JP4757046B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device which is a heating device that heats a material to be heated by nipping and conveying the material to be heated. In particular, the present invention relates to an image forming apparatus including a fixing device that fixes a toner image carried on a transfer material by heating and pressing.

  Conventionally, a heat roller system is used as a heating device that heats and fixes an unfixed toner image that is indirectly formed (that is, transferred) or directly supported on a transfer material by an image forming means such as an electrophotographic process as a permanently fixed image on the transfer material surface. The heating device is widely used.

  In recent years, a film heating type heating apparatus has been put into practical use from the viewpoint of quick start and energy saving. There has also been proposed an electromagnetic induction heating type heating device for generating heat from a metal film itself. Each will be described below.

a) Film heating type heating device A film heating type heating device has been proposed in, for example, Patent Documents 1 to 4 listed below.

  FIG. 3 shows a schematic configuration of a film heating type heating apparatus. The heating device of the film heating system includes a heat-resistant film 20 (hereinafter, a fixing belt) sandwiched between a ceramic heater 23 as a heating body and a pressure roller 21 as a pressure member, and a pressure nip portion N (hereinafter, referred to as a pressure contact nip N). , Fixing nip portion). In the fixing nip N, a transfer material P on which an unfixed toner image t is formed and supported is introduced between the fixing belt 20 and the pressure roller 21 and is nipped and conveyed together with the fixing belt 20. Accordingly, the unfixed toner image t is fixed on the transfer material surface by the pressure of the pressure roller 21 in the fixing nip portion N while applying heat of the ceramic heater 23 to the transfer material P via the fixing belt 20.

  In recent years, with the downsizing of image forming apparatuses, the outer diameter (film outer diameter) of the fixing belt 20 tends to be reduced. However, the pressure roller 21 having an elastic layer needs to have a certain size in order to secure a fixing nip. Further, when the fixing belt 20 and the pressure roller 21 have the same diameter, the offset toner continues to rotate in the same cycle, and the fixing belt 20 and the pressure roller 21 may be damaged. For this reason, the fixing belt 20 and the pressure roller 21 often have different outer diameters.

  This film heating type heating device can be configured as an on-demand type device by using a low heat capacity member for the ceramic heater 23 and the fixing belt 20. In this on-demand type apparatus, it is only necessary to energize the ceramic heater 23 as a heat source only when an image forming operation is performed to generate heat at a predetermined fixing temperature. As a result, there are advantages such as a short waiting time from the power-on of the image forming apparatus to the state in which the image forming operation can be executed, and a significant reduction in power consumption during standby.

b) Heating device using a metal film for a fixing belt In recent years, with the increase in speed and color of image forming apparatuses, in a heating device of a film heating system, a metal film such as SUS (Steel Use Stainless) or nickel as a fixing belt. There has been proposed a heating apparatus using the. Further, a heating device using a fixing belt in which an elastic layer is provided on a metal film has been proposed.

  Conventionally, a heat-resistant resin or the like has been used as the base material of the fixing belt. However, with the increase in the speed of the image forming apparatus, it has become necessary to increase the heat conductivity of the fixing belt and more efficiently transfer the heat of the ceramic heater to the transfer material. Therefore, it is preferable to use a metal having a higher thermal conductivity than the resin as the fixing belt substrate. A heating device using such a metal fixing belt is optimal for a metal sleeve having sufficient strength and excellent durability in order to constitute a long-life heating device, with a thickness of 20 μm to 100 μm. (For example, see Patent Document 5 or Patent Document 6 below).

  Further, with the colorization of the image forming apparatus, it has become necessary to provide an elastic layer on the base material of the fixing belt. Examples of such a fixing belt and an image forming apparatus are disclosed in, for example, Patent Document 7 or Patent Document 8 below.

  This is because in the conventional film heating device, the surface of the fixing belt cannot follow the shape of the toner image in the portion where the toner image is transferred in multiple, and the unevenness of the fixing property occurs partially. . This unevenness of fixing property appears as uneven glossiness of the image. Further, in OHT (transparent sheet for overhead projector), there is a problem of uneven transmission, and this unevenness of transparency appears as an image defect when projected.

  In contrast, by providing an elastic layer on the fixing belt, the elastic layer is deformed along the toner layer, so that the non-uniform toner is enveloped by the elastic layer and uniformly heated. A uniform fixing of the toner image is achieved.

c) Electromagnetic Induction Heating Type Heating Device For example, Patent Document 9 below discloses an induction heating device that induces eddy currents in a metal layer (heating layer) of a fixing belt by magnetic flux and generates heat by its Joule heat. Yes. This can generate heat directly from the fixing belt by using the generation of induced current, and achieves a more efficient fixing process than a heat roller type heating device using a halogen lamp as a heat source.

  Such an electromagnetic induction heating type heating device uses a thin metal of about 50 μm as a fixing belt. Further, when an electromagnetic induction heating type heating device is applied to a color image forming apparatus, a fixing belt having an elastic layer on a metal layer is used.

<Temperature control>
The temperature control of the heating device is performed as follows. That is, the output of the thermistor as a temperature detection element provided on the ceramic heater is A / D converted and taken into the CPU. And based on the information, the phase of AC voltage and the wave number control etc. which are supplied with electricity to a heating body by triac are performed. Thus, the heating body energizing power is controlled.

At this time, the target temperature setting is changed in a plurality of stages in accordance with the number of prints of one job in consideration of an increase in the pressure roller temperature caused by overlapping the number of prints (for example, see Patent Document 10 below). Further, with the downsizing and quick start of the image forming apparatus as described above, the fixing belt and the pressure roller have become smaller in diameter. Therefore, when the heat capacity of the pressure roller is reduced and the heat of the pressure roller is taken away by the transfer material due to the passage of the transfer material, the transfer material (mainly the rear end of the transfer material) at the part where the temperature has dropped. The fixability of the toner image sometimes deteriorated. In response to this, the fixing temperature adjustment temperature is increased from the front end to the rear end of the transfer material within one transfer material (see, for example, Patent Document 11 below).
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP 2003-045615 A JP 2003-156554 A Japanese Patent Laid-Open No. 10-10893 Japanese Patent Laid-Open No. 11-15303 Japanese Utility Model Publication No. 51-109739 Japanese Patent Laid-Open No. 2004-117853 JP 2001-100588 A

  However, as described above, with the colorization of the image forming apparatus, the thermal conductivity of the heating member is lowered by providing an elastic layer on the base material of the fixing belt, and a heat storage effect is produced like the pressure roller. End up. Therefore, according to the conventional example, the supply of heat from the fixing belt to the transfer material is greatly insufficient. As a result, there is a problem that non-uniformity due to insufficient heat supply occurs not only in the pressure roller cycle but also in the fixing belt cycle. This periodic unevenness appears notably as gloss unevenness particularly in a color image that requires high gloss.

The present invention has been made in view of such problems, and an object of the present invention is to provide a fixing device capable of suppressing the occurrence of uneven gloss and obtaining a stable image quality.

  The present invention has been made to solve the above-described problems, and includes the following configuration.

(1) A cylindrical fixing belt, a heater that contacts the inner surface of the fixing belt, a pressure roller that forms a fixing nip with the heater via the fixing belt, and a temperature detection that detects the temperature of the heater. And a control means for controlling the power supplied to the heater so that the detected temperature of the temperature detecting element maintains a set temperature, and the recording paper carrying the toner image is sandwiched and conveyed at the fixing nip portion. In a fixing device that heats and fixes a toner image on a recording sheet,
The control means includes: a first control for gradually increasing the set temperature within a period in which one sheet of recording paper moves through the fixing nip, and a period of the circumference of the pressure roller; Can be set in a period during which the fixing nip portion is moved, and the set temperature is gradually increased with the circumference of the fixing belt as a cycle. The second control is the first control. The fixing device is set when the temperature of the pressure roller is higher than when the control is set.
(2) When a plurality of recording sheets are continuously fixed, the second control is set in a period in which the number of processed sheets is larger than a period in which the first control is set. The fixing device according to 1).
(3) The fixing device according to (1), wherein the first control is started after the recording paper has passed through the fixing nip portion for one round of the fixing belt .

According to the present invention, it is possible to provide a fixing device that can suppress the occurrence of uneven glossiness and obtain stable image quality.

  The best mode for carrying out the present invention will be described based on the following examples.

  However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

  Hereinafter, a heating apparatus according to the present embodiment and an image forming apparatus including the heating apparatus will be described by taking a full-color image forming apparatus employing the above-described heating apparatus of the film heating method as an example. FIG. 2 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment.

  The image forming apparatus according to this embodiment is a full-color image forming apparatus that obtains a full-color image by superimposing four color toner images of yellow, cyan, magenta, and black using an electrophotographic system. The process speed of the full-color image forming apparatus according to the present embodiment is 90 mm / sec. The number of printed sheets per minute is 16 US letter size paper. Further, the time (FPOT) to the first print (First Page Out) is about 15 seconds. However, the process speed, the number of printed sheets per minute, and the FPOT are naturally not limited to these.

  In FIG. 2, 1Y, 1C, 1M and 1K are photosensitive drums as image carriers, and 3Y, 3C, 3M and 3K are charging rollers as charging means. 2Y, 2C, 2M and 2K are developing rollers as developing means for developing the electrostatic latent image, and 4Y, 4C, 4M and 4K are cleaning blades as cleaning means for the photosensitive drums 1Y to 1K. is there. The image forming apparatus according to the present embodiment uses a so-called all-in-one toner cartridge in which the photosensitive drums 1Y to 1K, the charging rollers 3Y to 3K, the developing rollers 2Y to 2K, the cleaning blades 4Y to 4K, and the like are collected in one container. ing.

  Examples of the toner cartridge include a yellow cartridge, a magenta cartridge, a cyan cartridge, and a black cartridge in which a yellow (Y), magenta (M), cyan (C), and black (K) toner is filled in a developing container (not shown). I am using it.

  Further, an optical system as an exposure unit that exposes the photosensitive drums 1Y to 1K to form an electrostatic latent image is provided corresponding to each toner cartridge. In this embodiment, a laser beam scanner 5 which is a laser scanning exposure optical system is used as an optical system.

  Scanning light based on the image data from the laser beam scanner 5 exposes the photosensitive drums 1Y to 1K uniformly charged by the charging rollers 3Y to 3K. Thereby, electrostatic latent images corresponding to the image data are formed on the surfaces of the photosensitive drums 1Y to 1K. Further, by setting the developing bias applied to the developing rollers 2Y to 2K from a bias power source (not shown) to an appropriate value between the charging potential and the latent image (exposure portion) potential, the toner is charged to a negative polarity. The The negatively charged toner is selectively attached to the electrostatic latent images on the photoconductive drums 1Y to 1K, whereby development is performed.

  The monochromatic toner images developed on the photosensitive drums 1Y to 1K are transferred onto an intermediate transfer belt 6 as an intermediate transfer member that rotates at a substantially constant speed in synchronization with the photosensitive drums 1Y to 1K. The intermediate transfer belt 6 is driven by a driving roller 7 and is stretched by a tension roller 8. Primary transfer rollers 9 </ b> Y, 9 </ b> C, 9 </ b> M, and 9 </ b> K as primary transfer units transfer the toner images on the photosensitive drums 1 </ b> Y to 1 </ b> K to the intermediate transfer belt 6. A toner image is primarily transferred to the intermediate transfer belt 6 by applying a primary transfer bias having a polarity opposite to that of toner from a bias power source (not shown) to the primary transfer rollers 9Y to 9K.

  After the primary transfer of the toner image, the transfer residual toner remaining on the photosensitive drums 1Y to 1K is removed by the cleaning blades 4Y to 4K. In this embodiment, a urethane blade is used as the cleaning blade.

  The above operation is performed in synchronization with the rotation of the intermediate transfer belt 6 for each color of yellow, magenta, cyan, and black, and a primary transfer toner image of each color is sequentially superimposed on the intermediate transfer belt 6 to form a full color toner image. At the time of monochrome image formation (monochrome mode), the above operation is performed only for the target color.

  A transfer material as a material to be heated set in a transfer material cassette 10 serving as a transfer material supply unit is fed by a feed roller 11. In this embodiment, the transfer material is the recording paper P. The fed recording paper P is conveyed by a registration roller 12 to a nip portion between the intermediate transfer belt 6 and a secondary transfer roller 13 as a secondary transfer unit at a predetermined timing. A bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 13 by a bias applying unit (not shown), whereby the primary transfer full-color toner image formed on the intermediate transfer belt 6 is collectively transferred onto the recording paper P. Is done. Reference numeral 14 denotes a secondary transfer roller facing roller.

  The secondary transfer residual toner remaining on the intermediate transfer belt 6 after the secondary transfer is removed by a cleaning blade 15 as an intermediate transfer belt cleaning unit. In this embodiment, the intermediate transfer belt 6 is cleaned with a urethane blade in the same manner as the cleaning blades 4Y to 4K.

  The full-color toner image secondarily transferred onto the recording paper P passes through a heating device F as fixing means, and is melted and fixed onto the recording paper P to become an output image of the image forming apparatus. Hereinafter, the heating apparatus F will be described in detail.

  FIG. 3 is a schematic cross-sectional view of the heating device F according to this embodiment. The heating device F according to the present embodiment is a film heating type heating device, and is also a pressure rotating body driving type (tensionless type) heating device.

In FIG. 3, reference numeral 20 denotes a fixing belt as a heating member. The fixing belt 20 has an outer diameter of 18 mm. Further, the fixing belt 20 is formed by forming a 200 μm-thick silicone rubber layer on a belt made of SUS having a thickness of 30 μm by a ring coating method, and further, a PFA resin having a thickness of 30 μm as a release layer. The tube is covered. For the silicone rubber layer, it is desirable from the viewpoint of temperature rise to use a material having as high a thermal conductivity as possible and to reduce the heat capacity of the fixing belt 20. In this embodiment, a material having a thermal conductivity of about 4.2 × 10 ⁻¹ W / m · K and a silicone rubber having a high thermal conductivity was used. The heat capacity of the fixing belt 20 thus formed was measured and found to be 28.5 J / K.

  Reference numeral 21 denotes a pressure roller as a pressure member. The pressure roller 21 has an outer diameter of 20 mm. The pressure roller 21 is formed by forming a silicone rubber layer having a thickness of about 3 mm by injection molding on a stainless steel core bar having an outer diameter of 14 mm and coating a PFA resin tube having a thickness of about 40 μm thereon. The heat capacity of the pressure roller thus formed was 204 J / K. Further, the pressure roller 21 is disposed such that both end portions of the core metal are rotatably supported by bearings between the back and front side plates of the image forming apparatus frame (not shown).

  Reference numeral 22 denotes a heater holder as a heating body holding member, which has a substantially semicircular arc shape in cross section and has heat resistance and rigidity. The heater holder 22 is formed of a liquid crystal polymer resin having high heat resistance, and holds the fixing heater 23 described later and plays a role of guiding the fixing belt 20. In this example, DuPont Zenite 7755 was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C. The fixing belt 20 is loosely fitted on the heater holder 22.

  Reference numeral 23 denotes a fixing heater as a heating body, which is disposed on the lower surface of the heater holder 22 along the longitudinal direction of the heater holder 22. The fixing heater 23 of this embodiment forms a resistance heating element by applying a conductive paste containing a silver / palladium alloy on a substrate of aluminum nitride into a film having a uniform thickness by screen printing. This is a ceramic heater with a glass coating made of pressure-resistant glass.

  The configurations of the fixing belt 20, the pressure roller 21, the heater holder 22, and the fixing heater 23 are not particularly limited to these.

  The pressure roller 21 is rotationally driven at a predetermined peripheral speed in the direction of the arrow in the drawing by a driving unit (not shown). Accordingly, the cylindrical fixing belt 20 is driven and rotated. In addition, the fixing heater 23 is energized, and the fixing heater 23 is heated to a predetermined temperature and the temperature is adjusted. In this state, the recording paper P carrying the unfixed toner image t is introduced into the fixing nip N between the fixing belt 20 and the pressure roller 21. The introduced recording paper P has the unfixed toner image carrying surface side of the recording paper P in the fixing nip portion N in close contact with the outer surface of the fixing belt 20, and the fixing nip portion N is nipped and conveyed in the paper passing direction together with the fixing belt 20. It will be done.

  In this nipping and conveying process, the heat of the fixing heater 23 is applied to the recording paper P via the fixing belt 20, and the unfixed toner image t on the recording paper P is heated and pressurized on the recording paper P and melted and fixed. The The recording sheet P that has passed through the fixing nip N is separated from the fixing belt 20 by the curvature, and is discharged by a fixing discharge roller (not shown).

  The temperature control system of the heating device F will be described with reference to FIG. A thermistor 24 as a temperature detection element is disposed in contact with the fixing heater 23. The thermistor 24 is connected to a CPU 25 as a control means via an A / D converter 26 as shown in FIG. Further, the CPU 25 controls the energization to the fixing heater 23 via the triac 27. This energization control is performed, for example, by controlling the phase or wave number of the AC voltage. That is, the CPU 25 controls the energization of the fixing heater 23 by the triac 27 based on the temperature information signals of the pressure roller 21 and the heating body 23 output from the thermistor 24 and A / D converted by the A / D converter 26. It is set to be.

  At this time, the target temperature setting is changed in a plurality of stages according to the number of prints of one job in consideration of an increase in the pressure roller temperature caused by overlapping the number of prints. Further, in order to compensate for the insufficient supply of heat from the pressure roller 21 to the recording paper P, control is performed to increase the temperature according to the rotation period of the pressure roller 21.

  However, as described above, with the colorization of the image forming apparatus, since the elastic layer is provided on the base material of the fixing belt 20, the thermal conductivity is lowered by that amount, and a heat storage effect is produced like the pressure roller. End up. As a result, the supply of heat from the fixing belt 20 to the recording paper P is greatly insufficient. As a result, gloss unevenness occurs due to insufficient supply of heat not only in the pressure roller period but also in the fixing belt period. There was a case. Details are described below.

  FIG. 5 shows temperature transitions of the pressure roller 21 and the fixing belt 20 during continuous paper feeding. In the graph, the vertical axis represents temperature, and the horizontal axis represents the number of printed sheets. The pressure roller temperature gradually increases from the start of printing to the vicinity of the 60th sheet, and tends to saturate at around 120 ° C. after the 61st sheet. On the other hand, the fixing belt temperature tends to increase rapidly to around 140 ° C. after several prints start, and then gradually decrease. This is because the temperature adjustment temperature is lowered according to the number of prints in consideration of the temperature rise of the pressure roller temperature.

  FIG. 6 shows the temperature transition of the fixing belt 20 and the pressure roller 21 in the recording paper. The temperature change of the pressure roller 21 is as large as Δ15 ° C. until the 60th print, and the heat capacity is relatively large after the 61st sheet where the pressure roller temperature is saturated (204 J / K in this embodiment). As small as Δ5 ° C. On the other hand, the temperature change of the fixing belt is Δ10 ° C. regardless of the number of prints because the heat capacity is small (28.5 J / K in this embodiment).

  That is, the gloss unevenness of the pressure roller cycle described above occurs remarkably before the pressure roller temperature reaches the saturation temperature, and hardly occurs after saturation. On the contrary, after the pressure roller temperature is saturated, the uneven glossiness of the fixing belt having a smaller heat capacity than that of the pressure roller 21 becomes conspicuous.

  The heating device according to the present embodiment is configured to prevent the gloss unevenness by performing temperature control that changes the temperature control temperature switching period according to the number of prints based on the recognition described above.

  Hereinafter, temperature control in the present embodiment will be described with reference to Table 1 and FIG.

  Table 1 shows the switching cycle of the temperature adjustment temperature in the recording paper according to the number of prints in this embodiment. Note that the number of prints shown in the table indicates the number of prints in the case of continuous printing from the cold state (the temperature of the pressure roller 21 is at room temperature).

  In Table 1, when the temperature of the pressure roller is not saturated, that is, the first to the 60th sheet where the supply of heat from the pressure roller 21 to the recording paper P is large, the temperature control temperature in the recording paper is adjusted to the leading edge of the paper. From the rear to the rear end, the pressure is controlled so as to increase at a pressure roller cycle (62.8 mm). Then, after the 61st sheet where the pressure roller temperature starts to saturate, control is performed so that the temperature adjustment temperature is raised at the fixing belt cycle (56.5 mm).

<Experimental example>
Hereinafter, the result of a comparative experiment between the heating apparatus having the configuration of this example and the conventional heating apparatus will be described. The conventional heating device used as a comparative example performs control to switch the temperature control temperature in the recording paper at a pressure roller cycle (62.8 mm) regardless of the number of prints. For the above-mentioned two types of controlled heating devices, the gloss unevenness level when the paper was continuously fed from the cold state was compared. FIG. 7 shows the experimental results.

  When the number of prints is 1 to 60, the temperature adjustment temperature is switched in the pressure roller cycle, and therefore gloss unevenness occurs in the fixing belt cycle. After the 61st sheet where the pressure roller temperature is saturated, the comparative example causes gloss unevenness of the fixing belt cycle. On the other hand, in this embodiment, since the temperature control temperature is switched in the fixing belt cycle, gloss unevenness in the fixing belt cycle does not occur. Further, gloss unevenness of the pressure roller cycle hardly occurs because the heat capacity is larger than that of the fixing belt 20 and the pressure roller temperature is saturated.

A major feature of the present embodiment is that temperature control is performed to change the temperature control temperature switching cycle according to the number of prints based on the above-described recognition. As a result, it is possible to provide a fixing device and an image forming apparatus that suppress and prevent gloss unevenness and prevent deterioration of image quality in continuous printing.

  In Example 1, the occurrence of gloss unevenness was suppressed / prevented by performing temperature control in which the temperature control temperature switching cycle is changed according to the number of printed sheets. However, before the pressure roller temperature is saturated, that is, in the first half of continuous printing, gloss unevenness of the fixing belt cycle still occurs.

  FIG. 8 shows the gloss unevenness. Gloss unevenness of the fixing belt cycle with a small heat capacity appears remarkably at the leading edge (first round) of the recording paper, and the gloss unevenness of the pressure roller cycle having a larger heat capacity than the fixing belt 20 tends to appear remarkably toward the rear end of the paper. is there.

  In this embodiment, the gloss unevenness is prevented by changing the temperature control temperature switching period in the recording paper.

  Hereinafter, temperature control in the present embodiment will be described with reference to FIG. 1, Table 2, and FIG. In addition, about a present Example, only a different point from Example 1 is demonstrated, the same code | symbol is attached | subjected about the structure same as Example 1, and description is abbreviate | omitted.

  FIG. 1 is a diagram illustrating a temperature control temperature switching cycle in one recording sheet in the present embodiment. In FIG. 1, the vertical axis represents the temperature control temperature, and the horizontal axis represents the temperature control temperature switching cycle.

  In this embodiment, the temperature control temperature switching period in the recording paper is made to correspond to the above-described gloss unevenness, and the first round is the fixing belt period (56.5 mm), and the pressure roller period (62.8 mm) thereafter. ). However, for the second round, since the period converted from the leading edge of the recording paper is different between the fixing belt 20 and the pressure roller 21, it is set to a period obtained by subtracting one round of the fixing belt from the two rounds of the pressure roller. Yes. Regarding the control according to the number of prints, as shown in Table 2, the switching cycle described above is applied to the first to 60th continuous prints, and as described in the first embodiment for the 61st and subsequent prints. The fixing belt cycle.

<Experimental example>
Hereinafter, the result of the comparative experiment between the heating device according to the present embodiment and the conventional heating device will be described. The heating device used as a comparative example is a heating device that performs temperature control of the first embodiment, and performs control to always switch the temperature control temperature in the recording paper at a pressure roller cycle (62.8 mm) regardless of the number of prints. A heating device was used. For these three types of controlled heating devices, the level of gloss unevenness when the paper was continuously fed from the cold state was compared. FIG. 9 shows the experimental results.

  About the structure of a comparative example and Example 1, as described in Example 1, when the number of printed sheets is 1 to 60, gloss unevenness of the fixing belt cycle occurs. However, in the first embodiment, in the second half of continuous printing (after the 61st sheet), the temperature control temperature is switched at the fixing belt cycle. Therefore, in Example 1, uneven glossiness of the fixing belt cycle does not occur. On the other hand, in the temperature-controlled heating apparatus of this embodiment, since the temperature control temperature switching period in the recording paper is changed, gloss unevenness does not occur regardless of the number of prints. As a result, it is possible to suppress uneven gloss that has occurred in the fixing belt cycle.

A major feature of the present embodiment is that temperature control is performed to change the temperature control temperature switching cycle in one sheet of recording paper based on the above-described recognition. As a result, it is possible to provide a fixing device and an image forming apparatus that suppress and prevent gloss unevenness and prevent deterioration of image quality in continuous printing.

  In the first and second embodiments, the case where continuous printing is performed from a cold start (the temperature of the pressure roller 21 is room temperature) has been described. However, the present invention is not particularly limited thereto. For example, during intermittent printing, the same effects as in the first and second embodiments can be obtained even if the following control is performed. For example, during intermittent printing, the print interval is measured by a timer or the like that measures the print interval. When the measurement result is equal to or smaller than the predetermined value, the number of intermittent prints is counted in the same manner as the number of sheets in continuous printing, and the same temperature control as in continuous printing is performed. On the other hand, when the print interval is larger than the predetermined value, the temperature of the fixing heater 23 is detected by the thermistor 24, and the temperature control temperature switching cycle is changed according to the detection result. Thereby, it becomes possible to suppress the temperature rise of the pressure roller 21, and the same effects as in the first and second embodiments can be obtained even during intermittent printing.

  Further, the heat capacities of the fixing belt 20 and the pressure roller 21 in Examples 1 and 2 are defined as 28.5 J / K and 204 J / K, respectively, but are not particularly limited thereto. For example, if the heat capacity is 10 J / K or more (heat capacity having a heat storage effect) or more, the same effect can be obtained.

  The process speed of the image forming apparatuses according to the first and second embodiments is defined as 90 mm / sec. However, the process speed is not particularly limited to this, and the same effect can be obtained even when the process speed is 25 mm / sec or more. Obtainable. In particular, since the heat transfer is delayed as the process speed increases, the effect of the present invention is increased.

  In the first and second embodiments, the full-color image forming apparatus has been described as an example. However, the present invention is not particularly limited thereto, and may be an image forming apparatus capable of forming a monochrome image. Even if the present invention is applied to a heating device in the image forming apparatus, the same effect can be obtained.

  Moreover, although Example 1 and 2 demonstrated the heating apparatus of the film heating system as an example, it is not specifically limited to this. For example, it may be an electromagnetic induction heating type heating device or a thin roller type heat fixing device with a small heat capacity, and the same effect can be obtained even if the present invention is applied to the heating device.

  In the first and second embodiments, the printer is described as an example of the image forming apparatus, but the present invention is not particularly limited thereto. For example, another image forming apparatus such as a copying machine or a facsimile machine, or an image forming apparatus such as a combined machine combining these functions, a transfer material carrier, and a transfer material carried on the transfer material carrier. An image forming apparatus that sequentially superimposes and transfers toner images of the respective colors may be used. Even if the present invention is applied to a heating device in the image forming apparatus, the same effect can be obtained.

The figure which shows the switching cycle of the temperature control temperature in Example 2 Schematic sectional view of an image forming apparatus according to Embodiments 1 and 2 Schematic cross-sectional view of a heating device according to a conventional example and Examples 1 and 2 Block diagram showing temperature control system of heating device The figure which shows the temperature transition of the fixing belt and pressure roller in Example 1. FIG. The figure which shows the temperature transition of the fixing belt and pressure roller in Example 1. FIG. The figure which shows the experimental result of Example 1 and a comparative example Diagram explaining uneven gloss in recording paper The figure which shows the experimental result of Example 2 and a comparative example

Explanation of symbols

20 Fixing belt (corresponding to heating member)
21 Pressure roller (corresponding to pressure member)
23 Fixing heater (corresponding to heating element)
24 thermistor (corresponding to temperature sensing element)
25 CPU (corresponding to control means)
N Fixing nip P Recording paper (supports transfer materials and heated materials)

Claims (3)

A cylindrical fixing belt; a heater that contacts the inner surface of the fixing belt; a pressure roller that forms a fixing nip portion with the heater via the fixing belt; and a temperature detection element that detects the temperature of the heater; Control means for controlling the power supplied to the heater so that the temperature detected by the temperature detection element maintains a set temperature, and recording is performed while nipping and conveying the recording paper carrying the toner image at the fixing nip portion. In a fixing device that heats and fixes a toner image on paper,
  The control means includes: a first control for gradually increasing the set temperature within a period in which one sheet of recording paper moves through the fixing nip, and a period of the circumference of the pressure roller; Can be set in a period during which the fixing nip portion is moved, and the set temperature is gradually increased with the circumference of the fixing belt as a cycle. The second control is the first control. The fixing device is set when the temperature of the pressure roller is higher than when the control is set. 2. The second control is set in a period in which the number of processed sheets is larger than a period in which the first control is set when a plurality of recording sheets are continuously fixed. Fixing device. 2. The fixing device according to claim 1, wherein the first control is started after the recording paper passes through the fixing nip portion for one rotation of the fixing belt .