JP2010145665A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device of an external heating system, which can efficiently transmit heat to a fixing member from an external heating device and is high in heat efficiency, and to provide an image forming apparatus having the fixing device. <P>SOLUTION: In the area 35 of the surface of the fixing member 20, to which heat is transmitted by the external heating device 70, a quantity of heat generated by the external heating device 70 is made larger on the downstream side than that on the upstream side in the moving direction of the surface of the fixing member 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device that is mounted on an image forming apparatus such as a printer, a copying machine, or a facsimile using electrophotographic technology or electrostatic recording technology, and heat-fixes an unfixed image on a recording material, and such a fixing device. The present invention relates to an image forming apparatus using the. In particular, the image forming apparatus includes a fixing member, a pressure member that comes into contact with the surface of the fixing member, and an external heating device that heats the surface of the fixing member from the outside. An unfixed toner image is formed on the pressure contact portion between the fixing member and the pressure member. The present invention relates to a fixing device and an image forming apparatus that introduce a carried recording material and perform heat fixing.

  In an image forming apparatus that employs an electrophotographic system such as a copying machine, a printer, or a facsimile, a heat fixing device is used as a fixing device that fixes an unfixed toner image transferred onto a recording material such as transfer paper or OHP onto the recording material. Is widely used. As a heat-fixing device, a pressure roller (pressure member) is pressed against a heated fixing roller (fixing member), and an unfixed toner image is heated and melted while the recording material is nipped and conveyed by both rollers. A heat roller type for fixing is widely used. FIG. 9 attached to the present application shows a schematic diagram of the heat roller type fixing device.

  In this example, the fixing roller 50 is provided with a heating body (heat source) 53 such as a halogen lamp in a hollow cored bar 51 made of aluminum or stainless steel, and a fluororesin or the like for preventing toner offset on the outer surface. The release layer 52 is provided. Further, the pressure roller 60 is formed with an elastic layer 62 formed of silicone rubber or the like on the outside of the cored bar 61 or a sponge elastic layer 62 formed by foaming silicone rubber, and the outer layer is similar to the fixing roller 50. A release layer 63 such as a fluororesin is formed.

  In the case of an image forming apparatus using a high-speed machine or color toner, the fixing roller 50 is provided on the outer surface of the hollow cored bar 51 in place of the release layer 52 in order to sufficiently satisfy the toner fixing property. An elastic layer having a thickness of about 2 mm such as silicone rubber is provided. With this configuration, the efficiency of heat transfer to the recording material and the toner is improved by wrapping the toner on the surface of the fixing roller that has become soft.

  However, in this heat roller fixing method, it takes a long time (warm-up time) until the fixing roller surface reaches the fixing temperature after the heating of the fixing roller 50 is started. This is because it takes time until the heat from the heat source 53 disposed on the inner surface of the fixing roller 50 is transmitted to the surface of the fixing roller.

  Therefore, from the viewpoint of ease of use, it is necessary to preheat the fixing roller 50 during standby, and there is a problem that large power is consumed during warm-up and standby.

  In order to solve such problems, a fixing device configured to heat the fixing roller 50 from the outside (hereinafter referred to as “external heating fixing device”) has been proposed.

  Various methods have been proposed for heating the fixing roller 50 from the outside. For example, Patent Documents 1, 2, 3 and the like include an external heating device 70 as shown in FIG. There has been proposed one in which a small-diameter heating roller 71 is brought into contact with the outer peripheral surface of the fixing roller.

  In this case, the small-diameter heating roller 71 of the external heating device 70 is heated in a short time by a heat source 72 such as a built-in halogen heater. As a result, the surface of the fixing roller 50 having the elastic layer 52 formed of silicone rubber, foamed silicone rubber or the like on the outer surface of the hollow metal core 51 is directly applied by the heating roller 71 disposed on the side opposite to the pressure roller 60. Heated. Therefore, the temperature raising speed on the surface of the fixing roller 50 can be increased.

  Furthermore, Patent Document 4 proposes an example of an external heat fixing device that can improve thermal efficiency.

  In the external heating and fixing device of Patent Document 4, as shown in FIG. 11 attached to the present application, a plate-like heater 73 having a small heat capacity is used as a heat source of the external heating device 70. A plate-like heater 73 carried by the heat insulating stay holder 74 is in sliding contact with the fixing roller 50 to heat the fixing roller 50. The amount of heat generated by the heater 73 is performed via the temperature detection element 75.

  Further, in this example, the pressure member 60 has a structure in which a flexible rotating body 64 is brought into contact with the fixing roller 50 via a sliding member 66 held by a holder 65.

  In this configuration, since the heat capacity of the heater 73 itself is small, the heater 73 starts up quickly. Furthermore, unlike the type of heating with the small-diameter heat roller 71 shown in FIG. 10, the contact surface with the fixing roller 50 is fixed in a sliding state, so that the heat from the heater 73 is transferred to the contact portion. Never be taken away from. Therefore, it becomes possible to transfer heat more efficiently.

  Further, Patent Documents 5 and 6 propose non-contact type external heat fixing devices using a radiant heat source instead of the contact type heat source as described above.

  This non-contact type external heating and fixing apparatus has a structure in which a heating body (heat source) 76 such as a halogen lamp is included in a curved reflecting plate 77 as an external heating apparatus 70 as shown in FIG. Is done. Further, a fixing roller 50 having an elastic layer 52 formed of silicone rubber, foamed silicone rubber, or the like is disposed on the outer surface of the hollow metal core 51 at the opening notch 78 of the reflection plate 77, and is heated by the heating body 76. Only the outer surface is heated. The surface temperature of the fixing roller 50 is detected by the temperature detection unit 58. In this example, the pressure roller 60 has the same configuration as that shown in FIG.

  Even in the case of this heat fixing device, the surface of the fixing roller 50 can be rapidly heated to heat the fixing roller 50 from the outside, and the warm-up time is shortened compared to the heat roller fixing device shown in FIG. Is done. The power consumption can be reduced by shortening the temperature raising time of the fixing roller 50.

  As described above, the method of rapidly heating the surface of the fixing roller from the outside has an effect that the rise time can be shortened and the power consumed during standby can be reduced as compared with the heat roller method having a heat source inside. Yes.

  However, the above-described fixing method has the following problems.

  In order to shorten the warm-up time, the elastic layer of the fixing roller 50 is formed in a sponge shape such as foamed silicone rubber, and when a roller with a PFA tube covered as a release layer on the surface is used, Warm-up time is reduced. However, it is necessary to set the surface temperature of the fixing roller at which the toner image on the recording material can be fixed at the pressure contact portion between the fixing roller 50 and the pressure roller 60, that is, the fixing nip N.

  This is because the heat capacity becomes small because the fixing roller 50 gives priority to heat insulation, and it becomes difficult to secure a sufficient amount of heat necessary for heat fixing at the fixing nip portion N.

  In addition, since the surface of the fixing roller has a heat insulating property, the amount of heat from the external heating device 70 is not positively transferred. Therefore, the temperature of the external heater is maintained sufficiently higher than the surface temperature of the fixing roller. There was a need. For this reason, high heat resistance is required for the external heater holding member and members around the external heater. In particular, it is necessary to select an element that operates at a higher temperature, such as a safety element disposed on the back surface of the heater, and a more expensive element has to be used.

  Further, if it is limited to the external heating device 70 using a non-contact type heat source as shown in FIG. 12, a large electric power has to be supplied to the radiant heat source 76. As a result, the radiant heat source and the temperature around the radiant heat source become extremely high. For example, the recording material is wound around the fixing roller 50 due to a jam or the like, or the rotation of the fixing device is stopped due to some problem. In addition, the recording material may be exposed to a very high temperature.

  As a method for avoiding this, Patent Document 7 proposes that the elastic layer of the fixing roller is divided into two layers, the lower layer is a heat insulating layer, and the uppermost layer is a high thermal conductive silicone rubber layer. It is trying to solve the above problems by storing heat in

  However, in order to ensure the releasability to the toner, it is necessary to further form a fluororesin layer as a release layer on the surface of the fixing roller.

  Usually, the fluororesin layer has a low thermal conductivity. According to the study by the present inventors, even if the fluororesin layer is formed of a thin layer of about 10 μm to 20 μm, the fluororesin layer is It turned out that it became a barrier layer and the following problems occurred.

  That is, it takes time to diffuse the heat from the external heating device to the high thermal conductive elastic layer that is the heat storage layer of the fixing roller. Therefore, in order to spread a sufficient amount of heat to the high thermal conductivity elastic layer that is the heat storage layer of the fixing roller, the temperature of the external heater is set high, and the temperature of the surface of the fixing roller is accordingly maintained, and eventually maintained at a high temperature. I have to do it.

  As one method for solving this problem, it is conceivable to increase the thermal conductivity of the fluororesin layer serving as a thermal barrier layer. If heat from the external heating device is easily transferred to the fixing roller by increasing the thermal conductivity of the fluororesin layer, heat can be efficiently transferred to the fixing roller even if the temperature of the external heater is set low. Will be able to. In order to increase the thermal conductivity of the resin, a method of mixing a heat conductive filler is conceivable mainly, and the present inventors have also confirmed that the heat conductivity is improved by mixing various fillers.

  However, the harmful effect is also great, and the biggest one is a decrease in releasability. In addition, mixing of the filler affects the flexibility and surface properties of the resin, leading to a decrease in durability and adhesiveness. Further, the loss of flexibility leads to difficulty in handling after manufacturing, and affects the manufacturing method and the manufacturing yield.

Therefore, since it is required to design the filler with an amount of mixing that satisfies both of these adverse effects and the thermal conductivity, the above problem cannot be solved only by the method of mixing the filler.
Japanese Patent Laid-Open No. 04-159585 JP 09-204114 A JP-A-10-301434 JP 2003-186327 A Japanese Patent Laid-Open No. 7-152271 Japanese Patent Laid-Open No. 9-54510 JP 2002-123117 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an external heating type fixing device with higher thermal efficiency and an image forming apparatus including such a fixing device, which efficiently transfers heat from the external heating device to the fixing member. is there.

The above object is achieved by a fixing device and an image forming apparatus according to the present invention. In summary, according to the first aspect of the present invention, there are provided a fixing member, a pressure member that forms a pressure contact portion in contact with the surface of the fixing member, and a heating body that heats the surface of the fixing member from the outside. An external heating device with
In a fixing device for performing heat fixing by introducing a recording material carrying an unfixed toner image into a pressure contact portion between the fixing member and the pressure member,
In the heat transfer region by the external heating device on the surface of the fixing member, a heat generation amount of the external heating device is larger on the downstream side than on the upstream side in the moving direction of the surface of the fixing member. Is done.

According to a second aspect of the present invention, in an image forming apparatus comprising: an image forming unit that forms an unfixed toner image on a recording material; and a fixing device that thermally fixes the unfixed toner image on the recording material.
An image forming apparatus is provided in which the fixing device is a fixing device having the above-described configuration.

  According to the present invention, in the heat transfer region by the external heating device on the surface of the fixing member, the amount of heat generated by the external heating device is made larger on the downstream side than on the upstream side in the moving direction of the surface of the fixing member. As a result, the temperature difference between the surface of the fixing member that rises in the heat transfer region and the surface of the external heating device can be continuously increased, and heat is efficiently transferred to the surface of the fixing member in the heat transfer region. be able to.

  Therefore, the external heating type fixing device of the present invention improves the heating efficiency of the fixing roller by the external heater, has a short warm-up time, and is excellent in on-demand characteristics.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1
(Overall configuration of image forming apparatus)
FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus 100 to which a fixing device according to the present invention is applied.

  In this embodiment, the image forming apparatus 100 includes a sheet feeding device including a sheet feeding tray 1, a sheet stacking table 2, and a sheet feeding roller 3. The recording material 37 stacked on the sheet stacking table 2 in the sheet feeding tray 1 is picked up one by one from the uppermost recording material by the sheet feeding roller 3 and sent to the registration unit by the conveying roller 4 and the conveying roller 5. . The recording material 37 is fed to the image forming unit constituted by the image forming process means after the conveying direction is aligned by a resist unit composed of the registration roller 6 and the registration roller 7.

  The image forming unit includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 80 as an image carrier. Around the photosensitive drum 80, a charger 81 for charging the photosensitive drum 80 as an image forming process means, a developing unit 82 for developing the latent image on the photosensitive drum with toner, and residual toner on the photosensitive drum are removed and stored. A cleaner 83 or the like is disposed. These image forming process means are configured as a unit as a toner cartridge 9. The laser scanner unit 10 as an exposure unit is configured by unitizing a polyhedral mirror, a polyhedral mirror rotating motor, a laser unit, and the like.

  The laser beam L based on the image information is irradiated from the laser scanner unit 10 and the photosensitive drum 80 uniformly charged by the charger 81 is exposed. A latent image based on the image information is electrophotographic on the photosensitive drum 80. Formed by the method. The latent image is developed with toner as a developer by a developing device 81, and the developed toner image is transferred onto the recording material 37 conveyed from the photosensitive drum 80 by the transfer roller 12.

  After the transfer of the toner image, the recording material 37 is conveyed to the fixing device 20, where the transferred toner image is heated and fixed. The fixing device 20 includes a fixing roller 50, a pressure member 60, and an external heating device 70. Thereafter, the recording material P is discharged onto a discharge tray 17 by a discharge unit including an intermediate discharge roller 15 and a discharge roller 16.

  A cooling fan 18 is attached to the side surface of the image forming apparatus main body 100A for cooling a temperature rising portion such as an image forming unit and an electrical board in the apparatus. Cool by taking in. Further, a temperature detection means 19 such as a thermistor is attached in the vicinity of the cooling fan 18. The temperature detection means 19 detects the temperature of the environment in which the image forming apparatus 100 is installed when air outside the apparatus is taken in by the cooling fan 18, and the temperature control sequence of the heating and fixing apparatus 20 based on the detection result. To give feedback.

  In the image forming apparatus 100 described above, the configuration of a fixing device that heat-fixes an unfixed toner image on a recording material as a permanent image on the recording material will be described below.

(Fixing device)
FIG. 2 shows the structure of the fixing device 20 in the first embodiment. The fixing device 20 according to the present exemplary embodiment includes a fixing roller 50 as a fixing member in which a pressure contact portion, that is, a fixing nip portion 28 is formed by being pressed against each other, and a pressure roller 60 as a pressure member. Further, the fixing device 20 includes an external heating device 70 that is an external heating unit that heats the fixing roller 50. That is, the fixing device 20 of this embodiment is a fixing device of a fixing member external heating type. With such a configuration, the recording material 37 carrying the unfixed toner image 36 is introduced into the nip portion 28, and is nipped and conveyed to fix the unfixed toner image on the recording material 37.

  In this embodiment, the fixing member having a roller shape, that is, the fixing roller 50 has an outer diameter of about 18 mm. Specifically, an elastic layer 22 made of low thermal conductive silicone rubber having a thickness of about 3 mm is provided on the outer side of a stainless steel core 21 having a diameter of 12 mm, and a release layer 23 made of a fluororesin having a thickness of 30 μm is further provided on the outer side. Are sequentially provided.

  The low thermal conductivity elastic layer 22 is formed of an elastic layer (a foam rubber layer) in which a hollow filler is dispersed in a silicone rubber layer, a gas portion is provided in a cured product, and a heat insulating action is enhanced.

  These hollow fillers include micro-balloon materials, such as glass balloons, silica balloons, carbon balloons, phenol balloons, acrylonitrile balloons, vinylidene chloride balloons, alumina balloons, zirconia balloons, shirasu balloons, etc. It doesn't matter.

  In the silicone rubber layer in this example, it is desirable that the cured product (silicone rubber) has a thermal conductivity of 0.15 W / mK or less, preferably 0.13 W / mK or less, so that the thermal conductivity is achieved. It is preferable to adjust to. If the thermal conductivity is high, the heat from the external heating device 70 is easily absorbed inside, and the temperature on the surface of the fixing roller is difficult to rise. Therefore, the heat conductivity is as low as possible, the thermal conductivity is low, and the heat insulation effect is high. This is advantageous for the rise of the fixing roller 50.

  The pressure member having a roller shape, that is, the pressure roller 60 has the same configuration as the fixing roller 50 described above, and has an outer diameter of about 18 mm. Specifically, an elastic layer 26 made of low thermal conductive silicone rubber having a thickness of about 3 mm is provided on the outside of a stainless steel core 25 having a diameter of 12 mm, and a release layer 27 made of a fluororesin having a thickness of 30 μm is further provided on the outside. Are sequentially provided.

  In the present embodiment, as described above, both the fixing member 50 and the pressure member 60 will be described by taking a roller-shaped member as an example, but the shape is not limited to the roller.

  In this embodiment, the pressure roller 60 is arranged in parallel with the fixing roller 50 in the axial direction, and is in pressure contact with the fixing roller 50 with a total pressure of 98N. At this time, a fixing nip portion 28 is formed between the fixing roller 50 and the pressure roller 60, and the nip width W1 is about 5 mm.

  The external heating device 70 is means for heating the fixing roller 50 from the surface side of the fixing roller 50, and uses a part of a conventionally known film heating type ceramic heater unit.

  That is, in the present embodiment, the external heating device 70 includes a ceramic heater 30 as a heating body, a heat insulating stay holder 31 that is a support body that supports the heat insulation of the heater 30, and a metal stay 32 that backs up the heat insulating stay holder. It has. Further, a temperature detection element 33 such as a thermistor and a safety element (not shown) such as a temperature fuse are installed on the surface opposite to the surface on the fixing roller side of the ceramic heater 30.

  3A and 3B are schematic views of the ceramic heater 30. FIG. FIG. 3A is a schematic cross-sectional view of the ceramic heater 30 and shows a cross-sectional view taken along the line CD shown in FIG. 3B. FIG. 3B shows a B surface of the ceramic heater 30 shown in FIG.

  The ceramic heater 30 is a plate-shaped heater having an insulating ceramic such as alumina or aluminum nitride on a substrate 38. The heater 30 has, on the surface thereof, a line having a thickness of about 10 μm and a width of about 1 to 5 mm by screen printing or the like along the longitudinal direction with an energization heating resistance layer 39 which is a heating element such as Ag / Pd (silver palladium). It is formed by coating in the shape of a strip or strip. In the present embodiment, although not limited to this, the energization heating resistor layer 39 having two patterns in parallel along the longitudinal direction is formed.

  On the fixing roller side (surface side) of the heater 30 which is a heating body, a protective sliding layer 40 is provided to protect the energization heating resistance layer 39 of the heating body within a range that does not impair the thermal efficiency. The material of the protective sliding layer 40 is mainly a glass coat, but a material such as polyimide or fluororesin may be used. In this embodiment, alumina is used for the substrate 38, silver palladium is used as the material for the energization heating resistance layer 39, and glass coat is used as the protective sliding layer 40.

  Two Ag / Pt electrodes 41 having a size of about 3.7 mm × 3.7 mm are formed in the vicinity of one longitudinal end of the substrate 38. In the present embodiment, one end of the energization heating resistor layer 39, which has two patterns, and the electrode 41 are connected by a conductive layer 42a made of the same material as that of the electrode 18 and are in a conductive state. The other ends of the energization heat generating resistance layer 39 having two patterns are connected to each other by a conductive layer 42b.

  In the ceramic heater 30, the heat generation amount on the upstream side and the downstream side is changed in the moving direction of the fixing member, that is, the rotation direction of the fixing roller 50, by changing the pattern of the energization heat generation resistance layer 39. I can do it. That is, if the energization heating resistor layer 39 is formed only on the downstream side in the substrate, the amount of heat generation on the downstream side can be increased. Conversely, if the energization heating resistor layer 39 is formed only on the upstream side, the upstream side The calorific value on the side can be increased. In addition to this, if a wide energization heating resistor layer 39 is provided on the upstream side and a narrow energization heating resistance layer 39 is provided on the downstream side, two patterns having a large amount of heat generation on the downstream side can be formed due to the difference in specific resistance. Can be formed. On the other hand, it is also possible to form two patterns with a large amount of heat generation on the upstream side.

  In this embodiment, by changing these patterns, the amount of heat generation on the upstream side and the downstream side is changed, and the difference in the temperature increase rate of the fixing roller at that time is compared. This will be described after the description of the remaining members.

  The heat insulating stay holder 31 that holds the ceramic heater 30 is formed of a heat resistant resin such as liquid crystal polymer, phenol resin, PPS, or PEEK, and the lower the thermal conductivity, the higher the heat efficiency when heating the surface of the fixing roller. Therefore, a hollow filler such as a glass balloon or a silica balloon may be included in the resin layer.

  As described above, the thermistor 33 for detecting the temperature of the ceramic substrate 38 raised in response to the heat generated by the energized heat generating resistor layer 39 is disposed on the opposite surface of the fixing roller 50 of the ceramic heater 30. The temperature of the heater 30 is controlled.

  A safety element (not shown) arranged at the same position as the thermistor 33 is a temperature fuse that operates at a predetermined temperature, cuts off the electric power supplied to the heater when the heater is abnormally heated, It is arranged for the purpose of preventing dangerous conditions that become extremely hot.

  The external heating device 70 composed of the above members is a sheet-like sliding member having heat resistance with respect to the fixing roller 50 by a pressing means (not shown) with the ceramic heater 30 on the fixing roller 50 side, that is, Pressure is applied through the heat-resistant sliding sheet 34. Thereby, a heat transfer region, that is, a heating region 35 is formed between the ceramic heater 30 and the fixing roller 50. In this embodiment, the external heating device 70 is in pressure contact with the fixing roller 50 with a total pressure of 98 N, and the width W2 of the heating region 35 is approximately 5.0 mm.

  The heat-resistant sliding sheet 34 used in this example is formed of a polyimide sheet having a thickness of 30 μm. A filler for the purpose of improving heat conduction is mixed, and the heat from the ceramic heater 30 is efficiently transmitted to the fixing roller 50.

  The material of the heat-resistant sliding sheet 34 in the present embodiment is not limited to the above polyimide, and other resin materials such as PEEK, PES, PPS, etc. may be used. In addition to the resin material, it is also preferable to use a metal material such as aluminum, stainless steel, or phosphor bronze.

  When using a resin material, it is desirable to mix a filler for improving thermal conductivity as described above. Examples of the material include BN, aluminum, alumina, and aluminum nitride, but other materials may be used.

  It is desirable that PFA, PTFE, FEP or the like having good slidability is thinly coated on the fixing roller 50 side on which the heat resistant sliding sheet 34 abuts. In this embodiment, PFA resin having a thickness of 6 to 8 μm is coated.

  Further, in order to efficiently transmit heat, it is preferable that the surface roughness of the contact surface of the heat-resistant sliding sheet 34 with the ceramic heater 30 and the contact surface with the fixing roller 50 is small. Moreover, it is also preferable to interpose heat resistant grease excellent in thermal conductivity between the ceramic heater 30 and the heat resistant sliding sheet 34 in order to improve heat transfer.

  The heat-resistant sliding sheet 34 in the present embodiment is fixed by being wound around the heat-insulating stay holder 31 and sandwiching it between the metal stays 32 that back up the heat-insulating stay holder 31.

  These fixing members for the heat-resistant sliding sheet 34 fix the heat-resistant sliding sheet 34 at the same position during printing and non-printing, and the heat-resistant sliding sheet 34 is rotated during the rotation of the fixing roller 50. Is fixed while being rubbed against the fixing roller 50.

  In the configuration as described above, when the fixing roller 50 is driven to rotate, the fixing roller 50 is rotated while being rubbed and rubbed via the heater 30 of the external heating device 70 and the heat-resistant sliding sheet 34. Accordingly, the pressure roller 60 is driven to rotate. Thereafter, the ceramic heater 30 is energized to generate heat, and the surface of the fixing roller 50 is heated. Temperature detection information is input to a control circuit (not shown) by the thermistor 33 provided on the opposite surface of the fixing roller 50 of the ceramic heater 30. The control circuit controls the power supply of the external heating device 70 to the heater 30 so that the detected temperature of the ceramic heater 30 input from the thermistor 33 is maintained at a predetermined temperature (fixing temperature). As a result, the surface temperature of the fixing roller 50 is adjusted to a predetermined temperature.

  Next, the heating capability of the fixing roller 50 in a predetermined time of the fixing device 20 in this embodiment was confirmed. In detail, the heat generating layer pattern of the ceramic heater 30 described above was variously changed, and the temperature change of the fixing roller 50 at that time was measured and compared.

  First, with reference to Table 1, the pattern of the energization heating resistor layer 39 of the ceramic heater 30 used in the experiment will be described.

  The used ceramic substrate 38 is alumina, and in FIG. 3B, the length L in the longitudinal direction is 270 mm, and the width in the sheet passing direction of the recording material (hereinafter referred to as “substrate width”) W is 6. A 0 mm one was used. By changing the pattern of the energization heating resistor layer 39, the heaters (1) and (2) were produced as the heater 30 of Example 1, and the heaters (3), (4) and (5) were produced as comparative examples. Table 1 shows a list of heaters.

  First, items common to the heaters (1) to (5) will be described.

  A glass coat is used for the protective sliding layer 34 of all the heaters 30 and the thickness thereof is about 50 μm. When a plurality of patterns are arranged, they are connected in series, and the resistance is adjusted to be 25Ω for all the heaters. The material was silver palladium, and the resistance value was adjusted by changing the blending ratio. Further, all the thermistors 33 for detecting the temperature of the ceramic heater 30 are arranged at the center position of the ceramic substrate 38 in the substrate width direction.

  In the heater (1), one energization heating resistance layer (heating element) 39 having a width of 1.0 mm is disposed in a downstream region as viewed from the center of the substrate 38 in the substrate width direction. In the present embodiment, the width W2 of the heating region 35 formed by the fixing roller 50 and the ceramic heater 30 is 5.0 mm, and the heating element 39 disposed on the downstream side is also included in the heating region. Yes. Although the heater surface temperature distribution in the heating region has a peak where the heat generation pattern exists, a temperature gradient is obtained such that the temperature decreases from the downstream side where the heating element 39 exists toward the upstream side. In the heating region, the heat generation ratio between the upstream side and the downstream side is 0: 1.

  In the heater (2), two energization heating resistance layers (heating elements) 39 are disposed, and the width of the heating elements 39 on the upstream side and the downstream side is changed to change the amount of generated heat. The width of the heating element 39 is 1.5 mm for the upstream heating element and 0.75 mm for the downstream heating element. As a result, the heat generation ratio of the upstream and downstream heating elements is adjusted to be 1: 2.

  In the heater (3), two energization heating resistance layers (heating elements) 39 having a width of 1.0 mm are arranged for a substrate width of 6.0 mm. Although the heater surface temperature distribution in the heating region slightly has a peak where the heat generation pattern exists, there is no large temperature gradient over the entire region and uniform heat generation is achieved.

  In the heater (4), two energization heating resistance layers (heating elements) 39 are arranged in the same manner as the heater (1), but the width of the upstream heating element and the downstream heating element is 0.75 mm, respectively. And 1.5 mm. Thus, the amount of heat generation is changed, and the heat generation ratio of the upstream and downstream heating elements is adjusted to be 2: 1.

  In the heater (5), one energization heating resistor layer (heating element) 39 of 1.0 mm is disposed for a substrate width of 6.0 mm. It is located in the upstream region as viewed from the center in the substrate width direction of the substrate 38. When the heating region is formed, the heating element 39 is present only in the upstream portion. Since the heating element 39 does not exist on the downstream side, the heating ratio between the upstream and the downstream is 1: 0.

  As described above, five types of heaters 30 with different amounts of heat generation on the upstream side and the downstream side were produced. These heaters 30 were incorporated into the fixing device 20 of the present embodiment and experiments were conducted. When the fixing roller 50 was raised from room temperature, the time to reach 150 ° C. was monitored. The ceramic heater 30 was supplied with electric power of 500 W, and the rotation speed of the fixing roller 50 and the pressure roller 60 rotated in accordance with the fixing roller 50 was rotated at 115 mm / sec. The surface temperature of the fixing roller 50 was monitored by a non-contact temperature sensor (model number: IT550S, manufactured by HORIBA, Ltd.). In addition, when the temperature detection element 33 arranged on the back surface of the heater reached 200 ° C., a control circuit was assembled so as to adjust the temperature at the same temperature based on the temperature information from the thermistor 33. The results are summarized in Table 2.

  In the heater (1), the energization heat generation resistance layer 39 is disposed only on the downstream side, and the heat generation ratio between the upstream side and the downstream side is set to 0: 1. At this time, the time for the fixing roller surface temperature to reach 150 ° C. was 5.6 sec.

  In the heater (2), the width of the energization heat generating resistance layer 39 on the upstream side and the downstream side is changed, and the heat generation amount on the downstream side is increased. At that time, the heat generation ratio of the upstream and downstream heating elements 39 was 1: 2. At this time, the time for the fixing roller temperature to reach 150 ° C. was 5.8 sec, which was 0.2 sec later than that of the heater (1).

  In the heater (3), the energization heat generation resistance layer 39 was arranged on both the upstream side and the downstream side, and the heat generation ratio was 1: 1. At this time, the time for the fixing roller temperature to reach 150 ° C. was 6.0 sec, which was slower than the heater configurations (1) and (2) in the first embodiment.

  In the heater (4), the width of the heating heating resistance layer 39 on the upstream side and the downstream side is changed to increase the heat generation amount on the upstream side. At that time, the heat generation ratio of the upstream and downstream heating elements 39 was 2: 1. At this time, the time for the fixing roller temperature to reach 150 ° C. was 6.2 sec, which was slower than the heaters (1) and (2) of Example 1 and the heater (3) of the comparative example.

  In the heater (5), the energization heat generation resistance layer was disposed only on the upstream side, and the heat generation amount on the upstream side was further increased. At this time, the time for the fixing roller to reach 150 ° C. was 6.4 sec, and the rise in the surface temperature of the fixing roller was the slowest among the heaters used in this experiment.

  As described above, when the fixing roller temperature is 150 ° C., the heating element 39 is provided upstream and downstream, and the heating element 39 is provided only on the upstream side of the heater that is considered to generate heat substantially uniformly. It was found that a heater with a large upstream heat generation rate is inferior in roller heating rate. Conversely, it has been found that a heater having a heating element 39 only on the downstream side and having a large amount of heat generation on the downstream side has a higher roller heating rate.

  Next, the temperature distribution on the heater surface was verified using a heat transfer simulation using a finite element method. In heaters (1), (3), and (5), the results of simulation of the heater surface temperature distribution after 6 seconds from the start of energization are shown in FIG. In the graph, the left side is the upstream side of the heating region 35, and the right side is the downstream side of the heating region 35.

  The heater (1) is a heater in which the ratio of upstream and downstream heating elements is 0: 1 by disposing the heating element 39 only downstream. It can be confirmed that the temperature rises from the upstream side to the downstream side.

  The heater (3) is a heater having an upstream and downstream heat generation ratio of 1: 1. Overall, the temperature is generally uniform except that the temperature on the downstream side is higher and that a temperature peak is observed near the position of the heating element.

  The heater (5) is a heater in which the heating element 39 is disposed only on the upstream side, so that the upstream and downstream heating ratio becomes 1: 0. It can be confirmed that there is a temperature peak at the portion where the upstream heating element 39 is located, and the temperature tends to decrease toward the downstream side.

  It was confirmed by simulation that the surface temperature of the heater can be made higher in the portion where the heat generation ratio is high by changing the heat generation ratio. Accordingly, it has been found that by increasing the heat generation ratio on the downstream side of the heating region 35, the difference from the surface temperature of the fixing roller can be kept large, and the fixing roller 50 can be heated more efficiently.

  Although the results are not shown for the heaters (2) and (4), an intermediate temperature distribution between the heater (1) and the heater (3) is obtained for the heater (2), and the heater (4) An intermediate temperature distribution between 1) and heater (5) is obtained.

  The above experiment and simulation results will be described with reference to FIG.

  FIG. 5 shows that a certain point on the surface of the fixing roller passes through the heating nip portion 35 when the electric power W is applied to the heater and the surface of the rotating fixing roller 50 is heated. The temperature rise is schematically shown. In FIG. 5, it is assumed that the surface of the fixing roller moves in the right direction. That is, the left side is upstream and the right side is downstream.

First, consider a state where uniform heat is generated. Although it depends on the arrangement of the heating element 39, a temperature distribution is generally common in that the temperature slightly decreases at the end where the heating element 39 cannot be arranged and slightly increases in the center. FIG. 5 shows a heater having two heating elements 39. Because of the uniform heat generation, the heater surface is considered to be substantially constant at A ° C. on average. There, one point on the surface of the fixing roller having a temperature of B ° C. is a heating nip portion 35.
Suppose that you have entered. The temperature difference between the heater 30 and the fixing roller 50 immediately after the entry is ΔT ₁ , and at this time, a heat amount of Q ₁ is supplied from the heater 30 to the fixing roller 50. As a result, the surface of the fixing roller is heated. While the temperature of the heater is constant at A ° C., the temperature of the fixing roller rises in the heating nip, so the temperature difference between the heater 30 and the fixing roller 50 becomes smaller, and the temperature difference ΔT at the inlet at the nip outlet. Δt ₁ which is smaller than ₁ . At this time, the amount of heat supplied from the heater 30 to the fixing roller 50 is q ₁ which is smaller than the initial Q ₁ .

  That is, although the fixing roller surface temperature is greatly increased in the initial stage of the heating nip, the temperature difference with the heater is reduced as the fixing roller surface temperature is increased, and the amount of heat transferred is reduced. Temperature rise rate is slow. Therefore, as shown in FIG. 5, as the heater 30 moves from the upstream side to the downstream side, the gradient of the temperature rise becomes smaller.

  On the other hand, the case where the heater 30 whose downstream heat generation amount is larger than the upstream heat generation amount is considered. At this time, the surface temperature of the heater is not uniform and has a gradient, and it is assumed that the downstream side is (A + a) ° C. and the upstream side is (A−a) ° C. Since the same electric power W is input, if it is averaged from upstream to downstream, it is A ° C.

As in the case of uniform heat generation, it is assumed that one point on the surface of the fixing roller having a temperature of B ° C. has entered the heating nip. The upstream heater temperature is (A−a) ° C., and the temperature difference between the heater 30 and the fixing roller 50 immediately after entering is ΔT ₂ . Amount of heat transferred from the heater 30 to the fixing roller 50 at this time is Q _2. ΔT ₂ is smaller than ΔT ₁ because the heater temperature is lower than that during uniform heat generation. Accordingly, since Q _{2 is} also smaller than Q ₁ , the fixing roller temperature rising speed on the upstream side of the heating nip 35 is slower than that during uniform heat generation.

  As the fixing roller 50 rotates, the fixing roller temperature rises as one point on the surface of the fixing roller moves from the upstream side to the downstream side in the heating nip. The difference between the heater temperature and the fixing roller temperature becomes smaller, and the inclination of the temperature rise of the fixing roller 50 gradually becomes smaller.

However, in the heater 30 in which the downstream heat generation amount is larger than the upstream heat generation amount, the heater surface temperature is inclined. As a result, the temperature difference between the heater 30 and the fixing roller 50 can be kept large on the downstream side as compared with the case where heat is uniformly generated throughout the heater. In particular, when the temperature difference between the heater 30 and the fixing roller 50 at the downstream end is Δt ₂ , if Δt ₁ = Δt ₂ , the fixing roller temperature is higher than the uniform heat generation because the heater temperature is higher. It will be possible. Even if Δt ₁ <Δt ₂ , the heat flow q _{2 at} this time is larger than q ₁ , and a larger amount of heat flows from the heater to the fixing roller than in the case of uniform heat generation. . Therefore, the fixing roller temperature can be made higher than at least during uniform heat generation.

  The above heat transfer is repeated during the start-up operation. As a result, even if the same power and the same time are required for start-up, the fixing roller can be warmed more effectively by increasing the downstream heat generation amount. The roller temperature can be increased.

  As described above, in Example 1, it was found that the heating rate of the fixing roller 50 can be increased by increasing the heat generation amount of the heater 30 on the downstream side of the upstream side. As a result, it is possible to configure an external heating type fixing device that rises faster.

  That is, the external heating type fixing device of this embodiment improves the heating efficiency of the fixing roller by the external heater, has a short warm-up time, and has excellent on-demand characteristics.

Example 2
Next, another embodiment of the fixing device according to the present invention will be described.

  The entire configuration of the fixing device 20 in the second embodiment shown in FIG. 6 is the same as that of the fixing device 20 in the first embodiment described with reference to FIG. 2 and FIG. The same reference numerals are assigned, the description of the first embodiment is used, and the description thereof is omitted here.

  In the second embodiment, the position of the heater unit 70 as an external heating device is shifted in the upstream direction or the downstream direction of the heating region 35 formed by the heater unit 70 and the fixing roller 50. By doing so, it is possible to change the heat generation distribution in the heating region.

  That is, as shown in FIG. 6, if the heater unit 70 is shifted to the upstream side of the heating region 35, the heat generation peak can be moved to the upstream side of the heating region 35. Is shifted to the downstream side of the heating region 35, the exothermic peak can be shifted to the downstream side of the heating region 35.

  The exothermic peak moves larger as the shift amount of the heater unit 70 is increased. However, if the heater unit 70 is excessively shifted, the heating element 39 of the heater 30 may be detached from the heating region 35. If the heating element 39 of the heater 30 is removed from the heating region 35, the heat of the heating element 39 becomes difficult to be taken away by the fixing roller 50, and there is a possibility that the temperature of that part will rise abnormally. In order to reduce this, for example, the material of the sliding member 34 sandwiched between the heater 30 and the fixing roller 50 may be made of a metal having a high thermal conductivity. A state that deviates from the above is not preferable.

  Therefore, the shift amount of the heater unit 70 is also determined by the size of the heating element pattern on the heater.

  In the above configuration, an external heating device, that is, the heater unit 70 is brought into pressure contact with the fixing roller 50 and the elastic layer of the fixing roller 50 is compressed, so that a heating nip (heat transfer region) having a shape matching the shape of the heater 30 is obtained. The configuration forming 35 has been described.

  On the other hand, it is also preferable to configure the heat transfer area, that is, the heating area 35 to have a shape that follows the curvature of the fixing roller 50.

  For example, instead of the sliding member 34, which is the heat-resistant sliding sheet described in the first embodiment and is interposed between the heater 30 and the fixing roller 50, as shown in FIG. Alternatively, the sliding member 43 may be formed of a curved sheet metal having a curvature. The heater 30 is disposed on the opposite surface of the curved sheet metal 43 that contacts the fixing roller 50. In this way, the heating layer length along the rotation direction of the fixing roller 50 is further increased as compared with the case where the elastic layer of the fixing roller 50 is compressed to form the heating region 35 along the shape of the heater 30. It can be formed longer.

  By interposing the curved sheet metal 43 between the heater 30 and the fixing roller 50, it becomes possible to form a heating region 35 larger than the heater width W. For example, if the long heating region 35 can be formed, the position of the heat generation peak can be greatly shifted from the center of the heating region 35. For example, as shown in FIG. 8, the ratio of the heat generation amount on the upstream side and the downstream side of the heating region 35 can be greatly changed by adopting a configuration in which the heating region 35 is long on the downstream side.

  In FIG. 8, as described above, the curved sheet metal 43 has a shape projecting upstream in the rotation direction of the fixing roller 50. As a result, the position of the heater 30 is not changed by changing a support member (not shown), but the heating region 35 formed by the curved sheet metal 43 and the fixing roller 50 is expanded to the upstream side of the fixing roller 50 from the heater 30. Thus, the heater 30 is relatively positioned on the downstream side of the heating region 35.

  The upstream area of the heating area 35 transfers heat from the heater 30 by the curved sheet metal 43 to apply heat to the fixing roller 50. On the other hand, in the area downstream of the heating area 35, the distance from the heater 30 is close, so that heat is more preferentially applied to the fixing roller 50. Accordingly, the downstream area has a larger amount of heat applied to the fixing roller 50 than the upstream area of the heating area 35.

  Various shapes of the curved sheet metal 43 are conceivable, and it is preferable that the curved sheet metal 43 is changed according to a necessary rotation speed and a fixing device rising speed. Further, the shape is not limited to a curved surface, and is a member having a shape along the outer surface of the fixing roller 50. For example, a polygonal shape combining a plurality of planes may be used. Moreover, the shape comprised by a plane and a curved surface may be sufficient, and the shape which curved the planar member may be sufficient. Further, the material is preferably as excellent in thermal conductivity as possible, but is not limited to metal. For example, it may be a ceramic material having good thermal conductivity such as alumina or aluminum nitride, or may be a resin material such as polyimide.

  As described above, as in the second embodiment, the position of the heater unit 70 can be changed, or the shape of the sliding member 43 interposed between the heater 30 and the fixing roller 50 can be changed. With this configuration, the heat generation amount on the downstream side of the heating region 35 formed by the heater 30 and the fixing roller 50 can be made larger than the heat generation amount on the upstream side. As a result, heat can be more efficiently transmitted to the fixing roller 50.

  That is, the external heating type fixing device of the present embodiment improves the heating efficiency of the fixing roller by the external heater as in the first embodiment, has a short warm-up time, and has excellent on-demand characteristics.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of an embodiment of an external heating type fixing device according to the present invention. 3A and 3B are schematic views of a ceramic heater, in which FIG. 3A is a cross-sectional view taken along the line C-D in FIG. 3B, and FIG. 3B is a plan view illustrating a B surface in FIG. 6 is a graph showing a simulation result of a heater surface temperature in Example 1. It is explanatory drawing of the effect of Example 1. FIG. It is a schematic block diagram of the other Example of the external heating type fixing device which concerns on this invention. It is a schematic block diagram of the other Example of the external heating type fixing device which concerns on this invention. It is a schematic block diagram of the heat transfer area | region vicinity in the other Example of the external heating type fixing device which concerns on this invention. It is the schematic of the heat roller fixing device of the external heating system which is a prior art example. It is the schematic of the heat roller fixing device of the external heating system using the heat roller which is a prior art example. It is the schematic of the heat roller fixing device of the external heating system using the plate-shaped heater which is a prior art example. It is the schematic of the fixing device of the external heating system using the radiant heat source which is a prior art example.

Explanation of symbols

20 Fixing device 28 Fixing nip (pressure contact)
30 Ceramic heater (heating body)
33 Thermistor (Temperature sensing element)
34 Heat-resistant sliding sheet (sliding member)
35 Heating area (heat transfer area)
37 Recording material 38 Substrate 39 Current-generating heating resistance layer (heating element)
43 Curved sheet metal (sliding member)
50 Fixing roller (fixing member)
60 Pressure roller (Pressure member)
70 External heating device (heater unit)
80 Photosensitive drum (image carrier)
81 Charging device 82 Developing device 83 Cleaner 100 Image forming apparatus 100A Image forming apparatus main body

Claims (5)

A fixing member, a pressure member that forms a pressure contact portion in contact with the surface of the fixing member, and an external heating device that includes a heating body that heats the surface of the fixing member from the outside.
In a fixing device for performing heat fixing by introducing a recording material carrying an unfixed toner image into a pressure contact portion between the fixing member and the pressure member,
In the heat transfer region by the external heating device on the surface of the fixing member, the heat generation amount of the external heating device is larger on the downstream side than on the upstream side in the moving direction of the surface of the fixing member.   The fixing device according to claim 1, wherein the heating body of the external heating device is in contact with the surface of the fixing member via a heat-resistant sliding member to heat the surface of the fixing member.   The fixing device according to claim 2, wherein the sliding member is a sheet-like member having heat resistance.   The fixing device according to claim 2, wherein the sliding member is a heat conductive member having a shape along a surface of the fixing member. In an image forming apparatus comprising: an image forming unit that forms an unfixed toner image on a recording material; and a fixing device that thermally fixes the unfixed toner image on the recording material.
The image forming apparatus according to claim 1, wherein the fixing device is a fixing device according to claim 1.

Images