. A heat generation distribution in which the heat generation amount is the highest is obtained. This is because the voltage between the contact portions of the power feeding member is the highest and the current density is high. In the present embodiment, the heat generation amount on the diagonal line between the feeding members to which the voltage is applied is 104% of the heat generation amount as compared with the region of the minimum heat generation amount (marked with a circle in the figure).
On the other hand, when the pair of power supply members that apply a voltage of 100 V at intervals of 0.1 second is periodically switched to AC as the first mode and BD as the second mode, the maximum heat generation region is as shown in FIG. 8 (A) and the broken line part of FIG. 8 (B) are repeated alternately. At this time, the maximum heat generation amount was 102% of the minimum heat generation amount. That is, the temperature unevenness in the fixing belt can be reduced. When the maximum and minimum heat generation ratio is 104% without using this embodiment and the temperature adjustment temperature is 180 ° C., the difference between the maximum and minimum belt temperatures is 2 ° C. By using this embodiment, the maximum and minimum calorific value ratio was 102%, and the difference between the maximum and minimum fixing belt temperatures at a temperature adjustment temperature of 180 ° C. was 1 ° C. As a result, uneven glossiness in the fixed image of the solid image can be reduced, leading to an improvement in image quality.

<< Third Embodiment >>
FIG. 9A is a cross-sectional view in the longitudinal direction of the present embodiment, and FIG. 9B is a view showing the arrangement of the power feeding members as seen from the longitudinal direction. The same reference numerals as those in the embodiment described above denote the same members. In the above-described embodiment, the electrode layer on the one end side and the electrode layer on the other end side are both used as the same electrode layer during the paper passing operation and in the standby state of the image heating apparatus. Separate electrode layers are used. That is, external electrode layers 50 and 51 exposed to the outside are provided outside the base layers 131b and 131c as electrode layers used during the paper passing operation. The external electrode layers 50 and 51 are formed in a ring shape along the circumferential surface on one end side and the other end side of the heating rotator, and are electrically connected to one end side and the other end side of the resistance heating layer 132, respectively. Is conductive. Further, internal electrode layers 52 and 53 that are not exposed to the outside are provided inside the resistance heating layer 132 as electrode layers used during standby. The internal electrode layers 52 and 53 are formed in a ring shape along the circumferential surface on one end side and the other end side of the heating rotator, and are electrically connected to one end side and the other end side of the resistance heating layer 132, respectively. Is conductive.

  Here, the internal electrode layers 52 and 53 are provided between the base layer 131a and the base layer 131b and between the base layer 131a and the base layer 131c in the longitudinal direction. The base layers 131a, 131b, and 131c are made of the same material as the base layer 131 of the above-described embodiment. Also in this embodiment, the elastic layer 133 is provided outside the resistance heating layer 132, and the surface release layer 134 is provided outside.

  In the present embodiment, power supply members A1 and A2 are provided as a pair of power supply members that are used during the paper passing operation and locally heat the nip portion. During the paper passing operation, a voltage is applied to the pair of power supply members A1 and A2. Is applied. Further, power supply members B1 and B2 are provided as a pair of power supply members that are used during standby to heat the entire heating rotator, and a voltage is applied to the pair of power supply members B1 and B2 during standby.

  In the present embodiment, when the power feeding members A1 and A2 that are used during the sheet passing operation and come into contact with the external electrode layers 50 and 51 fail, the power feeding members B1 and B2 that come into contact with the internal electrode layers 50 and 51 are replaced with A1 ′ and A2. It can be used by being displaced to the position '.

  In relation to the second embodiment, a further pair of power feeding members E1 and E2 is provided at a position displaced 180 degrees in the circumferential direction of the power feeding members B1 and B2 in the configuration of the present embodiment, and B1 and E2 are used. The first mode and the second mode using B2 and E1 may be performed periodically during standby.

(Modification)
As described above, the elastic layer 133 and the outer surface release layer 134 are provided outside the resistance heating layer 132. However, one or both of the elastic layer 133 and the surface release layer 134 are not provided. You can also. In addition, although a flexible film is used for the resistance heating layer 132, the present invention is not limited to this, and the resistance heating layer 132 may be formed of a rigid resistance heating element.

118 ..Thermistor, 120 ..Fixing belt, 122 ..Pressure roller, 123 ..Inlet guide, 124 ..A / D converter, 125 ..CPU, 126.
135 .. Electrode layer, A, B, C.

Claims (9)

A heating rotator having a resistance heating layer that generates heat when energized, and a pressure rotator that forms a nip portion with the heating rotator, and sandwiches a recording material carrying an image at the nip portion. An image heating apparatus that conveys and heats an image,
It is formed in a ring shape along the peripheral surface at one end side and the other end side of the heating rotator, and is electrically connected to one end side and the other end side of the resistance heating layer, respectively. An electrode layer,
A pair of power supply members in contact with the electrode layer on the one end side and the electrode layer on the other end side to apply a voltage from a power supply device to generate heat in the resistance heating layer, the resistance heating A pair of first power supply members for locally generating heat at a portion corresponding to the nip portion is different from a pair of first power supply members for generating heat entirely from the resistance heat generation layer. A pair of second power supply members;
An image heating apparatus, wherein a voltage is applied to the pair of first power supply members during a sheet passing operation of the image heating apparatus, and a voltage is applied to the pair of second power supply members during standby. .   The image heating apparatus according to claim 1, wherein the heating rotator is in a non-contact state with the pressurizing rotator during the standby.   The electrode layer on the one end side and the electrode layer on the other end side are also used as the same electrode layer during the paper feeding operation of the image heating apparatus and in the standby state, respectively. Image heating device.   2. The image according to claim 1, wherein the electrode layer on the one end portion side and the electrode layer on the other end portion side are used as separate electrode layers during the paper feeding operation of the image heating device and during standby, respectively. Heating device.   Of the pair of the first power supply member and the pair of the second power supply member, the power supply member in contact with the electrode layer on the one end side is also used as the same power supply member, and the heating rotation The power supply member that is provided at a position corresponding to the position of the nip portion in the circumferential direction of the body, while the power supply member that contacts the electrode layer on the other end side is related to the pair of the first power supply members. It is provided at a position corresponding to the position of the nip portion in the circumferential direction, and is provided at an opposite position displaced by 180 degrees in the circumferential direction from a position corresponding to the position of the nip portion with respect to the pair of the second power supply members. The image heating apparatus according to claim 3.   On the one end side and the other end side of the heating rotator, 180 in the circumferential direction from the position corresponding to the position of the nip portion and the position corresponding to the position of the nip portion in the circumferential direction of the heating rotator, respectively. The power supply member is provided at a position opposite to the second power supply member, the position corresponding to the position of the nip portion on the one end side and the position of the nip portion on the other end side as a pair of the second power supply member A first mode using a position on the opposite side displaced 180 degrees in the circumferential direction from a position corresponding to the position on the opposite side displaced 180 degrees in the circumferential direction from a position corresponding to the position of the nip portion on the one end side. A second mode using a position corresponding to the position of the nip portion at the position and the other end side, and periodically using the first mode and the second mode during standby of the image heating apparatus. Features and Image heating apparatus according to claim 3 that.   The image heating apparatus according to claim 1, further comprising: an elastic layer provided outside the resistance heating layer; and a surface release layer provided outside the elastic layer.   The image heating apparatus according to claim 1, wherein the electrode layer is an external electrode layer exposed to the outside.   The image heating apparatus according to claim 1, wherein the electrode layer is an internal electrode layer that is not exposed to the outside.