JP2013167662A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device capable of reducing deterioration of contact reliability between an end portion of a roller supporting an external heating belt and an external heating belt when the roller has a crown shape.SOLUTION: An image heating device (9) includes an image heating member (101) for heating an image formed on a recording material in a nip portion (N), and an external heating belt (105) for heating the image heating member by being in contact with the surface of the image heating member. The image heating device (9) further includes rotatable first and second stretching rollers (103, 104) between which the external heating belt is stretched, and heating means (114) for heating at least an end region of the first stretching roller (103) in a direction of the rotational axis of the first stretching roller(103). In the image heating device (9), the outer diameters of the first and second stretching rollers are larger in the central portions than in the end portions, respectively. The difference between the outer diameter of the central portion of the first stretching roller and the outer diameter of the end portions thereof is smaller than the difference between the outer diameter of the central portion of the second stretching roller and the outer diameter of the end portions thereof.

Description

  The present invention relates to an image heating apparatus such as a fixing apparatus having an external heating belt for heating an image heating member for heating a toner image formed on a recording material.

  In recent years, image forming apparatuses such as copiers, printers, and multifunction machines have been required to have high speed, high image quality, color, and energy saving. Further, there is a demand for multimedia compatibility and high productivity (number of printed sheets per unit time) that can support various recording materials such as thick paper, rough paper, embossed paper, and coated paper.

  In an image forming apparatus to which an electrophotographic system is applied, it is necessary to improve the heating performance of a fixing device (image heating device) in order to increase the productivity with a recording material having a large basis weight. However, the amount of heat required for fixing a recording material (thick paper) having a large basis weight is significantly larger than that of a recording material (thin paper) having a small basis weight. Therefore, at the time of fixing thick paper, a large amount of heat is deprived of the fixing roller as the image heating rotator, and the surface temperature of the rotator is lowered, which may cause a fixing failure.

  On the other hand, an external heating configuration in which an external heating device is brought into contact with the surface of the fixing roller to heat the fixing roller from the outside is known as a configuration for reducing the temperature drop on the surface (see Patent Document 1). In the external heating configuration described in Patent Document 1, an endless belt-shaped external heating belt is stretched (suspended) on a plurality of support rollers each having a halogen lamp as a heating element. Thereby, the heat of the halogen lamp is transmitted through the support roller in the order of the external heating belt and the surface of the fixing roller, thereby reducing the temperature drop on the surface of the fixing roller.

  When using an external heating belt, in order to reduce the phenomenon that the external heating belt moves to one side, in the support roller that stretches the endless belt, the outer diameter of the central portion in the axial direction is set to be larger than the outer diameter of both end portions. There is a method to set a larger value. That is, the support roller is configured to have a crown shape in which the outer diameter of the central portion is larger than the outer diameter of the end portion. Thus, by making the support roller into a crown shape, the belt is positively distorted to generate an internal stress difference, thereby effectively suppressing the deviation of the belt.

JP 2004-198659 A

  However, when the support roller is crown-shaped, there is a possibility that a gap is likely to occur between the external heating belt and the support roller at the end of the support roller.

  If such a gap occurs, the supply of heat from the support roller to the external heating belt is hindered at the end of the external heating belt, and a temperature difference occurs between the center and the end of the external heating belt. Will occur. Therefore, the amount of heat supplied from the external heating belt to the fixing roller also differs between the central portion and the end portion.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image heating apparatus capable of reducing a decrease in contact between a roller end and a belt when a roller supporting an external heating belt is crowned.

  The present invention includes an image heating member that heats an image formed on a recording material at a nip portion, an external heating belt that contacts the surface of the image heating member and heats the image heating member, and the external heating belt. A first tension roller and a second tension roller that are rotatable to be stretched; and a heating unit that heats at least an end region of the first tension roller in a rotation axis direction of the first tension roller. In the image heating apparatus, the outer diameter of the center portion of the first stretching roller and the second stretching roller is larger than the outer diameter of the end portion, and the outer diameter and the end portion of the center portion of the first stretching roller are The image heating apparatus is characterized in that the difference from the outer diameter is smaller than the difference between the outer diameter of the center portion and the outer diameter of the end portion of the second stretching roller.

  The present invention also provides an image heating member that heats an image formed on a recording material at a nip portion, an external heating belt that contacts the surface of the image heating member and heats the image heating member, and the external heating belt. A rotatable first stretching roller and a second stretching roller, and heating means for heating at least an end region of the first stretching roller in the rotation axis direction of the first stretching roller; In the image heating apparatus, the outer shape of the first stretching roller is a straight shape, and the outer diameter of the central portion of the second stretching roller is larger than the outer diameter of the end portion. is there.

  According to the present invention, when the roller that supports the external heating belt has a crown shape, it is possible to reduce a decrease in contact between the roller end portion and the belt.

1 is a schematic configuration diagram of a fixing device having an external heating belt configuration according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating an image forming apparatus in which the fixing device of FIG. 1 can be mounted. (A), (b) is a graph which shows the temperature transition of the surface of the fixing roller in the comparative example with this embodiment. 6 is a table showing the lowest point temperature of the surface temperature at the center and the end of the fixing roller due to the difference in the shape of the support roller. (A), (b) is a figure which shows the relationship between the shape of a support roller, and the light distribution of a halogen heater, and the heat supply to an external heating belt. It is a schematic block diagram of the fixing device provided with the external heating belt structure in 2nd Embodiment which concerns on this invention.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 2 is a cross-sectional view showing the overall configuration of the image forming apparatus. In the following embodiments, the image heating apparatus of the present invention will be described with reference to a fixing apparatus that fixes an unfixed toner image on a recording material. This image heating apparatus is a recording that carries a fixed image or a semi-fixed image. It can also be implemented as a heat treatment apparatus that adjusts the surface properties of an image by heating and pressing a material.

<First Embodiment>
First, the image forming apparatus 100 will be described with reference to FIG. The image forming apparatus 100 is a tandem type full color laser printer in which first, second, third, and fourth image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 130. In FIG. 2, the external heating unit 32 described later is not shown.

  As shown in FIG. 2, the image forming apparatus 100 is provided with first, second, third, and fourth image forming portions Pa, Pb, Pc, and Pd, and toner images of different colors are latent. Formed through image, development and transfer processes. Each of these image forming portions Pa, Pb, Pc, and Pd includes a dedicated image carrier (in this example, electrophotographic photosensitive drums 3a, 3b, 3c, and 3d), and on each of the photosensitive drums 3a, 3b, 3c, and 3d. Each color toner image is formed.

  An intermediate transfer belt 130 is installed adjacent to the photosensitive drums 3a, 3b, 3c, and 3d, and the toner images of the respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are primarily transferred onto the intermediate transfer belt 130. Transferred and transferred onto the recording material P at the secondary transfer portion. Further, the recording material P onto which the toner image has been transferred is fixed as a recorded image after the toner image is fixed by heating and pressing in the fixing device 9. The image forming units Pa to Pd and the intermediate transfer belt 130 constitute an image forming unit that forms a toner image (image) on the recording material. The fixing device 9 fixes the toner image formed on the recording material by the image forming unit to the recording material.

  Drum chargers 2a, 2b, 2c, 2d, developing devices 1a, 1b, 1c, 1d, primary transfer chargers 24a, 24b, 24c, 24d, and the outer periphery of the photosensitive drums 3a, 3b, 3c, 3d, respectively Cleaners 4a, 4b, 4c, and 4d are provided. Laser scanners 5a, 5b, 5c, and 5d are installed above the image forming apparatus 100.

  In the laser scanners 5a, 5b, 5c and 5d, a light source device (not shown) and a polygon mirror are arranged. These laser scanners 5a to 5d scan the laser light emitted from the light source device by rotating the polygon mirror, and deflect the light beam of the scanning light by the reflection mirror. A latent image corresponding to an image signal is formed on the photosensitive drums 3a, 3b, 3c, and 3d by condensing and exposing on the buses of the photosensitive drums 3a, 3b, 3c, and 3d by an fθ lens (not shown). It is formed.

  The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners as developers, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images.

  The intermediate transfer belt 130 is driven to rotate in the direction indicated by the arrow E in FIG. 2 at the same peripheral speed as the photosensitive drums 3a, 3b, 3c, and 3d. The yellow toner image of the first color formed and carried on the photosensitive drum 3a is formed by the primary transfer bias applied to the intermediate transfer belt in the process of passing through the nip portion between the photosensitive drum and the intermediate transfer belt 130. Intermediate transfer is performed on the outer peripheral surface of the intermediate transfer belt by an electric field and pressure.

  Reference numeral 11 denotes a secondary transfer roller, and this secondary transfer roller 11 is disposed in parallel with the intermediate transfer belt 130 so as to be in contact with the lower surface portion. The secondary transfer roller 11 sandwiches the intermediate transfer belt 130 against the roller 14 out of the three rollers 13, 14, 15, which are stretched around the intermediate transfer belt 130. A secondary transfer nip portion is formed between the belt 130 and the belt 130. A desired secondary transfer bias is applied to the secondary transfer roller 11 by a secondary transfer bias source.

  Transfer of the composite color toner image superimposed and transferred onto the intermediate transfer belt 130 to the recording material P is performed as follows. That is, the recording material P is fed from the sheet feeding cassette 10 to the contact nip between the intermediate transfer belt 130 and the secondary transfer roller 11 at a predetermined timing through the registration roller 12 and the pre-transfer guide (not shown). At the same time, a secondary transfer bias is applied from a bias power source. The composite color toner image is transferred from the intermediate transfer belt 130 to the recording material P by the secondary transfer bias.

  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 belt 130, and a composite color toner image corresponding to the target color image is obtained. Is formed. The composite color toner image is formed from the four side edges of the recording material P leaving a certain margin.

  The photosensitive 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 the subsequent formation of the next latent image. The toner and other foreign matters remaining on the intermediate transfer belt 130 are wiped off by bringing a cleaning web (nonwoven fabric) 19 into contact with the surface of the intermediate 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 the toner image is fixed by applying heat and pressure. In the duplex printing mode, the recording material P fed from the paper feeding cassette 10 passes through the registration roller 12, the pre-transfer guide, and the contact nip between the intermediate transfer belt 130 and the secondary transfer roller 11. Then, after the recording material P is fixed on one side by the fixing device 9, the recording material P is guided to the reversing path 17 through the switched switching member (flapper) 16.

  Thereafter, the recording material P is reversed by the reversing roller 18 and guided to the double-sided path 30. Then, the recording material P again passes through the contact nip between the registration roller 12, the pre-transfer guide 31, the intermediate transfer belt 130 and the secondary transfer roller 11, and after the second side is transferred, the both sides are fixed by the fixing device 9. Fixing process is performed. The switching member 16 is switched during the double-sided image formation of the recording material P, and the recording material P fixed on both sides is discharged out of the image forming apparatus 100 as a recorded image.

  Next, the configuration of the fixing device 9 which is an image heating device according to the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic configuration diagram of a fixing device 9 having an external heating belt configuration in the present embodiment. As described above, the image forming apparatus 100 fixes the image forming units Pa to Pd that form toner images on the recording material and the toner image formed on the recording material by the image forming unit to the recording material P. The image heating device of the present invention is applied to the fixing device 9.

  As shown in FIG. 1, the fixing device 9 has a casing (not shown) that houses the external heating unit 32, the fixing roller 101, the pressure roller 102, and the like. The fixing device 9 rotates an image formed on the recording material P at a fixing nip portion (nip portion) N to form a fixing nip portion N by pressing the fixing roller 101 as an image heating member and the fixing roller 101. A possible pressure roller 102 and an external heating unit 32 are provided.

  That is, the fixing device 9 is configured to pass the unfixed toner (toner image) K on the recording material P through the fixing nip portion N and fix it on the recording material P, and carries the unfixed toner K. The recording material P is fixed by being nipped at the fixing nip portion N and heated.

  The fixing roller (image heating member) 101 is configured to be rotationally driven at a predetermined speed, for example, a peripheral speed of 500 mm / sec, in the direction of arrow A by a drive source (not shown). Specifically, the fixing roller 101 includes a metal core made of a cylindrical metal (in this embodiment, made of aluminum) having an outer diameter of 74 mm, a thickness of 6 mm, and an axial length of 350 mm. A silicone rubber (in this embodiment, JIS-A hardness 20 degrees) is covered with a thickness of 3 mm as a heat-resistant elastic layer on the mandrel. On the elastic layer, a fluororesin (in this embodiment, PFA (polytetrafluoroethylene) tube) is coated with a thickness of 100 μm as a heat-resistant release layer in order to improve releasability with the toner. ing.

  For example, a halogen heater 106 with a rated power of 1200 W is disposed as a heating element inside the cored bar of the fixing roller 101, and the fixing roller 101 is heated from the inside so that its surface temperature becomes a predetermined temperature. . The surface temperature of the fixing roller 101 is detected by a thermistor 121 as temperature detecting means that contacts the fixing roller 101. Based on the detected temperature, the heater control means 140 as temperature control (adjustment) means turns on / off the halogen heater 106 to control it to a predetermined target temperature, for example, 200 ° C.

  The pressure roller (pressure member) 102 is pressed against the fixing roller 101 with a predetermined pressure by a pressing unit (not shown), and forms a fixing nip portion N with the fixing roller 101. The pressure roller 102 is driven to rotate at a predetermined peripheral speed (for example, 500 mm / sec) in the direction of arrow B as the fixing roller 101 is driven to rotate by a driving unit (not shown).

  Specifically, the pressure roller 102 includes a cored bar made of cylindrical metal (made of aluminum in this embodiment) having an outer diameter of 54 mm, a thickness of 5 mm, and an axial length of 350 mm. A silicone rubber (in this embodiment, JIS-A hardness 15 degrees) is coated with a thickness of 3 mm as a heat-resistant elastic layer on the metal core. On the elastic layer, a fluororesin (in this embodiment, a PFA tube) as a heat-resistant release layer is coated with a thickness of 100 μm in order to improve releasability with the toner.

  Further, a halogen heater 107 having a rated power of 300 W, for example, is disposed as a heating element in the core of the pressure roller 102, and the pressure roller 102 has an internal surface temperature of a predetermined temperature. Has been heated from. The surface temperature of the pressure roller 102 is detected by a thermistor 122 serving as temperature detection means that contacts the pressure roller 102. Then, based on the detected temperature, the heater control means 140 controls the halogen heater 107 to be turned on / off so that it becomes a predetermined target temperature, for example, 130 ° C.

  Next, the external heating unit 32 provided in the fixing device 9 and constituting one of the features of the present invention will be described in detail with reference to FIG.

  That is, as shown in FIG. 1, an external heating belt 105 that heats the fixing roller 101 in contact with the surface of the fixing roller 101 is disposed on the outer peripheral surface of the fixing roller 101. The external heating belt 105 is stretched (suspended) by a first support roller 103 and a second support roller 104 upstream of the first support roller 103 in the rotation direction of the fixing roller 101. The external heating belt 105 is configured in an endless shape that contacts the fixing roller 101 and heats the fixing roller 101.

  The first support roller 103 constitutes a rotatable first tension roller that stretches the external heating belt 105 and has at least heating means, and the second support roller 104 stretches the external heating belt 105. The 2nd tension roller which can rotate is comprised. The first and second support rollers (first and second stretching rollers) 103 and 104 press the fixing roller (image heating member) 101 via the external heating belt 105.

  The first and second support rollers 103 and 104 that stretch the external heating belt 105 are evenly pressed against the fixing roller 101 with a predetermined pressure by a pressure mechanism (pressure means) 33. The external heating belt 105 is configured to be able to contact / retreat with respect to the fixing roller 101 by the operation of the pressure mechanism 33, and between the external heating nip 105 and the fixing roller 101 in a state of being in contact with the fixing roller 101. Form. The external heating belt 105 pressed by the fixing roller 101 is driven (rotated) along with the main rotation of the fixing roller 101.

  The external heating belt 105 has a layer of a metallic base material (stainless steel, nickel, etc.) having an outer diameter of 60 mm, a thickness of 50 μm, and a length of 350 mm, for example. In order to prevent the external heating belt 105 from adhering to the toner, for example, a fluororesin (in this embodiment, a PFA tube) is coated with a thickness of 20 μm as a heat-resistant sliding layer. Such an external heating belt 105 contacts the outer surface of the fixing roller 101 at a predetermined speed in the direction of arrow C in FIG. 1, for example, a peripheral speed of 500 mm / sec, and is driven to rotate as the fixing roller 101 rotates. Then, the fixing roller 101 is heated.

  A cleaning roller 108 is disposed between the first and second support rollers 103 and 104 on the outer peripheral surface of the external heating belt 105. The cleaning roller 108 has a structure having a porous material layer such as sponge on the outer peripheral surface of the core metal, and is pressed against the external heating belt 105 with a predetermined pressure by a pressing means (not shown). The surface of the external heating belt 105 is cleaned.

  The first support roller 103 that stretches the external heating belt 105 is disposed on the downstream side in the rotation direction of the fixing roller 101. The first support roller 103 includes a cored bar made of cylindrical metal (in this embodiment, made of aluminum) having an outer diameter of 30 mm, a thickness of 3 mm, and an axial length of 350 mm, for example. On this mandrel, in order to prevent abrasion with the inner surface of the external heating belt 105, a fluorine-based resin (in this embodiment, a PFA tube) as a heat-resistant sliding layer has a thickness of, for example, 20 μm. It is covered.

  In addition, a halogen heater 114 having a rated power of 1000 W, for example, is disposed inside the core of the first support roller 103. In FIG. 5B, the halogen heater 114 is light-distributed so as to heat the end region of the first support roller 103, and the internal temperature is adjusted so that the surface temperature of the external heating belt 105 becomes a predetermined temperature. Heat from. The halogen heater 114 constitutes a heating unit that heats at least the end region of the first support roller 103 in the rotation axis direction of the first support roller (first stretching roller) 103.

  The surface temperature of the external heating belt 105 is detected by a thermistor 123 as temperature detecting means that contacts the contact region D1 between the first support roller 103 and the external heating belt 105. Then, based on the detected temperature, the heater control means 140 turns on / off the halogen heater 114 to control (temperature adjustment) so as to reach a predetermined target temperature, for example, 220 ° C.

  On the other hand, the second support roller (second stretching roller) 104 that stretches the external heating belt 105 contacts the inner surface of the external heating belt 105 and heats the external heating belt 105 from the inside. The second support roller 104 in the present embodiment is formed in a crown shape in which the outer diameter of the central portion in the width direction is larger than the outer diameters at both end portions in the width direction so as to suppress the deviation of the external heating belt 105 in the width direction. 2 tension roller is constituted.

  In the second support roller 104, the outer diameter of each axial end portion is set to, for example, 30 mm, the outer diameter of the axial center portion is set to be, for example, 300 μm larger than the outer diameter of both end portions, The outer shape (first outer diameter) has a crown shape that is larger than the outer diameter (second outer diameter) at both ends. The second support roller 104 includes a cored bar made of cylindrical metal (made of aluminum in this embodiment) having a thickness of 3 mm and an axial length of 350 mm, for example. On this mandrel, in order to prevent abrasion with the inner surface of the external heating belt 105, a fluorine-based resin (in this embodiment, a PFA tube) as a heat-resistant sliding layer has a thickness of, for example, 20 μm. It is covered.

  Further, for example, a halogen heater 115 with a rated power of 1000 W is disposed inside the core of the second support roller 104. The halogen heater 115 is distributed so as to heat the central region of the second support roller 104 (see FIG. 5B), and is heated from the inside so that the surface temperature of the external heating belt 105 becomes a predetermined temperature. To do.

  The halogen heater 115 heats the second support roller (second stretching roller) 104, that is, a second heating unit that heats the central portion in the width direction that intersects the rotation direction (arrow C direction) of the external heating belt 105. Configure. The halogen heater (heating means) 114 heats the end portion of the first support roller 103 from the center portion, and the halogen heater (second heating means) 115 heats the center portion of the second support roller 104 from the end portion. The heating distribution is set so as to.

  The surface temperature of the external heating belt 105 is detected by a thermistor 124 serving as a temperature detection unit that comes into contact with the contact region D2 between the second support roller 104 and the external heating belt 105. Then, based on the detected temperature, the heater control unit 140 turns on / off the halogen heater 115 to control (temperature adjustment) so as to reach a predetermined target temperature, for example, 220 ° C.

  Here, the reason why the target temperature of the external heating belt 105 is set higher than the target temperature of the fixing roller 101 is as follows. That is, when the temperature of the external heating belt 105 is kept higher than the temperature of the fixing roller 101, the external heating is performed with good response (heat sensitivity accuracy) to the temperature drop due to the recording material of the surface temperature of the fixing roller 101. This is because heat can be supplied from the belt 105 to the fixing roller 101.

  In the present embodiment, as shown in FIG. 5B, the first support roller 103 is configured in a straight shape including a halogen heater 114 that is distributed so as to heat its end region. As described above, the second support roller 104 is configured in a crown shape that incorporates a halogen heater 115 that is distributed so as to heat its central region. In the first support roller 103, the difference in outer diameter between the width direction center portion intersecting (orthogonal) with the rotation direction of the external heating belt 105 and both width direction end portions is the outer diameter of the width direction center portion of the second support roller 104. It is comprised in the shape of the dimension which does not exceed the crown amount which subtracted the outer diameter of the width direction both ends. (Straight shape in this embodiment)

  The arrangement configuration of the present embodiment described above that can heat the central portion of the sheet passing area wider than the end portion in the axial direction immediately before the external heating belt 105 enters the external nip portion Ne with the fixing roller 101 is suitable. It is believed that there is. However, the arrangement is not limited to this, and the positional relationship may be reversed such that the downstream first support roller 103 is disposed upstream and the upstream second support roller 104 is disposed downstream. Almost the same effect can be obtained.

  Next, the influence of the shape of the first support roller 103 and the second support roller 104 on the temperature transition of the fixing roller 101 during continuous paper feeding will be described through an experiment using the following comparative configuration example.

In this experiment, the following configuration example (i) and configuration example (ii) are configured so that the effect of the shape of the support roller can be easily understood.
(i) An example in which both the first and second support rollers 103 and 104 of the present embodiment are configured in a crown shape in which the outer diameter of the central portion in the axial direction is larger by 300 μm than the outer diameters of both end portions.
(ii) An example in which both the first and second support rollers 103 and 104 of the present embodiment are configured to have a straight shape in which the central part and both end parts in the axial direction are the same.

  Hereinafter, these configuration examples (i) and (ii) will be described with reference to FIGS. 3 and 4 for comparison. 3A and 3B are graphs showing the results of an experiment comparing the surface temperature of the fixing roller 101 in each of the configuration examples (i) and (ii), and showing the temperature transition of the surface of the fixing roller. is there. FIG. 4 is a table showing the lowest point temperature of the surface temperature at the center and the end of the fixing roller due to the difference in the shape of the support roller.

  In order to compare the effects of the shapes of the first and second support rollers 103 and 104, the heating regions of the halogen heaters 114 and 115 built in the first and second support rollers 103 and 104 are made to be the entire support roller. The heater has been changed.

  3A and 3B, the horizontal axis represents time (seconds), and the vertical axis represents the fixing roller surface temperature (the surface temperatures (° C.) of the center portion and the end portion of the fixing roller 101 in the sheet passing area). ). 3A and 3B, the point at which the first recording material has entered the fixing nip N (see FIG. 1) is indicated by A, and the point at which the last recording material has passed through the fixing nip N is shown. This is indicated by B.

In this experiment, A3 size plain paper having a basis weight of 209 g / m ² was used as a recording material, the recording material was continuously fed, the conveyance speed was 660 mm / sec, and the printing speed was 70 ppm. went.

  FIG. 3A shows a case where both the first and second support rollers 103 and 104 are configured in a crown shape that is set to be 300 μm larger than both ends in the central portion in the axial direction. In this case, when the first recording material enters the fixing nip portion N (point A), heat is removed from the fixing roller 101 by the recording material, so that the fixing roller surface temperature decreases at both the end portion and the central portion. However, due to the thermal response of the halogen heater 106 inside the fixing roller and the supply of heat from the external heating belt 105, the surface temperature of the fixing roller 101 is such that the end portion is lower than the central portion from the point B passes. It can be seen that the temperature rises.

  In the configuration example (i), since both of the support rollers 103 and 104 that stretch the external heating belt 105 have a crown shape, there is a gap between the end portions of the external heating belt 105 and the support rollers 103 and 104. Is caused by As a result, the amount of heat supplied from both the support rollers 103 and 104 to the end of the external heating belt 105 is reduced, so that the surface temperature at the end of the fixing roller 101 is lower than that at the center. For this reason, there is a possibility that fixing failure occurs at the end of the recording material.

  FIG. 3B shows a case where both the first and second support rollers 103 and 104 are formed in a straight shape having the same outer diameter in the axial direction as a whole. In this case, when the first recording material enters the fixing nip portion N (point A), the surface temperature of the fixing roller 101 decreases at both the end portion and the central portion. However, due to the thermal response of the halogen heater 106 inside the fixing roller and the supply of heat from the external heating belt 105, the surface temperature of the fixing roller 101 is the same at both the end and the center from the point B passes. You can see that it rises.

  In the configuration example (ii), since both the support rollers 103 and 104 for stretching the external heating belt 105 have a straight shape, the external heating belt 105 and the both support rollers 103 and 104 are in good contact with each other. This is because a sufficient amount of heat could be supplied even in the section.

  FIG. 4 is a table showing the lowest point temperatures of the surface temperatures of the center portion and the end portion of the fixing roller 101 depending on the shapes of the support rollers 103 and 104 in the configuration examples (i) and (ii). .

  In FIG. 4, in the configuration example (i) in which both the first and second support rollers 103 and 104 are crown-shaped, the lowest point temperature of the center surface temperature is 197 ° C., and the lowest surface temperature of the end portion. The point temperature was 185 ° C. In the configuration example (ii) in which the first and second support rollers 103 and 104 are both straight, the lowest point temperature of the center surface temperature is 197 ° C., and the lowest point temperature of the end surface temperature. Was 194 ° C.

  The above also applies to the external heating belt configuration of the present embodiment to which the present invention is applied. 5 (a) and 5 (b) are schematic cross-sectional views showing the configuration of the external heating belt to which the present invention is applied.

  In FIG. 5A, the halogen heaters 114 and 115 are provided in the entire axial direction so that the entire surfaces of the support rollers 103 and 104 are heated without causing the first and second halogen heaters 114 and 115 to have light distribution. ing. In FIG. 5B, the halogen heater 115 disposed inside the second support roller 104 having a crown shape is used as a light distribution at the center, and the halogen heater 114 disposed inside the first support roller 103 having a straight shape. Is the light distribution at both ends. In both configuration examples of FIGS. 5A and 5B, the second support roller 104 has a crown shape as described above in order to control the displacement of the external heating belt 105. In the present embodiment, a heater that heats at least the end of the straight roller is used. In this embodiment, the heater is also used for the crown-shaped roller.

  In FIG. 5A, the entire area of each surface of each of the support rollers 103 and 104 is heated without causing the halogen heaters 114 and 115 to have light distribution. As described above, the adhesion between the end of the straight roller heated by the heater and the external heating belt 105 is enhanced, so that the end of the external heating belt 105 can be obtained even if the shape of one of the rollers is a crown. The temperature drop of the part can be reduced.

  Since the second support roller 104 has a crown shape for controlling the shift of the external heating belt 105, the second support roller 104 and the external heating belt 105 are in good contact with each other at the center, but both end portions Then there is a gap between them. As a result, the amount of heat supplied from the second support roller 104 to the end of the external heating belt 105 becomes small, and the difference in the amount of heat supplied from the external heating belt 105 to the fixing roller 101 becomes large between the end and the center. There is. Therefore, when both the rollers are heated over the entire area, the temperature difference between the end portion and the center portion can be reduced by adjusting the heating amount of the crown-shaped roller.

  Thus, the amount of heat supplied from the crown-shaped second support roller 104 to the end of the external heating belt 105 is reduced, but the amount of heat supplied to the end of the external heating belt 105 is supplied by the straight first support roller 103. Is done. Therefore, the temperature drop at the end of the external heating belt 105 can be reduced.

  In FIG. 5B, the halogen heater 115 disposed inside the crown-shaped second support roller 104 has a central light distribution, and the halogen heater 114 in the straight-shaped first support roller 103 has both end portions. Light distribution. In this case, the first support roller 103 positively heats both ends of the external heating belt 105, and the second support roller 104 positively heats the central portion of the external heating belt 105. As a result, the amount of heat can be evenly supplied to the central portion and both ends of the external heating belt 105, and the surface temperature of the external heating belt 105 can be made uniform.

  Therefore, according to the configuration shown in FIG. 5B, the second support roller 104 that stretches the external heating belt 105 is crowned, so that the shift of the external heating belt 105 during driving can be controlled. At the same time, the temperature drop at both ends of the external heating belt 105 due to the support roller having a crown shape can be prevented by making the first support roller 103 straight. Moreover, the surface temperature of the external heating belt 105 can be made uniform by determining the light distribution of the heating sources (halogen heaters 114 and 115) arranged inside according to the shapes of the support rollers 103 and 104.

  In this embodiment, the crown amounts of the first and second support rollers 103 and 104 that stretch the external heating belt 105 are changed according to the light distribution state of the halogen heaters 114 and 115 in the support rollers. That is, the second support roller 104 has a crown shape in which the outer diameter of the central portion in the axial direction is larger than the outer diameters of both ends, and the first support roller 103 has a straight shape that is less than the crown amount of the second support roller 104. It is configured as.

  The first support roller 103 has a crown shape instead of a straight roller, and the difference between the center portion and the end portion of the first support roller 103 is larger than the difference between the center portion and the end portion of the second support roller 104. A small configuration may be used. Thus, the outer diameter of the center part of the first support roller 103 and the second support roller 104 is larger than the outer diameter of the end part, and the outer diameter of the center part of the first support roller 103 and the outer diameter of the end part are The difference can be configured to be smaller than the difference between the outer diameter of the center portion and the outer diameter of the end portion of the second support roller 104.

  As described above, the central portion of the external heating belt 105 is effectively affected by the halogen heater 115 in the axially central portion of the second support roller 104 while the crown-shaped second support roller 104 effectively suppresses the deviation of the external heating belt 105. Can be heated. At the same time, the entire surface of the external heating belt 105 is uniformly heated by appropriately supplying the amount of heat to the both ends of the external heating belt 105 by both axial ends of the first support roller 103, and from the external heating belt 105. The efficiency of heat conduction to the fixing roller 101 can be improved.

  In this embodiment, for example, the halogen heater 115 is removed from the second support roller 104 while the first support roller 103 distributes the first halogen heater 114 in the entire axial direction as shown in FIG. It is also possible to configure as described above. In this case, the crown-shaped second support roller 104 does not heat while suppressing the deviation of the external heating belt 105, and the halogen heater 114 of the first support roller 103 covers the entire width direction of the external heating belt 105. Heat. Also in this case, the same effect as described above can be obtained.

  According to the embodiment described above, the outer diameter of each central portion of the first and second support rollers 103 and 104 is larger than the outer diameter of each end portion, and the outer diameter and end of the central portion of the first support roller 103 are The difference from the outer diameter of the part can be made smaller than the difference between the outer diameter of the center part of the second support roller 104 and the outer diameter of the end part. Further, according to the present embodiment, the outer shape of the first support roller 103 is a straight shape, and the outer diameter of the central portion of the second support roller 104 can be larger than the outer diameter of the end portion. Accordingly, when the roller that supports the external heating belt 105 has a crown shape, it is possible to obtain a remarkable effect that the contact between the roller end portion and the external heating belt 105 can be reduced.

<Second Embodiment>
Next, a second embodiment according to the present invention will be described with reference to FIG. In the present embodiment, the same reference numerals are given to the parts common to the configuration described in the first embodiment, and the description thereof is omitted. FIG. 6 is a schematic configuration diagram of a fixing device 9 having an external heating belt configuration in the present embodiment.

  In order to maintain the surface temperature of the fixing roller 101 at a higher temperature, a configuration that can supply more heat from the external heating belt 105 to the fixing roller 101 is desired. For this purpose, it is necessary to enlarge the external nip portion Ne formed by the external heating belt 105 and the fixing roller 101 as compared with the configuration of FIG.

  Here, as a method of enlarging the external nip portion Ne, the present applicant stretches the external heating belt 105 around these support rollers in a state where the peripheral length of the external heating belt 105 is increased and the number of support rollers is increased. We focused on the points that can be realized by doing this.

  This can be realized by the configuration shown in FIG. That is, in the external heating unit 34 of this embodiment, the external heating belt 105 as an external heating member is disposed on the outer peripheral surface of the fixing roller 101. The external heating belt 105 is stretched (suspended) by an upstream fifth support roller 118, an intermediate fourth support roller 117, and a downstream third support roller 116 in the rotation direction of the fixing roller 101. . The external heating belt 105 is configured in an endless shape that contacts the fixing roller 101 and heats the fixing roller 101.

  The third, fourth, and fifth support rollers 116, 117, and 118 that stretch the external heating belt 105 are evenly pressed against the fixing roller 101 with a predetermined pressure by a pressure mechanism (pressure means) 35. The external heating belt 105 is configured to be able to contact / retreat with respect to the fixing roller 101 by the operation of the pressurizing mechanism 35, and the external nip portion Ne between the external heating belt 105 and the fixing roller 101 in a state of being in contact with the fixing roller 101. Form. The external heating belt 105 pressed by the fixing roller 101 is driven (rotated) along with the main rotation of the fixing roller 101.

  On the outer peripheral surface of the external heating belt 105, a cleaning roller 108 for cleaning the surface of the external heating belt 105 is disposed between the third support roller 116 and the fourth support roller 117. The cleaning roller 108 is pressed against the external heating belt 105 with a predetermined pressure by a pressing unit (not shown). The cleaning roller 108 has a porous material layer such as sponge on the outer peripheral surface of the cored bar.

  The external heating belt 105 has a layer of a metal base material (stainless steel, nickel, etc.) having an outer diameter of 70 mm, a thickness of 50 μm, and a length of 350 mm, for example. In order to prevent adhesion with the toner, a fluorine resin (in this embodiment, a PFA tube) is coated with a thickness of 20 μm as a heat-resistant sliding layer. The external heating belt 105 is driven (rotated) in accordance with the main rotation of the fixing roller 101 at a predetermined speed, for example, a peripheral speed of 500 mm / sec, in the direction of arrow C in FIG. The external heating belt 105 heats the fixing roller 101 while being in contact with the outer peripheral surface of the fixing roller 101.

  The third support roller 116 that stretches the external heating belt 105 is disposed on the downstream side in the fixing roller rotation direction. The third support roller 116 has an outer diameter set at, for example, 30 mm, an axially central portion set at, for example, 300 μm larger than both ends, and has an overall crown shape. The third support roller 116 includes a cored bar made of cylindrical metal (in this embodiment, made of aluminum) having a thickness of 3 mm and an axial length of 350 mm, for example. On the mandrel, in order to prevent abrasion with the inner surface of the external heating belt 105, a fluorine-based resin (in this embodiment, a PFA tube) as a heat-resistant sliding layer is coated with a thickness of 20 μm, for example. ing.

  The fourth support roller 117 that stretches the external heating belt 105 has a straight shape that is equal to or less than the crown amount of the third support roller 116, and is disposed upstream of the third support roller 116 in the fixing roller rotation direction. ing. The fourth support roller 117 also contacts the inner surface of the external heating belt 105 and heats the external heating belt 105.

  The fourth support roller 117 includes a metal core made of cylindrical metal (in this embodiment, made of aluminum) having an outer diameter of 30 mm, a thickness of 3 mm, and an axial length of 350 mm, for example. On this mandrel, in order to prevent abrasion with the inner surface of the external heating belt 105, a fluorine-based resin (in this embodiment, a PFA tube) as a heat-resistant sliding layer is coated with a thickness of 20 μm, for example. Has been.

  A halogen heater 119 for heating the fourth support roller 117 having a rated power of 1000 W, for example, as a heating element is disposed inside the core of the fourth support roller 117. The external heating belt 105 is heated from the inner surface by the fourth support roller 117 so that the surface temperature becomes a predetermined temperature.

  The surface temperature of the external heating belt 105 is detected by a thermistor 125 as temperature detecting means that comes into contact with the contact region D3 of the fourth support roller 117 and the external heating belt 105. The heater control unit 140 turns on / off the halogen heater 119 based on the detected temperature, and controls (temperature adjustment) so as to reach a predetermined target temperature, for example, 220 ° C.

  The fifth support roller 118 has a straight shape equal to or less than the crown amount of the third support roller 116, and is made of, for example, a cylindrical metal having an outer diameter of 30 mm, a thickness of 3 mm, and an axial length of 350 mm (this embodiment). Then, an aluminum cored bar is provided. On this mandrel, in order to prevent abrasion with the inner surface of the external heating belt 105, a fluorine-based resin (in this embodiment, a PFA tube) as a heat-resistant sliding layer is coated with a thickness of 20 μm, for example. Has been.

  A halogen heater 120 that heats the fifth support roller 118 with a rated power of 1000 W, for example, as a heating element is disposed inside the core of the fifth support roller 118. The external heating belt 105 is heated from the inside by the fifth support roller 118 so that the surface temperature becomes a predetermined temperature.

  The surface temperature of the external heating belt 105 is detected by a thermistor 126 as temperature detecting means that contacts the contact region D4 of the fifth support roller 118 and the external heating belt 105. The heater control unit 140 turns on / off the halogen heater 120 based on the detected temperature, and controls (temperature adjustment) to a predetermined target temperature, for example, 220 ° C.

  Here, the reason why the target temperature of the external heating belt 105 is set higher than the target temperature of the fixing roller 101 is as follows. That is, when the temperature of the external heating belt 105 is kept higher than the temperature of the fixing roller 101, the external heating belt has a good response (heat sensitivity accuracy) to the drop of the surface temperature of the fixing roller 101 due to the recording material. This is because heat can be supplied from 105 to the fixing roller 101.

  In the present embodiment, the third support roller 116 is a crown-shaped roller, and the fourth and fifth support rollers 117 and 118 are straight-shaped rollers incorporating halogen heaters 119 and 120. The fifth support roller 118 is a straight roller with a built-in halogen heater 120 in order to heat it to a predetermined temperature immediately before the external heating belt 105 enters the external nip Ne with the fixing roller 101. Further, in order to prevent the external heating belt 105 from being shifted, the third support roller 116 in which the winding amount of the external heating belt 105 is larger than that of the fourth support roller 117 has a crown shape.

  In the above embodiment, the crown-shaped third support roller 116 does not have a halogen heater (second heating means), and the straight-shaped fourth and fifth support rollers 117, 118 have halogen heaters 119, 120 built-in. doing. In the present embodiment, the third support roller 116 is a crown in which the outer diameter of the central portion in the width direction is larger than the outer diameters at both ends in the width direction so as to suppress the shift in the width direction intersecting the rotation direction of the external heating belt 105. It is comprised as a 2nd tension roller made into the shape.

  The light distribution state of the halogen heaters 119 and 120 is, for example, that the fourth support roller 117 is disposed at both ends like the first support roller 103 in FIG. 5B, and the fifth support roller 118 is the second support roller in FIG. It is good also as a center arrangement like 2 support rollers 104. Alternatively, the fifth support roller 118 is arranged at both ends like the first support roller 103 in FIG. 5B, and the fourth support roller 117 is like the second support roller 104 in FIG. 5B. A central arrangement is also possible.

  As described above, in the present embodiment, the third support roller 116 is configured as the second stretching roller, and the fourth and fifth support rollers 117 and 118 are the first tension rollers having heating means (halogen heater 119 or 120). It is configured as a rack roller.

  The embodiment configured as described above is suitable as the fixing device 9 to which the present invention is applied. However, the present invention is not limited to this arrangement configuration, and other arrangement arrangements may be possible. Of course.

  As described above, when the entire surface of the support roller is heated in a state where the support roller of the external heating belt 105 has a crown shape having a heating source therein, a gap is generated between the external heating belt and the end of the support roller, thereby supporting the support roller. Heat supply from the roller to both ends of the external heating belt is hindered.

  Therefore, in the present embodiment, the support roller for stretching the external heating belt 105 includes a third support roller 116 for controlling the shift of the external heating belt 105 during rotation driving, and a third support roller for heating the external heating belt 105. 4 and the fifth support rollers 117 and 118. Thus, by changing the shape of the support roller for each function, the surface of the external heating belt 105 can be uniformly heated while controlling the shift of the external heating belt 105 during driving.

  According to the configuration of the present embodiment, the third support roller 116 that stretches the external heating belt 105 is crowned, so that the shift of the external heating belt 105 during driving can be controlled. Further, the fourth and fifth support rollers 117 and 118 are formed in a straight shape, and the halogen heaters 119 and 120 are disposed as heating sources inside, whereby the surface temperature of the external heating belt 105 can be made uniform.

  As described above, the crown amounts of the third, fourth, and fifth support rollers 116, 117, and 118 that stretch the external heating belt 105 are changed in accordance with the presence or absence of heating means and the light distribution state inside the support roller. Yes. That is, the third support roller 116 has a crown shape in which the outer diameter of the central portion in the axial direction is larger than the outer diameters of both end portions, and the fourth and fifth support rollers 117 and 118 are less than the crown amount of the second support roller 104. It has a certain straight shape. Thereby, while effectively controlling the shift of the external heating belt 105 by the crown-shaped third support roller 116, both end portions of the external heating belt 105 and the halogen heaters 119 and 120 of the fourth and fifth support rollers 117 and 118 and The center part can be heated effectively. For this reason, the entire surface of the external heating belt 105 can be heated uniformly.

  According to this embodiment, the outer diameter of each central part of the fourth and fifth support rollers 117 and 118 is larger than the outer diameter of each end part, and the outer diameter and the end part of the central part of the fourth support roller 117 are the same. The difference from the outer diameter can be made smaller than the difference between the outer diameter of the center portion of the fifth support roller 118 and the outer diameter of the end portion. Further, according to the present embodiment, the fourth support roller 117 has a straight outer shape, and the outer diameter of the center portion of the fifth support roller 118 can be larger than the outer diameter of the end portion. As a result, the same effects as those of the first embodiment can be obtained.

  At the same time, by stretching the external heating belt 105 with the three support rollers 116, 117, and 118, the effect that the contact surface between the external heating belt 105 and the fixing roller 101 can be further increased can be obtained. Thereby, the amount of heat supplied to the fixing roller 101 can be more effectively performed.

  The fourth support roller 117 (or roller 118) has a crown shape instead of a straight roller, and the difference between the center portion and the end portion of the fourth support roller 117 (or roller 118) is the same as that of the third support roller 116. You may make it a structure smaller than the difference of a center part and an edge part. As described above, the outer diameter of the center portion of the fourth support roller 117 (or the fifth support roller 118) and the third support roller 116 is configured to be larger than the outer diameter of the end portion. The difference between the outer diameter of the center portion and the outer diameter of the end portion of the fourth support roller 117 (or the fifth support roller 118) is the difference between the outer diameter of the center portion and the outer diameter of the end portion of the third support roller 116. It is also possible to adopt a configuration that is smaller than the difference.

  DESCRIPTION OF SYMBOLS 9 ... Image heating apparatus (fixing apparatus), 101 ... Image heating member (fixing roller), 103, 117, 118 ... 1st stretching roller (1st support roller, 4th support roller, 5th support roller), 104, 116: second stretching roller (second support roller, third support roller), 105: external heating belt, 114, 119, 120: heating means (halogen heater), 115: second heating means (halogen heater), N ... Nip part (fixing nip part), P ... Recording material

Claims (4)

An image heating member that heats an image formed on a recording material at a nip portion, an external heating belt that contacts the surface of the image heating member to heat the image heating member, and a rotation that stretches the external heating belt In an image heating apparatus comprising: a first tension roller and a second tension roller that are possible; and a heating unit that heats at least an end region of the first tension roller in a rotation axis direction of the first tension roller. ,
The outer diameter of the central portion of the first stretching roller and the second stretching roller is larger than the outer diameter of the end portion, and the difference between the outer diameter of the central portion of the first stretching roller and the outer diameter of the end portion. Is smaller than the difference between the outer diameter of the center portion and the outer diameter of the end portion of the second stretching roller. An image heating member that heats an image formed on a recording material at a nip portion, an external heating belt that contacts the surface of the image heating member to heat the image heating member, and a rotation that stretches the external heating belt In an image heating apparatus comprising: a first tension roller and a second tension roller that are possible; and a heating unit that heats at least an end region of the first tension roller in a rotation axis direction of the first tension roller. ,
2. The image heating apparatus according to claim 1, wherein an outer shape of the first tension roller is a straight shape, and an outer diameter of a central portion of the second tension roller is larger than an outer diameter of an end portion.   The image heating apparatus according to claim 1, wherein the first stretching roller and the second stretching roller press the image heating member via the external heating belt.   And a second heating unit for heating the second stretching roller, wherein the heating unit heats an end portion of the first stretching roller from a central portion, and the second heating unit is configured to be the second stretching roller. The image heating apparatus according to any one of claims 1 to 3, wherein a heating distribution is set so as to heat a central portion of the first portion more than an end portion thereof.

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