JP2013088735A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device 100 that is provided with an external heating member 103 that contacts and heats a heating rotating body 101 and an external heating member 104 that contacts and heats a pressure rotating body 102, and prevents thin paper from being curled and reduces glossiness unevenness on a first surface during double-sided printing on thick paper; and an image forming apparatus.SOLUTION: A temperature of a first external heating member 103 that contacts a heating rotating body 101 and a temperature of a second external heating member 104 that contacts a pressure rotating body 102 are adjusted depending on a basis weight of a recording material. Accordingly, thin paper can be prevented from being curled, and glossiness unevenness on a first surface during double-sided printing on thick paper can be reduced.

Description

  INDUSTRIAL APPLICABILITY The present invention is an image for heating an image on a recording material, which is suitable for use as a fixing device mounted in an image forming apparatus such as an electrophotographic system or an electrostatic recording system (copying machine, printer, multifunction machine, facsimile, etc.). The present invention relates to a heating device.

  Examples of the image heating device include a fixing device that fixes an unfixed image formed on a recording material, and a glossiness imparting device that improves the glossiness of an image by reheating the image fixed on the recording material.

In recent years, image forming apparatuses such as copiers, printers, and multifunction machines have been required to have higher speed, higher image quality, higher color, and energy saving. Furthermore, multimedia compatibility that supports various recording materials such as thin paper, thick paper, rough paper (rough paper), uneven paper (embossed paper, etc.), coated paper (gloss coated paper, matte coated paper, etc.) In addition, high productivity (the number of images formed per unit time) is also required. In particular, in order to increase the productivity of a recording material having a large basis weight (g / m ² ) such as cardboard, the fixing performance for fixing the toner to the recording material is improved by improving the recording material heating performance of the fixing device. There is a need to improve.

  However, the amount of heat required for toner fixing of 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. For this reason, if toner fixing is performed on a recording material with a large basis weight at the same fixing speed as a recording material with a small basis weight, the heating rotator of the fixing device that heats the toner is deprived of heat and the surface temperature decreases. The problem of poor fixing may occur. Therefore, when fixing toner on a recording material having a large basis weight, in order to ensure fixability (adhesive force between the toner and the recording material), the fixing speed is reduced, that is, the fixing process is performed with reduced productivity. This is the current situation.

  As such a heating rotator, for example, a heat-resistant elastic layer such as silicone rubber or fluorine rubber is coated on a metal pipe-shaped cored bar in which a heating source such as a halogen heater is disposed, and the elastic layer A fixing roller having a structure in which a release layer such as a fluororesin is formed is generally used. In such a fixing roller, heat from the halogen heater is blocked by a metal core or an elastic layer having low thermal conductivity and is not easily transmitted to the surface of the fixing roller.

  There is also a structure in which an elastic layer is not provided as a fixing roller. In the case of this structure, the surface temperature decrease is small because of the absence of the elastic layer, but the heat is blocked as the thickness of the core metal increases, so that the surface temperature decrease occurs similarly. Further, in the absence of this elastic layer, in a recording material with large irregularities, the toner in the recesses is difficult to contact the fixing roller, and the toner in the recesses may cause poor fixing.

  In particular, in the case of a color image, the surface of the unfixed image cannot be melted uniformly, and fixing unevenness, gloss unevenness, and color unevenness may occur, and image quality may deteriorate. Therefore, it is preferable to cover the heating rotator with an elastic layer in view of compatibility with various recording materials and image quality.

  In any case, in order to prevent a decrease in the surface temperature of the fixing roller, a structure in which a high-power halogen heater is disposed in the fixing roller and heated rapidly can be considered. However, in the case of this structure, the core metal temperature of the fixing roller suddenly increases, and due to the thermal deterioration of the adhesive layer between the core metal and the elastic layer, or the thermal deterioration of the adhesive layer between the core metal and the release layer, There is a possibility that peeling between the core metal and the elastic layer or peeling between the core metal and the release layer may occur.

  Furthermore, the elastic layer is softened or hardened due to heat, and the change in the hardness of the fixing roller increases, and the width of the fixing nip portion (the width in the roller circumferential direction) with the pressure roller as the pressure rotating body changes. There is also a possibility that the elastic layer may be destroyed due to a change in fixing property due to the deterioration or softening deterioration.

  Accordingly, an external heating type fixing device has been proposed as a technique for improving the heating performance of the recording material and improving the productivity in order to prevent a decrease in the surface temperature of the fixing roller due to the passing of the recording material. This is a system in which the fixing roller is heated not only from the internal heater but also from the outside by bringing an external heating member into contact with the fixing roller.

  In addition, a pressure rotator that presses against a heating rotator of a fixing device to form a fixing nip portion generally does not have a heating source inside. Therefore, when a recording material is passed, the surface temperature is In response to the heat of the heating rotator, the temperature gradually rises and reaches a certain temperature. Therefore, the fixing property is not good in the initial printing from the standby state. As the number of continuous prints increases, the fixability gradually improves.

  In order to improve the fixing property at the initial stage of printing, a fixing device has a heating source inside a pressure roller as a pressure rotator and raises the surface temperature of the pressure roller to a predetermined temperature during standby. Has been proposed.

  Such a pressure roller is formed by, for example, coating a heat-resistant elastic layer such as silicone rubber or fluorine rubber on a metal pipe-shaped cored bar in which a heating source such as a halogen heater is disposed. It has a structure in which a release layer such as a fluororesin is formed thereon.

  However, the fixing device having a heating source inside the pressure roller has good fixability since the surface temperature of the pressure roller is maintained at a predetermined temperature in the initial printing from the standby state. However, when the number of continuous prints is increased, the recording material is deprived of heat, so that the surface temperature of the pressure roller is gradually lowered and the fixability is lowered.

  In addition, the pressure roller forms a fixing nip portion in pressure contact with the fixing roller, and in order to improve the fixing property, the width of the fixing nip portion is increased and the time for supplying heat to the recording material is increased. There is a need to. For this purpose, a method of increasing the thickness of the elastic layer of the pressure roller is effective.

  However, when the thickness of the elastic layer of the pressure roller is increased, the heat of the internal heating source hardly reaches the surface. Therefore, in order to prevent a decrease in the surface temperature of the pressure roller, a structure in which a high-power halogen heater is disposed in the pressure roller and heated rapidly can be considered.

  However, in this structure, the cored bar temperature of the pressure roller rises rapidly, so that the cored bar and the elastic layer may be peeled off due to thermal deterioration of the adhesive layer between the cored bar and the elastic layer. There is. Furthermore, the elastic layer is softened or hardened due to heat, and the change in the hardness of the pressure roller increases. The change in the fixing property due to the change in the width of the fixing nip, or the softening deterioration progresses and the elastic layer breaks. There is also a possibility of being done.

  Therefore, as a technique to improve the heating performance of the recording material and improve productivity in order to prevent the surface temperature of the pressure roller from being lowered due to the recording material passing, fixing by an external heating method in which the pressure roller is heated from the outside. An apparatus has been proposed (Patent Document 1). In this method, an external heating member is brought into contact with the pressure roller to heat the pressure roller from the outside.

  These external heating type fixing devices have the advantage of improving the fixability and productivity by preventing the surface temperature of the fixing roller and pressure roller from decreasing. Also, the fixing roller or pressure roller core metal temperature is lowered to prevent the separation between the core metal and the elastic layer, the separation between the core metal and the release layer, or the thermal deterioration of the elastic layer. In addition, there is an advantage that the life of the pressure roller can be extended.

JP 2004-138949 A

  In the fixing device in which the fixing roller and the pressure roller are each provided with, for example, an external heating roller as an external heating member, the surface temperature of the pressure roller can be easily changed. Therefore, it is possible to further improve the quality of output materials of different recording materials from thin paper to thick paper, depending on how the pressure roller surface temperature is set.

  Specifically, at the time of thin paper printing, the recording material has low rigidity, and thus the curling of the recording material becomes large. Due to the curl, there is a high possibility of problems such as jams caught on the recording material conveyance path, corner breaks of the recording material, and image position misalignment between the front and back surfaces during double-sided printing.

  On the other hand, when printing on both sides of thick paper, there is a high possibility that gloss unevenness due to pressure roller temperature unevenness will occur in the first image. This is because the pressure roller has a large temperature difference between the sheet and the sheet passing portion, and a large temperature drop in the circumference of the pressure roller during sheet passing. Therefore, when the image on the first side comes into contact with the pressure roller during printing on the second side during double-sided printing, the unevenness in the glossiness of the image on the first side that contacts the pressure roller occurs due to the temperature unevenness of the pressure roller. It is because it will do. In particular, this gloss unevenness tends to occur remarkably in a recording material having a smooth surface of cardboard.

  Therefore, the present invention has been proposed in view of the above circumstances. The purpose is to provide a wide range of recordings by optimizing the control of the temperature of the external heating member that heats the pressurizing rotator in an image heating apparatus equipped with a heating rotator and a pressurizing rotator, respectively. It is to realize output of high-quality images to the material.

  Accordingly, the present invention provides a heating rotator that contacts and heats an image formed on a recording material, a pressurizing rotator that pressurizes the heating rotator and forms a nip portion that sandwiches and conveys the recording material, and the heating A first external heating member that contacts the surface of the rotating body to heat the heating rotating body, and a second external heating member that contacts the surface of the pressure rotating body and heats the pressing rotating body And an image heating apparatus that controls the temperature of each of the first external heating member and the second external heating member so as to be a predetermined set temperature. The image formed on the recording material having a temperature higher than the first basis weight is set to the set temperature of the second external heating member in the first mode for heating the image formed on the recording material having the basis weight of. From the set temperature of the second external heating member in the second mode High and setting.

  The present invention also relates to a heating rotator that contacts and heats an image formed on a recording material, a pressurizing rotator that pressurizes the heating rotator and forms a nip portion that sandwiches and conveys the recording material, and the heating A first external heating member that contacts the surface of the rotating body to heat the heating rotating body, and a second external heating member that contacts the surface of the pressure rotating body and heats the pressing rotating body And an image heating apparatus that controls the temperature of each of the first external heating member and the second external heating member so as to be a predetermined set temperature. The image formed on the recording material smaller than the first basis weight is heated at the set temperature of the second external heating member in the first mode for heating the image formed on the recording material having the basis weight of. Than the set temperature of the second external heating member in the second mode And characterized in that the fence set.

  According to the present invention, it is possible to output a high-quality image to a wide range of recording materials by optimizing the control of the temperature of the external heating member that heats the pressure rotator for the external heating type image heating apparatus. . More specifically, curling can be reduced when the recording material is thin paper, and gloss unevenness on the first surface during double-sided printing when the recording material is thick paper or glossy paper can be reduced. In addition, it is possible to secure fixability in a low temperature environment and reduce curl in a high humidity environment.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. 1 is a schematic configuration diagram of a fixing device according to a first embodiment. FIG. 3 is a block diagram of a control system of the fixing device. The control flow figure concerning a 1st embodiment. The control flow figure concerning a 2nd embodiment. The control flow figure concerning a 3rd embodiment. The control flow figure concerning a 4th embodiment.

  The present invention will be specifically described below with reference to examples. These examples are examples of the best mode of the present invention, but the present invention is not limited to these examples.

<First Embodiment>
(1) Description of Configuration of Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as an image fixing apparatus 100. This image forming apparatus is a four-color full-color electrophotographic image forming apparatus of an intermediate transfer tandem system. This is a device capable of forming a color image on a recording material (transfer material) P based on electrical image information (image signal) input from a host device 200 to a control circuit unit (CPU) 130 as control means.

  The host device 200 is an image reading device (image reader), a personal computer (PC), a terminal on a network, a partner facsimile, a word processor, or the like, and is connected to the control circuit unit 130 via an interface unit. The control circuit unit 130 exchanges various electrical information with the operation panel 131 including the various operation keyboards 131a and the display 131b and the host device 200. The control circuit unit 130 monitors and controls the operation of each device in the image forming apparatus, and comprehensively controls the image forming operation of the image forming apparatus according to a predetermined control program and a reference table.

  The image forming apparatus has a plurality of image forming units. In the present embodiment, units U (UY, UM, UC, UBk) as first to fourth image forming units are arranged in the horizontal direction (lateral direction) in order from the left side to the right side in the drawing. The toner images of different colors are formed by parallel processing. Each unit U is an electrophotographic image forming mechanism having the same configuration except for the color of the developer (hereinafter referred to as toner) accommodated in each developing device.

  Each unit U of this example is a cylindrical (drum type) electron whose surface layer is made of an OPC (organic optical semiconductor), for example, as a rotatable (movable) image carrier on which an electrostatic latent image is formed. It has a photographic photoreceptor (hereinafter referred to as a drum) 1. Each drum 1 is rotationally driven at a predetermined speed in a counterclockwise direction indicated by an arrow by a driving means (not shown). Further, around the drum 1, there are a charging roller 2, an image exposure device 3, a developing device 4, a primary transfer roller 5, and a drum cleaning device 6 as process means acting on the drum 1 along the drum rotation direction.

  The charging roller 2 is a charging unit that charges the surface of the drum 1. The charging roller 2 is driven to rotate in contact with the drum 1 and is applied with a predetermined charging bias. As a result, the surface of the rotating drum 1 is uniformly charged to a predetermined polarity and potential. The image exposure apparatus 3 is an image exposure unit that exposes the surface of the drum 1 that has been charged with exposure light (laser light or the like) according to image information. By this charging and exposure, an electrostatic latent image corresponding to image information is formed on the surface of the drum 1.

  The developing device 4 is a developing unit that visualizes the electrostatic latent image formed on the surface of the drum 1 as a toner image (developer image). In this embodiment, yellow (Y) toner is stored in the developing device 4 of the first unit UY. The developing device 4 of the second image forming unit UM contains magenta (M color) toner. The developing device 4 of the third image forming unit UC contains cyan (C color) toner. The developing device 4 of the fourth image forming unit UBk contains black (Bk) toner.

  The drum cleaning device 6 is a cleaning unit that removes primary transfer residual toner on the surface of the drum 1, and cleaning members such as blades and brushes are disposed.

  An intermediate transfer belt device 7 is disposed below the first to fourth units UY, UM, UC, and UBk. The belt device 7 includes a flexible endless belt 8 that is an intermediate transfer member, and a drive roller 9, a support roller 10, and a backup roller 11 as a plurality of belt stretching members that stretch the belt 8. . The drive roller 9 is disposed on the first unit UY side. The support roller 10 is disposed on the fourth unit UBk side. The backup roller 11 is disposed below the drive roller 9 and the support roller 10.

  The belt 8 is driven to rotate (circulation movement) at a peripheral speed corresponding to the peripheral speed of the drum 1 in the clockwise direction of the arrow by driving the driving roller 9 by a belt driving motor (not shown) controlled by the control circuit unit 130. Is done.

  In each unit U, the primary transfer roller 5 is disposed inside the belt 8. Each roller 5 is in pressure contact with the lower surface of the corresponding drum 1 via an ascending belt portion between the roller 9 and the roller 11. A contact portion between each drum 1 and the belt 8 is a primary transfer portion (primary transfer nip portion) T1. The rollers 10, 11, 5 rotate following the belt 8 rotated by the roller 9. Further, an intermediate transfer cleaning device 12 for cleaning the belt surface after the secondary transfer is disposed facing the belt suspension portion of the roller 9, and cleaning members such as blades and brushes are disposed. .

  The secondary transfer roller 13 is in contact with the backup roller 11 with the belt 8 interposed therebetween. A contact portion between the belt 8 and the roller 13 is a secondary transfer portion (secondary transfer nip portion) T2. The roller 13 rotates following the belt 8 rotated by the roller 9.

  The operation when the full-color mode (full color image formation) is selected is as follows. The control circuit unit 130 drives the drive unit of the image forming apparatus based on the image formation start signal. Thereby, the drum 1 of each unit U is rotationally driven. The belt 8 is also rotationally driven. In synchronism with this drive, the charging roller 2 uniformly charges the surface of the drum 1 to a predetermined polarity and potential in each unit U at a predetermined control timing.

  Each image exposure device 3 performs pattern exposure on the surface of each drum 1 in accordance with image information of each color (color separation image of a full color image). As a result, an electrostatic latent image corresponding to the image information of the corresponding color is formed on the surface of each drum 1 with a predetermined control timing. Then, the electrostatic latent image is developed as a toner image by the developing device 4.

  By the electrophotographic image forming process operation as described above, a Y color toner image corresponding to the Y color component image of the full color image is formed on the drum 1Y of the first unit UY. The toner image is primarily transferred onto the belt 8 at the primary transfer portion T1 of the unit UY. An M color toner image corresponding to the M color component image of the full color image is formed on the drum 1M of the second unit UM. The toner image is primary-transferred at the primary transfer portion T1 of the unit UM, superimposed on the Y-color toner image already transferred onto the belt 8.

  Further, a C color toner image corresponding to the C color component image of the full color image is formed on the drum 1C of the third unit UC, and the toner image is already on the belt 8 in the primary transfer portion T1 of the unit UC. The transferred Y color + M color toner image is superimposed and primarily transferred. A Bk color toner image corresponding to the K color component image of the full color image is formed on the drum 1Bk of the fourth unit UBk. In the primary transfer portion T1 of the unit UBk, the toner image is superposed on the Y color + M color + C color toner image already transferred onto the belt 8 and is primarily transferred.

  In each unit U, the primary transfer of the toner image from the drum 1 to the belt 8 is performed by applying a primary transfer voltage to the roller 5. That is, a primary transfer voltage having a predetermined potential and a polarity opposite to the normal charging polarity of the toner is applied to the roller 5. This is done by the electric field generated by this applied voltage and the nip pressure of the primary transfer portion T1.

  In this way, a four-color full-color unfixed toner image of Y color + M color + C color + Bk color is synthesized and formed on the belt 8 (multiple transfer formation). In the present embodiment, the color order is Y color, M color, C color, and Bk color. In each unit U, the primary transfer residual toner remaining on the surface of the drum 1 after the primary transfer of the toner image to the belt 8 is collected by the drum cleaning device 6. The cleaned drum 1 is again charged uniformly and uniformly by the charging roller 2 and repeatedly used for image formation.

  On the other hand, the recording material P is fed from the paper feed mechanism unit 14 at a predetermined control timing. In the present embodiment, the paper feed mechanism unit 14 includes upper and lower paper feed cassettes 15, 16, and 17. Further, it has a manual feed tray (multipurpose tray) 18. Further, it has an intermediate tray 19 for the double-sided image forming mode.

  Then, the cassette 15 or 16 or 17 designated in advance, or the sheet feeding roller 20 of the manual sheet feeding tray 18 is driven. Then, one sheet of recording material P is separated and fed from the cassette or tray corresponding to the driven paper feed roller 20 and enters the third sheet path 23 through the first sheet path 21 or the second sheet path 22. Then, the recording material P reaches the registration roller pair 24 to correct skew, and is adjusted in registration to be synchronized with the image portion on the belt 8 and introduced into the secondary transfer portion T2.

  As a result, the four-color superimposed toner image on the belt 8 side is secondarily transferred collectively and sequentially onto the surface of the recording material P that is nipped and conveyed by the secondary transfer portion T2. This secondary transfer is performed by applying a secondary transfer voltage to the roller 13. That is, a secondary transfer voltage having a predetermined potential that is opposite to the normal charging polarity of the toner is applied to the roller 13. This is done by the electric field generated by this applied voltage and the nip pressure of the secondary transfer portion T2.

  The recording material P passing through the secondary transfer portion T2 is separated from the belt 8, introduced into the fixing device 100 by the fourth sheet path 25, and nipped and conveyed by the fixing nip portion, whereby the toner image on the recording material is heated. Pressurized and fixed as a fixed image. The fixing device 100 will be described in detail in the next section (2). On the other hand, the secondary transfer residual toner on the belt 8 after the secondary transfer of the toner image to the recording material P is collected by the intermediate transfer cleaning device 112. The belt 8 from which the secondary transfer residual toner has been removed is repeatedly used for primary transfer for image formation.

  When the designated mode is the single-sided image forming mode, the recording material P that has exited the fixing device 100 is advanced from the fifth sheet path 26 to the sixth sheet path 27 on the upper surface of the flapper by the first flapper 29. The paper is discharged to the paper discharge tray 28 as a single-sided full-color formed product.

  When the double-sided image forming mode is specified, the first image-formed recording material P that has exited the fixing device 100 is routed from the fifth sheet path 26 to the seventh sheet path 30 by the first flapper 29. Is changed to the side. Further, after being introduced into the switchback sheet path as the eighth sheet path 30, it is switched back and conveyed, introduced into the ninth sheet path 33 by the second flapper 32, and conveyed to the intermediate tray 19. Once stored.

  The recording material P on the tray 19 is separated and fed by a sheet feeding roller 20 driven at a predetermined control timing, enters the third sheet path 23 again through the first sheet path 21, and is turned upside down. In this state, it is reintroduced into the secondary transfer portion T2. As a result, a toner image is formed on the second surface of the recording material P. Thereafter, as in the single-sided image forming mode, the sheet passes through the fourth sheet path 25, the fixing device 100, the fifth and sixth sheet paths 26 and 27, and is discharged to the tray 28 as a double-sided image formed product. .

  Further, for example, in the case of a black monochromatic mode (monochromatic image formation) or a 2-3 color mode, image formation on the drum 1 is executed in an image forming unit of a necessary color. At this time, the drum 1 in the unnecessary image forming unit is rotated idly. Then, the toner image is primarily transferred onto the belt 8 at the primary transfer portion T1, and further transferred to the recording material P at the secondary transfer portion T2 and introduced into the fixing device 100. The

(2) Fixing device 100
FIG. 2 is a transverse right side view of the main part of the fixing device 100, and FIG. 3 is a block diagram of a control system of the fixing device 100.

  Here, regarding the fixing device 100, the front surface is a surface (or the side) when the apparatus is viewed from the recording material inlet side, and the rear surface is the opposite surface (or the side: recording material outlet side). Left and right are left or right when the apparatus is viewed from the front. The longitudinal direction of the fixing device 100 or a member constituting the fixing device 100 is an axial direction (thrust direction) of the rotating body, a direction orthogonal to the recording material conveyance direction in the recording material conveyance path surface, or a direction parallel to the direction. is there. The short direction is a direction parallel to the recording material conveyance direction. Up or down is up or down in the direction of gravity. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction.

  The fixing device 100 of this example includes a fixing roller 101 as a heating rotator, a pressure roller 102 as a pressure rotator, a fixing external heating roller 103 as a first external heating member, and a second external heating member. A pressure external heating roller 104 is provided.

(2-1) Fixing roller 101
The fixing roller 101 has a configuration in which a heat-resistant elastic layer 101b and a heat-resistant release layer 101c are sequentially laminated on the outer peripheral surface of a cylindrical metal core 101a. The core metal 101a is made of aluminum having an outer diameter of 74 mm, a thickness of 6 mm, and a length of 350 mm, for example. The elastic layer 101b is made of, for example, silicone rubber having a thickness of 3 mm (for example, JIS-A hardness 20 degrees), and covers the outer peripheral surface of the cored bar 101a. The release layer 101c is made of, for example, a fluororesin (eg, a PFA tube) having a thickness of 100 μm and covers the surface of the elastic layer 101b in order to improve the releasability with the toner.

  The left and right ends of the fixing roller 101 are rotatably supported between the left and right side plates (not shown) of the fixing device casing 100a (FIG. 1) via bearing members. The fixing roller 101 is rotationally driven in a clockwise direction indicated by an arrow A at a predetermined peripheral speed, for example, 500 mm / sec, by a driving source (fixing motor) M100 controlled by the control circuit unit 130.

  In addition, a halogen heater 111 having a rated power of 1200 W, for example, which generates heat when energized as a heating source is disposed in the cored bar 101 a over almost the entire length of the fixing roller 101. Electric power is supplied to the heater 111 from the power supply unit S111 controlled by the control circuit unit 130. Further, a thermistor 121 as a first temperature detecting means is disposed in elastic contact with the longitudinal central portion of the outer surface of the fixing roller 101.

(2-2) Pressure roller 102
The pressure roller 102 also has a configuration in which a heat-resistant elastic layer 102b and a heat-resistant release layer 102c are sequentially laminated on the outer peripheral surface of a cylindrical metal core metal 102a. The metal core 102a is made of stainless steel having an outer diameter of 50 mm, a thickness of 5 mm, and a length of 350 mm, for example. The elastic layer 102b is made of, for example, silicone rubber having a thickness of 5 mm (for example, JIS-A hardness 24 degrees), and covers the outer peripheral surface of the cored bar 101a. The release layer 102c is made of, for example, a fluororesin (eg, a PFA tube) having a thickness of 100 μm and covers the surface of the elastic layer 102b in order to improve the releasability with the toner.

  The pressure roller 102 is arranged in parallel to the fixing roller 101 below the fixing roller 101, and both left and right end portions are rotatable between the left and right side plates of the fixing device casing 100a via a bearing member. It is supported and arranged. The left and right bearing members are slidably moved in directions toward and away from the fixing roller 101 with respect to the side plates, and the fixing roller 101 is pressed by a pressing means (not shown: compression reaction force of an elastic member). It is biased to move in the direction approaching. As a result, the pressure roller 102 is pressed against the fixing roller 101 with a predetermined pressing force against the elasticity of the elastic layers 101b and 102b in a free state.

  By this pressure contact, a fixing nip portion N1, which is a first nip portion having a predetermined width, for example, about 10 mm width, is formed between the rollers 101 and 102 in the roller circumferential direction. When the pressure roller 102 is in pressure contact with the fixing roller 101, the pressure roller 102 is rotated in the clockwise direction indicated by an arrow B following the rotational driving of the fixing roller 101.

  In addition, a halogen heater 112 having a rated power of 600 W, for example, which generates heat when energized as a heating source is disposed in the metal core 102 a over almost the entire length of the pressure roller 102. Electric power is supplied to the heater 112 from the power supply unit S112 controlled by the control circuit unit. Further, a thermistor 122 as a second temperature detecting means is elastically contacted with the longitudinal center portion of the outer surface of the pressure roller 102.

  Further, the pressure roller 102 is moved away from the fixing roller 101 by the separation means H102 controlled by the control circuit unit 130 in a direction away from the fixing roller 101 against the pressing force of the pressure means (or applied from the fixing roller 101). The pressure release state: the same applies hereinafter). Specifically, the separating means H102 can be constituted by an electromagnetic solenoid plunger device, a mechanism using a cam and a lever, or the like. That is, the pressure roller 102 performs a pressure contact operation and a separation operation with respect to the fixing roller 101 by the urging force of the pressure unit and the separation unit H102 controlled by the control circuit unit 130.

(2-3) Fixing external heating roller 103
A fixing external heating roller 103 as a first external heating member that contacts and heats the fixing roller 101 has heat resistance for improving the releasability from the toner on the outer peripheral surface of a cylindrical metal cored bar 103a. The release layer 103b is covered. The core metal 103a is made of, for example, a cylindrical metal (for example, made of aluminum) having an outer diameter of 30 mm, a thickness of 3 mm, and a length of 350 mm. The release layer 103b is, for example, a 15 μm fluororesin (for example, PFA coat).

  The fixing external heating roller 103 is arranged in parallel to the fixing roller 101, and both left and right end portions are rotatably supported between the left and right side plates of the fixing device casing 100a via bearing members. It is installed. The left and right bearing members are arranged so as to be slidable in the direction approaching and distant from the fixing roller 101 with respect to the side plates, and are moved in the direction approaching the fixing roller 101 by a pressurizing means (not shown). It is energized. Accordingly, the fixing external heating roller 103 is pressed against the fixing roller 101 with a predetermined pressing force against the elasticity of the elastic layer 101b in a free state.

  By this pressure contact, an external heating nip portion N2, which is a second nip portion having a predetermined width, for example, a width of about 5 mm, is formed between the rollers 101 and 103 in the circumferential direction of the roller. The fixing external heating roller 103 rotates in the counterclockwise direction indicated by an arrow C following the rotational driving of the fixing roller 101 in a state where the fixing external heating roller 103 is pressed against the fixing roller 101.

  In addition, a halogen heater 113 having a rated power of 800 W, for example, which generates heat when energized as a heating source is disposed in the cored bar 103 a over almost the entire length of the fixing external heating roller 103. Electric power is supplied to the heater 113 from the power supply unit S113 controlled by the control circuit unit 130. In addition, a thermistor 123 as a third temperature detecting means is disposed in elastic contact with the longitudinal central portion of the outer surface of the fixing external heating roller 103.

  Further, the fixing external heating roller 103 is moved in a direction away from the fixing roller 101 against the pressure of the pressing means by the separating means H103 controlled by the control circuit unit 130, and is held in a state separated from the fixing roller 101. Is done. That is, the fixing external heating roller 103 performs a pressing operation and a separating operation with respect to the fixing roller 101 by the urging force by the pressing unit and the separating unit H103 controlled by the control circuit unit 130.

(2-4) Pressurized external heating roller 104
A pressure external heating roller 104 as a second external heating member that contacts and heats the pressure roller 102 is also provided on the outer peripheral surface of the cylindrical metal core 104a to improve the releasability from the toner. The heat-resistant release layer 104b is covered. The metal core 104a is made of, for example, a cylindrical metal (for example, aluminum) having an outer diameter of 30 mm, a thickness of 3 mm, and a length of 350 mm. The release layer 104b is, for example, a 15 μm fluororesin (for example, PFA coat).

  The pressure external heating roller 104 is arranged in parallel to the pressure roller 102, and both left and right end portions are rotatably supported between the left and right side plates of the fixing device casing 100a via bearing members. Arranged. The left and right bearing members are arranged so as to be slidable in a direction approaching the pressure roller 101 and a direction away from the pressure roller 101 with respect to the side plate, and in a direction approaching the pressure roller 102 by a pressure means (not shown). The movement is energized. Thereby, the pressure external heating roller 104 is pressed against the pressure roller 102 with a predetermined pressing force against the elasticity of the elastic layer 102b in a free state.

  By this pressure contact, an external heating nip portion N3 that is a third nip portion having a predetermined width, for example, a width of about 5 mm, is formed between the rollers 102 and 104 in the circumferential direction of the roller. While the pressure external heating roller 104 is in pressure contact with the pressure roller 102, the pressure external heating roller 104 rotates in the clockwise direction of the arrow D following the rotation of the pressure roller 102.

  In addition, a halogen heater 114 having a rated power of 800 W, for example, which generates heat when energized as a heating source is disposed in the cored bar 104 a over almost the entire longitudinal direction of the pressure external heating roller 104. Electric power is supplied to the heater 114 from the power supply unit S114 controlled by the control circuit unit 130. Further, a thermistor 124 as a fourth temperature detecting means is elastically contacted with the longitudinal central portion of the outer surface of the pressure external heating roller 104.

  The pressure external heating roller 104 is moved away from the pressure roller 102 by the separation means H104 controlled by the control circuit unit 130 in a direction away from the pressure roller 102 against the pressure of the pressure means. Kept in a state. That is, the pressure external heating roller 104 performs a pressure contact operation and a separation operation with respect to the fixing roller 101 by the urging force by the pressure unit and the separation unit H104 controlled by the control circuit unit 130.

(2-5) Fixing Operation When the image forming apparatus is on standby (when the control circuit unit 130 is waiting for input of an image formation start signal), the main motor (not shown) of the image forming apparatus is stopped. . Further, the fixing motor M100 of the fixing device 100 is also stopped.

  During standby, the separation means H102, H103, and H104 are turned on to prevent deformation or distortion of the elastic layer 101b of the fixing roller 101 and the elastic layer 102b of the pressure roller 102. As a result, the pressure roller 102, the fixing external heating roller 103, and the pressure external heating roller 104 are held apart from the fixing roller 101 and the pressure roller 102.

  If the rollers 101, 102, 103, and 104 remain pressed without being separated during standby, deformation or distortion of the elastic layer at the fixing nip N1 and the external heating nips N2 and N3 remains during printing. There are things to do. For this reason, horizontal streaks, gloss streaks (gloss unevenness), and the like may occur on the image, and image quality may deteriorate. Therefore, it is preferable to separate the rollers during standby as in the present embodiment.

  When an image formation start signal is input from the host device 200 or the operation panel 131 to the control circuit unit 130, the control circuit unit 130 activates the main motor and operates the image forming mechanism unit for image formation according to a predetermined image formation sequence program. To start.

  For the fixing device 100, the control circuit unit 130 turns off the separating means H102, H103, and H104. As a result, the pressure roller 102, the fixing external heating roller 103, and the pressure external heating roller 104 are converted into a state where they are in predetermined pressure contact with the fixing roller 101 and the pressure roller 102 by the urging force of the pressure unit, respectively. The

  Further, the fixing motor M100 is activated, and the fixing roller 101 is rotationally driven in a clockwise direction indicated by an arrow A at a predetermined speed, for example, a peripheral speed of 500 mm / sec. The pressure roller 102 and the fixing external heating roller 103 are rotated counterclockwise by arrows B and C, respectively, following the rotation of the fixing roller 101. The pressure external heating roller 104 rotates in the clockwise direction indicated by an arrow D following the rotation of the pressure roller 102.

  In addition, power is supplied from the power supply units S111 to S114 to the halogen heaters 111 to 114, respectively, and the fixing roller 101, the pressure roller 102, the fixing external heating roller 103, and the pressure external heating roller 104 are internally provided by the heat generated by the heaters. Is heated from.

  The surface temperature of the fixing roller 101 is detected by the thermistor 121, and the detected temperature is input to the control circuit unit 130. The control circuit unit 130 supplies power from the power source unit S111 to the halogen heater 111 so that the surface temperature of the fixing roller 101 is maintained at a predetermined target temperature, for example, 180 ° C., based on the detected temperature information input thereto. Is controlled (ON / OFF control, etc.) to control the temperature.

  The surface temperature of the pressure roller 102 is detected by the thermistor 122, and the detected temperature is input to the control circuit unit 130. The temperature control function unit of the control circuit unit 130 generates a halogen from the power source unit S112 so that the surface temperature of the pressure roller 102 is raised to a predetermined target temperature, for example, 120 ° C. and maintained based on the input detected temperature information. The temperature is controlled by controlling the power supply to the heater 112.

  The surface temperature of the fixing external heating roller 103 is detected by the thermistor 123, and the detected temperature is input to the control circuit unit 130. The temperature control function unit of the control circuit unit 130 starts from the power source unit S113 so that the surface temperature of the fixing external heating roller 103 is raised to a predetermined target temperature, for example, 210 ° C., based on the detected temperature information input thereto. The temperature is controlled by controlling the power supply to the halogen heater 113.

  The surface temperature of the pressure external heating roller 104 is detected by the thermistor 124, and the detected temperature is input to the control circuit unit 130. The temperature control function unit of the control circuit unit 130 receives power from the power supply unit S114 so that the surface temperature of the fixing external heating roller 103 is raised to a predetermined target temperature, for example, 170 ° C. based on the detected temperature information input thereto. The temperature is controlled by controlling the power supply to the halogen heater 114.

  In the above state, the recording material P carrying the toner image K is conveyed from the secondary transfer portion T2 side (image forming portion side) to the fixing nip portion N1 of the fixing device 100 from the direction of arrow E and introduced. In the present embodiment, recording materials of various sizes of large and small are introduced into the fixing device 100 by so-called center reference conveyance with the center of the recording material width as a base line.

  Then, the recording material P is nipped and conveyed by the fixing nip portion N1 to pass through and is heated and pressurized, and the toner image K is fixed to the recording material P as a fixed image.

  At this time, the portion of the surface of the fixing roller 101 and the surface of the pressure roller 102 where the recording material P is deprived of heat at the fixing nip portion N1 rises to a predetermined temperature as follows. That is, the amount of heat from the halogen heaters 111 and 112 inside the roller, heated from the fixing external heating roller 103 by the external heating nip N2, and heated from the pressure external heating roller 104 by the external heating nip N3 to a predetermined temperature. To rise. Thereafter, the fixing operation is performed by repeatedly applying heat to the recording material P at the fixing nip portion N1.

  On the other hand, the portion of the fixing external heating roller 103 where the heat is taken by the fixing roller 101 at the external heating nip portion N2 is heated by the amount of heat from the halogen heater 113 inside the roller and rises to a predetermined temperature. In addition, the portion of the external heating nip portion N3 of the external pressure heating roller 104 where heat is removed by the pressure roller 102 is heated by the amount of heat from the halogen heater 114 inside the roller and rises to a predetermined temperature. Thereafter, the fixing operation is performed by repeatedly applying heat to the fixing roller 101 at the external heating nip portion N2 and to the pressure roller 102 at the external heating nip portion N3.

(2-6) Thermistors 121-124
A thermistor that detects the surface temperatures of the fixing roller 101, the pressure roller 102, the fixing external heating roller 103, and the pressure external heating roller 104 will be described. As described above, in the present embodiment, the introduction of the recording material of various large and small width sizes to the fixing device 100 is performed by the central reference conveyance with the recording material width center as the base line. Accordingly, the thermistors 121 to 124 that detect the surface temperature of each roller are at least the recording material passing area (sheet passing part) of the minimum width that can be passed through the apparatus, or the passing area corresponding part (sheet passing part). Corresponding part).

  Each of the thermistors 121 to 124 is arranged at a substantially central portion in the longitudinal direction of each roller. However, the thermistors 121 to 124 may be within the range of the width of the minimum width size paper or the range corresponding to the width of the minimum width size paper. For example, you may arrange | position in the position remove | deviated from the approximate center part of this longitudinal direction.

  The thermistors 121 to 124 are temperature control thermistors that respectively control the halogen heaters 111 to 114 so as to maintain the surface temperatures of the rollers of the sheet passing unit and the sheet passing corresponding unit at a predetermined target temperature.

  The thermistor 121 is arranged so as to detect the surface temperature of the fixing roller 101, and further on the downstream side of the external heating nip portion N2 in the rotation direction of the fixing roller 101 and on the upstream side of the fixing nip portion N1 in the rotation direction of the fixing roller 101. It is preferable to arrange.

  The thermistor 122 is arranged so as to detect the surface temperature of the pressure roller 102, and further downstream of the external heating nip portion N3 in the rotation direction of the pressure roller 102 and in the rotation direction of the pressure roller 102 in the fixing nip portion N1. It is preferable to arrange on the upstream side.

  Further, the thermistors 121 to 124 may be either contact type or non-contact type temperature detection means for the detection target.

(2-7) Temperature Control of External Heating Members 103 and 104 In the present embodiment, the control circuit unit 130 is connected to the fixing external heating roller 103 and the pressure externally according to the basis weight of the recording material passed through the apparatus. The temperature control set temperature of the heating roller 104 is adjusted as follows. That is, the direction of reducing curl when the recording material is thin paper, that is, a recording material with a small basis weight, and reduction of gloss unevenness on the first side when printing on both sides when the recording material is a thick paper, that is, a recording material with a large basis weight. It adjusts in the direction.

Here, in this embodiment, regarding the basis weight g / m ² of the recording material,
For thin paper (first basis weight recording material) 50 g / m ² or more and less than 64 g / m ^{2 For} plain paper (second (third) basis weight recording material) 64 g / m ² or more Less than 180 g / m ² -For thick paper (recording material having a third (second) basis weight), the amount is 180 g / m ² or more and less than 300 g / m ² .

  Table 1 shows the basis weight of the recording material to be passed at the time of printing and the set temperature of the temperature control of each roller 101 to 104 of the fixing device 100 in the present embodiment (first embodiment: basis weight vs. temperature control). ). Table 2 shows, as Comparative Example 1, the basis weight of the recording material during conventional printing and the set temperature for temperature control of each roller.

  In the present embodiment, as shown in the control flow charts of Table 1 and FIG. 4, the control circuit unit 130 performs the following controls 1) and 2).

  1) When the recording material to be passed through the apparatus has a basis weight of thin paper, the roller 103 as the first external heating member has a predetermined temperature higher than the set temperature when the recording material has a basis weight of plain paper. Adjust the temperature to a lower set temperature. The roller 104, which is the second external heating member, is adjusted to a preset temperature that is higher than the preset temperature when the recording material has a basis weight of plain paper.

  In this embodiment, a thin paper mode can be selected as the first mode, a plain paper mode can be selected as the second mode or the third mode, and a thick paper mode can be selected as the third or second mode. In addition, it is the structure which has a detection apparatus which can detect the basic weight of a recording material, or the numerical value equivalent to a basic weight, Comprising: The structure which switches from a 1st mode to a 3rd mode based on a detection result may be sufficient.

  2) When the recording material to be passed through the apparatus has a basis weight of thick paper, the roller 103 is adjusted to a preset temperature that is higher than the preset temperature when the recording material has a basis weight of plain paper. Adjust the temperature. The temperature of the roller 104 is adjusted to a preset temperature that is lower than the preset temperature when the recording material has a basis weight of plain paper.

  As a result, it is possible to achieve both curl reduction of thin paper and first-surface gloss unevenness reduction during double-sided printing of thick paper.

  Here, the basis weight detection of the recording material will be described. Regarding the basis weight of the recording material, for example, the basis weight information of the recording material used by the user can be input to the control circuit unit 130 from the host device 200 or the operation panel 131. In addition, a recording material information automatic detection means 140 is provided that automatically detects the basis weight of the recording material fed from the paper feed mechanism unit 14 by measuring factors such as thickness, rigidity, electrical resistance, and vibration attenuation. Then, the detected basis weight information can be input to the control circuit unit 130. The control circuit unit 130 adjusts each roller temperature of the fixing device 100 according to Table 1 based on the input recording material basis weight information.

  More specifically, when printing plain paper, for example, as shown in Tables 1 and 2, each roller temperature is set to “medium” (plain paper setting). Each roller temperature setting when printing plain paper is the same in Table 1 and Table 2.

  First, when printing thin paper, as shown in Comparative Example 1 in Table 2, for example, in order to supply heat according to the basis weight of the recording material, the fixing roller temperature is low, the fixing external heating roller temperature is low, The pressure roller temperature was low, and the pressure external heating roller temperature was low. With this setting, the temperature of the fixing external heating roller and the pressure external heating roller are lowered by lowering the temperature of the fixing roller and the pressure roller than when printing on plain paper, thereby reducing the amount of heat supplied to the recording material. Was.

  However, in such a setting, the temperature difference ΔT between the fixing roller 101 and the pressure roller 102 is as large as 75 ° C. For this reason, the curling of the recording material becomes large when printing on thin paper. Due to this curl, the recording material is jammed in the conveyance path after fixing, the recording material is bent, and when printing on both sides, the registration of the front and back (image alignment) becomes unstable due to the curling of the recording material. There was a great possibility that problems such as misalignment of the front and back images would occur.

  Therefore, in this embodiment, when printing thin paper, for example, as shown in Table 1, fixing roller temperature: low, fixing external heating roller temperature: low, pressure roller temperature: high, pressure external heating roller temperature: high , And.

  With this setting, at the time of thin paper printing, the fixing external heating roller temperature is lowered and the pressure external heating roller temperature is raised, thereby lowering the fixing roller temperature and raising the pressure roller temperature. Therefore, the temperature difference ΔT between the fixing roller temperature and the pressure roller temperature can be reduced to 20 ° C. Compared with Comparative Example 1 in Table 2, ΔT is a decrease of 55 ° C. from 75 ° C. to 20 ° C., and compared with plain paper in Table 1, ΔT is 40 ° C. from 60 ° C. to 20 ° C. Decrease in degrees Celsius.

  Therefore, in this embodiment of Table 1, compared with the thin paper setting in Comparative Example 1 in Table 2 and the plain paper setting of this embodiment in Table 1, ΔT is reduced to reduce the thin paper after fixing. Curling could be reduced. Therefore, by reducing the curl of the thin paper, it has been possible to reduce the occurrence of the jamming, corner breakage, front and back image position misalignment, and the like, which have been problems in the past.

  Here, a mechanism for curling the recording material due to a temperature difference between the fixing roller 101 and the pressure roller 102 will be described.

  When the temperature difference ΔT between the fixing roller 101 and the pressure roller 102 is large, that is, the fixing roller temperature is usually higher than the pressure roller temperature. For this reason, when the fixing roller temperature is high and the pressure roller temperature is low, the amount of moisture on the fixing roller surface side is large and the amount of moisture on the pressure roller surface side is small in the recording material. Therefore, the difference in the degree of shrinkage between the front and back of the recording material occurs due to the difference in the amount of moisture decrease between the front and back of the recording material, and the curling of the recording material occurs on the fixing roller surface side. The larger the temperature difference ΔT, the larger the curl amount, and the smaller the temperature difference ΔT, the smaller the curl amount.

  In particular, the curl amount is large in a high humidity environment where the recording material has a small rigidity and a small basis weight, and the recording material has a large moisture content.

  In order to prevent this curl, it is effective to make the temperature difference between the fixing roller 101 and the pressure roller 102 smaller from the above-described curl generation mechanism. Therefore, in the present embodiment, when printing thin paper, the fixing roller temperature is set low and the pressure roller temperature is set high to reduce the temperature difference between the fixing roller and the pressure roller, thereby reducing curling. It is.

  Here, in order to set the pressure roller temperature high, the pressure roller temperature is lowered by passing the recording material through the fixing nip portion N1. Therefore, it is necessary to set the temperature of the pressure external heating roller 104 high, supply a large amount of heat to the pressure roller 102, and maintain the surface temperature of the pressure roller 102 high. In order to maintain the surface temperature of the pressure roller 102 high, it takes time for the amount of heat to reach the surface because the elastic layer 102b is provided only by the internal heater 112 of the pressure roller 102. The external pressure heating roller 104 is essential.

  On the other hand, in order to set the fixing roller temperature low, it is necessary to set the temperature of the fixing external heating roller 103 low, reduce the amount of heat supplied to the fixing roller 101, and keep the surface temperature of the fixing roller 101 low. It is. Since the pressure roller temperature is set higher as the fixing roller temperature is lowered, the fixability of thin paper is good.

  Next, when printing on thick paper, conventionally, as shown in Comparative Example 1 of Table 2, for example, the amount of heat corresponding to the basis weight of the recording material is supplied, so the fixing roller temperature is high, and the fixing external heating roller temperature is high. The pressure roller temperature was high, and the pressure external heating roller temperature was high. With this setting, the temperature of the fixing external heating roller and the pressure external heating roller are increased to increase the temperature of the fixing roller and the pressure roller, thereby increasing the amount of heat supplied to the recording material, compared to when printing on plain paper. By doing so, the fixing property of the cardboard was secured.

  However, in the case of such a setting, as described above, since the temperature of the pressure roller 102 is high, there is a high possibility that the problem of uneven glossiness will occur on the first side during double-sided printing of thick paper. This is because if the pressure roller temperature is high, the toner image on the first side is remelted by the high-temperature pressure roller when fixing the second side of the thick paper. At this time, if the toner image on the first side can be uniformly remelted, the gloss only increases and gloss unevenness does not occur.

  However, the surface temperature of the pressure roller 102 is high because it contacts the fixing roller 101 between the sheets, and the temperature of the sheet passing portion is low. There was a high possibility that uneven glossiness between papers would occur.

  Further, since the thick paper takes more heat from the pressure roller 102 than the thin paper, the surface temperature of the pressure roller 102 is greatly reduced. Therefore, for a recording material longer than one rotation of the pressure roller 102, the surface temperature is high at the first rotation of the pressure roller, so that the increase in gloss is large, and the surface temperature is low after the first rotation of the pressure roller. . For this reason, there is a great possibility that uneven glossiness in the circumferential direction of the pressure roller that causes a small increase in gloss will occur.

  Here, the inventors have found that the inter-paper gloss unevenness and the circumferential gloss unevenness hardly occur when the pressure roller temperature is low. This is because by setting the pressure roller temperature low, the absolute value of the gloss increase due to remelting of the first side during double-sided printing is reduced, and gloss unevenness is less noticeable. Further, the surface temperature of the pressure roller 102 is somewhat affected by the fixing device and the toner material. However, when the temperature is about 100 ° C. or less, the gloss unevenness is hardly noticeable and almost at a problem-free level. is there.

  Therefore, in this embodiment, when printing thick paper, for example, as shown in this embodiment in Table 1, the fixing roller temperature is high, the fixing external heating roller temperature is high, the pressure roller temperature is low, and the pressure external heating is performed. Roller temperature: Low.

  With this setting, during at least double-sided printing of thick paper, the fixing external heating roller temperature is raised and the pressure external heating roller temperature is lowered to raise the fixing roller temperature and lower the pressure roller temperature. Therefore, the pressure roller temperature can be maintained at about 100 ° C. This is a 40 ° C. decrease from 140 ° C. to 100 ° C. compared to Comparative Example 1 in Table 2, and a 20 ° C. decrease from 120 ° C. to 100 ° C. compared to the plain paper in Table 1.

  Therefore, in this embodiment of Table 1, compared to the thick paper setting in Comparative Example 1 of Table 2 and the plain paper setting of this embodiment in Table 1, the pressure roller temperature is lowered to reduce both sides of the thick paper. Gloss unevenness on the first side during printing could be reduced.

  Therefore, in the present embodiment, when printing on both sides of thick paper, the fixing roller temperature is set high and the pressure roller temperature is set low to reduce gloss unevenness on the first side.

  Here, in order to set the pressure roller temperature low, the temperature of the pressure external heating roller is set low, the amount of heat supplied to the pressure roller is reduced, and the surface temperature of the pressure roller is kept low. is necessary.

  On the other hand, in order to set the fixing roller temperature high, the fixing roller temperature is lowered by passing the recording material through the fixing nip portion N1. Therefore, it is necessary to set the temperature of the fixing external heating roller high, supply a large amount of heat to the fixing roller, and maintain the surface temperature of the fixing roller high. In order to maintain the surface temperature of the fixing roller at a high level, only the internal heater of the fixing roller has an elastic layer, so it takes time for the amount of heat to reach the surface. is there.

  Further, even when the fixing roller has no elastic layer, in order to keep the surface temperature of the fixing roller high, the core metal temperature of the fixing roller becomes high, so that an external fixing heating member is essential. The fixing roller temperature contributes more to the fixing property than the pressure roller temperature, and the fixing roller temperature is set higher because the pressure roller temperature is lowered. It is.

  Therefore, in this embodiment, when printing thin paper (small basis weight), the temperature of the first external heating member is low, and the temperature of the second external heating member is high. When printing on thick paper (large basis weight), the temperature of the first external heating member is high, and the temperature of the second external heating member is low. As a result, it was possible to achieve both curl reduction of thin paper and reduction of glossiness unevenness on the first side during double-sided printing of thick paper.

  In this embodiment, it is possible to select a single-side mode in which an image is formed only on one side of the recording material and a double-side mode in which an image is formed on both sides of the recording material. At this time, in this embodiment, the set temperatures in the single-side mode and the double-side mode are the same set temperatures, and the set temperatures are based on Table 1.

  In this embodiment, the fixing device in which the halogen heater 112 is disposed inside the pressure roller 102 has been described. However, the effect of the present invention is the same in a fixing device in which the halogen heater 112 is omitted. If there is no halogen heater 112, the thermistor 122 may be omitted.

  When there is no heating source inside the pressure roller 102, the pressure external heating roller 104 is brought into contact with the pressure roller 102 even during standby, and a drive source (not shown) for rotating the pressure roller 102 is added and rotated. good. Therefore, even during standby, the surface of the pressure roller 102 is heated at a predetermined temperature by the pressure external heating roller 104, so that the fixability is improved. Further, when there is no heating source inside the pressure roller 102, a pressure external heating roller 104 for heating the pressure roller 102 is essential.

<Second Embodiment>
In the present embodiment, the control circuit unit 130 sets the temperature control of the fixing external heating roller 103 and the pressure external heating roller 104 according to the type (paper type) of the recording material that is passed through the apparatus. It is characterized by adjusting the temperature as follows. In other words, when the recording material is glossy paper, adjustment is made in a direction to reduce gloss unevenness on the first side during duplex printing.

  Table 3 shows the type of recording material to be passed during printing and the set temperature for temperature control of each of the rollers 101 to 104 of the fixing device 100 in the present embodiment (second embodiment: paper type vs temperature control). . Table 2 shows, as Comparative Example 1, the paper type of the recording material at the time of conventional printing and the set temperature for temperature control of each roller.

  As shown in the control flow charts of Table 3 and FIG. 5, when the recording material to be passed through the apparatus is glossy paper (coated paper), the control circuit unit 130 uses plain paper as the recording material for the roller 103. The temperature is adjusted by adjusting to a preset temperature higher than the preset temperature in a certain case. In this embodiment, the coated paper is a paper whose surface is coated with a resin.

  Further, the roller 104 is adjusted by adjusting the temperature to a preset temperature lower than the preset temperature when the recording material has a basis weight of plain paper. As a result, it is possible to reduce the gloss unevenness on the first side during double-sided printing on a paper type with high glossiness, for example, coated paper. Note that, similarly to the first embodiment, the set temperatures of the single-side mode and the double-side mode are also common in this embodiment.

  Here, the paper type detection of the recording material will be described. As the type of the recording material, for example, the type information of the recording material used by the user can be input from the host device 200 or the operation panel 131. As the recording material type information, for example, on the operation panel 131, for example, “plain paper (quality paper)”, “double-side coated paper”, “single-side coated paper”, “recycled paper”, “OHT”, “embossed paper” The user selects the type of recording material used by the user. In an image forming apparatus having a plurality of paper feed cassettes for storing recording materials, it is preferable to select the type of recording material for each paper feed cassette.

  Further, a recording material information detecting means 140 for automatically detecting the type of recording material fed from the paper feed mechanism unit 14 by measuring a factor such as glossiness is provided, and the detection type information is controlled. Input to the circuit unit 130 is also possible. The control circuit unit 130 adjusts each roller temperature of the fixing device 100 according to Table 3 based on the input recording material type information.

  More specifically, when printing plain paper, each roller temperature is set to “medium” as shown in Tables 3 and 4, for example. Each roller temperature setting at the time of printing plain paper is the same in Table 3 and Table 4.

When printing glossy paper (medium basis weight, 64-180 [g / m ² ]), for example, double-sided coated paper, conventionally, for example, as shown in Comparative Example 2 in Table 4, the amount of heat corresponding to the type of recording material is set. To supply,
Fixing roller temperature: High Fixing external heating roller temperature: High Pressure roller temperature: High Pressure external heating roller temperature: High

  With this setting, the temperature of the fixing external heating roller and the pressure external heating roller are increased to increase the temperature of the fixing roller and the pressure roller, thereby increasing the amount of heat supplied to the recording material, compared to when printing on plain paper. By doing so, the fixing property of the coated paper was secured.

  Here, the coated paper has a higher thermal conductivity than the plain paper having the same basis weight because of the coated layer. Therefore, in order to melt the toner on the coated paper, more heat is consumed by the fixing roller and the pressure roller in the coated paper than in the plain paper. Therefore, in order to ensure the fixing property, it is necessary to increase the temperature of the fixing roller 101 and the pressure roller 102 and supply more heat.

  In addition, there are various types of coated paper, and gloss coated paper with high glossiness requires a larger amount of heat because of its thick coat layer in order to ensure fixing properties, and gloss coated paper with low glossiness. Since the coat layer is thin, not much heat is required.

  However, in such a setting, since the temperature of the pressure roller 102 is high, there is a high possibility that the problem of uneven glossiness will occur on the first side during double-sided printing of coated paper. This is because, as described above, if the pressure roller temperature is high, the toner image on the first surface is remelted by the high-temperature pressure roller 102 when the second surface of the coated paper is fixed. Further, as described above, this gloss unevenness includes inter-paper gloss unevenness and circumferential gloss unevenness.

  The gloss unevenness is more noticeable in the gloss coated paper than the plain paper because the gloss of the toner image is greatly increased when the surface of the recording material is smooth. Further, even with coated paper, matte coated paper whose recording material has a non-smooth surface is less likely to cause gloss unevenness because the increase in gloss of the toner image is small. Therefore, the case where the coated paper of this embodiment is a double-sided gloss coated paper will be described.

  Here, in the coated paper, when the pressure roller temperature is low, gloss unevenness is less likely to occur as in the case of thick paper. When the pressure roller surface temperature is about 100 ° C. or less, The gloss unevenness is more suitable because it is at a level with almost no problem.

  Therefore, in the present embodiment, when coated paper is printed, as shown in Table 3, for example, fixing roller temperature: high, fixing external heating roller temperature: high, pressure roller temperature: low, pressure external heating roller temperature: Low.

  With this setting, during at least double-sided printing of the coated paper, the fixing external heating roller temperature is raised and the pressure external heating roller temperature is lowered to raise the fixing roller temperature and lower the pressure roller temperature. Therefore, the pressure roller temperature can be maintained at about 100 ° C. This is a 40 ° C. decrease from 140 ° C. to 100 ° C. compared to Comparative Example 2 in Table 4, and a 20 ° C. decrease from 120 ° C. to 100 ° C. compared to the plain paper in Table 1.

  Therefore, in the present embodiment shown in Table 3, compared with the coated paper setting in Comparative Example 2 in Table 4 and the plain paper setting in the present embodiment shown in Table 3, the pressure roller temperature is lowered to reduce the coating paper. It was possible to reduce uneven glossiness on the first side when printing on both sides of paper.

  Therefore, in the present embodiment, during double-sided printing of glossy paper (coated paper), the fixing roller temperature is set high and the pressure roller temperature is set low to reduce gloss unevenness on the first side.

  The fixing roller temperature has a larger contribution than the pressure roller temperature, and the fixing roller temperature is set higher because the pressure roller temperature is lowered. It is good.

  Therefore, in the present embodiment, when printing plain paper, the temperature of the first external heating member is medium and the temperature of the second external heating member is medium. When glossy paper is printed, the temperature of the first external heating member is high, and the temperature of the second external heating member is low. As a result, it was possible to reduce the first-side gloss unevenness when printing on both sides of glossy paper.

<Third Embodiment>
In the present embodiment, the control circuit unit 130 sets the temperature adjustment temperature of the roller 103 as the first external heating member and the temperature of the roller 104 as the second external heating member according to the environmental temperature. It is characterized in that it is adjusted in a direction to ensure the fixing property.

  Table 5 shows the environmental temperature at the time of printing and the temperature control setting temperature of each of the rollers 101 to 104 of the fixing device 100 according to the present embodiment (third example: environmental temperature vs. temperature control). Here, in this embodiment, regarding the environmental temperature, 20 ° C. is set as a set temperature, 20 ° C. or higher (set temperature or higher) is set as a normal temperature environment, and less than 20 ° C. (lower than set temperature) is set as a low temperature environment.

  As shown in the control flow charts of Table 5 and FIG. 6, when the environment is a low temperature environment, the control circuit unit 130 sets a predetermined temperature for the rollers 103 and 104 than the set temperature when the environment is a normal temperature environment. The temperature is adjusted to a high preset temperature. Thereby, fixability can be ensured in a low-temperature environment, for example, according to the environmental temperature.

  That is, as shown in Table 5, during printing in a normal temperature environment, the temperature of the roller 103 as the first external heating member is medium: the temperature of the roller 104 as the second external heating member is medium. At the time of printing in a low temperature environment, the temperature of the roller 103 is high and the temperature of the roller 104 is high. Thereby, fixability can be secured even in a low temperature environment.

  Here, environmental temperature detection will be described. The environmental temperature is detected by, for example, an environmental detection unit 150 disposed in the image forming apparatus main body. The environment detection unit 150 is preferably arranged in the vicinity of the outer peripheral surface that is not easily affected by the heat of the image forming apparatus main body in order to detect the environment of the atmosphere outside the image forming apparatus. The environment information is detected by the environment detection unit 150, and the control circuit unit 130 obtains the environment information. Further, the control circuit unit 130 adjusts each roller temperature of the fixing device 100 according to Table 5 based on the environmental information, and in the case of the present embodiment, based on the environmental temperature.

More specifically, when printing in a normal environment of plain paper (medium basis weight, 64-180 [g / m ² ]), for example, an environment of 20 ° C. or higher, as shown in Table 5, for example, each roller Set the temperature to the “medium” setting. Conventionally, when printing on plain paper, printing has been performed at an environmental temperature of less than 20 ° C., for example, at an environmental temperature of 20 ° C. or higher in Table 5 regardless of the environmental temperature.

  However, in such a setting, in a low temperature environment, since the temperature of the recording material is also low, there is a high possibility that the problem that the fixing property is lowered occurs. Therefore, in this embodiment, at the time of printing in a low temperature environment, for example, as shown in Table 5 below 20 ° C., fixing roller temperature: high, fixing external heating roller temperature: high, pressure roller temperature: high, external pressure The heating roller temperature is high.

  With this setting, at the time of printing in a low temperature environment, the fixing roller temperature and the pressure roller temperature are increased by increasing the fixing external heating roller temperature and the pressing external heating roller temperature. Therefore, in this embodiment of Table 5, as compared with the setting of 20 ° C. or higher, the amount of heat supplied to the recording material is increased at the setting of less than 20 ° C., thereby ensuring the fixing property of the recording material even in a low temperature environment. can do.

  Here, in order to set the fixing roller temperature and the pressure roller temperature high, the fixing roller temperature and the pressure roller temperature are lowered by passing the recording material through the fixing nip portion N1. Therefore, the fixing external heating roller temperature and the pressure external heating roller temperature are set high, a large amount of heat is supplied to the fixing roller 101 and the pressure roller 102, and the surface temperatures of the fixing roller 101 and the pressure roller 102 are set. It is necessary to keep it high.

  In order to keep the surface temperatures of the fixing roller 101 and the pressure roller 102 high, the internal heaters 111 and 112 of the fixing roller 101 and the pressure roller 102 respectively have elastic layers 101b and 102b. It takes time to reach the heat amount. Therefore, the fixing external heating roller 103 and the pressure external heating roller 104 are essential.

  Therefore, in the present embodiment, when printing in the normal temperature environment, the temperature of the first external heating member: medium, the temperature of the second external heating member: medium, when printing in the low temperature environment, the first external heating member The temperature of the second external heating member is high. As a result, the fixing property can be secured even in a low temperature environment.

  In this embodiment, the temperature rise width of the pressure external heating roller is set to be larger than the temperature rise width of the fixing external heating roller. The reason is as follows. In the case of a low temperature environment, the temperature of the recording material is low. In order to obtain sufficient fixability, it is necessary to warm the low-temperature recording material. If the recording material is heated by the fixing roller, it is necessary to increase the temperature increase of the fixing roller, and as a result, the toner on the surface is excessively melted.

  Therefore, in this embodiment, the pressure roller actively heats the recording material, so that the temperature increase of the fixing roller can be reduced. As a result, the toner on the fixing roller is excessively melted (hot) Offset) can be reduced.

  In this embodiment, the case of plain paper has been described. However, when the environmental temperature is less than 20 degrees as in this embodiment, the temperature of the fixing roller 101 is + 5 ° C., the temperature of the fixing external heating roller 103 is + 10 ° C., and the temperature of the pressure roller. Is set to + 20 ° C., and the temperature of the pressure external heating roller is set to + 30 ° C.

<Fourth Embodiment>
In this embodiment, the control circuit unit 130 increases the temperature adjustment set temperatures of the roller 103 as the first external heating member and the roller 104 as the second external heating member, respectively, according to the environmental humidity. It adjusts in the direction which reduces the curl in a humid environment, It is characterized by the above-mentioned.

  Table 6 shows the environmental humidity during printing and the set temperature of the temperature control of each of the rollers 101 to 104 of the fixing device 100 in the present embodiment (fourth embodiment: environmental humidity vs. temperature control). Here, in this embodiment, the absolute moisture amount calculated from the environmental temperature and the relative humidity is used as the environmental humidity. The absolute water content is the water content [g / Kg] per 1 kg of air. As the absolute moisture content, for example, 13 [g / Kg] is an installation value, and less than 13 [g / Kg] (less than the installation value) is a normal humidity environment, and 13 [g / Kg] or more (more than the installation value) is high. It is a humid environment.

  As shown in the control flow charts of Table 6 and FIG. 7, when the environment is a high humidity environment, the control circuit unit 130 sets the roller 103103) to a predetermined temperature higher than the set temperature when the environment is a normal humidity environment. Adjust the temperature to a lower set temperature. The temperature of the roller 104 is adjusted to a preset temperature that is higher than the preset temperature when the environment is a normal humidity environment. Thereby, the curl of the recording material can be reduced according to the environmental humidity, for example, in a high humidity environment.

  That is, as shown in Table 6, when printing in a normal humidity environment, the temperature of the first external heating member: medium, the temperature of the second external heating member: medium, when printing in a high humidity environment, the first The temperature of the external heating member is low, and the temperature of the second external heating member is high. Thereby, curl can be reduced even in a high humidity environment.

  Here, environmental humidity detection will be described. The environmental temperature / humidity is detected by, for example, the environment detection unit 150. The environment detection unit 150 is preferably arranged in the vicinity of the outer peripheral surface that is not easily affected by the heat of the image forming apparatus main body in order to detect the environment of the atmosphere outside the image forming apparatus. The environment information is detected by the environment detection means 150, and the control circuit unit 130 obtains the environment information. Further, the control circuit unit 130 adjusts each roller temperature of the fixing device 100 according to Table 6 based on the environmental information, and in the case of the present embodiment, based on the absolute moisture amount calculated from the environmental temperature and humidity. .

More specifically, when printing a normal paper (medium basis weight, 64-180 [g / m ² ]) in a normal humidity environment, for example, when the absolute water content is less than 13 [g / Kg], for example, Table 6 Each roller temperature is set to “medium” as shown in FIG. Conventionally, when printing on plain paper, regardless of the environmental humidity, for example, the normal humidity environment shown in Table 6, that is, the absolute water content: less than 13 [g / Kg], the high humidity environment, that is, the absolute water content: 13 g / Kg] or more was also printed.

  However, in such a setting, the moisture content of the recording material becomes large even in plain paper in a high humidity environment. For this reason, the curling of the recording material is increased, and as described above, there is a high possibility that problems such as jamming of the recording material, corner breakage, and image position misalignment between the front and back sides will occur.

  Therefore, in this embodiment, when printing in a high humidity environment, for example, as shown in Table 6 in which the absolute water content is 13 [g / Kg] or more, the fixing roller temperature is low, the fixing external heating roller temperature is low, the heating is Pressure roller temperature: high, pressure external heating roller temperature: high.

  With this setting, when printing in a high humidity environment, the fixing external heating roller temperature is lowered and the pressure external heating roller temperature is raised, thereby lowering the fixing roller temperature and raising the pressure roller temperature. Therefore, the temperature difference ΔT between the fixing roller temperature and the pressure roller temperature can be reduced to 25 ° C. Compared with the absolute water content of Table 6 below 13 [g / Kg], ΔT decreases by 35 ° C. from 60 ° C. to 25 ° C.

  Therefore, since the printing has been conventionally performed under the setting of the normal humidity environment (absolute water content: less than 13 [g / Kg]) even in a high humidity environment (absolute water content: 13 [g / Kg] or more), the curling of the recording material. Was getting bigger. On the other hand, in Table 6, curling after fixing in a high humidity environment could be reduced by changing the temperature setting of each roller in a high humidity environment to reduce ΔT. Therefore, by reducing the curl in a high humidity environment, it has been possible to reduce the occurrence of jamming, corner folding, front and back image position misalignment, and the like, which have been problems in the past.

  Here, in order to set the pressure roller temperature high, the pressure roller temperature is lowered by passing the recording material through the fixing nip portion N1. Therefore, it is necessary to keep the surface temperature of the pressure roller 102 high by setting the temperature of the pressure external heating roller 104 high and supplying a large amount of heat to the pressure roller 102. In order to maintain the surface temperature of the pressure roller 102 high, it takes time for the amount of heat to reach the surface because the elastic layer 102b is provided only by the internal heater 112 of the pressure roller 102. The external pressure heating roller 104 is essential.

  On the other hand, in order to set the fixing roller temperature low, it is necessary to set the temperature of the fixing external heating roller 103 low, reduce the amount of heat supplied to the fixing roller 101, and keep the surface temperature of the fixing roller 101 low. It is. Since the pressure roller temperature is set higher as the fixing roller temperature is lowered, the fixability in a high humidity environment is good.

  Therefore, in the present embodiment, when printing in a normal humidity environment, the temperature of the first external heating member is medium, and the temperature of the second external heating member is medium. At the time of printing in a high humidity environment, the temperature of the first external heating member is low, and the temperature of the second external heating member is high. As a result, curling could be reduced even in a high humidity environment. In this embodiment, the case of plain paper has been described. However, when the absolute water content is 13 [g / Kg] or more as in this embodiment, the temperature of the fixing roller 101 is −5 ° C. and the temperature of the fixing external heating roller 103 is −10 with respect to Table 3. The temperature of the pressure roller is set to + 30 ° C, and the pressure of the pressure external heating roller is set to + 30 ° C.

  The numerical values and schematic diagrams in each of the above-described embodiments are examples for simplifying the description, and can be arbitrarily determined according to the configuration and settings of the image forming apparatus and the fixing apparatus.

  Further, the present invention is not limited to the fixing device described in each embodiment, and can be applied to other types of fixing devices such as any combination of the embodiments.

  Therefore, in the present embodiment, the external heating roller is used as the external heating member. However, for example, the external heating performance is improved by using an external heating belt in which a belt is stretched around a plurality of external heating rollers as the external heating member. The effect of the present invention is also the same in the fixing device.

  In this embodiment, the halogen heater is used as the heating source. However, the effect of the present invention is equivalent to a fixing device using another heating source such as a resistance heating element or an electromagnetic induction heating method. .

  The image heating device according to the present invention is not limited to use as the fixing device of the embodiment. It can also be effectively used as a gloss increasing device (image modifying device) that increases the gloss of the image by heating the image fixed on the recording material.

  The image forming apparatus is not limited to the electrophotographic system of the embodiment, and forms a mono-color image or a full-color image (multicolor image) on a recording material in an image forming unit by various other principle processes and systems such as an electrostatic recording system. It can be an image forming apparatus.

  DESCRIPTION OF SYMBOLS 100 ... Fixing apparatus, 101 ... Fixing roller (heating rotary body), 102 ... Pressure roller (pressure rotary body), 103 ... Fixing external heating roller (1st external heating member), 104... Pressurized external heating roller (second external heating member), 111, 112, 113, 114... Halogen heater (heating source), 121, 122, 123, 124. ), 130... Control circuit (CPU: control means), 140... Recording material information detection means, 150... Environment detection means (temperature / humidity detection means), P. ..Toner (image)

Claims (10)

A heating rotator that contacts and heats an image formed on the recording material, a pressure rotator that pressurizes the heating rotator and forms a nip portion that sandwiches and conveys the recording material, and a surface of the heating rotator. The first external heating member that heats the heating rotator, the second external heating member that contacts the surface of the pressure rotator and heats the pressure rotator, and the first In the image heating apparatus, comprising: a control means for controlling the temperature of the external heating member and the second external heating member so as to reach a predetermined set temperature.
The control means sets the set temperature of the second external heating member in the first mode for heating the image formed on the recording material of the first basis weight to a recording material larger than the first basis weight. An image heating apparatus, wherein the temperature is set to be higher than a set temperature of the second external heating member in the second mode for heating the formed image.   The control means sets the set temperature of the first external heating member in the first mode for heating the image formed on the recording material of the first basis weight to a recording material larger than the first basis weight. The image heating apparatus according to claim 1, wherein the image heating apparatus is set to be lower than a set temperature of the second external heating member in the second mode in which the formed image is heated. A heating rotator that contacts and heats an image formed on the recording material, a pressure rotator that pressurizes the heating rotator and forms a nip portion that sandwiches and conveys the recording material, and a surface of the heating rotator. The first external heating member that heats the heating rotator, the second external heating member that contacts the surface of the pressure rotator and heats the pressure rotator, and the first In the image heating apparatus, comprising: a control means for controlling the temperature of the external heating member and the second external heating member so as to reach a predetermined set temperature.
The control means sets the set temperature of the second external heating member in the first mode for heating the image formed on the recording material of the first basis weight to a recording material smaller than the first basis weight. An image heating apparatus, wherein the temperature is set to be lower than a set temperature of the second external heating member in the second mode in which the formed image is heated.   The control means sets the set temperature of the first external heating member in the first mode for heating the image formed on the recording material of the first basis weight to a recording material smaller than the first basis weight. The image heating apparatus according to claim 3, wherein the image heating apparatus is set higher than a set temperature of the second external heating member in the second mode in which the formed image is heated.   Setting temperature of the second external heating member when heating the image formed on the first surface of the recording material and setting of the second external heating member when heating the image formed on the second surface of the recording material The image heating apparatus according to claim 1, wherein the temperatures are the same.   Setting temperature of the first external heating member when heating the image formed on the first surface of the recording material and setting of the first external heating member when heating the image formed on the second surface of the recording material 6. The image heating apparatus according to claim 1, wherein the temperatures are the same.   The setting temperature of the second external heating member when the recording material coated with resin is passed through the recording material with the first basis weight is the same as the set temperature when passing the recording material with the first basis weight. 7. The image heating apparatus according to claim 1, wherein the temperature is lower than a set temperature of the external heating member.   The set temperature of the first external heating member when the recording material coated with resin is passed through the recording material with the first basis weight is the first temperature when the recording material with the first basis weight is passed. The image heating apparatus according to claim 1, wherein the image heating apparatus is set to be higher than a set temperature of one external heating member.   When the environmental temperature is lower than the set temperature, the set temperature of the second external heating member and the set temperature of the first external heating member are increased to increase the set temperature of the second external heating member. The image heating apparatus according to any one of claims 1 to 8, wherein the image heating device is larger than a range in which the set temperature of the first external heating member is increased.   2. The absolute temperature of the first external heating member is decreased when the absolute water content is equal to or higher than a set value, and the set temperature of the second external heating member is increased. The image heating apparatus according to claim 9.